Abstract
The stress corrosion cracking (SCC) susceptibility of duplex stainless steel tubulars in oxidant-free NaCl/H2S solutions simulating downhole sour gas well environments has been evaluated. The alloys tested had compositions of 21 to 25 pet Cr, ∼5 pct Ni, and ∼3 pct Mo and included both annealed and cold reduced products. The SCC tests were conducted in autoclaves pressured with H2S/CO2 and H2S /CO2/CH4 gas mixtures. Test specimens included a variety of statically loaded specimens (U-bends, C-rings, notched C-rings, tensiles, and precracked double cantilever beams) as well as dynamically strained specimens. SCC susceptibility increased with yield strength, comparing specimens stressed to their yield point. In Cl−/H2S solutions free of oxidants, SCC initiated under anodic (pitting corrosion) rather than cathodic conditions, similar to a Cl−/H2S synergism promoting both pitting and active corrosion. SCC susceptibility was measured over the full range of test temperatures: 23 ‡C to 288 ‡C. The composition-temperature region of SCC immunity has been partially defined and is largely dependent upon minimizing the H2S partial pressure, NaCl content, and the acidity established by the CO2 partial pressure.
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