Stainless steel will rust, even the better grades will tarnish, although the marine grade is very resistant. If you look at your kitchen stainless steel you will notice it may say 18/8 or 18/10, a higher grade. The first number refers to the chromium and the second to nickel. When you take cutlery out of your dishwasher you may well find tarnish marks on it from the aggressive action of the cleaning chemicals.
Colin