This sounds like a poster child for stress corrosion cracking - which would greatly impact the toughness of the material. Most steels (including stainless) become significantly more brittle under stress when exposed to high chloride environments like seawater while under load - much more than standard fracture mechanics would suggest. Basically there's chloride penetration and then hydrogen generation at the grain boundaries within the metal structure, which significantly reduces the toughness and allows for rapid and catastrophic failure easily.