How are vessels that are subjected to external pressure (1 atm) strengthened besides using Stiffeners?

Question

external pressure = 1 atm (101325 Pa)
material of pressure vessel = Marraging Steel (UTS = 450 N/mm2)
shape of pressure vessel = Rectangular c/s

external pressure = 1 atm (101325 Pa)
material of pressure vessel = Marraging Steel (UTS = 450 N/mm2)
shape of pressure vessel = Rectangular c/s

Note = Increasing the wall thickness is not an option

Answer 1

If you wish to make the walls of this vessel stiffer without increasing wall thickness or changing material then have the sheet metal vendor place strengthening darts in all the panels during the punching or forming process. These are done with a 'V'-shaped punch and die that plasticly deforms the material (to the inside or outside as required) in the shape of a trough (think of them as louvers that are not completely punched through), is quite efficient and, if done during the blank panel production process on a turret punch, almost no cost will be added to the process. Most good sheet metal shops should be able to advise you concerning this. This will not improve the welded seams of your container, but it will stop the walls from flexing and bowing. It has been my experience that this is where most pressure vessels fail. I was a managing engineer for 30 years with firms that produced pressure vessels and many other parts and helped redesign oil line transmission filter stations and vapor purge points, some rectangular, that were hydrostatic tested to 1750 PSI (over 60 bar). Without a print I cannot offer any more, but would offer more detail if you email me more information. A sphere or a cylinder as stated by others is much more user friendly.

Answer 2

(I work as a vessel engineer at a large corp and have been to ASME Section VIII classes). If a vessel is in a pump out situation where it pulls vacuum there is nothing you can do about it. Is there a way to put a vacuum breaker on the vessel perhaps? We have some stiffened rectangular vessels but the braces are all over the place and the equations are quite complicated. Also keep in mind that if your are doing repair/modifaction work that has impact on a pressure vessel you must have a firm do the work that has an ASME R-Stamp.
If this is a big vessel i would suggest a vacuum breaker or switching out to a cylindrical vessel with eliptical heads.

Answer 3

Build the vessel with a material like concrete and use prestressed reinforcing steel inside the walls. The steel is stretched before the concrete is poured and the stress is relieved after the concrete sets up. What you a left with is a container whos walls are pushing on themselves axially. Any pressure applied to the vessel must overcome the prestress before it will have any effect on the structure. We do this on bridges and silos all the time.

Answer 4

You should do a search for vacuum chambers to see how many people do this.

The most economical way of strengthening a chamber is with some type of stiffener on the outside. The actual design depends on the vessel, level of vacuum, size, etc....

If you wanted to get fancy you could build some type of external structure around the chamber and connect the two. It's a way of doing it besides using stiffeners but it would be more work and cost more money.

Simple stiffeners on the outside would be the way to go.

Answer 5

The other choices are to increase the wall thickness of the vessel or if you have the latitude, change to a cylinder shape.

A change to a longer narrower rectangular shape might also reduce the possibility of failure from external pressure.

I would not use pressure since the pressure will eventually fail and you will have a collapsed tank.

Answer 6

If you can't make the material thicker and you can't use stiffeners, I would say the only option left would be to apply an equal pressure to the inside of the vessel to balance the forces acting on the walls.

Answer 7

Pressure vessels are almost always cylindrical or spherical/toroidal or a combination thereof. I have seen one rectangular one heavily braced with external stiffeners on a high pressure valve. My only suggestion is to encase your vessel in a suitably designed vessel in which a vacuum is established to protect your rectangular vessel.

Answer 8

You say you want to increase the external pressure capability of the vessel, but not add stiffeners and not increase the wall thickness.

Good luck.....

Answer 9

if your design accept, use additional partisions but keep the bottom and top open for free flow

Answer 10

you maybe could build it usind a two layer sheeting, or a laminated type material. or pressurise it using the regulator pricipal on a scuba diving tank ???????????.