Fatigue of X65 steel in the sour corrosive environment—A novel experimentation and analysis method for predicting fatigue crack initiation life from corrosion pits

Oil and gas pipelines manufactured from API-5L Grade X65 steel are generally subjected to cyclic loading their internal surfaces frequently exposed corrosive sour fluids. Exposure of these environments often leads localized corrosion (pitting) decreased fatigue life. Corrosion pits geometrical discontinuities that may promote cracking by acting as stress raisers. In order optimize asset inspection repair scheduling, it is important understand the behavior in particular, ability predict crack initiation pit. To achieve this level understanding, conducting tests an environmental condition replicating field environment important. This paper presents test protocol results testing using bespoke laboratory apparatus undertake situ a under uniaxial loading. The selected represent processes likely occur at oil production were carried out on smooth samples obtain S-N curve specific well pre-pitted samples. An electrochemical method used create Also, model proposed life pit, local stress-based technique, which has been validated experimental results. Post-test fractography was scanning electron microscopy (SEM). performance our approach demonstrated. innovation anticipated encourage other workers employ similar small-scale requiring toxic challenging environments.