Analysis of Vessel Nozzle Junction and Rationalization of Allowable Nozzle Loads Through FEM

Abstract

Cylindrical vessels are widely used in pressure vessels and piping systems of petrochemical, fossil and nuclear power plants. Under different loading conditions the stress concentration will occur at the junction area. In addition due to discontinuity of the geometry & difficulties during welding & defect detected there, the junction region will become the weakest point & the failure source of the whole structure. Thus a reliable & accurate analysis method for shell nozzle junction is necessary.

This dissertation illustrates the design and analysis of pressure vessel. 3D model of the vessel nozzle junction is created using Ansys 8.0 series, and elastic-plastic limit load analysis have been done for the 30& 90 degree lateral vessel nozzle junction under increasing internal pressure loading. The spread of plastic area, deformation pattern are studied. The dissertation addresses recommendations & advanced design guidelines for the plastic analysis of the cylindrical vessel nozzle lateral intersection.

Generally the predominant loading in pressure vessels is internal and/or external pressure However in most cases additional non-pressure loads do occur & their effect must be evaluated in order to guarantee the integrity of the vessel. The dissertation illustrates the behavior of the nozzle load due to the piping on shell with varying shell diameter, internal pressure, and temperature. Four sets of nozzles i.e. 12”, 18”, 24”& 30” have been taken to investigate the behavior of the loads. The maximum allowable nozzle loads have been calculated at the various severe conditions with the F. E. A. package nozzle –pro.

The axial force, circumferential & longitudinal moments are found to be sever in the context of discontinuity. These major three nozzle loads have been plotted on the 3D graph to provide a correlation between the nozzle loads. Both linear & parabolic correlation has been presented so that any practice engineer can easily check the value of allowable for the considered nozzle sizes. Similarly surfaces can be generated for another nozzle size.