All:

For over 20 years, and as recently as several months ago, we have been getting large (16,000-27,000 ft^2) code stamped process heat exchangers for PET plants with one tubeheet integral to shell and channel, and the other tube sheet integral to shell and extended as flange. This appears to be a TEMA "BEN" type exchanger.

So far, no issues have been raised as per UHX-13.2: "The two tubesheets shall have the same thickness, material, and edge conditions" from vendors. So, I am not sure if ASME has made this exchanger "illegal" now (actually since 2003!!)

I have had two replys on other posting (eng-tips) pointing out that the rule eliminates some other TEMA type exhcangers they feel are legal combinations (such as mine). Their view is that its not illegal to do and get code stamp, it just invalidates UHX-13 proceedures and puts one into U-2(g). One mentioned UHX-10, but I don't see how UHX-10 a, b, or c) will then point to d) in this particular case.

And, the statement seems pretty inclusive to me.

The only "out" that I (maybe) see is from "UXH-13.1 Scope" that says "...tubesheets MAY {rather than the legalise "shall"} have one of the four configurations...", with the implication that a mixed configuration is not one of consideration, thus nullifying everything below UHX-13.1. But each end is clearly one of the four, so...

Comments please!

Second, if it IS a legal exchanger, how does one analyze? I am not experienced on this type of analysis, but I thought tubesheet analysis (even TEMA) assumes that the two ends of the tube bundle/sheet/shell structure are structurally "mirrored".

Thanks
John