pressurised welded orthogonal tank 1

[melcys]

Hello!

Has anyone had any experiences in designing welded orthogonal stainless steel pressurised tank? The pressure is about 3 bar and ss sheet thickness is about 3mm. Since the tank is about 1m^3, so I have added stiffeners around. I'm currently referring to the 'Welded Structures' by Omer Blodgett and 'Plates and shells' by S. Timoshenko if I'm not mistaken of the book titles. my queries are, how close should I place the stiffeners from the edge, and do I have to consider the moments experiened by the weld at the lap joints or butt joint instead at the edges of the panels? There is no frame for the tank. does it need one?

regards, mel

 

[ksuengrng]

Mel,

When I would designing orthogonal, or rectangular tanks/vessels, the vertical stiffener's would taper down to the chime around the bottom of the vessel, and then be welded to this chime. This same stiffener would also taper into the top angle/stiffener that went around the top of the vessel.

At the pressures you are talking about, along with the sheet thickness shown, I would think the top of this vessel would also require reinforcement. The stiffenere's for the top and the vertical stiffeners must be welded together to transmit the loads effectively to the slab or pad, through anchorage, that the vessel is resting on.

As for framework, I would say that it would depend upon the physical dimensions of the vessel. If the Height/Length ratio is high, horizontal stiffener's may be required, and they would also need to be welded to one another, as well as welded into the vertical stiffeners.

Be sure to look at the bottom of the vessel also, as well as anchorage. This will also play a vital part in your stiffening, as well as location of stiffeners and anchors. Should the bottom require stiffener's, you may look at attaching/designing an anchor into the bracing.

One other option is to look at increasing the sheet/plate thickness of this vessel. Paying a little bit more for steel is less than paying your welders to cut and weld bracing into each other; not to mention the amount of heat that can be produced when welding the braces on that could tend to warp the 3mm sheet quite quickly.

Spacing of the stiffener's would be best utilized by referring to Roark's Formulas for Stress and Strain. Watch your deflections to be sure they don't exceed allowable limits. (See the forum on Vessels and the input from Butelja) Excellent information here on deflections.

Hope that helps in some sort of way.

 

[prex]

I agree with ksuengrng: a thickness of 3 mm for such pressure and volume makes nonsense to me.
I think the pitch of stiffeners will be less than 100 mm (there's a formula in ASME VIII for this).
Also you must dimension the stiffeners, including buckling, and account for many details (e.g. corners), as discussed by ksuengrng, that require structural experience if you want to avoid mistakes.
Concerning the frame, if you mean supports for the tank, this is a minor problem: as long as you get a tank resisting that pressure, it will be perfectly able to stay on it's stiffeners.
I suggest also, besides increasing the wall thickness to some 8 mm, considering the use of internal stays, in the form of round bars or of plates (partitions): this will require much less welding and added weight.
prex
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