bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Weld Induced Residual Stresses on Pipe Crack Opening Areas and Implications on Leak-Before-Break Considerations
Authors: Fredette Lee , Brust F. W.
Published: August 2008

The USNRC is anticipating updating their leak-before-break (LBB) procedures. One of the technical areas of concern in the existing procedures is the prediction of the crack-opening-displacements (COD) needed for estimating the postulated leakage crack size for a prescribed leakage detection capability. If cracks develop in the welded area of a pipe, as is often the case, residual stresses in the weld may cause the crack to be forced closed. Earlier studies have shown that pipe welding produces high residual stresses with a sharp stress gradient ranging from tension to compression through the thickness of the welded area of the pipe. The current guidelines are inadequate to predict crack size based on leak rates for cracks in welded areas of pipes. The current guidelines rely on the calculation of the crack-opening-displacement as related to pipe loading. Values from the current guidelines are used to predict a crack’s cross sectional area and, in turn, to determine the severity of an existing crack by monitoring in-service leakage rates. The equations currently in use are applicable to service loaded pipe material only. Residual stresses caused by cold work, welding, etc. are neglected. This study uses two and three dimensional finite element models and weld residual stress calculation software created at Battelle Memorial Institute to develop correction factors to be used with the traditional design equations. The correction factors will compensate for the effects of welding induced residual stresses on cracks in pipe welds. This study concentrates on type 316 stainless steel material properties, but the COD corrections should be equally applicable to all stainless steels, and also can be used for ferritic steels. A test matrix of pipe radius, thickness, and crack size was used to develop the equation correction factors. Pipe wall thicknesses (t) of 7.5 mm (0.295 in.), 15 mm (0.590 in.), 22.5 mm (0.886 in.), and 30 mm (1.181 in.) were studied in pipes with mean radius to thickness ratios of 5, 10, and 20. Cracks with half-lengths in radians of π/16, π/8, π/4, and π/2 were introduced in these virtual pipes. The matrix of results was used to produce correction factors for crack opening displacement equations applicable to a broad range of pipe sizes.
Three-Dimensional Analysis of In-Process Distortion Control in Fillet Welded Joints by Additional Cooling
Authors: Mochizuki Masahito , Takahashi Nobuki , Toyoda Masao
Published: August 2008

Control of welding distortion should be performed during the welding procedure rather than making adjustments after welding. Numerical simulation with three-dimensional model of in-process distortion control in fillet welds is studied in this paper. Moving arc processes and the deposition of the weld metal are considered in the analysis with temperature-dependant material properties. Additional cooling of the weld metal near the melting zone while keeping a fixed distance is done during the welding process so that the transient thermal distortion becomes smaller. The effectiveness of the additional cooling method is evaluated.
Effect of Small Amount of Bismuth on Corrosion Resistibility of Austenitic Stainless Steel Weld Metals
Authors: Hara Yasuhiro , Shiga Keisuke , Nakazawa Nobuo
Published: August 2008

Flux-cored are welding (FCAW) has increased recently because of high welding efficiency. However, a small amount of bismuth in the weld metals was a residue from the flux component that was added for improving slag detachability. The effect of small amount of bismuth in austenitic stainless steel weld metal on corrosion behavior in wet corrosion environment is not adequately clear because there is little reported to date. In the present research, the effect of bismuth which remained in the weld metal on the corrosion behavior of 308-type weld metal in wet corrosive solution was examined by using different bismuth containing weld metal. Measurement of the anodic polarization curve in a sulfuric acid solution, determination of pitting potential and conducting stress corrosion cracking (SCC) tests in a chloride solution, and implementation of boiling nitric add solution tests were conducted. In addition, the corrosion behavior of the FCAW weld metal was compared with that of Bi-free weld metals by shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) to clarify how the corrosion behavior varies between the welding processes. In this research, no noticeable adverse effect of bismuth remained in the 308-type austenitic FCAW weld metals was observed in corrosion test.
Experimental Investigation of Constraint Effects on Creep Crack Growth
Authors: Bettinson Adam D. , O’Dowd Noel P. , Nikbin Kamran M. , Webster George A.
Published: August 2008

In this work the effects of specimen size and type on creep crack growth rates in stainless steel are examined. Experiments have been carried out on high constraint compact tension specimens (CT) and low constraint centre cracked panels (CCP) of ex-service 316H stainless steel. All testing was carried out at 550°C. Constraint effects have been observed in the data, with the large CT specimens having the fastest crack growth rate and the small CCP specimens the slowest. These trends are consistent with those that would be predicted from two parameter (C*–Q) theories. However, it is found that a constraint dependent creep crack growth model based on ductility exhaustion overpredicts the constraint dependence of the crack growth data.
Creep and Creep-Fatigue Strength Property of a Long-Term Used Boiler Weldment Parts of 2.25Cr-1Mo Steel
Authors: Ogata Takashi
Published: August 2008

The purpose of this study is to make clear effect of material degradation on creep and creep-fatigue properties of a weldment. Materials used in this study were a weldment of a boiler super header operated for about 200,000 hours (U weld joint) and a simulated as-received weldment (S weld joint). In the U weld joint, although creep cavities were not observed at all, significant coarsening of carbide precipitation and low dense dislocation structure were observed at all locations in the weldment compared with microstructure of the S weld joint. Creep rupture time of the U weld joint is shorter than that of the S weld joint at higher stress region, while the discrepancy of the rupture strength tends to disappear as stress level becomes lower. Strain controlled creep-fatigue tests with 1 hour and 10 hours strain hold time at the maximum tensile strain were performed at strain range of 0.3% and 0.5% on S and U weld joints. No difference of failure life between materials was observed. Reduction in failure life by introducing strain hold period becomes larger as decreasing strain range level indicating that creep-fatigue interaction is enhanced under lower strain range. Based on the nonlinear damage accumulation model, a simplified creep-fatigue life prediction method of weldments under creep-fatigue loading conditions was proposed. It was demonstrated that failure lives under the long-term creep-fatigue conditions were well predicted by the simplified prediction method.
Thermal-Hydraulic Response in the Discharge Piping With Water Pool
Authors: Bang Young S. , Ahn Hyung J. , Kim In-G. , Kim Hho J.
Published: August 2008

Thermal-hydraulic response in the discharge piping at the upstream of water pool following the opening of the safety relief valve is analyzed. To predict the basic pressure wave propagation and interaction with reflection wave, the RELAP5/MOD3 code is used. Pressure wave propagation behavior in a simple geometry is calculated and the effect of the important parameters including the loss factor, the pipe configuration, the water slug inflow, the valve opening time, and subdivision of sparger are investigated. And the affecting factors influencing the pressure wave propagation and their mechanisms are discussed.
Measurement of Pressure Drop in a Liquid Metal Reactor Fuel Assembly
Authors: Choi Seok Ki , Choi Il Kon , Lee Kil Yong , Nam Ho Yun , Choi Jong Hyeun , Choi Hoon Ki
Published: August 2008

An experimental study has been carried out to measure the pressure drop in a 271-pin fuel assembly of a liquid metal reactor. The rod pitch to rod diameter ratio (P/D) of the fuel assembly is 1.2 and the wire lead length to rod diameter ratio (H/D) is 24.84. Measurements are made for five different sections in a fuel assembly; inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. A series of water experiments have been conducted changing flow rate and water temperature. It is shown that the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly are much larger than those in other regions. The measured pressure drop data in a wire-wrapped fuel assembly region is compared with the existing four correlations. It is shown that the correlation proposed by Cheng and Todreas fits the best with the present experimental data among the four correlations considered.
An Experimental Study of EFB Behavior of Large Model Tank
Authors: Tazuke Hideyuki , Yamaguchi Satoru , Akiyama Hiroshi , Sakurai Tomoki , Chiba Toshio
Published: August 2008

We recognized the importance of the seismic capability against earthquakes of the thermal power plant on the occurrence of the Hyogoken-Nanbu Earthquake in 1995. In this respect, seismic proving tests on the equipment of the thermal power plant had been planned and carried out. Vibration tests and FEM analysis were performed to demonstrate the seismic capability of the equipment. A liquefied natural gas (LNG) tank was selected as one of the subjects. One of the remarkable nonlinear phenomena of an actual large tank was Elephant Foot Bulge (EFB). To investigate the EFB behavior of the tank, vibration test of the large scale model tank and FEM analysis were conducted. Then we estimated EFB behavior of the tank.
Stochastic Stability of Some Hamiltonian Systems
Authors: Jedrzejewski F.
Published: August 2008

Stochastic stability plays an important role in modern theories of nonlinear structural dynamics. Recently, more realistic models based on stochastic modelling and Itoˆ calculus, like flow induced vibrations and seismic excitations have been proposed. In this paper, the almost-sure asymptotic stability of some hamiltonian systems subjected to stochastic fluctuations is investigated. Dynamical systems are reduced to Itoˆ stochastic differential equations for the averaged hamiltonian by using a new stochastic averaging method. The stability of the original system is determined approximately by examining the behavior of the averaged hamiltonian. Analytical expressions for the stochastic stability exponents are obtained. The proposed procedure is illustrated on the Rayleigh Van der Pol Oscillator.
Penetration With High-Speed Friction
Authors: Jones S. E. , Davis Robert N. , Hughes Mary L. , Toness Odin A.
Published: August 2008

Work on friction dates back more than two hundred years. Some of the work applies to dynamic situations in which the influence of speed may be a factor (see Kragelskii [5]). But, most of the work does not apply to the velocity regime observed in high-speed penetration problems. This has become an issue because of the Air Force’s interest in smaller and more versatile air launched weapons. Earlier work focused on conventional friction models. Jones and Rule [2] considered optimal design of the penetrator nose in a high friction environment using Coulomb friction. Later, Jones, et al [3] used constant friction equivalent to target shear strength. While the results of these analyses were largely satisfactory, they did not completely capture the essence of the work done by friction. Recently, the authors [4] proposed a simple velocity-dependent engineering model to account for friction in high-speed penetration events. A critical velocity controlled the initiation of friction and the amount of work done by friction. The results were very satisfactory and correlated very well with experimental observations from range tests. However, there were a number of tedious integrations and numerical evaluation of some difficult integrals. In this paper, several simplifying assumptions are made which replace the numerical integration with closed form solutions. The results, while somewhat different, agree in principle with those given earlier. The same trends are observed and the correlation with independently performed experiments is excellent. Additionally, the zero asymptotic limit is replaced and its effect is considered.
Intensive Quenching Theory and Application for Imparting High Residual Surface Compressive Stresses in Pressure Vessel Components
Authors: Aronov Michael A. , Kobasko Nikolai I. , Powell Joseph A. , Freborg Andrew M. , Ferguson B. Lynn
Published: August 2008

An alternative method for the hardening of steel parts has been developed as a means of providing steel products with superior mechanical properties through development of high residual compressive stresses on the part surface, and involves the application of intensive quenching during heat treatment. This processing method, commercially patented under the name IntensiQuench SM, imparts high residual compressive stresses on the steel surface, thus allowing for the use of lower alloy steels, reduction or elimination of the need for carburization and shot peening, and providing for more cost-effective heat treating. Intensive quenching also provides additional environmental benefits, as the process uses plain water as the quenching media in contrast to traditional heat treatment practices which typically employ hazardous and environmentally unfriendly quenching oil. This paper presents an overview of the theory and application of intensive quenching, as well as provides experimental and computational data obtained for a variety of steel products. Also presented will be results of computer simulations of temperature, structural and stress/strain conditions for a typical pressure vessel during intensive quenching.
Comparison of Methods for Calculating Stress Intensity Factors for a Closure Thread
Authors: Kendall David P.
Published: August 2008

Non-mandatory Appendix D of Section VIII, Division 3 of the ASME Boiler and Pressure Vessel Code [2] provides a method for calculating the stress intensity factors for the region of a thread root of a threaded closure. This method involves calculation of the distribution of stress acting on a plane normal to the axis of the thread. This distribution is fitted with several different cubic equations for different regions and the coefficients of these cubic equations are entered into an equation to calculate the distribution of stress intensity factor for each region. The values of stress intensity factor for each region after the first one are shifted to obtain a continuous distribution. Neubrand and Burns, 1999 [1] determined the distribution of stress intensity factor for a specific closure thread using weight function methods. In the present paper the stress intensity factors for this same closure design were calculated using the method from Appendix D of Division 3 as described above. Distributions are also calculated using a proposed modification of this method, and also by the method given in Appendix D for cracks in areas of the vessel at which the gradient of the stress distribution is less steep.
Leak-Before-Burst Testing of a High Pressure Tube
Authors: Koerner Peter , Hiller Waldemar , Wink Rolf
Published: August 2008

High pressure systems like a LDPE-reactor may store a great amount of energy in the form of compressed gas. The way in which this energy is released in case of a failure is of paramount importance to the safety of the plant and its personnel. Catastrophic failure modes with a large gas release and possible metal splintering have to be avoided as far as technically possible. Therefore the failure mode needs to be analysed during the design of a high pressure system and taken into account. One important criterion for a safe pressure component is that a leak-before-burst behaviour can be ensured. This paper discusses the requirements for demonstration of this failure mode according to the design code for high pressure vessels ASME section VIII division 3. A full scale parts test using a DN-80, PN-3500 reactor tube section of a tubular LDPE-plant has been used to compare the code requirements with experimental results.
The Effect of Plasticity on Process-Zone Predictions of DHC Initiation at a Flaw in CANDU Reactor Zr-Nb Pressure Tubes
Authors: Scarth Douglas A. , Smith Ted
Published: August 2008

Delayed Hydride Cracking (DHC) in Zr-2.5 Nb alloy material is of interest to the CANDU industry in the context of the potential to initiate DHC at a blunt flaw in a CANDU reactor pressure tube. The material is susceptible to DHC when there is diffusion of hydrogen atoms to the flaw, precipitation of hydride platelets, and development of a hydrided region at the flaw tip. The hydrided region could then fracture to the extent that a crack forms, and is able to grow by the DHC crack growth mechanism. A procedure for evaluating DHC initiation at a blunt flaw that takes into account the effect of flaw geometry has been developed. This methodology can, in principle, be applied to any flaw that is found during in-service inspection. The methodology is based on representing the stress relaxation due to hydride formation, and crack initiation, by a process zone. The authors have presented predictions of DHC initiation on the basis of elastic conditions in the surrounding zirconium alloy matrix material outside of the process zone in papers presented at the 1999, 2000 and 2001 ASME PVP Conferences. In the present paper, the effects of plasticity in the surrounding zirconium alloy matrix material have been incorporated into a simple theoretical process-zone model for DHC initiation, as well as into an engineering process-zone model that is suitable for evaluation of in-service flaws. The resulting process-zone model calculations and comparisons with DHC initiation experiments demonstrate that DHC initiation predictions can be overly-conservative if plasticity is not taken into account.
LBB Assessment on Ferrite Piping Structure of Large-Scale LMFR
Authors: Yoo Y. S.
Published: August 2008

These days, the interest on LBB behavior becomes to be rising in the step of design of LMFR structural components in Japan. The governing service loading of LMFR can be identified thermal expansion stress and thermal transient stress because the operation temperature is higher than that of LWR and the liquid metals contain higher heat transfer coefficient than water. On that reason, the ferrite steel which yields less thermal expansion is considered to be desirable for the piping components of LMFR in the viewpoint of high temperature structural integrity. This study deals with LBB assessment of the primary piping components of LMFR subjected to a series of transients and the results may envision the use of ferrite steel for LMFR components.
Ductile Fracture Behavior of Carbon Steel Cracked Pipes With Moderate-Toughness
Authors: Miura Naoki , Kashima Koichi , Miyazaki Katsumasa , Hisatsune Masakazu , Hasegawa Kunio
Published: August 2008

To achieve a rational maintenance program for aged light water reactor components, it is important to establish and to improve the flaw evaluation criteria. The current flaw evaluation criteria such as ASME Boiler and Pressure Vessel Code Section XI are focused on Class 1 piping, which usually shows relatively higher toughness. On the other hand, flaw evaluation criteria suitable for Class 2 and Class 3 piping with moderate-toughness are also required because some Class 2 and Class 3 piping systems are as important to plant risk analysis as Class 1 piping. In this study, fracture experiments by four-point bending were conducted for circumferentially cracked pipes. Tested pipes were made of moderate-toughness carbon steel, STPT410 carbon steel. Ductile fracture behavior and load-carrying capacity were compared with those from elastic-plastic fracture mechanics analysis. As a result, it was ascertained that ductile fracture behavior could be well predicted by fracture mechanics analysis using J-integrals. A Z-factor approach applicable to moderate-toughness pipes was also discussed.
Validation of Constraint Based Methodology in Structural Integrity – VOCALIST: Project Overview
Authors: Lidbury David , Bass Richard , Keim Elisabeth , Bhandari Surender , Connors David , Eisele Ulrich , Nilsson Karl-Frederick
Published: August 2008

VOCALIST (Validation of Constraint Based Methodology in Structural Integrity) is a shared cost action project co-financed by the European Commission under the Fifth Framework of the European Atomic Energy Community (EURATOM). The motivation for VOCALIST is based on the observation that the pattern of crack-tip stresses and strains causing plastic flow and fracture in components is different to that in test specimens. This gives rise to the so-called constraint effect. Crack-tip constraint in components is generally lower than in test specimens. Effective toughness is correspondingly higher. The fracture toughness measured on test specimens is thus likely to underestimate that exhibited by cracks in components. The purpose of VOCALIST is to develop validated models of the constraint effect, and associated best practice advice, with the objective of achieving (i) an improved defect assessment methodology for predicting safety margins; (ii) improved lifetime management arguments. The work is intended to be of benefit to both plant operators and their regulators. The project started in October 2000 and will run for thirty-six months. The main achievements to date are as follows: • Identification and assessment of current issues affecting the application of constraint-based fracture assessment methods in practical situations. • Materials selection and identification of test matrices. • Initiation of characterisation testing. • Detailed definition of analytical programme and alignment with experimental programme. • Definition of test conditions for Benchmark and Features tests. • Procurement and execution of Benchmark tests. • Procurement and execution of scoping Features tests. This paper provides an overview of VOCALIST, describes its various Work Packages, and provides an up-to-date summary of progress as the project reaches mid-term.
A Probabilistic Application of the R6 Detectable Leakage Leak-Before-Break Procedure
Authors: Beardsmore D. W. , Yellowlees S. F. , Sharples J. K. , Ainsworth R. A. , Budden P. J.
Published: August 2008

This paper presents an assessment of circumferential defects in pipes which combines the Detectable Leakage, leak-before-break Procedure of R6 with the probabilistic assessment principles contained in R6. It shows how the equations which determine the stability of cracks and those that describe the rate of leakage can be formulated, and how Monte Carlo calculations can be carried out, to determine the limiting crack sizes for leakage detectability and crack stability. A leak-before-break case can be made if the minimum size required for a detectable leak is less than the size at which disruptive fracture would occur. A large number of independent calculations can be carried out, from which the probability of making a leak-before-break case can be established for any specified defect size. Results of calculations are presented using a series of histograms to demonstrate the probabilities obtained. The effect of including a statistical coupling between the material’s yield stress and fracture toughness is also examined.
Code Based Failure Avoidance Assessments of the NESC-1 Large Scale Pressurised Thermal Shock Experiment
Authors: Smith Michael C.
Published: August 2008

The NESC-1 large scale pressurised thermal shock experiment was designed partly as a test of the performance of structural analysis methodologies. One of the activities performed by the NESC network was a “codes and standards” round robin, which applied national failure avoidance codes to the defects in the NESC-1 cylinder. Six procedures were applied: ASME Section XI, R6 and BS PD6493:1991 (UK), KTA (Germany), SKIFS 1994:1 (Sweden), and RCCM/RSEM (France). The results were uniformly pessimistic. All the assessments predicted acceptable defect sizes in the range 1–10mm, nearly two orders of magnitude smaller than the large defects in the NESC-1 cylinder which produced only very limited crack growth during the test. The reasons for this excessive pessimism were reviewed using the R6 assessment as a representative example. Three major areas of pessimism were identified: the defect model used to represent real defects in the test cylinder, the methods used to estimate crack driving force in the presence of thermal shock stresses that cause plastic flow, and the transition fracture toughness model used. Excess pessimism in predictions of crack driving force can be minimised by use of an appropriate defect model (through-clad for surface defects, sub-clad for buried defects), and by taking account of the effects of plasticity on secondary stresses in estimates of crack driving force. Fracture toughness curves based upon the traditional ASME approach with safety factors are very pessimistic for the NESC-1 material. A statistical lower bound based upon the Master Curve provides a much better description of the material behaviour.
Experiences in Examining and Dispositioning Flaws in Zr-2.5Nb Pressure Retaining CANDU Reactor Components
Authors: Celovsky Andrew , Slade John
Published: August 2008

CANDU reactors use Zr-2.5 Nb alloy pressure tubes, as the primary pressure boundary within the reactor core. These components are subject to periodic inspection and material surveillance programs. Occasionally, the inspection program uncovers a flaw, whereupon the flaw is assessed as to whether it compromises the integrity of the pressure-retaining component. In 1998, such a flaw was observed in one pressure tube of a reactor. Non-destructive techniques and analysis were used to form a basis to disposition the flaw, and the component was fit for a limited service life. This component was eventually removed from service, whereupon the destructive examinations were used to validate the disposition assumptions used. Such a process of validation provides credibility to the disposition process. This paper reviews the original flaw and its subsequent destructive evaluation.
Cracking in Alloy 600/182 Reactor Vessel Head Penetrations
Authors: Frye Charles R. , Alley Tom , Arey Melvin L. , Robinson Michael R.
Published: August 2008

During the last fourteen months (December 2000 through February 2002), a large effort has been expended in examining and repairing cracks in reactor vessel head penetrations on the three Oconee reactor vessel closure heads. It is a typical maintenance practice during refueling outages to inspect the top of the head to detect flange leaks or other sources of boron on the top of the head. These inspections also meet requirements imposed by the Nuclear Regulatory Commission in response to numerous leaks in alloy 600 components throughout the nuclear industry [1]. When leaks were first detected, inspections and repairs of the Oconee heads resulted in large radiation doses and long outages. Each subsequent outage has shown improvement in both dose and execution time for the repairs. Metallurgical examinations have confirmed the mechanism of cracking and industry efforts have resulted in improvements in the technologies of both inspection and repair. The results of some of the metallurgical examinations are presented along with a description of some of the improvements in welding and inspection.
Crack Opening Areas During High Temperature Operation
Authors: Yellowlees S. F. , Hooton D. G. , Sharples J. K. , Budden P. J. , Dean D. W.
Published: August 2008

This paper presents results from two-dimensional finite element analyses of a centre cracked plate under both plane stress and plane strain conditions. The plate has been loaded in tension and secondary creep conditions have been assumed. The variation of the crack opening area with time has been calculated. It has been shown that the rate of change of the crack opening areas reduces with time up to the redistribution time which approximates the time to achieve steady creep conditions. Thereafter, the rate of change of crack opening area is constant. From curve fits to finite element results, a simplified expression for the rate of change of crack opening area of a stationary crack has been derived in terms of the elastic crack opening area, the creep strain rate, the elastic strain and two characteristic crack lengths (one for a strain field dominated by elastic strains and one for a strain field dominated by creep strains). This expression predicts the rate of change of the crack opening area both during the transient period up to the redistribution time and at all times thereafter.
A Corotational Flow Rule for Rigid Plastic Hardening Materials Based on Logarithmic Strain Tensor
Authors: Naghdabadi Reza , Yeganeh Mehdi , Saidi Alireza
Published: August 2008

In this paper a flow rule for rigid plastic hardening materials based on von Mises yield criterion is introduced. This flow rule relates the corotational rate of the logarithmic strain tensor to the difference of the deviatoric Cauchy stress and the back stress tensors. Using different corotational rates in the proposed flow rule, the deviatoric Cauchy stress tensor is calculated for rigid plastic isotropic, kinematic and combined hardening materials in the simple shear problem at large deformations. For the purpose of verification, the results for different corotational rates are compared with the results presented in referenced articles.
Stochastic Meshless Analysis of Elastic-Plastic Cracked Structures
Authors: Rao B. N. , Rahman S.
Published: August 2008

This paper presents a stochastic mesh-free method for probabilistic fracture-mechanics analysis of nonlinear cracked structures. The method involves enriched element-free Galerkin formulation for calculating the J-integral; statistical models of uncertainties in load, material properties, and crack geometry; and the first-order reliability method (FORM) for predicting probabilistic fracture response and reliability of cracked structures. The sensitivity of fracture parameters with respect to crack size, required for probabilistic analysis, is calculated using a virtual crack extension technique. Numerical examples based on mode-I fracture problems have been presented to illustrate the proposed method. The results from sensitivity analysis indicate that the maximum difference between sensitivity of the J-integral calculated using the proposed method and reference solutions obtained by the finite-difference method is about six percent. The results from reliability analysis show that the probability of fracture initiation using the proposed sensitivity and meshless-based FORM are very accurate when compared with either the finite-element-based Monte Carlo simulation or finite-element-based FORM. Since all gradients are calculated analytically, the reliability analysis of cracks can be performed efficiently using meshless methods.
Evaluation of Coalescence Criteria for Parallel Cracks
Authors: Kamaya Masayuki
Published: August 2008

When multiple cracks approach one another, the stress intensity factor (SIF) is likely to change due to the interaction of the stress field. Since the change in the SIF is not always conservative in structural reliability evaluations, this interaction between multiple cracks must be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code (Sec. XI) provides a flaw characterization method for considering multiple crack interactions. In Sec. XI, adjacent cracks are replaced by a coalesced single combined crack if they are located within a certain distance. However, no systematic analysis of the SIF for interacting parallel surface cracks is provided. Furthermore, the background of the coalescence criterion prescribed in Sec. XI is not clear. In this study, the SIF of interacting parallel cracks was calculated using the finite element method. A coalescence criterion for parallel cracks was then proposed based on the calculation results. A simplified mesh generation method was adopted in order to improve the complexity of the mesh generating procedure, which uses a transitional mesh, referred to as a “Tie Block.”
Determination of the Fatigue Limit: Comparison Between Experimental Tests and Statistical Simulations
Authors: Mansur Tanius Rodrigues , Pinto Joa˜o Ma´rio Andrade , Soares Wellington Antonio , Palma Ernani Sales , Colosimo Enrico A.
Published: August 2008

Fatigue limit’s of steel specimens were determined using experimental test’s and numerical simulations. The simulation was based on life distribution parameters taking into account a log-normal model. The obtained experimental results are quite close to those obtained by simulation.
Static Strength Properties of an Aluminum Alloy Honeycomb Sandwich Panel and Strength Reliability Evaluation of an Actual Car Body Structure
Authors: Takeichi Michifumi , Okuno Sumio , Okazaki Masato , Tsuruda Hitoshi , Kawano Shunichi
Published: August 2008

The hollow extrusion-type material made from aluminum alloys has recently attracted attention, and it has been used for the car bodies of high-speed railway vehicles. Hollow extrusions are laminating board structures that consist of a two-sheet board and slanting material known as a double skin structure. The double skin structure is advantageous in attaining a lightweight car body structure and in increasing rigidity in case it bends outside and the pressure load at the time of the run in tunnel acts, since rigidity is high. In this study, static tests were carried out for component models and for an experimental full-sized car body, in which aluminum honeycomb panels are applied as outside plates to improve pressure resistance, while their requisite light weight and rigidity are maintained. Experiments were conducted to determine tensile strength, bending strength and the shearing strength of the honeycomb panel. The stresses of an actual car body were under 30 MPa, which is low compared with strength of the honeycomb panel. An actual car body, then, has sufficient strength reliability.
Effects of Local Peak Stress Distribution on the Ratchet Limit
Authors: Yanagida Nobuyoshi , Tanaka Masaaki , Yamashita Norimichi , Yamamoto Yukinori
Published: August 2008

Alternative stress evaluation criteria suitable for Finite Element Analysis (FEA) proposed by Okamoto et al. [1],[2] have been studied by the Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) in Japan. Thermal stress ratchet criteria in plastic FEA are now under consideration. Two criteria are proposed: (1) Evaluating variations in plastic strain increments, and (2) Evaluating the width of the area in which Mises equivalent stress exceeds 3Sm. To verify of these criteria, we selected notched cylindrical vessel models as prime elements. To evaluate the effect of the local peak stress distribution on these criteria, cylindrical vessels with a semicircular notch on the outer surface were selected for this analysis. We used two notch configurations for our analysis, and the stress concentration factor for the notches was set to 1.5 and 2.0. We conducted elastic-plastic analysis to evaluate the ratchet limit. Sustained pressure and alternating enforced longitudinal displacements which causes secondary stress were used as parameters for the elastic-plastic analysis. We found that when no ratchet was observed, the equivalent plastic strain increments decreased and the area in which Mises equivalent stress exceeds 3Sm are below the certain range.
The Modified Rate Approach Method to Evaluate Fatigue Life Under Synchronously Changing Temperature and Strain Rate in Elevated Temperature Water
Authors: Tsutsumi Kazuya , Higuchi Makoto , Iida Kunihiro , Yamamoto Yutaka
Published: August 2008

The fatigue life of steel in elevated temperature water is strongly affected by the composition of the environmental water, temperature and strain rate. The effects of these parameters on fatigue life reduction have been investigated experimentally in these years. One problem to be discussed is the fact that the previous experiments which leaded main conclusions on the environmental effects were generally executed by keeping a set of experimental parameters constant. In the transient condition in an actual plant, however, such parameters as temperature and strain rate are not constant. In order to evaluate fatigue damage in an actual plant on the basis of experimental results under constant temperature and constant strain rate conditions, the modified rate approach method was developed. The method can be applicable to changing temperature condition and strain rate condition separately. In the present study, an additional model is proposed with considering that both temperature and strain rate change simultaneously in an actual plant. The applicability of this method is discussed and verified experimentally. The fatigue lives predicted by this method are scattered within the factor of 2 or 3 bands against test results even when several parameters changed synchronously.
A Proposal of Fatigue Life Correction Factor Fen for Austenitic Stainless Steels in LWR Water Environments
Authors: Higuchi Makoto , Iida Kunihiro , Hirano Akihiko , Tsutsumi Kazuya , Sakaguchi Katsumi
Published: August 2008

The fatigue life of austenitic stainless steel has recently been shown to undergo remarkable reduction with decrease in strain rate and increase in temperature in water. Either of these parameters as a factor of this reduction has been examined quantitatively and methods for predicting the fatigue life reduction factor Fen in any given set of conditions have been proposed. All these methods are based primarily on fatigue data in simulated PWR water owing to the few data available in simulated BWR water. Recent Japanese fatigue data in simulated BWR water clearly indicated the effects of the environment on fatigue degradation to be milder than under actual PWR conditions. A new method for determining Fen in BWR water was developed in the present study and a revised Fen in PWR water is also proposed based on new data. These new models differ from those previously used primarily with regard to the manner in which strain amplitude is considered to affect Fen in the environment.
Effects of Water Flow Rate on Fatigue Life of Ferritic and Austenitic Steels in Simulated LWR Environment
Authors: Hirano Akihiko , Yamamoto Michiyoshi , Sakaguchi Katsumi , Shoji Tetsuo , Iida Kunihiro
Published: August 2008

The flow rate of water flowing over a steel surface is considered to be one of the most important factors influencing the fatigue life of the steel, because the water flow produces differences in the local environment. The effect of the water flow rate on the fatigue life of carbon, low alloy, and austenitic stainless steels was therefore investigated experimentally. Fatigue testing of low (S = 0.008 wt%) and high (S = 0.016 wt%) sulfur content carbon steels and a low alloy steel was performed at 289°C for various dissolved oxygen concentrations (DO) of less than 0.01 and 0.05, 0.2, and 1 ppm, and at various water flow rates. Three different strain rates of 0.4, 0.01, and 0.001%/s were used in the fatigue tests. For high sulfur carbon steel (S = 0.016 wt%), the effect of a high water flow rate on mitigating fatigue life reduction was more clearly observed at a lower strain rate, irrespective of the DO. This effect of high water flow rate was most notable at a DO of 0.2 ppm, which was the DO level that produced a significant sulfur effect. This indicates that the mechanism responsible for the mitigation of fatigue life reduction is the flushing effect of the water, which eliminates the locally corrosive environment. For high sulfur carbon steel (S = 0.016 wt%), no benefit of a high water flow rate was found at a DO of 0.01 ppm. This was because the environmental effect is insignificant at this low DO level. For low sulfur carbon steel (S = 0.008 wt%) and low alloy steel (S = 0.008 wt%), a high water flow rate had little effect on mitigating fatigue life reduction even at a DO of 0.2 ppm. This indicates that the sulfur is much less influential in low sulfur steel than in high sulfur steel. Fatigue testing of Type 316 nuclear grade stainless steel (316NG) and Type 316 stainless steel (SUS316) was performed at 289°C and 320°C for DO levels of less than 0.01 and 0.05, and 0.2. For austenitic stainless steel, no mitigating effect at a high water flow rate was found. It should be noted rather that there is a possibility that a high water flow rate decreases the fatigue life because a tendency to a slight decrease in fatigue life with an increasing flow rate was observed.
Fatigue of Piping and Vessel Welds: ASME’s FSRF Rules Revisited
Authors: Dong P. , Hong J. K. , Osage D. , Prager M.
Published: August 2008

Fatigue design rules for welds in the ASME Boiler and Pressure Vessel Code are based on the use of Fatigue Strength Reduction Factors (FSRF) against a Code-specified fatigue design curve generated from smooth base metal specimens without the presence of welds. Similarly, Stress Intensification Factors (SIF) that are used in the ASME B31 Piping Codes are based on component S-N curves with a reference fatigue strength based on straight pipe girth welds conducted by Markl et al in 1950s. Typically, the determination of either the FSRF or SIF requires extensive fatigue testing to take into account the stress concentration effects associated with various types of component geometry, weld configuration, and loading conditions. As the fatigue behavior of welded joints is being better understood, it has been generally accepted that the difference in fatigue lives from one type of weld to another is dominated by the difference in stress concentration. However, general finite element procedures are currently not available for effective determination of such stress concentration effects. This is mainly due to the fact the stress solutions at a notch (e.g., at weld toe) are strongly influenced by mesh size at and near a weld, resulted from notch stress singularity. In this paper, a mesh-insensitive structural stress method is used to re-evaluate the S-N test data ranging from Markl et al in 1950s, to those by Heald and Kiss on nuclear piping in 1970, to the most recent piping weld S-N data by Scavuzzo et al in 1998. The major findings are as follows: (a) The mesh-insensitive structural stress method provides a simple and effective mean for characterizing stress concentrations at vessel and pipe welds. (b) The structural stress based parameter provides an effective measure of stress intensity at welds, which can be related to fatigue lives. (c) Once the mesh-insensitive structural stress are used, the S-N data processed thus far can be reasonably consolidated into one narrow band. Therefore, single master S-N curve for vessel and piping welds can now be established, regardless of piping weld types or geometries (straight pipe girth welds, different types of flange welds, elbow welds, Mitre bends, etc.), and can be used to general a master fatigue design curve.
Probabilistic Approach for Creep-Fatigue Evaluation in Liquid Metal Cooled Fast Reactor
Authors: Kawasaki Nobuchika , Chuman Yasuharu , Tanaka Yoshihiko , Asayama Tal
Published: August 2008

A procedure to calculate crack initiation probabilities by creep-fatigue damage is explained in this paper with a calculation example. Material properties of 316FR are determined as probabilistic distributions from test data. As the result yield stress, fatigue property, cyclic stress-strain relation and creep property are input into a creep-fatigue evaluation as the probabilistic distributions. The crack initiation probability is calculated with the condition for the Japanese commercialized sodium cooled fast breeder reactor. As the result, the allowable thermal cycles in the present design becomes 5 × 10−9 cumulative crack initiation probability.
Flow Accelerated Corrosion Behavior of CANDU Feeder Piping Characterized by High Temperature Rotating Cylinder Electrode
Authors: Kim Jun Hwan , Kim In Sup , Chung Han Sub
Published: August 2008

To test the flow accelerated corrosion in nuclear power plant environment with ease, High Temperature Rotating Cylinder Electrode (HTRCE) was developed. The main design concept of HTRCE is to assure stable operation of working electrode up to highest possible rotation speed in a severe environment, to insulate electrode housing except working electrode surface against external fluid, and to extract corrosion parameter from the rotating cylinder to outside of the autoclave safely. From the results of corrosion experiment at high temperature water, HTRCE has been proved as an effective device to evaluate the velocity sensitivity in high temperature water environment.
Design Criterion of Fatigue Analysis on Plastic Basis by ASME B&PV Code
Authors: Kalnins Arturs , Dowling Norman E.
Published: August 2008

The paper investigates the current rules for fatigue analysis on plastic basis of the ASME Boiler and Pressure Vessel Code. It addresses the question: When these rules are used for a vessel or component, is it designed with respect to crack initiation or failure? Using available fatigue test data, the question is answered for blunt double-notch plate specimens made of AISI 4340 steel. When the rules are applied to these specimens, it is found that they are designed with respect to the initiation of a crack of a certain length that decreases as the strain range increases. The plate specimens are not designed with respect to failure. It is concluded that for geometries that exhibit a strain range gradient away from the surface, the number of cycles allowed by the current rules includes the initiation phase but not the propagation phase of a fatigue crack. If this result is unsatisfactory, new rules have to be written.
Fatigue Crack Growth Rate of Medium and Low Sulfur Ferritic Steels in Pressurized Water Reactor Primary Water Environments
Authors: Eason Ernest D. , Nelson Edward E. , Heys Graham B.
Published: August 2008

Models of fatigue crack growth rates for medium and low sulfur ferritic pressure vessel steels in pressurized water reactor (PWR) primary environments are developed based on a recent collection of UK data and the EPRI Database for Environmentally Assisted Cracking (EDEAC). The combined UK and EDEAC database contains a broader range of experimental conditions specific to PWRs than either database by itself. Both probabilistic and conventional crack growth rate models are developed that reduce unnecessary conservatism for medium and low sulfur PWR primary water applications and eliminate the explicit dependence on rise time that caused difficulties applying prior models.
Development of a Water Environment Fatigue Design Curve for Austenitic Stainless Steels
Authors: Leax Thomas R.
Published: August 2008

Technical support is provided for a fatigue curve that could potentially be incorporated into Section III of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code. This fatigue curve conservatively accounts for the effects of light water reactor environments on the fatigue behavior of austenitic stainless steels. This paper presents the data, statistical methods, and basis for the design factors appropriate for Code applications. A discussion of the assumptions and methods used in design curve development is presented.