Alyeska Pipeline launched a corrosion detection pig today in the 8-inch fuel gas line, which parallels the trans-Alaska pipeline from Pump Station 1 to Pump Station 4. This high resolution magnetic corrosion detection pig will scan the fuel gas line for corrosion which may reduce pipe wall thickness. A corrosion detection pig was last run in the fuel gas line in April 1993; minimal corrosion was detected during previous pig runs.

The fuel gas line is 10-inches in diameter from Pump Station 1 to Mile Post 34 and 8-inches from Mile Post 34 to Pump Station 4 (approximately 115 miles south). The computer in the pig does not have enough memory to track the entire length of the 8-inch section of the line. The pig will be run twice to gather information from the entire length of the fuel gas line. The pig launched today is expected at Pump Station 4 on Wednesday; the trip takes about 44 hours. The second pig run is scheduled to begin Thursday. Data from the current pig run is expected in approximately three months. At that time, engineers will determine if the fuel gas line needs to be excavated, inspected for corrosion and repaired if necessary.

The fuel gas line carries natural gas from the North Slope fields to supply fuel for pump stations north of the Brooks Range. Pump stations south of the Brooks Range are fueled with liquid turbine fuel.

During an annual maintenance inspection of the mainline valves, the clapper on Check Valve 90, 30 miles south of Pump Station 9, was found to be locked in the open position. The clapper was released and valve was successfully function tested. The valve clapper is believed to have been locked in the open position in September 1997, during maintenance work. A complete investigation of the situation is underway.

Check valves are designed to prevent the reverse flow of oil in the pipeline. The valve clapper is held open by the flow of oil and drops closed automatically when oil flow stops or is reversed. If the clapper is locked in the open position, the valve will not respond if oil flow stops or reverses.

The north end of the pipeline was idled briefly at 3:55 p.m. Saturday when a component in a control panel for the pumps at Pump Station 4 failed and the suction pressure at the pumps increased above the set point for the station. An automatic logic system, designed to protect the pipe from over-pressuring, activated and automatically idled Pump Station 4 and Pump Station 3. Operators in the Operations Control Center in Valdez idled Pump Station 1 when the other pump stations were idled.

The pipeline was restarted at 4:00 p.m. by operating the pumps at Pump Station 4 in a manual control mode. The failed component was replaced at Pump Station 4 and the pipeline was back at normal operation by 5:45 p.m.

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