bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the Truth Loading Conditions of a Austenitic CT Specimen During a SCC Experiment
Authors: Marie S. , Guerre C. , Herms E.
Published: May 2012

With the aim to investigate the influence of strain hardening on the stainless steels susceptibility to stress corrosion cracking, tests were conducted in PWR environment on CT specimens, taken from a 316L stainless steel sheet cold rolled to 40% in thickness reduction. The initial cracks obtained by the fatigue pre-cracking have an atypical ‘V’ shape with smaller propagation in the center of the CT thickness compared to nominal propagation observed at both sides. The initial explanation was to consider a stress intensity factor derived from classical reference solution on the basis of a straight crack front, and considering the local value of the crack depth in the equation. This assumption raised several problems analsyes in this paper. This particular shape of the initial defect may be related to several factors, and partly to the 40% cold rolling. It is likely that the hardening is not uniform, with a higher rate at the specimen sides than in the central area. In addition, significant residual stresses due to the gradient of mechanical properties are observed. Due to the high rate of work hardening by rolling of the sheet metal, a gradient of the mechanical properties through the thickness was determined, and the residual stresses profile induced by this process was measured. The variations obtained are consistent with each other: the material is more hardened in the vicinity of specimen surface and residual stresses are compressive in nature in the central part of the specimen and of tensile type on the flanks. All these data were firstly considered in order to assess their role regarding the particular form of the initial crack front obtained after fatigue: the 3D finite element calculations taking into account the true shape of the crack front demonstrate the relationship between the characteristics of the experimental crack front obtained after fatigue pre-cracking and the residual stresses. Moreover, from the residual stresses measured on the plate where samples have been machined/prepared, the residual stresses field in the specimen after its machining is calculated and then taken into account in the mechanical analysis. The characteristics of this field in addition to the mechanical loading applied during SCC testing can explain the crack propagation behavior observed experimentally.
RCC-MRx Appendix A16 Methodology for the Analytical J Calculation Under Thermal and Combined Thermal + Mechanical Loadings for Pipes and Elbows and Related Assessment Tool MJSAM
Authors: Marie S. , Ne´de´lec M. , Delaval C.
Published: May 2012

RCC-MRx code provides flaw assessment methodologies and related tools for Nuclear Power Plant cracked components. An important work has been made in particular to develop a large set of compendia for the calculation of the parameter J for various components (plates, pipes, elbows,…) and various defect geometries. Also, CEA in the frame of collaborations with IRSN, developed a methodology for J analytical calculation for cracked pipes and elbows submitted to thermal and combined mechanical and thermal loadings. This paper presents first the development of this methodology and an overview of the validation strategy, based on reference 2D and 3D F.E. calculations. The second part of the paper presents the last version of the MJSAM tools which is based on the 2010 version of the appendix A16 of the RCC-MRx code. All compendia (for KI, J and C* calculation) and all defect assessment procedures have been implemented in the tool: It covers crack initiation and propagation under fatigue, creep, creep-fatigue and ductile tearing situations. Sensitivity and probabilistic analyses can also been performed with this tool, directly linked to Microsoft Excel software for the results exploitation.
Harmonic Response of a Piping System Considering Pipe - Support Friction via HFT Method
Authors: Argu¨elles Jose´ , Casanova Euro , Asuaje Miguel
Published: May 2012

The harmonic response of piping systems is in general estimated considering linear behavior, i.e. neglecting pipe-support dry friction, shocks between adjacent pipes or between pipe and supports, unidirectional supports, gaps, etc. Under this hypothesis, harmonic analysis is straight forward for a forcing frequency and not specially demanding in terms of computational cost. On the contrary, if any nonlinearity is taken into account, integration in time is required until the system achieves a steady-state solution, which demands dealing with initial conditions, intensive computation and long calculation times. In the particular case of support friction, vibration amplitudes calculated using the linear assumption may be well overestimated for some systems or conditions, thus misguiding designers and analysts, which traduces in excessive cost in system construction. In this work, the Hybrid Frequency-Time method (HFT) is used to calculate the steady state amplitudes of a piping system subjected to harmonic excitations and considering pipe-support friction. Comparisons between a full integration scheme and the proposed methodology are presented and discussed for a typical system. Results show that the HFT method is a valid practical option to estimate the harmonic response of a piping system when considering support friction.
A Proposal for the Maximum KIc for Use in ASME Code Flaw and Fracture Toughness Evaluations
Authors: Kirk Mark T. , Stevens Gary L. , Erickson Marjorie , Yin Shengjun Sean
Published: May 2012

Nonmandatory Appendices A [1] and G [2] of Section XI of the ASME Code use the KIc curve (indexed to the material reference transition temperature, RTNDT) in reactor pressure vessel (RPV) flaw evaluations, and for the purpose of establishing RPV pressure-temperature (P-T) limits. Neither of these appendices places an upper-limit on the KIc value that may be used in these assessments. Over the years, it has often been suggested by some of the members of the ASME Section XI Code committees that are responsible for maintaining Appendices A and G that there is a practical upper limit of 200 ksi√in (220 MPa√m) [4]. This upper limit is not well recognized by all users of the ASME Code, is not explicitly documented within the Code itself, and the one source known to the authors where it is defended [4] relies on data that is either in error, or is less than 220 MPa√m. However, as part of the NRC/industry pressurized thermal shock (PTS) reevaluation effort, empirical models were developed that propose common temperature dependencies for all ferritic steels operating on the upper shelf. These models relate the fracture toughness properties in the transition regime to those on the upper shelf and, combined with data for a wide variety of RPV steels and welds on which they are based, suggest that the practical upper limit of 220 MPa√m exceeds the upper shelf fracture toughness of most RPV steels by a considerable amount, especially for irradiated steels. In this paper, available models and data are used to propose upper bound limits of applicability on the KIc curve for use in ASME Code, Section XI, Nonmandatory Appendices A and G evaluations that are consistent with available data for RPV steels.
Advances in Development of J-Integral Experimental Estimation, Testing and Standardization
Authors: Zhu Xian-Kui
Published: May 2012

The J-integral is an important concept in the elastic-plastic fracture mechanics, and serves as a critical material parameter to quantify the toughness or resistance of ductile materials against fracture. The relation between the J-integral and crack extension has been widely used as the resistance curve of ductile materials in fracture mechanics design and in structural integrity assessment. Experimental testing and evaluation have played a central role in providing reliable fracture toughness properties to fracture mechanics analysis. Since the J-integral concept was proposed, extensive efforts of investigations have been made to develop its experimental estimation method, testing technique and standardization, as evident in the ASTM E1820 — a commonly used fracture toughness testing standard. In recent years, significant progresses of the J-integral fracture testing and experimental estimation have been achieved, and a part of them was accepted and updated in ASTM E1820. To better understand and use this fracture testing standard, the present paper gives a brief review of historical efforts and recent advances in the development of the J-integral experimental estimation and standard testing.
Limit Load Analysis of Cylindrical Vessels Under Internal Pressure and Axial Strain
Authors: Zhu Xian-Kui
Published: May 2012

Strain-based design is a newer technology used in safety design and integrity management of oil and gas pipelines. In a traditional stress-based design, the axial stress is relatively small compared to the hoop stress generated by internal pressure in a line pipe, and the limit state in the pipeline is usually load-controlled. In a strain-based design, however, axial strain can be large and the load-carrying capacity of pipelines could be reduced significantly below an allowed operating pressure, where the limit state is controlled by an axial strain. In this case, the limit load analysis is of great importance. The present paper confirms that the stress, strain and load-carrying capacity of a thin-walled cylindrical pressure vessel with an axial force are equivalent those of a long pressurized pipeline with an axial tensile strain. Elastic stresses and strains in a pressure vessel are then investigated, and the limit stress, limit strain and limit pressure are obtained in terms of the classical Tresca criterion, von Mises criteria, and a newly proposed average shear stress yield criterion. The results of limit load solutions are analyzed and validated using typical experimental data at plastic yield.
Determination of Burst Pressure for Line Pipes With Long Blunt Defects
Authors: Zhu Xian-Kui , Leis Brian N.
Published: May 2012

Burst pressure is the maximum load in a pipeline. Its accurate prediction is critical to the safety design, integrity assessment and operational management of the pipeline. This paper overviews the commonly-used corrosion assessment methods, including ASME B31G, Modified B31G, LPC and PCORRC criteria, and describes three theoretical solutions of burst pressure for defect-free pipes in terms of Tresca criterion, von Mises criterion and ZL criterion — a newly proposed average shear stress yield criterion and the associated flow rules. These three theoretical solutions are extended to those for corroded pipes with infinitely long corrosion defects. Followed this, an elastic-plastic finite element analysis is performed using the commercial software ABAQUS with an aim to demonstrate numerical determination of burst pressure corresponding to the Mises and ZL solutions. The corrosion assessment methods are then applied to evaluate the burst pressure for six corroded line pipes with real long corrosion defects. It is concluded that the ZL solution and the PCORRC criterion can determine reasonable and conservative predictions for corroded pipelines with very long corrosion defects.
Finite Element Analysis for J-Integral of Axial Through-Wall Cracked Elbow Under Bending Moment
Authors: Liu Wei-Ju , Tsai Bor-Jiun , Chen Jien-Jong , Du Yan-Shiun , Liu Wei-Sheng
Published: May 2012

Leak-before-break (LBB) assessment of nuclear piping involves ductile fracture analysis of pipes or elbows with postulated through-wall cracks. Due to the fact that the crown part of an elbow is one of the positions that crack initiation occurs in most frequently, the calculation of J-integrals to investigate fracture behavior are important research topics. This paper proposes a 3-D finite element model of an elbow embedded with an axial through-wall crack to estimate the J-integral parameters under bending moment. The J-integral values can be calculated by using ABAQUS and taking into account the effects of geometrical and model of material in non-linear analysis. The results show that the non-linear deformation and contact condition of crack surfaces play important roles for the J-integral values. In addition, the J values estimated by the proposed model are more conservative and realistic than previous studies.
Elastic Follow-Up Factor for Cruciform Plate Under Bi-Axial Loading
Authors: Lee Kuk-Hee , Kim Yun-Jae , Ainsworth Robert A. , Dean David , Jin Tae-Eun
Published: May 2012

This paper derives analytical solutions of the elastic follow-up factor for power-law creeping cruciform plates under bi-axial displacements to investigate the effect of multi-axial stress states on elastic follow-up behaviors. Validity of the proposed solutions is checked against the results from finite element analyses using power-law creep material. Based on proposed solutions, effects of the biaxiality, geometry, Poisson’s ratio and creep exponent on elastic follow-up factors are discussed. Present results show that the elastic follow-up factor for structure with structural discontinuity can be significantly affected by the multi-axial stress states.
The Design of Ultra-Large Hydraulic-Balance Oil Tank With Double-Shell
Authors: Cao Guowei , Chen Zhiping , Guo Wenjing
Published: May 2012

Large-scale oil tanks are being studied all along because they have a series of advantages. For example, they can reduce the cost of manufacturing and management of the facilities, and save land. So the volume of oil tanks becomes larger and larger during their development. However, without on-site heat treatment, the thickness of the shell of traditional oil tanks is restricted to 200,000 m3. In this paper, a new structure named Ultra-large Hydraulic-Balance oil tank with double-shell was put forward. With the method of hydraulic-balance, oil tanks of this structure could be larger than 200,000 m3. Besides expounding the working principle in detail, a 200,000 m3 oil tank with double-shell was also designed in the paper according to API 650, and the finite element model was used to analyze the stress including intensity and distribution of both shells in order to test and verify its security. Furthermore, its economy was analyzed by comparing with traditional oil tanks. Finally, the problem caused by the difference of liquid lever as well as was discussed. Results show that Ultra-large Hydraulic-Balance oil tank with double-shell owned advantages including rational construction, economy and easy manufacturing.
Impact Response Analysis of a Coaxial Double-Pipe Structure by Using Spectral Element Method
Authors: Nishida Akemi , Iigaki Kazuhiko
Published: May 2012

A coaxial double-pipe structure is to be used in the primary and auxiliary coolant system of a high-temperature gas-cooled reactor. In order to study the vibration characteristics of the coaxial double-pipe structure, hammering experiments were performed using specimens of the structure. Because the structural responses obtained in the experiments contained high-frequency components, impact response analysis was performed by using the spectral element method, which has high accuracy in the high-frequency region. A comparison between analysis results and experiment results showed good agreement between them. We also performed parametric studies on the damping properties of the specimens. The damping properties determined from the experiment results indicated that the inner and outer pipes had different damping properties.
Study on the Interaction of Multiple Flaws in Ductile Fracture Process
Authors: Suga Kazuhiro , Miyazaki Katsumasa , Kawasaki Shota , Arai Yohei , Kikuchi Masanori
Published: May 2012

Study on the interaction of multiple cracks during ductile crack growth processes is important for the integrity evaluation of nuclear structure. The ductile fracture processes are well simulated using Gurson’s constitutive equation and taking into account of void growth during plastic deformation. In this study, two through wall cracks are assumed to exist in a plate in tension and the interaction between two cracks is studied. By changing the initial crack length, horizontal distance and vertical distance between inner crack tips, more than twenty cases are simulated. Interaction behavior between two crack tips is studied precisely. Criteria to evaluate maximum load in the ductile fracture processes are discussed.
NESC VII European Project: Demonstration of Warm Pre Stressing Effect in Biaxial Loading Conditions—Bending Tests on 18MND5 Cruciform Specimens
Authors: Jacquemoud C. , Yuritzinn T. , Marie S. , Moinereau D. , Nedelec M. , Chapuliot S.
Published: May 2012

In the framework of NESC VII European project, a large experimental program has been dedicated to demonstrate the Warm Pre Stressing (WPS) effect in different testing configurations. One of the CEA (France) contributions to this project is the realization of five point bending tests on large cruciform specimens considering different WPS loading cycles. The five cruciform specimens, sponsored by EDF (France) and IRSN (France), are made of 18MND5 steel. Two of them have been tested on a same LCF (Load-Cool-Fracture) loading cycle, including an isothermal preloading at TWPS = −30°C followed by a cooling down to TFRAC = −150°C at a constant load before an isothermal reloading up to fracture at TFRAC. The results presented in this paper give a successful demonstration of the Warm Pre Stressing effect in biaxial loading conditions on a LCF cycle.
Evaluation of the Active Plasticity Hypothesis as a Relevant Justification of the Warm Pre-Stressing Effect
Authors: Jacquemoud C. , Marie S. , Nedelec M.
Published: May 2012

This study aims to evaluate the relevance of the active plasticity hypothesis in predicting the risk of cleavage fracture during a WPS loading cycle. We define a critical loading path, along which the active plasticity hypothesis might fail. On this critical loading path, Beremin local model is compared to a stress-based criterion model. The chosen critical loading path is a LTF (Load-Transient-Fracture) cycle, including an isothermal preloading up to F1WPS = 42 kN at TWPS = −25°C followed by a cooling down to TFRAC = −150°C with a progressive loading up to F2WPS = 45 kN before an isothermal reloading up to fracture at −150°C. The final loading level (F2WPS = 45 kN) is chosen so that the plasticity is not active during the cooling phase while the stress-based criterion is. Two sets of experiments, performed on normalized compact tensile specimens made of 16MND5 steel, have demonstrated that the active plasticity was a necessary condition for cleavage fracture.
Deformation State Evaluation Around Deep Drilled Hole After Three-Dimensional Stress Release
Authors: Kitano Houichi , Okano Shigetaka , Mochizuki Masahito
Published: May 2012

Deep hole drilling technique (DHD) has received much attention as a method for measurements of thorough thickness residual stresses in recent years. In the past, however, the measurements of residual stresses by DHD technique have been limited to evaluation for in-plane stress and stress in through thickness direction. In the present study, the effect of shear stresses in through thickness direction on deformation states around the through thickness hole after stress release is discussed by theoretical approaches. In addition, the method for evaluating shear stresses in cutting direction is proposed from the result obtained by the previous theoretical investigation. Then, an unequal three-dimensional residual stress field is evaluated by DHD (or iDHD) technique and the proposed method using measurement changes obtained by numerical analysis. Finally, the reasons why the differences between the evaluation results and the stress distributions on the center line of the trepanned core are exits are clarified for high-accuracy evaluation.
Hot Isostatic Pressing of Inconel 600 and 690 Powders for Pressure Retaining Components
Authors: Jelfs Timothy C. , Burdett W. Barry
Published: May 2012

Hot Isostatic Pressing (HIP) has been used for many years to consolidate porosity in cast metal shapes to improve mechanical properties. When applied to fine metal powders, it is possible to produce Near Net Shape (NNS) items and more complex geometry components that are fully dense and offer an attractive set of properties at reduced cost. NNS items produced from HIPed powder deliver cost savings by reducing initial material usage and subsequent machining costs. Powder production and HIP processing are automated methods, which provide protection against forging route obsolescence. Setup costs are lower and batch sizes are smaller, which makes HIPping particularly well suited to small numbers of high integrity components. HIPed powder microstructures are isotropic and equiaxed, with uniformly fine grain sizes not normally achieved in heavy section components, which facilitates ultrasonic NDE examination. Improved features to facilitate NDE are readily incorporated into the HIP assembly. Inclusion contents are lower and of more benign geometry, easing fracture assessment. In a broad program of testing, Rolls-Royce has established (1) that HIPed powder 316L/304L components, in items up to several tons in weight, have equivalent or slightly better strength, toughness and corrosion resistance than the wrought equivalents. Rolls-Royce are extending their activities to HIPing of Inconel alloys. The first phase has been to HIP test samples of Inconel 600 and Inconel 690 alloys. Initial testing has produced promising results in line with expectations of wrought material. There has also been the opportunity to vary the HIPing cycle to assess the effect of processing parameters on the final product. An ability to HIP Inconel components is thought to be of benefit in new plant construction, where material is often not readily available in required thick section. The adaptability and good control of the HIP technique also shows promise as a manufacturing route for future high temperature materials which will be required in Generation 4 civil builds.
Effect of the Groove Shape on Residual Stress Distribution of Narrow Gap Welds
Authors: Soh Na-Hyun , Huh Nam-Su , Yang Jun-Seok
Published: May 2012

Recently, in Korea, the reactor coolant main loop piping and the steam generator have been connected with narrow gap welding (NGW) method after the replacement of steam generator of Korean nuclear power plants. The NGW method has many advantages, for instance, the reduction of welding time and the shrinkage of weld, and the small deformation of a component resulting from the small groove angle and welding bead width. In the actual welding process with NGW, some different groove shapes have been adapted. Noting that the distribution of a weld residual stress is significantly affected by welding conditions, for instance, shape of weld groove, direction of welding and width of weld groove etc., the weld residual stress due to NGW with different welding conditions should be accurately investigated for its application to life assessment considering actual conditions since these residual stress distributions can affect the susceptibility of parent and weld material to the primary water stress corrosion cracking (PWSCC) which is one of main issues in the nuclear component integrity. In this context, the present paper investigates the distribution of the weld residual stress as well as the deformation behavior of ER308L weld due to NGW using the nonlinear 2-dimensional (2-D) finite element (FE) analysis in which the detailed actual welding process of NGW was simulated. In particular, the effect of shape of weldment, i.e., the shape of welding groove (“single-side weld” and “double-side weld”) and the width of weld, on the residual stress is emphasized. Based on the FE results, the relevant groove shape is discussed in the sense that it provides lower residual stress values at the inner surface of pipe, which might reduce susceptibility to PWSCC.
Global Ratcheting by Elastic-Plastic FEA According to ASME Section VIII Rules
Authors: Kalnins Arturs , Rudolph Ju¨rgen
Published: May 2012

A framework of global ratcheting is developed for which the ratcheting measure is incremental permanent change of shape of a vessel or component. The changes of shape are such that they reduce the resistance to collapse, and, upon extended cycling, can lead to eventual failure by collapse. A ratcheting check is designed to prevent this failure. This framework fits the ratcheting rules that are currently in the 2010 Section VIII of the ASME B&PV Code. Tools are provided for ratcheting assessment based on this framework, and examples are presented that illustrate their application.
Variables Affecting Nut Factors for Field Assembled Joints
Authors: Cooper William G. , Heartwell Timothy M.
Published: May 2012

A great deal of research has been done to determine how to ensure a reliable bolted flange connection. Using a proper bolt torque value during installation helps achieve this goal. Many of the variables used during the calculation of a bolt torque value are easily quantified, but the nut factor has yet to be accurately determined. This paper provides an overview of research recently completed to determine what the real world nut factor is in varying applications.
Stress Corrosion Cracking Susceptibility of Type 16MnR Low-Alloy Steel in Oil Refining Environment
Authors: Lu Zhiming , Li Zhaoai , Zhu Chenhui , Gao Honggang
Published: May 2012

The stress corrosion cracking susceptibilities of type 16MnR low-alloy steel in simulated oil refining environment were investigated by slow strain rate test. Many research works have been done to study the single solution parameter effect on the stress corrosion cracking, such as H2S concentration or Cl− content, but less had been done for the interactive effect of the multiparameter. In this work, the separate and interactive effects of H2S concentration, Cl− content, temperature and pH value on stress corrosion cracking susceptibilities were studied. By stepwise regression analysis of test results, the effect notabilities of medium parameters on stress corrosion cracking susceptive index were revealed. It could be conclude that the effect of H2S concentrations was most notable to susceptive indexes, there was no notable correlativity between Cl− content and susceptive indexes, temperature and H2S played interactive role on the susceptive indexes.
Failure Analysis of Expansion Joint Bellows of Gas Pipelines
Authors: Lu Zhiming , Li Zhaoai , Zhu Chenhui , Gao Honggang
Published: May 2012

Some expansion joints bellows used in buried gas pipeline in east China cities cracked after 1∼2 years service, the cracks usually located at top of the bellows, they expand nearly 48% of total circumference and the whole thickness. The material of the bellows was austenitic stainless steel plate. In order to research the crack causes, one typical failure bellows was chosen in this work, the specimen cut near the crack were analyzed by the macro-analysis, micro-analysis, chemical composition analysis, optical microscopy and electron microanalysis. The results showed that the chloride ion and sulfide in water of pipeline well and the high additional stress due to deviation of alignment of the two side pipeline ends were the main causes, the interaction effects of aggressive and high stress lead to stress corrosion crack of the top of bellows.
A Risk-Informed Assessment of ASME Section XI, Appendix E
Authors: Gamble Ronald , Server William , Bishop Bruce , Palm Nathan , Heinecke Carol
Published: May 2012

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code [1], Section XI, Non mandatory Appendix E, “Evaluation of Unanticipated Operating Events”, provides a deterministic procedure for evaluating reactor pressure vessel (RPV) integrity following an unanticipated event that exceeds the operational limits defined in plant operating procedures. The recently developed risk-informed procedure for Appendix G to Section XI of the ASME Code [2, 3], and the development by the U.S. Nuclear Regulatory Commission (NRC) of the alternate Pressurized Thermal Shock (PTS) rule [4, 5, 6] led to initiation of this study to determine if the Appendix E evaluation criteria are consistent with risk-informed acceptance criteria. The results of the work presented in this paper demonstrate that Appendix E is consistent with risk-informed criteria developed for PTS and Appendix G and ensures that evaluation of RPV integrity following an unanticipated event would not violate material or operational limits recently defined using risk-informed criteria. Currently, Appendix E does not have evaluation criteria for BWR vessels; however, as part of this study, risk-informed analyses were performed for unanticipated heat-up events and isothermal, overpressure events in BWR plant designs.
Simulation of the Vibration of a Steam Generator Tube Subjected to Fluidelastic Forces Induced by Two-Phase Cross-Flow
Authors: Sawadogo Teguewinde , Mureithi Njuki
Published: May 2012

A computer simulation of the vibration of a tube bundle subjected to fluidelastic forces induced by two-phase cross flow is carried out. Two fluidelastic instability models are compared in the simulations: the Connors model and the quasi-steady model. In the quasi-steady model, the fluid forces are expressed in terms of the quasi-static drag and lift force coefficients and their derivatives which are determined experimentally. The consideration of the angle of incidence induced by the relative tube displacement with respect to the fluid introduces a velocity dependent term in the fluid force expression. The simulation has been done using ABAQUS. The ABAQUS user subroutine VUEL provides the required interface and information to calculate and apply the fluid forces to the structure. The fluidelastic forces applied to each element are calculated using the element displacement and velocity, the tube instantaneous frequency, a flow retardation parameter and the fluid damping and stiffness components. A typical U-tube in a steam generator subjected to a non-uniform two-phase flow was considered in the simulations. The tube support contact was modeled using the ABAQUS contact pair algorithm. The Anti-Vibration-Bars (AVB) limiting the tube vibration in the out-of-plane direction in the U-bend region were also included in this model. As the simulation was nonlinear because of the loose supports, a Fast Fourier Transform technique was used to estimate the tube instantaneous frequency. The quasi-steady fluidelastic force was compared to the fluidelastic force of the Connors model. The instability growth rate of the Connors model was found to be higher than that of the quasi-steady model. The impact forces at the supports and the AVB are also extracted. These forces can be used to calculate the work rate and estimate the tube wear.
Radioactive Material Packaging Torque Requirements Compliance
Authors: Watkins Robert W. , Leduc Daniel R. , Smith Allen C.
Published: May 2012

Shipping containers used to transport radioactive material (RAM) in commerce employ a variety of closure mechanisms. Often, these closure mechanisms require a specific amount of torque be applied to a bolt, nut or other threaded fastener. It is important that the required preload is achieved so that the package certification testing and analysis is not invalidated for the purpose of protecting the public, workers, and environment. Torque compliance as a means of ensuring closure preload, is a major factor in accomplishing the package functions of confinement/containment, sub-criticality, and shielding. This paper will address the importance, as a matter of operational practice, of applying proper torque to package closures, discuss torque value nomenclature, and present one methodology to ensure torque compliance is achieved.
Modelling and Data Interpretation of Small Punch Creep Testing
Authors: Li R. , Hyde T. H. , Sun W. , Dogan B.
Published: May 2012

The small punch testing (SPT) technique has been proposed for use in determining the creep properties of materials for which only a very small volume of material is available. A draft code of practice on SPT has been produced. However it is not, as yet, generally accepted that the data obtained from small punch tests can be directly related to those which would be obtained from conventional uniaxial creep tests. For this reason, the development of techniques suitable for the interpretation of SPT data has become very important. In this paper, a set of uniaxial creep test data has been characterised in such a way as to gain an improved understanding of the correlation between the data from small punch tests and corresponding uniaxial creep tests. Finite element (FE) analyses of small punch creep tests, using a damage mechanics based creep model, have been performed. The effect of large deformation on the determination of material properties for a creep damage model, has been investigated to take into account the large deformation nature of small punch tests. An equivalent stress, σeq, proposed by the draft code, was used to relate the SPT results to the corresponding uniaxial creep test results. A preliminary assessment of the use of small punch test results, in determining creep properties, has been presented, which includes comparisons of the failure life and equivalent minimum strain rate results obtained from SPTs with the corresponding uniaxial creep test data. Future work related to the interpretation of SPT is briefly addressed.
Ratcheting Responses of Strain Hardening Plasticity Models
Authors: Indermohan H. , Reinhardt W.
Published: May 2012

Nuclear reactor components are often subjected to combinations of sustained and cyclic stresses due to the application of internal pressure and transient temperature loads. During the thermal transients, the interaction of such stresses could cause cyclic plastic deformation, which may either lead to shakedown or ratchetting behavior. Design criteria meant to guard against ratcheting are established in Section III of the ASME Code. The criteria are based on perfectly plastic material behavior. However, materials undergo strain hardening upon reaching the yield strength. For elastic-plastic analysis, NB-3228.4 does not contain any guidance on modelling of material hardening, leaving it to the analyst to justify their choice. Although it is widely known that some plasticity models are inadequate for modeling cyclic plasticity, there has been little published study of the effect various plasticity models have on the ratchet boundary. This paper compares the ratchet boundary obtained from bilinear and Chaboche kinematic hardening material models with that obtained from perfect plasticity. The investigation is carried out for simple examples such as the classical Bree problem and a thin plate under biaxial loading.
A Simplified Methodology for Extremely Low-Probability Rupture Prediction for PWR LBB Applications
Authors: Xu Heqin , Nana Ashok , Mahmoud Samer , Killian Doug
Published: May 2012

The leak-before-break (LBB) applicability is stated in General Design Criterion 4 (GDC-4) of Title 10 of the Code of Federal Regulation Part 50 (10 CFR 50). GDC-4 requires that analyses reviewed and approved by the U.S. Nuclear Regulatory Commission (NRC) demonstrate that the probability of fluid system piping rupture is extremely low under conditions consistent with the design basis for the piping, in order that dynamic effects associated with postulated pipe ruptures in nuclear power units may be excluded from the design basis. Standard review plan 3.6.3 (SRP-3.6.3) further requires a simultaneous safety margin of two and ten on the flaw size and leak rate detectability, respectively, for deterministic analyses, believing that the very conservative and restrictive safety margins would lead to extremely low probability of fluid system piping rupture. The technology advancements of recent years make it possible to numerically quantify the probability of rupture with confidence. Planned for completion within the next six years, a long-term, large-scale assessment tool, xLPR, is currently being developed by the U.S. NRC, in cooperation with the nuclear industry, to assess the extremely low probability of rupture. The tool will include comprehensive evaluations both before and after through-wall cracks are developed in the degraded components. In this study, we are going to utilize a simplified methodology to investigate the probability of piping rupture for a postulated through-wall crack. The conditional probability, when multiplied by the probability of having a through-wall crack during the life time of plant service, produces an overall probability of piping rupture. The major quantifiable uncertainties, such as the uncertainties associated with the material tensile properties and fracture toughness, and flow-path crack morphology parameters will be modeled as correlated random variables in this paper. Efficient Dimension-Reduction methods will be applied to predict this conditional probability and the results will be compared with the Monte Carlo simulation method. As a sample application of the proposed method, the relationship between the magnitude of the conditional probabilities and the required leak rate detection capability will be established.
Evaluation of the Minimum Temperature Requirements for the RPV Closure Head Flange Region in 10 CFR 50 Appendix G
Authors: Focht Eric M.
Published: May 2012

Title 10 of the Code of Federal Regulations, Part 50 Appendix G (10CFR50 App. G) prescribes the pressure-temperature (P-T) limits for light water power reactors by incorporating American Society of Mechanical Engineers (ASME) Boiler & Pressure Vessel Code, Section XI, Appendix G (ASME App. G) by reference. The P-T limits in ASME App. G are based on the fracture toughness of the vessel limiting material accounting for irradiation effects. The fracture toughness of the limiting material is determined based on the plane strain fracture toughness, KIc, indexed to the material reference temperature, RT NDT. Prior to the 2000 Addenda of ASME App. G, fracture toughness was based on the arrest fracture toughness, KIa, but the approval of Code Case N-640 [1] in 1998 changed the fracture toughness basis to KIc. In addition to the P-T limits determined by ASME App. G, 10CFR50 App. G sets additional minimum temperature requirements that limit the operating pressure based on other factors such as the minimum unirradiated reference temperature, RTNDT(u), of the material in the closure head flange region. This paper presents an analysis of the closure head flange region minimum temperature requirements based on both KIa and KIc. Recommendations for potential alternative minimum temperature requirements are made for normal operation and hydrostatic test conditions.
Comparison of ASME B31.12 Versus B31.3 for Hydrogen-Containing Piping in Refinery Services
Authors: Shargay Cathleen , Livingston Hilliard L. , Moukabaa Hani , Duggan Kyle
Published: May 2012

For more than fifty years the oil refining industry has been using American Society of Mechanical Engineers (ASME) B31.3 “Process Piping” for the design of piping systems in hydrogen-containing services. In 2008, ASME B31.12 “Hydrogen Piping and Pipelines” was released, which caused uncertainty within the refining industry about which Code to apply in these services. The foreword of B31.12 states that it “applies to design, construction, operation, and maintenance requirements for piping, pipelines, and distribution systems in hydrogen service. Typical applications are power generation, process plants, refining, transportation, distribution, and automotive filling stations.” Typical refinery services containing hydrogen include a gamut of applications. Some operate at high pressures and/or temperatures; some also contain water, hydrogen sulfide (H2S) and/or other corrosives and others are pure hydrogen at mild conditions. This paper describes the various services along with a summary of associated material degradation or cracking mechanisms and the measures used to prevent piping failures. This is followed by a discussion about whether the more rigorous requirements of B31.12 provide safeguards for these potential degradation mechanisms. A comparison of the two Codes in design, materials, fabrication and non-destructive examination (NDE) requirements is provided along with qualitative estimates of the cost differences. This comparison should help new design and construction projects choose which Code to apply. The paper also has suggestions for clarifying the scope of B31.12.
The Dynamic Load Factor of Pressure Vessels in Deflagration Events
Authors: Xu Yu , Young Kuao-John
Published: May 2012

There are vessels that could be subjected to rapidly rising pressure load during deflagration events. The dynamic load factor (DLF) which accounts for dynamic load effects in such events can be used to bridge the gap between transient and static pressure loads. This paper addresses the issues in estimating the DLF for a deflagration event. A unified methodology for estimating the DLF is first presented. The methodology is then validated with existing references. Key parameters determining DLFs are identified during the validation. Case studies are used to illustrate how to use the methodology. Finally, this paper is concluded with the findings and a suggested procedure for estimating DLFs in deflagration events.
Practical Considerations in Improving Practices Related to Bolted Piping Joints in a Chemical Manufacturing Site
Authors: Lick Wendy W.
Published: May 2012

A focused effort was initiated to improve the performance of gaskets in bolted piping joints at a large manufacturing site of Eastman Chemical Company. The facility includes many miles of pipe, ranging in age from brand new to several decades old, containing a multitude of process fluids at a wide range of process conditions. In accord with the Responsible Care initiative of the American Chemistry Council, there is strong desire continually “to identify, reduce and manage process safety risks.” This led to the formation of a team to identify initiatives that will provide a better understanding of the causes of failed gaskets in bolted piping joints, and a structured approach to prevent failures. The results include educational initiatives, improvements in standards and their use, a structured approach to risk assessments of critical piping systems, and the beginning of a long-term, data-driven approach to investigate failures of gaskets in bolted piping joints and apply the knowledge gained.
Carrying Capacity of Strain-Hardening Austenitic Stainless Steel Pressure Vessels Under Hydrostatic Pressure
Authors: Deng Yang-chun , Chen Gang
Published: May 2012

To reduce the waste of austenitic stainless steels due to their low yield strengths, the strain hardening technology is used to significantly improve their yield strength, in order to increase the elastic load carrying capacity of austenitic stainless steel pressure vessels. The basic principle of strain-hardening for austenitic stainless steel pressure vessels and two common models of strain hardening, including Avesta Model for ambient temperature and Ardeform Model for cryogenic temperature, were briefly introduced. However, it was fully established by experiments, the lack of a necessary theoretical foundation and the safety concern affect its widespread use. In this study, we investigated the load carrying capacity of strain-hardening austenitic stainless steel pressure vessels under hydrostatic pressure, based on the elastic-plastic theory. To understand the effects of strain hardening on material behavior, the plastic instability loads of a round tensile bar specimen were also derived under two different loading paths and validated by experiments. The results of theoretical, experimental and finite element analyses illustrated, considering the effect of material strain hardening and structural deformation, at ambient temperature, the static load carrying capacity of pressure vessels does not relate to the loading paths. To calculate the plastic instability pressures, a method was proposed so that the original dimension and original material parameters prior to strain hardening can be used either by the theoretical formula or finite element analysis. The safety margin of austenitic stainless steel pressure vessels under various strain hardening degrees was quantitatively analyzed by experiments and finite element method. A 5% strain as the restrictive condition of strain hardening design for austenitic stainless steel pressure vessels was suggested.
Different Structural Integrity Assessment Methods for Pipe Containing Circumferential Through-Thickness Crack
Authors: Jiang Huifeng , Chen Xuedong , Fan Zhichao
Published: May 2012

Heretofore, several kinds of codes are applicable to the structural integrity assessment for pipe containing defects, i.e. API 579, R6 and BS 7910 etc. In this paper, different methods from API 579-1/ASME FFS-1: 2007 and R6-2000 were employed to assess the integrity of pipe containing a circumferential through-thickness crack. However, there was a significant difference between the calculated load ratios by these two codes, although the calculated fracture ratios were very close. To verify these results, elastic-plastic finite element analysis was carried out to calculate the limit load and the load ratio. Additionally, the experimental results and our previous engineering experience were also referred to. The final results imply that the larger load ratio obtained from R6-2000 rather than API 579 code is more reasonable for the pipe with good fracture toughness.
Technical Basis of Fatigue Crack Growth Rate Curve for Ni-Base Alloy Weld Metal in Air Environment
Authors: Ogawa Takuya , Narazaki Chihiro , Itatani Masao , Hirano Akihiko , Nagase Hiroshi , Yoneda Hideki
Published: May 2012

Recently, incidents of SCC in Ni-base alloy weld metal of BWR components have been reported. When the defects are detected by inspection, structural integrity assessment should be performed for the technical judgment on continuous service based on the Rules on Fitness-for-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers Code (JSME FFS Code). The structural integrity assessment includes fatigue crack growth analysis. However, fatigue crack growth analysis for Ni-base alloy is impossible since the fatigue crack growth rate curves in air and the BWR environment are not prescribed yet in the JSME FFS Code. The curve in air environment is needed for the structural integrity assessment of the flaw when the embedded flaw repair which is one of the repair techniques to isolate the defect from water environment by seal welding is applied. In this study, fatigue crack growth tests in air environment were performed for Ni-base alloy weld metal. Based on the test data, fatigue crack growth rate curves with ΔKth of Ni-base alloy weld metal were investigated. It is found that fatigue crack growth data in the Paris region hardly depend on the test temperature and the stress ratio, whereas data around ΔKth are dependent on them. Hence, the curve in the Paris region was regarded as the same curve despite the difference of the test temperature and the stress ratio. The minimum ΔK of final crack growth data in the ΔK decreasing test was adopted as ΔKth of the curve.