bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens - Surface Finishing Effect for Notched Specimens of Carbon Steel
Authors: Takanashi Masahiro , Wang Yun , Hirano Akihiko , Kitamura Yoshihide
Published: November 2024

The DFC1 and DFC2 subcommittees of the Japan Welding Engineering Society developed a new approach to fatigue analysis. A part of the approach has been revised and incorporated into JSME Environmental Fatigue Evaluation Method for Nuclear Power Plants 2022 Edition, which also includes the factor for the effect of surface finish. Considering the factor was devised on the basis of limited tests and literature reviews, the subsequent subcommittees, DFC3 and DFC4, investigated the effect of surface finish on the fatigue strength. This paper presents the effect of surface finish on the fatigue strength of carbon steel in a series of studies by the subcommittees. Initially, four series of smooth round bar specimens were prepared. One series was polished, while the other three were machined to target surface roughness levels of Rz = 6.3, 25, and 50 μm, respectively. Strain-controlled fatigue tests were conducted on these specimens. The fatigue strength of Rz = 6.3 μm was comparable to that of the polished specimen. However, it reduced with an increase in surface roughness. The fatigue strength ratio of the polished specimen to the machined specimen was defined as the factor for the effect of surface finish, Ksf. The maximum value of Ksf was about 1.15, which rose in the high-cycle region. Subsequently, considering that actual components typically fatigue at structural discontinuities, load-controlled fatigue tests were conducted on round notched specimens, with the notch root polished and machined to Rz = 25μm. The Ksf was obtained in the same manner as for the smooth specimen. It was hence affirmed that the Ksf of JSME, developed from the smooth specimen test results, is applicable to structural discontinuities where fatigue failures arise in actual components.
Hillside Nozzle Crack Analysis Comparison Using FAD and Crack Driving Force Methods With 3-D Crack Meshes
Authors: Thorwald Greg
Published: November 2024

Computing accurate crack assessments, such as via methods described in the API 579-1/ASME FFS-1 standard, helps support reliable pressure vessel operation, maintenance and inspection. When solutions of the actual crack geometry or location are not available, three-dimensional (3-D) crack meshes can be used in Finite Element Analysis to compute the solutions. Two crack assessment methods are used in this paper to assess postulated cracks in the weld connecting a hillside nozzle to the vessel’s elliptical head. The first method is the Failure Assessment Diagram, and the second method is the crack driving force.

Both crack assessment methods concurred that the cracks are sub-critical. The deeper crack case located at the side of the nozzle gave the largest J-integral value of the examined cracks and was less than the material estimated toughness. Weld residual stress was included in the analyses by a simplified method applying a delta temperature to the weld zone nodes to cause contraction in the weld, resulting in tensile residual stress.

When using 3-D crack meshes, the crack driving force method may be advantageous to include both weld residual stress and pressure loading within a single elastic-plastic model, and the analysis needs to converge only to the design pressure. The FAD method uses elastic analyses to compute the stress intensity for each load category (i.e., primary, secondary, or residual), which are quicker to run. In this analysis, an estimated reference stress was used because the elastic-plastic analysis of the pressure load to compute the reference stress did not provide sufficient results.
A Thermal Striping Evaluation Methodology for Natrium™ Internal Components Using Frequency Response Function Solutions
Authors: Xu Heqin , Riordan Tom , Bhuiyan Shafiq , Koneru Saradhi , Cohen Michael
Published: November 2024

Liquid sodium is used as the coolant in the Natrium (a TerraPower and GE-Hitachi technology) reactor design because of its outstanding thermal properties. Sodium becomes liquid at above 98°C and remains in liquid state up to a very high temperature of 883°C at atmospheric pressure. This feature allows the reactor to have a high operating temperature while maintaining a sufficient margin to avoid boiling of the coolant under all design basis events, without any pressurization as is typically utilized in a light water reactor (LWR) design. On the other hand, there are certain critical structural mechanics issues for the components in contact with high temperature liquid sodium. Besides the design basis thermal transients, the primary coolant streams flowing out of the fuel assemblies and control assemblies may experience incomplete mixing of hot and cold jet flows, causing a special thermal hydraulics phenomenon called thermal striping. The thermal striping may have a temperature fluctuation over 50°C at frequencies of 0.1 to 10 Hz. The temperature fluctuation in the flow may also be caused by thermal stratification at the interface of the horizontal relatively hot and cold streams. Due to the high frequency temperature fluctuation in the liquid sodium, the structures in contact with the flow are subjected to nontrivial cyclic thermal stresses which may cause high cycle fatigue (HCF) damage to the structures. The structures containing both liquid sodium and cover gas may also experience temperature fluctuation due to free surface level fluctuation at the liquid/gas interface where the cover gas and the liquid sodium have very different thermal conductivities. This paper presents frequency response function (FRF) solutions to evaluate the thermal striping limits of the Natrium internal components against the fatigue crack propagation prevention criteria while considering the cyclic range of thermal stresses and stress intensity factor due to the thermal striping on one side of a component, and various boundary conditions on the other side.
Elastic-Plastic Finite Element Analysis Utilizing Detailed Crack Profiles
Authors: Holloman Ryan , Blanks Daniel , Martinez Miguel , Thorwald Greg , Turnquist Michael
Published: November 2024

Operators are required to mitigate any known risk identified during a pipeline inspection, meaning all detected crack-like defects must be investigated. While defects with depths or lengths exceeding the limits set by the pipeline owner will be repaired, shallower or shorter crack-like defects are often evaluated using engineering analysis and judgement. Deterministic assessment based on modern fracture mechanics is commonly used to inform the mitigation process. However, these assessments often assume lower bound material properties and generalize the crack shape as semi-elliptical for simplicity and conservatism, potentially rendering overly conservative results.

Through evolving in-line inspection (ILI) technology, ultrasonic imaging technologies can now capture the true profile of a crack-like defect. Rather than assuming a semi-elliptical crack based on a single depth and length measurement, detailed crack shape analysis now offers reduced conservatism and improved accuracy. However, averaging techniques are often used to characterize a detailed crack shape given that closed-form fracture mechanics models such as API 579-1/ASME FFS-1 Fitness-for-Service (API 579) or MAT-8 require an assumed semi-elliptical geometry.

An alternative deterministic assessment is provided that can be executed with the detailed crack profile using elastic-plastic finite element analysis to calculate burst pressure and remaining life. Three-dimensional (3-D) crack meshes of the detailed crack profiles are generated using the ILI data, enabling the J-integral to be accurately computed along the entire crack front. The maximum crack front J-integral value is compared to the pipe’s toughness to determine the predicted burst pressure. The 3-D custom shape crack results can then be compared to the API 579 and MAT-8 fracture models. This alternative approach reduces conservatism, which can aid operators and reduce costs while maintaining asset integrity.
Electromagnetic Lithium Ring Compression for Magnetized Target Fusion Application: Trajectories
Authors: Dick Jean-Sebastien , Sirmas Nick , Bernard Scott , Santos Lemuel , Forysinski Piotr
Published: November 2024

To achieve commercially relevant fusion conditions in a magnetized plasma, rapid and efficient heating must surpass heat loss. In Magnetized Target Fusion (MTF) experiments, which heat plasma by compression, a magnetic flux conserver made of metal is essential for plasma confinement, and an understanding of the compression trajectory of this plasma liner is crucial to the design and operation of the machine.

In this work, lithium rings, 527 mm in diameter and 55 mm in height, were produced by centrifugal casting and electromagnetically compressed using a high voltage power supply with capacitor energy ranging from 100 kJ to 250 kJ. High speed cameras were used to track the trajectories of the inner and outer edges of the top surface of the ring, as well as its inner edge at the equator. Magnetic field sensors were positioned at a number of radial locations to measure the change in magnetic flux density during ring compression. Ring parameters, such as thickness and temperature, were explored to attain symmetric compression trajectories free of buckles.

A 2D-axisymmetric numerical model was developed using the ANSYS LS-DYNA software package to predict compression trajectories and evaluate the energy efficiency of the compression. The aim of this work is to assess the use of concentric coil electromagnetic compression, also known as a theta-pinch, in magnetized target fusion using a solid lithium liner and to validate the LS-DYNA model. Close agreement between simulation and experiment was observed. This research contributes to advancing Magnetized Target Fusion technologies, with implications for future fusion energy applications.
Comparative Study of Crack Shape on the Ductile Fracture Response of Cracked Pipelines
Authors: Zhang Xinfang , Yoosef-Ghodsi Nader , Kainat Muntaseer , Leung Juliana Y. , Adeeb Samer
Published: November 2024

Buried pipelines are subjected to various types of loads, including external pressure from soil overburden and internal pressure from pressurized fluids. These loads can induce axial and hoop stresses, which are the primary factors leading to the formation of integrity threats, such as cracks. The presence of cracks can render a pipeline susceptible to failure, posing a significant threat to its operation, safety, and the environment. This underscores the importance of promptly detecting and evaluating even seemingly minor surface defects, as they can significantly damage the structural integrity of the pipeline. It is also crucial to accurately predict the failure pressures of pipelines with cracks to ensure that the operating pressure remains below this critical limit with an adequate margin of safety. A variety of approaches exist for assessing cracks in pipes, including empirical approaches such as MAT-8, Ln-Sec and CorLAS™ models, as well as numerical approaches like the extended finite element method (XFEM). XFEM is a powerful tool to estimate the failure pressures of pipelines containing cracks. It extends the capabilities of the traditional Finite Element Method (FEM) and offers a more effective means of simulating crack propagation. In ABAQUS, initial cracks can be modelled in either sharp or blunted shapes. However, it is uncertain whether the shape of the crack affects the failure pressures of cracked pipelines. For this purpose, detailed parametric studies are necessary to investigate the implications of pre-existing cracking shapes on the ductile fracture response of pipes subjected to pure mode I loading.
Fitness-for-Service Analysis of a Light Water Reactor Pressure Vessel Under Complex Operating Conditions
Authors: Tran Minh N. , Muransky Ondrej , Spencer Benjamin W.
Published: November 2024

Conventional power-generation plants, including nuclear plants, have been traditionally designed to provide a steady baseload energy capacity, optimizing output efficiency while minimizing variable costs. However, the growing adoption of large-scale renewable energy-generation systems, which rely on intermittent sources such as solar and wind, has introduced more variability into the energy supply in interconnected electricity grids. As a result, the next generation of power plants needs to operate in what is known as load-following mode, requiring flexible adjustments in electricity production to align with the energy demand on the grid. This transition from the steady baseload operation to load-following operating conditions can significantly increase the number of times various plant components are exposed to transient stresses. This increased thermomechanical cycling can lead to accelerated material degradation, thereby elevating the risk of premature component failure. It becomes imperative to conduct a comprehensive analysis of fatigue, creep-fatigue, and stress corrosion cracking life to assess the resilience of the various engineering components under these flexible load-following operating conditions.

This study aims to develop a comprehensive numerical model of a light-water reactor pressure vessel (RPV) to investigate its degradation under various operating scenarios. This coupled thermomechanical finite element analysis evaluated the stress response of the RPV caused by considering fluctuations in thermal and mechanical loads caused by the varying pressure and temperature occurring during the load-following operation. Critical locations on the RPV are subsequently identified based on the stress response. The stress intensity factors for the postulated flaws at those locations are then calculated, followed by an evaluation of the reactor’s life in accordance with the American Society of Mechanical Engineers Boiler and Pressure Vessel Code Section XI. This comprehensive life assessment covers a number of transients expected during the flexible load-following operation, providing invaluable insights into the RPV’s structural integrity. Moreover, the development methodology can be adapted to other reactor components, as well as components of conventional power stations affected by varying operating conditions.
Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens (5) - Application of Elastic-Plastic FE Analyses for Notched Specimens of Carbon Steel
Authors: Nakane Motoki , Wang Yun , Takanashi Masahiro , Hirano Akihiko , Kitamura Yoshihide
Published: November 2024

The DFC3 and DFC4 subcommittees of the Japan Welding Engineering Society had investigated the effect of mean stress on fatigue properties of notched carbon steel and mean stress correction methods. In these studies, small specimens were adopted for fatigue tests and these tests are conducted by load control because the cross section of the notch root is too narrow to measure the strain. However, it is very important to understand the strain or stress state at the notch root to evaluate the fatigue test results.

In this study, an elastic-plastic analysis method for circular notched carbon steel specimens was investigated to contribute to the setting of fatigue test conditions and the evaluation of test results. The equivalent strain amplitudes calculated from the analyses were almost consistent with the S-N curves of smooth specimens and this agreement showed the validity of the application of the analytical method to circular notched specimens. Furthermore, the loading conditions for fatigue tests of circular notched specimens subjected mean stress were examined. The results indicated that fatigue tests with mean stress of about 5 MPa to 17 MPa and 9 MPa to 17 MPa can be expected for the notched specimens with stress concentration factor Kt = 1.5 and Kt = 1.8, respectively.
Validation Program for Seals and Flange Gaskets in Hydrogen and Hydrogen-Methane Blends Applications
Authors: Lejeune Hubert , Felten Jérémy
Published: November 2024

There is an increasing interest in hydrogen as a clean energy carrier in decarbonizing energy systems. Hydrogen’s various production paths and use for storing and transporting energy make it a flexible option for linking diverse sources of power generation with transmission and distribution networks. Large-scale hydrogen consumption will require a well-developed hydrogen transport infrastructure. For example, the European Hydrogen Backbone (EHB) initiative, bringing together more than thirty energy infrastructure operators, is working on the definition of hydrogen infrastructure including existing and new pipelines. Seals are identified as key components for the performances of these infrastructures, but a lack of recognized test protocols and available test data are reported by the end-users.

In this context, with several partners, Cetim (Technical Center for Mechanical Industry) has launched in 2022 a testing program on different seal types (“O”-rings, gaskets and dynamic seals) to evaluate their sealing performances and integrity (including Rapid Gas Decompression) with 100% hydrogen, 20% hydrogen - 80% methane blends and 100% helium (or 100% methane) as a reference gas. Long term thermal ageing was also involved to check the performances stability. This paper will identify facilities presently in use for validation, the testing protocols with which these tests are conducted and most importantly, their results.
Analysis and Treatment of Pipeline Vibration in Centrifugal Compressors
Authors: Wang Chengwen
Published: November 2024

While going through the startup process of a centrifugal compressor unit, the pipline of compressor tertiary outlet bypass to a gas expander and supporting structure was observed to be shaking abnormally. The shaking was significant enough that worker feld foot numbness on the steel grating and at a level that the owner was afraid of approaching the piping. The initial assumption was that the piping or the piping supports had been improperly designed. After being reinforced with the supports, the vibration still hadn’t been alleviated.

Further investigation revealed that the root cause of the problem was a flow-generated pulsation of the compressor that excited the pipeline shell mode. But the project’s start-up schedule was tight, and had no time to use CFD to analysis the reason. meantime it’s hard to change the excitation of the compressor and the mode of piping. The ultimate solution to the problem was the “flow-splitters” method to reduce the pulsation. we installed two porous noise reduction plates on the original flange of the pipeline. At last the vibration dropped to an acceptable range in the shortest possible time, ensuring the start-up progress. It provided a practical basis for the treatment of pipeline vibration of large centrifugal compressor in the future.
Present Status of the FRACTESUS Project: Numerical and Experimental Round Robins on Irradiated and Unirradiated Materials
Authors: Bonny Giovanni , Uytdenhouwen Inge , Altstadt Eberhard , Arffman Pentti , Cicero Sergio , Obermeier Florian , Petit Tom , François Pierrick , Tanguy Benoît , Swan Helen , Wilcox Hannah
Published: November 2024

The FRACTESUS project aims to determine the effect of specimen size on the fracture toughness properties. The project has entered its last year and many preliminary data are available. In this contribution, we report on the status of the three main inter-laboratory round robins (RR) that have been completed: i) numerical round robin; ii) experimental round robin on unirradiated materials; and iii) experimental round robin on irradiated material. The numerical round robin is completed by nine different laboratories and shows that the different numerical tools and set-ups used by the different laboratories provide comparable and consistent results. The experimental round robin on six unirradiated materials is completed by 13 different laboratories (> 480 fracture toughness tests). Except for the 73W weld material, the reference temperatures T0 obtained from MC(T) specimens by the different laboratories compares well to the ones obtained from large (mostly 1T-C(T)) specimens. The experimental round robin on the irradiated 73W weld material is performed by seven different laboratories (> 112 fracture toughness tests). Similar to the unirradiated case, T0 obtained from the MC(T) data set largely underestimates T0 from large specimens by about the same amount.
An Application for Crystal Plasticity Finite Element in Updating Industrial Integrity Assessment Practices
Authors: Horton Edward W. , Mostafavi Mahmoud , Knowles David , Chevalier Marc
Published: November 2024

Within the nuclear sector, structural integrity assessments must be performed to prove a plant is still safe to operate. Currently these assessments are conservative out of necessity, however if this conservatism could be reduced power plants could remain in operation for longer. To help increase the accuracy of predictions better material models can be used which take account of detailed features that are not completely considered, such as microstructure variation in fabricated component. Crystal plasticity (CPFE) is a technique that accounts for microstructure, so has the potential to help inform future revisions of integrity assessments. In this work CPFE is used in conjunction with the assessment code R5 to predict the life of a volume of material. The mesh within this volume is changed to represent microstructures often seen in service. It was found that CPFE was able to predict similar life to an inelastic model produced using suggestions from R5. The CPFE model also showed that different microstructures give a varying mechanical response which is something traditional continuum models are not directly capable of modelling.
Allowable Stress and Allowable Flaw Sizes Estimated by Converted Tensile Properties From Hardness for Austenitic Stainless Steel Pipe
Authors: Ha Yoosung , Yamaguchi Yoshihito , Hasegawa Kunio , Negyesi Martin
Published: November 2024

If a flaw in a high-toughness ductile pipe of a power plant is detected during periodic in-service inspection, stress applied at the flaw location of the pipe is compared with an allowable stress. When the applied stress is less than the allowable stress, the plant can operate continuously for a certain evaluation period in accordance with ASME Code Section XI. The flow stress given by the average of yield strength and ultimate tensile strength is an important material parameter for allowable stress. Recently, many fitness-for-service codes and technical reports have adopted conversions from hardness measurement values to yield strength and ultimate tensile strength. In this paper, we introduced the flow stress obtained from converted tensile properties from Vickers hardness using the presented equations for austenitic stainless steel. The allowable stress and allowable crack depths (sizes) estimated by the Vickers hardness were compared with those determined by actual tensile properties. As a result, the flow stress converted from hardness was about 1.5 times larger than that obtained by actual flow stress. The allowable flaw sizes calculated by the flow stress converted from hardness gave an appropriate indication when the allowable or applied stress was very low. However, the flow stress converted from hardness gave unconservative allowable stress, when the applied stress was large. Since the results are based on one available hardness measurement, other hardness measurements should be necessary to confirm these preliminary conclusions.
Structural Health Monitoring Using Time-Augmented Response Spectrum and Deep Learning
Authors: Aeba Takaki , Fukasawa Tsuyoshi
Published: November 2024

Institutions in the United States and Europe have highlighted the necessity for structural integrity assessment and issued guidelines for it. However, due to the lack of established standards for structural integrity evaluation, there is a demand for concrete methods. Techniques commonly used in structural health monitoring, such as Fourier and Wavelet transforms, are not physical quantities like acceleration and thus cannot be directly applied to seismic design. The response spectra used in seismic design lack temporal information. This paper proposes a time-frequency spectrum that is highly compatible with seismic design and includes temporal information. Furthermore, for the precision enhancement of structural integrity assessment, a deep learning model has been developed to determine structural integrity based on the multifaceted information provided by the proposed spectrum. The applicability of a structural health monitoring method combining these elements was verified using analysis and test data focused on plastic deformation. The validation results show that this method enables precise judgments, estimation of the time of anomaly occurrence, and visualization of the decision-making basis of deep learning.
Large Openings on Cylindrical Shell Subject to Axial Compression
Authors: Lu James , Millet Barry , Kirkpatrick Kenneth , Mosher Bryan , Hundl Jacob
Published: November 2024

Vertical vessels experience axial compression due to equipment dead weights, vessel contents and environmental loads. ASME BPVC Section VIII Division 2, Paragraph 4.5.17 provides rules for reinforcement of openings in cylindrical and conical vessels subject to axial compression. The rules outlined in the Code only apply to openings not exceeding 25% of the vessel diameter or 80% of the stiffening ring spacing. Openings exceeding these limits are required to be designed by analysis per Section VIII Division 2, Part 5. The rules in Part 4 of Section VIII Division 2 are quite restrictive for vessel manufacturers as a vessel smaller than 8’-0” in diameter with a 24” inner diameter manway would require a specialized analysis per the rules in Part 5 of the Code for which the majority of fabricators would require an outside consultant to perform, resulting in higher engineering costs for small diameter Division 2 vessels. Most of these vessels are not even subject to significant axial loads or bending moments. Pressure vessels designed to ASME BPVC Section VIII Division 1, European Standards EN 13445 and British Standard PD 5500 do not require opening designed for axial compression. This paper examines the effects of reinforcement for openings greater than the 25% of vessel diameter for vessels subject to axial compression and investigates the possibility of modifying the Code rules to increase the opening size limit to more than 25% of vessel diameters.
A Case Study on the Effects of Geometry and Stress Around Various Pin-Connected Members
Authors: Wiseman Phillip , Darade Animesh Anil , Sharma Timilsina Ayushma
Published: November 2024

Pin connections are commonly used in various applications revolving around civil and mechanical engineering. It is also an essential component in pipe support including both hangers and restraints, thus, understanding their current requirements is crucial. This paper involves a case study where different geometry of pin-connected members are examined on multiple stress conditions using finite element analysis (FEA) tools. Varied dimensions of pin and hole as well as multiple locations of the hole has been analyzed under various stress conditions. The stress distribution around the hole has been analyzed in this paper. The goal is to compare that stress distribution along the pin connected members, i.e., the hole, the pin, the connecting unit, and study which configuration would be suitable for which particular condition. The analytical data obtained using FEA and the stress distribution calculations has been used to compare and to select one of the most effective configurations. The primary purpose of the paper is to examine and optimize the effectiveness of pin-connected loads while considering their geometric restrictions. This optimization process involves finding the most efficient design for these members to ensure safety and reliability. The paper focuses on dimensional and stress regulations as per the ASME Boiler and Pressure Vessel Code and AISC 360 and takes into account the latest industry standards and guidelines to ensure compliance with current best practices. The paper investigates an analytical way to understand how the allowable stresses are handled in a certain geometric restriction and how the stress ratio is compared with geometric restriction of the pin, the hole and stress distribution around the hole.
Small Punch Tests to Evaluate the Tensile Properties of Highly Irradiated LYRA-10 RPV Model Steels
Authors: Naziris Frideriki , Adamech Marek , Marques Pereira Viviam , Martin Oliver , Bakker Theo , Kolluri Murthy
Published: November 2024

In the past few years, miniature testing techniques to evaluate the mechanical properties of structural materials of nuclear reactors have gained interest due to the limited number of irradiated surveillance specimens and strict safety regulations. One of such miniature testing techniques is the Small Punch Testing (SPT) method, which uses tiny discs to estimate mechanical properties such as tensile properties, fracture toughness and the ductile-to-brittle transition temperature of the examined material.

As described in the ASTM E3205 standard: Standard Test Method for Small Punch Testing of Metallic Materials, empirical relations are used to correlate the yield strength and the ultimate tensile strength to the SPT parameters determined from the investigated material. The validity of these empirical relations at high fluence irradiation needs to be further studied and understood to assess the potential applicability of the SPT technique for the evaluation of the effect of high-fluence irradiation in reactor pressure vessel (RPV) steels and for the implementation of this testing method in surveillance programs of existing nuclear power plants.

In this current work, SPT tests have been performed on six RPV model steels in the as-received and highly neutron irradiated state. These alloys were part of the joint NRG-JRC irradiation campaign LYRA-10 and resemble VVER and PWR RPV steels with tailored chemical compositions to study the synergetic effect of Ni, Mn and Si in the high fluence regime. The tensile properties of these materials prior and after irradiation are correlated with the SPT results and the shifts in SPT fitting parameter βp0.2 as effect of irradiation and chemical composition are studied to evaluate the effectiveness of this technique for screening of irradiation-induced hardening.
Circumferential and Off-Axis Crack Fatigue Growth Susceptibility in Buried Steel Pipelines
Authors: Lamborn Lyndon , Hogan James , Ferguson James , Skow Jason
Published: November 2024

While the industry generally discounts fatigue growth of circumferential and off-axis cracks in mainline pipe as being a credible threat, it has occurred. Three instances of girth weld and one instance of spiral weld crack fatigue growth are examined in this presentation and modeled for fatigue growth due to internal pressure fluctuation effects. Metallurgical findings for vintage girth weld fatigue growth are presented with potential root causality elements. A cutout indicating circumferential crack growth dormancy is likewise modeled to check model realism.

Using a surviving flaw approach and observed axial fatigue growth non-susceptibility downstream of pump stations, an off-axis flaw fatigue growth susceptibility methodology is proposed. Based on surviving flaw methods, stress intensity comparisons are employed to project the likelihood of fatigue growth in spiral weld cracks over a range of spiral weld angles. Sensitivity to superimposed axial tensile stress is projected based on the family of da/dN curves produced using the Walker theory.

A risk framework approach is proposed with baseline susceptibility considerations to assist operators to determine where fatigue growth of circumferential and off-axis cracking merits consideration. Potential risk treatment options are proposed with recommendations for future work.
Evaluation of Stresses in Saddle (Q-lip) Type Nozzles With Weaker Material Strength Compared to the Pressure Vessel Shell
Authors: Kuscu Koray , Singh Mandeep
Published: November 2024

ASME BPVC Section VIII Division 1 and 2 provide various design configurations for reinforcing nozzle openings in pressure vessels. One of these configurations is integrally reinforced saddle (Q-lip) type nozzle forgings, which are utilized when the nozzle to shell junction is required to be radiographically examined. These types of nozzles provide smoother geometrical transition at the nozzle to vessel junction, which results in reduced stress concentrations. In addition, these nozzles do not require a corner fillet weld, enhancing their performance if they are subject to cyclic (fatigue) loads. When the strength of the pressure vessel shell and the nozzle are similar, the nozzle to shell junction does not require any special consideration in the design. However, when the nozzle has a weaker material compared to the shell, connection between the two requires a refined design to address the local stresses. This paper aims to provide an insight to the stress distribution and potential design implications for such nozzle types and material combinations. Accordingly, various nozzle and pressure vessel geometries are designed using ASME Section VIII Code. Stresses are calculated using Finite Element Method at the vicinity of the nozzle to shell junction including the nozzle saddle transition and at the shell.
Parametric Study on the Vibration of Small-Bore Piping Branch Connections – Update
Authors: van Zyl Gys , Brodzinski Richard , Swindell Rob , Wally Gernot
Published: November 2024

In vibration service, small-bore piping connections, especially unsupported cantilever configurations, are associated with a high level of concern as potential fatigue crack initiation locations. In PVP2022-84119 the results of a study that was performed to characterize the relationship between vibration and stress amplitude of small-bore branch connections are presented. This work presents an update to the earlier study. The parametric finite element study was expanded to include contoured fittings and fittings with integral flanges and a different parametric distribution for the branch lengths was used. In the original parametric study, a random distribution of run pipe diameter and thickness and branch pipe diameter, thickness, and length was used to evaluate a few thousand different small-bore configurations. In this work the original distribution of parameters was compared with a typical site parameter set and the set of parameters used in this study was modified accordingly. Improvements were also made in the statistical analysis of the results, and the frequency dependance of a non-dimensional stress-to-velocity factor was investigated. Finally, the data set of natural frequencies obtained from the finite element analyses was used to develop optimized coefficients for an approximate equation to estimate the natural frequency from the geometry and mass properties of a small-bore piping connection.
Review of Standards for Liquid Hydrogen Storage Vessels
Authors: Li Keming , Guo Xiao , Shen Tao , Gao Yi , Han Yisong , Zheng Jinyang
Published: November 2024

Safe and efficient storage of liquid hydrogen is a challenge due to its extreme low temperature (20K). The development of standards is a key support for the construction of liquid hydrogen storage vessels. This paper presents an overview of current standards for liquid hydrogen storage vessels, including ISO 13985—2006 Liquid hydrogen — Land vehicle fuel tanks, CGA H-3—2019 Standard for cryogenic hydrogen storage, and three Chinses standards GB/T 40060—2021 Technical requirements for storage and transportation of liquid hydrogen, T/CATSI 05006—2021 Special technical requirements for static vacuum-insulated liquid hydrogen pressure vessels, and T/CATSI 05007—2023 Special technical requirements for transportable vacuum-insulated liquid hydrogen pressure vessels. Scopes of application including vessel types, pressure and volume are given for each standard. Materials for construction of liquid hydrogen storage vessels are presented, and the standard requirements and test data for materials used at cryogenic temperature are discussed. Designs of inner vessels, outer jackets, insulation system, support system, piping and safety accessories are summarized. Accelerations due to the movement of vessels, and calculation of inner tank and outer jacket thicknesses are mainly compared. Special requirements on forming, welding, heat treatment, and cleaning are presented. Routine tests including pressure testing, vacuum integrity testing, cold filling testing, and mass spectrometer leak detector testing, and type tests such as burst testing and thermal autonomy testing for fuel tanks, and normal evaporation rate and hold-time measuring are summarized.
Evaluating the Effectiveness of Bracing Designs in Reducing the Vulnerability of Small-Bore Piping Connections to Vibration
Authors: Wally Gernot , Bottomley Ian
Published: November 2024

Cantilever type Small Bore Connections (SBCs) in process piping are vulnerable to excitation from internal flow-induced turbulence (FIT). Current industry standard guidelines provide conceptual guidance for the design of SBCs where most of these guidelines arise from parametric numerical analyses carried out on unsupported cantilever-type SBC arrangements. As mitigation, the guidelines recommend the use of welded braces to increase the natural frequency of the SBC to a level where less vibration energy is available in the system to excite it, thereby reducing the dynamic stresses at the welded connections to acceptable levels. The available guidelines do not provide an approach to quantify the benefit provided by a particular welded bracing design or an assessment criterion against which to assess it. This paper seeks to address these issues as follows:

Welded bracing design evaluation for FIT: A parametric finite element study on thousands of different configurations was performed to determine how different welded bracing designs and parameters influence the natural frequencies of SBCs. The underlying parametric data set is based on design guidelines currently used by different engineering companies in actual processing facilities around the world and includes factors such as bracing concepts (2-way, 4-way), bracing profiles (flat-bar, angle bar) and overall bracing length. The study also provides a comparison of different attachment methods such as welded directly to the pipes (with and without reinforcement pad) or welded to a flange and how these methods affect the natural frequencies and consequently the fatigue performance of the SBCs.

SBC acceptance criteria: This paper also introduces the concept of a “cut-off frequency” for SBCs. It will be shown that if the natural frequency of a SBC exceeds this cut-off frequency it is very unlikely that a turbulence driven excitation, with single or multi-phase flow, can result in dynamic stresses on the SBC connection that will be sufficient to pose a fatigue threat. This part of the study utilizes the flow conditions gathered over several hundred real-life flow analyses and site assessments from which conservative “worst-case” flow conditions for single-phase flow and multi-phase flow were extracted.
Interpretation of the Progressive Deformation in Tube Plates
Authors: Billon François , Jourden Erwan
Published: November 2024

When we carry out a fatigue analysis in a tube plate and we exceed the 3Sm rule in the ligament between 2 holes, the question which then arises is: how to consider the elastic-plastic correction factor Ke?

The objective of our study is to propose an answer to the question by carrying out an elastic-plastic analysis of the tubesheet Elementary Representative Portion (ERP), made of 9 holes, by varying the stresses applied to the ERP and by analyzing, for different stress states and from the fatigue curve, the number of allowable cycles obtained with an elastic calculation and the number of allowable cycles obtained with an elastic-plastic calculation, in order to evaluate at this stage the consideration of the elastic-plastic correction factor.
Impact of General and Local Metal Loss on the API 579-1 Omega-Method Creep Analysis
Authors: Scano Lorenzo , Piccini Francesco , Palomba Salvatore
Published: November 2024

Creep and metal loss are typical and concomitant damage mechanisms of pressure equipment operated at high temperature. The phenomena influence and compete with one another: the loss of wall thickness acts as a stress-riser, fostering the inelastic strain accumulation due to creep; on the other hand, the stresses redistribute and relax due to the exposure in the creep range, especially in the case of localized corrosion.

API 579-1 [1] does not provide clear indications on how to deal with concurring damage mechanisms. For Level 3 assessments in the creep range a common and conservative approach is to carry out fully-corroded FEA, i.e., inelastic creep analyses in the ultimate condition of metal loss. In a previous part of the research [2], an FEA-based comparison was made with progressively-corroding finite-elements models for both general and local metal loss. The investigation was performed for a straight-section of a low-alloy pipe and the creep damage was calculated, at every integration step, according to the Larson-Miller method, as given by API 579-1 Part 10. The simplified approach was found conservative, in terms of creep damage, by a factor greater than 2 for uniform and greater than 1.4 for localized corrosion.

Given that the Larson-Miller theory is a stress-based methodology for accounting for creep damage, and considering the impact of stress redistribution and relaxation combined with the wall thickness loss, the API 579-1 Omega method (strain-based) was then taken into account in the inelastic FEA in the present work. The new investigation kept the same geometry and boundary conditions in terms of creep and corrosion rates in order to perform a direct comparison of the overall level of conservativism of the simplified approach when the creep is evaluated via the Omega method. The analysis shed also light on the notch-effect given by local metal loss and on its impact on the accumulated creep damage evaluated via stress or strain methodologies with and without ongoing corrosion.
Metallic Seal Ring Reusability
Authors: Payvar Reza
Published: November 2024

Metal-to-metal seals, exemplified by well-established designs like inverted T-shaped metallic seal rings, have emerged as preferred choices for both self-energized and pressure-energized sealing solutions. These seal designs find extensive application in clamp connections, compact flanges, or practically any metallic seal seat machined to provide the required diametrical interference and contact profile. By employing high-strength materials with elevated specified minimum yield strength, the reusability of these seals is substantially enhanced, consequently extending their operational lifespan from a sealability perspective.

Unlike the classical ratcheting model of Bree, which is based on the combination of primary membrane stress and alternating secondary bending stress in the same direction, ratcheting in this context may occur solely due to secondary stresses during the make-up (assembly) and break-out (disassembly) phases. This study centers on simulating the makeup and break-out cycles of these seals. The primary objective revolves around evaluating how key design parameters — specifically seal sizing and yield strengths — impact the distribution of plastic strain and the overall potential for reusability of the seal rings. In pursuit of this goal, a comprehensive assessment utilizes an elastic-plastic stress analysis method, as detailed in section 5.5.7 of ASME VIII Div. 2.

The study’s findings affirm that employing a minimum specified yield strength of 75 Ksi significantly enhances the reusability and operational lifespan of these seal types. This conclusion is in harmony with empirical insights gathered from various industries and is consistent with existing acceptance criteria, notably the stand-off value, which provides a quantitative measure of reusability potential.
ASME CC N-900 Revision Discussion (No.1) Effect of Triaxiality Factor on Allowable True Strain Amplitude
Authors: Shibukuwa Kenichi , Wen Jie , Takanashi Masahiro , Funasaki Kenji
Published: November 2024

In 2019, ASME Section III and JSME published a code case (ASME CC N-900[1]/JSME NC1 CC-008[2]) regarding seismic design codes for piping by using elastic-plastic analysis. As shown in PVP2023-107170[3] “Seismic Design Method of Crossover Piping Across Building Isolation Boundary”, while it would be clear that this code case using elastic-plastic analysis allows for a reasonable seismic design of the piping, there are few examples of actual seismic design works by using this code case. The reasons why the seismic evaluation method based on elastic-plastic analysis of piping has not been applied to actual design works include conservative strain-based criteria based on both Triaxiality Factor [TAF] and allowable true strain amplitude.

Therefore, this paper reports the studies result on the conservatism of allowable true strain amplitude of current ASME CC N-900 [1] based on the relationship between fatigue strength (life) and triaxiality factor [TAF] of pipe fittings, in order to establish a seismic evaluation method based on elastic-plastic analysis of piping in actual seismic design work.
A Failure Monitoring Method for Liquid Hydrogen Storage Tanks Based on Distributed Temperature Sensing and Digital Twin Technology
Authors: Li Chaoyuan , Yang Hong , Xue Jiacheng , Li Xiang , Zhang Haotian , Zhang Shouhua
Published: November 2024

Taking a typical high-vacuum-multilayer-insulation (HVMLI) liquid hydrogen horizontal storage tank as the object, a failure monitoring method of liquid hydrogen storage tank based on the temperature field of tank interlayer is discussed by combining real-time detection with numerical simulation. For the HVMLI structure, the outermost temperature of the insulation layer is calculated by the layer-by-layer heat transfer calculation method. Based on Fluent, the heat and mass transfer simulation of the tank model was carried out. Based on the MultiZone mesh division of the combination of tetrahedron and hexahedron, the energy equation, the standard K-epsilon turbulence model and the solar radiation model were selected to calculate the stable temperature field cloud map of the tank interlayer. Three common failure modes are simulated. The results show that compared with the normal working conditions, the outermost temperature field of the insulation layer will change significantly under the three failure modes. Combined with the conventional parameters such as the liquid level of the inner tank and the interlayer pressure, a multi-parameter fusion liquid hydrogen storage tank failure criterion is proposed, which can effectively judge the liquid phase leakage of the inner tank, the gas phase leakage of the inner tank, the leakage of the outer tank and the damage of the local insulation layer. Based on DTS technology, the safe and effective measurement of the temperature field on the outer surface of the insulation layer can be realized, and the twin model of liquid hydrogen storage tank driven by sensing data can be established to effectively judge the failure state.