Stallionbreed, Code permits use of either, your choice. Should be a negligable difference between the two, if not check your work :)

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

Use which ever one is easier to get dimensions. UG-27(c) is ID based, App. 1-1(a) is OD based, which is also why you get a slight difference in thickness.

Thanks all for the replies.

The equipment that I'm looking appears to have a 2% difference between the two equations.

While that may not seem like much, as you imagine if the thickness is closer to the higher reading would it be risky to go with the higher Tmin? It will help increase the inspection interval but i wouldn't want to do that if there is a risk of failure...

Is this a question of new design or existing equipment?

It looks like the OD-based formula shown in Appendix 1 was derived from the ID-based formula in UG-27(c), but they substituted T required for T actual. Not quite identical. So if you were to rate the cylinder to the calculated MAWP, both equations would give the exact same result, but if you make your cylinder thicker than is required to support the internal pressure the results will differ.

A 2% difference is nothing to be concerned about (to get a 2% difference your cylinder would have to be a lot thicker than the required thickness). Use whichever equation you prefer.


-Christine

Sorry for the late replies

TGS4: existing

Christine74: Thanks for pointing that out I didn't realize that.