Official Answer
Answer
Elgiloy (a Co-Cr-Ni alloy) is selected for spiral retaining rings in subsea oil and gas tools due to its exceptional resistance to Sour Gas ($H_2S$) and its ability to maintain high strength at cryogenic and elevated temperatures. It is NACE MR0175 compliant, meaning it is resistant to sulfide stress cracking. The material's high modulus of elasticity ($E \approx 30 \times 10^6$ psi) and excellent fatigue endurance make it superior to 17-7PH in environments where cyclic loading and extreme corrosion coexist. Processing involves cold working followed by age hardening to achieve tensiles exceeding 250 ksi.
