Galvanic risk of Beta C titanium Pins in Duplex/Super Duplex 2

[Ibreakstuffdigitally]

Hello

We're in the process of designing some Beta C titanium shear pins for a super duplex component. The assembly will spend most of it's operational life fully immersed in sea water. The actual stainless alloy has yet to be determined, It will be manufactured by others, and our control over that material choice may be somewhat limited.

Before we go through the rather lengthy process of load testing and qualifying a batch of material for the pins, we need to evaluate the potential risk of eating the stainless steel part. The ti pin is about two orders of magnitude smaller, but I'm still concerned.

Could anyone suggest a good technical reference for this? mil-std-889 doesn't list duplex, but austenitic grades are listed as incompatible with ti in seawater (not the same I realize)

The shear pins are going to have to be replaced on a regular schedule anyway, probably every 6 months or so. As such, coating them with something ablaitive may be an option. Any suggestions on a coating solution would also be very much appreciated. Even a wet assembly compound might be viable considering the geometry.

Thanks in advance for any suggestions or references.

 

[SJones]

See attachment.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[EdStainless]

Good ref Steve

In this combination there is no risk. A superduplex (any of them) will be fully corrosion resistant in seawater. They are galvanically very similar.

The risk in this type of situation is not to the SS part, but to the Ti. If there is any corrosion then hydrogen will be evolved and the Ti is at risk form hydrogen embrittlement.

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[Ibreakstuffdigitally]

Thankyou both for the information. I'll have to look into the risk of hydrogen embrittlement of titanium. We've had titanium couplers operate in similar service for years with no corrosion issues, so it's not something I'd considered, but the geometry here is definitely different.

We had some hydrogen embrittlement issues in plated bolts once a few years back and I have no interest in putting the design at risk of that.

 

[EdStainless]

I have seen it happen to Ti inserted into 316, but not higher alloys

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