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(searched for: doi:10.1007/s00158-012-0789-1)
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Published: 12 May 2021
by MDPI
Materials, Volume 14; https://doi.org/10.3390/ma14102520

Abstract:
The experimental and numerical analyses of the pressure vessels with different flat ends are presented and discussed in the paper. The main aim of the study is to propose the optimal flat head end geometry. The analyses are focused on the comparison of standardized geometries and with the proposed elliptical cut-out. The experimental tests with the application of strain-gauge measurements and numerical modeling of the pressure vessel are conducted. The behavior under low and high pressures and the influence of the residual welding stresses, material properties, and geometrical tolerances on the level of the plastic deformation in the flat end is discussed. It is presented that the rules given in the recent standard are not sufficient for optimal selection of the optimal geometry. It is observed that in certain geometries the deviations of the pipe thickness may lead to a significant increase of the equivalent stresses. The residual welding stresses have a significant influence on the stress and strain level—particularly in the stress relief groove (SRG). The performed study and comparison of the different geometries allow for the proposal of the optimal shape of the flat end. It appeared that the pressure vessels with SRG are the most optimal choice, particularly when elliptic shapes are in use. In some cases (i.e., pipe with wall-thickness equal to 40 mm and the flat end with circular SRG), the optimal configuration is reached for dimensions beyond the admissible by code range.
Zhaohua Huang, , Chenhui Jia, Xianqing Lei, Zhuangya Zhang, Zhenyu Ma
International Journal of Pressure Vessels and Piping, Volume 192; https://doi.org/10.1016/j.ijpvp.2021.104398

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Published: 13 December 2019
by MDPI
Materials, Volume 12; https://doi.org/10.3390/ma12244194

Abstract:
The application of flat ends in pressure boilers is inevitably associated with the presence of stress concentration, which is observed in the vicinity of the junction of the cylinder and the closing flat plate. The analyzed flat end plates with stress relief grooves fall into the group of solutions recognized by the respective Standards of Calculations of Pressure Vessels. Unfortunately, no clear evidence is given in the Standards on how to choose the best groove parameters. This opens up the problem of the optimal choice of the groove parameters providing a minimum stress level. Even for the optimal values defining the stress relief groove geometry, certain plastic deformations are observed in the groove area for materials which exhibit elastic-plastic properties. Such a situation is completely unacceptable during exploitation, and a suitable reduction of the operating pressure is necessary. This paper discusses the effectiveness of other designs for flat ends used in pressure vessels. The proposed modifications took the form of external ribs applied around the top of the endplate circumference. The dimensions of these ribs were set using parametric optimization. The results of the study encouraged the authors to perform a more general analysis with the use of topology optimization. The results of all performed studies proved that the reduction of stress concentration and the full elimination of plastic deformation are possible. All numerical calculations were made using the finite element code (FEM), Ansys.
, Gun Young Park, Chul Kim
Journal of Pressure Vessel Technology, Volume 142; https://doi.org/10.1115/1.4045027

Abstract:
Type II storage vessel, which consists of a metallic liner hoop wrapped with a carbon fiber-resin composite to work at high pressure, has been widely adopted as the fuel container for compressed natural gas (CNG) vehicles. The general vessel, manufactured by welding enclosures to an open-end cylinder, shows uniform thickness throughout the whole liner, while the high pressure vessel, fabricated by the deep drawing and ironing (D.D.I) and spinning processes, has the integral junction part of cylinder with increased end thickness along the meridian direction. This study established a design method for improvement of failure resistance and inner capacity of the seamless CNG pressure vessel (Type II) through finite element analysis with consideration of thickness variation. Autofrettage pressure is used to enhance fracture performance and fatigue life of the vessel, and variations of stress behaviors in the liner and composite were analyzed during the autofrettage process. The influence of the composite on generation of compressive residual stress was investigated. In order to verify advantages of the D. D. I. and the spinning processes for structural safety at the end closure, the stress distribution considering thickness variation was compared with that with uniform thickness, and the maximum inner capacity objective satisfying structural reliability was obtained. The inner capacity of the proposed model with the ratio of major axis to minor axis, 2.2, was expanded by 4.5. Theoretical equivalent stresses were compared with those from the simulations, and the technique of FEM was verified.
, Jerzy Lewinski, Rafal Cichy
Journal of Pressure Vessel Technology, Volume 140; https://doi.org/10.1115/1.4039844

Abstract:
The paper is a review work devoted to dished heads of various meridian shapes. Geometry of the shells of revolution, the membrane state, and the edge effect occurring in the shells are described. Exemplary analytical and numerical finite element method (FEM) studies of torispherical, ellipsoidal, Cassini-ovaloidal, and untypical special dished heads are presented. The results of the above-mentioned two methods are compared. Moreover, numerical research of elastic buckling of the above-mentioned selected heads under external pressure is carried out. Literature related to each of the considered head types is quoted and discussed, with special attention paid to the works developed in the 21st century. In concluding remarks, the stress concentration and buckling of these structures are commented, with consideration of the head meridian shapes.
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