Abstract
Environmentally assisted cracking of line pipe is considered from the perspective of effective loading, acknowledging the possibility of corrosion fatigue. The mechanical and environmental driving forces responsible for crack initiation and crack growth in near neutral pH soil environments are identified and their interactions are discussed. With ΔK controlling crack growth mechanically at normal pipeline operating conditions, both dissolution and hydrogen are found to be essential environmental components. Stress intensifiers have a pertinent role in the cracking process, as they are associated with the majority of pipeline failures. The importance of stress intensifiers in crack initiation and propagation is explored within the realm of the identified crack growth driving forces. Elastic-plastic finite element studies of growing cracks at the toe of a weld and at the bottom of a pit indicate that the presence of these stress intensifying features enhance the probability of small crack growth by increasing the chances that mechanical thresholds of K and ΔK are satisfied and by increasing the frequency of damaging operating pressure cycles.
