Computer modelling application in life prediction of high temperature components

Abstract

Defects introduced in pressure vessel components during fabrication processes act as potential sources for damage accumulation and subsequent catastrophic failure. Cracks nucleate at these stress risers and propagate aided by fatigue type of loading, corrosion and creep. Analysis of crack growth under conditions of ‘time-dependent fatigue’ is very important for the life prediction of pressure vessel components. In this paper the interaction of creep-hot corrosion and low cycle fatigue is analyzed based on the energy expended for the nucleation of damage at the advancing crack front. The total damage accumulation is divided into that due to (i) fatigue, (ii) corrosion and (iii) creep for modelling purpose. The analysis yields a relation in terms ofJ-integral which is applicable to both crack propagation and final failure. A corrosion-creep parameter (F _i ) has been introduced at the crack propagation stage and raw data from different sources have been analyzed for different types of loading and compared with the theoretical predictions. The total energy in tension which includes the tension going time, appears to be a good parameter for the prediction of time-dependent fatigue life.