Investigation On The Limit And Burst Pressures For The Vessels With Nozzle

At present, cylindrical shell intersection configurations are very common structural components in many industries, such as piping, transportation, nuclear and power engineering, chemical and petro-chemical, aerospace, construction, etc. Because of the variety of geometric parameters, fabrication methods and loads, it is very difficult to calculate the local stresses in the cylinder-nozzle intersection area. An overall analysis about the cylindrical shell structures with nozzles becomes an important project. It has been an attentive problem in the field of pressure vessel research since 1950's. The action of different loads (internal pressure, external pressure, moments and temperature) leads to local stresses in the intersection region with high stress concentration caused by the geometric discontinuity. In addition, due to the difficulties arising during welding and defects detected there, the intersection region will become the weakest point and the failure source of the whole structure. In this thesis, a study of plastic behaviors and limit loads, burst pressure, failure location were made by experiment and three-dimensional nonlinear finite element analysis on cylinder shell intersection structures subjected to internal pressure. The main works in this study are including: 1. To gain the load-strain curves by the measurement technique of strain, strain gages were used on the three test vessels with different nozzle locations under different loads. 2. Besides the vessels used in the experiment, three analysis models were studied by three-dimension nonlinear finite element method and a series of data and conclusions were obtained. 3. Analysis and comparison between the finite element analysis and experiment results for stress concentration factor, limit load, burst pressure and failure location were performed. 4. Burst pressure and failure location of cylinder shell intersection structures were obtained based on a series of analysis and comparison. Further more, the influence of different nozzle locations on burst pressure and failure location was obtained, which could be used in the practical engineering. Some conclusions were obtained through the studies above: 1. It is a feasible method to study the limit load and burst pressure for cylindrical shell intersection structures under internal pressure through the nonlinear FEM. 2. Critical area appeared at cylinder-nozzle intersection area, longitudinal section is the dangerous section of the structure under internal pressure. 3. The stress concentration is local obviously. The stress rapidly decreases to the normal stress level with the increase of the distance from the opening. 4. The strain criterion to estimate the burst pressure has been deemed more reasonable approach. The burst pressure is determined by dp dε=0. This point can be obtained by the nonlinear FEM. 5. The maximum equivalent plastic strain through the wall thickness occurs in the longitudinal plane for arc-length method. This coincides with the experimental result. This point can be regarded as the failure location. 6. The stress concentration factor is reduced with the increase of the angle β, but the values of limit load and burst pressure are increased. Also the changes of nozzle location depressed the influence on intensity of cylinder shell intersection structures.