User blog comment:Unownshipper/Metallurgists Wanted: Rapture's Natural Resources/@comment-3967731-20140811034544/@comment-75.36.139.103-20140811135946

Stainless doesnt do great in Salt Water. Monel is better but a quick search didnt find mention of whether pressure makes a big difference (it does for some materials).

The main problem is Monel is more than half Nickel (upto ~70%)and most of the rest is Copper. SO you back to where do you get those in the ocean  (and in the quantities for construction purposes).