Relationships Between Pitting, Stress, and Stress Corrosion Cracking of Line Pipe Steels

This paper presents observations about the results of an investigation into the relationships between pitting, stress, and stress corrosion cracking of line pipe steels. This work showed that the number of stress corrosion cracks varied exponentially with specimen stress. The cracks generally nucleated from pits, whose depths followed a lognormal distribution. A mathematical analysis of the crack number and pit depth data supports the hypothesis that a crack nucleates from the bottom of a pit when the stress concentration at the bottom of the pit reaches a critical value. The increase in crack number with stress results from the corresponding decrease in the critical pit depth, and hence an increase in the number of critically sized pits. The number of critically sized pits was found to increase exponentially with stress.