Inspection Opening WRC 107 Question

[wsmith22]

I have a 20" od x .25" wall inspection opening in a 36" od x .25" wall shell. Per Section VIII, Div.1, the reinforcement calculation passes. However, the WRC 107 calculation fails. The only load to be considered is the weight of the flange/cover/nozzle of the opening, and since it is located on the top of the vessel, this loading opposes the shell pressure. Does it make sense that the WRC 107 calculation fails?

Thanks in advance for your input.

 

[TomBarsh]

The Code rules for area replacement are based on heuristic principles to prevent failure of the shell at the opening. While stress considerations were involved in developing the rules, odd results such as this can sometimes occur. What's happening is that the opening meets the rules of UG-37 for area replacement but even so the shell has high local stresses. Analyzing the effect of nozzle loads with WRC-107 and adding the resulting stresses to those resulting from pressure results in the high stress becoming apparent, since now we're talking in terms of "stress", not "area". I've run into this a few times.

 

[Bobfromoh]

I just ran a quick 107 check and got about 3200 psi stress.
That doesn't seem to be overstressed. The flange combination is about 470 lb for 150 flanges. The access is on a horizontal shell.
How does this compare to your numbers?

 

[wsmith22]

I included pressure trust by mistake.

Anybody have any background on when kb and kn? If you are including effects of thermal stresses, should kb=0?