110ksi strength grade modified 13Cr steels, that are categorized as "13-5-2" in ISO13680, have been developed and widely used as an OCTG tubing material for CO2 environments containing small amounts of H2S. However, the application limits are not clear due to the complex interaction of the environmental-related factors, such as chloride concentration, pH and H2S partial pressure, on the sulfide stress cracking (SSC) and high temperature stress corrosion cracking (SCC) resistance. A 110ksi strength grade super 13Cr steel, UNS S41426, was evaluated for its SSC resistance in accordance with Method A of NACE TM0177-96. The SSC-resistance domains for 110ksi grade super 13Cr steel are proposed as a function of Cl- concentration, pH and H2S partial pressure. The influence of Cl concentration was larger for the lower pH or higher H2S partial pressure environments. The SCC resistance was evaluated by the four-point bent beam test technique. The SCC-resistance domain in 0.001MPa H2S environment at 175°C was influenced by Cl- concentration and pH. Super 13Cr steel suffered from SCC at low pH and high Cl- ion concentration even within the SSC-resistance domain. From these test results, it is suggested that the cracking resistance should be evaluated at the maximum service temperature, as well as at 25°C, when evaluating the application limits for super 13Cr steels.

Subject
Materials, Hydrogen concentration, Chloride ion concentration, Passive films, Partial pressures, Cracking resistance, Steel, Environments, Cracking, Sulfide stress cracking, Chlorides, Stress corrosion cracking, Chloride stress corrosion cracking
Keywords:
super 13Cr steel, super martensitic stainless steel, SSC, SCC, H2S
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2009
Association for Materials Protection and Performance (AMPP)
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