bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations Arising From Exponential Fitting Methods to a Charpy V-Notch Energy Database From Tata Steel
Authors: Horn Anthony J. , Axe Thomas M.
Published: May 2012

Charpy testing across a range of temperatures is a cost effective way to characterise the ductile-to-brittle transition region. It is often convenient to fit a curve to Charpy data through the transition region: a commonly used method is to use a continuous tan-h fit, a single mathematical expression that links lower shelf, transition region and ductile upper shelf behaviour in one continuous curve. Using this method, the temperature dependence of Charpy energy is a unique feature of each individual steel with some steels exhibiting steep transition curves and some shallow curves. In contrast to Charpy data, fracture toughness data are usually analysed by partitioning upper shelf and transition region data. The transition region data is generally accepted to fit a universal temperature dependence, the Master Curve, as proposed by Wallin [1] and standardised in ASTM E1921 [2]. Recent research on nuclear pressure vessel steels [3, 4] has indicated that when Charpy data is assessed using a similar method to that used for fracture toughness data, a common exponential temperature dependence is observed. This paper presents the current results from an on-going investigation aimed at assessing the effect of exponential curve fitting methods on a large dataset of Charpy V-notch energy data from Tata Steel. The Tata Steel data cover a wide range of parent plate steels. The results are compared to the recent studies on nuclear pressure vessel steels and a similar exponential temperature dependence is observed.
Burst Pressure Evaluation of Axially Flawed Tubes Considering the Effect of Support Plate
Authors: Oh Chang Kyun , Kim Hyun Su , Youm Hag Ki , Kim Hong Deok , Chung Han Sub
Published: May 2012

Heat exchangers are widely used in power plants as well as petrochemical facilities. Typical heat exchangers consist of a number of thin-walled tubes and several support plates. Operating experience of the heat exchangers has shown that flaws of various morphologies frequently occur in the tubes. Therefore, an accurate integrity assessment of the cracked tube is quite important from the viewpoint of safety and reliability. The heat exchanger tubes are supported at regular intervals by the support plates, and rotations as well as translations of the tubes are partially restrained. It was reported that the burst pressures for the circumferential through-wall cracks are significantly affected by the support plates, and existing limit load solutions differ from the actual burst pressure. However, the effect of the support plate on the burst pressure of axially flawed tubes has not been fully investigated. This paper evaluates detailed burst pressures and crack opening displacements for the tubes with axial flaws considering the effect of the support plates through three-dimensional finite element analyses.
Development of Compact Small Punch Creep Testing Equipment
Authors: Watanabe Hajime , Kanaya Akihiro , Kusumoto Junichi , Tsurui Takafumi
Published: May 2012

Japan has many aged thermal power plant facilities and some boilers in such facilities have been in operation for more than 100,000 hours, so the importance of creep residual life evaluation of components exposed to severe conditions has been increasing. Although creep residual life of such components can be evaluated by destructive methods relatively accurately, they significantly affect the component to be sampled, take a long time to carry out and are high-cost. To solve these problems, Kobe Material Testing Laboratory Co., Ltd. and Kyushu Electric Power Co., Inc. have jointly developed compact-sized and less expensive small punch creep testing equipment for accurate creep residual life evaluation. Outer dimensions of developed equipment are 660W × 335D × 807H (mm); weight is 130kg. Small punch creep test can be conducted by this testing equipment, in order to identify creep property using 8mm diameter and 0.5mm thickness specimens taken from tubes or pipes of thermal power plant facilities, and evaluate remaining life. The testing equipment is expected to improve efficiency and reduce costs to evaluate material characteristics and creep residual life for facilities in power plants and various industries.
Mitigation of Stress Corrosion Cracking Based on Residual Stress Improvement by Water Jet Peening (WJP)
Authors: Fukaya Masashi , Yoshikubo Fujio , Hatoh Hisamitsu , Matsui Yuji , Tamura Yoshiaki , Matsumoto Yoichiro
Published: May 2012

We have developed a practical peening technology using cavitating water jet. Water jet peening (WJP) is a preventive maintenance technology for nuclear power plants. WJP changes the residual stress on weld surfaces of reactor internals from tensile to compressive to mitigate the stress corrosion cracking (SCC). The operating conditions of WJP are controlled on the basis of ‘JSME Codes for Nuclear Power Generation Facilities.’ WJP has several advantages of operation, especially no foreign material is left in the reactor vessel since only water is injected, and wide range of the residual stress improvement is obtained since the cavitating flow spreads along the weld surface. We have also developed a prediction method of the residual stress improvement by WJP using a combination of a cavitating jet simulation and a residual stress simulation. We numerically simulated impulsive bubble pressure that varied in microseconds in the cavitating jet with ‘bubble flow model’. The bubble collapse energy was estimated by the bubble pressure. The residual stress simulation was conducted under the input conditions obtained from the bubble collapse energy. The residual stress distributions on and under the weld surface were predicted. The distributions were compared with measured data, and the result confirmed that the developed method for predicting the compressive residual stress after WJP was valid.
Application of USP to Steam Generator Nozzles
Authors: Mori Norimasa , Yamamoto Takeshi , Eto Masahiro , Narita Marekazu , Fujita Jun , Kamiyoshi Atsushi
Published: May 2012

An effective countermeasure against stress corrosion cracks in pipe welds is to improve the residual stress. A new ultrasonic shot peening (USP) technique for steam generator (SG) nozzles will be introduced as a means to improve the residual stress of SG nozzles with Alloy 600 welds. This method changes the residual stress on the inner surface from tensile stress to compressive stress by applying plastic strain to the surface via the collision force of the shot material during the shot peening. Our group has successfully performed 14 USP operations in actual plants in Japan.
Application of L-SIP to Pressurizer Nozzles
Authors: Watanabe Masaru , Ueda Takeshi , Okimura Koji , Wakabayashi Kazuhiro , Akaba Takashi , Kamo Kazuhiko , Ohta Takahiro , Nakama Shohei , Kobayashi Hiroyuki
Published: May 2012

It has long been known that the most effective in a countermeasure for stress corrosion cracking in pipe and nozzle welds is by reducing the residual stress in the portion of the weld exposed to the corrosive environment. An irradiated laser stress improvement process (L-SIP) was introduced as a method to improve residual stress inside steel pipes and nozzles. L-SIP has been applied to the pressurizer nozzles in actual plant, Tsuruga unit 2 Japan, for the first time in the world. The nozzles to which this process was applied are the surge nozzle (September 2007), safety nozzles, relief nozzle and spray line nozzle (April 2010). L-SIP can be applied without inner surface cooling because the high power laser beam can generate the sufficient temperature difference without such cooling. Where necessary to achieve optimum temperarure difference, water cooling may also be applied at the inner surface. At Tsuruga unit 2, L-SIP was successfully applied to the spray line nozzle in air-cooling mode, and the surge nozzles, 3 safety nozzles and relief nozzle in water-cooling mode.
Fatigue Crack Growth Behavior of Threaded Pipe Couplings
Authors: Van Wittenberghe Jeroen , De Baets Patrick , De Waele Wim
Published: May 2012

Threaded couplings are used in various applications to connect steel pipes. To maintain a secure connection, such couplings are preloaded and during service additional dynamic loads can act on the connections. The coupling’s threads act as stress raisers, initiating fatigue cracks, which can cause the connection to fail in time. Accurate knowledge of the fatigue behavior, taking into account crack initiation and propagation is necessary to understand the fatigue mechanisms involved. In this study, the fatigue behavior of tapered couplings with NPT threads is studied. This is done by analyzing the results of an experimental four-point bending test. The fatigue crack propagation is monitored using an optical dynamic 3D displacement measurement device and LVDTs to measure the crack opening. At certain times during the test, the load ratio is changed to apply a number of beach marking cycles. This way a fine line is marked in the fracture surface. These marked crack shapes are used as input for a finite element model. The measured deflection and crack opening are compared to the results of the numerical simulations. Using this methodology a distinction is made between fatigue crack initiation and propagation. By analyzing the fracture surface it was observed that once the crack is initiated, it propagates over a wide segment of the pipe’s circumference and subsequently rapidly penetrates the wall of the pipe. The observed crack growth rates are confirmed by a fracture mechanics analysis. Since the appearing long shallow crack is difficult to detect at an early stage the importance is demonstrated of accurate knowledge of the fatigue behavior of threaded connections in order to define acceptable flaw sizes and inspection intervals.
Benchmark Analysis on the Failure Probability Assessment of Piping With Stress Corrosion Cracks
Authors: Arakawa Manabu , Narumi Kentaro , Machida Hideo , Onizawa Kunio
Published: May 2012

This paper describes the benchmark analysis of two probabilistic fracture mechanics (PFM) codes developed for structural reliability evaluation of primary loop recirculation system (PLR) piping of a boiling water reactor (BWR) in which the stress corrosion cracking (SCC) has been observed frequently in recent years. The two codes PASCAL-SP and PEPPER-M used for benchmark analysis have been independently developed by Japan Atomic Energy Agency (JAEA) and TEPCO systems Corporation (TEPSYS), respectively. After the validity of the procedure of analysis in these codes was conformed, the reliability assessment of PLR piping containing cracks due to stress corrosion cracking (SCC) was carried out according to some regulatory requirements and the rules on fitness-for-service in Japan. The analytical results from both codes were well in agreement. Through comparison of the results, influences of some items and input parameters on failure probabilities were identified.
Modeling Grain Boundary Damage Evolution in As-Measured 3D Microstructure
Authors: Simonovski I. , Cizelj L.
Published: May 2012

In recent years we have seen a development of novel experimental techniques that enable one to non-destructively characterize polycrystalline microstructures. These techniques hold significant advantages over approaches like serial sectioning since the specimen is not destroyed in the characterization process. This is of immense value in advancing our understanding of materials and multiscale computational models. In particular, processes at the small length scales like the initiation and early development of grain boundary damage can now be measured more closely while the resulting simulations can now be directly compared to the experimental data. The task is, however, far from being simple as extremely complex geometry needs to be coupled with advance constitutive models for the bulk grain material and the grain boundaries themselves need to be combined. In this work a model, based on a X-ray diffraction contrast tomography data of a stainless steel wire with a diameter of 0.4 mm is presented. 3D topology and crystallographic orientation of individual grains are directly transferred into a finite element model. Grain boundary damage initialization and early development is then explored for a number of cases, ranging from isotropic elasticity up to crystal plasticity constitutive laws for the bulk grain material. In all cases the grain boundaries are modeled using the cohesive zone approach. Also, the stability of the simulations and measures aimed at improving it are reported upon.
Laser Peening Technology as the SCC Mitigation for Reactor Internals
Authors: Miyasaka Hiroyuki , Yoda Masaki , Chida Itaru , Ishigaki Tatsuya
Published: May 2012

Stress Corrosion Cracking (SCC) is one of the major concerns for aged nuclear reactors. SCC-susceptible materials have been employed in a wide variety of applications in the nuclear industry. Laser Peening (LP) is a method for the SCC mitigation that eliminates surface tensile stress using impulsive effect of high-pressure plasma induced by irradiation with high-power laser pulses in the water. To apply LP to nuclear reactor internals, Toshiba has developed a new process which needs no protective coating on the materials and optimizes the conditions for the laser irradiation. Its effects for stress improvement and SCC-mitigation of laser-peened materials were confirmed through SCC tests for austenitic stainless steels and nickel-based alloys. Also integrity of the laser-peened materials was confirmed through various examinations. Toshiba developed the LP system for the core shroud and the reactor bottom part of BWRs, and has been applying it to actual Japanese nuclear reactors since 1999. For PWRs, Toshiba developed the system for Bottom-Mounted Instrumentation (BMI) nozzles and other Reactor Vessel (RV) nozzles, and has been applying it to Japanese PWRs since 2004. So far Toshiba has already completed LP operations for 2 PWR plants and 8 BWR plants in Japan. In consideration of extending the LP system to BWRs and PWRs overseas, a portable LP system equipped with a small size laser oscillator has been developed. We confirm the possibility that the portable LP system makes the outage period shorter.
Evaluation of Sealing Performance and FEM Calculations in Bolted Flange Connections With Ring Joint Gasket Subjected to Internal Pressure
Authors: Tenma Kentaro , Kikuchi Tsutomu , Sawa Toshiyuki , Horiuchi Kazuhide
Published: May 2012

The bolted flange connections with ring joint gasket have been used to seal the inner fluid at higher pressure under higher temperature condition. Assembly procedures and tightening methods for the type of gasket have typically been empirically determined. Generally, it is known that the bolt preload which is required to seal the inner fluid in the connections using the ring joint gasket is not higher than that of the connections using sheet gaskets and spiral wound gaskets. However, no research for the evaluation of sealing performance in the bolted flange connections with metal ring gasket has been conducted. In this paper, the leakage tests for the bolted flange connections with the ring joint gasket were conducted in the case where the maximum pressure is 10MPa. Measuring the leak rate of inner fluid using the pressure drop method, the sealing performance of the connections with the ring joint gasket was evaluated. In addition, using the FEM stress calculations, the flange hub stress distributions and the flange groove stress distributions were examined as the evaluation for the flange strength. As the result, it is found that the stress distribution at the contact surfaces between the ring joint gasket and the flange groove depends on the bolt tightening procedure. In the leakage tests, it was observed that the amount of the leakage (He gas) depends on the stress distributions at the groove stress which is affected due to the bolt tightening method.
Analysis of Residual Stresses in a Pressurizer Surge–Nozzle Weldment
Authors: Obermeier Florian , Nicak Tomas , Meier Gottfried , Keim Elisabeth
Published: May 2012

Residual stresses and distortion of welded structures have a significant influence on their functionality and their lifetime. In Pressurized Water Reactor (PWR) piping systems, residual stresses in dissimilar metal welds extensively increase their susceptibility to primary water stress corrosion cracking (PWSCC). An accurate crack initiation and growth assessment is essential to assure that no severe component failure will occur due to SCC or any other stress induced mechanism. Therefore it is necessary to develop methods for a proper residual stress and distortion prediction. Numerical welding simulations have developed fast during the recent years but no universally accepted guidelines for a reliable prediction of residual stresses have been established so far. In order to support further validation of developed methods the U.S. NRC launched an international round robin program. Its main intention is to benchmark different numerical approaches by direct comparison with experimental data obtained from a provided mock-up. This paper shows the contribution of AREVA NP Germany to this round robin. A two dimensional axis-symmetric analysis of a pressurizer surge nozzle – safe end – pipe weldment will be presented. The residual stresses are calculated by means of an uncoupled transient thermal and mechanical finite element analysis using the ABAQUS Code. In addition some comments on the selection of the material model and its effect on the resulting residual stresses will be given.
Development of LBB Assessment Method for Japan Sodium Cooled Fast Reactor (JSFR) Pipes (4): Verification of Crack Opening Displacement Assessment Method for Thin Wall Pipes Made of Mod.9Cr-1Mo Steel
Authors: Wakai Takashi , Machida Hideo , Yoshida Shinji , Kawashima Fumiko , Kikuchi Koichi , Xu Yang , Tsukimori Kazuyuki
Published: May 2012

For sodium pipes of Japan Sodium cooled Fast Reactor (JSFR), the continuous leak monitoring will be adopted as an alternative to a volumetric test of the weld joints under conditions that satisfy Leak-Before-Break (LBB). The sodium pipes are made of ASME Gr.91 (modified 9Cr-1Mo) steel. Thickness of the pipes is small, because the internal pressure is very low. Modified 9Cr-1Mo steel has a relatively large yield stress and small work hardening coefficient comparing to the austenitic stainless steels which are currently used in the conventional plants. In order to discuss about the LBB of the sodium pipes made of modified 9Cr-1Mo steel, the coolant leak rate from a through wall crack must be estimated properly. Since the leak rate is strongly related to the crack opening displacement (COD), an appropriate COD assessment method must be established to perform LBB assessment. However, COD assessment method applicable for JSFR sodium pipes — thin wall and small work hardening material — has not been proposed yet. Therefore, the authors have proposed a COD assessment method applicable to thin walled large diameter pipe made of modified 9Cr-1Mo steel. In this method, COD is calculated by classifying into three components of elastic, local plastic and fully plastic. This paper describes the improved COD assessment method and verifies the validity of the method based on the results of a series of four-point bending tests at elevated temperature using thin wall modified 9Cr-1Mo steel pipe containing a circumferential through wall crack. As a result, COD values calculated by the proposed method were in a good agreement with the experimental results for the uniform pipe without weld. In the case that the crack was machined at weld metal or heat affected zone (HAZ), proposed method predicted relatively larger COD than the experimental results. The causes of such discrepancies were discussed comparing with the results of finite element analyses. Based on these examinations, the rational leak rate evaluation method in LBB assessment was proposed.
A Novel Cutting Strategy for Reducing Plasticity Induced Errors in Residual Stress Measurements Made With the Contour Method
Authors: Traore Yeli , Bouchard P. John , Francis John , Hosseinzadeh Foroogh
Published: May 2012

The contour method (CM) has emerged as a valuable technique for the measurement of residual stresses (RS). The method involves cutting the sample in which residual stresses are to be measured, using wire electric discharge machining (EDM), and measuring the deformation that occurs on the newly created surface, which can be related to the residual stresses that existed beforehand. The contour method provides a full 2-D map of the stresses acting in a direction normal to the plane of the cut. It is ideally suited to measurements in power plant welds since, unlike diffraction-based techniques, it is not affected by microstructure gradients, and it is well suited to thick section components. However, as with other mechanical strain relief techniques, it is prone to errors arising from plasticity when residual stresses close to the yield strength of material are encountered. This paper describes contour method measurements in an AISI Type 316L austenitic steel three-pass. A novel cutting and restraint strategy is applied in an attempt to reduce plasticity errors following optimisation studies simulating the cutting process using the finite element (FE) method.
Assessment of Error and Pressure Influence on Total Equivalent Stress Amplitude Calculation by WRC107
Authors: Liu Fujun , Qian Yueqiang , Ling Zhangwei , Kong Shuai , Zheng Mulin
Published: May 2012

Bulletin WRC107 is most commonly used in attachment design, but still some uncertainties make it difficult to ensure safety in recent use. Two problems in fatigue evaluation were addressed here, first the bulletin is based on shell theory and some other assumption, and for various condition the calculation error is unknown; second pressure is not considered in calculation. To the first problem, an assessment was performed by comparing the total equivalent stress results of WRC107 and of finite element method (FEM). To the second problem, a method from Chinese standard HG20582-1998 Specification for Stress Calculation of Steel Chemical Vessels (HG method) was introduced as a supplement, and the reliability was studied. The results show that, total equivalent stress amplitude calculated by WRC107 may be underestimated, and its error mainly depends on parameters β and γ. Complemented by HG method, WRC107 could be used in calculation of shell under pressure and external loading.
Development of LBB Assessment Method for Japan Sodium Cooled Fast Reactor (JSFR) Pipes (5): Crack Growth Assessment Method for Pipes Made of Mod.9Cr-1Mo Steel
Authors: Wakai Takashi , Machida Hideo , Yoshida Shinji , Tokiyoshi Takumi , Kikuchi Koichi , Xu Yang , Tsukimori Kazuyuki
Published: May 2012

For sodium pipes of Japan Sodium cooled Fast Reactor (JSFR), the continuous leak monitoring will be adopted as an alternative to a volumetric test of the weld joints under conditions that satisfy Leak-Before-Break (LBB). The vessels of JSFR are connected by thin wall pipes with a large diameter made of modified 9Cr-1Mo steel and the internal pressure of the pipes is very low. Modified 9Cr-1Mo steel has relatively large yield stress and small work hardening coefficient compared to the austenitic stainless steels which are currently used in the conventional plants. Therefore, these material characteristics of modified 9Cr-1Mo steel must be taken into account in LBB assessment, as well as geometrical and structural features of JSFR pipes. In order to demonstrate LBB aspects of the JSFR pipes, the authors have proposed a LBB assessment flowchart and developed assessment methods of unstable fracture and crack opening displacement (COD) for the thin wall pipes with large diameter made of modified 9Cr-1Mo steel. This paper studies the master curve to estimate the crack length when a postulated initial crack unexpectedly grows and penetrates the pipe thickness. In order to obtain the fatigue crack and creep crack growth characteristics of modified 9Cr-1Mo steel pipes, fatigue crack and creep crack growth tests were conducted using compact tension (CT) specimens and crack growth rates for both fatigue and creep at elevated temperature were obtained. Based on the obtained material characteristics and the results of a series of crack growth calculations, a relationship between the penetrated crack length and the ratio of membrane to total stress, so called as master curve, was proposed. In this study, master curves were proposed for pipes made of modified 9Cr-1Mo steel as a function of pipe geometry, i.e. the ratio of radius to thickness.
Numerical Simulation and Experimental Research on Crack Magnetic Flux Leakage Field
Authors: Liu Fujun , Zheng Mulin , Kong Shuai , Ling Zhangwei , Qian Yueqiang
Published: May 2012

Magnetic flux leakage (MFL) testing is widely used to inspect and characterize defects in pipelines, storage tanks and other structures. In this paper, based on the Maxwell Equations, numerical simulation and experimental research of crack magnetic flux leakage field were carried out. The three-dimensional models of cracks were established, the influence of the generalized crack parameters to the magnetostatic MFL field, including depth, width, inclination angle and crack spacing, was discussed. The relationship between defect parameters and MFL amplitude was obtained. The amplitude is significantly affected by the inclination angle. Therefore, single direction inspection may lead to undetected in practice. While the two cracks interval is less than 5 mm, the MFL fields would overlap. Furthermore, the experimental investigations were developed, and the results agree well with that of the simulation. The conclusions could provide valuable reference for inspection.
Modelling Acoustic Sources in Pipework
Authors: Goyder H. G. D.
Published: May 2012

The internal gas flow within a pipework system can generate large noise levels which may be sufficient to cause vibration and fatigue damage. The sources of such noise can be modelled by means of acoustic oscillations of inflow and outflow from a point location. Single and multiple point locations (monopoles and dipoles) within pipework are analysed to determine the different wave structures they generate. Use is made of frequency domain methods within which the effects of damping can be included by using reflection coefficients which allow some energy to leave the system. In order to model the source strength some data (due to Graf and Ziada) are analysed to determine how the source is linked to the flow within the pipework. Use is again made of frequency domain methods to represent this data. The source is found to contain a mixture of negative and positive damping which depends on the flow rate in a non-linear manner. Throughout this investigation the physical nature of the mechanisms involved is emphasised and the use of frequency domain methods is found to be successful.
The Effects of Loadings on Welding Residual Stresses and Assessment of Fracture Parameters in a Welding Residual Stress Field
Authors: Wei Liwu , He Weijing , Smith Simon
Published: May 2012

The level of welding residual stress is an important consideration in the ECA of a structure or component such as a pipeline girth weld. Such a consideration is further complicated by their variation under load and the complexity involved in the proper assessment of fracture mechanics parameters in a welding residual stress field. In this work, 2D axi-symmetric FEA models for simulation of welding residual stresses in pipe girth welds were first developed. The modelling method was validated using experimental measurements from a 19-pass girth weld. The modeling method was used on a 3-pass pipe girth weld to predict the residual stresses and variation under various static and fatigue loadings. The predicted relaxation in welding residual stress is compared to the solutions recommended in the defect assessment procedure BS 7910. Fully circumferential internal cracks of different sizes were introduced into the FE model of the three-pass girth weld. Two methods were used to introduce a crack. In one method the crack was introduced instantaneously and the other method introduced the crack progressively. Physically, the instantaneously introduced crack represents a crack originated from manufacturing or fabrication processes, while the progressively growing crack simulates a fatigue crack induced during service. The J-integral values for the various cracks in the welding residual stress field were assessed and compared. This analysis was conducted for a welding residual stress field as a result of a welding simulation rather than for a residual stress field due to a prescribed temperature distribution as considered by the majority of previous investigations. The validation with the 19-pass welded pipe demonstrated that the welding residual stress in a pipe girth weld can be predicted reasonably well. The relaxation and redistribution of welding residual stresses in the three-pass weld were found to be significantly affected by the magnitude of applied loads and the strain hardening models. The number of cycles in fatigue loading was shown to have little effect on relaxation of residual stresses, but the range and maximum load together governed the relaxation effect. A significant reduction in residual stresses was induced after first cycle but subsequent cycles had no marked effect. The method of introducing a crack in a FE model, progressively or instantaneously, has a significant effect on J-integral, with a lower value of J obtained for a progressively growing crack. The path-dependence of the J-integral in a welding residual stress field is discussed.
Effect of Welded Mechanical Heterogeneity on Local Stress and Strain Ahead of Growing Crack Tips in the Piping Welds
Authors: Zhao Lingyan , Xue He , Tang Wei , Fang Xiurong
Published: May 2012

Primary loop recirculation (PLR) piping weld joints are more susceptible to stress corrosion cracking (SCC). But it is difficult to accurately predict SCC growth rate in PLR piping weld joints because the material and mechanical properties in weld joints are quite complicated. Especially, it is provided that hardening in the weld heat-affected zone (HAZ) might play an important role in promoting SCC growth. Considering welded mechanical heterogeneity, the local stress and plastic strain fields ahead of growing crack tip in 316L PLR piping weld joints are analyzed, the effect of constant stress intensity factor (KI) and constant loading on SCC behaviors of PLR piping weld joints is investigated in this study. The results show that the mechanical fields of SCC tips behave quite differently under constant KI and constant loading because of welded mechanical heterogeneity and advanced crack length, which demonstrate that the effect of constant loading on the stress and strain ahead of the growing crack tip is bigger than that of constant KI.
Finite Element Simulation of Sealing Performance in Bolted Flange Joints of Longitudinal Baffle Type Heat Exchanger
Authors: Yamanaka Hiroshi
Published: May 2012

Bolted flange joints are used in heat exchangers and piping of oil refineries, chemical refineries and various other industries. Above all, it is reported that bolted flange joints of longitudinal baffle type heat exchanger are easy to leak as compared with other type heat exchangers in start up of units. In this study, outside influence on operating and structure of longitudinal baffle type heat exchanger which affect sealing performance were analyzed using finite element analyses to prevent leakage accidents. As a result, it is understood that the sealing performance in bolted flange joints decreases remarkably when the shell of heat exchanger transforms like a bow with a rise in temperature. In addition, it is clarified that retightening, increases in bolt preload and thickness of gasket keep sealing performance well in bolted flange joints of longitudinal baffle type heat exchanger.
Numerical and Experimental Evaluation of Residual Stresses in Dissimilar Weld Joints
Authors: Ayrault Danie`le , Bonaventure Alix , Asserin Olivier , Montay Guillaume , Klosek Vincent
Published: May 2012

This paper describes finite element modelling of residual stresses in tubular dissimilar weld joints. To validate numerical approach, residual stresses are determined experimentally in various locations of the welded specimen by using complementary methods such as neutron diffraction technique and increment hole drilling method combined to speckle interferometry. Dissimilar metal weld specimens (DMW), representative of configurations in primary coolant circuit of pressurized water nuclear reactors, are produced using AISI 316L stainless steel and low alloy carbon 16MND5 steel as base materials and a nickel based filler metal (Inconel 82) for buttering of the ferritic side and the filling between the buttered pipe and stainless steel one. The simulation of the manufacturing procedure of the DMW specimen is firstly performed thanks to an equivalent heat source. Secondly, the mechanical behaviour is calculated by using the computed thermo-metallurgical history for each welded pass. The “birth and death” elements method is used to simulate the addition of filler metal for this multi-pass welding configuration. A relatively good agreement is observed between the calculated and experimental results.
FEM Stress Analysis and the Sealing Performance Evaluation of Pipe Flange Connections Subjected to External Bending Moments and Internal Pressure
Authors: Horiuchi Kazuhide , Takagi Yoshio , Sawa Toshiyuki
Published: May 2012

In previous study, the characteristics of the pipe flange connections such as the contact gasket stress distribution and the sealing performance of the connection subjected to bending moments are examined. The result suggests that the leakage increases as the bending moment increases. However, a design method for the connection subjected to bending moment is not taken into consideration. The sealing performance of the connection for the different loading history is changed due to non-linearity and hysteresis of non-asbestos gasket. After the pipe flange connections are tightened, bending moment prior to internal pressure is applied due to misalignment of the connections with bolts and nuts. So, it is necessary to examine the difference in the sealing performance due to different loading history and to establish a design method for the connections subjected to bending moment and internal pressure. In this study, the difference in the sealing performance due to different loading history is examined and pipe length in each usage condition is determined for the two loading histories using tensile strength of hub side and allowable leak rate of soppy bubble method to establish a design method of flange subjected to bending moment. The result suggests the average contact gasket stress for the different loading history is changed due to non-linearity and hysteresis of non-asbestos gasket and pipe length in each initial contact gasket stress is determined for the two loading histories.
Investigation on Different Tightening Sequences on Several Bolted Flange Types, Dimensions and Their Associated Gasket Types
Authors: Lejeune Hubert , Birembaut Yves , Riedl Alexander , Schunemann Arne
Published: May 2012

In the last years, several projects have been performed on alternative tightening sequences in the US and in Japan. This work has led to the publication of documents introducing alternative tightening procedures as JIS B 2251:2008 / HPIS Z 103 TR (JAPAN) and the new revision of ASME PCC-1:2010. In this study, the required bolt torque is calculated according EN1591-1 [1] (EN standard for bolted flange calculation according to a given tightness class) to achieve a given tightness class for each investigated gasket (6 types) and flange type (CLASS/PN)/dimension (from 4″/DN100 to 16″/DN400). The calculated bolt torque is then applied using a hydraulic torque wrench following three tightening sequences based on Legacy cross-pattern of ASME PCC-1:2010, alternative pattern #1 of ASME PCC-1:2010 and HPIS Z 103 TR. The bolted flange connection is then pressurized with Helium. The load for each bolt is continuously monitored using strain gauges, through the bolt-up phase and during pressurization. The average obtained bolt load, the bolt load scatter, the evolution of bolt load versus passes and elapsed time are compared for all the tested configurations (tightening sequence/ bolted flange type & dimension/ gasket type). A “Quality factor” is defined enabling comparison between the tightening quality (according to several criteria) of the different investigated tightening sequences in the tested configurations.
Using a Probabilistic Approach in the Brittle Fracture Deterministic Integrity Assessment of a Nuclear Reactor Pressure Vessel
Authors: Beaufils Romain , Meister Eric , Ardillon Emmanuel
Published: May 2012

This work deals with the possibility of the life extension of nuclear power plants in France. The aim is to justify the resistance of the pressure vessel, which is non-replaceable. The brittle fracture deterministic integrity assessment of the nuclear Reactor Pressure Vessel (RPV) is based on the analysis of a flaw under the austenitic cladding of the RPV. The demonstration of the RPV resistance is controlled by the regulations. It is proposed here to use a probabilistic method by propagating uncertainties into the deterministic mechanical model in order to quantify conservatism of the deterministic method. The regulatory requirements must be respected and the purpose of the work presented here is thus to link the probabilistic result to the deterministic method.
Evaluation of Leakage Probability of Non-Asbestos Fiber Sheet Gasket at Elevated Temperature Based on Percolation Theory: Characteristics Under Internal Pressure
Authors: Hagihara Masahiro , Tsuji Hirokazu , Yamaguchi Atsushi
Published: May 2012

A long-term life prediction method for a compressed fiber sheet gasket under a high-temperature environment is studied. Non-asbestos compressed fiber sheet gaskets are now being used as a substitute for asbestos in the bolted flange joint, for instance chemical plants and oil plant facilities. Consequently, there is a real need for a technology to predict the lifetime of non-asbestos compressed fiber sheet gaskets quantitatively. We have previously reported that the facing surface which was formed the gasket and flange was visualized with scanning acoustic tomography (SAT). Voids were observed on the facing surface of the gasket and increased with the increase in exposure time at high temperature. If a leakage path for inner fluids was created by the increasing number of voids, the leak occurs on the facing surface of the gasket surface. The probability of a leak due to voids and the lifetime of this gasket were predicted by applying the percolation theory, which describes the connectedness of voids and clusters. In this report, the influence of internal pressure of test flange joint upon the rate of increase is studied.
Comparison of Creep-Fatigue Evaluation Methods With Notched Specimens Made of Mod.9Cr-1Mo Steel
Authors: Ando Masanori , Hirose Yuichi , Karato Takanori , Watanabe Sota , Inoue Osamu , Kawasaki Nobuchika , Enuma Yasuhiro
Published: May 2012

In a component design at elevated temperature, creep-fatigue is one of the most important failure modes, and assessment of creep-fatigue life in structural discontinuity is important issue to evaluate structural integrity of the components. Therefore a lot of creep-fatigue life evaluation methods were proposed until now. To compare and assess these evaluation methods, a series of creep-fatigue tests was carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo steel, which it is a candidate material for a primary and secondary heat transport system components of JSFR (Japan Sodium-cooled Fast Reactor). Mechanical creep-fatigue tests and thermal creep-fatigue tests were performed by using conventional uni-axial push-pull fatigue test machine and thermal gradient generating system with an induction heating coil. Stress concentration levels were adjusted by varying the diameters of notch roots in the both tests. In the test, creep-fatigue lives, crack initiation and propagation processes were observed by digital micro-scope and replica method. Besides those, a series of elastic Finite Element Analysis (FEA) were carried out to predict the number of cycles to failure by several creep-fatigue life evaluation methods. Then these predictions were compared with test results. Several types of evaluation methods which are stress redistribution locus (SRL) method, simple elastic follow-up method and the methods described in JSME FR (Fast Reactor) code were applied. The applicability and conservativeness of these methods were discussed. It was appeared that SRL method gave rational prediction of creep-fatigue life with conservativeness when the factor of κ = 1.6 was applied for all the conditions tested in this study. Comparison of SRL method and simple elastic follow-up method indicated that SRL method applied factor of κ = 1.6 gave the smallest creep-fatigue life in practicable stress level. JSME FR code gave an evaluation 70∼100 times conservative lives comparing with the test results.
Pipe Rupture Analysis Considering Fluid-Structure Interaction
Authors: Hamamoto Yukari , Toyoda Makoto
Published: May 2012

Global warming is caused by the emission of greenhouse gases, like CO2. Nuclear energy is one of the main sources of low-carbon energy. In the events of serious accidents, a nuclear power plant may emit radioactivity that is harmful to human health. Nuclear power should be used after enough evidence of its safety is provided. Measures for safety of nuclear power plants, such as autogenous control and LBB, have been developed. Moreover, there is requirement with respect to the design, safety, equipments components and systems of nuclear plant. For example, it is necessary to place components that restrain pipe whip behavior, and to design peripheral equipments that may be affected by high-pressured fluid in pipe rupture accidents [1], [2]. In the case of pipe rupture that occurs to structures such as nuclear plants and steam generators, a pipe deforms releasing its inner high-pressured fluid. In previous studies, the pipe whip behavior analyses have been performed by using blowdown thrust force that is estimated by fluid analysis. In this study, we simulate pipe whip behavior and reduction of blowdown thrust force by releasing inner fluid to the atmosphere. The analysis model is an elbow pipe and high-pressure fluid running inside. We considered fluid-structure interaction effect in the analysis because ovalization of the cross-section of the elbow part as well as a change of the elbow torus radius affects fluid flow blowing out from the ruptured part of the pipe.
Complex Crack Stability in Dissimilar Metal Welds: Background and Test Plan
Authors: Rudland D. , Scott P. , Olson R. , Cox A.
Published: May 2012

Typically in flaw evaluation procedures, idealized flaw shapes are assumed for both subcritical crack growth and critical crack stability analyses. Past NRC-sponsored research have developed estimation schemes for predicting the load-carrying capacity of idealized flaws in nuclear grade piping and similar metal welds at the operating conditions of nuclear power reactors. However, recent analyses have shown that growth of primary water stress corrosion cracks (PWSCC) in dissimilar metal (DM) welds is not ideal; in fact, very unusual complex crack shapes may form, i.e., a very long surface crack that has a finite length through-wall crack in the same plane. Even though some experimental data on base metal cracks exist to demonstrate that complex shaped cracks in high toughness materials fail under limit load conditions, other experiments demonstrate that the tearing resistance is significantly reduced. At this point, no experimental data exists for complex cracks in DM welds. In addition, it is unclear whether the idealized estimation schemes developed can be used to predict the load carrying capacity of these complex-shaped flaws, even though they have been used in past analyses by the nuclear industry. Finally, it is unclear what material strength data should be used to assess the stability of a crack in a DM weld. The NRC Office of Nuclear Regulatory Research (RES), with their contractor Battelle Memorial Institute, has begun an experimental program to confirm the stability behavior of these complex shaped flaws in DM welds. A combination of thirteen full-scale pipe experiments and a variety of laboratory experiments are planned. This paper will summarize the past base metal complex-cracked pipe experiments, and the current idealized flaw load carrying capacity estimation schemes. In addition, the DM weld complex cracked pipe experimental test matrix will be presented. Finally, plans for using these results to confirm the applicability of idealized flaw stability procedures are discussed.
Numerical Interpretation of the Endurance Test on FATHER Mixing Zone Mock-Up
Authors: Stephan Jean-Michel
Published: May 2012

For a better understanding of thermal fatigue in piping mixing zone, EDF, CEA and AREVA ANP have developed a mock-up named FATHER. Tests performed on the mock-up have given access to fluid temperature thermal fluctuations and external surface strains. Tests were completed by an endurance test. Examinations revealed the presence of numerous cracks at different locations. EDF R&D has performed a numerical interpretation of the test, in relation with different specimen fatigue tests (HCF tests on polished specimens, influence of surface roughness, influence of mean stress,…) and with the use of different fatigue criteria (RCC-M, Fatemi-Socie, Dang Van…). Numerical results are compared with the results of examinations. A comparison is done with results obtained by codified methodologies for nuclear plants.