Corrosion between Titanium Fastners and 316 Stainless Steel Tubing

[RGNCJN]

thread307-108364

We currently have a product where we are supplying Titanium ASTM B348 Grade 2 Bolts, washers, and nuts specified by our customer. These bolts will be in contact with 316 Stainless steel sleeves that we have bonded into our polyurethane parts. The possible contact areas will be between the washers and the pipe ends and between the threads of the bolts and the i.d. of the pipe. We are worried about possible corrosion between the two dissimilar metals. These parts will be in an offshore environment. They may be wetted with salt water but I don not believe they will be submerged. Is anyone aware of any issues between these two metals? I linked a thread that I found through searching but no follow up was given. All that was said is that there may be a problem. Any assistance would be greatly appreciated.

 

[cloa]

Do you have an estimate of the relative surface areas?

Try googling Galvanic corrosion Titanium and 316.


e.g.

http://cat.inist.fr/?aModele=afficheN&cpsidt=13468193

 

[SJones]

Galvanic corrosion should not be too much of an issue as the two materials are not too far apart in the galvanic series. The most probable mode of attack will be crevice corrosion of the 316.

Steve Jones
Materials & Corrosion Engineer

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

 

[RGNCJN]

I appreciate the responses gentlemen. I have looked up galvanic corrosion and have noted that the two materials are not that far from each other on the chart. But I have read that the distance from each other on the chart doesn't necessary have anything to do with the rate of corrosion. The rate of corrosion has more to do with the enviromental conditions and the relative surface areas. The sleeve is a 5/8" O.D. .049" wall thickness. The washers are standard 1/2" washers.

SJones where would you see crevice corrosion being a problem? Are you referring to the interface of the SS sleeve and the bottom of the washer? If you do feel this is where the problem will arise how would you recommend preventing this?

I have included a sketch of the bolted cross-section in question. The yellow is polyurethane. Hope this helps.

 

[EdStainless]

I am with SJones on this. Crevice corrosion of the 316 is the most likely problem. The Ti will look inert in this environment.

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Plymouth Tube

 

[SJones]

Initially at the washer-sleeve interface and, as the corrosion progresses and opens up a gap, further down into the sleeve-thread region. The titanium shouldn't be affected too much. You might get a bit of rust staining showing on the outside after a while, but it wouldn't appear to be a critical failure mode for the arrangement as shown. As to preventing it, you have to keep moisture and salt from penetrating under the washer - reliably! Assess whether the arrangement can tolerate some metal loss on the sleeve near the interfaces. If not, then change the 316.

Steve Jones
Materials & Corrosion Engineer

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

 

[EdStainless]

For a medium term fix you could try to fill the internal gaps with a stiff synthetic grease. This might keep enough water out to slow the 316 corrosion.

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Plymouth Tube

 

[RGNCJN]

Thank you for the responses gentlemen. I think I will recommend the grease as an option I may also look at using some silicone.