Prediction of Fatigue Crack Initiation Life Based on Pit Growth

Fatigue crack initiation behavior of low-alloy steel in 90 C deionized water was investigated. It was observed that the corrosion fatigue process composed three stages, namely, pit growth, crack formation from the pit, and corrosion fatigue crack propagation. The pit size was found to increase with time (t) following the relation: pit size ∝ t1/3. The crack formation from the pit was determined from the stress intensity factor (linear elastic fracture mechanics parameter), which was calculated by assuming that the pit was a sharp crack. The critical pit condition (ΔK)P was 1.2 MPam for 2.5NiCrMoV and 3.5NiCrMoV in 90 C water containing dissolved oxygen. Using these results, a residual life prediction method for fatigue crack initiation based on in-service inspection was proposed.