Cleaning pig runs amok at Alyeska terminal

Refrigerator-sized device diverts into manifold, breaks up; incident doesn’t stop oil movement as operator uses alternate flow path

Wesley Loy

For Petroleum News

The operator of the trans-Alaska pipeline has a stuck pig at the Valdez oil terminal. And it’s likely to stay stuck.

A pig is a tool that slides through the pipeline to clean it, or to test for problems such as corrosion.

Back in the spring, a cleaner pig ran off course and was “ingested” into a manifold, an arrangement of piping and valves designed to control oil flow.

The pig broke apart, and much of it remains stuck. The incident didn’t interrupt the flow of oil into the terminal or onto tankers, said a spokeswoman for system operator Alyeska Pipeline Service Co.

But a nonprofit organization that monitors oil industry activity at Valdez said “efforts to recover the pig and reestablish normal operations including the resumption of routine pigging were both extensive and protracted.”

Tool temporarily lost

The pig was about the size of a refrigerator and was built from fairly flexible polyurethane parts, she said. The device is designed to break into smaller pieces if it encounters significant barriers or pressure.

Alyeska sends cleaner pigs down the pipeline about once a week to scrap out wax that can build up inside the line, which is 48 inches in diameter.

On May 10, a pig arrived as scheduled at the Valdez Marine Terminal at the end of the 800-mile pipeline.

But something happened to divert the pig’s path.

“As the pig arrived, the pressure relief system was triggered, likely by the incoming wax cloud,” Egan said.

The pig should have gone to a trap, or chamber, where it can be retrieved after a run through the pipeline. But on this occasion, operators found no pig when they opened the trap.

A search determined the pig had followed the oil on a “path of least resistance,” going into what’s known as the relief system manifold in the terminal’s East Metering building.

Pig parts blocked some of the relief valve piping.

The incident did not force a terminal shutdown. Rather, Alyeska was able to use an approved alternate flow path to take oil around the relief system, Egan said.

Alyeska removed a portion of the obstruction, an investigation was conducted, and regulators were kept informed, she said.

‘Encased in concrete’

The council monitors the terminal and the tankers that load crude oil in Valdez.

In a memo prepared in advance of the board meeting, council staffers provided their own understanding of what happened with the errant pig.

“In May, a pig approaching the Valdez Marine Terminal happened to be forced into a section of piping buried under reinforced concrete rather than continuing on to its intended destination, the VMT’s pig trap,” the memo said. “That section of piping was the header piping for the relief system. From subsequent investigatory efforts, the pig appears to be located at the tail end of the relief header piping, blocking flow through one of the four relief valves. Alyeska has not attempted to extract the pig from the header as the piping is encased in several feet of concrete. ....”

The memo continued: “Initially, regulators permitted Alyeska to continue moving oil into the terminal by using a longstanding alternate operating procedure that does not require the relief or backpressure system for safe operation. Once the relief system was confirmed operational with three relief valves, normal routing of oil was resumed. Regulators were engaged throughout the process.”