By the time a massive oil-pipeline spill was discovered in March on Alaska's North Slope, the job of BP's senior corrosion engineer had been left unfilled for more than a year, according to an internal company audit.

This vacancy, and others, hindered BP's (BP) ability to maintain a "strategic view" of its corrosion prevention activities, the audit found.

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The audit also noted that BP Exploration Alaska Inc. had left vacant the top job in its pipeline-corrosion oversight division in Alaska for more than six months in 2005. That division, formally known as the Corrosion, Inspection and Chemicals Group, was headed until the end of 2004 by Richard C. Woollam, who on Thursday refused to testify under oath before a House subcommittee.

Despite Woollam's silence, lawmakers blasted other executives of the London-based oil giant on Thursday for pipeline maintenance lapses and sought explanations for what may have caused the March discharge of more than 200,000 gallons of oil in the Alaskan tundra.

In responding to lawmakers, Steve Marshall, the president of BP Exploration Alaska, said at one point during the hearing that Woollam's "abrasive nature" may have intimidated workers from raising questions about pipeline safety and integrity. Marshall refused to make a direct link between Woollam's behavior and what he admitted were "in hindsight" inadequate pipeline maintenance procedures on the North Slope.

Lost in that exchange with lawmakers, however, was the fact that after transferring Woollam to a non-supervisory job in Houston in January 2005, the company did not fill the vacancy he left until July of that year.

As of June 2006, when the internal audit was completed, BP still hadn't filled the vacancy left by its former senior corrosion engineer. A BP spokesman could not immediately say whether that position has been filled yet.

The audit said BP Exploration Alaska's "operations integrity" position was also vacant as of June, and it noted that the leader of its "maintenance and reliability team" was "fairly new" to the job.

"Such factors reduce the capacity of the teams to take a broader strategic view of the corrosion management programme," the audit concluded.

The audit was conducted by a team of BP PLC employees that were led by John Baxter, the company's director of engineering.