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.
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
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