A mechanistic study on near-neutral pH stress corrosion cracking of pipeline steel

Abstract

This chapter investigates the roles of dissolved hydrogen in material and anodic dissolution in the near-neutral pH stress corrosion cracking (SCC) process of pipeline steel. A modified Devanathan-type dual cell is used in SCC tests to independently control both the dissolved hydrogen concentration in specimens and the anodic dissolution current density on the test surface. The experimental results show that both dissolved hydrogen in the pipeline steel and anodic dissolution promote crack initiation over a wide potential range. At high anodic dissolution rates, the crack initiation is retarded owing to the dissolution of the potential crack nuclei. The experimentally-measured crack growth rate decrease almost monotonically with increasing applied potential, but the anodic dissolution has no significant impact on crack growth rate. These results clearly indicate that the crack propagation process is controlled mainly by a hydrogen-induced crack mechanism. The chapter also proposes a preliminary chemo-mechanical model for the near-neutral pH SCC based on theoretical analysis and electrochemical measurements. According to this model, SCC is controlled by a synergistic mechanism of hydrogen- and anodic dissolution-induced plasticity.