ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V03AT00A001. doi:10.1115/PVP2017-NS3A.

This online compilation of papers from the ASME 2017 Pressure Vessels and Piping Conference (PVP2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Design and Analysis: 2nd International Symposium on Coke Drum Life Cycle Management

2017;():V03AT03A001. doi:10.1115/PVP2017-65060.

Shell bulging and cracking in coke drums have been documented for decades. Most of the literature on the subject attributes these failures to severe spatial and temporal thermal gradients that develop during the quench part of the operating cycle. While transient thermal gradients can be severe and can cause excessive stresses, they alone cannot explain all types of observed shell damage in drums. In this paper, the authors present and discuss observations that suggest that when a cooling shell contracts during quenching, the interaction of the cooling shell with the in-situ coke in the drum can induce substantial hoop and axial stresses in its wall. The manner and degree to which this resistance plays a role in causing damage appears to depend on the type of coke produced and the way drums are operated.

Topics: Coke , Failure
Commentary by Dr. Valentin Fuster
2017;():V03AT03A002. doi:10.1115/PVP2017-65066.

A novel approach to mechanical integrity was utilized for addressing failures in an old set of coke drums. Using a rigorous routine of inspections, assessments, and long-term repairs, drums which had suffered accelerated deterioration, unpredicted cracks, and loss of containment were transformed to a reliable set of vessels. Despite old age and thin walls, due to the success of this strategy and results of a fatigue test program, plans to replace these vessels were canceled and the time between turnarounds is being considered for an increase. In this paper, we describe the approach that was used and compare results from this set of drums to another set at the same facility that was managed differently.

Topics: Coke
Commentary by Dr. Valentin Fuster
2017;():V03AT03A003. doi:10.1115/PVP2017-65077.

Cracks on skirt attachment welds in coke drum fabricated in 1979 installed in a coker plant in Japan were completely repaired by the team of authors in 2016. Coke drums undergo cyclic operations typically in the temperature range from ambient temperature to about 500°C (930°F). Consequently, repetitive large thermal stress which leads to cracks is developed in skirt attachment portion of coke drum. Usually, the existence of serious cracks that need to be repaired extensively is recognized by the regular inspections such as plant turnarounds, whereas the overall schedule of turnarounds from shutdown to start-up is planned carefully in advance with consideration in terms of production loss as well. Accordingly, time constraint becomes a critical problem to consider when an appropriate countermeasure is expected. Although the authors have faced this kind of problem due to serious cracks detected at turnaround, weld repair for entire circumferential seam of skirt attachment and post weld heat treatment for the repaired area have completed satisfactorily. This paper summarizes the actual repair and inspection methods including the work flow from the planning stage in order to accomplish the repair work within the limited turnaround period and achieve the expected quality for further use.

Topics: Maintenance , Coke
Commentary by Dr. Valentin Fuster
2017;():V03AT03A004. doi:10.1115/PVP2017-65098.

Throughout the refining industry, there is a need to increase the return on investment of aging assets. Remaining life technology application and development is widely adopted to increase value from existing infrastructure and equipment. In this paper, an innovative way of continuing to utilize compromised vessels was creatively pursued. The technique and principles can be applied to vessels or equipment that is known to have shape deficiencies without having to replace sections, components, whole shells, drums, towers or casings. In this way, the costly rebuild work and greater loss of production can be avoided. Replacement was circumvented in a Delayed Coking Unit (DCU) for a Canadian oilsands upgrader.

In this case study, principles were taken from the building transportation and moving industry and applied to lifting and tilting of 145ft (44.2m) high coke drums. The ability to tilt and re-align a vessel of 14 storey (equivalent height) thin shell coke drum was believed to be possible and was subsequently performed successfully, at this location, multiple times. These were the largest coke drums in the world (at the date of their fabrication in 2006). The design and engineering issues are discussed in detail, including the techniques and analysis, stability, protection against buckling and finally; inspection and verification.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A005. doi:10.1115/PVP2017-65161.

Many of the Cr{1-1/4 to 2-1/4}-Mo{1/2 to 1} pressure vessels in the refining and petrochemical industries such as process reactors, distillation columns, separators, pressurized storage vessels, and heat exchangers are typically vertical columns, most often supported by a circular skirt. Typically, design considerations for these vessels and support skirts are for operating under continuous “steady-state” conditions, where temporary stresses due to short-term “transient” events such as start-up and shutdown are often ignored. Consequences of dynamic and cyclic loading play a very significant role in their life and performance. For Coke drums, survey data from API shows that the skirt-to-drum attachment weld and adjoining area appears to be the most problematic, frequently experiencing low-cycle fatigue cracking due to concentrated stresses.

A methodology for repairing the skirt attachment weld of Cr-Mo pressure vessels is provided. When designing a repair approach, consideration should include material and aged condition, extent and location of defects, welding process and consumables, and codes, standards, and regulatory guidelines. When repair by weld metal buildup to rebuild a skirt-attachment weld configuration is considered, weld procedure qualification and adequate mock-ups should be performed in order to ensure a sound repair. Further, when invoking a code compliant repair without post-weld heat treatment by controlled deposition welding or temper bead techniques, proper training of welder operators should be conducted to ensure the techniques are implemented properly.

A case study is provided for a Coke drum, where the original design and fabrication of the skirt attachment included an initial SAW weld metal buildup on the 2.25Cr (P5A) cone followed by an SMAW/GTAW attachment weld to the 1.25Cr skirt (P4). During a plant shutdown, a surface breaking crack was detected in the skirt to shell attachment weld by Dye Liquid Penetrant Testing (D-LPT) and confirmed with Magnetic Particle Testing (MPT). Subsequent examination by Phased Array Ultrasonic Testing (PAUT) discovered a large number of volumetric indications, oriented towards the knuckle section internally. The repair approach consisted of 1) Completely remove the existing skirt and the attachment weld (knuckle) in segments, 2) Inspect the cone for remaining flaws, 3) Excavate and repair flaws in cone using temper bead technique, 4) Rebuild knuckle area for skirt to cone attachment with an increased radius using temper bead welding techniques, 5) Install new skirt sections using controlled deposition welding technique. Temper Bead and Controlled Deposition repair welding techniques were utilized to avoid conventional post-weld heat treatment requirements, significantly improving the turn-around time in the field.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A006. doi:10.1115/PVP2017-65222.

As throughput is increased and cycle times are reduced for delayed cokers, many owners are experiencing an increased occurrence of repairs and drum failures. Typically, other equipment in the facilities are upgraded while the coker unit is left unchanged and is expected to perform under more severe cyclic conditions. The operators are required to keep increasing the throughput and decrease the cycle time to meet targeted production. Most Coke drum failures are due to the high cyclic thermal stresses. Cyclic thermal stresses along with their increased occurrence lead to premature failures and cracking. It can be shown that by adding a 3rd drum to a 2 drum unit, the drum life can be extended by several fold, possibly eliminate the need to replace the coke drums and at the same time increase throughput.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A007. doi:10.1115/PVP2017-65264.

Aging coke drums and their connected overhead piping in delayed coking units experience fatigue cracks which most commonly occur at the skirt junction and high stress pipe welds.

This paper presents 2-case studies of this new cost-effective repair methodology with fatigue resistant design upgrade. The first case study applies to coke drum weld build-up solid skirt crack repair and the second for overhead vapor line weld crack repair.

This paper presents new field repair methodology which could also improve long term fatigue resistance. It also suggests optimizing the thermal operation & thermal gradients of coke drums for further reliability improvement.

Based on FEA, successful field execution and our experience, these case studies demonstrate a long term improvement in reliability and fatigue life of the order of 2.5 to 3 or higher especially if combined with thermal operation optimization.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A008. doi:10.1115/PVP2017-65412.

Several studies recognized that cracks in delayed coke drums resulted from low cycle fatigue induced by cyclic thermal stress [1], [2], [3]. According to a coke drum survey coordinated by API in 1996 [1], there are two different areas where cracks are produced. The first zone is located at the shell to skirt weld, and the second at the bulged areas found in the cylindrical section. In the second case, from 145 coke drums 57% reported that had shell bulging problems. Of the drums that bulged, 87 % also showed cracks.

Recently, it has been reported the use of a novel weld repair procedure on bulged sections of a drum. In this repair, the bulge is overlaid with weld metal on the inside or outside on the bulge depending on the bulge shape. It has been reported that this repair procedure can stop further bulging on the shell, but detailed information about its influence has not yet been published.

Finite element analysis of several bulged patterns that were identified from some laser mappings are used to compare the level of the stress after a weld overlay repair is made. The study was carried out running a sequentially-coupled thermo-mechanical analysis. The assessment shows the influence of the thickness and the extent of the weld overlay on the level of stress on bulged coke drums. The results indicated that depending on the initial bulged shape this repair method either reduces or increases the level of the stress. When an inward deformation pattern is observed, an external reinforcement is recommended; however, when an outward deformation pattern is developed in a coke drum, an external weld overlay repair is not recommended.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A009. doi:10.1115/PVP2017-65414.

Coke drums are subjected to batch cycles processing residue from refineries and upgrading the fuel streams back to the plant for further processing. As a result of operating conditions, these vessels are subjected to severe non-uniform thermal gradients that lead to localized hot and cold spots. The predominant failure mode in the coke drum shell is therefore the natural, but unwanted, progression of bulges and corrugations and eventual cracking. According to a coke drum survey coordinated by API in 1996 from 145 coke drums, 57% were found to have shell bulging problems. A common trend to increase profitability in coke drum units is reducing operational cycle length; which aggravates bulging and cracking mechanisms on these vessels.

As part of the bulging monitoring process, laser mapping and bulge severity factor (BSF) analysis were conducted in a total of six coke drums. The vessel that exhibited the most significant bulges was subsequently instrumented with strain gauges and thermocouples in three specific regions. Finite element analyses (FEA) of the instrumented regions were performed using the laser mapping and 2-dimensional temperature gradients as inputs, and compared with the strain gauge measurements. The assessment shows the level of damage produced during operation, as well as the changes in damage from one cycle to the next. The usage factor can be used as a decision criterion by operation personnel for potential changes, as well as aiding in decision making on when to repair, replace or reinforce the sections of interest.

Topics: Fatigue , Coke
Commentary by Dr. Valentin Fuster
2017;():V03AT03A010. doi:10.1115/PVP2017-65415.

Coke drums are thin walled pressure vessels that are subjected to severe thermal cyclic operation, which causes low cycle thermal fatigue. Because of that, they are considered as the vessels with the highest failure rate in a refinery according to API survey conducted in1996.

In the last decade, a new technology in bottom blocking valve systems for coke drums has been introduced which induces a change in the traditional center feeding system to lateral feeding system; basically with the main goal to increase operators safety. Taking into account the mechanical integrity and remaining life of coke drums, the central feeding system has traditionally been considered as the best option, however; this hypothesis has not been fully demonstrated.

Two central fed coke drums were heavily instrumented with strain gauges and thermocouples in bulged zones identified after performing a bulge severity analysis (BSA). Thermocouple arrays and several strain gauges were installed in eight specific locations of the drums. This instrumentation was installed three months before installing bottom blocking valves in the drums, and consequently, changing their feeding system to lateral. A statistical analysis was performed using 40 thermal cycles of the two coke drums with central feeding system and 120 thermal cycles of the same coke drums after changing to lateral feeding system. The usage factor was estimated for each cycle considering the axial stress amplitude and a fatigue strength reduction factor of 2 for the ASME S-N design curve Fig. KD-320.2. Finally, the remaining life was estimated for each instrumented zone taking into consideration that the coke drums would have the same cumulative damage in the future.

The results show that average remaining life at instrumented zones (considering all locations) of one coke drum increased when the lateral feeding system was introduced; while the average remaining life at instrumented zones for the second coke drum remained practically unchanged after the lateral feeding system was put in to service.

Topics: Coke
Commentary by Dr. Valentin Fuster
2017;():V03AT03A011. doi:10.1115/PVP2017-65699.

Coke drum is typical industrial equipment which experiences complex thermal and mechanical cyclic load during its operation, and the thermal stress which is produced by the drastic change of temperature is the main cause of the cracking failure of coke drum. This paper aims at coke drum with 1.25Cr–0.5Mo steel, and is based on iterative algorithm. Then we simulate the process of liquid medium climbing the inner surface of coke drum in the stages of oil filling and water quenching with dynamic thermal boundary, and carry out the numerical calculation of transient temperature field of coke drum in main process stages for one operating cycle. After the comparison of simulated temperature values with the measured temperature data at several locations on the outer surface of coke drum, the appropriate equivalent coefficients of convective heat transfer will be obtained. The variation rules of transient temperature field for the key parts of coke drum are discussed. Based on the simulation results of temperature field, the thermal-structure coupling analysis of coke drum is carried out, and the variation characteristics of thermal stress on coke drum are studied later.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A012. doi:10.1115/PVP2017-65807.

It is well known that coke drums are subjected to severe operating conditions that can lead to progressive plastic strain accumulation and related fatigue damage and cracking. The difficulties of performing an insightful, useful coke drum analysis are numerous. There are a variety of uncertainties and randomness in temperature and stress during the heating and quench portions of the cycle that limits the value of conventional analysis for remaining life prediction. Further complicating the issue, the progression of damage in coke drums often involves gross plasticity, permanent dilation, and variable bulging in the pressure boundary. Since the accumulation of damage in the drum is a history (or path) dependent process, a snapshot of strain or even distortion data has limited value in quantifying damage or remaining life. Additionally, ASME Code elastic-based fatigue methods, with plasticity correction factors, that have been used for coke drum assessments in the past are technically invalid when ratcheting (incremental plastic strain accumulation) is occurring. More modern fatigue methods and damage models may be required to address the permanent irreversible damage and material degradation that is produced during cycling.

To date, there are no standard methodologies developed in the refining industry for coke drum life prediction, as is evidenced by the first edition of API Technical Report 934-G [1] (published in April 2016) as well as the limited analytical work typically performed to validate coke drums during the design phase. Simplified approaches have generally been used to attempt to define trends rather than developing more fundamental analytical insight into structural response. API 934-G [1] generally attributes cracking in the bottom cones and skirts of coke drums to cyclic thermal stresses introduced during the fill and water quench portions of the operating cycle, but indicates that weld misalignment can also be a contributor to crack initiation and propagation. In this study, the thermal-mechanical behavior of multiple coke drum skirt designs, including forged, welded, and sliding configurations is investigated using elastic and elastic-plastic finite element analysis (FEA), and corresponding fatigue life predictions are discussed for each type of design. Additionally, the effect of skirt slots is quantified. Finally, a cyclic plasticity material model is employed to establish shake-down, and a modern strain-based fatigue method is implemented, including a critical-plane approach as documented in Part 14 of API 579-1/ASME FFS-1, Fitness-For-Service, (API 579) [2], Welding Research Council (WRC) Bulletin 550 [3], and Reference [4]. These results are compared to more conventional base metal and welded fatigue predictions.

Topics: Coke , Fatigue life
Commentary by Dr. Valentin Fuster
2017;():V03AT03A013. doi:10.1115/PVP2017-65870.

Assessment of a coke drum for seismic stability is generally a well-documented load case, with ample examples and historical design experience. However, the long-term effects of non-uniform temperature distributions have in many cases led to a phenomenon in coke drums commonly referred to as the “banana effect”. The banana effect leads to out-of-plumb, and local weakening of the shell due to bulging, and creates a more vulnerable structure where the contributions of tilting angle and effective seismic loads vary with each stage of the coking cycle. This paper outlines one practical approach to this challenging problem, along with the derivations and analytical techniques necessary to support the resulting conclusions. The framework developed was able to compare the influences of tilting and seismic accelerations independently, even when acting simultaneously. Using this technique, the analysis was able to efficiently predict a relationship between an expected seismic load and the critical drum tilt angle, with only minor adjustments needed to account for non-linear vertical distribution of the shear force.

Topics: Coke , Vessels
Commentary by Dr. Valentin Fuster
2017;():V03AT03A014. doi:10.1115/PVP2017-65875.

Slide valves used to unhead coke drums have had a significant impact on the safety and efficiency of the unheading process in these vessels. Therefore, many refiners have changed to the inherently different inlet flow nozzle configurations that the slide valves have introduced. Single-side entry and dual-side entry have been common alternatives used as a result of the implementation of slide valves. Both of these configurations can depart from a centralized flow pattern and can create adverse flow and temperature distributions. Furthermore, these changes manifest themselves throughout the vessel with measureable mechanical integrity consequences in the cone, skirt, shell, and piping. This paper analyzes historic measured skin thermocouple data as a function of elevation of the coke drum. A total of three different refinery sites were included in this study; two of them having dual-side inlets, and one of them having a single-side entry. A statistical comparison was performed using the measurements focusing on the data that causes mechanical integrity problems in coke drums: temperature differences around the circumference and elevations, peak fill and peak quench rates.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A015. doi:10.1115/PVP2017-65903.

The reliability of coke drums has become a central theme to many refineries worldwide as high value products are recovered from refinery residuum. The severe thermal gradients inherent in the coking process have led to ever more frequent failures from cracks in bulges, skirts and cones, which reduce productivity and jeopardize the safe and reliable operation of coke drums. An intrinsically-safe coke drum health monitoring system rated for operation in hazardous environments, consisting of high temperature strain gauges and thermocouples was installed on a coke drum at a refinery in the United States. Specific locations identified as high risk areas through a combination of engineering analyses, inspections and historical repairs were targeted for monitoring. The health monitoring system calculates the cumulative damage and damage rates at critical locations through the quantification of thermal transient gradients and measured strains, and analyzes the trends over time. Of particular interest are two high damage events recorded with the health monitoring system that closely preceded the propagation of a through wall crack, approximately one week after the events. This paper performed a post-mortem analysis of the event, and shows how the data obtained via health monitoring systems can be used for prioritizing inspections and the potential for anticipation of failures. By analyzing damage accumulation trends from specific operational practices, the impacts of process changes on the expected life of the coke drum can be assessed. Finally, a detailed review of the maintenance and inspection records, results of the on-line Non-Destructive Examination (NDE), laser mapping, and bulged severity assessment were used to prepare a detailed inspection and repair plan for a forthcoming turnaround. The damage accumulation trends captured with an Equipment Health Monitoring System (EHMS) were used to optimize operating parameters of the coke drums referred to in this paper. This together with the execution of detailed inspection plan and comprehensive repairs are allowing a safe and reliable operation of these drums.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A016. doi:10.1115/PVP2017-66118.

Jagged cracks were observed in SA240 Type 405 stainless steel cladding of Inconel 625 overlay repaired coke drums. It is found that intergranular cracking is the dominant fracture mode in the fine-grained heat-affected zone (FGHAZ) of the boat specimens. The sensitization effect from the operation and welding thermal cycles leads to the depletion of Cr with the preferential precipitation of Cr-rich M23C6 carbides along the grain boundaries. The cladding FGHAZ has the largest frequency of grain boundaries with higher local strain levels and the highest fraction of grain boundary Cr-rich M23C6 carbides. Thermal stress distributions predicted by finite element analysis clearly show the maximum shear stress to exhibit the typical “jagged” pattern near the cracked regions. Thermal expansion coefficient and strength mismatch among the shell base metal, cladding, and overlay is believed to have caused the unique jagged maximum shear stress distribution in the cladding HAZ of Inconel 625 overlay. The magnitude of this thermal stress can reach the yield strength of the cladding at 900 °F (482 °C) service temperature, therefore, provides the driving force for the jagged cracking formation in the sensitized HAZ.

Commentary by Dr. Valentin Fuster

Design and Analysis: CFD in Design and Analysis

2017;():V03AT03A017. doi:10.1115/PVP2017-65310.

The mixture energy equation of the pipeline is developed. By introducing the mass transfer between the two phases, the two-fluid model is extended to two phase flow simulation in pipeline. Taking the space limit of the pipe in pipeline multiphase flow into account, the combined continuity equation is established to represent the interaction between phases, and a segregated solution method is promoted and adopted in this study. A numerical method coupled with phase behavior, flow pattern and hydro-thermodynamic is presented through combing mixture energy equation and two-fluid model developed in transient condition, and is used to simulate the transient-state two-phase in gas-condensate pipeline. In discretization, high-resolution scheme is adopted for conquering nonphysical oscillation caused by step distribution of air void fraction on premise of at least second accuracy. Simulation results have a good performance on the fluctuation of the pipeline multiphase flow and on depressing the dispersion and dissipation. Compared with the OLGA (a commercial software), the maximum difference of the liquid phase fraction is 0.075, the pressure is 0.08MPa and the temperature is 0.6°C.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A018. doi:10.1115/PVP2017-65669.

A three-dimensional computational fluid dynamics (CFD) model has been established for the simulations of supercritical LNG heat transfer in a horizontal tube of an intermediate fluid vaporizer (IFV). The influences of inlet pressure and mass flux on heat transfer have been studied. The predictive capabilities of different heat transfer coefficient (HTC) correlations, which is vital for the economic and reliable design of an IFV, have been evaluated. The results indicate that the Jackson correlation gives more accurate HTC predictions for supercritical LNG at the relatively small mass flux, with a maximum deviation of 10% and an average deviation of 6%; while for the cases with larger mass flux, a modification to the Jackson-Hall correlation works well. Detailed flow and heat transfer characteristics and buoyancy effect have also been analyzed. The reported findings would provide insight into the supercritical LNG vaporization process and give guidance to the design optimization of an IFV.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A019. doi:10.1115/PVP2017-66001.

During vacuum drying of used nuclear fuel canister, helium pressure is decreased to as low as 67 Pa to promote evaporation and removal of water remaining in the canister following draining operation. At low pressures associated with vacuum drying, there is a temperature jump (thermal resistance) between the solid surfaces and helium in contact with them. This temperature jump increases as the pressure decreases (rarefied condition), which contributes to the fuel assembly’s temperature increase. It is important to keep the temperature of the fuel assemblies below 400°C during vacuum drying to ensure their safety for transport and storage.

In this work, an experimental apparatus consisting of a 7×7 array of electrically heated rods maintained between two spacer plates and enclosed inside a square cross-section stainless steel pressure vessel is constructed to evaluate the temperature of the heater rods at different pressures. This geometry is relevant to a BWR fuel assembly between two consecutive spacer plates. Thermocouples are installed in each of the 49 heater rods, spacer plates and enclosure walls. They provide a complete temperature profile of the experiment. Different pressures and heat generation relevant to vacuum drying conditions are tested. The results showed that the maximum temperature of the heater rods increases as the pressure decreases. The results from these experiments will be compared to computational fluid dynamics simulations in a separate work.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A020. doi:10.1115/PVP2017-66002.

Computational fluid dynamics simulations of a 7×7 array of heated rods within a square-cross-section enclosure filled with rarefied helium are performed for heat generation rates of 50 W and 100 W and various helium pressures ranging from 105 to 50 Pa. The model represents a section of nuclear fuel assembly between two consecutive spacer plates inside a nuclear canister subjected to during vacuum drying process. A temperature jump model is applied at the solid-gas interface to incorporate the effects of gas rarefaction at low pressures. The temperature predictions from simulations are compared to measured temperatures. The results showed that when helium pressure decreased from 105 to 50 Pa, the maximum temperature of the heater rod array increased by about 14 °C. The temperatures of the hottest rod predicted by simulations are within 4°C of the measured values for all pressures. The random difference of simulated rod temperatures from the measured rod temperatures are 3.33 °C and 2.62 °C for 100 W and 50 W heat generation rate.

Commentary by Dr. Valentin Fuster

Design and Analysis: Composite Materials and Structures

2017;():V03AT03A021. doi:10.1115/PVP2017-65265.

Wrinkle bending was a vintage technique in pipeline construction for aligning pipe sections. However, this process causes severe geometry changes over the pipeline structure and thus stress concentrations are developed. These stress concentrations have the potential to cause catastrophic pipeline failure due to internal pressure cycles, seismic effects and temperature changes. Different techniques have been studied and examined to mitigate the destructive effects that wrinkle bends pose to pipeline integrity. Composite repair methods and materials have been proven as one of the most reliable and efficient technologies to repair different pipeline defects. Designing an economical composite repair for a wrinkled pipe with proper performance requires precise design considerations. Finding an economical balance can be achieved multiple ways, such as performing experimental tests or applying analytical formulas and procedures. Each of these two methods has its own drawbacks: cost, errors and time can prevent accurate experimental tests and poor accuracy. Applicability of suggested analytical design equations can render certain analyses useless. To technically and economically improve the design and application processes of composite repair systems for wrinkle bends, elastic finite element analysis (FEA) was performed. The FEA analysis was conducted to study the effects of applying composite repairs on the elastic stress concentration factor of the wrinkle section of a Grade X52 carbon steel pipe. Moreover, a nonlinear kinematic hardening material model was developed and calibrated for this same steel. An elastic-plastic FEA was implemented to evaluate the stress-strain response of a wrinkled pipe subjected to a cyclic bending loading and constant internal pressure. Different strain based fatigue life estimation approaches were used to estimate the fatigue life enhancement achieved by utilizing a proprietary composite repair installation method.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A022. doi:10.1115/PVP2017-65365.

The increase in stiffness to weight ratio and relative ease of manufacturing fibre reinforced composite pressure vessels, have put such vessels at the forefront of technology. However only limited research and specific codes pertaining exclusively to composite pressure vessel design can be found in literature. The ASME Boiler and Pressure Vessel (BPVC) Section X Code and the European design codes EN 13121-3:2016 (GRP tanks and vessels for use above ground) together with EN 13923:2005 (Filament wound FRP pressure vessels — materials, design, manufacturing and testing) are some of the few known design codes applicable to composite pressure vessels. These codes utilise both design by rule (DBR) and design by analysis (DBA) methods. The authors believe that more studies along the DBA route would benefit the composite pressure vessel design community and make it more accessible to designers and engineers. A similar scenario has already been seen in the last 10 to 15 years for steel pressure vessel design codes when DBA based on inelastic analysis was introduced. In line with these thoughts, this study compares the different design methods to prevent buckling and applies finite element analysis (FEA) to analyse a hemispherical GFRP pressure vessel head subjected to external pressure. The effect of material damage and geometrical imperfections on the final collapse failure is examined and discussed.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A023. doi:10.1115/PVP2017-65366.

Composite pipes are currently being used in a multitude of applications varying from civil to oil and gas applications. Pipes are generally connected together by means of pipe elbows that in turn are subjected to bending moment and pressure loading. This study looks into the effect of combined loading on the first ply and ultimate failure load of pipe elbows. The influence of pressure loading followed by a bending moment versus firstly applying bending moment followed by subsequent pressure loading, on the ultimate catastrophic failure, is investigated through numerical methods. The combined bending moment and pressure load ramping is also studied. Design by analysis finite element damage mechanics numerical methods are applied to investigate post first ply failure and stress redistribution. The study shows that different loading combinations can give rise to different damage mechanisms and ultimately failure loads. A safe design load envelope for a typical fibre-reinforced pipe elbow and following first ply failure and ultimate catastrophic is established and discussed.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A024. doi:10.1115/PVP2017-65764.

Nowadays, fiber reinforced composites are widely used in variety of industrial applications such as aircraft structures, automotive, pressure vessels and piping, etc. Aircraft standard fabrication process requires certain level of vacuum compaction (debulking) during the lay-up process, and a standard bagging method for curing in an autoclave. Every compacted component cured in an autoclave needs to be vacuum bagged employing edge breathers or bleeders and surface breathers. This process is repetitive and time consuming, and therefore needs further investigation. In this research, the combined effect of the removal of compaction and edge breathing on the thermomechanical behavior of plain weave woven laminated composites is studied. Tests have been conducted on 12 lamina plain weave composite specimens. Results indicated an insignificant difference on the thermomechanical properties between compacted and non-compacted specimens. Tensile, ILSS, flexural and DSC tests confirm that for the 12 lamina specimens compaction and edge breathing are not needed.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A025. doi:10.1115/PVP2017-65888.

Additive manufacturing (AM) allows for product development with light weight, fewer machining constraints, and reduced costs depending on the application. While AM is an emerging field, there is limited research on the use of AM for pressure vessels or implementation in high stress environments. Depending on the design approach and limitations of traditional material-removal fabrication techniques, AM parts can achieve high strength-to-weight ratios with reduced manufacturing efforts. Coupling AM with alternative metal and composite materials allows for unique designs that have high strength-to-weight ratios for pressure-based applications. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has conducted research on a number of these composite designs, focusing on the use of carbon fiber or metal plating with the AM materials.

Before implementing AM in field tested prototypes, JHU/APL performed strength limitation tests on AM pressure vessels (PVs) in the laboratory to prove their effectiveness. PVs constructed with varying thicknesses and coating techniques were divided into three groups, each with a uniform wall thickness that provided a congruent surface area to withstand higher pressures. These PVs were then paired with one of three coating/plating technologies, forming a trade matrix of varying AM thicknesses and plating techniques. Once fabricated and plated, these test PVs were hydro-statically tested at increasing pressure levels. This pressure testing demonstrates that the use of AM to create PVs, when paired with specific plating techniques, can result in structures with significant strength capabilities at lighter than normal PV weights.

Furthermore, JHU/APL has begun to test the AM PVs in a number of research projects. Such testing is desired because these unique parts can be easily manufactured in shapes and volumes that were previously unattainable through common manufacturing techniques. AM parts are now commonly used in air-frames; however, in higher pressure underwater scenarios AM’s capabilities are unproven. JHU/APL has begun to apply this new and emergent field to the effective design of AM PVs, which can play a significant role in the field of underwater vehicles and similar projects.

Commentary by Dr. Valentin Fuster

Design and Analysis: Design and Analysis of Bolted Joints

2017;():V03AT03A026. doi:10.1115/PVP2017-65087.

In calculating the bolt stresses under lateral loads, such as caused by the differential thermal movement between two components — problems often found in the reactor internal design, the boundary condition of the bolt is usually conservatively assumed to be in a guided-cantilever beam mode, i.e., the bolt head is not allowed to rotate. In reality, the bolt head could rotate to a certain degree and, furthermore, the bolt head could slip, a form of loosening, under the lateral loads.

A series of lateral load-deflection tests was conducted on bolts of different sizes and different lengths, with different preloads, to study the bolt behaviors, including when the bolts start to slip and what is the effect of preloading on the slippage. Furthermore, finite element studies were conducted to correlate the test results to find the proper boundary condition to be used in the bolt stress calculation.

Topics: Stress
Commentary by Dr. Valentin Fuster
2017;():V03AT03A027. doi:10.1115/PVP2017-65371.

Spiral Wound Gaskets have widespread use in the Process Industry, with adequate results in both piping and equipment applications. The current revision of ASME B16.20-2012 provides several details of gasket construction and dimensions. Paragraph 3.2.6 of the referenced standard has been the object of many discussions, and some question its effectiveness since it does not assure a suitable sealing performance. This paper proposes to address this issue showing results of sealability tests with many different sizes of gaskets. It also proposes a test protocol that could eventually rewrite Paragraph 3.2.6 with a protocol for sealability in addition to the compression evaluation.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A028. doi:10.1115/PVP2017-65439.

A lens gasket is a specific type of metallic ring gasket that is usually only deployed in high pressure gas applications where a high integrity bolted flange joint is required. Lens gaskets are not common in ASME design and there are no ASME rules that guide the design of flanges with lens gaskets, nor are there ASME standards to control lens gasket specifications.

Lens gaskets present a special challenge when determining target bolt tension values for flange assembly. For calculating target bolt tension, the gasket seating width is an important parameter. With lens gaskets, the gasket seating width depends on the applied bolt tension, therefore calculation of bolt tension is by nature an iterative process. In these flange joints, the lens gasket has spherical machined surfaces that are in contact with conical gasket seats in the flanges. At low bolt tensions, gasket contact is nearly equivalent to line contact. At high bolt tensions, finite contact widths are developed, sometimes involving plastic deformation of the gasket.

This paper will present a method that was developed to determine target bolt tension for a lens gasket bolted flange. Reference will be made to European standards that address lens gaskets, and the results of finite element analysis studies that were used to validate the calculation method will be presented. The successful deployment of the outcome of this work for all the lens gasket flange joints on a plant will be discussed.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A029. doi:10.1115/PVP2017-65506.

Nut Factor is used to establish a bolt load for a given applied torque in bolted joint assembly. In previous papers the effects of different factors influencing Nut Factor results were examined, which included the type of anti-seize, bolt and nut material, bolt diameter and amount of anti-seize applied. This paper examines those factors further and then includes additional factors which have been shown to have significant effect on the measured Nut Factor.

The knowledge of these factors has been used to adjust the proposed ASTM specification for determining Nut Factor. It is also relevant to application in the field and to ensure that any testing conducted in a laboratory will be applicable in the field.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A030. doi:10.1115/PVP2017-65507.

This paper outlines recent work in the field of pressure boundary bolted joint integrity and the effect of corrosion on bolted joint components. It summarizes recent analysis and testing which determined the risk to joint integrity or catastrophic failure associated with corrosion of the joint components; bolts, nuts and flanges.

The paper details, at a high level, the work performed and outlines the limits to corrosion that can be applied in the field for each component as an inspection limit to trigger planned replacement or emergency shut down.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A031. doi:10.1115/PVP2017-65550.

This paper presents a summary of recent testing into bolt relaxation, which occurs at temperatures above 230°C (450°F). Bolt relaxation is problematic for pressure boundary bolted joints as it can lead to joint leakage in the longer term. In addition, it should be a major consideration at the design phase, with selection of the appropriate bolt material limited not by the creep or yield limit of the material, but by the point where bolt relaxation becomes significant.

Preliminary test results for different bolt materials at different temperatures are presented in this paper. The test results allow for some very high level observations regarding the acceptable design limits for different bolt and nut material combinations.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A032. doi:10.1115/PVP2017-65610.

For the girth flange of heat exchangers, the circumferential temperature distribution of shell and connecting flange due to inside fluid will affect tightness of the girth flange, however this effect is not considered in present design codes. It is important to know the key characteristics of flange tightness to minimize the risk of leakage. In past studies, the effects of circumferential temperature distribution on flange tightness were investigated at high temperature operations. The effects of partial cooling on flange tightness might be severer than circumferential high temperature distribution.

In this paper, the effects of partial cooling on flange tightness were studied. The flange tightness was evaluated by wideness of partially cooled region (liquid level) of heat exchanger and gasket recovery characteristics parametrically. Based on these studies, it was concluded that the gasket contact pressure was decreased by the partial cooling of heat exchanger and the effects of the above mentioned factors were summarized quantitatively.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A033. doi:10.1115/PVP2017-65800.

This paper explores torque wrench accuracy, one source of the overall inaccuracy associated with bolted flange joint assembly. The accuracy and repeatability of various pneumatic torque wrenches were tested and analyzed. Pneumatic torque wrenches were benchmarked against a hydraulic wrench which has a lower perceived bolt load scatter. The testing was performed on two mock-up flanges, NPS 8 Class 150 and NPS 16 Class 300 raised-face flanges with spiral-wound gaskets. The analysis compares the accuracy and repeatability of the following: each tool versus its manufacturer’s claims; duplicate models of the same tool; and overall tool type (pneumatic or hydraulic) versus another tool type. Because accuracy is closely related to tool calibration, torque wrench calibration method and frequency are also discussed.

There are several methods of applying axial load through torque that have been used within the industrial assembly of Bolted Flanged Joint Assemblies (BFJA’s). The most common tool used within the industry is the manual torque “clicker” wrench which traditionally allows an assembler to reach 600ft/lbs. While companies make wrenches that achieve higher amounts of torque, they are harder on the assembler to use so other tools, such as hydraulic and pneumatic torque wrenches (Powered Equipment), that require less physical strength are used instead. This paper will discuss the accuracy and repeatability of pneumatic and hydraulic wrenches and compare them to the manufacturer’s/industry standards.

Topics: Torque
Commentary by Dr. Valentin Fuster
2017;():V03AT03A034. doi:10.1115/PVP2017-65826.

Although heat exchangers are built according to international codes and proved to be leak tight by hydrotesting at ambient temperature, leak of stainless steel heat exchangers girth flanges at the tubesheet gaskets likely occurs during startup and operation at high temperatures. Accordingly, evaluation of the design to assure leak free operation considering anticipated thermal events is required.

WRC 510 bulletin [4] introduces a simplified analytical method to address this issue and provides safe guarding against leakage.

This study is performed on solid 300 series stainless stationary tubesheet flanged with girth flanges having the same or different material of construction.

A thermal finite element analysis is performed to obtain the transient temperature distribution through a girth flanges and stationary tubesheet assembly of a heat exchanger using SOLIDWORKS® SIMULATION [7]. The model of the flanged joint consists of two girth flanges with a tubesheet and gaskets in between. Thermal time dependent transient analysis of the above model is conducted to compute the temperature distribution in the flanged joint assembly for different time steps.

Further, these temperature distributions are used to compute the expansion, deflection and rotation for the flanged joint parts using WRC 510 bulletin [4] equations.

The study determines both the permissible heating rates during startup and the temperature limits, for the example studied, which are suitable for using solid 300 series stainless tubesheet for both material types of the girth flanges to have the most leak tight & economical assembly when the minimum design metal temperature allows these materials.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A035. doi:10.1115/PVP2017-65993.

Since its original issue in 2000, ASME PCC-1 has provided guidance to the user for establishing target torque values for bolted flanged joint assembly. The original tables were developed based on a reference bolt stress of 50 ksi (345 MPa) with guidance provided for making adjustments using other bolt stress values. Despite its attempts to provide clarity, the industry perception has been that the 50 ksi (345 MPa) reference bolt stress is a mandatory requirement, which has never been the intent. This paper reviews the basis of the original Table 1M/Table 1 values provided in PCC-1, and provides a forecast of future improvements utilizing a new concept called a Target Torque Index based on a unit bolt stress, allowing the user to utilize the guidance in Appendix O of PCC-1 to define the appropriate bolt stress for their particular situation.

Topics: Torque
Commentary by Dr. Valentin Fuster

Design and Analysis: Design and Analysis of Piping and Components

2017;():V03AT03A036. doi:10.1115/PVP2017-65025.

High acoustic energy has the potential to cause vibration induced fatigue in a piping system at integral attachments such as welded pipe supports. Although recognized as a potential failure location, there is no established design curve and fatigue life equation among industry guidelines. In this paper, acoustic induced vibration (AIV) at welded supports is evaluated using Finite Element Analysis. Peak stress and the associated minimum fatigue life is calculated for various types of welded supports under the same acoustic excitation. By comparing the stress level to that of a branch connection, for which design limit for AIV have been published, the design limit and fatigue life equation for welded pipe supports is developed. The use of partial reinforcement pad to mitigate AIV risk is also discussed.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A037. doi:10.1115/PVP2017-65026.

Pipe bends (e.g. 90° and 45°) are trimmed at pipe fabricator shop to suit the required angle per design. However, B31.3 Code requires all pipe bends that are trimmed more than 3° from its original configuration to be treated as an unlisted component. In addition, the stress formulas provided in the ASME B31.3 Code are only intended for 90° elbows without considering the effect of bend angle. The objective of this study is to evaluate stresses in elbows of various bend angles and to provide a design justification for the field disposition. To serve this purpose, elbows with outer-diameter sizing from 4 to 60 inches and angle ranging from 25 to 75 degrees have been studied and compared with 90° bends under the same loading conditions. The results reveal that the stresses are reduced in the trimmed elbow. And the reduction trend in the stresses due to trimming can be predicted by the bend angle and the flexibility characteristic.

Topics: Stress
Commentary by Dr. Valentin Fuster
2017;():V03AT03A038. doi:10.1115/PVP2017-65043.

The use of compression joints in ASME Nuclear Class 2 and 3 small diameter piping systems has become increasingly popular because their installation does not require welding, and therefore saves time, money, and radiation dose. An important question is whether these types of joints can be a practical alternative to socket welds in piping systems subject to vibration. There have been numerous operating experience events where socket welds have developed cracks due to high cycle fatigue. On the other hand, parts of compression joints plastically deform the pipe to grip and create their sealing connection; the application of a high cycle vibration load to an already plastically strained pipe might lead to premature failure. It is desired to know whether at least one type of compression joint would perform better or worse than socket welds in such an environment.

In this paper, a testing methodology is described, in which one supplier’s coupling joint design was tested for vibration loading in tubing assemblies of varying sizes. The intended application for these joints is in an Electro-Hydraulic Control system at a northeastern Boiling Water Reactor plant. Industry experience reports have identified past vibration problems in this system at other plants. A test setup was devised, in which multiple specimens could be tested simultaneously by adjusting specimen natural frequency, shake table speed, and input acceleration. Fatigue Strength Reduction Factors were derived, allowing the resistance to fatigue failure to be quantified. Both compression joints and socket welds were tested using the same procedures, in order that the fatigue damage resistance could be compared between the two types of joints.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A039. doi:10.1115/PVP2017-65053.

Sleeve and socket welds are often used in small bore nuclear power plant pipework where access is too limited to allow a conventional butt-weld. These welds are also used in process plants and pipelines as a permanent repair to reinforce areas such as cracks and corrosion that might threaten the structural integrity of the component. The fillet weld associated with this type of joint is particularly susceptible to lack of fusion defects which can be problematic to detect using conventional volumetric inspection techniques. The stress concentration associated with this type of defect will impact the fatigue life and pressure retaining ability of the joint.

This paper provides examples of Copper/Nickel (CuNi) sleeve weld defects and presents an approach for determining the fatigue life of socket welds due to pressure cycling within a Pressurised Water Reactor (PWR) environment. This approach is based on modelling lack of fusion features using a database of sleeve and socket weld Non-Destructive Testing (NDT) records and calculating the stress range in the remaining ligament using textbook calculations. Sensitivity studies presented herein show the impact of lack of fusion and pipe size/thickness on fatigue life.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A040. doi:10.1115/PVP2017-65094.

Piping caters a major role in the process industries wherein stress intensification factor (SIF) express the Piping flexibility of the system. A typical Piping system consists of combination of pipes and various fittings with intersection geometries namely bend, tee, reducer, etc. A SIF is a multiplier on nominal bending stress so that the effect of geometry and welding can be considered in a flexibility analysis. An attempt has been made to compare the SIF values among ASME Piping B31.3, Welded Research Council (WRC) Bulletin 329, Paulin Research Group (PRG) empirical data and shell-based finite element analysis (FEA) for various tee sections based on in-plane and out-plane bending moments through this paper. The bending moment which causes tee to open/close in the plane formed by two limbs of tee is called in-plane bending moment. The bending moment which causes branch of tee to displace out of the plane retaining run pipe steady is called Out-plane bending moment.

ASME B31.3 provide guidelines to evaluate SIF values through empirical formulation as per Appendix-D with few limitations listed below.

1. Valid for d/D < 0.5 only

2. Non-conservative for 0.5 < d/D < 1.0

3. Valid for D/T ≤ 100

4. SIF values calculated with respect to header pipe. There is no difference in SIF values for header and branch pipe and it is the average value.

WRC 329 was published in 1987 and has not been updated taking ASME B31.3 latest edition into account. PRG carried out SIF for the various sizes and types of tee fittings and prepared correlation equations through detailed FEA using nonlinear regression and test data.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A041. doi:10.1115/PVP2017-65096.

The Reactor Inner Zone Inlet Header (RIZIH) temperatures have raised more rapidly in the CANDU units in general, compared to the original aging predictions. The RIZIH high temperature alarms are required to be monitored to prevent operation outside the safe operating envelope as supported by the safety analysis. To prevent RIZIH temperature alarms, increasing RIZIH temperatures are being mitigated through changes in unit operating conditions which have caused power derates (as low as 87% Full Power) and a loss of revenue. In order to address the above concerns, a CANDU utility has initiated a study to evaluate multiple design alternatives and develop the best design option to improve RIZIH temperatures control. Seven design alternatives were assessed to a sufficient level based on their risk, suitability, economics, and effectiveness in managing RIZIH temperature with minimum system level impacts to interfacing systems. The study concluded that the external feedwater bypass of High Pressure Heater is the preferred option.

Topics: Temperature , Design
Commentary by Dr. Valentin Fuster
2017;():V03AT03A042. doi:10.1115/PVP2017-65114.

Knife gate valves are common in process piping plants in the petrochemical industry. In this study a failure analysis is undertaken on a large knife gate valve attached on top of a Y-piece as part of a purge bin outlet in a polyethylene production facility. A large crack was discovered on the knife gate valve shortly after its installation and operation of the facility. The study outlines a methodology, based on the finite element method, to analyze failure of such units. It starts out by determining the stress intensification factors for a Y-piece by conducting an FEA, which are used in CAESER II piping software to determine the operational loads on the valve. The loads are used as inputs for a non-linear FEA model of the valve accounting for material failure based on continuum damage mechanics approach. The FEA results suggest that the operational loads are not the root cause to the observed failure on the gate valve. It is rather attributed to internal casting defects and the lack of post-heat treatment of the valve.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A043. doi:10.1115/PVP2017-65144.

Buried pipeline systems may traverse sections in moving soil masses. Large strains may be accumulated in buried pipes under long-term ground movements, and it may affect the performance of the pipes. It is a common practice in that a stress relief procedure is applied to the pipe by removing the soil around the pipe to allow the pipe to spring back to its initial state. Pipeline engineers and designers need to assess the frequency of stress relief to maintain the integrity of the pipeline to prolong its operation. The frequency of applying necessary remediation measures depend on; the rate of soil displacement, soil-pipe interaction, severity of loading, and soil conditions.

A physical model has been designed and fabricated to investigate these critical effects on soil-pipe interaction. This model comprises a steel circular soil chamber (1.5 m in diameter and 1.2 m in height) rested on a rail system, and a steel pipe (150–300 mm in diameter) being embedded in a compacted soil inside the chamber. This system has unique features: (i) facilitating the pipe be subjected to relative displacements in complex oblique (combined longitudinal-transverse) loading, (ii) simulating the low soil displacement rates in the field (50 mm per year), and (iii) testing of different soil types. Test results obtained from this research program will be used to evaluate the existing guidelines (e.g., American Lifelines Alliance (ALA) and Pipeline Research Council International (PRCI)).

Commentary by Dr. Valentin Fuster
2017;():V03AT03A044. doi:10.1115/PVP2017-65237.

The coal oil slurry valves are located between the high pressure and intermediate pressure separators in the direct coal liquefaction unit. Because of the high pressure drop between the valve inlet and outlet, the cavitation occurs immediately once the coal oil slurry enters into the valve. Simultaneously, the severe erosion wear are also found on the valve components. Therefore, the erosion-cavitation wear has become a serious problem in the running of valve. In this paper, a numerical-experimental investigation on the erosion-cavitation wear of coal oil slurry valve is conducted. The cavitation experiments are used to verify the numerical modeling and calculation. Moreover, the expressions of functions used in the particle erosion model are defined from the erosion experiments in the high temperature environment. In the numerical simulation, the areas with the high risk of erosion-cavitation wear are predicted. The results showed that the most serious erosion-cavitation wear occurs on the top of valve spool. The particle erosion can also be found around the spool head. The numerical prediction of erosion-cavitation wear can be verified by the comparison between numerical results and actual failure morphology.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A045. doi:10.1115/PVP2017-65333.

Impact analyses for storage and transportation cask drop tests were performed using the explicit dynamic finite element analysis code to demonstrate analytical accuracy and benchmark the analytical code. The test series for this benchmarking were provided by Sandia National Laboratories (SNL) as the Structural Evaluation Unit Benchmark Problem Statement. 30 foot and 120 foot drop test cases in which the test unit was dropped from 30 feet and 120 feet onto an essentially rigid target were selected as the benchmarking problems. A comparison of deformation and acceleration between the actual cask drop tests and those predicted by explicit dynamic finite element analysis performed using LS-DYNA was performed in this paper. The simulation results showed reasonably good agreement with respect to deformation and acceleration between the calculated and the measured result by adjusting the material properties of the impact limiter to match the amount of crush.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A046. doi:10.1115/PVP2017-65382.

The reaction moment calculations of Hinged and Gimbal expansion joints, designed according to the “Standards of Expansion Joint Manufacturers Association” (EJMA), consider the bellows spring rate and pin friction. The reaction moment due to the lateral pressure forces should also be considered. Metal bellows subjected to angular movement extends one side and contracts the opposite, generating a lateral force caused by the media pressure.

This paper evaluates the lateral force reaction moment in a hinged expansion joint with the hardware designed for angular movements. For this purpose prototypes were built and the moments evaluated, simulating actual field conditions.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A047. doi:10.1115/PVP2017-65481.

Environmental fatigue evaluation is a key technology to extend Nuclear Power Plant design life. Since USNRC issued the RG 1.207 in 2007, many studies on fatigue evaluation in Light water Reactor coolant environments have been carried out by referencing documents such as NUREG/CR-6909, EPRI-TR-1025823, ASME BPVC Sec. III NB-3600/3200 Code, ASME Code Case, and so on. These documents presented environmental fatigue evaluation methods about each single-metal such as carbon steels, low-alloy steels, nickel-chromium-iron (Ni-Cr-Fe) alloys, and austenitic stainless steels. However, the environmental fatigue evaluation method for interface of dissimilar metal welding is mostly insufficient. Dissimilar metal welding has been widely used in nuclear industry. If environmental fatigue analysis method for dissimilar metal welding is developed, it will facilitate the design of piping for more safety. Therefore, the development of environmental fatigue evaluation for the interface of dissimilar metal welding should be studied. This paper presents environmental fatigue evaluation for the interface of dissimilar metal welded piping. The environmental fatigue evaluation for a dissimilar metal welded piping model was performed based on above documents.

Topics: Fatigue , Metals , Pipes
Commentary by Dr. Valentin Fuster
2017;():V03AT03A048. doi:10.1115/PVP2017-65488.

Polyethylene pipe reinforced by winding steel wires (PSP) is new type of polymer-matrix composite pipe, which is widely used in petroleum, chemical engineering, and water supply, etc. PSP is composed of a thermoplastic core pipe (HDPE), an outer cover layer (HDPE), and steel wire skeleton sandwiched in the middle. The steel wire skeleton is formed by crossly winding steel wires integrated with HDPE matrix by cohesive resin. In traditional analysis models of PSP, components of PSP were considered linear elastic, and steel wire skeleton was assumed to be orthotropic composite layer based on the classical laminated plate theory. Although achieving good results in engineering applications, traditional models neglected the material nonlinearity of steel wires and HDPE matrix, which was significant to failure analysis. In the present paper, a new finite element model was constructed using commercial software ABAQUS[1], based on the actual steel wire spiral structure of PSP. Steel wires and HDPE matrix were modeled separately, which were both represented by solid elements, and the interaction between steel wires and HDPE was characterized by tie interaction. Experimental result of short-term burst pressure of PSP was used to validate the nonlinear model. Compared with the experimental result, the calculation results of the nonlinear model agreed well. Furthermore, the effect of the nonlinear material property of components on the calculation results were investigated, and the short-term mechanical responses of PSP were determined and analyzed through the nonlinear model.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A049. doi:10.1115/PVP2017-65578.

Polyethylene (PE) pipe, particularly high-density polyethylene (HDPE) pipe, has been successfully utilized to transport cooling water for both non-safety-related applications and safety-related applications in nuclear power plant (NPP). However, concerns of a lack of non-destructive examination (NDE) procedures and qualifications specialized for HDPE pipe impede its broader application. Traditional approximation without considering effects of acoustic dispersion could work for PE pipe with a small inspection depth. But for PE pipe of large size used in nuclear power plant, effects of acoustic attenuation and dispersion accumulate with depth, and have influence on waveforms of target pules, which brings great challenges to the energy concentration when performing ultrasonic phased-array inspection for PE pipe in NPP. In this paper, a theoretical method applying Szabo’s causal convolutional propagation operator based on causality theory was presented to obtain wave equations of ultrasound in PE considering both attenuation and dispersion, in which attenuation coefficient and phase velocity were used to separately characterize acoustic attenuation and dispersion. Then, an experimental method using ultrasonic spectroscopy technology was proposed to confirm the proposed model, and a good agreement was obtained. The results indicated that attenuation coefficient of PE had an approximately linear relation with frequency and that phase velocity rose logarithmically with frequency. Finally, effects of attenuation and dispersion on amplitude spectrum and waveform in time domain of the target signal were investigated. Frequency downshift and time delay shift had an influence on image resolution and focus capability, and were believed to be a restriction of current inspection technology. This work also theoretically proved that lower testing frequencies (less than 2.5MHz) could improve the inspection effectiveness of the applied inspecting systems for HDPE pipes in NPP applications.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A050. doi:10.1115/PVP2017-65634.

Waterhammer is the phenomenon which occurs due to rapid valve operation or sudden stop of pumps. When the waterhammer occurs, unbalanced pressure between elbows causes transient load on piping system. In the piping design against the waterhammer, it is necessary to evaluate the strength and the displacement of piping system against the transient load, and required to provide adequate piping supports. In the piping design, dynamic analysis and static analysis with DLF (Dynamic Load Factor) are often conducted to consider dynamic effect of the water hammer load. The piping support often regarded as rigid in the piping system analysis, however, because of support characteristic (flexibility, plastic behavior, sliding friction), the dynamic response of piping system changes from analysis result with rigid support. For this reason, support characteristics shall be considered adequately. Nevertheless, effect of the support characteristics on the piping design has not been discussed sufficiently.

In this paper, to clarify the effect of the support characteristics against the waterhammer load, a series of the nonlinear dynamic analyses were conducted. Based on the analysis results, the response spectra and the ductility charts considering the nonlinearities of the piping system were created. the design approach to properly control the displacement of piping system based on the nonlinear response spectra and ductility charts, is proposed, and the dynamic response against waterhammer load in the piping system of LNG loading line is discussed.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A051. doi:10.1115/PVP2017-65744.

As codes and standards employ the beam theory to evaluate stress in piping systems, large diameter piping is therefore outside the domain of these codes and standards. To investigate any failure modes in these piping systems, more general codes such as ASME Sec. VIII Div.2 must be used. Research has shown that estimating local stress is important near the shoe support tip especially for large diameter piping systems and aboveground pipelines. To evaluate protection against local failure under an applied design load, a more accurate estimation method of ASME Sec. VIII Div.2, part 5 is applied by using elastic-plastic stress analysis procedures. For this purpose, finite element analysis is carried out along with distributed gravity loading and design pressure. Furthermore, parametric FEA studies are conducted on the effect of the ratio of pipe diameter to thickness, as well as the width and wrap angle of shoe support on the local stress of shoe support. The FEA results have been compared to semi-empirical formula for local stress in shoe support developed by AWWA standard.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A052. doi:10.1115/PVP2017-65756.

The bending moments imposed on welded plate anchors that are part of embedded pipe wall penetrations are often overestimated in the structural evaluations of these penetrations. For this type of restraint, the pipe is embedded in a concrete wall penetration with a welded plate mounted on the surface of the wall. This penetration is typically modeled with a single 6 degree of freedom (DOF) restraint at the plate in the pipe stress analysis. This approach can lead to overestimated loads on the welded plate and the mounting anchor bolts because no credit is taken for reaction on the embedded portion of the pipe. A significant portion of the bending moments from piping on both sides of the penetration is transferred directly to the concrete wall by the normal reaction on a fully grouted pipe, thus reducing loads on the steel plate and the mounting anchored bolts. The objective of this study is to determine load factors for bending moments from both sides of the pipe penetration on the anchored steel plate. A parametric study is performed using ANSYS models of a pipe fully embedded in a concrete wall penetration with a welded plate mounted on one side of the wall by anchor bolts. Various pipe diameters, concrete wall thicknesses and plate thicknesses are considered. For each model, the loading on the plate is compared to the loading applied at the free end of the pipe. Load factors are developed for use in the structural evaluation of the welded plate and the mounting anchor bolts. The maximum compressive bearing pressure at the concrete wall is also calculated for use in the structural evaluation of these types of pipe supports.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A053. doi:10.1115/PVP2017-65797.

The use of the Load and Resistance Factor Design (LRFD) for Class 2 nuclear piping can be an alternative of the traditional Allowable Stress Design (ASD) method currently used in the ASME Boiler Pressure Vessel Code, Section III, Div. 1 providing the benefit of a known and consistent reliability for the designed piping. The design uncertainties and the necessary safety margin are evaluated for each equation for all service levels by considering the applied loads (e.g., earthquake, deadweight, internal pressure, etc.) and the resistance of steel, in the form of either the yield or ultimate strength, as separate variables described by their mean value, distribution, and coefficient of variation. The procedure yields different partial safety factors for each load and the resistance in opposition to the one safety factor used in each of the ASD equations of the Code. Although LRFD equations have been developed in the past, a range of possible partial safety factors were assigned to the variables, corresponding to different levels of reliability. This paper discusses the method used, namely calibration, for achieving same reliability as in the Code equations, and the progress made to assess a minimum target reliability index or else acceptable probability of failure for the LRFD equations that consider the earthquake load for pressurized pipes as well as the design for internal pressure for Class 2 nuclear pipes made of carbon steel.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A054. doi:10.1115/PVP2017-65818.

Pipe bends are frequently used to change the direction in pipeline systems and they are considered one of the critical components as well. Bending moments acting on the pipe bends result from the surrounding environment, such as thermal expansions, soil deformations, and external loads. As a result of these bending moments, the initially circular cross-section of the pipe bend deforms into an oval shape. This consequently changes the pipe bend’s flexibility leading to higher stresses compared to straight pipes. Past studies considered the case of a closing in-plane bending moment on 90-degree pipe bends and proposed factors that account for the increased flexibility and high-stress levels. These factors are currently presented in the design codes and known as the flexibility and stress intensification factors (SIF). This paper covers the behaviour of an initially circular cross-sectional smooth pipe bend of uniform thickness subjected to in-plane opening/closing bending moment. ABAQUS FEA software is used in this study to model pipe bends with different nominal pipe sizes, bend angles, and various bend radius to cross-sectional pipe radius ratios. A comparison between the CSA-Z662 code and the FEA results is conducted to investigate the applicability of the currently used SIF factor presented in the design code for different loading cases. The study showed that the in-plane bending moment direction acting on the pipe has a significant effect on the stress distribution and the flexibility of the pipe bend. The variation of bend angle and bend radius showed that it affects the maximum stress drastically and should be considered as a parameter in the flexibility and SIF factors. Moreover, the CSA results are found to be un-conservative in some cases depending on the bend angle and direction of the applied bending moment.

Topics: Pipe bends
Commentary by Dr. Valentin Fuster
2017;():V03AT03A055. doi:10.1115/PVP2017-65996.

This paper describes a novel approach for optimizing a district heating distribution network under various flow rate conditions. For district heating systems, the demand or the flow and pressure at each node varies over the time of year. The flow control that affects the operational cost can be based on the variable speed and the on/off control on serial pumping or pressure controlled valves. In the pipe system design, the topology, or the pipe layout, and the pipe diameter is optimized using genetic algorithms. Standardized methods are used for calculating the pipe thickness, supports, anchors and the thermal expansion loops. The interconnection between the pipe system and the pump station design is discussed. The objective is to minimize the total or life cycle cost (capital maintenance and operational cost), subject to ensuring demands or constraints at all points. The results are compared to classical methods where the pump station and the pipe system are designed separately and the improvements are discussed.

The problem is formulated by developing an objective function where the optimization parameters define the pump arrangement, pipe system topology, and pipe diameters. The pump station and pipe system optimization consist of selecting components from a pre-defined set of elements and is implemented with discrete decision variables. Optimization of pipe elements consists of optimizing the diameter, after the topology has been defined, and is implemented with discrete variables. Flow distribution and pressure analysis is performed. Thicknesses, pressure classes, supports, expansion loops and anchors are not part of the optimization parameters, but are determined during the evaluation of the objective function. Each time the objective function is evaluated, the pipe system is designed in a sub-optimization according to given loads. The pressure head constraints are used to design the pumping curves. The method is tested on a district heating system in Reykjavik, Iceland.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A056. doi:10.1115/PVP2017-65997.

In geothermal power plants, the steam system is a costly component of the infrastructure in terms of construction requirements. The steam system consists of geothermal wells, well head equipment, pipelines and separators connecting wells to the separators and the separators to the power plant. This paper describes an approach for optimum design of a steam system, with focus on topology and route selection for pipelines transporting two-phase fluid from geothermal wells to a separation station and single-phase pipelines from the separator stations to the power plant.

This article proposes a new approach for selecting the locations of the separators and power plant and routes for both two phase-flow and single-phase flow pipelines in a geothermal steam gathering system. Multiple weighted distance maps calculated by uniform cost Dijkstra’s algorithm are used to find the optimum location of a site for a steam separator based on the flow capacity of geothermal wells. The two-phase flow routes are monotonic and the incline is slight in order to minimize the pressure drop and the slug flow conditions in the pipeline. Once the location of separators has been optimized, the optimum location of the power plant can be determined based on the route selection for both the pipelines transporting steam to the power plant and the pipelines transporting the used geothermal fluid from the power plant to the injection wells. The objective is to minimize both cost and visual effects.

A comparison of this method to traditional methods shows that when the method described in this paper is used, shorter routes and cheaper systems can be designed with less environmental impact.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A057. doi:10.1115/PVP2017-66019.

The ALBA Synchrotron Light Source in Barcelona (Spain) requires a reliable, stable and adequate cooling system for its optimal operation. The current design with four long and intricate consumption lines with a ring type piping layout (270 m perimeter) and a common return pipe is believed to compromise the operability and to promote the trapping of air pockets. In order to improve its performance, a better understanding of the thermo-fluid dynamic behaviour is required that permits to opmitize the system and to anticipate unexpected failures. For that, a detailed 1D model has been built with Flowmaster® software comprising all the components and the various regulation mechanisms to control fluid temperature and pressure. Preliminarily, the model has been validated in steady state operating conditions against experimental measurements showing good agreement. Then, a series of specific steady and transient numerical simulations have been carried out to determine the system response. In particular, the effects of blockage and leakage as well as the increase or decrease of heat duty have been analysed. Furthermore, the best flow distribution through the rings has also been found to reduce the air content by maximizing the velocities.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A058. doi:10.1115/PVP2017-66113.

In a previous paper, it was demonstrated that a tight radius bend with uniform wall thickness equal to the pressure based thickness of the corresponding straight pipe does not meet the linear elastic criteria of NB-3221 Design Loadings. It was also demonstrated that the allowable wall thickness circumferential distribution of the ASME B&PV Code SEC XI Code Case N-597-2 achieves a uniform linear elastic stress intensity over the entire bend that meets the linear elastic criteria of NB-3221. As stated by the ASME B&PV Code under NB-3221, the provisions of NB-3228 may provide relief from certain of the linear elastic stress limits if plastic analysis techniques are applied.

In this paper, the plastic collapse analysis approach of the COG FFSG is adopted to explore the relative safety margin when analyzing various Class 1 tight radius pipe bends’ configurations made of Carbon Steel SA-106 Grade B. In addition to the power law material model, three elastic plastic material models are constructed based on ASME B&PV Code Section II Part D material properties. The pressure-based thickness for the same size straight pipe is uniformly used in modelling the tight radius bends (no increased thickness on the intrados). It is demonstrated that the results from the ASME B&PV based flow stress model are marginal and that the ASME B&PV based bi-linear material model and the limit analysis results are not meeting the collapse pressure criterion. It is also demonstrated that the uniform pressure-based thickness along with the power law material model meets the requirements for the adopted plastic collapse pressure providing a considerable life extension.

Commentary by Dr. Valentin Fuster

Design and Analysis: Design and Analysis of Pressure Vessel, Heat Exchangers, and Components

2017;():V03AT03A059. doi:10.1115/PVP2017-65023.

It could be argued that pressure equipment design is fully mature. Aside from placing increased attention on regions of localized stress, offered by Finite Element Analysis (FEA), there is little else that can be done, from a design standpoint, to reduce manufacturing costs of pressure equipment. This paper builds on previous work undertaken by the authors that questioned the use of weld efficiency based on partial and no volumetric inspection. It proposes a new class of pressure vessel where the fabricator has control over the weld efficiency factor, thus enabling the opportunity for reduction in pressure vessel costs for a certain range of products. This paper addresses three key topics:

1. The historical basis and justification for the use of weld efficiency factors;

2. The design principles behind the proposed new vessel class, and;

3. The advantages, conditions and challenges faced in implementing the new vessel class.

The intent of this paper is to explore the opportunity for an advancement in pressure equipment design and its fabrication.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A060. doi:10.1115/PVP2017-65120.

The data needed to fully benchmark a simulation is frequently inadequate. The analyst is then challenged to make assumptions or otherwise determine how the simulation can be appropriately used to predict future outcomes. A thermal analysis will be presented where temperature data is available at several locations throughout the structure, but information on boundary conditions and thermal properties of the structure is limited. The unknown variables are parameterized and bounded based on the underlying physics and available data for ‘typical’ values. Simulations are then run and a fitting score is used to determine the ranges of the inputs which gave the best overall fit to the test data for the entire structure, avoiding bias of focusing on the single location of interest. In this process, multiple combinations are found that yield similar fit scores, but the variables were confounded and the available data could not support one set of values over another. The resulting ranges of input values were then used in the follow-on analysis work, allowing results to be found as a range of likely values in terms of the input uncertainties. Statistical methods were also applied to the results, allowing determination of which inputs had the greatest impact on the results, and thus identifying where future efforts should be focused to distinguish the variables and provide greater accuracy in the method.

Topics: Simulation
Commentary by Dr. Valentin Fuster
2017;():V03AT03A061. doi:10.1115/PVP2017-65188.

This paper provides a FEA of a specific type of Quick-Actuating Closure which uses an external cylindrical retaining ring. An equation is provided to find the minimum coverage angle of the retaining ring so that the ring will not rotate when loaded by the closure door.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A062. doi:10.1115/PVP2017-65220.

This paper provides designers a methodology for determining membrane and bending stresses in cylinders with loads applied through rectangular attachments having a length to width aspect ratio greater the four (4). This paper extends the original work done by Bijlaard [1] and Dodge [2] as well as the work published in Welding Research Council WRC Bulletins. Bulletins 107 [3] and 537 [4] are limited to aspect ratios of four (4) and Bulletin 198 [2] is limited to aspect ratio of ten (10). This method provided also adds more precision to the Kellogg [5] method which was based on the work of Roark [6]. The data, curves and formulas presented in this paper are the result of a parametric finite element study across the geometry range. Attachments were analyzed with a slender attachment orientation parallel and perpendicular to the axis of the cylinder. Geometric parameters were varied over a range of cylinder diameter & thickness and attachment length & width. This study is limited to small displacement theory. This paper also provides a methodology for analysis of the attachment from the loadings.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A063. doi:10.1115/PVP2017-65246.

In case of fire occurring in an Oil and Gas facility, pressurized vessels may be exposed to fire. Though the entire system will be depressurized once a fire is detected, vessels may rupture, leading to risk of flammable, toxic or cryogenic fluid being released into atmosphere. Therefore, pressure vessels should be designed to withstand internal pressure without rupture during exposure to fire, at least until the system pressure can be decreased to a safe level. A pressure vessel rupture study should be conducted in addition to design code calculation in order to ensure a safe design in case of fire. As part of the recent trend for safer plant design, demand for pressure vessel rupture studies is growing and becoming a necessary requirement.

In our previous presentation (PVP2015-45260 [1]), the material data for carbon steel (SA-516 Gr.70) and stainless steel (SA240 type304 and type304L) at high temperature range were obtained through material testing and were presented as our study result. And in the other presentation (PVP2016-63184 [6]) that we’ve made, procedure for pressure vessel rupture study by FEM using the above mentioned material data was developed.

For the present research, material testing in a dynamic condition wherein a more similar condition to an actual fire case were performed and comparison between the test results and FEM analysis was done. In conclusion, recommendation for the application of the pressure vessel rupture study was justified and necessity for further development of the above mentioned study was determined.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A064. doi:10.1115/PVP2017-65287.

There are enormous tubes in large fixed tubesheet heat exchangers making it difficult to model all the tubes and tubesheet connections in detail for a finite element (FE) analysis. Alternatively, an equivalent solid plate with various simplified tube connections are employed in the FE modeling. But this fails to yield an accurate stress field around the connecting region of tubes and the tubesheet. Given that the maximum stress of the equivalent solid plate generally occurs adjacent to the solid tubesheet, a novel finite element modeling methodology is proposed in this paper. A two part process is used. The first part is a coarse FE model and the second part is a more detailed FE model. In the coarse FE model, the equivalent solid plate is employed in the central region of the tubesheet with simplified tube connections such as equivalent cylinder by multi-points contacting. And quasi detailed tube and tubesheet connections are used in the coarse FE model for the region adjacent to the solid plate, in which the tube and the tubesheet are simply connected with same nodes. This means that both tubesheet and tubes are established in this quasi detailed FE modeling region. Although both the weld and contacting condition between the tube and the tubesheet are not included, the coarse model is enough to yield a believable stress field for the determination of the maximum stress point of the quasi detailed FE modeling region. In the second part, the sub-model methodology is utilized in the predetermined maximum stress point, in which the detailed connecting structure of the tube and the tubesheet is included, such as the weld and the contact condition. The proposed modeling methodology is helpful to have an insight into the stress around the connecting region of the tube and tubesheet for the effective evaluation of the tubesheet and the connection.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A065. doi:10.1115/PVP2017-65423.

Failure has been observed to occur on grade P91 alloy flat head closures in Heat Recovery Steam Generators (HRSG), operating at high temperature (>538°C) and high pressure (>125 bar), after a relatively low in-service life. Since creep is expected to be the major failure mechanism, creep analysis and creep life prediction were conducted on four commonly used flat head designs. We have previously shown that failure of welded P91 material is highly dependent on the material properties in the Heat Affected Zone (HAZ). As such we modeled a common multilayer welding procedure to determine the local material properties of both the Coarse Grain and Fine Grain HAZ for each flat head design. Once the final material properties were obtained, we exposed each simulated flat head to typical operational conditions and calculated the total stress (pressure + thermal) and temperature at each node. With this we then used a Deformation Mechanism Map (DMM) for the P91 alloy to determine the creep rate at each node. This allowed us to identify areas that are accumulating creep strain from different creep mechanisms and therefore susceptible to creep and to approximate the creep life.

Finally, a comparison made between the four commonly used flat head designs by ASME to show which design is more desired with respect to welding process.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A066. doi:10.1115/PVP2017-65469.

With improvement in innovative manufacturing technologies, e.g. automated tow-placement, it is now possible to fabricate any complex shaped structural design for practical applications. This innovative manufacturing technology allows for the fabrication of curvilinearly stiffened pressure vessels and pipes. Compared to straight stiffeners, curvilinear stiffeners have been shown to have better structural performance and weight savings under certain loading conditions. In this paper, an optimization framework for optimal structural design for curvi-linearly stiffened composite pressure vessels and pipes is presented. Non-Uniform Rational B-Spline (NURBS) curves are utilized to define curvilinear stiffeners over the surface of the pipe. An integrated tool using Python, NURBS-based Rhinoceros 3D, MSC.PATRAN and MSC.NASTRAN is implemented for performing topology optimization of curvilinearly stiffened cylindrical shells. Rhinoceros 3D is used for creating the geometry, which later can be exported to MSC.PATRAN for finite element model generation. Finally, MSC.NASTRAN is used to perform structural analysis. A hybrid optimization technique, consisting of Particle Swarm Optimization (PSO) and Gradient Based Optimization (GBO), is used for finding the optimized locations of stiffeners, optimal geometric dimensions for stiffener cross-sections and the optimal layer thickness for the composite skin. Optimization studies show that stiffener placement influences the buckling mode of the structure. Furthermore, the structural weight can be decreased by optimizing the stiffener’s cross-section and skin thickness. In this paper, a cylindrical pipe stiffened by orthogonal and curvilinear stiffeners under internal pressure and bending load is studied. It is shown that curvilinear stiffeners lead to a potential 8% weight saving in the composite laminated skin as compared to the case of using straight stiffeners.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A067. doi:10.1115/PVP2017-65538.

This paper presents research work about the design and optimization of pressure vessels using Hybrid Heuristic Gradient Projection (HGP), Sequential Quadratic Programming (SQP) and Genetic Algorithms (GA). The design is concerned with the pressure loading conditions, intended internal utility volume, geometrical dimensions and the induced stresses. Cylindrical pressure vessels with hemispherical ends are considered. They are required to hold a definite volume under a specific pressure. The thicknesses of each hemispherical part and the cylindrical part satisfy the recommended ASME code. The design also satisfies allowable stress constraints. The design multi-objectives are to generate the optimum geometry to satisfy required specifications, performance and cost requirements. A developed HGP, SQP and GA algorithms are utilized to perform the optimization. The efficiency of the procedure is indicated and the optimum results in the form of optimum design charts are presented.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A068. doi:10.1115/PVP2017-65607.

The phenomenon of condensation with noncondensable gas widely exists in many industrial processes. In this paper, the effect of noncondensable gas on condensation heat transfer inside corrugated low finned tubes is investigated experimentally. Air is mixed into steam playing the role of noncondensable gas. The effects of gas mixture inlet conditions and condensation tubes structural parameters are investigated. The results show that the influence mechanism inside corrugated low finned tubes is similar with that inside smooth tubes. The heat transfer coefficient decreases as noncondensable gas fraction increases. However, the decreasing rate is gradually reduced. Increasing inlet mass flux could enhance the heat transfer coefficient especially at small heat transfer rate. And the heat transfer coefficient decreases with the increase of inlet pressure. The heat transfer coefficients inside smaller pitches tubes are higher than that inside larger pitches tubes, and the declining rate is also slightly faster. When the noncondensable gas fraction is large enough, the difference of heat transfer coefficients between different enhanced tubes can be ignored. Tube with the largest protrusion height has the highest heat transfer coefficient. And the gap of heat transfer coefficients between different protrusion heights is larger than that between different pitches. This shows that the protrusion heights have greater influence on condensation compared with pitches.

Topics: Condensation
Commentary by Dr. Valentin Fuster
2017;():V03AT03A069. doi:10.1115/PVP2017-65766.

Depending on plant/site location, it may be advantageous to dress a vertical vessel, in horizontal position, prior to erection. Dressing refers to the installation of items attached to the vessel such as internals, insulation, piping, ladders, platforms, electrical cable trays, lighting, etc. The decision to dress a vessel may be due to safety, schedule or economic reasons. Dressing a vessel results in higher lifting loads.

Vessel Codes address loadings to be considered when designing a vessel in its operating position and not necessarily for lifting. Since the Codes do not address erection loadings, engineering judgment must be used in their consideration and analysis in order to avoid overstressing the vessel. In some cases, erection loads govern the design thickness of the vessel.

Lifting analysis in the context of this paper is the evaluation of stresses in the vessel when it is initially picked up from the horizontal position. This paper discusses the compressive stresses which usually govern in the lifting analysis of thin-walled vessels. Different methods used in literature and industry are presented in the paper. Some Owners/Users, engineering firms, and fabricators use the Factor B in ASME Section II, Part D, Subpart 3 as the limiting criterion for compressive stresses. In some cases, this criterion is too conservative. This paper presents the application of alternative buckling criteria for lifting analysis.

Topics: Design , Vessels
Commentary by Dr. Valentin Fuster
2017;():V03AT03A070. doi:10.1115/PVP2017-65786.

Modern petrochemical and chemical facilities consist of a significant number of pressure vessels. Adequate design of pressure vessels and their foundations have a significant impact on the safety and economics of such facilities. The design of pressure envelope components is well developed and specified in pressure vessel codes. A more less developed but significant aspect of the design of pressure vessels is the design of the vessel support and foundation. To adequately design the vessel support/foundation, engineers shall consider all the applicable loads on the vessel from attached piping and determine whether these loads could potentially entirely translate to the vessel base support/foundation. While methodology to determine these piping loads is well developed in literature and codes, there is a lack of guidance on how to determine the effect of these piping loads on the base support/foundation loading.

This paper is a continuation of the paper presented at the PVP2016 conference (63694 “Effects of Piping Loads on Vessel Supports and foundation” [1]), where the effect of piping loads on a vessel support/foundation was discussed. The paper demonstrated that when flexibility was introduced into a simple piping system, the loads transferred to the foundation/supports were reduced. This paper expands the study by evaluating piping loads from a more complex piping system attached to a tall vessel. To observe the differences, two different vessel heights and three different shell thicknesses are evaluated. The effect of piping loads (loading at the base) is calculated when the vessel and the nozzles are considered rigid and when flexibilities are introduced into the system. The more flexibility is introduced into the system, the more reduction in base loads is observed.

Topics: Stress , Pipes , Vessels
Commentary by Dr. Valentin Fuster
2017;():V03AT03A071. doi:10.1115/PVP2017-65858.

In ASME Section VIII, Division 1, rules are provided for calculating the thickness of 2:1 ellipsoidal heads in UG-32. UG-32(c) also states that “an acceptable approximation of a 2:1 ellipsoidal head is a torispherical head with a spherical radius of 0.9D and a knuckle radius of 0.17D”. However, calculating the thickness of a torispherical head with those “equivalent” dimensions results in a thicker head. This result is inherently inconsistent, which starts to bring into question the so-called equivalency.

Code Case 2260 further perpetuates this equivalency by providing alternative rules for calculating the thickness of torispherical heads, and then permitting the engineer to calculate 2:1 ellipsoidal heads implementing this 90-17 equivalency.

Additionally, the calculation methodology for a 2:1 ellipsoidal head in ASME Section VIII, Division 2 uses the torispherical head calculation methodologies and directly implements this 90-17 equivalency. However, this calculation method results, for the same allowable stress basis, in a completely different thickness from the above three methods.

This paper reviews the past 90+ years of work on this topic, and presents some theoretical treatment of the different head geometries. A review of the current Code rules is presented, with a comparison of results for several sizes. A survey of head fabricators is presented to show the actual geometries produced for use in ASME pressure vessels. Finally, conclusions regarding whether or not the 2:1 ellipsoidal head is in fact equivalent to the 90-17 torispherical head are presented, and recommendations for future revisions to both ASME Section VIII, Division1 and Division 2 are provided.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A072. doi:10.1115/PVP2017-66093.

A high-pressure (HP) steam super heater located in the primary reformer of Ammonia Plant of Saudi Arabian Fertilizer Company (SAFCO) has ruptured twice in two different tubes, in 2009 and again in 2014. On both occasions, the repair was performed by removing and plugging the failed tube. In January 2015, the new plug that was installed in 2014 failed and led to an emergency shutdown. The older plug was found to be in good condition. An investigation was initiated to determine the reason for failure of one plug within nine months of operation while another was still in good condition after 6 years of operation. The failed plug was subjected to a metallurgical failure analysis where visual and stereoscopic inspection, scanning electron microscopy, metallographic examination, and chemical analysis were performed. The two plugs had different geometric designs, and thermal and static structural finite element analyses were performed to compare the 2009 and 2014 designs. Based on the outcome of the investigation, the cause of failure and the reason for the discrepancy in lifetimes of the two plugs was determined. This paper will present the conclusions of the metallurgical failure analysis and design review which was performed, and the improved repair design that was developed as a result of the investigation.

Commentary by Dr. Valentin Fuster
2017;():V03AT03A073. doi:10.1115/PVP2017-66138.

Steam turbines need to be safer and more reliable when used in nuclear power plants. In order to ensure long-term reliability of nuclear power equipment, a high safety factor is usually adopted in the design of low-pressure (LP) inner casing of steam turbines. It not only leads to larger self-weight of LP outer casings and fundamental load, but also causes higher manufacturing and transportation costs. In this paper, the stress and deformation behaviors of the LP outer casings of steam turbines are first evaluated using the numerical finite element analysis. Then, two optimization design methods, size optimization and topology optimization are used to conduct the weight reduced optimization design of inner casing, in combination with the design standards, so that the structural efficiency and performance of LP inner casings are achieved. At the same time, the self-weight and related costs are also greatly reduced. This study proposes a more optimized structural design of LP inner casings of steam turbines, and it offers considerable economic benefits.

Commentary by Dr. Valentin Fuster

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