I'm trying to apply for ABSA CRN approval some HX I manufacture.
Such units have NTIW tubesheets and are excluded by the scope of UHX per UHX-10.
I calculated those tubesheets according to TEMA R, feeling confident that this could be the soultion, but the Revisor rejected the calculation since NTIW models are excluded from TEMA too.
TEMA RCB-7.3 (1) mention such configuration, but obviously desn't give any solutions, leaving all the issue in the hand of the inspector.
Now the ABSA revisor "suggested" to calculate the tubesheets with the following approach
1. calculate the perforated area with TEMA R considering the radius passing throught the outmost tube
2. calculate the unperforated areas with UG-34, considering the tubesheet as an un-stayed flat end.

I consider such approach not only overly conservative, but especially for the point 2 something not applicable.

UG-34 considers the pressure only by one side. So which pressure should I consider in my calculation? The shellside or tubeside one?
Furthermore which sketches do I use? The one welded to the shell or the other one with the flanged extension bolted?
If I consider the flanged one I would calculate an unstayed plate retained only by the bolts. That's not corrected since it  doesn't consider the other side welded. In such way I would calculate some kind of "floating" end.

So now I need to find a good solution in compliance with U-2(g) and I would like to avoid the FEA calculation for now.

Any suggestions?

Thanks in advance

ReddeV