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Nozzle reinforcement, Div. 1 vs B31.3

Nozzle reinforcement, Div. 1 vs B31.3

Nozzle reinforcement, Div. 1 vs B31.3

(OP)
ASME B31.3 section 304.3.3, equation (6) imposes a multiplier [2-sin(beta)] to the required area A1 while Div 1 does not have this multiplier. For a 45 degree hill-sided nozzle or branch, this multiplier is 1.29, which means it needs 29% more area than Div. 1. Anyone knows why ?

If more area needed is for stress concentration due to skew angle, why Div 1 is not doing that ? I thought Div 1 should be more stringent than B31.3 to make vessel fail-proof. Note that a vessel can be as slender and long as a header pipe. When people doing pipe stress analysis, they model the vessel as a pipe. In other words, the overall behavior for a vessel with branch/nozzle has no difference in B31.3 from stress point of view.

I do not think different safety factors in both codes is the reason, because you can find the same allowable stress in many cases on both codes.



RE: Nozzle reinforcement, Div. 1 vs B31.3

"I thought Div 1 should be more stringent than B31.3 to make vessel fail-proof".
Your thinking is correct. The Div 1 works with design pressure/temperature, while the B31.3 works with the pipe rating (pressure/temperature), for the same process condition. Just remember the vessel is designed say for 1000 kPa @ 50 deg C, but the pipe rating is Class 150 (1830 kPa @ 50 deg C). See the difference? OK, perhaps a bit oversimplified, but essentially the above is correct.
Cheers,
gr2vessels

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