bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconstituted Mini Tensile Specimens
Authors: Kovács Attila , Horváth Ákos , Horváth Márta , Szenthe Ildikó , Gillemot Ferenc
Published: October 2018

In order to evaluate the fracture toughness and Master Curve, the exact values of the tensile and yield strengths determined at the fracture toughness testing temperature are required. The fracture toughness should be measured around the T0 reference temperature to obtain valid results. Tensile properties — if exists — are generally measured at room temperature, and at the maximum operation temperature of the pressure vessel. If T0 reference temperature is different from these temperatures a correction formula is used for interpolation or extrapolation. Several times even no reliable tensile results are available, especially in the case of irradiated specimens. Use of irradiated Charpy remnants is a solution to produce tensile bars. A specific method has been developed to produce 12 pieces of flat 2*1 mm cross section tensile specimens made from one half Charpy specimens using stud weld reconstitution. The specimen cutting is made using thin molybdenum wire spark cutting. In order to do so difficulties of handling the small radioactive specimens needed to be solved, special grips were developed for the tensile machine to clamp the miniature tensile specimens. A laser extensometer was used to measure the strain and a video microscope was used to determine the cross section after the fracture without touching the specimen. The paper presents the results obtained on more than 200 irradiated small tensile specimens. These results had been compared to the old surveillance ones.
Interaction of Longitudinal Corrosion Defects on a Pipeline
Authors: Land Jason C. , Yahner Thomas , Harper William V. , Brongers Michiel P. H. , Kobs Jeffrey
Published: October 2018

Longitudinal corrosion defects in pipelines can be formed from external or internal metal loss, from selective seam corrosion, or from clustering of corrosion defects in the longitudinal direction. Standard assessments of such defects are traditionally performed on an individual basis, but research has shown that unique challenges arise when multiple defects are present on the same pipe joint. Multiple longitudinal defects can be evaluated using a combined probability of failure (PoF) methodology based on the dependence of the interaction. This paper presents results of such an evaluation, in which finite element analysis (FEA) was applied to calculate energy densities at the most sensitive defect elements. The methodology provided a measure of the interaction dependence. The combined statistical interaction of defects can be calculated using an adaptation of the inclusion-exclusion principle, where overlapping non-linear energy densities are calculated.
Temporary Acceptance of Leaking Brazed Joints
Authors: O’Sullivan J. E. (Jim) , Hacker Kevin J.
Published: October 2018

Minor leakage in brazed joints is occasionally detected in nuclear power plant Class 3 piping systems such as emergency service water cooling lines for equipment room and containment area coolers. Detection of such leakage often causes the system to be taken out of service for performance of repair/replacement activities to restore the piping to its original condition. This can lead to plant shutdowns or outage delays which are very costly, and often at increased safety risk, to accomplish the repairs. To avoid such costs and increased risk, a method is needed to establish structural adequacy of leaking brazed joints so that leakage can be controlled and monitored until the next planned opportunity for replacement of the brazed joint.

During industry testing performed in the late 1950s, over 1200 lap joint tensile test specimens were brazed in a round-robin series of tests performed by 10 laboratories. The results of these tests showed that very little overlap is needed in a brazed lap joint to obtain full strength in the joint. In fact, braze metal shear strength exceeded piping collapse strength in all cases when the braze overlap was only 2.3 times the thickness of the members being brazed. Similar testing was performed by the U.S. Navy, and resulted in development of a NAVSEA document that established a conservative percentage of bond required for MIL F-1183 brazed fittings to prevent structural failure of a leaking brazed joint.

This paper discusses an ASME Section XI Code Case that has been developed to incorporate the results of this testing into a methodology for temporary acceptance of leakage of brazed lap joints in copper, copper-nickel, and nickel-copper ASME Code Class 3 nuclear piping systems.
Application of an a priori Jacobian-Based Error Estimation Metric to the Accuracy Assessment of 3D Finite Element Simulations
Authors: Rainsberger Robert B. , Fong Jeffrey T. , Marcal Pedro V.
Published: October 2018

The determinant of the Jacobian matrix is frequently used in the Finite Element Method as a measure of mesh quality.

A new metric is defined, called the Standard Error, based on the distribution of the determinants of the Jacobian matrices of all elements of a finite element mesh. Where the Jacobian norm can be used to compare the quality of one element to another of the same type, the Standard Error compares the mesh quality of different versions of a finite element model where each version uses a different element type.

To motivate this new Standard Error, we investigate the geometric meaning of the Jacobian norm on 3D Finite Elements. This mesh quality metric is applied to 8, 20, and 27 node hexahedra, 6 and 15 node prisms, 4 and 10 node tetrahedra, 5 and 13 node pyramid, and 3, 4, 6, 8, and 9 node shell elements. The shape functions for these 14 element types, or more precisely their first partial derivatives, are used to construct the Jacobian Matrix. The matrix is normalized to compensate for size. The determinant of the Jacobian is calculated at Gaussian points within each element. Statistics are gathered to form the Standard Error of the mesh.

To illustrate the applicability of this a priori metric, we present two simple example problems having exact answers, and two industry-type problems, a pipe elbow with a crack and a magnetic resonance imaging (MRI) birdcage RF coil resonance, both having no analytical solution.

Significance and limitations of using this a priori metric to assess the accuracy of finite element simulations of different mesh designs are presented and discussed.
Use of Mini-CT Specimens for Fracture Toughness Characterization of Low Upper-Shelf Linde 80 Weld Before and After Irradiation
Authors: Sokolov Mikhail A.
Published: October 2018

Mini-CT specimens are becoming a highly popular geometry for use in reactor pressure vessel (RPV) community for direct measurement of fracture toughness in the transition region using the Master Curve methodology. In the present study, Mini-CT specimens were machined from previously tested Charpy specimens of the Midland low upper-shelf Linde 80 weld in both, unirradiated and irradiated conditions. The irradiated specimens have been characterized as part of a joint ORNL-EPRI-CRIEPI collaborative program. The Linde 80 weld was selected because it has been extensively characterized in the irradiated condition by conventional specimens, and because of the need to validate application of Mini-CT specimens for low upper-shelf materials — a more likely case for some irradiated materials of older generation RPVs. It is shown that the fracture toughness reference temperatures, To, derived from these Mini-CT specimens are in good agreement with To values previously recorded for this material in the unirradiated and irradiated conditions. However, this study indicates that in real practice it is highly advisable to use a much larger number of specimens than the minimum number prescribed in ASTM E1921.
Proposal of New Combination Criterion for Pipe With Circumferential Multiple Cracks Based on Ductile Failure Simulation
Authors: Lee Myeong-Woo , Hasegawa Kunio , Kim Yun-Jae
Published: October 2018

In this paper, the combination rule for circumferential multiple-cracked pipe assessment is investigated using finite element damage analysis. The FE damage analysis based on the stress-modified fracture strain model is validated against limited fracture test data of two circumferential surface cracked pipes. Then systematic parametric study is performed using FE damage analysis for symmetrical surface cracked pipes. Failure bending stresses are calculated using the combination rule and the net-section collapse load approach for single crack provided in ASME BPV Code. It is found that predicted failure bending stress using the combination rule might be non-conservative when the distance between two cracks is short. To overcome the problem, a new combination criterion based on crack dimensions is proposed and compared with numerical data.
Design and Optimization of High-Pressure Hydrogen Cylinders for Intermodal Container Transportation
Authors: Chen Jialei , Shi Jianfeng , Zhang Chuck
Published: October 2018

Hydrogen as a next generation energy carrier, is a clear and zero emission fuel with growing application in various fields. Intermodal transportation is an important issue for the safety and economic use of hydrogen fuel in distributed sites. Hydrogen is usually transported in high-pressure cylinders on trucks with bounded space. In this paper, we investigated different cylinder designs, packing strategies and their impact on the storage density, which is defined as the weight of hydrogen divided by the storage space, and then found out the optimal design and packing strategy. The high-pressure hydrogen gas was considered as real gas, and the stress distribution was analyzed for the 4130 steel cylinders based on the thick-wall cylinder model. Two different head designs of sphere and elliptical head were considered and discussed. A high storage density strategy with cylinder geometric parameter design, hydrogen gas pressure and cylinder packing methods were proposed. An exploration of the carbon fiber cylinder showed the potential of the composite material as a storage cylinder in high-pressure storage situations.
A Study on the Pressure-Temperature Limit Curve Under High Cooling Rate for the Reactor Using Finite Element Method
Authors: Choi Ye-Rin , Kim Min-Kyu , Kim Jae-Hee , Ryu Tae-Young , Yang Jun-Seog , Kim Moon Ki , Choi Jae-Boong
Published: October 2018

Demands for the safety of the Nuclear Power Plant (NPP) are increasing because of some accidents during decades. For the safety of the NPP, maintaining integrity of the reactor is one of the most important part. For the integrity evaluation of the Reactor Pressure Vessel (RPV), evaluation methods such as Upper Shelf Energy (USE), Pressurized Thermal Shock (PTS), and Pressure-Temperature (P-T) limit curve, etc. have been suggested by the ASME Code with consideration of neutron irradiation embrittlement. Among them, The P-T limit curve suggests limitations for the temperature and pressure during the operation of the RPV. The ASME Code Section XI Appendix G (Sec. XI App. G) suggests a method to generate P-T limit curves of the RPV [1]. There is restriction on the operation procedure; the cooling rate of the reactor is limited to 100 °F/hr or less and the available temperature range for the equations at the ASME Code is also limited to 100 °F/hr. However it is needed to cool down the reactor very fast at the severe accident condition to control the reactor to the stable condition and this sudden temperature drop can cause a thermal shock in the reactor. Therefore it is important to compensate the risk by accurately prepared P-T limit curve with high cooling rate for severe accidents in the NPP. In this study, researchers try to expand the limitation of the cooling rate for the P-T limit curve from 100 °F/hr to 200 °F/hr. Finite Element Analysis (FEA) for integrity evaluation and comparison of results using ASME Code equations were carried out.
Development of Burst Pressure Estimation Equations for Steam Generator Tubes With Multiple Axial Surface Crack
Authors: Kim Ji-Seok , Lee Myeong-Woo , Kim Jin-Weon , Kim Yun-Jae
Published: October 2018

In this paper, the burst pressure estimation equations for steam generator tubes with multiple axial surface cracks are proposed based on the local collapse load approach concept. The proposed equations are for a single axial surface crack, two collinear axial surface cracks and two non-aligned axial surface cracks. The proposed equations are validated against experimental tube burst test results and finite element damage analysis for twin cracks. Predicted burst pressures agree well with the experimental results and FE analysis results, suggesting validity of the proposed equations to estimate burst pressures for twin axial surface cracks.
FE Welding Residual Stress Analysis and Validation for Spent Nuclear Fuel Canisiters
Authors: Gim Jae-Min , Kim Ji-Soo , Kim Yun-Jae , Lam Poh-Sang
Published: October 2018

Spent Nuclear Fuel (SNF) Canisters are large welded stainless steel structures without post-weld heat treatment, possibly leaving large welding residual stresses (WRS). For CISCC assessments for SNF canisters, the estimation of the weld residual stress accurately is very important because tensile stress can make crack initiate. In this paper, the welding procedure for the SNF canisters is simulated through a FE analysis. Two-dimensional FE WRS analysis is performed for both longitudinal welding and circumferential welding. To simulate the welding procedure, heat analysis and stress analysis are conducted separately. The results are compared with the experimental mock-up canister WRS data conducted at the Sandia National Laboratories. It seems that FEA could sufficiently confirm the experimental data.
Application of Energy-Based Damage Model to Simulate Ductile Fracture Under Cyclic Loading and Validation Against Piping System Test Data
Authors: Youn Gyo-Geun , Nam Hyun-Suk , Kim Hune-Tae , Lee Jong-Min , Kim Yun-Jae
Published: October 2018

In this paper, a method to predict ductile fracture under low cyclic loading condition is proposed. Then it is compared with test results of surface cracked pipes which is conducted by Battelle Institute. A&F nonlinear kinematic hardening model is adopted to describe material behavior under cyclic loading condition and energy-based damage model is applied to simulate ductile crack growth. The energy-based damaged model is depending on multi-axial fracture strain energy. To apply this model, two parameters should be determined from tensile and C(T) test results under monotonic loading condition. One is multi-axial fracture strain energy Wf and the other is critical damage value ωc. From the determined damaged model, it is enable to simulate surface cracked pipe tests under low cyclic loading condition.
The Size Effect on J-R Curve for Construction Steels and its Prediction by Simplified Mechanical Model
Authors: Stratil Ludek , Siska Filip , Hadraba Hynek , Dlouhy Ivo
Published: October 2018

Evaluation of mechanical properties from a small amount of test material is essential in a process of development of new alloys and monitoring of degradation and damage of in-service components. Miniaturization of test specimen together with a specimen reconstitution technique enable direct method of evaluation of mechanical properties if only a limited amount of material is available. Modern types of construction steels and alloys possess improved metallurgical and mechanical properties and also demonstrate a high level of fracture toughness. In these cases, correlation and correction of size effect on fracture toughness between different specimen sizes are needed. Within this contribution the size effect of J-R curve for two sizes of three-point-bend specimens is solved. The J-R curves of three-point-bend specimens with cross-section 10 × 10 mm and 3 × 4 mm of P91 and Eurofer97 steel were determined at room temperature. The existence of size effect is proven as larger specimens demonstrate higher J-R curves than smaller specimens for both steels. Simplified mechanical model based on fracture energies initially proposed by Schindler et al. is applied to describe experimentally determined J-R curves and to predict the observed size effect between used specimen sizes.
Further Validation of the Strain-Life Weighted (SNW) Fen Method for Plant Realistic Strain and Temperature Waveforms
Authors: Currie Chris , Morley Andrew , Leary Daniel , Platts Norman , Twite Marius , Wright Keith
Published: October 2018

Environmentally assisted fatigue of nuclear plant materials in the Pressurised Water Reactor (PWR) coolant environment is a phenomenon that has been extensively studied over the past 30 years. Methods for accounting for the PWR environment in an ASME Section III fatigue assessment are presented in NUREG/CR-6909. The deleterious effect of environment is described through a Fen factor dependent upon strain rate, temperature and the dissolved oxygen content of the water. The formulae which describe the Fen are based upon correlations observed in test data, predominantly from tests conducted with constant temperature and strain rate (triangular or sawtooth loading). Actual loading histories encountered during service are far more complex, with both strain rate and temperature, and therefore Fen, varying through the cycle. NUREG/CR-6909 Draft Rev 1 recommends the Modified Rate Approach (MRA) to account for this type of loading.

There is a substantial and growing body of data for conditions in which the strain rate and/or temperature change within the load cycle, for which MRA does not generally perform well in describing the deleterious effect of environment in these complex waveform conditions. In particular, MRA does not predict the observed difference in life when the temperature is varied in-phase or out-of-phase within the strain waveform, or when the slow portion of the strain rate is moved from the top to the bottom of the waveform.

An alternative approach called the Strain-Life Weighted (SNW) Fen method was presented in PVP2017-66030 and additional validation testing was proposed.

This paper develops the SNW method further into a general approach for all stainless steels and presents additional new validation data, including a range of isothermal and non-isothermal plant realistic waveforms and a more extensive review of open literature data.

It is concluded that the SNW method offers a significant improvement in fatigue life prediction capability for plant realistic complex waveforms compared to MRA and provides residuals similar to that of standard waveform data. It is thus considered to be suitably validated to propose a code case for use in ASME Section III fatigue assessments.
Thermal Fatigue Evaluation Based on the Methods for Structural Stress Determination According to EN 13445-3 Annex NA: Comparison With Other Codes
Authors: Trieglaff Ralf , Beckert Martin , Rudolph Jürgen , Friers Daniel
Published: October 2018

The European Pressure Vessel Standard EN 13445 provides in its part 3 (Design) a simplified method (Clause 17) and a detailed method for fatigue assessment (Clause 18) of unwelded and welded components. Clause 18 “Detailed Assessment of Fatigue Life” is under principal revision within the framework of the European working group “CEN/TC 54/WG 53 – Design methods” in order to reach a significant increase in user-friendliness and a clear guideline for the application.

This paper is focused on the new recommendations for the thermal fatigue evaluation given in the new informative annex NA “Instructions for structural stress oriented finite element analyses using brick and shell elements”. In this annex NA different application methods for the determination of structural stresses are explained in connection with the requirements for finite element models and analyses.

This paper will give a short overview of the proposed approaches of structural stress determination in the new draft annex NA of the revised EN 13445-3 with special recommendations for thermal fatigue evaluation application. This constitutes an extension of the usual and established application of the structural stress approach for welds subjected to mechanical loading conditions. It will present the current state of the approaches based on the results of fatigue analyses according to EN 13445-3 Clause 18 for two different application examples. For validation purposes, these different approaches are compared with the results of Clause 17 of the EN 13445 and other pressure vessel design codes.
Effect of Autoclave Process Variables on Film Adhesive Bond With Polycarbonate Adherends
Authors: Jagatap Shraddha , Nassar Sayed A.
Published: October 2018

This study investigates the effect of autoclave curing process variables on the bond strength between film adhesive and polycarbonate adherends. Bond strength is measured in terms of the tensile shear load transfer capacity (LTC). Studied variables include cure temperature, cure pressure and their respective rates as well as the duration of cure time. Test coupons are made of two layers’ polycarbonate lexan adherends that are autoclave-bonded using aliphatic polyether film adhesive (Huntsman PE399). The relative significance of variables and variable combinations are investigated for their effect on the bond strength. Experimental test data shows interaction between autoclave variable cure temperature in combination with cure time, temp ramp rate and pressure ramp rate have significant effect on bond strength and failure mode.
Simplified LBB Guidance: Stage 1 — Development of a New Software Tool and Initial Scoping Calculations
Authors: Gill Peter , Sharples John , Aird Chris
Published: October 2018

This study is focussed on establishing more simplified Leak-before-Break (LbB) guidance for inclusion into Section III.11 of the R6 procedure. The approach adopted has involved the development of a universal software tool for LbB simplified assessments which can be used to perform initial scoping calculations to demonstrate typical LbB cases. It is envisaged that this simplified methodology will enable plant assessment engineers to be more informed on which sites on plant are likely to have LbB successfully applied and to be able to undertake LbB assessments in a more simplistic way than is currently available. Using the developed software tool, a range of LbB calculations for different cracks and loading conditions have been performed to provide guidance on where LbB is more likely to be applied on plant. Loading conditions include primary and secondary stresses, where through-wall changes have been accounted for. The pipe geometries included in this study have been defined by the inner radius and the wall thickness, calculated by minimum pipe thickness required according to meet the design rules of ASME III. The pipe inner radius varies from 40mm to 200mm (80mm to 400mm inner diameter (ID)). All pipe outer diameters are less than 0.5m. All cracks considered in this study are through-wall and circumferential. Pipe material properties are chosen to be broadly representative of an Austenitic Stainless Steel, where the fracture toughness varies from 100 to 180MPa√m and the yield stress is 150MPa.
The Role of Uncertainty in Machine Learning As an Element of Control for Material Systems and Structures
Authors: Elenchezhian Muthu Ram Prabhu , Raihan Md Rassel , Reifsnider Kenneth
Published: October 2018

Recurrent neural networks (RNN) have been used to interpret data in situations wherein our knowledge of the active physics is incomplete. The currency of these methods is the data that are generated by a physical system. Unfortunately, if we are uncertain about the physics of the system, we also do not know the level of uncertainty in the data that we use to represent it.

Typically, data provided to an RNN is provided by measurements of system state information, e.g., data that define speed, position, accelerations, configurations of system elements (like the flaps and elevators on an airplane) etc. But recently, data are being collected that indicate the state of the materials themselves that are used to construct the system. Material state may include the defect state of the materials such as the crack density and patterns in composite material in structural elements (obtained from health monitoring data).

In this paper, we address the question of teaching a control system (e.g., for testing equipment, aircraft control systems, health monitoring systems, etc.) to recognize composite material degradation during service and to adjust applied loads and fields as part of a control scheme to avoid failure of the material during service.

Topics will include defining a proper cost function for the above objectives, formulation of a ‘failure hypothesis’ as a regression function, and the quantification of uncertainty when the physics of the situation is not completely defined. Examples of machine learning techniques for a uniaxial fatigue loading of composite coupons with a circular hole are presented. Example models are random forest regression algorithms and artificial neural networks for linear regression.
Inter-Laboratory Results and Analyses of Mini-C(T) Specimen Testing of an Irradiated Linde 80 Weld Metal
Authors: Server William , Sokolov Mikhail , Yamamoto Masato , Carter Robert
Published: October 2018

An irradiated low-upper-shelf Linde 80 weld metal has been tested by four laboratories as part of an inter-laboratory assessment of use of the miniature compact tension [mini-C(T)] test specimen for Master Curve fracture toughness evaluation following ASTM E1921. The preliminary results from each of the laboratories have been compiled and evaluated together to assess the validity and use of the mini-C(T) specimen for an irradiated reactor pressure vessel material which can exhibit ductile crack growth at low temperatures relative to cleavage initiation fracture toughness. The preliminary results from this mini-C(T) testing can also be compared to extensive specimen test results from larger C(T) specimens of the same irradiated material. Comparisons of the results from each of the laboratories and some inter-laboratory differences in the fracture testing are assessed. The evaluations indicate reasonable agreement between the mini-C(T) and larger specimen results, but the selection of test temperature and the number of test specimens needed to obtain reliable results are more difficult when testing a low-upper-shelf toughness material.
Buckling Instability Analysis and Stiffeners Optimization Design for Large Vacuum Spherical Tanks
Authors: Xu Yongsheng , Deng Guide , Sun Liang , Yang Zhirong , Suo Hongchao
Published: October 2018

The main failure mode of a large vacuum spherical tank, subjected to uniformly external pressure, is buckling of thin shell. Taking a large vacuum spherical tank with volume of 18000m3 for research objects, the different calculation methods of buckling pressure between the ASME standard, analytic method and finite element method, were compared and analyzed. Using ANSYS software, the buckling pressure of stiffened spherical tanks were analyzed, and the optimum design of the thickness, height and quantity of stiffeners are studied. The results of analysis showed that the anti-instability ability of the large vacuum spherical tank can be improved significantly by a reasonable arrangement of stiffeners.
Effect of Chronological Order of Cyclic Loads With Different Amplitudes on Fatigue Crack Growth
Authors: Miura Naoki , Nagai Masaki
Published: October 2018

When cracked bodies are subjected to cyclic loading, fatigue crack growth evaluation is often required from the viewpoint of the assurance of fitness-for-service. For cyclic loading with constant amplitude, crack growth can be calculated by integrating a fatigue crack growth rate law provided by the Paris law in terms of stress intensity factor range. However, the cause of cyclic loading supposed in actual structures is not simple. For an example of LWR (Light Water Reactor) plants, a number of datasets of cyclic loading with different amplitudes is necessary for specific transient events. And the chronological order of individual transients cannot be determined. In this paper, a universal procedure to deal with multiple transients was developed in case that the chronological order of the transients was indefinite. Cyclic loading sequence such that the loadings were lined up in the order corresponding to larger amplitude gave the most conservative crack growth prediction among the possible sequences from the set of the specific transient events. Nevertheless the effect of the sequence was quite limited and the differences in fatigue crack growth were much less than the accuracy of the analysis outputs.
Fatigue Crack Growth for Ferritic Steel Under Negative Stress Ratio
Authors: Yamaguchi Yoshihito , Hasegawa Kunio , Li Yinsheng
Published: October 2018

Crack closure during fatigue crack growth is an important phenomenon for predicting fatigue crack growth amount. Many experimental data show that fatigue cracks close at not only negative loads but also positive loads during constant amplitude loading cycles, depending on applied stress levels.

The Appendix A-4300 in the ASME Code Section XI provides two equations of fatigue crack growth rates expressed by stress intensity factor range for ferritic steels under negative stress ratio. The boundary of two fatigue crack growth rates is classified by the magnitude of applied stress intensity factor range with the consideration of crack closure.

The objective of this paper is to investigate the influence of the magnitude of the stress intensity factor range on crack closure. Fatigue tests have been performed on ferritic steel specimens in air environment at room and high temperatures. Crack closures were obtained as a parameter of stress ratio. It was found that crack closure occurs at a smaller applied stress intensity factor range than the definition given by the Appendix A-4300.
Development of Crack Evaluation Models for Probabilistic Fracture Mechanics Analyses of Japanese Reactor Pressure Vessels
Authors: Lu Kai , Masaki Koichi , Katsuyama Jinya , Li Yinsheng
Published: October 2018

In Japan, a probabilistic fracture mechanics (PFM) analysis code PASCAL has been developed by Japan Atomic Energy Agency for structural integrity assessment of reactor pressure vessels (RPVs). The most recent release is PASCAL Version 4 (hereafter, PSACAL4) which can be used to evaluate the failure frequency of RPVs considering neutron irradiation embrittlement and pressurized thermal shock events. For the integrity assessment of RPVs, development of crack evaluation models is important. In this study, finite element analyses are performed firstly to verify the stress intensity factor calculations of cracks in PASCAL4. In addition, the applicability of the crack evaluation models in PASCAL4 such as the location of embedded cracks, crack shape and depth of surface cracks, and the increment of crack propagation is investigated. Based on sensitivity analyses of crack evaluation models for Japanese RPVs using PASCAL4, the effects of these evaluation models on failure frequency are clarified. From the analysis results, crack evaluation models recommended to the failure frequency evaluation for a Japanese model RPV are discussed.
Progress Report on Stress Intensity Factor and J-Integral Estimation for Nuclear Fuel Canisters Under Mechanical Loading
Authors: Kim Ji-Su , Gim Jae-Min , Kim Yun-Jae , Lam Poh-Sang
Published: October 2018

Due to the interaction of welding residual stress (WRS) and salt environment, cracks can be generated and grow in the Spent Nuclear Fuel (SNF) Canisters. In this paper, two fracture mechanics parameters, stress intensity factor and J-integral, for the canisters with axial cracks subjected to the mechanical loading are calculated by finite element analysis. The structural integrity assessment codes, API 579-1 and R6, are used to verify the procedure. For every external surface crack and through-wall crack, the stress intensity factor follows well the existing evaluation codes, API 579-1. The reference stress-based J-integral prediction of R6 procedure is the most accurate to use the tresca-based limit load as the reference stress.
Evaluation of Fracture Toughness CTOD Testing and its Standard Test Methods for SENB Specimens
Authors: Zhu Xian-Kui , McGaughy Tom
Published: October 2018

Crack-tip opening displacement (CTOD) is an important fracture mechanics parameter. Due to different definitions, existing CTOD test methods may determine different CTOD toughness for stationary and growing cracks even for a standard specimen, such as single edge notched bend (SENB) specimen. In the USA, ASTM 1820 uses the J-integral conversion method to determine CTOD, whereas in the UK, BS 7448 adopts the plastic hinge model to determine CTOD. In contrast, ISO 12135 uses the plastic hinge model to determine the initiation CTOD, but the J-conversion method to determine a CTOD-R curve. Thus, those standards may determine different CTOD values for the same material, leading to a long-time dispute. Recently, a double clip gage (DCG) method was used in the oil and gas industry to measure CTOD. As such, there are three typical CTOD test methods: plastic hinge model, J-conversion method, and DCG method.

To better understand those CTOD test methods for SENB specimens, the present paper first gives a brief review of CTOD standard test methods. This includes the CTOD definitions, plastic hinge model, J-conversion method, modified plastic hinge model, and DCG method, BS 7448, ASTM E1820, and ISO 12135. Those CTOD test methods are then evaluated using available test data for various ductile steels in literature. The experimental results of CTOD at fracture initiation and crack tearing are compared, and the differences are discussed.
Assessment Methods and Technical Challenges of Remaining Strength for Corrosion Defects in Pipelines
Authors: Zhu Xian-Kui
Published: October 2018

This paper presents a technical review of remaining strength assessment methods, major technical challenges and on-going progress for line pipes containing metal loss defects. A brief review is first given to burst prediction models for defect-free pipes, including the strength solutions and flow solutions of burst pressure and their experimental validations. Followed are more detailed review and evaluation of existing corrosion assessment methods, including three-generation models developed for low to high strength pipeline steels. Major challenges to improve the corrosion models are then discussed in regard to full-scale testing, numerical modeling, material failure criteria, constraint effects, and applications to real corrosion defects. Finally, on-going progress is presented for developing improved assessment models to predict more accurate remaining strength of corroded pipelines.
Two- and Three-Dimensional Weld Residual Stress Analysis of a Weld Overlay Mockup of a VVER Feedwater Nozzle Dissimilar Metal Weld
Authors: Ku Francis H. , McCracken Steven L.
Published: October 2018

Weld overlay (WOL) is a popular repair technique to mitigate stress corrosion cracking (SCC) in dissimilar metal weld (DMW) in U.S. pressurized water reactor (PWR) design. The WOL technique is being considered as a SCC mitigation technique for DMW in Russian water-water energetic reactor (WWER or VVER) design. A WOL mockup on a VVER super emergency feedwater nozzle DMW has been fabricated, which represents the first WOL on VVER with the goal to mitigate SCC and the first WOL in Czech Republic civilian nuclear power plants. This paper presents the two- and three-dimensional finite element analyses performed to assess the weld residual stresses in the WOL mockup. The analysis evaluates the stress distribution and changes in the DMW before and after the WOL application, as well as compares the results to established industry guidelines and comparable WOLs on U.S. PWR.
Limit Load Analysis of a Torispherical Head With Thermal Hot Spot Damage
Authors: Mehrizi Amir , Nakhodchi Soheil , Adibi-Asl Reza
Published: October 2018

Vessel dished heads are widely being used in storage tanks or pressure vessels. These heads are available in different shapes including hemispherical, ellipsoidal and torispherical heads. In this paper, pressure limit load of torispherical head with thermal hotspot damage is investigated. Thermal hotspots are one of the common types of in-service degradation in some pressurized components and can be considered as damage. This type of damage is usually caused by the loss of refractory lining on the inside wall of pressure components or due to a misdistribution of the flow within vessels containing catalysts. Hotspot damage potentially jeopardizes the integrity of the components [1]. In the current research, the impact of a thermal hotspot on the load carrying capacity of various shapes of torispherical heads is investigated using numerical simulation. Also, sensitivity analysis has been performed to investigate the effect of location of thermal hot spots and thickness in the torispherical heads, with and without thermal hot spot damage.
Parameter Study of a Thermal Analysis of a Bead-on-Plate Weld
Authors: Alexandratos Spyridon A. , Shi Lei , O’Dowd Noel P.
Published: October 2018

Failures in engineering components operating at high temperature often initiate in welded joints, particularly in the heat-affected zone (HAZ) adjacent to a weld. This is due to the inhomogenous microstructure of the weld and adjacent material due to the different thermal histories experienced during the weld cycle. It is therefore important to accurately predict the temperature distributions arising during welding and the subsequent effect on material microstructure. The NET TG1 bead-on-plate weld geometry is examined in this work. This geometry is a single weld bead laid on the surface of an AISI 316L austenite steel plate. Experimental data from the TG1 study are available to validate different weld simulation techniques. Here, a sensitivity study to the thermal properties is carried out and the influence on the HAZ temperatures and grain size is examined. The study shows that the conductivity and the specific heat capacity significantly affect the temperature prediction in the HAZ with a similar influence on predicted grain size following welding. Results are presented for a stainless steel (316L) and a martensitic steel (P91) plate.
Improvement of Target Flaw Sizes of CASS Pipe for PD Approval Using PFM Code Preface
Authors: Nishi Wataru , Hirota Takatoshi , Ochi Mayumi , Takagoshi Daiki , Hojo Kiminobu
Published: October 2018

In order to determine the target flaw depths for performance demonstration (PD) of nondestructive testing of cast austenitic stainless steel (CASS) pipes, probabilistic fracture mechanics (PFM) code, “PREFACE”, was developed to evaluate ductile fracture and plastic collapse considering change in mechanical properties due to thermal aging and uncertainties of the mechanical properties. In the previous study[1], the tables of the target flaw depths for the highest ferrite content material of the Japanese CASS pipes at the fully saturated thermal aging condition were calculated for several flaw lengths and several stress levels by the PREFACE code. However, the sensitivity study of the ferrite content on the target flaw depth revealed that the fully saturated thermal aging condition may not be the most severe condition for the target flaw depth. In this study, the PREFACE code was modified to improve the dependency of ferrite content on true stress-strain curve and to apply limit load method directly at the failure mode of plastic collapse. To confirm of the correct relation between ferrite content and aging time, deterministic sensitivity analyses were performed. For validation of the PFM function, the results of the deterministic analysis and PFM analysis were compared.
Stress and Distortion Simulation of Additive Manufacturing Process by High Performance Computing
Authors: Huang Hui , Chen Jian , Carlson Blair , Wang Hui-Ping , Crooker Paul , Frederick Gregory , Feng Zhili
Published: October 2018

Numerical simulation is an efficient way to better understand the thermal and mechanical evolution during metal additive manufacturing (AM) and to design and optimize the process. However, with today’s computational tools, pass-bypass thermal-mechanical numerical simulation of the metal AM process is extremely time-consuming. In this study, a new finite element code recently developed in house at Oak Ridge National Lab was used for additive manufacturing simulation. Our new code effectively utilizes GPU based high-performance computers to allow for realistic simulation of the transient thermal and mechanical response of materials during additive manufacturing. A benchmark study on a cylinder model by powder bed selective laser melting was carried out and distortion profile was compared to the experimental measurements. The accuracy and efficiency of the code was also demonstrated by analyzing a wire and arc additive manufacturing (WAAM) model which consists of a base plate and four deposited layers.
Limits of Applicability of the Notch Failure Assessment Diagram
Authors: Horn Anthony J. , Aird Chris
Published: October 2018

Structural integrity assessment codes such as R6 [1] and BS7910 [2] provide guidance on the assessment of flaws that are assumed to be infinitely sharp using the Failure Assessment Diagram (FAD). In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as those associated with lack of fusion, porosity or mechanical damage. Several Notch Failure Assessment Diagram (NFAD) methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. This paper uses mechanistic modelling to define the limits of applicability of the NFAD approach in terms of ρ/a, where ρ is the notch root radius and a is the notch depth. The work concludes that the NFAD can be used to assess notches with ρ/a values of up to unity.
A Local Approach to Assess Effects of Specimen Geometry on Cleavage Fracture Toughness in Reactor Pressure Vessel Steels
Authors: Sarzosa Diego F. B. , Savioli Rafael , Ruggieri Claudio , Jivkov Andrey , Beswick Jack
Published: October 2018

This work presents recent improvements in the micromechanical failure criterion based on the Weibull stress (σw) concept for prediction of cleavage fracture in ferritic steels. The model is applied in SE(B) specimens extracted from an ASTM A533 pressure vessel steel having different levels of stress triaxiality at the crack tip. Nonlinear 3D finite element models with dimensions matching the tested specimens were built to provide the necessary crack tip stresses at the fracture process zone for calculation of the σw-J evolution from wich the variation of characteristic toughness values (J0) between different cracked geometries can be estimated. Application of this methodology for the material used at this study is able to predict J0 for SE(B) specimens with very shallow crack size ratio a/W = 0.05, short crack a/W = 0.2 and deep crack a/W = 0.4. The reported fracture toughness values for specimens having very shallow crack size ratio is an additional contribution of this study.
Optimization of Curing Conditions and Nanofiller Incorporation for Production of High Performance Laminated Kevlar/Epoxy Nanocomposites
Authors: I. Mourad Abdel-Hamid , Al Mansoori Mouza S. , Al Marzooqi Lamia A. , Genena Farah A. , Cherupurakal Nizamudeen
Published: October 2018

Kevlar composite materials are getting scientific interest in repairing of oil and gas pipelines in both offshore and onshore due to their unique properties. Curing is one of the major factor in deciding the final mechanical performance of laminated Kevlar/epoxy nanocomposites. The parameters such as curing time, temperature and applied pressure during the hot pressing will affect chemistry of crosslinking of the epoxy matrix and interaction of epoxy with the Kevlar fiber. The present study is carried out to evaluate the optimal curing conditions of the Kevlar/epoxy nanocomposites. Three different nanofillers (namely Multi walled Carbon nanotubes (MWCNT), Silicon Carbide (SiC) and Aluminum Oxide (Al2O3)) are incorporated in different weight percentage. Differential Scanning Calorimetry (DSC) and Thermo-Gravimetric Analysis (TGA) tests are carried out to determine the thermal stability and optimal curing conditions. Mechanical performance is investigated by conducting flexure, and drop weight tests. The results show that, the optimal curing temperature for maximizing the mechanical properties is at 170°C. Peeling off the Kevlar layers are observed for nanocomposite samples cured under 100°C. Mechanical strength of the composites is enhanced by optimizing the curing conditions and nanofiller contents.
Leak Before Break Fracture Assessment for X70 Steel Pressurized Tubes With Axial Surface Crack
Authors: El-Sayed Mohamed , El Domiaty Aly , I. Mourad Abdel-Hamid , Lotfy Mohamed
Published: October 2018

In oil and gas pipelines, cracks can initiate from regions of high stress concentration or from defects due to either manufacturing or corrosion or both. The cracks under service may grow due to applied load and form stable through-thickness cracks causing leak prior to catastrophic failure. If this leak-before-break (LBB) takes place, then there is a possibility of preventing catastrophic failure. Therefore, LBB analysis is an important requirement for the safe design and re-assessment of pipelines life. This paper presents a simplified approach for the failure assessment utilizing LBB concept of pressurized pipes having an axial crack.
Structural Capacities of Flanged Joints
Authors: Kirkemo Finn
Published: October 2018

Flanged joints are used in high pressure applications such as process piping, pressure vessels, risers, pipelines and subsea production systems. These flanges are subjected to external loads in addition to pressure. A brief description of high pressure flanges standards is given. Design of high pressure flanged joints are covered in many design codes. A review of allowable stresses, load factors for bolting, flanges and bolt preload requirements has been made for the following codes: ASME VIII-2, ASME VIII-3, ASME B31.3 Chapter IX, API 6A, API 6X, API 17D, API 17TR7, API 17TR8, API 17G, EN 1591-1 and NORSOK U-001. This paper also presents analytically based structural load-capacity (ultimate strength) design equations for flanged joints. The design equations are used to calculate rated working pressure and flange-face separation load-capacity of API 6A type 6BX flanges. Future code recommendations for flange design are provided.