Pressure Vessel Force and Pressure

What is force?

Force can be described in pounds or tons.  We intuitively think of force in weight which is a fair description.  Is there a difference between 10-psi and 1000-psi?

Yes, there is a 100-times difference in pounds. This becomes very important when a pressure vessel contains steam, air, volatile gases, compressible gas/fluid, or substances that have internal energy such that when exposed to the atmosphere the substance expands violently. Steam is a good example where there is an expansion process of 1604-times [saturated steam].

Question: Imagine a vessel with a 1-foot diameter cover that is fastened to a pressure vessel and there is 10-psi pushing outward against the cover. How much force is being applied to the cover?

A) 10-psi    B) 10,000-pounds    C) 1,131-pounds    D) 101-pounds

Answer C) 1130-pounds. 

That is over 1/2-ton of force with only 10-psi. The point here is 10-psi can be as deadly as 1000--psi. Finally, we can never under estimate the care needed in keeping pressure vessels in top condition. Force = 10-psi x p r ² [don’t forget to convert ]

Lets try another question. A tank is 50-foot tall with atmospheric [exposed to the outside air] pressure at the top and it contains water. How much pressure [psi] is at the bottom of the tank?

A.) 0-psi     B.) 22-psi     C.) 25-psi     D.) 53-psi

Answer B) 22-psi. 

Gradually, as we come down the tank wall the pressure increases; therefore, the thickness of the tank wall would have to increase in order to retain the water. p = g x 50-feet [don’t forget to convert & g = 62.4 lbs../ft³ ]