TransAlaska Pipeline: Corroded and A Severe Safety Issue -- Agency

The pipeline is corroded due partly to decreased capacity.

The 800-mile pipeline ships 12 percent of the domestic oil supply.

A reason for the increased corrosion is limited use. Oil began flowing through the 48-inch diameter pipeline in 1977. At its peak, the pipeline carried 2.1 million barrels per day.

Capacity has dropped starting in the late 1980's. According to Alyeska Pipeline Service data, between 2000 and 2010, total annual capacity has dropped 38 percent. Today the pipeline operates at less than one-third of the 2.1 million barrels per day that flowed soon after it was built.

The decrease in oil flow is accompanied by a drop in crude oil temperatures, which leads to corrosion. The lower temperatures also create the risk that the water mixed with crude oil may freeze in case the pipeline needs to be temporarily shut down.