How much pressure can a 55 gallon steel drum withstand?

Answer 1

Depends on whether the pressure is acting from within or without and at what point failure would be deemed.

If distension of the ends of the barrel is tolerable, then depending on the condition of the barrel and thickness (this can vary), pressures of many tens of pounds per square inch can be stored inside - and possibly even a couple of hundred pounds per square inch, though this would certainly be an unsafe pressure for a typical steel drum.

BUT

IF the pressure is applied from the outside (simply atmospheric would suffice) - effectively pumping down the barrel to produce a vacuum, then you will find that a barrel will collapse into itself some time BEFORE even a soft vacuum is approached. As little as 10psi can wreck the barrel - even less if the barrel has a few "starter dents".

You can do this without a vacuum pump with a small fire and a few pints of water. Place the water in the barrel and place the barrel on the fire. Wait until the water is boling vigourously and expelling a large volume of steam. then remove the barrel from the fire (or extinguish fire) and carefully observe the steam coming from the barrel opening. As soon as the steam has almost stopped, add the cap, sealing the barrel. Now, you can either wait for the water to cool and the steam to condense back to water - or you can speed things along a little by throwing cold water onto the barrel.

With the steam condensing (which has already displaced most of the air), you start generating a fairly impressive vacuum, the barrel will go from being perfectly formed to crushed (by atmospheric pressure) in one very dramatic movement lasting no more than a couple of hundred milliseconds.

Makes a very good visual science experiment when trying to demonstrate just what atmnospheric pressure is - and how much force it can exert.