bluuebunny/crossref_metadata_2025 huggingface dataset:
Impacting Effects of Seismic Loading in Feeder Pipes of PHWR Power Plants
Authors: Kumar R.
Published: February 2008

The core of a pressurized heavy water reactor (PHWR) consists of a large number of fuel channels. These fuel channels are connected to the feeder pipes through which the heavy water flows and transports heat from the reactor core to the steam generators. The feeder pipes are several hundreds in number. They run close to each other with small gaps and have several bends. Thus they represent a complex piping system. Under seismic loading, the adjacent feeder pipes may impact each other. In this paper a simplified procedure has been established to assess such impacting effects. The results of the proposed analysis include bending moment and impact force, which provide the stresses due to impacting effects. These results are plotted in nondimensional form so that they could be utilized for any set of feeder pipes. The procedure used for studying the impacting effects includes seismic analysis of individual feeder pipes without impacting effects, selection of pipes for impact analysis, and estimating their maximum impact velocity. Based on the static and dynamic characteristics of the selected feeder pipes, the maximum bending moment, impact force, and stresses are obtained. The results of this study are useful for quick evaluation of the impacting effects in feeder pipes.
Bending Stresses at Longitudinal Weld Joints of Pressurized Cylindrical Shells due to Angular Distortion
Authors: Ong L. S. , Hoon K. H.
Published: February 2008

This article presents a simple second-order theory for the determination of bending stresses which arise at the longitudinal welded joint of a pressurized, cylindrical shell subject to peaking, i.e., angular misalignment. Although this problem has been studied quite extensively over the years by a few authors and a few versions of simple formulas are available for the calculations of bending stresses at the welded joint, it is noted these formulas show considerable discrepancies when compared with the finite element solutions. As the additional bending stresses at the weld joint will lead to a shorter fatigue life of the joint, an improved theory to predict the peak stress at the weld joint, such as the one presented in this article, would be important and of interest to the design engineer and vessel inspector. The present theory has been validated against finite element results and shown to be extremely accurate.
A Finite Element for the Analysis of Shell Intersections
Authors: Koves W. J. , Nair S.
Published: February 2008

A specialized shell-intersection finite element, which is compatible with adjoining shell elements, has been developed and has the capability of physically representing the complex three-dimensional geometry and stress state at shell intersections (Koves, 1993). The element geometry is a contoured shape that matches a wide variety of practical nozzle configurations used in ASME Code pressure vessel construction, and allows computational rigor. A closed-form theory of elasticity solution was used to compute the stress state and strain energy in the element. The concept of an energy-equivalent nodal displacement and force vector set was then developed to allow complete compatibility with adjoining shell elements and retain the analytical rigor within the element. This methodology provides a powerful and robust computation scheme that maintains the computational efficiency of shell element solutions. The shell-intersection element was then applied to the cylinder-sphere and cylinder-cylinder intersection problems.
Vibrations of Fiber-Reinforced Laminated Deep Shells
Authors: Kumar V. , Singh A. V.
Published: February 2008

This paper deals with a numerical method for the free vibrational analysis of laminated deep shells. The strain-displacement relations are obtained for a general laminated shell geometry described by orthogonal curvilinear coordinates. Parabolic variation of transverse shear stresses along the thickness and the effects of rotary inertia are included in the formulation. The displacement fields are represented by Bezier patches. The shape and size of these patches are controlled by certain arbitrary points called control points. Owing to the special characteristics of these control points, the treatment of displacements, slopes, curvatures, etc., at a particular edge becomes very simple. Hence, the enforcement of boundary conditions along the edges is straightforward. Ritz-type solution procedure is used for the eigen-analysis of the shell structure. Numerical examples involving laminated spherical, conical, and cylindrical shells are investigated in detail. Such shell geometries usually have planes of symmetry; hence, only one-quarter of the shell is analyzed in this study. Good convergence of the natural frequencies is observed by using eighth-order Bezier functions. The results are compared with the existing sources in the literature. The influences of material strength and number of layers on the natural frequencies are also examined.
Study on the Stress Concentration at the Round Corners of Flat Heads in Pressure Vessels Subjected to Internal Pressure
Authors: Chen H. , Jin J. , Yu J.
Published: February 2008

Results from finite element analysis were used to show that the stress index kσ and the nondimensionalized highly stressed hub length kh of a flat head with a round corner in a pressure vessel subjected to internal pressure are functions of three dimensionless parameters: λ ≡ h/dt, η ≡ t/d, and ρ ≡ r/t. Approximate formulas for estimating kσ and kh from λ, η, and ρ p are given. The formulas can be used for determining a suitable fillet radius for a flat head in order to reduce the fabricating cost and to keep the stress intensity at the fillet under an acceptable limit.
Failure Cause Analysis—A Structural Approach
Authors: Gandhi O. P. , Agrawal V. P.
Published: February 2008

The paper presents a methodology to analyze failure cause of a system using structural approach based on digraph and matrix method. Failure causality digraph models the failure cause considering contributing events and their interaction in terms of cause-effect relation, i.e., causality. Failure cause function (VPF − fc) is obtained from the permanent matrix, obtained from the digraph, which is characteristic of the failure cause. The procedure is useful, not only for the analysis, but also for identification, comparison, and evaluation of the failure cause. The coefficients of similarity and dissimilarity, and identification set based on these are also proposed. These are useful for comparison of two failure causes. In addition, failure cause index (Ifc) derived from VPF − fc is proposed which evaluates and ranks failure causes of the system. The method permits analysis, identification, and comparison at design as well as operating state of the system and provides the user directions for minimizing the failure causes leading to improvement of the system reliability. The procedure is developed using an example of weld defects.
A New Method of Nondestructive Measurement for Assessment of Material Degradation of Aged Reactor Pressure Vessels
Authors: Ara K. , Ebine N. , Nakajima N.
Published: February 2008

A method, MIM (magnetic interrogation method), is proposed for nondestructive measurement of radiation damage of nuclear reactor pressure vessels. The method relies on good correlation between the levels of radiation-induced hardness change and magnetic coercivity change in pressure vessel steel. A part of the pressure vessel to be inspected is magnetized with two-pole magnetic yokes through the overlay clad of nonmagnetic stainless steel, and magnetic field distributions on the surface of overlay clad are measured in the vicinity of the poles of magnetic yokes. Then, the coercivity distribution in the direction of thickness in the pressure vessel steel is inversely estimated from the measured magnetic field distribution patterns with aid of static magnetic field analysis. The level of radiation damage such as hardness change is assessed with relation to the estimated coercivity distributions.
Constraint Effects of Clad on Underclad Crack
Authors: Miyazaki N. , Ikeda T. , Ochi K.
Published: February 2008

The finite element method is applied to two-dimensional elastic-plastic analyses for underclad crack problems. The analyses are performed for rectangular specimens with an underclad crack, which are composed of A533B class 1 steel and a clad material, to obtain the fracture mechanics parameter J-integral and the stress distribution ahead of a crack tip. The Q-factor proposed by O’Dowd and Shih is calculated from the stress distribution ahead of a crack tip, and the constraint effect of a crack tip due to a clad material or the effect of a clad material on the fracture toughness of a base material is discussed in terms of the Q-factor. Clad thickness, crack length, and the material property of a clad material are varied to examine their effects.
A Study on the Buckling of Rectangular Bellows Under Pressure Loads
Authors: Nishiguchi I. , Tanaka M. , Kaji Y. , Muto Y. , Koizumi K.
Published: February 2008

We have studied the buckling behavior of rectangular bellows under pressure loads. Our final objective is to establish the design guidelines for the rectangular bellows of an experimental fusion reactor, the ITER, the International Thermonuclear Experimental Reactor. Based on the numerical investigation by the FEM, we proposed a simplified method to evaluate the buckling pressure. The evaluation method of the buckling pressure for circular bellows can be found, for example, in the standards of the expansion joint manufacturers association in the U.S.A. (EJMA Standards). For rectangular bellows, however, investigation of the buckling behavior is limited, and EJMA does not provide a method for evaluating the buckling pressure. Therefore, we investigated the buckling behavior of rectangular bellows by the FEM and proposed a simplified evaluation method based on the half-pitch model.
A Serviceability Approach for Carbon Steel Piping to Intermittent High Temperatures
Authors: Ratiu M. D. , Moisidis N. T.
Published: February 2008

Carbon steel piping (e.g., ASME SA-106, SA-53), is installed in many industrial applications (i.e., diesel generator exhaust manifold) where the internal gas flow subjects the piping to successive short time exposures at elevated temperatures up to 1100°F. A typical design of this piping without consideration for creep-fatigue cumulative damage is at least incomplete if not inappropriate. Also, a design for creep-fatigue, usually employed for long-term exposure to elevated temperatures, would be too conservative and will impose replacement of the carbon steel piping with heat-resistant CrMo steel piping. The existing ASME Standard procedures do not explicitly provide acceptance criteria for the design qualification to withstand these intermittent exposures to elevated temperatures. The serviceability qualification proposed is based on the evaluation of equivalent full temperature cycles which are presumed/expected to be experienced by the exhaust piping during the design operating life of the diesel engine. The proposed serviceability analysis consists of: (a) determination of the permissible stress at elevated temperatures, and (b) estimation of creep-fatigue damage for the total expected cycles of elevated temperature exposures following the procedure provided in ASME Code Cases N-253-6 and N-47-28.
Technical Basis for the Extension of ASME Code Case N-494 for Assessment of Austenitic Piping
Authors: Bloom J. M.
Published: February 2008

In 1990, the ASME Boiler and Pressure Vessel Code for Nuclear Components approved Code Case N-494 as an alternative procedure for evaluating flaws in light water reactor (LWR) ferritic piping. The approach is an alternate to Appendix H of the ASME Code and allows the user to remove some unnecessary conservatism in the existing procedure by allowing the use of pipe specific material properties. The Code case is an implementation of the methodology of the deformation plasticity failure assessment diagram (DPFAD). The key ingredient in the application of DPFAD is that the material stress-strain curve must be in the format of a simple power law hardening stress-strain curve such as the Ramberg-Osgood (R-O) model. Ferritic materials can be accurately fit by the R-O model and, therefore, it was natural to use the DPFAD methodology for the assessment of LWR ferritic piping. An extension of Code Case N-494 to austenitic piping required a modification of the existing DPFAD methodology. Such an extension was made and presented at the ASME Pressure Vessel and Piping (PVP) Conference in Minneapolis (1994). The modified DPFAD approach, coined piecewise failure assessment diagram (PWFAD), extended an approximate engineering approach proposed by Ainsworth in order to consider materials whose stress-strain behavior cannot be fit to the R-O model. The Code Case N-494 approach was revised using the PWFAD procedure in the same manner as in the development of the original N-494 approach for ferritic materials. A lower-bound stress-strain curve (with yield stress comparable to ASME Code specified minimum) was used to generate a PWFAD curve for the geometry of a part-through wall circumferential flaw in a cylinder under tension and bending. Earlier work demonstrated that a cylinder under axial tension with a 50-percent flaw depth, 90 deg in circumference, and radius to thickness of 10, produced a lower-bound FAD curve. Validation of the new proposed Code case procedure for austenitic piping was performed using actual pipe test data. Using the lower-bound PWFAD curve, pipe test results were conservatively predicted (failure stresses were predicted to be 31.5 percent lower than actual on the average). The conservative predictions were attributed to constraint effects where the toughness values used in the predictions were obtained from highly constrained compact test specimens. The resultant development of the PWFAD curve for austenitic piping led to a revision of Code Case N-494 to include a procedure for assessment of flaws in austenitic piping.
Flow-Induced Wear in Steam Generator Tubes—Prediction Versus Operational Experience
Authors: Au-Yang M. K.
Published: February 2008

Many nuclear steam generators have accumulated more than 10 effective-full-power-years of operation. Eddy-current inspections revealed that a number of these steam generator tubes, notably those located in high local cross-flow regions, have indications of wear at some support plate elevations after 5 to 10 yr of effective-full-power operations. In the last 5 yr, a number of technical papers on nonlinear tube bundle dynamics has been published to address the effect of tube and support plate interactions. At the same time, test data relating wear and tube wall thickness losses for different material combinations and different support plate geometries became available. Based on the available data in the literature, as well as data obtained in the author’s affiliation, this paper assesses the cumulative tube wall wear after 5, 10, and 15 effective-full-power years of operation of a typical commercial nuclear steam generator, using different wear models. It is hoped that this study will shed some light on the probable mechanism that caused the observed wear in today’s operating nuclear steam generators.
Analytical Study on Fatigue Strength Reduction Factor of Small-Diameter Socket-Welded Pipe Joints
Authors: Higuchi M. , Nakagawa A. , Iida K. , Hayashi M. , Yamauchi T. , Saito M. , Sato M.
Published: February 2008

Four-point bending and rotating bending fatigue tests were conducted on socket-welded joints made of carbon, stainless, and Cr-Mo steels for clarification of the effects of diameter, welding pass sequence and post-weld heat treatment (PWHT) on fatigue strength. The results were evaluated quantitatively. Fatigue strength of socket-welded joints was found to strongly depend on weld pass sequences in fillet welds, this being possibly due to large change in residual stress distribution at roots and toes. The effects of residual stress were thus examined quantitatively by comparison of fatigue strength of PWHT stress-free specimens with that of as-welded specimens. By the modified Goodman’s method, the lowest S-N curve corresponding to maximum tensile residual stress and the highest S-N curve corresponding to maximum compression residual stress were obtained for different steels and diameters. Conventional S-N data of socket-welded joints were situated between these two limiting curves. Based on the lowest curve, fatigue strength reduction factors of socket-welded joints were proposed.
Pipe Whip: In-Plane Whipping of Bent Cantilever Pipes
Authors: Reid S. R. , Yang J. L.
Published: February 2008

The dynamic elastic-plastic behavior of a bent cantilever pipe subjected to an in-plane force pulse at its tip is described. A theoretical model based on a large deflection formulation of dynamic beam theory is described. This takes into account the plastic hardening-softening behavior which is characteristic of a pipe when it is subjected to large changes in curvature. This beam model was first formulated and applied by Reid et al. (1995b, 1996), who demonstrated that it was able to describe quite accurately the characteristics of freely whipping, straight cantilever pipes. The present paper extends this model to enable it to be applied to bent cantilever pipes and covers cases in which the bend angle is opened or closed. Previous attempts (Wang, 1991) to analyze these problems using a rigid, perfectly plastic model were not completely successful due to the inability to identify admissible modes of deformation for all circumstances. A systematic program of pipe whip tests has been carried out in UMIST on right-angled bent pipes. To illustrate the validity and use of the theoretical model, two typical cases are considered and the results compared with the experimental data extracted from high-speed films of the tests. Excellent agreement between the two is demonstrated.
Effect of Tube-to-Tube Ties on Fluidelastic Instability of Tube Arrays Exposed to Crossflow
Authors: Eisinger F. L. , Rao M. M.
Published: February 2008

Tube-to-tube ties and their arrangement within the tube array are shown to affect the onset of fluidelastic instability. The influence of tie arrangement for a single tube row and for an in-line tube array is obtained by numerical simulation using S. S. Chen’s unsteady flow theory. Maps of dimensionless critical velocities for groups of tubes consisting of two, three, four, and five tubes tied to each other are developed for several design configurations. It is shown that the stability limits can be raised by appropriate choice of tube group and tie location.
The Initiation of Environmentally Assisted Cracking in Semi-Elliptical Surface Cracks
Authors: James L. A.
Published: February 2008

A Criterion to predict under what conditions EAC would initiate in cracks in a high-sulfur steel in contact with low-oxygen water was recently proposed by Wire and Li (1996). This EAC initiation criterion was developed using transient analyses for the diffusion of sulfides plus experimental test results. The experiments were conducted mainly on compact tension-type specimens with initial crack depths of about 2.54mm. The present paper expands upon the work of Wire and Li by presenting results for significantly deeper initial semi-elliptical surface cracks. In addition, in one specimen, the surface crack penetrated weld-deposited cladding into the high-sulfur steel. The results for the semi-elliptical surface cracks agreed quite well with the EAC initiation criterion, and provide confirmation of the applicability of the criterion to crack configurations with more restricted access to water.
Buckling Analysis of Thick-Walled Composite Pipe Under Torsion
Authors: Huille A. , Yang C. , Pang S.-S.
Published: February 2008

Composite pipes have been utilized in the petrochemical industries where corrosion resistance and light weight are important. There is a need to calculate the buckling load for the pipe under torsion which develops from the structural loadings. An analytical model of composite pipe in torsion is developed during this study. Laminated anisotropic plate theory is utilized to derive the kinematics and constitutive relations of the pipe wall laminates. Solutions are obtained by using the Ritz method with suitable boundary conditions. Good agreement is found when comparing the present results with the analytical and experimental results from previous research.
Limit Load Analysis of Perforated Disks With Square Penetration Pattern
Authors: Rogalska E. , Ka¸kol W. , Guerlement G. , Lamblin D.
Published: February 2008

Limit load analysis of perforated disks with a square penetration pattern is presented. The results of limit analysis are used to obtain yield surfaces for solid material equivalent to perforated disk based on homogenization approach. Theoretical and experimental results are compared. Approximations of the yield surfaces are proposed.
On Design Formulas of U-Shaped Bellows
Authors: Hamada M. , Tsuda T.
Published: February 2008

The applicability of the following four design formulas of the single-ply unreinforced U-shaped bellows is examined: 1) Kellogg’s formula, 2) formula of EJMA, 3) formula by Hamada and Takezono, 4) formula by Hamada et al. Examination is carried out by comparing results of the design stress and the fatigue life estimated by these four formulas with each other and with experimental data.
A Probabilistic Model for Creep-Fatigue Failure
Authors: Harlow D. G. , Delph T. J.
Published: February 2008

We outline here a method for incorporating the scatter observed in creep rupture times and fatigue cycles-to-failure into a probabilistic model for creep-fatigue failure. We do this within the context of the well-known damage fraction summation rule. Various numerical methods for calculating the probability of failure for given creep-fatigue loading cycles are discussed.
The Effect of Water Flow Rate Upon the Environmentally Assisted Cracking Response of a Low-Alloy Steel: Experimental Results Plus Modeling
Authors: James L. A. , Lee H. B. , Wire G. L.
Published: February 2008

The presence of a critical concentration of sulfides at the tip of a crack is thought to be a prerequisite for environmentally assisted cracking (EAC) in low-alloy steels. Sulfides can be “supplied” to the crack tip by a growing crack intersecting and dissolving embedded MnS inclusions present in the steel as an impurity. Sulfides can be removed from the crack tip by diffusion, ion migration, fatigue pumping, or convection induced within the crack by external water flow. EAC can result when the supply of sulfides exceeds the loss by mass transport. This paper presents results of experiments conducted on relatively large semi-elliptical surface cracks subjected to mean free stream velocities of 0.56, 1.71, and 5.00 m/s. The two higher velocities resulted in mitigation of EAC, while the lowest did not. A computational fluid dynamics computer code, FIDAP®, was employed to model the interaction between the flow within the crack cavity and the free stream flow. The model demonstrated that the two highest free stream velocities produced a significant interaction between the two regimes, but that the lowest free stream velocity produced minimal interaction. Thus, there was good qualitative agreement between the experimental and analytical results.
Load Distribution Between Threads in Threaded Connections
Authors: Grewal A. S. , Sabbaghian M.
Published: February 2008

Threaded connections are commonly employed in axial load-bearing equipment and pressure vessel components. There are a number of parameters that affect the load distribution between the threads and the stress concentration at the thread roots. These include the thread form, the thickness of walls supporting the threads, the pitch of threads, number of threads engaged, and the boundary conditions. In this paper, the influence of these parameters on the load distribution between threads is reported. Load distribution analyses in threaded connections is performed by analytical and by finite element methods. Square and buttress-type threads have been considered. Three-dimensional nonlinear finite element analyses on threaded connections have been performed using MSC/NASTRAN finite element code. The effect of clearance between the nonmating faces of threads as well as the presence of a flexible media between the mating faces of threads are investigated.
Classical Versus Improved Thin Shell Theories: A Theoretical Argument or a Design Concern?
Authors: Simos N. , Chassapis C.
Published: February 2008

Differences in the response of thin nonshallow spherical shells resulting from the choice of the adopted shell theory (classical or improved) are addressed analytically and through a series of representative shell problems. The analytical approach utilized to study the variation between the two theoretical models is based on the response resulting from Singular loads. The differences are quantified in a set of problems that reflect on the assumptions used in formulating the analytical description of the two theories in question. The broad scope of this paper is to examine the impact of shear deformability, introduced by the improved theory on the stress field when amplified under specific loading and geometric conditions, when those are of primary concern to the engineers. Such cases associated with stress concentration around cutouts, interaction of shells with nozzles, stress field in the vicinity of concentrated surface loads, etc. The mathematical formulation is based on the derivation of appropriate Green functions and the computational scheme is formed upon a special type of boundary integral equation. Comparison solutions for stress concentration around circular cutouts of twisted and sheared shells, stress amplification in the junction of shell with nozzles, and local stress field induced by concentrated loads are presented for the two theories.
Weight-Saving Plastic Design of Pressure Vessels
Authors: Porowski J. S. , O’Donnell W. J. , Reid R. H.
Published: February 2008

Within the last two decades, the use of elastic finite element analyses to demonstrate design compliance with the rules of the ASME Code has become a generally accepted engineering practice. Linearized stresses from these analyses are commonly used to evaluate primary stresses. For redundant structures or complex structural details, the use of such analyses, instead of simple equilibrium models, often results in significant overconservatism. Direct use of finite element results is often preferred because equilibrium solutions are not unique and effective equilibrium models are not easily constructed for complex three-dimensional structures. However, finite element analyses include secondary stresses, even for pressure, mechanical, and shock loading. For primary stress evaluation, the ASME Code allows the use of inelastic methods based on lower-bound solutions and plastic analysis. For primary stresses, the Code requires equilibrium to be satisfied without violating the yield strength of the material. The use of finite element inelastic analysis to partition mechanically induced stresses into the primary and secondary categories was introduced by Porowski et al. (1993). The latter provides a detailed discussion of the technical approach and the results for the axisymmetric junction between the plate and shell in a pressure vessel. This example was selected by the Session Organizer as a benchmark case to compare the efficiency of various analytical approaches presented at the Session. The authors have since used this approach to design more efficient structures. The practical application of this method to reduce the weight of complex redundant structures designed to meet primary stress limits is described herein for a more complex three-dimensional case. Plastic design utilizes the ability of actual materials to find the most efficient load distribution. A heat exchanger subjected to pressure, accelerations, and nozzle external loads is evaluated as a practical example. The results of elastic analyses are compared with those obtained by inelastic analyses. It is shown that inelastic analyses can be used effectively to reduce the weight of structures using only modern PCs for the engineering computations, as illustrated in this paper.
A Study on the Large Ductile Deformations and Perforation of Mild Steel Plates Struck by a Mass—Part II: Discussion
Authors: Jones N. , Kim S.-B.
Published: February 2008

An experimental study into the ductile deformations and static and impact perforation of mild steel plates is reported in Part I. These results are discussed in this article and compared with other experimental data reported in the literature. The accuracy of various empirical formulas for the impact perforation of plates is also examined.
Effects of Compressibility on Flow Characteristics and Dynamics of Swing Check Valves—Part II
Authors: Botros K. K. , Roorda O.
Published: February 2008

Part II of this paper is concerned with two aspects of the dynamic behavior of swing-type check valves, namely, slamming of the disk and the maximum attainable reverse flow as the valve closes due to flow deceleration. Both aspects are well understood in incompressible flows, but not as well in applications involving fluids of relatively higher compressibility. A systematic approach in studying these phenomena in compressible flows is followed, and where possible, comparison with incompressible flow applications (e.g., water) is made. Both experimental and numerical investigations were carried out and results presented. Measurements were taken on an NPS 4 test rig in air and in water to provide fundamental comparisons of the two applications. The numerical investigation was based on the solution of the full equation of motion of the swing disk, including damping and counterbalance weights, and utilizing the valve opening-flow characteristics model developed in Part I in a quasi-steady manner. Transient flows in the connecting piping system upstream and downstream of the valve were analyzed based on the standard method of characteristics to solve the full one-dimensional conservation equations. Good agreement was obtained between numerical and experimental results which allowed further numerical investigations of the effects of various parameters in applications involving fluids of relatively higher compressibility.
An Experimental Investigation of the Interaction of Primary and Secondary Stresses in Fuel Plates
Authors: Swinson W. F. , Battiste R. L. , Yahr G. T.
Published: February 2008

If the load is not relieved as a structure starts to yield, the induced stress is defined as primary stress. If the load relaxes, as a structure begins to yield the induced stress is defined as secondary stress. In design, it is not uncommon to give more weight to primary stresses than to secondary stresses. However, knowing when this is good design practice and when it is not good design practice represents a problem. In particular, the fuel plates in operating reactors contain both primary stresses and secondary stresses, and to properly assess a design there is a need to assign design weights to the stresses. Tests were conducted on reactor fuel plates intended for the advanced neutron source (ANS) to determine the potential of giving different design weights to the primary and secondary stresses. The results of these tests and the conclusion that the stresses should be weighted the same are given in this paper.
An Explicit Weight Function for Semi-Elliptical Surface Cracks
Authors: Beghini M. , Bertini L. , Gentili A.
Published: February 2008

An explicit weight function which allows determination of the stress intensity factor for a semi-elliptical surface crack under arbitrary loading is proposed. It was derived by the approximate solution valid for an embedded elliptical crack in infinite body, and a suitable corrective function to account for the free surface effect was obtained on the basis of several accurate stress intensity factor solutions found in literature. By this weight function and a simple numerical quadrature, the SIF at any point of the crack front can be calculated for any loading condition. The method requires negligible time for model preparation and elaboration and little computing resources. It was tested for many crack shapes and loading conditions, and an accuracy of a few percent in the stress intensity factor evaluation was observed. This suggests using the proposed weight function in many practical problems, typical for pressure vessel technology, in which several fracture mechanics analyses are required.
Minimum Weight Design of Pressure Components Using R-Nodes
Authors: Mangalaramanan S. P. , Seshadri R.
Published: February 2008

A simple procedure uses the r-nodes to achieve minimum weight design of mechanical components and structures. The method is based on two linear elastic finite element analyses (or more) in order to arrive at a component configuration that would correspond to the minimum weight design. The proposed method is applied to pressure component configurations of practical interest.
Corrosion Fatigue Crack Growth in Clad Low-Alloy Steels—Part I: Medium-Sulfur Forging Steel
Authors: James L. A. , Auten T. A. , Poskie T. J. , Cullen W. H.
Published: February 2008

Corrosion fatigue crack propagation tests were conducted on a medium-sulfur ASTM A508-2 forging steel overlaid with weld-deposited alloy EN82H cladding. The specimens featured semi-elliptical surface cracks penetrating approximately 6.3 mm of cladding into the underlying steel. The initial crack sizes were relatively large with surface lengths of 30.3–38.3 mm, and depths of 13.1–16.8 mm. The experiments were conducted in a quasi-stagnant low-oxygen (O2 < 10ppb) aqueous environment at 243°C, under loading conditions (ΔK, R, and cyclic frequency) conducive to environmentally assisted cracking (EAC) in higher-sulfur steels under quasi-stagnant conditions. Earlier experiments on unclad compact tension specimens of this heat of steel did not exhibit EAC, and the present experiments on semi-elliptical surface cracks penetrating cladding also did not exhibit EAC.
Corrosion Fatigue Crack Growth in Clad Low-Alloy Steels—Part II: Water Flow Rate Effects in High-Sulfur Plate Steel
Authors: James L. A. , Lee H. B. , Wire G. L. , Novak S. R. , Cullen W. H.
Published: February 2008

Corrosion fatigue crack propagation tests were conducted on a high-sulfur ASTM A302-B plate steel overlaid with weld-deposited Alloy EN82H cladding. The specimens featured semi-elliptical surface cracks penetrating approximately 6.3 mm of cladding into the underlying steel. The initial crack sizes were relatively large with surface lengths of 22.8–27.3 mm, and depths of 10.5–14.1 mm. The experiments were initiated in a quasi-stagnant low-oxygen (O2 < 10 pph) aqueous environment at 243°C, under loading conditions (ΔK, R, cyclic frequency) conducive to environmentally assisted cracking (EAC) under quasi-stagnant conditions. Following fatigue testing under quasi-stagnant conditions where EAC was observed, the specimens were then fatigue tested under conditions where active water flow of either 1.7 m/s or 4.7 m/s was applied parallel to the crack. Earlier experiments on unclad surface-cracked specimens of the same steel exhibited EAC under quasi-stagnant conditions, but water flow rates at 1.7 m/s and 5.0 m/s parallel to the crack mitigated EAC. In the present experiments on clad specimens, water flow at approximately the same as the lower of these velocities did not mitigate EAC, and a free stream velocity approximately the same as the higher of these velocities resulted in sluggish mitigation of EAC. The lack of robust EAC mitigation was attributed to the greater crack surface roughness in the cladding interfering with flow induced within the crack cavity. An analysis employing the computational fluid dynamics code, FIDAP, confirmed that frictional forces associated with the cladding crack surface roughness reduced the interaction between the free stream and the crack cavity.
An Axisymmetric Method of Elastic-Plastic Analysis Capable of Predicting Residual Stress Field
Authors: Jahed H. , Dubey R. N.
Published: February 2008

Linear elastic solution of an axisymmetric boundary value problem is used as a basis to generate its inelastic solution. This method treats the material parameters as field variables. Their distribution is obtained as a part of solution in an iterative manner. Two schemes of updating material parameters are discussed and compared. A procedure for calculation of residual stress field is presented. Application of the method to autofrettage is presented. Residual stress calculation based on actual material curve, isotropic and kinematic hardening models, and variable Bauschinger effect factor (BEF) is carried out. It is concluded that consideration of dependency of BEF on plastic strain makes significant changes to residual hoop stress near the bore for low-level autofrettage. However, this dependency is insignificant for high-level autofrettage. Results obtained here are shown to be in good agreement with experimental and finite element results.
Modeling and Simulation of Crack Initiation and Growth in Particulate Composites
Authors: Kwon Y. W. , Lee J. H. , Liu C. T.
Published: February 2008

A micro/macromechanical approach was used to model and simulate crack initiation and crack propagation in particulate composite structures. The approach used both the micromechanical and macromechanical analyses in tandem. The micromechanical analysis was based on a simplified micromechanical model and damage mechanics at the micro-level, and the macromechanical analysis utilized the finite element method. In using these methods, crack initiation and growth in a general shape of composite structure were investigated with an efficient computational effort. It was assumed that a crack initiates and/or propagates when localized damage is saturated. As a result, the crack length was assumed to be the size of the saturated damage zone. Matrix crack initiation and propagation at circular notch tips were simulated using this approach. Modeling and simulation were also conducted for cases of nonuniform particle distribution in particulate composite structures. Predicted results showed a good agreement with the experimental data.
Conceptual Models for Understanding the Role of the R-Nodes in Plastic Collapse
Authors: Mangalaramanan S. P.
Published: February 2008

The r-nodes (redistribution nodes) are locations in mechanical components and structures that are load-controlled, and therefore insensitive to material constitutive relationships. These locations and their respective equivalent stress values can be approximately determined on the basis of two linear elastic analyses. By invoking equilibrium considerations, a simple relationship can be established between the “combined r-node equivalent stress” and the plastic collapse loads. On account of its load-controlled nature, the combined r-node equivalent stress can be identified with the reference stress, which is extensively used in carrying out pressure component integrity assessments. The concept of r-nodes is also related to the primary stresses in pressure components, and in designing mechanical components and structures for minimum weight. This paper proposes simple phenomenological models in an attempt to characterize the functioning of r-nodes.
Designing Piping Systems Against Acoustically Induced Structural Fatigue
Authors: Eisinger F. L.
Published: February 2008

Piping systems adapted for handling fluids such as steam and various process and hydrocarbon gases through a pressure-reducing device at high pressure and velocity conditions can produce severe acoustic vibration and metal fatigue in the system. It has been determined that such vibrations and fatigue are minimized by relating the acoustic power level (PWL) to being a function of the ratio of downstream pipe inside diameter D2 to its thickness t2. Additionally, such vibration and fatigue can be further minimized by relating the fluid pressure drop and downstream Mach number to a function of the ratio of downstream piping inside diameter to the pipe wall thickness, as expressed by M2 Δp = f(D2/t2). Pressure-reducing piping systems designed according to these criteria exhibit minimal vibrations and metal fatigue failures and have long operating life.
Prediction of Failures of Low-Pressure Steam Turbine Disks
Authors: Liu C. , Macdonald D. D.
Published: February 2008

Localized corrosion phenomena, including pitting corrosion, stress corrosion cracking, and corrosion fatigue, are the principal causes of corrosion-induced damage in electric power-generating facilities and typically result in more than 50 percent of the unscheduled outages. In this paper, we describe a deterministic method for predicting localized corrosion damage in low-pressure steam turbine disks downstream of the Wilson line, where a condensed, thin electrolyte layer exists on the steel disk surfaces. Our calculations show that the initiation and propagation of stress corrosion cracking (SCC) is not very sensitive to the oxygen content of the steam, but is sensitive to the conductivity of the condensed liquid layer and the stresses (residual and operational) that the disk experiences in service.
Effects of Residual Stress on Fatigue Strength of Small-Diameter Welded Pipe Joint
Authors: Yamashita T. , Hattori T. , Iida K. , Nomoto T. , Sato M.
Published: February 2008

Bending fatigue tests were conducted to investigate the fatigue strength of small-diameter socket welded pipe joints. In most cases of large-diameter socket joints, a fatigue crack started from the root of the fillet weld, though the stress amplitude at the root was smaller than that at the toe of the fillet weld. Additionally, the fatigue strength was affected by the weld bead sequence. The residual stress was considered to be one of the important parameters governing fatigue strength; therefore, its effects were investigated. In several types of pipe joints, the local stress and residual stress distributions were calculated by finite element analysis. The residual stresses were compressive at the toe and tensile at the root of the socket welded joints. Based on these results, the effects of residual stresses on the fatigue strength are discussed for small-diameter welded pipe joints in the present work.
The Influence of Higher Modes and Support Gaps on the Seismic Response of Piping Systems Containing Snubbers
Authors: Abu-Yasein O. A. , Lay C. , Pickett M. A. , Madia J. , Sinha S. K.
Published: February 2008

In this study of flexible piping systems (0.6 to 6.6 Hz), it was shown that the fundamental mode was not always the most significant mode of vibration. This study also concluded that variations in support condition do not significantly influence response in terms of nodal stress, fundamental frequency, and contribution of higher modes. In terms of support stiffness, the ratio of the magnitude of the gap (the total of all the mechanical tolerances and deadbands in the snubber support system) to the magnitude of the support nodal displacement was found to be more important than the actual magnitude of the gap. Additionally, when the magnitude of the nodal displacement exceeded the gap magnitude by a factor of about five or more, support stiffness was found to remain relatively constant.
Numerical Simulations of Full-Scale Corroded Pipe Tests With Combined Loading
Authors: Roy S. , Grigory S. , Smith M. , Kanninen M. F. , Anderson M.
Published: February 2008

The ANSI/ASME B31G guideline has been useful to pipeline operators in assessing the integrity of corroded line pipe. Because large safety margins have had to be incorporated, the guidelines can be excessively conservative, which in turn can force costly repairs and replacements that may not actually be necessary. On the other hand, because the current guidelines consider only pressure loading and neglect bending and axial compression, they could give nonconservative failure predictions when combined loading exists. Therefore, a study was initiated to develop a theoretically sound methodology for assessing the integrity of corroded line pipe subjected to combined loading. A key step in the successful application of this methodology is the development of a sophisticated three-dimensional finite element procedure that can accurately simulate full-scale pipe tests under conditions of combined loading. This paper describes thirteen full-scale failure tests on artificially corroded pipes subjected to simultaneous internal pressure, bending, and longitudinal compression and presents a detailed account of the finite element analysis procedure that was developed to simulate these tests numerically. Additional finite element analyses that were conducted to investigate the effect of key parameters on failure, and to expand the corroded pipe failure database, are also discussed.
On Free Vibrations of an Embedded Anisotropic Spherical Shell
Authors: Chen W. Q. , Ding H. J.
Published: February 2008

In this paper, free vibrations of a spherically isotropic spherical shell embedded in an elastic medium of Pasternak type are studied by using a six-mode shell theory that includes effects of shear deformation, rotary inertia, and transverse normal strain. The separable homogeneous solution for displacements and stresses in a deep spherical shell is derived and two classes of vibrations are obtained by the introduction of five auxiliary variables. Numerical results are compared with those predicted by two simpler shell theories mentioned in the paper and those by three-dimensional elastic theory.
Optimal Design of Laminated Cylindrical Pressure Vessels for Maximum External Pressure
Authors: Walker M. , Reiss T. , Adali S.
Published: February 2008

Finite element solutions are presented for the optimal design of hemispherically and flat-capped symmetrically laminated pressure vessels subjected to external pressure. The effect of vessel length, radius, and wall thickness, as well as bending-twisting coupling and hybridization on the optimal ply angle and buckling pressure are numerically studied. Comparisons of the optimal fiber angles and maximum buckling pressures for various vessel geometries are made with those for a hybrid pressure vessel. The well-known golden section method is used to compute the optimum angle in each case.
Cracks Emanating From an Erosion in a Pressurized Autofrettaged Thick-Walled Cylinder—Part I: Semi-Circular and Arc Erosions
Authors: Levy C. , Perl M. , Fang H.
Published: February 2008

Erosion geometry effects on the mode I stress intensity factor (SIF) for a crack emanating from the erosion’s deepest point in an autofrettaged, pressurized, thick-walled cylinder are investigated. The problem is solved via the FEM method and knowledge of the asymptotic behavior of short cracks. Autofrettage, based on von Mises yield criterion, is simulated by thermal loading and SIFs are determined by the nodal displacement method. SIFs are evaluated for a variety of relative crack lengths, a0/W = 0.01 – 0.45, emanating from the tip of erosions of different geometries. In Part I of this paper, two configurations are considered: (a) semi-circular erosions of relative depths of 5 percent of the cylinder’s wall thickness, W; and (b) arc erosions for several dimensionless radii of curvature, r′/W = 0.05 – 0.4. While deep cracks are almost unaffected by the erosion, the effective SIF for relatively short cracks is found to be significantly enhanced by the presence and geometry of the erosion and might reduce the vessel’s fatigue life.