HX Modification

[picasa]

Modification needs to be done to an existing shell and tube HX (Carbon Steel). Originally HX is four-pass. It needs to be made two-pass. That requires that the old partitions (that are off-center) are taken out and new one be put in at the center line. Does this require re-stamping the vessel? Do calculations need to be done again for the tubesheet thickness? Please provide any references discussing this issue. Does TEMA allow such modification to the tubesheet? What does ASME Section VIII say about this modification?

 

[jte]

picasa-

The pass partition plates are internals which are not part of the ASME (or, as far as I know, TEMA) design. As such, you can pretty much do what you want with them. Cutting out the old ones is a non-Code job. The only thing to be careful with is that the weld of the new partition plate to the shell should be of the usual PV quality using a "weldable" (per VIII) steel and approved by the AI. Whether or not such a change would require an R stamp is up to the AI, though I would expect it to be chalked up as the old "repair of a routine nature" variety.

I would not expect any impact on the tubesheet thickness, as you are not changing the design pressure and presumably you are keeping the pass partition plate groove at the same depth as the original grooves were.

References... Don't have any that spring into my head at this point.

jt

 

[rmw]

If the pressure boundary is cut on or welded to, I have seen it interpreted as a modification, and not just a "R stamp" type repair (which infers putting it back to its original state). The tubesheet is part of this pressure boundary, as are the channel pressure boundaries.

I would check very closely with your AI or governing body to ascertain before hand how they view it before planning to make this change.

rmw