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

摘要

In the production of a tubular reactor for a high pressure polyethylene plant the autofrettage processwas used to produce a compressive residual stress at bore, which will increase the fatigue strength ofthe reactor. The autofrettage residual stress in the reactor will, however, gradually relax duringoperation. It is necessary to investigate the influence of residual stress relaxation on the fatiguestrength of the reactors. In the design only fatigue crack initiation life was considered as its fatiguestrength. What the fatigue crack propagation life is was not known. In this paper, fatigue crackpropagation life of a reactor with residual stress was analysed using Paris' equation. Based on theresults 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 residualstress can greatly increase crack initiation life of plain reactors. However, since crack propagation lifeof the reactors is short, effort should be taken to prevent crack initiation on the inner or outer surfaceof the reactor caused by other factors.