bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple Model of Lu¨ders Behaviour in a Novel Compact Tension Specimen for Investigation of Residual Stress Effects
Authors: Wenman Mark R. , Plant Robert D.
Published: July 2008

Residual stress effects on defects have been investigated by the use of a novel compact tension (CT) specimen. Mild steel CT specimens have been preloaded in compression to generate a plastic zone around the notch prior to precracking. Upon unloading, the specimen contains a residual tensile stress, around the notch tip, into which a defect such as a prefatigue crack can be introduced. The effect of the residual stress on fatigue crack growth and final fracture is then investigated. Here, the uniaxial tensile behaviour of the steel used shows Piobert-Lu¨ders behaviour typical of certain ferritic pressure vessel steels. The mechanical preloading process has been modelled via a finite element (FE) analysis. The plastic deformation behaviour, taken from tensile test data, has been incorporated into the CT specimen model, first ignoring the Lu¨ders behaviour and then including it via a simple plastic model of the phenomenon. The model of Lu¨ders behaviour was tested on a FE model, of an uniaxial tensile test, before it was applied to the CT specimen. The result of this test was the generation of a realistic propagating band of plastic instability along the gauge length of the tensile specimen. Results for FE models of CT specimens, with and without the Lu¨ders behaviour, were then compared to real preloaded CT specimens. The models using only a lower yield point and ignoring Lu¨ders behaviour under predict the deformation of real specimens. The incorporation of plastic data containing an upper yield point predicts with reasonable accuracy the preloading cycle and as a result the shape of the residual stress field generated. Hardness maps have been made, by the use of scanning indentation mechanical microprobe (SIMM), of the free surface, of preloaded specimens. These maps reveal the strain profile of the surface and Lu¨ders bands emanating from the notch region are clearly visible. The FE model of the CT specimen, including Lu¨ders behaviour, shows Von Mises stress contours in a similar pattern to the Lu¨ders bands in the real specimen. Finally, some specimens were precracked, using cyclic compression, and then fractured at lower shelf temperatures (-140°C) to reveal the precrack shape; this matched the predicted shape of the maximum principal stress field responsible for driving crack growth. The lower shelf fracture toughness of preloaded specimens was found to be considerably reduced from reference toughness specimens with no preload. This suggests that the tensile residual stress was dominant over any benefit gained from warm pre-stressing the material.
An Experimental Investigation of the Fatigue Crack Growth Behavior of a Pressure Vessel Material
Authors: Wang Xiaogui , Gao Zengliang , Zhao Tianwen , Ding Fei , Jiang Yanyao
Published: July 2008

An experimental investigation was conducted on 16MnR, a pressure vessel material widely used in China. Standard compact specimens were subjected to several different R-ratios (the ratio of the minimum load over the maximum load in a loading cycle) and loading amplitudes. Three different notch sizes ranging from very sharp notch to blunt notch were used. In addition to constant amplitude load, experiments were conducted with overloads being applied at different crack lengths. Two-step high-low sequence loading experiments were conducted to study the influence of the loading sequence. The experimental results show that the R-ratio has an insignificant influence on crack growth of the material. A single overload at the start of crack growth from a notch results in a crack arrest. The application of an overload during a constant amplitude loading experiment retards the crack growth significantly. A higher constant amplitude loading history has a great influence on the crack growth in the subsequent lower constant amplitude loading. The size of the notch together with the R-ratio has a great influence on the early crack growth from the notch.
Comparison of Experimental to Theoretical Pipe Strains During Water Hammer
Authors: Leishear Robert A.
Published: July 2008

Experimental strains during water hammer were compared to theoretical equations for strain. These equations were derived from the basic equations of motion, which lead to equations for the hoop stress and hoop strain. In this particular case, a sudden pressure increase traveling in a pipe was measured, and the hoop strains resulting from this fluid transient were also measured. Measuring the strains at numerous locations along the pipe permitted comparison of the strains as a function of position with respect to the fluid shock wave. This comparison of strains at different positions along the pipe permits analysis of the vibratory nature of the strain in the pipe wall. Essentially, the equations of motion provide an approximate technique to find the maximum stress and strain due to water hammer.
The Comprehensive Discussion of the Pipe Wall Thinning of Secondary System in BWR and PWR Nuclear Power Plants
Authors: Ohira Taku , Hoshino Tomohiko
Published: July 2008

The behaviors of pipe wall thinning of secondary systems in The Japan Atomic Power Company (JAPC)’s BWR and PWR nuclear power plants were compared in this paper, to discuss the effects of respective factors contributing to corrosion protection of pipe. The rates of pipe wall thinning in single-phase flow environment, in both BWR and PWR, depend on temperature. Nevertheless, the rate of pipe wall thinning in PWR is more than that in BWR. The rates of pipe wall thinning at elbow of pipe, bending of pipe, straight run of pipe and reducer areas are mutually different, although they are located in the same line. Especially, the rates of pipe wall thinning at elbows of pipes, bendings of pipes, straight runs of pipes and reducers, which are located closely downstreams of the pumps discharge nozzles, elbows, orifices or bent pipes, depend on not the temperature but the pipe configuration.
Simulation of FSI Using a Monolithic Code
Authors: Capron Nicolas , Souli M’hamed , Mompean Gilmar
Published: July 2008

The main concern in fluid-structure interaction problems is the computation of fluid forces that act on a rigid or deformable structure. However, the majority of numerical test consists in employing two different codes to separately solve pressure of the fluid and structural displacements. In this paper, a monolithic with an ALE formulation approach is used to implicitly calculate the pressure of an incompressible fluid applied to the structure. The velocity-pressure formulation is decoupled by the projection method proposed by Gresho.
Special Phased Array Applications for Pipeline Girth Weld Inspections
Authors: Moles Michael , Labbe´ Simon
Published: July 2008

Ultrasonic phased arrays present major improvements over conventional multiprobe ultrasonics for inspecting pipeline girth welds, both for onshore and for offshore use. Probe pans are lighter and smaller, permitting less cutback; scans are quicker due to the smaller probe pan; phased arrays are considerably more flexible for changes in pipe dimensions or weld profiles, and for different scan patterns. More important, some of the potential advantages of phased arrays are now becoming commercially available. These include: • Compensating for variations in seamless pipe wall thickness. • Wedge temperature compensation. • Improved focusing for thick and thin wall inspections. • Premium inspections for risers, tendons and other components. • Small diameter pipes. • Multiple displays. • Clad pipe. The paper describes the latest phased array UT results for special applications.
Evaluation of Stress Concentration Factors by Finite Element Analysis
Authors: Strzelczyk Andrzej T. , Ho San S.
Published: July 2008

In the ASME Code fatigue evaluation, the total stress at the critical region of a structure is often calculated as a product of nominal stress and the SCF (stress concentration factor). The SCF values are usually taken from technical material like the Welding Research Bulletin [1] or Peterson’s Stress Concentration Factors book [2]. However, the published data do not cover all stress concentration cases; furthermore, many results are ambiguous or with limited accuracy. This paper recommends direct evaluation of the stress concentration by finite element analysis. It presents examples of automatic generation of finite element models which apply to practical cases. The examples show that the finite element method is an effective way for stress concentration assessment; the method can give accurate (convergent) results for a wide variety of cases of geometry and loading conditions.
Nozzle Reinforcement: Constant vs. Variable
Authors: Taagepera Jaan , McKay Mike
Published: July 2008

Section VIII Divisions 1 and 2 require shell openings to be reinforced using a cross sectional area replacement philosophy. Although the state of stress in a shell opening varies with the location along the nozzle to shell intersection most nozzle reinforcement is designed as though there is no variation. Openings in the shell which are reinforced with excess thickness available in the shell, nozzle neck, or weld are defined as “integrally reinforced.” Section VIII acknowledges the variation in stress for these integrally reinforced nozzles with respect to the orientation of a section cut through the opening. The use of a factor F to reduce the required reinforcement proportionally is allowed. In this paper, stresses developed due to internal pressure in integrally reinforced shell openings reinforced continuously are evaluated. These stresses are compared with those in the case where reinforcement is varied using the F factor. Continuously integrally reinforced nozzles have a constant amount of reinforcement area about the nozzle centerline while those reinforced with a variable area of reinforcement do not. This lack of symmetry is most likely to be developed through additional weld buildup on either the shell or nozzle neck or with a larger fillet on the attachment weld. The costs of each type of construction are compared. It is found that in some cases reinforcing a nozzle with a variable reinforcement area applied through weld buildup may be substantially less expensive than the typical reinforcing pad approach. A guideline of having 70% of the area required available within the shell and nozzle and weld is suggested as a criteria to evaluate the potential to benefit from a variable reinforcement approach.
The Study on Crack Dynamic Propagation in the Rich Gas Transmission Pipelines
Authors: Zhuang Z. , Yang X. B. , Feng Y. R. , Huo C. Y. , Zhuang C. J.
Published: July 2008

Based on the theories of dynamic fracture mechanics and the DWTT (Drop Weight Tear Test), the whole process of crack dynamic propagation of rich gas pipeline is simulated with the finite element method. The decompression behaviour of rich gas is considered and a three-stage linear decompression mode is put forward to simulate the behaviour of rich gas phase transition in ruptured pipeline, and the pressure plateau caused by the phase transition of rich gas is calculated by a multi-parameter state equation. The dynamic parameter (the CTOA, Crock Tip Opening Angle) varied with the crack location is obtained under various conditions, such as different gas components, different initial pressure, and different SDR (Standard Dimension Ratio). Through comparison of experimental data and numerical results, the reliability of engineering is valuated in rich gas transmission pipelines.
The Mechanics Basis of Residual Stress Profiles in Proposed API 579 Appendix E
Authors: Dong P. , Cao Z.
Published: July 2008

In this paper, the mechanics basis underlying the parametric through-thickness residual stress profiles proposed for the revised API 579 Appendix E are presented. The proposed residual stress profiles are governed to a large extent by a unified parametric function form valid for a broad spectrum of pipe and vessel welds. The functional relationship is established based on the comprehensive knowledge base developed within a recent major international joint industry project (JIP) under the auspice of Pressure Vessel Research Council (PVRC) and a large amount of residuals stress measurement data from recent literature. One of the most important features associated with the proposed revision is that residual stress profile is uniquely determined by two important sets of governing parameters: (1) parameters relevant to pipe geometry, i.e., r/t and t; (2) a parameter related to welding linear heat input Q (J/mm), referred to as the characteristic heat input Qˆ which has a dimension of J/mm3. As a result, the corresponding through-wall residual stress distribution exhibits a continuous change as a function of r/t, t, and Qˆ, instead of falling into a few discrete and unrelated profiles, as seen in the current Codes and Standards.
Penetration of Fine Foundry Sand by Rigid Projectiles
Authors: Stoltz Brian C. , Hankins Melissa D. , Torres Karen L. , Jones Stanley E.
Published: July 2008

In another paper [1], the authors presented an approach to penetration of a particulate target. This theory is based on the friction that the particles of target material present to the entire penetrator surface, including its shank. The shank of the penetrator affords a very large surface area compared to that of the nose. Even modest friction acting on the shank can provide a fairly large retarding force. Normal pressure acting on the projectile is assumed to be velocity-squared dependant, as indicated by a number of methods, including cavity expansion modeling [2]. Penetration of sand and soil has been considered by numerous investigators, e.g. [3–5]. These investigations did not directly address the frictional component of the net resisting force acting on the penetrator. A series of laboratory scale penetrations tests were performed. Data from these tests was used to evaluate the parameters in the model. Fine foundry sand is a high-density medium (1960 kg/m3) with a small amount of friction. This contrasts the target used by the authors in [1], which had a sizable amount of friction. Results from the theory are in excellent agreement with the experiments with velocities as high as 630 m/sec.
An Overview of 3-D Geometric Models to Describe Brittle Fracture in Polycrystalline Ferritic Steels
Authors: Flewitt P. E. J. , Smith G. E. , Hughes G. M. , Crocker A. G.
Published: July 2008

Flaws that can be present within pressure vessels, pipework and other engineering components are assessed using the principles of fracture mechanics. In general, failure avoidance methodologies are used for assessments. In these, mechanical properties and fracture toughness of the particular materials, taking account of the thermo-mechanical history, are important input parameters. In addition, however, it is necessary to support these approaches with an understanding of the underlying fracture mechanisms. In the case of lower shelf brittle fracture of ferritic materials, various approaches have been adopted to provide an understanding of the initiation and growth of these cracks. Certainly polycrystalline ferritic steels are widely used for construction of engineering components. Although a truly multiscale problem, this overview describes the key features of 3D geometric models that can be used to consider brittle fracture of a variety of polycrystalline materials, including bcc materials, in the intermediate microscale range of 10−6 to 10−3 m. Results of the modelling applied to the brittle fracture of bcc polycrystalline ferritic materials are presented, particularly with respect to predicted crack paths as an initiated crack propagates across the model. In this situation, brittle cleavage and intergranular brittle fracture are addressed. One particular application is the effect of prior grain boundary creep damage, arising from plant service history, on the subsequent lower shelf brittle fracture of ferritic steel components. The implications of this 3D modelling of polycrystalline material are discussed.
The Interrelationships of KIa, KIc, and JIc, and the Implications of These Relationships on Use of Fracture Models Over the Ranges of Hardening Observed in Ferritic Steels
Authors: EricksonKirk Marjorie , EricksonKirk Mark , Williams Tim
Published: July 2008

Models to predict the fracture and arrest behavior of ferritic steels, particularly those in use in the nuclear industry, have long been under development. The current, most widely accepted model of fracture toughness behavior is the ASTM E1921-02 “Master Curve” that is used to predict the variation of the mean cleavage fracture toughness with temperature in the transition temperature region as well as predicting the scatter of data about the mean at any given temperature. Recently, models describing the variation of arrest fracture toughness and of ductile initiation toughness with temperature have also been proposed. A study has been conducted with the goal of assessing how the scatter in cleavage initiation toughness may vary with temperature and level of irradiation embrittlement, which utilizes the crack arrest and ductile crack initiation models to redefine limits of applicability of the Master Curve-assumed Weibull distribution by developing empirically-derived interrelationships between the three models. These relationships are expected as all three parameters, KIc, KIa, and JIc, are controlled by the flow behavior of the material. There is a physical basis for viewing the crack arrest toughness as an absolute lower bound to the distribution of crack initiation toughness values for a fixed material condition and temperature. This physically based relationship, borne of the fact that both cleavage crack initiation toughness and cleavage crack arrest toughness are controlled by dislocation mobility, has brought about the suggestion that crack arrest toughness could be used to modify the lower tails of the crack initiation fracture toughness distribution. Using both empirical evidence and a hardening model proposed by Natishan and Wagenhofer, we investigate the relationship between initiation and arrest toughness and the implications on use of toughness models.
Structural Response of Piping to Internal Gas Detonation
Authors: Shepherd Joseph E.
Published: July 2008

Detonation waves in gas-filled piping or tubing pose special challenges in analysis and prediction of structural response. The challenges arise due the nature of the detonation process and the role of fluid-structure interaction in determining the propagation and arrest of fractures. Over the past ten years, our laboratory has been engaged in studying this problem and developing methodologies for estimating structural response. A brief overview of detonation waves and some key issues relevant to structural waves is presented first. This is followed by a summary of our work on the elastic response of tubes and pipes to ideal detonation loading, highlighting the importance of detonation wave speed in determining flexural wave excitation and possibility of resonant response leading to large deformations. Some issues in measurement technique and validation testing are then presented. The importance of wave reflection from bends, valves and dead ends is discussed, as well as the differences between detonation, shock wave, and uniform internal pressure loading. Following this, we summarize our experimental findings on the fracture threshold of thin-walled tubes with pre-existing flaws. A particularly important issue for hazard analysis is the estimation of loads associated with flame acceleration and deflagration-to-detonation transition. We give some recent results on pressure and elastic strain measurements in the transition regime for a thick-wall piping, and some remarks about plastic deformation.
Neutron Diffraction Evaluation of Residual Stress for Several Welding Arrangements and Comparison With Fitness-for-Purpose Assessments
Authors: Paradowska Anna M. , Price John W. H. , Ibrahim Raafat , Finlayson Trevor , Blevins Richard , Ripley Maurice
Published: July 2008

In this research the neutron diffraction technique was used to investigate and compare the residual stress characteristics in a several weld arrangements. This research has focused on the effects on residual stress of: • restraint condition applied during welding, • the start and end of the weld for a single bead, and • increasing the number of passes. The measured residual stress distributions are normalized by the yield strength of the material and compared with distribution provided in fitness-for-purpose procedures. It is found that the current safety assessment procedure BS 7910 and R6 Level 1 are significantly conservative. For a less conservative assessment R6 Level 2 is recommended, however even this assessment is often conservative, in particular for transverse residual stresses.
An Overview of GMAW Including Applications, Common Problems and Solutions
Authors: Henderson Michael R.
Published: July 2008

Gas Metal Arc Welding (GMAW) is said to be one of the easiest welding processes to learn and use. Because of its high deposition rates and little post-weld cleaning required, GMAW is a popular choice for a variety of applications including almost all commercially important metals. Another factor contributing to the widespread use of GMAW is the various modes of metal transfer including short circuit, spray, surface tension transfer (STT), etc. These different modes of transfer enable GMAW to be tailored to different situations. For instance, some applications may require deep penetration or other applications may be for welding very thin sections. However, these factors along with others may result in inferior welds if not monitored closely. Problems such as weld porosity, lack of fusion, and lack of shielding gas coverage can all lead to inadequate welds which can lead to larger problems if not corrected. Many common drawbacks to the GMAW process can be remedied quite easily with proper time and attention. Taking the time and effort to produce a sound weld may, however, negate the superior deposition rates of GMAW thereby limiting its use to fewer applications. This welding process can be extremely effective when used properly. However, the key is to not sacrifice weld quality for the sake of production. GMAW applications, modes of transfer, along with common problems and solutions associated with the process will all be discussed and detailed.
Reinvestigation of a Heat Exchanger Flange Leak
Authors: Porter Mike , Martens Dennis
Published: July 2008

In a paper presented in 1994 [1], the authors examined a heat exchanger flange to ascertain the cause for a leak. This examination was conducted using Finite Element (FE) analysis procedures. At that time, it was not practical to accurately model the interaction between the flanges and gaskets as a function of time and the resultant temperature. In the ensuing time period, the available FE technology has improved dramatically. Faster computers and new parallel solver technology allow modeling of the flange components that was not practical 10 years ago. In this paper, the authors will re-examine the exchanger system using current technology and discuss the improved insight that this new technology provides to the problem solution.
Seismic Analysis of a Pressure Vessel
Authors: Porter Mike , Martens Dennis , McGuffie Sean
Published: July 2008

The seismic analysis of ASME Section VIII Div 1 [1] industrial pressure vessels has typically been accomplished using rather simplified “equivalent static force” procedures. As detailed by Bardia et al [2], the equivalent static force from an earthquake event is developed from tabular data in building codes. In general, these procedures have proven to be safe and effective. However, this method assumes that deformation may occur but containment will be maintained. A similar assumption of deformation is contained in the modification factor used in building codes. If the vessel is expected to function after a specific earthquake event, such methods are not adequate for design. This paper addresses a more detailed procedure of seismic analysis that involves a finite element analysis of the vessel incorporating the interaction of the piping and the vessel. This methodology provides a better understanding of the localized stresses, such those as at vessel nozzles with pipe attached. This methodology may be used to analyze a vessel for a design that can be subjected to a specific earthquake response spectrum with minimal deformation and probable return to operation status.
Hydrodynamic Modeling of Detonations for Structural Design of Containment Vessels
Authors: Rodriguez Edward A. , Romero Christopher
Published: July 2008

Los Alamos National Laboratory (LANL), under the auspices of the U.S. Department of Energy (DOE) and the National Nuclear Security Administration (NNSA), has been conducting confined high explosion experiments utilizing large, spherical, steel pressure vessels to contain the reaction products and hazardous materials from high-explosive (HE) events. Structural design of these spherical vessels was originally accomplished by maintaining that the vessel’s kinetic energy, developed from the detonation impulse loading, be equilibrated by the elastic strain energy inherent in the vessel. In some cases, the vessel is designed for one-time use only, efficiently utilizing the significant plastic energy absorption capability of ductile vessel materials [1]. Alternatively, the vessel can be designed for multiple use, in which case the material response is restricted to the elastic range [2]. Within the last decade, designs have been accomplished utilizing sophisticated and advanced 3D computer codes that address both the detonation hydrodynamics and the vessel’s highly nonlinear structural dynamic response. This paper describes the hydrodynamic modeling of HE reaction products phase, which produces transient pressures resulting in an impulsive load on the vessel shell. Modeling is accomplished through either (a) empirical/analytical methods utilizing a vast experimental database developed primarily for the Department of Defense (DoD) or (b) through application of numerical hydrodynamics codes, such as the Sandia National Laboratories (SNL) shock-wave physics code, CTH [3], which accurately model the thermochemistry and thermophysics of a detonation. It should be noted that this paper only addresses blast load prediction using the methods stated and does not include an assessment of structural response methods.
Fatigue Analysis of Compound Cylinder Subjected to Repeated Internal Pressure
Authors: Patil Sunil A.
Published: July 2008

The cylindrical vessels are used for storing fluids at high pressure. If the magnitude of the internal/external pressure is closer to the yield strength of the material used, then no thickness of the material will prevent the failure of the vessel. Hence shrink-fitted compound cylinders are used, which can store the fluids at higher pressure closer to the yield stress of the material. Optimally designed compound cylinder has equal maximum hoop stress in both — the inner and outer cylinders. The value of this hoop stress is closer to the value of yield stress of the material used. Such compound cylindrical vessels can be used in future automobile and space vehicles for storing gaseous fuels. In such case, the compound cylinder will be subjected to repeated loading — the internal pressure varying from zero to maximum value. In this paper, an effort is made to analyze the compound cylinder under fatigue loading by using ANSYS DesignSpace FEA software. The analysis is interesting because the inner cylinder is subjected to fluctuating hoop stress varying in magnitude and direction; and the outer cylinder is subjected to hoop stress varying in magnitude only. Finally an effort is made to find out the optimum thickness of both the cylinders under fatigue loading.
Development of a New Generation Computer Code (PRO-LOCA) for the Prediction of Break Probabilities for Commercial Nuclear Power Plants Loss-of-Coolant Accidents
Authors: Rudland David L. , Xu Heqin , Wilkowski Gery , Scott Paul , Ghadiali Nu , Brust Frederick
Published: July 2008

In order to aid the Nuclear Regulatory Commission (NRC) in the process of making a risk-informed revision of the design-basis break size requirements for operating commercial nuclear power plants, a new probabilistic computer code (PRO-LOCA) is being developed, This code will aide the NRC in predicting leakage and rupture probabilities for critical piping systems as a function of break sizes. The PRO-LOCA code incorporates many enhancements in technology developed since some of the earlier probabilistic codes (e.g., PRAISE) were developed. These enhancements include improved crack stability analyses, improved leak rate models, improved weld residual stress solutions, improved crack initiation models, and new material property data. In addition, new degradation mechanisms, not previously considered in codes such as PRAISE were added. This included the addition of primary water stress corrosion cracking (PWSCC) for dissimilar welds in pressurized water reactors (PWRs). This paper reviews the development of the PRO-LOCA code by giving a brief description of its capabilities and the models embedded in the code. The current version of the PRO-LOCA code was used for a series of sensitivity analyses in order to test the robustness of the code for a full range of input parameters and to identify which input parameters have the greatest effect on the predicted leakage probabilities. The results from these sensitivity analyses are presented, as well as comparisons with other PFM codes (PRAISE). Details of which parameters appear to affect the leakage probabilities and the plans for future improvements to the code conclude this paper.
Detonation Chamber of Chemical Munitions: Its Design Philosophy and Operation Record at Kanda, Japan
Authors: Asahina Joseph K. , Shirakura Takao
Published: July 2008

Destruction of chemical weapons is a technical area that involves extensive international cooperation, with open discussion among a wide variety of participants aimed at elimination of these weapons of mass destruction. The most common methods for destruction of chemical weapons are: (1) chemical neutralization and (2) incineration after separation of the chemical agent from the weapon’s explosive charge. When the munitions are stockpiled, the agent and the explosive charge are easily separated by means of reverse assembly or water jet cutting. However, for munitions that are not stockpiled, complete separation of agent and explosive charge is nearly impossible.
Determination of C2 Stress Index of Back-to-Back Welded Piping Bends Using Finite Element Method
Authors: Vlaicu Dan , Aggarwal Manohar Lal , Li Ming
Published: July 2008

In current ASME Boiler and Pressure Vessel Code, the C2 stress index for back-to-back elbows welded together is taken as the product of the C2 index of the elbow and the C2 index of the girth butt weld. In recent years, many finite element analyses studies have been conducted on the elbow C2 index itself which have found that the code C2 value is conservative. The girth butt weld C2 given in the code resulted from analytical studies on transition joint between two straight pipes. While the code considers that the secondary stress due to the weld reinforcement including the effect from the mismatch to be small and practically negligible for a thick pipe, it recommends a formula to calculate C2 for weld in a thin pipe of thickness less than 0.237”. The purpose of this paper is to present an approach that C2 caused by weld mismatch can be determined by finite element analysis. Back-to-back bends are modeled with 2 typical configurations: in-plane and out-of-plane. Parametric studies of linear elastic secondary stresses are carried out to determine the “worst possible” two bend central line mismatch. The stress indices at elbows and weld location are established. It is found that the C2 index based on the code formula is overly conservative for back-to-back welded pipe bends and the multiplication by the C2 index of the weld is not needed.
Effect of Biaxial Stress on Crack Driving Force
Authors: Shen G. , Tyson W. R.
Published: July 2008

A stress-strain equation of Ramberg-Osgood type is proposed to correlate the longitudinal stress with longitudinal strain of a thin plate when a constant stress is applied transversely. The same approach can be used to correlate the axial stress with axial strain for a thin-walled pipe in axial tension with internal pressure. The proposed stress-strain equation relating the longitudinal stress and strain closely approximates that of deformation theory. The effect of a secondary stress (hoop stress) on the J-integral for a circumferential crack in a pipe under axial load and internal pressure is evaluated by finite element analysis (FEA). The results show that the J-integral decreases with internal pressure at a given axial stress but increases with internal pressure at a given axial strain. It is concluded that while a secondary stress may be safely neglected in a stress-based format because it decreases the driving force at a given applied stress, it should not be neglected in a strain-based format because it significantly increases the driving force at a given applied strain.
Standardisation of High Temperature Crack Growth Testing of Weldments
Authors: Dogan B. , Ceyhan U. , Nikbin K. , Dean D.
Published: July 2008

A European collaborative effort has been made to produce a Code of Practice (CoP), with participation from the European Structural Integrity Society (ESIS) TC11-Working Group on High Temperature Testing of Weldments (WG on HTTW) and EC project CRETE. The prepared CoP is based on the authors’ and project partners’ long years of experience in the subject field of high temperature testing, deformation studies and crack growth on various materials studied in internal, European and international projects. The code is being processed for ISO standardization by the International Institute of Welding (IIW), Select Committee Standardization (SC STAND). Guidelines are established for material and specimen selection. The document aims at giving advice on testing, measurements and analysis of creep crack initiation and growth data for a range of creep brittle to creep ductile materials. It may be used for material selection criteria and inspection requirements for damage tolerant applications. In quantitative terms, it can be used to assess the individual and combined effects of metallurgical, fabrication, operating temperature, and loading conditions on welded components for high temperature service. The present paper reports on the standardisation of high temperature crack initiation and crack growth testing in weldments. The material behaviour in service, including significance of creep and loading, substantiates the testing and data analyses procedure for design as well as fitness-for-purpose assessment.
Hydrogen Storage Tank Systems and Materials Selection for Transport Applications
Authors: Dogan B.
Published: July 2008

The present international socio-economic drive for renewable energy use for sustainable development with environmental protection directs attention to hydrogen as energy carrier. Hydrogen production and storage, and fuel cell (FC) technologies have been intensively worked on in Europe including European Commission (EC) supported projects via Framework Programs (FPs), as well as various national and international cooperative programs including those of International Energy Agency (IEA) and International Partnership for Hydrogen Economy (IPHE). The hydrogen storage is required for transport applications as dense as possible to achieve high gravimetric and volumetric density. The storage of hydrogen in liquid, gas and solid forms are associated with low temperature cooling, higher pressures up to 700 bar and integrated higher volume and weight, respectively. The liquid and pressurized gas storage systems are relatively advanced in present applications. On the other hand, the system safety and reliability, hence the public acceptance as well as economic feasibility have been the main drives for solid and hybrid hydrogen applications. The use of solid hydrogen is predicted by the automotive industry to ultimately dominate the hydrogen transport application market. The bottleneck in solid hydrogen application is metal hydride production to meet the quantitative targets for vehicles mainly following the US DOE goals set for years up to 2015. System requirements need also be met for a present target of e.g. 75kWel fuel cell cars aiming at a 400km driving distance with 4 kg of hydrogen. This necessitates a gravimetric storage density of over 6 wt. per cent. The present paper will address the hydrogen storage tank system for on-board applications including storage tank materials, system design, production technologies and system safety. An overview will be presented on the current state-of-the-art of European and international progress on storage materials integrated into on-board storage tank system. The European current programs on hydrogen storage technologies for transport applications including design, safety and system reliability will be addressed.
Flow Interaction With Composite Wall
Authors: Hamadiche Mahmoud , Kizilova Natalya
Published: July 2008

Stability of the steady flow of a viscous liquid through the thick-walled multilayered viscoelastic tubes with different rheological properties of the layers for no stress boundary conditions at the outer surface of the tube is investigated. The eigen values of the system are found. The influence of the material parameters of the layers and the Reynolds number on the spatial and temporal amplification rate of the most unstable mode is investigated. It is shown that the system can be stabilized by increasing the shear modules of the inner and middle layers. The temporal amplification rate significantly decreases and becomes negative with increasing the shear modules of the outer layer, that corresponds to temporal stability of the system. The comparative study of the obtained dependences with the solution of the same problem at no displacement boundary conditions is carried out. The results may be applied to the fluid flows in the ducts of different technical devices as well as to the blood flow in the arteries and veins which are composed of three layers with different functions, structure and material parameters.
Investigation of Hydrogen Assisted Cracking in Pressure Vessels
Authors: Homrossukon Samerjit , Mostovoy Sheldon , Todd Judith A.
Published: July 2008

Hydrogen assisted cracking (HAC) has been investigated in high strength 4140 and low strength Z17D pressure vessel steels, charged at −50 mA/cm2 in 1N H2SO4 + 25 mg/1 As2O3 and tested under three-point bend decreasing load. The HAC growth rate for Z17D steel (1.4×10−7 cm/s) was found to be approximately two orders of magnitude slower than that of 4140 steel (3.3×10−5 cm/s), while the threshold stress intensity factor for Z17D steel (∼37 MPa√m) was significantly higher than that of 4140 steel (∼7 MPa√m). This research will show that a single analytical model, based on the hypothesis that hydrogen both reduces crack resistance (R) and increases crack driving force (G), can explain HAC in 4140 and Z17D steels. The model predicts the hydrogen concentration required to initiate HAC as a function of the stress intensity factor and yield strength of the steel. Hydrogen-induced reduction of R was found to dominate HAC in 4140 steel, while hydrogen-induced reduction of R was combined with an increase in G for HAC cracking of Z17D steel.
Ventilation Duct Fire Dampers and Shock Valves
Authors: Borresen Bent A. , Saeter Olav , Uldalen Stein Erik
Published: July 2008

Buildings located in industrial gas production areas are normally designed to withstand explosion pressures from a design accidental event in the plant. To protect personnel and equipment inside buildings, installation of shock valves is the normal procedure. Experience with shock valves is, however, that they require maintenance, are expensive, have corrosion problems, and add pressure losses in the ventilation system. Alternatives are to reinforce fire and gas dampers in areas where shock pressures are moderate. Design pressures and possible effects of damping chambers and location of dampers are important variables. The paper summarizes some of the main results and conclusions provided from a study done for the Norwegian company Hydro Oil & Energy. The main conclusions drawn are as follows: Fortification shock waves have normally significantly shorter durance compared to explosion pressures from a typical accident in a gas process plant, and fortification design guidelines should not be used directly. Dampers should be designed to withstand pressures 1.5–1.8 times the side-on shock pressures unless the dampers are mounted flush with the building wall or roof, due to the reflecting shock pressure from a closed damper mounted inside a ventilation duct.
Seismic Considerations for the Transition Break Size: An Overview of the Methodology
Authors: Wilkowski G. , Xu H. , Krishnaswamy P. , Chokshi N. , Shaukat S. , Hiser A. , DeGrassi G. , Johnson J. J. , Olson R.
Published: July 2008

This paper describes the results of a study, sponsored by the U.S. Nuclear Regulatory Commission (NRC), to assess potential seismic effects on the postulated transition break size (TBS) in the proposed risk-informed revision of the regulatory requirements for the emergency core cooling system (ECCS) contained in Title 10, Section 50.46, of the Code of Federal Regulations (10 CFR 50.46). The full report was provided on the NRC web site in mid-December 2005. The primary focus of this paper is to provide a summary of the study’s approach and results which was conducted to facilitate review and comment concerning the proposed rule and statement of considerations (SOC), entitled “Risk-Informed Changes to Loss-of-Coolant Accident Technical Requirements; Proposed Rule,” which the NRC published in the Federal Register (70 FR 67598) on November 7, 2005.
Examination of Service Cracks in CRDM Nozzles and Relevance to Flaw Evaluation Procedures
Authors: Wilkowski G. , Rudland D. , Xu H.
Published: July 2008

In Section XI of the ASME B&PV Code, a flaw evaluation procedure was recently developed for axial surface cracks in control-rod-drive mechanism (CRDM) nozzles in PWR reactor pressure vessel heads, i.e., Code Case N694-1 and IWB-3660. Some of the aspects of the analysis procedures are not rigorously defined due to numerous unknown aspects of this complicated problem. The U.S. operators of PWR plants were required by the NRC to make inspections of their CRDM nozzles and report the inspection results. The data was recently analyzed to assess how the flaw sizes develop and how that might provide guidance to the ASME flaw evaluation criterion. The results from numerous plants showed that the surface cracks tend to develop with a relatively constant aspect ratio for a certain plant, but that aspect ratio can significantly change from plant to plant. Using weld residual stresses and operating stresses with rigorous K-solutions for the depth and length of the surface cracks and the PWSCC crack growth rates, however, predicts surface flaws that would be much shorter in length than occur in service. It is suggested that rather than calculating the length of the surface flaws using the K-solutions, that the growth in the depth direction be calculated using the K-solutions (with some additional guidance) and the length be based on the aspect ratios found in the particular plants.
Measurement of Residual Stress in as Received and Repaired Clad Components
Authors: Ohms Carsten , Truman Chris , Wimpory Robert C. , Gripenberg Hans , Smith David , Youtsos Anastasius G.
Published: July 2008

The application of welded austenitic stainless steel claddings to thick ferritic steel pressure vessels has been used as a means of protection of pressure vessels operating in corrosive environments for decades. Cladding could — in some ways — be considered a predecessor of modern coating techniques that for many reasons is still applied in “modern” times. The process of cladding introduces considerable residual stresses because of the large amount of thermal energy added to the component locally, and because two dissimilar materials are joined with different thermo-mechanical properties. Such residual stress fields around the materials interface are of considerable interest as they could strongly contribute to the generation and propagation of interfacial cracks. The assessment of such stresses by experimental means is particularly challenging because of the size clad components would normally have and because of the sharp stress gradient that would be expected near the materials interface. Clad components containing weld repairs are even more complicated to investigate. Three residual stress measurement methods applied to various clad components are presented in this paper: neutron diffraction, deep hole drilling and the ring core method. Residual strains and stresses have been measured by these methods in a non-repaired clad component and in three components containing weld repairs of different sizes. The measurement methods are described with giving emphasis to their respective strengths and weaknesses for these particular applications. In the case of neutron diffraction three different experimental approaches have been used. The way, in which the measurement techniques have been applied on the different components, is explained and an overview of the experimental results is given. In several cases good agreement between test results has been obtained. For example, all tests show a high tensile stress in the cladding layer of the non-repaired component. In other cases, stress magnitudes found were not in excellent agreement, amongst others due to differences in specimen preparation. The paper is concluded with a critical revue of the applicability of these stress measurement methods to welded claddings based on the results obtained.