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ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V001T00A001. doi:10.1115/ETAM2018-NS.
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This online compilation of papers from the ASME 2018 Symposium on Elevated Temperature Application of Materials for Fossil, Nuclear, and Petrochemical Industries (ETAM2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Materials Properties of Candidate Materials

2018;():V001T01A001. doi:10.1115/ETAM2018-6706.
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Predictions as to 105 hrs creep rupture strength of grade 91 steel have been made recently. The predictions should be verified by some means, since they are based on certain assumptions. A formula for predicting long-term creep rupture lives should correctly describe long-term data points used in its formulation. Otherwise the formula cannot properly predict further longer-term creep rupture lives. On the basis of this consideration, the predictions are examined with long-term creep rupture data of the steel. In the predictions three creep rupture databases were used: data of tube products of grade 91 steel reported in NIMS Creep Data Sheet (NIMS T91 database), data of T91 steel collected in Japan, and data of grade 91 steel collected by an ASME code committee. Short-term creep rupture data points were discarded by the following criteria for minimizing overestimation of the strength: selecting long-term data points with low activation energy (multi-region analysis), selecting data points crept at stresses lower than a half of proof stress (σ0.2/2 criterion), and selecting data points longer than 1000 hrs (cut-off time of 1000 hrs). In the case of NIMS T91 database, a time-temperature parameter (TTP) analysis of a dataset selected by the multi-region analysis can properly describe the long-term data points. However, the TTP analyses of datasets selected by the σ0.2/2 criterion and by the cut-off time of 1000 hrs from the same database overestimate the long-term data points. The different criteria for data selection have more substantial effects on predicted values of the strength of the steel than difference of the databases.

Topics: Creep , Steel , Rupture
Commentary by Dr. Valentin Fuster
2018;():V001T01A002. doi:10.1115/ETAM2018-6712.
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Type IV damage has been found at several ultra-supercritical (USC) plants that used high-chromium martensitic steels in Japan, and the assessment of the remaining life of the steels is important for electric power companies. The assessment of the remaining life needs long-term creep data for over 10 years, but such data are limited. We have attempted to assess the remaining life by creep tests and by microstructural observation of Grade 91 steels welded pipes which were used in USC plants for over 10 years. Following the results of microstructural observation of USC plant pipes, we find that microstructures, especially distribution of MX precipitates, have large effect on the creep life of Grade 91 steels.

Topics: Creep , Steel
Commentary by Dr. Valentin Fuster
2018;():V001T01A003. doi:10.1115/ETAM2018-6720.
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A creep strength of welded joint of ASME Grade 91 steel in a region exceeding 100,000 hours was examined in this work. Creep tests were conducted on the steel used at USC plants for long-term, and remaining creep life of the material for operating condition was calculated on a fitting curve using Larson-Miller parameter. Total creep life of the material, which means a creep life at initial state, was presumed to be a summation of the service time at the plants and the remaining creep life. The estimation was conducted for welded joints used at five plants for long-term, and all results lay within 99% confidential band by the creep life evaluation curve of the material proposed by Japanese committee in 2015, while a significant heat-heat variation of creep strength was found even in the region exceeding 100,000 hours. Creep tests on base metals related to each welded joint were also conducted, and the estimation results of the total creep life of the base metals were compared to those of the welded joints. It was suggested that the heat-heat variation of the welded joints eminently depends on the creep life property of the corresponding base metal.

Topics: Creep , Steel , Welded joints
Commentary by Dr. Valentin Fuster
2018;():V001T01A004. doi:10.1115/ETAM2018-6732.
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This paper presents ongoing research at NETL aimed at gaining fundamental understanding of high-entropy alloys (HEAs) formation and their properties, and developing highperformance HEAs for high-temperature fossil energy applications. First-principles density functional theory (DFT), Monte Carlo simulation, and molecular dynamics simulation are carried out to predict enthalpy of formation, the entropy sources (i.e., configurational entropy, vibrational entropy, and electronic entropy), and elastic properties of model single-phase HEAs with the face-centered cubic, body-centered cubic and hexagonal closed-packed structures. Classical elastic theory, which considers the interactions between dislocations and elastic fields of solutes, has also been used to predict solid solution strengthening. Large-size (∼7.5 kg) HEAs ingots are produced using vacuum induction melting and electroslag remelting methods, followed by homogenization treatment resulting in greater than 99% homogeneity. Subsequent thermomechanical processing produces fully-wrought face-centered cubic microstructures. The tensile behavior for these alloys have been determined as a function of temperature, and based on these results screening creep tests have been performed at selected temperatures and stresses.

Topics: Alloys , Entropy
Commentary by Dr. Valentin Fuster
2018;():V001T01A005. doi:10.1115/ETAM2018-6741.
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Nickel-base alloys are required for many of the components in advanced ultra-supercritical steam and CO2 power systems operating at temperatures and pressures exceeding 1202°F (650°C) and 3.6 ksi (25 MPa). Age-hardened alloys offer a distinct advantage over traditional solid solution strengthened alloys by virtue of their significantly higher creep strength. This makes it possible to reduce wall thickness and thereby minimize total construction cost. INCONEL alloy 740H (UNS N07740) is an age-hardened alloy that was developed and extensively characterized for advanced ultra-supercritical steam boilers. Material testing by the A-USC Consortium and US Department of Energy led to ASME Code Case 2702 covering UNS N07740. Alloy 740H is the first age-hardened nickel-base alloy permitted for welded construction for use in the creep limited temperature regime. More recent development work on the alloy has focused on applications for supercritical CO2 systems. Various laboratories have reported on oxidation properties of the alloy under simulated operating conditions. This paper focuses on the manufacturing and properties of tubing and fittings that are being applied for the various advanced ultra-supercritical steam and supercritical CO2 projects now planned or underway. As many of the structures are constructed by welding, a review of welding practices is presented, including dissimilar welds and their properties.

Commentary by Dr. Valentin Fuster
2018;():V001T01A006. doi:10.1115/ETAM2018-6742.
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TerraPower has developed sophisticated computational analysis tools to support the design and fabrication of high temperature components to be used in the Traveling Wave Reactor (TWR). One of the key material properties required to predict material damage and remaining lifetime of key in-reactor components is the thermal creep rupture time. Although TerraPower optimized ferritic-martensitic (FM) HT9 steel has shown consistent improvement in yield stress and creep rupture strength through uniaxial tensile tests, extrapolations of existing test data are still needed to fully support the complex analysis used in the TWR design.

Traditional Larson-Miller analysis for creep rupture was used to compare the TerraPower optimized HT9 steel to the existing historical database. The results of the Larson-Miller analysis were compared to the results from the Wilshire analysis to explore the relative advantages and disadvantages of each method. The best estimate values for fitting constants and activation energies were determined for both methods, taking into account the effects of the higher yield stress observed in TerraPower optimized HT9 compared to historic HT9.

Likewise, the best estimate creep rupture stresses for TerraPower optimized HT9 at various times and temperatures were determined by extrapolations using both the Larson-Miller and Wilshire analysis. The allowable stresses of historical and TerraPower optimized HT9 steels were compared to those of existing materials (9Cr-1Mo-V) in the ASME high temperature code. The comparison of analysis methods and rupture stresses demonstrate that TerraPower FM steel thermal creep performance and analysis methods are comparable to existing ASME qualified materials for high temperature applications.

Commentary by Dr. Valentin Fuster
2018;():V001T01A007. doi:10.1115/ETAM2018-6745.
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Increasing global demands for energy are spurring research efforts to improve the efficiency of fossil power plants while simultaneously reducing the emission of greenhouse gases. Current research reveals that a power plant’s efficiency increases when it is operated at Advanced Ultra Super Critical (A-USC) temperatures and pressures. These operating conditions require some plant components to be made from nickel-based superalloys. Previous research has established HAYNES® 282® alloy1 (UNS N07208), a Ni-Cr-Co-Mo-Ti-Al precipitation hardenable alloy, as a viable choice for A-USC applications. For such components, current interest is focused on the development of a single step age hardening treatment. An earlier paper presented the mechanical properties of an 8-hour single step age hardening heat treatment at 800°C (1472°F)/8 hr/AC. This paper will review preliminary results of a shorter single age treatment: 800°C (1472°F)/4 hr/AC.

Topics: Alloys
Commentary by Dr. Valentin Fuster
2018;():V001T01A008. doi:10.1115/ETAM2018-6748.
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The realization of advanced thermal power plants with increased efficiencies requires the development of new materials with enhanced capabilities in respect to high temperature strength and steam oxidation behavior. The change in the environmental policy and the increasing contribution of renewable energy sources into the public electric grid has changed the operation mode of the existing power plants in Europe. Instead of quasi stationary operation, for which the conventional thermal power plant fleet was designed, cyclic operation modes will dominate the power plant service lifetime. The creep-fatigue phenomena, however, may be responsible for significant lifetime reductions compared with the original design lifetime. Revamping of the existing power plants by application of “stronger” materials with improved steam-oxidation behavior, allowing wall thickness reduction can be a possible way to address the topic. Recently, Vallourec developed a new high-Cr ferritic-martensitic steel that combines excellent creep rupture strength properties and enhanced steam oxidation resistance of 12%Cr steels such as VM12-SHC or X20CrMoV11-1. Industrial products were successfully manufactured and the creep and steam oxidation properties were validated.

Commentary by Dr. Valentin Fuster

Fabrication, Construction, and Heat Treatment Methods

2018;():V001T02A001. doi:10.1115/ETAM2018-6704.
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Extrusion process produces semi-finished product that provides significant savings in machining and fabrication of the finished components. Plymouth Engineered Shapes (PES) employs forward extrusion techniques to produce products up to 40 feet long that are utilized in power generation, nuclear, and petrochemical applications where it is critical to meet or exceed ASME piping, boiler and pressure vessels code specifications. The extrusion process has been successfully employed to manufacture components such as various types of valve bodies, manifolds, adapters and more that are targeted for elevated temperature applications up to 1200°F and under high pressures up to 10,000 PSIG. Critical product characteristics include flatness, straightness, twist, angularity, surface quality and dimensions over the full length. This paper presents an overview of the carbon steel and stainless steel extrusion process, the room temperature and elevated temperature mechanical properties, metallographic characterization, testing requirements and the applications of such products. Properties are also be compared to those produced by the conventional hot rolling and forging operations.

Commentary by Dr. Valentin Fuster
2018;():V001T02A002. doi:10.1115/ETAM2018-6714.
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Requirements for post-weld heat treatment (PWHT) of steels for pressure boundary component applications have been defined in terms of exceeding a minimum Charpy impact energy in an attempt to overcome the risk of brittle cracking. This approach can be excessively conservative since it does not properly assess resistance to cracking under the relatively static conditions encountered in pressure service. It is well established that under these conditions, cracking resistance, brittle or ductile, is more properly characterized using fracture toughness (KIc/JIc) type tests. The current paper describes room temperature fracture testing conducted via Charpy testing, fracture toughness testing, and tube (burst) pressurization of Grade 91 weldments after different PWHT conditions. The results obtained highlight (a) the excessive conservatism associated with use of Charpy data for assessing burst, (b) the value of fracture toughness testing to measure the sensitivity of fracture resistance to changes in PWHT (not seen in the Charpy data), and (c) the response of tube weldments with known flaws to pressurization. The observed burst pressure results are consistent with predictions made by analysis using the fracture toughness test results. Detailed analysis, including information from post-test examination of tube weldments and a fracture mechanics-based interpretation of test data for component flaw tolerance, provide a quantitative basis for specifying repair procedures and quality assurance methods for such welds. The findings illustrate the need to utilize long-established material fracture toughness testing methods and related properties to establish rules for construction and for post-construction repair. This is particularly true for the creep strength enhanced ferritic (CSEF) steels where the elevated temperature behavior may be compromised by potentially over-tempering weldments to meet requirements based simply on the results from inexpensive but inappropriate tests such as the Charpy test.

Commentary by Dr. Valentin Fuster
2018;():V001T02A003. doi:10.1115/ETAM2018-6715.
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Corrosion conditions in the Chemical and Oil and Gas Industries are such that equipment must withstand pressure and corrosion at high temperatures.

Due to the fact that in many cases only the internal surface is exposed to corrosive attack, and so only that surface needs to be protected, savings on material costs can be achieved by taking advantage of the weld overlay technique.

Weld overlay, through the choice of alloy, is selected to resist to the corrosive attack. Parent material can be selected based on the required strength at temperature.

In recent years, highly corrosion resistant Nickel Chromium-Molybdenum Alloys have been developed to operate in the most severe corrosive environments.

One of the recent developments in this family of materials, is Alloy 59 UNS N06059 that is replacing Hastelloy C-2000 UNS N06200 and Hastelloy C-22 UNS N06022. Nickel-Chromium-Molybdenum alloys are the most versatile nickel alloys, because they contain molybdenum, which protects against corrosion under reducing conditions, and chromium which protects against corrosion under oxidizing conditions.

Wrought products produced from these alloys are processed to obtain a homogeneous austenitic grain structure. Weld overlay or weld deposit, due to the fundamental differences in processing compared to base material, result in a more heterogeneous metallurgical grain structure that in general shows however a good level of corrosion resistance.

Weld or Weld overlay features are highly dependent on electric parameters, filler metal, technique, base material temperature, etc., and for this reason the general settings of the welding process need to be finalized and tested, with the intent of optimizing all these parameters in order to allow the best corrosion results.

A research activity has been carried out by ALFA LAVAL OLMI to define a processes and parameters’ selection in order to obtain a weld deposit with a behavior as close as possible to wrought Alloy 59 base material.

Commentary by Dr. Valentin Fuster
2018;():V001T02A004. doi:10.1115/ETAM2018-6716.
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Diffusion bonding was conducted on cold-worked Alloy 600. Cold-work of 50 % was applied prior to diffusion bonding in order to incite recrystallization and limit grain growth. Tensile testing was conducted at room temperature and 550 °C for evaluation of joint efficiency, while premature brittle failure at the bond-line was observed for most diffusion bonding conditions. It was found that such premature failure was related to a planar bond-line that indicated lack of grain boundary diffusion across the bonding surfaces. Additional application of post-bond heat treatments did not result in significant bond-line migration. Microstructural analyses revealed the existence of Cr-rich carbides and Ti-rich precipitates along the bond-line, which prevented bond-line migration by acting as pinning points.

Commentary by Dr. Valentin Fuster

Failure Mechanisms in Elevated Temperature Regime

2018;():V001T03A001. doi:10.1115/ETAM2018-6708.
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A simplified J-integral evaluation method applicable to unstable failure analysis in Leak Before Break (LBB) assessment of Sodium-cooled Fast Reactor (SFR) in Japan was proposed. Mod.9Cr-1Mo steel is supposed to be a candidate material for the coolant systems of SFR in Japan. This steel has relatively high yield strength and poor fracture toughness comparing to those of conventional austenitic stainless steels. In addition, SFR pipe has small thickness and large diameter. Furthermore, in SFR, primary stresses are insignificant and displacement controlled secondary stresses are predominant. Therefore, the load balance in such piping system changes by crack extension and R6 (2-parameter) method (hereinafter “2-parameter method”) [1] using J-integral is applicable to unstable failure analysis for the pipes under such loading conditions. As a J-integral evaluation method for circumferential through-wall crack in a cylinder, EPRI has proposed a fully plastic solution method. However, the geometry of SFR pipe and material characteristics of Mod.9Cr-1Mo steel exceed the applicable range of EPRI’s method. Therefore, a series of elastic, elasto-plastic and plastic finite element analyses (FEA) were performed for a pipe with a circumferential through-wall crack to propose a J-integral evaluation method applicable to such loading conditions. J-integrals obtained from the FEA were resolved into elastic, local plastic and fully plastic components. Each component was expressed as a function of analytical parameter, such as pipe geometries, crack size, material characteristics and so on. As a result, a simplified J-integral evaluation method was proposed. The method enables to conduct 2-parameter method using J-integral without any fracture mechanics knowledge.

Commentary by Dr. Valentin Fuster
2018;():V001T03A002. doi:10.1115/ETAM2018-6709.
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Grade 91 steel has been widely utilized in power plants over the last 20 years. Its specification for worldwide power plant construction has dramatically increased since the acceptance of Code Case 1943 for this material in 1983. Recent evaluation of a combination of ex-service Grade 91 steel components and virgin material has provided a unique opportunity to independently assess the performance of a combination of base metals and weldments. This approach has been grounded in the fundamental objective of identifying and quantifying metallurgical risk factors in 9%Cr creep strength enhanced ferritic (CSEF) steels and in Grade 91 steel in particular.

Identification of metallurgical risk factors is essential in the integration of a meaningful life management strategy for complex 9%Cr CSEF steels. In particular, there is a need to link the damage developed either in-service or through well-controlled testing to features in the material. These features may include, but not be limited to, carbonitride precipitates (and distribution of these phases along grain boundaries, e.g. M23C6 and MX-type), inclusions developed as a consequence of the steel making process (such as MnS, Al-rich or complex Ca-modified) and intermetallic phases which evolve in-service (Laves or Z-phase) or through product forming (AlN or BN). Identification and linking of these particles to damage is considered a critical need for widely used 9%Cr CSEF steels as Grade 91 steel can show widely variable behavior with respect to creep ductility whilst Grade 92 shows a marked and consistent trend to low creep ductility.

In this study, the evaluation of damage is detailed for an ex-service Grade 91 steel heat which exhibited a marked susceptibility to the evolution of in-service damage. This evaluation focuses on the evolution of HAZ damage under well-controlled, uniaxial creep test conditions using feature, cross-weld creep tests. For interrupted and failed samples, evaluation of damage was performed using state-of-the-art scanning electron microscopy (SEM) based techniques. Particular emphasis was made to link the post-test condition with the as-fabricated weldment and the parent material condition. It will be shown that there is a significant population of cavities associated with second phase particles, and particularly inclusions and intermetallic phases resulting from steel making and product manufacturing processes.

Topics: Heat , Steel , Damage
Commentary by Dr. Valentin Fuster
2018;():V001T03A003. doi:10.1115/ETAM2018-6713.
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It has been identified that in-service carburization of austenitic stainless steels in the UK Advanced Gas Cooled Reactor (AGR) fleet can impact upon creep-fatigue crack initiation, which is assessed using the R5 Volume 2/3 assessment methodology.

Material properties for the carburized layer have been derived through testing of preconditioned specimens. These properties have been used to propose a simplified assessment methodology for the treatment of creep-fatigue crack initiation in carburized specimens. The methodology accounts for the negative impacts of carburization, such as the reduced creep ductility, but does not benefit from the potentially positive impacts, such as the increased creep deformation resistance.

At relatively low strain ranges, typically seen by plant components, these simplifications generally result in a very conservative creep-fatigue lifetime prediction. However, at short dwell times (in load control) at high strain ranges (in strain control) the methodology has the potential to be non-conservative when the stress mismatch between the carburised layer and bulk material is severe due to differing cyclic stress-strain properties. Therefore pragmatic limits of application must be applied to the simplified approach. This paper explores these limitations of the simplified assessment advice, the impact on plant assessments and how current research is looking at how less conservative assessment methodology can be developed.

Commentary by Dr. Valentin Fuster
2018;():V001T03A004. doi:10.1115/ETAM2018-6719.
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Premature creep cracking in fabricated large bore branch connections in Grade 91 steel (9Cr-1Mo-VNbN) piping continues to be a commonly observed failure mechanism in high energy applications. Failures have been observed in components fabricated to the requirements of both ASME Section I and B31.1 codes. This paper presents the application of a physically-based creep continuum damage constitutive model developed for Grade 91 steel to the assessment of a large bore fabricated branch connection. For a specific component geometry and operating conditions, model predictions for the expected location and timing of crack initiation as well as for the crack growth behavior have been made. In addition, as validation, trends in the simulated behavior are compared to information from case studies of large bore branch cracking and failure in service. The physically-based continuum damage model is shown to accurately predict both the location and timing of local crack initiation as well as the observed crack growth behavior.

Commentary by Dr. Valentin Fuster
2018;():V001T03A005. doi:10.1115/ETAM2018-6734.
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CSEF (creep strength enhanced ferritic) steels and austenitic steels are widely used for USC boiler tubes. It is important to evaluate creep life of these parts because metal temperature is indeterminable in superheater and reheater tubes. Almost investigations were conducted under higher stress, short time creep tests, but the pressure for the boiler pipe and tube at actual plant were very low. It is therefore necessary to establish creep life method under long time region time test at various stresses. The purpose of this work is to establish creep life evaluation in high Cr ferritic steels and austenitic steels with long time creep ruptured data. The creep life evaluation methods are based on hardness and microstructure changes.

Topics: Creep , Boiler tubes
Commentary by Dr. Valentin Fuster

Elevated Temperature Design Methods

2018;():V001T04A001. doi:10.1115/ETAM2018-6710.
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Realistically simulating the creep response of welded components can help quantify the risk associated with operating inservice, high-temperature equipment and can validate new component designs in the power generation and petrochemical industries. Detailed finite element analysis (FEA) is employed in this study and is coupled with generalized, non-linear creep simulation techniques to investigate the elevated temperature response of welds. Depending on original heat treatment, creep damage progression is known to be accelerated by the mismatch in properties of the base metal, weld deposit, and heat affected zone (HAZ). This mismatch results in stress intensification that can accelerate creep damage near a weldment (typically in or adjacent to the HAZ). In this paper, the effect of implementing an elastic damage parameter that adjusts the stiffness of the material as a function of creep damage is examined. This type of damage mechanics model has a significant impact on the predicted damage evolution near weld deposits and can realistically mimic observed in-service failures. Additionally, commentary on different creep damage failure criteria is provided. The simulations presented utilize the Materials Properties Council (MPC) Omega creep methodology, with particular emphasis on the behavior of high-temperature, low chrome (1-1/4 Cr 1/2 Mo) piping with longitudinal weld seam peaking.

Application of these techniques to high-temperature, low chrome piping is relevant as there have been numerous related catastrophic failures in the power generation and petrochemical industries attributed to weld seam peaking. Commonly, weld peaking occurs during fabrication due to angular misalignment of rolled plate. Furthermore, for many fusion-welded piping fabrication standards, no tolerance for peaking is specified. Local peaking can induce significant local bending stresses, and for components that operate in the creep regime, the presence of peaking can lead to an increased risk for creep crack initiation, propagation, and eventual rupture. An overview of some well-known historical low chrome piping failures is provided in this paper, and a literature review on existing creep analysis and peaking measurement methodologies is offered. Additionally, the remaining life of low chrome piping systems is estimated and the sensitivity in results to variations in key parameters is highlighted; these parameters include operating temperature, magnitude of peaking, and the effect of heat treatment. The simulation techniques discussed in this paper are not only valuable in estimating remaining life of in-service components, but detailed analysis can help establish recommended weld seam peaking fabrication tolerances, appropriate manufacturing practices, and practical inspection intervals for high-temperature piping systems.

Commentary by Dr. Valentin Fuster
2018;():V001T04A002. doi:10.1115/ETAM2018-6711.
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Uncertainty in modeling the creep rupture life of a full-scale component using experimental data at microscopic (Level 1), specimen (Level 2), and full-size (Level 3) scales, is addressed by applying statistical theory of prediction intervals, and that of tolerance intervals based on the concept of coverage, p. Using a nonlinear least squares fit algorithm and the physical assumption that the one-sided Lower Tolerance Limit ( LTL ), at 95 % confidence level, of the creep rupture life, i.e., the minimum time-to-failure, minTf, of a full-scale component, cannot be negative as the lack or “Failure” of coverage ( Fp ), defined as 1 - p, approaches zero, we develop a new creep rupture life model, where the minimum time-to-failure, minTf, at extremely low “Failure” of coverage, Fp, can be estimated. Since the concept of coverage is closely related to that of an inspection strategy, and if one assumes that the predominent cause of failure of a full-size component is due to the “Failure” of inspection or coverage, it is reasonable to equate the quantity, Fp, to a Failure Probability, FP, thereby leading to a new approach of estimating the frequency of in-service inspection of a full-size component. To illustrate this approach, we include a numerical example using the published creep rupture time data of an API 579-1/ASME FFS-1 Grade 91 steel at 571.1 C (1060 F) (API-STD-530, 2007), and a linear least squares fit to generate the necessary uncertainties for ultimately performing a dynamic risk analysis, where a graphical plot of an estimate of risk with uncertainty vs. a predicted most likely date of a high consequence failure event due to creep rupture becomes available for a risk-informed inspection strategy associated with an energy-generation or chemical processing plant equipment.

Commentary by Dr. Valentin Fuster
2018;():V001T04A003. doi:10.1115/ETAM2018-6727.
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This paper overviews recent advances in developing novel alloy design concepts of creep-resistant, alumina-forming Fe-base alloys, including both ferritic and austenitic steels, for high-temperature structural applications in fossil-fired power generation systems. Protective, external alumina-scales offer improved oxidation resistance compared to chromia-scales in steam-containing environments at elevated temperatures. Alloy design utilizes computational thermodynamic tools with compositional guidelines based on experimental results accumulated in the last decade, along with design and control of the second-phase precipitates to maximize high-temperature strengths. The alloys developed to date, including ferritic (Fe-Cr-Al-Nb-W base) and austenitic (Fe-Cr-Ni-Al-Nb base) alloys, successfully incorporated the balanced properties of steam/water vapor-oxidation and/or ash-corrosion resistance and improved creep strength. Development of cast alumina-forming austenitic (AFA) stainless steel alloys is also in progress with successful improvement of higher temperature capability targeting up to ∼1100°C. Current alloy design approach and developmental efforts with guidance of computational tools were found to be beneficial for further development of the new heat resistant steel alloys for various extreme environments.

Commentary by Dr. Valentin Fuster
2018;():V001T04A004. doi:10.1115/ETAM2018-6733.
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The majority of studies of the heat transfer inside the hot box treats the heat transfer as a steady-state process. This paper demonstrates that this approach cannot be applied to the most dangerous cases of the cyclic thermal stress. The significant thermal gradients may occur in the skirt to shell junction of a high-temperature vessel and set up critical thermal stresses. It is a common practice to use a hot box to equalize temperatures of a shell and a skirt support. Reduction of thermal gradient results from a radiative heat transfer inside this hot box. Where a heating/cooling rate is high enough, as in coke drums, for example, the accounting of transient alters radically the distribution of a thermal stress state, and allows us to reconsider the mechanics of the fracture growth in the skirt to shell weld. This paper proves that during the cooling of coke drums some parts of the skirt support have higher temperatures than the shell, which causes tensile circumferential stresses in the weld. The intensity of the radiative heat transfer falls rapidly, when cooling a shell down to 247 °C, which leads to the increase of thermal gradients in the weld zone. This paper proposes a solution to the thermal problem in 2D, and strain-state analysis — in 3D, due to the presence of skirt slots equally spaced around skirt circumference, which increases the circumferential flexibility. The two-dimensional thermal field has been interpolated to a three-dimensional hexagonal grid for solving the thermo-strength transient problem.

Commentary by Dr. Valentin Fuster
2018;():V001T04A005. doi:10.1115/ETAM2018-6737.
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This paper outlines several procedures for developing allowable compressive stress rules in the creep regime (time dependent regime). The rules are intended for the ASME Boiler and Pressure Vessel codes (Sections I and VIII). The proposed rules extend the methodology presently outlined in Sections I, II-D, and VIII of the ASME code for temperatures below the creep regime into temperatures where creep is a consideration.

Commentary by Dr. Valentin Fuster
2018;():V001T04A006. doi:10.1115/ETAM2018-6749.
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In general Section I of the ASME Boiler Code was originally developed for industrial boilers through to sub-critical boilers operating at relatively low temperatures and pressures under steady state conditions. Current and future boilers do and will operate at higher temperatures and pressures under cyclic loading requiring a more detailed assessment and examination to ensure safe and reliable operation.

Design by Analysis (DBA) methods will be fundamental to the assessment process for key boiler components. It is intended that the Code will incorporate several DBA methods, ranging in complexity, to allow the user some flexibility to select the method appropriate to the design conditions.

The methods currently being considered include an elastic approach based on Section VIII Division 2, a simplified inelastic approach, an inelastic approach based on the Omega method from API 579, the Section VIII Division 2 Code Case 2843 based on the Section III Part NH rules utilizing the strain deformation method and a new Section III Code Case based on the EN 13445 approach.

This paper will look at the key aspects of the methods and highlight the limitations of each.

Topics: Boilers , Design
Commentary by Dr. Valentin Fuster

Experience With Subcritical/Supercritical Boilers, Petrochemical Components, and Advanced Nuclear Vessels at Elevated Temperatures

2018;():V001T05A001. doi:10.1115/ETAM2018-6721.
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A fitness-for-service (FFS) evaluation was performed on a cogeneration power plant high pressure steam line. The piping system included a Gr 91 to Gr 22 dissimilar metal weld (DMW) between an SA-335 Gr P91 pipe and an SA-335 Gr P22 reducer. This unit had accumulated more than 100,000 service hours. The FFS project included as-built and as-found piping stress analyses, redistribution of creep stresses, weld residual stress estimates, review of the nondestructive examination (NDE) results, evaluation of the plant information data, and a fracture mechanics evaluation.

Due to tapering of the Gr P22 pipe to match the wall thickness of the Gr P91 pipe at the DMW interface, the Gr P22 pipe wall thickness was not in compliance with the ASME B31.1-2000 Code minimum wall thickness (MWT). In addition, an inspection of the single groove girth DMW revealed ultrasonic indications along the fusion face of the weld. The lack of side wall fusion (LSWF) can be considered as a planar and crack-like indication, so a fracture mechanics evaluation was performed.

The piping stress analysis revealed that the DMW was subject to low axial stresses. A creep life fraction evaluation was performed for the material that does not have the LSWF indication, considering conservative creep rupture data, weld performance degradation, redistributed creep stresses, and multiaxial stresses in the DMW. Due to the low stresses, the life fraction analysis estimated more than 50 years of remaining creep life.

Failure Assessment Diagrams (FADs) were developed to evaluate the component integrity for various combinations of crack depths and lengths. The reported indications should not compromise the integrity of the component subject to the typical plant operation during the next 12 years and the component is fit for continued operation.

The crack propagation evaluation determined that the DMW has a predicted minimum safe operating life of at least 12 years if operated as in the past. Because the wall thickness of the tapered reducer is below the ASME B31.1 Code allowable MWT, it was recommended that the DMW be examined during a scheduled outage within 5 years and the component be replaced with Gr P91 material during a major outage within 8 years.

Commentary by Dr. Valentin Fuster

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