Limit Analysis Of Pressure Vessels With Pad Reinforcement Under In-plane Moment On Nozzles

The cylindrical shell structures with nozzles have now been widely used in pressure vessels and piping system. 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 a conspicuous problem in the field of pressure vessel research from the 1950's.The stress concentration often occurs in the cylinder-nozzle intersection area due to the pressure and different external loads. This thesis was supported by PVRC. A study of plastic behaviors and limit loads was carried out through experiment and three-dimensional nonlinear finite element analysis on cylinder shell structures subjected to In-plane moment on nozzles. The flexibility factors of these structures were also studied.The main works in this study are including:1. To gain the load-displacement and load-strain curves by the measurement technique of displacement and strain using displacement sensors and strain gages on the six test vessels with different d/D ratios under different loads.2. Besides the vessels used in the experiment, six 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 intensity factor, limit load, and flexibility factor were performed.4. Limit analysis was conducted on a series of parametric analysis models with different values of d/D, t/T and D/T. Also, the correlation equations about limit moment were 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 for cylindrical shell intersection under In-plane moment on nozzle through the nonlinear FEM.2. Critical area appeared at cylinder-nozzle intersection area and edge of reinforcement pad, longitudinal section is the dangerous section of the structure under In-plane moment on nozzle.3. Stress distribution appears anti-symmetrical characteristic in longitudinal section of cylinder-nozzle about the nozzle central line.4. The stress concentration is local obviously. The stress rapidly attenuates to the normal stress level with the increase of the distance from the opening, and thescope is about 2.0*/Rtmm.5. A reinforcement pad reduces effectively the stress concentration of cylinder-nozzle intersection area, and increases the limit load of the structure, therefore it is an effective reinforcement approach.6. The limit loads obtain by load-displacement and load-strain curves are agreement very well. So in order to predigest the procedure of test, displacement measurement method is recommended.7. The verifying result indicates that the correlation equations from this work for limit load is of preferable reliability and application value.