Corrosion of titanium rivets in ali/steel holes

[StevenKatzeff]

Hi,

I am hoping someone can help me with the following problem:

I have 3 metals in contact: An OS212 Steel bracket (Passivated+painted) connected via titanium rivets(Anodized) to an Al2024-T351-HDT Sheet (Anodized+painted). Although all three components have some form of corrosion protection, locally at the rivet holes, both the Steel and Ali parts are bare (I assume this as the holes are drilled after surface treatment). This leaves the bare Steel and Ali hole material in contact with the anodized titanium rivets. The spec calls for the titanium fasteners to be wet installed, but this was not done. The Steel and Ali parts themselves however have been wet installed and there is a decent layer of coating between them. As the relevant specs are sparse on info, my question is threefold:

1) Is the anodized protection on the titanium fastener enough to ensure no corrosion between the bare metals and the titanium.
2) To what extent will wet installing the fasteners protect the parts from corrosion. i.e. How can one rely on a coating on a driven rivet?
3) If there is a corrosion problem, what steps should be taken to repair the assemblies already in service.


Thanks,

 

[CoryPad]

What kind of rivet? Most rivets are deformed, so the anodizing would not survive.

1) No, that is why the wet installation was recommended.
2) The wet installation allows the protective organic coating to coat all surfaces then cure in place for barrier protection.
3) Spray protective coating over the fastener area or maybe remove the rivet (e.g. drilling) then wet install a new rivet.

 

[StevenKatzeff]

Thanks Corypad.

One more question:

Would it make a difference if the rivet positions are painted over after installation? Assuming the paint stays intact, is there still a concern of corrosion with the dry installed rivets?

 

[TomDOT]

Paint never stays intact.


....it's just the timeframe that varies.

 

[TVP]

IF everything stays dry (no electrolyte), then coating after installation can delay corrosion. TomDOT is correct, paint won't remain intact forever. Timeframe depends on environment (temperature including cycling, chemicals present, etc.), stresses (in-service and residual), etc.