Concerned about the potential for corrosion, inspectors for the Trans-Alaska Pipeline System flagged a segment for replacement in a 2008 risk assessment, according to Reuters and The Hill. As we've noted, a leak was detected along that segment earlier this month, necessitating emergency shutdowns of the pipeline.

The disclosure of the earlier risk assessment was made by the pipeline operator, Alyeska Pipeline Service, in response to a request from Rep. Edward Markey, a Massachusetts Democrat, for more information about the pipeline’s prior inspections.

The attempt to inspect this particular section of the pipeline for corrosion was last made in 2008, but was halted because the line was underground and encased in cement [PDF]. Removing the cement for an inspection would risk damaging the pipeline, the company said, so instead it was flagged for replacement. Here’s Reuters, quoting the company’s CEO:

"A risk assessment completed in October 2008 recommended not removing the concrete, but rather, replacing the pipeline."

Alyeska said it had planned to replace the stretch of pipe in question as early as this year. In 2009, Alyeska began the design and engineering work needed before replacing the stretch, said spokeswoman Michelle Egan. "There has been progress made. The work that was required has begun," she said.

In 2007, Alyeska appeared before the House Energy and Commerce committee and testified that accelerated corrosion was not a threat to the integrity of the Trans-Alaska Pipeline System. It also touted “new corrosion monitoring locations at Pump Station One,” the area where the latest leak was found, according to Rep. Markey’s letter to the company.

The leak was not detected by the company’s leak detection system, but by someone walking by on operator rounds, according to the company. Pipeline operations were resumed on Friday, according to a joint command center that has been responding to the incident.

Alyeska also disclosed in its response that the pipeline has had at least 20 spills since 2001—adding up to about 400,000 gallons of spilled oil, the Hill reported.

That count doesn’t include other spills in Alaska from pipelines operated separately by BP. As we’ve noted, Alyeska has strong ties to BP, its largest single shareholder, and though it is technically a separate company, almost all of Alyeska's CEOs have been executives on loan from BP. (The current CEO is one of only two exceptions.) BP’s own maintenance reports have also shown problems with severe corrosion throughout its pipeline system.