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Subsea pipelines and umbilicals are used for the transportation of fluids and electrical power between subsea installations and floating production units (FPUs). The installation and maintenance of these systems can be expensive. In a conventional subsea field development, the produced fluids can be transported from the well to a FPU where they can be offloaded to a tanker (surface ship). In the case of carbon dioxide (CO2) injection into the well, the direction of flow is reversed, i.e., CO2 flows from the tanker to the FPU, down the riser base and through the subsea pipelines to the well. This offloading process is weather-dependent and cannot be performed in severe weather conditions, i.e., strong winds and large waves. This paper presents a novel subsea shuttle tanker system proposed by Equinor ASA designed to be a possible alternative to subsea pipelines, umbilicals, and tanker ships. The subsea shuttle is intended to operate submerged under the sea surface to transport liquid CO2 from an existing offshore/land facility where CO2 is captured to a subsea well where the CO2 is injected into the reservoir. As the shuttle is subsea, it can operate under any type of weather conditions. Even though the subsea shuttle is proposed as a vehicle for liquid CO2 transport, it can also transport other types of cargo such as hydrocarbons, injection fluids, electrical power, or subsea tools. The paper will discuss the most important design considerations surrounding the subsea shuttle tanker. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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 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]

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]

The gas-liquid cylindrical cyclone (GLCC) is a simple, compact, and low-cost separator, which provides an economically attractive alternative to conventional gravity-based separators over a wide range of applications. Over the past 22 years, more than 6500 GLCCs have been installed around the world by the petroleum and related industries. However, to date no systematic study has been carried out on its structural integrity. The GLCC inlet section design is a key parameter, which is crucial for its performance and proper operation. This paper presents finite element analysis simulation results aimed at investigating the effect of various parameters on the inlet section structural integrity. Finally, recommendations on design modifications are presented, directed at strengthening the inlet section. [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]

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]

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]

Seamless pressure vessels (tubes) are designed per Department of Transportation (DOT) Specification 3AAX or 3 T. These tubes are used in over- the-road transport of high pressure gases. In tube trailer, these tubes are supported at ends from outside threaded necks. This paper describes the technical basis which was used in developing CGA C-23 document, which provides guideline on inspection and evaluation of tubes neck mounting surfaces. API-579/ASME FFS-1 standard and test data were used in developing the guideline for acceptance rejection criteria of the tube neck containing local thin areas and thread wear, respectively. [ABSTRACT FROM AUTHOR]

For finding out reliable limit load multipliers in pressure vessel components or structures using simplified limit load methods, proper estimation of reference volume is important. In this paper, two empirical methods namely elastic reference volume method (ERVM) and plastic reference volume method (PRVM) for reference volume correction are presented and compared. These reference volume correction concepts are used in combination with mα-tangent method and elastic modulus adjustment procedure to achieve converged limit load multiplier solution. These multipliers are compared with nonlinear finite element analysis results and are found to be lower bounded. Elastic reference volume method is the simplest method for reference volume correction when compared to plastic reference volume method. [ABSTRACT FROM AUTHOR]

The elastic analysis of two different kinds of radially heterogeneous pressure vessels is conducted in this paper. As a first kind of heterogeneous pressure vessels, a multilayered pipe with different material properties in different layers is considered. Another kind of heterogeneous pressure vessels is a thick hollow cylinder made of functionally graded material (FGM). On the basis of the finite difference method, the time-dependent deformation, strain and stress distributions of both kinds of heterogeneous pipes are obtained under the different kinds of thermomechanical loadings. In this investigation, it is assumed that the pressure and temperature are symmetrical about the axis of the cylinder. Also, the material properties are considered to be independent of temperature. Results obtained from the present method are compared with the existing data. [ABSTRACT FROM AUTHOR]

The circumferential flaw evaluation procedures in ASME Boiler and Pressure Vessel Code Section XI nonmandatory Appendix C are currently limited to straight pipes under pressure and bending loads without consideration of torsion loading. The Working Group on Pipe Flaw Evaluation of the ASME Boiler and Pressure Vessel Code is developing guidance for considering the effects of torsion by a mean of an equivalent bending moment, which is a square root of sum square combination of bending moment and torsion load with a weighted factor for torsion moment. A torsion weighted factor, Ce, is established in this paper using large strain finite element limit load analysis with elastic perfectly plastic materials. Planar flaws and nonplanar flaws in a 10.75 in. (273 mm) OD pipe are investigated. Additionally, a finite element J-integral calculation is performed for a planar through wall circumferential flaw with elastic plastic materials subjected to bending and torsion load combinations. The proposed Ce factor for planar flaws is intended for use with the ASME B&PV Code Section XI, Appendix C for limit load and Elastic Plastic Fracture Mechanics (EPFM) circumferential planar flaw evaluations. [ABSTRACT FROM AUTHOR]

In the pressure vessel and piping and power industries, creep deformation has continued to be an important design consideration. Directionally solidified components have become commonplace. Creep deformation and damage is a common source of component failure. A considerable effort has gone into the study and development of constitutive models to account for such behavior. Creep deformation can be separated into three distinct regimes: primary, secondary, and tertiary. Most creep damage constitutive models are designed to model only one or two of these regimes. In this paper, a multistage creep damage constitutive model is developed and designed to model all three regimes of creep for isotropic materials. A rupture and critical damage prediction method follows. This constitutive model is then extended for transversely isotropic materials. In all cases, the influence of creep damage on general elasticity (elastic damage) is included. Methods to determine material constants from experimental data are detailed. Finally, the isotropic material model is exercised on tough pitch copper tube and the anisotropic model on a Ni-based superalloy. [ABSTRACT FROM AUTHOR]

The use of large, high pressure liquid petroleum gas (LPG) storage bullets has become a common, and often assumed safe, practice in the petrochemical industry. The Engineering Equipment and Materials Users Association (EEMUA) is an organization that has attempted to address design aspects related to mounded or buried bullets; Publication No. 190 published by the EEMUA (2000, Guide for the Design, Construction and Use of Mounded Horizontal Cylindrical Vessels for Pressurized Storage of LPG at Ambient Temperatures, EEMUA, London, England.) became a standard practice in the industry. However, the design recommended, and therefore addressed, by Publication 190 is for bullets directly supported by soil (i.e., without saddle supports). However, it has been noticed by the authors that many users are requesting these storage bullets be supported by saddles resting on foundations in order to minimize the chance of unexpected settling and any motion of the bullets underground. The large span of these bullets requires more than two saddles adding to the complexity of the design due to statically indeterminate construction, differential settlement, and uneven supports. This paper focuses on major issues related to the design of such bullets. First, the loads induced by mound weight, pressure due to mound, and the loads due to longitudinal thermal expansion and soil resistance to this expansion is analyzed. Next, a method for calculating the multiple saddle reactions and bending moments at spans and supports is provided. A simplified method for assessing the effect of differential settlement between saddles is proposed. [ABSTRACT FROM AUTHOR]

In this paper, the formulae for elastoplastic stress distribution in layered cylindrical vessel layers with gaps have been provided. These formulae are based on the modified Pimshtein formulae for the elastic stress of layers. Plane strain with ideal elastoplastic model of materials is adopted. A practice example is presented to show how the formulae can be used for elastoplastic stress calculation. The hoop, radial, axial, and Von Mises equivalent stresses are obtained. The calculation result showed that the stress state of layered cylindrical vessel is more complex than that of monobloc cylindrical shell due to the interlayer gaps. The stress distribution is discontinuous. Calculation results obtained theoretically were compared to those obtained by finite element method (FEM). It shows that the results from the proposed formulae are in good agreement with finite element results. [ABSTRACT FROM AUTHOR]

In this paper, a modified weld structure of the layered urea reactor has been provided. In the modified structure, new circumferential weld can improve the stress status of the urea reactor. It has the both advantage of separated and integrated layered pressure vessel. This modified design is based on the stress status analysis and the requirement of leak detection. In order to evaluate the modified structure, stresses of original and modified urea reactor shell with interlayer gaps were calculated via Finite element software ANSYS 12.0. The calculation result shows that the maximum stress of the modified structure is reduced obviously in the same condition, and the leak of liner also can be detected effectively. [ABSTRACT FROM AUTHOR]

One of the critical issues for reactor pressure vessel (RPV) structural integrity is related to the pressurized thermal shock (PTS) event. Therefore, within the framework of safety assessments special emphasis is given to the effect of PTS-loadings caused by the nonuniform azimuthal temperature distribution due to cold water plumes or stripes during emergency coolant injection. This paper describes the method used to predict the thermal mechanic boundary conditions (system pressure and wall temperature). Using a system code the pressure and global temperature distributions were calculated, systematically varying the leak size and the location of the coolant water injection. Spatial and temporal temperature distributions in the main circulation pipes and at the RPV wall were predicted by mixing analyses with a computational fluid dynamics (CFD) code. The model used for these calculations was validated by post-test calculations of a UPTF (upper plenum test facility) experiment simulating cold leg injection during a small break loss of coolant accident (LOCA). Comparison with measured temperatures showed that the modeling used is suitable to obtain enveloping results. Fracture mechanics analyses were carried out for circumferential flaw sizes in the weld joint near the core region and between the RPV shell and the flange, as well as for axial flaws in the nozzle corner. Stress intensity factors KI were calculated numerically using the finite element program ansys and analytically on the basis of weight and polynomial influence functions using stresses obtained from elastic finite element analyses. Benchmark tests revealed good agreement between the results from numerical and analytical calculations. For all regions of the RPV investigated and the most severe transients it was demonstrated that a large safety margin against brittle crack initiation exists and brittle fracture of the RPV can be excluded. [ABSTRACT FROM AUTHOR]

The available design formulas for flat heads and blind end closures in the ASME Code, Section VIII, Divisions I and 2 are based on bending theory and do not apply to the design of thick flat heads used in the design of high pressure vessels. This paper presents new design formulas for thickness requirements and determination of peak stresses and stress distributions for fatigue and fracture mechanics analyses in thick blind ends. The use of these proposed design formulas provide a more accurate determination of the required thickness and fatigue life of blind ends. The proposed design formulas are given in terms of the yield strength of the material and address the fatigue strength at the location of the maximum stress concentration factor Introduction of these new formulas in a nonmandatory appendix of Section VIII, Division 3 is recommended after committee approval. [ABSTRACT FROM AUTHOR]

Assessment of multiple volumetric flaws is one of the most common problems relating to pressure vessels and piping components. Under the current fitness for service rules, such as ASME, BS, and so on, multiple volumetric flaws are usually recharacterized as an enveloping volumetric flaw (defined as a single larger volumetric flaw) as well as multiple cracklike flaws, following their assessment rules. However the rules proposed in their codes will not often agree and their justification is unknown. Furthermore, they can provide unrealistic assessment in some cases. In this paper the interaction between two differently sized nonaligned volumetric flaws such as local thin areas is clarified by applying the body force method. Unlike multiple cracklike flaws, the effect of biaxial stresses on the interaction is evident. Based on the interaction that indicates the magnification and shielding effects and reference stress solutions, a new procedure for multiple volumetric flaws is proposed for assessing the flaws in the p-M (pressure-moment) diagram, which is a simple assessment procedure for vessels with volumetric flaws. [ABSTRACT FROM AUTHOR]

This paper proposes an optimization technique for increasing the structural integrity of a light-weight composite blast containment vessel. The vessel is cylindrical with two hemispherical ends. It has a steel liner that is internally reinforced with throttles and gusset plates and wrapped with a basalt-plastic composite. A computationally-efficient finite element model of the blast containment vessel was proposed and verified in an earlier work. The parameters of the vessel are incorporated within an iterative optimization procedure to decrease the peak strains within the vessel, which are caused by internal blast loading due to an explosive charge placed at the center of the vessel. The results of the proposed procedure are validated for different initial guesses of the design variables. [ABSTRACT FROM AUTHOR]

Nuclear safety-piping is designed according to the ASME Boiler and Pressure Vessel Code, Sections III, NB-, NC-, and ND -3600 that use the allowable stress design method (ASD). The potential use instead of reliability-based design equations for nuclear piping could benefit the structural design by providing, among others, consistent reliability levels for piping. For the development of such equations, not only the probabilistic characteristics of the design variables are needed, but also the quantification of the uncertainties introduced by the strength models that are used in order to estimate the resistance of pipes subjected to different loadings. This paper evaluates strength models, and therefore provides necessary information for the reliability-based design of pipes for burst or yielding due to internal pressure and for excessive bending. [ABSTRACT FROM AUTHOR]

High temperature (>300°F, 149°C) water has been found to greatly accelerate fatigue crack growth rates in carbon and low-alloy steels. Current ASME Code fatigue design curves are based entirely on data obtained in air. While a factor of 2 on life was applied to the air data to account for environmental effects, the actual effects have been found to be an order of magnitude greater in the low-cycle regime. A great deal of work has been carried out on these environmental effects by talented investigators world- wide. The ASME Code Subgroup on Fatigue Strength has been working for 20 years on the development of new fatigue design methods and curves to account for high temperature water environmental effects. This paper presents an overview of the data and analyses used to formulate proposed new environmental fatigue design curves, which maintain the same safety margins as existing Code fatigue design curves for air environments, and a historical summary of ASME Code Work in this field. [ABSTRACT FROM AUTHOR]

Infrared thermography is a nondestructive evaluation method with an increasing span of applications. In this paper the pixel-level image fusion of infrared light and visible light image for infrared thermography and its application in nondestructive testing (NDT) of pressure vessel are studied. First in the image fusion, different mode image registration has been done based on feature corners. The corners and curves relative to each corner are extracted using the curvature scale space method. A new shape context descriptor for each corner is computed as the criterion to match the corners. Marks can then be added to pick up the corners, especially if there are no distinct matching feature corners between the different mode images. Two fusion methods, contrast modulation and transparent fusion, are introduced to fuse the visual and infrared light images. The experimental results show that the methods are good for pixel-level image fusion. Finally the method is applied to inspection of pressure vessel. The research indicates that image fusion for infrared thermography can facilitate defect location and interpretation of inspection results. [ABSTRACT FROM AUTHOR]

Current fatigue analyses of metallic structures undergoing variable amplitude loading, including pressure vessels, are mostly based on linear cumulative damage concepts, as proposed by Palmgren and Miner This type of analysis neglects any sequential effects of the loading history. Several studies have shown that linear cumulative damage theories can produce inconsistent fatigue life predictions. In this paper both fatigue damage accumulation and cyclic elastoplastic behaviors of the P355NL1 steel are characterized using block loading fatigue tests. The loading is composed of blocks of constant strain- controlled amplitudes, applied according to two and multiple alternate blocks sequences. Also, loading composed by blocks of variable strain-controlled amplitudes are investigated. The block loading illustrates that fatigue damage evolves nonlinearly with the number of load cycles, as a function of the block strain amplitudes. These observations suggest a nonlinear damage accumulation rule with load sequential effects for the P355NL1 steel. However, the damage accumulation nonlinearity and load sequential effects are more evident for the two block loading rather than for multiple alternate block sequences, which suggests that the linear Palmgren-Miner rule tends to produce better results for more irregular loading histories. Some phenomenological interpretations for the observed trends are discussed under a fracture mechanics framework. [ABSTRACT FROM AUTHOR]

Most current flange design methods use an equivalent pressure to treat bolted flange connections subjected to external bending loads. This oversimplified approach together with the lack of a proper assessment of the actual affected tightness make these methods inadequate for modern flange design. The substitution of the external applied moment by an equivalent pressure is excessively conservative and not realistic since it assumes that the achieved tightness is that of a gasket unloaded entirely to a minimum stress whereas in reality only a small section of it is, the rest of it is actually at a much higher stress. The successfulness of a valid analytical approach in yielding to an acceptable solution resides in its ability to account for the circumferential distribution of the gasket contact stress and its effect on leakage. This paper presents an analytical model based on the flexibility of the flange to treat flanges subjected to bending loads such as those produced by external moments and misalignments and capable of integrating leakage around the gasket circumference. The bolted joint sealing performance in the presence of such loads is evaluated using the new Pressure Vessel Research Council (PVRC) gasket constants Gb, a, and Gs, obtained from room temperature tightness (ROT) tests. The analytical results including leakage predictions are validated by comparison to those obtained numerically by finite element analysis and experimentally on different size flanges. The overconservatism of the equivalent pressure is demonstrated. [ABSTRACT FROM AUTHOR]

Between 1973 and 1990 four units of the Russian nuclear power plants type WWER-440/ 230 were operated in Greifswald (former East Germany). Material probes from the pressure vessels were gained in the frame of the ongoing decommissioning procedure. The investigations of this material started with material from the circumferential core weld of unit 1. First, this paper presents results of the reactor pressure vessel (RPV) fluence calculations depending on different loading schemes and on the axial weld position based on the Monte Carlo code TRAMO. The results, show that the use of the dummy assemblies reduces the flux by a factor of 2-5 depending on the azimuthal position. The circumferential core weld (SNO.1.4) received afluence of 2.4 x 10[sup19] neutrons/cm[sup2] at the inner surface; it decreases to 0.8 x10[sup19] neutrons/cm[sup2] at the outer surface. The material investigations were done using a trepan from the circumferential core weld. The reference temperature T[sub0] was calculated with the measured fracture toughness values, K[subJc], at brittle failure of the specimen. The K[subJc] values show a remarkable scatter The highest T[sub0] was about 50°C at a distance of 22 mm from the inner surface of the weld. The Charpy transition temperature TT[sub41J] estimated with results of subsized specimens after the recoveiy annealing was confirmed by the testing of standard Charpy V-notch specimens. The VERLIFE procedure prepared for the integrity assessment of WWER RPV was applied on the measured results. The VERLIFE lower bound curve indexed with the Structural Integrity Assessment Procedures for. European Industry (SINTAP) reference temperature, RTT[sub0][supSINTAP], envelops the K[subJc] values. Therefore for a conservative integrity assessment the fracture toughness curve indexed with a RT representing the brittle fraction of a data set of measured K[subJc] values has. to be applied. [ABSTRACT FROM AUTHOR]