Besides 316 SS, are there any other stainless grades especially suitable for service in a salt water environment and in pressure applications, i.e. pressure piping, and vessels in off shore facilities?
As EdStainless mentioned, superaustenitic stainless steels were specifically developed for seawater usage. Outokumpu, Sandvik, and Allegheny Ludlum all have a great deal of technical information available from their websites. Use the following links for more information:
I just noticed that the link I provided earlier for Sandvik is for the Sandvik Powdermet group, which is only one of their activities related to marine applications. The following link has information on the traditional wrought stainless steel products that Sandvik offers for offshore/oil & gas applications:
Zeron 100 is another superduplex stainless that is commonly used for offshore applications and seawater RO units. Superduplex and 6-Mo superaustenitics do have higher strength than 316L so keep that in mind when designing pressure applications you might be able to reduce the wall thicknesses and save on the initial cost.