Case Of Internal Pressure Research Articles

축방향 관통균열 배관의 새로운 탄소성 J-적분 및 COD 계산식

This paper proposes engineering estimation equations of elastic-plastic J and COD for axial through-wall cracked pipes under internal pressure. Based on detailed 3-D FE results based on deformation plasticity. the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalized crack length, and the strain hardening. Based on these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against the 3-D FE results based on deformation plasticity. For more general application to general stress-strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress concept. Such a re-formulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic-plastic 3-D FE results using actual stress-strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimations.

Elastic–plastic J and COD estimates for axial through-wall cracked pipes

This paper proposes engineering estimation equations of elastic–plastic J and crack opening displacement (COD) for axial through-wall cracked pipes under internal pressure. On the basis of detailed 3D finite element (FE) results using deformation plasticity, the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalised crack length, and the strain hardening. On the basis of these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against 3D FE results based on deformation plasticity. For more general application to general stress–strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress (RS) concept. Such a re-formulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed RS based J and COD estimation equations are compared with elastic–plastic 3D FE results using actual stress–strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimates.

Quantification of pressure-induced hoop stress effect on fracture analysis of circumferential through-wall cracked pipes

This paper provides engineering J and crack opening displacement (COD) estimation equations for through-wall cracked (TWC) pipes under internal pressure and under combined internal pressure and bending. Based on selected 3-D FE calculations for the TWC pipe under internal pressure using power law materials, elastic and plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the normalised crack length and the mean radius-to-thickness ratio. These developed GE/EPRI-type solutions are then re-formulated based on the reference stress concept. Such re-formulation not only provides simpler equations for J and COD estimation, but also can be easily extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic–plastic 3-D FE results using actual stress–strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimates.

Creep Relaxation in Multilayer Wrapped Vessels

One of the common methods of construction of vessels for high to ultra-high pressure applications is the wrapping technique. In this method, relatively thin plates (normally in the range of 6 mm) are rolled to proper curvature, wrapped around the core or the preceding layers and then welded. In this fashion, a prestress is gradually built in the cylinder wall which would compensate and moderate the extreme stresses due to internal pressure. Relying on such prestress, however, should be done only with careful consideration of stress relaxation that will take place while the vessel is in service, especially in high temperature services. In this paper, the initial stresses due to wrapping are obtained. These stresses are due to shrinkage of the weld as well as the plate affected by the heat of welding. The power function stress-creep strain rate is employed to predict the relaxation of interface pressure between any two adjacent layers. The creep stress distribution based on relaxing interface pressures are given as a function of time. In such vessels, in order to maintain the same safety factor as existed when the vessel was constructed, the internal pressure must be decreased with time. A relationship between the internal pressure and time, based on a constant safety factor, is obtained. Alternately, for the case of internal pressure being kept at the same level, a relationship is obtained that would give the decreasing safety factor or the vessel as a function of time.

Stress Analysis of Multilayer Bellouws

Expansion bellows are widely to absorb thermal expansion of tubes in pipeline system. Considering narrow piping space and small number of special positions where pipes are strongly fixed, the designing of pipelines for ship service requests the expansion bellow to have shorter effective length and smaller spring rate.The accurate stress-strain analysis concerning the deformation of bellows is necessary in order to assure the safety of the pipeline system. However, the mechanical behaviour of multilayer bellows has not been sufficiently analysed.Stress and strain applied to a monolayer bellow and a multilayer bellow during loading of axial deflection and internal pressure were experimentally measured with strain gage, and also calculated with the aid of elastic finite element method. The measurement and calculation were conducted with a 200 A-diameter bellow made of type 304 stainless steel.In the course of the finite element analysis, the gap/friction elements were developed to model the inter-surface between each layer of the mutilayer bellow. The friction coefficient was assumed to be 0 or 10000.When axial deflection was applied to a monolayer bellow, it was found that the calculated results from the finite element method were in good accordance with the experimental results from actual measurement. In case of a multilayer bellow, the calculated results coincided well with the observed results when the friction coeffecient was 0. It was noted that strain and stress generated in a multilayer bellow were much smaller than those in a monolayer bellow.In case of internal pressure, the finite element results of a monolayer bellow fitted to the measured results. The measaured values of stress and strain in a multilayer bellow were nearly equal to those in a monolayer bellow. Whereas the calculated values of stress and strain in a multilayer bellow with the friction coefficient of 0 were a little larger than the observed values. However, it was confirmed that the finite element method was more suitable for the stress analysis of multilayer bellows than the EJMA equation.Multilayer bellows have an advantage over monolayer bellows with respect to endurance because smaller amount of stress is generated through loading, in the former than the latter.

The finite deformation of a pressurized circular tube for a class of compressible materials

This investigation is concerned with the problem of a hollow circular cylinder subjected to uniform internal and external pressure within the equilibrium theory of finite elasticity. The tube is composed of homogeneous, isotropic,compressible materials of special type, namely harmonic materials. Explicit closed-form solutions for the deformation and stress fields are obtained. The true stress distribution, expressed as a function of the undeformed coordinates, is shown to be essentially independent of material properties. The two cases of internal pressure only, and external pressure only, are examined in detail. In the former case, there is a critical value of the applied pressure at which the maximum hoop stress in the tube, occurring at the inner surface, becomes unbounded. Results appropriate for thin shells are also obtained. For the case of external pressure only, a critical value of the applied pressure exists for which closing of the cavity is predicted. For nearly solid cylinders, or equivalently, for a cavity in an unbounded medium, explicit results are provided for the corresponding stress concentration factor.

The pressurized hollow sphere problem in finite elastostatics for a class of compressible materials

This investigation is concerned with the problem of a hollow sphere subjected to uniform internal and external pressure within the equilibrium theory of finite elasticity. The sphere is composed of homogeneous, isotropic, compressible materials of special type, namely harmonic materials. Explicit closed-form solutions for the deformation and stress fields are obtained. The true stress distribution, expressed as a function of the undeformed coordinates, is shown to be essentially independent of material properties. The two cases of internal pressure only, and external pressure only, are examined in detail. In the former case, there is a critical value of the applied pressure at which the maximum hoop stress in the sphere, occurring at the inner surface, becomes unbounded. Results appropriate for thin shells are also obtained. For the case of external pressure only, a critical value of the applied pressure exists for which the cavity closes. The maximum hoop stress does not always occur at the cavity wall. For nearly solid spheres, or equivalently, for a cavity in an unbounded medium, explicit results are provided for the corresponding stress concentration factor. For sufficiently small values of applied pressures, all the foregoing results coincide with those of classical linear isotropic elastostatics.

Stress Analysis and Stress Index Development for a Trunnion Pipe Support

A finite element stress analysis is presented of a trunnion pipe anchor. The structure is analyzed for the case of internal pressure and various end moment loadings. Stress results were post-processed and decomposed into average and linear varying (through the wall thickness). These decomposed values were then interpreted within the ASME Boiler and Pressure Vessel Code to estimate primary and secondary stress indices. Several computer runs were made for a variety of structural sizes and empirical formulas were developed expressing the stress indices as a function of certain dimensionless ratios.

OPTIMUM DESIGN OF FLANGED AND FLUED EXPANSION JOINTS

Optimum design of flanged and flued expansion joints used in heat exchangers is presented. Minimization of the reaction transferred by the expansion joint to the tube sheet or anchor is considered as the objective function. The structure is analysed by the finite element method. Design criteria based on stress limitations are used as constraints. The problem turns out to be a nonlinear optimization problem under multiple loading conditions. Optimization is carried out by the improved move limit method of sequential linear programming. The progress of optimization is discussed and results are presented for two values of nondimensional expansion. For each value four cases of internal pressure have been considered. The optimum configuration of structure is discussed in detail.

Analytical and Experimental Stress Analysis of a Cylinder-to-Cylinder Structure

This paper presents a comparison of stress results obtained using the FESAP three-dimensional finite element computer program with results obtained from experimental testing. The comparison was obtained for the case of internal pressure applied to a cylinder-to-cylinder structure with a variable shell thickness at the juncture and a D/d of 1.6. The experimental testing conducted at the Babcock & Wilcox Research Center, Alliance, Ohio, consisted of strain gage testing followed by a “stress freezing” photoelastic analysis. The numerical analysis was performed at the Babcock & Wilcox Nuclear Equipment Division using the FESAP three-dimensional isoparametric element with incompatible modes. The model mesh was generated with the program FEMEG which is briefly discussed. The paper includes a detailed description of both the experimental and analytical studies. It is concluded that FESAP, with the eight-node incompatible mode element can accurately and economically predict the structural response of complex components.

Analysis of the transition zone in combined metal/reinforced-plastic shells

The bending stresses in the conical joint zone of cylindrical shells composed of two different materials are determined for the case of internal pressure. The effect of the length of the joint on these stresses is investigated using parameters typical of steel and glass-reinforced plastic.