Design And Analysis Of Shrink Fitted Multilayer Pressure Vessel Under Mechanical Loads

Abstract

Multilayer pressure vessels are widely used in field of heavy equipment engineering such as chemical & gas plant, ammonia converter, heat exchanger, fertilizer industry etc. Fatigue life , load bearing capacity of monoblock cylinders can be considerably improved by inducing residual (compressive) hoop stresses near the bore of cylinder. To enhance load bearing capacity different processes such as shrink fit and autofrettage are usually employed. The present work discusses the design & analysis of a multi-layer shrink fitted pressure vessel, discontinuity stress analysis at junction, weld neck flange stress analysis and wind analysis.

In the shrink-fitting problems, considering long hollow cylinders, the plane strain hypothesis can be regarded as natural. Using shrink fit process, it is possible to reduce the tangential stresses across wall thickness. The residual stresses of multi layer cylinders subjected to shrink fit processes have been determine analytically & successfully validated by using finite element analysis. The stress distribution in monoblock cylinder and compound cylinder are compared in this report. The analytical results of stress distribution is calculated and validated through finite element results.

Design of the juncture of the two parts is a major consideration in reducing discontinuity stresses. In this dissertation effort is made to compute stresses at junction of hemispherical head to cylindrical shell. This stresses near the juncture are called discontinuity stresses, they are analyzed using design by analysis guideline provided in ASME Sec. VIII Div 2 part 5.

The report present results of parametric study using design of experiment (DOE), taguchi approach of integrally weld neck flanges and results are analyzed using the analysis of variance (ANOVA). The values of stress in weld neck flange are obtained for a range of taper hub thickness, nozzle neck thickness, flange thickness and gasket outside diameter, when flange subjected to internal pressure. The results obtained have been compared with guidance given in ASME Sec. VIII Div 2, Para. 4.16 pressure vessel code. The predicted results from taguchi method and ANOVA are validated using PV Elite software.

The first requirement in vessel design is to determine loads & the condition to which vessel subjected during operation. These loads are wind load, earthquake, dead loads, piping loads etc. In this paper wind analysis of tall vertical pressure vessel is carried out using IS 875 code and effort is made to validate results using Finite element analysis.