Northwest Pipeline said that a 111-mile portion of its idled 26-inch diameter line between Sumas and Washougal, WA, is back in service, providing an additional 131,000 Dth/d of much needed pipeline capacity along the I-5 corridor. The capacity increase will allow customers to transport more gas to markets in southern Washington, Oregon and California and to the Jackson Prairie storage field.

About 268 miles of the 1950s vintage pipeline was taken out of service last year after two ruptures occurred, one in May and another in December. There were no explosions nor any injuries from the pipeline ruptures. However, the federal Office of Pipeline Safety (OPS) and the Pipeline Safety Division of the state Utilities and Transportation Commission ordered the company to test and repair defective segments of the pipeline, which was installed in 1956.

On June 22, Northwest successfully returned to service the last of four hydro-tested segments of its 26-inch line. The hydrostatic testing program began on March 12 and was completed on May 24. A total of 54 separate hydrostatic tests were conducted with only one failure, the company said.

In April, regulators granted the first return to service for a 16-mile segment of pipeline between Mt. Vernon and Snohomish. A 16-mile segment between Chehalis and Washougal was placed in service in May. Earlier this month, 45 miles between Ft. Lewis and Chehalis was placed is service and the OPS approved the return of the 32-mile Sumas-to-Mt. Vernon, WA segment on June 17 (see NGI, June 21). Northwest expects that the restored capacity will meet typical market need.

The company is looking at a combination of factors that could have produced the stress-corrosion cracking that led to the ruptures, including the type of steel, the coating used on the pipe and the moist environment in which it operates (see NGI, June 16, 2003).

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