hi,everybody!
Can somebody tell me how to calculate the wall thickness of piping under external pressure?And anybody knows the calculation software---MAR?
Is it ok to use Bresse fomular here?
The way from BPV Code SEC VIII DIVISION 1 UG28 is complicated,and the answer based on the Bresse fomular is different from which based on BPV Code,So the Bresse fomular is not applicable?
I am confused,somebody help me!
Thanks very much!

I don't know about Bresse formula , but what I can suggest to you is : follow the code you are using. If it is B31.1 or B31.3, you have to use UG-28.I think the rules of UG-28 are straightforward and not complex at all.Sample calculation has been provided in the code as how to compute the required moment of inertia.

Some simplistic treatment of this problem can be found in Timoshenko's : " Strength of Materials, Part II".

I read the Bresse formula and the UG-28 carefully,it is obviously that the Bresse formula is more conservative than UG-28.It seems the critical external pressure is determined by S/D,and have nothing to do with L/D in Bresse formular(S---minimum required thickness of pipe;D---outside diameter of pipe;L---total length).As a preconditon,the pipe line is very long,and the value of L/D is very large.
My comprehension is right?I cann't sure.May somebody give some suggestion to me?
Best regards!

Bresse-Bryan formula refers to INFINITE length cylindrical shells, and that's why you will not find the Length/Diameter (L/D) ratio within this formula. It is a theoretical formula used only for preliminary and conservative estimations.

ASME Sect. VIII (UG-28)calculation procedure regards all possible practical situations (I mean short length, medium length and long length cylindrical shells), and, what it cannot be ignored, involves also the safety coefficients that take into account the inherent initial distortions of the shell wall.

I suggest you to use ASME Sect. VIII method (applied for the LARGEST L/D ratio that is available). Moreover, as probably you noted, ASME B 31 Codes (B 31.3 for instance, at par. 304.1.3 - Straight Pipe Under External Pressure) IMPOSE this approach ("To determine wall thickness and stiffening requirements ..., the procedure outlined in the BPV Code, Section VIII, Division VIII, UG-28 through UG-30 SHALL BE FOLLOWED ...").

The exceptions are also described there and refers to Diameter/Thickness (D/T) ratio values lower than 10.

Regards,

Dorin Popescu