bluuebunny/crossref_metadata_2025 huggingface dataset:
Risk-Informed Assessment of French Stress Corrosion Cracking Operational Experience Relative to the Fleet of Pressurized Water Reactors in the United States of America
Authors: Rudland David , Leech Matthew , Homiack Matthew , Nellis Christopher
Published: November 2024

During a typical inservice inspection on October 21, 2021, at Civaux Unit 1 (a 4-loop, 1450 MW pressurized water reactor (PWR)) in France, Électricité de France (EDF) found circumferential cracking at several locations near an elbow in a non-isolable section of piping in the emergency core cooling system (ECCS). Through destructive examination, EDF determined that the root cause of the cracking was intergranular stress corrosion cracking (IGSCC) caused by stresses associated with thermal stratification. Weld residual stress (WRS) may have also played a role in the cracking. After discovery of this cracking, EDF expanded its inspections to other similarly designed plants and identified many cracks in similar locations in the safety injection and residual heat removal systems. The French response to this operational experience (OE) is still ongoing.

The U.S. industry responded to this OE by developing a focus group organized by the Pressurized Water Reactor Owners Group (PWROG) and the Electric Power Research Institute (EPRI). This focus group assessed applicability of the OE to the U.S. fleet of PWRs and the associated safety implications. While the industry focus group found no direct evidence of this type of cracking in the U.S. PWR fleet and, therefore, no safety issues, it did recommend a modification to inspection methods to better identify IGSCC in these welds. In parallel, the U.S. Nuclear Regulatory Commission (NRC) staff conducted both qualitative and quantitative analyses using a risk-informed approach to assess the safety significance of the OE and determine what regulatory actions, if any, were appropriate. This paper discusses the NRC staff’s results, which consisted of detailed probabilistic fracture mechanics (PFM) analyses to estimate loss of coolant accident frequencies that were then used in a probabilistic risk assessment (PRA) to determine the impact of the OE (assuming it occurs) on the core damage frequencies of the U.S. PWR fleet. The results suggest that the risks to U.S. PWRs are low and that the industry-planned inspection method modifications can maintain adequate safety margins and performance monitoring.
On the Required Distance to Major Structural Discontinuity From Local Metal Loss Area
Authors: Ishizaki Yoichi , Ameya Hiroyasu
Published: November 2024

API 579-1/ASME FFS-1 Fitness for Service Part 5 local metal loss Level 2 assessment requires a sufficient distance between local metal loss area and neighboring major structural discontinuity based on S.Timoshenko’s model [1] [2]. The model assumed a concentrated force and moments on a cylindrical shell. A sufficient distance to settle down the bending moment from the point was evaluated.

Occasionally, a flaw is observed around a major structural discontinuity, and the required distance limits the application of Lv.2 assessment. While the model would be well applicable for piping nozzles and supporting attachments that takes external force and moment, some of those limiting components, such as stiffeners, vessel heads and manway nozzles in kind, are not taking any external forces and moments. They might affect to the local metal loss area in a different manner than piping nozzles and such. In 2023 ASME PVP, S.Bouse et al. [2] discussed the effect of ellipsoidal head and hemisphere head in their paper ; PVP 2023-106371 Re-Evaluating the Minimum Required Distance Between Local Thin Area In Cylinder and an Ellipsoidal Head. The conclusion was that ellipsoidal heads was beneficial for local metal loss assessment based on FEM model data. The outcome is incorporated in 2021 version of API579-1/ASME FFS-1 Fitness-For-Service, table 4.2 [3].

To discuss which type of “Major Structural Discontinuity” would be beneficial for local metal loss assessments one step further, it would be important to consider the significance of Folias factor, Mt, and surface correction factor, Ms, of current API579-1/ASME FFS-1 Part 5 assessment. As discussed in our previous paper [4], authors reorganized the significance and derivation of Mt and Ms. Based on the model of Ms, the pressure load working on remaining ligament underneath flaw was equal to flow stress level and the surplus pressure load was traveling to side ligaments. The idea of model indicated RSF would be increased according to the increase of side ligament cross section. If this was true, stiffening ring, manway nozzles and flanges would be a good candidate to exempt from current “Distance to Major Structural Discontinuity”, Lmsd, requirement [3] in addition to ellipsoidal head. Because those components simply exist on cylindrical shells provides extra cross section without any significant external forces and moments on cylindrical shell unlike piping nozzles.

In this paper, using FEM models of stiffening rings and ellipsoidal heads as example cases, an interaction mechanism between “Major Structural Discontinuity” and flaw will be discussed considering the concept of Ms model. This would contribute to enhance the “distance to major structural discontinuity” criteria discussion.
A Comparative Study on Creep-Fatigue Evaluation Methodologies For Natrium™ Reactor Internal Components Using Elastic and Inelastic Analysis
Authors: Xu Heqin , Riordan Tom , Bhuiyan Shafiq , Cohen Michael
Published: November 2024

Per ASME Code Section III Div. 5, design of a Class A component for elevated temperature service must meet the functional requirements specified in the Design Specifications (NCA-3211.19) to be acceptable. Also it needs to satisfy the requirements for a design by analysis, either in HBB-3200 or in the Design Rules for components, while under the loadings described in HBB-3111.2 and the Design Specifications; and satisfies the general design rules of HBB-3130 and the applicable design rules for components. The creep-fatigue assessment is part of the Code requirements to meet the strain and deformation limits for a design by analysis for a Class A metallic pressure boundary component as required in HBB-3200, and a Class SM metallic core support structure as required by HGB-3200. As suggested by the Code, the analysis can be either elastic analysis, elastic perfectly plastic analysis, or inelastic analysis. Although the inelastic analysis is more complicated than the elastic analysis method considering the required time-dependent material properties to account for plasticity and creep, the elastic analysis method has more complicated rules than the inelastic analysis since the elastic strain range must be adjusted to account for plasticity and creep. The adjustments are usually over-conservative that makes it difficult to pass the required limits under most design situations by elastic analysis method. This paper compares the creep-fatigue evaluation procedures and results using elastic analysis method and inelastic analysis method, emphasizing the safety margin each analysis method can achieve.
Experimental and Numerical Analyses for the Evaluation of Heat Fluxes of a Fire Reference Test
Authors: Gleim Tobias , Feldkamp Martin , Quercetti Thomas , Wille Frank
Published: November 2024

Packages for the transport of high-level radioactive material are designed to endure severe accidents. To obtain approval, these transport packages must adhere to the specification-based criteria of the IAEA SSR-6 [1]. To ensure compliance with these requirements, specific mechanical and thermal tests need to be appointed with respect to the package type. Typically, IAEA SSR-6 [1] prescribes mechanical tests followed by a thermal fire test as part of a cumulative test sequence. To approve the fire test, BAM uses a reference package representing the original package in its outer geometry for characterizing the actual fire and its impact on the package. This serves a dual purpose: it allows the precise adjustment of experimental parameters for the package design to be approved, and it provides input parameters for thermomechanical simulations, cf. [2]. With the help of this methodology for characterizing boundary conditions of the package, temperature evolutions within the reference package can be studied in a Finite-Element Analyses (FEA). This helps to compare the experiments with the numerical simulations on the case of the reference package, but also serves at the same time for preliminary simulations with the package design to be approved.

The thermal test consists of a 30-minute fully engulfing 800°C pool fire or an equally severe fire, e.g. a propane gas fire. The fire reference test is performed prior to the regulatory fire test with the package design to be approved. The fire reference package in the described case is a closed sheet 316L steel cylinder with a wall thickness of 10 mm, a length of 182 mm, and a diameter of 102 mm. The package was instrumented with thermocouples and filled with heat resistant insulating material.
Investigation of the Very High Cycle Fatigue (VHCF) Behavior of AISI 347 and 304L Austenitic Stainless Steels Including Their Welds for Reactor Internals at Ambient and Operating Temperature
Authors: Rudolph Jürgen , Veile Georg , Regitz Elen , Smaga Marek , Fischer Udo , Grimm Michael , Weihe Stefan , Beck Tilman
Published: November 2024

The fatigue assessment of safety relevant components is of importance with regard to safety and reliability of nuclear power plants. Due to their excellent mechanical and technological properties as well as their corrosion resistance austenitic stainless steels are often used for reactor internals. Internals are subject to mechanical and thermo-mechanical loading in all fatigue regimes. This work presents the current status of the research project VHCF-II with the goal of improved fatigue life prediction for safety assessment of the materials AISI 304L, AISI 347 and ER 347. For improved fatigue life prediction, the static and cyclic material behavior is characterized at ambient and operation relevant temperatures. A detailed characterization of the material behavior is required to determine the components’ fatigue life up to 109 load cycles with Ultrasonic Fatigue Testing Systems (UFTS) working at 20 kHz. The characterized material data serve the purpose to expand the data for improving methods of fatigue calculations. For this purpose, numerical simulations of thermo-mechanically loaded components with focus on their welded joints are conducted. Experiments are conducted in order to further validate the methods of fatigue life assessment under operating conditions of nuclear power plants. Foreseen and ongoing work of the VHCF-II project is presented in this paper.
Damage Model Investigations to Predict Crack Initiation in a Tension Test for a Ductile Steel
Authors: Rainey Samuel , Smith Steven
Published: November 2024

Guarding against the initiation of cracks in pressure vessel design is of essential importance. In this paper, a damage model is investigated on its ability to estimate the initiation of cracks in standard uniaxial specimens. The damage model is used to predict the formation of a crack in a Q345R pressure vessel steel uniaxial tensile specimen during monotonic loading. An FEA mirroring the conditions of the original test is conducted, and the damage model applied to evaluate the stress and strain states at locations in the tensile specimen. It is found that the damage model can accurately predict the fracture strain, fracture location, and fracture orientation of the original tensile test specimen by identifying the load increment during which the cumulative damage on a given plane exceeds a critical value.
Testing Fracture Toughness of Composite Repair Bonding
Authors: Al Shabibi Abdullah M. , Al Ismaili Abdul-Majeed A. , Al Ghatrifi Mohammed A. , Al Kindi Hisham I. , Al Mashrafi Hussam S.
Published: November 2024

Pipelines, in petroleum industry in particular, are exposed to defects that can result in reducing their capacity of transferring oil. Composite repair wrapping is a new emerging method of repairing defected pipelines. To realize the extent of the load capacity for the repaired defected pipeline, it is important to understand the failure criteria for the composite wrapping. The aim of this study is to experimentally determine the failure pressure of a pipe with a through-wall defect repaired with a composite material. Defects of different sizes are to be considered.
Research on Stress in Obround and Out-of-Roundness Shells
Authors: Jin Yao
Published: November 2024

Using the closed-form solution of obround shell, the stress and displacement of obround shells were theoretically analyzed. With the straight segment introduced, the maximum stresses and displacement of obround shells increase significantly. The length of the straight segment is a key factor in determining the maximum stress and location. For obround shells, the maximum stress is the function of two dimensionless geometrical parameters. Parameter study results show that for most engineering applications, the maximum stress occurs in the middle section of the curved segment. The maximum displacement appears in the middle of the straight segment. The stress increment caused by the out-of-roundness of cylindrical shells was studied. A cylindrical shell with out-of-roundness is treated as an elliptical shell. Two methods are proposed to estimate the maximum stress in the out-of-roundness shells. The ovalized cylindrical method simplifies the numerical analysis model. Complex out-of-roundness details are replaced by ellipse. The virtual obround method provides a theoretical analysis tool. The analysis results show that the stress increase of out-of-roundness shell depends not only on the amount of distortion, but also on the type of distortion. The equivalent out-of-roundness is defined to normalize the distortion according to stress concentration level for each distortion type. Based on existing design codes, simply limiting the measured diameter differences does not appear to be sufficient. The analysis results show that even within the range of out-of-roundness value accepted by the codes, the stress increment caused by out-of-roundness may exceed expectations. In some situations, especially for thin- to medium-walled shells, the minimum required wall thickness estimated by the existing codes may be underestimated.
Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens - Application of Elastic-Plastic FE Analyses for Notched Specimens of Low Alloy Steel
Authors: Takagoshi Daiki , Nomura Yuichiro , Asada Seiji , Kitamura Yoshihide
Published: November 2024

DFC and DFC2 subcommittees in the Japan Welding Engineering Society developed a new approach in fatigue analysis methodology. This fatigue analysis methodology has made several modifications and has been incorporated into the JSME Environmental Fatigue Evaluation Method 2022 Edition (JSME S NF1-2022). Research on the effects of surface finishing and mean stress on the fatigue lives of notched specimens were followed by DFC3 and DFC4 subcommittees. In this paper, the application of elastic-plastic Finite-Element Analysis (FEA) for fatigue evaluation of notched specimens of low alloy steel was investigated.

To verify the applicability of a simple analytical method to the fatigue life evaluation, elastic-plastic FEA were performed simulating fatigue testing with positive mean stress for notched specimens of low alloy steel, JIS-G3120 SQV2A. Local stress-strain behaviors at the notch root and mean stresses changes with increasing number of fatigue cycles were investigated by these analyses.

As a result of FEA, in the case of lower stress amplitude, plastic deformation occurred only at the first cycle and local mean stress was constant. On the other hand, in the case of higher stress amplitude, cyclic plastic deformation occurred throughout all cycles and local mean stress became lower with increasing fatigue cycles. After sufficient number of fatigue cycles were applied, local mean stress at the notch root became almost zero. These results were consistent with fatigue test results of SQV2A in another research, in which mean stress had little effect on the fatigue lives of notched specimens. Also, it was confirmed that the fatigue lives of notched specimens could be arranged on the identical S-N curve based on the fatigue lives of smooth specimens by using the equivalent strain amplitude, εaeq estimated by FEA. From these results, it was concluded that FEA is applicable for the evaluation of the fatigue lives of notched specimens.
Simulation of Crack Growth in Mini-C(T) Fracture Tests in the Ductile-to-Brittle Transition Using a Cohesive Zone Model: Application to Reactor Pressure Vessel Steels
Authors: Somera Audrey , Perales Frédéric , Vincent Pierre-Guy
Published: November 2024

The goal of this study is to simulate crack growth in mini-C(T) fracture tests using a Cohesive Zone Model (CZM) in order to derive the evolution of the toughness in the Ductile-to-Brittle Transition (DBT) region. The calibration method used is adapted from [1] and only requires low-temperature experiments. For a given temperature, it is assumed that the cohesive energy increases with the fracture probability, and that the shape of the CZM traction-separation law varies from a triangle to a trapezoid when the cohesive energy is greater than a value identified using elasto-plastic simulations. The cohesive parameters are determined using two calibration procedures. The first is performed using two experimental load-displacement curves. The second involves finding the cohesive energy leading to the right fracture toughness value given by the master curve for three different temperatures and two fracture probabilities. An exponential evolution of the cohesive energy with temperature is proposed. Cohesive energy is also assumed to depend on fracture probability.

Simulations of mini-C(T) toughness tests are then performed for cumulative failure probabilities of 2%, 50% and 98% at different temperatures. A good agreement is observed between the toughness computed from the simulations and the master curve approach.
Fundamental Study on Passive Safety Characteristics of Piping System Against Excessive Earthquake
Authors: Horinouchi Riku , Yamamoto Yotaro , Kasahara Naoto
Published: November 2024

As a lesson learned from the accident at the Fukushima Daiichi Nuclear Power Plant, it has become important not only to prevent failure occurrence, but also to mitigate failure consequence to catastrophic failure after an accident.

In this study, the behavior of bent round rods and support structures simulating a piping system subjected to vibration loading was tested and analyzed to demonstrate that the piping system has passive safety characteristics against excessive earthquake.

In the vibration tests, bent round rods and support points simulating the piping system were subjected to vibration loads. As a result of the vibration test, the natural frequency of the piping system, response acceleration, elbow strain, displacement, and other data were obtained. In the vibration analyses, a model was created under the same conditions as the vibration test and analyzed using finite element method analysis. As a result of the vibration analyses, data on the reaction force applied to each support point and the reaction force applied to the fixed end point during vibration were obtained.

Based on these results, it was concluded that the piping system transitions to a passive safety structure in which seismic forces are less likely to be transmitted from the floor to the piping system because the natural frequency of the piping system falls below the frequency of seismic waves due to failures in the support structure that have little effect on the cooling function.
Allowable Circumferential Flaw Sizes Based on Code Given and Actual Measured Flow Stresses for High Toughness Ductile Pipes Subjected to Bending and Tensile Loads
Authors: Negyesi Martin , Ha Yoosung , Hasegawa Kunio , Lacroix Valery
Published: November 2024

Allowable stresses for pipes are determined by combining failure stresses and safety factors. When predicting the plastic collapse failure stresses for high toughness ductile pipes, flow stresses of the pipe materials are indispensable. The flow stress is usually given by the average of the yield strength and the ultimate tensile strength. Inservice Inspection of the American Society of Mechanical Engineers (ASME) Code Section XI states to use the yield strengths and the ultimate tensile strengths defined by the ASME Code Section II Materials. The ASME Code Section XI also states that actual measured yield strengths and ultimate tensile strengths are possible to be used, alternatively. Values of yield strength and ultimate tensile strength given by the ASME Code Section II are conservative, corresponding to lower bound values. Then, it is easily inferred that the allowable stresses calculated by the code given flow stress are lower than the allowable stresses calculated by the actual measured flow stress. The objective of this paper is to compare the plastic collapse failure and allowable stresses based on both the code and actual flow stresses for pipes with circumferential flaws subjected to bending and tensile loading. In addition, it is demonstrated that allowable flaw sizes based on both flow stresses do not differ much at low allowable stress. However, when the allowable stress is large, the allowable flaw size based on the code flow stress is substantially lower compared to that based on the actual flow stress.
Advanced Vibrational Fatigue Monitoring Approaches With Varied Technical Application Fields
Authors: Rudolph Jürgen , Ziegler Rainer , Kopinec Milan , Bruckmüller Florian
Published: November 2024

Numerous industrial structures are subjected to vibrations which may induce fatigue damage and which can often not easily be mitigated by design and damping measures. In order to manage and control this ageing mechanism and to prevent unexpected fatigue damage a monitoring system is needed which is able to predict fatigue damage before it occurs. It is composed of a hardware part and a software part. The hardware consists of simple and robust accelerometers or displacement sensors that measure the vibrations at a few key selected points of the structure. The software is a program that identifies the contribution of each dynamic vibration mode in the measured vibrations and transforms this information into an estimation of remaining lifetime at each location of interest. Implementation steps are the one-time generation of a digital twin of the monitored structure, the continuous acceleration measurement and the cyclic signal processing. The comparison of each single mode displacement with the modal basis of the digital twin leads to the stress time history (full stress tensor as a function of time) at the fatigue relevant locations of the structure. A rainflow algorithm allows for the counting of the cycles and the identification of partial and cumulative fatigue usage factors. Extrapolation of results allows for a remaining fatigue lifetime estimation. The visualization of results includes the plot of fatigue usage as a function of operation time. Potential application examples are given in terms of distillation columns (chemical industry), wind mill tower structures (wind energy industry) and piping systems (chemical industry, nuclear and conventional power plants) including small bore piping with well-known fatigue sensitivities at socket welds. An exemplary hardware layout for wind mill tower structures will be given.
Design-by-Analysis Rules for ASME SECTION III, Division 5, Class B Components
Authors: Mahajan Heramb , Jetter Robert , Sham Ting-Leung , Wang Yanli
Published: November 2024

The current rules for elevated temperature ASME Section III, Division 5, Class B components, other than piping, were basically adapted from the Design-by-Rule approach for Section VIII, Division 1 vessels. A goal of the proposed new rules is to explicitly account for the design life and cyclic service while recognizing the less-rigorous requirements commensurate with lesser safety consideration. Further goals are to maximize the use of modern computational technology, for example finite element analysis in conjunction with reference stress concepts, and to avoid the need for stress classification. This paper summarizes the work done to address these issues. A summary of the design-by-analysis for primary loads, strain limit evaluation, and creep-fatigue damage assessment is presented. The proposed design-by-analysis creep-fatigue damage calculation approach uses a new elastic follow-up-based Isochronous Stress Strain Curve stress relaxation procedure. A set of sample problems are selected to validate the proposed design-by-analysis rules for creep-fatigue damage assessment. The proposed Class B rules are evaluated against the Class A elastic design rules and the experimental data obtained from a family of a simplified model test-based key-feature test results. The proposed Class B creep-fatigue damage assessment methodology yields conservative design cycles estimates compared to the experimental results.
Girth Weld Defect Identification Method and Application Research Based on MFL Internal Detection
Authors: Zhao Yatong , He Renbi , Shi Lei , Zhou Liguo
Published: November 2024

Aiming at the limitations of weld non-excavation inspection technology, non-excavation identification difficulties and other problems, this paper carries out the internal inspection and identification of oil and gas pipeline weld defects based on magnetic flux leakage internal inspection. We establish a finite element leakage simulation model containing defects in the circumferential weld, and identify and extract the inversion characteristics of the defect signal; according to the finite element analysis results, we guide and complete the internal inspection draw test and signal analysis, compare and contrast the characteristics of the draw test signal and the simulation inversion signal, and validate the validity of the simulation results; we study the method of characterizing the leakage signal of the circumferential weld and establish a method of classifying and identifying the defects based on the peak of the leakage signal characteristics. The method can be used for the identification and evaluation of weld defects under non-excavation conditions, which greatly reduces the cost associated with excavation inspection and provides technical support for the automatic identification of weld defects.
Preliminary Investigation of the Effects of Neutron Irradiation on the Weibull Modulus of Graphite
Authors: Campbell Anne A.
Published: November 2024

The tensile strength distribution of graphite has historically been estimated via the two- and three-parameter Weibull distributions due to the flaw distribution within the material. This is apparent within the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Section III “Rules for Construction of Nuclear Facility Components”, Division 5 “High Temperature Reactors”, Subsection HH “Class SN Nonmetallic Core Components”, Subpart A “Graphite Materials”, where the materials data sheet (MDS) requires the calculation of both the two- and three-parameter Weibull distributions of the tensile strength for as-manufactured graphite. There is not currently a requirement to determine Weibull distribution of the strength of graphite post-irradiation, mainly because no results have been reported that suggest whether the Weibull parameters, most importantly the Weibull modulus, changes due to neutron irradiation damage. An irradiation program was performed at Oak Ridge National Laboratory where graphite grade ETU-10 was exposed to neutron damage at a range of temperatures and final neutron fluences. Within this experiment, ten strength coupons were irradiated at each temperature and fluence combination which when analyzed can provide information as to whether irradiation damage has altered the Weibull modulus. This paper will focus on the analysis of the post-irradiated equibiaxial flexural strength change via a Weibull analysis of each individual data set and discussion as to whether there appears to be statistically significant changes to the Weibull parameters.
Investigation of the API 579-1/ASME FFS-1 KPTC Stress Intensity Factor for Bending Stress
Authors: Altstadt Steven , Mellings Sharon , Bouse Scott , Butchers Ryan
Published: November 2024

The API 579-1/ASME FFS-1 2021 (API 579-1) Fitness-For-Service stress intensity factor solution for a plate with a through-wall center crack (KPTC) subject to bending stress was investigated. Finite element (FE) models of through-thickness center cracked plates subjected to bending stress fields were created and used to estimate stress intensity factors (KI) along the crack fronts, which were then used to establish influence coefficient values. For fitness-for-service applications it is a common practice to extrapolate K along the crack front to obtain an effective K at the surface. The method chosen for extrapolation can have a modest impact on the results. The method of extrapolation used for this assessment is similar to other through-thickness crack solutions in API 579-1. The new influence coefficient values presented herein are recommended for fitness-for-service assessments that involve KPTC subjected to bending stress. Most of the FE results were cross checked against results generated using the dual boundary element method, which showed excellent agreement. The comparison of the newly calculated stress intensity factors to the existing API 579-1 KPTC values showed modest differences for some cases and substantial differences for others. The largest differences were associated with high plate width-to-thickness ratios. The new influence coefficients were also compared to values published by Marie et al (2007). Good agreement was found for almost all cases, but there were some notable discrepancies for high plate width-to-thickness ratios. A comparison was also conducted for the BS7910 solution, which showed that the solution generally overpredicts the stress intensity factor. Some cautionary notes are provided to help delineate the range of applicability for fitness-for-service assessments.
Evaluation of Corrosion Resistance of Stainless Steel Piping With Fillet Weld on External Side in Comparison to Back Shielding Condition
Authors: Takahashi Atsushi , Tsuda Takahiro
Published: November 2024

Back shielding by inert gas is required to not only single-sided butt joints but also fillet joints of piping in accordance with specification or standard such as API RP582 [1] where chromium content of base metal is high, e.g., greater than 2.5 %, and wall thickness is thin, e.g., 1/4” (6.5 mm) or lesser, for preventing oxidation in atmospheric environment by welding heat input.

However, the volume of back shielding space on inside piping by fillet welding, such as joints between run pipe and piping support or reinforcing pad, is sometimes too large to purge oxygen out with economical rationality due to limitation of place of back shielding isolations, especially during piping erection period at construction site.

Recently, non-backing gas practices with gas metal arc welding in short circuit mode (GMAW-S) [2] and gas tungsten arc welding (GTAW) [3] have been developed and implemented to single-sided butt joints of stainless steel (SS) process piping in oil and gas industries with successful results [4]. Therefore, oxidation of the fluid-contacting side can be considered as nonmaterial from a corrosion resistance viewpoint regardless of welding method and back shielding.

This paper presents study results of corrosion resistance of fillet welds on SS piping in comparison to back shielding conditions and introduces the possibility of omission of back shielding for fillet welds.
Evaluation of Cr-Mo Steels Welds Produced by Gas Tungsten Arc Welding With High Silicon Solid Filler Rod to Omit Back Shielding – Second Report
Authors: Mori Koki , Takahashi Atsushi , Zhou Bin , Isono Shinya , Takauchi Hideaki
Published: November 2024

Where single-sided welding is applied to the fabrication and erection of piping, back shielding by inert gas and its maintenance for the first few layers are required for low alloy steels (LAS), stainless steels (SS) and nonferrous alloys to obtain good weldability and quality of welds.

However, installation and removal of back shielding isolations inside piping for the joint and the adjacent areas to be welded are sometimes impractical due to piping layout and construction sequence such as closure joints. And the unexpected remaining isolations sometimes become concerns for obstructing fluid flow or damaging piping components such as valves and rotating equipment during commissioning or after operation.

To solve the concerns, high silicon solid filler rod was experimented to 9Cr-1Mo steels welding by gas tungsten arc welding (GTAW) to omit back shielding, and positive results of the R&D were introduced in ASME PVP2023[1]. The same concept using high silicon solid filler rod for GTAW was expanded to welding for 5Cr-0.5Mo steels and properties of the welds were studied by comparison to the welds produced by different concentration of silicon in filler rods for the conventional GTAW with back shielding. This paper discusses and evaluates the potential of the GTAW with high silicon solid filler rod which can omit the inert gas back shielding for Cr-Mo steels and expected applications with the filler rod.
Aging Embrittlement of 1¼Cr–½Mo–Si and 1Cr–½Mo Steels
Authors: Sakata Mikihiro , Le Nevé Charles
Published: November 2024

Toughness degradation can be observed when 1¼Cr-½Mo-Si or 1Cr-½Mo steels are used at temperatures exceeding 500 °C (932 °F) for an extended period of time. However, research addressing this phenomenon is limited. Although temper embrittlement is one of the causes of toughness degradation of 1¼Cr-½Mo-Si and 1Cr-½Mo steels, embrittlement mechanisms have not yet been fully elucidated. This study comprises two parts. First, published information, experimental studies and the authors’ experiences on the aging embrittlement of 1¼Cr-½Mo-Si and 1Cr-½Mo steels were reviewed, focusing on both long-term operation and fabrication heat treatment (i.e., post-weld heat treatment). Second, Charpy impact toughness data obtained from vintage 1¼Cr-½Mo-Si and 1Cr-½Mo steels used at temperatures exceeding 500 °C (932 °F) for an extended period of time (up to approximately 45 years) were statistically analyzed. The majority of these steels were acquired from pressure vessels or piping in catalytic reforming or fluid catalytic cracking units that began operation in the 1970s or earlier. This study will help understand and predict the aging embrittlement of 1¼Cr-½Mo-Si and 1Cr-½Mo steels.
Third-Generation Test Facility for Strain-Controlled EAF
Authors: Seppänen Tommi , Arilahti Esko , Alhainen Jouni , Juvalainen Juho , Moilanen Pekka , Solin Jussi
Published: November 2024

Meeting the stringent requirements of strain-controlled testing standard ASTM E606 in simulated reactor coolant is challenging. Two earlier generations of bellows-based testing devices have proven direct strain control to be possible in deoxygenated PWR water at up to 350 °C and 150 bar. To meet future research demands, a third-generation device has been designed and is in the final phase of commissioning.

The first-generation miniature bellows loading device was designed as a prototype to prove the applicability of the technology for strain-controlled fatigue testing. All standard criteria for valid experimental results were not aimed to be met with the prototype, but the technology was successfully demonstrated. This encouraged later development of the second-generation “FaBello” devices. FaBello was designed to comply, as far as possible, with ASTM E 606. However, pneumatic load train and certain technology-related boundary conditions placed limits on the range of controllable test parameters.

With the emphasis on overcoming past limitations without straying from standard requirements, the third-generation “FaVite” devices were designed. Through the various improvements FaVite can be used to generate quantitative experimental results to assist in filling multiple environmentally-assisted fatigue knowledge gaps, as outlined in an EPRI report.

This paper gives a technical overview of the main challenges in conducting valid LCF experiments in simulated reactor coolant environment. Some proven solutions are introduced as well.
Continuum and Crystal Plasticity Coupled Finite Element Modelling to Explore Complex Loading Conditions
Authors: Allen Christopher , Coules Harry , Truman Christopher
Published: November 2024

Components in civil nuclear power plants are subject to high temperatures and pressures. Current methods to perform structural integrity assessments on said components are often overly conservative and cannot predict complex loading conditions. This is partially due to these approaches accounting for only macroscopic material behaviour and ignoring behaviour at a granular level. This has led to increased popularity in crystal plasticity finite element (CPFE) modelling due to its ability to simulate macroscopic and mesoscopic behaviour from a mechanistic perspective. A key factor in the accuracy of CPFE modelling is the boundary conditions applied. Periodic conditions allow the simulation of uniaxial stress states however, exploring more complex loading conditions is challenging.

This paper presents a multiscale methodology to apply complex loading conditions to a CPFE model. The material used in this study is Type 316H stainless steel. A macroscopic finite element model is produced of the desired component. At the region of interest, the resulting displacements generated are interpolated and applied to the surfaces of a CPFE model. To partially validate this approach, uniaxial and biaxial simulations have been performed.

The uniaxial simulations demonstrate that this approach captures uniaxial behaviour accurately at the macro- and meso-scale, as evidenced by comparisons with lattice plane deformation measured by diffraction techniques. The biaxial simulations match qualitatively well with experimental findings, but more quantitative comparisons must be drawn to exhibit the predictive capabilities.
Technical Basis for Fatigue Crack Growth Rules in Gaseous Hydrogen for ASME B31.12 Code Case 220 and for Revision of ASME VIII-3 Code Case 2938-1
Authors: San Marchi Chris , Ronevich Joseph A. , Bortot Paolo , Ortolani Matteo , Xu Kang , Rana Mahendra
Published: November 2024

Emerging hydrogen technologies span a diverse range of operating environments. High-pressure storage for mobility applications has become commonplace up to about 1,000 bar, whereas transmission of gaseous hydrogen can occur at hydrogen partial pressure of a few bar when blended into natural gas. In the former case, cascade storage is utilized to manage hydrogen-assisted fatigue and the Boiler and Pressure Vessel Code, Section VIII, Division 3 includes fatigue design curves for fracture mechanics design of hydrogen vessels at pressure of 1,030 bar (using a Paris Law formulation). Recent research on hydrogen-assisted fatigue crack growth has shown that a diverse range of ferritic steels show similar fatigue crack growth behavior in gaseous hydrogen environments, including low-carbon steels (e.g., pipeline steels) as well as quench and tempered Cr-Mo and Ni-Cr-Mo pressure vessel steels with tensile strength less than 915 MPa. However, measured fatigue crack growth is sensitive to hydrogen partial pressure and fatigue crack growth can be accelerated in hydrogen at pressure as low as 1 bar. The effect of hydrogen partial pressure from 1 to 1,000 bar can be quantified through a simple semi-empirical correction factor to the fatigue crack growth design curves. This paper documents the technical basis for the pressure-sensitive fatigue crack growth rules for gaseous hydrogen service in ASME B31.12 Code Case 220 and for revision of ASME VIII-3 Code Case 2938-1, including the range of applicability of these fatigue design curves in terms of environmental, materials and mechanics variables.
T-Slot Design and Fatigue Life Assessment of Coke Drum Skirt to Cone Knuckle Weld Joint
Authors: Scandroli Tony , Nassif Omar
Published: November 2024

Coke drums experience failures in through-wall cracking throughout their operating life, resulting from low cycle fatigue at the skirt to cone weld joint and keyhole slot ends. In some cases, drums built without keyholes have experienced 360° through-wall cracking within five years of operation. Keyholes are added to the skirt to mitigate low-cycle fatigue failures and extend the life of the drums. Typical designs terminate the slots with top and bottom holes, hence, keyhole slots. Once a skirt modification with keyhole slots and the coke drum is put into service, cracks at the top keyholes have been discovered as few as two years later. Depending on the crack size, there is little concern about these cracks breaching the pressure boundary of the drum. However, if unattended, they will continue to grow over time, and a breach of the coke drum’s pressure boundary is more likely. This paper presents T-Slots as an alternative to conventional keyhole design. An iterative methodology was used to compare changes in keyhole slots and T-Slots using finite element analysis (FEA) to optimize the geometry and placement. Several crotch radii, standard keyhole slot sizes, and T-slots are examined to find an optimum design with the most extended service life before fatigue crack initiation. T-slots were the most effective in extending the operating life of the Coke drum skirt to cone joints and slot ends.
Blast-Induced Failure Analysis of Liquid Ammonia Storage Tank
Authors: Slovenec Derek E. , Wood Joan , Kummari Seetha Ramudu , Prueter Phillip E.
Published: November 2024

Ammonium nitrate (AN) is a widely used compound in the agriculture and mining industries that, if improperly handled, poses a significant explosive hazard, as evidenced by the 2020 Port of Beirut explosion. In the wake of this event, the Australian government required failure analysis studies for all bulk AN storage. This paper details one such failure analysis study where bulk solid AN was stored at a mining facility that also featured a large, double-walled, refrigerated API 620 storage tank containing liquid ammonia. The goal of this study was to determine the quantity of solid AN that, if an explosion were to occur, could cause failure of the tank, potentially resulting in a significantly larger explosion. Nonlinear dynamic finite element analysis (FEA) was performed to simulate blast overpressure wave propagation and incidence upon the exterior tank wall and system response including contact between inner and outer tank walls. The tank was subjected to blast scenarios ranging from the equivalent of 77,000 lbsTNT up to 420,000 lbsTNT to study its behavior from essentially elastic response through effectively certain loss of containment. There is no industry standard or published code establishing failure criteria for a tank or pressure vessel subjected to an external explosion. Therefore, various sources were used to inform the criteria defining structural failure of the tank, including the United States Department of Defense Unified Facilities Criteria 3-340 (DOD UFC 3-340-02), ASME Boiler and Pressure Vessel Code Section VIII Division 3 (ASME VIII-3), and ASME VIII-2. Comparisons were made between these methods, and a range of AN quantities likely to cause failure of the tank is proposed. This study highlights the challenges of blast analysis, failure-level response simulation, and, ultimately, quantifying the consequence of cascading failure events.
Probabilistic Critical Initial Flaw Size Analysis in the Circumferential Welds of Layered Pressure Vessels
Authors: Kirby Matthew L. , Riha David S. , Cardinal Joseph W. , Hobbs Joel R. , Stoltz Brian C.
Published: November 2024

NASA operates as many as 300 non-code layered pressure vessels (LPVs) across their research and space flight centers. Many of these mission critical assets are operating beyond their expected service life, but replacement of these LPVs is cost prohibitive. Thus, NASA is interested in assessing fitness-for-service (FFS) and extending the life of these vessels when it is safe to do so. Since FFS of non-code LPVs comes with distinctive challenges, NASA has developed an alternate standard for FFS. Structural analysis under the alternative standard includes logic for performing probabilistic fracture mechanics assessments to estimate the cumulative distribution function (CDF) of critical flaw sizes for known and postulated flaws in key regions of the vessel. The resulting CDFs are predictive distributions that represent the current state of knowledge about the critical flaw size captured by models and data. This paper describes the probabilistic critical initial flaw size method employed by the alternative standard, and demonstrates its use to analyze a surface crack in the circumferential weld of a 9-layer vessel. It also discusses unique aspects of the probabilistic results and presents an approach for interpreting the probabilistic results in light of the deterministic critical initial flaw size solution.
Effect of Strength on Mechanical Properties of Linepipe Steel in High Pressure Hydrogen Environment
Authors: Imayama Hikaru , Izumi Daichi , Shimamura Junji , Nishihara Yoshihiro , Okano Hiroshi
Published: November 2024

In this paper, the fundamental material behavior and mechanical properties of linepipe steel in a high-pressure hydrogen environment were investigated. A fracture toughness test was carried out using the unloading compliance method (described in ASTM E1820) in 21-MPa hydrogen using bainitic steel of various strengths as the test material. Compared with the linepipe base material, namely American Petroleum Institute (API) grade X65, the fracture toughness of API grade X80 was inferior but that of API grade X70 was superior. The fatigue crack growth characteristics in hydrogen were inferior to those in air, with the effect of strength being small. The effect of strength on the hydrogen embrittlement of bainitic steel for linepipes was examined based on the change in fracture form after the test, presence of hydrogen trap sites, and hydrogen diffusion coefficient for the steel.