bluuebunny/crossref_metadata_2025 huggingface dataset:
Coefficients of Friction in Dependence on Aging State of Elastomers – Experimental Identification and Numerical Simulation of the Experiment
Authors: Weber Mike , Zaghdoudi Maha , Brandt Guido , Kömmling Anja , Jaunich Matthias , Wolff Dietmar
Published: November 2022

Elastomer seals are mounted as barrier seals in lid systems of containers designed for transport and disposal of negligible heat generating radioactive waste and as auxiliary seals in spent fuel storage and transportation casks (dual purpose casks (DPC)). When the behavior of mounted seals under normal and hypothetical accident conditions of disposal and transport is to be simulated, a comprehensive knowledge of their complex mechanical properties at every state of aging is necessary. In previous works, BAM’s efforts in experimental investigations on specimen artificially aged at different temperatures and times and the implementation of the found results in finite element material models were presented. Additionally, our approaches to reproduce the aging process itself and to extrapolate the results of artificially accelerated aging to longer times were presented. Numerical simulations have shown that the behavior of the seal during mounting and one-sided pressurizing and the resulting performance values such as leakage rate strongly depend on the coefficient of friction (COF) between flange and seal. The friction coefficient, in turn, depends on the aging state of the elastomer material as several publications suggest (see below).

Dynamic COF between an exemplary ethylene propylene diene rubber (EPDM) material and a stainless steel ball were determined by using a self-designed linear oscillation tribometer. Unaged and artificially aged EPDM specimen stored for 30 days and 100 days at a temperature of 150 °C were tested. A stainless steel ball (d = 10 mm) is brought in contact with the specimen’s surface und loaded by normal forces of 2.5 N, 5 N, 10 N and 20 N. During a reciprocating movement of the EPDM sheet, the horizontal force/friction force is continuously measured, and the COF can be derived.

It is well known that friction is a complex phenomenon especially in soft materials. It cannot be excluded that the measured friction force is influenced by additional force components, resulting from the ball’s grooving through the elastomer’s surface. This force depends on the penetration depth of the ball and on the resistance of the elastomer in its different states of aging. The latter results from microstructural changes i.e., chain scission and additional crosslinking that occur during aging which in turn influence the softening or hardening of the material.

A finite element (FE) ABAQUS® model was developed to reproduce the measurement process. It should help to better understand the physical mechanisms and to quantify the percentage of measured forces resulting from real friction on the one hand and forces resulting from unintended side effects that could falsify the result on the other hand. The behavior of the elastomer in its different states of aging is reproduced by a FE material model already presented in previous works of BAM.
INCEFA-SCALE (Increasing Safety in NPPs by Covering Gaps in Environmental Fatigue Assessment - Focusing on Gaps Between Laboratory Data and Component-Scale)
Authors: McLennan Alec , Cicero Roman , Mottershead Kevin , Courtin Stephan , Que Zaiqing , Cicero Sergio
Published: November 2022

INCEFA-SCALE is a five-year project supported by the European Commission HORIZON2020 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 continue work, advancing the ability to predict lifetimes of Nuclear Plant components when subjected to Environmental Assisted Fatigue loading (EAF).

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. EPRI, in the USA, is leading a series of component-scale environmental fatigue tests that are expected to advance data availability significantly; however, the ability to address transferability of laboratory-scale tests to real component geometries and loadings will still be constrained by limited test data. This is the knowledge gap addressed by INCEFA-SCALE. The project strategy will be (1) the development of comprehensive mechanistic understanding developed through detailed examination of test specimens and MatDB datamining, and (2) testing focussed on particular aspects of component-scale cyclic loading. The project will initially survey and understand the vast amount of test data within JRC’s MatDB database (from the predecessor INCEFA-PLUS project, and from other external sources such as USNRC, EPRI, MHI and the AdFaM project). In parallel, the test programme needs have been agreed, and protocols agreed for managing data, testing, and material examinations consistently. Testing commenced after one year and will run for three years. Finally, the project will deliver guidance on the use of laboratory-scale data for component-scale applications.

This paper will report the first year of the project and detail the preparations completed to ensure the project maximises the achievement of its objectives.
Practical Application of Inline Inspection Tool With Combination of Eddy Current and Deformation Technology
Authors: Geng Liyuan , Feng Qingshan , Chang Jinglong , Huo Xiaotong , Qu Jie
Published: November 2022

In the actual process of magnetic flux leakage inline inspection, the following four problems are often encountered: 1) There are many impurities in pipelines, which seriously interfere with the results of magnetic flux leakage inline inspection; 2) Girth weld misalignment cannot be accurately detected by magnetic flux leakage inline inspection because MFL signals are complex in girth welds; 3) The minimum passage of magnetic flux leakage inline inspection tool is poor when negotiating with pipeline geometry restrictions, so in practice geometry inline inspection normally perform prior to magnetic flux leakage inline inspection to validate the tool passage risk and avoid tool stuck incident, this will lead to tremendous extra efforts, as well as expenses; 4) The magnetic flux leakage inline inspection tool is normally heavier due to mechanical design and strong magnetic attraction force with metal surface, which lead to a much higher driving/pulling force.

To solve these problems above, this paper propose the inline inspection tool with combination of eddy current and deformation technology. This inline inspection tool has the advantage of light weight and lower friction force, which lead to a comparative lower driving/pulling force. It can detect the metal loss on the inner wall of pipelines and weld misalignment of girth welds while realizing geometry inspection.

By comparing the inspection results with the high-resolution magnetic flux leakage inline inspection results, it is concluded that the inspection tool combined with the eddy current and deformation technology inline inspection technology can replace the high-resolution magnetic flux leakage inline inspection tool when focusing on the inner metal loss of pipe wall.
Impact of General and Local Metal Loss on the API 579-1 Creep Residual Life
Authors: Scano Lorenzo , Piccini Francesco
Published: November 2022

Creep and corrosion are typical damage mechanisms of pressure components operated at high temperatures and they are frequently evaluated using the relevant sections of the API 579-1 [1] standard. When a general or local metal loss is expected or assessed via Non-Destructive-Examination (NDE) on a pressure equipment in the creep regime, the time-dependent corrosive phenomenon has a direct impact on the time and stress-dependent creep residual life and the two damage mechanisms are competing and reinforcing one another. For these cases, an API 579-1 Level 3 creep assessment shall necessarily take into account the metal loss induced by the corrosive environment to be effective in predicting the component residual life. In this work, the impact of corrosion on the creep life evaluated according to API 579-1 and the Larson-Miller theory was evaluated for the special case of a low-alloy piping component exposed to both general and local metal loss with variable corrosion and creep rates. A finite-element model was set-up incorporating the inelastic steady-state creep law, the API 579-1 time-fraction creep damage and the progressive metal loss due to uniform and localized corrosion. A parametric analysis was finally carried out to investigate the role of the corrosion rate, and the related, augmented stress field on the overall API 579-1 creep damage.
Experimental Investigation on the Fatigue Strength for Different Tightening Procedures and Materials in Metric Screws
Authors: Fini Stefano , Croccolo Dario , De Agostinis Massimiliano , Olmi Giorgio , Robusto Francesco , Scapecchi Chiara
Published: November 2022

The aim of this present paper is to investigate the influence of some joint design parameters on the fatigue strength of metric screws. This investigation involved different screws strength grades (8.8 and 12.9). The experimental tests were carried out on black oxidized M6 screws, coupled with steel nuts of the corresponding strength class. Both screws and nuts were tested in “as received” lubrication condition. The screws were tested untightened and tightened with the tightening torque causing yielding (100% of the yield stress). A preliminary test to evaluate the tightening torque providing the desired equivalent stress on the screw was carried out. A tightening machine bench which was able to measure the tightening load and the friction coefficients both in the underhead and in the thread was used. The tests were run controlling the tightening torque and the spindle speed. In the following tests, the screws were tightened at the desired tightening torque and then untightened by means of the aforementioned tightening machine bench. Then the screws and the nuts were assembled on an ad hoc test fixture and tested on a resonant testing machine in order to evaluate the screw fatigue limit according to the international standard ISO 3800. The experimental results were processed by means of statistical tools of two-way ANOVA and Fisher Test in order to evaluate the effect of each parameter on the fatigue response of the screws.
Overview of Standards on Pressure Cycling Test for On-Board Composite Hydrogen Storage Cylinders
Authors: Huang Qianghua , Li Xiang , Li Jiepu , Liu Yitao , Li Xin , Zhu Chaoyang
Published: November 2022

As the fuel storage component for hydrogen fuel cell vehicles, on-board composite hydrogen storage cylinders have developed rapidly in recent years. The safety of on-board composite hydrogen storage cylinders in fuel cell vehicles raises wide concerns in the society. The pressure cycling test is used to simulate repeatedly charging and discharging process of hydrogen storage cylinders in service conditions, verify the fatigue resistance of gas cylinders at ambient temperature or extreme temperature, and to test the impact of extreme temperature conditions on the burst strength of hydrogen storage cylinders. Currently, some relevant standards or standard drafts have been drawn up by the international organizations, which stipulate the ambient cycling test method and extreme temperature cycling test method for on-board composite hydrogen storage cylinders. The pressure cycling test methods of composite hydrogen storage cylinders in various standards were compared and analyzed, such as test object, test medium, environment temperature and humidity requirements, test frequency, cycle pressure range, cycle times, qualification indicators, etc. Furthermore, the problems that need to be further studied in pressure cycling test methods were pointed out. Finally, the corresponding suggestions when deploying the pressure cycling test were given.
Development of Screening Technology for Hydrogen Embrittlement Compatibility of Pipeline Steels and Welds Using Simple In-Situ Tests in High-Pressure Environments
Authors: Shin Hyung-Seop , Min Eunsu , Kang Sungbeom , Baek Un-Bong
Published: November 2022

Simple screening technology for hydrogen embrittlement (HE) of steels for hydrogen energy facilities using the in-situ small punch (SP) test method has been established. The HE behaviors of API X70 steel base metal and welds for pipelines were investigated using the relative reduction of thickness (RRT) obtained by the in-situ SP test. As a result, it was found that API X70 steel exhibited similar HE sensitivity regardless of test conditions and weld regions. In this study, to give data application reliability to the RRT obtained by the in-situ SP test of ferritic steels, a simple in-situ slow strain-rate tensile (SSRT) test method using a hollow-type specimen was devised. It was used to evaluate the HE sensitivity of the API X70 steel and welds at various temperatures, and the obtained relative reduction of area (RRA) was used to compare to the RRT by in-situ SP test. As a result, it can be found that RRT by in-situ SP test showed a generally good relationship with RRA by the SSRT, even though some variation existed depending on the test temperature, confirming that the in-situ SP test can be effectively applied to the HE sensitivity screening of pipeline steels and welds in high-pressure hydrogen environments.
Technological Progress on Safety Assurance for Hydrogen Storage and Transportation Pressure Equipments in China
Authors: Chen Xuedong , Fan Zhichao , Xu Shuangqing , Xu Peng , Liu Xiaoliang
Published: November 2022

Hydrogen is important clean, secondary energy and is considered to be one of the important solutions to achieve the goal of “peak carbon dioxide emission and carbon neutrality”. The industrial chain for hydrogen includes the production, storage, transportation, refueling, and terminal utilization, etc. The safe and efficient storage and transportation of hydrogen is a bottleneck problem that needs to be solved urgently in the development of hydrogen industry. The needs for development of hydrogen energy in China have been briefly introduced in the context of carbon peaking and carbon neutrality goals. The failure modes and damage mechanisms of the typical hydrogen storage and transportation pressure equipments have been discussed. The current development status of hydrogen storage and transportation pressure equipments, in terms of the design, manufacturing and maintenance technologies, has been reviewed. Combined with the development trends such as high-pressure, low-temperature, large-capacity and high-density, etc., and focused on different application scenarios including gaseous and liquid hydrogen, technical challenges have been analyzed on safety utilization of hydrogen storage (stationary storage at the refueling stations and on-board storage on fuel cell vehicles) and transportation pressure equipments. The relevant research suggestions on the long-term safety guarantee of the hydrogen storage and transportation pressure equipments have been proposed.
Quantitative Probabilistic Seismic Resilience Assessment of Industrial Facilities
Authors: Kalemi Bledar , Paolacci Fabrizio , Caputo Antonio C. , Corritore Daniele , Quinci Gianluca
Published: November 2022

Seismic events could expose industrial facilities to huge economic losses due to production capacity loss. The loss of production capacity and economic losses are not only influenced by direct damages that occur to a facility due to earthquakes, but also they are highly related to recovery process. Recovery process is a function of plant preparedness, recovery plan, and its applicability. In order to have a clear view of economic losses in a process plant in case of seismic events, plant resilience can be useful. Consequently, this paper presents a comprehensive framework for the quantification of seismic resilience of a process plant, at plant level. After the introduction of resilience definition and process plant resilience metrics, a probabilistic methodology for calculation of seismic resilience of plant is presented; furthermore, scenario-based analysis for calculation of risk and resilience metrics is introduced and explained. Finally, case study of a black carbon plant is used to show the applicability of scenario-based analysis for calculation of risk and resilience performance metric. Resilience index, expected annual losses and operational capacity curve are used as performance metrics for process plant. The proposed methodology is the first steps toward a risk and resilience targeted design/assessment of process plants under seismic loading.
Low-Alloy SA-533 Steels as Alternative to ASME SA-516 Carbon Steel for Fabrication of Lightweight FPSO Vessels
Authors: Ngomo Valéry , Guyot Evelyne , Lancini Ivan , Cornut Dany
Published: November 2022

One of the biggest challenges in the design of an Floating Production Storage and Offloading (FPSO) plant is managing the weight of the facilities within the limited space and weight capacity of the ship. Weight reduction allows simplification of the load distribution on the ship, which is critical because the motions of the structure due to sea current and waves may affect the vessel performance. In this context, the use of high strength steels for pressure vessels reduces the weight by permitting thinner vessels and lighter supporting steel structures.

Compared to ASME SA-516 Grade 70 steel, commonly used for pressure vessels, ASME SA-533 Class 2 steel provides approximately 30–50% greater allowable stress when vessels are designed in accordance with ASME Section VIII Division 1 or 2. Therefore, special considerations are needed to ensure sufficient impact toughness of the welds and to balance toughness, tensile and hardness properties required by the severe service condition.

This paper aims at summarizing some technical data on high strength carbon steel SA-537 class 2 and low-alloy steel SA-533 type C class 2. A case study will illustrate the weight savings that can be achieved with these grades. In addition, characterization results obtained on base material from laboratory tests as well as welded joints will be provided, including hardness survey as regard to ANSI/NACE MR0175 / ISO 15156. Finally, a world-class manufacturer of pressure equipment will provide some feedback on the recent fabrication of pressure vessels in ASME SA-533 Type C grade for an offshore project in Western Africa.

This contribution demonstrates the interest of high strength steels for the fabrication of lighter pressure vessels, and their potential use for severe conditions such as low-temperature or sour service.
Study on Ultrasonic Phased Array Imaging Technique for Direct Contact Inspection on Double Curved Surface
Authors: Cheng Jingwei , Fan Zhichao , Chen Xuedong , Bu Yangguang , Wang Haibin , Wang Zhe
Published: November 2022

Ultrasonic testing technique is commonly used for nondestructive inspection of pressure vessels and pipelines. Normally, ultrasonic phased array system can effectively and efficiently image different types of defects within the structures through direct contact method. However, the double curved geometries of inspection targets (e.g. pipe elbows, pipe weld joints and turbine blades) give rise to challenges in direct contact between probe and surface. Therefore, based on the full matrix capture and total focusing method (TFM), this paper uses a conventional phased array transducer with flexible wedge to detect and image a double curved sample with different depths of side drilled holes. The test specimen is fabricated in a ring shape with an outer diameter of 150 mm, an inner diameter of 100 mm and a 2 mm high weld reinforcement. It is found that the full matrix data can be captured to image the structure interior by either extracting the surface profile or directly imaging with preset surface dimensions. The proposed technique has also demonstrated its capability on realizing high-resolution imaging of 1 mm side drilled holes at different depths. Our promising results show that the method has the ability to reliably locate and quantitatively evaluate the defects with complexly shaped structure.
Filament Wound Composite Pipes Subject to Torsion and Bending Loads
Authors: Farrugia Nicole , Camilleri Duncan , Ellul Brian , Muscat Martin
Published: November 2022

Filament winding has been extensively used to fabricate fibre reinforced composite pipes. The fibres are primarily oriented in such a way to increase the structural efficiency of the pipes to withstand internal pressure, that namely load the pipes in the hoop direction. However, the various intricate pipe systems and connections will also subject these pipes to torsional and bending loads. In this study different fibre orientation lay-up sequences consisting of four E-Glass /polyester resin layers were fabricated using a standard four-axis filament winding machine and experimentally subjected to torsion and bending load tests. During the curing process the samples were also vacuum bagged to minimise the void content. The respective volume fractions are also identified through ignition loss tests. The load versus deformation and ultimate failure load were recorded. The onset of first ply failure was also identified through acoustic/vibration measurements and observable differences in load/deformation plots. Different failure modes were observed ranging from buckling failure to matrix failure. The primary failure mode for pipes subject to bending was either compressive or tensile failure at the upper or lower strands of the pipe as a result of the imposed bending stresses. On the other hand, buckling or shear failure was observed in the pipes subject to torsional loading. The best fibre orientation based on loading conditions was identified. In the case of bending, the load carrying capacity increased when fibres are oriented closer to the axial direction, however care is to be taken to ensure that the pipes do not buckle. In the case of torsional loading, pipes with fibres oriented at 45° were able to sustain the highest load.
Energy-Based Very Low Cycle Fatigue Crack Growth Simulation for Seismic Application
Authors: Hwang Jin-Ha , Kim Yun-Jae , Kim Jin-Weon
Published: November 2022

In the previous studies, the energy-based damage model was developed by simulating cracked pipe fracture behaviour under seismic loading. The multi-axial fracture strain energy density, the parameter of energy-based damage model, was determined by standard tensile test data and monotonic cracked pipe test data. Very low cycle fatigue crack growth was simulated by applying the multi-axial fracture strain energy density under monotonic loading. When the previous energy-based damage model was applied to simulate cracked pipe fracture test under seismic loading, the simulated results were good agreement with experimental data under high load amplitude reverse cyclic loading and displacement controlled large scale cyclic loading. However, the conservative predicted results are shown in pipe test with low load amplitude and different load ratio.

In this paper, the energy-based damage model was improved by incorporating the effect of load amplitude and load ratio on multi-axial fracture strain energy density. The cyclic multi-axial fracture strain energy density increased by depending on the load amplitude and load ratios. The improved damage model was applied by pipe fracture test under seismic loading with various load amplitudes and load ratios. The pipe tests were subjected by using circumferential through-wall crack (TWC) and surface crack (SC) pipe specimen. The seismic loading consisted of two load amplitudes and two load ratios. The simulated results were compared with experimental data and validated.
A Recurrent Neural Network Method for Condition Monitoring and Predictive Maintenance of Pressure Vessel Components
Authors: Halliday Chris , Palmer Iain , Pready Nigel , Joyce Mark
Published: November 2022

High-fidelity physics simulations such as finite element analyses (FEA) provide accurate solutions to complex physical problems that are encountered in equipment subjected to transient conditions. However, such simulations come with significant computational expense, which often prevents them from being used for condition monitoring as a ‘digital twin’. Physics-based reduced order models (ROMs) seek to reduce this computational cost by using classical equations, augmented with empirical factors, to predict some unknown physical quantity of interest over time. Such ROMs are fast to run and simple to tailor for different load cases, but often require significant bespoke development effort. Additionally, developing the formulation of such ROMs becomes increasingly difficult as the complexity of the modelled physical phenomena increases.

Advances in Artificial Intelligence and Machine Learning have resulted in techniques that are ideally placed to address the shortfalls of ROMs and maintain their benefits. A common problem that a physics-based ROM attempts to solve is predicting an unknown time-varying parameter (such as stress) based on a set of known time-varying parameters. Recurrent Neural Networks (RNNs) are well suited to tackle exactly this problem as an RNN-ROM.

An RNN-ROM has been developed and validated against finite element analyses for a piece of rotating machinery subjected to complex thermal transients. Transient thermal datasets were extracted from locations of interest in an FEA representation of a rotating component and used as inputs to the RNN-ROM to predict time-dependent transient thermal behavior. The results were compared to the high-fidelity finite element model from which the input data was extracted; these results showed significantly improved accuracy compared to physics-based ROMs.
Case Study of Probability of Loss of Containment Due to Overpressure
Authors: Nunez Joseph , Hay Clifford
Published: November 2022

This research explores the equation in API 581 for determining the probability of loss of containment due to overpressure from a failure of a pressure relief device to open on demand. This paper explores the basis for the equation as presently written in API 581 and how that relates to the ASME Code for pressure vessels; specifically ASME Section VIII Division 1. A generic form of the equation is derived which can be broadly applied to equipment designed to any code of construction that provides a design margin on plastic collapse. This paper then provides several case study comparisons of the generic equation applied to various codes of construction; ASME VIII Division 1 (current edition), ASME VIII Division 2 (Class 1 and Class 2), and ASME B31.3. Results using a burst pressure design margin and isochronous creep rupture design margins are explored. Finally, a comparison with the nuclear service level elastic limits is provided for qualitative benchmarking.

This research provides end users engaged in risk based inspection activities for PRDs with information that can more accurately define the risk of loss of containment for equipment other than pressure vessels constructed to ASME VIII Division 1. This will allow more accurate results when determining inspection intervals for PRDs in accordance with the procedures in API 581.
Probabilistic Fracture Mechanics Codes for Piping International Benchmark – Part 1: Deterministic Comparisons
Authors: Homiack Matthew
Published: November 2022

This paper describes deterministic benchmark comparisons of 14 probabilistic fracture mechanics (PFM) codes. The benchmark problem focused on determining the leak-before-break behavior of a nickel-based alloy weld in a large-bore piping system of a pressurized-water reactor. The modeled degradation mechanism was primary water stress-corrosion cracking (PWSCC). The benchmark problem was deterministically analyzed with the PFM codes using their models for crack growth rates, stress-intensity factors, crack-opening displacements (CODs), crack transition from inside surface-breaking cracks to through-wall cracks, leak rates, and crack stability. Several output quantities of interest relevant to leak-before-break behavior were then compared. Other outputs as a function of the simulated component operating time were also compared, including the crack lengths and depths, stress-intensity factors, inside and outside surface CODs, and leak rates. An interpretation of these comparisons is provided in relation to the underlying models to better understand the effects of the different modeling approaches. Insights from this study will be used to inform probabilistic comparisons of the PFM codes, which will be presented in a subsequent paper.
Earthquake NaTech Risk Assessment, Monitoring and Management of Cylindrical Liquid Storage Tanks With Floating Roof in Major-Hazard Industrial Plants
Authors: Salimbeni Michela , De Angelis Maurizio , Vezzari Valerio , Ciucci Mariano
Published: November 2022

Earthquake is one of the natural events which is part of NaTech events (Natural Hazard Triggering Technological Disasters), due to interaction between natural and industrial risks. Industrial plants employ cylindrical liquid tanks with floating roof for storage of volatile and flammable products. Damages due to earthquakes affecting tanks with floating roof can cause major accidents involving dangerous substances, like hazardous releases, fires and explosions, especially due to the convective motion of the fluid caused by seismic excitation. The aim of this work is to inform about the most common damages in case of seismic event and to give some advice to seismic risk management through monitoring of critical elements of liquid storage tanks with floating roof. During an earthquake, damages to structural and non-structural elements can occur, and the non-structural elements are often the most involved in major accidents. In order to mitigate the consequences of a major accident, a monitoring system of the tank for management of the seismic risk can be installed, integrating new dedicated sensors into the existing monitoring network. The fiber optic sensors FBG (Fiber Bragg Grating) and FSI (Fiber Segment Interferometry) are a robust, multifunctional and removable alternative to the sensors already in use in the industrial field.
Accurately Predicting Transient Fluid Forces in Piping Systems Part 1: Fundamentals
Authors: Lang Scott A. , Walters Trey W.
Published: November 2022

Changes in the operation of piping systems — like valve closures or pump starts — propagate pressure waves that travel at acoustic velocity throughout the fluid. These pressure waves have considerable effect on forces, potentially generating dynamic loads upwards of 10,000 lbf (50 kN) in common configurations.

Some estimation methods used in industry for estimating transient forces neglect terms that may be important in some cases. Calculating forces due to these transients without simplification for transient liquid or gas flow is presented here in detail.
Combining Weld Residual Stress Predictions and Measurement for Use in Probabilistic Structural Integrity Assessments
Authors: Coules Harry , Simpson Christopher , Mostafavi Mahmoud
Published: November 2022

The use of residual stress information in probabilistic fracture assessments is hindered by difficulties in the quantification of uncertainty. At the same time, it is often necessary to consider residual stress data derived via two or more independent methods in an assessment: typically from a model of the process which introduced the stress, and from a direct physical measurement. The uncertainty in single weld process models is difficult to quantify and is strongly dependent on the process being modelled, the material constitutive behaviour assumed, and so on. Likewise, most experimental techniques for measuring deep residual stresses on welded metallic components, including relaxation methods such as Deep Hole Drilling and diffraction-based methods, also have multiple physical sources of uncertainty associated with them. This makes the uncertainty associated with single measurements difficult to estimate reliably.

We explore the use of inverse-variance weighting to combine such datasets through “characteristic” uncertainties derived from prior round robin studies, and we use data from the NeT TG4 residual stress measurement and modelling round robin to illustrate this approach. Although it requires some significant simplifications, it allows convenient synthesis of residual stress data while gaining more realistic uncertainty estimates than are typically available from single measurements. This is significant because straightforward yet robust uncertainty estimates will be key for enabling future structural integrity assessment methodologies.
Evaluation of Hydrogen Embrittlement Sensitivity of 4130X Material Based on the Disc Method
Authors: Zhai Jian-Ming
Published: November 2022

In order to evaluate the hydrogen embrittlement sensitivity of 4130X material, the effect of curvature radius of the high-steel ring on material failure mode and blasting pressure was firstly carried out, and then the hydrogen embrittlement sensitivity index was evaluated for disc samples with different surface roughness. The test results show that when the curvature radius of the high-steel ring is 0.5 mm, 1.5 mm, 2.0 mm, the material is mostly destroyed by shear. When the curvature radius is greater or equal to 4.0 mm, the material will be destroyed in the form of blasting. The blasting strength tested in hydrogen environment of 4130X materials decreases when the surface roughness increase from 0.1 to 4.1 μm.

For the HE sensitivity evaluation of 4130X by DPT method, it is recommended that the curvature radius should be greater or equal to 4.0 mm, and the surface roughness between 0.1 and 1.5 μm can meet the DPT requirements.
Accurately Predicting Transient Fluid Forces in Piping Systems Part 2: Applications
Authors: Lang Scott A. , Walters Trey W.
Published: November 2022

Part 1 of this series discussed in detail how to accurately calculate the reactions induced by pressure transients that travel at acoustic velocity in either liquid or gas piping systems. Part 2 applies these methods to a variety of realistic examples to further illustrate their use and to demonstrate areas in which traditional or simplified methods may impart significant error.
Investigating Weld Interface Cracking of 1.25Cr-0.5Mo Steel External Weld Repair with Alloy 625 Filler Metal due to Low-cycle Fatigue Failure
Authors: Zhang Shutong , Giorjao Rafael A. , Berkson Jacque W. , Penso Jorge A. , Guo Haixia , Yuen Simon , Ely Lisa , Ramirez Antonio J.
Published: November 2022

Welding repair has been widely used to restore the structural integrity of coke drums compromised by cracks due to low-cycle fatigue failure among other damaging mechanisms. Nevertheless, due to the heterogeneous mechanical and metallurgical properties, repair welds are susceptible to re-cracking during subsequent operations. The API 1996 report has shown that 88% of outer-diameter (OD) repair welds have experienced re-cracking in coke drums. The re-cracking susceptibility downgrades the efficiency of welding repair to extend coke drum operation life and may increase the complexity of coke drum maintenance. Hence, addressing the low-cycle fatigue failure of weld becomes a critical issue to optimize welding repair for coke drum maintenance. Alloy 625 is a commonly used Ni-based filler metal to perform coke drum repairs due to its good thermal and metallurgical compatibility with the base metal. However, weld metal dilution close to the weld interface changes local microstructure and mechanical properties from the rest part of the weld. In this study, an external repair welds of 1.25Cr-0.5Mo steel under as-received (Normalized and Tempered) and service-aged conditions with Alloy 625 using HP-GTAW process are evaluated based on low-cycle fatigue tests and failure analysis. Weld transition samples are extracted to encompass the transition from weld metal to base metal at the gage section. Low-cycle fatigue tests are performed at 0.7%, 1.0%, 1.5% and 2.0% strain amplitudes. Interfacial cracks are observed at lower strain amplitudes (0.7% and 1.0%) and failures at higher strain amplitudes tend to occur at the base metal region. Metallurgical characterizations are performed to characterize the microstructure at weld interface and measure the mechanical properties through micro hardness. Interfacial cracks are examined using Scanning Electron Microscopy. This study helps clarify how microstructure and mechanical properties contribute to the interfacial cracking of the Ni-base alloy and steel dissimilar joint.
PTFE Gasket Material Performance Variation With Thickness
Authors: Bausman Anita , Wilson Jeffery
Published: November 2022

Polytetrafluoroethylene (PTFE) is an excellent gasket material, chemically, but it has relatively poor mechanical performance. As a result, much effort has gone into improving the mechanical performance of PTFE-based gasket materials. Methods to improve mechanical performance include the addition of fillers (glass fibers, glass microspheres, silica, barium sulfate, carbon, etc.) and the manipulation of the microstructure (micro-cellular, expanded, restructured, etc.). These various forms of PTFE materials can have widely varying mechanical performance. PTFE materials that are chemically the same will have significantly different mechanical performance if the manufacturing process and microstructure are different. An example is the performance of amorphous, virgin PTFE sheet compared to fibrillated, expanded PTFE (ePTFE) sheet. The thickness of a gasket material is another structural difference that results in different mechanical performance.

This paper explores the difference in the mechanical performance of two common filled PTFE (fPTFE) materials that end-users often consider functionally the same at several industrially important thicknesses. The gasket materials are both barium sulfate-filled, restructured PTFE sheet materials. The mechanical performance of each material is compared for three thicknesses using the Hot Blowout Thermal Cycling test (HOBTC, ASTM WK61856 Rev 10-9-2020). [1] The thicknesses are 0.79 mm (0.031 inch), 1.60 mm (0.063 inch), and 3.18 mm (0.125 inch). The authors selected these thicknesses for performance review because of their usage in the industry. The thinnest, 0.79 mm (0.031 inch), is commonly used for instrument service. Very little performance data is publicly available on this thickness. The medium thickness, 1.60 mm (0.063 inch), is most commonly used in piping flanges. The thickest reviewed for this paper, 3.18 mm (0.125 inch), is commonly used for pressure vessels but also shows up in piping. Leakage testing according to the Room Temperature Tightness test (ROTT or ASTM F2836 Standard Practice for Gasket Constants for Bolted Joint Design) [2] was performed on the thinner 0.79 mm (0.031 inch) materials. HOBTC and ROTT testing was performed on an amtec TEMES fl.ai1 test fixture over the latter half of 2021 at the authors’ company. This data will demonstrate to the end-user how different the mechanical behavior can be of the same gasket material differing only in how thick it is.
Hydrogen Induced Cracking Susceptibility in the Heat Affected Zone of SA-508 Pressure Vessel Steel
Authors: Velasquez Joshua D. , Alexandrov Boian T. , McCracken Steven L.
Published: November 2022

ASME Case N-888, Similar and Dissimilar Metal Welding Using Ambient Temperature SMAW and Machine GTAW Temper Bead Technique, requires a 48-hour hold time before nondestructive examination (NDE) can be performed to ensure hydrogen-induced cracking (HIC) did not occur. The aim of this work is to assess and characterize the HIC susceptibility of SA-508 pressure vessel steel. The results from this study will be used to consider potential elimination of the NDE hold time requirement in Case N-888. The Gleeble™ thermo-mechanical simulator was used to recreate CGHAZ for five weld conditions; as-welded, post-weld heat treated (PWHT), and four single-reheat temperatures of 675 °C, 700 °C, 725 °C, and 735 °C to simulate temper bead welding (TBW). Metallurgical characterization revealed a tempered martensitic microstructure for all TBW and the PWHT conditions. The 735 °C TBW sample developed ferrite along the prior austenite grain boundaries. The single reheats to 675 °C, 700 °C and 735 °C reduced the as-welded CGHAZ hardness from 425HV0.5 respectively to 313, 298, and 278HV0.5. A fourth TBW condition was added at 725 °C to eliminate ferrite formation seen at 735 °C. The TBW at 725 °C produced a microstructure of tempered martensite with a hardness of 298HV0.5. The HIC susceptibility is being evaluated using the Delayed Hydrogen Crack Test (DHCT) developed at the Ohio State University. Samples of SA-508 steel with the five CGHAZ microstructural conditions are loaded at 90% of the base metal yield strength and simultaneously electrolytically charged with hydrogen. The HIC susceptibility is ranked by the time to failure (full specimen separation) and sustained mechanical energy.
Study on Alternative Bounding Approach for ASME Code Section XI Appendix L
Authors: Shim Do Jun , Tran Minh N.
Published: November 2022

Current Equivalent Single Crack (ESC) tables in ASME Code, Section XI, Nonmandatory Appendix L were developed using a probabilistic fracture mechanics (PFM) approach which included outdated K solutions and fatigue crack growth rates. Recent study demonstrated that the current ESC tables can be non-conservative when using the latest K solutions and fatigue crack growth rates. However, significant effort is needed to update and maintain the ESC tables. Hence, the ASME Code Committee Task Group on Appendix L has been discussing potential approaches to eliminate ESC from Appendix L. Present study was performed to develop an alternative bounding evaluation approach without using the ESC tables. Fatigue crack growth calculations for the ranges of pipe dimensions considered in Appendix L were performed. The objective was to identify options for potentially simplifying the Appendix L methodology. Two possible options were proposed. Option 1 was to use the allowable flaw depth from a 1:6 flaw and apply it to evaluate the fatigue crack growth of an initial 360° flaw. Option 2 was to use the allowable flaw depth of a 360° flaw and apply it to evaluate the fatigue crack growth of an initial 1:6 flaw. The time for a postulated initial flaw to reach the allowable flaw size for both options was calculated. The current study demonstrated that the flaw tolerance analysis using ESC is not bounded by either Option 1 or Option 2 when using the membrane-to-gradient cyclic stress ratio Δσm /Δσg = 0.0. However, when a more reasonable lower bound membrane-to-gradient cyclic stress ratio (i.e., Δσm /Δσg = 0.1) was used to determine the ESC, Option 1 results bounded most of the cases considered in the present study.
Ductile Damage Model Development and Validation of 316L Laser Powder Bed Fusion Steel Under Multiaxial Stress Conditions
Authors: Hales Theo , Rønneberg Tobias , Hooper Paul , Davies Catrin Mair
Published: November 2022

Laser powder bed fusion (LPBF) is an additive manufacture technique which builds components up in layers from a powder feedstock, using a scanning laser to selectively melt the powder into the required shape. The process of LPBF can often introduce defects into the structure of a part, since the powder may not fully melt and leave holes, or pores, in the sample. Excessive laser power may also cause the powder to vaporise and create pores. In whatever manner these pores are formed, they can significantly impact the properties of the finished component. Since pores and small defects already exist in LPBF components, the void growth and ductile fracture behaviour of LPBF components under multiaxial stress conditions needs to be characterised and predicted. In this work, notched bar tensile tests have been performed on samples with a range of notch acuities and hence multiaxial stress states. These tests have enabled ductile damage models to be calibrated and finite element (FE) simulations of the notched bar tests performed. The model was validated by comparison to the experimental results. The model agrees well with the results in many cases assessed in this work, but sometimes suffers from discrepancies and premature failure due to variability in material tensile properties, emphasising the need for sensitivity studies.
Analysis of Plastic Deformation of Pipes Due to Deflagration to Detonation Transition Using Static Equivalent Pressure
Authors: Müller Matthias , Bernhardi Otto-Ernst , Denecke Jens , Schildberg Hans-Peter , Schmidt Jürgen
Published: November 2022

Explosions of premixed gases with DDT, the transition from deflagration to detonation, are a risk in the process industry with potentially catastrophic consequences. Robust and simple design methods are required for industrial use. Such a simplified design method based on finite element analysis is proposed to model the dynamic behavior of pipes loaded by gas explosions of premixed gases including DDT.

First, it is reviewed how the pressure load of the gas explosion and the resulting material behavior has been modeled in previous publications. The analytical equations are then extended for describing the pressure load as a function of time and location by considering the leading compression wave as it affects the pressure load of the overdriven detonation. The extended analytical equations are parameterized using Chapman-Jouguet conditions and experimental results from publications for both static equivalent pressure and the location of the DDT. To describe the plastic material behavior at high strain rates, the well-known Johnson-Cook plasticity model is used. The material parameters of the model are derived from simple experiments, which are available in an industrial environment. The comparison of a finite element simulation with experimental data shows that the concept of equivalent static pressure can be extended to an FEM analysis, which in the future will allow the sizing of complete pipe systems including tees, bends and flanges while considering plastic deformation.
Influence of High-Pressure Hydrogen Gas and Pre-Charged Hydrogen on Fatigue Crack Initiation and Fatigue Life of 255 Super Duplex Stainless Steel
Authors: Kagay Brian , Ronevich Joseph , San Marchi Chris
Published: November 2022

High strength austenite-ferrite duplex stainless steels are a potential alternative to austenitic stainless steels for components in hydrogen gas storage systems. Since these components experience cyclic loading from frequent pressurization and depressurization, the effect of hydrogen on the fatigue behavior of duplex stainless steel must be understood. To determine the influence of hydrogen on fatigue crack initiation and fatigue life of a 255 super duplex stainless steel, circumferentially notched tensile (CNT) specimens were fatigue tested in the as-received condition in air, with pre-charged internal hydrogen in air, and in the as-received condition in high pressure hydrogen gas. The direct current potential difference (DCPD) method was used to detect crack initiation so that S-N curves could be produced for both (i) cycles to crack initiation and (ii) cycles to failure. An electropolished CNT specimen was also cycled in the as-received and hydrogen pre-charged conditions but interrupted just after crack initiation. The microstructural locations of small fatigue cracks were then identified with scanning electron microscopy and electron backscatter diffraction (EBSD). High pressure hydrogen gas and pre-charged hydrogen decreased the fatigue life of 255 duplex stainless steel by a nearly identical amount. The effects of hydrogen on fatigue crack initiation and fatigue life of 255 duplex stainless steel are discussed and compared to austenitic stainless steels.