A 3/4 inch Natural gas line broken - gas is flowing for 180 minutes at 30 psi how much has been released ?

Answer 1

0.75 ID pipe has area = (Pi) * (Radius) * (Radius)
= (Pi) * (0.75 / 2) * (0.75 / 2) = 0.4418 in2

For mass flow rate, use (Pressure) * (Area)
= (30) * (0.4418) = 13.25 lb

Average density of natural gas = 0.05 lb/ft3

Volume flow of gas = (Mass Flow) / (Density)
= (13.25) / (0.05) = 265 ft3/min

Now, having this flow for 180 minutes means
(Total Volume released) = (Volume flow) * (Time)
= (265) * (180) = 47700 ft3

Answer 2

The pressure alone does not specify the state point of the gas, so the solution is indeterminant. With pressure and temperature, for instance, one could calculate the density, then together with the cross sectional area the flow rate can be determined ( rho * Area * V).

If it were air flowing, for which the specific heat ratio, cp/cv, is 1.4, and the gage pressure is 30, then the expansion ratio across the break is slightly > 1.8 suggesting the flow would be choked.

With methane, however, the specific heat ratio is different and the flow is not likely to be choked. The specific heat ratio is influenced by the molecular structure and the number of atoms in the molecule.

Answer 3

Enough to level an entire neighborhood when it hits an ignition source. That is a high pressure local distribution line. The usual one that comes into your house is 2-5 psi and could take down one home in a few minutes worth of leaking.