To conduct a hydrostatic pressure test on its gas pipelines , PG&E first obtains all needed work permits , coordinates with local agencies and provides gas to customers temporarily from an alternative source.
1. The section of pipeline to be tested is excavated , vented of gas and cut open at both ends. The inside is mechanically cleaned before testing.
2. A “test head”, a piece of pipeline with a hose at one end , is welded to one end of the underground pipe being tested. Another test head is attached to the other end of the tested section
3. The pipeline is filled with water through the hose.
4. The pipeline is pressurized to a specified pressure, much higher than normal operating pressure – for example , 600 psi if maximum allowable pressure is 400 psi.
5. The test pressure is is held and monitored for at least 8 hours.
6. Pipe sections that fail the test are replaced with new pipe that has already passed a pressure test.
7. Pipe is emptied of water , dried and returned to service.