Managing Pipeline Corrosion
Alyeska’s Preventive Maintenance Program

Pipeline corrosion is the deterioration of metal resulting from a reaction with the internal or external environment of the pipe, which changes the iron contained in pipe to rust. External corrosion occurs from the natural chemical interaction between the exterior of the pipeline and the soil, air, or water surrounding it. Internal corrosion results from a chemical attack on the interior of the pipe from naturally-occurring foreign materials in the oil being transported.

Alyeska’s corrosion control strategies are designed to address both internal and external corrosion on the TAPS mainline and other facilities. Alyeska has programs to prevent corrosion in its storage tanks, at pump station and Valdez Marine Terminal piping and on the 150-mile fuel natural gas line which fuels the northern pump stations. Alyeska spends millions of dollars each year on integrity management – which includes corrosion prevention and control.

Smart pigs -- which are effective in detecting both internal and external corrosion -- are run every three years to inspect for corrosion. A pig is a mechanical device that is pushed through the pipeline by the oil. They move with the oil and measure pipe wall thickness and deformities. Engineers evaluate the data and compile a list of specific locations that need to be investigated by visual inspection, which in some cases requires excavating the pipe to physically examine the area in question.

In 29 years of TAPS operation, 60 smart pigs have been run to inspect the mainline. Several thousand excavations have resulted in examining over 5 miles of pipe with evidence of corrosion or other damage and making repairs as needed.

On the pipeline, internal corrosion is controlled by the flow of oil which moves or sweeps settling water and sediment down the pipeline. Alyeska runs cleaning pigs along the length of the system every 7 to 14 days to remove wax, sediment or other deposits that naturally occur on the mainline pipe walls and may contribute to corrosion.

“Controlling corrosion extends the life of the pipeline and helps protect the environment,” Kevin Hostler, Alyeska President and CEO, said. “It is critical to our core mission of moving oil safely."

External corrosion occurs wherever moisture contacts steel pipe. Cathodic protection (CP) is provided to prevent external corrosion on the mainline, station piping and tanks. CP systems are monitored annually to determine if protection levels are adequate and adjusted as needed. To maintain external conditions, Alyeska uses procedures such as re-coating, re-taping, repairing insulation jackets, or applying sleeves - steel bands that completely encircle the pipe to reinforce pipe strength. In extreme cases, the affected pipe will be replaced.

At pump stations and at the Valdez Marine Terminal, sediment and water can settle to the bottom of the pipe in certain settings which may create a potentially corrosive environment. Alyeska uses CP coupons to test internal corrosion, and injects corrosion inhibitor where corrosion rates indicate it is needed. Since pigs can not be placed in pump station piping, Alyeska uses external ultrasonic measurements to detect corrosion.

In the life of a pipeline, corrosion is a certainty. At the same time, with proper maintenance and prevention, it can be managed to maintain the safety of the pipeline and the longevity of the entire system.