Susceptibility of 316L Stainless Steel to Chloride Stress Corrosion Cracking in Low Dissolved Oxygen Environment

Abstract It is widely referenced that chloride stress corrosion cracking (CSCC) of austenitic stainless steel will not occur provided that the concentration of dissolved oxygen (DO) is kept low enough. However, field evidence has suggested otherwise, with suspected cases of CSCC occurring even in the absence of oxygen. These instances were linked with either formation waters (high MgCl2 content) or refinery applications (deposition of NH4Cl salts). While there is plenty of research on MgCl2 solutions, the literature on NH4Cl corrosion is relatively sparse. This study focuses on determining the 316L threshold for CSCC in the absence of oxygen in concentrated NH4Cl environments. The experiments were conducted in de-aerated (DO < 20 ppb) ammonium chloride solutions. Slow strain rate tensile testing (SSRT) was carried out at a strain rate of 4x10-7s-1 in temperatures ranging from 60 to 105 °C and concentrations ranging from 15 to 40 wt.%. The results showed stable pit growth above 80 °C and branching cracks, indicative of CSCC, at temperatures above 95 °C, even in de-aerated systems. This indicates that dissolved oxygen may not be a pre-requisite for CSCC in highly concentrated chloride solutions.