ASME VIII - UG-37 "area in excess thickness" vs UG-29 "combined ring cross section&qu

[jbesson]

Hy Engineers,

My today's concern is regarding ASME VIII - UG-37 "area in excess thickness" vs UG-29 "combined ring cross section".

Let's consider a vessel working under external pressure.
Stiffeners are installed and partial length of the shell is considered (and combined) with the stiffener to check the inertia required by stiffeners to resist to buckling under external pressure as permitted by UG-29.

In paralell we've a nozzle that is requiring reinforcement and we consider for area calculation the "area in excess thickness available in the shell" as permitted by UG-37.

Problem is that the UG-37 "area in excess thickness" and UG-29 "combined ring cross section" are overlaping meaning that we're considering the same section for two differents stress.

ASME doesn't specify if we can consider UG-37 "area in excess thickness" and UG-29 "combined ring cross section" only under condition that areas are not overlapping...

Shall we check if those areas are overlapping or not, it seems that software (Autopipe Vessels and Sicapwin) don't make this verification...

 

[DSB123]

Because normally you don't locate a nozzle so close to the stiffeners that the areas overlap. Think you may be on dodgy ground using the same area for both assessments similar to when you have two nozzles close together. However on the other side the required area for a nozzle due to external pressure is less than for the same internal pressure. You could always reduce the diameter you are assuming contributes to the reinforcement of the nozzle such that the areas do not overlap and see if it passes the reinforcement check . if it does than all is well. Remember you do not have to take the full diameter of the applicable reinforcement zone into account if you do not have to.

 

[jbesson]

Hy DSB123 and thanks for your answer.
I'm 100% in line with all points of you mail.
For clarity i'm working on PV only subject to external pressure, thus with a lot of stiffeners. Large nozzles are frequently crossing one or two stiffeners and sometimes they're just fitting between two stiffeners and it's in that configuration that the areas are overlapping.

The reason of my thread is that I sadly realized yesterday that the two softwares I used for PV calculations are not checking this particular point...

 

[SnTMan]

jbesson, that's what engineers do

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[prex]

IMO your softwares are correct. The area contributing to the ring inertia is not really a stressed material because of its participation in the inertia: the only actual stress in the shell is the uniform compressive stress due to external pressure, and you account for this one in the nozzle reinforcement calculation.

prex
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