PROPAGATION OF STRESS-CORROSION CRACKS IN STEAM-GENERATOR TUBES

A model suitable to describe the propagation of stress corrosion crack s in steam generator tubes made of Inconel-600 is proposed in this pap er. It concentrates on axial cracks located in the tube expansion tran sition zones which are assumed to be through-wall. The residual stress field is therefore considered as the major contributing factor drivin g short cracks while operational stresses dominate the growth of longe r cracks. An estimate of residual hoop stresses is obtained using a no n-linear finite element simulation of the tube to tube-sheet rolling p rocess. Scatter of the residual stresses due to the stochastic variati ons of the dominant influencing parameters was studied. The crack prop agation model utilizes linear-elastic fracture mechanics theory. In pa rticular, both crack tips are modelled to propagate with different vel ocities due to the highly asymmetric stress field. Provisions are also made to account for the reactor coolant temperature and chemical comp osition effects. The model performance is demonstrated by a numerical example considering the crack propagation data from D4 steam generator s during a 15 month operational cycle as recorded by subsequent non-de structive tube examinations.