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RESEARCH PAPERS

J. Pressure Vessel Technol. 1988;110(4):343-347. doi:10.1115/1.3265614.

A simplified method for determining the J -integral for elastic-plastic conditions using the stiffness gradient method is described. Power law hardening material is shown to simplify the J -integral estimation, rendering elastic and fully plastic J solution terms. Numerical results are obtained for an interior complete circumferential crack in a pipe and compared to the analogous EPRI handbook solution. Because the stiffness gradient method is based on external displacement and forces, and not directly dependent on the stresses, it is sufficient to use relatively coarse finite element meshes to detemine the J -integral instead of highly refined and costly meshes required in most conventional J -integral computations.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):348-354. doi:10.1115/1.3265615.

The damage-related internal variables are introduced as associated with kinematical (deformation) measures. Two basic damage tensors relative to finite damage are defined through macro-micro transition for the Lagrangian velocity gradient and the Eulerian one. Both reduce to a small-damage tensor as the finite deformation measures reduce to their common infinitesimal strain counterpart. The damage mechanism by cavity growth from hard inclusions is examined. The systematic procedure is proposed to settle up the damage evolution equation. It is based on the datum of the local velocity field within an elementary cell viewed as an element containing an inner cavity and subject to displacement boundary conditions compatible with homogeneous deformation of outer faces. Experimental procedure is employed to verify the hypotheses regarding the local velocity field in the cell and evolutive cavity forms in a two-dimensional case. Artificial cylindrical inclusions are embedded in a metal plate, periodicity of their spacing being respected. The laser-speckle measurements of displacement increments are performed within a unit-cell chosen as the whole element is loaded to plasticity range. They permit to evaluate the “local” smoothed velocity field perturbed by cavity presence.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):355-360. doi:10.1115/1.3265616.

Integral equations are derived to calculate the stresses and displacements in the neighborhood of a load-carrying rigid attachment in a shallow cylindrical shell. The integral equation formulation is simplified by modifying existing Green functions for the unbounded shell to account for simply supported boundary conditions at the ends of the vessel. The resulting equations are solved numerically. Three forces and three moments applied to the attachment are the loadings considered. Results for circular attachments agree with those found by other authors using different solution methods and with experiments.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):361-366. doi:10.1115/1.3265617.

The present paper is an extension of work on stresses in corner radii already described by the authors in previously published references [1 and 2]. Whereas the original study concerned itself with pressure effects only and the second reference gave the initial version of the work dealing with thermal effects, the report included here gives more recent results concerning specifically thermal loads. As before, the results are limited to inside corner radii between cylinders and flat heat closures. Similarly, the analysis is based on a systematic series of finite element calculations with the significant parameters covering the field of useful design boundaries. The 334 elements containing some 1800 degrees of freedom ensure a realistic determination of local stresses and a large number of complete solutions enables the presentation of smooth design curves. The results are condensed into a rapid method for the determination of peak stresses needed for performing fatigue analysis in pressure vessels subjected to a significant, variable thermal load. The paper takes into account the influence of the film coefficient, temporal temperature variations, and material properties. A set of coefficients provides a convenient method of stress evaluation suitable for design purposes.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):367-373. doi:10.1115/1.3265618.

Two normally intersecting cylinders under different internal pressures in each of the cylinders is solved analytically. The inclusion of nozzle fillet, insert plate and inner nozzle broadens the applicability of this analytical method in the design and analysis of pressurized cylinder-to-cylinder intersection. The current numerical solution scheme has been incorporated in the computer code NUTSHELL. Comparisons of NUTSHELL solutions and experimental or finite element results have also been presented.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):374-386. doi:10.1115/1.3265619.

The finite element analyses are carried out for the several piping components (D /T ≧ 100) subjected to in-plane or out-of-plane moment. For the stress evaluation of the chemical plant piping systems, ANSI B31.3 is usually applied. But the stress intensification factors and flexibility factors in this code are mainly for a heavy-wall-thickness pipe, so it is necessary to reconsider these factors for a thin-wall-thickness pipe with a large diameter. In our study, several finite element analyses using MSC/NASTRAN program were performed on the pipe bends (elbow or miter bend, 0.01 ≦ h ≦ 0.2) and the unreinforced fabricated tees (50 ≦ D /T r ≦ 300, 0.5 ≦ d /D ≦ 0.95, 0.25 ≦ T b /T r ≦ 0.95), and the empirical formulas for the flexibility factors and the stress indices, due to out-of-plane or in-plane moment, were proposed. Experimental stress analyses for the piping components with D /T r = 127 were also carried out, and it was confirmed that the results agreed well with the numerical ones.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):387-392. doi:10.1115/1.3265620.

Thin-walled spherical pressure vessels, the bending and compressive stiffnesses of which are small in comparison with their tensile stiffness, are discussed using membrane theory. In the first part of the paper linear membrane theory is used to analyze the statics of supports for large spherical pressure vessels. The reactions from such supports which are tangential or almost tangential to the pressure vessel surface, require reinforcements so as to distribute the reactions into the wall without causing undue stress concentrations and/or wrinkling. The size and contour of such reinforcing elements depend, of course, on the magnitude of the reactions as well as the internal pressure. In the second part of the paper, nonlinear membrane theory is used to analyze the geometry of wrinkled domains in such membrane pressure vessels. Using an Eulerian formulation, the parameters of the first and second fundamental forms of the surface are treated as key variables and are determined from the analysis as functions of the curvilinear coordinates referred to the current deformed configuration. The solution technique is applied to a simple example.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):393-401. doi:10.1115/1.3265621.

The objective of this paper is to provide analysis results of displacements and localized stresses in horizontal pressure vessels which were determined by using the three-dimensional finite element method. The analysis models utilized realistic geometry, including saddle supports, vessel heads and actual boundary conditions. The results give a detailed distribution of displacements and local stresses in the saddle support area, and show that the maximum stress is located at the horn of the saddle. A comparison of the results for different saddle locations, (A /L ), was performed, and a reasonable location for the supports is suggested. Also, examples of parametric analyses and dimensionless design curves for calculating localized stresses are presented. The latter results should prove to be an invaluable aid in the generation of a new design code for horizontal vessels.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):402-404. doi:10.1115/1.3265622.

Stress redistribution in a butt-welded pipe during later mechanical and thermal treatments is studied numerically by use of a thermoelastoplastic FE-model. It is proposed that the influence of the welding process on the redistribution can be modeled using a simplified approach. Here the welding residual stress field is simulated with an equivalent radial line load. Two standard treatments, one mechanical and one thermal, are studied with this simplified approach. Both treatments are performed after the welding is completed. The calculations show that both treatments can be used to turn (detrimental) tensile welding residual axial stresses on the inner surface at the weld into compressive ones.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):405-412. doi:10.1115/1.3265623.

During seismic or blade/impeller loss events, the potential for rubs in rotating nuclear and fossil fuel power plant components is quite high. Generally, such events involve interactions between blade/impeller tips and machinery components. This also includes the possibility of seal casing rubs. The paper will develop methodologies to: (i) evaluate the blade impeller-casing rub event; (ii) establish the associated stress, strain and force fields; (iii) enable signature analysis defining blade/impeller/seal particpation; and (iv) establish procedure enabling evaluation of blade/impeller/seal fatigue life. Additionally, the paper will present benchmarking examples of prototypical power plant components, i.e., feedwater pumps and steam turbines.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):413-421. doi:10.1115/1.3265624.

Design layout of ducts and supports systems which make up the heating, ventilating and air-conditioning systems (HVAC) is based upon the Japanese Industrial standard (JIS)[1] for hanger support systems conforming to SMACNA[2] standards of high-rigidity design, where emphasis is placed on buildings containing duct systems. However, since high-rigidity systems involve raising the rigidity of the total system, the weight and number of support structures have to be increased, thus posing economic problems. On the other hand, hanger systems are problematic due to their structural weakness. Therefore, we have tried to apply low-rigidity ducts and a support system which rely heavily on the strength of the ducts themselves. To accomplish this we tried to lengthen the duct support span, to lighten the support structures, and to establish a reasonable design method for the duct system. Further, the effectiveness of the present design margin can be confirmed by a duct system test using a shaker table. Our study mainly consisted of experiments: performing duct element tests to study rigidity and strength, using the shaker table to estimate dynamic characteristics and response characteristics of a duct system model, and studying the calculations of the duct beam model.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):422-429. doi:10.1115/1.3265625.

Exact analytical solutions for free vibration of straight tubes have been known for many years, with solutions for curved tubes being developed more recently. In this paper it is shown how these solutions can be exploited to obtain similar solutions for the free vibration of U-tubes. All of the required interface boundary conditions are developed in detail and it is shown how advantage can be taken of U-tube symmetry where it exists. Illustrative results of two studies are presented. This represents, to the author’s knowledge, the first comprehensive analytical study of the U-tube free vibration problem.

Commentary by Dr. Valentin Fuster

PRESSURE VESSEL AND PIPING CODES

J. Pressure Vessel Technol. 1988;110(4):430-443. doi:10.1115/1.3265626.

Preface. Code criteria defined. Evolution of ASME Boiler and Pressure Vessel Code. How the Code operates today. Design by rule. Evolution of design by analysis. Types of stress and their significance. Failure modes. Strength theories. Design loads. New or unusual designs. Code Cases. Interpretations. Stress limits for design by rule and design by analysis. Elevated temperature design. Recent developments. A glimpse at the future. References.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):444-450. doi:10.1115/1.3265627.

This paper establishes limits on piping material strains for ASME Boiler and Pressure Vessel Code Level D loadings that ensure a limitation of deformation and provide suitable safety margins. In establishing the strain limits, potential piping failure modes due to compressive wrinkling and low-cycle fatigue are considered. A stress-strain correlation methodology to convert linear, elastically calculated Code Class 2 and 3 equation (9)-Level D stresses to strains is established. This correlation is based on the fatigue evaluation procedure of the Code and is verified by comparison with test results. A detailed discussion of test results compared with the stress-strain correlation methodology is also presented.

Commentary by Dr. Valentin Fuster

DESIGN DATA AND METHODS

J. Pressure Vessel Technol. 1988;110(4):451-456. doi:10.1115/1.3265628.

An approach to the problem of predicting reaction forces that can occur during pipe failure is provided. Use is made of experimental data measuring crack propagation speed to determine the pipe rupture forces. The results of this paper are for pipelines carrying subcooled liquid water, but may be applied to other fluids. The reaction forces during pipe failure are compared with steady-state values.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Pressure Vessel Technol. 1988;110(4):457-460. doi:10.1115/1.3265629.

Grain storage silos are essentially pressure vessels, but unlike liquid or gas storage vessels, grain in silos is not always distributed axisymmetrically. Remnant grain obtained from discharging underneath along a diametrical line forms grain ungulas. This produces uneven pressures around the circumference of the silo. The resulting forces have led to buckling in some steel storage silos. This article demonstrates how to approximately calculate these forces in the silo and shows why they can cause buckling of an improperly designed tank. Sufficient base anchorage is suggested as the most effective means for elimination of this buckling problem.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):460-463. doi:10.1115/1.3265630.

In the early design stage of pressure vessels the configuration of the piping systems is not yet established; hence forces transmitted by the piping systems to the nozzles in the pressure vessels cannot be determined. This often leads to the design of nozzles in pressure vessels guided by consideration of pressure loadings such as the area-replacement method. However, it is true that in many cases the stresses due to external loads can be more critical than those due to the internal pressure. Therefore, engineers often redesign the piping system several times by adding more pipe bends or special restraints for a hot piping system to reduce the reactions at a previously designed nozzle so that the resulting stresses at the nozzle are within the acceptable limit. This paper introduces a rational mechanism whereby the stresses due to the unforeseen external loads can be minimized in the early design stage of the nozzle. An appropriate analysis is discussed which is based on the classical thin shell theory. Analyses using this method allow one to obtain the minimum stresses at a nozzle in a pressure vessel head or a spherical vessel for moment and thrust loadings.

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Pressure Vessel Technol. 1988;110(4):464. doi:10.1115/1.3265631.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 1988;110(4):464-465. doi:10.1115/1.3265632.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

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