Joint efficiency - UG-27 ASME BPVC

[MartinVT]

Hi everyone!

This is my first thread here, and I’m sure it won’t be the last!
I’ve searched the forum for an answer, but I haven’t found one—so I’m relying on your expertise.

I’m designing a vessel according to ASME BPVC Section VIII, Division 1 (2023), and I’m calculating the pipe per UG-27(b).
My question concerns the joint efficiency to use. I came across the 4th answer in this thread : https://www.nationalboard.org/PrintPage.aspx?NewsPageID=144. I have a similar vessel setup: a pipe, two nozzles spaced 1500 mm apart, and two flanges.

No ligament efficiency — got it;
Cylinder joint — okay;
Nozzle joint — okay;
But why are the circumferential joints multiplied by two? Is this related to converting circumferential to longitudinal joints? If so, how is that done?

I’ve seen rules for converting ligament efficiencies (UG-52/53), but not for joint efficiencies.
Also, where exactly in UG-27 does it say that I should use longitudinal joint efficiencies only ?

Thanks in advance, and have a great weekend!

Martin

 

[Geoff13]

But why are the circumferential joints multiplied by two?

Not sure where you're reading this. Let me take a guess, and if I'm on the wrong track ask a follow-up question with the specific sentence or formula.

With a simple free-body diagram you can figure out the basic thin-plate membrane forces. The load in the hoop direction of a cylinder, which will be resisted by the longitudinal weld, is PR per unit length. The load in the axial direction of a cylinder, which will be resisted by the circumferential welds, is PR/2 per unit length. Other shapes (spherical, conical, ellipsoidal, etc) will have different formulas.

Also, where exactly in UG-27 does it say that I should use longitudinal joint efficiencies only ?

Joint efficiency is only related to the weld type and level of inspection as described in Table UW-12, not the direction of the weld / stress.