bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Stability of a Plate Supported by Air Pressure (Analysis of Two Degree-of-Freedom Coupled System of Translational and Rotational Motions)
Authors: Takeda Masakazu , Suda Takahiro , Sugawara Yoshiki , Watanabe Masahiro
Published: November 2023

This paper presents a stability analysis and exciting mechanism of coupled vibration of translation and rotation of a plate supported by air pressure. In stability analysis, the basic equation of fluid flow and the equation of motion of the plate are separated into the steady-state equation and the unsteady-state equation by the perturbation method. The unsteady-state equations are then Laplace transformed, and the steady-state terms obtained by solving the steady-state equations are substituted. The Laplace transformed equations are rearranged to obtain the characteristic equations for the vibration of the plate. The vibration characteristics and unstable condition of the self-excited vibration of the plate are calculated using the characteristic equations. The stability of the plate is affected by the air flow rate, the mass of the plate, the volume of chamber supplying air. we clarified those influences on the instability conditions of the self-excited vibration. Furthermore, the fluid force acting on the plate is separated into factors such as compressibility and viscosity. This is necessary for analyzing the effect of the work done by the fluid force derived from these factors on the dynamic stability of the system. The results reveal a critical factor for the occurrence of self-excited vibration; additionally, the detailed exciting mechanism of translational and rotational vibration is discussed.
Assessment of Gage Length Effects on Cylindrical Austenitic Stainless Steel Fatigue Specimens in Air and High-Temperature Water Environment
Authors: Baykal B. Aydin , Spätig Philippe , Seifert Hans-Peter
Published: November 2023

This paper addresses the specimen gage length on the fatigue behavior of 316L austenitic stainless steels when tested in air and light water reactor environment. In fatigue testing, the overall spread of the data tends to be high due to high natural random error and also unknown systematic errors arising from ambiguous or poorly constrained standards. Identifying and mitigating sources of systematic error can reduce the high spread in fatigue data and significantly increase the reliability of fatigue life approximations under a specific set of test conditions. In order to reduce sources of systematic error, we have explored the effect of the gage length of 316L stainless steel specimens in two different environments. For this purpose, a minimum of three low-cycle fatigue tests were performed for each set of conditions with 0.3% and 0.6% strain amplitude using gage lengths of 20, 27 and 34 mm. The effect of the high-temperature BWR environment results in a strong reduction of the fatigue life in comparison with tests carried out in air at room temperature. The effect is usually quantified in literature using the Fen factor defined as the ratio of the fatigue life in air at room temperature to the fatigue life in a light water reactor (LWR) environment. Fen factors were calculated for each set of conditions and specimen gage lengths using room temperature air tests as reference and compared with existing literature.
Numerical Prediction of Fracture Toughness of a Reactor Pressure Vessel Steel Based on Experiments Using Small Specimens
Authors: Metzler Timo , Gaganidze Ermile , Aktaa Jarir
Published: November 2023

Due to limited availability of irradiated material and safety concerns when testing large, irradiated specimens, a major effort is being made in nuclear materials research to establish small specimen testing techniques for determining the fracture resistance of reactor pressure vessel (RPV) steels. The ASTM E1921 standard is used extensively to estimate fracture toughness of ferritic steels in the ductile-to-brittle transition region. Because of the inherent low constraint of small specimens, many test results exceed the fracture toughness limit specified in the standard, resulting in wasted material. To avoid this problem, finite element analysis using the cohesive zone model is applied to predict the fracture toughness of standard-sized specimens based on small specimen test results. Those tests were carried out within the framework of the FRACTESUS project using miniaturized compact tension specimens. The parameters of the cohesive zone model are calibrated by means of a hybrid experimental-numerical approach. After identification of the parameters on small specimens, the simulation of a standard-sized geometry is performed, and the resulting fracture toughness is compared to the small specimen data.
Probabilistic Leak Before Break
Authors: Brigante Francesco , Pasti Fabio , De Haan-De Wilde F. H. E.
Published: November 2023

The Double Ended Guillotine Break (DEGB) is a pipe failure mode in nuclear power plant installations which is the postulated root cause of a Loss Of Coolant Accident (LOCA). Pipe whip restraints and jet impingement shield are safety systems that mitigate the effects of this postulated accident. The Leak Before Break (LBB) failure mode occurs when a small leak from a cracked pipe is detected prior to the DBEG failure. The application of this failure mode and the detection of cracked pipes would increase defense in depth and justify the removal from the plant of the pipe whip restraints and the jet impingement shield, decreasing costs and maintenance time. In this study a probabilistic assessment is performed with an in-house developed LBB software. The assessment models the complexity of the physical model and the diversity of the systems with stochastic input variables for the material properties and crack parameters. The developed deterministic code is based on the UK procedure for assessing the integrity of structures containing defects (R6). The Detectable Leak Before Break (DLBB) procedure is used, which is based on the Failure Assessment Diagram (FAD) Option 1 assessment procedure. The structural integrity assessment is then coupled with the Henry-Fauske two-phase critical flow model for the evaluation of the leakage rate. A sensitivity analysis is performed to reduce the number of probabilistic variables. The output from the assessment is the probability of defect detection prior to structural failure. The Second Order Reliability Method (SORM) is the probabilistic method used. The probabilistic results are then compared with the safety factors currently used for deterministic LBB assessments.
Seismic Dynamic Response Analysis of Liquid Storage Tank Under Uneven Foundation Settlement Based on Fluid-Structure Interaction
Authors: Huang Jiayi , Chen Zhiping , Jiao Peng
Published: November 2023

Large storage tanks are commonly used to store liquefied petroleum gas, liquefied natural gas, etc. In actual service process, the storage tank is not only vulnerable to foundation settlement, but also prone to structural damage caused by accidental loads such as earthquakes. This paper proposed a seismic dynamic response analysis method for storage tanks under uneven foundation settlement. Through the wet modal analysis, the self-vibration characteristics of the storage tank were obtained. Using a two-way fluid-solid coupling method, the structural response of the tank under combined action of settlement and seismic load was studied. The results showed that when the tank with uneven foundation settlement was subjected to seismic load, the maximum mises stress, maximum circumferential stress, and maximum axial compressive stress increased by 56.7%, 28.5%, and 30.8% respectively compared to the tank without settlement, and the maximum stress occurred at the location of the circumference angle deflection of about ± 25°, where was exactly the position that the maximum stress occurred under the action of uneven settlement alone. Under the combined action of seismic load and uneven settlement, the storage tank was in its elastic stage with no large deformation most of the time. The maximum deformation recovered from 8.21mm to 3.83mm at the end of the seismic load. These results can provide some theoretical reference for seismic design of storage tank and earthquake damage investigation.
Additive Manufacturing and Regulatory Testing of Canisters for Spent Nuclear Fuel Management
Authors: Martinez Oscar , Giuliano Dominic , Tang Wei , Nogradi Paul , Adeniyi Abiodun , Lowe Lance
Published: November 2023

The back end of the nuclear fuel cycle focuses on the interim storage, transportation, and final disposition of the spent nuclear fuel (SNF) from reactors. Commercial light-water nuclear power stations across the United States operate with fuel assemblies that are irradiated for up to 6 years (planned) in the reactor pressure vessel. After their planned irradiation, the fuel assemblies are moved to a spent fuel pool within the facility complex. After the SNF is removed from the fuel pool, it is typically inserted into a welded metal canister that can be transferred between overpacks for storage, transportation, and possibly disposal. Most dry storage systems used in industry today use dual-purpose canisters (DPCs), which designed for use in storage and transportation overpacks but are not specifically designed for disposal. Triple-purpose canisters, designed for disposal in addition to storage and transportation, have also been researched. Traditional manufacturing methods for spent fuel canisters involve fusion welding along the length or circumference of the canister, resulting in high-tensile residual stresses in the joint weld zone (WZ) and heat-affected zone (HAZ).

This paper documents work in which spent fuel canister designs were printed by wire arc additive manufacturing (AM) using the 316L SS welding wire to demonstrate (1) the feasibility of SNF canister fabrication using this advanced manufacturing method and (2) the dynamic response of the AM canister design when subjected to the federally mandated Normal Conditions of Transport (NCT) and Hypothetical Accident Conditions (HAC) physical tests for Type B packages. This paper focuses on the canister printing design and structural tests. The AM 3D-printed design, regulatory testing, and post-test evaluation of the canister tested to the 10 CFR 71.71 and 10 CFR 71.73 requirements are presented herein. One AM canister design was subjected to the penetration, free drop, and puncture test. Before and after the dynamic structural tests, the AM canister design was scanned with a handheld scanner to capture a 3D CAD geometry to compare to the 3D-printed canister design in the deformed shape. The scanned geometry was sectioned in areas with deformation, and the cross section profile was measured to determine accurate and repeated results of the deformed shape of the AM canister design.
Shaking Table Test on a Piping System Model for Developing High-Quality Simulation Model
Authors: Nakamura Izumi , Shibutani Tadahiro , Kuriyama Yukihisa , Kasai Naoya
Published: November 2023

A shaking table test on a piping system model was conducted to develop a reliable inelastic Finite Element Method (FEM) analysis model for a piping system. The purpose of this experiment was to obtain the data until failure, which can then be utilized to validate the numerical model. In this experiment, the test model was designed so that failure would occur at the tee pipe joint, because there are few data for failure behavior of tee pipe joint.

The experimental data until failure could be obtained successfully by the excitation tests performed by E-Defense. The result showed that fatigue failure at the tee pipe joint was the failure mode.

In addition to the excitation data, configuration data of the tee pipe and material data were also obtained. Based on these actual data, the pre-FEM analysis model was prepared prior to the excitation test. The analysis model could well predict the failure position qualitatively.
The Role of Internal vs External Hydrogen on Fracture Resistance of Austenitic Stainless Steels
Authors: Ronevich Joseph A. , Balch Dorian , San Marchi Chris
Published: November 2023

Austenitic stainless steels are used in high-pressure hydrogen containment infrastructure for their resistance to hydrogen embrittlement. Applications for the use of austenitic stainless steels include pressure vessels, tubing, piping, valves, fittings and other piping components. Despite their resistance to brittle behavior in the presence of hydrogen, austenitic stainless steels can exhibit degraded fracture performance. The mechanisms of hydrogen-assisted fracture, however, remain elusive, which has motivated continued research on these alloys. There are two principal approaches to evaluate the influence of gaseous hydrogen on mechanical properties: internal and external hydrogen, respectively. The austenite phase has high solubility and low diffusivity of hydrogen at room temperature, which enables introduction of hydrogen into the material through thermal precharging at elevated temperature and pressure; a condition referred to as internal hydrogen. H-precharged material can subsequently be tested in ambient conditions. Alternatively, mechanical testing can be performed while test coupons are immersed in gaseous hydrogen thereby evaluating the effects of external hydrogen on property degradation. The slow diffusivity of hydrogen in austenite at room temperature can often be a limiting factor in external hydrogen tests and may not properly characterize lower bound fracture behavior in components exposed to hydrogen for long time periods. In this study, the differences between internal and external hydrogen environments are evaluated in the context of fracture resistance measurements. Fracture testing was performed on two different forged austenitic stainless steel alloys (304L and XM-11) in three different environments: 1) non-charged and tested in gaseous hydrogen at pressure of 1,000 bar (external H2), 2) hydrogen precharged and tested in air (internal H), 3) hydrogen precharged and tested in 1,000 bar H2 (internal H + external H2). For all environments, elastic-plastic fracture measurements were conducted to establish J-R curves following the methods of ASTM E1820. Following fracture testing, fracture surfaces were examined to reveal predominant fracture mechanisms for the different conditions and to characterize differences (and similarities) in the macroscale fracture processes associated with these environmental conditions.
Design of a Lab-Scale Multi-Zone Autoclave for LDPE High-Pressure Polymerization Systems
Authors: Gockel Lena , Ständecke Laura , Schreiner Nicola , Busch Markus
Published: November 2023

Low-density polyethylene (LDPE) is produced industrially in high-pressure tubular or autoclave reactors at pressures up to 3000 bar. Autoclave reactors usually have a high height-to-diameter ratio and are divided into multiple reaction zones with additional feed points along the reactor axis. On the other hand, most laboratory reactors are stirred vessels with only one reaction zone and one feed stream. Consequently, the two types of reactors differ significantly in their residence time behavior, and typical temperature profiles of industrial autoclaves are difficult to establish at laboratory scale. In this work, a lab-scale multi-zone autoclave for high-pressure polymer synthesis is constructed. A division into three reaction zones is realized by a tailored stirrer design. Different stirrers are evaluated both experimentally and simulatively. The focus is on a rapid mixing of the feed and clean separation of the reaction zones. Experimentally, tracer experiments with ink in water are carried out. Computational Fluid Dynamics (CFD) is used to bridge the gap to high-pressure operating conditions.
Ultrasonic Phased Array Detection of Crack-Like Defects in Welds Based on Multi-Mode Total Focusing Method
Authors: Bu Yangguang , Fan Zhichao , Chen Xuedong , Cheng Jingwei , Chen Wei , Wang Zhe , Wang Haibin
Published: November 2023

As a critical structural component within pressure vessels, weld can be frequently found with harmful defects during service, such as microcracks with different orientations. Therefore, regular inspections of welds from pressure equipment are very important. Compared to traditional ultrasonic NDT, ultrasonic phased array total focusing method is a new postprocessing imaging method that is more accurate for defect localization. The inspection of defects in the weld often necessitates prior knowledge to scan multiple times using different inspection surfaces and angles to increase detection coverage, which is time-consuming and labor-intensive. In this study, a multi-mode ultrasonic phased array total focusing method (TFM) for crack-like defects with different orientation is proposed, and the multi-mode imaging method is applied to the inspection of butt welds and fillet welds to achieve effective and quantitative detection of defects in different orientations. In addition, according to the actual size of the detection object, the sound beam incident state and imaging parameters are calculated based on intelligent algorithms, and the optimum imaging view is selected. As a result, a multi-mode imaging method that can comprehensively cover the weld area is obtained. Experimental results show that the multi-view method delivers different sensitivity to different defect orientations, which can better suppress noise than single-view imaging, and improve the probability of detection for crack-like defect.
Effect of Friction on Structural Capacities of a Subsea Intervention System Equipment
Authors: Sepehri Ali , Bansal Gaurav
Published: November 2023

The offshore oil and gas industry is drilling into and producing from wells in high-pressure, high-temperature (HPHT) environments. This has created a greater demand to develop more advanced tools and new technology to safely overcome the challenges in these operations. Due to the sensitivity and potential impact on the environment, the industry is striving to homogenize the design and acceptance criteria. The API 17G is the industry standard for offshore intervention operations. This standard adopts the methodologies from ASME Boiler Pressure Vessel Code (BPVC) Section VIII, Div. 3.

The objective of this study is to evaluate structural capacity of a subsea intervention system equipment according to API 17G standard by utilizing Yielding Load Method for single and combined loads per elastic-plastic analysis with no strain hardening. The assembly has multiple tightly fitted parts that can slip and slide upon application of external loads. Large deformations (nonlinear geometry) shall be included when analyzing such models. Contacts are modeled with friction. Therefore, application of real friction value is important for accuracy of results that are representative of realistic operations. A sensitivity study is conducted to assess the effect of friction on the structural capacity. In addition, absence of through section yielding criterion is also verified.
History and Technical Scope of Code Case N-513
Authors: Parker Stephen M. , McCracken Stephen L. , McGill Robert O. , Patten Ioannis D.
Published: November 2023

ASME Section XI Case N-513-6, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping and Gate Values [1], is one of the most widely implemented code cases within the U.S. nuclear industry. The primary purpose of the Code Case is to provide evaluation criteria for flaws within moderate energy, safety-related piping to allow for continued plant operation without repair/replacement until the next scheduled refueling outage. Utilities may avoid an unscheduled plant shutdown provided structural integrity is demonstrated and other requirements are met. Periodic examinations of the flaw during the temporary acceptance period are required by N-513 to ensure the flaw has not grown beyond the acceptable flaw size. N-513 is typically implemented to disposition flaws found in service water piping made of carbon steel that is exposed to raw water where active corrosion mechanisms exist. The Code Case can also be applied to stainless steel and nonferrous material components.

The purpose of this paper is to provide a history of N-513, its technical scope, current ASME Code and U.S. regulatory status, as well as proposed changes for an upcoming revision. This paper also provides a secondary benefit of consolidating the history and development of this important nuclear industry flaw evaluation methodology for traceability and knowledge transfer purposes.
Operational Experience With Application of Appendix G Methods for Irradiated Pressure Vessels
Authors: Edge Nathan , Cairns Scott , Dutton Oliver
Published: November 2023

ASME III Appendix G provides a non-mandatory approach for obtaining the allowable loadings for ferritic pressure-retaining components based on the principles of Linear Elastic Fracture Mechanics (LEFM). Its purpose is to derive a relationship between Temperature and allowable Pressure of a ferritic vessel in order to prevent it from being subjected to high pressure (and therefore stress) when the metal temperature is low and potentially susceptible to non-ductile failure. The purpose of this paper is to present operational experience using ASME III Appendix G to form operational boundaries for specific irradiated pressure vessels. An overview of the historic and recent use of ASME III Appendix G is presented alongside observations on improvements and relaxations of conservatisms inherent to this method. A discussion is also presented regarding alternative methods which link the calculation of maximum allowable pressure during low temperature operation to the defect tolerance assessments produced in support of safety cases, whilst maintaining appropriate levels of conservatism in the assessment. The conclusion of the paper is that whilst ASME III Appendix G generally supports the provision of reasonable operational boundaries for irradiated ferritic pressure vessels there are a number of alterations and revisions required for specific components, and indeed specific regions of components, where standard methods result in pessimistic limitations to performance.
Research on Flow Induced Vibration Tandem Towers Under Passive Control
Authors: Wang Jiawei , Tang Bowen , Tan Wei
Published: November 2023

The flow-induced vibration (FIV) of the tower is one of the important reasons for tower failure. It is very important to take effective manual measures to control FIV for the safety and operation of the tower. Helical strakes can effectively interfere with the Karman vortex street and suppress vortex-induced vibration of isolated structures. Due to the vortex structure interaction, the mechanism of FIV control of helical strakes on tandem cylinders remains to be studied. The idealized model of a multi cylinder system with elastic support has been recognized in many fields, such as aviation engineering, nuclear engineering, ocean engineering, and wind engineering. Therefore, in this paper, the tandem cylinders wind tunnel experiment is designed, and a helical strakes installed on the wall of the cylinder model of the tower is designed. The structural dimensions and shapes are mainly involute, square, and D-shape. The vibration respond of the cylinder model at different distances are explored, and the effects of different sections, screw pitches, and helical strakes fin heights on the crosswind vibration response of the cylinder model are investigated. Compared with a series of smooth cylinders, the vibration amplitude of the cylinder with a D-shape helical strakes is reduced by 89%. Furthermore, based on a D-shaped section, the influence of two parameters of helical strakes h (fin height) and P (pitch) on the amplitude response of tandem cylinders is explored, and the parameters of optimal D-shaped helical strakes under different spatial arrangements are given. The research results can be used for the vibration reduction research of tandem towers.
Response of Buried Pipelines Under Permanent Ground Movements: Physics-Informed Deep Neural Network Approach
Authors: Taraghi Pouya , Li Yong , Yoosef-Ghodsi Nader , Fowler Matt , Kainat Muntaseer , Adeeb Samer
Published: November 2023

Long-distance underground pipelines are inexorably constructed over harsh geological fields exposing them to geohazards resulting in both transient and permanent ground movement. The permanent ground movements caused by landslides, liquefaction, ground subsidence, slope failures, fault movement, etc., can result in large deformation threatening the safety and integrity of the pipelines. Therefore, evaluation of the structural response, i.e., displacement and strain fields of the buried pipelines exposed to the permanent ground displacement is a major concern for the industry. The mechanical and physical behavior of the pipelines subjected to ground movement can be described mathematically using nonlinear Partial Differential Equations (PDEs) by adopting the Euler-Bernoulli beam theory with large deformation. The model takes into account the nonlinearities caused by the pipe-soil interaction and pipe geometry. Various methods, including the Finite Element Method (FEM) and Finite Difference Method (FDM), can be used to solve the nonlinear PDEs and thus predict the structural response. However, the FEM usually requires complicated simulation using costly commercial software. Also, both the FE and FD methods are mesh-dependent. On this basis, this research endeavor proposes and utilizes an inexpensive, novel, easy-to-implemented, simulation-free, and meshless method to get the response. As a result, Physics-Informed Neural Networks (PINNs), deep-learning neural networks that consider the underlying law of physics in PDEs, can be a potential strategy to deal with PDEs with high complexity. To this end, the neural networks thoroughly learn based on the incorporated physical laws together with the boundary and/or initial conditions, eliminating the need for large training datasets. The obtained structural response, applicability, and accuracy of the predicted results of the proposed method are assessed by comparison with the obtained results from FEM.
Potential of Variational Auto-Encoder as an Alternative to a Welding Residual Stress Profile Sampling Model
Authors: Oh Changsik , Kim Jin-Gyum , Kang Sung-Sik , Lee Sangmin
Published: November 2023

Primary Water Stress Corrosion Cracking (PWSCC) is a significant degradation mechanism for probabilistic Leak-Before-Break evaluation. Welding residual stress profiles, which have a great influence on the evaluation results, are difficult to measure and have a large uncertainty due to very limited data. Therefore, constructing welding residual stress profiles by reflecting the actual characteristics is an important part in the probabilistic evaluation.

This paper analyzed whether a generation model based on artificial neural networks could be an alternative to a sampling model of welding residual stress profiles. The network selected in this study is the Variational Auto-Encoder (VAE), which is well-known for learning the distribution of training data. Like the Auto-Encoder, the VAE is based on deep neural networks composed of an encoder and a decoder, but additionally learns the probability distribution of the input data. Systematically constructed sinusoidal wave training data sets were used to investigate the characteristics of the VAE. Amplitude and phase changes were made to generate the training data sets showing the self-balancing nature of the welding residual stress profile. The results showed that the generated data well represented the features of the training data, and demonstrated its potential as an alternative to a welding residual stress profile sampling model.
INCEFA-SCALE Project – Phases 1 and 2 of Testing Programme
Authors: Beswick Jack , Doremus Luc , Martin Oliver , Le Roux Jean-Christophe
Published: November 2023

INCEFA-SCALE is a five-year project supported by the European Commission HORIZON 2020 programme. It is the successor to the INCEFA-PLUS programme that ran from 2015 to 2020. INCEFA-SCALE kicked off in September 2020. The objective is to advance the ability to predict lifetimes of Nuclear Plant components when subjected to Environmental Assisted Fatigue (EAF) loading.

It has been generally observed by nuclear plant operators that there appears to be a disconnect between the perceived difficulty of providing an acceptable assessment result with the current EAF methodologies and the good service experience with regard to this specific degradation mechanism. It is internationally recognised that a possible contributor to this discrepancy is the transferability of laboratory-scale tests to real nuclear components. This is the key knowledge gap addressed by INCEFA-SCALE. To address this gap, the project has identified specific loading, geometric and environmental conditions which are not fully understood and may be considered excessively pessimistically in assessment. The conditions include variable amplitude and multiaxial loading, stress raising features such as notches, and the transferability of results between air and PWR environments, and between specimens with differing surface finishes, under the complex loading scenarios under consideration. Test matrices have been designed to deepen the understanding of specific materials’ (stainless steels) fatigue performance under these conditions, and the testing is well underway at the time of writing.

This paper will give an overview of the INCEFA-SCALE testing carried out to date, from the first two one-year phases of the testing programme. The testing and associated analysis has been designed to better understand the material behaviour at the component scale, and assess the applicability of models, developed elsewhere in the project, to predict the lives of these components, which are in turn informed by comprehensive characterisation of the material after failure. The test results are presented in a manner to allow comparison between the experimental fatigue lives and those predicted with standardised assessment procedures, such as NUREG/CR-6909, with comment on how more advanced models (addressed in a different paper), could be used to improve predictions.
Repeatability and Uncertainty Study of Strain Measured on Coupled Fluid-Structure Vessels in Response to High Intensity Proton Pulses
Authors: Jiang Hao , Winder Drew , Liu Yun
Published: November 2023

Spallation Neutron Source (SNS) produces neutrons through spallation reactions with the short pulse (∼0.7 μs) operated at a repetition rate of 60 Hz with 1.0 GeV protons onto the mercury target in a stainless-steel vessel. Each pulse causes a distributed pressure field in the mercury, with pressures exceeding 20 MPa. Dynamic high-pressure waves created by the proton pulses interact with the stainless-steel vessel. Fluid-structure interaction causes stress cycles in the target vessel and leads to fatigue cracks and cavitation of the mercury, which leads to further damage. Strain measurements are critical for understanding and improving the lifetime of the target vessels. The measurements also allow evaluation of the efficacy of pulse mitigation techniques such as injecting small helium gas bubbles into the flowing mercury.

Since 2015, researchers at SNS have used fiber-optic sensor systems to measure dynamic strain responses of the target vessels. An abundance of mercury target strain data has been collected. We would like to use these strain data to validate simulation results. It is important that the uncertainty of the measurements is quantified as part of the validation process. This paper focuses on the repeatability and uncertainty study in strain measurement data of SNS target vessels. The potential reasons causing the variance associated with measurements are investigated and discussed.
An Approach to Include the Effects of Plasticity in the Calculation of Crack Opening Areas for Through-Wall Cracks Subject to Combined Primary and Secondary Loading
Authors: James Peter , Brayshaw William , Sharples John
Published: November 2023

The work presented within this paper looks at estimates of crack opening area (COA) under elastic-plastic material conditions.

Developing leak before break (LbB) arguments with secondary (thermal or weld) stresses present is challenging. This potentially results from defect assessment methods like R6 not including guidance on the effect of plasticity on COA estimations in the presence of the secondary stresses, where the COA would be expected to increase compared to the elastic COA. The corresponding elastic-plastic stress intensity factor (KJ) could, conversely, reduce compared to handbook elastic solutions for stress intensity factor (KI).

Current practise within an LbB assessment in the UK would be to assume a plasticity correction is applied to KI, calculated using the R6 failure assessment diagram (FAD) as a J estimation scheme, to provide KJ. COA’s are evaluated elastically to ensure that the assessment under-estimates real-plant scenarios and is therefore generally conservative. Including plasticity in COA evaluations will allow assessment of COA to be more accurate, and therefore provide a reduction in conservatism compared to current guidance when a defect is in the presence of a single load type or when different loading types are combined.

This paper presents an approach which allows plasticity to be included in COA evaluations by calculating an additional crack opening as a result of plasticity, based on crack tip opening displacement and an enhancement calculated from the contributions of elastic and plastic reference strain (and is therefore consistent with the reference stress methods contained in R6 and elsewhere). This resulting crack opening area is then added to the elastic COA (COAe) calculated from the solutions published in a previous ASME PVP paper by France et al. The results of this approach are compared to elastic-plastic FEA results, where the primary membrane and secondary through-wall bending stresses were investigated when in isolation and combined with respect to K and COA.

The method outlined herein provides an increase in crack opening and therefore a reduction in conservatism compared to the FEA results, whilst remaining conservative; i.e. elastic-plastic COA prediction (COAep) is less than the FEA results.

Where a secondary through-wall bend has been applied in isolation, the restriction of crack overclosure (inclusion of crack face contact) in the FEA generates greater opening at the tensile surface. This is not replicated in the COAep method developed in this work and would need further development.

Under combined loading, the inclusion of plasticity in COAep has a small effect as the primary and secondary stresses are low and the secondary stresses relax due to plasticity, ensuring the response remains nominally elastic and is therefore consistent with existing methodology.
Graphite Material Model Calibration for Conceptual Design and Core Configuration Studies
Authors: Young Amanda , Horne Graeme , Gray Richard , Kent Daniel , Joyce Mark
Published: November 2023

Nuclear graphite is a candidate moderator material for many high temperature advanced reactor concepts. However, the material properties of graphite used in this application evolve during service, principally as a function of fast neutron dose, irradiation temperature and, if relevant, radiolytic oxidation. In these applications, the graphite moderator components also define the core geometry, including channels for coolant and reactivity control devices. One of the most significant threats to the core structure continuing to meet its design requirements is graphite dimensional change, which can cause significant deformation in the components through life.

This paper proposes an approach to this problem by defining a semi-empirical model for the behaviour of graphite in a nuclear environment which can be calibrated to experimental data. It can then be used by Finite Element (FE) software to provide a prediction of expected behaviour of core components. Whilst this approach is used to support continued operation of the UK fleet of Advanced Gas-cooled Reactors (AGRs), it is also judged appropriate to inform the pre-conceptual design stage of new reactor core designs. Being able to rapidly assess different core configuration options and their compliance with the guidance in ASME Section III Division 5 is a valuable tool in the early stages of design, particularly when irradiated material data is sparse.

Once a best estimate prediction has been made a robust approach to sensitivity studies is required, aimed at ensuring that a particular core design is tolerant to material evolution uncertainty. This should enable design work to proceed in parallel to the collection of detailed material evolution information significantly reducing risk and the time to complete the system design and assurance process.
Re-Evaluating the Minimum Required Distance Between a Local Thin Area in a Cylinder and an Ellipsoidal Head
Authors: Bouse Scott D. , Hill Lance , Altstadt Steven , Sarzynski Melanie
Published: November 2023

Many of the assessment procedures in API 579 / ASME FFS-1 require that flaws to be assessed must be located a minimum distance away from a Major Structural Discontinuity to ensure that the disruptions caused by the discontinuity do not adversely affect the conservatism of the calculations. Flaws in a cylinder with a Distance to Major Structural Discontinuity (Lmsd) less than 1.8*sqrt(Dt) are typically excluded from basic assessments, regardless of the type of discontinuity (or flaw) in question. This work explores the impact of a Local Thin Area (LTA) in a cylindrical shell as the discontinuity approaches a 2:1 ellipsoidal head. In this paper, the authors populated an Elastic-Plastic parametric study spanning a wide range of cylindrical thickness-to-diameter ratios (D/t), flaw sizes (both longitudinal and circumferential), materials, flaw severities, and proximity to both 2:1 ellipsoidal heads and hemispherical heads in order to characterize the responses. The results imply the existence of several classes of structural discontinuity, along with conditions under which some discontinuities might either act to support or de-stabilize a cylindrical shell against plastic collapse. The authors demonstrate that under supportive conditions, an LTA in a cylinder can approach certain discontinuities with negligible effects. In some cases, the limiting load reliably increases due to the interaction with the discontinuity. The work concludes with broader observations on discontinuity types and the circumstances under which those discontinuities might be found to be beneficial.
Oxidation Properties of Graphitic Packings Used in Low Emission Valves
Authors: Girão Carlos D. , Ruffin Mark , Pontes João H.
Published: November 2023

Flexible Graphite is used in a variety of seals because of its good thermal resistance, chemical stability and high conformability. It is widely used throughout the industry, and it is present in most low emission packing solutions associated to some content of PTFE. However, graphite will show appreciable oxidation when exposed to air at elevated temperatures and PTFE is subject to thermal degradation thus leading to mass loss and consequently reducing sealing performance. With the growing need to evaluate Fugitive Emission at higher temperatures, API 622 has introduced in March of 2022 a High Temperature Testing Procedure to access seal performance at 400°C, and modified its Packing Ring Weight Loss Test procedure to include a 24h hold at 593°C to measure seal mass loss. The scope of this paper is to evaluate the effect of temperature on low emissions packings composed of graphite and PTFE. The influence of test method in the oxidation rate of inhibited graphite from different sources, using thermogravimetric analysis and a muffle oven are investigated at temperatures ranging from 400°C to 700°C. A comparison is presented among different forms of graphite — tape, yarn and packing. Additional comparative weight loss data are reported among packings with PTFE, without PTFE, tested exposed to air, and confined in a test rig simulating a stuffing box.
Uniaxial Creep Properties of 316L Stainless Steel Manufactured by Laser Powder Bed Fusion
Authors: Sandmann Paul , Milne Amy J. , Davies Catrin Mair
Published: November 2023

316L stainless steel has long been used in high temperature applications. As a well-established laser powder bed fusion (LPBF) alloy, there are opportunities to utilise additive manufacturing in such applications. However, to date there is limited creep data on LPBF material. Uniaxial round bar creep tests have been performed at 700 °C and characterised using power-law relations to evaluate the creep strain and rupture properties of LPBF 316 L. Samples were manufactured in two orientations denoted (i) vertical i.e. loading direction parallel to the build direction and (ii) horizontal, i.e. loading direction perpendicular to the build direction. The creep response was found to be anisotropic with specimen build orientation, with samples loaded perpendicular to the build direction (Horizontal) exhibiting faster minimum creep rates than samples built parallel to the build direction (Vertical). This was mainly attributed to the columnar grain structure revealed by electron back scattering diffraction (EBSD), which was aligned with the build direction of the LPBF samples. The vertical samples generally exhibited significantly longer rupture lives than horizontal samples, unless influenced by deleterious porosity. The results were compared to existing test data performed at 650 °C and similar trends were seen at both temperatures, though higher creep rates and shorter rupture times resulted from the higher temperature, as expected.
Fatigue Crack Initiation and Fatigue Life Testing of High-Strength Austenitic Stainless Steel Tubing With Internal Hydrogen
Authors: San Marchi Chris , Ronevich Joseph A. , Pohl Johan , Ramseyer Severin , Cortinovis Davide , Eckmann Stefan
Published: November 2023

Austenitic stainless steels have been extensively tested in hydrogen environments; however, limited information exists for the effects of hydrogen on the fatigue life of high-strength grades of austenitic stainless steels. Moreover, fatigue life testing of finished product forms (such as tubing and welds) is challenging. A novel test method for evaluating the influence of internal hydrogen on fatigue of orbital tube welds was reported, where a cross hole in a tubing specimen is used to establish a stress concentration analogous to circumferentially notched bar fatigue specimens for constant-load, axial fatigue testing. In that study (Kagay et al, ASME PVP2020-8576), annealed 316L tubing with a cross hole displayed similar fatigue performance as more conventional materials test specimens. A similar cross-hole tubing geometry is adopted here to evaluate the fatigue crack initiation and fatigue life of XM-19 austenitic stainless steel with high concentration of internal hydrogen. XM-19 is a nitrogen-strengthened Fe-Cr-Ni-Mn austenitic stainless steel that offers higher strength than conventional 3XX series stainless steels. A uniform hydrogen concentration in the test specimen is achieved by thermal precharging (exposure to high-pressure hydrogen at elevated temperature for two weeks) prior to testing in air to simulate the equilibrium hydrogen concentration near a stress concentration in gaseous hydrogen service. Specimens are also instrumented for direct current potential difference measurements to identify crack initiation. After accounting for the strengthening associated with thermal precharging, the fatigue crack initiation and fatigue life of XM-19 tubing were virtually unchanged by internal hydrogen.
Effect of Hydrogen Partial Pressure on Fatigue Crack Growth Rates of Low Alloy, Quenched and Tempered Steels
Authors: Bortot Paolo , Ortolani Matteo , San Marchi Christopher , Ronevich Joseph
Published: November 2023

Low alloy, quenched and tempered Cr-Mo and Ni-Cr-Mo steels are commonly used for construction of seamless pressure vessels for hydrogen gas storage. Designing such vessels for high-pressure gaseous hydrogen service requires knowledge of fatigue crack growth rates and fracture toughness in the service environment at the design pressure. Measurement of these properties is challenging, and only a few laboratories in the world are equipped to make these measurements at very elevated pressure up to 103 MPa (15,000 psi) which are of interests for pressure vessels to be used as buffers in hydrogen refueling stations. In recent years, these properties for common low alloy steels were published in the ASME Boiler and Pressure Vessel Code Case 2938-1, therefore allowing design and construction without the need for dedicated testing. However, the fatigue crack growth rate curves published in the CC were determined from test data at 100 MPa and above and may be over-conservative for lower pressure applications. Prior publication PVP2019-93907 ([1]) in fact, already proposed a correction factor of fatigue crack growth rates based on hydrogen fugacity. Since then, new data were generated at lower pressures i.e. 55 MPa (8,000 psi). This paper presents the new findings and discusses the applicability of the previously proposed equation, which could allow reducing conservatism in current design of pressure vessels.
Structural Capacity Analysis of Subsea Equipment
Authors: Karpanan Kumarswamy , Kirkemo Finn
Published: November 2023

Subsea oil and gas production equipment such as risers, manifolds, trees, wellheads, tubing hangers, tubing heads, blow out preventers, etc., are predominantly designed to criteria of API 6X, API 6A, API 16A, API 17D, API 17G, ASME VIII-2, ASME VIII-3, and NORSOK U-001 design codes. These industry codes provide design criteria to verify failure modes such as plastic collapse, fatigue failure, ratcheting, local strain failure, brittle failure, etc. Among these failure modes, plastic collapse and fatigue failure can be considered as the primary failure modes. A detailed review of plastic collapse design criteria from these codes and standards is discussed in this paper. These codes allow elastic (linear), limit load (elastic perfectly plastic), and elastic-plastic finite element analysis (FEA) to estimate the structural capacity. Some of these codes allow geometric nonlinearity in limit load FEA and some are not. All elastic-plastic analyses are solved with geometric nonlinearity.

For this study, four components are considered which represent many subsea equipment. A pressure vessel (cylindrical shell) with internal pressure, open-end vessel (cylindrical shell) with external pressure, load shoulder, and pipe (cylindrical shell) bending are considered. Three materials with yield to tensile strength ratio of 0.53, 0.79, and 0.89 are considered in this study. A detailed review of plastic collapse criteria design criteria from these codes and standards is discussed in this paper for the four cases above.