Crews repair corrosion areas identified by pigging data

Crews near Pump Station 1 recently installed a pressure containing metal sleeve to repair areas of external corrosion on the pipeline, and have since reburied the pipe at that location.

Each year, Alyeska plans to investigate and repair mainline pipe based on data provided by “smart pigs.” The pigs use sensor technologies, such as ultrasonic and magnetic sensors, to locate external and internal metal loss or mechanical defects along the pipeline.

This “pigging” process is a regularly scheduled operation along TAPS. After receiving a report from an inspection run in 2006, Integrity Management Engineers identified corrosion at Milepost 0.13, just outside of the Pump Station 1 facility, which required investigation.

The corrosion area at Milepost 0.13 was one of only a few locations that met Alyeska’s criteria for investigation and will be examined this year. The first investigation location was completed at Milepost 22.87 earlier this year and required repair of the pipeline coating, but no mechanical repair. A third location, at Milepost 784.5, will be investigated this spring.

Integrity management teams use various methods to detect corrosion along the pipeline. The pig – an inline mechanical device – assists in this effort. A pig is designed to travel through the pipe without stopping the flow of oil as it performs cleaning and inspection operations.

The sleeve repair work at Milepost 0.13 was completed in March and required excavation of approximately 20 feet of underground pipeline where the inspection pig had detected corrosion.

Alyeska removed the coating from the pipeline, sandblasted the pipe’s surface and laid out grids in the areas where the corrosion was located, in order to obtain accurate measurements of the pipe wall thickness. Integrity Management Engineers calculated the remaining strength of the corrosion area and determined it was safe to continue operation of the pipeline at its current operating pressure. As a safety precaution, however, it was decided to temporarily lower the safety relief pressure set point of the pipeline until the repair sleeve was installed. Workers fitted the pipe corrosion area with the metal repair sleeve and welders mobilized to make final repairs within days of when the pipe corrosion was inspected.

“Once the repair was made, the line was restored back to full operating pressure conditions,” said Tom Webb, Engineering Integrity Manager. “These safety precautions did not impact the pipeline operating conditions or throughput levels.”