Steam pipe protective coating under insulation
Steam pipe protective coating under insulation
(OP)
What is an acceptable and economical method of protective coating for steam pipe under insulation (calcium silicate)?
Pipe is for cyclic loading between 450 degF and ambient. Not in high moisture zone.
I was told NACE prohibit hot galvanized coating (zinc based) under insulation. Do not know the reasoning behind it.
Want to know what the general practice is for the case. Thanks.
Pipe is for cyclic loading between 450 degF and ambient. Not in high moisture zone.
I was told NACE prohibit hot galvanized coating (zinc based) under insulation. Do not know the reasoning behind it.
Want to know what the general practice is for the case. Thanks.
It boils down to simple math.





RE: Steam pipe protective coating under insulation
On steam pipes where we a problem similar to yours we will lag the Cal-Sil and finish it with some type coating. We exclusively use SS weather coating for these pipes. It's the Cal-Sil that will more than likely need the protection from water. If ever the insulation gets wet it needs replacing as it will never effectively dry in service.
http://www.dampney.com/Products/ProductLines.asp
RE: Steam pipe protective coating under insulation
Why do you think you need to?
RE: Steam pipe protective coating under insulation
Forgot to mention the A106B pipe material.
pennpiper: Does pipe need to be galvanized or better without?
I was told I should be concerned about under insulation corrosion. But is corrosion from inside more than from outside for steam pipe?
Thanks.
--It boils down to simple math--
RE: Steam pipe protective coating under insulation
Do not use galvanized in Steam Service or any other service above 350F.
Corrosion under insulation is a big problem if one doesn't keep the weather barrier in good condition, which is hard to do in today's economic times. There just any money for maintenance but plenty to replace a failed line.
Generally corrosion or erosion is from the inside is the biggest problem with carbon steels in a poorly operated steam service. If a steam line remains above 100C about the only problem you will see external is you have poorly maintained insulation and drops of water hits the pipe you eventually have trouble.
pennpiper,
At one time our pipe specs called for silicate based coating or aluminizing on any steam service under 300 Lbs. This was in the days of tar paper and chicken wire with "bull" mastic. Never was told why, just do it, yes sir.
RE: Steam pipe protective coating under insulation
Stainless steels that are insulated can be corroded by some types of insulation.
RE: Steam pipe protective coating under insulation
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RossABQ,
At one time before low chloride insulation became available we would take the Cal-Sil clam shells and lag the inside with A Cloth and coat with Sodium Silicate. We still did this + coating the lines until we lost the A cloth.
Addenda:
All black iron pipe used to come with a heavy coating. On fittings you could tell by the color who made them. All I recall is that Taylor Forge was green.
RE: Steam pipe protective coating under insulation
I would have owner to get invilved and make this decision.
--It boils down to simple math--
RE: Steam pipe protective coating under insulation
There is a small temperature range where the galvanic potential between steel and Zinc reverses. If there is moisture (there will be bacause it will condense from the air breathing in and out of the insulation as it heats and cools) and any damage to the paint surface on the pipe you will get very agressive corossion.
NACE have a paper on it. Last I saw it recommended several coats of a silicone based paint and be careful not to scratch it.
Make sure you have inspection panels in the cladding and open them regularly. Then every now and then open a section you have not previously inspected. You will be shocked if you find this damage and will realise the importance of the measures suggested here.
Regards
Dennis Kirk-Burnnand
Dennis Kirk Engineering
www.ozemail.com.au/~denniskb
RE: Steam pipe protective coating under insulation
Service - Insulated parts (carbon steel) exposed to temperatures up to 400 deg C
Location - Indoor/Outdoor
In the works
Surface preparation - Blasting to ISO 8501-1 grade Sa 2.5
Surface profile to ISO 8503 ' medium (G,S)
Primer, Weldable inorganic zinc ethyl silicate, 25microns DFT
At site
Surface preparation - Cleaning and derusting mechanical damages to ISO 8501-1 grade Sa 2 or St3
Touch up, Weldable inorganic zinc ethyl silicate 25microns DFT
RE: Steam pipe protective coating under insulation