Sealing Issue - marine environment

[stevenmon]

Hello,

I work for a company that manufacturers Marine Instrumentation. We try and use Plastics or Titanium whenever possible but in this case we have a 316 SS part (passivated) fastened to a Delrin Housing. The 316 SS Part has an Oring Face seal against the Delrin Housing. We always see corrosion between the two parts (my guess is stagnant seawater near the Oring is causing the corrosion). I need some help on solving the problem.


1. I am looking at using another grade of stanless since Titanium in this case is cost prohibitive. Could someone reccomend one?

2. My other option is to coat the Stainless with some type of epoxy or coating. Can a Oring worthy surface finish be maintained with an Epoxy? My guess is not.

Thanks
Steve

 

[MikeHalloran]

A properly designed o-ring cavity has more volume than the o-ring itself, so even if the o-ring is still sealing, there are places where water could collect in the joint and cause corrosion outside the sealing line.

You could use a Quad Ring(r), which has two sealing lines, and fills the corners of the cavity a little better.

You could pre-pack the groove with silicone high vacuum grease, which is relatively resistant to seawater.

You could use a laser-cut or die cut flat rubber sheet gasket.

You could use a formed- in- place RTV gasket. Some RTV grades sold for electronics use don't emit acetic acid on cure, so would be less likely to corrode the stainless.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Capntom]

How about Bronze or Nitronic 50 ??

 

[stevenmon]

Thanks for the responses. Another issue I forgot to mention is that the pressure requirement is 1000psi.

I am leaning towards coating the stainless part with some type of marine epoxy but I am not sure if I can control the epoxy in the Oring groove or lap it to guanratee a smooth and uniform surface. Is this possible? If I mask the Oring surface it defeats the purpose of coating the part since the salt water will attack the groove.

Is there some type of Gel or Grease that can help?

 

[unclesyd]

Here is one you might try, Krytox.

We use it on Kalrez, Viton and Silicone O-rings in some very rugged services.

http://www.dupont.com/lubricants/en/index.html

 

[mshimko]

I found from a previous project that o-rings form one of the most severe crevices, due to the compliant nature of the o-ring.

An epoxy coating in the area of the o-ring may work, but it carries some risk.

If you do try an epoxy; you'll need to provide locally a near optimum surface prep (SP-10 or better), then apply probably 2-coats of epoxy, then sand lightly to provide a smooth sealing surface.

The risks include crevice corrosion UNDER the epoxy.

As an example of the issues involved; years ago a lab actually tried gold plating to prevent crevice corrosion in an o-ring seal area. After 6-months of exposure in a test loop this joint was leaking. We removed the flange, and the gold plating just fell out! It turned out the "tie-layer" between the piping and gold was active compared to both the piping & gold and was quickly consumed by galvanic corrosion.

Our "final" solution in this case was weld cladding of a slightly more noble material. You should consider a similar solution if it's not too costly.

 

[stevenmon]

Thanks again for the input. Any ideas on some type of plating? Nickel?

It is looking more and more like Titanium is the only real answer as it will introduce more and more labor associated with applying an epocy/lapping etc.

 

[mshimko]

From my memory, the "standard" cladding material to prevent crevice corrosion of CRES would be an inconel. I do not recommend plating for the reasons stated in my previous post.