Clamped CS shoe for SS Pipe--Corrosion issue

[cjabhijit]

thread378-337956

Dear All,

I am in a situation wherein there is a 2" SS Drain piping to be supported by CS bolted clamped shoe.
There are no insulators like liners etc. to avoid the contact in between the 2 different metals CS with SS.

Kindly advice on this at the earliest about how this is done or the above situation is acceptable?

What are the various ways to avoid the SS to CS contact in above situation?

Thanks & Regards,
Abhijit

 

[pennpiper]

Use a non-conductive Poly-wrap between the SS Pipe and the CS Clamp.

Sometimes its possible to do all the right things and still get bad results

 

[moltenmetal]

Your concern in this case should be limited to concerns over corrosion of the carbon steel part, not the stainless steel part. Any service where you'd be concerned about damage to the SS part, the carbon steel part is already so marginal in corrosion resistance that it won't be long for this world.

In practice, SS/CS galvanic joints don't tend to be much of a problem except again in services where the CS is already of marginal corrosion resistance.

We've used galvanized steel pipe shoes in contact with stainless steel pipe for at least the two decades I've been with my present company, and have never heard from a client that there's been a problem. In milder external corrosion situations, we've also used painted carbon steel shoes in contact with stainless steel pipe, again without problems in two decades. The coatings are NOT good enough in that case to eliminate galvanic coupling between the pipe and the shoe/structure.

Galvanized parts should not be used in contact with pipe above 200 C (400 F), since the galvanizing is of little if any benefit at these temperatures- and well above these temperatures, the risk of liquid metal embrittlement is at least a theoretical possibility.

 

[EdStainless]

If there are chlorides in the environment (near the coast) then corrosion of the CS and Cl combined can corrodes the SS pipe.
If you are not near salt water and these are exposed to rain they should be fine.
Isolating them is safest.

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P.E. Metallurgy, Plymouth Tube

 

[cjabhijit]

Thanks for your advice pennpiper will check out on that.
However, pls note provision for the same is not there in my support standard. If want to deviate, I need to get approved from Client as it is additional material/scope.

Moltenmetal,
It looks like you are of the opinion that I should overlook this problem & move forward. The support standard itself is not talking about it.
But I still feel that I should have a word with Client however, I wanted to make the grounding before I take it up to Client.

EdStainless,
Yes it is coastal environment then I need to isolate.
Pls share ways of isolating per your experience?

Thanks & Regards,
Abhijit

 

[EdStainless]

I have usually seen HDPE inserts used for isolation.
They need to have drain holes in them also.
I am sure that there are other things that will work.
Just make sure that there are no chlorides and that it cannot absorb moisture.

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P.E. Metallurgy, Plymouth Tube