ASTM A 453 grade 660,class A,B,C and D fastener rusted in our system and now I am looking for reason why this material rusted by looking properties and High temp fasteners this is the best fastener to use as per knowledge to high strength and high temp application.We used 316SS washer with this bolt its ok or not?Some of those bolts are mixed with black oxide coating may be thats the reason to rusting those bolts. I am not getting any conclusion on this and getting more and more confused Please help me. These fastener are used in seawater application.Any alternative for 660 bolt? What if i do passivate these bolt and use it it give me more corrosion resistance or not? Thanks in Advance for help.