bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of Welding Residual Stress Model Using Results From a Pressurizer Surge Nozzle Mockup
Authors: Killian Doug
Published: May 2012

Although numerical welding simulation is now commonly used in the nuclear industry to predict residual stresses in reactor vessels and associated piping components, there are currently no universally accepted guidelines for performing such analysis. Moreover, due to the complexity of the calculations and varying analytical procedures among analysts, there remains a need to validate predictions of residual stress against benchmark studies. As part of an industry initiative to manage the degradation of dissimilar metal welds in pressurized water reactor piping that are susceptible to primary water stress corrosion cracking, the U.S Nuclear Regulatory Commission embarked on a multi-phased program to validate welding residual stress models. The aim of Phase II of this program is to obtain measured residual stresses from a pressurizer surge nozzle dissimilar metal weld mockup for use in comparisons with numerically predicted stresses. This paper presents results of finite element analysis for various stages during the fabrication of a 14–inch pressurizer surge nozzle mockup, including an Alloy 82 dissimilar metal weld between a stainless steel safe end and carbon steel nozzle, an inside surface weld repair (back weld) and fill-in weld (weld build-up), and a stainless steel “field” weld attaching a section of straight pipe to the safe end. The NRC validation program was structured to allow participants to first calculate results using their own material properties, and then tune their welding simulations to thermocouple data. This was followed by reanalysis using NRC-supplied material properties. The program was conducted as a round robin analysis among an international group of participants and formatted as a blind validation project wherein results were submitted to the NRC prior to receipt of thermocouple and material property data. Results were obtained for both kinematic and isotropic hardening rules to study the effect of these two extreme measures of material characterization on the development of residual stress. Predicted stresses are then compared to measured stress data obtained by the deep-hole drilling technique at multiple locations through the thickness of the weld. The NRC residual stress model validation project serves as a valuable contribution to the understanding of how residual stresses are developed in dissimilar metal welds. The correlation of calculated residual stresses with measured data from a relevant mockup also serves to increase confidence in predicting crack growth in these primary pressure boundary welds by removing much of the uncertainty previously associated with residual stress input to crack growth analysis.
Assessment of Residual Stress in Fracture Mechanics Coupons
Authors: Hill Michael R. , VanDalen John E. , Prime Michael B.
Published: May 2012

This paper describes measurements of residual stress in coupons used for fracture mechanics testing. The primary objective of measurement is to quantify the distribution of residual stress acting to open (and/or close) the crack across the crack plane. The slitting method and the contour method are two destructive residual stress measurement methods particularly capable of addressing that objective, and these were applied to measure residual stress in a set of identically prepared compact tension (C(T)) coupons. Comparison of the results of the two measurement methods provides some useful observations. Results from fracture mechanics tests of residual stress bearing coupons and fracture analysis, based on linear superposition of applied and residual stresses, show consistent behavior of coupons having various levels of residual stress.
Fatigue Crack Growth Rate and Fracture Resistance of Heat Affected Zone of Type 316L Stainless Steel With Narrow Gap Welds
Authors: Lee Ho-Jung , Kim Minu , Jang Changheui , Cho Sun-Young , Yang Jun-Seog
Published: May 2012

In nuclear power plants, the automated narrow gap welding (NGW) technique has been widely used in joining pipes in primary coolant system. Meanwhile, to apply the leak-before-break (LBB) design, mechanical properties of the structural materials of piping systems should be evaluated, especially at various welded joints. In this study, the fatigue crack growth rate (FCGR) and fracture resistance of stainless steel weld fusion zone and nearby heat affected zone (HAZ) were evaluated to support the LBB application. Tests were performed at plant operating temperature (315°C) and room temperature. FCGR test results showed higher crack growth rate in HAZ and the weld fusion zone compare to the base metal. Fracture resistance tests showed higher fracture toughness in HAZ compared to the weld fusion zone. By analyzing the microstructures in the weld fusion zone and HAZ, their effects on crack growth rate were discussed. Also, the crack growth behavior in circumferential direction was compared with that in radial direction which was previously reported.
Pre Test Calculations on TOPFLOW PTS Experiment With NEPTUNE_CFD Code
Authors: Martin A. , Raynaud C. , Pe´turaud P. , Heib C. , Dubois F. , Huvelin F. , Barbier A.
Published: May 2012

Hypothetical Small Break Loss Of Coolant Accident is identified as one of the most severe transients leading to a potential huge Pressurized Thermal Shock on the Reactor Pressure Vessel (RPV). This may result in two-phase flow configurations in the cold legs, according to the operating conditions, and to reliably assess the RPV wall integrity, advanced two-phase flow simulations are required. Related needs in development and/or validation of these advanced models are important, and the ongoing TOPFLOW-PTS experimental program was designed to provide a well documented data base to meet these needs. This paper focuses on pre-test NEPTUNE_CFD simulations of TOPFLOW-PTS experiments; these simulations were performed to (i) help in the definition of the test matrix and test procedure, and (ii) check the presence of the different key physical phenomena at the mock-up scale.
Study of Residual Stresses Heterogeneities in a Ring Norem Hardfaced Sample by Neutron Diffraction
Authors: Mathieu Jean-Philippe , Kelleher Joe F. , Steuwer Axel
Published: May 2012

Iron-based hard-facing alloys, such as Norem, are considered to be good substitutes for Co-based ones where radiological activation is an issue. This work aims at studying residual stresses inside Norem02 Plasma Transferred Arc deposits. A standard test sample used by a valve manufacturer is taken as an example: it consists of a stainless steel (AISI 316L) disk with circular weld bead deposits of Norem hard-facing on both sides. Residual stresses were investigated using neutron diffraction on the ENGIN-X beam line. As expected, experimental results tends to indicate the welding overlap zones to be affected by reheating. Since previous works indicates quite limited metallurgical influence of high temperature re-heating on the deposited material, it is expected to be possible to capture this effect by further finite element modelling of the welding process, in order to study its influence on further in-service behaviour of valves.
Simultaneous Measurement of Velocity and Temperature Downstream of a Heated Cylinder
Authors: Bencs Pe´ter , Szabo´ Szila´rd , Borda´s Ro´bert , Za¨hringer Katharina , The´venin Dominique
Published: May 2012

Bluff bodies placed in a flow, such as electrical transmission lines, cartridge heaters, pipes of heat exchangers, factory chimneys and so on, often have a different temperature compared to that of the surroundings. The structure of the flow developing around bluff bodies has been investigated for a long time (Adrian, 1991; Williamson, 1996). The Ka´rma´n vortex street was and is examined by numerous researchers, both experimentally and numerically. Nevertheless, the question arises as to how this vortex street is modified by a heated cylindrical bluff body. What is the influence of heating on the frequency of the detaching vortices, the structure of the vortices and the location of the detachment? Many of these questions have already been answered by the help of numerical simulations and of measured velocity distribution using Particle Image Velocimetry (PIV) and the vortex distributions obtained from this (Venkatakrishnan and Meier, 2004). A further question is the heat loss caused by the vortex structure and the forced convection. To tackle this question, the Background Oriented Schlieren (BOS) method is applied here. At the same time, first steps have been taken towards determining temperature and vortex distributions simultaneously, which are introduced in this paper. Main objective and novelty of this work is the solution for the mentioned measurement problem with a single camera.
Performance Evaluation of Product Type Magnetic Damper Using Eddy-Current Damping Effect
Authors: Furuya Osamu , Ogata Keiji
Published: May 2012

Response control techniques such as a base-isolation and a vibration control have been a general vibration reduction system for upgrading of seismic safety or habitability improvement in civil and architectural structure after Kobe earthquake. In such state in Japan, an application of the vibration reduction device to a small-scale structure has been carried out actively in recent years. Especially, in the important institution of the cities such as refuge place, hospital, school, information and communication institution where function maintenance is needed, it is important to maintain its performance of the machinery and equipment in the facility with an upgrade of structural seismic safety. Moreover, in the future, upgrading of seismic safety of the particular equipments is urgent business. This study has been examined a compact and low cost damping device for a base-isolation system of light weight mechanical structures like a computer server rack. In this paper, experimental and analytical results on the performances of the product type damping device using damping effect caused by Eddy-Current are described.
New Approach to Stress-Strain Curve Prediction Using Ball Indentation Test
Authors: Brumek Jan , Strnadel Bohumi´r , Dlouhy´ Ivo
Published: May 2012

This work is concerned with the method for predicting stress-strain behavior of material using instrumented indentation technique. High strength low alloy steel with different thermal treatment was taken into the analysis. Heat treatment for the steel was performed to obtain different mechanical properties. Assessment of mechanical properties was done by using inverse technique of the finite element analysis. The results were confronted with conventional test parameters and prediction procedure defined such Automated Ball Indentation Technique (ABIT). Comparison of the material curves shows good agreement with tensile test properties which makes this non-destructive method suitable for industrial application.
The Best-Estimate Plus Uncertainty (BEPU) Challenge in the Licensing of Current Generation of Reactors
Authors: Petruzzi A. , Muellner N. , D’Auria F. , Mazzantini O.
Published: May 2012

Within the licensing process of the Atucha II PHWR (Pressurized Heavy Water Reactor) the BEPU (Best Estimate Plus Uncertainty) approach has been selected for issuing of the Chapter 15 on FSAR (Final Safety Analysis Report). The key steps of the entire process are basically two: a) the selection of PIE (Postulated Initiating Events) and, b) the analysis by best estimate models supported by uncertainty evaluation. Otherwise, key elements of the approach are: 1) availability of qualified computational tools including suitable uncertainty method; 2) demonstration of quality; 3) acceptability and endorsement by the licensing authority. The effort of issuing Chapter 15 is terminated at the time of issuing of the present paper and the safety margins available for the operation of the concerned NPP (Nuclear Power Plant) have been quantified.
Materials Information Management Systems for Energy Applications
Authors: Marsden William M. , Cope Elizabeth R.
Published: May 2012

Materials property data, and broader materials information, are essential to the wide range of people and functions in engineering enterprises involved in the design and construction of power generation facilities. This paper focuses on how this complex and specialist information must be managed, and how it can be deployed most effectively to those who need it. There are many different types of data to be considered, but they all begin as test results of one form or another. Generating this test data represents a major cost for many organizations. Applying it effectively can give them a major competitive advantage — for example, avoiding problems in design, gaining more understanding of the performance of materials, and ultimately reducing maintenance costs or enabling asset life extension. Yet few organizations have in place any systematic system to manage materials data. Not only does this mean that they are not making best use of their investment in this asset, it means that they can actually waste large amounts of time and money, in searching for the right data, or in duplicating tests that have already been done. This paper concentrates on the practical challenges involved, and on the technical details of how these challenges can be solved, drawing on the experience of developing the GRANTA MI materials information management system in collaboration with a consortium of leading aerospace, energy, and defense organizations. Three use-case scenarios are explored in which the management and application of materials data are important. These are: support for engineering design, statistical process control, and materials selection. For each use-case, the technical requirements for any corporate materials data management system are identified. Significant overlaps are found between the requirements for the different areas, indicating that a well-designed system can both meet a broad range of specific needs, and help to integrate different aspects of an organization’s operations. It is then appropriate to discuss the actual software tools required to meet these needs. These include tools to capture and consolidate materials data, to analyze and apply the data, to maintain a corporate materials information resource, and to deploy materials data enterprise-wide to the different functions (e.g., Design, and Quality Assurance) and roles (e.g., design engineers, stress analysts, and process improvement managers) that require it. The paper closes by providing guidelines on best practice regarding implementation of materials data management technology.
Guidelines for Repair Welding of Pressure Equipment in Refineries and Chemical Plants: Part 1—General
Authors: Yamamoto Eiichi , Tahara Takayasu , Matsushita Yukinobu , Minami Fumiyoshi
Published: May 2012

Responding to the needs in petroleum and chemical industries, the Japan Welding Engineering Society (JWES) has been worked to establish a repair welding guideline on pressure equipment in refineries, petrochemical and other process industries. As accomplishments, JWES published Guideline for Repair Welding on Pressure Equipment in 2009. The paper describes Part 1 of the guideline which covers typical material degradations of the pressure vessels, equipment diagnosis and role of repair welding and standard repair welding procedures.
Integrity Concept for Piping Systems With Corresponding Leak and Break Postulates in German Nuclear Power Plants
Authors: Ilg Ulf , Nagel Gerhard , Ko¨nig Gu¨nter , Schu¨mann Dirk , Mayinger Wolfgang , Widera Martin
Published: May 2012

In order to exclude the possibility of catastrophic failure of safety relevant pressure-retaining components in nuclear power plants during operation, the “integrity concept” is applied in Germany. It has been developed over the past 30 years on the basis of the safety criteria of the guidelines for damage precautions, as set by the German Advisory Committee on Reactor Safeguards (RSK-LL) and the basic safety concept. The integrity concept is based on the requirements of proven basic safety characteristics: design, construction, material, and manufacturing. Complementary elements (so-called redundancies) also have to be considered: the principle of inspections by multiple parties, the worst-case principle, the principle of plant monitoring and documentation, as well as the principle of verification. This includes consideration of possible operational damage mechanisms in terms of interaction between causes and consequences as well as consideration of any new knowledge, if necessary in the framework of additional safety analyses. The integrity concept is applied in German PWR plants, i.e. the main coolant lines and their connecting lines, as well as in German BWR plants with large main steam and feedwater lines within the pressure-retaining boundary (primary system) up to the outer containment. A fracture mechanics safety analysis with postulated defect sizes as well as the experimental basis of load behavior are essential parts of the integrity concept. The measures determined and verified in this way guarantee that no major deviations from design values occur. This is confirmed by periodic in-service inspections. The advantage of this concept is the application of reduced leakage assumptions for important safety-related pipe systems, i.e. either through application of a conservative postulate of 0.1 F according to RSK-LL or reduced leak sizes. The operational experience gained with this concept has been positive in all German PWR and BWR plants. This paper demonstrates that the German integrity concept has been proven to be successful over the past 30 years and reflects the state of the art. Its implementation in plants and its incorporation in the German Nuclear Codes (KTA rules) contribute to the safety of German nuclear power plants in terms of precautionary damage prevention.
New Computational Procedures for Evaluation of Fracture Surfaces of the Drop Weight Tear Test of the Piping Steel
Authors: Zˇidli´k Pavel , Ferfecki Petr , Strnadel Bohumi´r
Published: May 2012

Drop weight tear test (DWTT) is one of the standard methods for evaluation of the ductility of large-dimensional structural components, such as pipelines used for gas and/or oil transportation. In general, the pipelines are even used in places with temperatures close to −40 °C, and in such environments, it is necessary to guarantee the resistance of the material used for pipeline against the initiation of unstable fracture. Currently, the percentage portion of the ductile fracture of the DWTT specimen is determined by an expert evaluator. The objective of this paper is to introduce new procedures working on the principle of deterministic, statistical and fractal description of the fracture surface. For the proposed computational procedures, the fracture surface of the test specimen is scanned at the macroscopic level using the 3D-Cam scanner. The newly investigated procedures show highly sensitive to the determination of the percentage portion of the ductile fracture on the tested DWTT specimens. The developed procedures to assess the fracture surfaces of the DWTT specimens contributes to making the results of this test more correct, objective and also increases the reliability and safety of the manufactured pipelines.
Stress and Deformation Analyses of Large Diameter Blind Flange Connections Subjected to Bolt Loads and Internal Pressure
Authors: Kobayashi Takashi , Kogasaka Masahiro , Nishiura Kengou , Kazuaki Uchiyama
Published: May 2012

Leakage problems caused in large diameter gasketed flanged connections in piping systems are closely related to deformation of flanges caused by the high thrust force and rather low rigidity of the flanges. Therefore, it is necessary to understand the deformation characteristics of flanged connections when they are tightened and pressurized. In this study, experiments were carried out using a 16-inch gasketed flanged connection to examine the stress and strain in the flanges. In order to clarify the deformation characteristics of the gasketed flanged connection, a method to analyze stresses and deformations of a gasketed flanged connection was demonstrated using the classical theory by Timoshenko. Recently, finite element analysis (FEA) has widely been used in the analysis of gasketed flanged connections. However, analyses of flanged connection based on the analytical method using strength of materials are still important when parametric calculations of flanged connection are necessary. The experimental results and the analytical ones were compared and discussed to clarify the sealing behaviors of large diameter gasketed flanged connection.
H∞ Direct Output Feedback Control of High-Speed Elevator Systems
Authors: Chang Chang-Ching , Lin Chi-Chang , Su Wu-Chung , Huang Yuan-Po
Published: May 2012

The more the development of super high-rise buildings, the faster the speed of elevator in order to shorten the riding time of elevator and the waiting time of passengers. With the increase of elevator speed, the horizontal vibration of passenger car becomes more significant resulting in the decrease of serviceability and safety of elevator, and the discomfort of passengers. The horizontal vibration is mainly generated from the elevator wheels running on rough and winding guide rails. In this paper, a four degree-of-freedom (DOF) elevator system was established to examine the characteristics of the excitations and to analyze the dynamic responses of the elevator. An active mass driver (AMD) was developed to reduce the horizontal acceleration of passenger car in the elevator based on H∞ direct output feedback control algorithm. The optimal control force is obtained from the multiplication of direct output measurements by a pre-calculated time-invariant gain matrix. To achieve optimal control performance, the strategy to select both control parameters γ and α was investigated extensively. Numerical verification results show that decrease in γ or increase in α yields better control performance with an acceptable magnitude of control force. The selective ranges of γ and α making a controlled system become overdamped or unstable were found. To assure system stability and control efficiency, the upper bound of α were derived and illustrated graphically. An optimum design flowchart was also proposed. Finally, a full-scaled high-speed elevator system was investigated to prove the applicability and control effectiveness of the proposed AMD system.
Comparative Assessment of Turbulence Models for Prediction of Flow-Induced Corrosion Damages
Authors: Das Kaushik , Basu Debashis , Mintz Todd
Published: May 2012

The present study makes a comparative assessment of different turbulence models in simulating the flow-assisted corrosion (FAC) process for pipes with noncircular cross sections and bends, features regularly encountered in heat exchangers and other pipeline networks. The case study investigates material damage due to corrosion caused by dissolved oxygen (O2) in a stainless steel pipe carrying an aqueous solution. A discrete solid phase is also present in the solution, but the transport of the solid particles is not explicitly modeled. It is assumed that the volume fraction of the solid phase is low, so it does not affect the continuous phase. Traditional two-equation models are compared, such as isotropic eddy viscosity, standard k-ε and k-ω models, shear stress transport (SST) k-ω models, and the anisotropic Reynolds Stress Model (RSM). Computed axial and radial velocities, and turbulent kinetic energy profiles predicted by the turbulence models are compared with available experimental data. Results show that all the turbulence models provide comparable results, though the RSM model provided better predictions in certain locations. The convective and diffusive motion of dissolved O2 is calculated by solving the species transport equations. The study assumes that solid particle impingement on the pipe wall will completely remove the protective film formed by corrosion products. It is also assumed that the rate of corrosion is controlled by diffusion of O2 through the mass transfer boundary layer. Based on these assumptions, corrosion rate is calculated at the internal pipe walls. Results indicate that the predicted O2 corrosion rate along the walls varies for different turbulence models but show the same general trend and pattern.
Numerical Evaluation of Corrosion Condition for Pressurized Water Reactor Secondary Cooling System
Authors: Das Kaushik , Mintz Todd , Basu Debashis
Published: May 2012

Flow-accelerated corrosion (FAC) in a pressurized water reactor (PWR) feedwater piping system is considered the leading degradation process that has been blamed for a number of accidents and incidents. One of the challenging issues in estimating FAC in piping is the hydrazine (N2H4) oxygen (O2) reaction rate and its subsequent impact on the wall mass transfer. N2H4 is injected in the system to maintain a stable pH in the water and also to act as an O2 scavenger. Previous research results indicate a varying degree of FAC rate dependence on the presence of N2H4 in the system. The N2H4-O2 reaction is also a complex function of temperature and pipe material. The present paper presents a two-part analysis that uses computational fluid dynamics (CFD) tools to investigate the N2H4-O2 reaction and its subsequent impact on mass transfer. In the first part of the analysis, chemistry and flow of water with dissolved O2 and N2H4 is simulated to assess different reaction mechanisms available in the literature. Results obtained from this study are compared with available experimental data for benchmarking. The numerical results were able to capture the general pattern of reaction rate as a function of temperature. Numerical simulations were also carried out to accommodate the surface effects on the reaction, but results indicate that such accommodations will yield useful results only if the geometrical extent of the near-wall-zone, where surface effects are prevalent, is well known. In the second part of the analysis, numerical simulations were carried out for a U-bend pipe. A number of restrictive assumptions were made to assess the dependence of O2 mass-transfer rate on N2H4-O2 reaction. Hydrodynamic results show the secondary flow pattern within the bend section. Results are also presented for the Sherwood number ratio at the pipe wall with and without reaction. Results indicate that the N2H4-O2 reaction decreases the O2 flow rate toward the wall. This calculation also shows that secondary flow in the bend affects the wall mass transfer pattern.
Reference Volume Consideration in the mα-Tangent Method Based Linear Elastic Analysis
Authors: Adibi-Asl R. , Hossain M. M. , Mahmood S. L. , Gudimetla P. S. R. , Seshadri R.
Published: May 2012

Limit loads for pressure components are determined on the basis of a single linear elastic finite element analysis by invoking the concept of kinematically active (reference) volume in the context of the “mα-tangent” method. The resulting technique enables rapid determination of lower bound limit load for pressure components by eliminating the kinematically inactive volume. This method is applied to a number of practical components with different percentages of inactive volume. The results are compared with the corresponding inelastic finite element results, or available analytical solutions.
Seismic Fragility Evaluation of a Buried Auxiliary Cooling Water System Pipeline for Liquefaction-Induced Soil Settlement
Authors: Erbay O¨mer O. , Kan Frank W. , Hashimoto Philip S. , Bayraktarlı Yahya , Zuchuat Olivier
Published: May 2012

Seismic fragility evaluation of the buried Auxiliary Cooling Water System (ACWS) intake pipeline of the Mu¨hleberg Nuclear Power Plant (KKM) was conducted to determine its performance when subjected to liquefaction-induced soil settlement. This evaluation utilized nonlinear analysis as a rigorous alternative to more approximate methods due to the importance of the ACWS to plant safety. The ACWS intake line is constructed of welded steel pipe with a nominal outside diameter of 23.6 in. (600 mm) and a wall thickness of 0.22 in. (5.6 mm). The line was modeled and analyzed using computer program Abaqus, considering nonlinearities of the pipe material and pipe-soil interaction. Failure of the pipe is initiated by local wrinkle-type buckling at the wall penetration followed by local ductile tearing. Failure criterion for local tearing is expressed in terms of effective plastic strain including the effects of triaxiality at the critical section. Parameters critical to the pipe settlement capacity include pipe yield and ultimate strengths, pipe effective strain capacity, and soil yield strength and displacement. The variabilities in the pipe settlement capacities were calculated considering varabilities of the critical parameters by the Separation-of-Variables Method recommended by EPRI TR-103959. The 1% non-exceedance probability (NEP) settlement capacities were determined to be well in excess of the 99% NEP settlements estimated by the geotechnical investigation. Based on this comparison, it was concluded that the probability of ACWS intake line failure due to soil liquefaction is negligible.
Welding Residual Stress Modeling Benchmark Comparison Study
Authors: Good B. , Ng C. , Bamford W. , Broussard J.
Published: May 2012

Welding residual stress modeling is currently performed by researchers around the world using a wide variety of modeling methods to predict the final stress state of a completed weld. Among the key modeling assumptions used to perform a residual stress simulation are: • The geometric setup of the model, including boundary condition and assumptions. • The thermal and structural model simulating the welding process including lumping of weld passes. • The strain hardening input properties and hardening law. Researchers from Dominion Engineering, Inc. (DEI) and Westinghouse Electric Co. (WEC) have performed a benchmark comparison studying these key modeling assumptions and their results on the predicted welding residual stress distributions. Researchers from DEI and WEC have completed independent studies to validate their respective methods for calculating residual weld stress. In addition to the comparative evaluation, brief descriptions of the individual validations will be included in this paper. The weldment selected for evaluation is a typical reactor pressure vessel (RPV) outlet nozzle dissimilar metal safe end weld in a pressurized water reactor plant. This weld joins a low alloy steel nozzle to a stainless steel safe end using Alloy 182 weld material; this weld is completed in the manufacturing shop. The safe end is then field welded to the stainless steel reactor coolant loop piping. The residual stress distributions in the dissimilar metal welds, like the one selected, are important in predicting stress corrosion crack growth in Reactor Coolant System (RCS) components. The fabrication drawings for the selected RPV outlet nozzle were provided to both organizations, and independent residual stress simulations were performed using the best effort modeling techniques from each organization. This paper investigates the impact of the key modeling assumptions described above on the differences in the predicted welding residual stress distributions between the two simulation techniques. The results from the modeling comparison are provided in this paper.
Stress Relaxation Behavior in PWHT of Welded Components
Authors: Zhang Jinmiao , Dong Pingsha , Song Shaopin
Published: May 2012

This paper is focused on the discussion of weld residual stress relaxation in a uniform post weld heat treatment (PWHT). In particular, the paper is attempted to address a fundamental issue related to the PWHT stress relaxation behavior, i.e., what is the dominant stress relaxation mechanism in PWHT? Is it due to creep or material strength reduction at elevated temperature? The paper starts with a simplified 3-bar weld model to demonstrate how weld residual stress is developed and relaxed. It then follows with an example of thick section narrow groove weld to highlight the results and conclusions. The results clearly indicate that creep mechanism plays a dominant role in the stress relaxation of PWHT. Several other important observations related to the stress relaxation are also summarized.
Changing the Frequency of Inspections for PWSCC Susceptible Welds at Cold Leg Temperatures
Authors: Palm Nathan A. , Bamford Warren H. , Harrington Craig
Published: May 2012

A project has been completed under the sponsorship of the EPRI Materials Reliability Program to evaluate the acceptability of returning to an inservice inspection (ISI) frequency of ten years for the large diameter cold leg pipes (525 to 580F), with Alloy 82/182 dissimilar metal (DM) welds. This effort addresses alternative inspection requirements with a frequency of 7 years that have recently been imposed in order to address the potential for service induced Primary Water Stress Corrosion Cracking (PWSCC) of these welds. Careful review of the service experience shows that cracking has only been observed in the hot leg piping locations with DM welds, and the cold leg locations continue to exhibit very reliable service. There are a number of technical and practical arguments in favor of making this change, even beyond the excellent service experience, and these arguments are summarized in this paper. • Pulling the reactor vessel (RV) core barrel is a serious activity which can entail many risks, so additional pulls should be avoided. Inspection at a frequency of less than 10 years involves additional core barrel pulls. • The flaw tolerance of these large diameter cold leg pipes is very good, and example calculations show that reasonably large flaws are acceptable for ten years. • The probability of cracks initiating in cold leg piping is significantly lower than that for piping at hotter temperatures, and a detailed model has been developed to demonstrate this. Actions are underway to revise the relevant inspection requirements, back to a more typical Section XI ten-year interval, using this technical work as a basis.
Damage Assessment on Low Cycle Fatigue Properties of Cyclic Pre-Strained Austenitic Stainless Steel
Authors: Fujimura Nao , Oguma Hiroyuki , Nakamura Takashi
Published: May 2012

The effects of cyclic pre-strain on low cycle fatigue properties of austenitic stainless steel were investigated, and the fatigue damage was assessed based on several parameters such as the full width at half maximum (FWHM) of diffracted X-ray profile and surface roughness of specimens. The strain-controlled tests were conducted under strain ratio Rε = −1 and various constant total strain ranges. Also the change in remnant fatigue lives were investigated when the cyclic pre-strain were applied to the specimens under the different number of cycles which were determined with reference to the usage factor UFpre ranged from 0.2 to 0.8. As a result, the remnant fatigue life of the pre-strained samples became shorter than that of the sample without pre-strain as the UFpre increased. The relationship between the pre-strain damage expressed in UFpre and the remnant fatigue damage in UFpost was roughly described by the cumulative linear damage law: UFpre + UFpost = 1. Namely, the cyclic pre-strain affected the remnant fatigue lives. In order to evaluate the effects of cyclic pre-strain on fatigue lives more precisely, the damage in the cyclic pre-straining processes was estimated by using FWHM and surface roughness. The FWHM of the specimens with pre-strain once decreased with increase in UFpre, and then increased after showing a minimum value. The surface roughness of specimens increased linearly with an increase of the number of pre-straining cycles. These results suggested that the damage due to pre-strain can be assessed by means of FWHM and surface roughness of specimens.
Evaluation of Torsion and Bending Collapse Moments for Pipes With Local Wall Thinning
Authors: Hasegawa Kunio , Li Yinsheng , Bezensek Bostjan , Hoang Phuong
Published: May 2012

ASME B&PV Code Section XI provides fully plastic bending fracture evaluation procedures for pressurized piping components containing flaws subjected to bending and membrane loads. The piping components in power plants may experience only bending moments but also occasionally small torsion moments, simultaneously. Currently, there is a lack of guidance in the Section XI for combined loading modes including torsion. Finite element analyses were conducted in this paper for 24-inch diameter straight pipes with local wall thinning. The pipe was subject to combined bending and torsion moments. It is shown that the effect of torsion moment on plastic collapse bending moment for the pipes depends on the local wall thinning sizes. In addition, it is found that the equivalent moments defined as the root of the sum of the squares (RSS) of the torsion and bending moments is equal to pure bending moments, when wall thinning depth is shallow.
Investigation on Creep-Rupture Failure Time of HDPE Pipe Under Hydrostatic Pressure
Authors: Xu Cheng , Xu Ping , Shi Jianfeng
Published: May 2012

There are three typical failure modes of high density polyethylene (HDPE) pipe under hydrostatic pressure, which are relatively caused by creep, slow crack growth, and degradation. The duration time of HDPE pipe under hydrostatic pressure before creep-rupture failure is predicted based on a viscoelastic constitutive model. It is found that, hoop stress increases due to reduction in wall thickness of HDPE pipe because of creep, while yielding stress decreases owing to the decrease in creep rate. When the hoop stress approaches the yielding stress, the pipe will quickly deform and then structural failure will follow.
Plastic Collapse Loads for Flat Plates With Dissimilar Non-Aligned Through-Wall Cracks
Authors: Hasegawa Kunio , Miyazaki Katsumasa , Saito Koichi
Published: May 2012

When multiple flaws are offset flaws, alignment rules are used to determine whether the flaws should be treated as non-aligned or as coplanar. The alignment rules are provided in fitness-for-service codes, and the rules are based on comparison of flaw dimensions. Quasi-static tensile tests were performed on Type 304 stainless steel flat plate specimens with two dissimilar through-wall offset flaws at ambient temperature. It can be seen that, in the experiments, plastic collapse loads were independent of non-alignment dimensions, when the counterpart flaw lengths are smaller enough compared with the main flaw lengths.
An Automatic Procedure for the Application of the Italian Standard for Creep-Operated Pressure Equipment
Authors: Grisolia Ottaviano
Published: May 2012

The Section two of the guideline [1] to the Italian technical procedure [2] concerns issues on high-temperature component assessment: it suggests, among others, the first-choice method for calculating expended life under creep conditions. One may get the time to rupture at operation temperature directly through the model chosen for the curve Larson-Miller parameter - stress. The author has written a computer program for finding the best fitting model’s regression coefficients: it features the least squares analysis on points (test temperature, ultimate strength at 100000 hours) available in literature for any creep-sensitive material. A few of both the points and linear system coefficients allow providing also a simplified pocket PC program: it features the analysis for third-grade polynomial model, which may commonly fit the curve. Aim of the work is to provide both a model-functions database for most used materials in high-temperature applications and a ready-at-hand tool for life assessment.
A Novel Fracture Mechanics Specimen to Investigate the Effect of Residual Stress and Crack-Tip Constraint on Fracture
Authors: Kamel Simon , Vanagosoom Tiyaporn , Shanthenu Prakash , Davies Catrin M. , Nikbin Kamran M.
Published: May 2012

A novel fracture toughness specimen design is presented for investigating the effects of residual stress and crack tip constraint on fracture. The specimen design, denoted here as an SC(T) specimen, is a hybrid of a blunt-notched C(T) specimen and an SEN(T) specimen. The SC(T) specimen is mechanically pre-compressed on the C(T) load line to introduce a residual stress in the ligament ahead of a blunt notch. Following pre-compression, a crack is introduced into the tensile residual stress field. The SC(T) specimen can then be loaded either on the C(T) or SEN(T) load line to examine the effects of residual stress under high constraint or low constraint conditions respectively. Finite element analysis is performed to examine the sensitivity of the specimen dimensions on crack tip constraint and to demonstrate the introduction of residual stress into the specimen.
Realistic Modeling of the Failure of Composite Pipes Under Ring Deflection and Internal Pressure Loading Conditions
Authors: Faria Hugo
Published: May 2012

Realistic numerical models of the behavior of glass-fiber reinforced plastic (GFRP) pipes under two loading conditions — ring deflection and internal pressure — representative of their typical applications were developed and experimentally validated. A 2D modeling approach was implemented, using cohesive elements to accurately represent at the layer/laminate level the damage mechanisms leading to failure of these composite structures and estimate their ultimate strength under those loading conditions. The innovative and advantageous feature of these models is their ability to identify the load level at which damage is initiated, its location and the way it propagates thus giving a realistic assessment to the composite pipes’ behavior. Inter-layer delamination and transverse fiber breakage were identified as main damage mechanisms occurring up to the catastrophic failure of the pipes. The numerical-experimental procedure conducted in this study allowed also to determine the proper values of material’s physical properties such as inter- and intra-layer energy release rates governing the failure mechanisms.
Material Report in Support to RCC-MRx Code 2010: Stainless Steel Parts and Products
Authors: Ancelet Olivier , Lebarbe´ Thierry , Dubiez-Le Goff Sophie , Bonne Dominique , Ge´lineau Odile
Published: May 2012

This paper presents the Material Report dedicated to stainless steels parts and products issued by AFCEN (Association Franc¸aise pour les re`gles de Conception et de Construction des Mate´riels des Chaudie`res Electro-Nucle´aires) in support to RCC-MRx 2010 Code. The RCC-MRx Code is the result of the merger of the RCC-MX 2008, developed in the context of the research reactor Jules Horowitz Reactor project, in the RCC-MR 2007, which set up rules applicable to the design of components operating at high temperature and to the Vacuum Vessel of ITER (a presentation of RCC-MRx 2010 Code is the subject of another paper proposed in this Congress; it explains in particular the status of this Code). This Material Report is part of a set of Criteria of RCC-MRx (this set of Criteria is under construction). The Criteria aim at explaining the design and construction rules of the Code. They cover analyses rules as well as part procurement, welding, methods of tests and examination and fabrication rules. The Material Report particularly provides justifications and explanations on requirements and features dealing with parts and products proposed in the Code. The Material Report contains the following information: Introduction of the grade(s): codes and standards and Reference Procurement Specifications covering parts and products, applications and experience gained, • Physical properties, • Mechanical properties used for design calculations (base metal and welds): basic mechanical properties, creep mechanical properties, irradiated mechanical properties, • Fabrication: experience gained, metallurgy, • Welding: weldability, experience gained during welding and repair procedure qualifications, • Non-destructive examination, • In-service behaviour. In the article, examples of data supplied in the Material Report dedicated to stainless steels will be exposed.
The History of BS 7910 Flaw Interaction Criteria
Authors: Bezensek Bostjan , Sharples John , Hadley Isabel , Pisarski Henryk
Published: May 2012

Assessment of flaws and flaw-like indications in engineering components is commonly performed using fitness for service procedures such as the BS 7910 to demonstrate margins for continued operation or to find a limiting state. An individual or multiple flaw indications may be found in a component as a result of fabrication or degradation during operation. Most fitness for service codes provide guidance for assessment of multiple flaws. This consists of simplifying the actual indications into flaws more amenable to analysis using engineering criteria. The subject of this paper is the flaw interaction criteria used by the BS 7910 procedure. The criteria have been refined several times since the 1980 version of the BS 7910 predecessor document PD 6493. This paper will summarise the changes and provide plausible explanations to the changes supported by the experimental data and numerical analysis. A proposed way forward for the 2012 edition of BS 7910 flaw interaction and characterisation will conclude the paper.
Fracture Assessment of Pipes Having Multiple Flaws Based on Ramberg–Osgood-Type Stress–Strain Relationships
Authors: Machida Hideo , Hamanaka Tetsuya , Takahashi Yoshiaki , Miyazaki Katsumasa , Iwamatsu Fuminori , Saito Koichi , Itatani Masao , Narazaki Chihiro , Hojo Kiminobu
Published: May 2012

This paper describes a fracture assessment method for a pipe having multiple circumferential flaws. According to Fitness-for-Service (FFS) codes for nuclear facilities published by the Japanese Society of Mechanical Engineers (JSME), the fracture strength of a high-ductility pipe having a circumferential flaw is evaluated using the limit load assessment method assuming the elastic–perfectly-plastic stress–strain relationship. In this assessment, flow stress is used as a proportional stress. However, previous experimental results [1, 2, 3] show that a crack penetrates before the entire flawed pipe section reaches the flow stress. Therefore, stress concentration at a flaw was evaluated on the basis of the Dugdale model [4], and the fracture strength of the crack-ligament was evaluated. This model can predict test results with high accuracy when the ligament fracture strength is assumed to be tensile strength. Based on this examination, a fracture assessment method for pipes having multiple flaws was developed considering the stress concentration in the crack-ligament by using the realistic stress–strain relationship (Ramberg–Osgood-type stress–strain curve). The fracture strength of a multiple-flawed pipe estimated by the developed method was compared with previous experimental results. When the stress concentration in the crack-ligament was taken into consideration, the fracture strength estimated using the Ramberg–Osgood-type stress–strain curve was in good agreement with experimental results, confirming the validity of the proposed method.