bluuebunny/crossref_metadata_2025 huggingface dataset:
Creep-Fatigue Damage Evaluation of Grade 91 Steel Using Interrupt Creep Fatigue Test
Authors: Ro Uijeong , Kim Jeong Hwan , Lee Hoomin , Kang Seok Jun , Kim Moon Ki
Published: October 2018

The Sodium Fast-cooled Reactor (SFR), are generation IV nuclear power plants, have a target operating temperature of 550°C which makes creep-fatigue behavior more critical than a generation III nuclear power plants. So it is important to understand the nature of creep-fatigue behavior of the piping material, Grade 91 steel. The creep-fatigue damage diagram of Grade 91 steel used in ASME-NH was derived using a conventional time-fraction testing method which was originally developed for type 300 stainless steels. Multiple studies indicate that the creep-fatigue damage diagram of Grade 91 steel developed using this testing method has excessive conservatism in it. Therefore, an alternative testing method was suggested by separating creep and fatigue using interrupted creep tests. The suggested method makes it possible to control creep life consumption freely which was difficult with the previous method. It also makes it easier to observe the interaction between creep and fatigue mechanisms and microstructural evolution. In conclusion, an alternative creep-fatigue damage diagram for Grade 91 steel at 550°C was developed using an interrupt creep fatigue testing method and FE model simulation.
Experiences in Developing a Practical Algorithm of Identification and Attenuation of Pressure Pulsation and Piping Vibration in Gas Reciprocating Compressor Plants and Other Systems
Authors: Rydlewicz Maciej , Rydlewicz Wojciech
Published: October 2018

This paper presents results of research on practical engineering solutions to suppress pressure pulsation and mechanical vibrations in piping systems. It concerns both new build and retrofitted plants. Analyses were performed according to ASME B31, EN-13480 and API 618 codes. Solutions were considered for natural gas reciprocating compressor stations (gaseous media) and liquid hydrocarbons plant with various pumps.

Pressure pulsation in a piping system is a source of dynamic forces. Unbalanced pressure layout in the piping system results in the presence of dynamic forces that may excite mechanical vibrations [1,7, 22, 23, 24].

In industrial applications, mechanical vibrations are present mostly in resonant conditions. Since hundreds of eigenvalues can characterise the piping system, it is crucial to identify the key ones, which are likely to be excited to vibrate. Therefore, it is necessary to allow adequate modelling and subsequent analysis of the fluid-structure interaction with available engineering tools.
Moving Liquid Column With Entrapped Gas Pocket and Fluid-Structure Interaction at a Pipe’s Dead End: A Nonlinear Spring-Mass System
Authors: Tijsseling Arris S. , Hou Qingzhi , Bozkuş Zafer
Published: October 2018

Moving liquid columns and entrapped gas pockets are basic ingredients in the industrial processes of starting flow and pipe filling. Within limits, the liquid columns can be modeled as masses and the gas pockets as springs. Such a simple model already gives useful estimates of maximum pressures and temperatures in the gas pockets. Herein we consider a gas pocket located at a closed pipe end which is being compressed by a liquid column. In particular the situation is considered where the mass-stiffness ratios of the liquid-gas system and the vibrating dead end are of the same order of magnitude, so that fluid-structure interaction must be taken into account. This leads to interesting nonlinear behavior of the twofold spring-mass model representing the system. Any acoustic effects (wave propagation) are ignored. The study aims at finding dimensionless dynamic load factors and vibration frequencies in pipe systems filled with liquid and gas.
Study on Flow Induced Vibration Analysis and Evaluation for Heat Transfer Tube of Steam Generator
Authors: Huang Xuan , Qi Huan-Huan , Cai Feng-Chun , Feng Zhi-Peng , Liu Shuai
Published: October 2018

The heat transfer tube of steam generator is an important part of the primary loop boundary, the integrity is crucial to the safe operation of the whole reactor system; the flow induced vibration is one of the main factors leading to the failure of heat transfer tube in steam generator. Both ASME and RG1.20 have made a clear requirement for the analysis and evaluation of the flow induced vibration of steam generator. The flow induced vibration of heat transfer tube in two-phase flow is the difficult and important content in the analysis. In this paper, the finite element model of heat transfer tube is established and the modal analysis is carried out. Then in order to evaluate the influence of two-phase flow in the secondary side and support boundary constraint, the analytical results are compared with the natural frequencies of the heat transfer tube measured in the two-phase flow test. On the basis of accurate simulation of the dynamic characteristics of heat transfer tube in two-phase flow, the paper calculate the turbulent excitation response and the fluidelastic instability ratio aiming at the main mechanism causing the flow induced vibration of heat transfer tube in two-phase flow. Firstly, the modified PSD of turbulent excitation is proposed on the foundation of root mean square displacement amplitude of heat transfer tube measured in two-phase flow test. The calculation result of the amplitude of heat transfer tube with different void fraction can envelope the test result by using the modified PSD as input, and the safety margin is reasonable. Then we also verify whether the analysis conclusion of fluidelastic instability is in agreement with the test. Finally, the analytical technique is applied to the analysis of flow induced vibration of steam generator to verify the design of structure. The paper studies on flow induced vibration analysis and evaluation a heat transfer tube of steam generator in two-phase flow. The analysis program of flow induced vibration on the basis of the test results. The investigation can be used for the risk prediction and evaluation of flow induced vibration of heat transfer tube in two-phase flow, solve the technical difficulties of flow induced vibration analysis in two-phase flow, and provide the technical support for the flow induced vibration analysis of steam generator.
Bolted Flange Joint Made of Glass Fibre Reinforced Polymer (GFRP) for Oil and Gas Pipelines
Authors: Aljuboury Muhsin , Rizvi Md Jahir , Grove Stephen , Cullen Richard
Published: October 2018

The objective of this work is an experimental and numerical investigation for a bol Richard Cullen ted composite flange connection for composite pipes, which are used in the oil and gas applications, and obtain a joint with high strength and high corrosion resistance. For the experimental part, we have designed and manufactured the required mould, which ensures the quality of the composite materials and controls its surface grade. Based on the ASME Boiler and Pressure Vessel Code, Section X, this GFRP flange has been fabricated using biaxial glass fibre braid and polyester resin in a vacuum infusion process. Numerically, an investigation is carried out using 3D finite element analysis (FEA) of a bolted GFRP flange joint including flange, pipe, gasket and bolts. This model has taken into account the orthotropy of the GFRP material and the non-linear behaviour of the rubber gasket material for both the loading and non-loading conditions. Furthermore, the leakage propagation between the flange and the gasket has also been simulated in this investigation by using the pressure-penetration criteria PPNC in ANSYS. Finally, the flange has been tested under the internal pressure and the agreement between the experimental and numerical results is excellent.
Modeling Hypervelocity Impacts Using Smoothed Particle Hydrodynamics
Authors: Ganser M. , van der Linden B. , Giannopapa C. G.
Published: October 2018

Hypervelocity impacts occur in outer space where debris and micrometeorites with a velocity of 2 km/s endanger spacecraft and satellites. A proper shield design, e.g. a laminated structure, is necessary to increase the protection capabilities. High velocities result in massive damages. The resulting large deformations can hardly be tackled with mesh based discretization methods. Smoothed Particle Hydrodynamics (SPH), a Lagrangian meshless scheme, can resolve large topological changes whereas it still follows the continuous formulation. Derived by variational principles, SPH is able to capture large density fluctuations associated with hypervelocity impacts correctly. Although the impact region is locally limited, a much bigger domain has to be discretized because of strong outgoing pressure waves. A truncation of the computational domain is preferable to save computational power, but this leads to artificial reflections which influence the real physics. In this paper, hypervelocity impact (HVI) is modelled by means of basic conservation assumptions leading to the Euler equations of fluid dynamics accompanied by the Mie-Grueneisen equation of state. The newly developed simulation tool SPHlab presented in this work utilizes the discretization method smoothed particle hydrodynamics (SPH) to capture large deformations. The model is validated through a number of test cases. Different approaches are presented for non-reflecting boundaries in order to tackle artificial reflections on a computational truncated domain. To simulate an HVI, the leading continuous equations are derived and the simulation tool SPHlab is developed. The method of characteristics allows to define proper boundary fluxes by removing the inwards travelling information. One- and two-dimensional model problems are examined which show excellent absorption behaviour. An hypervelocity impact into a laminated shield is simulated and analysed and a simple damage model is introduced to model a spallation failure mode.
Standards-Based Technologies for Exchanging Fatigue Test Data
Authors: Austin Tim , Lin Lianshan , Métais Thomas
Published: October 2018

Fatigue testing campaigns are a common feature in the design and operation of advanced engineering systems in the aerospace and power generation sectors. The resulting data are typically of a high inherent technical and financial value. Presently, these data are typically transferred between departments and companies by way of ad-hoc solutions reliant on obsolete or proprietary technologies, including CSV files, MS Excel® files, and PDFs. In these circumstances there is significant potential for data loss, inconsistency, and error. To address these shortcomings, there is a need for a systematic means of transferring data between different digital systems. With this in mind, a series of CEN Workshops on engineering materials data have taken place with a view to developing technologies for representing and exchanging engineering materials data. Most recently, a CEN Workshop on the topic of fatigue test data has delivered data formats derived from the ISO 12106 standard for axial strain-controlled fatigue testing. This paper describes the methodology for developing the data formats and demonstrates their use in the scope of the INCEFA-PLUS project on increasing safety in nuclear power plants by covering gaps in environmental fatigue assessment.
J-R Curve Prediction of Pre-Strained Stainless Steel 316 Material Using FE Damage Analysis Method
Authors: Seo Jun-Min , Kim Ji-Soo , Kim Yun-Jae
Published: October 2018

In this study, a method to predict J-R curve of SUS316 material using FE damage analysis is proposed. As experimental data, tensile and fracture toughness test results of cold worked SUS316 are used. The damage model used in this study is multi-axial fracture strain model and the model is determined by simulating the tensile and fracture toughness test according to the procedure in R6 code [1]. A pre-strain constant is newly introduced to consider pre-strain damage caused by the pre-strain, and the damage for various degrees of pre-strain are calculated. As a result, the predicted J-R curves using FE damage model show good agreement with the experimental data.
Limit Strains of X70 Pipes With a Semi-Elliptical Crack Based on Initiation and Ductile Tearing Criteria
Authors: Kang Ju-Yeon , Jang Youn-Young , Huh Nam-Su , Kim Ki-Seok , Cho Woo-Yeon
Published: October 2018

Crack-tip opening displacement (CTOD) and J-integral have been used for elastic-plastic fracture parameters as a crack driving force (CDF) and crack resistance curve to evaluate tensile strain capacity (TSC) of cracked pipelines based on strain-based design (SBD). The TSC can be determined by using two kinds of failure criteria. One is based on the limit state corresponding to an onset of stable crack growth and the other is tangency approach which determines an onset of unstable crack growth by comparing crack driving force and resistance curve. For this reason, the accurate calculation of crack driving force and crack resistance curve is highly required to determine TSC.

In the present study, the TSCs for X70 pipelines with a circumferential semi-elliptical surface crack were estimated based on both crack initiation and ductile tearing criteria using crack driving force diagram (CDFD) method. The CDF curves of cracked pipelines were calculated through the detailed elastic-plastic finite element (FE) analyses. Crack resistance curves were obtained from experimental data of single edged notch tension (SENT) specimens. Both the CDF and crack resistance curves were represented using CTOD and J-integral, respectively. As for loading conditions, axial strain and internal pressure were considered. The TSCs based on CTOD were compared with those based on J-integral to investigate the effect of choice of the fracture parameters on TSC. From the FE results, the TSCs based on ductile tearing allowed higher TSCs than those based on crack initiation. Although there were some differences between the TSCs using CTOD and J-integral, the effect of choice of fracture parameter on TSC with internal pressure was not significant.
Applicability of Nonlinear Kinematic Hardening Models to Low Cycle Fatigue Simulation of C(T) Specimen
Authors: Kim Hune-Tae , Youn Gyo-Geun , Lee Jong-Min , Kim Yun-Jae , Kim Jin-Weon
Published: October 2018

To perform low cycle fatigue analysis on nuclear structural materials under cyclic loading, cyclic hardening rules should be determined. In this study, the determination of linear and nonlinear kinematic hardening model parameters based on limited material test data is proposed. Chaboche model parameters are determined from hysteresis loops for the purpose of comparison. Simulation of cyclic C(T) test is performed using the hardening models. In cyclic C(T) test, SA508 Gr.1a low alloy steel and SA312 TP316L stainless steel were taken and incremental loading sequence was adopted. In the loading sequence, displacement control was used for loading steps and load control was applied for unloading steps to maintain constant load ratio. A constant displacement increment was applied after each cycle. The simulation results using A&F model and Chaboche model are compared to verify the applicability of A&F model.
Experimental Study on Characteristics of Condensation and Flow Resistance Inside Horizontal Corrugated Low Finned Tubes
Authors: Ren Bin , Tang Xiaoying , Lu Hongliang , Fu Dongliang , Du Yannan , Wang Shaojun , Song Pan , Ding Ju
Published: October 2018

It is the simplest and most feasible method to enhance heat transfer by replacing the smooth tube with various kinds of special-shaped enhanced tubes. In this paper, the characteristics of condensation and flow resistance inside horizontal corrugated low finned tubes were studied experimentally. The effects of steam inlet conditions and condensation tubes structural parameters were analyzed. The results showed that the heat transfer performance inside corrugated low finned tubes was greater than that inside smooth tubes. Like inside smooth tubes, the heat transfer coefficients increased with the vapor quality and steam mass flux. But the enhancement rate showed the opposite trend. And the heat transfer coefficients inside corrugated low finned tubes increased with the decrease of pitch and increase of protrusion height. Meanwhile, the variation trend of pressure drop gradient changing with inlet conditions and construal parameters was consistent with trend of heat transfer coefficient. The performance evaluation criteria were used to evaluate the comprehensive performance. It was found that the maximum performance evaluation factor was acquired at the minimum vapor quality and mass flux. The maximum value was 2.24 happened in the tube with pitch of 6 mm and height of 0.7mm. Finally, both the correlation for heat transfer coefficient and correlation for pressure drop gradient were developed by fitting experimental data. And this would provide calculation foundations for the design of horizontal condensers with corrugated low finned tubes.
Influence of Hydrogen and Oxygen Impurity Content in a Natural Gas / Hydrogen Blend on the Toughness of an API X70 Steel
Authors: Briottet Laurent , Ez-Zaki Hamza
Published: October 2018

The European Union is intending to reduce their carbon emissions by up to 80–95% by 2050. This will imply the increase of electricity coming from variable renewable energy sources. Producing hydrogen from this electricity is one way to facilitate the integration of such intermittent sources. Currently, there is no consensus in the world on the allowed amount of hydrogen in the natural gas with the aim to use the natural gas existing transportation grid to transport such mixture. The object of the present study is to provide additional experimental data concerning the effect of the hydrogen content in a N2/H2 mixture on the toughness of an API X70 steel dedicated to gas transport. The toughness has been measured in terms of Crack Tip Opening Displacement under a total pressure of 85 bar. The mechanical results are compared to existing results. It is confirmed that 1% H2 induces a significant decrease of the material toughness. Moreover, the content of O2 impurity in the N2/H2 mixture has been considered and its effect on HE mitigation has been quantified for an O2 content ranging between 10 vol. ppm and 100 vol. ppm. Finally, several approaches to take into account the effect of H2 in the NG/H2 blend on the design or on the service life of gas pipelines will be discussed.
Numerical Investigations on the Interaction of Cracks in Quasi-Laminar Crack Fields
Authors: Swacek Christian , Schuler Xaver , Seidenfuss Michael
Published: October 2018

Non-destructive testing measurements in the Belgian nuclear power plants Doel 3 and Tihange 2 revealed a high quantity of indications in the upper and lower core shells of the reactor pressure vessels. The most likely explanation is that the indications are hydrogen flakes positioned in segregated zones of the base material of the pressure vessel. These hydrogen flakes have a laminar and quasi-laminar orientation to the pressure retaining surface. Under mechanical loading the crack tips undergo predominantly mixed mode loading conditions, where the induced stress and strain fields of the single crack tips influence each other. Due to these specific loading conditions, the assumptions for classical standardized fracture mechanical methods are not met. Currently, there is no verified concept for the evaluation of such kind of crack fields.

Therefore the mechanical behavior of components with laminar crack fields and the interaction of cracks in such crack fields are investigated in an ongoing research project. Relevant parameters to describe crack fields in terms of crack size, crack location and crack orientation are derived from literature and own nondestructive measurements. Damage mechanical approaches are used in finite element calculations to investigate the interaction of cracks. Advanced damage mechanical models will be used to investigate crack initiation, crack growth and coalescence of cracks in crack fields. According to the results, representative parameters for crack fields will be derived and critical crack formations determined. The results will be evaluated and compared with state of the art approaches and standards.
2018 RCC-MRx Code Edition: Context, Overview, On-Going Developments
Authors: Pétesch Cécile , Lebarbé Thierry , Gelineau Odile , Vallot Damien , Blat-Yrieix Martine
Published: October 2018

The 2018 edition of the RCC-MRx Code (1) will be issued, by the end of the 2018, in French and English versions by AFCEN (Association Française pour les règles de Conception et de Construction des Matériels des Chaudières Electro-nucléaires). This Code set up rules applicable to research reactor components (coming from the RCC-MX 2008 developed in the context of the Jules Horowitz Reactor project), to reactor components operating at high temperature (coming from the RCC-MR 2007) and to the Vacuum Vessel of ITER (also coming from the RCC-MR 2007).

This edition takes the benefits of an important feedback of the users, such as Jules Horowitz Reactor or ASTRID project, but also from ITER and MYRRHA projects.

In parallel, in compliance with the EC’s objectives and its own policy of openness, AFCEN proposes to make its codes evolve, taking into account the needs and expectations of European stakeholders (operators, designers, constructors, suppliers ...) through a workshop called CEN Workshop 64 phase 2. The end of the workshop, planned for 2018, will allow to integrate recommendations issued from this work in the code.

This paper gives an overview of the performed work and also identifies the work to be done for a development of a standard such as RCC-MRx code.
Prediction of Elbow Flow Dynamics Using Correlated Wall Pressure Data
Authors: Baramili André , Chatellier Ludovic , David Laurent , Ancian Loïc
Published: October 2018

The present study focuses on the analysis of the flow-induced vibration phenomenon typically encountered on piping systems containing an elbow. The correlation between the turbulent flow through the elbow and the dynamic forcing it yields on the piping walls was assessed experimentally. A closed water loop containing a transparent elbow was designed in order to develop fully turbulent duct flow condition. Particle Image Velocimetry (PIV) was applied in the transparent zone in order to provide unsteady data on the flow dynamics through the elbow; simultaneously, wall pressure fluctuations were measured on and around the elbow. Several flow configurations were tested in order to obtain a large coupled database linking the flow features to the resulting dynamic excitation on the walls. Finally, Partial Least Square Regression (PLSR) was applied in order to harvest the correlated information contained in multiple pressure signals at multiple time-delays and build a relationship capable of estimating the temporal evolution of the velocity field using a set of measured wall pressure signals.
Analysis of a Weld Overlay to Address Fatigue Cracking in a Stainless Steel Nozzle
Authors: Marlette S. E. , Udyawar A. , Broussard J.
Published: October 2018

For several decades the nuclear industry has used structural weld overlays (SWOL) to repair and mitigate cracking within pressurized water reactor (PWR) components such as nozzles, pipes and elbows. There are two known primary mechanisms that have led to cracking within PWR components. One source of cracking has been primary water stress corrosion cracking (PWSCC). Numerous SWOL repairs and mitigations were installed in the early 2000s to address PWSCC in components such as pressurizer nozzles. However, nearly all of the likely candidate components for SWOL repairs have now been addressed in the industry. The other cause for cracking has been by fatigue, which usually results from thermal cycling events such as leakage caused by a faulty valve close to the component. The PWR components of most concern for fatigue cracking are mainly stainless steel. Thus, ASME Section XI Code Case N-504-4 would be a likely basis for SWOL repairs of these components, although this Code Case was originally drafted to address stress corrosion cracking (SCC) in boiling water reactors (BWR). N-504-4 includes the requirements for the SWOL design and subsequent analyses to establish the design life for the overlay based on predicted crack growth after the repair.

This paper presents analysis work performed using Code Case N-504-4 to establish the design life of a SWOL repair applied to a boron injection tank (BIT) line nozzle attached to the cold leg of an operating PWR. The overlay was applied to the nozzle to address flaws found within the stainless steel base metal during inservice examination. Analyses were performed to calculate the residual stresses resulting from the original fabrication and the subsequent SWOL repair. In addition, post-SWOL operating stresses were calculated to demonstrate that the overlay does not invalidate the ASME Section III design basis for the nozzle and attached pipe. The operating and residual stresses were also used for input to a fatigue crack growth (FCG) analysis in order to establish the design life of the overlay. Lastly, the weld shrinkage from the application of overlay was evaluated for potential impact on the attached piping, restraints and valves within the BIT line. The combined analyses of the installed SWOL provide a basis for continued operation for the remaining life of the plant.
Imaging Hydrogen in Stainless Steel Alloys by Kelvin Probe Force Microscopy
Authors: McNamara J. D. , Duncan A. J. , Morgan M. J. , Korinko P. S.
Published: October 2018

Kelvin probe force microscopy (KPFM) was used to image austenitic stainless steel (SS) samples (Type 304L) fabricated by the laser engineered net shaping (LENS®) process. The samples were hydrogen charged (H-charged) and subsequently cut and polished. The surface contact potential difference (CPD) of the samples was measured using the KPFM technique, a form of atomic force microscopy. A set of uncharged samples was also studied for reference and changes in the CPD were on the noise level. For H-charged samples fabricated by the LENS® process, the resulting surface potential images show a change in CPD of about 10 – 20mV around cell-like boundaries (5–10 μm in size) and grain boundaries (50–100 μm in size). The significant change in the CPD is affected by variation of the local work function, which indicates the presence of hydrogen. The elemental composition of the LENS® samples was studied using energy dispersive spectroscopy (EDS) which showed an increase in the atomic percentage of Cr and a decrease in Ni around the cell-like boundaries. The existence of intercellular ferrite on the sub-grain boundaries may explain the propensity of hydrogen to segregate around these regions. The finer grain structure of LENS® samples compared to that of forged or welded samples suggests that the hydrogen can be dispersed differently throughout this material than in traditionally forged austenitic SS. This study is conducted to elucidate the behavior of hydrogen with respect to the microstructure of additively manufactured stainless steel alloys.
Influence of Hydrogen on Tensile and Fatigue Life Properties of 304/308 Austenitic Stainless Steel Butt Welded Joints
Authors: Okazaki Saburo , Matsunaga Hisao , Nakamura Masami , Hamada Shigeru , Matsuoka Saburo
Published: October 2018

To investigate the influence of hydrogen on the tensile and fatigue life properties of welded joints of 304/308 austenitic stainless steels, slow strain rate tensile (SSRT) tests and fatigue life tests were conducted in laboratory air using hydrogen exposed specimens. The specimens were fabricated from welded plates, and to elucidate the role of weld structure on hydrogen-induced degradation, the welded joint was solution-treated. In the SSRT tests of the as-welded (AW) joint, a non-exposed specimen failed at the base metal (BM), whereas a hydrogen-exposed specimen failed near the weld toe. In the case of the solution-treated-welded (STW) joint, the non-exposed specimen failed at the part of solution treated weld metal, whereas an H-exposed specimen failed near the weld toe. As a result, internal hydrogen significantly degraded the elongation of the AW joint.

In the fatigue test, all the specimens failed near the weld toe. Internal hydrogen degraded the fatigue life considerably. However, the pre-charging led to little, if any, reduction in the fatigue limit. Similarly to the AW joint, hydrogen gas exposure notably degraded the fatigue life of the STW joint and led to little reduction in the fatigue limit. To investigate the relationship between the hydrogen-induced degradation and strain-induced martensitic transformation during fatigue testing, the volume fraction of ferrite in the broken specimens was measured by a ferrite scope. The volume fraction of martensitic transformation increased with an increase in the stress amplitude. These experimental results implied that the hydrogen-induced fatigue life degradation in the welded joint was closely related to the martensitic transformation during the fatigue process. The mechanisms of both the degradation in fatigue life and nondegradation in fatigue limit will be discussed further.
Determination of Safety Factors for Repair of Buried Nuclear Safety Related Metallic Pipe Using Carbon Fiber Reinforced Polymer
Authors: Marohl Michael P. H. , Ojdrovic Rasko
Published: October 2018

Buried piping is subject to unique environmental exposure, loading, and restricted access once put into service. Buried piping is susceptible to various corrosion mechanisms on the outside of the pipe as well as internal corrosion mechanisms similar to other aboveground piping. Inspection, repair and replacement of buried piping to address such issues are inherently difficult and costly due to the access issues. To address such difficulties and avoid excavation, a carbon fiber reinforced polymer (CFRP) repair can be applied to the internal diameter of a buried pipe to provide a structural pressure boundary to strengthen or replace the existing piping over a specified length.

Pipe repairs using CFRP have traditionally been designed using a Load and Resistance Factor Design (LRFD) approach for determining the demand and the strength of the repair. However, inclusion of CFRP design rules into allowable stress design (ASD) based Section XI of the ASME Boiler and Pressure Vessel Code, which has not adopted LRFD, requires use of safety factors applied to the strength for the appropriate design rules. Both ASD and LRFD have the same philosophy that the stress from the applied loads must be less than the material strength by a certain factor, and the basic difference between the two approaches is how to determine the appropriate factor of safety to cover all unknown variations in load, material strength, installation, and other.

This paper provides a basis for development of safety factors for design of CFRP repairs of nuclear safety related buried metallic piping to meet the required maximum acceptable probability of failure and reliability in accordance with NEI 96-07.
Analyzing Accuracy, Repeatability, and Overall Performance of Torque Tools and Patterns on Multiple Flange Geometries
Authors: Hamilton Scott , Mahoney Dan , Wright Jason
Published: October 2018

Many different variables need to be considered when a bolted flange is to be assembled. Past research on this topic has focused on nut factors, bolting patterns, gaskets, etc. However, there has been little research on the performance of torque as an assembly method.

The performance of various powered and manual torque wrenches is investigated, including accuracy (achieved bolt load versus target bolt load), repeatability (variation in achieved bolt load), and time to assemble. This study compared performance of seventeen different tools including pneumatic, hydraulic, and manual torque wrenches, across four different flange size/rating combinations utilizing two assembly method (Legacy Star and Modified Legacy Star).

This paper builds on the work described in PVP2017-65800 Determining Accuracy and Repeatability of Torque through Powered Equipment. A larger number of flange assemblies were performed compared to the PVP2017-65800 work, using a greater number of tools and flange configurations.

The results of the tests are provided and the implications of the findings discussed, including consideration of tool selection, assembly pattern selection, personnel competence and training, and bolted flange joint component selection and inspection.
Derivation of Transverse Tensile Properties of Alloy 690 Steam Generator Tubes Using Ring-Tensile Specimen and Finite Element Analysis
Authors: Kim Jongmin , Kim Minchul
Published: October 2018

Transverse tensile properties of the Alloy 690 steam generator tube used in Korean PWR(pressurized water reactor) nuclear power plant is one of the main properties to analyze creep rupture caused by the hoop stress in the severe accident conditions. Transverse tensile properties of steam generator tubes cannot be obtained directly machined from the tubes and it is also difficult to make miniaturized flat tensile specimens due to their geometry limitations. The ring-tensile specimens are widely used to measure the tensile properties in the circumferential direction, but membrane and bending stresses are mixed in the ring-tensile specimen during the test due to the shape of ring-tensile specimens. Therefore, obtaining the transverse tensile properties need the inverse analysis using finite element analysis and optimization process. In this study, ring-tensile tests were carried out using 3-piece loading mandrel. The stress-strain curve of ring-tensile specimen in transverse direction is derived by comparing the load-displacement curves of the finite element analysis with those of test. The load-displacement curves from tests agree well with the finite element results. Use of finite element analysis and optimization process as used in this work is effective to predict the transverse tensile properties of ring-tensile specimen.
Orientation Dependence of Hydrogen Accelerated Fatigue Crack Growth Rates in Pipeline Steels
Authors: Song Eun Ju , Ronevich Joseph A.
Published: October 2018

One of the most efficient methods for supplying gaseous hydrogen long distances is by using steel pipelines. However, steel pipelines exhibit accelerated fatigue crack growth rates in gaseous hydrogen relative to air. Despite conventional expectations that higher strength steels would be more susceptible to hydrogen embrittlement, recent testing on a variety of pipeline steel grades has shown a notable independence between strength and hydrogen assisted fatigue crack growth rate. It is thought that microstructure may play a more defining role than strength in determining the hydrogen susceptibility. Among the many factors that could affect hydrogen accelerated fatigue crack growth rates, this study was conducted with an emphasis on orientation dependence. The orientation dependence of toughness in hot rolled steels is a well-researched area; however, few studies have been conducted to reveal the relationship between fatigue crack growth rate in hydrogen and orientation. In this work, fatigue crack growth rates were measured in hydrogen for high strength steel pipeline with different orientations. A significant reduction in fatigue crack growth rates were measured when cracks propagated perpendicular to the rolling direction. A detailed microstructural investigation was performed, in an effort to understand the orientation dependence of fatigue crack growth rate performance of pipeline steels in hydrogen environments.
Numerical Study on Longitudinal Distance Effect on Failure Stress of Non-Aligned Twin Cracked Pipe
Authors: Nguyen Thanh-Long , Lee Myeong-Woo , Hasegawa Kunio , Kim Yun-Jae
Published: October 2018

In this study, the effect of longitudinal distance H between non-aligned twin cracks is investigated using finite element damage analysis. The FE damage analysis based on the stress-modified fracture strain model is used to calculate the failure stress of non-aligned twin cracked pipe. Parametric study on the axial distance H between non-aligned twin cracks with various crack depths and lengths were conducted and compared with predictions using the alignment rules and the net-section collapse load approach for single crack provided in ASME Code. It is shown that the trend of the predicted collapse bending stresses for the non-aligned twin cracked pipes using FE damage analysis are different from the ones using the alignment rule.
New Fatigue Screening Criteria for the Fitness-for-Service Assessment of In-Service Process Piping Vibrations
Authors: Bifano Michael F. P. , Breaux Lyle , Feller Anthony J. , Brodzinski Richard
Published: October 2018

Commonly used piping vibration screening limits are typically justified by experience and lack a well-documented technical basis. This paper presents technical background for future Level 1 Fitness-for-Service (FFS) vibration screening criteria. The criteria assess the risk of fatigue in process piping due to bending mode type vibrations. Finite element analysis (FEA) of 20,000 randomly generated candidate-piping models and high-cycle welded joint fatigue curves for both constant amplitude and variable amplitude loading form the stress limits and basis for the proposed criteria. Most importantly, the proposed criteria aligns with historically used allowable vibration limits rooted in substantial experience. The allowable stress basis implemented in this paper considers periodic and random vibrations making it applicable to situations of mechanically induced, two-phase flow induced, turbulent-induced vibration of single-phase process fluid, or wind-induced, which may be manifested as either periodic or random. To reduce conservatism, limits are set for butt-welded and non-butt welded mainline piping to prevent use of a single blanket limit that may lead to unnecessary piping support alterations/additions, or costly piping configuration changes and unit downtime. Furthermore, the proposed Level 1-type criteria are consistent with previously proposed FFS Level 2 and 3 piping vibration fatigue evaluations [1] intended for inclusion in the ASME FFS-1/API 579 (API 579) Fitness for Service Standard [2].
Subsea Tree Connector Capacity Chart per the Elastic-Plastic Analysis Methodology
Authors: Sepehri Ali , Harbert Stuart , Wilhelmi Joe
Published: October 2018

The oil and gas industry is currently drilling into and producing from wells in high-pressure, high-temperature (HPHT) environments. This has created a greater demand to develop more advanced tools and new technology to safely overcome the challenges in these operations. The Bureau of Safety and Environmental Enforcement (BSEE) requires equipment operating in HPHT environments to pass a design verification analysis. The design verification shall be evaluated using finite element analysis (FEA) per ASME Boiler Pressure Vessel Code (BPVC), Section VIII, Division 3 [1] and API 17TR8 [2].

The objective of this study is to generate a pressure-bending-tension (PBT) capacity chart per the elastic-plastic analysis methodology (global collapse criteria) outlined in KD-230 [1] for a subsea tree connector. The PBT capacity chart covers a wide range of normal operating conditions. Results indicate that the structural capacities from the elastic-plastic analysis methodology are higher than those determined by the standard elastic analysis methodology.
Formula for Estimation of Effective Applied Load at Cracked Section Considering Compliance Change and its Application Under Dynamic Loading Conditions
Authors: Kim Yeji , Oh Young-Jin , Kim Yun-Jae , Hwang Il-Soon
Published: October 2018

The refinement of the piping integrity assessment methods has emerged as a priority issue, in response to heightened concerns about the beyond design basis accident following several events. The compliance change in structures may have a significant influence on the fracture estimation. For instance, the deformation of a crack in the piping system may result in a decrease of the applied moment at the cracked section. To consider these effects, the authors have developed the general formula for prediction of the effective applied moment at circumferential cracked section based on the elastic beam theory. Using the developed formula, one can evaluate the extent of the load reduction at a crack position due to the change in compliance. This paper aims to expand the applicability of the formula for dynamic loading conditions. By conducting the time history analysis using FE model accompanying the comparisons with the piping system experiment results, it was confirmed that the formula is also available for dynamic loading conditions. It is expected that the proposed formula can be implemented in sthe piping integrity assessment to consider the restraint effect.
Code Case N-822 for Pin Brazing Non-Structural Attachment Tabs for Buried Pipe Cathodic Protection
Authors: McCracken Steven L. , Mohr Nick
Published: October 2018

Cathodic protection (CP) is one of the primary methods to protect buried piping and pressure components from corrosion and is a critical element in asset management of buried piping at nuclear power plants. Implementation of cathodic protection requires non-structural attachments to the buried piping for electrical leads and connections. The method of attaching copper-copper alloy CP leads to carbon steel piping and components using traditional arc welding processes can be difficult and time consuming. A two-step process is frequently used where a carbon steel weld tab is first welded to the pipe or component by a traditional arc welding process. The copper-copper alloy CP lead is then joined to the carbon steel weld tab by the exothermic welding process.

An alternative to this cumbersome two-step process is pin brazing which is an automatic brazing process that uses electric current resistance to heat the interface between a pin capsule and the component. An arc between the pin capsule and the outside surface of the electrical connector is then used to melt the capsule or pin that contains the brazing filler metal. The process is similar to stud welding in that the brazing pin is loaded into an automatic pistol and the brazement is made when the trigger is pulled. ASME Section XI Code Case N-882 delineates rules and requirements for application of pin brazing on Class 2 and 3 pressure boundary components. This paper provides the background and description of the pin brazing process with a summary of the technical basis for Case N-882.
Trial Study of the Master Curve Fracture Toughness Evaluation by Mini-C(T) Specimens for Low Upper Shelf Weld Metal Linde-80
Authors: Yamamoto Masato
Published: October 2018

The Master Curve (MC) method can be used to directly determine fracture toughness of ferritic reactor pressure vessel (RPV) materials. CRIEPI has been working on the development of a testing technique to apply very small C(T) (called Mini-C(T)) specimens for the MC method. The appropriateness of using Mini-C(T) specimens for several materials including un-irradiated plate, forging, weld metal and irradiated plate has been demonstrated. Through a series of investigations, it was determined that more invalid data, due to ductile crack growth (DCG), can occur when using small size specimens.

Linde-80 weld metal, used in the fabrication of some RPVs, is known as low upper shelf material, which tends to exhibit more DCG than high upper shelf materials. In the present study, two sets of 15 Mini-C(T) specimens were machined and pre-cracked from irradiated Linde-80 weld metal. Each set of specimens were provided to two different laboratories (A and B). The laboratories separately conducted the MC tests. DCG occurred even in the lower test temperature condition. About half of specimens for lab A showed excessive DCG and were subjected to the censoring. Some of specimens were rejected since the test temperature is outside of the specified range (T-To < −50°C). As a result, lab A could not obtain valid To with 15 specimens. Lab B also experienced DCG, however were able to obtain a sufficient number of valid KJc data points to determine a valid To. The obtained ToQ (lab A) and To (lab B) are sufficiently close to each other and suggests that Mini-C(T) can be used even for the low upper shelf material if the number of available specimens are sufficiently large. The combined dataset from labs A and B estimated To = 31.5°C, which is in the scatter band of To obtained by pre-cracked Chapry (PCCv), 0.5TC(T) or 1TC(T) specimens in a past Heavy-Section Steel Irradiation (HSSI) project. The overall result suggests that To can be estimated using Mini-C(T) specimens for the lower upper shelf weld material, but 15 is a marginal number of specimens for a valid estimation.
Exploring Finite Element Validation for Weld Residual Stress Prediction
Authors: Benson Michael L. , Raynaud Patrick A. C. , Wallace Jay S.
Published: October 2018

The U.S. Nuclear Regulatory Commission staff has analyzed results from the weld residual stress round robin study, conducted in 2014. An uncertainty quantification scheme was applied to the dataset in order to compare and contrast results from independent analysts. The uncertainty quantification scheme provides a rigorous framework within which to make judgement calls about appropriate modeling guidelines and potential validation schemes. This paper will explore various options for guidelines and validation approaches, as informed by a statistical analysis of the dataset.
An Effect of Nozzle Flexibilities/Stiffness on Equipment Nozzle Loads and Local Stresses
Authors: Pathre Sujay S. , Govindan K.
Published: October 2018

The loads on the equipment nozzles are generally generated by the piping stress engineer by doing the stress analysis of entire closed loop systems. Subsequently the nozzle loads are passed on to the engineers of the pressure vessel equipment. The value of the loads which have been worked out for the nozzle mostly depends upon the methods/concept by which the piping stress engineer has evaluated the piping loop. Nozzle flexibility/stiffness is the important parameter in evaluation of various components of nozzle loads. The objective of this paper is to explain the effect/influence of flexibility/stiffness generated from three different methods (Anchor, WRC and Finite element method) on nozzle load evaluation and shell/nozzle junction stresses.

WRC297 bulletin [6] gives the reference to nozzle flexibility in the appendix A, example no.3.

The work presented in this paper is an attempt to compare the nozzle loads calculated by evaluating the flexibilities/stiffness in various methods. Further an attempt has been made to consolidate the results of junction local stresses obtained by the various methods of stiffness/flexibilities which would result in realistic results and overall code acceptable stresses without the results being either overly conservative or unconservative.
Alternative Characterization Rules for Multiple Surface Planar Flaws
Authors: Dulieu Pierre , Lacroix Valéry , Hasegawa Kunio , Li Yinsheng , Strnadel Bohumir
Published: October 2018

When multiple surface flaws are detected in pressure components, their potential interaction is to be assessed to determine whether they must be combined or evaluated independently of each other. This assessment is performed through the flaw characterization rules of Fitness-For-Service (FFS) Codes. However, the specific combination criteria of surface flaws are different among the FFS Codes. Most of the time, they consist of simple criteria based on distance between flaws and flaw depth. This paper aims at proposing alternative characterization rules reflecting the actual level of interaction between surface planar flaws. This interaction depends on several parameters such as the relative position of flaws, the flaw sizes and their aspect ratio. Thanks to numerous three-dimensional XFEM simulations, best suited combination criteria for surface planar flaws are derived by considering the combined influence of these parameters.