Duplex stainless steel is widely used in the oil and gas industry due to its inherent resistance to localised corrosion and stress corrosion cracking. However, duplex stainless steel can still be susceptible to stress corrosion cracking in H2S-containing environments, if the environmental conditions are aggressive enough. Thus, published limits exist in ISO(1) 15156 (NACE(2) MR0175) to constrain use of the material to safe environments (in terms of chloride content, temperature, pH2S and pH). Testing under conditions outside of these published limits is permitted to assess whether a material may be suitable for use outside of the limits. Constant load tests were carried out on a wrought duplex stainless steel (UNS S31803) under conditions suggested to be a sour service limit for the material. All specimens suffered localized corrosion and cracking. Surface finish and microstructural analyses were carried out to investigate their influence on the localized corrosion and SCC resistance of the material.

The results of the SCC tests showed that wrought UNS S31803 was not resistant to environmentally-induced cracking or corrosion in the test environment (100,000mg/l chloride, pH4.5, 80°C, 0.35bar pH2S). A difference in surface finish did not have a significant effect on the degree of corrosion or cracking.

Subject
Surface finishing, Test methods, Materials, Microstructure, Grinding, Roughness, Corrosion cracking, Corrosion resistance, Duplex stainless steel, Localized corrosion, Chlorides, Stress corrosion cracking, Chloride stress corrosion cracking
Keywords:
Duplex stainless steel, stress corrosion cracking, constant load, H2S, sour
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2017
Association for Materials Protection and Performance (AMPP)
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