Donut Shaped Pressure Vessel

[millsjj]

Hi,

I am currently designing a pressure vessel system for hot water with a max temp of 99C and operating pressure of 160psi. The part is shaped like a donut with wholes through one face to allow for hot water piping to be welded as this unit will be part of an outlet manifold. I am double checking the strength calculations as this is a part I have inherited and is not my own design. I am wondering the best way of checking this part as it does not fit in well with the standard ASME pressure vessel calcs.

My approach thus far has been break the part into two components, the outer and inner tube. I have treated the outer tube as if it is a standard pipe with internal pressure and used standard ASME calcs to ensure strength. I have then treated the inner diameter as if it is a standard pipe with external pressure acting on it. I feel like this should satisfy the criteria but I would like to see if anyone else has some advice as I wouldn't consider myself an expert on all things ASME.

I have attached a drawing below to give an understanding of the geometry.

Thanks

 

[SnTMan]

millsjj, I think that under Sec VIII, Div 1, that's about the best you can do. Keep in mind a little extra steel is cheap insurance

Regards,

Mike

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

 

[prex]

If I correctly understand your sketch (drawing?), you also have two flat faces, and there are other important details not covered in the sketch: how are flat walls joined to shells, how are nozzles attached, and possibly other.

prex
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[chicopee]

Your description is confusing. Are the "wholes" going thru both flat sides?; Are the "wholes" to be considered the firetubes or water tubes"?. Inside of the doughnut, I see no inlet or outlet, so are you building some form of a Bomb? More details about this project would help.

 

[millsjj]

Hi Guys,

Sorry for the typo on 'wholes' that chicopee so readily pointed out. The 'holes' are to accommodate piping that will be welded in place. They go through one side as they function as an inlet whilst there is a single outlet on the top of the component. This will have 4" piping welded in place. The unit is manufactured by welding sheet metal along the seams of the faces.

My understanding, which may well me wrong, is that if there was no inner hole then this part could be regarded as a simple cylinder. I could treat the part as a standard cylindrical pressure vessel but also accommodate for the welded connections. The inner hole that makes this a donut shape is the main thing I am unsure of but please feel free to correct my interpretation!

I have attached another sketch with more details.

Thanks

 

[GenB]

How are the two parts welded? under what code of construction? You cannot Calc as inner and outer.

 

[TomBarsh]

I once designed a "donut" vessel for a Section III application. Topologically it was similar to what is in your sketch (but very much larger) and it was divided into about 8 chambers (think of a number of your donuts stacked up). The diameter was around 22 feet and height was about 40 feet. It was very low pressure (but extremely high temperature) and was made from thin stainless plate.

The outer cylinder was designed for the chamber's internal pressure. The chamber's internal pressure produced an interesting effect on the inner cylinder: the inner cylinder was subject to "external pressure" from the chamber's internal pressure for purposes of circumferential compressive stress; but the chamber's internal pressure produced longitudinal tension in the inner cylinder, quite the opposite of a typical vacuum vessel. If anything, the combination of longitudinal tension and circumferential compression produced a condition more susceptible to buckling (I think of those woven tubular "handcuffs" given away at fairs when I was a kid, you'd stick a finger in each end and as you tried to pull your fingers out the woven tube would constrict and get tighter). Just eyeballing it, your donut wouldn't seem to be prone to buckling of the inner cylinder, but that all depends on the pressure, temperature, material, thickness, etc.

 

[millsjj]

@GenB,

yes the two parts are welded together in compliance with Div IV of ASME, Heating Boilers. Can you specify why you cannot calc as inner and outer? My approach is to consider the end with the opening for the piping as a tube sheet with stays, then the external wall as standard pressure vessel. I have treated the inner as a cylindrical part under external pressure and from theses calcs it seems like 1/2" 316L sheet metal is strong enough.

@TomBarsh

I can see how that would be a possibility, would not have expected that myself, but I think that I my part is at such a low temp and small height that this would not be an issue.