304 is more prone to develop rust stains than 316, be prepared to rub the surface down now and then to remove the rust.

But with these steels there is more than can be seen by the eye. If there are welds the risk for weld decay must be considered. The scientific term for this phenomenon is carbide precipitation, and it lowers the corrosion resistance in a narrow area adjacent to the weld, and can cause sudden failure under load. Unfortunately this happens in the marine environment after some time has passed.

The problem is that weld decay is not readily apparent, nothing can be seen, and if it is not known what the manufacturer has done to prevent it corrosion testing is needed in order to find out if it will occur.

If the right kind of stainless is used the trouble is avoided, there should be a letter L following to the notation, i.e. 304L.

Also stainless without the L can be used, but in this case solution annealing is necessary. This means heating the welded item to 1050 deg C, and then quenching it in water. This procedure prevents weld decay on thin parts which are cooled down quickly enough.

Find out from the supplier whether either of these preventions has been used. If he has no idea it would be advisable to do corrosion testing first, or find another supplier

Lars