bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of High Temperature Stability on Microstructures of 25Cr35NiNb Alloy Prepared by Laser Additive Manufacturing
Authors: Li Jizhan , Fan Zhichao , Chen Tao , Zhou Yu
Published: November 2022

The performance of static casting 25Cr35NiNb alloy pipe fittings with complex shapes for ethylene cracking furnace is insufficient, which affects the safe operation of equipment, and becomes an urgent problem to be solved in this field. Laser additive manufacturing (LAM) technique is suitable for the fabrication of complex components with high performance. 25Cr35NiNb alloy prepared by LAM is different from that prepared by static casting or centrifugal casting due to the solidification with the cooling rate of 102∼105 K/s in a tiny molten pool. In order to fabricate complex pipe fittings by LAM, the performance of 25Cr35NiNb alloy prepared by LAM needs to be clarified and the mechanism also needs to be revealed.

This paper focuses on the mechanism of high temperature stability on microstructures of 25Cr35NiNb alloy prepared by LAM. Firstly, two kinds of 25Cr35NiNb alloy deposits were prepared by LAM with different processing parameters. Secondly, heat treatments were executed in the temperature range from 850°C to 1275°C for 25Cr35NiNb alloy deposits. Then, the microstructures of 25Cr35NiNb alloy were observed by optical microscope (OM) and scanning electron microscopy (SEM). It is found that the finer the microstructures of the original deposits was, the better the high temperature stability of microstructures was. The results of electron probe microanalysis (EPMA) show that the distribution of Nb and Ti elements in the original deposits affects the high temperature stability of microstructures. The finer microstructure has the more uniform distribution of Nb and Ti elements, which improves the high temperature microstructural stability.
Investigations on the Failure Behavior of Specimens Containing Crack Fields Made by Additive Manufacturing
Authors: Stumpfrock Ludwig , Weber Ulrich , Weihe Stefan , Seidenfuss Michael , Mally Linda
Published: November 2022

Laminar and quasi-laminar orientations of hydrogen flakes with an inclination up to 16° to the pressure retaining surface were found in pressure vessels of Belgian nuclear power plants. Because of their orientation, these crack tips undergo predominantly mixed-mode loading conditions under internal pressure and the induced stress and strain fields of the single crack tips influence each other.

In a former paper, the failure behavior under mixed-mode loading conditions was investigated at RT (Room Temperature) in the upper shelf and in the lower transition region of the steel 22NiMoCr3-7, respectively. In this paper, the failure behavior will be shown for many different levels of material toughness (beginning from upper shelf down to the lower shelf region) on experiments.

Additionally numerical simulations are carried out with extended micromechanical based damage mechanics models. For the description of ductile failure mode the Rousselier model is used and the Beremin model to calculate the probability of cleavage fracture. To simulate the sensitivity for low stress triaxiality damage by shear loading, the damage mechanics model was enhanced with a term to account for damage evolution by shear. For numerical simulations in the transition region of brittle-to-ductile failure a coupled damage mechanics model (enhanced Rousselier & Beremin) will be used. In this paper, the current state of the ongoing research project is presented.
Optimization Design of Focusing Electromagnetic Acoustic Transducer for Crack Detection of Pressure Structure
Authors: Wang Zhe , Fan Zhichao , Su Yuanlian , Cheng Jingwei , Wang Haibin , Bu Yangguang
Published: November 2022

High-precision detection of crack is of great significance to ensure the safety of pressure equipment in service. Electromagnetic ultrasound has the advantages of no coupling agent, no surface pretreatment, and non-contact. However, several problems such as low energy conversion efficiency and poor sound field directivity limit the application in crack detection. This paper designs a multi-layer line-focusing electromagnetic acoustic bulk wave transducer (MLF-EMAT). A simulation model containing MLF-EMAT is established based on the Lorentz force and magnetostrictive force transduction mechanism. The influence of some transducer parameters (wire width, wire thickness, coil turns, lift-off distance) on the echo response of crack has been studied. The orthogonal experimental design method is used to optimize the controllable parameters of the transducer. When the width of the permanent magnet is equivalent to the width of the coil, the larger the number of coil layers, the larger the amplitude of the echo response of crack. An experimental platform for electromagnetic ultrasonic testing is established, and several line-focusing electromagnetic acoustic transducers with multiple parameters are prepared. The comparison results show that the optimized MLF-EMAT significantly improves the signal-to-noise ratio of echo response of crack. The amplitude of echo wave is increased by about 78% compared with that before optimization, and the detection accuracy of crack notch depth is up to 0.05 mm. The MLF-EMAT proposed in this study lays the foundation for the application of crack detection or monitoring of pressure vessels and pipes under complex working conditions.
Investigation of Surface Finish Effect on Fatigue Strength of Carbon and Low Alloy Steels
Authors: Asada Seiji , Hirano Akihiko , Wang Yun , Itatani Masao , Takanashi Masahiro , Nomura Yuichiro , Ochi Fumihiro , Ogawa Takeshi
Published: November 2022

The subcommittees on Design Fatigue Curve (DFC) and Design Fatigue Curve 2 (DFC2) in Atomic Energy Research Committee of the Japan Welding Engineering Society (JWES) developed a new fatigue analysis method. A design fatigue curve by this method is established by applying factors on stress and cycles, which have been derived by statistical analysis, to the best-fit curve using tensile strength as a variable considering the mean stress correction called the Smith-Watson-Topper approach. For high cycle region, the variable amplitude effect of EN 13445 is employed.

This fatigue analysis method was brought to the JSME Code Committee, and the JSME reviewed this method, and decided to incorporate it into the JSME Environmental Fatigue Evaluation Method with some modifications including the fatigue strength reduction factor for surface finish effect. This paper addresses surface finish effect on fatigue strength of carbon and low alloy steels.

To perform further investigation for surface finish effect on fatigue strength of carbon and low alloy steels, the DFC3 Subcommittee was established with the support of a Japanese utility project. A series of fatigue tests for surface finish effect was performed for carbon and low alloy steels in the utility project, and the fatigue test data were evaluated by the DFC3 Subcommittee. In this paper, the series of fatigue tests are introduced and discussed. Finally, the validity for the fatigue strength reduction factor for surface finish effect developed by the JSME Committee has been confirmed based on the above fatigue tests.
Study on Leakage Monitoring Method of Supercritical CO2 Long-Distance Pipeline
Authors: Guo Xiaolu , Fan Zhichao , Xu Shuangqing
Published: November 2022

The carbon capture, transportation and storage technology is an important option to achieve carbon peak and carbon neutralization. In order to prevent the pipeline fracture propagation, human injury and medium loss during the longdistance CO2 pipeline leakage, it is necessary to establish the on-line leakage monitoring technology. At present, there is not enough understanding of the law of pressure response and phase change during the leakage of CO2 pipeline, and there is still a lack of accurate leakage monitoring method based on the propagation law of decompression wave. Based on the release experiment data in the industrial scale pipeline, combined with the theoretical analysis, the pressure drop-rebound mechanism as a result of wave propagation at the moment of rupture was studied. The attenuation law of decompression wave strength will be researched for the establishment of the monitoring method of pipeline leakage position and orifice diameter. The reliability of the monitoring method considering the effect of flow state on the leakage characteristics of CO2 pipelines was studied and a modified algorithm for higher measurement accuracy was proposed. This study was of great significance to the stability and safe operation of CO2 long-distance pipeline system.
Effect of the Bending Stiffness of Bolted Flange Joints on the Dynamics of Aero-Engine Rotors
Authors: Zhu Linbo , Pan Hu , Yang Yilong , Bouzid Abdel-Hakim , Hong Jun
Published: November 2022

Bolted flange joints are used to connect adjacent disks and drums in aero-engine rotors. The flange mating contact surfaces usually move relative to each other and deform when they are subjected to numerous combinations of loads during normal operation. Consequently, the local bending stiffness of the bolted flange joint is altered considerably affecting the overall rotor stiffness and therefore the rotor dynamics.

This paper presents a study on the effect of the bending stiffness of bolted flange joints on the dynamic characteristics of an aero-engine rotor. A method to calculate the bending stiffness is proposed using an equivalent model based on an axial spring and bending beam stiffnesses. The relationship of the structure geometry, loading and assembly conditions of the bolted flange joints, and the bending stiffness loss are obtained. Furthermore, a dynamic model of an aero-engine high-pressure compressor rotor is developed using the transfer matrix method that incorporates the bending stiffness effect of the bolted flange joint. Based on this model, the influence of bending stiffness on the natural frequency and the steady-state response is discussed. The results show that the stiffness loss of bolted flange joint has a significant impact on the rotor dynamics. The structure geometry, loading, and assembly conditions can be used to control the dynamic response of aero-engine rotors.
Investigations on Multi-Stage Tests and Transient Endurance Limit Behavior Under Low-, High- and Very High Cycle Fatigue Loads
Authors: Schopf T. , Weihe S. , Rudolph J.
Published: November 2022

The fatigue analyses included in nuclear rules of KTA [1]–[2] and ASME [3] are based on defined loads (specified or measured loads and frequencies). It is assumed that highly cyclic loadings or resonance vibrations are avoided by appropriate design. Often these loads are recorded by measurements during commissioning or during operation. In particular, in pressure vessel and reactor internals such vibrational excitations cannot be excluded, so that fatigue loadings in the HCF regime and even in the VHCF regime can occur. Since these kinds of loading situations also appear in combination with fatigue loadings in the LCF regime, load collectives are to be considered, as they are not explicitly taken into account in the current analysis of the nuclear regulations. Furthermore, no generally validated method, especially a consolidated damage accumulation model is available. Furthermore, design fatigue curves for austenitic steels in the applicable international design codes were extended by extrapolation from originally 106 up to 1011 load cycles [1]–[3]. However, the existing database for load cycles equal to or above 107 is still insufficient. Therefore, international efforts are currently ongoing in order to expand the database through international co-operations and compile a safe high cycle fatigue (HCF) database [4]. This is particularly important in combination with the influence of the cooling medium and its consideration according to established international standards as the database of the Argonne National Laboratory ANL [5] for fatigue behavior under medium conditions. For the range from HCF to VHCF and for their combination with LCF loads (collective effect) and the currently discussed limit values above which the cooling medium has an effective influence on the fatigue strength are not sufficiently consolidated. These aspects gain in importance particularly in the long-term operation context. A recently finished cooperative research project aims at contributing to closing these mentioned gaps by generation of a data and assessment basis for the fatigue behavior of welded austenitic stainless steels at high numbers of load cycles [6].

The following topics will be discussed in detail in the paper:

• Fatigue behavior at variable amplitude loading (combination of LCF / HCF and LCF / VHCF)

• Development of a fatigue assessment methodology under consideration of the transient endurance limit and damage accumulation effects including assessment and adaptation of appropriate fatigue damage parameters
Stud Bolt Thread Engagement: A Fitness for Service Approach
Authors: Cranford Colton M.
Published: November 2022

In the pressure equipment industry, codes of construction stipulate that fastener assemblies shall exhibit thread engagement through the full depth of the nut. In many older facilities and in locations with poor quality control, assemblies may be found on in-service equipment which do not have full thread engagement and do not meet the requirements of the code of construction. This is often found during the routine visual inspection of equipment and is flagged as a construction code deficiency requiring attention. Current post construction code guidance on fastener assemblies is ambiguous on how to handle fasteners with less-than-full thread engagement exceeding one thread of shortfall. The perceived risk of such a lack of thread engagement may lead maintenance organizations to perform costly and high-risk remediation activities, such as in-service “clamping” or “single stud replacement,” also known as “hot-bolting.” However, in many situations, fastener assembly strength can be proven to be sufficient for a given joint through analytical evaluation. Using a combination of innovative and existing thread strength and flanged joint considerations, the minimum required length of engagement, and, thus, the maximum allowable lack of engagement, can be safely determined for most fasteners on flange connections. This paper reviews some of the most important fastener strength considerations to propose a post-construction evaluation technique to determine the fitness for service of less-than-fully engaged fastener assemblies.
Evaluation of Welding Techniques for Stainless Steels Piping Without Use of Backing Gas
Authors: Sanagavaram Chakradhar , Chiluvuri Sivakumar , Penso Jorge
Published: November 2022

Austenitic Stainless steel SS304L and SS316L are extensively used as piping material for cryogenic and corrosive services in an LNG plant. GTAW welding process is a widely used welding process for joining stainless steel pipe work in pipe fabrication yards. For pipe welding, the GTAW process uses inert backing gas or purge gas (e.g. Argon) to prevent oxidation of root pass in order to achieve the weld quality. Welding large diameter stainless steel pipes using GTAW with inert gas introduces significant risk of asphyxiation when a welder enters the pipe that has resulted in fatalities based on industry references. A large LNG project mandated that only welding techniques without backing gas were permitted for joining stainless steel pipes of size > 24”. The project team evaluated four alternative welding techniques with no backing gas and Advanced or Modified Short-arc GMAW was selected. Initial scope covered cryogenic services and later extended to include corrosive / wet (aqueous) services.

This paper discusses the approach the project chose including the literature evaluation from the industry experiences, non-backing gas welding qualification and test protocols, curating technical specification, PQR testing and developing WPS’s and welder training and qualification program at the module fabrication yards. The paper also presents the knowledge, experiences gained, and challenges faced in implementing the non-backing gas welding for joining large size stainless steel pipe work in an extensive scale spanning multiple piping module fabrication yards globally.
Overview of Suitable Methodologies for Threshold Stress Determination by Small Punch in Aggressive Environments
Authors: Andrea Calvo Laura , Arroyo Martinez Borja , Álvarez Laso José Alberto , Gutiérrez-Solana Federico , Cicero González Sergio , Lacalle Calderón Roberto
Published: November 2022

The Small Punch Test is a recently standardized technique successfully employed for estimating the tensile, creep and fracture properties of metallic materials, and is considered as one of the most suitable options for evaluating mechanical properties when materials are in shortage. Several advances have been made in order to apply this methodology for mechanical characterizations in aggressive environments. The first tests were carried out pre-embrittling the samples in environment and then testing them in air. Subsequent methodologies proposed tests in environment after pre-embrittling the samples in order not to lose part of the embrittling capacity while testing; in these scenarios the punch rate has an enormous influence on environmental characterizations. The most recent works propose to implement in the Small Punch Test the step loading methodology collected in ASTM F1624 standard, which solves these problems by applying steps at a constant load which gradually increases until the sample fails. In this work, guidelines for the application of Small Punch Tests to determine the threshold load in aggressive environment are given, based on tests results under hydrogen embrittlement scenarios. A range of punch rates for constant punch displacement is provided, together with the suitable step times when applying the step loading technique, and a correlation to estimate the threshold stress based on Small Punch samples tested with this novel technique.
Verification and Applicability of a Simplified Method for Analyzing Blast Overpressure in Vertical Pressure Vessels
Authors: Hundl Jacob , Millet Barry , Mosher Bryan , Kirkpatrick Kenneth
Published: November 2022

A simplified method for analyzing pressure vessel response to blast overpressure incidents was developed in a previous study that demonstrated the ability to apply, evaluate and interpret the results of an overpressure incident on vertical pressure vessels without the use of advanced FEA software. The previous study was primarily focused on the development of the simplified method from existing literature and the step-by-step implementation of the method in an example case. The method itself was only applied to one example case and compared to a control case. This paper will verify the simplified method and determine its applicability by evaluating the response of several different vessels to different overpressure values and comparing the results to control cases performed using the CONWEP model in ABAQUS. The sampling of vessels will be determined by using common vessel diameters with different diameter to length ratios. The simplified method developed in the previous study will also be further refined by the application of Newmark’s Method, which allows for the evaluation of the dynamic response of a system to a time-history loading. Newmark’s Method is an average acceleration scheme that is primarily used in structural analysis to measure seismic response. The results from the analysis, along with a comparison between the data from the simplified method and the control case, will be discussed.
Fatigue and Fracture of Pipeline Steels in High-Pressure Hydrogen Gas
Authors: San Marchi Chris , Ronevich Joseph A.
Published: November 2022

Decarbonizing natural gas networks is a challenging enterprise. Replacing natural gas with renewable hydrogen is one option under global consideration to decarbonize heating, power and residential uses of natural gas. Hydrogen is known to degrade fatigue and fracture properties of structural steels, including pipeline steels. In this study, we describe environmental testing strategies aimed at generating baseline fatigue and fracture trends with efficient use of testing resources. For example, by controlling the stress intensity factor (K) in both K-increasing and K-decreasing modes, fatigue crack growth can be measured for multiple load ratios with a single specimen. Additionally, tests can be designed such that fracture tests can be performed at the conclusion of the fatigue crack growth test, further reducing the resources needed to evaluate the fracture mechanics parameters utilized in design. These testing strategies are employed to establish the fatigue crack growth behavior and fracture resistance of API grade steels in gaseous hydrogen environments. In particular, we explore the effects of load ratio and hydrogen partial pressure on the baseline fatigue and fracture trends of line pipe steels in gaseous hydrogen. These data are then used to test the applicability of a simple, universal fatigue crack growth model that accounts for both load ratio and hydrogen partial pressure. The appropriateness of this model for use as an upper bound fatigue crack growth is discussed.
Comparison of Stresses in Flexible Shell Element Expansion Joint of a Heat Exchanger for Code Application When Made of Multiple Flexible Shell Element
Authors: Mathkar Ameya , Gopalakrishnan Shyam , Pathre Sujay S.
Published: November 2022

To reduce shell and tube longitudinal stresses and tube-to-tubesheet joint stresses in a fixed tubesheet heat exchanger, expansion joints are provided. In addition to providing pressure integrity, the expansion joints provide flexibility for thermal expansion. ASME Sec. VIII Div.1 provides the methodology for evaluation of stresses in the expansion joint in both corroded and non-corroded condition for loading conditions under mechanical loads only, thermally induced displacements only or both. However, when it comes to the design rules, the ASME Sec. VIII Div. 1 leaves it to the user to perform the design calculations by a method (i.e., stress analysis) that can be shown to be appropriate for expansion joints.

For thick bellow expansion joints, it is a common practice for the industry to adopt the methodology described in TEMA for performing the design calculations. The latest TEMA (10th Edition) in comparison to the previous edition has modified the methodology for applying the loading conditions for spring rate and stress determinations.

It is a common practice for the industry to model the half-length symmetry flexible shell element in the Finite Element Analysis for determination of stresses and spring rate. This approach holds good when the heat exchanger comprises only one flexible shell element. However, in the industry owing to complex application requirements at times, it is a requirement to have multiple identical flexible shell elements or multiple non-identical flexible shell elements. The TEMA standard provides rules for FEA when multiple flexible shell elements are provided in an expansion joint. The methodology described in TEMA has certain conditions of applicability and holds good provided those criteria are met. However, when the stipulated criteria are not met, the TEMA standard leaves it to the discretion of the designer to approximately model the geometry for spring rate and stress determination.

The work reported in this paper is an attempt to evaluate the spring rate and determine the stresses for multiple flexible shell elements by means of FEA and verification of Code compliance and review of literature.
Numerical Investigation of Ductile Crack Propagation of Circumferentially Cracked Pipes Subjected to Multiaxial Loading at Room and Low Temperatures
Authors: Li Yuhao , Paredes Marcelo
Published: November 2022

Failure in pipes containing an initial crack under multi-axial loading condition is of common occurrence in industry and engineering applications. Current fitness-for-service codes and design standards cover partially part of this complex type of failure mode where the stress states may change abruptly from one state to another due to the combinatory nature of the applied loads. However, the torsional moment is mostly disregarded in the analysis for being apparently negligible in front of the bending moment and axial force, whose combined effects on crack-tip stress-strain fields have been very well investigated in the past. Based on recent research efforts to understand its effect, it has found that torsion in combination with axial force and bending moment, in fact, increases structural strength and delay fracture propagation, whose intensity varies depending on the crack configurations. Inspired by previous observations, this work takes a step forward in understanding effects of combined torsion with bending and axial force under harsh environments such as low temperature levels. A comprehensive numerical investigation is carried out using a newly developed constitutive model to describe failure at low temperatures on multi-axially loaded cracked pipes made of 316L stainless steel. Kinetic phase transformation and temperature dependent fracture criterion are implemented to accurately capture mechanical response at different temperature levels. Even though, experimental observations of these simulations were not available, their outcomes were quite consistent with some already published results performed on similar materials and loading conditions.
Compatibility of Medium Density Polyethylene (MDPE) for Distribution of Gaseous Hydrogen
Authors: Shrestha Rakish , Ronevich Joseph A. , Fring Lisa , Simmons Kevin , Meeks Noah D. , Lowe Zachary E. , Harris Timothy J. , San Marchi Chris
Published: November 2022

Numerous projects are looking into distributing blends of natural gas and different amounts of gaseous hydrogen through the existing natural gas distribution system, which is widely composed of medium density polyethylene (MDPE) line pipes. The mechanical behavior of MDPE with hydrogen is not well understood; therefore, the effect of gaseous H2 on the mechanical properties of MDPE needs to be examined. In the current study, we investigate the effects of gaseous H2 on fatigue life and fracture resistance of MDPE in the presence of 3.4 MPa gaseous H2. Fatigue life tests were also conducted at a pressure of 21 MPa to investigate the effect of gas pressure on the fatigue behavior of MDPE. Results showed that the presence of gaseous H2 did not degrade the fatigue life nor the fracture resistance of MDPE. Additionally, based on the value of fracture resistance calculated, a failure assessment diagram was constructed to determine the applicability of using MDPE pipeline for distribution of gaseous H2. Even in the presence of a large internal crack, the failure assessment evaluation indicated that the MDPE pipes lie within the safe region under typical service conditions of natural gas distribution pipeline system.
Effect of Trapped Fluid on Expandable Liner Hanger Performance in Geothermal Applications
Authors: Yin Shengjun , Zhong Allan , Abir M. D. , Gharesi Abdolreza
Published: November 2022

A metal-to-metal sealing expandable liner hanger (ELH) was designed for high pressure/high temperature (HPHT) applications [1]. It has been proven to be very robust for geothermal applications in deep well simulator testing, with temperatures up to 575°F. A potential scenario when using this ELH for geothermal applications is that fluid could be trapped between the expanded hanger and casing ID. The trapped fluid can induce a pressure change from a significant temperature rise because fluids typically have much higher thermal expansion coefficients than metals. When the temperature rises, the trapped fluid can generate significant pressure between the hanger and the casing. On the other hand, the volume change on the cavities can reduce the trapped pressure if the temperature change is not large enough and may help to increase anchoring capacity. The full fluid-structural interaction needs to be considered to accurately evaluate the effect of trapped fluid on expandable liner hanger performance.

This paper illustrates how a surfaced-based fluid cavity finite element model can be utilized to simulate fluid-structural interaction between the structure and the trapped fluid [2, 3]. The model accounts for the coupling between the deformation of the surrounding structure and the pressure from the trapped fluid acting on the structure. This methodology was applied to investigate the effects of trapped fluid on the ELH performance when subjected to high pressure/high temperature applications.

With a specific well condition in consideration, it was observed that: 1) the pocket (cavity) pressure after expansion was lower than the hydrostatic pressure, as per design intention; 2) the net effect was that the hydrostatic pressure squeezed the hanger which improved the ELH hang weight capacity.

In the extreme well conditions where the trapped fluid pressure may reduce the hanger anchor capacity, a novel design concept was developed to mitigate trapped fluid pressure effect.
Nickel Cladded Structural Components for Advanced Reactors
Authors: Barua B. , Messner M. C. , Sham T.-L.
Published: November 2022

The aggressive corrosive environment along with higher operating temperature in molten salt reactors present significant challenges to existing structural materials that have been qualified in the ASME Section III, Division 5 Code for high temperature cyclic service. Corrosion resistant claddings offer an attractive near-term solution to mitigate corrosion concerns and enable the use of ASME Code qualified materials for advanced reactor structural components. Nickel provides good corrosion resistance to molten salts as well as good thermal and mechanical compatibility with existing ASME Code qualified materials, and therefore can be used as a cladding material for structural components in molten salt reactors. However, there are currently no ASME design rules for cladded components to guard against creep-fatigue failure and ratcheting strain accumulation under high temperature cyclic service. Recently, we have developed new design rules for components cladded with creep-compliant materials (e.g. nickel clad on 316H base metal) for high temperature cyclic service. These design rules require design parameters that can be established through relatively short-term testing for the clad material. This work shows how the design parameters for nickel are developed using fatigue and creep-fatigue test data. Finally, the paper walks through a sample problem detailing the application of the design rules to 316H components cladded with nickel.
Numerical Approaches for Bolt Interactions in Flange Gasket Assemblies
Authors: de la Roca Leonardo , Meira Igor , Girão Carlos D. , Carlos Veiga José
Published: November 2022

In most industrial plants, the maintenance of the piping system is a crucial part of the site’s health and integrity, as leakage can often lead to costly losses and even disastrous accidents with the loss of life. An incorrect assembly of a bolted flange joint will most likely form a leak path in the sealing surface and lead to joint failure. Standards such as the ASME PCC-1 Guidelines for Pressure Boundary Bolted Flange Joint Assembly, have the purpose of guiding towards safer procedures of gasket installation in bolted flange connections, where specific gasket assembly methods regarding recommended fastening torque and bolt sequence are described in detail. However, to this day, said guidelines are not strictly followed. The lack of training concerning the recommended methods leads to unqualified flanged joint assemblers and hence the most common cause of gasket failure, which is an improper installation. Therefore, there is a need to produce instructional tools, physical in nature or not, that help raise awareness to the recommended, standardized, gasket installation methods and good practices in bolted flanged joint assemblies, aiming to reduce the volume of industrial plants’ leakage caused by improper installation, preventing further health and environmental problems. The present work describes a set of mathematical methods designed for flange assembly training simulations, intended to be used as an educational tool to enhance the abilities and knowledge of assemblers. The work includes methods of calculating elastic interactions between bolts and other common phenomena characteristics of flange tightening.
Advanced Structural Integrity Assessment Tools for Safe Long Term Operation - ATLAS+ Project: Status of the Activities of the WP3 on Modelling in 2020 & 2021
Authors: Blouin Arnaud , Marie Stéphane , Nicak Tomas , Timperi Antti , Gill Peter
Published: November 2022

The main objective and mission of the ATLAS+ project was to develop advanced structural assessment tools to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems.

ATLAS+ WP3 focused mainly on ductile tearing prediction for large defects in piping and associated components: Several approaches have been developed to accurately model the ductile tearing process and to take into account phenomena such as triaxiality effects, or the ability to predict large tearing in industrial components. These advanced models include local approach coupled models or advanced energetic approaches. Unfortunately, the application of these tools is currently rather limited to R&D expertise. However, because of the continuous progress in the performance of calculation tools and accumulated knowledge, in particular by members of the ATLAS+ consortium, these models can now be considered as relevant for application in the context of engineering assessments.

WP3 was planned to:

• Illustrate the implementation of these models for industrial applications through the interpretation of large scale mock-ups (with cracks in weld joints for some of them),

• Make recommendations for the implementation of the advanced models in engineering assessments,

• Correct data from the conventional engineering approach by developing a methodology to produce J-Δa curve suitable case by case, based on local approach models,

• Improve the tools, guidance and procedures for undertaking leak-before-break (LBB) assessments of piping components, particularly in relation to evaluating structural representative fracture toughness J-Resistance curves and the influence of weld residual stresses.

To achieve these goals, WP3 was divided into 4 sub-WPs. This paper presents the progress of the work performed in each sub-WP after 48 months of activities.
ATLAS+ European Project - General Method for the Components J-R Curve Derivation
Authors: Nicak Tomas , Blouin Arnaud , Marie Stephane , Ancelet Olivier
Published: November 2022

The main objective and mission of the European Project ATLAS+ project was to develop advanced structural assessment tools to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems. ATLAS+ WP3 was focused mainly on ductile tearing prediction for large defects in components. Several approaches have been developed to accurately model the ductile tearing process and to take into account phenomena such as the triaxiality effect, or the ability to predict large tearing in industrial components. These advanced models include local approach coupled models or advanced energetic approaches. Unfortunately, the application of these tools is today rather limited to R&D or expertise. However, because of the continuous progress in the performance of the calculation tools and accumulated knowledge, in particular by members of ATLAS+, these models can now be considered as relevant for application in the context of engineering assessments.

Although there are analytical solutions for calculation of J-Integral values for many standard specimen geometries (i.e. CT or SENT), limited or no formulas are available for more complex structures such as pipes, elbows, T-junctions, pressure vessels etc.

Therefore, there is a need to develop a methodology which can be used for derivation of J-R curves for an arbitrary component geometry on the basis of experimental results obtained by testing small size laboratory specimens.

To achieve this goal Framatome GmbH used combined local approach (GTN model) and elastic-plastic calculations to determine J-R curves whereas Framatome France used analytical methodologies to derive the J-R curves from local approach results (GTN model). In both cases, the Δa and J values were calculated at the deepest point of the crack front.

This paper shows promising results and concludes there is a significant margin in the fracture mechanics assessment based on material properties obtained by testing highly constrained standard specimens compared to more realistic structural situations.
Assessment of Safety Valve Escape Pipework
Authors: Vorster Willem J. J. , Roy Jonathan , Gilroy Daniel G. , Pollock Jack A. , Clarkson David M. , Beveridge Andrew J. , Strong Alistair
Published: November 2022

This paper discusses fitness for purpose (FfP) structural integrity assessments of Safety Relief valve (SRV) vent pipes that were inadequately designed and maintained. The FfP assessments identified several latent errors with the pipework design. The absence of a fault schedule in combination with the latent errors led to a discernable anomaly in the safety case which was finally address but resulted in long outage delays and spiraling costs due to the large number of assessments, inspections and modifications required to achieve and demonstrate integrity.

The FfP assessments discussed here consider all failure mechanisms which were identified as being relevant during steam discharge. These include plastic collapse, ratchetting, creep rupture and creep-fatigue and required a series of complex assessments to sentence the SRV pipes for return to service. The Computational Fluid Dynamics (CFD), pipe stress analysis and Finite Element Modeling (FEM) required to demonstrate integrity are discussed. The plant modification and repair solutions required to achieve integrity before the pipes could be returned to service are presented. The method used to apply CFD loads to pipe stress models without double accounting for static pressure stresses in the Finite Element Analyses (FEA), is describe here. Novel analysis techniques used to speed up assessments and the historic plant data reviews that were required to substantiate the claims on historic damage are reviewed.
Flanges Impact Testing Exemption Assessment
Authors: Robles Roberto , Muñoz Miguel , Santana Antonio
Published: November 2022

Over the last decade, multiple carbon steel flanges brittle fracture failures have led the industry to issue a global alert on standard ASTM A105 flanges toughness values at temperatures higher than −20°F (−29°C), the minimum temperature allowed by the current editions of ASME B16.5 and ASME B31.3. The ASME BPV VIII Subgroup Toughness penalized these components by assigning the material the UCS-66 Curve A and modified UCS-66(c) to limit the minimum temperature of standard A105 flanges to 0°F (−18°C), unless the flanges have been normalized and manufactured to fine grain practice, after which they can be used down to the temperature permitted by ASME B16.5.

In order to determine whether these changes would provide acceptable toughness values, nineteen (19) flanges were purchased from local manufacturers in both as-forged and normalized conditions and were subjected to several tests including charpy testing at various temperatures, McQuaid-Ehn, hardness testing, metallography, grain sizing, and chemical analysis. The results suggest that complying with UCS-66(c) does not necessarily guarantee acceptable toughness results for flanges that were normalized and manufactured to fine grain practice, and this is attributed to low Mn:C ratios and possibly uncontrolled heat treatment procedure. On the other hand, a number of non-normalized standard flanges have been found to provide very low toughness values at temperatures as high as 32°F (0°C), despite the current state of UCS-66(c) allowing use down to a minimum temperature of 0°F (−18°C).

In view of the above, this paper discusses and evaluates some of the possible additional technical requirements that users could specify to minimize the risk of brittle fracture on standard ASTM A105 flanges, as well as a number of methods to guarantee better toughness performance in standard flanges.
Effect of Trace Water Vapor on Measurement of Fatigue Crack Growth Rates in Hydrogen Gas at Low ΔK
Authors: Nibur Kevin , Somerday Brian
Published: November 2022

Anomalous and inconsistent results were observed while performing fatigue crack growth tests in hydrogen gas on 4130X Cr-Mo steel when the stress-intensity factor range (ΔK) was less than 10 MPa m1/2. Two particular abnormal characteristics were noted: i) sequential measurements of fatigue crack growth rate (da/dN) vs. ΔK from a single test specimen were not repeatable at lower ΔK, and ii) at constant ΔK ∼8 MPa m1/2, da/dN never reached a steady-state level, as crack growth rates continuously increased as a function of time. It was hypothesized that both of these characteristics could be related to water vapor in the hydrogen gas. This hypothesis was tested by varying the environment in the test chamber through modification of the pressure purging and vacuum evacuation procedures. The resulting water vapor levels in the hydrogen test gas were either higher or lower than the nominal value, and measurements of fatigue crack growth rates in these environments confirmed the hypothesis that water vapor governed da/dN at lower ΔK. One consequence of such water vapor-dominated fatigue crack growth rates is that the da/dN vs. ΔK relationship in dry hydrogen gas at lower ΔK cannot be reliably represented by the da/dN vs. ΔK relationship measured in humid air. As a result, when the lower-ΔK portion of the da/dN vs. ΔK relationship in hydrogen gas is constructed from the da/dN vs. ΔK relationship in air, fatigue crack growth rates can be overestimated by as much as an order of magnitude.
Quantification of the Tempering Response for Temper Bead Welding of SA-508 Low Alloy Steel
Authors: Jang Eun , Luo Yuxiang , Alexandrov Boian , McCracken Steven L. , Tatman Jon , Barborak Darren
Published: November 2022

The objective of this work is to demonstrate the tempering response quantification approach for process - property optimization in the heat affected zone (HAZ) of SA-508 Gr. 2 Cl. 1 (formerly designated as SA-508 Cl. 2) subjected to temper bead welding (TBW).

The tempering response in the CGHAZ and ICHAZ was quantified by a series of TBW thermal history simulations, followed by microstructural characterization and hardness measurements. Tempering response predictive equations were developed utilizing a version of the Grange Baughman parameter (GBP), modified to reflect the thermal histories in multi-pass welding.

In parallel, the accuracy of the tempering response quantification and predictive hardness equations were validated. Validation was achieved through experimental welding with thermal history acquisition, determination of a predicted hardness value using the recorded thermal data, and comparison of the predicted values with micro-hardness measurements.
Guidance on the Suitability of Design Codes and Assessment Procedures for Deploying High Temperature Advanced Modular Reactors in the UK
Authors: Chevalier Marc , James Peter , Underwood Nick
Published: November 2022

The UK government has committed to achieving “net-zero” carbon emissions by 2050. Advanced Modular Reactors (AMRs) are small Generation IV reactor that operate at high temperatures. These reactors could play a significant role in providing low carbon electricity generation and decarbonising other industrial processes by utilising heat directly. However the structural integrity challenges for such high temperature plant have been demonstrated in experimental Generation IV plant and the AGR fleet in the UK.

Ensuring the design codes are fit for purpose to satisfy the UK regulatory requirements, including Generic Design Assessment (GDA) and also producing a reliable design that results in a commercially viable plant, is essential. Therefore, the “Establishing AMR Structural Integrity Codes and Standards for UK GDA” (EASICS) project was established to identify the suitability and shortfalls of existing design codes and assessment procedures.

The headline deliverable from the EASICS project was a guidance document, aimed towards vendors looking to deploy AMRs in the UK. However many of the issues raised are relevant to AMR technology regardless of the regulatory regime. This paper provides a summary of the EASICS guidance document. This includes a review of the regulatory requirements for design substantiation in the UK (which unlike many other countries requires consideration of defect tolerance), status of existing design codes (i.e. ASME III Div. 5 and RCC-MRx) and assessment procedure (i.e. R5/R6), comment on the notable technical differences between the available design codes and assessment procedures, highlighting what has been learnt from previous operation of high temperature nuclear plant (including Generation IV reactors and the AGRs in the UK), and an overview of the conclusions.

The conclusions consider the strengths, weaknesses and gaps in the currently available design codes and assessment procedures for commercial deployment of AMRs. It also identifies the development required to address perceived shortfalls and how design codes and assessment procedures may have to be used congruently to provide a solution on a timescale consistent with the UKs ambition for AMR deployment.
Crack Growth in Carbon and C-0.5Mo Steels in High Temperature Hydrogen: Laboratory Data and Fitness for Service Modelling
Authors: Rollins Brandon C. , Sutton Nathaniel
Published: November 2022

High temperature hydrogen attack (HTHA) is a known degradation mechanism in the refining industry for carbon and low alloy steels operating at temperatures above 400°F in hydrogen service. Historically the integrity of operating equipment subject to these conditions has been ensured by using the empirically derived Nelson Curves to identify safe operating regions. This approach was largely successful, but failures still occurred and, in some cases, required overly conservative operational limits. Additionally, this approach did not allow for a defect tolerance approach to fitness for service (FFS) assessments. An on-going joint-industry project (JIP) has been addressing these issues by generating laboratory crack growth data and developing models to apply the acquired knowledge in FFS assessments.

A testing program was conducted on three (3) C-0.5 Mo steels to generate crack growth data in hydrogen at a range of temperatures (316 to 399°C [600 to 750°F]), 5.52 MPa (800 psig H2) hydrogen pressure, and stress intensity values between (10.5 to 35.4 MPa√m [9 to 32 ksi√in]). These results were used to validate and refine a crack growth model based on the creep crack growth fracture mechanics approach, C*. The results of the test program and modeling efforts are described in detail.