bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study for Proposal of Welded Joint Strength Reduction Factors of Modified 9Cr-1Mo Steel for Japan Sodium Cooled Fast Reactor (JSFR)
Authors: Wakai Takashi , Onizawa Takashi , Kato Takehiko , Date Shingo , Kikuchi Koichi , Satoh Kenichiro
Published: January 2014

This paper proposes provisional welded joint strength reduction factors (WJSRF) of modified 9Cr-1Mo steel (ASME Gr.91) applicable to the structural designing of “Japan sodium cooled fast reactor (JSFR)”. In the welded joints of creep strength enhanced ferritic steels including modified 9Cr-1Mo steel, creep strength may obviously degrade especially in long-term region. This phenomenon is known as “Type-IV” damage. The authors had proposed provisional allowable stress for the welded joints made of the steel in PVP 2010 conference, taking creep strength degradation due to “Type-IV” damage into account. Available creep rupture data of the welded joints made of the steel provided by Japanese steel venders were collected. The temperature range was from 500 to 650°C. The database was analyzed by stress range partitioning method. The creep rupture data were divided into two regions of short-term and long-term and those were individually evaluated by regression analyses with Larson Miller Parameter (LMP). The difference in the creep failure mechanisms between short-term and long-term regions is taken into account in this method. Boundary between these regions was half of 0.2% proof stress of the base metal at corresponding temperature. First order polynomial equation of logarithm stress was applied. For conservativeness, allowable stress was proposed provisionally considering design factor for each region. JSME (Japan Society of Mechanical Engineers) published a revised version of the elevated temperature design code in last year. Modified 9Cr-1Mo steel was officially registered in the code as a new structural material for sodium cooled fast reactors. The creep rupture curve for the base metal of the steel was standardized by employing stress range partitioning method, same as for the welded joint. However, second order polynomial equation of logarithm stress was applied in the analysis for the base metal. In addition, the creep rupture data obtained at 700°C were included in the database and data ruptured in very short term, i.e. smaller than 100 hours, were excluded from the analysis. Thus, there are some differences between the procedures to determine the creep rupture curves for base metal and welded joint made of modified 9Cr-1Mo steel. This paper discusses the most feasible procedure to determine the creep rupture curve of the welded joint of the steel by performing some case studies to focus on physical adequacy and harmonization with the determination procedure of the creep rupture curve for the base metal. Then, the WJSRF are provisionally proposed based on the design creep rupture stress intensities. In addition, the design of JSFR pipes was reviewed taking WJSRF into account.
A Micromechanics Approach for Assessing the Applicability of Precracked Charpy Specimens to Determine the T0 Reference Temperature
Authors: Savioli Rafael G. , Ruggieri Claudio
Published: January 2014

This work describes an application of a micromechanics model for cleavage fracture to determine the reference temperature for pressure vessel steels from precracked Charpy (PCVN) specimens. A central objective is evaluate the effectiveness of the Weibull stress (σw) model to correct effects of constraint loss in PCVN specimens which serve to determine the indexing temperature T0 based on the Master Curve methodology. Fracture toughness testing conducted on an A285 Grade C pressure vessel steel provides the cleavage fracture resistance data needed to estimate T0. Very detailed non-linear finite element analyses for 3-D models of plane-sided SE(B) and PCVN specimens provide the evolution of near-tip stress field with increased macroscopic load (in terms of the J-integral) to define the relationship between σw and J from which the variation of fracture toughness across different crack configurations is predicted. For the tested material, the Weibull stress methodology yields estimates for the reference temperature, T0, from small fracture specimens which are in good agreement with the corresponding estimates derived from testing of much larger crack configurations.
A Parametric Study of Independent Support Motion Method for the Steam Supply Piping Connected to the HP Turbine of APR 1400
Authors: Kim Dae Soo , Lee Joon Ho , Kim In Yeung
Published: January 2014

The steam supply piping connected to the high pressure (HP) turbine of APR1400 (Korea’s advanced power plant 1400 MW-class) is a typical example of multi-supported piping system, and it is routed from the Containment building to the Turbine building via the Main Steam Isolation Valve House in the Auxiliary building. In the seismic analysis of this piping system, using the Enveloped Response Spectrum (ERS) method, a commonly used methodology for seismic analysis of nuclear power plant piping in industry circles, generates overly conservative analysis results. Therefore, Time History Method (THM) which applies excitation characteristic of each support attached to individual building was used to eliminate unnecessary conservatism. However, it was noticed that the Time History Method requires considerable amount of labor and time in generating combined time history equivalent to the spectrum applied for each support although it is regarded as the most exact and realistic method for seismic analysis. The nuclear industry has been making lots of efforts in finding out the mathematic logicality and practical applicability to resolve this issue. This paper deals with parametric research on combination effects of responses between support groups, damping effects, and modal combination method with close modes in applying the Independent Support Motion (ISM) method to the analysis model of the steam supply piping connected to the high pressure turbine of APR1400. Quantitative assessment and comparison with the analysis results of the ERS method and THM were also carried out. As a result, it is shown that the analysis results of the ISM method together with the SRSS combination between support groups, 4% damping with ±15% spectrum peak broadening and grouping of modal combination are remarkably similar to those of THM.
Development of Regulation on Accident Management and Statistics Analysis on Accident for China Special Equipment
Authors: Yang Jingbiao , Zheng Jiong , Luo Weijian , Li Xufeng
Published: January 2014

Regulations on safety supervision and accident management of special equipment since 1979 were analyzed in order to clarify the rules and characteristics of safety supervision for China’s special equipment. The accident management process of special equipment gradually tends to be standardized and procedural. In addition, the number development and accident evolvement trend of special equipment in China since 1979 were studied aiming at obtaining the characteristics and rules of the special equipment development, and a guideline is provided for the safety supervision of special equipment in China. On the whole, the accident rates and mortality rates per ten thousand equipments gradually decrease in the stages investigated in this paper, but compared with the corresponding accident rates of special equipment in developed countries, there is a space for the accident rates and mortality rates of China’s special equipment to decline.
Numerical Analysis of Heat Transfer and Flow in a Passive Condensation Heat Exchanger
Authors: Jo Jong Chull , Do Kyu Sik , Lee Yong Kab
Published: January 2014

A PWR design incorporates a passive auxiliary feedwater system equipped with one passive condensation heat exchanger (PCHX) which consists of inclined V-shaped tube bundles submerged in a water pool of which the top is open to the atmosphere. During the PCHX operation, saturated steam flows into the PCHX where steam is condensed inside of the tubes by cooling the outer side with the pool water. Then, the condensate flows out passively by gravity. Because the thermal-hydraulic characteristics in the PCHX determine the condensation mass rate and the possibility of thermal stratification-induced fatigue of the pool tank wall, system instability and waterhammer, it is important to understand the phase change flow in the PCHX. In this paper, the complex phase change heat transfer and multi-phase flow in a PCHX tube model were numerically simulated. The single fluid multi-component flow model with the equilibrium phase change model was employed for the condensation phase change flow inside the tube and the two-fluid model with the wall boiling model and the equilibrium phase change model was used for the boiling-induced natural convection outside the tube in the pool. Based on the present numerical simulation, the characteristics of the heat transfer and flow in the PCHX are discussed and illustrated for some typical results.
Development of Ultimate Strength Evaluation Method for Piping Subjected to Seismic Loads
Authors: Machida Hideo , Chitose Hiromasa , Yamazaki Tatsuhiro
Published: January 2014

This paper reports the results of the study on the failure modes and limit loads of piping in nuclear power plants subjected to cyclic seismic loading. By investigating the past fracture tests and earthquake resistance tests, it became clear that dominant failure mode of piping was fatigue, and the effect of ratchet strain was negligible. Until now, the stress generated with the acceleration of an earthquake was classified into the primary stress. However, the relationship between the input acceleration and the seismic response displacement of the pipe observed from earthquake resistance tests is non-linear, and increasing rate of displacement is lower than that of input acceleration in elastic-plastic stress condition. Therefore, the seismic loading can be treated as displacement controlled loading. To evaluate the reliability-based critical acceleration, a limit state function was defined taking the variations in the fatigue strength or some parameters into consideration. By using the limit state function, the reliability was evaluated for the typical piping of boiling water reactor (BWR) plants subjected to cyclic seismic loading, and a partial safety factors were calculated. Based on these results, a fatigue curve corresponding to the target reliability was proposed.
The Correction of Stress Intensity Factor for Crack Growth Evaluation Under Steep Residual Stress Distribution and Steep Yield Strength Distribution
Authors: Yasuoka Tetsuo , Mizutani Yoshihiro , Todoroki Akira
Published: January 2014

Welds and heat affected zones have the distribution of the residual stress or the yield strength. The crack growth evaluation is conventionally conducted using stress intensity factor in those regions. However, the stress intensity factor may be invalid when the residual stress distribution or yield strength distribution changes in the vicinity of a crack tip. The reason is that the distributions around the crack tip affect the plastic zone size and the stress intensity factor inappropriately represents the stress state in the vicinity of a crack tip. In this study, the residual stress distribution and yield strength distribution was assumed along the crack propagation path and the validity of the stress intensity factor was discussed on that condition. As a result, the stress intensity factor tended to be invalid when the steep residual stress distribution or the steep yield strength distribution. When the steep distribution exists, the crack growth evaluation should be conducted using a parameter considering the elastoplastic behavior near the crack tip. For that purpose, the authors proposed new method of the plastic zone correction using a differential term of the stress intensity factor. The new method was demonstrated through the case study for stress corrosion cracking of nuclear power plants.
Effects of Stress on Pitting Corrosion Behavior of Low-Carbon Steel
Authors: Cao Huaixiang , Zhang Hao , Qiu Xingqi
Published: January 2014

Low-carbon steel Q235B was widely used in low or middle pressure equipments, which were not only withstanding the corrosive effect of the environment or medium, but also the high stress in service processes. In this paper, acetic acid accelerated corrosion test of low-carbon steel Q235B under the action of various stress levels was conducted, and its pitting corrosion behavior was studied by corrosion morphology, pitting corrosion parameters, scanning electron microscope (SEM) and energy disperse spectroscopy (EDS). The results showed that, the degree of pitting corrosion of low carbon steel Q235B with stress was more serious than that of non-stress. And the corrosion started from grain boundary, which was corroded before grain itself, and then grains fell off or dissolved. Furthermore, it would have the tendency of deep hole corrosion with stress, which was more of a threat to the structural safety of pressure vessels.
Determination of Tensile Properties of Power Plant Steels by Testing of Miniature Specimens
Authors: Klevtsov Ivan , Dedov Andrei
Published: January 2014

Long-term operation of the power plant components in the conditions of the creep leads to the degradation of the short-term mechanical properties of the material. Therefore, in order to predict the degree of the metal degradation and integrity of the component the determination of the mechanical properties of the actual component in service material is required. Since the standard tests requiring a significant volume of sample material cannot be applied the technique of the tensile testing of miniature flat plate specimens has been developed in Tallinn University of Technology and described in this paper. The results of the tests of miniature flat plate specimens have been compared with testing results of cylindrical specimens with standard size and at the same time the comparison has shown a good agreement of the results. The data analysis has also shown the high repeatability of the tests results of miniature specimens. Thus, the developed technique of the miniature flat plate specimens testing could be considered as accurate and reliable method and could be definitely used for evaluation of the tensile properties of the metal.
Derivation of Design Fatigue Curves for Austenitic Stainless Steel Grades 1.4541 and 1.4550 Within the German Nuclear Safety Standard KTA 3201.2
Authors: Schuler Xaver , Herter Karl-Heinz , Rudolph Jürgen
Published: January 2014

Titanium and niobium stabilized austenitic stainless steels X6CrNiTi18-10S (material number 1.4541, correspondent to Alloy 321) respectively X6CrNiNb18-10S (material number 1.4550, correspondent to Alloy 347) are widely applied materials in German nuclear power plant components. Related requirements are defined in Nuclear Safety Standard KTA 3201.1. Fatigue design analysis is based on Nuclear Safety Standard KTA 3201.2. The fatigue design curve for austenitic stainless steels in the current valid edition of KTA 3201.2 is essentially identical with the design curve included in ASME-BPVC III, App I (ed. 2007, add. July 2008 respectively back editions).

In the current code revision activities of KTA 3201.2 the compatibility of latest in air fatigue data for austenitic stainless steels with the above mentioned grades were examined in detail. The examinations were based on statistical evaluations of 149 strain controlled test data at room temperature and 129 data at elevated temperatures to derive best-fit mean data curves. Results of two additional load controlled test series (at room temperature and 288°C) in the high cycle regime were used to determine a technical endurance limit at 107 cycles. The related strain amplitudes were determined by consideration of the cyclic stress strain curve. The available fatigue data for the two austenitic materials at room temperature and elevated temperatures showed a clear temperature dependence in the high cycle regime demanding for two different best-fit curves. The correlation of the technical endurance limit(s) at room temperature and elevated temperatures with the ultimate strength of the materials is discussed.

Design fatigue curves were derived by application of the well known factors to the best-fit curves. A factor of SN = 12 was applied to load cycles correspondent to the NUREG/CR-6909 approach covering influences of data scatter, surface roughness, size and sequence. In terms of strain respectively stress amplitudes in the high cycle regime, for elevated temperatures (>80°C) a factor of Sσ = 1.79 was applied considering and combining in detail the partial influences of data scatter surface roughness, size and mean stress. For room temperature a factor of Sσ = 1.88 shall be applied.

As a result, new design fatigue curves for austenitic stainless steel grades 1.4541 and 1.4550 will be available within the German Nuclear Safety Standard KTA 3201.2. The fatigue design rules for all other austenitic stainless steel grades will be based on the new ASME-BPVC III, App I (ed. 2010) design curve.
The Effect of Fluid-Resonant Coupling in High-Speed Impinging Planar Jet Flows
Authors: Arthurs David , Ziada Samir
Published: January 2014

This study investigates the effect of fluid-resonant coupling, i.e. the coupling between unstable modes of an impinging jet with resonant acoustic modes occurring between the nozzle and the impingement surface, on the self-excited oscillations of high-speed impinging planar jet. In order to investigate this phenomenon, a series of experiments have been performed using a high-speed impinging planar jet with varying nozzle thickness (h) and impingement distance (xo), for a single Mach number in the compressible flow regime. The test results reveal that the jet oscillation is controlled by a fluid-dynamic mechanism for small impingement distances, where the unstable mode of the jet is controlled by the impingement ratio. At larger impingement distances, the response is dominated by a fluid-resonant mechanism, in which the various hydrodynamic modes of the jet couple with different resonant acoustic modes occurring between the nozzle and the impingement surface. Within the fluid-resonant regime the system produces acoustic tones that are excited predominantly as a function of the impingement distance, with the nozzle thickness and impingement ratio having only minor effects on the tone frequency. Flow visualization images show that the same unstable mode is excited for multiple nozzle thicknesses at a constant impingement distance, despite the wide variations in associated impingement ratio.
On the Adequacy of Shell Models for Predicting Stresses and Strains in Thick-Walled Tubes Subjected to Detonation Loading
Authors: Bitter Neal P. , Shepherd Joseph E.
Published: January 2014

This paper analyzes the adequacy of shell models for predicting stresses and strains in thick-walled tubes subjected to detonation loads. Of particular interest are the large axial strains which are produced at the inner and outer surfaces of the tube due to bending along the tube axis. First, comparisons between simple shell theory and a static finite element model are used to show that the axial strain varies proportionally with wall thickness and inversely with the square of the axial wavelength. For small wavelengths, this comparison demonstrates nonlinear behavior and a breakdown of the shell model. Second, a dynamic finite element model is used to evaluate the performance of transient shell equations. This comparison is used to quantify the error of the shell model with increasing wall thickness and show that shell models can be inaccurate near the load front where the axial curvature is high. Finally, the results of these analyses are used to show that the large axial strains which are sometimes observed in experiments cannot be attributed to through-wall bending and appear to be caused instead by non-ideal conditions present in the experiments.
Validating the Mechanical Nature of the Test Speicmen Thickness Effect on Fracture Toughness in the Transition Temperature Region
Authors: Meshii Toshiyuki , Lu Kai , Takamura Ryota
Published: January 2014

This paper considered the test specimen thickness (TST) effect on the fracture toughness of a material Jc, in the transition temperature region, for 3PB (i.e., SE(B) for ASTM standard) specimens. Fracture toughness tests and elastic-plastic finite element analyses (FEA) with non-standard test specimens, on the point that the specimen thickness to width to ratio B/W was varied in the range of 0.25 to 1.5, were conducted. Based on these tests and FEA results, it was demonstrated that Jc showed tendency to saturate to some lower bound for B/W = 1.5. This tendency was similar with that predicted by our previous work, which assumed the TST effect on Jc as an out-of-plane crack-tip constraint issue. Because the TST effect on Jc (such as Jc ∝ B(−1/2)) together with Jc’s bounding nature for large B could not be predicted by the weakest link model but out-of-plane constraint assumption worked, it was concluded that the TST effect is mainly mechanical in nature.
Development of Limit State Design for Fast Reactor by System Based Code
Authors: Watanabe Daigo , Chuman Yasuharu , Asayama Tai , Takaya Shigeru , Machida Hideo , Kamishima Yoshio
Published: January 2014

Limit state design was newly developed in order to apply the margin exchange which is one of the innovative concepts of the System Based Code (SBC). It was shown that limit state design method is applicable to plant design instead of current design criteria. In this report, working example of a reactor vessel of a Fast Reactor subject to thermal load is conducted to demonstrate this concept. As the result allowable stress was increased by changing the acceptance criteria from current design criteria to limit state design criteria.
Effect of the Loading Rate on Failure of Composite Pressure Vessel
Authors: Chou Heng-Yi , Bunsell Anthony , Mair Georg , Thionnet Alain
Published: January 2014

A multi-scale model has been successfully applied to the simulation of the effects of pressurisation rate on damage accumulation in carbon fibre/epoxy plates and composite pressure vessels. The results of the simulations agree with experimental results and reveal that the point at which the structures become unstable in a monotonic pressurisation test depends on the speed of loading. The faster the loading rate the higher the applied stress at which the composite structure becomes unstable. The mechanism which governs this behaviour is seen to be the viscoelastic nature of the matrix material through which stresses are transferred from broken to neighbouring intact fibres. At loading rates that allow greater relaxation of the resin around fibre breaks neighbouring fibres are subjected to increased loads over a significantly greater length, leading to further earlier breaks.
Structural Integrity for Nuclear Power Plant Against Excessive Load on Design Extension Condition
Authors: Watanabe Daigo , Hojo Kiminobu
Published: January 2014

This paper introduces an example of structural integrity evaluation for Light Water Reactor (LWR) against excessive loads on the Design Extension Condition (DEC). In order to assess the design acceptance level of DEC, three acceptance criteria which are the stress basis limit of the current design code, the strain basis limit of the current design code and the strain basis limit by using Load and Resistance Factor Design (LRFD) method were applied. As a result the allowable stress was increased by changing the acceptance criteria from the stress basis limit to the strain basis limit. It is shown that the practical margin of the LWR’s components still keeps even on DEC by introducing an appropriate criterion for integrity assessment and safety factors.
Displacement Based Failure Criterion Applicable to Finite Element Analysis Results for Wall-Thinned Pipes Under Pressure Load
Authors: Meshii Toshiyuki , Yoshii Kan
Published: January 2014

In this work, a failure criterion applicable to large strain elastic-plastic Finite Element Analysis (EP FEA) results was proposed in order to predict the burst pressure of wall-thinned straight pipes. The key finding was that, though the pipe material was strain-hardening material, and though the pipe was locally wall-thinned, the outer surface radial displacement at the flaw center obtained from the EP FEA tended to diverge with the increase in pressure, even though the strain was very low compared to the true strain of fracture. This tendency was validated by the image processing displacement measurement results from the systematic burst tests of wall-thinned pipes. By comparing the EP-FEA results with the test results, the proposed criterion predicted the burst pressure within a maximum 10% difference. Advantage of the criterion is that it uses the true stress and strain relationship below the true tensile strength, and the ambiguous near fracture relationship is not necessary.
Investigation on In-Flow Fluidelastic Instability of an Array of Tubes
Authors: Hirota Kazuo , Morita Hideyuki , Hirai Jun , Iwasaki Akihisa , Utsumi Seiho , Shimamura Kengo , Kawakami Ryoichi
Published: January 2014

Fluidelastic instability (FEI) remains the most important vibration mechanism in steam generators. Fluidelastic instability of an array of tubes thought to be mainly occurred in the cross-flow direction. In the present day, some researchers reported possibility of occurrence of fluidelastic instability in the in-flow direction. However, the phenomenon of the in-plane FEI has not been well recognized compared to the transverse FEI.

In this study, air flow tests using cantilevered straight cylinder array of tubes in triangular configuration were conducted. It is confirmed that the in-flow FEI could be occurred and the critical flow velocity in the in-flow direction is larger than that of in the cross flow direction. Furthermore, the relationship between P/D of an array of tubes and the critical flow velocity in the in-flow direction was also investigated.
Study on Wind-Induced Vibration of a Super-High Tower
Authors: Chen Zhiwei , Qian Caifu , Yang Guoyi , Li Xiang , Yin Lijun
Published: January 2014

In this paper, wind-induced vibration of a super-high tower is numerically studied. The natural frequencies of the tower are calculated. Karman’s Vortex Street is simulated and the alternate lateral forces across the wind are obtained. It is found that with the wind speed range of 0–52.3m/s acting on the tower, the maximum vortex shedding frequency is lower than the second natural frequency of the tower. Resonance of the tower could occur at the first natural frequency with the horizontal force amplitude 241.5N/m. For high towers, it is suggested that the wind actions in across the wind and fatigue strength checks should also be considered in the design approach.
Tests and Discussions on the Impact Work of the S30403 Austenitic Stainless Steel at 20°C and -196°C
Authors: Chen Zhiwei , Yang Guoyi , Qian Caifu , Li Xiang , Wang Haoyang
Published: January 2014

In this paper, impact tests on the S30403 austenitic stainless steel at 20°C as well as −196°C were carried out. Both base plate and welded joint including weld and heat-affected zone are tested to measure the impact work KV2. It is found that when the temperature of the testing environment is decreased from 20°C to −196°C, both the impact work KV2 for the base plate and welded joint are decreased remarkably. Specifically, the impact work KV2 for the base plate decreases by 19–29% while that for the welded joint decreases by as much as 53.8%. In addition, impact tests with different size of specimens show the impact work KV2 with 5×10×55mm specimens is about 0.53–0.54 times that with 7.5×10×55mm specimens, much lower than 2/3, the ratio of two specimens’ cross section areas, indicating that rules in relevant steel or equipment standards regarding impact tests using small specimens need to be revised.
Study on the Failure Mode of Cracking Through the Fitting of Electrofusion Joint
Authors: Zheng Jinyang , Luo Xiangpeng , Shi Jianfeng , Zhong Sijia
Published: January 2014

Electrofusion (EF) technique has been widely used in polyethylene and its composite pipeline system. The strength of the EF joint is regarded as higher than that of present pipe, for the EF joints are usually failed at the pipe when subjected to internal pressure. However, several recent studies from different researchers have revealed that the EF joint may fail by cracking through the fitting in the long-term hydraulic pressure tests. In this study, the structure parameter and loading condition were taken into consideration to investigate the failure mechanism of this failure mode. The progress of crack initiation and propagation was studied by FEA method and linear elastic fracture mechanics theory. EF joints with different structure and welding parameters were analyzed to find out the design factors which would have major influence on the failure mode of cracking through the fitting. The analytical results show a reasonable agreement with experimental observations, and also reveal that the length of inner cold welding zone has a great influence and should be carefully determined in the designation of EF fittings.
Optimization in Polymer Composite Piping Design
Authors: Mertiny Pierre , Baier Horst
Published: January 2014

Polymer composite piping that is composed of a fiber reinforcement phase embedded in a continuous polymer matrix is associated with high specific strength and excellent corrosion properties. The fiber reinforcement is often considered to dominate the mechanical performance of composite structures. Consequently, principal design parameters for composite piping are usually associated with the fiber architecture, which in many practical applications has been limited to simple angle-ply configurations. Nevertheless, the function of the polymer phase is not limited to merely providing rigidity to the otherwise pliable fiber architecture. In fact, the often quoted high strength of composites is sustained by a load-sharing mechanism that the matrix enables between filaments. In this manner, the effect of localized flaws and filament damage is mitigated, and only the accumulation of numerous micro damage events leads to component failure. An additional function of the polymer matrix is to prevent ingress of fluid into the composite and possible leakage in pressure-bearing components. The design of composite piping therefore needs to consider a matrix-sensitive damage criterion. In view of variable loading conditions and multi-angle fiber architectures this study investigates design optimization techniques intended to yield better performance in terms of strength and especially fluid permeation resistance.
Comparison Between Full System Hydrotest and Local Hydrotest Methods for Pipe Butt Welds
Authors: Brown Warren
Published: January 2014

This paper presents an overview of an in-depth study into the stresses generated at a piping butt weld during hydrotest. A distinction is made between hydrotest conditions that are simply a leak test and those test which also test the structural integrity of a piping system. The work is also extended to include hydrotest of the butt weld at a B16.5 welding neck flange. The stress levels generated by four different methods of local hydrotest are examined and compared to a full system hydrotest. Conclusions regarding the suitability of the different methods to detect weld flaws are made and guidance is provided for determining which methods should be used during hydrotest of pipe welded joints, including those made at the butt weld of B16.5 flanged joints. This work is an extension of previous work that examined strain gauge stress measurement of local hydrotest methods (CARBER® [1]) and subsequent FEA assessment of the stress fields (Brown [2]).
Fatigue Improvement of Welded Elements and Structures by Ultrasonic Peening
Authors: Kudryavtsev Yuri , Kleiman Jacob
Published: January 2014

The ultrasonic impact treatment (UIT) is relatively new and promising process for fatigue life improvement of welded elements and structures. In most industrial applications this process is known as ultrasonic peening (UP). The beneficial effect of UP is achieved mainly by relieving of tensile residual stresses and introducing of compressive residual stresses into surface layers of a material. The secondary factors in fatigue improvement by UP are decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the material. Fatigue testing of welded specimens showed that UP is the most efficient improvement treatment as compared with traditional techniques such as grinding, TIG-dressing, heat treatment, hammer peening and application of LTT electrodes. The developed computerized complex for UP was successfully applied for increasing the fatigue life and corrosion resistance of welded elements, elimination of distortions caused by welding and other technological processes, residual stress relieving, increasing of the hardness of the surface of materials. The UP could be effectively applied for fatigue life improvement during manufacturing, rehabilitation and repair of welded elements and structures. The areas/industries where the UP process was applied successfully include: Shipbuilding, Railway and Highway Bridges, Construction Equipment, Mining, Automotive, Aerospace. The results of fatigue testing of welded elements in as-welded condition and after application of UP are considered in this paper. It is shown that UP is the most effective and economic technique for increasing of fatigue strength of welded elements in materials of different strength. These results also show a strong tendency of increasing of fatigue strength of welded elements after application of UP with the increase in mechanical properties of the material used.
Simulating Natural Axial Crack Growth in Dissimilar Metal Welds due to Primary Water Stress Corrosion Cracking
Authors: Rudland D. , Shim D.-J. , Xu S.
Published: January 2014

For axial subcritical crack growth in dissimilar metal (DM) welds due to Primary Water Stress Corrosion Cracking (PWSCC), the crack growth in the length direction is limited to the weld width since the base materials are not susceptible to this type of cracking mechanism. However, the crack may continue to grow in the depth direction until it penetrates the wall thickness. Since the weld width can be much less than the pipe wall thickness, axial cracks have the potential of growing much deeper than they are long. Published stress intensity factor influence functions for semi-elliptical axial cracks in pipe suggest that as the half crack length (c) becomes smaller than the crack depth (a), the stress intensity factor at the deepest point of the crack begins to decrease. These solutions suggest that in many cases, these types of cracks may arrest before penetrating the wall thickness. However, natural flaw growth using the Advanced Finite Element Method (AFEA) suggests that these cracks will not arrest and the stress intensity factor does not decrease in a manner suggested by idealized flaw growth analyses using semi-elliptical crack influence functions.

In this paper, modifications to idealized flaw growth analyses are proposed to predict the natural PWSCC axial crack growth within DM welds. A series of modified flaw growth predictions are presented and compared to published AFEA results. The simplistic rules developed in the paper allow the use of standard influence functions in predicting the time to leakage for axial cracks in DM welds without having to conduct the more complex AFEA analyses.
French Methodology Proposal for Environmentally Assisted Fatigue Assessment
Authors: Métais Thomas , Courtin Stéphan , Genette Pierre , Lefrançois André , Massoud Jean-Paul , De Baglion Laurent
Published: January 2014

Environmental assisted fatigue is a phenomenon that has been investigated over the past 30 years through many test campaigns in various laboratories around the world. It is receiving nowadays an increased level of attention as many nuclear plants will see their life-time extended to up to 60 years. To provide a set of rules for this significant life extension, international codes have already proposed code cases to formally integrate these effects.

More particularly, the ASME code has based itself on the NUREG/CR-6909 [1] to elaborate the Code Case N-792 [2] and suggests a modification of the fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which multiplies the typical usage factor.

In France, the EDF and AREVA objective is also to more explicitly integrate these effects in the RCC-M code basing itself on international methodologies but also results from French in-house testing campaigns [3]. The approach in this paper is globally similar to the one in the ASME code: it will indeed consist in an update of the fatigue curve as well as the calculation of an environmental penalty factor. Nevertheless, the methodologies differ in their detailed implementation, as was already hinted in previous papers discussing the French methodology [4–5]. This paper will present the proposal as well as highlight the differences with the ASME methodology.
Accurate Monitoring of Pipe and Structural Vibrations by Remote RADAR Observations
Authors: Guarnieri Andrea Monti , D’Aria Davide , Speziali Filippo , Giunta Giuseppe
Published: January 2014

The paper describes an innovative RADAR-based methodology to monitor vibrations in pipes and structures. RADARs sense vibrations from zero to thousands of kHz with a spatial sensitivity that goes down to a few micrometers in the best cases and they never saturates even for very large motions. Furthermore, they do it remotely, say tens of meters. The paper provides a critical analysis of performance of such technique and a cross-validation with both controlled vibration in laboratories and measures from accelerometers in campaigns in compression gas stations.
Direct Use of the Fracture Toughness Master Curve in ASME Code, Section XI, Applications
Authors: Server William , Cipolla Russ
Published: January 2014

The ASME Code, Section XI, has adopted the indirect use of the fracture toughness Master Curve to define an alternative index (RTT0) rather than RTNDT for using the Code KIC and KIa curves in Appendices A and G. RTT0 is defined as T0 + 19.7°C (T0 + 35°F), where T0 is the Master Curve reference temperature as defined in ASTM Standard Test Method E 1921. This alternative approach was first approved in ASME Code Case N-629 for Section XI and Code Case N-631 for Section III. Most recently this approach has been integrated directly into the Code, Section XI, and will be published in the 2013 Edition. When this alternative indexing approach was developed, it was recognized that the direct use of the Master Curve itself also could be used as an alternative to the Code KIC curve. A Code Case for the direct use of the fracture toughness Master Curve has been developed and has been presented to Section XI for approval. This paper provides the technical basis for using the fracture toughness Master Curve as an alternative to the Section XI KIC curve. An adjustment to the Master Curve at very low temperatures is included which alleviates a potential problem for low temperature overpressure (LTOP) protection setpoints as would be determined using the existing Code KIC curve.
Modelling and Simulation of Radial Ring Rolling Process Based on Finite Element Analyses
Authors: Feng Zhengkun , Champliaud Henri
Published: January 2014

Ring rolling is widely used to produce seamless rings for critical structural components in assembly industries, such as machinery, aeronautics, energy and automotive. The complex process is characterized by high nonlinearity, unsteady and asymmetrical three-dimensional deformation, dynamic contact boundary conditions caused by the rotations of ring and rolls. A numerical model based on dynamic explicit finite element approach is proposed in this paper to simulate the process behaviors. An expanded ring has been obtained by numerical simulations with the model. Strain and stress analyses have been performed on the rolled ring.
The Role of Grain Size in Predicting Cleavage Fracture Toughness of Pressure Vessel Steels
Authors: Erickson Marjorie , Cochran Kristine B. , Bass B. Richard , Williams Paul T.
Published: January 2014

A theoretical, multi-scale model has been developed to predict the fracture toughness of ferritic steels in the ductile-to-brittle fracture mode transition temperature region. The new model is being implemented into the DISlocation-based FRACture (DISFRAC) computer code at the Oak Ridge National Laboratory (ORNL) and will permit fracture safety assessments of ferritic structures with only tensile properties and microstructural information (grain and carbide size) required as input. The theoretical basis of this model provides a means of predicting fracture behavior outside of the ranges of data currently used in deriving empirically-based models and should provide a means of improving the understanding of fracture behavior in the fracture mode transition region. Dislocation distribution equations, derived from dislocation theory developed by Yokobori et al., are combined with modified boundary layer solutions to account for the stress state local to various microstructural features believed to control fracture behavior. Terms are included to account for microcrack initiation in brittle grain boundary particles, propagation of the microcrack into the first ferrite grain and then through subsequent grain boundaries accounting for local tilt and twist grain misorientation across boundaries. This paper summarizes the DISFRAC model and provides the results of a study performed to investigate the role of grain size in microcrack initiation, propagation and the resulting prediction of fracture toughness.
BWR Steam Dryer Issues and Lessons Learned Related to Flow Induced Vibration
Authors: Basavaraju Chakrapani , Manoly Kamal A. , Murphy Martin C. , Jessup William T.
Published: January 2014

Steam dryers in Boiling Water Reactors, located in the upper steam dome of the reactor pressure vessel, are not pressure retaining components and are not designed and constructed to the provisions of Section III of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code. As such, these components do not correspond to any specific safety class referenced in the Code. Although the steam dryers in BWRs perform no safety function, they must maintain the structural integrity in order to avoid the generation of loose parts that may adversely impact the capability of other plant equipment to perform their safety functions. Therefore guidance from Section III of the ASME Code is utilized in the design and fabrication of replacement dryers as well as for design modifications of the existing dryers for extended power uprates. The majority of licensees of operating nuclear plants are applying for EPU, which generally increases the thermal power output to 20% above the original licensed thermal power. Nuclear power plant components such as steam dryers can be subjected to strong fluctuating loads and can experience unexpected high cycle fatigue due to adverse flow effects while operating at EPU conditions. However, there are some unique challenges related to steam dryer operation at EPU conditions requiring special considerations to prevent fatigue damage from the effects of flow induced vibration. This paper examines the issues and lessons learned related to FIV considerations during EPU reviews of BWR steam dryers.
Simplified Computation of the Welding Process on a Steam-Generator Divider Plate
Authors: Rossillon Frédérique , Depradeux Lionel
Published: January 2014

The integrity of structures in nuclear power plants has to be assessed to meet given safety criteria. For a better understanding of the in-service loads in welded areas of PWRs components, the residual stresses resulting from the welding process have to be estimated. For that purpose, numerical simulations of welding have proved efficient but still require some improvement in terms of computation time reduction to be widely used in an industrial context.

This paper focuses on the residual stress fields in a double V butt weld on a steam generator divider plate. To set a reference, a 2D simulation of multi-pass welding was performed taking into account the whole non-linear thermo-mechanical history. Two simplified method were then carried out to estimate the residual stress field. The first method consists of modeling macro-beads by merging passes together. The second considers only a reduced number of appropriately selected passes in the analysis. Both methods are confronted to the full multi-pass simulation, set as a reference simulation, and their respective efficiency and robustness are discussed.

The main feature of this work, the RNP method, based on a reduced number of appropriately selected passes, gives a good reproduction of the stress fields and strongly reduce the computation time. A significant improvement is observed: CPU time is divided by 10 times with this predictive method.
A Time Saving Method to Compute Multi-Pass Weld Residual Stresses
Authors: Depradeux Lionel , Rossillon Frédérique
Published: January 2014

In order to obtain the residual stress field resulting from the welding process, numerical simulations of multi-pass welding have demonstrated their efficiency and have become an interesting alternative to practical measurements. However, in the context of engineering studies, it remains a difficult task to compute residual stresses for a very high number of passes with reasonable computation times. In this paper, a time-saving method is proposed to simulate the welding process, ensuring an accurate reproduction of the residual stress field with drastically reduced computation times. The method consists in including in the simulation only the last deposited pass, or a reduced number of appropriately selected passes. For a given material and a given heat input, the choice of remaining passes depends on the geometrical parameters. The method is applied to various geometries of austenitic pipes girth welds, which have been widely studied in the literature and standards. The results, confronted to multipass simulations including all the passes, and to literature results, are very satisfactory. Quasi-identical residual stress fields are computed in both cases with computation times divided by a factor comprised between 7 up to 12. Further computations are in progress on other configurations than girth-weld pipes, and more complex 3D geometry like J weld of bottom head nozzles.
Quasi-Static Approach of Damping Forces Exerted Upon a Long Cylinder Oscillating in an Axial Flow
Authors: Divaret Lise , Berland Julien , Berro Hassan , Cadot Olivier , Doaré Olivier , Moussou Pierre
Published: January 2014

This study investigates the flow around a cylinder in a near-axial flow at a Reynolds number of 27000. Both CFD calculations and experiments are performed. Time-mean values of lift force coefficient are investigated against the inclination of the cylinder in the domain of low inclinations (< 15°). Pressure distribution and flow profiles are also measured and extracted from the CFD calculation results for a characteristic inclination α = 5°. Numerical results for force and pressure show fair agreement with experiments for inclination below 5° and reveal that at low angles, the lift force is proportional to the angle. In the framework of a quasi-static approach, the instantaneous damping force exerted on a cylinder oscillating in axial flow is equivalent to the normal force exerted on a cylinder placed in an oblique flow.