Pacific Gas and Electric Co. (PG&E) has completed roughly 20 hydrostatic tests of pipeline segments involving the temporary use of compressed natural gas (CNG) and liquefied natural gas (LNG). The pipeline segments passed their pressure tests, and the use of CNG/LNG also passed, according to utility officials.
Most recently, PG&E completed pressure tests on transmission pipe in the Santa Cruz region, about 80 miles southwest of San Francisco. This required the combination utility to take the area's primary gas supply line out of service.
"In order to maintain safe and uninterrupted service for 46,500 customers during these tests, we launched our LNG/CNG support program. PG&E injected more than 3.5 million pounds of LNG into its distribution system,” the spokesperson said.
The project took 20 days in August. "We successfully hydro tested five miles of transmission pipe," the spokesperson said. Two years of planning went into the Santa Cruz test.
Four years ago, with the sting of the San Bruno pipeline failure and explosion still being strongly felt, PG&E agreed to a "very, very aggressive schedule" to validate the maximum allowable operating pressure of all of its high consequence area pipelines that had not been pressure tested (see Daily GPI, March 31, 2011). The testing continues, and in Santa Cruz an 89-member CNG/LNG project team worked to make sure retail natural gas utility customers were unaffected.
On the Santa Cruz project there were nearly 120,000 miles driven for the mobile fueling operation, involving 171 truckloads of LNG and another 45 CNG truckloads. The LNG supplies amounted to about 81 MMcf.
LNG was shipped via truck from the Clean Energy Fuels Corp. liquefaction facilities in Boron, CA, in the Southern California Mojave Desert to Santa Cruz, more than 300 miles to the north.
"Truck-trailers with LNG/CNG made nearly constant deliveries to the injection sites in the region," the PG&E spokesperson said. "Given the complexity of this project, the LNG/CNG team safely tested the system for 48 hours prior to relying upon it to ensure customers would not be affected. The team operated 32 tankers, five portable compressors, and three vaporizers,"
PG&E said it will continue to use the LNG/CNG approach while the high-pressure safety tests of the transmission pipelines continue.