Rectangular opening in pressure vessel

[daniel1978]

Dear All

My client has vessel and they want to make rectangular opening into the shell. so both PVelite and Compress can not calculate stress on shell due to rectangular Cut/opening( correct me if i am wrong) even nozzle pro . so i wonder if any one here knows any reference to calculate (except FEA Softwar) to calculate the stress on shell?

 

[gr2vessels]

Make the openings obround in accordance with UG-36.

 

[prex]

You can calculate the opening as if it was circular with a diameter equal to the diagonal of the rectangle, though this may be unnecessarily conservative if the rectangle is in the shell and the long side is along the circumference.
However you should prevent your client that rectangular openings are strongly discouraged (though not prohibited) by ASME VIII: an obround opening is recommended.

prex
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[daniel1978]

Actually they try to cut abround opening, but it seem they need to cut huge part 47"x17" in 121" ID cylinder. the rectangular has four round corner. so what i undrestand from your reply is that i can calculate an opening with equal diameter of ~50" which is eaual to diagonal of the rectangular?

 

[SnTMan]

daniel1978, carefully study UG-37 and Appendix L, L 7.7. You need to evaluate opening reinforcement in both the longitudinal and circumferential directions. Either direction may govern. PVElite (and other software) will do this for round openings, for other shapes, not likely. And, oh yeah, PVElite DOES NOT "calculate stress on shell due to rectangular Cut/opening", rather it performs opening reinforcement calculations per UG-37.

Maybe time to crack the Code book, get out the pencil and paper.

Regards,

Mike

 

[prex]

SnTMan, this opening is outside the dimensional limits per UG-36(b)(1), so the example in L-7.7 is not of much help, and we are very likely out of the reach of any PV design software.
For large openings the code requires to use either 1-7 in combination with UG-36 or 1-10 alone. Both of these chapters seem (silently) fully applicable to round openings only (they refer to the nozzle neck radius R_n) and bothe refer to U-2(g) for specific points. I don't think this opening can be treated with plain code means, an in depth special analysis is required.

prex
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[XL83NL]

I don't think this opening can be treated with plain code means, an in depth special analysis is required.

So FEA acc. VIII-2?

 

[SnTMan]

prex, I cited example 7.7 because it shows how an opening is treated in the two directions. UG-36, -37 etc. of course invoke the various Appendii(?) for large openings as required. Speaking in short hand a bit I suppose.

Agreed, the software I am familiar with will not likely adequately address this opening.

As to whether it can be designed per normal rules, possibly not, based on info available I couldn't say.

Regards,

Mike

 

[saplanti]

Rectangular openings have a lot more problems than the oval or round openings. The nozzle/shell connection will subject to stress intensification due to the complex stress distribution. I guess the designers needs to provide 4 ring stiffeners (2 will be next to the opening) in circumferential direction, and at least 2 horizontal (next to the opening) in longitudinal direction which will connect all 4 circumferential stiffeners. Ring and longitudinal stiffeners can be rectangular or L or T shape by depending on the stress level and geometry under consideration.

In this way you may reduce the stresses at the corners of rectangular openings under internal pressure and other effects. (Please do not forget that there will be a thrust force due to the opening end plate.) However I recommend to verify this application by FEA analysis (design by analysis) with a model that includes all the components in the area.

 

[jtseng123]

daniel1978,
what is the purpose of that opening ? In revamp, big rectangular hole is cut to bring in and out internals quickly. If that is the case, you don't need any code calculation. Just a simple calculation like opening in the skirt. Normally, use L or T steel to temporally reinforce the opening.

We also have rectangular opening come with duct for service, size like 90" x 50" in a FCC unit for a big regenerator. No need to use FEA but just utilize what in the code to reinforce the opening and the duct. Many guys above have touched the point.

Or, is it really a "manway" ?

 

[daniel1978]

jtseng123
thanks for answering my question. The purpose of the opening is to cut a sample to inspect shell plate. So they need to cut big chunk of shell to do inspection (microscopic inspection) which they could not do it in place. This exercise is different from Man way and duct opening. So what I thought FEA would be the best solution for this problem. But I want to make sure nowhere in code address these opening.
Regards,

 

[SnTMan]

You're gonna put it back right? Not subject to pressure while open, right? Or what?

Regards,

Mike

 

[JStephen]

If you cut a piece out and weld it back in, or cut a piece out and replace it with identical material, there's not any stress analysis involved. You would need to refer to the appropriate codes for the work- typically, National Board Inspection Code. And need the appropriate stamps to do the work.

I would think there's got to be a better way of accomplishing whatever it is you're trying to do, though. You'd think if it was microscopic inspection, they could core out a pretty small plug.

 

[daniel1978]

there will be no pressure, this vessel will be like skirt for above vessel untill inspection shinish. then they will decide to use the vessel or change it. to answer to your question they are not replace piece untill inspection finiches. the only load will be weight from top vessel and attachment in to bottom vessel.