Answer
316 Stainless Steel is preferred for marine environments due to the addition of molybdenum ($2-3\%$), which provides superior resistance to chloride-induced pitting and crevice corrosion compared to 302 or 304 stainless. However, 316 cannot be hardened by heat treatment; its strength is derived solely from cold working (drawing and coiling). This limits its maximum tensile strength to approximately $160-185$ ksi, which is lower than the $200+$ ksi achievable with 17-7PH. Consequently, for a 316 ring to match the thrust capacity of a 17-7PH ring, it may need to be thicker or have a deeper groove. In subsea applications where the ring is static, 316 is ideal, but for dynamic or high-load applications, a higher-strength superalloy like Inconel 625 might be required.
