Aluminium coating on super duplex? 1

[Chiller]

It has been requested by our clients that super duplex under insulation must be Alumium thermal spray coated.

Are there anybody with such experience, or thoughts to whether this is a suitable thing to do?
Will the application of heat when coating have effects on the macro structure of super duplex to create a problem?

Many thanks in advance

 

[mcguire]

That's an odd one. Aluminum coating of stainless is, to my knowledge, only done on 409 and 439 for exhaust applications for oxidation resistance. There's no reason why it can't work with a super-duplex.
The problem won't come during aluminizing, which is fast and at a low enough temperature that sigma won't form. My question would be, "What service temperature does your client anticipate that would require aluminizing?" If it's high enough that oxidation would be a problem then sigma will probably be a problem.

 

[TVP]

Since it is thermal spray, is it possible that your customer wants the coating to be aluminum oxide, not metallic aluminum?

 

[EdStainless]

I am sure that this a themal spray AL coating of nearly pure metalic Al. It is not reacted with the base metal as in aluminizing. It is meant to be a sacrifical annode protecing against under depsoit corrosion.
Some companies wrap the piping with Al foil prior to insulating. Most use an epoxy paint to protect the SS.

I don't see why this won't work. Just make sure that the surface temp never exceeds 600F. I have seen Al sprayed onto cardboard.
What are you going to use as a sealer? A ureathane? These systems work much better if there is a sealer.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[unclesyd]

We used an Al spray coating, flame or thermal arc, for corrosion protection. The coating was Al based wtih a couple of % Si.
We did't use it on SS.
Our larger SS vessel were coated with a "?black silicate?" based paint if the vessel was insulated.

 

[hacksaw]

believe you problem has to do with contamination of superdulex stainless by the insulation; the alumize has the effect of a diffusion barrier.

 

[YLWEA]

About 20 years ago we used thermal sprayed anodic coatings to prevent external SCC of stainless steel piping. Process fluid was oxygen free and nearly neutral pH so no ID cracks, but if it dripped on the ajacent piping the oxygenated and highly concentrated (by evaporation) fluid caused cracking. Our testing of various coatings suggested that the benefits were from the galvanic difference between coating and substrate instead of or in addition to the barrier effect. I agree with previous posters who said there is little danger of hurting the duplex by this process.