Role of Stress in Transgranular Stress Corrosion Cracking of Transmission Pipelines in Near-Neutral pH Environments

摘要

Transgranular stress corrosion cracking (TGSCC) of carbon steel pipelines occurs on buried transmission lines that are protectively coated and subjected to cathodic protection. Analysis of failed pipelines and previous research suggest that hydrogen is involved in the cracking process. The objective of this research was to further the understanding of the mechanism of TGSCC by determining how stresses affect hydrogen diffusion into the pipeline steel and crack initiation. Slow strain rate test results with varying load conditions on plain and notched samples indicate that stress concentration is required in order for the hydrogen to accumulate in sufficient quantity to induce quasi-cleavage fracture behavior. One source of stress concentration on pipeline steels was determined to develop from preferential dissolution of surface inclusions in near-neutral pH environments, leading to pitting and development of cracks at stresses lower than yield strength. Results from this study provide an insight into the hydrogen-driven mechanism of TGSCC by understanding the conditions of hydrogen diffusion into the pipeline and the sites of hydrogen accumulation. [PUBLICATION ABSTRACT]