Prediction of Corrosion Fatigue Crack Initiation Life Based on Corrosion Pit Growth

Corrosion fatigue crack initiation behavior of low alloy steel in deionized water has been investigated. It was observed that the corrosion fatigue process was composed of three stages, namely, corrosion pit growth, formation of a crack from the corrosion pit and corrosion fatigue crack propagation. The corrosion pit size was found to increase with time ,t, following the relation: corrosion pit size∝t1/3. The formation of a crack from the corrosion pit was determined by the stress intensity factor, by assuming the corrosion pit is a sharp crack. The critical pit condition (ΔK)p was 1.2MPam for 2.5NiCrMoV and 3.5NiCrMoV in 90°C water containing dissolved oxygen. Based on the above mentioned results, a residual life prediction method for corrosion fatigue crack initiation based on in service inspection was proposed.