bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Tertiary Creep Damage Behavior of a Transversely-Isotropic Material Under Multiaxial and Periodic Loading Conditions
Authors: Stewart Calvin M. , Gordon Ali P.
Published: January 2011

Despite the advent of single crystal turbine blades, the aerospace and industrial gas turbine industries have continued to use directionally-solidified turbine blades due to higher manufacturing yields. These transversely-isotropic turbine blades are subjected to high temperature multiaxial cyclic loading conditions which lead to complex creep strain histories. Few tensor-based constitutive models have been developed that accurately model creep-damage behavior. This paper describes an anisotropic tertiary creep damage model for transversely-isotropic materials. The model is a tensorial expansion of the Kachanov-Rabotnov isotropic creep damage formulation. The analytical techniques required to determine the associated material constants are derived and demonstrated. The model is shown to accurately model a directionally-solidified Ni-base superalloy. A parametric study under biaxial and hydrostatic loading is conducted and the resulting creep strain tensor is evaluated. A series of periodic loading simulations are conducted to examine the stress-strain behavior and damage evolution during ratcheting.
Design and Analysis of LPG Storage Bullets Supported on Multiple Saddles
Authors: Stefanovic Radoslav , Noman Yaser
Published: January 2011

The use of large, high pressure Liquid Petroleum Gas (LPG) storage bullets has become a common, and often assumed safe, practice in the petrochemical industry. The Engineering Equipment and Materials Users Association (EEMUA) is an organization that attempted to address design aspects related to mounded or buried bullets. Publication No. 190 published by the EEMUA [1] became a standard practice in the industry. However, the design recommended, and therefore addressed, by Publication 190 is for bullets directly supported by soil (i.e. without saddle supports). However, it has been noticed by the authors that many users are requesting these storage bullets be supported by saddles resting on foundations in order to minimize the chance of unexpected settling and any motion of the bullets under ground. The large span of these bullets requires more than two saddles adding to the complexity of the design due to statically indeterminate construction, differential settlement and uneven supports. This paper focuses on major issues related to the design of such bullets. First, the loads induced by mound weight, pressure due to mound, and the loads due to longitudinal thermal expansion and soil resistance to this expansion is analyzed. Next, a method for calculating the multiple saddle reactions and bending moments at spans and supports is provided. A simplified method for assessing the effect of differential settlement between saddles is proposed.
Flaw Evaluation in Elbows Through French RSEM Code
Authors: Faidy Claude
Published: January 2011

During the past 20 years many works have been done on duplex stainless steel elbows from EDF plants. These elbows are manufactured with cast CF8M material sensitive to thermal ageing and sensitive to cast defects. After an important work the fitness for service has been derived: acceptance of a crack of 10 × 20mm on the outer surface of the elbows in any particular location for all type of design transients: level A, B, C and D, with corresponding safety factors. Consequently, EDF developed a set of material data: • stress-strain curves; • crack initiation laws for cast defects; • crack growth laws for cast defects; • toughness data versus ageing for this material; and different models for flaw evaluation like: • crack growth in operation; • critical crack sizes based on J approach. All the models developed on cracked elbows can be used for a larger number of nuclear and non-nuclear applications. The paper will describe all the content of the RSEM 2007 concerning this problem of flaw evaluation in elbows.
Nozzle Blend Radius Peak Stress Correction Factors for 2-D Axisymmetric Finite Element Models
Authors: Walter Matthew C. , Sommerville Daniel V.
Published: January 2011

Two dimensional (2-D) axisymmetric finite element models (FEMs) are often used as a simplified means of modeling cylindrical nozzles that intersect cylindrical pressure vessels. An axisymmetric model represents the vessel as a spherical shell rather than a cylindrical shell. Therefore, analysts must correct the stresses predicted by the 2-D model to account for the three dimensional (3-D) effects caused by the true nozzle geometry, which are not represented by the 2-D axisymmetric simplification. This paper presents total stress correction factors for the nozzle blend radius region of Boiling Water Reactor (BWR) Feedwater, Core Spray and Recirculation Inlet nozzle geometries. The correction factors are defined by taking the ratio of the total hoop stress from the 3-D nozzle FEM to the total hoop stress obtained from the 2-D nozzle FEM. Eighteen (18) separate nozzle designs were evaluated. These cases are considered to span the range of dimensions expected for General Electric type BWR-2 through BWR-6 Feedwater, Core Spray, and Recirculation Inlet nozzles.
Review of Section VIII, Division 1 and 2 Changes, 2008–2010
Authors: Pastor Thomas P.
Published: January 2011

Three years ago the major event within Section VIII was the publication of the new Section VIII, Division 2. The development of the new VIII-2 standard dominated Section VIII activity for many years, and a new standard has been well received within the industry. As expected with any new standard, some of the material that was intended to be published in the standard was not ready at the time of publication so numerous revisions have taken place in the last two addenda. This paper will attempt to summarize the major revisions that have taken place in VIII-2 and VIII-1, including a detailed overview of the new Part UIG “Requirements for Pressure Vessels Constructed of Impregnated Graphite”. I have stated in the past that the ASME Boiler and Pressure Vessel Code is a “living and breathing document”, and considering that over 320 revisions were made to VIII-1 and VIII-2 in the past three years, I think I can safely say that the standard is alive and well.
The Relation Between the Peak Stress for a Blunt Flaw and the Stress Intensity Factor for an Equivalent Crack
Authors: Smith Edwin
Published: January 2011

The paper presents arguments to support the view that the often quoted relation σp = Lim[μKI/(πρ)1/2] as ρ (flaw root radius of curvature) tends to zero, with σp being the peak flaw-tip stress, KI, the effective stress intensity factor, and μ = 2, is strictly valid only for the case of an infinitely deep parabolic flaw. The importance of the parameter μ is highlighted with regards to the problem of fracture initiation at the root of a blunt flaw.
ASME Division IV Magnetic Confinement Fusion Energy Devices
Authors: Sowder William , Barnes Richard W.
Published: January 2011

There is an on-going effort within the ASME Section III Codes and Standards organization approved by the ASME Board of Nuclear Codes and Standards to develop rules for the construction of fusion-energy-related components such as vacuum vessel, cryostat and superconductor structures and their interaction with each other. These rules will be found in Division IV of Section III entitled “Magnetic Confinement Fusion Energy Devices (BPV III)”. Other related support structures, including metallic and non-metallic materials, containment or confinement structures, fusion-system piping, vessels, valves, pumps, and supports will also be covered. The rules shall contain requirements for materials, design, fabrication, testing, examination, inspection, certification, and stamping. The formation of a new Work Group Fusion Energy Devices that will develop these rules is just beginning to develop its membership and future working group support structures.
Research on the Powder Consolidation by Using Shock Compaction Method
Authors: Nishi Keijiro , Ide Makoto , Terasawa Nozomi , Irie Seiichi , Itoh Shigeru
Published: January 2011

Shock compaction of powder by using an underwater shock wave is studied and the technical advantages are reported. In this research, we propose a technique for shock compaction of copper/diamond powders by using an underwater shock wave generated by the detonation of explosive. This process produces a composite material in which the particles are strongly bonded due to melting caused by strong deformation and rapid solidification at the particle surface. The improvement of the thermal conductivity of the composite material collected is expected, because the diamond has a high thermal conductivity. Good compacts of composite materials in which diamond particles were dispersed in the copper matrix were obtained in this experiment, and their microstructures and thermal properties were examined. Moreover, pressure measurements and numerical calculations were performed to assess the effect of the pressuring condition in the explosive container.
Microstructure Observation of Inconel Alloy 617 Creep-Tested in He Environment at 950°C
Authors: Lee Gyeong-Geun , Kim Woo-Gon , Kim Yong-Wan , Park Ji Yeon
Published: January 2011

The very high temperature gas reactor (VHTR) has been chosen by the Generation IV International Forum as one of the next-generation nuclear reactors. Due to the high operating temperatures of VHTR, Inconel alloy 617 is being considered as a primary candidate material for the intermediate heat exchanger (IHX) of the VHTR. In this study, the microstructures of creep specimens under various creep loads in a He environment were investigated. As the creep time increased, the thickness of Cr-oxide on the outer layer of the specimens clearly increased, and delaminated after a long creep time. Depths of the decarburized zones in the specimens increased slowly with creep time. However, precipitates at grain boundaries near the surface disappeared before the bulk diffusion of Cr in the matrix. It is considered that decarburization caused by minor gas impurities in He caused the reduction in creep rupture time.
Mechanism of Compressive Residual Stress Introduction on Surfaces of Metal Materials by Water-Jet Peening
Authors: Ishibashi Ryo , Hato Hisamitsu , Yoshikubo Fujio
Published: January 2011

Water-jet peening (WJP) has been applied to several Japanese nuclear power plants as a method of preventive maintenance against stress corrosion cracking. WJP introduces compressive residual stress reaching hundreds of micrometers in depth, comparable with shot peening (SP), and much smaller plastic deformation at the processed surfaces than SP does. The causes of these features are investigated from the perspective of the impact processes on the surfaces. Pulse-load propagation simulation through elasto-plastic calculations using a finite-element method program was applied to analyze the effects of various parameters of the impact processes on the depth profiles of the residual stress and the amount of plastic deformation on the surface of austenitic stainless steels processed with either WJP or the SP. The calculated depth profiles of residual stress and plastic deformation were similar in some degree to the experimental results of an XRD residual-stress analysis and a plastic-strain analysis using both cross-sectional hardness measurements and EBSD analysis. The analysis reveals that the depth of the compressive residual stress tends to increase as the size of the loaded spot during impact increases. The average and maximum observed load spots using WJP were 0.25 and 0.95 mm in diameter, respectively. These diameters were respectively 1.3 and 4.8 times as large as the calculated diameter of a load spot using SP. The reason that the depth of the compressive residual stress using WJP is comparable with that using SP is considered to be the fact that the sizes of the load spots during the impact with WJP are in the same range as those with SP. Shots impact the surface during the SP process, while shock waves generated by the extinction of cavitations impact the surface during the WJP process. The analysis reveals that the shots deform the surface locally with much higher surface pressure in the early stages of the impact, while shock waves deform the surface evenly throughout the wave passage across the surface. It is inferred from these analyzed results that the media impacting the surface make a difference in the hardness and microstructure of the processed surface.
Effect of KIII on Fatigue Crack Growth Behavior
Authors: Kikuchi Masanori , Wada Yoshitaka , Ohdama Chikako
Published: January 2011

Mixed mode fatigue tests are conducted using surface cracked specimen. Slant surface cracked specimens are made where crack angle is 15°, 30°, 45° and 60°. It is shown that factory roof is made at deepest point of surface crack due to ΔKIII, and crack growth rate decreases by the factory roof. Fatigue crack growth is simulated using S-version FEM (Finite Element Method) using crack growth criteria. It is shown that conventional crack growth criteria are not available to predict fatigue crack growth with factory roof. In this study, modified criterion for the prediction of crack growth rate is proposed. By using this criterion, fatigue crack growth simulation is conducted, and results are compared with those of experiments and discussed.
Stability of Time-Averaged Cylinder Wake and Receptivity to Inlet Flow Pulsation
Authors: Lu Liang , Papadakis George
Published: January 2011

In this paper, the linear stability analysis (LSA) is utilized to investigate the stability of time-averaged cylinder wake past a circular cylinder at Re = 200 and its receptivity to inlet flow pulsation. An in-house finite volume method is used to solve the full N-S equations as well as the linearised set for small perturbations around the time-averaged flow. The solution of the latter set provides information about the stability of the wake. It is found that the most unstable eigenmode has a small negative real part and an imaginary part that closely marches the Strouhal number of vortex shedding. This finding agrees with the results of other investigators. Inlet flow pulsation appears as a forcing term in the linearised equation set. Both cross-stream and streamwise velocity components in the separating shear layers are strongly affected by pulsation. The effect of pulsation is spatially localised in the near wake. Increasing the pulsation frequency reduces the spatial extent within which pulsation plays an important role.
Free Vibrations of Fluid–Solid Structures With Strong Coupling
Authors: Voss Heinrich , Stammberger Markus
Published: January 2011

Free vibrations of fluid-solid structures are governed by unsymmetric eigenvalue problems. A common approach which works fine for weakly coupled systems is to project the problem to a space spanned by modes of the uncoupled system. For strongly coupled systems however the approximation properties are not satisfactory. This paper reports on a framework for taking advantage of the structure of the unsymmetric eigenvalue problem allowing for a variational characterization of its eigenvalues, and structure preserving iterative projection methods. We further cover an adjusted automated multi-level sub-structuring method for huge fluid-solid structures.
Development of LBB Assessment Method for Japanese Sodium Cooled Fast Reactor (JSFR) Pipes: 1—Study on the Premise for the Standardization of Assessment Procedure
Authors: Wakai Takashi , Machida Hideo , Enuma Yasuhiro , Asayama Tai
Published: January 2011

This paper describes the premise for the standardization of Leak Before Break (LBB) assessment procedure applicable to Japanese Sodium cooled Fast Reactor (JSFR) pipes made of modified 9Cr-1Mo steel. For the early commercialization of the SFRs, economic competitiveness is one of the most essential requirements. Japan Atomic Energy Agency (JAEA) proposes an attractive plant concept and studies the applicability of some innovative technologies to the plant. One of the most practical means to reduce the construction costs is to reduce the total amount of structural materials. To meet the requirements, modified 9Cr-1Mo steel has attractive characteristics as a main structural material of SFRs, because the steel has both excellent thermal properties and high temperature strength. By employing the steel as the main structural material, remarkably compact plant design can be achieved. Since the ductility and toughness of the steel is relatively inferior to those of conventional austenitic stainless steels, a LBB assessment technique suitable for the pipes made of modified 9Cr-1Mo steel may be required. In addition, since the SFR pipes are mainly subjected to displacement controlled thermal loads, it is expected that fast unstable fracture is unlikely. Taking both material and structural features into account, the framework to establish a precise LBB assessment procedure for SFR pipes must be organized. For the standardization of the LBB procedure, the main investigation items were defined as follows: (1) Approval of the assessment flowchart eliminating uncertainty due to small scale leakage, e.g. self plugging phenomenon and influence of crack surface roughness on leak rate. (2) Proper selection of LBB assessment objects in JSFR. (3) Distinguishment between the matters covered by a design code and LBB, i.e. assumption of initial flaw(s). (4) Development of creep and/or fatigue crack extension assessment technique, including collection of necessary material data. (5) Development of unstable fracture assessment technique. (6) Development of leak rate evaluation technique. (7) Characterization of loads for LBB assessment. (8) Standardization of the procedure as the Japan Society of Mechanical Engineers (JSME) code.
A Prediction of V-Factor for the Cracked Pipe Under Combined Mechanical and Thermal Stresses With Elastic Follow-Up
Authors: Song Tae-Kwang , Lee Kuk-Hee , Oh Chang-Young , Kim Yun-Jae , Ainsworth Robert A. , Nikbin Kamran
Published: January 2011

In this paper, a prediction of V-factor, the correction factor for the plasticity interaction between the primary stress and secondary stress, for the cracked pipe under combined mechanical and thermal stresses with significant elastic follow-up is presented. Recently, present authors suggested enhanced V-factor solution using failure assessment curve, which is less conservative than R6 code. However, this solution is limited to weak elastic follow-up condition. The degree of elastic follow-up is related to the variations of Vo with β according to this study. Based on this observation, a prediction solution for the V-factor which can be applied to the crack assessment ranging from weak elastic follow-up condition to strong elastic follow-up condition is proposed.
Digital Image Evaluation Method for Digital Radiography
Authors: Mori Masako , Kashiwa Toshibumi , Aoki Yoshimitsu
Published: January 2011

Digital radiography is becoming one of the common radiographic testing techniques in various industries. However, to apply this new technique to nuclear components, one big issue is how to evaluate the images and ensure that the images have enough quality to be used as inspection record. In film radiography, the IQI, which stands for Image Quality Indicator, have been used to ensure that the films have enough quality to detect any specified defects in the products. In this paper, new alternative IQI that was developed in our previous study for digital radiography to evaluate digital image quality is tested and evaluated. In addition, new image evaluation criteria are also developed and evaluated by calculating MTF, which stands for Modulation Transfer Function, from the IQI images of the products. Finally, the recommended procedures to evaluate radiographic testing image are summarized.
RBI Technology for Boiler Superheater of Power Station
Authors: Liu Fujun , Ding Shoubao , Kong Shuai , Song Dan , Hu Dongming , Guo Xiaolian , Jin Nanhui
Published: January 2011

Risk-Based Inspection (RBI) has been wide used in petrochemical industry all over world with good performance. But its application in power station boiler is rarely reported. The “four tubes” of the power station boiler, namely economizer, water-cooling wall, superheater and reheater tubes, are prone to blast due to the direct fire heating, and it causes non-plan shutdown and leads to severe influence to safety. In this paper, the failure mechanisms of power station boiler were analyzed, the calculation of modification factors for high-temperature smoke erosion and high-temperature creep was researched. Considering the specific situations in China, the probability of failure modification factor based on remaining life was proposed. Then, the method of economic loss calculation was established based on the differences between the petrochemical equipment and the power station boilers, and the proper classification scope was established according an investigation. At last, a superheater project was carried out, the risk was fixed and the proper management and inspection suggestions were proposed.
Recent Progress of the Stationary Pressure Vessel Regulations and Standards in China
Authors: Shou Binan , Chen Gang , Xie Tiejun
Published: January 2011

The recent development of the stationary pressure vessel regulations and standards was introduced in this paper. The important technical changes in the regulations and standards which have been issued in the year of 2009 were also analyzed. Compared between the Chinese essential safety requirements and the relative codes in the U.S., the feasibility of the mutual cooperation between China and the U.S. standardization organizations were discussed.
Analysis of the Partial Safety Factor Method Using Probabilistic Techniques
Authors: Lindley B. A. , James P. M.
Published: January 2011

Partial Safety Factors (PSFs) are scaling factors which are used to modify the input parameters to a deterministic fracture mechanics assessment in order to consider the effects of variability or uncertainty in the values of the input parameters. BS7910 and SINTAP have adopted the technique, both of which use the First Order Reliability Method (FORM) to derive values for PSFs. The PSFs are tabulated, varying with the target probability of failure, p(F), and the Coefficient of Variance (COV) of the variable. An accurate assessment of p(F) requires a probabilistic method with enough simulations. This has previously been found to be time consuming, due to the large number of simulations required. The PSF method has been seen as a quick way of calculating an approximate, conservative value of p(F). This paper contains a review of the PSF method, conducted using an efficient probabilistic method called the Hybrid probabilistic method. The Hybrid probabilistic method is used to find p(F) at a large number of assessment points, for a range of different PSFs. These p(F) values are compared to those obtained using the PSF method. It is found that the PSF method was usually, and often extremely, conservative. However there are also cases where the PSF method was non-conservative. This result is verified by a hand calculation. Modifications to the PSF method are suggested, including the establishment of a minimum PSF on each variable to reduce non-conservatisms. In light of the existence of efficient probabilistic techniques, the non-conservatisms that have been found in the PSF method, coupled with the impracticality of completely removing these non-conservatisms, it is recommended that a full probabilistic assessment should generally be performed.
Weld Residual Stress Analysis and the Effects of Structural Overlay on Various Nuclear Power Plant Nozzles
Authors: Zhang Tao , Brust Bud , Wilkowski Gery , Ranganath Sam , Wang Lihua , Tsai Yao Long , Huang Chin-Cheng , Liu Ru-Feng
Published: January 2011

Welding is a commonly used and one of the most important material-joining processes in industry. The incidences of defects had been located by ultrasonic testing (UT) in various pressurizer nozzle dissimilar metal welds (DMW) at nuclear power plants. In order to evaluate the crack propagation, it is required to calculate the stress distribution including weld residual stress and operational stress through the wall thickness in the weld region. The analysis procedure in this paper included not only the pass-by-pass welding steps, but also other essential fabrication steps of surge, safety/relief and spray nozzles. In this paper, detailed welding simulation analyses have been conducted to predict the magnitude of these stresses in the weld material. To prevent primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR) on susceptible welded pipes with dissimilar metal welds, the weld overlay process has been applied to repair nuclear reactor pipe joints in plants. The objectives of such repairs are to induce compressive axial residual stresses on the pipe inside surface, as well as increase the pipe thickness with a weld material that is not susceptible to stress-corrosion cracking. Hence, understanding the residual stress distribution is important to evaluate the reliability of pipe joints with weld overlay repairs. The finite element results in this paper showed that, after deposition of the DMW nozzle and stainless steel welds, tensile weld residual stresses still exist at regions of the DMW through the thickness. This tensile weld residual stress region was significantly reduced after welding the overlay. The overlay weld also provides a more uniform and large compressive region through the thickness which has a beneficial effect on the structural integrity of the DMW nozzle welds in the plant.
Estimation Uncertainty in the Determination of the Master Curve Reference Temperature
Authors: Sham T.-L. Sam , Eno Daniel R.
Published: January 2011

The Master Curve Reference Temperature, T0, characterizes the fracture performance of structural steels in the ductile-to-brittle transition region. For a given material, this reference temperature is estimated via fracture toughness testing. A methodology is presented to compute the standard error of an estimated T0 value from a finite sample of toughness data, in a unified manner for both single temperature and multiple temperature test methods. Using the asymptotic properties of maximum likelihood estimators, closed-form expressions for the standard error of the estimate of T0 are presented for both test methods. This methodology includes statistically rigorous treatment of censored data, which represents an advance over the current ASTM E1921 methodology. Through Monte Carlo simulations of realistic single temperature and multiple temperature test plans, the recommended likelihood-based procedure is shown to provide better statistical performance than the methods in the ASTM E1921 standard.
Flow Stress in a Notched Austenitic Stainless Steel Specimen Under Combined Tension and Bending
Authors: Izawa Satoru , Matsubara Masaaki
Published: January 2011

A load history-dependence of tension and bending does not exist in the brittle fracture where linear elastic fracture mechanics is applicable. However, load history-dependency does exist in a plastic collapse load of a member. The load history-dependency of plastic collapse load of a single-edge cracked member subjected to combined tension and bending for accurate structural integrity evaluation was studied in this paper. For this purpose, the authors developed a statically indeterminate fracture mechanics failure testing system, which examines of the load history-dependency of the plastic collapse of the member, by applying an axial force and a bending moment. The plastic constraint factor, the plastic collapse load and the 0.2% proof strength all exceeded the upper bound solution. Therefore, the flow stress is used in place of the plastic collapse load as an effective stress. In general, the flow stress is typically used at the average of the proof stress and the tensile strength. This paper describes the experimental result of the load history-dependency of the flow stress in a single-edge notched specimen test. The experimental result showed the load history-dependency on the flow stress in single-edge notched members subjected to combined tension and bending. A method for evaluating the flow stress from the stress intensity versus displacement chart is also described. The flow stress of the notched ductile materials followed the upper-bound solution regardless of the load history. The effect of the combined loading on the flow stress was considered using both the tangent intersection method with the evaluation chart. A method for evaluating the flow stress from the distribution of plastic collapse load on the upper-bound solution is given. The proposed a method showed that this flow stress is in fairly good agreement with that obtained by the upper-bound solution.
Effect of Creep Mismatch Factor on Stress Redistribution in Welded Branch Pipes
Authors: Han Jae-Jun , Kim Yun-Jae , Lee Kuk-Hee
Published: January 2011

This paper describe steady state stress distribution into the weld metal of welded branch components using detailed three dimensional elastic creep finite element analyses. In order to show the effect of the loading mode, this research is carried out under various loading conditions such as internal pressure, in-plane bending to the branch pipe and out-of-plane bending to branch pipe. Also, to generalize the unique aspect, three geometries of branch components including welded large bore branch, medium bore branch, and trunnion are considered. It is a well-known fact that the creep strain rate of welds material is faster than that of parent material. Therefore, the creep exponent and constants for the parent and weld metal are systematically varied to analyze under-matching, even-matching and over-matching conditions in creep. It can be shown that mismatch effect can be quantified as mismatch factor with specific characteristics.
Effects of Scatter in Bolt Preload on the Sealing Performance of Pipe Flange Connections Under Internal Pressure (Case Where the Nominal Diameter of Pipe Flange Connection is 20″)
Authors: Takagi Yoshio , Sawa Toshiyuki , Torii Hiroyasu , Omiya Yuya
Published: January 2011

It has been well known that a scatter in axial bolt forces in pipe flange connections tightened by the torque control method is substantial. In practice, pipe flange connections with the large nominal diameter tightened by the torque control method have been used in chemical industry, and so on. In our study, the characteristics of the connections with smaller nominal diameter (less than 8″) have been shown. So, in an optimum design of pipe flange connections with gaskets, it is necessary to understand the characteristics of the pipe flange connections with large nominal diameter under internal pressure and the contact gasket stress distributions due to the scatter in axial bolt forces in the connections tightened by the torque control method. In this paper, the experimental and FE analyses were done to evaluate the effect of scatter in axial bolt force on the gasket stress distribution and the sealing performance of pipe flange connections with 20″ nominal diameter. Two types of torque controlled assembling procedures, that is, ASME PCC-1 and JIS B 2251 procedures, are evaluated as an assembling procedures and an effect of scatter in the axial bolt forces obtained from the above methods is examined. Then, the effect of scatter in the axial bolt forces on the sealing performance of the connection is evaluated. The contact stress distribution in the larger pipe flange connection with 20″ nominal diameter under internal pressure is analyzed using FEM by taking into account a non-linearity and a hysteresis. The measured scatter in the axial bolt forces is applied in the FEM calculations.
Variation in Mechanical Properties, Microstructures and Fracture Behavior of 304 Stainless Steel During Low-Cycle Fatigue
Authors: Ye Duyi , Xu Yuandong , Xiao Lei , Cha Haibo
Published: January 2011

A series of experiments, including constant amplitude low-cycle fatigue tests, post-fatigue tension to failure tests, LOP (TEM) observations, and SEM examinations, were performed at room-temperature to investigate the variation of the static mechanical properties, microstructures and fracture behavior of 304 austenitic stainless steel during low-cycle fatigue. The changing characteristics of various static mechanical property parameters, including the strength parameters, stiffness parameter, ductility parameters and strain hardening exponent during fatigue damage process of the stainless steel were obtained experimentally and their micromechanisms were discussed by analyzing both the deformation microstructures and the fracture features of the cyclically pre-deformed specimens. It was shown that the austenite / martensite transformation resulting from the accumulation of cyclic plastic strain was mostly responsible for the variation in the strength, ductility and strain hardening ability of the stainless steel during fatigue damage process. The depletion of the inherent ductility in the material due to fatigue damage evolution led to the ductile-to-brittle transition (DBT) in the fracture modes. Based on the macro- / micro-experiments regarding the exhaustion of the ductility during fatigue damage, the ductility parameter was suggested as a damage indicating parameter for the present stainless steel in further studying the fatigue damage mechanics model as well as the residual fatigue life prediction method.
Stress and Strain Locus of Perforated Plate in Inelastic Deformation: Strain-Controlled Loading Case
Authors: Watanabe Osamu , Bubphachot Bopit , Matsuda Akihiro
Published: January 2011

Plastic strain of structures having stress concentration is estimated by using the simplified method or the finite element elastic solutions. As the simplified methods used in codes and standards, we can cite Neuber’s formula and elastic follow-up procedure. Also we will cite stress redistribution locus (abbreviated as SRL) method recently proposed as the other simplified method. In the present paper, inelastic finite element analysis of perforated plate, whose stress concentration is about 2.2∼2.5, is carried out, and stress and strain locus in inelastic range by the detailed finite element solutions is investigated to compare accuracy of the simplified methods. As strain-controlled loading conditions, monotonic loading, cyclic loading and cyclic loading having hold time in tension are assumed. The inelastic strain affects significantly life evaluation of fatigue and creep-fatigue, and the stress and strain locus is discussed from the detailed inelastic finite element solutions.
Influences of Inner Pressure and Overload on Low Cycle Fatigue Behaviors of Elbow Pipes With Local Wall Thinning
Authors: Sato Kyohei , Takahashi Koji , Ogino Kanako , Urabe Yoshio , Ando Kotoji
Published: January 2011

Low cycle fatigue tests were conducted using 100A elbow pipe specimens with or without local wall thinning. Local wall thinning of 50% of the nominal pipe wall thickness was machined on the inside of the test elbows to simulate metal loss due to flow-accelerated corrosion. The local wall thinning area was machined at the extrados, which has been reported to be the section most likely to suffer local wall thinning. Low cycle fatigue tests were carried out under displacement control using pipe with local wall thinning at the extrados to investigate the influences of an inner pressure of 0∼12 MPa. To simulate seismic events, low cycle fatigue tests were also carried out on pipe with or without wall thinning to investigate the influences of cyclic overloads. No differences in fatigue life were caused by an inner pressure of 3 MPa. However, degradation of fatigue life was caused as inner pressure increased from 6 MPa to 12 MPa. The fatigue lives of overloaded pipes were similar to those of non-overloaded pipes. In addition, three-dimensional elastic-plastic analyses were carried out using the finite element method. The crack penetration area and the crack growth direction were successfully predicted by the analyses.
Analysis of the Dynamic Response of a Controlled Detonation Chamber
Authors: Simoens B. , Lefebvre M. H. , Asahina J. K. , Minami F. , Nickell R. E.
Published: January 2011

Detonation chambers (either mobile or fixed) are used worldwide for a wide range of applications. At present, a 1/7 scale model of a 1 ton detonation chamber is available for extended testing in Belgium. The chamber is a single wall cylindrical vessel with semi-elliptical ends. Each time an explosive charge is fired in the vessel, that vessel is submitted to a number of deformation cycles. A series of strain gages measure the deformation of the vessel walls. Experimental peak strains and vibration frequency can be compared to predicted values based on simple formulas. Measured values are reasonably close to the estimated values. The influence of the shape of the charge is studied. The shape has an important influence on the chamber response. For a fixed charge mass, a spherical charge causes less deformation than a cylindrical charge and is therefore advantageous from a fatigue point of view.
Improvement of the Threshold Stress Intensity Factor for Stress Corrosion Cracking in SUS316 by Tensile Overload
Authors: Takahashi Koji , Miyazaki Yuji , Hashikura Yasuaki , Ando Kotoji
Published: January 2011

The effects of overload on the threshold stress intensity factor (KISCC) for stress corrosion cracks (SCC) in stainless steel were studied. Tensile overload was applied to a wedge opening loaded specimen of SUS316, and SCC tests were carried out to determine the resultant KISCC. As a result, the value of KISCC was found to increase with increasing stress intensity factor by tensile overload. The effects of tensile overload on KISCC and the threshold stress intensity factor range for fatigue (ΔKth) were compared. It was found that the effect of tensile overload on KISCC was larger than that of ΔKth.
Characterization of Leakage Through Gaskets by a Two-Stage Numeric Approach Using Transport Equations
Authors: Kurz Hariolf , Roos Eberhard
Published: January 2011

The present discussion on environmental impact leads to the need to reduce fugitive emissions in the processing industry. In Europe, the IPPC requires national governments to put standards — such as VDI-guideline 2290 [1] — into place that force plant operators to meet the best available techniques. In this study, an approach is presented, to estimate the effects of inhomogeneous gasket stresses, geometry changes and combinations of different gasket materials to improve the sealing performance and reduce fugitive emissions. Compression and leakage tests according to DIN EN 13555 [2] formed the basis to characterize the gasket pressure-closure behaviour and permeability of a homogeneous stressed sheet gasket material. Provided that linear pressure dependency is applicable, transport-theory according to heat conduction can be applied to calculate the effects of inhomogeneous gasket stress distribution or variation of gasket geometry such as gasket width. The method implies a two-stage procedure. In the first step, the local gasket stress distribution and thus the corresponding permeability in a flange connection is calculated. The local permeability is allocated for each element in terms of a unique material definition. Solving the steady state in the second step under inner and ambient pressure-constraint leads to the internal pressure distribution, local leakage flow and the overall leakage rate. The approach is applied and verified at an inhomogeneous stressed sheet gasket and enables us to predict the reduction in the leakage rate by factor 3000 of an prestressed PTFE-sheet gasket due to the decreased gasket width.
Presentation of a Toughness Benchmark on a Low Ductility Material: 6061-T6 Aluminium
Authors: Ancelet O. , Marie S. , Allais L. , Wident P. , Brianc¸on L. , Guilbaud D. , Bonne D. , Bonnot A. F.
Published: January 2011

The aluminum alloy 6061-T6 is a material used for some part of experimental reactor for its interesting physical and mechanical proprieties. To respect the European rules on pressure equipments, a material must present some minimal characteristics for toughness and ductility. In particular, a preventive analysis against abrupt break can be performed in order to ensure the integrity of the structure. In this frame, some characterizations of the toughness were undertaken. Some tests present singular propagation at the beginning of the crack propagation. These singular crack propagation brings some difficulties in the interpretation of the testing and in the J0,2BL/JIC determination. It is the reason why a benchmark on the determination of this value for such material was organized between three different laboratories: the LISN of the French atomic commission (CEA), the LC2M of the CEA and the CESMAN of the DCNS industry. All participants receive a piece of the same material and realize some toughness testing according to its own usage. The benchmark allows comparing the different experimental methodology (machining specimen, pre-crack, testing conditions, equipments …) and the interpretation methodology (ASTM 1820 and ISO 12135 application). This leads to propose a list of recommendations on the realization of the toughness testing and more specifically some necessary adaptation of the ASTM 1820 and ISO 12135 standard for such material.
Statistical Assessment of Effect of Hydride Non-Ratcheting Conditions on Delayed Hydride Cracking Initiation in CANDU Pressure Tubes
Authors: Gutkin Leonid , Scarth Douglas A. , Bickel Grant A.
Published: January 2011

In-service flaws in CANDU Zr-Nb pressure tubes are evaluated for initiation of delayed hydride cracking (DHC) according to Canadian nuclear standards. A flaw may be under hydride ratcheting conditions or under hydride non-ratcheting conditions, depending on the hydrogen concentration at the flaw location. Under hydride ratcheting conditions (higher hydrogen concentrations), flaw-tip hydrides do not completely dissolve at normal operating temperature and incrementally accumulate with each reactor heatup/cooldown cycle. On the contrary, under hydride non-ratcheting conditions (lower hydrogen concentrations), the flaw-tip hydrides completely dissolve at normal operating temperature, so that no incremental hydride accumulation occurs with each reactor heatup/cooldown cycle. Experiments have demonstrated that the resistance to DHC initiation under hydride non-ratcheting conditions is substantially higher than that under hydride ratcheting conditions. A single-valued lower-bound hydride non-ratcheting factor had been proposed to conservatively quantify this behaviour. However, such a factor does not account for the experimentally observed variation in the relative increase in the threshold stress for DHC initiation under hydride non-ratcheting conditions with respect to that under hydride ratcheting conditions. In this paper, this problem has been addressed statistically by evaluating the probability of DHC initiation at the in-service flaws. The predicted probability of DHC initiation has been found to increase with increasing the applied stress and the stress concentration at the flaw tip and to decrease with increasing the threshold stress intensity factor for DHC initiation. All these trends are consistent with our fundamental understanding of the DHC initiation phenomenon. Also, the predicted probability of DHC initiation is higher for hydride ratcheting conditions than for hydride non-ratcheting conditions. On the basis of this analysis, the hydride non-ratcheting factor has been represented as a distributed parameter, suitable for use in the probabilistic assessments of delayed hydride cracking initiation.
Comparison Between J and Collapse Load Approaches Applied to Fracture Test Results on Ni Base Alloy 600 Surface Cracked Plates
Authors: Gilles Philippe , Andrieu Yann , Amzallag Claude
Published: January 2011

The paper presents a fracture mechanics analyses of CT and surface cracked plate specimens (CCT) made from material Inconel 600. The main issue is to determine whether the plates fracture by ductile tearing or collapse with the aim of determining a simplified fracture assessment of steam generator partition plates. The paper compares J based analyses to several collapse load formulae. It is shown that estimating the tearing initiation load is almost unachievable in the present tests designed as demonstrative tests. It is also proven that most of the case collapse load formulae are very conservative. The results contribute to evidence that partition plates exhibit sufficient safety margins to failure up to the end of service life in spite of the presence of a very deep initial crack.
Viscoelastic Finite Element Modeling of Bimodal High Density Polyethylene (HDPE) Piping Materials for Nuclear Safety-Related Applications
Authors: Shim Do-Jun , Krishnaswamy Prabhat , Hioe Yunior , Kalyanam Sureshkumar
Published: January 2011

The U.S. Nuclear Regulatory Commission (USNRC) has recently approved Relief Requests for the use of high density polyethylene (HDPE) piping in safety-related applications. The ASME Boiler and Pressure Vessel Code, meanwhile, has developed Code Case N-755 that defines the design and service life requirements for PE piping in nuclear plants though it has not as yet been approved by the USNRC. One of the issues of concern is premature failure of PE piping due to slow crack growth (SCG) that can initiate due to a combination of sustained loads, elevated temperatures, and a pre-existing defect. Understanding and predicting the SCG behavior is an essential step in developing a methodology for predicting the service life of PE piping. The first step in studying the failure process in a polymer under a constant sustained load is the selection of a suitable constitutive model to represent the time-dependent behavior of the material. In this paper, uniaxial tensile creep tests were performed for a bimodal HDPE (PE4710) piping material. This creep data was used to determine the viscoelastic material constants for this bimodal HDPE using a power-law creep model. These material constants were used in finite element (FE) analyses to study the viscoelastic behavior of the bimodal HDPE. As a first step, the FE model was verified by comparing the results from numerical simulations and experiments for a set of uniaxial tensile creep tests. The FE model was then applied to study the viscoelastic behavior of a SCG specimen. The time dependent stress and strain fields were investigated.
An Approach Based on Code Case 2605 for Fatigue Evaluation of Vanadium Modified Materials Reactor
Authors: Panwala M. Sohel M. , Desai D. H. , Mehta S. L.
Published: January 2011

The recent increase in demand of petroleum product has been fulfilled by increase in capacity of refineries. The increases in capacity of refineries have been established by using the heavy wall thickness reactor of material such as 2.25Cr-1Mo-0.25V. The ASME Section VIII Division 2 curves do not extend to creep regime and also and also there is no method in Division 2 to analyze for fatigue or screening using the fatigue curves which is required for material with UTS greater than 80 ksi. Hence, ASME gives the guide lines for the fatigue evaluation & analysis in presence of creep by the Code Case 2605. Code Case 2605 gives the design requirements for fatigue in presence of creep for this material by involving creep ratcheting and creep relaxation procedures. The creep model given in Code Case 2605 is not available in any commercial software like ANSYS, ABAQUS & others. Hence, usercreep model is developed & compiled in FORTRAN software. This usercreep model has been used in ANSYS by TBOPT command from outside ANSYS through FORTRAN. The most critical skirt to bottom head & shell junction in reactor has been analyzed for fulfilling the requirement of Code Case 2605. The elastic perfectly plastic material curve is also used to calculate the plastic strain along with creep strain as required by Code Case 2605. The 0.00071 of accumulated creep damage has been induced at 1,000,000 Hr. Hence, the time of 1,000,000 Hr governs the creep relaxation analysis of Code Case 2605 for fatigue evaluation in spite of limit given on accumulated creep damage in this specific case.