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The need for integrity evaluations and remaining life assessments of boilers arises from technical, economic, and legal reasons. The pulp and paper industry has less experience and tradition in using this engineering discipline when compared to other industries such as oil, petrochemical, and power generation. The pertinent Brazilian legal standard (NR-13) is concise in establishing this requirement, without providing details of applicable technical procedures. Furthermore, recovery boilers are a special type of steam generator, being very specific as to their inherent in-service degradation mechanisms and inspection needs. In view of the above scenario, pulp and paper mill engineers often have doubts and encounter diverse interpretations of the official regulations when they need to carry out integrity evaluations of quarter-century old recovery boilers. This paper relates CENIBRA's recent experience in evaluating its recovery boiler No. 1. [ABSTRACT FROM AUTHOR]

The manhole sealing performance of a kettle agitator directly affects the production efficiency and safety of the whole pressure vessel. This paper investigated the market demand for the reliability of manhole seal rings. First, the objective weight was determined by the rough set method and the subjective weight was determined by an analytic hierarchy process. The subjective weight and objective weight were integrated organically to obtain a scientific and effective comprehensive evaluation model. Then, the method of Quality Function Deployment is applied to transform the user requirements into the technical characteristics of the seal ring. The technical c haracteristics of the sealing ring are converted into the influencing factors of the reliability of the sealing ring by the transformation matrix, and the weight of the factors is determined according to the triangular fuzzy number. Finally, the most important factors affecting the reliability of the seal ring were studied by finite element analysis. This paper provides a theoretical basis for studying the reliability design of seal ring. [ABSTRACT FROM AUTHOR]

Copyright of China Textile Leader is the property of China Textile Information Center and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper provides a critical review of the advancements made in the application of the variable material properties (VMP) method over the past two decades. The VMP method was originally proposed in 1997 (Jahed and Dubey, 1997, ASME J. Pressure Vessel Technol., 119(3), pp. 264-273; Jahed et al., 1997, Int. J. Pressure Vessels Piping, 71(3), pp. 285-291) and further developed in 2001 (Parker, 2001, ASME J. Pressure Vessel Technol., 123(3), p. 271) as an elastoplastic method for the analysis of axisymmetric problems. The model was originally developed as a boundary value problem to predict the spatial distribution of stress. However, since 1997, it has been extended to include thermal effects to solve thermomechanical residual stresses; time domain to solve creep of disks and cylinders; finite deformation to solve cylinders under large strains; numerical solutions to make them more efficient; and asymmetric hardening behavior to accommodate nonslip deformation modes. These advancements, made over the past 20 years, are reviewed in this paper, and future trends and frontiers are discussed. [ABSTRACT FROM AUTHOR]

In order to develop the knowledge base necessary to design deep sea pressure vessels, it is essential to understand the full chain from design and manufacturing through nondestructive testing (NDT) and characterization to long-term behavior under hydrostatic pressure. This paper describes results from European and national research programs focusing on the use of composites for underwater applications over the last 20 years. Initial tests on small glass/epoxy cylinders were followed by large demonstration projects on carbon/epoxy cylinders with implosion pressures of up to 600 bar, corresponding to 6000 m depth. Numerical modeling has enabled end closures design to be optimized for test performance. Thin and thick wall cylinders have been tested under quasi-static, and long-term loading. Both thermosetting and thermoplastic matrix composites have been tested to failure, and the influence of defects and impact damage on implosion pressure has been studied. These deep sea exploitation and exploration studies were performed for oceanographic, military, and offshore applications, and extensive data are available. The aim of this paper is to indicate existing results, particularly from European projects, in order to avoid costly repetition. [ABSTRACT FROM AUTHOR]

Applicable design codes for power plant components and pressure vessels demand for a design check against progressive plastic deformation. In the simplest case, this demand is satisfied by compliance with shakedown rules in connection with elastic analyses. The possible noncompliance implicates the requirement of ratcheting analyses on elastic-plastic basis. In this case, criteria are specified on maximum allowable accumulated growth strain without clear guidance on what material models for cyclic plasticity are to be used. This is a considerable gap and a challenge for the practicing computer-aided engineering engineer. As a follow-up to two independent previous papers PVP2013-98150 ASME (Kalnins et al., 2013, "Using the Nonlinear Kinematic Hardening Material Model of Chaboche for Elastic-Plastic Ratcheting Analysis," ASME Paper No. PVP2013-98150.) and PVP2014-28772 (Weitze and Gilman, 2014, "Additional Guidance for Inelastic Ratcheting Analysis Using the Chaboche Model," ASME Paper No. PVP2014-28772.), it is the aim of this paper to close this gap by giving further detailed recommendation on the appropriate application of the nonlinear kinematic material model of Chaboche on an engineering scale and based on implementations already available within commercial finite element codes such as ANSYS® and ABAQUS®. Consistency of temperature-dependent runs in ANSYS® and ABAQUS® is to be checked. All three papers together constitute a comprehensive guideline for elastoplastic ratcheting analysis. The following issues are examined and/or referenced: (1) application of monotonic or cyclic material data for ratcheting analysis based on the Chaboche material model, (2) discussion of using monotonic and cyclic data for assessment of the (nonstabilized) cyclic deformation behavior, (3) number of backstress terms to be applied for consistent ratcheting results, (4) consideration of the temperature dependency (TD) of the relevant material parameters, (5) consistency of temperature-dependent runs in ANSYS® and ABAQUS®, (6) identification of material parameters dependent on the number of backstress terms, (7) identification of material data for different types of material (carbon steel, austenitic stainless steel) including the appropriate determination of the elastic limit, (8) quantification of conservatism of simple elastic-perfectly plastic (EPP) behavior, (9) application of engineering versus true stress-strain data, (10) visual checks of data input consistency, and (11) appropriate type of allowable accumulated growth strain. This way, a more accurate inelastic analysis methodology for direct practical application to real world examples in the framework of the design code conforming elastoplastic ratcheting check is proposed. [ABSTRACT FROM AUTHOR]

Fitness-For-Service (FFS) assessments are quantitative engineering evaluations, which are especially used in oil and gas industry. Crack-like flaws is one of the major failure modes of pressure vessels. The main purpose of this paper is to study the residual strength evaluation of crack-like flaws pressure vessels. Firstly, domestic and foreign FFS assessments about crack-like flaws pressure vessels have been studied in the paper. Secondly, the assessments in API579 have been studied. Then this paper introduced the software of crack-like flaws assessments which is based on BS structure and is completed by Sql server and Visual studio with C# and database. An example has been given to obtain a software result, which is compared with a handed result in order to verify the accuracy of software. [ABSTRACT FROM AUTHOR]

Wire-winding technique is usually applied to increase strength to weight ratio, to improve the fatigue life and prevent rapid failure of structures with high sensitivity. Most of the relations, which are presented for wire-winding analysis, are specially introduced for wire-wound pressure vessels. The purpose of this paper is to present a new approach for stress analyzing in wire layers of wire-wound frames, which are subjected to tensile forces and used to carry the load from the closures of pressure vessels too. The required wire-winding force will be obtained based on constant effective stress in all layers at maximum applied force. In this work, after reviewing the theoretical background of wire-winding, a new approach called "constant effective stress theory" is presented. In comparison with previous published works, in this paper, the problem has been specially defined for a rectangular frame, the wire mantles have been considered as discrete elements, and Von Mises yield criterion is applied on the model at maximum applied force. The logical steps of this approach are done in four steps. First, the critical points of the wires are obtained. The maximum stress is defined according to Von Mises criterion. Then, tensile stress is obtained in all layers at working condition. In third step, tensile stress is calculated at nonworking condition, and finally, the required wire-winding force is obtained for all layers. The results are compared with Harkegard's theory and have been validated by finite element method. They show that the value of the required tensile stress during wire-winding will be reduced considerably. In addition, by assuming a final small gap at maximum applied force between frame members, yoke, and column, this stress would be reduced more. Furthermore, there is a very good agreement between the results of new approach and finite element method. [ABSTRACT FROM AUTHOR]

This paper reviews the literature on variational method in limit load analysis and presents both analytical and numerical approaches. One of the most successful applications of variational method in theory of plasticity is limit load analysis. The main objective of the limit load analysis is to estimate the load at the impending plastic limit state of a body. However, for complicated problems it may be very difficult to find the exact limit load. Therefore, based on the extremum principles of limit load analysis, the lower-bound theorem or the upper bound theorem is employed to estimate the limit load directly without considering the entire loading history. In general, limit load analysis plays an important role in design and fitness-for-service assessment of pressurized vessels and piping. [ABSTRACT FROM AUTHOR]

Autofrettage is a metal forming technique widely incorporated for strengthening the thick-walled cylindrical and spherical pressure vessels. The technique is based on the principle of initially subjecting the cylindrical or spherical vessel to partial plastic deformation and then unloading it; as a result of which compressive residual stresses are set up. On the basis of the type of the forming load, autofrettage can be classified into hydraulic, swage, explosive, thermal, and rotational. Considerable research studies have been carried out on autofrettage with a variety of theoretical models and experimental methods. This paper presents an extensive review of various types of autofrettage processes. A wide range of theoretical models and experimental studies are described. Optimization of an autofrettage process is also discussed. Based on the review, some challenging issues and key areas for future research are identified. [ABSTRACT FROM AUTHOR]

In pressure vessel and pipe inspection, ultrasonic nondestructive evaluation plays a pivotal role in both in-situ and laboratory examinations. Scanning acoustic microscopy (SAM) has been a well-recognized laboratory tool for both visualization and quantitative evaluation of pressure vessel and piping materials at the microscale since its invention in 1974. While there have been multiple advances in SAM over the past four decades, some issues still remain to be addressed. First, the measurement speed is limited by the mechanical movement of the acoustic lens and the sample stage. Second, a single-element transducer with an acoustic lens forms a predetermined beam pattern for a fixed focal length and incident angle, thereby limiting control of the inspection beam. Here, we propose to develop a phased-array probe as an alternative to overcome these issues. Preliminary studies to design a practical high-frequency phased-array acoustic microscope probe were explored. A linear phased-array, comprising 32 elements and operating at 5 MHz, was modeled using PZFlex, a finite element method software. This phased-array system was characterized in terms of electrical input impedance response, pulse-echo and impulse response, surface displacement profiles, mode shapes, and beam profiles. Details of the construction of the model and the results are presented in this paper. Development of a phased-array acoustic microscope probe will significantly enhance scanning acoustic microscopy techniques for detecting surface and subsurface defects and microstructural changes in laboratory samples of pressure vessel and piping materials. [ABSTRACT FROM AUTHOR]

The paper is a review work devoted to dished heads of various meridian shapes. Geometry of the shells of revolution, the membrane state, and the edge effect occurring in the shells are described. Exemplary analytical and numerical finite element method (FEM) studies of torispherical, ellipsoidal, Cassini-ovaloidal, and untypical special dished heads are presented. The results of the above-mentioned two methods are compared. Moreover, numerical research of elastic buckling of the above-mentioned selected heads under external pressure is carried out. Literature related to each of the considered head types is quoted and discussed, with special attention paid to the works developed in the 21st century. In concluding remarks, the stress concentration and buckling of these structures are commented, with consideration of the head meridian shapes. [ABSTRACT FROM AUTHOR]

This research paper is concerned with the mechanical behavior of the cylindrical vessels with hillside nozzles when subjected to both pressure and nozzle bending loads in cyclic forms. The influence of hillside angle on shakedown (SD) limits of the connection under cyclic pressure and combined steady pressure with cyclic nozzle bending is investigated. A shell finite element analysis model is built for the assembly using five different hillside angles ranging from 0 deg to 40 deg. Shakedown limits are determined by a direct technique known as the nonlinear superposition method (NSM). Bree diagrams for cyclic out of plane opening (OPO)/in plane (IP) nozzle moments combined with steady internal pressure are determined. The results show an increase in both OPO and IP shakedown moments as the hillside angle is increased. In addition, the OPO shakedown limit moments for all hillside angles were found to be insensitive to the level of internal pressure; this differs from the IP shakedown moment which starts to decrease with pressure for the high pressures. [ABSTRACT FROM AUTHOR]

In structural integrity analysis of reactor pressure vessels (RPVs), a postulated shallow crack is subjected to biaxial far-field stresses. However, the fracture toughness Kc or Jc, which is an important material property for the structural integrity assessment of RPVs, is usually obtained from testing deeply cracked compact tension (C(T)) or single-edged bending (SE(B)) specimens under uniaxial loading. Thus, the fracture toughness data do not reflect the biaxial loading state that cracks in a RPV are subjected to. Cruciform bending specimen was therefore developed to simulate the biaxial stress state. In this paper, a series of finite element (FE) simulations of the cruciform specimens containing different crack geometries and of different material properties are conducted. The crack tip stress fields are analyzed, and the constraint is investigated using the J-A2 theory. The results show that the biaxial effect is material property dependent which could be useful for the optimization of the test method and the better design of cruciform specimens. The trends about the biaxial loading effect revealed in this study would also be helpful in estimating the safe operating life of RPVs. [ABSTRACT FROM AUTHOR]

In recent years, jet fire accidents caused by gas tank or pipe leakage are often reported to cause more serious losses and even induce a series of other accidents, especially for high pressure jet fires. This paper presents an integrated model which couples the leakage process model of Abel-Noble equation of state (AN-EOS), the notional nozzle model and the flame size (flame length and lift-off height) model. The model can be used to predict the variation of jet flame length induced by the unsteady leakage of high pressure flammable gas. The lift-off height correlation is proposed after a review on the jet fire behavior, and then the AN-EOS leakage process model is evaluated through a testing on the vessel gas pressure variation against the measurement in literature. The integrated model is finally evaluated through a testing on the variation of flame length with vessel gas pressure against the measurement in literature. Results indicate that the integrated model is applicable for jet flame length prediction. More experimental data on high pressure horizontal hydrogen jet fires is needed for evaluation and validity of the integrated model. [ABSTRACT FROM AUTHOR]

In this paper, the spherical vessel-pipe gas explosion test system is developed to study the effects of initial pressure, vessel volume and pipe length on the explosion of hydrogen-air premixed gas. The experimental system consists of an explosive device, an ignition device, a data acquisition device and an automatic gas distribution device. The explosive device consists of a 113 L or 22 L spherical vessel connected with pipe. The experimental results showed that, the maximum explosion pressure in the spherical vessel connected with pipe decreases with pipe length, the hydrogen maximum explosion pressure at the end of the pipe decreased when the spherical vessel is connected. The maximum explosion pressure in the isolated spherical vessel and the isolated pipe terminal increased linearly with the initial pressure. In the spherical vessel connected with pipe, the maximum explosion pressure in the spherical vessel and pipe terminal increased with the initial pressure, but there is no linear relationship between the maximum explosion pressure and the initial pressure. In the spherical vessel connected with pipe, the change in maximum explosion pressure in the spherical vessel is small, and the maximum explosion pressure at the pipe terminal clearly increased as the volume of the vessel increased. When a hydrogen explosion occurs in the spherical vessel connected with pipe, there is a significant oscillation in the spherical vessel and terminal of the pipe. The maximum explosion pressure rising rate in spherical vessel increases with the vessel volume, The maximum explosion pressure rise rate at the pipe terminal decreases with the vessel volume. The maximum hydrogen explosion pressure rising rate at the pipe terminal increases with the pipe length, the maximum hydrogen explosion pressure rising rate in the large spherical vessel decreases with the pipe length. In the spherical vessel connected with pipe, the maximum explosion pressure in the spherical vessel decreases with the pipe length. The maximum hydrogen explosion pressure in the pipe terminal increased with the pipe length. When the spherical vessel is connected with the three-section pipe, the maximum hydrogen explosion pressure in the pipe terminal reaches 1.78 MPa, which is a quasi-detonation state. [ABSTRACT FROM AUTHOR]

Bolted flange joints are extensively used to connect pressure vessels and piping equipment together. They are simple structures that offer the possibility of disassembly. However, they often experience leakage problems due to a loss of tightness as a result of a nonuniform distribution of gasket contact stresses in the radial and circumferential direction. Many factors contribute to such a failure; the flange and gasket stiffness and bolt spacing design combination being one of them. In our recent paper, the effects of bolt spacing were investigated based on the theory of circular beams resting on a linear elastic foundation (Do, T. D., Bouzid, A. H., and Dao, T.-M., 2011, "Effect of Bolt Spacing on the Circumferential Distribution of Gasket Contact Stress in Bolted Flange Joints," ASME J. Pressure Vessel Technol., 133 (4), 041205). This paper is an extension of the work in which an analytical solution based on the real nonlinear gasket behavior is developed. This study focuses on the distribution of the gasket contact stress of two large diameter flanges, namely, a 52 in. and a 120 in. heat exchanger (HE) flanges. The nonlinear gasket behavior solution is compared to the Finite Element Analysis (FEA) and the linear gasket behavior solution for evaluation and comparison. [ABSTRACT FROM AUTHOR]

Copyright of DYNA - Ingeniería e Industria is the property of Publicaciones Dyna SL and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tensile strength and Ductile-Brittle Transition Temperature (DBTT) are the essential parameters for the strength analysis of reactor pressure vessels at various stages of operation, as well as for the validation of the lifetime extension. This paper reviews the changes in yield strength and DBTT under irradiation on the example of the Russian RPV steels: VVER-440 (15KhMFA steel and welds) and VVER-1000 (15Kh2NMFA steel and welds) as well as the functional dependences, developed in the last 10-15 years, to determine the DBTT of VVER RPV steels. The review is based on papers selected by a group of experts under the EC Project 'Nuclear Knowledge Preservation and Consolidation', coordinated by JRC Petten. [ABSTRACT FROM AUTHOR]

The paper tries to describe the history of the radiation effects study in WWER type reactor pressure vessels - from their design, manufacturing and operation point of view. The paper shows the time evolution and also institutions that were and are included in this research and development study. Main effort has been concentrated on development and realisation of steels and welding joint with low susceptibility to radiation damage as neutron fluences on reactor pressure wall in WWER type reactors are relatively high. [ABSTRACT FROM AUTHOR]

A thermal stress problem of a long hollow cylinder was considered in this paper. The outer surface of the cylinder was adiabatically insulated, and the inner surface was heated axisymmetrically by a fluid with sinusoidal temperature fluctuations (hereafter called as thermal striping), whose temperature amplitude (ΔT) and angular velocity (ω) were constant. The heat transfer coefficient h was also assumed to be constant. The stress intensity factor (SIF) due to the thermal stress for a given cylinder configuration varies not only with these three parameters ΔT, ω, and h, but also with time. The temperature and, as a result, SIF fluctuation amplitude soon became constant (Meshii, T, and Watanabe, K., 2004, "Stress Intensity Factor of a Circumferential Crack in a Thick-Walled Cylinder Under Thermal Striping," ASME J. Pressure Vessel Technol., 126(2), pp. 157-162), which hereafter is called as steady state. If one is interested in fatigue crack growth (assuming Paris law) under this thermal stress, because the SIF range soon converges to a constant, it seemed important to know the maximum value of the steady state SIF range for a given cylinder configuration, for all possible combinations of ΔT, ω, and h. This maximum SIF evaluation is time consuming. Thus in this paper this maximum steady state SIF range for four typical surface cracks' deepest point, inside a hollow cylinder for all possible combinations of ΔT, ω, and h were presented as a first step. Thin-to thick-walled cylinders in the range of mean radius to wall thickness parameter rm/W = 10.5-1 were considered. Crack configurations considered were 360 deg continuous circumferential, radial, semi-elliptical in the circumferential and radial directions. Normalized crack depth for all cases was in the range of a/W = 0.1-0.5. In case of semi-elliptical crack, the normalized crack length a/c was all in the range of 0.063-1. [ABSTRACT FROM AUTHOR]

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code specifies design curves for the fatigue life of structural materials in nuclear power plants. However; the effects of light water reactor (LWR) coolant environments were not explicitly considered in the development of the design curves. The existing fatigue-strain-versus-life (c-N) data indicate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives in water relative to those in air can be a factor of 15 lower for austenitic stainless steels and a factor of ≈30 lower for carbon and low-alloy steels. This paper reviews the current technical basis for the understanding of the fatigue of piping and pressure vessel steels in LWR environments. The existing fatigue s-N data have been evaluated to identify the various material, environmental, and loading parameters that influence fatigue crack initiation and to establish the effects of key parameters on the fatigue life of these steels. Statistical models are presented for estimating fatigue life as a function of material, loading, and environmental conditions. An environmental fatigue correction factor for incorporating the effects of LWR environments into ASME Code fatigue evaluations is described. This paper also presents a critical review of the ASME Code fatigue design margins of 2 on stress (or strain) and 20 on life and assesses the possible conservatism in the current choice of design margins. [ABSTRACT FROM AUTHOR]

The paper presents new experimental results on the collapse of unstiftened aluminum alloy circular cylinders suffering elastic and plastic nonsymmetric bifurcation buckling under external hydrostatic pressure. These results complement the results given in two previous Marine Technology papers written by the senior author, which were intended for the structural design of near-perfect unstiffened and ring-stiffened circular conical shells under external hydrostatic pressure. The present paper presents a structural design chart for geometrically imperfect circular cylinders under uniform external pressure, which is more likely to be used than the design charts for the previous near-perfect vessels because it represents the more "usual" case. In addition to an experimental analysis, theoretical analyses were also carried out. An analytical solution by von Mises was used, together with a finite element analysis solution, using the Shell 93 element of the ANSYS computer package. Comparison between ANSYS and the analytical solution was reasonable. A design chart is provided, which looks like it could be quite useful for practical purposes. [ABSTRACT FROM AUTHOR]

The technology for pressure equipment design continues to advance each and every day. The ASME Boiler and Pressure Vessel Code has been keeping pace with these advances over the last 92 years. As far back as the 1960s, it was recognized that the special requirements for design of pressure vessels operating at pressures over 2000 psi (13.7 MPa) called for special rules, and ASME issued Sec. VIII, Division 2 of Alternative Rules for Pressure Vessels. Since that time, the understanding of failure mechanisms and advances in material science, nondestructive testing, and computer-aided design has progressed to the stage where a new approach was needed not only in the content of design codes but in the way they are presented and organized. This paper introduces the newly issued ASME Sec. VIII, Division 2 of 2007 edition and explores the technical concepts included and the new format designed for ease of use. Included are results of test exercises sponsored by ASME giving actual applications of the new Code for design of vessels. This paper demonstrates ASME's commitment to provide manufacturers and users of pressure equipment with the most up-to-date technology in easy to use standards that service the international market. [ABSTRACT FROM AUTHOR]

Modern diesel common-rail injection systems supply fuel from a high-pressure vessel. The injection event causes an instantaneous drop in the rail pressure, as the stored mass is diminished. Pressure variations are also affected by the dynamics of the high-pressure pump that supplies fuel to the rail to compensate for the emptying process due to the injection. This paper proposes the possibility of diagnosing the injection process from measurement of the rail pressure. Different data treatment techniques are explored and evaluated in this paper to propose an effective method for the diagnosis of common-rail injection systems. [ABSTRACT FROM AUTHOR]

Composite pressure vessels are extensively used in unmanned spacecraft systems due to high specific strength of composites, which provides higher mass savings as compared to metallic vessels. The most common example is their use as liquid propellant tanks. Being a part of spacecraft, composite vessels are exposed to space environment, and therefore, may be subjected to hypervelocity impacts (HVI) by orbital debris or micrometeoroids. This paper analyzes the manufacturing features such as filament winding pattern and defects of fabrication that may influence the response of composite pressure vessels to HVI, and discusses the ways to introduce those features into the numerical modeling. [ABSTRACT FROM AUTHOR]

The paper addresses the Bauschinger effect under complex stress state in materials with deformation-induced anisotropy whose strain hardening is described by the isotropic-kinematic (translational) type hardening hypothesis. The Bauschinger effect is analyzed using the model based on the yield surface conception and graphical-analytical method of construction of constitutive equations under complex loading. As an example, cylindrical pressure vessels with closed and open ends subjected to autofrettage are considered. The tension-compression Bauschinger effect in the axial and hoop directions as well as the Bauschinger effect under reversed torsion with respect to the longitudinal axis is determined. The role of such factors as the level of prestraining under autofrettage, relation between isotropic and kinematic components of the strain hardening, and chemical composition of the material is analyzed. The results obtained are presented in the form of plots. [ABSTRACT FROM AUTHOR]

Pressure vessels are subject to deterioration processes, such as corrosion and fatigue, which can lead to failure. Inspections and repairs are performed to mitigate this risk. Large industrial facilities (e.g., oil and gas refineries) often have regularly scheduled shutdown periods during which many components, including the pressure vessels, are disassembled, inspected, and repaired if necessary. This paper presents a decision analysis framework for the risk-based maintenance (RBM) planning of corroding pressure vessels. After a vessel has been inspected, this framework determines the optimal maintenance time of each defect, where the optimal time is the one that minimizes the total expected cost over the lifecycle of the vessel. The framework allows for multiple defects and two failure modes (leak and burst), and accounts for the dependent failure events. A stochastic gamma process is used to model the future deterioration growth to determine the probability of vessel failure. The novel growth model presents a simple method to predict both the depth and length of each corrosion defect to enable burst analysis. The decision analysis framework can aid decision makers in deciding when a repair or replacement should be performed. This method can be used to immediately inform the decision maker of the optimal decision postinspection. A numerical example of a corroding pressure vessel illustrates the method. [ABSTRACT FROM AUTHOR]

In this paper, we present an exploratory study on the evaluation of reliability levels associated with the piping design equations specified by ASME Boiler and Pressure Vessel (BPV) Code, Section III. Probabilistic analyses are conducted to evaluate reliability levels in straight pipe segments with respect to performance functions that characterize the different failure criteria using advanced first-order reliability method (AFORM). One important failure criterion considered in this study relates to the plastic instability which forms the basis of piping design equations for emergency and faulted load level conditions as defined in the ASME code. The code-specified definition of plastic instability is based on the evaluation of a collapse moment which is defined using the moment-curvature curve for a particular component. In this study, we use elastic-perfectly plastic, bilinear kinematic hardening, and multilinear kinematic hardening stress-strain curves to develop closed-form expressions for the moment-curvature relationship in a straight unpressurized pipe. Both the pressurized and the unpressurized loading conditions are considered. The closed-form reliability is evaluated using Monte Carlo simulation because of the complex nature of the closed-form expression. The reliability values are calculated with respect to the maximum allowable moment specified by the code design equations that use deterministic safety factors. [ABSTRACT FROM AUTHOR]

Pressure vessels that undergo repairs are normally pressure tested to verify their structural integrity before returning into service. Conventionally, the entire vessel is pressure tested, according to the relevant construction code. In this paper, partitioning the pressure vessel is suggested as an equivalent alternative test arrangement, where pressure testing is limited to the zone where a repair has been performed. Use of such an arrangement would alleviate potential concerns associated with the conventional testing method. Procedures are provided to specify the position of the partition relative to the repair location, in order to maintain the state-of-stress to that achieved in a conventional pressure test. Validity of this approach has been demonstrated for a repaired full-circumferential welded joint in the wall of a cylindrical pressure vessel. [ABSTRACT FROM AUTHOR]

The so-called "in-vessel retention (IVR)" is a severe accident management strategy, which is widely adopted in most advanced nuclear power plants. The IVR mitigation is assumed to be able to arrest the degraded melting core and maintain the structural integrity of reactor pressure vessel (RPV) within a prescribed hour. Essentially, the most dangerous thermal-mechanical loads can be specified as the combination of critical heat flux (CHF) and internal pressure. The CHF is the coolability limits of RPV submerged in water (~150°C) and heated internally (~1327°C), it results in a sudden transition of boiling crisis from nucleate to film boiling. Accordingly, from a structural integrity perspective, the RPV failure mechanisms span a wide range of structural behaviors, such as melt-through, creep damage, plastic deformation as well as thermal expansion. Furthermore, the geometric discontinuity of RPV created by the local material melting on the inside aggravates the stress concentration. In addition, the internal pressure effect that usually neglected in the traditional concept of IVR is found to be having a significant impact on the total damage evolution, as indicated in the Fukushima accident that a certain pressure (up to 8.0 MPa) still existed inside the RPV. This paper investigates structural behaviors of RPV with the effects of CHF and internal pressure. In achieving this goal, a continuum damage mechanics (CDM) based on the "ductility exhaustion" is adopted for the in-depth analysis. [ABSTRACT FROM AUTHOR]

The brittle fracture prevention model is of great importance to the safety of pressure vessels. Compared to the semi-empirical approach adopted in various pressure vessel standards, a model based on Master Curve technique is developed in this paper. Referring to ASME nuclear code, the safety features including the lower bound fracture toughness and a margin factor equal to 2 for the stress intensity factor produced by primary stress are adopted in the new model. The technical background of the brittle fracture model in ASME VIII-2 has been analyzed and discussed, and then its inappropriate items have been modified in the new model. Minimum design temperature curves, impact toughness requirements, and temperature adjustment for low stress condition are established on the basis of new model. The comparison with the relevant curves in ASME VIII-2 is also made. The applicability of the new model is verified by the measured fracture toughness and impact toughness data of several kinds of pressure vessel steels. The results suggest that the minimum design temperature and the impact test requirements derived by the new model are compatible with each other. More testing data of different steels to check this model is necessary for further engineering application. [ABSTRACT FROM AUTHOR]

Analytical evaluation procedures for determining the acceptability of flaws detected during in-service inspection of nuclear power plant components are provided in Section XI of the ASME Boiler and Pressure Vessel Code. Linear elastic fracture mechanics based evaluation procedures in ASME Section XI require calculation of the stress intensity factor. Article A-3000 of Appendix A in ASME Section XI prescribes a method to calculate the stress intensity factor for a surface or subsurface flaw by making use of the flaw location stress distribution obtained in the absence of the flaw. The 2015 Edition of ASME Section XI implements a number of significant improvements in Article A-3000. Major improvements include the implementation of an alternate method for calculation of the stress intensity factor for a surface flaw that makes explicit use of the Universal Weight Function Method and does not require a polynomial fit to the actual stress distribution and the inclusion of closed-form equations for stress intensity factor influence coefficients for cylinder geometries. With the inclusion of the explicit weight function approach and the closed-form relations for influence coefficients, the procedures of Appendix A for the calculation of stress intensity factors can be used more efficiently. A review of improvements that have been implemented in Article A-3000 of Appendix A in the 2015 Edition of ASME Section XI is provided in this paper. Example calculations are provided for illustration purpose. [ABSTRACT FROM AUTHOR]

In response to the appeal for environmental protection and the efficient utilization of energy, local governments in China actively promote time-of-use (TOU) electricity tariffs for manufacturing enterprises. Motivated by a real-life industrial scenario of large special-purpose pressure vessel production, this paper addresses an energy-efficient two-stage flow shop scheduling problem under TOU tariffs to minimize the total electricity cost and the mean tardiness. Since the problem is computationally intractable, we focus on developing a multi-objective discrete differential evolution (MDDE) algorithm. Specifically, based on the optimal properties of the problem, we tailor an encoding scheme that consists of two job sequences and an idle time vector. The novel mutation and crossover operators are designed to generate the trail individuals, and the hypervolume contribution indicator is incorporated into the bi-criteria selection operator to measure the quality of the solution. Furthermore, two neighborhood structures are designed to iteratively improve the non-dominated solutions in the external archive set. We evaluate the performance of the MDDE algorithm via extensive computational experiments. The experimental results indicate that the MDDE algorithm can obtain the good approximate Pareto front, and it outperforms the well-known NSGA-II, SPEA2 and MOEA/D algorithms in solution quality. • A new energy-efficient scheduling problem under TOU tariffs is studied. • The encoding scheme is tailored based on the optimal properties. • Neighborhood search can improve the quality of approximate Pareto front. • The proposed MDDE algorithm performs well in real-life industrial scenario. [ABSTRACT FROM AUTHOR]

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The design of pressure vessel is an extremely professional job which has heavy workload, repeated work, and rich accumulated knowledge, and it has good characteristics of serialization, generalization, standardization. Generic 3D CAD systems are not suitable for pressure vessel design. On the contrary, customized development based on 3D CAD system is needed. In this paper, a new pressure vessel design system based on Chinese 3D CAD system named SINOVATION was developed to improve design efficiency and accuracy. First, the functions and construction of pressure vessel design system were presented with the analysis of the traditional design process of pressure vessels. Second, related design specifications were managed and used flexibly in pressure vessel design system, and general parts library and standard parts library were established to improve parts reuse and accumulation. Finally, a guiding design mode was accepted for typical vessels and components to design same product series while direct modeling function was used for atypical pressure vessels. The results show that this method is helpful for embedded use of design specifications, standards and knowledge, and also provides an extensive interface for product updates and diversification. Statistical data reports and accurate engineering drawings are generated automatically based on 3D models. The quality, efficiency, and consistence are greatly improved. With the implementation and application, the system has been highly commended by customers in Chinese pressure vessel industry, especially in petrochemical industry. [ABSTRACT FROM AUTHOR]

Piping components in power plants may experience combined bending and torsion moments during operation. There is a lack of guidance for pipe evaluation for pipes with local wall-thinning flaws under the combined bending and torsion moments. ASME boiler and pressure vessel (B&PV) Code Section XI Working Group is currently developing fully plastic bending pipe evaluation procedures for pressurized piping components containing local wall thinning subjected to combined torsion and bending moments. Using elastic fully plastic finite element (FE) analyses, plastic collapse bending moments under torsions were obtained for 4 (114.3)-24 (609.6) in. (mm) diameter pipes with various local wall-thinning flaw sizes. The objective of this paper is to introduce an equivalent moment, which combines torsion and bending moments by a vector summation, and to establish the applicable range of wall-thinning lengths, angles, and depths, where the equivalent moments are equal to pure bending collapse moments. [ABSTRACT FROM AUTHOR]

Strength mismatching between weld metal and parent material is common in pressure vessel industry. To carry out the fracture assessment of weld defects, it is required to accurately estimate the reference stress or limit load for the flawed section. Weld strength mismatch introduces complexity in determination of the limit load. Although it is acceptable to use the weaker material properties in the assessment, it can be overly conservative. Industrial standards R6 and BS7910:2013 provide the methods for weld strength mismatch, but no limit load ratio solutions are available for semi-elliptical surface and embedded flaws which are the most common cracks in pressure vessels and pipework. It is useful to understand whether the existing limit load ratio solutions in R6 and BS7910 can be used for surface and embedded flaws. This paper reviews the assumptions used in the existing reference stress solutions and discusses its suitability for mismatch conditions. The effects of weld strength mismatch on limit loads of the surface and embedded flaws are studied using 3D elastic-plastic finite element analyses. The results are compared with the R6 and BS7910 solutions. The validity of the handbook solutions of through-wall flaws for surface and embedded flaws in plate and the mismatch effect on limit loads are discussed. [ABSTRACT FROM AUTHOR]

Stress and damage analyses are performed on a composite pressure vessel with aluminum liner under internal pressure through numerical simulations. The variational thickness and wound angle of the head is reflected in the finite element model in accordance with the actual structure. A progressive damage model considering four failure modes are adopted for the composite, i.e., the fiber tension and compression, the matrix tension and compression. The regularities of the initiation and distribution of the various damages are studied, and the effects of the damage evolution on the determinations of the burst pressure and the autofrettage pressure are analyzed. The effects of the autofrettage pressure on the mean stress and the stress amplitude of the liner under zero and service pressures are also discussed. The conclusions in this paper are helpful to the design and use of composite pressure vessels. [ABSTRACT FROM AUTHOR]

The paper outlines the writer's involvement with pressure-related equipment over a period of some sixty years. It highlights some of the achievements of the author and his colleagues originally presented in a plenary lecture at Shanghai during the fourteenth international Pressure Vessel Conference, ICPVT-14, and includes commentary on recent developments in pressure design and analysis. [ABSTRACT FROM AUTHOR]

Q345R steel is the most commonly used material in fabrication of the pressure vessels and boilers in China, due to its excellent properties. In 2010, ASME code case 2642 accepted Q345R steel for use in construction of pressure vessels. The code case specified impact test exemption curve A for the impact test requirements for Q345R. However, this provision severely limits the application of this material at low temperature, since most of the minimum design metal temperature (MDMT) of curve A is above the freezing point. In this paper, a series of tests (such as uniaxial tensile test, impact test, and fracture toughness test) were carried out at low temperature to investigate the mechanical properties of Q345R steel plates with thickness of 36-80?mm. This study of low temperature usage of Q345R steel was conducted using the fracture mechanics assessment procedure of API 579-1/ASME FFS-1. The fracture toughness is given by master curve (MC) method in the transition regime. The results show that Q345R can be used at lower temperature and that classifying Q345R steel into curve D is appropriate. [ABSTRACT FROM AUTHOR]

The shell-to-bottom joint of hydrocarbon storage tanks is a critical location which may experience fatigue cracking and requires evaluation of the local cyclic stresses especially in the case of elevated temperature tanks. The fill/draw down cycle of the stored liquid causes low cycle fatigue near this joint and hence a fatigue evaluation is recommended. The peak alternating stress at this location, used to enter the fatigue curves is currently determined using a pseudo-elastic analysis that represents strain range due to inelastic deformations. API 650 employs beam on elastic foundation theory for this analysis. This theory is being used for tanks resting fully on earthen foundation as well as those on concrete ring wall. This paper studies the validity of using this theory for tanks with concrete ring wall foundation which are much more rigid compared to earthen foundations. Some of the difficulties in the current practice are highlighted. An alternative to the current model is presented for the determination of stresses in such tanks. The results are validated using finite element analysis. The results show that the current practice needs to be revised or rejustified in an alternative manner. [ABSTRACT FROM AUTHOR]

The paper reports on recent progress in numerical shakedown and limit analysis based on Melan's lower bound shakedown theorem. After explaining the theoretical foundations of their approach, the authors describe in detail the numerical scheme, in particular the underlying optimization via interior point methods. Numerous examples mostly related to pressure vessel technology are presented, illustrating the potential of the method. [ABSTRACT FROM AUTHOR]

This paper deals with the effectiveness of two isolation systems for the seismic protection of elevated steel storage tanks. In particular, the performance of high damping rubber bearings (HDRB) and friction pendulum isolators (FPS) has been analyzed. As case study, an emblematic example of elevated tanks collapsed during the Koaceli Earthquake in 1999 at Habas pharmaceutics plant in Turkey is considered. A time-history analysis conducted using lumped mass models demonstrates the high demand in terms of base shear required to the support columns and their inevitable collapse due to the insufficient shear strength. A proper design of HDRB and FPS isolator according to the EN1998 and a complete nonlinear analysis of the isolated tanks proved the high effectiveness of both isolation systems in reducing the response of the case tank. Actually, the stability conditions imposed by the code and a reduced level of convective base shear obtained with the second isolation typology suggests the use of FPS isolators rather than HDRB devices. [ABSTRACT FROM AUTHOR]

China has very ambitious goals of expanding its commercial nuclear power by 30 GW within the decade and wishes to phase out fossil fuels emissions by 40-45% by 2020 (from 2005 levels). With over 50 new nuclear power plants under construction or planned and a design life of 60 years, any discussions on structural integrity become very timely. Although China adopted its nuclear technology from France or USA at present time, e.g., AP1000 of Westinghouse, the construction materials are primarily "Made in China." Among all issues, both the accumulation of the knowledge base of the materials and structures used for the power plant and the technical capability of engineering personnel are imminent. This paper attempts to compile and assess the mechanical properties, Charpy V-notch impact energy, and fracture toughness of A508-3 steel used in Chinese nuclear reactor pressure vessels (RPVs). All data are collected from open literature and by no means complete. However, it provides a glimpse into how this domestically produced steel compares with western RPV steels such as USA A533B and Euro 20MnMoNi55. [ABSTRACT FROM AUTHOR]

Commonly used design codes for power plant components and pressure vessels include rules for ratcheting analysis that specify limits on accumulated strain. No guidance is provided on the use of the material model. The objective of the paper is to provide guidance that may be helpful to analysts. The Chaboche nonlinear kinematic (NLK) hardening material model is chosen as an appropriate model. Two methods are selected for its calibration that can determine the parameters for stainless steels. One is manual that requires no outside software and the other uses finite element software. Both are based on the monotonic stress-strain curve obtained from a tension specimen. The use of the Chaboche parameters for cases when ratcheting is caused by cyclic temperature fields is selected as the example of an application. The conclusion is that the number of allowable design cycles is far higher when using the parameters with temperature dependency than those at the constant maximum temperature that is being cycled. [ABSTRACT FROM AUTHOR]

In this paper, the J-R curves of two cracks (A508 HAZ crack 2 and A508/Alloy52Mb interface crack 3) located at the weakest region in an Alloy52M dissimilar metal welded joint (DMWJ) for connecting pipe-nozzle of nuclear pressure vessel have been measured by using single edge-notched bend (SENB) specimens with different crack depths a/W (different constraint). Based on the modified T-stress constraint parameter τ*, the equations of constraint-dependent J-R curves for the crack 2 and crack 3 were obtained. The predicted J-R curves using different constraint equations derived from the three pairs of crack growth amount all agree with the experimental J-R curves. The results show that the modified T-stress approach for obtaining constraint-dependent J-R curves of homogeneous materials can also be used for the DMWJs with highly heterogeneous mechanical properties (local strength mismatches) in nuclear power plants. The use of the constraint-dependent J-R curves may increase the accuracy of structural integrity design and assessment for the DMWJs of nuclear pressure vessels. [ABSTRACT FROM AUTHOR]

This paper overviews the effects of some precipitates in Fe-Ni base boilers materials. The volume fraction of these precipitates is usually below 10% for maintaining the microstructure stability and manufacture ability. They appear in a number of morphologies, but all of them improve the creep strength when they exist in small size. For the alloys serviced below 650°C, the strengthening precipitates disperse within the matrix and maintain their diameter below 100 nm during long time exposure. For the alloys serviced above 650°C, the strengthening precipitates are normally larger than 100 nm in equivalent diameter. They may experience long growth duration and thus keep their size below 500 nm. Meanwhile, the precipitates may improve creep strength when they are dispersed over the grain boundaries. [ABSTRACT FROM AUTHOR]

To demonstrate the structural integrity of a reactor pressure vessel, a detailed stress analysis is required to be carried out accounting for the transients during various operating conditions of the reactor. For thick-wall reactor pressure vessels, the temperature gradient across the vessel thickness is time-dependent during the operating transients and adds to the complexities in estimating the stress field across the vessel wall thickness. The design of such thick vessels needs to be supplemented with a detailed thermal stress analysis taking in to account the time-dependent variations. The present paper discusses the detailed thermo-mechanical stress analysis carried out for reactor pressure vessel of Tarapur Atomic Power Station-1 and 2. A complete evaluation of temperature and resulting stress distribution across the vessel wall thickness, in a non-steady state is obtained using a numerical model. In this model, the temperature of the inside surface of the vessel is considered to change according to various transients, viz., reactor startup, shutdown and emergency condition. The analysis results indicate that the most stressed location in RPV wall is clad-vessel interface and the governing transient is emergency shutdown condition. The results have been used for structural integrity assessment of reactor pressure vessel. Studies have also been carried out for re-circulation nozzle for its structural integrity assessment to preclude the possibilities of crack initiation or propagation. [ABSTRACT FROM AUTHOR]

Aiming at reducing the drawbacks of traditional forming process of large-scale austenitic stainless steel ellipse heads, the draw-bead was introduced to the forming process in this article. Three types draw-bead were considered in this paper: the round draw-bead, the rectangular draw-bead and edge-bead. Accordingly, a finite element model was built to simulate the forming process of ellipse heads. Meanwhile, the geometrical parameters were optimized in terms of the forming quality, the maximum thinning ratio and the maximum punch force by using the finite element analysis and design of experiment. The single-factor experiment was adopted to find out the possible significant factors and the reasonable range of these factors. The influencing factors, such as the type of draw-bead, the distance between the center of the draw-bead and inside of die, the height of the draw-bead, and the roundness radius of die, were researched. By means of orthogonal test and multi-objective experiment, the optimum parameter combination of draw-bead was found. [ABSTRACT FROM AUTHOR]