B31.1 45¦ Branch Connection

[vikramkaku]

I am currently working on designing branch connection sitting at 45° on the header pipe. I was doing area replacement calculations as per para 104.3.1 of B31.1-2001. To calculate area to be replaced (A7) it multiplies by the factor (2-Sin 45). I don't understand why this factor is included, because if we actually measure this area it is just tmh*d1.
Also, is it possible to qualify branch connection for B31.1 using Finite element analysis??

Thanks for ur help.

Vikram

 

[JohnBreen]

Hi vikramkaku,

Regarding the area replacement rules, the best (albeit short) answer is: the Code is correct, just do as you are directed to do.

You may qualify a B31.1 component by using Finite Element Method. Things to remember: the B31 Pressure Piping Codes do not calculate true elastic stresses in components - do not be surprised when FEA calculated stresses differ from those calculated by B31 (beam theory) rules; do not mix methodologies and allowable stresses - if you use FEA, use the rules (and allowable stresses from ASME B&PV Code, Section VIII, Division 2.

The B31 Codes provide a simplified approach to analysis, the Codes do not intend to preclude more rigorous analysis when it is appropriate. Document everything you do and include the documentation in the stress report to the client.

Regards, JOhn.