AISI 420/410 Modified Martensitic Stainless Steel Bar Stock Materials Sulphide Stress Cracking (SSC) Resistance in Mildly Sour Environments

UNSⁱⁱⁱ S41000 and UNS S42000 martensitic stainless steels bar stock alloys are often selected for downhole completion equipment due to their good performance in oil and gas environments. In accordance with the ISO^iv 15156 / ANSI^v NACE^vi MR0175 Part 3¹ guidelines, UNS S41000 and UNS S42000 quenched and tempered to 22 HRC have a maximum ppH2S limit of 10 kPa (1.5 psi). For H₂S levels exceeding 10 kPa (1.5 psi), the most common selection is precipitation hardened nickel alloys.

Martensitic stainless steels are desirable as the lowest cost oil and gas corrosion resistant alloys and knowing their corrosion performance application windows for well construction materials is critical to their safe application. Similarly, it is possible that more stringent specification of these grades could extend their utility to more severe environments, decreasing reliance on PH-Ni alloys which are expensive and increase the lead time for equipment.

Earlier work identified² the effect of restricting the nickel (Ni) content in 13Cr tubing to ≤ 0.2 wt.% to reduce the threat of both localized corrosion and Sulfide Stress Cracking (SSC). Therefore, limiting the Ni content in alloys UNS S41000 and UNS S42000 should provide a similar effect, improving their corrosion performance in more demanding conditions. The currently generally accepted Ni content limits are ≤ 0.5 wt.% and ≤ 0.2 wt.% for UNS S41000 and UNS S42000 respectively.

The present paper provides insight into the SSC performance of UNS S41000 and UNS S42000 bar stock alloys when the Ni content is ≤ 0.2 wt.% compared to a Ni content ≤ 0.5 wt.%. The SSC results support the hypothesis that a Ni content limit of ≤ 0.20 wt. %, brings a performance benefit to UNS S41000 and UNS S42000 bar stock alloys, extending their application to more severe oil and gas production environments.

Evidence is also presented on the effect of inclusions and the need for quality control on inclusion type and size, especially with respect to pitting corrosion resistance in aggressive production environments and during acid treatment well interventions and stimulations.