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What coating for steam coil used in caustic solution

September 8, 2011

we are looking at coating a 2" carbon steam coil, approx temp 340 F.
It is installed in a tank to contain a caustic solution up to 50%
Looking at all options. metallizing last resort, 25' of piping

Dave Korn
applicator - Burnaby B.C. Canada

First of two simultaneous responses -- September 9, 2011

Sir:

No coating for mild steel coil is required for a caustic soda [affil links] (sodium hydroxide) solution.

Regards, Dr. Thomas H. Cook, Hot Springs, South Dakota, USA

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA

Second of two simultaneous responses -- September 9, 2011

We used plain black steel pipe in our caustic cleaner, but it was less concentrated and a lot lower temp.
The major problem with really hot pipes is that they get a coating on them that is like rock and it destroys the heat transfer.
I am not aware of any coating that would be worth the additional cost. I doubt if it would be worth using stainless steel.

For steel, use sched 80 fittings as that is where we had the eventual failures with sched 40. (have I got these sizes confused with pvc??)

James Watts
- Navarre, Florida

Hi. I believe that James is correct on every point. In the plating industry, with which I am familiar, the closest process we have is black oxiding, which operates at about 275° F ±, and a substantial caustic concentration approximating yours. It does not attack the steel tanks, but coils are pretty much useless as James explained. Direct gas firing under the tank is pretty universal.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 12, 2011

I agree with the response from James Watts. In this bath, any hardness at all will form scaling on the heating coil and sludge in the tank. If you use softened water for make-up, it will at least slow this down and minimize the problem.

Lyle Kirman
consultant - Cleveland Heights, Ohio
September 13, 2011

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