ASME Conference Presenter Attendance Policy and Archival Proceedings

2016;():V003T00A001. doi:10.1115/IPC2016-NS3.

This online compilation of papers from the 2016 11th International Pipeline Conference (IPC2016) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Operations, Monitoring and Maintenance: Automation and Measurement

2016;():V003T04A001. doi:10.1115/IPC2016-64014.

Invariably, oil pump station piping layouts may contain multiple dead-legs brought about by closed valves at one end of side branches, while flows continue through the main runs. During the transportation of heavy crude through the pump station, these dead-legs will be filled with this crude. When a light crude batch is introduced next into the pipeline, following the heavy crude ahead, two phenomena will occur. First, contamination between batches at the interface of the two crudes will occur due to axial turbulent diffusion along the length of the pipeline itself. Second, as the light crude flows through the pump station, and passes by each dead-leg containing residual heavy crude from the preceding batch, the heavy crude trapped in these dead-legs will start to drain out into the passing light crude in the main run. This causes further contamination and spreading of the mixing zone between the two batches. The second source of contamination, which is addressed in this paper, could cause appreciable contamination particularly for large dead-leg sizes and numbers. A computational fluid dynamics (CFD) model has been developed to quantify the drainage rate of the contaminating crude into the main stream and its impact on widening the mixed zone (contamination spread) between the two batches. Two drainage mechanisms of the heavy crude in the dead-legs into the main stream of the light crude have been identified and quantified. Finally, potential innovations to mitigate contamination due to dead legs are presented and quantified for their respective effectiveness in minimizing the contamination spreads between batches of different crudes.

Commentary by Dr. Valentin Fuster
2016;():V003T04A002. doi:10.1115/IPC2016-64080.

Gas pipeline internal surface typically undergoes degradation for a variety of reasons such as fouling of the pipe inner surface, erosion, corrosion and deposits of objectionable materials that occasionally enter the gas stream at receipt points. Accurate monitoring of the pipe internal surface condition can hugely benefit the planning of cleaning activities. Theoretically the pipe wall roughness for a given pipe segment can be extracted based on measured flow data and other system parameters. The challenge lies in the fact that measured data all contain varying degrees of uncertainty, and the system becomes more complex to analyze when it contains different segments connected in series or parallel like many typical gas gathering and lateral networks. This paper demonstrates the application of the Error-in-Variable Model (EVM) using the Markov Chain Monte Carlo (MCMC) solution method in analyzing a complex pipeline network on the TransCanada NGTL System. EVM, a well-established Bayesian parameter estimation technique, accounts for uncertainties in the measured variables, such as flow and pressure data, when determining the most probable estimates of unknown parameters such as pipe internal wall surface roughness. In this work, the EVM problem is solved using the MCMC Metropolis-Hastings algorithm. The MCMC approach is demonstrated to be robust, easy to implement and capable of handling large quantities of data. It has the potential to analyze complex networks and monitor the pipe wall surface condition on-line with SCADA data. Using this method, the internal wall surface roughness for the segments of interest in this network were extracted from measured data collected before and after the pigging operation. Results demonstrate the model’s capability in estimating the degradation of the pipe wall internal surface and the effectiveness of pigging. Details on implementation and challenges in applying such methodology to analyze complex gas networks are discussed.

Commentary by Dr. Valentin Fuster
2016;():V003T04A003. doi:10.1115/IPC2016-64118.

Leakage in oil and gas infrastructure, often cause significant financial losses, severe damage to the environment and raises public concern. In order to minimize the impact of spills, quick detection of a leak and a rapid response are needed. The systems currently employed to detect pipeline leakage range from simple visual checking to complex hardware and software systems such as mass balance, pressure point analysis, flow deviation, acoustic emission systems, and fibre-optic-based sensing technologies. These methods are useful, but there are certain limitations. The main drawback of the majority of these leak detection technologies is that they detect leakage indirectly, often unable to detect the leakage until the major spill.

The preventive monitoring system and direct detection of hydrocarbon leakage are urgently needed to enable fast response and timely repairs with less deleterious effects. Research is being conducted for the development of a functional prototype and environmental testing of in-situ carbon nanotube (CNT) nanocomposite based sensors for hydrocarbon leakage detection. The CNT nanocomposite offers a unique approach to the direct hydrocarbon leakage detection in pipelines and aboveground storage tanks (ASTs).

Expanding the study from the previous report of sensor characteristics under the optimal ambient condition, it was further investigated to identify the sensor performance under harsh conditions such as the underground (exposed to the soil) with compost and moisture, high pressure, changing temperature and long-term exposure to the outdoor environment. Investigation of the sensor behavior is studied, and a performance matrix is developed that accounts for the change in sensor response to various environmental conditions. Results showed that the proposed CNT nanocomposite sensor was applicable under given conditions with immediate responses while maintaining high sensitivity to the hydrocarbon leakage.

Once a list of sensor detection specifications is defined, it is anticipated that the CNT sensor technology is applicable as part of a robust, reliable and accurate early detection system for the pipeline industry.

Commentary by Dr. Valentin Fuster
2016;():V003T04A004. doi:10.1115/IPC2016-64160.

Remote communications to field devices for data monitoring and controls has greatly reduced operating costs, reduced downtime, and helped to optimize our industry. With the ever growing threat of cyber-attacks, the need for securing that data is becoming a more common topic of discussion. Whether collecting SCADA or Measurement data from the field, doing remote configuration, or even sitting dormant, it is important to keep the line of communication to your devices secure. This presentation will discuss potential threats and examples of cyber-attacks. It will cover industry standards, types of cyber security, and the importance and best practices for securing data for Measurement and/or SCADA and control systems.

Commentary by Dr. Valentin Fuster
2016;():V003T04A005. doi:10.1115/IPC2016-64193.

Canada and the United States have vast energy resources, supported by thousands of kilometers (miles) of pipeline infrastructure built and maintained each year. Whether the pipeline runs through remote territory or passing through local city centers, keeping commodities flowing safely is a critical part of day-to-day operation for any pipeline. Real-time leak detection systems have become a critical system that companies require in order to provide safe operations, protection of the environment and compliance with regulations. The function of a leak detection system is the ability to identify and confirm a leak event in a timely and precise manner. Flow measurement devices are a critical input into many leak detection systems and in order to ensure flow measurement accuracy, custody transfer grade liquid ultrasonic meters (as defined in API MPMS chapter 5.8) can be utilized to provide superior accuracy, performance and diagnostics.

This paper presents a sample of real-time data collected from a field install base of over 245 custody transfer grade liquid ultrasonic meters currently being utilized in pipeline leak detection applications. The data helps to identify upstream instrumentation anomalies and illustrate the abilities of the utilization of diagnostics within the liquid ultrasonic meters to further improve current leak detection real time transient models (RTTM) and pipeline operational procedures. The paper discusses considerations addressed while evaluating data and understanding the importance of accuracy within the metering equipment utilized. It also elaborates on significant benefits associated with the utilization of the ultrasonic meter’s capabilities and the importance of diagnosing other pipeline issues and uncertainties outside of measurement errors.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T04A006. doi:10.1115/IPC2016-64218.

The prevailing leak detection systems used today on hazardous liquid pipelines (computational pipeline monitoring) do not have the required sensitivities to detect small leaks smaller than 1% of the nominal flow rate. False alarms of any leak detection system are a major industry concern, as such events will eventually lead to alarms being ignored, rendering the leak detection system ineffective [1].

This paper discusses the recent work focused on the development of an innovative remote sensing technology that is capable of reliably and automatically detecting small hazardous liquid leaks in near real-time. The technology is suitable for airborne applications, including manned and unmanned aircraft, ground applications, as well as stationary applications, such as monitoring of pipeline pump stations. While the focus of the development was primarily for detecting liquid hydrocarbon leaks, the technology also shows promise for detecting gas leaks.

The technology fuses inputs from various types of optical sensors and applies machine learning techniques to reliably detect “fingerprints” of small hazardous liquid leaks. The optical sensors used include long-wave infrared, short-wave infrared, hyperspectral, and visual cameras. The utilization of these different imaging approaches raises the possibility for detecting spilled product from a past event even if the leak is not actively progressing.

In order to thoroughly characterize leaks, tests were performed by imaging a variety of different types of hazardous liquid constitutions (e.g. crude oil, refined products, crude oil mixed with a variety of common refined products, etc.) in several different environmental conditions (e.g., lighting, temperature, etc.) and on various surfaces (e.g., grass, pavement, gravel, etc.). Tests were also conducted to characterize non-leak events. Focus was given to highly reflective and highly absorbent materials/conditions that are typically found near pipelines.

Techniques were developed to extract a variety of features across the several spectral bands to identify unique attributes of different types of hazardous liquid constitutions and environmental conditions as well as non-leak events. The characterization of non-leak events is crucial in significantly reducing false alarm rates. Classifiers were then trained to detect small leaks and reject non-leak events (false alarms), followed by system performance testing. The trial results of this work are discussed in this paper.

Commentary by Dr. Valentin Fuster
2016;():V003T04A007. doi:10.1115/IPC2016-64355.

Pigging operations are common procedures for pipeline maintenance. However, questions still remain about pig dynamics due to the difficulties to accurately describe this complex phenomenon. Consequently, most predictions of pig dynamics are based on empirical knowledge deduced from experimental data and numerical models developed considering simplified physical models, without calculate transient pig-flow interaction and neglecting 3D aspect of flow dynamics. Therefore, to present an actual 3D transient model, this paper proposes a novel CFD methodology using a static mesh in a moving control volume. Forces acting on the pig are dynamically computed by a Fluid-Structure Interaction (FSI) approach; pig velocity is obtained for each time instant and it is set as a variable boundary condition. This method was validated with experimental results and it may be used to describe a wide range of rigid body motion immerse in a flow. This approach is then utilized to obtain the transient simulation of a pig launch in a straight water pipeline. Numerical predictions of the static grid method were compared with those obtained using moving mesh simulations. Results show that the pig reaches a terminal velocity higher than average flow velocity and a huge difference on predictions of maximum pressure drop (through the pig) between steady state based models and transient models. Additionally, it was simulated a 2D model to observe the differences between 2D and 3D simulations on the flow characteristics and pig motion features, which shows an important increase of the pressure drop on 3D model over 2D and high pig acceleration in the 3D simulation.

Commentary by Dr. Valentin Fuster
2016;():V003T04A008. doi:10.1115/IPC2016-64371.

Many different approaches have been adopted for identifying leaks in pipelines. Leak detection systems, however, generally suffer from a number of difficulties and limitations. For existing and new pipelines, these inevitably force significant trade-offs to be made between detection accuracy, operational range, responsiveness, deployment cost, system reliability, and overall effectiveness. Existing leak detection systems frequently rely on the measurement of secondary effects such as temperature changes, acoustic signatures or flow differences to infer the existence of a leak.

This paper presents an alternative approach to leak detection employing electromagnetic measurements of the material in the vicinity of the pipeline that can potentially overcome some of the difficulties encountered with existing approaches. This sensing technique makes direct measurements of the material near the pipeline resulting in reliable detection and minimal risk of false alarms. The technology has been used successfully in other industries to make critical measurements of materials under challenging circumstances. A number of prototype sensors were constructed using this technology and they were tested by an independent research laboratory. The test results show that sensors based on this technique exhibit a strong capability to detect oil, and to distinguish oil from water (a key challenge with in-situ sensors).

Topics: Pipelines , Leakage
Commentary by Dr. Valentin Fuster
2016;():V003T04A009. doi:10.1115/IPC2016-64372.

One of the challenges of transporting highly viscous crude oil is to ensure that the flow of oil will be delivered. It is also necessary to keep the operational standards and conditions along sections of pipes and fittings. Today, with low oil prices, it is important to minimize energy losses through the pipelines and accessories. However, new designs are often based on correlations that have not been developed for heavy oil water mixtures and are not frequently reported in the literature. Moreover, conventional calculations do not take into account the presence of accessory lines, or simply consider by empirically adding an extra percentage of energy loss or according to the engineer design test. Even more, the current correlations that could estimate accessory loss do not work well for viscous fluids and are even less suitable for the case of two-phase mixtures. For example, Gardel correlation [1] was made for water flow through yee type accessories. Applying this correlation to viscous fluids result in high deviations, more than 500% compared to CFD simulations. The present work attempts to predict the fluid dynamics behavior and the energy losses of these viscous fluids and mixtures (oil - water) going through a Yee type confluence.

All simulations were carried out using ANSY CFX® v14.5. Mesh number of elements was optimized using Pipe-It® (optimization software). A grid independence study was also carried out automatically in Pipe-It® to ensure the quality of results. Several conditions have been simulated: angle confluence of 45°–75°, diameter ratio 2–7, oil viscosity from 10 to 105 cP, and water cut of 0–1. As the main result, a correlation that predicts the behavior of viscous mixtures in their passage through yee type confluences was developed using a genetic algorithms technique [2]. This correlation takes into account: viscosity, fluid fractions, input speeds, confluence angle and other parameters that are not normally considered by other authors. Therefore, it may be used in mixtures of water with light and heavy crude oil. Finally, correlations with 10% deviation compared to CFD simulations were obtained.

Topics: Crude oil , Junctions
Commentary by Dr. Valentin Fuster
2016;():V003T04A010. doi:10.1115/IPC2016-64405.

Real-time leak monitoring of pipelines is a need that is growing with the aging of the assets and the rise of the population living in their close proximity. While traditional deployment of external monitoring solutions on legacy assets may require extensive construction and trenching on the pipeline right-of-way, a new class of self-powered and wirelessly communicating devices provides an intriguing alternative. These devices are installed on the right-of-way with no need for mechanical excavation and allow continuous monitoring of a pipeline over long distances. Their low-power requirement makes it possible to operate the monitoring system continuously on battery power and their wireless communication is established through a self-forming network. These attributes make real-time monitoring possible without requiring any wiring to be deployed on the right-of way. The devices take advantage of the pipe’s characteristics that guide the acoustic waves generated by the leak along the pipeline to detect leaks. These characteristics make the detection possible even from a device that is not in close proximity of the leak.

Since device spacing is a key parameter in the cost of monitoring with the leak detection system, it is important to understand the parameters that govern the propagation of leak sound on pipelines. Testing was performed for this purpose to validate the ability of these novel acoustic sensors in an outdoor test facility under a variety of leak conditions. This testing evaluated the propagation of acoustic waves emanating from small leaks on a buried pipe. This was achieved by pressurizing the pipeline to different levels of pressure and inducing leaks through various orifice sizes. The acoustic disturbances induced by these leaks were measured by sensors deployed at various stations on the pipe. The results of this testing demonstrated the ability of such an approach to be used for detecting very small disturbances in soil from an offset position caused by leaking liquids.

Commentary by Dr. Valentin Fuster
2016;():V003T04A011. doi:10.1115/IPC2016-64471.

Pipeline ruptures have the potential to cause significant economic and environmental impact in a short period of time, therefore it is critical for pipeline operators to be able to promptly detect and respond to them. Public stakeholder expectations are high and an evolving expectation is that the response to such events be automated by initiating an automatic pipeline shutdown upon receipt of rupture alarm. These types of performance expectations are challenging to achieve with conventional, model-based, leak-detection systems (i.e. CPM–RTTMs) as the reliability measured in terms of the false alarm rate is typically too low.

The company has actively participated on a pipeline-industry task force chaired by the API Cybernetics committee, focused on the development of best practices in the area of Rupture Recognition and Response. After API’s release of the first version of a Rupture Recognition and Response guidance document in 2014, the company has initiated development of its own internal Rupture Recognition Program (RRP). The RRP considers several rupture recognition approaches simultaneously, ranging from improvements to existing CPM leak detection to the development of new SCADA based rupture detection system (RDS). This paper will provide an overview of a specific approach to rupture detection based on the use of machine learning and pattern recognition techniques applied to SCADA data.

Commentary by Dr. Valentin Fuster
2016;():V003T04A012. doi:10.1115/IPC2016-64488.

This paper will demonstrate that with limited instruments at the terminals and platforms only, it is feasible to monitor the integrity of offshore pipelines effectively. Some examples of applications will be shown, including both crude oil and natural gas pipelines.

The statistical volume balance technology based on flow and pressure measurements at the inlets and outlets only provides the detection and location of leaks. The paper describes the performance of these leak detection systems for incidents ranging from small leaks to pipeline rupture.

To help operators run pipelines safely and cost effectively, real-time transient models are used to calculate the flow, pressure, temperature, density and other fluid properties along the pipeline. Instead of using measured flow and pressure, the operators rely on these calculated values to take operational decisions. The combination of hydraulic modelling and statistical leak detection provides the operators with the information and confidence in the integrity of their pipelines. In the event of any incident the operators can take actions quickly and correctly to minimize the consequences.

Commentary by Dr. Valentin Fuster
2016;():V003T04A013. doi:10.1115/IPC2016-64670.

Natural gas leakage from unmanned facilities, such as compressor stations, gathering sites, and block valve locations, can pose significant economic and safety impacts. Additionally, methane, the primary constituent of natural gas, is a powerful greenhouse gas with 84 times the global warming potential of carbon dioxide on a mass basis over a 20-year period (IPCC 2013). Due to the remote location of many of these facilities, fluid leaks can persist for extended periods of time. Continuous leak detection systems would facilitate rapid identification and repair of leaks. However, existing technologies, such as infrared cameras, are cost-prohibitive to be installed at a high number of sites and are instead used in periodic monitoring as part of leak detection and repair programs. Such periodic monitoring does not provide for quick detection of “fat tail” leaks that dominate the emissions from gathering and transportation systems (Mitchell et al. 2015, Subramanian et al. 2015).

A unique and innovative arrangement of various stakeholders was utilized to initiate a technology development and testing program aimed at expedited deployment of low-cost technologies at high numbers of sites. The technologies targeted for this work were low enough in cost to economically justify the installation of such sensors at every gas gathering and transportation site. This work was driven by an environmental advocacy organization under a partnership with eight different oil and gas companies and technical oversight from various universities, non-profits, and government agencies to give a wide perspective on the needs of such technology.

Four different technologies were developed and tested in realistic release environments. The technologies ranged from sensors modified from automobile-based technology to laser-based systems used for monitoring gases in coal mines. The systems were treated as “end-to-end” units whereby all components (e.g., sensor, data acquisition, enclosures, etc.) needed to perform according to the provided specifications. The testing involved controlled releases under numerous environmental conditions and with different gas compositions. The largest focus of the testing was on outdoor releases where the systems had to detect the transient nature of gas plumes.

The primary objectives of the testing were to determine the readiness of the technologies for pilot testing in the field and identify continuous improvement opportunities. The project demonstrated that there are newly-developed technologies that could be deployed as low-cost continuous monitoring solutions for the gas industry.

Topics: Sensors , Methane , Emissions
Commentary by Dr. Valentin Fuster
2016;():V003T04A014. doi:10.1115/IPC2016-64675.

In this paper, a new leak detection system based on a pattern recognition algorithm in a shut-in condition of a pipeline is presented. For a fully shut-in pipeline, the governing fluid dynamic equations are simplified to the thermodynamic state postulates. Hence, the shut-in section can be treated as a closed thermodynamic system with no mass flow in or out of the system boundaries. The system always contains the same amount of matter, but heat and work can be exchanged across the boundaries of the system. The pattern recognition algorithm presented in this paper automatically monitors the pressure drop patterns and generates an alarm when the pattern of pressure gradients matches the leak signatures. The algorithm takes into account the effect of thermal cooling and other operational complexities to enhance the reliability performance of the scheme. Results of the performance of the shut-in leak detection system are presented and discussed in this paper. Both simulated and historical leak scenarios during shut-in state are used to investigate the performance of the shut-in leak detection scheme.

Topics: Pipelines , Leakage
Commentary by Dr. Valentin Fuster
2016;():V003T04A015. doi:10.1115/IPC2016-64698.

In the operation of hydrocarbon liquid pipelines, Computational Pipeline Monitoring (CPM) systems are used for software based leak detection. When installed, CPM systems must meet the regulatory requirements such as API 1130 in the USA and CSA Z662 in Canada. API RP 1130 provides several methods that can be used to test a CPM system: forced parameter testing, simulated leak test (SLT), and fluid withdrawal testing (FWT).

Leak tests are performed to establish and verify the leak detection capabilities of the installed CPM system and in some cases test the response of the personnel. One of the primary interests in leak testing is the realism or hydraulic accuracy of the leak signature, in order that the reported leak sensitivity results of the test are reflective of the real performance of the CPM system.

Simulated leak tests (SLT’s) use an offline pipeline model to generate hydraulically accurate data which can be fed into the CPM model. SLT’s provide the most flexible and hydraulically accurate solution to simulating leaks, compared to some of the other API RP 1130 compliant test methods. SLT’s do not have leak location restrictions and also correctly models the flow and pressure hydraulic signature of a leak.

The paper outlines a novel approach and method to leak simulation, based on its size and shape of the leak hole. This method can be used to represent various sizes of a leak, ranging from a pin hole to a large rupture along the seam. Implementation of the method in a simulator developed with commercial software is discussed. The results of the simulation, namely the hydraulic signatures from the simulated leak and the CPM response, are compared with the widely used leak simulation method using a constant leak rate. Finally, possible applications of this method are considered.

Commentary by Dr. Valentin Fuster
2016;():V003T04A016. doi:10.1115/IPC2016-64704.

While natural gas pipelines already benefit from airborne, remote detection of leaks [1, 2], oil pipeline leak detection has been for a long time reliant on SCADA systems limited in their capability to detect very small leaks, and/or visual inspection of the right of way (line flyers, pipeline employees or members of the public). This paper presents a novel and complementary way of detecting small leaks (i.e. sensitivity of 0.1 L/minute, 1 barrel/day) of oil (crude or refined products) using an optical detection system mounted on an airborne platform (UAV, plane or helicopter). The scope of this paper is based on the requirements provided by TransCanada, namely sensitivity (herein referred as LOD — Limit of Detection) and accuracy (herein referred as spatial resolution) as similar to their description in API 1130, while the topic of reliability is addressed in our noted concerns on the false alarms that may be generated in Infrared-DiAL based systems due to soil reflectivity. Robustness, as described in API 1130, was out of scope.

Keeping in mind the requirement of airborne operation, three different approaches for the detection of leaks along long pipeline ROWs were studied. Infrared Differential Absorption lidar (IR-DiAL), UltraViolet Raman lidar (UV-Raman lidar) and UltraViolet Laser-Induced Fluorescence lidar (UV-LIF lidar) have been tested in realistic conditions. In the first round of tests, laboratory spectral measurements of vapors in a closed cell were performed. In the second round of tests, the breadboards were placed in a mobile laboratory and the light beams aimed at a large open at 40 to 50 meters and reflected off a sand target. Finally, the mobile laboratory with the breadboards was installed at ∼40 meters from a leak simulator. The leak simulator was made by using a large sand container in which petroleum products were leaked.

Intermediate scale leak simulator tests showed that it is clearly a challenge to correlate a measured concentration to an actual leak size. Tests have also shown that there is a strong concentration gradient in the air above a leak. This indicates that a better overall detection performance should be obtained with a measurement using the air next to the ground, and that it is feasible to detect a leak of less than 1 barrel/day.

UV-Raman tests performed in the outdoors suggested a Limit Of Detection (LOD) of the system below 1 500 ppm-m when detecting all hydrocarbons. Because of the hardware that would be needed to lower this detection limit, results suggest abandoning the Raman technique for remote leak detection from an airborne platform.

IR-DiAL showed the best sensitivity for the detection of hydrocarbons (< 1 ppm-m of LOD). However the effective LOD will be reduced because of the soil spectral reflectance variations that may lead to a high false alarm rate for concentrations of hydrocarbons lower than 235 ppm-m.

The UV-absorption approach was also briefly tested, suggesting a LOD for benzene of between 1.5 and 2.5 ppm-m. The UV absorption of benzene is not affected by ground spectral reflectance variations. This is an approach that will be investigated further.

Topics: Pipelines , Leakage
Commentary by Dr. Valentin Fuster

Operations, Monitoring and Maintenance: Geohazards

2016;():V003T04A017. doi:10.1115/IPC2016-64065.

Longwall mining operations could compromise the integrity of high pressure pipelines by way of surface subsidence and soil strains. Prior to implementing field programs for monitoring subsidence, a preliminary mitigation/stress analysis study should be designed to determine the possible effects of the longwall mining operations on the pipeline(s). If the stress analysis indicates possible high stresses beyond the allowable limits of a pipeline, then a mitigation plan should be developed and implemented. Regardless of the anticipated stress level in a pipeline, a strain monitoring program is usually recommended.

The purpose of this paper is to discuss the design of a pipeline strain monitoring program, which includes the installation of strain gages at critical locations along two adjacent pipelines. The study area includes a 12 inch diameter steel pipeline (for natural gas transport) and a 12 inch HDPE pipeline for water transport. The study area is located in a mountainous region of West Virginia.

Prior to the field program, a laboratory pilot study was performed with strain gages on a test section of HDPE pipe to determine the best mounting procedures. The field implementation program included the installation of strain gages on the gas and water pipelines. Multiplexers, data loggers, a solar array and a satellite modem for 24/7 data transfer were installed, and monitored throughout the study. During the field implementation program several meteorological and geologic events occurred which caused some design changes in the field program.

Commentary by Dr. Valentin Fuster
2016;():V003T04A018. doi:10.1115/IPC2016-64199.

This paper presents a methodology which uses past bank erosion behaviour as a predictor of future performance. The methodology employed in the bank erosion study consists of the following main steps: identifying a reach to examine, classifying the watercourse, estimating key hydrotechnical properties, obtaining historical air photographs of the reach, georeferencing or orthorectifying the airphotos, mapping the position of the channel edge, obtaining the historical records of nearby gauges to estimate the return period of floods that have occurred between successive pairs of historical air photographs, and finally combining the results to provide correlations between the rates of bank erosion and the rarity of the floods that have occurred.

More than 70 bank erosion studies have been completed in the past two years at a variety of watercourses. This paper provides three case histories that illustrate the methodology and then proceeds to provide some tentative relationships that could be used to focus future bank erosion studies on those sites most active, and used to provide a preliminary estimate of the amount of bank erosion that could be expected in both design settings and existing pipeline integrity evaluations.

In this study wandering rivers are more laterally active than other channel pattern types. Although the smallest floods do not cause large-scale changes to the banks, significant bank erosion can be caused by either moderate (20-year) or extreme (100-year) events with a rough trend to larger bank erosion in larger floods. No significant correlation between the time elapsed between successive air photos and the magnitude of erosion was found, suggesting that bank erosion is an event-driven process rather than time dependent.

Topics: Erosion , Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T04A019. doi:10.1115/IPC2016-64219.

Enbridge Liquids Pipelines (Enbridge) operates over 26,000 km of liquid pipelines in Canada and the US, administers a system-wide geohazard management program to identify, investigate and monitor geohazards, and performs remediation as required. An integral part of the geohazard management program is real-time flood monitoring, where pipeline watercourse crossings affected by flooding are identified and flood levels monitored. Watercourse crossings where the pipelines have a high potential to become exposed, to span, and potentially to fail during a flood event are studied in more detail.

This flood monitoring program automatically monitors publicly available real-time stream gauge flow measurements and compares these measurements to estimated discharge thresholds for the crossing under evaluation. Thresholds are related to the current pipeline depth of cover (DOC) and the amount of scour that can occur over a range of flood magnitudes. Thresholds include: 1) the estimated peak flow to expose the top of the pipe, “exposure flow”, 2) the estimated peak discharge and associated flow velocities that could create enough free spanning pipe for the onset of vortex induced vibration (VIV) fatigue failure, “flow of concern”, and 3) where additional mechanical assessment taking account of specific pipe properties, data requirements and circumstances has been carried out, the “critical flow”, the estimated average peak flow and duration that has the potential to result in product release due to VIV once a sufficient pipe span length has developed, “critical flow”.

This paper is a case study of an assessment and flood monitoring of one of Enbridge’s Mississippi River pipeline crossings, which has a history of flood-related pipeline exposure and subsequent mitigations. During real-time monitoring of a 2015 flood event the “exposure flow” and “flow of concern” thresholds for this crossing were exceeded, resulting in a decision by Enbridge to shut down the pipeline. Subsequent surveys revealed that the pipe had become exposed and was spanning adjacent to the previously remediated area. The previous mitigation likely limited the length of pipe exposure and pipe span. Added complexity was encountered during the post shutdown DOC survey, which needed to be completed as quickly and safely as possible after flood levels declined to allow for an assessment of the actual condition of the pipeline prior to restart.

This paper presents a methodology that could allow pipeline operators to identify river crossings susceptible to pipe exposure, and the potential for freespan development, due to flooding, by providing an understanding of what is likely happening to the cover over the pipe at a particular crossing during a flood event. This provides a tool to better manage pipeline river crossings experiencing flooding.

As far as the authors are aware, this case study represents the first time a pipeline has been shut down based on real-time flows and thresholds in the United States.

Topics: Pipelines , Floods , Rivers
Commentary by Dr. Valentin Fuster
2016;():V003T04A020. doi:10.1115/IPC2016-64222.

Because pipelines can cover extensive distances through diverse terrain, they are subject to various geohazards, including slope failure and earthquake damage, which can have costly environmental and monetary impacts over their designed operational lifetime. Here, we show how geophysical investigative techniques can be used to complement other geotechnical investigation methods to provide a detailed understanding of site geology to best inform geohazard assessments. We pay particular attention to how multiple geophysical methods can be used to obtain spatially continuous measurements of subsurface physical properties, and layer and structural geometries. The geophysical data can then be used to either interpolate or extrapolate geotechnical engineering properties between and away from boreholes and excavations, or optimize the locations of subsequent boreholes or excavations. To demonstrate the utility of our integrated approach of incorporating geophysical methods to geohazard assessments, two case studies are presented. The first case study shows how electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and multichannel analysis of surface wave (MASW) datasets are used to constrain the thickness and extent of potentially sensitive glaciomarine clay layers that are subject to slope instability and structural failure along a proposed pipeline route near Kitimat, British Columbia (BC). A second case study describes how high-resolution ground-penetrating radar (GPR) and seismic reflection surveys are used to locate and characterize fault strands that may cause future ground deformation at a proposed pipeline crossing of the Tintina/Rocky Mountain Trench fault in northeastern BC.

Commentary by Dr. Valentin Fuster
2016;():V003T04A021. doi:10.1115/IPC2016-64378.

Ground deformation from natural or anthropogenic processes is a significant factor in the integrity management plan for natural gas distribution networks. Rapid or large scale deformation can pose an immediate rupture threat. Smaller, more gradual or repeated ground deformations may lead to material stresses, damage and strain accumulation, posing a longer-term threat. Satellite monitoring can play a key role in pipeline integrity management programs by measuring ground deformation over an entire pipeline network, at high spatial and temporal resolutions with the ability to capture both rapid large scale and subtle, repeated ground movement over a longer period of time.

Millimeter accuracy ground deformation estimates are derived from radar satellite imagery using InSAR, a well-established and validated remote sensing technique. InSAR is an effective tool for rapidly identifying new regions requiring ground geotechnical surveys, deriving estimates of deformation rate, extents, and evolution of deformation patterns, for validating or extending traditional ground-based measurements, and for forward-looking operational monitoring.

We present the results of InSAR ground deformation monitoring over a natural gas distribution pipeline network in Saskatchewan, Canada. At the case study site, small diameter pipelines (up to 40 years old) have been subjected to ground slumping from a retrogressive landslide affecting multiple lakeshore communities and compounded in recent years by a high water table. Some locations have recently experienced slumping at rates greater than 50 cm/yr leading to important structural issues with roads, buildings, water mains, and gas pipelines.

The ground movement analysis is based on RADARSAT-2 satellite imagery acquired at 24-day intervals over a short period in 2015. Thousands of suitable measurement points were identified over two communities on opposite shores of the lake. The measured InSAR deformation time series showed deformation toward the lake. The extents of the deformation are clearly delineated by the InSAR measurements.

Commentary by Dr. Valentin Fuster
2016;():V003T04A022. doi:10.1115/IPC2016-64515.

Land disturbance associated with the progressive expansion of a major pipeline and power corridor, along with extensive timber harvesting, triggered the reactivation of an ancient, 100 million cubic meter deep-seated landslide in northern Alberta. The landslide threatened six major transmission pipelines, and caused a loss of containment in one of the pipelines. The level of landslide activity and associated pipeline damage was surprising given the relatively subtle disturbances in relation to the massive scale of the slide. Given the very shallow 4.5 degree slope inclination and the lack of any surface expression of distress over most of the slope area, this case history underscores the importance of considering regionally specific geological conditions within pipeline geohazard evaluations. An intensive, multi-pronged program was adopted to stabilize and manage the landslide, including a series of targeted surface and ground water control measures that produced an approximate 100-fold reduction in movement rates. This demonstrates that the sensitivity of slides in the region to subtle changes is a negative factor for triggering landslides, but can also be a positive factor for stabilizing them.

Topics: Landslides
Commentary by Dr. Valentin Fuster
2016;():V003T04A023. doi:10.1115/IPC2016-64594.

Vibrating wire (VW) strain gauges have been used by the pipeline industry for over 50 years as part of landslide hazard management programs. This paper provides technical and operational guidelines for the use of these strain gauges based on 20 years of experience managing active but slow moving landslides. Guidelines are provided for the use of strain gauges during 1) routine monitoring 2) cut outs and 3) strain relief. Examples of expected strain gauge responses are provided along with technical considerations for interpreting data. Given the relatively small size of the gauges in relation to the length of pipeline within most landslides, techniques are provided to best locate the gauges including the use of 1) visual/on-site geotechnical assessments, 2) geotechnical monitoring technologies and 3) smart pigging technologies (caliper, IMU and axial strain technologies). Limitations, reliability, and alternatives to VW gauges are also discussed.

Commentary by Dr. Valentin Fuster

Operations, Monitoring and Maintenance: Operations and Maintenance

2016;():V003T04A024. doi:10.1115/IPC2016-64012.

Expeller performance has been evaluated in terms of the capability to create suction pressure at the throat. This formulation has been used to assess the effectiveness of evacuating combustible gases from an isolated, depressurized, pipeline section involving mainline block valves up to two times normal spacing with an intermediate vent stack. Additionally, the effects of elevation changes that promote buoyancy driven flows are accounted for in time as the interface between air and gas travels along the pipeline section during expelling. Two expelling strategies were introduced and assessed. These are simultaneous expelling, in which gas is expelled from the pipeline section from both ends, and sequential expelling, in which an intermediate vent stack is used to expel gas from the upstream and downstream segments. The effects of elevation changes and the location of the intermediate vent stack determine the best strategy for expelling so as to maximize the purge velocity in the section of a pipeline to be purged, while maintaining the mean flow velocity in the pipe above the minimum purge velocity to prevent air-gas stratification. It was found that for a ‘Flat-’ or a ‘Cusp-type’ elevation profile it is advantageous to follow a sequential expelling procedure using one expeller at the intermediate vent stack location. In the case of a ‘Vee-type’ elevation profile, a simultaneous expelling procedure is a better option in terms of expelling time, at the cost of needing to deploy two expellers to different sites quite far apart. Air ingress location depends on the expelling strategy and elevation profile.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T04A025. doi:10.1115/IPC2016-64076.

Natural gas accepted into the pipeline at receipt points is subject to gas quality specifications to ensure that downstream laterals and mainlines are not subjected to operational upsets, and that the integrity of the pipeline and related facilities is not compromised. One of the specifications is the maximum hydro-carbon dew point (HCDP) at the pipeline operating pressure. Occasionally, gas plants encounter operational upsets that result in a higher HCDP. If the HCDP exceeds the ground temperature, condensation of heavier hydrocarbon can potentially occur along the lateral. Ideally, after an upset has been detected and the producer has been shut in, the lateral would be pigged to remove the condensed hydrocarbons. However, if the lateral is unpiggable, the only way to remove the liquids is to evaporate them into a flow of dryer gas. The present paper compares two potential courses of action which may be taken after a high HCDP is detected at a receipt point on an unpiggable line: (a) flowing dry gas from the producer after the source of upset is corrected, or (b) pulling dryer gas back from the operator’s mainline through the lateral to the producer. In order to determine the most appropriate course of action for a given upset, the state of the lateral during and after the upset must first be accurately quantified. In the present paper, the state was modelled based on the governing equations of fluid flow including heat transfer and condensation, the GERG-2008 equation of state, and empirical liquid-hold-up equations. The effect of flow parameters (e.g., gas composition, lateral elevation profile, ground temperature, etc.) on the upset severity is explored. Subsequently, models for forward flow and pull back are presented, and the criteria for selecting when either course of action is appropriate are discussed.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T04A026. doi:10.1115/IPC2016-64104.

An experimental study was conducted to evaluate the performance of various filler materials used in Type B tight-fit and stand-off steel sleeve designs. Full-scale testing was performed to examine the performance of three filler materials and two sleeve types reinforcing four separate dents subjected to cyclic internal pressure. All filler materials were installed with the test pipe at 55°F and allowed to cure for 7 days. The metric for comparing filler material performance was stress concentration factors (SCFs) measured in the dents in the unrepaired and repaired configurations. The filler materials included a two-component epoxy, an epoxy-based grout, and a cement-based grout. The average SCF for the unreinforced dents was 5.64, while after reinforcement the average SCF was 1.2 (an average reduction of 79%).

The results of this study generated two important findings. First, the stand-off sleeve design was able to provide reinforcement similar to what was measured for the tight-fit sleeve. Second, the study determined that the cement-based grout actually slightly outperformed the epoxy-based grout, the latter being the filler material of choice prior to this study. This paper provides readers with practical information and data on the performance of competing filler material types, while also presenting a systematic method for evaluating different methods of reinforcement.

Commentary by Dr. Valentin Fuster
2016;():V003T04A027. doi:10.1115/IPC2016-64127.

In pipeline integrity threat management, the comparison of In-Line Inspection (ILI) and field results (trending) is typically used as an effective approach to determine the performance of ILI tool. ILI and field trending typically influences the integrity threat management of unmitigated features. Hence, pipeline operators should ensure collecting an adequate number of excavated ILI features from the field which are statistically relevant and represent the entire population of ILI data. The number of the trended data points is considered a sample from the entire population of ILI reported features. Nevertheless, it is considered a biased sample since it is drawn from the ILI population based on selective threat mitigation criteria. This paper describes several sampling methodologies with a focus on advantages and disadvantages of each approach. A Bayesian approach is introduced as an appropriate approach to the integrity sampling problem.

Commentary by Dr. Valentin Fuster
2016;():V003T04A028. doi:10.1115/IPC2016-64150.

The disconnect between the optimization systems of upstream production and downstream demand poses a legitimate problem for China’s refined oil industry in terms of overproduction waste. Established methods only partially model the refinery system and are unable to integrate detailed production plans or meet market demands. Therefore, the research on production scheduling optimization combined with the demand of downstream pipeline network has very real applications that not only reduce the consumption of human/material resources, but also increase economic efficiency. This paper aims to optimize the production scheduling of refined oil transportation based on the demand of downstream product pipelines by analyzing the relationships between crude oil supply, refinery facility capacities and refinery tanks storage. The new model will minimize the refined production surplus therefore minimizing refinery costs and wastage. This is done by implementing models custom designed to optimize the three subsystems of the overall process: oil product blending scheduling optimization, producing and processing equipment scheduling optimization, and mixed crude oil scheduling optimization. We first analyzed the relationship between all the production units from the crude oil to the distributional destinations of oil products. A mathematical model of the refinery production scheduling was then built with minimum total surplus inventory as the objective function. We assumed a known downstream demand and used a step by step model to optimize oil stocks. The oil blending plan, production scheduling, amount of crude oil, and refined oil mixing ratios were all derived from the model using three methods: a nonlinear method called Particle Swarm Optimization (PSO), the simplex method and the enumeration method. The evidence laid out in this paper verifies our models functionality and suggests that systems can be significantly optimized by using these methods which can provide solutions for industries with similar challenges. Optimization of the refinery’s overall production process is achieved by implementing models for each of the three distinguished subsystems: oil blending model, plant scheduling model, and the mixed crude oil refining model. The demand dictates the final production quantities. From those figures we are able to place constraining limits on the input crude oil. The refined oil production scheme is continuously enhanced by determining the amount of constituent feed on the production equipment according to the results of previous production cycle. After optimization, the minimum surplus inventory of the five oil components approach their lower limits that were calculated using our models. We compare the literature on scheduling optimization challenges both in China and abroad while providing a detailed discussion of the present situation of Chinese refineries. The interrelationships of production processes on each other are revealed by analyzing the system and breaking it down to three fundamental parts. Basing the final production predictions on the downstream demand, we are able to achieve a minimum refinery surplus inventory by utilizing a comprehensive refinery scheduling model composed of three sub-models.

Topics: Optimization
Commentary by Dr. Valentin Fuster
2016;():V003T04A029. doi:10.1115/IPC2016-64154.

Conventional pipeline maintenance and modification work requires removal of fluids from inside the pipeline section where work will be performed. In order to complete this task, the pipeline must either be depressurized (blown down) or temporarily isolated.

Depressurization can be costly because the pipeline cannot stay in service during the time of decommissioning, intervention and re-commissioning, and depend significantly on factors like pipeline size, length and pressure. As a result, valuable production is lost and downstream customers may be affected. Also, the significant environmental issues associated with the removal of pipeline inventory further escalate the overall costs and complexities of the maintenance/repair process. Depressurization might not even be an option for repair/maintenance work on long pipeline sections.

An alternative to depressurization of the entire pipeline is isolation of the pipeline section requiring maintenance or repair. This method allows the pipeline to stay in service, production downtime and loss of pipeline product are kept to a minimum, with associated environmental and economic benefits.

A wide range of methodologies, both intrusive (such as hot tapping and plugging) and non-intrusive (inline isolation plugs), can be used to isolate in-service pipeline sections. Both approaches are well accepted in the industry, with the choice of one over the other being largely governed by factors such as location and accessibility of the pipeline, operating pressures, pipeline inventory, and costs.

Some maintenance/ repair operations using isolation methods require a facility shutdown. These cases often require double barriers to safeguard personnel and facility equipment during pipeline maintenance. Although the philosophy, definition, and requirements of double barriers have been described in various international codes and standards, certain misconceptions persist surrounding double barrier terminology and its application to pipeline pressure isolation tools. The objective of this paper is to clarify the concepts of double barrier isolation, and to examine how both intrusive and non-intrusive methods can be used to provide double barrier isolation that meets the accepted requirements. The paper also addresses methods that can be used when standard isolation is not practical.

Commentary by Dr. Valentin Fuster
2016;():V003T04A030. doi:10.1115/IPC2016-64168.

This paper introduces basic research conducted to develop a numerical analysis technique for water hammer analysis. The CIP (Cubic Interpolated Profile) scheme was applied to obtain more accurate results without greatly causing a spatial interpolation error depending on the Courant number in the method of characteristics. Regarding this technique, the authors derived a well-formed error formula by applying a linear stability analysis. Characteristics of the interpolation error were clarified by comparing existing interpolation schemes with the method of characteristics. The interpolation error of CIP scheme was superior to the Spatial Linear Interpolation Scheme, was approximately equal to the Time Linear Interpolation Scheme and the cubic spline interpolation scheme with sufficient number of computational grids. The calculation efficiency of the CIP scheme was superior to the other schemes excepting the Spatial Linear Interpolation Scheme.

Topics: Water hammer
Commentary by Dr. Valentin Fuster
2016;():V003T04A031. doi:10.1115/IPC2016-64208.

An electrical Variable Frequency Drive (VFD) is a device that controls a motor by varying the frequency and voltage supplied to the motor. Frequency (or hertz) is directly related to the motor’s speed (RPMs). If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement which in turn controls the output of the connected equipment, in this case a pipeline pump (i.e. flow and pressure).

This device is important in pipeline applications as it provides the operator with improved control over the critical parameters of the pump and in doing so increases pumping efficiency while reducing energy costs.

Enbridge Liquids Pipelines has gradually introduced more VFD units on its mainline pumping systems since 1994. To date, 50% of the mainline pumps in the Enbridge Liquids Pipeline network operate under the control of a VFD. There is now sufficient historical operating data on those assets in order to quantify the benefits related to this particular system. This paper focuses on the operational reliability aspects of the VFDs and equipment controlled by the VFD. This includes failure probabilities and throughput performance over the life cycle of the system but excludes technical implications such as VFD selection, application, specification or design.

From a pure maintenance perspective, VFDs contribute to a marked improvement on pumps in terms of failure reduction. For general pump failures including components such as mechanical seals, bearings, shaft, wear rings or couplings, it is demonstrated that the probability of failure is lower on pumps combined with VFDs compared to pumps without VFDs. In terms of mean time between repairs (MTBR), this equates to an increase of 65% relative to pumps with VFDs.

All mainline pumps in Enbridge are driven by electric motors. With regards to drive motor failures, there is also a significant reduction in repairs; MTBR increases by approximately 25% on VFD driven electric motors.

Another factor which can enhance the benefits associated with VFDs is the sparing options. In Enbridge Liquids Pipelines, there are two types of sparing options related to VFDs:

• Dedicated VFDs (1 VFD controlling a single mainline pump)

• Shared VFD (1 VFD shared between a set of mainline pumps) with back-up across the line starting.

The throughput performance between the above mentioned existing options has been shown to differ substantially. On a specific pipeline built initially with shared VFDs then fitted with Dedicated VFDs, the number of pump failures decreased by 60% leading to a throughput loss reduction of 66%.

However, while the VFD helps preserve the asset it runs in conjunction with, the VFD itself introduces a high frequency of failures in the overall pumping system. For the systems studied in Enbridge pipelines, adding a VFD increases the frequency of downtime events by 118%. However, these failures are short in duration which in the long term add up to less downtime (276% less) on a pumping system with VFD.

Finally, VFD units have a high capital cost which can double the cost of ownership of a pumping system over the life cycle of the asset. However, this cost can be offset by the increase in availability provide by the VFD but this needs to be vetted through a Life Cycle Cost analysis.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T04A032. doi:10.1115/IPC2016-64210.

Blowdown is a planned or unplanned release of pressurized natural gas from stations, equipment (vessels) or pipelines. In high pressure pipelines, the blowdown leads to low temperatures within the fluid and high vent rates due to larger gas inventory volumes. Blowdown is a hazardous operation, and for this reason several methods have been proposed to improve the accuracy in the estimation of the blowdown rate and the blowdown time in pipelines. In general, these approaches include either physical volume or pipe models with numerical and analytical methods of solution. For instance, a very simple approach for the estimation of the blowdown time is presented by American Gas Association (AGA); this approach can be used a as first-approximation to verify the size of the blowdown stack/valve. Another well-known simple method to predict gas-line blowdown times was presented by Weiss, Botros and Jungowski (WBJ) (1988); this method involves the application of correction factors that regards the pipeline as a volume. However, due to the transient nature of the blowdown and the proven accuracy of their formulation, in recent years transient simulations have been performed using commercial simulation software. This work compares simplified approaches and an acknowledged transient method integrating significant effects of fluid mechanics (quasi-steady flow for one phase), heat and mass transfer and rigorous thermodynamics. This transient method is extensively used by process design engineers since it is included as a calculation tool or utility in commercial simulation software. Experimental data taken from acknowledged literature allows estimating the level of accuracy of these approaches. Due to the complexity and sometimes non-availability of the transient models included in commercial simulation software, a novel and innovative simplified hybrid approach is presented in this work. This approach includes novel and improved correlations as well as numerical solutions of a physical model that can be easily translated into a computational code or sequentially structured in a spreadsheet. This method allows for estimating relevant variables associated to the pressure – time computation and the optimal sizing of blowdown stack/valves in gas pipelines, based on recommended gas blowdown times; these times were estimated considering a balance between the maximum permissible blowdown duration and the minimum wall and fluid temperatures that can safely be contained in the pipeline. Finally, comparisons between the results obtained by using commercial software and the novel approach are presented, showing a fair level of accuracy of this method (7.6 % maximum error percentage) considering its simplicity with regard to the transient modelling.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T04A033. doi:10.1115/IPC2016-64211.

Over the past two decades, a significant amount of research has been conducted on the use of composite materials for the repair and reinforcement of pipelines. This has led to vast improvements in the quality of composite systems used for pipeline repair and has increased the range of applications for which they are viable solutions (including corrosion and mechanical damage). By using composite repair systems, pipeline operators are often able to restore the structural integrity of damaged pipelines to levels equal to or even in excess of the original undamaged pipe. Although this research has led to substantial advancements in the quality of these repair systems, there are still specific applications where questions remain regarding the strength, durability, and effectiveness of composite repair systems, especially in elevated temperature, harsh environment conditions.

This program initially involved composite repair systems from six manufacturers. The test group included both carbon and E-glass based systems. Performance based qualifications were used to reduce the size of the test group from the initial six systems down to three. The experimental study consisted of small-scale testing efforts that ranged from tensile tests performed over a range of temperatures to 10,000-hour material coupon tests at elevated temperatures. The elevated temperatures used for testing were intentionally selected by the operator to reflect the 248 °F design temperature of the target pipeline.

Using small-scale qualification testing outlined in ASME PCC-2 – Repair of Pressure Equipment and Piping standard (Article 4.1, Nonmetallic Composite Repair Systems: High-Risk Applications) as a foundation, the test program described in this paper was able to demonstrate that, when properly designed, and installed, some composite materials are able to maintain their effectiveness at high temperatures. This study combined short-term and long-term testing of composite systems and demonstrated the advantages of a 10,000 hour test when aging properties are unknown. Finally, the study showed that, although high-temperature reinforcement using composite repair systems is feasible and commercially available, this capability is not standard practice across the composite repair industry. Proper analysis and verification using experimental methods, including full scale testing should be conducted prior to installation of a composite repair system in these types of harsh conditions.

Commentary by Dr. Valentin Fuster
2016;():V003T04A034. doi:10.1115/IPC2016-64212.

This paper discusses the benefit of using single-tap double block and bleed (DBB) technology to isolate large diameter (24-inch and 36-inch) natural gas transmission lines during tie-in of a pig launcher and receiver in Surrey, British Columbia, Canada. The pipeline, which is owned by FortisBC, is the only source of supply for the city of Coquitlam, the Vancouver Island system, and a major power generation facility. As such, shutting down the line was not an option. Instead, the project required a bypass. However, the footprint of the jobsite was too small for a traditional bypass. In addition, the jobsite’s location adjacent to a major highway and a tight timeline meant that first time isolation success was mandatory.

Commentary by Dr. Valentin Fuster
2016;():V003T04A035. doi:10.1115/IPC2016-64262.

The aim of this article is to investigate uneven distribution of oil-gas two phase flow in parallel petroleum processing pipelines. On-site analysis on BZ35-2 central platform A and SZ36-1 central platform N/O (two typical platforms in China’s Bohai Bay) shows that uneven distribution is originated mainly by two sources: flow rate difference and dryness difference. A 3-dimensional numerical model of two-phase flow in T-junction before parallel processing units was built. Flow and dryness distribution under different operating conditions were simulated. It is demonstrated that unevenness of flow rate grows worse as the total flow rate increases or operating pressure difference between parallel units becomes larger. Moreover, unevenness of dryness is mainly caused by phase split in a tee. It can be concluded that the phase split will be more obvious when parallel units are located at different heights or gas volume fraction of feed stream and inlet flow rate is small. Besides, flow rate distribution has an effect on dryness distribution. There is a specific flow ratio that will cause the most serious phase split.

Finally, according to the conclusions, modification scheme for BZ35-2 central platform A piping layout was proposed. And this work may provide some guidance for process design and practical operation of parallel units.

Topics: Pipes , Petroleum
Commentary by Dr. Valentin Fuster
2016;():V003T04A036. doi:10.1115/IPC2016-64267.

Drag reduction agents (DRA) with its special properties adhering to the inner wall of gas pipeline can reduce the pipe surface roughness and turbulent velocity of gas flow. Injecting DRA into the natural gas pipeline is a potential and economical method which decreases the energy consumption and enhances gas delivery throughput. The premise that DRA can be used on site is to pass the performance test in laboratory, so reasonable DRA test system are designed through simulating the operation conditions of natural gas transmission pipelines. Emphatically improving the pumping system, atomization injection system and test pipe section. The pumping system adopts separation design pattern which can avoid various DRA samples blending drastically. The atomization injection system provides full atomized space for DRA solution which can ensure atomization injection process to carry out ideally. The test pipe section can replace quickly and ensure a higher measuring accuracy. The proposed approach above can perfect the test system for DRA used in gas transmission pipeline and can provide important guidance to the industrialized application of DRA.

Commentary by Dr. Valentin Fuster
2016;():V003T04A037. doi:10.1115/IPC2016-64311.

A study was conducted to evaluate the use of E-glass/epoxy composite materials for reinforcement of large-diameter elbows. Using a combination of sub-scale and full-scale testing, the study demonstrated that when properly designed and installed, composite materials can be used to reduce strain in reinforced elbows considering bending loads of up to 3.6 million ft-lbs (4.88 million N-m), cyclic pressures between 720 psi (4.96 MPa) and 1,440 psi (9.93 MPa), and burst testing. The stresses measured in the composite material were well below designated ASME PCC-2 design stresses for the composite materials. During testing, there was no evidence that previously applied bending loads reduced the overall burst pressure capacity of the composite-reinforced elbows. Finite element modeling was used to optimize the geometry of the composite reinforcement. The resulting design guidance from this study was used to provide direction for possible reinforcement of large-diameter elbows for in-service pipelines.

Commentary by Dr. Valentin Fuster
2016;():V003T04A038. doi:10.1115/IPC2016-64320.

Pattern recognition using correlation analysis (Cij) method is useful for non-destructive testing of physical objects, including pipes. An evaluation of the technique based on Computer Simulation Technology (CST) models has demonstrated the advantages of using the technique to detect and classify pipe wall thinning (PWT) in pipes. Given enough increments, the technique can be refined to detect any possible combination of PWT attributes. For this research 71 different simulations were modeled for purposes of calibration of the system, based on five varied properties of the modeled PWT instances. These properties include: location (29 simulations based on distance from origin and two lengths of PWT, for a total of 58 simulations), width (standardized at 25.4mm), depth (four simulations as radius of PWT at 78.74mm, 81.28mm, 83.82mm, and 86.36mm), length (four simulations as percentage of circumference: 25%, 50%, 75% and 100% circumferential PWT) and type of defect (five simulations based on five discrete profiles).

Microwaves were simulated from port 1 and port 2, with a sweeping frequency range (0.5 GHz bandwidth), analyzed as S11 and S21 for measuring and calibrating the response to the standards. The resulting waveforms became the standard patterns against which 11 unknown simulations were compared, sometimes using S11 waveforms for comparison, and at other times S21.

The correlation analysis technique was able to distinguish parameters for the unknown test cases. The technique is able to determine the correlation between the resonance frequency peak (RFP) and waveform for an unknown case, and those of nearby calibration models, via pattern recognition. For example, 0.847 and 0.872 correlations to two standard patterns for an unknown RFP which appears midway between two standard RFPs, produces a peak for the unknown that is equidistant from the RFPs for the standards.

Commentary by Dr. Valentin Fuster
2016;():V003T04A039. doi:10.1115/IPC2016-64328.

This paper describes the performance of the ultrasonic normal incidence method as a technique for inspection of the middle zone of wall thickness of LSAW (Longitude Submerged Arc Welding) steel pipes. Generally, the tandem method is applied to LSAW seam inspection of the middle zone of wall thickness. However, it is difficult to adjust the locations and angles of each probe.

Therefore, the normal incidence method using one probe for inspection of the middle zone of wall thickness was studied. Because the probe arrangement is simple, it is possible to reduce the time and effort required to adjust the probe location and angle. In the normal incidence method, it is possible to transmit and receive a mirror reflection because the ultrasonic wave is transmitted perpendicularly to a planar flaw under a high refraction angle. As a result of comparison experiments of the normal incidence method and tandem method, the amplitude of the echo from flat bottom drilled hole (F.B.H.) is 12dB higher in the normal incidence method than in the tandem method. The normal incidence method also has wide area sensitivity in the circumferential direction, however, the amplitude of the reflection echo changes ±25% when the incidence angle of the pipe changes ±0.3°. Thus, in practical applications, strict control of the deviation of the pipe incidence angle is necessary. This suggests that the reliability of this technique can be improved by compensating for sensitivity variations, for example, fluctuations associated with tracking backlash.

Commentary by Dr. Valentin Fuster
2016;():V003T04A040. doi:10.1115/IPC2016-64480.

Predicting the effects of entrapped gas or vapor formation on surge is very important in design and operation of liquid pipelines. This paper identified the scenarios in which entrapped air and vapor formation need to be considered in pipeline operation and design. Useful modeling methods utilizing common liquid pipeline transient hydraulics software are provided. Validation of the presented methods was completed using experimental data from published literature. Examples are presented in showing the implementation of the provided modeling methods on real pipeline design scenarios. Finally, advantages and limitations of the presented methods was discussed. The methods presented in this paper enable pipeline operators and design engineers to properly estimate the complicated surge issues such as the influence of air bubble venting and column separation and collapse using commonly available single phase hydraulics tools. The operators and engineers will benefit from the provided methods in finding and validating reliable surge mitigation solutions and creating pipeline design with higher integrity level. The paper also presents the limitation of the methods and continuous improvements that can be achieved in the future.

Commentary by Dr. Valentin Fuster
2016;():V003T04A041. doi:10.1115/IPC2016-64495.

This paper applies state-of-the-art integrity management and life extension methodologies to address degradation and failure modes specific to CALM buoy export terminals. The main objectives are to (1) classify the components of the export terminal according to their criticality, (2) establish risk-based inspection and maintenance plans to reduce or mitigate risk to acceptable levels and (3) assess remaining life.

The method is applied to a CALM buoy operating off the coast of Colombia. This buoy serves as the oil export terminal for all crude oil transmitted by the Ocensa pipeline, which has a capacity of 560 kBPD or around 60% of total Colombia oil production. The buoy is nearing the end of its design life, and options for life extension have been investigated based on an integrity assessment of the current condition of the equipment. As part of the assessment, detailed plans for future Risk Based Inspections (RBI) and Mitigation, Intervention, and Repair (MIR) have been developed.

Topics: Life extension , Buoys
Commentary by Dr. Valentin Fuster
2016;():V003T04A042. doi:10.1115/IPC2016-64521.

According to the 2015 AER database there are approximately 473,000 km of high pressure pipelines in Alberta alone, ∼93,000 km of which have been discontinued. Of these 93,000 km of discontinued lines approximately half have been abandoned. When a pipeline is abandoned it is typically flushed out, marked and has all corrosion protection and monitoring systems removed.

In the absence of corrosion protection all pipelines will inevitably corrode. This can create long term issues for abandoned pipelines. Two of the critical issues are potential ground subsidence and the creation of unintended water conduits. Ground subsidence is caused when an abandoned pipeline corrodes to the point of allowing the surrounding soil to fall into the empty pipe. Ground stability issues can result depending on the size and depth of the pipeline. Stability issues can appear suddenly in the form of sinkholes, slow slumping troughs or cracks in the earth and anything in between. Regarding unintended water conduits the main concern centres on a pipeline under or near water crossings or in areas of saturated soil. The pipeline corrosion can eventually provide a mechanism for water (or other constituents) to enter and migrate through the empty pipe and then be discharged further down the line. This uncontrolled migration can potentially have environmental impacts depending on what gets transported and where it ends up being discharged.

One common industry method to protect abandoned lines from the issues described above is to backfill them with foam or grout. Backfilling areas of abandoned lines can help protect against ground instability and subsidence as the line corrodes away. Creating plugs or cutting/capping abandoned pipelines can protect against the possibility of water conduits. The use of paste technology is not common to the industry in this regard however it can provide many benefits over current foams and grouts. This paper will discuss paste technology and it use as a backfill option for pipeline abandonment.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T04A043. doi:10.1115/IPC2016-64531.

The problem of identifying and forecasting potential scheduling conflicts and the impact to quality and delivery targets is a very real and complex problem. The most effective way to meet the above business objective is to develop a terminal simulation model that combines elements of a mass balance system (MBS), operational rules/procedures and operator behavioral patterns.

This paper is a case study describing the approach in designing a detailed pipeline tank terminal simulation model with an objective to identify and quantify complex and possibly unresolvable operating conflicts/events occurring given a current pipeline, tank or terminal configuration and then comparing this with other configuration options. In addition, the model will be able to measure quality impacts (measured by quantifying the volume of degraded product) that results from resolving the operating conflicts for each evaluated configuration.

We will demonstrate how the resultant model allows a terminal operator to effectively understand quality impacts to batches delivered through the pipeline tank terminal as a function of operational procedures and system configuration changes.

Commentary by Dr. Valentin Fuster
2016;():V003T04A044. doi:10.1115/IPC2016-64687.

Continuous economic development demands safe and efficient means of transporting large quantities of crude oil and other hydrocarbon products over vast extensions of land. Such transportation provides critical links between organizations and companies, permitting goods to flow between their facilities. Operation safety is paramount in transporting petroleum products in the pipeline industry. Safety can affect the performance and economics of pipeline system. Pipeline design codes also evolve as new technologies become available and management principles and practices improve. While effective operation safety requires well-trained operators, adequate operational procedures and compliance with regulatory requirements, the best way to ensure process safety is to implement safety systems during the design stage of pipeline system.

Pressure controls and overpressure protection measures are important components of a modern pipeline system. This system is intended to provide reliable control and prevent catastrophic failure of the transport system due to overpressure conditions that can occur under abnormal operating conditions. This paper discusses common pressure surge events, options of overpressure protection strategies in pipeline design and ideas on transient hydraulic analyses for pipeline systems. Different overpressure protection techniques considered herein are based on pressure relief, pressure control systems, equipment operation characteristics, and integrated system wide approach outlining complete pressure control and overpressure protection architecture for pipeline systems. Although the analyses presented in this paper are applicable across a broad range of operating conditions and different pipeline system designs, it is not possible to cover all situations and different pipeline systems have their own unique solutions. As such, sound engineering judgment and engineering principles should always be applied in any engineering design.

Topics: Design , Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T04A045. doi:10.1115/IPC2016-64691.

Oil & Natural Gas Corporation Ltd. (ONGC) operates a 42” gas pipeline that originates from an offshore platform and terminates at an onshore plant. The pipeline has operated for two decades and transmits 17% of India’s gas needs.

Unfortunately, the buried pipeline became exposed at Landfall Beach, likely due to the unpredictable impact of natural forces over a period of time. The shifting shoreline eroded resulting in the pipeline being exposed, which threatened its integrity. Stopgap arrangments were made to protect the pipeline from being hit and moved by continual tides, but that temporary measure also proved ineffective against the forces of the nature. The seasonal tropical storms worsened the situation.

ONGC rose to the challenge and decided to carry out permanent remedial measures, including re-routing of the affected segment of the pipeline and its associated station valve.

The situation presented several challenges. Because the pipeline was responsible for a large percentage of India’s gas needs, it was important to keep the pipeline live. Additionally, the worksite was a popular beach recreation area, so safety was a top priority.

ONGC contacted T.D. Williamson India Private Ltd. (TDW) for an isolation solution using double block and bleed methodogy to meet both of these concerns.

Commentary by Dr. Valentin Fuster

Materials and Joining: Crack Propagation and Arrest

2016;():V003T05A001. doi:10.1115/IPC2016-64011.

The Battelle two-curve method is widely used throughout the industry to determine the required material toughness to arrest ductile (or tearing) pipe fracture. The method relies on accurate determination of the propagation speed of the decompression wave into the pipeline once the pipe ruptures. GASDECOM is typically used for calculating this speed, and idealizes the decompression process as isentropic and one-dimensional. While GASDECOM was initially validated against quite a range of gas compositions and initial pressure and temperature, it was not developed for mixtures containing hydrogen. Two shock tube tests were conducted to experimentally determine the decompression wave speed in lean natural gas mixtures containing hydrogen. The first test had hydrogen concentration of 2.88% (mole) while the second had hydrogen concentration of 8.28% (mole). The experimentally determined decompression wave speeds from the two tests were found to be very close to each other despite the relatively vast difference in the hydrogen concentrations for the two tests. It was also shown that the predictions of the decompression wave speed using the GERG-2008 equation of state agreed very well with that obtained from the shock tube measurements. It was concluded that there is no effects of the hydrogen concentration (between 0–10% mole) on the decompression wave speed, particularly at the lower part (towards the choked pressure) of the decompression wave speed curve.

Commentary by Dr. Valentin Fuster
2016;():V003T05A002. doi:10.1115/IPC2016-64017.

Pipelines transporting compressible hydrocarbons like methane or high-vapor-pressure liquids under supercritical conditions are uniquely susceptible to long-propagating failures in the event that initiation triggers this process. The unplanned release of hydrocarbons from such pipelines poses the risk for significant pollution and/or the horrific potential of explosion and a very large fire, depending on the transported product. Accordingly, the manufacturing procedure specification (MPS) developed to ensure the design requirements are met by the steel and pipe-making process is a critical element of the fracture control plan, whose broad purpose is to protect the environment and ensure public safety, and preserve the operator’s investment in the asset.

This paper considers steel specification to avoid long-propagating shear failures in advanced-design larger-diameter higher-pressure pipelines made of thinner-wall higher-grade steels. Assuming that the arrest requirements can be reliably predicted it remains to specify the steel design, and ensure fracture control can be affected through the MPS and manufacturing procedure qualification testing (MPQT). While standards exist for use in MPQTs to establish that the MPS requirements have been met, very often CVN specimens remain unbroken, while DWTT specimens exhibit features that are inconsistent with the historic response and assumptions that underlie many standards. In addition, sub-width specimens are often used, whereas there is no standardized means to scale those results consistent with the full-width response required by some standards. Finally, empirical models such as the Battelle two curve model (BTCM) widely used to predict required arrest resistance have their roots in sub-width specimens, yet their outcome is widely expressed in a full-size context.

This paper reviews results for sub-width specimens developed for steels in the era that the BTCM was calibrated to establish scaling rules to facilitate prediction in a full-size setting. Thereafter, issues associated with the use of sub-width specimens are reviewed and criteria are developed to scale results from such testing for use in the MPS, and MPQT, which is presented as a function of toughness. Finally, issues associated with the acceptance of data from unbroken CVN specimens are reviewed, as are known issues in the interpretation of DWTT fracture surfaces.

Commentary by Dr. Valentin Fuster
2016;():V003T05A003. doi:10.1115/IPC2016-64052.

Prediction of crack arrestability of higher grade line pipe steel microalloyed with niobium in full scale burst tests based on laboratory simulation tests including Charpy impact, DWTT and CTOD is rendered difficult, as the full scale burst test is found to be far more sensitive to microstructure variables than current laboratory tests. This paper deals with nano-scale TiN-NbC composite precipitate engineering as an alternative approach to strain-induced precipitation of NbC to produce thicker gage plate or coil with enhanced toughness and resistance to ductile fracture propagation of line pipe steel. Microstructure engineering is based on identification of key microstructural parameters to which target properties can be related, and engineer the target microstructure through design of base chemistry and optimization of processing schedules. Nano-scale precipitate engineering based on control of spacing and size of TiN-NbC composite precipitate offers a new approach to achieve excellent strength and toughness (300J at −60C) of line pipe steels through control of target microstructure consisting of: (i) refinement of austenite grain size (under 30 microns) of transfer bar before pancaking, (ii) high volume fraction of acicular ferrite with adequate plasticity to increase resistance to ductile fracture propagation, (iii) high density and uniform dispersion of high angle grain boundaries that arrest micro-cracks to suppress brittle fracture initiation, (iv) less intensity of unfavorable {100}<011> texture component that facilitate the propagation of brittle fracture, (v) suppression of ultra-fine precipitates in the matrix, thereby enlarging plastic zone ahead of the crack tip to blunt the tip of the crack, and (vi) suppression of coarse brittle constituents (carbides or MA products) that initiate brittle fracture. Experimental results are presented on thermo-mechanically rolled X-90 and K-60 that validate the concept of microstructure engineering using TiN-NbC composite precipitate engineering to enhance strength and fracture toughness.

Commentary by Dr. Valentin Fuster
2016;():V003T05A004. doi:10.1115/IPC2016-64058.

Arrest of fast ductile fracture in the design of gas pipelines has traditionally been assured by specifying Charpy absorbed energy (Cv) of pipe steel based on the Battelle two-curve method. However, the Charpy test has been shown to be inadequate to characterize crack propagation in modern high-strength, high-toughness pipe steels. For steels with Cv more than approximately 100 J, fracture arrest methodologies based on Cv can lead to non-conservative predictions. The problem is that the Charpy specimen is too small to characterize full-scale fracture, and for tough steels the ductility can be so high that the Charpy specimen bends without fracturing completely. To overcome these limitations, the use of a larger full-thickness specimen, the “Drop-Weight Tear Test” (DWTT) specimen, has been proposed. The test is instrumented to measure the force on and displacement of the impactor during crack propagation. The data is interpreted to yield the “crack-tip opening angle” (CTOA), which is constant during steady-state crack growth and characterizes the propagation resistance. The CTOA has been proposed for some time as a suitable property to assess fracture propagation and arrest in high-pressure gas pipelines, but up to now a standard test method for measurement of the CTOA has not been available. To remedy this situation, a draft standard has been developed by the authors and is being balloted by ASTM E081.

In this paper, the CTOA parameter and CTOA-based fracture arrest methodology will be introduced briefly. The background and development of the draft ASTM standard test method for determination of CTOA using the drop-weight tear test (DWTT) specimen will be reviewed including the procedure and the results of an international round robin. In the CTOA test method, the only adjustable parameter is the rotation factor (rp). Using a modified Xue-Wierzbicki damage mechanics model and a statistical analysis, rp has been determined to be a weak function of yield strength, Charpy absorbed energy and specimen thickness. Although no physical model has been developed to explain the interplay of these factors, they are all related to the extent and distribution of plastic deformation ahead of the crack. The technical background and quantification of rp will be described in this paper. It is intended to apply the CTOA test method to a broad range of steels, including thin (less than 6 mm) and thick (larger than 20 mm) pipe steels.

Topics: Weight (Mass)
Commentary by Dr. Valentin Fuster
2016;():V003T05A005. doi:10.1115/IPC2016-64112.

Two full scale burst tests for the assessment of different crack arrestor designs were carried out on the pipes that will be used in the Coastal GasLink (CGL) Pipeline project. The tests supported by LNG Canada and TransCanada Technology Management Program were conducted at the Spadeadam test site of DNV GL, United Kingdom (UK), on 1219 mm (48 inch) outside diameter CSA Z245.1 Category II Grade 550 pipe at a nominal pressure of 13.38 MPa (1,940 psig) with 80% SMYS and temperature of −5°C, and with a gas representative of the richest gas envisaged for transport in the CGL pipeline project.

The reservoirs are spaced with a gap between the reservoir ends of approximately 130 m, where the test section, comprising eleven pipe lengths and a tie-in pup, was installed. The centre of the test section consisted of an 18.5 mm thick low toughness initiation pipe. The remaining pipes were referenced as 1E to 5E in the easterly direction and similarly 1W to 5W in the westerly direction. The propagation pipes (1E and 1W) with 18.5 mm wall thickness, used to establish steady-state propagation, were located immediately either side of the central initiation pipe.

For the first test, two crack arrestor pipes with 29.6 mm wall thickness were installed adjacent to the propagation pipes in the west and east directions, with a lead-in transition of 18.5 mm wall thickness for a distance of 130 mm then a 4:1 taper running back to the full pipe wall thickness. To the east, the first crack arrestor pipe had an average Charpy Vee-notch (CVN) energy of 246 J and to the west it had an average CVN energy of 341 J at the inboard end. In both directions, the fracture propagated from the initiation pipe, through the propagation pipes (1E/1W) before arresting in the first 29.6 mm thick crack arrestor pipes (2E/2W). In both directions, the arrest resulted in the fracture turning at the toe of the tapered transition on the front end of crack arrestor pipes 2E and 2W.

The pipe arrangement for the second test was similar to the first one. In the east direction, in order to optimize crack arrestor design, two 24.7 mm wall thickness pipes replaced the 29.6 mm pipes which were used in the first test. In the west direction, the test section contained four 18.5 mm wall thickness test pipes arranged with a progressively increasing Charpy energy, up to 452 J. A low toughness, 18.5 mm thick pipe (5W), with a 1.8 m long Clock Spring® crack arrestor completed the test section. To the east, the fracture propagated from the initiation pipe through pipe 1E before arresting near the inboard end of the crack arrestor pipe 2E. In the west direction, the fracture was observed to run through all four of the pipes arranged with increasing CVN energy, before being arrested by the Clock Spring® crack arrestor fitted to the fifth pipe.

Commentary by Dr. Valentin Fuster
2016;():V003T05A006. doi:10.1115/IPC2016-64119.

In recent years, considerable doubt has arisen over the prediction of the level of toughness required to arrest a propagating fracture in higher-strength line pipe. It has been clear for many years that the most widely used traditional approach, the Two-Curve Method (TCM) developed at Battelle in the early 1970s, could not be applied directly when the required toughness, expressed as full-size Charpy energy, exceeded about 80–90 J. Initially, this issue was addressed by the adoption of empirical correction factors, but more recently, there have been indications that this approach is no longer effective for modern, high-strength materials. Additional information, which in general can only be derived from well-characterized burst tests, is essential to furthering understanding of the fracture arrest problem under conditions that are typical of modern, long-distance, large-diameter pipeline design.

In the context of the Coastal GasLink (CGL) project, TransCanada has carried out a program of full-scale burst testing at the Spadeadam test site of DNV GL. The tests were supported by LNG Canada and the TransCanada Technology Management Program. These tests are described in another paper at this conference [1]. Though most of the testing was directed towards the assessment of different crack arrestor designs, one half of one test contained a run of four pipes of progressively increasing Charpy energy, up to a very high level (over 450 J). The fracture was observed to run through all four pipes, before being arrested by a crack arrestor fitted to a fifth pipe having lower toughness.

Nearly all approaches to determining requirements for fracture arrest depend, directly or indirectly, on relationships between fracture velocity (for given levels of fracture resistance) and the driving force, generally considered to be directly related to the pressure in the plane of the crack tip. By comparing measured fracture velocity with the crack tip pressure determined either directly at pressure transducer locations or by comparison with propagation velocities within the expansion wave, conclusions can be drawn regarding the accuracy of existing relationships. Most previous work regarding correction factors has been based simply on discrepancies between predicted and observed propagation and arrest behaviour. Direct comparisons of observed and predicted fracture speed potentially provide much more data and focus more clearly on where model deficiencies may lie. The current analysis focuses on comparisons with the predictions of the traditional TCM and those of a transient model developed by JFE. While data from the present work are clearly limited, this approach appears to present a way of recalibrating fracture velocity formulations that may extend the range over which traditional, Charpy-based approaches can be applied. For the future, the incorporation of additional results from other recent, well-characterized burst tests would be extremely valuable in this respect.

Commentary by Dr. Valentin Fuster
2016;():V003T05A007. doi:10.1115/IPC2016-64240.

TransCanada, on behalf of the Coastal GasLink (CGL) project, has carried out two full-scale burst tests [1, 2] at the Spadeadam test site of DNV GL, to validate the effectiveness of crack arrestors and refine the propagation control design for the large-diameter, X80 linepipe required for this project. The tests were supported by LNG Canada and TransCanada Technology Management Program. For these full-scale burst tests, Grade 550linepipe having Charpy energies from 125 to over 450 J were produced using thermomechanical controlled processing (TMCP) technology.

This paper describes propagation and arrest properties of the X80 linepipe materials having various Charpy energy values from the aspect of crack propagation energy and crack propagation speed relationships from instrumented Charpy and press-notched (PN) and static pre-cracked drop-weight tear (SPC-DWT) tests, together with in-situ observation of crack propagation by high-speed video camera. It was found that crack propagation speed is greatly affected by crack propagation energy measured by both Charpy and instrumented DWT tests. The crack propagation energy is lower in DWTT specimens with a higher separation index. It is not clear whether the crack propagation energy is only affected by the separations. However, the crack velocity is higher in DWTT specimens with a higher separation index. It is assumed that the crack propagation speed might be not only affected by separation but also low propagation energy. The testing data obtained from Charpy and instrumented DWT tests are compared with the fracture speed data measured from the full-scale burst test. The correlation between Charpy energy and crack propagation energy in DWTT is also compared with the predictions of an empirical equation.

Commentary by Dr. Valentin Fuster
2016;():V003T05A008. doi:10.1115/IPC2016-64308.

This paper describes the results of pressure vessel fracture test which called West Jefferson and/or partial gas burst testing using Grade API X65 linepipe steel with high Charpy energy that exhibits inverse facture in the Drop Weight Tear Test (DWTT).

A series of pressure vessel fracture tests which is as part of an ongoing effort by the High-strength Line Pipe committee (HLP) of the Iron and Steel Institute of Japan (ISIJ) was carried out at low temperature in order to investigate brittle-to-ductile transition behavior and to compare to DWTT fracture behavior. Two different materials on Fracture Appearance Transition Temperature (FATT) property were used in these tests. One is −60 degree C and the other is −25 to −30 degree C which is defined as 85 % shear area fraction (SA) in the standard pressed notch DWTT (PN-DWTT). The dimensions of the test pipes were 24inches (609.6 mm) in outside diameter (OD), 19.1 mm in wall thickness (WT). In each test, the test pipe is cooled by using liquid nitrogen in the cooling baths. Two cooling baths are set up separately on the two sides of the test vessel, making it possible to obtain fracture behaviors under two different test temperatures in one burst test. The test vessel was also instrumented with pressure transducers, thermocouples and timing wires to obtain the pressure at the fracture onset, temperature and crack propagation velocity, respectively.

Some informative observations to discuss appropriate evaluation method for material resistance to brittle facture propagation for high toughness linepipe materials are obtained in the test. When the pipe burst test temperatures are higher than the PN-DWTT transition temperature, ductile cracks were initiated from the initial notch and propagated with short distance in ductile manner. When the pipe burst test temperatures were lower than the PN-DWTT transition temperature, brittle cracks were initiated from the initial notch and propagated through cooling bath. However, the initiated ductile crack at lower than the transition temperature was not changed to brittle manner. This means inverse facture occurred in the PN-DWTT is a particular problem caused by the API DWTT testing method. Furthermore, results for the pipes tested indicated that inverse facture occurred in PN-DWTT at the temperature above the 85 % FATT may not affect the arrestability against the brittle fracture propagation and it is closely related with the location of brittle fracture initiation origin in the fracture appearance of PN-DWTT.

Commentary by Dr. Valentin Fuster
2016;():V003T05A009. doi:10.1115/IPC2016-64317.

Three partial gas pipe burst tests were conducted to assess the brittle-to-ductile transition temperature and brittle fracture arrestability of a heavy-walled TMCP line-pipe steel. This steel had a very high Charpy energy (400 J) which is typical of many modern line-pipe steels. In standard pressed-notch DWTT specimen tests this material exhibited abnormal fracture appearance (ductile fracture from the pressed notch prior to brittle fracture starting) that occurs with many high Charpy energy steels. Such behavior gives an invalid test by API RP 5L3, which makes the transition temperature difficult to determine.

The first burst test was conducted in a manner that is typical of a traditional West Jefferson (partial gas vessel) burst tests. The crack was initiated in the center of the cooled vessel (with a partial air gap), but an unusual result occurred. In this test a ductile fracture just barely started from each crack tip, but one of the endcaps blew off. The pipe rocketed into the wall of a containment building. The opposite endcap impacted the wall of the building and brittle fractures started there with one coming back to the center of the vessel. The implication from this test was that perhaps initiation of the brittle fracture in the base metal gives different results than if the initial crack came from a brittle location.

The second burst test used a modified West-Jefferson Burst Test procedure. The modification involved cutting a short length of pipe at the center of the vessel and rotating the seam weld to the line of crack propagation. The HAZ of the axial seam weld had a higher dynamic transition temperature. The initiation flaw was across one of the center girth welds so that one side of the initial through-wall crack had the crack tip in the base metal while the other side initiated in the seam weld HAZ. On the base metal side, the crack had about 220 mm of crack growth before reaching steady-state shear area, i.e., the shear area gradually decreased as the fracture speed was increasing. On the other side, a brittle fracture was started in the HAZ as expected, and once it crossed the other central girth weld into the base metal, the fracture immediately transformed to a lower shear area percent. These results along with those from the first burst test suggest that the DWTT specimen should have a brittle weld metal in the starter notch region to ensure the arrestability of the material.

The final burst test was at a warmer temperature. There was a short length of crack propagation with higher shear area percent, which quickly turned to ductile fracture and arrested.

In addition various modified DWTTs were conducted and results were analyzed using an alternative brittle fracture arrest criterion to predict pipe brittle fracture arrestability.

Commentary by Dr. Valentin Fuster
2016;():V003T05A010. doi:10.1115/IPC2016-64332.

Good material properties are required to ensure the safe and reliable design of oil and gas transmission pipelines. The main objective of the study, presented in this paper, is to examine the influence of high strain rates on the hardening and ductile fracture behaviour of an API 5L X70 pipeline steel by means of a combined experimental/numerical approach. For this purpose, the impact toughness of the material is assessed using instrumented Charpy V-notch (CVN) impact tests at a wide range of temperatures. To characterize the mechanical response of an X70 pipeline steel subjected to high strain rates, split Hopkinson tensile bar (SHTB) experiments are performed. These experiments allow deriving the true effective stress versus plastic strain, strain rate and temperature. Both the CVN and SHTB tests results are used for fundamental material research and constitutive material modelling. For the numerical simulations, the modified Bai-Wierzbicki (MBW) model is applied. The MBW model represents the influence of the stress state on the plastic behaviour and the onset of damage, and quantifies the microstructure degradation using a dissipation-energy based damage evolution law. The model hence allows for an accurate prediction of the ductile fracture mechanisms. The combined experimental/numerical approach is then used to simulate the upper shelf ductile fracture behaviour of an API X70 pipeline steel for high strain rate and Charpy tests. Based on the available experimental data, a new parameter set has been determined. Using these new material parameters, good correlations between numerical simulations and experimental observations have been obtained for both the split Hopkinson tensile bar tests and the Charpy impact tests.

Commentary by Dr. Valentin Fuster
2016;():V003T05A011. doi:10.1115/IPC2016-64365.

Fracture control studies for new gas transmission pipelines usually produce a specified minimum Charpy energy, often including “correction factors”, which will ensure that a crack will arrest in the body of the pipe. The basic pipeline parameters such as pressure, pipe grade, diameter and wall thickness will be fixed early in design, and the reservoir and process engineering design will set limits on the extremes of the gas composition.

The inverse case, where the gas composition in an existing pipeline is to be changed from the original design basis, is more challenging. Changes in composition can arise from ageing of the reservoir supplying a pipeline, or opportunities for the operator to generate additional revenue from 3rd party access. Sales gas specification limits for general purpose natural gas transmission often have broad limits, which can be met by a wide range of compositions.

As a wide range of gas compositions can give the same crack driving force, determining the composition limits is a “many to one” problem without a unique solution. This paper describes the derivation of an envelope of richer gas compositions which gave an acceptable probability of crack arrest in an existing pipeline which had originally been designed for a very lean gas mixture. Hence it was necessary to limit the amount of rich third party gas to ensure that the crack driving force did not increase sufficiently to propagate a long running fracture.

Manufacturing test data for the linepipe were used with the EPRG probabilistic approach to derive a characteristic Charpy energy which would achieve a 95% probability of crack arrest in 5 joints or fewer. After “uncorrecting” the high Charpy energy, the value was used with the Battelle Two Curve model to analyse a range of gas compositions and derive an envelope of acceptable compositions. Sensitivity studies were carried out to assess the effects of increasing the temperature and of expanding the limits for nitrogen and carbon dioxide beyond the initial assumptions.

It is concluded that for a specific case it will be possible to solve the inverse problem and produce composition limits which will allow increased flexibility of operation whilst maintaining safety.

Commentary by Dr. Valentin Fuster
2016;():V003T05A012. doi:10.1115/IPC2016-64456.

A third full-scale fracture propagation test has been conducted using a dense phase carbon dioxide (CO2)-rich mixture (approximately 10 mole percent of non-condensables), at the DNV GL Spadeadam Test & Research Centre, Cumbria, UK, on behalf of National Grid, UK.

The first and second tests, in 914 mm (36 inch) outside diameter pipe, also conducted at the Spadeadam Test & Research Centre, showed that predictions made using the Two Curve Model and the (notionally conservative) Wilkowski et al., 1977 correction factor were incorrect and non-conservative. An additional correction was required in order to conservatively predict the results of the two tests.

A third full-scale test was necessary to evaluate the fracture arrest capability of the line pipe for the proposed 610 mm (24 inch) outside diameter Yorkshire and Humber CCS Cross-Country Pipeline, because the predictions of the first and second tests were non-conservative, and it was unclear if and how the results of these tests could be extrapolated to a different diameter and wall thickness.

The third test was designed to be representative of the proposed cross-country pipeline, both in terms of the grade and geometry of the pipe, and the operating conditions.

The test section consisted of seven lengths of pipe: an initiation pipe and then, on either side of the initiation pipe, one transition pipe and two production pipes. The (in total) four production pipes are representative of the type of line pipe that would be used in the proposed cross-country pipeline.

A running ductile fracture was successfully initiated; it propagated through the transition pipes on both sides, and then rapidly arrested in the production pipes. The result of the test demonstrates that a running ductile fracture would arrest in the proposed Yorkshire and Humber CCS Cross-Country Pipeline.

The main experimental data, including the layout of the test section, and the decompression and timing wire data, are summarised and discussed.

Furthermore, the implications of the three tests, in two different pipe geometries, for setting toughness requirements for pipelines transporting CO2-rich mixtures in the dense phase are considered.

Commentary by Dr. Valentin Fuster
2016;():V003T05A013. doi:10.1115/IPC2016-64466.

Carbon Capture and Storage (CCS) is an approach to mitigate global warming by capturing and storing carbon dioxide (CO2) from large industrial emitters. Pipelines will play a significant role in the transportation of CO2 in CCS projects. National Grid has an interest in this, and has carried out research to investigate the requirements for the safe design and operation of CO2 pipelines.

CO2 pipelines are susceptible to long running fractures which are prevented by specifying an adequate pipe body toughness to arrest the fracture. There is no existing, validated methodology for setting pipe body toughness for pipelines transporting dense phase CO2 with impurities. The methods for estimating the pipe body toughness are semi-empirical so full scale fracture propagation tests are required to validate and extend these methods.

As part of a major research programme into pipeline transportation of dense phase CO2, National Grid conducted two full scale fracture propagation tests using 900 mm diameter pipe in 2012. The tests demonstrated that the current natural gas practices for setting pipe body toughness was incorrect and non-conservative for dense phase CO2 pipelines. National Grid recognises the importance of understanding fracture arrest as it required to ensure design code compliance, impacts on pipeline design and provides reassurance to stakeholders.

As the results of the two tests cannot be used directly to set the toughness requirements for a specific project pipeline, a third full scale test was necessary to confirm the fracture arrest capability of the pipe for the proposed pipelines.

A third full scale fracture propagation test was conducted in July 2015. A propagating ductile fracture was initiated and successfully arrested in linepipe representative of that to be used on the proposed project.

Commentary by Dr. Valentin Fuster
2016;():V003T05A014. doi:10.1115/IPC2016-64561.

In linepipe steels, there has been a growing interest in using damage mechanics that provides physical models of the fracture process which are embedded into a two- or three-dimensional finite element (FE) model. Among the various damage models, the cohesive zone model (CZM) has recently been used to simulate the ductile crack growth behavior in linepipe steels because of its computational efficiency and it requires only two parameters which can be determined in experiments. While CZM is not yet to be used as predictive tool, but it has a great application in crack arrestor design as well as in providing insight to ductile crack propagation.

In this paper, the authors have demonstrated some practical applications of CZM in linepipe steels. The CZM was used to simulate the ductile crack propagation in full-scale pipes which was able to capture the global deformation as well as the experimental crack speed. The model was then used to determine the effect of anchor blocks at the end of the pipe in a large diameter full-scale burst test. Later, the model was used to simulate two small diameter pipe tests with steel crack arrestors to mimic two arrestor cases with one showing crack propagation and the other showing crack arrest. The CZM model was also applied to demonstrate the circumferential ring-off behavior of a small diameter pipe test with rigid crack arrestor. The arrestor model was then extended to simulate a large diameter full scale Mojave burst test with “soft crack arrestor (SCA)”. A single element FE model was developed to verify the SCA material which was later extended with stain-based failure criteria. Finally, ductile crack growth in full-scale pipe with SCA was demonstrated to show that the FE CZM model can be used to optimize the design of SCA.

Commentary by Dr. Valentin Fuster
2016;():V003T05A015. doi:10.1115/IPC2016-64569.

In this paper the results will be presented for burst tests from a Joint Industry Project (JIP) on “Validation of Drop Weight Tear Test (DWTT) Methods for Brittle Fracture Control in Modern Line-Pipe Steels by Burst Testing”. The JIP members for this project were: JFE Steel as founding member, ArcelorMittal, CNPC, Dillinger, NSSMC, POSCO, Tenaris, and Tokyo Gas.

Two modified West Jefferson (partial gas) pipe burst tests were conducted to assess the brittle-to-ductile transition temperature and brittle fracture arrestability of two 48-inch diameter by 24.6-mm thick X65 TMCP line-pipe steels. These steels had very high Charpy energy (350J and 400J) which is typical of many modern line-pipe steels. In standard pressed-notch DWTT specimen tests, these materials exhibited abnormal fracture appearance (ductile fracture from the pressed notch prior to brittle fracture starting) that occurs with many high Charpy energy steels. Such behavior makes the transition temperature difficult to determine.

The shear area values versus temperature results for these two burst tests compared to various modified DWTT specimens are shown. Different rating methodologies; DNV, API, and a Best-Estimate of steady-state fracture propagation appearance were evaluated.

Commentary by Dr. Valentin Fuster
2016;():V003T05A016. doi:10.1115/IPC2016-64585.

Running fracture control is a very important technology for gas transmission pipelines with large diameter and high pressure. The Battelle two-curve (BTC) model developed in the early 1970s has been widely used in pipeline industry to determine arrest toughness in terms of the Charpy energy. Because of its semi-empirical nature and calibration with test data only for grades up to X65, the BTC does not work for higher grades. Simple corrections were thus proposed to extend the BTC model to higher grades, but limited to those grades considered. Moreover, the BTC model only predicts the minimum arrest toughness, but not arrest distance.

To fill the technical gaps, this paper proposes a modified two-curve (MTC) model and a fracture arrest distance model in reference to the Charpy energy. The MTC model coupling with an arrest distance algorithm can predict fracture arrest toughness and arrest distance in one simulation of numerical integration for a single pipe or a set of multiple pipes with given toughness. Two sets of full-scale burst test data for X70 and X80 are used to validate the proposed model, and the results show good agreements between the predictions and full-scale test data of arrest toughness and arrest distance as well. The MTC model is then applied to optimize a design of pipe segment arrangements for a mockup full-scale burst test on a high-strength pipeline steel. The MTC simulation results confirm the experimental observation that different pipe arrangements determine different arrest toughness and arrest distance for the same grade pipes.

Commentary by Dr. Valentin Fuster
2016;():V003T05A017. doi:10.1115/IPC2016-64610.

This paper reports an extension of a previous study that compared methods of evaluating J by the crack mouth opening displacement and by surface strain gradients. Here, the surface strain gradients are measured by three-dimensional digital image correlation. The results herein represent a small test matrix that involved evaluation of the J-integral for clamped single-edge notched tensile specimens from API 5L X65 base-metal, weld metal and the adjacent heat affected zone; the J-integral was evaluated by a standardized procedure utilizing the crack mouth opening displacement (CMOD) and by the contour integral method on an external surface strain contour. Digital image correlation provides sufficient full-field strain data for use by this method and is considerably more robust than surface-mounted strain gage instrumentation. A series of validity checks are presented that demonstrate that the data are useful and valuable. Experimental determination of the J-integral is not limited to thoroughly analyzed test geometries and may be achieved with limited instrumentation. Furthermore, the method described does not require a determination of crack size nor any instrumentation that requires access to the crack mouth.

Commentary by Dr. Valentin Fuster

Materials and Joining: Materials

2016;():V003T05A018. doi:10.1115/IPC2016-64021.

Much of the established data from SENT tests has been generated on ductile materials in the form of tearing resistance curves (R-curves) in terms of J. The testing of SENT specimens is now standardised in BS 8571 [1] and there is potential to use SENTs for high and low temperature tests, but there is little recently published data showing SENT behaviour at low temperature. This paper presents a comparison of fracture toughness data for equivalent SENT and SENB specimens in three different steels as ductile-to-brittle transition curves over a range of temperatures. SENT specimens in comparison to SENBs show higher fracture toughness on the upper shelf, lower transition temperature, but also a much steeper transition from ductile to brittle behaviour. It is therefore important to characterise SENT behaviour at the lowest anticipated service temperatures to ensure that this sudden change in fracture behaviour will be avoided in service.

This paper also describes methods for carrying out SENT tests at very low temperatures, including the use of threaded ends to allow testing inside a temperature controlled test chamber, while preventing the specimen from yielding at locations away from the intended notch tip.

Commentary by Dr. Valentin Fuster
2016;():V003T05A019. doi:10.1115/IPC2016-64099.

For safety reasons, the demands made on line pipe steels have been continuously increasing in recent years. The focus is on the steels’ mechanical, weldability and toughness properties, in particular. In addition to this typical pattern of increasing demands, it is also observable that customers increasingly require an integrated process and quality control system, from the steel-making process right through to ultimate plate production. Awareness of the potentials available in the production of the steel and of the plate, and their interaction in process improvement, is an essential factor in the meeting of such demands for comprehensive process control.

Both steelmaking plant and rolling-mill processes are increasingly being automated via the incorporation of sophisticated control and instrumentation technology. This creates optimum conditions for precise adjustment of these processes on the criteria of product quality.

The methods of process adjustment using the latest quality-evaluation tools, such as SILENOS (Steel Inclusion Level Evaluation by Numerical Optical Systems) and THEMiS (Testing for Heterogeneous Microinclusions and Segregation) are examined here. SILENOS is a new procedure for the assessment of steel cleanliness in which particle diameters of above 20 micron are analysed using computer-tomographic images.

A special CNC milling machine, a high-resolution scanner and a laser spectrometer examine the layers of metal by removing a large number of 10 μm layers in order to obtain a statistically correct evaluation. An automated procedure determines the concentration, size, geometry and chemical composition of the particles.

THEMiS was developed for assessment of the quality of the centre zone of slabs. Centre segregation in slabs is monitored and non-metallic inclusions evaluated simultaneously. A large number of spark-spectrometric analyses are performed perpendicular to the centreline segregation for this purpose. The classical spectrometric analyses and individual sparks are evaluated. This permits precise description of centre segregation by measurement, and also assessment of non-metallic inclusions of between 1 and 10 μm in the centre zone. The cleanliness and quality of the centre zone can then be described with very great accuracy and a new confidence level.

These specific measuring instruments are used for control of the steel-making processes at HKM (Hüttenwerke Krupp Mannnesmann) and at SMGB (Salzgitter Mannesmann Grobblech) in order to accommodate end-customers’ requirements and are directly correlated to production data and can be used for a product improvement.

This paper’s topic is the evaluation of an integrated improvement and quality assurance process extending from the very start of steel production, and including the interlinking of the properties of the cast slabs and the ultimate outcome in the form of the final plate. The benefits for the end customer and milestones along this evaluation route are examined and discussed.

Commentary by Dr. Valentin Fuster
2016;():V003T05A020. doi:10.1115/IPC2016-64143.

Large-diameter spiral-welded pipes are employed in demanding hydrocarbon pipeline applications, which require an efficient strain-based design framework. In the course of a large European project, numerical simulations on spiral-welded pipes are conducted to examine their bending deformation capacity in the presence of internal pressure referring to geohazard actions, as well as their capacity under external pressure for offshore applications in moderate deep water. Numerical models that simulate the manufacturing process (decoiling and spiral cold bending) are employed. Subsequently, the residual stresses due to cold bending are used to examine the capacity of pipe under external pressure and internally-pressurized bending. A parametric analysis is conducted to examine the effect of spiral cold forming process on the structural behavior of spiral welded pipes and the effect of internal pressure on bending capacity. The results from the present study support the argument that spiral-welded pipes can be used in demanding onshore and offshore pipeline applications.

Commentary by Dr. Valentin Fuster
2016;():V003T05A021. doi:10.1115/IPC2016-64147.

In recent years anisotropic pipe material properties have gained more interest due to offshore; strain based design and fracture arrest topics.

The effect of anisotropic UOE pipe material characteristic is analyzed in this contribution. Both, anisotropic strain dependent values (Lankford) and anisotropic strength dependent factors (Hill) are compared, and their impact on load bearing and plastic strain capacity is investigated.

Several common load cases as internal and external pressure as well as bending are investigated. An analysis of the structural behavior concerning burst pressure and transverse strain capacity, collapse pressure, maximum bending moment and critical buckling strain is performed depending on yield strength variation. Therefore the above load and strain capacities are investigated based on present material anisotropy as well as numerical parametric studies.

For the internal pressure as dominating load case, it was found that a higher yield strength in the longitudinal direction decreases burst pressure and increases transverse strain capacity. An increase of radial yield strength increases burst pressure as well as transverse strain capacity.

For collapse applications, higher radial and transverse yield strength is beneficial as well as a lower longitudinal yield strength.

Increasing longitudinal and radial yield strength leads to beneficial structural responses in terms of bending. Increase of transversal yield strength is thus not recommended as the maximum bending moment is not affected and critical buckling strain is decreased.

Further it becomes clear from the above various parametric studies that the structural behavior is prone to differ for every set of distinct anisotropic parameters and the load cases. On the other hand selection of distinct anisotropic material can promote the desired structural behavior.

Topics: Anisotropy
Commentary by Dr. Valentin Fuster
2016;():V003T05A022. doi:10.1115/IPC2016-64153.

As concerns for environmental impact of oil and gas transmission pipelines and overall public safety of the transmission pipeline systems are raised in the public domain, development of optimum toughness characteristics are a key attribute. Toughness performance as measured by charpy impact testing or drop weight tear testing (DWTT) is heavily influenced first by the average transformed grain size and more importantly the cross sectional uniformity/distribution. In addition, the crystallographic texture created can further improve or detract from the toughness performance.

The final transformed cross sectional grain size along with the uniformity/distribution is heavily influenced by the available total metallurgical reduction ratio, microalloy design, proper generation of the various recrystallization behavior types during rolling, critical per pass reductions and the final post rolling cooling rate. The final crystallographic texture is influenced by final rolling temperature, cooling rate and final cooling stop temperature. When the final cross sectional grain size and overall uniformity/distribution are marginal for optimum toughness, the addition of favorable crystallographic textures can enhance the toughness performance.

The challenge of producing optimum toughness on a thin slab caster, <100 mm thickness, is well known due to the available metallurgical reduction ratios. Typically, for API grade steels, a metallurgical reduction ratio ≥7:1 is required in order to achieve optimum toughness. However, in a thin slab caster the maximum metallurgical reduction ratios possible can be between 5:1 and 7:1 depending on the final thickness.

Nucor Steel Gallatin has been working to optimize the overall toughness of API X-grades for transmission pipeline steels in thicknesses up to 12.7 mm using their thin slab Compact Strip Production (CSP) production facility. By utilizing a proper understanding of reducing the as-cast thin slab, along with the key alloy/process attributes and recrystallization behavior kinetics during the rolling process to optimize the final transformed cross sectional grain size and more importantly the uniformity/distribution, a high level of toughness performance can be realized. In addition, a further understanding of the contribution of specific crystallographic textures can further improve the toughness performance of these grades.

This paper will discuss alloy/process parameters that have been studied and optimized to improve the low temperature toughness of API steels. In addition, toughness performance and metallographic characterization of different processing parameters will be presented.

Commentary by Dr. Valentin Fuster
2016;():V003T05A023. doi:10.1115/IPC2016-64157.

The oil and gas industry in North America operates an aging infrastructure of pipelines, 70% of which were installed prior to 1980 and almost half of which were installed during the 1950s and 1960s. There is growing interest in having knowledge of pipe properties so that a safe operating pressure can be determined, yet there are a significant number of cases where records are incomplete. Current in-line inspection (ILI) technologies focus on defect detection and characterization, such as corrosion, cracking, and the achieved probability of detection (POD). As a part of the process in assessing defect significance it is necessary to know the pipe properties, so as to determine potential failure limits. The mechanical properties (yield strength, tensile strength and fracture toughness) of steel pipe must be known or conservatively estimated in order to safely respond to the presence of detected defects in an appropriate manner and to set the operating pressure. Material property measurements such as hardness, chemical content, grain size, and microstructure can likely be used to estimate the mechanical properties of steel pipe without requiring cut-outs to be taken from pipes for destructive tests.

There are in-ditch methods of inspection available or being developed that can potentially be used to determine many of the material characteristics and at least some mechanical properties. Furthermore, there is also potential ILI data to be used for obtaining some information. Advances in ILI technologies for this purpose are currently being explored by several interested parties. ILI companies are specifically focusing on relating magnetic measurements from eddy current and magnetic flux leakage measurements to mechanical properties. ILI also regularly uses ultrasound measurements for wall thickness determination. Potential application of advances in ultrasound measurements for grain size and other properties are being explored. However, nondestructive methods of inspection in common use today usually do not enable determination of either the material or mechanical properties, leaving the only alternative to be destructive testing. This is costly, time-consuming, and often not practical for pipe that is in-service.

ILI and in-situ techniques are reviewed in this paper and provide an analysis of a sample set of data is presented. The paper explores the possibility of obtaining mechanical property data from data potentially measurable by ILI and in-situ measurements. Ideally, results would allow mechanical property measurements desired to assess pipelines so as to ensure that at a specific operating pressure there is the proper response to anomalies that might pose a significant threat. The use of a multivariate regression analysis showed better results than the traditional two-variable regression plots, and may be key to determining which properties are necessary to provide the best results for reliably estimating the mechanical properties of pipe. However, there is still much work to done in understand and account for the many sources of variability within the pipe material, and how that relates to the resultant relationships between the mechanical and material properties.

Topics: Steel , Inspection , Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T05A024. doi:10.1115/IPC2016-64179.

Higher grade linepipes such as grade X80 have been developed and applied to long distance pipelines in order to reduce the cost of pipeline construction by using thinner pipes than is possible with conventional grades. Service pressures have also been increased in recent years for efficient gas transportation. In addition to the requirement of higher strength, running ductile fracture should be prevented in long distance and high pressure pipelines. Resistance to ductile fracture, as evaluated by Charpy energy, is an important material property for higher grade linepipes.

It has been reported that bainite single-phase steel tends to show higher Charpy energy than ferrite-bainite or bainite-MA (martensite-austenite constituent) dual-phase steels, since void nucleation is suppressed in single-phase steels compared with dual-phase steels. However, in higher grade steels with a bainite single phase, a small amount of MA grains generally remains due to the chemical stability of MA. Therefore, further reduction of MA is key to improving Charpy energy for higher grade linepipe steels. In order to achieve high Charpy energy by MA formation control, the optimum conditions of the plate manufacturing process were investigated. As a result, a high Charpy energy was achieved by the combination of controlled rolling and precise control of the accelerated cooling conditions, by which the MA phase was minimized.

Based on the above investigation, grade X80 high Charpy energy linepipes were trial-produced by applying JFE Steel’s optimized accelerated cooling (ACC) system with a high cooling rate and homogeneous temperature profile. Stable higher Charpy energy was achieved by minimizing MA formation and achieving a homogeneous microstructure by advanced cooling control.

Commentary by Dr. Valentin Fuster
2016;():V003T05A025. doi:10.1115/IPC2016-64183.

Large diameter spiral welded pipes are produced from hot rolled coil. The forming of a spiral pipe out of a coil is a sequence of cold deformation steps which are: decoiling, levelling and 3-roll forming (followed by seam welding). Obviously the material experiences a quite complex deformation history since several strain reversals occur during the different steps. A further complexity is that the strain history will even vary along the thickness as it mainly concerns bending deformation. It is therefore not at all surprising that the mechanical properties on pipe and coil are different. The steel manufacturer is able to control the production of the steel within well-defined process limits. Consequently he can guarantee the properties of his product, i.e. the coil. However, the spiral pipe manufacturer only has limited possibilities to control the steel properties but eventually he is responsible for the properties of his product, i.e. the pipe. A detailed understanding of how spiral pipe forming affects the mechanical properties would definitely help steel mills to specify and target coil strength to ensure the final pipe strength. Therefore an experimental study was launched in which a 4-point bending setup was used to reproduce the different forming steps on lab scale. The mechanical properties were measured at intermediate process steps, i.e. on coil, after levelling, after pipe forming and after subsequent flattening. The last step was included because, in practice, the mechanical properties along the pipe transverse direction are typically measured using flattened tensile samples, i.e. after introduction of an additional cold deformation step with strain reversal. The advantages of this experimental approach are twofold: first, one has full control and knowledge on the deformations introduced during the different steps. Second, the typical statistical variation of mechanical properties from coil to coil or even within one coil is far less pronounced as all samples are taken within a relatively short distance from each other. For a more detailed understanding of the experimental study, an efficient Finite Element model to simulate spiral pipe forming was developed in Abaqus. A nonlinear kinematic-isotropic hardening law was applied to describe the material behavior. In this way it was possible to capture both yield point elongation and the well-known Bauschinger phenomenon. This paper summarizes numerical and experimental results for a 16mm thick X70 grade, where different production parameters (leveller settings, ratio of wall thickness to outer diameter) were considered.

Commentary by Dr. Valentin Fuster
2016;():V003T05A026. doi:10.1115/IPC2016-64192.

Due to an ever increasing endeavor for the reduction of greenhouse gas emissions over the next few decades, with a gradually increasing demand for energy world-wide and despite a society which is becoming more and more civilized and industrialized, the actual challenge in handling this problem is intensified by decreasing sources of energy, a global economic recession as well as energy market instabilities.

Replacing fossil energy sources such as oil with alternative energy concepts is at best difficult because of the high initial investment costs needed installing alternative energy concepts.

As an answer to the problems faced, the industry offers several solutions ranging from advanced technologies with a high efficiency ratio such as fuel cell and hydrogen energy, up to and including alternative new or renewable energy sources such as solar, hydro and wind power.

One of the major solutions for the transitional period to economical and reliable renewable energies is considered to be the use of Liquefied Natural Gas (LNG).

To accommodate for these requirements, Salzgitter Mannesmann Line Pipe has continuously developed highly sophisticated materials in the form of bainitic pipes for the transportation of gaseous or liquefied medium at ultra-low temperatures.

In the first part of this presentation paper the process route as well as the material and pipe properties will be shown and explained. In cooperation with our construction partner Fernwaerme-Technik (FW), the bainitic pipes were used to construct a special multi-pipe system for the conveyance of liquefied natural gas (LNG) at a temperature of −162 °C. The pipe system as well as results from the field testing is presented below and tests have been conducted on this system for three years using liquid nitrogen. It can be shown, that not only the low temperature pipe material requirements for transportation of LNG are fulfilled, moreover it offers further potential as an alternative for the replacement of expensive austenitic steels applied at temperatures down to −196°C.

Commentary by Dr. Valentin Fuster
2016;():V003T05A027. doi:10.1115/IPC2016-64299.

The drop-weight tear test (DWTT) has been widely used to evaluate the resistance of linepipe steels against long brittle fracture propagation. However, there is an ambiguity in its evaluation if the inverse fracture appears (100% shear area prior to cleavage fracture from the notch) on the DWTT fracture surfaces. Although cause of the inverse fracture is not fully understood, compressive pre-straining near the impact hammer has been discussed as a possible cause.

In the present work, DWTTs for X65, X70 and X80 were performed. In addition to conventional DWTT specimen with a pressed notch (PN), PN specimen with a back slot and specimens with a chevron notch (CN) or a static pre-cracked (SPC) were examined. The fracture appearances were compared in the different strength and in the different initial notch type. The frequency of the inverse fracture appeared in these DWTTs were different in each material and each specimen type, but there were no cases free from the inverse fracture.

The inverse fracture was investigated by fractography and the hardness profiles along the under layer of the fracture surfaces. Also, the strain histories during impact in DWTTs were measured by the digital image correlation technique based on the high-speed camera images.

The DWTT specimen purpose is to evaluate the brittle crack arrestability of the material in a pressurized linepipe. The DWTT results should be examined with a manner of a running brittle crack in a pressurized linepipe. A large scale brittle crack arrest test, so called temperature gradient ESSO test was also performed for X65 mother plate. The shear area fraction measured in DWTT fracture appearance was compared with the local shear lip thickness fraction in ESSO test. The count of the inverse fracture was discussed in comparison with the long brittle crack arrest behavior in ESSO test.

Commentary by Dr. Valentin Fuster
2016;():V003T05A028. doi:10.1115/IPC2016-64302.

Elemental segregation during continuous casting of steel is an inherent part of the solidification process. After rolling, the segregation is evident through banding of the microstructure, particularly at the centerline where the enrichment of such elements as carbon, manganese, molybdenum and chromium, may locally increase the hardenability of the steel and result in the formation of harder microstructural features. While operational steps may be taken to minimize segregation during casting, complete elimination of segregation is almost impossible. Various slab rating systems have been defined over the years which are employed as a means to measure slab quality taking into account such factors as internal cracks and segregation. While these slab rating systems were intended to aid mill operators in assessing slab quality, in recent years slab ratings have been prescribed as a means of assessing pipe quality. In this study the properties of pipe produced from a slab with Mannesmann rating of 2 are compared to those of pipe produced from a slab with a rating of 3. The work has been supplemented by microprobe analyses to measure the degree of segregation. Increased levels of Mn and Si were found at the centerline of pipe processed from the Mannesmann 3 slab. In the final pipe, these centerline bands were 10 to 20 μm in thickness and exhibited increased hardness (HV 50g) in the Mannesmann 3 pipe as compared to the Mannesmann 2 pipe. Despite evidence of increased segregation, the mechanical properties (YS, UTS, Charpy, DWTT) of both pipes comfortably met X70 property requirements.

Commentary by Dr. Valentin Fuster
2016;():V003T05A029. doi:10.1115/IPC2016-64310.

The occurrence of Hydrogen Induced Stress Cracking (HISC) is well documented in offshore pipelines constructed from duplex steel. The conditions required for HISC to occur are exposure to water, presence of a negative electrical potential from cathodic protection, and application of a high tensile stress. There is evidence that through wall HISC crack growth can occur in forgings when these conditions are present for just a few hours.

Onshore pipelines may also be constructed from duplex steel to provide corrosion resistance, particularly flowlines carrying well fluids. Where the fluid has a high pressure or low temperature, high tensile stresses may occur. These stresses are further increased at localised stress raisers such as girth welds and attachment fillet welds. The presence of water in the soil and the use of cathodic protection is likely for most buried onshore pipelines. Therefore all the conditions necessary for HISC to occur may be present.

Guidance for assessing the susceptibility of offshore duplex steels to HISC is available in DNV-RP-F112, based on laboratory testing and industry experience following failures caused by HISC. However, historically it has not been commonplace to use duplex material for onshore high pressure pipelines, so no standard guidance is available. A detailed engineering assessment is therefore required. However, many onshore design engineers may not be familiar with the HISC failure mechanism, and may not consider it at all when designing a pipeline using duplex material.

This paper discusses recent experience in applying the design rules in DNV-RP-F112 in an onshore pipeline design project.

Firstly the paper covers the conditions necessary for hydrogen generation to occur. It discusses the differences between onshore and offshore cathodic protection systems, with reference to the electrical potential required for hydrogen generation. It concludes that in some situations, control of the cathodic protection potential will be the sole barrier to hydrogen generation, and thus its reliability can be of critical importance.

Secondly the paper describes the detailed analysis required to determine peak stresses and strains at localised stress raisers, for assessment against the limits provided by DNV-RP-F112. The definition of ‘peak’ stress and strain is discussed, since this is different from the definition more commonly used (for example in fatigue analysis). The HISC phenomenon is driven by dislocation movement due to applied stress, but DNV-RP-F112 provides limits in terms of both stress and strain. A method is presented to determine strains caused exclusively by stress and not by thermal expansion or the Poisson effect.

It is concluded that some interpretation of the DNV-RP-F112 guidance is needed for application in an onshore environment. Further work, including testing, is required to demonstrate whether the DNV-RP-F112 guidance can be applied reliably onshore.

Topics: Design , Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T05A030. doi:10.1115/IPC2016-64380.

A new method is proposed combining multiple synchronized digital image correlation setups (multi-DIC) and finite element model updating to identify the hardening behaviour and anisotropy of 23.5 mm thick X70 line pipe steel. Curved tensile samples have been cut from a coil. While performing a tensile test on those samples, the force was obtained from the load cell and the back and front surface strain fields were measured by means of two synchronized stereo digital image correlation setups. The tests on the curved samples are reproduced with FE simulations, applying the same boundary conditions as the experimental setup to obtain the numerical force and strain fields. While simultaneously minimising the discrepancy between the experimentally and numerically obtained force and strain fields, the strain hardening behaviour is identified beyond the point of maximum uniform elongation.

A profound understanding of the anisotropy is also mandatory because the hot rolling operation develops substantial anisotropy which has an important influence on the line pipe performance. Due to the 23.5 mm thick steel that is used in this work, it is possible to measure the front and side surfaces with two synchronized stereo digital image correlation setups. Because full field information is available in all 3 material directions (lateral, longitudinal and through thickness direction), a 3D anisotropic yield criterion can be identified. A prerequisite for stable and accurate identification of the yield locus parameters is that the governing parameters are sufficiently sensitive to the experimentally measured response. For this purpose, a double perforated specimen has been designed which includes a side perforation. The latter guarantees the necessary through-thickness information to inversely identify the 3D anisotropic yield function through multi-DIC and finite element model updating.

The presented procedure could potentially be used by line pipe manufactures to verify whether the mechanical properties meet the specified requirements. The proposed approach has some advantages compared to conventional methods to determine mechanical properties of large diameter pipe. The curved specimen geometry is modelled in the FE simulation, hence the detrimental effects of flatting the tensile specimen can be avoided. Further, the new approach enables to consider the complete wall thickness as opposed to conventional testing with round bar samples of which a part of the wall thickness is removed during manufacturing.

Topics: Steel , Anisotropy , Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T05A031. doi:10.1115/IPC2016-64399.

In recent years, large-diameter pipe producers around the world have witnessed a growing interest to develop gas fields in arctic environments in order to fulfill the energy demand. High-strength linepipe grades are attractive for economic reasons, because they offer the benefit of a reduced wall thickness at a given operating pressure. Excellent low-temperature toughness of the material is essential under these conditions. Modern high-strength heavy plates used in the production of UOE pipes are produced by thermomechanical rolling followed by accelerated cooling (TMCP). The combination of high strength and high toughness of these steels is a result of the bainitic microstructure and is strongly influenced by the processing parameters. For this reason, the relationship between rolling and cooling parameters of heavy plate production, the low-temperature toughness and the microstructure is at the center of attention of the development efforts at Salzgitter Mannesmann Forschung (SZMF) in collaboration Salzgitter Mannesmann Grobblech (SMGB).

It has been shown previously that a variation of the processing parameters has a direct influence on the microstructure and correlates with mechanical properties that are accessible via small-scale tests. Modern characterization methods such as scanning electron microscopy in combination with electron backscatter diffraction have broadened our understanding of the underlying mechanisms and have helped to define processing conditions for the production of heavy plates with optimized low-temperature toughness in small scale tests. Within the present paper, the results of a recent laboratory investigation of the effect of a systematic variation of rolling parameters on the microstructure and low-temperature toughness of as-rolled and pre-strained Charpy specimens are discussed. In these trials, final rolling temperatures above the onset of the ferrite-austenite transformation and cooling stop temperatures above the martensite start temperature were selected. The microstructure of the plates was investigated by scanning electron microscopy and electron backscatter diffraction. In a series of Charpy tests in a specific temperature range, it was found that plate material in the as-rolled condition is not strongly sensitive to variations of the selected processing parameters, whereas pre-straining the Charpy specimens made it possible to assess the potential of individual processing concepts particularly with regard to low-temperature toughness.

In addition to Charpy testing, the toughness was also quantified via instrumented drop-weight tear (DWT) testing. By comparing total energy values from regular pressed-notch DWT-test specimens to J-integral values determined in drop-weight testing of pre-fatigued DWT-test specimens, the impact of variations of specimen type on material tearing resistance is shown.

Commentary by Dr. Valentin Fuster
2016;():V003T05A032. doi:10.1115/IPC2016-64406.

Tough market conditions have seen the price of oil drop which with the subsequent uncertainty surrounding the industry have seen the oil and gas industry concentrate on reducing the cost of designing, installing and operating pipelines. A critical process for the industry is the procurement, manufacture and installation of appropriate linepipe. The method of installation is often dictated by the pipe size and the water depth that the pipe is to be laid in, however there are times when the choice of lay method is due to vessel availability and relative costs for each technique.

In early 2014, Tata Steel successfully manufactured and delivered 16"OD × 0.875”WT X65 submerged arc welded longitudinal (SAWL) linepipe for installation via the reel lay method. Notable features about this fact were the size, which represents the thickest 16” external diameter UOE pipe yet delivered by Tata Steel, and that this was to be the first UOE pipe to be installed by the reel lay method in the North Sea. The ability to manufacture small diameter thickwall linepipe was only possible due to recent operational developments including an established tooling programme and a fully validated Finite Element (FE) model of the UOE process, along with years of experience of integrating these tools into the manufacturing process.

This paper discusses the manufacturing challenges for small diameter thickwall linepipe, and how with the aid of modelling tools, innovative thinking and previous experience in supplying small diameter thickwall linepipe into two reel-installed projects, the pipe was manufactured and delivered with the properties shown to be compliant with DNV OS-F101 Supplementary Requirement P.

Commentary by Dr. Valentin Fuster
2016;():V003T05A033. doi:10.1115/IPC2016-64509.

Niobium is a common micro-alloying addition in high-strength low-alloy (HSLA) steels primarily to add strength to the final product. Detailed quantification of the various effects of niobium is critical for understanding the microstructure evolution in the heat affected zone (HAZ) of welds. Laser ultrasonics for metallurgy (LUMet) was used to measure austenite grain growth kinetics in two experimental HSLA steels during continuous heating. For higher heating rates that are of relevance for the HAZ, grain growth during heating is negligible and grain size is determined during the brief time at the peak temperature. Thermal histories were designed based on these tests to produce a variety of microstructures relevant for various positions in the HAZ i.e. coarse and fine grain regions. It was found that the dissolution of niobium carbonitrides has a strong effect on austenite decomposition, particularily in the case of large austenite grain sizes. Nb in solution significantly depresses transformation temperatures in refinement of bainitic microstructures, significantly increasing the hardness in the coarse grained HAZ.

Topics: Steel , Pipes
Commentary by Dr. Valentin Fuster
2016;():V003T05A034. doi:10.1115/IPC2016-64553.

Many older pipelines contain significant residual stress due to the forming process. Cold expansion or a normalizing heat treatment can virtually eliminate residual forming stresses, but these practices were less common in the past. In the absence of cold expansion or normalization, residual forming stresses can be reduced by hydrostatic testing or operating pressures, but not eliminated entirely. Residual stresses can contribute to fracture in pipelines, particularly when the material toughness is low.

This article presents a series of analyses that seek to quantify the magnitude of residual forming stresses as well as their impact on pipeline integrity. The pipe forming process was simulated with elastic-plastic finite element analyses, which considered the effect of subsequent loading on relaxation of residual stresses. A second set of finite element simulations were used to quantify the effect of residual stresses on fracture behavior.

Commentary by Dr. Valentin Fuster
2016;():V003T05A035. doi:10.1115/IPC2016-64568.

The mechanical properties of six industrially produced pipeline steels equivalent to API X52, X60, and X70 specifications were evaluated in the temperature range of 200–350 °C. The steels were tested in uniaxial tension at strain rates of 10−4 and 8 × 10−4 s−1 in the as-received condition and after a low temperature 100 h aging process under a 419 MPa tensile stress. Dynamic strain aging was identified in the tensile data with the observation of serrated yielding, minima in ductility and maxima in ultimate tensile strength with respect to temperature. In addition to minima in ductility, higher strength grade steels exhibited maxima in ductility at high temperatures and greater amounts of strengthening compared to the lower strength grade, both which could be attributed to the precipitation of carbides or nitrides during tensile deformation. The low temperature aging process resulted in increased yield strength due to static strain aging, slight changes to ultimate tensile stress and, no observable change in ductility. Thus, based on the results discussed it is suggested that pipeline steels can be designed based on room temperature tensile properties, using established corrections for such properties at elevated temperatures.

Commentary by Dr. Valentin Fuster
2016;():V003T05A036. doi:10.1115/IPC2016-64632.

Pipe grade is a dominant parameter in a pipeline’s service life. Critical decisions on the design, construction, and maintenance of pipelines are made on the basis of pipe grade. The implied assumptions or expectations are that pipes of the same grade would behave similarly and the experiences with a particular grade can be applied to all pipelines of the same grade. This simplification does not adequately take into account the other characteristics that are not represented by pipe grade, but can play a critical role in the safe and economical operation of pipelines. For instance, the evolution of steel-making processes and advancements in field welding practice can lead to significant differences in weld behavior among pipes of the same nominal grade.

Most of the design, construction, and maintenance practices in the pipeline industry were established before the extensive use of modern control-rolled and microalloyed steels. With the exception of a few isolated research projects, the impacts of the fundamental changes in the steel metallurgy in modern microalloyed steels have not been systematically examined and understood. For instance, these steels may have very low strain-hardening capacity as a result of the TMCP process and may be subject to high levels of heat-affected zone (HAZ) softening due to their ultra-low carbon low-hardenability steel chemistry. HAZ softening reduces the longitudinal pipe strain capacity of girth welds, and low strain-hardening can potentially have a negative impact on tolerance to anomalies such as corrosion or mechanical damage.

This paper starts with a brief review of linepipe manufacturing history with a focus on the chemical composition and rolling practices that directly affect the mechanical properties and the response to welding thermal cycles. The characteristics of linepipes made from modern microalloyed steels are contrasted with those made from vintage hot-rolled and normalized steels. The resulting mechanical properties of these two types of materials in the presence of welding thermal cycles are presented, and compared in terms of their behavior.

The consequence of the weld characteristics is shown using examples of girth welds subjected to longitudinal strains. The implications of the pipe and weld characteristics on the design, field girth welding, and maintenance of pipelines are highlighted. Future directions and best practices in linepipe alloying and manufacturing strategies, linepipe specifications, field girth welding, and building strain-resistance girth welds are briefly described. It is emphasized that assessing the performance of pipelines based on their grades has fundamental shortfalls, and that gaps in codes and standards can lead to unexpected outcomes in pipeline integrity. In the long-run, revising relevant codes and standards is necessary to ensure consistent and reliable applications of new materials in the entire industry.

Commentary by Dr. Valentin Fuster
2016;():V003T05A037. doi:10.1115/IPC2016-64659.

Pipe elbows are frequently used in a pipeline system to change the directions. Thermal expansion and internal pressure results in bending moments on the bends causing ovalization of the initial circular cross-section. The ability of the bend to ovalize will result in an increase in the bend flexibility when compared to straight pipes [1]. In case of bends subjected to internal pressure, the pipe will start to straighten out due to the difference between the intrados and extrados surface areas. The internal pressure causes unbalanced thrust forces tending to open up the elbow depending on its stiffness and surrounding constraints. These forces tending to cause ovalization of the cross section and causing the tendency of pipe bends to open up are termed the “Bourdon effect”. If these unbalanced thrust forces are not taken into consideration, unanticipated deformations and high stress levels could occur at the elbow location that may not be accounted for in traditional stress analysis [2]. A better understanding of the influence of the Bourdon effect on the elbow design parameters is required. Past studies have investigated the behaviour of pipe elbows under closing bending moment and proposed factors that account for the increased flexibility and high stress levels resulted from ovalization. These factors are used in the current design codes [3],[4] &[5] and known as the flexibility factor and stress intensification factor.

In this investigation, pipe elbows with different nominal pipe size and various bend radiuses to internal pipe radius ratios (R/r) are studied to get a better understanding of the Bourdon effect and its influence on the pipe stresses and deformations. Differential equilibrium equations are solved to derive a mathematical model to evaluate the unbalanced thrust forces resulted from the Bourdon effect on a pipe elbow. The forces evaluated from the derived model are compared to finite element model results and showed excellent agreement. A comparison between the CSA-Z662 code and the FEA results is conducted to investigate the applicability of the stress intensification factors used in the current design code for different loading cases. The study showed that the external bending moment direction acting on the pipe has a significant effect on the distribution of stresses on the pipe elbow and significantly depending on the level of applied internal pressure.

Topics: Pipes
Commentary by Dr. Valentin Fuster
2016;():V003T05A038. doi:10.1115/IPC2016-64695.

The anisotropy of tensile properties and impact toughness of X80 ferrite-bainite pipeline steels was investigated. The lowest strength values were found in longitudinal (L) direction, medium — in the direction of wall thickness (Z-direction), the highest — in transverse (T) direction. The anisotropy of the tensile properties is low and does not change significantly with the test temperature. The maximum variation in yield stress and tensile stress do not exceed the ranges of 100 MPa and 50 MPa respectively.

The anisotropy in toughness is more clearly pronounced. Impact toughness in both T and L directions is more than 250 J/cm2 at minus 20°C while in Z-direction it is less than 30 J/cm2 at the same temperature. Low Z-direction toughness determines the susceptibility of steel to splitting during ductile fracture propagation (formation of brittle cracks parallel to the rolling plane of the plate). Microstructure and crystallographic texture analyses showed that the susceptibility to splitting is controlled by a number of factors like the predominant orientation of cleavage crystallographic planes parallel to the rolling plane, morphology of the microstructure elements, and the distribution of “second” phases.

Commentary by Dr. Valentin Fuster

Materials and Joining: Welding

2016;():V003T05A039. doi:10.1115/IPC2016-64152.

Evaluation of mechanical performance of different regions can be difficult by using standard size samples due to the size limitation of weld metal and heat-affected zone (HAZ). At first, the microstructure of different regions was characterized and quantified by Scanning Electron Microscope, which indicate that the pipeline steel is a typical acicular ferrite steel. In this study the deformation behavior of different regions (base metal, weld metal and heat affected zone) in a welded joint of API X80 pipeline steel were studied by conducting uniaxial loading tests on miniature specimens with the cross section of 2×0.5mm and gauge length of 9mm. From the results of uniaxial tension in base metal and weld metal it is shown that the welding is overmatching. Compared to the base metal, the coarse grained HAZ exhibits a lower strength, while the fine grained HAZ exhibits a higher strength. Under near zero-to-tension cyclic stress loading, all regions of the welded joints exhibit progressive accumulation of plastic strain. Under the same stress level, the base metal shows the fastest ratcheting strain accumulation, which is the result of lower strength than other regions. This fact may indicate that the ratcheting behavior of the overall welded joint is highly dependence on that of base metal for the present case. But when under the same normalized stress level (σ = σ/σYS), the fine grained HAZ has the highest ratcheting strain accumulation, while the coarse grained HAZ has the lowest ratcheting strain accumulation, which reveals that the intrinsic resistance to ratcheting is yield strength dependent.

Commentary by Dr. Valentin Fuster
2016;():V003T05A040. doi:10.1115/IPC2016-64169.

For cross country pipeline welding in Canada, welding procedures shall be qualified in accordance with the requirements of CSA Z662 Oil and Gas Pipeline Systems. For pipeline facility and fabrication welding on systems designed in accordance with CSA Z662 or ASME B31.4, welding procedures qualified in accordance with the requirements of ASME Boiler & Pressure Vessel Code Section IX are permitted and generally preferred.

Welding procedures qualified in accordance with ASME IX provide advantages for pipeline facility and fabrication applications as a result of the flexibility achieved through the larger essential variable ranges. The resulting welding procedures have broader coverage on material thickness, diameter, joint configuration and welding positions. Similarly, ASME IX is more flexible on welder performance qualification requirements and accordingly a welder will have wider range of performance qualifications. When applied correctly, the use of ASME IX welding procedures often means significantly fewer welding procedures and welder performance qualifications are required for a given scope of work.

Even though ASME IX qualified welding procedures have been widely used in pipeline facility and fabrication welding, it is not well understood on how to qualify the welding procedures in accordance with ASME IX and meet the additional requirements of the governing code or standard such as CSA Z662 in Canada. One significant consideration is that ASME IX refers to the construction code for the applicability of notch toughness requirements for welding procedure qualification, yet CSA Z662 and ASME B31.4 are both silent on notch toughness requirements for welding procedure qualification.

This paper explains one preferred method to establish and develop an effective ASME IX welding procedure qualification program for pipeline facility and fabrication welding while ensuring suitability for use and appropriate notch toughness requirements. The paper discusses topics such as base material selection, welding process, welding consumable consideration and weld test acceptance criteria.

Commentary by Dr. Valentin Fuster
2016;():V003T05A041. doi:10.1115/IPC2016-64206.

In order to maintain pipeline operation during repair and maintenance work, operators typically install branch (i.e. hot-tap) and repair fittings (i.e. sleeves) onto flowing pipelines. In-service welding procedures must be designed for these installations per code requirement. Welding induced cracking during the installation of pressure containing repair fittings is a major concern when welding onto flowing pipelines. Repair fitting dimensions influence cooling rates and restraint conditions. A combination of high stress and brittle microstructures formed during the rapid cooling of high carbon equivalent vintage pipeline steel can create conditions that promote the formation of cracks. CSA Z662 and API 1104 specify essential variables (requirements) that aim to mitigate risk of cracking by qualifying the weld procedure to equal or more severe conditions than expected in the field. These essential variables can include material carbon equivalent, cooling rate, and level of restraint limitations to be applied during qualification of the weld procedure. This paper will focus on the creation of a safe welding procedure by pre-welding assessment of the phase transformations that occur during welding on liquid product vintage pipelines and modelling the influence of readily quantifiable variables on the level of restraint induced by repair fittings.

Finite element analysis (FEA) was utilized to study the thermal history of simulated in-service weld heat affected zones to approximate the stress and strain magnitudes (level of restraint) at the fillet weld toe of simulated sleeve repairs. Thermal analysis was conducted on various weld bead geometries to simulate the effects of cooling rates and tempering. To aid in the design of a safe weld procedure, two continuous cooling transformation (CCT) diagrams were constructed from a vintage 1960s API 5L X52 pipe with a carbon equivalent of 0.51% (CEN and IIW). This enabled the selection of optimal welding parameters that produced desirable HAZ microstructures. The modeling of restraint level accounted for the thermal expansion and contraction of a multi-pass fillet weld sequence on various pipe and sleeve thicknesses. The sleeve-on-pipe configuration was compared to the plate-on-plate configuration. Sleeve wall thickness was varied from 1 to 7 times the pipe wall thickness to account for any possible instances where a very thick fitting, such as emergency fittings (e.g. STOPPLE®), may be installed on a thin pipeline. Test welds were completed on the 1960s vintage pipeline steel with a high volume water flow loop to simulate operating conditions. The heat affected zone hardness values correlated well with those predicted by the FEA and CCT results.

Commentary by Dr. Valentin Fuster
2016;():V003T05A042. doi:10.1115/IPC2016-64238.

An instrumented indentation technique is proposed as a method to directly measure the local yield strength distribution in each zone of gas metal arc welds produced in X80 linepipe. The joints were produced with different microstructures and mechanical properties by applying shielding gases with varying Ar/CO2 ratios of 50 to 15% CO2 and the addition of a pure titanium wire into the weld pool was used to achieve in-situ alloying. The local yield strength distribution for each weld zone was then measured with instrumented indentation. The mapped yield strength distributions measured by instrumented indentation was compared to the hardness distribution. In addition, the yield strength of each zone obtained by instrumented indentation were then compared to tensile test results from Digital Image Correlation (DIC), in order to obtain stress-strain curves for each microstructural zone of the weld. The yield strength results obtained from both techniques are in good agreement, suggesting that instrumented indentation can be useful method to measure the local yield strengths of specific regions in a welded joint.

Commentary by Dr. Valentin Fuster
2016;():V003T05A043. doi:10.1115/IPC2016-64305.

Continuous cooling transformation behaviour of the single cycled grain coarsened heat affected zones (GCHAZs) produced with a peak temperature (Tp) = 1350°C and cooling times, Δt800-500 = ∼ 1 to 100 s was evaluated for three different X80 pipe steels having various content of C, Mn, Ni, Cr, Mo and microalloying elements that include Nb, V and Ti. Optical microscopy was initially used to characterize the simulated GCHAZ, which consisted of a range of coarse prior austenite grains that transformed to different fractions of mainly low carbon lath martensite/fine bainite, mixtures of upper bainite and/or granular bainite as a function of increasing cooling time. A consistent trend of decreasing microhardness with increasing cooling time occurred for the range of GCHAZs formed in the pipe steels. The significant differences in GCHAZ microhardness for Δt800-500 < 15 s is attributable to the respective pipe steel compositions and the resulting microstructures. The GCHAZ microstructures were further characterized by means of scanning electron microscopy with electron backscattered diffraction and transmission electron microscopy with focus to analyze features of the transformation products, fraction of high angle boundaries and the nature of microconstituents, including carbonitride precipitates and inclusions. The simulated GCHAZ Charpy-V-notch impact energy transition curves revealed a consistent upward shift towards higher temperatures with increasing cooling time (Δt800-500 = 6, 15 and 30 s). The primary factors contributing to the variations in impact toughness of the respective GCHAZs were the differences in the microstructure, hardness and detailed features, including fraction of high angle boundaries (packet size), and the presence of various M-A microconstituents.

Topics: Heat , Steel , Pipes , Cycles
Commentary by Dr. Valentin Fuster
2016;():V003T05A044. doi:10.1115/IPC2016-64321.

X80 line pipe with high longitudinal deformability (X80HD) has been developed and applied in the Strain Based Design (SBD) of pipelines in harsh environment such as seismic areas, permafrost areas, fault zones, etc. For SBD pipelines it is critical that the pipeline girth welds overmatch the tensile properties of the pipe material to avoid local strain accumulation in the girth weld during a strain event. Also, it is important that pipeline girth welds that may experience high strains in operation have sufficient toughness to ensure adequate resistance to failure by fracture.

The objective of this research was to gain a better understanding of the influence of chemical composition and essential welding variables on microstructure and properties of the HAZ regions formed in X80HD pipeline girth welds. In this study, by using the weld thermal simulation approach, the peak temperatures (Tp, representative of the distance to the fusion boundary) and the cooling times, particularly between 800 °C and 500 °C (t8/5, representative of the weld heat input), identical to those occurring in the girth weld HAZ of three different X80HD pipe steels, were artificially reproduced. It should be noted that t8/5 is influenced by both heat input and preheat temperature. The weld peak temperatures, Tp, from 500 °C to 1300 °C, in 100 °C increment, whereas the cooling times t8/5 from 5 to 30 seconds were in 5, 15, and 30 seconds, associated with the heat input range of self-shielded flux cored arc welding (FCAW-S). The thermal simulation specimens on tensile properties, Charpy impact toughness, and Vickers hardness were tested and analyzed. Microstructures of these simulated HAZ were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). Finally, the actual FCAW-S girth welding experiments were carried out. These girth welds were subjected to different testing for evaluation of microstructure and mechanical properties of X80HD girth welded joints. These included transverse weld tensile testing, microhardness map of the weld joint, Charpy V-notch impact testing of weld metal and HAZ, and microstructure analysis. The results demonstrated that softening occurs in the fine grained HAZ (FGHAZ) and the inter-critical HAZ (ICHAZ) of X80HD line pipe girth welds. The severity of HAZ softening depends on the steel chemistry and the heat input applied during girth welding. The metallurgical design of the X80HD pipeline steel and the optimization of the girth welding procedures were proposed.

Commentary by Dr. Valentin Fuster
2016;():V003T05A045. doi:10.1115/IPC2016-64361.

The challenges associated with the welding of high-strength pipeline steels, such as X-80 and X100, are well established. While there are many filler metals that provide either adequate strength or good impact toughness, it is difficult to find products that provide both. Add to that the need for all-position welding and high deposition rates, and the options become almost non-existent.

Several years ago, Hobart® Filler Metals began working on a line of flux-cored arc welding (FCAW) consumables that are unique in the welding industry. The products have a basic slag system, but do not operate like traditional EXXXT-5 electrodes. Traditional T-5 electrodes have a low-melting, fluid slag, which makes welding out-of-position especially difficult. They also have a high level of calcium fluoride, which affects the stability of the arc and causes weld spatter. While the weld metal mechanical properties and crack-resistance are excellent, the welder appeal and ease-of-use tend to be sorely lacking in most EXXXT-5 electrodes.

The new approach utilizes aluminum for deoxidation, which has the added benefit of very clean weld deposits. The composition has been carefully optimized with appropriate levels of carbon, silicon, nickel and manganese. Alternative fluorine sources are used in place of calcium fluoride, which results in very good welder appeal and all-positional capabilities, including vertical down. The novel use of aluminum in a gas shielded process results in very low oxygen, nitrogen and sulfur content, providing exceptionally clean, tough weld deposits.

Although the new products have been produced over a range of strength levels, the primary emphasis of this paper is on E691T5-GC (E101T5-GC) and E831T5-GC (E121T5-GC) electrodes. Testing shows that tensile strength levels ranging from 700–880 MPa (100–128 ksi) can be achieved, with toughness levels of 120 J at −60°C (90 ft-lbs at −76°F) or better. The highly basic slag, combined with low weld metal hydrogen (less than 4 ml/100 gm), provides excellent resistance to cracking. The product can be used in all positions, including vertically down, making it an especially appealing choice for welding high-strength pipe.

Commentary by Dr. Valentin Fuster
2016;():V003T05A046. doi:10.1115/IPC2016-64384.

Whilst there is extensive industry experience of under pressure welding onto operational natural gas and liquid pipelines, there is limited experience for Carbon Dioxide (CO2) pipelines, either in the gaseous or dense phase. National Grid has performed a detailed research program to investigate if existing natural gas industry under pressure welding procedures are applicable to CO2 pipelines, or if new specific guidance is required.

At IPC 2014 a paper was presented (IPC2014-33223) that dealt with the results from one part of a comprehensive trial program, which defined the cooling time from 250 °C to 150 °C (T250-150) in CO2 pipelines and compared them to the typical decay times for natural gas pipelines. The results from this part of the work identified that maintaining the pre-heat using the established guidance in T/SP/P/9 during under pressure welding on dense phase CO2 pipelines would be very difficult, leading to potential operational issues.

The previous paper gave a brief summary of the effect that cooling time had on the mechanical properties. The aim of this paper is to present the findings of the T800-500 weld decay trials in more detail including the full testing programme, detailing the affect that variables such as CO2 phase, CO2 flow velocity and the welding parameters had on the weld and heat affected zone (HAZ) hardness.

The main finding is that although there is an indication that a higher cooling rate measured in the weld pool (characterized by the cooling time from 800 °C to 500 °C) leads to increased hardness in the HAZ region, there are no clear correlations. No hardness values were recorded that were considered unacceptable, even for the dense phase CO2 case which delivered the fastest cooling time. A significant finding was the requirement for controlling the buttering run procedure. A discussion of the critical aspects, including the link between weld cooling time and hardness, is presented with guidance on how this essential variables need to be controlled.

The paper is aimed at technical, safety and operational staff with CO2 pipeline operators. Read in conjunction, this paper and the previous IPC paper form a comprehensive review of this critical work that is contributing to the development of dense phase CO2 transportation pipelines and will facilitate the implementation of Carbon Capture and Storage (CCS)1 projects which is a critical part of the transition to a low carbon economy.

Commentary by Dr. Valentin Fuster
2016;():V003T05A047. doi:10.1115/IPC2016-64388.

Historically, the manual metal arc welding (MMA) process has been used for welding of full encirclement split tees on hot tap connections for gas transmission pipelines. The National Grid high pressure gas transmission network currently consists of pipelines up to and including 1219 mm outside diameter. The large diameter pipes require split tee assemblies up to 80 mm thick. The arc time to complete welding can be considerable and requires multiple welders to complete welding in one continuous operation.

The qualification of a mechanised gas shielded flux cored arc welding (GSFCAW) procedure for welding the longitudinal seams on large diameter tee connections would realise significant operational and cost benefits over the MMA method. The equipment for mechanised field welding is readily available for a large number of applications across many industries. Recent advances in the technology suggest that a suitable mechanised procedure can be developed for the longitudinal weld seams of split tee assemblies.

The primary aim of this project was to qualify a mechanised GSFCAW process and set of procedures in line with the National Grid specification for welding longitudinal seams of split tee assemblies. A comprehensive welding and test schedule was performed using 50 mm tee material. Welding was performed using the Firefly welding system in three positions, flat, overhead and horizontal to cover the full range of welding positions required for tee connections with either horizontal or vertical off-take branches.

Based on the mechanical testing and non-destructive examination (NDE) results, the combination of process and consumables used in this project have been qualified in accordance with the National Grid specification.

A number of quality issues were observed during welding and recommendations to address these have been identified. The travel speeds achieved using the GSFCAW process are up to twice those recorded when welding a similar size fitting using MMA. Even after considering the remedial work required to rectify quality issues, the overall welding times recorded using the GSFCAW process were lower than those recorded on a similar size fitting welded on site using the MMA process.

Commentary by Dr. Valentin Fuster
2016;():V003T05A048. doi:10.1115/IPC2016-64390.

Wall thickness transition joints are used to connect energy pipeline segments; such as straight pipe to fittings with different wall thicknesses. The transition joint may be subject to axial forces and bending moments that may result in a stress concentration across the transition weld and may exceed stress based design criteria. Current engineering practices, such as CSA Z662, ASME B31.4, and ASME B31.8, recommend the use of back-bevel transition welded connections. An alternative transition weld configuration is the counterbore-taper design that is intended to reduce the stress concentration across the transition.

In this study, the relative mechanical performance of these two transition design options (i.e., back-bevel and counterbore-taper) is examined with respect to the limiting burst pressure and effect of stress concentrations due to applied loads. The assessment is conducted through numerical parameter study using 3D continuum finite element methods. The numerical modelling procedures are developed using Abaqus/Standard. The performance of continuum brick elements (C3D8I, C3D8RH, C3D20R) and shell element (S4R) are evaluated. The continuum brick element (C3D8RI) was the most effective in terms of computational requirements and predictive qualities.

The burst pressure limits of the transition weld designs were evaluated through a parameter study examining the significance of pipe diameter to wall thickness ratio (D/t), wall thickness mismatch ratio (t2/t1), material Grade 415 and Grade 483 and end-cap boundary condition effects. The limit load analysis indicated the burst pressure was effectively the same for both transition weld designs. The effect of pipe diameter, D/t, t2/t1, and counterbore length on the stress concentration factor, for each transition weld design, was also assessed. The results demonstrate the improved performance of the counterbore-taper weld transition; relative to the back-bevel design as recommended by current practice, through the relative decrease in the stress concentration factor. The minimum counterbore length was found to be consistent with company recommended practices and related to the pipe diameter and wall thickness mismatch.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T05A049. doi:10.1115/IPC2016-64427.

Pipelines may experience significant longitudinal strains when subjected to large ground motions, such as seismic activity, landslides, etc. For these conditions, a strain-based design (SBD) approach can be used. The use of higher strength steels (like X80) for SBD approach can enable significant construction cost savings. Costs can be further reduced through the use of a double jointing process in order to reduce the amount of field welding. However, it is challenging to achieve adequate girth weld properties for SBD scenarios involving higher strength steels by using conventional double jointing processes such as submerged arc welding (SAW).

Acicular ferrite interspersed in martensite (AFIM) has been previously identified as an advantageous high strength weld metal microstructure that can be applied in field pipeline construction. In this paper, a double jointing technology for X70+ SBD applications will be discussed. Excellent strength and toughness properties were achieved in double joint welds by using an optimized AFIM welding technology that included a tailored welding consumable wire and a high productivity GMAW-P weld process. Welding procedures are discussed along with mechanical properties achieved. Productivity comparisons suggest that a fully optimized GMAW-P welding process in the 1G-rolled welding position can have productivity comparable to a conventional SAW double jointing process.

Topics: Design , Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T05A050. doi:10.1115/IPC2016-64491.

Pipeline defects such as cracks, dents and corrosion often require permanent pressure retaining repairs. Full encirclement metallic repair sleeves with fillet-welded end connections to the pipeline are often used for this purpose. In-service failures have occurred at pressure retaining sleeves as a result of defects associated with the sleeve welds, such as hydrogen-induced cracks, undercut at the fillet welds and inadequate weld size. At present, accurate quantitative fitness for service assessments for circumferential defects in a sleeve fillet welds are difficult to carry out due to a lack of detailed stress intensity factor (SIF) solutions for finite length cracks.

The primary objective of the project presented in this paper [1] was to develop flaw acceptance criteria which will fill gaps in the available Engineering Critical Assessment procedures for metallic sleeve repairs on all grades of pipelines. SIF solutions for finite length sleeve-end fillet weld toe and root cracks were generated and used to develop parametric equations suitable for carrying out defect assessments. These equations can be used in the assessment of fatigue crack growth and/or fracture using failure assessment diagram (FAD) methods at sleeve end fillets alongside the results developed for other structural geometries in national standards. The equations were developed based on detailed finite element (FE) analyses of a wide range of sleeve end fillet weld cracking scenarios to estimate the SIFs at both the deepest point and the surface breaking point along the crack front.

Commentary by Dr. Valentin Fuster
2016;():V003T05A051. doi:10.1115/IPC2016-64549.

Microalloyed steels can achieve a good combination of strength and toughness through appropriate alloy design and thermomechanical controlled processing (TMCP). However, the mechanical properties can deteriorate as a result of the high heat input and thermal cycles that the steel experiences during welding. It is generally accepted that the portion of the heat affected zone (HAZ) adjacent to the fusion line, i.e., the coarse grain heat affected zone (CGHAZ), which is characterized by coarse grains and martensite-austenite (M-A) constituents, is the region with poorer toughness relative to the rest of the steel. In the present research work, modification to the conventional tandem submerged arc welding (TSAW) process is carried out by the addition of a cold wire during welding (CWTSAW), which induces changes to the geometry and properties of the weld joint. Microstructural analysis, mechanical property investigation and geometry analysis indicate overall improvement in the weld and the HAZ properties after cold wire addition. These improvements are explained in terms of an increase in the deposition rate and a decrease in the amount of heat introduced to the weldment. An X70 microalloyed steel was welded using both TSAW and CWTSAW processes. Charpy-V-notch impact testing and microhardness testing showed improvement in the HAZ mechanical properties for CWTSAW samples relative to TSAW samples. Microstructural analysis, using both optical microscopy and scanning electron microscopy (SEM), indicated the formation of finer prior austenite grains (PAG) and less M-A constituent within the CGHAZ of the CWTSAW samples. These improvements are due to lower actual heat introduced to the weldment and a relatively faster cooling rate.

Commentary by Dr. Valentin Fuster
2016;():V003T05A052. doi:10.1115/IPC2016-64564.

For more than two decades, CSA Z662 Annex K has provided a method for developing alternative acceptance criteria for weld flaws in mechanized welded pipelines. Increasingly, over the years, fracture mechanics practitioners have found the method overly conservative and restrictive with respect to brittle fracture criteria when compared to other accepted fracture mechanics-based engineering critical assessment ECA codes and methods. These limitations rendered the CSA Annex K method difficult to implement on pipelines constructed with materials not possessing optimal toughness and in cases requiring consideration of fracture toughness at temperatures lower than the typical minimum design metal temperature (MDMT) of −5°C. This paper presents experiences implementing CSA Z662-15 Annex K Option 2 methodology on a 610 mm diameter liquids pipeline and compares and contrasts the utility and benefits of the code revision. This pipeline required consideration for installation during winter months, necessitating installation temperatures as low as −30°C. In addition to evaluation of actual ECA results, analytical evaluations of the Option 2 methodology were also conducted considering parameters outside those used on the project.

The new Annex K Option 2 method was found to be of considerable benefit in preparation of a practical ECA. Since fracture toughness testing was conducted at the anticipated lowest installation temperature, the flaw criteria were, as expected, principally controlled by elastic/plastic crack growth consideration. The failure assessment diagram implemented into the CSA Z662-15 Annex K Option 2 provided tolerance for both longer and deeper flaws than that afforded by Option 1 (which resorts to the former 2011 Annex K method). Furthermore, the reduced restriction to the surface interaction ligament (p distance) offers additional advantages including increased flexibility in weld profile design and weld pass sequencing.

Fracture toughness (CTOD) testing of TMP pipeline steels used in the project at −30°C often produced transitional fracture toughness results. It was found that the particular project materials were quite sensitive to the level of test specimen pre-compression (an acceptable plastic straining method to reduce residual stress gradients) applied to the CTOD specimens to enhance fatigue crack-front straightness. It was found that optimizing the level of pre-compression (to achieve acceptable pre-crack straightness while minimizing plastic pre-strain) achieved a balance between fully satisfying testing requirements, providing a conservative assessment of CTOD, and facilitating a functional Annex K ECA.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2016;():V003T05A053. doi:10.1115/IPC2016-64596.

The single-edge notch tension (SENT) test is frequently used for the assessment of the integrity of welds with flaws in them; this is done since the SENT specimen has the same flaw orientation as a surface flaw in the weld, and has similar constraint that affects the brittle-to-ductile transition and upper-shelf value. Traditionally SENT specimens are machined with a rectangular cross-section from the weld, and the thickness might be reduced because of that machining operation. The toughness value of the constant thickness machined specimen is then used in a pipe fracture analysis. Of course real welds have crowns in the roots of the weldment, which are ignored in both the fracture specimen test and the pipe geometry fracture analysis. To assess the importance of the weld crown and root, SENT tests were conducted as an exploratory aspect to determine the effect on toughness. Additionally, assessment of results where the SENT specimen breaks in the weld or base metal outside the weld due to the reinforcing that is usually machined off and ignored were conducted. The use of a full-weldment cross-section in SENT testing can be done for axial seam welds or circumferential welds. The initial work was on axial seam welds, although there is ongoing work for circumferential welds as well.

Commentary by Dr. Valentin Fuster
2016;():V003T05A054. doi:10.1115/IPC2016-64614.

Transition welds joining pipes of unequal wall thickness are often used in gas and oil pipelines at road crossings, bends, fittings, and locations of class change. Pipeline operators have successively utilized a counterbore-tapered design for transition of unequal wall thickness. In the counterbore-tapered design, the wall thickness transition is moved away from a girth weld region, resulting in reduction of stress concentration near the girth weld, subsequently reducing the risk of hydrogen assisted cracking (HAC) and the driving force for fatigue crack growth.

The counterbore length (L) is an important design parameter in the design of the counterbore-tapered joint. The aim of specifying the minimum counterbore length is to ensure that any local moments caused by the interaction of longitudinal stress and the dissimilar wall thickness are satisfactorily attenuated when they reach the weld area. While determining the minimum counterbore length, the present counterbore-tapered design criteria considers the attenuation of the bending stress induced by the local moments but does not consider the bending stress magnitude. In certain cases, although the bending stress attenuation length is long, the magnitude of the bending stress is very small. The long counterbore length creates practical challenges for boring the pipe due to the limitation of boring tools. Since the magnitude of the bending stress is very small, it is not necessary to fully attenuate the bending stress. In this work, the minimum required counterbore length (L0) criteria was revised. The revised counterbore length criteria considered the magnitude of the bending stress and the stress attenuation, hence avoided the unnecessary long counterbore length. The revised criteria was based on an analytical solution and supported by detailed finite element analyses. The analyses showed that the minimum counterbore length can be greatly reduced for those cases required unnecessarily long counterbore length with negligible or small increase in the stress concentration in the weld area.

The present design method of counterbore-tapered joints allows only one value of taper angles at thickness transition, i.e., 14°. However, for some situations, creating the smoothness required with the 14° taper angle is difficult and an increase in the taper angle is preferred. In this work, it is shown that the stress concentration near the wall thickness transition and weld area for counterbore-tapered joints changes marginally by increasing taper angle from 14° to 30°.

Topics: Welded joints
Commentary by Dr. Valentin Fuster
2016;():V003T05A055. doi:10.1115/IPC2016-64629.

The mechanical properties of welds are governed by the final microstructure that develops as an interaction between the chemical composition and cooling rates produced by welding thermal cycles. For welds in modern microalloyed thermomechanically controlled processed (TMCP) pipeline steels, the microstructure and mechanical properties can be extremely sensitive to cooling rates. The development and qualification of welding procedures to achieve targeted mechanical properties is often an iterative process. Accurate knowledge of welding thermal cycles and cooling rates as a function of welding parameters is valuable for optimization of welding process development.

This paper covers the development, validation, and application of a girth welding thermal analysis tool. The core of the tool is a numerical model that has a two-dimensional, axi-symmetrical finite element procedure to simulate the transient heat transfer processes both in the weld metal and the heat affected zone (HAZ). The tool takes welding parameters, pipe and bevel geometry, and thermal properties as inputs and predicts thermal cycles and cooling rates in weld metal and HAZ. The comparison of thermal cycles between experimental measurements and the model predictions show the tool was robust and accurate.

This tool is particularly effective in understanding the thermal history and resulting microstructure and mechanical properties of welds produced with high-productivity gas metal arc welding (GMAW), such as mechanized dual-torch pulsed gas metal arc welding (DT GMAW-P). The tool was used in optimization of development and qualification of welding procedures of a DT GMAW-P process under a tight time schedule. The actual welds were fabricated according to the optimized welding procedures followed by the mechanical testing of welds. Good agreement was found between the predicted tensile properties and those from experimental tests. The welding procedures were qualified within the tight time schedule by avoiding iterative trials, and reducing the cost associated with the making of trial welds and mechanical testing by approximately 50%. This tool has also been applied in the application of essential welding variables methodology (EWVM) for X80 and X70 linepipe steels [1, 2].

Future applications of the tools include the revamp of the approach to essential variables in welding procedure qualification. In particular, the parameters affecting cooling rates may be “bundled” together towards the one critical factor affecting weld properties, i.e., cooling rate. The individual parameters may be varied beyond the limits in the current codes and standards as long as their combined effects make the cooling rate stay within a narrow band. It is expected that the same framework of approaches to GMAW processes can be extended other welding processes, such as FCAW and SMAW.

Commentary by Dr. Valentin Fuster
2016;():V003T05A056. doi:10.1115/IPC2016-64665.

Two kinds of industry trial X90 pipeline steel which had different chemical composition were chosen as experimental materials, and the grain coarsening, microstructure evolution characteristics and the variation rules of low-temperature impact toughness in weld CGHAZ of this two steel under different welding heat input were studied by physical thermal simulation technology, SEM, optical microscope and Charpy impact test. The results show that microstructure in weld CGHAZ of 1# steel is mainly bainite ferrite (BF) and most of the M/A constituents are blocky or short rod-like; the grains of 2# steel are coarse and there is much granular bainite (GB), meanwhile M/A constituents become coarse and their morphology is changing from block to elongated laths; alloy content of X90 pipeline steel under different welding heat input has great effect on the grain size of original austenite, and when heat input is lower than 2.0KJ/mm, Charpy impact toughness in CGHAZ of lower alloy content pipeline steel is good; as heat input increases, impact toughness in CGHAZ of 1# steel is on the rise, and it is high (between 260J and 300J) when heat input is between 2.0KJ/mm and 2.5KJ/mm and the scatter of impact energy is small; impact toughness of 2# steel decreases gradually and the impact energy has obvious variability.

Commentary by Dr. Valentin Fuster

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