bluuebunny/crossref_metadata_2025 huggingface dataset:
How Validates Residual Stress Effect on Fatigue Strength and SCC Evaluations?
Authors: Mochizuki Masahito , Toyoda Masao
Published: August 2008

The availability of several processes for residual stress control is discussed in order to verify residual stress effect on fatigue strength and SCC evaluations The effectiveness protecting from fatigue and stress-corrosion cracking is validated by numerical analysis and actual experiment. In-process control during welding is the easiest method to reduce residual stress without any treatment after welding process. Control of welding pass sequence for multi-pass weld is applied to cruciform joints and butt-joints with X-shaped groove. Other processes after welding are confirmed the validity of residual stress improvement. Water jet peening is useful for obtaining compressive residual stress on the surface, and the tolerance against both fatigue and stress-corrosion cracking is verified. Cladding of corrosion-resistant material is also effective for preventing stress-corrosion cracking by the metallurgical respect on the basis that residual stress at the interface to base metal should be considered carefully. The residual stress of the base metal near the clad edge is confirmed within the tolerance of crack generation. Controlling methods both during and after welding processes are found to be effective for assuring the integrity of the welded components.
Analysis of Vessel and Piping Weld Fatigue Data Using the Master S-N Curve Method
Authors: Dong P. , Hong J. K.
Published: August 2008

In support of the new revision of ASME Div 2 Codes, a unified master S-N curve approach has been developed using a mesh-insensitive structural stress procedure. The effectiveness of the new maser S-N curve approach has been demonstrated in a number of earlier publications for many joint types and loading conditions, including pipe and vessel welds. In this paper, additional S-N data for pipe girth welds and vessel welds are analyzed using the mesh-insensitive structural stress procedure and the master S-N curve approach. The data include full scale pipe tests for applications for deepwater risers and vessel tests in support of ASME Sec. III related applications, in which some tests incorporated welds with artificially machined flaws. In addition, a great deal more data from plate joints data in offshore and marine industries has become available to the authors. Again, both the effectiveness and the validity of the master S-N curve approach have been demonstrated by collapsing all these weld S-N data from a diverse industries with drastically different joint types, plate thicknesses, and loading modes.
Residual Stress Redcution by Using Weld Metal With Property of Low-Temperature Phase Transformation
Authors: Mochizuki Masahito , Toyoda Masao , Kubo Takahiro , Morikage Yasushi
Published: August 2008

Residual stress in welded joints by using a new weld metal with the property of low-temperature phase transformation is numerically analyzed. 10 % Nickel and 10 % Chromium are involved in the developed welding material for producing the property of martensitic phase transformation at a low temperature and for generating compressive residual stress. A fillet-welded joint between plate and stiffener is used for the numerical simulation of the thermal elastic-plastic finite-element analysis with coupling phase transformation effect. Moving heat source is considered by using the gradual deposition of the finite-element during welding. Distribution of the computed residual stress mostly agrees with the measuring values by strain gauge. Compressive residual stress distributes in the weld metal for both longitudinal and transverse directions with weld line. The effects of the material of weld metal and welding pass sequence on residual stress are investigated. Residual stresses on the weld toe and root are improved lower by using the low-temperature transformation weld wire than the conventional one, regardless of the sequence of welding deposition. It is found that the weld metal with property of low-temperature phase transformation is effective to reduce residual stress near weld metal.
Residual Stress Analysis in a Thick Dissimilar Metal Weld Based on Neutron Diffraction
Authors: Ohms Carsten , Katsareas Dimitrios E. , Wimpory Robert C. , Hornak Peter , Youtsos Anastasius G.
Published: August 2008

Residual stresses in welded structural components can significantly compromise their performance and lifetime. Non-destructive measurement of such stresses remains a challenging task and neutron diffraction, in principle similar to X-ray diffraction, is used in this study. At the High Flux Reactor (HFR) of the Joint Research Centre (JRC), Petten, the Netherlands, a facility is available to investigate residual stresses in components of up to 1000 kg — the Large Component Neutron Diffraction Facility (LCNDF). Residual stress measurements in a dissimilar metal weld are presented. The specimen investigated is a full-scale mock-up of a pressure vessel to primary piping bi-metallic weld. The specimen wall thickness is 51 mm. A key issue in applying neutron diffraction to welds is the reliable estimation of the stress-free lattice spacing in the heat affected zones and weld pool. The description of the test procedure and the resulting strain/stress data are presented in this paper. Based on this a predictive FEM model has been calibrated. Comparison of test data and numerical results clearly shows that the neutron diffraction method as applied at the HFR, although touching its limits in this study, is still capable of yielding 3-D stress analysis data in steel specimens of more than 50 mm thickness.
Numerical Simulations of Residual Stresses in Repair Welded Clad Structures
Authors: Hein Hieronymus
Published: August 2008

As a consequence of inspections of the Reactor Pressure Vessel (RPV) and dependent on the indicated imperfections the possibility of special repairs on the inner RPV wall should be taken into consideration in the future. The paper contains the main results from numerical simulations of repair weld simulations on clad structures with anticipated sub-clad defects. Various specimens with different dimensions and material compositions have been investigated. The numerical simulations were supported by experimental measurements if possible. A number of parameters were varied to aid the optimization of the repair weld like the temper bead technique, the weld bead sequence, the interpass temperature and others. Moreover, some modeling issues have been addressed like hardening models and lumping of beads. The results are discussed with respect to support the repair weld optimization and appropriate modeling.
Dissimilar Girth Joints Under Combined Cyclic Thermal and Mechanical Loading: Experimental and Numerical Investigations
Authors: Mohrmann Ralf , Denner Vale´rie , Hollstein Thomas
Published: August 2008

Experimental and numerical investigations were conducted to qualify dissimilar girth welds in tubes fabricated in 9% Chromium steels T91 and E911 and the austenitic steel X3 CrNiMoN 17-13 for service temperatures up to 625°C [1]. Girth welds were produced on tubes by different welding processes such as automatic and manual TIG welding as well as friction welding. Ni-based consumables (NiCr20Nb) were used in the arc welding processes and NiCr15Fe transition rings in case of friction welded joints. The girth welds were investigated in the annealed as well as in the quenched and tempered post weld condition. The tubes were tested under combined cyclic thermal and mechanical loading [1]. A full material characterization (tensile tests at different strain rates, creep tests, low cycle fatigue tests at temperatures up to 650°C) for base metals and weld metals as well as weld thermal simulated heat affected zones were performed. This data was used to apply a non-isothermal viscoplastic Chaboche-type material model. This model describes primary, secondary and tertiary creep as well as the softening and hardening during cyclic loading. The viscoplastic model was implemented in the finite element code ABAQUS. Each material zone (base metals, three different heat affected zone materials, weld metal) was treated separately. Various finite element simulations were performed to analyze and predict the in-service behavior of the welded tubes. The comparison of long term laboratory tests with these predictions are promising.
Stress Intensity Factors Due to Residual Stresses in T-Plate Welds
Authors: O’Dowd Noel P. , Nikbin Kamran M. , Lee Hyeong Y. , Wimpory Robert C. , Biglari Farid R.
Published: August 2008

Residual stress distributions in ferritic steel T-plate weldments have been obtained using the neutron diffraction method. It is shown that the transverse residual stress distribution for two plates of different yield strength are of similar shape and magnitude when normalised appropriately and peak stresses are on the order of the material yield strength. The resultant linear elastic stress intensity factors for these stress distributions have been obtained using the finite element method. It has been shown that the use of the recommended residual stress distributions in UK structural integrity procedures leads to a conservative assessment. The stress intensity factors for the welded T-plate have been shown to be very similar to those obtained using a smooth edge cracked plate subjected to the same local stress field.
The Impact of Fracture Toughness and Weld Residual Stress of Inconel 82/182 Bimetal Welds on Leak-Before Break Behavior
Authors: Williams Craig , Brust Bud , Scott Paul , Rudland Dave , Wilkowski Gery , Tregoning Robert , Santos Cayetano
Published: August 2008

Cracks have been discovered in Inconel 82/182 bimetal welds at the hot leg to reactor pressure vessel (RPV) nozzle welds at the V. C. Summer nuclear power plant in the United States and at the Ringhals plant in Sweden. One question raised by these incidents is what impact will cracks such as these have on the possible acceptability of leak-before-break for these large-diameter piping systems. In order to address this question, fracture toughness tests in both the L-C and L-R orientation with the crack centered in both the Inconel 82/182 weld as well as in the buttered region of the bimetal weld were conducted on specimens machined from a bimetal weld obtained from a cold leg from a cancelled CE plant. In addition, weld residual stress analyses have been conducted to assess the propensity for primary-water stress-corrosion cracking (PWSCC). As part of this paper, the results from both the fracture toughness tests and weld residual stress analyses will be discussed, along with their potential impact on LBB.
Modeling and Quantitative Prediction of Environmentally Assisted Cracking Based Upon a Deformation-Oxidation Mechanism
Authors: Shoji Tetsuo , Lu Zhanpeng , Peng Qunjia , Wang Shengchun , Takeda Yoichi , Kai Akira
Published: August 2008

In order to provide a quantitative tool for predicting EAC growth rates for austenitic alloys such as austenitic stainless steels, Alloys 600 and 182 in simulated LWR environments, a model based upon the synergistic effects of deformation and oxidation at the crack tip has been proposed. In this paper, the effects of hardening, variation of K with crack growth and oxidation kinetics on EAC growth rate are described with special emphasis on field applications. The results imply recent cracking incidences in BWR core shroud and Primary Loop Recirculation (PLR) piping and PWR Vessel Penetrations (VP). In particular, the significance of oxide analysis at the crack tip and also of a kinetic approach to oxidation under stress or strain condition is described. Potential future directions for mitigation of such cracking are discussed.
Study on Growth Direction and Characteristics of SCC in Nickel Base Weld Metal in High Temperature Oxygenated Water
Authors: Kuniya Jiro , Yamamoto Michiyoshi , Fujimori Haruo , Namatame Satoshi , Suzuki Shunichi
Published: August 2008

SCC growth direction and SCC characteristics in Ni base weld metal (DNiCrFe-1J) in high temperature oxygenated water have been studied. The following results were obtained. (1) Strong direction dependence was observed in which SCC propagated preferentially along the growth direction of columnar crystals, (2) Conventional average SCC length which can be calculated from the equation in which SCC area is divided by the entire CT specimen thickness was about 1/2–3/4 times the average individual SCC length on individual columnar crystals. This was because SCC does not go through the entire thickness of the CT specimen. On the other hand, maximum SCC length was almost equal to the average individual SCC length produced on individual columnar crystals. Thus, the average individual SCC length and/or maximum SCC length were judged to be appropriate lengths for obtaining the SCC growth rate of Ni base weld metal (DNiCrFe-1J).
Finite Element Modelling of Fatigue Damage Using a Continuum Damage Mechanics Approach
Authors: De Jesus A. M. P. , Ribeiro A. S. , Fernandes A. A.
Published: August 2008

In this paper, a fatigue model formulated in the framework of the Continuum Damage Mechanics (CDM) is presented. The model is based on an explicit definition of fatigue damage and introduces a kinematic damage differential equation formulated, directly, as a function of the number of cycles and the stress cycle parameters. The model is initially presented for uniaxial problems, which facilitates the identification of its constants. An extension of the fatigue model to multiaxial problems is also proposed. This model was implemented in a non-linear finite element code in conjunction with a constitutive model for cyclic plasticity. The cyclic plasticity model considered is based on a J2-plasticity theory with non-linear isotropic and kinematic hardenings. In order to enhance the description of the cyclic elastoplastic behaviour, is suggested the superposition of several non-linear kinematic hardening variables. Both fatigue and plasticity models are identified for the P355NL1 (TStE355) steel. Finally, the numerical model is used to predict the fatigue crack initiation for a welded nozzle-to-plate connection, made of P355NL1 steel, and results are compared with experimental fatigue data.
Design Criteria for Biaxial/Multiaxial Low Cycle Fatigue
Authors: Itoh Takamoto , Sakane Masao , Hata Takahiro
Published: August 2008

This paper discusses a design procedure for structural components subjected to proportional and nonproportional low cycle fatigue damage. Strain multiaxiality and nonproportional factor were introduced for discussing the procedure. The applicability of the multiaxial proportional and nonproportional parameters was examined for the accurate prediction of proportional and nonproportional fatigue lives. A design flow was presented that indicates judging method to use uniaxial, multiaxial proportional or nonproportional damage law. The necessary data for the judgment were the exponent of Coffin-Manson law, a constant that expresses the amount of additional hardening and strain history.
Life Prediction for Notched Components in Nonproportional Low Cycle Fatigue: Experiment and FEM Analysis
Authors: Sakane Masao , Itoh Tsuneo , Susaki Tomoshige , Kawazoe Yoshiyasu
Published: August 2008

This paper studies the low cycle fatigue of circumferential notched specimens of type 304 stainless steel in nonproportional loading. Strain controlled tension-torsion low cycle fatigue tests were carried out using the notched specimens under 15 strain paths. Crack initiation lives detected by a d.c. potential method were discussed in relation to the strain concentration factors and strain histories. Finite element analyses were carried out for evaluating the local strain at the notch root using elastic-perfectly plastic and bi-linear models. The maximum principal strain and nonproportional strain ranges conservatively estimated the crack initiation lives of the notched specimens.
Plastic Loads for Internally Pressurized Toroidal Shells
Authors: Blachut J.
Published: August 2008

Tests on two internally pressurized toroidal shells are described in the paper. These were laboratory scale models manufactured by welding 90°, 316L steel elbows. Outside diameter of toroids was about 310.0 mm, radius of the tube was about 41.0 mm and the wall thickness was about 3.0 mm. Comparison of experimental and numerical plastic loads, based on pressure versus volume change plots, is given. The magnitude of experimentally derived plastic loads was about 16.0 MPa which was close to numerical predictions. Both shells failed by developing cracks in welds, at nozzles, at pressure of about 33.0 MPa.
Fatigue Crack Growth Curve for Austenitic Stainless Steels in PWR Environment
Authors: Nomura Yuichiro , Tsutsumi Kazuya , Kanasaki Hiroshi , Chigusa Naoki , Jotaki Kazuhiro , Shimizu Hidetaka , Hirose Takashi , Ohata Hitoshi
Published: August 2008

Although reference fatigue crack growth curves for austenitic stainless steels in air environments and boiling water reactor (BWR) environments were prescribed in JSME S NA1-2002, similar curves for pressurized water reactors (PWR) were not prescribed. In order to propose the reference curve in PWR environment, fatigue tests of austenitic stainless steels in simulated PWR primary water environment were carried out. According to the procedure to determine the reference fatigue crack growth curve of BWR, which of PWR is proposed. The reference fatigue crack growth curve in PWR environment have been determines as a function of stress intensity factor range, Temperature, load rising time and stress ratio.
Evaluation of Environmental Effects on the Fatigue of Notched Specimen of Austenitic Stainless Steel Using Modified Rate Approach Method
Authors: Sakaguchi Katsumi , Asada Yasuhide , Itatani Masao , Saito Toshiyuki
Published: August 2008

Fatigue testing was conducted on notched specimens of austenitic stainless steel 316NG in high temperature water. Specimens were notched round bar with elastic stress concentration factors Kt of 1.4 and 3. For the specimen of Kt = 3, fatigue test was also performed in high temperature air. Environmental correction factor Fen recently proposed by Environmental Fatigue Tests (EFT) project in Japan Nuclear Safety Organization (JNES) was applied to the result of fatigue test to evaluate the environmental effects on fatigue life of notched specimen. Since the notch root strain varies non-proportionally to nominal strain in the elastic-plastic region, the modified rate approach method was applied to predict the fatigue life of notched specimen in the water, which was proposed to account for the environmental effect on fatigue life of nuclear component materials under varying conditions. Notch root strain and strain rate were calculated by FEM analysis. The difference between predicted and experimental fatigue lives in high temperature water was within factor of 2 for Kt = 3. The relationships between fictitious stress amplitude at notch root (= notch root strain amplitude multiplied by elastic modulus) and corrected fatigue life shows good coincidence with best fit curve for austenitic stainless steels. It is concluded that the modified rate approach method and current environmental correction factor Fen proposed by EFT project is applicable to predict fatigue life of the stress concentration when the notch root strain is adequately estimated.
Evaluation of Fatigue Damage on Operating Plant Components in LWR Water
Authors: Higuchi Makoto , Hirano Takashi , Sakaguchi Katsumi
Published: August 2008

The effects of LWR water environments on fatigue life reduction of LWR component materials have been evaluated quantitatively. The environmental correction factor Fen, which is determined by strain rate, temperature and dissolved oxygen content has been proposed for assessing this reduction in the case of carbon, low alloy and austenitic stainless steels. Equations to calculate Fen have been established based on fatigue data derived under constant test conditions but strain rate and temperature in actual transients are usually not constant. A method for calculating Fen under conditions of continuously changing strain rate and temperature was established in this study for use in assessing fatigue damage on actual transients, with due consideration to the effects of LWR water environments. The method should be found applicable to Class 1 vessels. It should be possible to determine the stress cycle and fatigue usage factor in air in accordance with the ASME B&PV Code Section III NB-3200. Fatigue damage in LWR water may be found by linear summation of the products of Fen and partial fatigue usage factor in stress cycles. The method is consisted of simple and detailed methods. The evaluation of Fen must be applied for the strain range in which the strain increases continuously. In the simple method, the entire range of stain increasing is used as one segment and the average strain rate and the highest temperature in it are used for computing Fen. In the detailed method, the strain increasing range should be divided into small segments and average strain rate and highest temperature in it are used for finding Fen and Fens in all segments are subsequently averaged by weighting with strain increment in it. The Fen by this latter procedure was found much less than with the former under a condition of considerable temperature change.
Integrity Assessment of Pressure Components With Local Hot Spots
Authors: Seshadri R.
Published: August 2008

Local hot spots can occur in some pressure vessels and piping systems used in industrial processes. The hot spots could be result of, for instance, localized loss of refractory lining on the inside of pressure components or due to a maldistribution of process flow within vessels containing catalysts. The consequences of these hot spots on the structural integrity of pressure components are of considerable importance to plant operators. The paper addresses structural integrity issues in the context of codes and standards design framework. The interaction of hot spots as is the case when multiple hot spots occur is addressed. An assessment method suitable for Level 2 “Fitness-for-Service” evaluation is discussed, and applied to a commonly used pressure component configuration.
B2' Stress Indices for Elbows Using Non-Linear Finite Element Analysis
Authors: Venkataramana K. , Bhasin V. , Vaze K. K. , Kushwaha H. S.
Published: August 2008

Nuclear power plants are designed to withstand earthquake loads without severe damage under service level D conditions. Under earthquake induced reversing dynamic load, nuclear power plant components may undergo plastic deformation. Plastic deformation in class I nuclear power plant piping systems is limited by Equation (9) of ASME Boiler & Pressure Vessel Code [14], Section III, NB-3652. In the year 2000, the ASME B&PV Code was revised to accommodate reversing dynamic loading in which the failure mode is fatigue ratcheting, instead of plastic collapse. This modified equation [16] contains B2′ index, which is given as a fraction of B2 index where, B2 is defined for monotonic loading [17]. In this study a new definition is proposed for calculating B2′ stress index which is given by B2′ = MCLcyclicRange,straightpipe/MCLcyclicRange,component, where MClcyclicRange is the range of collapse moment. Incremental elastic-plastic nonlinear finite element analyses are performed considering both material and geometric nonlinearities. Kinematic hardening, isotropic hardening and elastic-perfectly plastic material models have been used to model the material behavior during plastic deformation. Load deflection curves are obtained and from these curves collapse loads for monotonic and cyclic loading are determined. B2 and B2′ stress indices are computed for elbows using the proposed equation. The computed stress indices are compared with ASME Code values.
JSME Code on Protection Design Against Postulated Pipe Rupture for Nuclear Power Plants
Authors: Kitsukawa Keisuke , Yokota Hiroshi , Murayama Koichi , Ueda Hiroshi , Takada Yasukazu , Kobayashi Hideo
Published: August 2008

As one of the Codes for Nuclear Power Generation Facilities, “Rules on Protection Design against Postulated Pipe Rupture for Nuclear Power Plants (JSME S ND1-2002)” has been developed by the JSME Committee on Power Generation Facility Codes from October 2001 and published in December 2002. The code covers the design for protection against postulated pipe rupture in nuclear power plants and gives the basic plan of protection design, locations of postulated pipe rupture, methods of determining the rupture type and opening area, and a procedure for evaluating jet impingement phenomena. It is a special feature of the code that the LBB (Leak Before Break) concept is applied to the determination of the piping rupture type, which belongs to RCPB, or to the main steam and feed water system inside the PWR containment vessel. Types of piping material applicable to the LBB concept are austenitic stainless steel, carbon steel and low-alloy steel. Furthermore, the code provides the flow and the method of LBB evaluation. In this paper, we describe the major rules of the code, including an outline of LBB evaluation methods.
Application of Potential Drop Technique to the Inspection of Welded Boiler Pressure Parts
Authors: Hamada Seiichi , Ogawa Yasuki , Iida Hideo , Kuroiwa Tomoki , Kuroki Masahiko , Hayakawa Manabu
Published: August 2008

In this paper, a practical method using the electrical potential drop technique was discussed to evaluate the creep damage accumulated in the welded power piping such as main steam pipe and hot reheat pipe. Round robin experimental measurements conducted by the authors et al. as academic activities in the Japanese Society for Non-destructive Inspection showed that the potential drop technique is effective for the application to the inspection of welded boiler pressure parts. The authors have conducted additional experimental and numerical studies for verification focusing on the application of the pulsed direct current potential drop technique. The authors have proposed technical requirements on the potential drop technique for the application to the inspection of welded power piping to be implemented in JSME Codes for Thermal Power Generation Facilities (2003 Edition) as a non-mandatory appendix JA. And the practical on-line measurement in the high temperature and high pressure burst test using the repair-welded power piping has been conducted. In this burst test, Tokyo Electric Power Company has tried to monitor the creep damage accumulated in the seam-welded area using the commercialized tool based on pulsed direct current potential drop technique.
What’s New in ASME Section II, Materials, 2004
Authors: Gold Michael
Published: August 2008

The major changes that have happened, or that will happen soon, since the publication of the 2001 Edition, concern metrication of Part D, revising Tables 2A and 2B of II-D to be consistent with the U and Y-I tables; providing values for new Divisions and Sections of the construction codes; providing more information on what data is required for new materials; providing guidance on metallurgical phenomena that can affect behavior of materials used in code construction; and changes to make Section II, Part D more user friendly.
Application Experiences of ASME Section III Code in Korea
Authors: Choi Sung Pyo , Kim Nam Ha
Published: August 2008

ASME Section III has been the most important Code for the design and construction of nuclear components for over 30 years in Korea. During that time, some difficulties have been recognized in compliance with the Code due to the differences in industrial practices and regulatory system between Korea and the U.S. In case of NCA (General Requirements for Division 1 and 2), the administrative and procedural requirements have been applied as modified to suit domestic industry practices. For technical aspects, supplemental requirements have been added to ASME Code in order to satisfy regulatory guides. Preheating and PWHT requirements of ASME Section III are slightly different from those of ASME B 31.1. The differences are discussed in this presentation. With the issuance of MOST (Ministry of Science & Technology) notice 96-32 in 1996 regarding KEPIC (Korea Electric Power Industry Code) application, KEPIC MN has been used in selected documents instead of ASME Sec. III. Ulchin 5&6 is the first project that applied to KEPIC. The application of KEPIC - MN has been gradually expanding to the subsequent nuclear projects. For consistent use of KEPIC, some measures for foreign vendors’ application of KEPIC should be considered.
What’s New in Section VIII [2002 Through 2003]
Authors: Pastor Thomas P.
Published: August 2008

It has been a three years since I last prepared a summary of significant revisions to the Section VIII Pressure Vessel Code. In addition to the routine maintenance and upgrade revisions that occur in each annual addenda to the Code, there are several major activities under way that will have a significant impact on Section VIII in the future. One of these is the rewrite of Section VIII, Division 2. The second is the publication of the 2004 Edition of the Boiler Pressure Vessel (B&PV) Code in SI units.
Comparative Study: EN 13445/ASME Section VIII Div. 1 & 2
Authors: Preiss Reinhard , Zeman Josef L.
Published: August 2008

EN 13445 is a modern, complex standard, incorporating many different ideas from acknowledged national standards, and also some new ideas, based on relatively recent research in various fields of technology.
Technical Basis for Equations for Stress Intensity Factor Coefficients in ASME Section XI Appendix A
Authors: Cipolla Russell C. , Lee Darrell R.
Published: August 2008

The stress intensity factor (KI) equations in ASME Section XI, Appendix A are based on non-dimensional coefficients (Gi) that allow for the calculation of stress intensity factors for a cubic varying stress field for a surface crack, and linear varying stress field for a sub-surface crack. Currently, the coefficients are in tabular format for the case of a surface crack in a flat plate geometry. For the buried elliptical flaw, the Gi coefficients are in graphical format. The tabular/graphical form makes the computation of KI tedious when determination of KI for various crack sizes is pursued. In this paper, closed-form equations are developed based on a weight function representation for the KI solutions for a surface crack. These equations permit the calculation of the Gi coefficients without the need to perform tabular interpolation within the current tables in Article 3320 of Appendix A. The equations are complete up to a fourth order polynomial representation of applied stress, so that the procedures in Appendix A have been expanded. The fourth-order representation for stress will allow for more accurate fitting of highly non-linear stress distributions, such as those depicting high thermal gradients and weld residual stress fields. It is expected that the equations developed in this paper will be added to the Appendix A procedures. With the inclusion of equations to represent Gi, the procedures of Appendix A for the determination of KI can be performed more efficiently. This is especially useful in performing flaw growth calculations where repetitive calculations are required in the computations of crack size versus time. The equations are relatively simple in format so that the KI computations can be performed by either spreadsheet analysis or by simple computer programming languages. The format of the equations is generic in that KI solutions for other geometries can be added to Appendix A relatively easily.
Background and Technical Basis for the Evaluation of Flaws in PWR Reactor Vessel Head Penetration Regions
Authors: Bamford Warren , De Boo Guy
Published: August 2008

Acceptance criteria have been developed for indications found during inspection of reactor vessel in upper head penetrations. These criteria were originally developed for inside surface flaws, as part of an industry program coordinated by NUMARC (now NEI) in 1992. These criteria were not inserted into Section XI at the time, because inspections were not required for these regions. In developing the enclosed acceptance criteria, the approach used by the industry group was similar to that used in other portions of Section XI, in that an industry consensus was reached using input from the operating utility technical staff, each of the three PWR vendors, and representatives of the NRC staff. The criteria developed are applicable to all PWR plant designs. The discovery of leaks at Oconee, ANO-1, and several other plants, have led to the imposition of inspection requirements for head penetration regions, and therefore the need to develop criteria for indications in all portions of the tubes. This would include indications on the inside diameter of the tube, as well as on the outside diameter of the tube below the attachment weld, and flaws in the attachment weld itself. The criteria presented herein are limits on flaw sizes which are acceptable. The criteria are to be applied to inspection results. It should be noted that determination of the period of future service during which the criteria are satisfied is plant-specific and dependent on flaw geometry and loading conditions. It has been previously demonstrated by each of the owners groups that the penetrations are very tolerant of flaws. It was concluded that complete fracture of the penetration would not occur unless very large through-wall flaws were present; therefore, protection against leakage during service is the priority. The approach used here is more conservative than that used in Section XI applications where the acceptable flaw size is calculated by putting a margin on the critical flaw size. In this case, the critical flaw size is far too large to allow a practical application of this approach, so protection against leakage is the key element used to define the acceptance criteria. Also, the use of flaw acceptance standards tables is not allowed for this region, for penetrations which are susceptible to stress corrosion cracking. The acceptance criteria apply to all flaw types regardless of orientation and shape. The same approach is used by Section XI, where flaws are characterized according to established rules and their future predicted size is then compared with the acceptance criteria.
Main Surface Crack Propagation and Crack Initiation and Propagation on Counter Plain Surface Under Cyclic Bending
Authors: Gotoh Jin’ichiro , Usami Saburo , Morita Hiroshi
Published: August 2008

Cyclic bending is a dominant loading mode in structures sustaining thermal loads. Under cyclic bending loads, a crack also initiates and propagates on the counter surface while the main crack grows. And then, these cracks meet and penetrate the thickness of the component. Numerical analysis was performed for the evaluation of the main elliptical crack propagation and crack initiation and propagation at the counter surface under cyclic out-of-plane bending. An inelastic three-dimensional finite element analysis took crack opening and closure into account. When the front surface is in tension, the main crack opens and the compressive strain on the counter surface increases. Thus, deeper the main crack, larger the total strain range on the counter surface and this stimulates crack initiation on the counter surface. As the main crack propagates, the J-integral range at the deepest point decreases for deeper than 40 % of the plate thickness, and the crack grows slower. On the other hand, the J-integral range of the counter surface crack increase rapidly and crack propagation rate of the counter crack becomes larger than that of the main crack. Both the cracks on front and counter surfaces meet near 2/3 of the plate thickness of the component. The calculated crack propagation rates in both longitudinal and depth directions of the main and the counter surface cracks based on the J-integral ranges are close to the experimental ones.
Finite Element Analysis on the Failure Behavior of Straight Pipe With Wall Thinning
Authors: Inoue Ken , Takahashi Koji , Ando Kotoji , Ahn Seok Hwan , Nam Ki Woo , Hasegawa Kunio
Published: August 2008

Monotonic four-point bending tests were conducted using straight pipe specimens 102 mm in diameter with local wall thinning in order to investigate the effects of the depth, shape, and location of wall thinning on the deformation and failure behavior of pipes. The local wall thinning simulated erosion/corrosion metal loss. The deformation and fracture behavior of the straight pipes with local wall thinning was compared with that of non wall-thinning pipes. The failure modes were classified as local buckling, ovalization, or crack initiation depending on the depth, shape, and location of the local wall thinning. Three-dimensional elasto-plastic analyses were carried out using the finite element method. The deformation and failure behavior, simulated by finite element analyses, coincided with the experimental results.
Comparison of Predicted Transition Temperature Shifts Between Static Fracture Toughness and Charpy-V Impact Properties Due to Irradiation for an A508 Pressure Vessel Steel
Authors: Tanguy B. , Besson J. , Bouchet C. , Bugat S.
Published: August 2008

Nuclear pressure vessel steels are subjected to irradiation embrittlement which is monitored using Charpy tests. Reference index temperatures, such as the temperature for which the mean Charpy rupture energy is equal to 56 J (T56J), are used as embrittlement indicators. The safety integrity evaluation is performed assuming that the shift of RTNDT due to irradiation is equal to the shift of T56J. In this work a material model integrating a description of viscoplasticity, ductile damage and brittle fracture is used to simulate both the Charpy test and the fracture toughness test (CT geometry). The model is adjusted on an unirradiated material. It is then applied to irradiated materials assuming that irradiation affects hardening. It is shown that irradiation probably also affects brittle failure. The shift of RTNDT and the predicted shift of T100MPam are then compared for a given level of irradiation.
Probabilistic Assessment of Margins in Appendix G Methodology
Authors: Yoon K. K. , Gunawardane H. P. , Rosinski S.
Published: August 2008

The pressurized thermal shock (PTS) re-evaluation program has been developed at the US NRC with the interaction of the EPRI Materials Reliability Program to revisit the PTS issue using new technology developed over the last decade. The results are encouraging as more realistic assessments of reactor pressure vessel (RPV) integrity are now possible using the NRC probabilistic fracture mechanics code FAVOR. This technology is now being considered for application to the ASME Code Section XI Appendix G methodology for pressure-temperature limit curves. This paper is a first attempt to use a FAVOR-type code to evaluate the true safety margin of nuclear power plant operational pressure temperature limits, especially low temperature over pressurization events. Preliminary results indicate that there is ample room for relaxing these limits based on this probabilistic approach.
Comparison of J-Integral Values and J-R Curves Between Carbon Steel Compact Tension Specimen and Pipe Specimen
Authors: Takanashi Masahiro , Izumi Satoshi , Sakai Shinsuke , Miura Naoki
Published: August 2008

In the present study, the transferability of elastic-plastic fracture toughness from a small-scale to a large-scale specimen was experimentally confirmed for carbon steel pipe with mild toughness. Fracture toughness tests were carried out on a pipe specimen 318.5 mm in outer diameter, 10.3 mm in thickness and having a through-wall crack, and also on a compact tension specimen 9.7mm in thickness, 25.4 mm in width, that had been cut out from the pipe specimen. Test results indicated the J-integral value of the pipe specimen at the crack initiation to be nearly twice that of the CT specimen. Finite element analysis conducted on the two specimens indicated this difference to arise primarily from the constraint near the crack front. Discussion was also made of the effects of crack orientation on elastic-plastic fracture toughness of CT specimens. The J-integral value at crack initiation in the specimen whose crack direction coincided with the pipe axial was found to be almost 54 % more than for specimens whose crack direction was circumferential.
A Two-Parameter Description of the Behaviour of a Process Zone at a Crack Tip: Part I — General Theory
Authors: Smith E.
Published: August 2008

In quantifying the behaviour of a sharp crack, considerable use has been made of the cohesive process zone description of the non-linear micro-mechanistic processes that are operative in the immediate vicinity of a crack tip. With this description, the non-linearity is modelled so that it is confined to an infinitesimally thin strip, and the analysis is considerably simplified if the description is coupled with the assumption that the stress is uniform within the process zone. When the process zone size is very small compared with the crack size and other dimensions associated with a configuration (the so-called small-scale yielding situation), the crack tip stress intensity factor defines the various parameters associated with the crack: crack tip opening displacement vT, process zone size s, crack opening area A and the effective opening area AD of the process zone. The stress intensity factor relates to the first term in the expansion of the expression for the relative displacement of the faces of an elastic crack, or the expression for the stress ahead of an elastic crack. This paper shows how the various crack parameters vT, s, A and AD are also related to the second term in the expansion of the relative displacement expression, when we relax the assumption that the process zone is very small, i.e. when we proceed beyond the small-scale yielding situation.
Meshless Dynamic Relaxation Technique for Simulating Atomistic Models Subjected to External Forces Under the Periodic Symmetry
Authors: Pan Li , Metzger Don , Niewczas Marek
Published: August 2008

The movement of dislocations, under the potential energy and the external driving forces, affects the performance of materials in various applications. This paper demonstrates meshless Dynamic Relaxation (DR) technique and the Embedded Atom method (EAM) potential function for simulations of the relaxation of atomistic models with dislocation defects subjected to external forces. A newly developed periodic symmetry method is incorporated into the algorithm and applied to one coordinate direction of the atomistic model, as well as the net traction on the periodic boundary in order to mimic an infinite bulk with a finite number of atoms. Output stress and displacement components are used to visualize the results and are in agreement with theoretical analysis. The numerical treatments, such as the application of the new periodic symmetry technique in the EAM potential model, the convergence criterion, the unit length, the choice of damping ratios in different cases and the stable range of net traction, are studied. The example case, which illustrates the pure edge dislocation model with and without the external force along the periodic direction, is successfully implemented and presented in the paper.
Prediction of Trimming Process Parameters in Aluminum Sheet Materials Using FE Method
Authors: Situ Quan , Jain Mukesh K. , Metzger Don R.
Published: August 2008

The trimming process is an important step to achieve good dimension and shape of a final product. However, it requires a systematic study of the various parameters involved in material separation. The finite element method was utilized to simulate the trimming process of aluminum sheet materials in aspects of material properties, tooling conditions and process parameters, including different tool configurations, clearances and punch speeds. Punch load versus displacement diagrams and cut edge morphologies obtained from representative clearances and tool configurations were investigated. A two-dimensional plane strain trimming was analyzed using a rate independent material model. An experimentally measured fracture strain was utilized in FE modeling for fracture initiation and development using element deletion technique. A thermally coupled material model was tentatively tested. Results from simulations were compared with experiments and good agreement was obtained for most of the studied conditions. Optimal trimming process parameters such as specific tool configuration, clearance and punch speed are suggested.
Deformation Behaviour of a Transversely Loaded Garter Spring
Authors: Leitch Brian W.
Published: August 2008

The CANDU power generation system is based on a natural uranium fuelled reactor with a heavy water moderator. A unique feature of the CANDU reactor is the horizontal fuel channel that allows on-line re-fuelling and fuel management. Pressure tubes containing the fuel bundles and pressurized heavy water coolant are the in-core component of the fuel channel assemblies. Calandria tubes span the length of the reactor core and provide passageways for the pressure tubes through the reactor core. The calandria and pressure tubes are each approximately 6 meters long. The calandria tube separates the heavy water moderator (∼80°C) from the pressure tube (∼300°C). Both tubes are subjected to gravity loads but the pressure tube carries the additional load of the fuel bundles as well as experiencing high temperature and irradiation induced material effects. The pressure tube deflects under the combined loading and areas of the pressure tube could come into contact with the calandria tube. This contact would limit the operating efficiency and lifetime of the fuel channel. To maintain a gap between the pressure and calandria tubes, helical springs manufactured from rectangular cross-section wire are placed over the pressure tube. These helical springs are known as garter springs and four such springs are spaced along the pressure tube. Initially, there is no contact between the springs and the calandria tube, but as gravity forces and creep effects begin to act, the pressure tube sags and garter spring/calandria tube contact occurs. As the pressure tube continues to deform, a portion of the pressure tube weight, fuel and coolant is transmitted through the garter spring onto the calandria tube. The calandria tube, in turn, begins to deflect under the applied stresses. This creep deformation of the fuel channel takes place over many thousands of operating hours. Eventually, creep induces a permanent vertical deformation (sag) in the fuel channel. The sag of a fuel channel is an important factor in the operation of the structure and many methods are used to determine the general response of the pressure tube/calandria tube/garter spring system. These methods assume the garter spring is a rigid component. This paper specifically examines the garter spring behaviour with respect to the non-linear material and contact response between the pressure tube/garter spring/calandria tube components. A three dimensional (3-D) finite element solid model of the garter spring is used to determine the non-linear response of the helical garter spring to the transverse forces applied from 3-D shell finite element models of the pressure and calandria tubes. Comparison with experimental, crushing tests on garter springs illustrate the analytical model is well behaved. Applying the operating load to the 3-D model shows that the garter spring’s transverse deformation is small and that assuming the garter spring is a rigid component is valid.