2 replies to this topic

[manchester]

Hi,,I'm a newbie and I have one question.

I just saw a video of how a pressure vessel sunk due to vacuum. It says that vent valve is open (so that pressure on vessel is near atmospheric). Would somebody explain why this could happen? Why a vessel that stands on pressure above 5 barg, but it doesn't stand on atm pressure?

[katmar]

A cylinder will withstand more pressure from the inside than from the outside because when the pressure is inside, it forces the cylinder into the most stable geometric shape - a circle. However, when the pressure is outside (or vacuum inside) the pressure is forcing the cylinder into an unstable and weak shape.

Think of a Coke or beer can. It is very thin and flimsy, but holds the internal pressure easily. But once it has been opened you can crush it easily with your fingers from from the outside. When a vessel fails under vacuum or external pressure it will usually not tear or rupture - it simply deforms and collapses.

[djack77494]

katmar has supplied a good and accurate answer, and I don't have much to add. The OP is warned not to assume anything about a vessel's ability to withstand forces acting to cause a destructive deformation just because you know the vessel's ability to withstand hoop stresses. They're very different and not well related. Extending this a bit further, you may come across vessels that can withstand high temperatures. That gives you NO indication of the vessel's ability to withstand low temperatures. Again, they are not related.