Stainless steel is a wonderful product as long as it is of 316 grade
Stainless steel that is less than 316 is of no real use in the marine environment, it rusts. Even 316 has its problems and during my surveying of vessels from 12 to 30 metres I come across it being used in all sorts of ways, most of which are appropriate and in good order. However, occasionally I come across a problem that you would not think could occur.
One particular vessel had a stainless steel emergency fire main water system fitted during construction. Now four years on it had started to give problems. It leaked when tested. Further investigation revealed that the 40 mm diameter stainless steel pipe had rusted through in several places. (See the image below) This had happened because the pipework had not been completely drained of the salt water after testing, some time before, and had not been flushed through with fresh water as would be good practice. Salt water left in a confined space in a stainless steel fitting will corrode the metal. On this vessel all the pipework had to be replaced, very expensive.
OK, not all vessesl have fire main water systems, but these days many builders are using stainless steel fittings which, if not installed and maintained correctly, could give a problem in a relatively short timescale.
So the moral of this story is that stainless steel is a wonderful material, but like all metals in a marine environment it needs to be well maintained and definitely not taken for granted.