bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterisation of the Microstructure Evolution of Aged Grade 91 Steel
Authors: Che Chang , Liu Xiang , Huang Youqiao , Pan Qingchuan , Qian Gong
Published: October 2020

Grade 91 steel has high creep strength and has been used as the material of piping in 600°C USC power plants in China. The Grade 91 materials used in actual power plants are useful in estimating the changes of material properties caused by long-term aging and damage at low stress conditions. An understanding of the long-term microstructural evolution under actually used conditions is a key for the improvement of these heat resistant steels. In this article, microstructural evolution of Grade 91 steel under different service conditions in Chinese power plants was studied using optical microscope (OM), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) techniques. The results show, M23C6, MX (V-rich particles; Nb-rich particles), and Laves phases were found to precipitate. A quantitative characterisation of microstructure evolution was evaluated during long-term exposure, focusing on the size of precipitates (M23C6 carbides, Laves phase, MX phase) for the Grade 91 steel after long-term service.
Examination of Oscillating Frequencies Generated by Combustion Oscillation Considering Temperature Distribution in a Combustor Tube Fueled by Natural Gas and Hydrogen Mixture
Authors: Uemichi Akane , Mitani Kan , Yamasaki Yudai , Kaneko Shigehiko
Published: October 2020

A combustion oscillation experiment fueling a mixture of hydrogen and natural gas was performed. The results showed oscillating frequencies of around 350 Hz in the case of the town gas only, whereas oscillating frequencies of around 200 and 400 Hz were observed in the hydrogen-containing fuel case. We hypothesized that the oscillating frequencies shift may occur by changing the temperature-distribution inside the tube, which was caused by different combustion conditions with the fuel mixture. As a result, the possible oscillating frequencies of not only around 350 Hz but also around 200 and 400 Hz were obtained. Although three types of possible oscillating frequencies were obtained in our previous study, more detailed temperature distributions should be considered to clarify the effect of the changing fuel mixture composition. In this paper, representative one-dimensional temperature distributions were formed by the combination of measured and calculated temperature distributions in the combustion tube for the corresponding fuel mixture. To include the detailed temperature distributions, the acoustic network model was divided into enough small elements to express the temperature distributions, where each element was connected by the transfer matrix. Then, the possible oscillating frequencies were calculated, taking account of the influence of the temperature distributions.
Evaluation of Material Compatibility for Hydrogen Applications Using Performance Factors Obtained by In-Situ SP Test
Authors: Shin Hyung-Seop , Yeo Juho , Custodio Nick A. , Baek Un-Bong , Nahm Seung-Hoon
Published: October 2020

Recently, a simple screening technique based on the quantitative evaluation of the hydrogen embrittlement (HE) sensitivity of the metallic materials using an in-situ small-punch (SP) test method was developed by the author group. The in-situ SP test can be easily carried out even under a high-pressure hydrogen gas environment. It makes possible to investigate the HE behaviors of metallic materials quantitatively adopting as a characterizing performance factor of the relative reduction of thickness (RRT) measured at the fractured parts of specimen after SP tests. In this paper, the application of the newly established in-situ SP test method for the hydrogen compatibility screening of austenitic stainless steels was performed at room and low temperatures. The influence of punch velocity on RRT of the HE sensitivity was examined for various austenitic stainless steels. Their HE sensitivities were evaluated quantitatively using RRT and checked by comparing to a factor, the relative reduction of area (RRA) obtained by SSRT tests.
Failure Analysis of Flange Sealing Surface of Outlet Pipeline of Wax Oil Hydrogenation Reactor
Authors: Shi Jiqing , Wang Jielu , Song Wenming , Huang Chaopeng
Published: October 2020

Hydrogenation reactor is the core equipment of various hydrogenation units or hydrogenation processes. Because of the harsh service environment, the difficult manufacturing technology, the high requirements and the expensive cost, the safety of hydrogenation reactor is a very important problem. The outlet flange of hydrogenation reactor in a petrochemical company suddenly cracked after several years of use. The maximum depth of the crack from the sealing surface to the depth of the flange is 165 mm, the circumferential cracking range is about 130 degrees. The crack is in a circumferential and curved line along the sealing groove, and has small bifurcations at the tip. In order to ensure the safety of equipment operation and prevent the recurrence of this kind of accident, the causes of flange failure were systematically analyzed and the preventive measures are formulated. This paper reviewed the manufacturing quality data of the failed flange, and carried out a series of tests and analyses, such as macroscopic inspection, penetration testing, ultrasonic testing, mechanical properties test, chemical composition analysis, metallographic structure analysis, finite element stress check and so on. Combined with the use environment and the operation parameters of the flange, we preliminarily analyze that the cause of flange cracking may be manufacturing defects. In order to avoid the failure of flanges again, it is recommended that the flanges of the same batch should be tested one by one to ensure the safe and stable operation of the device.
Throttling Effect and Thermodynamic Characteristics of Supercritical CO2 Flowing Through Shut-Off Valve
Authors: Guo Xiaolu , Xu Peng , Xu Shuangqing
Published: October 2020

The supercritical flow of CO2 is widely applied in energy fields such as the carbon capture and storage technology and the Brayton cycle power generation technology. The shut-off valves are widely used in various systems of energy fields, and their use is related to the stability and safety of the system. Due to the throttling effect of supercritical CO2 flowing through the valve, the large temperature drop may cause the dry ice generation, the overpressure and the blockage, which have an important impact on the safety and stability of the whole system. At present, there are few researches on the throttling effect and thermodynamic characteristics of supercritical CO2 flowing through the shut-off valve. In this paper, the pressure and temperature changes before the valve inlet and after the valve outlet were studied, and the field of pressure, temperature and phase inside the valve were analyzed. It was found that the outlet pressure of the shut-off valve increased rapidly after the valve was opened, and the temperature decreased at the same time. With the decrease of system pressure, supercritical CO2 in front of the valve changed into gas-liquid two-phase and gas-phase successively, and CO2 after the valve changed into gas-phase, liquid-phase, gas-liquid two-phase and gas-phase successively. This study is of great significance to the stability and safe operation of energy systems.
Research and Development of Viscous Fluid Dampers for Improvement of Seismic Resistance of Thermal Power Plants: Part 10 — Damper to Suppress Relative Deformation Between Furnace and Cage
Authors: Minagawa Keisuke , Aida Kiyoshi , Fujita Satoshi
Published: October 2020

In Hokkaido Eastern Iburi Earthquake in 2018, strong ground motion attacked a coal-fired thermal plant. A connecting part of a furnace and a cage of a boiler in the power plant and steam tubes in that part were damaged. Consequently the damage of the power plant induced a large impact to society. Suppressing relative displacement between the furnace and the cage might be effective to reduce this kind of the damage, because the furnace and the cage vibrate independently during earthquakes. Therefore this paper proposes application of dampers to the connecting part of the furnace and the cage of the boiler based on the results of the Part 9. The dampers are installed horizontally between the furnace and the cage and suppress relative displacement. The length and shape of the furnace are different from the cage, thus amount of the thermal expansion is also different. Therefore the damper has to allow the difference of the amount of the thermal expansion. In addition, the damper has to generate large damping force from the small vibration. Thus a viscous damper with high viscosity fluid is applied as a damper which satisfies above-mentioned requirements. A seismic response analysis using a frame model was conducted in order to verify the effect of the damper and to investigate the influence of the damping capacity of the damper. As a results, it was confirmed that the relative displacement between the furnace and the cage can be suppressed by applying the damper.
Effect of High-Pressure Hydrogen and Water Impurity on Aluminum Alloys
Authors: San Marchi Chris , Schwarz Martina , Ronevich Joseph
Published: October 2020

Aluminum alloys are desirable in mobile fuel cell applications due to the combination of strength, hydrogen resistance, and low density. In dry hydrogen environments, the fatigue and fracture resistance of common structural aluminum alloys are not degraded compared to air environments. However, aluminum alloys can be susceptible to stress corrosion cracking in humid air, which raises questions about the potential deleterious effects of moisture impurities in high-pressure hydrogen environments. While this study does not address the effects of the air environment on aluminum hydrogen pressure components, we assess the fracture resistance of aluminum alloys in high-pressure hydrogen containing known amount of water. High-pressure gaseous hydrogen at pressure up to 100 MPa is shown to have no effect on elastic-plastic fracture measurements of common high-strength aluminum alloys in tempers designed for resistance to stress corrosion cracking. Complementary sustained load cracking tests in high-pressure hydrogen were also performed in gaseous hydrogen at pressure of approximately 100 MPa with water content near the maximum allowed in hydrogen standards for fuel cell vehicles. These tests show no evidence of environmental-assisted cracking at loading conditions approaching the onset of unstable fracture in this configuration. In summary, typical moisture content in fuel cell grade hydrogen (< 5 ppm) do not promote hydrogen-assisted fracture or stress corrosion cracking in the tested aluminum alloys.
An Overview of ASME Section III Class 2 and 3 Valve Design and Service Loading Rules
Authors: Farrell Ronald , Lambin Jason
Published: October 2020

In addition to providing an overview of the ASME Boiler and Pressure Vessel Code design rules applicable to Class 2 and 3 valves, where Class is defined in Section III of the ASME Code, Sub-Article NCA-2130, this paper offers some insight as to why the rules are as they are. The motivation comes from a request by the ASME Codes and Standards Committee, Components Subgroup, for the Valve Working Group to prepare this overview. The request came after discussing a question from a participant regarding how the “(Primary Membrane or Local) plus Bending” stress category should be addressed for a valve.

The paper goes beyond a basic overview of Code rules as it includes a discussion of the underlying valve standard ASME B16.34, looks at the valve rules in relation with the rest of the Code, and contributes some historical perspective. From a perusal of the Code both in general and during preparation of this paper, it is concluded that the valve Code rules could benefit from a few clarifications; thus, changes are proposed, and the Working Group is encouraged to consider them. In answer to the underlying question regarding the primary local stress category, it is shown that the need for a local stress evaluation would be rare for a valve.
Plasma Arc Welding for Code Compliance Nuclear Applications
Authors: Sun Dongmei (Donna) , Pistor Rob
Published: October 2020

Plasma Arc Welding (PAW) has been used for many critical applications due to its flexibility, reliability and high weld quality. In this paper, two code compliance plasma arc welding applications in the nuclear industry are discussed.

The first application is an innovative welding process using PAW with specially designed dual hot wire feeding system, namely Dual Hot Wire Gas Metal Plasma Arc Welding (GMPAW). The GMPAW process offers unique advantages for high deposition and low dilution weld overlay application. The second application is a remote weld overlay repair from pipe inside diameter (ID) for a highly radiated nuclear component using PAW process with remote machining and NDE capability.

In this paper, the benefits and advantages are provided for the aforementioned PAW applications. The versatility of plasma arc welding system configuration, as well as high quality and productivity can make plasma arc welding a good candidate for many critical code compliance applications.
Microstructural Evolution During a Solid State Tube Pinch Weld
Authors: Korinko Paul S.
Published: October 2020

Microstructure development is examined for a specialized spot weld that is used as a solid-state closure process for stainless steel tubing, referred to as pinch welding. In order to elucidate the microstructural evolution of the weld, a series of test welds were made at nominal conditions using both tubes, used in test articles and production like components. These pinch welds normally terminate after twelve cycles of a 60 Hz AC weld process. In this study, tubes with different thermal processing history were welded from one to twelve cycles and the microstructure and weld variables after each individual weld cycle number were characterized using radiography and optical metallography. Two etchants were used that highlighted different microstructural features. The study revealed that: (1) this type pinch weld is largely complete after about six cycles of 60 Hz AC current, half the weld time utilized; (2) the resistance, deformation, and closure length approach “steady state” conditions after six cycles; and (3) both oxalic and nitric acid electrolytic etchants are useful for highlighting specific microstructural attributes of type 304L stainless steel. Finally, two distinct microstructural regions can be identified for these welds: the edge of the weld which is driven by concentrated deformation, recrystallization and grain growth and the center region which is more typical of forge welding and micro-asperity breakdown followed by diffusion and grain-growth. The bond line of annealed tubes exhibits fewer indications and less contamination than that of the partially annealed and as-received cold worked tubes.
Increasing Fatigue Strength and Wear Resistance of Additive Manufactured Nickel Alloy (UNS N07718) by Ultrasonic Nanocrystal Surface Modification (UNSM) Treatment
Authors: Pyun Young Sik , Choi Seimi , Karimbaev Ruslan , Ro Jun Suek , Sanseong Choong Ho , Sembiring Jan , Kim Jong Seog , Amanov Auezhan , Kang Suk Hoon , Ahn Hee Sung
Published: October 2020

Additive Manufacturing (AM) which is also known as metal 3D printing technique is a promising process with a massive potential for developing a component for wide range applications for various industries. Recently, AM process was introduced to the nuclear power plant industry as AM is capable of manufacturing the substitution of aging and obsolete component. However, the AM component has inferior mechanical properties and performance in terms of fatigue strength and wear resistance compared to its conventionally manufactured counterpart. Ultrasonic Nanocrystal Surface Modification (UNSM) is one of mechanical surface modification treatment known for improving fatigue strength and wear resistance of wrought material. Hence, in this study effect of UNSM treatment on fatigue strength and wear resistance of additive manufactured material was investigated. The investigation was done to Ni-based alloy 718 (UNS N07718) as this material is used for nuclear power plant components and was manufactured with two different AM techniques namely Powder Bed Fusion (PBF) and Direct Energy Deposition (DED) processes. The evaluation was conducted by comparing the as-polished and UNSM-treated specimens for each AM processes by performing fatigue and tribo tests. This result will become a part of the technical basis for KEPIC Code Case development.
Environmental Fatigue Analysis Considering Thermal Stratification in Direct Vessel Injection Piping
Authors: Lee Bonghee , Nam Ilkwun , Park Sangyun , Kim Sookyum , Kim Yongbaek
Published: October 2020

Thermal stratification-induced stresses could lead to a serious failure and fatigue crack on piping systems. U.S. NRC Bulletin 88-08 [1] requires to investigate which unisolable pipings are subjected to the thermal stratification and to demonstrate compliance with applicable code limits during the piping design stage by incorporating the thermal stratification-induced stresses into the fatigue evaluation.

In this paper, the computational fluid dynamic (CFD) analyses considering both the out-leakage case by turbulent penetration and the in-leakage case by valve leakage were performed for the unisolable portion of the Direct Vessel Injection (DVI) piping between the reactor vessel nozzle and the first check valve to determine the change of temperature gradient on the pipe wall as a function of time due to the thermal stratification. And then the CFD-based temperature distributions on the pipe wall at each time interval were transformed as input data for the structural analysis to evaluate the stresses induced by the global bending moments and local stresses by the thermal stratification of the DVI piping.

The localized thermal stratification stress intensities were directly extracted from the 3-D model using the ANSYS program and were categorized as the three stress terms induced by ΔT1, ΔT2, and Ta - Tb defined in NB-3600 of ASME B&PV Sec. III [2], but including thermal stratification effects herein for the fatigue analysis. To evaluate the air environment- and LWR environment-based fatigue damages for the DVI piping, the bending moments and three local stress terms due to the thermal stratification were incorporated into the fatigue analysis. NB-3200/-3600 of ASME B&PV Sec. III- and Regulatory Guide 1.207-based cumulative usage factors [3, 4] were compared with each other to investigate the effects of fatigue damages considering the thermal stratification in the air and light water reactor (LWR) environments.
Properties of Cladding With Respect to RPV Integrity
Authors: Brumovský Milan
Published: October 2020

Inner surface of most of primary circuit components in PWR/BWR/WWER type reactors is covered by austenitic cladding that serves primarily as anticorrosion protection. This is also supported by the requirements for stress analysis of the vessel by most of the codes — austenitic cladding is not taken into account in the calculation of vessel wall thickness and on allowance of stress intensities for operating conditions. Its effect is taken, in some codes like for WWER components, in fatigue calculation and also for evaluation of vessel resistance against fast fracture during pressurized thermal shock (PTS) events.
Vibration of FRP Bypass Piping of Sea Water Intake System in Offshore Platform
Authors: Choi Capjoo , Chu Yeon-Young
Published: October 2020

Severe vibration is observed at FRP (Glass-Fiber-Reinforced Thermosetting-Resin) bypass line connected to discharge of sea water intake pump which is installed on offshore platform. To find out characteristic of the flow, CFD (Computational fluid dynamics) analysis is conducted, and result shows that it is produced by complex pulsating two phase flow formed by the high speed water jet at the resistance orifice which passes through several elbows. After CFD analysis, the force-time history result from CFD analysis is used in transient structural analysis. Based on the numerical analysis result, mechanical response of the pipe and structure for the initial piping system and reinforced piping system are verified and compared with criteria of Energy Institute guideline and NORSOK S-002. Also in order to demonstrate a validity of the numerical analysis and check soundness of the whole reinforced piping and structure system with vibration, site measurement is performed. Moreover, in order to check the stress level of piping, dynamic strain measurement is undertaken.

This paper discusses the details on history of bypass line design to avoid air entrapment not to damage on seawater pump, and how the vibration issue is approached, and finally compared with industry standard for safety. Further, the paper presents the numerical analysis result that makes design modifications implement for bypass piping and structure during a commissioning, and various evaluation method that verify the soundness of piping and structure based on field vibration measurement.
Crack Opening Areas Under Combined Primary and Secondary Loading
Authors: Brayshaw W. J. , James P. , Sharples J. , Aird C.
Published: October 2020

Leak-before-break is a methodology to assess whether a leak through a defect in a pressurised component can be detected prior to the defect attaining a critical size. Developing leak-before-break arguments in non-stress relieved piping components can be challenging, in part due to the lack of solutions available, including in R6, to predict the crack opening area (required to evaluate leak rate) for combined primary and secondary stresses under elastic-plastic conditions. This is because the nature of the secondary stresses is to relax with plasticity, which can be captured in the calculation of the crack driving force (elastic-plastic stress intensity factor), but methods to account for the additional crack-tip strain this induces and its influence on crack opening are not available. Here primary stresses are those resulting from an applied force, such as pressure, and secondary stresses are those which result from an internal mismatch and do not contribute to plastic collapse, such as thermal or residual stresses. There is, of course, potential for a higher accuracy of crack opening area evaluations from finite element analysis modelling approaches, which include elastic-plastic material properties, in the presence of combined loading scenarios.

In this study, a series of finite element analyses have been conducted whereby crack opening area and stress intensity factor have been calculated from circumferential through-wall defects, under the influence of combined primary and secondary stresses, where the magnitude and order of the combined stress has also been varied. The crack opening areas have been compared to current elastic ‘handbook’ solutions, which are conservative for primary stresses, to better understand the effect of plasticity on crack opening area and to help inform assessments when accounting for the inclusion of plasticity with secondary stresses.
Numerical and Experimental Residual Stresses of Different Welded Joint Configurations in Heavy Wall
Authors: Colombo Chiara , Monti Stefano , Guagliano Mario , Vergani Laura , Fiordaligi Emanuele , Fusari Fausto
Published: October 2020

Refinery equipment subjected to high pressure is commonly made of Vanadium high strength steels (2¼Cr1Mo¼V), characterized by high allowable stress and low toughness in the as welded condition, leading to potential wall cracking before the application of thermal treatments. Therefore, the decision to perform specific thermal treatments after welding is of paramount importance. These thermal treatments, which are quite expensive and time demanding for the manufacturer, are still under discussion and not supported by evident scientific findings. The paper presents a numerical and experimental study on a plate-to-plate weld and on a nozzle-to-plate weld, created as ad-hoc mock-ups. Experimental residual stresses are collected by an X-ray diffractometer in the as welded configurations. These values are used to validate a complex 3D numerical model, implemented with the finite element software Abaqus and its AWI plugin. Finally, this validated model allows for the identification of joint criticality through two parameters: the volume of plasticized material per unit of welded length and the strain-based assessment according with ASME code. Their application as tools to compare the criticality of different welded geometries and the effect of thermal treatments on the residual stress field are discussed.
Study of the Influence of Microstructure and Intergranular Carbides on the Oxidation Behavior of a Nickel Base Alloy 690 TT in Supercritical Water Nuclear Reactor Conditions
Authors: Sáez-Maderuelo Alberto , Ruiz-Lorenzo María Luisa , Perosanz Francisco Javier , Halodová Patricie , Prochazka Jan , Namburi Hygreeva
Published: October 2020

Alloy 690, which was designed as a replacement for the Alloy 600, is widely used in the nuclear industry due to its optimum behavior to stress corrosion cracking (SCC) under nuclear reactor operating conditions. Because of this superior resistance, alloy 690 has been proposed as a candidate structural material for the Supercritical Water Reactor (SCWR), which is one of the designs of the next generation of nuclear power plants (Gen IV).

In spite of this, striking results were found [1] when alloy 690 was tested without intergranular carbides. These results showed that, contrary to expectations, the crack growth rate is lower in samples without intergranular carbides than in samples with intergranular carbides. Therefore, the role of the carbides in the corrosion behavior of Alloy 690 is not yet well understood.

Considering these observations, the aim of this work is to study the effect of intergranular carbides in the oxidation behavior (as a preliminary stage of degenerative processes SCC) of Alloy 690 in supercritical water (SCW) at two temperatures: 400 °C and 500 °C and 25 MPa. Oxide layers of selected specimens were studied by different techniques like Scanning Electron Microscope (SEM) and Auger Electron Spectroscopy (AES).
Assessment of Compact Heat Exchanger Design According to the Simplified ASME Analysis Methodologies
Authors: Shaw Avinash , Jentz Ian W. , Mahajan Heramb P. , Hassan Tasnim
Published: October 2020

High thermal efficiency of Compact Heat Exchangers (CHX) makes them distinctly utile for application to Next Generation Nuclear Plants (NGNPs). The high temperature application and transient conditions of NGNP operation induce stresses in CHX. These induced stresses can be categorized under different classifications based on their cause and location. ASME Sec. III Div. 5 has different analysis methodologies based on failure modes, failure criteria to be assessed, and constitutive relationship considered. The primary objective of this study is to provide a description of the classification of stresses in CHX. Further, evaluation of CHX design is conducted according to simplified analysis methodologies in ASME Sec. III Div. 5: Elastic and Simplified Inelastic Analysis. These simplified analyses are performed following the submodeling technique. At the global level, the channeled core is replaced by an elastic orthotropic core for analysis. At the local level, the stresses and strains for critical regions are determined following the simplified analysis methods. The load controlled stresses are checked against HBB-3220 of ASME Sec. III Div. 5. For the Elastic Analysis Method, strains in critical sections in CHX are checked for thermomechanical cycle against the HBB-T-1320 of ASME Sec. III Div. 5 criteria. For Simplified Inelastic Analysis, critical sections are analyzed for strain limits following HBB-T-1330 of ASME Sec. III Div. 5. The analyses outcomes are compared and results are discussed.
Test Protocol Definition to Measure Fracture Toughness J-Parameter Using Non-Standard Four-Point Bending Specimens
Authors: Ferreira Denis Alves , Pascualinotto Junior Vagner , Sarzosa Diego F. B.
Published: October 2020

This work proposes a new test methodology to characterize the fracture toughness values for either brittle or ductile materials, such as steels of risers and pipelines used in the oil and gas industry by using non-standard four-point bending specimens. Four-point bending (4PB) specimens show to be reliable configuration to characterize fracture toughness values. The methodology involves obtaining compliance equations, stress intensity factors, the proportionality factors between the deformation energy and J-integral, known as η-factor. This study evidences the impact of geometry variation on the crack-tip constraint. Laboratory tests were performed with four-point bending specimens. These experiments were compared with experimental data of standardized geometries SE(B) and SE(T). The results from the preliminary experimental campaign validated the numerical analysis. Thus, the proposed equations can be used to obtain the fracture toughness values using four-point bending specimens.
Bounding Acoustic Load Development for Boiling Water Reactor Shroud and Shroud Supports
Authors: Walter Matthew , Qin Minghao , Sommerville Daniel
Published: October 2020

As part of the license basis of a nuclear boiling water reactor pressure vessel, a sudden loss of coolant accident (LOCA) event needs to be analyzed. One of the loads that results from this event is a sudden depressurization of the recirculation line. This leads to an acoustic wave that propagates through the reactor coolant and impacts several structures inside the reactor pressure vessel (RPV). The authors have previously published a PVP paper (PVP2015-45769) which provides a survey of LOCA acoustic loads on boiling water reactor core shrouds. Acoustic loads are required for structural evaluation of core shrouds; therefore, a defensible load is required. The previous research compiled plant-specific data that was available at the time. Since then, additional data has become available which will add to the robustness of the bounding load methodology that was developed. Investigations are also made regarding the shroud support to RPV weld, which was neglected from the previous study. This will allow a practitioner a convenient method to calculate bounding acoustic loads on all shroud and shroud support welds in the absence of a plant-specific analysis.
Ductile Tearing Prediction of Ferritic Pipe Material by GTN Model for ATLAS+ European Project
Authors: Hojo Kiminobu , Hirota Takatoshi , Ogawa Naoki , Kumagai Satoshi
Published: October 2020

The main objective and mission of the European project ATLAS+ (Advanced Structural Integrity Assessment Tools for Safe Long Term Operation) are to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems. This project includes the development and validation of advanced simulation tools based on fracture mechanics methods using physically based mechanistic models. In the Work Package 3 (WP3), benchmark calculations using different available models are conducted to investigate the accuracy and the capability of the different models for ductile crack growth of different constraint condition, such as laboratory specimens and piping structure, which were tested in the Work Package 1 (WP 1). The authors joined the WP3 activity and investigated the effect of the parameters of the GTN (Gurson-Tvergaard-Needleman) model on the fracture behavior of the specimens. In this paper, the parameters of the GTN model were calibrated to simulate the fracture behavior of CT specimens, notched tensile (NT) specimens and single edge notched tensile (SENT) specimens of ferritic pipe material and the applicability of the GTN model. The adjusted parameters by the CT specimen predicted the fracture behavior of the SENT specimens, but did not those of the NT specimens. The adjusted parameters by the CT specimens were applied to the piping structure mock-up and they predicted the maximum load in high accuracy.
A Parametric Study of Variable Crack Initiation Criterion in XFEM on Pipeline Steel
Authors: Lin Meng , Li Yong , Salem Mohammad , Cheng J. J. Roger , Adeeb Samer , Kainat Muntaseer
Published: October 2020

The integrity decisions for cracked pipelines can be made based on the conventional Finite Element Method (FEM). However, it is extremely time-consuming due to the requirement of remeshing to continuously conform to the geometric discontinuities as the crack propagates. The more recently developed Extended Finite Element Method (XFEM) provides a more robust approach in which a crack can propagate through the finite element analysis mesh and thus alleviates the requirement for remeshing. However, the current criteria for crack initiation and propagation in XFEM framework have not been calibrated to pipeline steels. The current built-in criterion in Abaqus assumes a fixed value as the damage strain. Crack initiation occurs after this strain is exceeded. However, the accuracy of numerical crack propagating path is questionable, especially in a side-grooved single edge notched tension (SENT) model. Faster crack initiation at specimen side over the center conflicts with the actual crack propagating path obtained from a physical test. This paper develops a new crack initiation criterion which defines a variable damage strain as a function of the stress configuration at the crack tip. The criterion is modified from the Mohr-Coulomb fracture criterion as a function of stress triaxiality and Lode angle parameters. The damage strain exponentially decreases as the stress triaxiality increases. This paper presents a parametric study on the effects of material parameters considered in the criterion on the development of damage strain locus. The new crack initiation criterion is applied to a side-grooved SENT model, in which the corresponding failure mechanism is defined by the user’s subroutine UDMGINI in Abaqus.
Stored Elastic Strain Energy of Pressure Vessels and Their Consequential Effect on High Speed Projectiles
Authors: Kumar Abhimanyu , Kim Minsu , Wesevich James , Dereli Ozer , Ozbey Mehmet C.
Published: October 2020

The technological development of pressure systems is closely associated with the growth of various technologies in petrochemical, oil services, power, and aerospace industry. The closed boundary system such as a pressure vessel, pipe, tube, and barrel, in which an unforeseen ill design or installation imbalance between interior and external pressure conditions can result into a hazardous situation, and an unexpected catastrophic failure of the system. These accidental failures most likely lead to escalation of events due to hazardous projectiles impacting the surrounding environment.

The kinetic energy contained in the projectile are dependent on the size of pressure vessel, density of the fluid (gas or fluid), and pressure of contained media. Numerous studies have shown the relationship between the contained media within the pressure vessel and fragment velocity. However, a gap still persists in regard to the effect of elastic strain energy of the vessel itself on the projectile velocity. In this study, we study the correlation between elastic strain energy of a pressure vessel and the projectile velocity. Several parameters, such as contained media, internal pressure, fluid nozzeling, volumetric expansion with respect to diameter and thickness of pressure vessel were considered to investigate their influence on the level of consequence in an accidental event. The findings of this study aim to provide important guidance for the design and operation of high pressure systems and testing.
Verification of Flange Rigidity Index for Standard Flanges Using Finite Element Analysis
Authors: Choi Junho , Kim Minsu , Dereli Ozer , Ozbey Mehmet , Wesevich James
Published: October 2020

A flange connection consists of the flange, gasket, bolts, and pipe. In a flange design stage, the flange rigidity index is checked to ensure the leak tightness of the flange connection. Technically, the flange rigidity index was theoretically derived by the function of flexure induced into the flange by both bolt tension and internal pressure. However, some of the factors used to calculate the flange rigidity index were determined by regression formulas. On the other hand, the rotation angle of the flange is also limited to determine the allowable bolt pre-tension. To better understand the flange rigidity index, flange rigidity index and flange rotation angle were compared. The flange rotation angle was calculated using Finite Element Analysis (FEA). For the evaluation model, NPS 3, 6, 12, 18, 24 for classes 150, 300, 600, 900, 1500 integral-type flanges were selected. Typical gasket seating and operating conditions were considered in this study. In gasket seating condition, the required minimum bolt load was applied. In operating condition, internal pressure and uniform temperature were simultaneously applied to the FEA model. From the analysis results, it was concluded that the specified flange rigidity indexes may underestimate the leak tightness for lower pressure and large flange types.
Verification of Stress Model in Dissimilar Materials of Varying Cladded Pipes Using a Similar Cladded Plate Model
Authors: Kogo Bridget , Wang Bin , Chizari Mahmoud , Wrobel Luiz
Published: October 2020

This paper continues previous research performed by the authors on the modelling of dissimilar welded joints with varying clad thicknesses. This study aims to validate the use of a clad plate model as a replacement to the previous clad pipe model. To fulfill the hypothesis of the study, possible deformation or angular shrinkages occurring at weld joints have been simulated using a commercial finite element software. In parallel, angular shrinkages have been validated using the experimental data with the underlying concept of Gaussian transformation of plates into pipes. The welding of the two dissimilar materials has been carried out in-house with the aid of a Tungsten Arc weld with dynamic measurement of the temperature profile in the vicinity areas of the welding track using high temperature thermocouples. It was discovered that for each deformation angle of 11.5°, 22.75°, 40° and 45°, there exists shrinkage of the order of 0.01mm. Transient temperature curves have been generated for different cladding thicknesses (of stainless steel and mild steel). Comparison of the measured data versus the simulation results shows close agreement.
Influence of Structural Interface Opening of Bolted Joints Under Eccentric Load
Authors: Imura Makoto , Koyama Takayuki , Iizuka Motonobu , Hayasaka Yasushi
Published: October 2020

It is important to evaluate the safety of bolted joint under a load eccentric to a bolt axis. We examined tapped thread joints, with which a clamped plate is tightened with bolts to a base body, by applying eccentric loads to the bolts. The structural interface opening between the clamped plate and base body occurs due to the eccentric load based on the principle of leverage. During the growth of the interface opening, nonlinearity noticeably appears on the tensional and bending components of bolt stress, and these stress components become larger than expected in an early phase before a fatal bolt pull-out occurs. However, an evaluation method taking into account nonlinearity has not been investigated.

We propose a normalized-bolt-stress evaluation method for tapped thread joints that takes into account the effect of the nonlinearity of bolt stress during interface opening. We conducted numerical calculations, experiments, and finite element analyses to quantitatively validate the stress under the following conditions: (i) tapped thread joints with the clamped plate thinner than the bolt diameter and (ii) load eccentric to the bolt axis. We confirmed that the bolt preload and lever ratio should be fixed at an initial phase, in which has no interface openings for the appropriate normalization. By using the normalized-bolt-stress evaluation method, strength evaluation becomes easily applicable to layout changes of bolted joints as a similarity rule.
Continued Study on the Effect of Mean Stress on Ground Storage Vessels for Hydrogen Fueling
Authors: Peters Daniel T. , Parr Myles
Published: October 2020

The use of high pressure vessels for the purpose of storing gaseous fuels for land based transportation application is becoming common. Fuels such as natural gas and hydrogen are currently being stored at high pressure for use in fueling stations. This paper will investigate the use of various levels of autofrettage in high pressure storage cylinders and its effects on the life of a vessel used for hydrogen storage. Unlike many high-pressure vessels, the life is controlled by fatigue when cycled between a high pressure near the design pressure and a lower pressure due to the emptying of the content of the vessels. There are many misunderstandings regarding the need for cyclic life assessment in storage vessels and the impact that hydrogen has on that life. Some manufacturers are currently producing vessels using ASME Section VIII Division 1 to avoid the requirements for evaluation of cylinders in cyclic service. There are currently rules being considered in all of ASME Section VIII Division 1 and Division 2, and even potentially for Appendix 8 of ASME Section X. Recommendations on updating the ASME codes will be considered in this report.
Acoustic Emission Characterization of Damage Patterns in Composite Scarf Joints Using Unsupervised Learning
Authors: Xu D. , Chen Z. P. , Liu P. F. , Wu J. H. , Jiao P. , Gu Y. N.
Published: October 2020

Interest in damage detection and damage pattern recognition of engineering structures by non-destructive techniques has been increasingly growing. As a non-destructive technique, acoustic emission (AE) has developed rapidly to detect dynamic defects and their evolution behaviors of composite structures, based on the transient elastic waves produced by rapid energy release due to the geometry change of structures. In this paper, AE technology is utilized to monitor the real-time condition of the composite scarf joint (SJ) under tensile loading. First, after AE signal acquisition, dimensionality reduction of eight AE features is realized by employing principal component analysis such that the Curse of Dimensionality can be avoided. Second, feature selection is continued by introducing two evaluation indexes, i.e., correlation coefficient and Laplacian score. Third, after the optimal cluster number is determined, damage pattern recognition is accomplished by introducing k-means++ algorithm which explores the distribution of each pattern in the space constructed by four informative AE features. Based on the clustering results, damage initiation and evolution in SJ specimens under tensile loading are subsequently explored. The shear failure of the adhesive layer which is a characteristic damage pattern for SJ specimens shows a relatively-high activity after the early stage. Matrix cracking and fiber/matrix interface debonding are two fundamental damage patterns which keep active in the whole process.
An Investigation Into the Robustness of a Crystal Plasticity Finite Element Model
Authors: Taylor Megan , Agius Dylan , Knowles David , Mostafavi Mahmoud
Published: October 2020

A crystal plasticity model has been developed for describing the plastic and viscoplastic behaviour of 316H stainless steel. The model has been used successfully to predict the macroscopic response of the material for monotonic and cyclic loading, however the robustness of the model is now being scrutinised to ensure that it captures the underlying mechanisms and local meso-scale deformation characteristics correctly. In order to look at this in more detail, the model has been scripted to allow simulation of diffraction studies on the grains. This is being used to compare the simulation output with neutron and synchrotron experiments.

A theoretical study has been completed which adjusts the values of each material parameter within the crystal plasticity finite element (CPFE) framework in isolation to analyse the effect each has upon the shape of the hysteresis loop and how this relates to predictions. A further study had been conducted to investigate the amount of scatter that is produced by altering the initial microstructure of a relatively small volume. The results show that changing the initial microstructure has a negligible effect on the subsequent stress-strain response. This indicates the influence that the grain morphology will have upon the diffraction measurements and that there is no need to consider this further when testing small specimens.

To conclude this investigation two further aspects of the model have being scrutinised; the effects of constraining boundary conditions and altering the local environment of a single grain, again to explore the influences which these may have on diffraction studies. The plane boundaries of the volume are currently fixed at zero displacement which will influence the local grains on these boundaries as they are over constrained, but should not alter the overall stress-strain response. To investigate this, grains within the model that have boundary conditions applied have be discarded from the final results to leave the response from the central volume that should be free of the boundary condition effects. The results show that the macroscopic response of the bulk volume and the central volume are very similar but when the individual grain family responses are analysed, it can be seen that the boundary condition do alter the response of the representative volume element (RVE). To analyse how the local environment surrounding a single grain affects its stress-strain response, a centrally located grain will be selected and kept constant while the orientation of the surrounding grains are randomly altered. It has been found that changing the local environment surrounding a single grain will impact the stress-strain response seen by that grain.
Ultrasonic Nondestructive Evaluation of Stress Corrosion Crack in Welded Steel Plate
Authors: Ma Zhaoyun , Yu Lingyu , Lam Poh-Sang , Sindelar Robert L. , Duncan Andrew J. , Truong Thanh-Tam , Chao Yuh J.
Published: October 2020

Stress corrosion cracking (SCC) has been observed in the high-level nuclear waste tanks that were constructed by welding carbon steel plates. This paper aims to establish an ultrasonic inspection system and its fundamental ability for SCC inspection and quantification on thick welded steel plates. A welded steel plate was fabricated without heat treatment by joining two carbon steel plates through gas metal arc welding (GMAW) procedure. SCC growth, which was initiated with starter cracks across the weld, were observed in a few weeks after submerging the plate in 5 molar (5M) sodium nitrate (NaNO3) solution at about 90 °C. The SCC is inspected with an ultrasonic guided wave system, which employs a piezoelectric transducer for guided wave actuation and a scanning laser Doppler vibrometer (SLDV) for wavefield sensing. The measured wavefield can immediately show wave interactions with the crack. Wavefield images are further generated for the crack length quantification. To demonstrate the crack sizing capability of using the piezoelectric transducer and SLDV, the previous results from the magnetic particle test (MT) are compared. Reasonable agreement in crack length measurement is obtained with the ultrasonic test imaging technique.