updated 8/2/2005 7:57:17 AM ET 2005-08-02T11:57:17

The installation of the wrong type of pipe spool is believed to have caused last week’s explosion and fire at the same BP plant where 15 people were killed in March, company officials said Monday.

An 8-inch section of heavy steel pipe, located between a compressor and heat exchanger on the Resid Hydrotreater Unit, failed on Thursday. No one was injured during the resulting blast and blaze.

The section failed because workers installed the wrong type of steel pipe spool on the outlet of the heat exchanger, BP spokesman Ronnie Chappell said.

The elbow-shaped pipe spool, believed to have been mistakenly installed when the unit underwent routine maintenance in February, is not designed to withstand higher temperatures. The unit combines heavy crude oil with hydrogen as part of the conversion to lighter products.

“Figuring out what occurred was relatively easy. The question now is how did that error occur, given we have pretty elaborate processes and procedures which govern this kind of work,” he said.

The investigation is expected to take two weeks.

The hydrotreater unit will remain off-line for at least a few more days.

Workers at the refinery will check that the correct piping is installed in other sections of the unit as well as in other pieces of equipment around the facility, Chappell said.

Investigators with the U.S. Chemical Safety and Hazard Investigation Board are conducting their own probe into the most recent accident.

The chemical safety board is also continuing its investigation into the March 23 blast, which occurred in a unit that boosts the octane level of gasoline. That explosion killed 15 contractors and injured more than 170 workers.

The Texas City refinery processes 433,000 barrels of crude oil a day and 3 percent of the nation’s gasoline.

© 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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