Tubesheet Flatness Requirement

[msutherland]

Does anyone know what the recommended tubesheet flatness spec is for sanitary shell and tube heat exchangers where the bonnet pass rib does not have an actual seal but the rib face is metal to metal seal to the tubesheet face in multi-pass units? I contacted TEMA but since that isn't listed in their guidelines they cannot provide a answer for the requirement.

 

[SnTMan]

msutherland, that's a new one on me, it this a common arrangement?

What size unit, what leakage can you tolerate? How would relative deformations between the tubesheet and pass ribs be accommodated?

I'd think sealing would be an iffy propostion unless a pretty viscous fluid is involved.

Flatness? The flattter the better, what can you achieve?

Regards,

Mike

 

[msutherland]

SnTMan, The intent is not to completely seal the pass rib to the tubesheet face as it would be sealed with an elastomer in other designs. All of our standard designs which range in diameter from 3” up to 20” are this design with no elastomer to act as a seal between the pass rib and tubesheet face and we try to limit the “gap” between the tubesheet and the pass ribs. On average this gap is less than 0.005” and since most of our applications which have a viscosity of a water-like substance and are not of a low flow rate we experience very little cross flow pass the pass partition. We have had cases where this gap on larger units may be closer to 0.010”. We have had a customer question us on what is the allowable limit on the gap based on industry standards in which TEMA has none.

 

[SnTMan]

msutherland, then your answer is that there is no industry standard, and you quote the Manufacturers (your) standard.

Not every feature is subject to "industry standards".

Regards,

Mike

 

[innovation2]

For a sanitary unit I would refer to 3A guidelines. In my opinion I don't believe that a gap/crack of this fashion would be acceptable as it could not be cleaned by CIP. A design revision would be required to meet the sanitary requirement. On units that we see that do not have gaskets that seperate partitions a 1/8" gap is required to provide CIP. Typically, I have only seen this configuration on units like a falling film HX.

 

[msutherland]

Thanks for the response innovation2. We actually went through a 3A audit and have our marking permission to 3A stamp this design.