Threadolet Formula for ASME B31.3 coil design

[merton]

Please see the following information below that was forwarded to my by a co-worker. Any suggestions would be greatly appreciated.

Thanks in Advance
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Given the following information

Design to ASME B31.3, 2004 Edition



After running the calculations with an increased CA of 1/8” the revised lower pressure ratings would be:

Pre-heat coil is 3” 2500# with a 5031 psi design pressure (was 5625 psi with 1/16 CA)

Re-heat coil is 3” 900# with a 1622 psi design pressure (was 2025 psi with 1/16 CA)

Design Temperature is -7 to 200F, MDMT -7F
Sour, 1/8” CA, Stress relieved and 100% radiography.



Each coil will have a 1/2" and 3/4" 6000# TOL; what is the correct formula to prove the threadolets will meet the design. The thread pitch h as per (B1.20.1) is:



1/2" 6000# TOL with 1/2 – 14 NPT h = 0.05714”
3/4" 6000# TOL with 3/4 – 14 NPT h = 0.05714”