Wells in oil, gas and geothermal production experience a broad spectrum of operating conditions in terms of temperature, depth, pressure and production environments, which govern material selection. For severe environments, where high strength and toughness combined with excellent corrosion and cracking resistance are required, a new superaustenitic stainless steel has been recently developed. Aiming for a minimum yield strength of at least 120 ksi (827 MPa), strain hardening enables the desired mechanical properties, allowing users to avoid well known but HISC susceptible and less cost effective precipitation hardened (PH) nickel alloys.
Product Number:
51322-17720-SG
Author:
Julia Botinha, Helmuth Sarmiento Klapper, Clara Herrera, Merlin Seifert, Bodo Gehrmann, Helena Alves
Publication Date:
2022
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Corrosion resistant alloys are used in oilfield applications where carbon and low-alloy steels are expected to be affected by corrosion, and they often represent a cost-effective alternative to chemical treatment, or where specific application-driven requirements are required. Several alloys from 13% chromium stainless steel up to highly-alloyed nickel and cobalt alloys have been successfully used in drilling, completion, production as well as offshore oilfield equipment, where corrosion resistance is of concern. Many drilling technology components, for example, require non-magnetic austenitic stainless steels. In demanding production environments involving very corrosive fluids at elevated temperatures, on the other hand, nickel alloys are preferred. While one of the disadvantages of stainless steels concerns their limited resistance to localized corrosion and stress corrosion cracking in halide-containing environments, nickel alloys, particularly those that are precipitation hardenable, might be susceptible to hydrogen-stress-induced cracking (HISC).
Due to its excellent resistance to localized corrosion and environmentally assisted cracking at elevated temperatures as well as high resilience to hydrogen-assisted cracking mechanisms, UNS N08034 – a superaustenitic stainless steel with increased nickel content and balanced additions of nitrogen and manganese – is a promising candidate for oil and gas applications. Its refined chemical composition improves manufacturing characteristics to allow the fabrication of large components, including good machinability and weldability. Its non-magnetic nature enables the use in directional drilling and reservoir characterization tools. Since one limitation of austenitic stainless steels is their strength, cold working has been used to increase the yield strength of UNS N08034 to values higher than 120 ksi (827 MPa). In this study, a manufacturing process was developed based on thermodynamic and laboratory studies and subsequently applied to mill production trials. This paper reports the results from mechanical testing as well as microstructural investigations and corrosion testing conducted on strain-hardened UNS N08034.
