Simulation of Post Weld Heat Treatment Process of the Pressure Vessel to Predict Its Deformation and Its Validation with Experimentation

Abstract

Heat treatment of materials is a fundamental metallurgical process. Materials are subjected to heat treatment to relieve internal stresses, reduce brittleness and to improve machinability. Nevertheless, heat treatment can generate unwanted stresses and deformations, a fact that has to be taken into consideration when designing or changing the sequence of manufacturing for a given component. One way to decrease cost and reduce time in product development can be to use simulation tools that can reliably predict the final properties and shape of a component. A decrease in cost and better knowledge of final properties already in product development can give the company a better market position and competitiveness. The objective of the work presented in this thesis is to develop efficient and reliable methods for simulation of heat treatment using the Finite Elements Method. The result of the simulation must be sufficiently accurate and completed within an acceptable time when the manufacturing simulation is to be used in product development. The models would enable us to predict residual stresses, distortion, final shape, after a heat treatment process. In order to develop simulation methodology case study of reactor type pressure vessel manufactured by L&T at hazira works is considered. In the simulation study, finite element schemes for simulation of the post weld heat treatment are developed. A linear elastic static analysis to replicate PWHT holding time and thereby to replicate deformation during that time, are performed using l-DEAS simulation module with shell as well as solid model. Transient thermal analysis with shell model has been also performed to simulate the vessel during entire PWHT cycle. The numerical scheme developed in this work is validated by the experimentation. Experimental setup was developed to continuously measure deformation of the reactor during 60 hour long PWHT cycle.