13Cr-5Ni-2Mo type Super Martensitic stainless steels (SMSS-13Cr) are often chosen for the manufacture of downhole completion equipment within the oil and gas production environment. SMSS-13Cr is primarily used in CO2 rich production environments where carbon/low-alloy steels are subject to high corrosion rates. Currently, different UNS grades of SMSS-13Cr with varying maximum hardness, yield strengths, and heat treatment requirements are listed for use in limited sour service in the NACE MR0175/ISO 15156-3 guidelines1. The hardness limits of the listed grades mainly pertain to the 95 ksi (655 MPa) Specified Minimum Yield Strength (SMYS) level. The environmental limits listed for the 95ksi MYS grade have similar maximum H2S partial pressure and minimum fluid pH values, but vastly different chloride concentration limits. While chloride ions can pit SMSS-13Cr type materials, it is not clear historically why the current limits reflect a difference between the UNS grades within the same alloy type.

This paper discusses a study in which the SSC resistance of two different SMSS-13Cr UNS bar grades, S41425 and S41427 quenched and tempered to 95 ksi MYS were evaluated in multiple simulated downhole production environments to study the main effects of H2S partial pressure, environmental pH, and chloride concentration. The SSC results provide comparison between cracking resistance of S41425-95 and S41427-95 in sour service environments. These results also offer insight for plausible limits on H2S partial pressure, environmental pH, and chloride concentration based on testing per current NACE MR0175/ISO 15156-3 guidelines.

Subject
Test methods, Water, Materials, Partial pressures, Cracking resistance, Condensed water, Salinity, Heat, Pitting, Sulfide stress cracking, Hardness, Chlorides, Quenching and tempering
Keywords:
Sulfide Stress Cracking (SSC), 13Cr-5Ni-2Mo, Super Martensitic Stainless Steel, S41425, S41427, bar stock, H2S, NACE MR0175/ISO 15156
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2022
Association for Materials Protection and Performance (AMPP)
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