PG&E regulates pressure on its gas transmission system through a series of safety measures, including pressure regulator stations and overpressure protection devices. These systems keep pressure within specified limits. They are inspected and maintained regularly.
PG&E reduced pressure in some pipelines to increase the margin of safety until the Maximum Allowable Operating Pressures (MAOP) could be validated through actions such as records validation, pressure tests, or pipe replacement.
Hydrostatic testing involves pressurizing a pipe with water to reveal potential weaknesses. Hydrostatic testing is a proven method for verifying a pipeline’s MAOP, or capability to operate at a safe level of pressure. Hydrostatic testing is also used in other industries to test items such as scuba tanks, fire extinguishers and air compressor tanks.
PG&E checks more than 5,700 miles of natural gas transmission pipelines for leaks, first by aircraft equipped with advanced laser detection technology, then by teams of gas field technicians using handheld detectors.
In addition, we use a variety of methods to survey, monitor, and test pipelines on a continuous basis, including using "smart pig" in-line inspection devices that travel the length of a pipeline to identify any internal issues, such as corrosion. PG&E is also conducting hydrostatic pressure tests on 150 miles of transmission pipeline, which involves filling the pipe with water at high pressures to reveal potential weaknesses.
Since January 2011, PG&E engineers have been working to digitize, review and verify more than one million paper records, and scrutinize newer computerized records. PG&E has records for pressure tests, or historical operating pressure information, for more than 90 percent of 1,805 miles of transmission pipelines located in high-consequence areas. We have also confirmed pressure test information for more than 30 percent of pipeline segments that were installed before regulations were enacted to require pressure tests.
For pipeline segments where we have an incomplete record, we are taking extra safety precautions as appropriate. These may include, but are not limited to, reducing pressure where advisable, excavating and surveying pipe, pressure testing or replacing pipe if necessary. We continue to search for and review our files for the remaining pressure test records.
Automated gas transmission pipeline valves stop the flow of gas to a ruptured pipeline section in less time than traditional manual valves. By quickly isolating and stopping the flow of gas, emergency responders can take action more quickly and the impact to the public and environment is reduced.
By early 2012, PG&E expects to install 29 automated valves on the San Francisco Peninsula, and expects to install 228 valves throughout the system by 2014.
Learn about the various testing methods PG&E performs as part of the maintenance activities for gas transmission pipelines.
Odorization of Natural Gas
Proper levels of odorization are verified by conducting periodic tests of the odorized gas.
We maintain cathodic protection systems on our steel pipelines to control corrosion.
Transmission pipelines are all surveyed for leaks at least once per calendar year. Distribution pipelines are surveyed for leaks at least once every five years.
Transmission pipelines are patrolled either aerially or on the ground on a quarterly basis.
Pipeline Integrity Assessment
Additional pipeline integrity assessments are performed regularly in accordance with federal regulations. Read more about Pipeline Safety Inspection and Testing