ASME BPVC Section VIII Div. 2 Paragraph 4.10.3.1(C)

[TylerM]

Paragraph 4.3.10.1 states the requirements for using the equations in Paragraph 4.3.10 to calculate the combined loading and allowable stresses. I understand 4.3.10.1(a) and (b) but I am slightly confused why 4.3.10.1(c) is there.

How does having an inside radius to thickness ratio less than three impact a pressure vessel?

Where did the value three come from?

I know later on in the book 5.2.1.3 states that vessels with R/t<4 should not be used because “nonlinear stress distributions associated with heavy wall sections (R/t<4) are not accurately represented by the implicit linear stress distribution”. is this reason the same for 4.3.10.1(C) and if so, why has the value changed from 3 to 4?

If anyone could shed some light on this requirement from 4.3.10.1(C) for me that would be greatly helpful.

Regards,
Tyler

 

[TGS4]

Very good question. There is no additional guidance on this provided in PTB-1, so we are left to speculate.

The two values you quoted should probably at the very least be consistent with each other. In my opinion, both numbers should be 5, but the 3 in 4.3.10 seems really pushing it.

Would you please submit an inquiry to the Code Committee on this matter. They should be looking into it b