rectangular pressure vessel with jacket for sterlizer

[MikeG7]

I have posted a similar thread in another pressure vesssel forum.
Can anyone advise on the method to analyse a rectuangular pressure vessel with welded on "U" sections (ribs) as reinforcements. ASME VIII Div.1 Appendix 13 deals with this issue only for the chamber under internal pressure if the style of the chamber has chamfered corners (Sketch A6), but the code does not deal with the external pressure which exists in the jacket portion of the vessel in question which should, according to me, be checked for 2 cases:
1. external pressure on the shell/chamber when the jacket is under positive pressure and acting ON the shell/chamber (which may also have a vacuum).
2. the internal pressure on the jacket. Note - jacket does not have any external stiffeners other than those welded outside of the shell over which the jacket is welded on.
Any comments would be appreciated. Do I have to refer to U-2(g)?
This vessel also has a sliding door not a bolted cover so any advise on that is also appreciated.!
For note - this vessel is required to be approved to PD 5500 as cat3 vessel, but that code (to my knowledge) does not deal with rectangular vessel shapes hence I refer to ASME code VIII Div1, appendix 13.

 

[brkmech1234]

Whether internal or extrenal pressure, the type of major stress induced is bending. Only a small value membrane stress will be compressive . I believe you can apply the same rules.

 

[MikeG7]

Thanks brkmech1234, that sounds reasonable and 1/2 my issue is solved, so what would I do for the jacket? It has internal stiffeners not like the external ones in ASME VIII Div 1 Appendix 13

 

[MikeHalloran]

For some reason, pressure vessels are usually cylindrical. You might find out why.

I investigated the collapse of the inner tube of a jacketed tube assembly. The collapse happened during routine leak testing of the jacket, to a very modest pressure. The resulting BANG could be heard over the normal deafening noise of my entire shop. Luckily no one was hurt, but we got to make a replacement at our considerable expense.

That tube was cylindrical. It would seem to me that a rectangular tube is effectively pre-buckled, which might make collapse of the inner tube somewhat less spectacular, or require considerable reinforcement to prevent collapse.

No expertise claimed here wrt to codes and such.


Mike Halloran
Pembroke Pines, FL, USA

 

[MikeG7]

MikeHalloran
Thanks for your comment, and to go into the reason for the vessel being rectangular would be digressing from the topic but essentially the vessel in question is a steam sterilizer and is common for rectangular cross section to maximize internal dimensions and accommodate sliding door closure arrangement.

 

[dhengr]

MikeG7:
I suspect you are not going to find any codes or standards which provide cookbook formulas for checking a rectangular pressure vessel subject to positive and/or negative pressure. Whatever the pressures and pressure vessel size. There is a big difference in the analysis and design of such a vessel when it is pressurized and acting primarily in tension, with secondary bending; and when it is pressurized and acting primarily in compression, with secondary bending and buckling. Sounds like you could use the help of someone who understands Structural Engineering and steel fabrication. Someone who understands plates and shells, and their stresses and buckling. Someone who can interpret the intent of some ASME codes, which may not apply to this exact problem, but who doesn’t need to blindly follow a prescription to reach a conclusion. Since you say this is commonly done, why don’t you ask the people who commonly do this?

Since you don’t describe your problem particularly well, provide any sketches or loads/pressures, sizes, etc. such that we could better understand what you are dealing with, I guess you are left with a very difficult structure to analyze without a recipe, or a cook.

 

[MikeG7]

Hi dhengr
I cannot explain it better than by looking at the Sketch 6A which I mentioned, and I attach a copy here. Except, it has a jacket over the reinforcings. The pressures are quite low for the shell is -100KPa vacuum and the jacket 240KPa gauge.
I mean to say that this equipment is common, i.e. there are many rectangular medical sterlilzers of this type but in my opinion if the 3rd party inspector does not find "cook book" references, there usually more complications in achieving compliance. I feel there are "cook book" aspects that can apply to this problem and already brkmech1234 gives some practical advice to one aspect.

 

[MikeG7]

sorry, attach did not work, here is it...

 

[Cockroach]

I appreciate your point and experience, MikeHollaran. I concur with your point on rectangular pressure vessels and circular geometries. This is best reviewed as an FEA, you may be able to approximate stresses using flat plate theory at a point well AWAY from the corners. But I would expect considerable stress difficulty in the corners regardless of gusset support. I also note maximum deflection at mid height down the length of this vessel. What sort of pressure are we talking? My guess is low, one atmosphere?

Regards,
Cockroach

 

[MikeG7]

The pressures are -100KPa internal to the chamber/shell and +240KPa in the jacket. The differential pressure is 340KPa.