Grade 660 Class A,B,C Fastener Rusted.

[ram18]

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 that's 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.

 

[Navin A S]

If the fasteners are being used in a seawater application, it is not recommended to use ASTM A 453 grade 660 as this material does not have adequate corrosion resistance for this type of environment. It is better to use a more corrosion resistant material such as 316 stainless steel or duplex stainless steel. Passivating the bolts may help improve their corrosion resistance, but the effectiveness of this will depend on the passivation process used and the environment in which the fasteners are exposed to. Alternatively, you could look into using other materials that are specifically designed for use in seawater environments, such as Titanium or Super Duplex Stainless Steel.