Exploring the Service Life Extremes of 716 in Highly Corrosive Environments

716 (UNS N07716UNS N07716) is a commonly selected alloy for multi-decade oilfield applications with established environmental guidance from NACE MR-0175. Based on thermodynamic calculations, the historical limit determined using low-pressure rated equipment could be extended by 3x by accounting for non-ideal H2S phase behavior effects. Slow strain rate testing at 204 °C with increasing H2S concentration determined a potential traditional ideal 800 psi H2S limit and non-ideal 1100 psi H2S limit. TM0177 c-ring testing was conducted at these concentrations with 1200–1360 psi CO2, 20–25% NaCl, with elemental sulfurElemental sulfur at pressures of 2300 and 15,000 psi total pressure for 90 days. One 15,000 psi sample of nine unexpectedly cracked in a lower stress area outside of the highest stress apex area. Further microstructural analysis was conducted. The highest ever reported H2S 716 testing simultaneously proved multi-decade use at least 200 psi H2S over the standard and the new revision allowing elemental sulfurElemental sulfur is problematic.