Stress Corrosion Cracking of 316L Stainless Steel in Concentrated Ammonium Chloride Solution with Very Low Dissolved Oxygen Levels

Slow strain rate testing has been used to investigate the susceptibility of 316L stainless steel to stress corrosion cracking (SCC) in high chloride and low dissolved oxygen (DO) brines. Tests have been performed for various temperatures and ammonium chloride (NH₄Cl) concentrations. The susceptibility to SCC was assessed in terms of ductility loss, detailed fractography, and cross-sectional inspections to identify the damage mechanisms. It is challenging to maintain long-term SCC experiments with very low DO levels. In this work, we showed that 3 h of sparging with high-purity nitrogen at a flow rate of 0.2 L/min was sufficient to reduce the DO in a 0.6 L test solution to approximately 10 ppb. However, over the full test duration of 7 d or 8 d with continuous nitrogen purging of the solution, the mean and maximum DO values were 17.4 ppb and 34.4 ppb in 40 wt% NH₄Cl, and 16.5 ppb and 41.8 ppb in 30 wt% NH₄Cl solutions at 95°C. For 316L stainless steel at the open circuit in ≥ 30 wt% (i.e., 6.1 M) ammonium chloride solutions with these very low DO levels, pitting corrosion was not seen at 60°C, became evident at 80°C and was severe at 95°C and above, while SCC was not seen at 60°C or 80°C, was possibly initiating at 80°C without propagating significantly and was severe at 95°C.