TAPS replaces, repairs valves in 3-year inspection program

Stopple plugs isolate Check Valve 122, north of Valdez, while the bonnet of the valve is removed and the valve accessed for repair. (Photograph by Mike Dinneen and provided by Alyeska Pipeline Service Co., Anchorage)

A main line valve (RGV 80) is lifted from its site at MP 519 near Delta Junction, south of the midway point on the Trans-Alaska Pipeline, to be analyzed for sealing problems. Another valve from the Alyeska inventory replaced it in a 29-hr operation that shutdown the pipeline at the end of September. (Photograph by David Predeger and provided by Alyeska Pipeline Service Co., Anchorage) [41,153 bytes]
The longest planned shutdown in the history of the Trans-Alaska Pipeline system (TAPS) ended in September with replacement of one main line valve and repair in-place of another, according to Alyeska Pipeline Service Co., Anchorage, which operates the system for its seven oil-company owner partners.

The project cost approximately $10 million and was accompanied by other maintenance work along the 800-mile crude-oil system.

Alyeska coordinated the pipeline shutdown with North Slope producers. Oil flow during the shutdown was approximately 10% of normal; stopple plugs were installed up and down stream of each of two major valve jobs to isolate it during repairs.

Alyeska says tanker loading at the Valdez marine terminal remained unaffected.

Sealing problems

Remote Gate Valve 80, a 48-in. valve at Mile Post (MP) 519, approximately 13 miles north of Delta Junction, was replaced with another gate valve from Alyeska's inventory.

The removed valve was cut from the line and sent to Texas where it is being inspected to determine why it was not sealing properly upon closure.

By mid-November, Alyeska returned the repaired and refurbished valve to company inventory for future use.

At the base of Keystone Canyon at MP 780, 20 miles north of Valdez, Check Valve 122 was repaired in place by replacement of the internal sealing elements.

A crew, entering the pipeline from the top of the check valve, discovered debris and sludge at the bottom of the valve. Alyeska believes this material was preventing the valve from sealing properly. The company says this project was the first time an in-service 48-in. main line valve was refurbished.

Simultaneous with these two major projects, Alyeska was carrying out a variety of smaller maintenance projects in various locations along the system.

Inspection program

TAPS has 177 block valves, of which 96 are remotely controlled gate valves and 81 are automatic check valves, the latter to prevent back flow in case of line-pressure loss.

In 1996, says Alyeska, the company conducted a review of its maintenance program for main line valves, in concert with the Joint Pipeline Office, the joint federal/state pipeline-monitoring agency. The review indicated that some improvement could be made in valve preventive maintenance, inspection, full operational testing, and personnel training.

Along the system, risk assessment was performed, integrity testing conducted on all valves, and an aggressive valve-sealing plan developed.

In 1997, Alyeska conducted extensive risk-assessment to establish minimum acceptable performance standards for all mainline block valves. The threshold for repair is whether the amount of oil leaking through a valve seal is theoretically enough to add to the volume of oil that would spill from a 1-in. pipeline leak.

The testing of main line-valve operation begun in 1997 will be completed in 2000. Through mid-1998, 77 of the 177 main line valves had been tested. Only the two repaired in September showed need of major attention, says Alyeska.