bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cooldown of LNG Loading Systems – An Integrated Approach. Part 1: Piping Stress Analysis
Authors: Bottomley Ian , Carr Nick , Nicolle Andre , Azarbadegan Alireza 
Published: November 2024

Abstract
A common understanding amongst designers and operators of LNG terminals is that cooling down large-bore stainless steel piping systems using Liquid Natural Gas (LNG) or Liquid Nitrogen (LN2) can lead to steep temperature gradients generating high stresses / strains and the potential for low-cycle fatigue failure.
The normal approach for cooling down LNG piping systems is that they are cooled down over a long period of time during the commissioning or Start-up phase and then kept cold through continuous recirculation of the LNG to minimize or avoid the need to cooldown again during normal operation. The slow cooldown approach is typically achieved by using a sufficient volume of boil-off gas generated from LNG or LN2. Cold gas ensures uniform cooldown of large-bore stainless steel piping systems to avoid excessive thermal stresses. However, using boil-off gas for the slow cooldown of LNG loading systems is not practical in all facilities, particularly in substantial piping systems with significant thermal mass where generating sufficient volumes of cold gas is impractical.
This paper presents the first part of a comprehensive study on a hybrid cooldown approach using liquid and boil-off gas to cool the LNG piping system. A multiphysics approach is adopted which includes CFD analysis to model the heat transfer from the liquid and gas to the pipe. The temperature gradients developed are then mapped to an FEA of the piping system to evaluate the impact of circumferential temperature gradient on local and global thermal stresses and thereby determine the fatigue life of the system.
This paper is Part 1 of a series of papers. This paper focusses on the results of investigations carried out to better understand the theory of how the temperature gradients and stresses will develop in a piping system and their sensitivity to the rate at which the cryogenic liquid enters the pipework. From this a strategy is developed which will ultimately provide the basis for a cooldown procedure.
Subsequent papers will cover the application of the cooldown procedure to the actual piping system. This will include a full CFD and FEA of the piping system combined with validation of the simulation from the commissioning of the live system. It is anticipated that Part 2 will be published in 2025.
Very Low Cycle Fatigue Evaluation of Pipe Elbow Under Dynamic Cyclic Loading and Experimental Validations
Authors: Song Hyun-Seok , Park Joo-Young , Kim Yun-Jae , Kim Jin-Weon 
Published: November 2024

Abstract
This paper reports the strain-based very low cycle fatigue evaluation results of SA403 WP316 stainless steel pipe elbow under dynamic cyclic loading condition. Very low cycle fatigue tests of a pipe elbow under dynamic cyclic loading were performed. A sine wave acceleration was applied to repeat opening and closing of the pipe elbow, and the internal pressure was applied or not applied depending on the test. Failure occurred by very low cycle fatigue crack inside the crown of the pipe elbow. The tests were simulated by finite element dynamic analysis using Rayleigh damping with 0.5% damping ratio and bi-linear kinematic hardening model of which parameters were determined by JSME Code Case rule. The simulation was validated by comparing the acceleration of the mass attached at one end of the pipe elbow specimen and the displacement between each end of the elbow specimen with experimental data. Using the simulation data, the very low cycle fatigue evaluation of pipe elbow under dynamic cyclic loading was performed to calculate the cumulative usage factor. In the evaluation, two strain-based evaluation methods were used: (1) ASME BPVC Sec. VIII Div. 2 Part 5 and (2) the model incorporating the void shrinkage effect. The method incorporating the void shrinkage effect significantly improves the evaluation results and still gives conservative results. Above conclusions are consistent with the findings for quasi-static cyclic loading.
Experimental Study on Mechanical Response of Defective Gas Pipeline Under Heavy Vehicle Load
Authors: Ren Fei , Shuai Yi , Lv Zhiyang , Mei Yuan , Xie Dong , Jiang Lu , Jiang Lumeng , Yu Shengyang 
Published: November 2024

Abstract
Pipeline is one of the infrastructure that ensures people’s livelihood and social production. With the acceleration of urbanization, the impact of vehicle overload on the safety of buried pipelines is becoming increasingly serious. Especially for buried defective gas pipelines with a long service life, when the pipeline ruptures due to vehicle loading, it can cause serious fire and explosion accidents, seriously affecting the safety of urban areas. Experimental study on mechanical response of defective gas pipeline under heavy vehicle load is carried out in the paper. The considered pipeline defect conditions include defect size and defect location. Based on the research results, it can be found that under vehicle overload conditions, the deformation variables of pipeline end defects are significantly lower than those in the middle. As the axial length of the defect increases, the strain at the defect site of the pipeline can decrease to a certain extent. Pipeline strain is more sensitive to defect size than defect location, and defect size may be a high-risk point for pipeline failure under heavy load conditions. There is consistency between the overall deformation of the pipeline and the strain test results. Pipeline deformation is more sensitive to defect size than defect location, but its overall characterization ability is not as good as the strain parameters at the defect location.
EPRG Full Scale Fatigue Crack Growth Test on a Modern Linepipe Material in Gaseous Hydrogen
Authors: Bezensek Bostjan , Huising Otto Jan , Bacchi Luca , Roovers Paul , Bertelli Emanuele 
Published: November 2024

Abstract
EPRG (European Pipeline Research Group) is performing full scale fatigue crack growth testing in high purity hydrogen gas on a 28” OD API5L X70 modern LSAW welded pipe. The test vessel also contains normal (250 HV10) and high hardness (300 HV10) girth welds. The vessel is seeded with EDM notches and weld flaws. The aims of the test are to assess the effect of hardness on fatigue crack growth and fracture, compare the small scale laboratory testing with full scale behaviour under cyclic pressure and compare the modern with vintage materials.
In the ongoing modern pipe test several notches have established fatigue crack growth and some have reached failure point. An accelerated fatigue crack growth was observed consistent with small scale test results and the recent HyBlend fatigue crack growth model. A small non-fatigue driven crack growth is observed under constant pressure following large pressure cycling and this is attributed to both, a transient remnant cyclic plasticity driving force and exceedance of the toughness value Jth (at Δa = 0mm) rather than due to a new subcritical crack growth mechanism (the da/dt effect). Further small scale testing is ongoing to confirm this observation. Design of hydrogen pipelines such that the Jth (at onset of crack growth) is not exceeded should mitigate this concern.
Remaining Useful Creep Life Evaluations of Three Main Steam Piping Systems With Girth Weld Creep Cracks
Authors: Cohn Marvin J. 
Published: November 2024

Abstract
Safety and reliability are the preeminent concerns in the design, operation, and maintenance of power piping systems. Main steam (MS) piping systems in power piping plants are subject to severe operating conditions including creep range temperatures, high pressures, high stresses, cycling, and malfunctioning supports. Over time, these factors lead to material degradation which can significantly reduce the long term integrity and safety of the piping system. The identification and evaluation of critical components is vital to ensuring the efficacy of these piping systems and is useful to make informed maintenance decisions.
Conventional designs of MS piping systems in the United States comply with the American Society of Mechanical Engineers (ASME) B31.1 Power Piping Code. While operating in the creep range, thermal expansion stresses gradually redistribute over time. However, the ASME B31.1 Code does not consider the evaluations of time-dependent thermal stress redistribution, multiaxial stress effects, through-wall stress redistribution, residual welding stresses, and time-dependent creep life consumption due to material creep degradation.
The MS piping system is one of the most critical high energy piping systems. Many of the MS piping system girth weld failures have accelerated creep damage due to a combination of high operating temperatures and unintended high stresses from malfunctioning supports.
Over the past two decades, a creep life consumption methodology has been used to predict material creep damage in MS piping system girth welds considering the most current site information. This methodology has been used to prioritize the most likely girth welds to have accelerated creep damage. Three MS piping systems with service-related girth weld creep cracks are evaluated with a creep life consumption methodology that considers base metal equivalent weld stresses, multiaxial stress factors, time-dependent stress redistribution, cumulative life consumption curves, and illustrations of color-coded piping system (remaining useful life) RUL contour plots. The piping system RUL contour plots provide a visual representation of the girth weld remaining creep lives, which facilitate prioritized inspection decisions.
Technical Basis for Inspection Optimization and Deferral of PWR Pressurizer Component Examinations
Authors: Cofie Nathaniel G. , Dedhia Dilip , Chesworth Scott T. , Shim Do Jun , Grizzi Robert 
Published: November 2024

Abstract
Pressurizer welds in pressurized water reactors (PWRs) are required to be inspected every ten years by ASME Code, Section XI. The results of a comprehensive survey of over forty years of examinations for pressurizer welds performed at 74 domestic and international PWR units showed that no known degradation has occurred in these welds. This demonstrated that pressurizer welds are very flaw tolerant and can accommodate a much longer inspection period. A comprehensive study involving stress analyses and probabilistic and deterministic fracture mechanics analyses supported this observation and determined that the inspection of these welds can be deferred beyond the current ten-year requirement without compromising plant safety. As an alternative to the inspection interval for PWR pressurizer welds provided in Section XI of the ASME Code, EPRI developed the technical basis for deferring these examinations for an extended period in EPRI Report 3002015905.
A Code Case has been introduced in ASME Code, Section XI that would allow the inspection of certain pressurizer weld components to be deferred to 30 years after the date of the last qualified inspection of each component type. Specifically, the Code Case addresses the following ASME Code, Section XI Examination Categories and Item Numbers:
• Class 1, Category B-B, pressure-retaining welds in vessels other than reactor vessels (Item Nos. B2.11, B2.12, B2.21 and B2.22), and
• Class 1, Category B-D, full penetration welded nozzles in vessels (Item No. B3.110).
The technical basis report has been used by at least 20 PWR units (with Salem Units 1 and 2 being the lead plant submittal) to request relief from the U.S. Nuclear Regulatory Commission (NRC) for deferral of these two pressurizer weld examination categories to greater than 10 years.
This paper provides the technical basis for the 30-year deferral of the examination of pressurizer weld components in support of the proposed Code Case using the results of the evaluations in the EPRI technical basis report plus additional evaluations that were performed to specifically address the 30-year deferral period and the lessons learned through the Request for Alternative process by the lead and follow-on plants.
Quantitative Characterization of Hydride Morphology in Support of Improving Cohesive-Zone Fracture Toughness Model for Zr-2.5Nb Pressure Tubes
Authors: Liu Cheng 
Published: November 2024

Abstract
The CSA Standard N285.8 requires evaluation of service conditions for protection against fracture of operating Zr-2.5Nb pressure tubes in CANDU®1 reactors, as well as demonstration of Leak-Before-Break. Zr-2.5Nb pressure tubes are susceptible to hydride formation when the solubility of hydrogen in the pressure tube material is exceeded. Experiments have shown that the presence of hydrides can reduce the fracture toughness of the pressure tubes, depending on hydrogen concentration, hydride distribution and temperature. An improved cohesive-zone based model has been developed to predict the fracture toughness of Zr-2.5Nb pressure tubes in the lower-shelf and transition temperature regimes. To support the model development, quantitative metallography of bulk hydrides has been performed on optical micrographs from metallographic samples taken from hydrided irradiated rising pressure burst test specimens, and from rolled joint regions of ex-service pressure tubes. The results of quantitative metallography have been analyzed statistically to characterize the variations of the hydride morphology and the matrix ligament distribution in the radial-circumferential plane of the pressure tube. Parametric distributions have been developed for bulk hydride length, bulk hydride orientation angle, and radial extent of matrix ligament between bulk hydrides. Engineering relations have been further developed to characterize the variation of the parametric distribution of bulk hydride orientation angle. This paper describes the methodologies used in the quantitative characterization of hydride morphology and discusses the results.
Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens - Surface Finishing Effect for Notched Specimens of Low Alloy Steel
Authors: Nomura Yuichiro , Takagoshi Daiki , Asada Seiji , Sugeta Atsushi , Kitamura Yoshihide 
Published: November 2024

Abstract
The DFC and DFC2 subcommittees in the Japan Welding Engineering Society developed a new approach of fatigue analysis method with support from the Japanese utilities. This fatigue analysis method had several modifications made and has been incorporated into the JSME Environmental Fatigue Evaluation Method 2022 Edition (JSME S NF1). Also, research on effects of surface finishing and mean stress on fatigue lives of notched specimens have been conducted by the DFC3 and DFC4. In this paper, the test plan and overview of the outcomes of the DFC3 and DFC4 are introduced.
In this series of research, effects of surface finishing on fatigue strength and relation between a fatigue strength reduction factor and mean stress correction have been investigated using notched specimens, of which materials are carbon steel (CS:JIS STPT370) and low alloy steel (LAS:JIS SQV2A). The applicability of the Ksf (factor for the effect of surface finishing) equation of the JSME S NF1 to notched specimens has been investigated and confirmed based on the experimental results.
The order of consideration of the fatigue strength reduction factor and mean stress correction may not need to be considered if the Smith Watson Topper (SWT) approach can be applied to mean stress correction. Hence, the applicability of the SWT approach with stress concentration and mean stress have been investigated and confirmed based on the experimental results.
In this study, the effect of surface roughness due to emery polishing and machining (Rz = 25μm) was confirmed using circumferentially notched specimens. Ksf(ε) of the circumferentially notched machined condition was almost equal to the surface finish effect coefficient Ksf of the smooth machined material of the same roughness. It was confirmed that the JSME Ksf equation can be applied to the circumferentially notched shape and evaluated on the conservative.
Study of Fatigue Properties of Graphite Materials Under Four-Point Bending
Authors: Zhou Junjie , Wu Tianhao , Sun Libin , Shi Li , Wang Xiaoxin 
Published: November 2024

Abstract
The structural integrity of graphite components, supporting the reactor core of HTGRs (High-Temperature Gas-Cooled Reactor), is essential to the operational safety of the reactor. Therefore, the fatigue performance of graphite structures has been an extremely significant issue in both academia and industry. Currently, the stress amplitudes of the fatigue tests of nuclear graphite are normally less than its tensile strength, which is unsuitable for some components with stress concentrations. In this paper, fatigue tests with four-point bending loading were carried out to investigate the fatigue behavior of the nuclear-grade graphite material IG110 at stress levels higher than tensile strength. The four-point bending fatigue test fixture was designed based on the ASTM test standard. Different samples were tested to study the stress concentration effects. In the test, the bending fatigue life of graphite materials under different stress levels was obtained. The fatigue properties of graphite materials under bending load were also analyzed. This study not only provides important experimental data and theoretical guidance for the engineering application of nuclear-grade graphite materials in HTGRs, but also provides useful experience and inspiration for the fatigue performance studies of other brittle materials.
Full Scale Three-Dimensional Moving Arc Weld Analyses of Control Rod Drive Mechanism J-Groove Welds and Implications on Cracking
Authors: Brust Frederick W. , Punch Ed , Twombly Elizabeth 
Published: November 2024

Abstract
Flaw indications have been found in some nozzle to stainless steel piping dissimilar metal (DM) welds and reactor pressure vessel heads (RPVH) control rod drive mechanism (CRDM) tube welds in pressurized water reactors (PWR) throughout the world. The nozzle and J-groove welds usually involve welding ferritic (often A508) nozzles using Alloy 182/82 weld metal. Many of the nozzles have been repaired by using A152/52 filler metal which is resistant to primary water stress corrosion cracking (PWSCC) but many of the CRDM welds remain A182/82 material. The welds may become susceptible to a form of corrosion cracking referred to as primary water stress corrosion cracking (PWSCC). It can occur if the temperature is high enough (usually &gt; 300C) and the water chemistry in the PWR is typical of operating plants. The weld residual stresses (WRS) induced by the welds are a main driver of PWSCC. Crack growth in the J-groove welds of the vessel heads remains a concern for the integrity of the heads.
Computational weld analyses were performed for nozzles of different angles including 0-degree (top dead center), 25-degree, and 53-degree nozzles years ago. In the past simplified weld analyses of the J-groove welds using a ‘lump pass’ analysis procedure and simple geometric symmetry assumptions of the j-groove welds were made. Here full moving arc solutions of the full J-groove welds are made without the simplified geometric assumptions made in the past. Here FE models were used in this project to perform analyses of a small angle (9-degree) and a large angle (46-degree) nozzle and compared to limited WRS measurements at several locations in similar size head nozzles.
This paper summarizes WRS fields that are developed in the J-groove welds and ramifications on crack growth in the welds. Discussion of crack growth in these heads and consideration of Code Case N-729 assessment of cracking in these welds and tubes is discussed as well.
An Examination of Margins Needed to Ensure Conservative Application of T0 to RPV Fracture Toughness
Authors: Hall J. Brian , Golchert Brian M. , Simpson Derek 
Published: November 2024

Abstract
Variation in fracture toughness of a heavy-section reactor pressure vessel (RPV) steel plate, forging or weld can be caused primarily by processing and chemical composition variation. Understanding the variation is paramount to enable application of the ASTM E1921 measured ductile-brittle transition temperature, T0, to RPV integrity evaluations. Variation in toughness in thick section forgings and plates can be caused by carbon segregation and through thickness by the quenching process. Variation in toughness can also be caused by variation in chemical composition of the elements that enhance irradiation embrittlement, primarily copper and nickel. The geometric scale of these variations varies. For example, carbon segregation in a large ring forging might be limited to one region while it is well documented that toughness increases near the surface where the cooling rate was high when quenching. For welds, copper and nickel might vary within and between weld beads and at least a significant portion of the variation is captured in a typical set of toughness specimens used to determine T0. This paper will look at many datasets where at least two sets of specimen tests from which T0 can be calculated are available from the same heat of steel. It will be assumed that one T0 measurement is used as the direct fracture toughness measurement and the 2nd (or more) are measurements from the irradiated RPV represented by the irradiated ductile-brittle transition temperature fracture toughness test results. One T0 measurement will be adjusted to the condition of the 2nd (or more) measured dataset with assessment of the margin needed to ensure an evaluation of the RPV would be bounding. This information will enable development of necessary margins in applying unirradiated and irradiated master curve fracture toughness measurements to an RPV component using relatively small samples.
Investigation of Fluidelastic Instability in Normal Square Tube Arrays Subjected to Air Flow
Authors: Elhelaly Amro , Hassan Marwan 
Published: November 2024

Abstract
A comprehensive set of wind tunnel experiments was carried out, focusing on the normal square (in-line) array subjected to air cross-flow. The array’s geometric influence, encompassing factors such as array size, type, pitch ratio, and flexibility level, on the stability threshold were investigated. For the first time, experimental observation of streamwise fluidelastic instability (SFEI) in the normal square array was confirmed. The findings highlight the important role played by the array’s pitch ratio and the number of flexible tubes in influencing the stability threshold, specifically in the transverse directions.