It says gas pipeline out side military base. Assuming the pipeline was going to the the base. I would say its a gas pipeline carrying cooking gas(mixture of propane and butane). Since most military including Pakistanis use oil(petrol/diesel/ATF) for most military purposes, the only reason you would need gas is cooking.
I don't know about Pak but in India there are standard pressures you are supposed to keep in pipes for gas transportation. By govt. regulations we are supposed to keep 100 psi pressure for short range transportation and 250 psi for long range. So the blast impact should tell you about what kind of pipe it was. But then I am no explosive expert.