Pressure testing pipe systems
by dbasinger on 08/01/02 at 07:31:14

I'm trying to determine the quantity of compressed nitrogen required to pressurize a closed piping network. The total volume system is 55-cubic feet. An air compressor will be used to pressurize to 125-psi.  What quantity of nitrogen stored at 2,500-psi will be required to boost the system pressure from 125-psi to 250-psi?

Re: Pressure testing pipe systems
by P.B on 08/19/02 at 07:49:43

Suppose you pump nitrogen inside the pipe net "AT CONSTANT TEMPERATURE" of 20°C . That is you realize an isothermic compression. Under this condition if you pump 55 cu.ft of nitrogen (that is the total pipe inside volume) you double the pressure of the pipe net. If the net pipe is at atmoshperic pressure (1 bar), after you have introduced 55 cu.ft, and the system reaches the starting temperature, the gauge will show 2 bar. So you you have to introduce 55 cu.ft x ... to reach the pressure you request. The pressure value is linear with the nitrogen volume when the gas temperature remains constant (p x V is costant). As compression produce heat then it is better you consider the compression process as "adiabatic". This is only a compression process problem that involves the compressor. At the end of the process, when final temperature reach the starting temperature (20°C) you will have an increase in pressure proportional to the volume of nitrogen you have pumped in the net.

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