Porcelain enamel coated pressure vessel 1

[grayseal]

My company currently manufactures (ASME Section VIII) autoclaves made from 304 stainless steel. I am considering making them out of carbon steel and coating them with porcelain enamel for corrosion resistance. Some questions I have include:
Can dissimilar metals (stainless steel welded to carbon steel) be coated? I am concerned about the difference in thermal expansion.
What base material can be used that is ASME approved?
Can threaded bosses be coated?
Can parts be cold straightened after the coating process?
Is there a rust inhibitor out there that can be welded over without affecting the weld or the welder?

Any help is appreciated.
Grayseal

 

[MJCronin]

grayseal,

Stainless steel can be welded directly to carbon steel.Most piping and ASME vessel fabricators have AWS weld proceedures already developed. I don't recall ever reading about porcelain coated stainless steel.

My understanding is that the two materials are far enough apart on the galvanic series to pose no corrosion problems.

However, I don't understand porcelain-coated carbon steel in a thermal cycling application ? (Autoclave) Wont there be trouble ? Have any of these units been made and have they been tested ? I would guess that you are setting yourself up for an eventual fatigue failure ?

MJC

 

[grayseal]

MJCronin,

Thanks for the response. I am not concerned with the weldability of carbon to stainless, but I don't know what will happen to the coating when it cools down from approximately 1600 degrees F (baking temprature of the coating). Since thermal expansion of stainless is three times that of carbon steel, I feel the coating may flake off.
As far as thermal cycling, I think this type of coating is used on the common house hold oven and possibly water heaters. I have room temperature cycled at 60 psi two different chambers. I did get some flaking in a location that had weld melt through. The coating will not stick to an oxidized surface.

grayseal