Company closes gas pipeline for repairs
April 30, 2009 · Updated 4:05 PM
By Dennis Box, The Courier-Herald
Northwest Pipeline has shut down for repairs a 286-mile stretch of natural gas pipeline running parallel to the Interstate 5 corridor after two ruptures. The first rupture occurred May 1 near Lake Tapps at the Puget Sound Energy hydroelectric facility and the second Dec. 13 close to Toledo, Wash.
The Department of Transportation Office of Pipeline Safety sent a corrective action order to Northwest Pipeline on Thursday shutting down the pipeline until the problems are repaired.
The 26-inch pipeline in question runs from Sumas, near the Canadian border, to Washougal, near the Oregon border, and was installed underground in 1956 with spurs running out from the main line to transfer stations. Northwest has a 30-inch pipeline that also runs through the north-south pipeline corridor east of I-5. That line was installed in 1971 and will provide natural gas to Northwest Pipeline customers while repairs are made.
The 46-mile section running out of the main line from Snohomish to Sumner, which ruptured near the PSE Lake Tapps hydroelectric facility, has been out of service since May while Northwest Pipeline makes external repairs to the line.
"We need to understand where the stress corrosion is coming from," said Grant Jensen, Redmond district manager for Northwest Pipeline. "Stress corrosion is a relatively new phenomena. It's probably been out there for years, but we're just beginning to recognize it."
The process for finding the problem sections of the pipeline involve using a new, high-tech detection machine known as a "smart pig." The smart pig is put inside the pipeline. It will run between compression stations, which are located every 50 miles, the entire length of the line. Using computerized sensors, the smart pig gathers information about the pipeline's integrity.
"Once we have that data, we know what to dig up, and which pipe to repair by recoating or replace," Jensen said.
Prior to using a smart pig detector, companies would hydro test with pressurized water or dig sections up and hope.
"The smart pig finds imperfections before they get to be problems. It's much more proactive," Jensen said.
Northwest Pipeline is a distribution company that transports natural gas to companies and municipalities through its pipeline system. A company or city purchases natural gas from a mine holder in Canada or the Rocky Mountains and contracts Northwest Pipeline to transport the gas.
A typical gas mine will drill more than 2,000 feet into the earth searching for pockets or voids in the rock containing gas.
Northwest Pipeline transports natural gas from the mines to seven states - Washington, Oregon, Idaho, Wyoming, Colorado, Utah and northern New Mexico.
Dennis Box can be reached at email@example.com