Pipeline Safety Inspection and Testing

PG&E has a comprehensive program to enhance the safety of its natural gas transmission pipeline system. We utilize a variety of tools to verify the status, strength and safety of our pipelines. These tools range from in-the-field leak surveys using sensitive detection equipment, to in-line inspections and pressure tests.

In-Line Inspections

There are many internal line inspection, or in-line inspection (ILI), devices available. These devices called “Smart Pigs” can be equipped with robotic cameras and sensors to check pipe thickness and welds, and can detect flaws and corrosion. The main disadvantage of Smart Pigs is the line has to be designed to accommodate these devices (i.e. Smart Pig insertion and extraction points, smooth transitions between pipe segments, minimum radius turns, , pipeline segments of the same diameter, no plug type valves, etc.). Many of PG&E’s pipelines were designed and constructed before Smart Pig technology was developed. These lines would require significant reconstruction to accommodate in line inspections.

Hydrostatic Testing

Hydrostatic testing involves pressurizing a pipe with water to reveal potential weaknesses. Hydrostatic testing is a proven method for verifying the capability of a natural gas pipeline to operate at a safe level of pressure (referred to as the maximum allowable operating pressure, or MAOP). Hydrostatic testing is also used to test such familiar items as scuba tanks, fire extinguishers and air compressor tanks.

Performing a hydrostatic test involves the following steps:

  1. The section of pipeline to be tested is removed from service and purged of all natural gas, and has the inside mechanically cleaned.
  2. The section is sealed on both ends and filled completely with water.
  3. The water is pressurized to the test pressure.
  4. The test pressure is held and monitored for a set period of time, typically 8 hours.
  5. If there is no significant loss of pressure, then the section of pipeline is emptied of water, dried thoroughly, and placed back into service.

If a section does not reach or hold the pressure that means that the pressure from the hydrostatic test has caused the pipe to either leak or rupture. If that occurs, the leak is located, repaired, and the pipe section is tested again. Sections that don’t pass a hydrostatic test are replaced.

State standards for hydrostatic testing new pipelines were established in 1961, and federal standards for hydrostatic testing were established in 1970. Pipelines installed after these regulations became effective were hydrostatically tested prior to being put into service.

Camera Inspection

Camera inspection involves excavating several holes along the length of the transmission line so we that we can insert a tethered camera that will record internal conditions of the pipe. The video footage from the camera will be relayed to a nearby monitoring and recording device. Trained professionals will then analyze it and determine if any additional actions are necessary.

Performing a camera inspection involves the following steps:

  1. PG&E crews will excavate several holes along the length of the transmission line so we can access the underground pipe. For the public’s safety, these holes will be securely covered when not in use.
  2. The pipeline is taken out of service temporarily, and sealed from the rest of the system.
  3. Gas will be re-routed and continue to flow to homes and businesses throughout the course of the project.
  4. Once the pipeline is closed at both ends, it will be purged of natural gas so the crew can open and work inside the pipe safely. At this point, depending on wind direction and other weather conditions, the smell of gas may be noticeable to nearby homes or businesses, along with a loud sound made by the equipment that forces air through the pipeline. The natural gas will quickly dissipate and will not be harmful.
  5. At this point, a camera will be inserted into the pipeline to record internal conditions.
  6. Video footage from the camera will be relayed to a nearby monitoring and recording device. Since the camera is tethered, it will travel until it reaches its maximum length.
  7. It will then be retrieved and re-inserted at the next excavation point. Extensive planning for camera insertion locations has been done in advance to optimize this phase of our work.
  8. As the camera travels the length of the pipe segment we are assessing, trained professionals will analyze the recording and determine if any additional actions are necessary.
  9. Once the full length of the segment is assessed, our crews will close and seal the pipeline and then restore the excavation sites.
  10. In order to return the pipeline to full service, we will purge the line to remove air from inside the pipe. At this point, there is a second chance of a natural gas odor and a loud noise from the work site. Again, the smell of gas will lessen as the purged air dissipates.

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