Oxygen cylinder pressures

[cutinoak]

Say we have an oxygen cylinder 8"diameter 50" tall (not sure of the exact dimensions). The pressure inside is at 2600 psi. If I find the area of inside the tank 8 x pi x 50= 1256, do I take 1256sq" x 2600 psi to find the total amount of force exerted inside the tank as 3,265,600 lbs, or is it still 2600 lbs?

Anthony

 

[MintJulep]

Neither.

Take a look at this.

http://web.mit.edu/course/3/3.11/

http://www/modules/pv.pdf

 

[rb1957]

i scanned the article and couldn't see an answer. whilst you're dead wrong with your 2nd answer (2600 lbs would only work if there was 1 in2 of area), you're closer with your first answer (but you don't have the complete area).

of course one interpretation of total force would consider that the pressure is acting in many directions, so the net force (thinking of force as a vector) would be very different to the above calculation ... it would in fact depend on something quite different to your calculation (a hint, it would involve pressure but nt as you're applying it).

think about it, post if you want another clue

 

[bvanhiel]

Net force would be zero. Since nothing is moving, all forces are balanced.

The total amount of force exerted is the total area times the force. Total force isn't a very useful number, and I don't think it would ever need to be calculated in the real world. Since looking for homework help is against forum rules, I'll politely assume that you are trying to calculate the forces that are exerting stresses on the cylinder. The link MintJulep provided has the equations you need.

-b

 

[rb1957]

actually, the net force i was thinking of was the weight, which would be a function of the volume and the pressure.

 

[cutinoak]

I work as a metal fabricator in a welding shop. Our safety committee wants everyone to volunteer and discuss safety under their own topic. I picked the discussing of oxy-acetylene torch and cylinders. I wanted to give the employees an idea of what would happen if a 2600 psi bottle blow up or valve was severed from tank. I heard of a 100 gallon air compressor tank blowing up in a shop and deaths occur with just 180 psi. Don't tell me their is no force. There is stored energy in the cylinder.

 

[israelkk]

The stored energy equals Pressure X volume. When you deal with pressure vessel the energy is a major concern and some times compared to TNT weight. The stress in the vessel wall is another major issue. The vessel walls see pressure which is force per unit area. You can not sum the total pressure multiplied but the surface area of the walls and call it a force. Force by definition is a vector meaning it has to have a direction. In the vessel the total force exerted by the gas pressure is zero. If there was a force the vessel would start to move and was not standing still.

 

[rb1957]

ah, yes ... but stored energy is different from force ... the energy is only released if there is a hole. also there is a difference between a tank exploding and knocking off the valve.

anyways, now we understand where yo're coming from, and what interests (and limitations, i'm assuming you'r not a trained engineer) you have lets give some constructive help.

your simple calc shows that pressurised tanks are indeed bombs. but other than being an impressively large number, i don't know quite what it shows. Force is a simple concept to grasp, unfortunately perhaps energy is a more useful engineering term. the energy inside the pressure vessel is something like pV (pressure*volume) ... this is dimensionally correct, but it's not my field and someone else will correct me within a nanosecond. it would be interesting to see how many sticks of dynamite this is equal to. this energy would be released if the tank exploded for some reason ... exploded, you'd better add in something for the acetylene reaction (as this'll release energy too.

but this only means something if the tank explodes, and it probably would be quite devastating in a closed environment. if you knock the valve off, the acetlyene will jet out of the cyclinder. here there'd be a force of p*A (pressure* the area of the valve). and the jet would have a velocity of something like sqrt(2*p/rho) ... 1/2*rho*V^2 = pressure (rho = density of gas, related to the pressure; pressure is strictly tank pressure-ambinent pressure, but near enough tank pressure for your question. it'd be interesting to see how the tank would react with the exhaust stream ... something like a balloon with the end released !! here, you'd have the force (pA) accelerating the tank (m*a, m=the mass of the tank = weight/g)

 

[bvanhiel]

Remember that various gases are stored under different conditions. Oxygen is a compressed gas, so the above approximations are applicable. CO2 is a liquid when compressed to 900psi at room temp, and so has a much greater energy density than the compressed oxygen for the same sized tank, but not the fire risk. Acetylene is dissolved under pressure in acetone... Each presents separate dangers if the tank is damaged.

-b

 

[MintJulep]

Googling for

gas cylinder safety

returns lots of hits. I suspect that you would be able to find some interesting pictures too.

 

[MintJulep]

You might also want to look at thread1088-156920