Stabilized austenitic stainless steel (SS) grade 347 is used extensively in high-temperature processes in the petroleum refining industry, while duplex SS (DSS) grade 2205 is a relatively newer material in the industry. Though these grades of SSs perform well in refinery process streams, there are incidents of failure of process equipment attributable to stress corrosion cracking (SCC). The paper deals with a study on the cracking susceptibility of SS grade 347 and DSS grade 2205 in refinery simulated process environments containing hydrogen sulfide and chloride. The paper also reports the electrochemical behavior of these SSs in the medium containing hydrogen sulfide and chloride. The electrochemical behavior of the alloys was assessed by cyclic polarization experiments. Slow strain rate test (SSRT) was used to evaluate the susceptibility of the alloys to SCC. The cyclic polarization studies indicate that the H2S – chloride synergism had a pronounced effect on the localized corrosion susceptibility of 347 SS, while the effect was marginal on the alloy DSS 2205. The SCC susceptibility of 347 SS and DSS 2205 is strongly influenced by hydrogen sulfide-chloride synergism. Initiation of corrosion pits and the sulfidation of active pits due to the synergism were the important steps in the initiation of SCC.
The corrosion modes and extents of three candidate alloys (UNS S31603, UNS S31000 and UNS N06625) was investigated under simulated hydrothermal liquefaction (HTL) conditions. The effect of alkaline catalysts (K2CO3), operating pressure and flow rate on corrosion was also examined. Results indicated that the three alloys underwent general oxidation in hot pressurized water, of which SS 316 exhibited worse corrosion resistance compared to SS 310 and Alloy 625. The addition of K2CO3 resulted in a significant increase in the corrosion rates of the alloys, likely due to the formation of soluble metal hydroxides in basic environment. Environmental loop tests showed that higher operating pressure led to a marginal increase in the corrosion rates of SS 310 and Alloy 625. Increasing flow rate from 9 to 15 had no noticeable effect on the corrosion rates of the alloys in hot pressurized water at 310 C and 10 MPa.