Fatigue strength and crack propagation life of in-service high pressure tubular reactor under residual stress

Abstract

In the production of a tubular reactor for a high pressure polyethylene plant the autofrettage process was used to produce a compressive residual stress at bore, which will increase the fatigue strength of the reactor. The autofrettage residual stress in the reactor will, however, gradually relax during operation. It is necessary to investigate the influence of residual stress relaxation on the fatigue strength of the reactors. In the design only fatigue crack initiation life was considered as its fatigue strength. What the fatigue crack propagation life is was not known. In this paper, fatigue crack propagation life of a reactor with residual stress was analysed using Paris' equation. Based on the results of an internal pressure fatigue test on a reactor with inner and outer surface artificial notches, the effects of residual stress and suitable SIF expression were also analysed. The autofrettage residual stress can greatly increase crack initiation life of plain reactors. However, since crack propagation life of the reactors is short, effort should be taken to prevent crack initiation on the inner or outer surface of the reactor caused by other factors.