How to depressurize high pressure gas from pig trap?

Answer 1

The trap should have two block valves, a vent and a drain valve.

Close the two block valves. Open the vent valve to relieve the pressure and then the drain valve to remove any liquid. Opening the drain valve first can cause the pressure from the trap to stir up any dirt and rocks that might be in the area causing a spark and possible fire.

You should also have on hearing protection when this is done because the noise from the vent valve can be quite high.

Leave the vent and drain valve open while you remove the end closure.

Answer 2

1. Make sure the upstream HP valve is closed
2. Open Drain Valve