Alexander Saul’s scientific contributions

Slow strain rate testing has been used to investigate the susceptibility of 316L stainless steel to SCC in high chloride and low dissolved oxygen brines. Tests have been carried out 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 hours 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 ~ 10 ppb. However, over the full test duration of 7 or 8 days with continuous nitrogen purging of the solution, the mean and maximum DO values were 17.4 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 open circuit in ≥ 30 wt % (i.e. 6.1M) 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 or 80 °C, was possibly initiating at 80 °C without propagating significantly, and was severe at 95 °C.

Corrosion of stainless steel in applied industrial environments continues to be an area of concern for various refining operators. It is well accepted that a certain concentration of dissolved oxygen is required for chloride stress corrosion cracking (SCC). However, there are some environments where it is suspected that chloride SCC can occur even in the absence of dissolved oxygen. The susceptibility to SCC of 316L stainless steel has been studied in the pursuit of extending operating boundaries at higher temperatures under low dissolved oxygen concentrations. Slow strain rate tensile (SSRT) tests have been carried out for various temperatures and ammonium chloride concentrations under low dissolved oxygen conditions. The susceptibility to SCC was assessed in terms of the relative reduction in area (RRA). Detailed fractography and cross section inspections were used to identify the damage mechanisms. The implications of this behavior and its influence on improving material selection have been discussed.