Investigating the mechanism of stress corrosion cracking of controllable rolling pipe steel X70 in near-neutral environment

Abstract

The results of investigating the mechanism of stress-corrosion cracking of a controllable rolling pipe steel X70 at a cathodic protection in near-neutral pH environment, using slow strain rate tests and polarization curves, are presented. Using the method of polarization curves, a critical range of potentials, namely, from −0.75 VAg/AgCl to −0.97 VAg/AgCl was determined, in which the steel stays in a non-equilibrium electrochemical state and anodic dissolution proceeds simultaneously with hydrogen reducing. It has been shown that in this range, the sensitivity of X70 steel to a stress-corrosion cracking is observed, which correlates with the loss of plastic properties and the appearance of a brittle component in the fracture. At the potential of −2.0 VAg/AgCl, the predominant cathodic reaction is hydrogen reducing at the tip of a crack and its walls. Here, the brittle fracture dominates, which correlates with the character of the fracture.