Challenges of Materials and Corrosion Management: Stress Corrosion Cracking (SCC) and Gaping in our Understanding of the Subject

An essential step in materials degradation is the determination of the failure mechanism. For example, stress, metallurgical (microstructure), or environment-assisted cracking (EAC), helps the determination of the fundamental cause of failure and recommendation on proper measures to prevent failure recurrence. In this context, environment-assisted cracking, or environmentally induced failure, is a form of corrosion that produces a failure/fracture in alloys with minimal corrosion. As for example, environmentally assisted cracks in linepipe steels are initiated either because of stresses in combination with environmental effects, as in SCC, or because of trapped hydrogen in the steel or HIC. To understand better the mechanism of the crack initiation process, key metallurgical and environmental elements that can affect the cracking phenomena were investigated and reviewed. The complexity of both cracking phenomena results from the dependence of SCC and HIC on multiple metallurgical, mechanical, and environmental parameters that may all influence both crack initiation and propagation. Cracking of linepipe steels is analyzed critically, with particular attention to the crack initiation process. The paper is divided into two parts: (i) stress corrosion cracking (SCC); and (ii) hydrogen-induced cracking (HIC) also referred to as hydrogen embrittlement (HE). Many non-metallic particles and stringers, and the anomalous microstructures are excellent trapping sites for diffusing H atoms and the initiation and growth of cracking.