Shell Tolerance for shells under external pressure

[PVchemEng]

For PV subject to external pressure, ASME VIII div.2 gives some rules for measuring maximum deviation using a segmental circular template (4.4.4.1 - (b)).

Herein is explained how to calculate max permissible deviation and how to calculate template chord lenght. eq 4.4.8 through 4.4.13.

For equations 4.4.9 and 4.4.11 some limits of applicability are given.

What if "ec" or "n" falls out of this limits?

 

[TGS4]

Then the vessel is not suitable for the specified external pressure in accordance with Division 2 (it fails the fabrication tolerances).

There may be an out for that would invoke Part 5, but I would discuss that with your AI.