Published: Mar 23, 2011 5:42 PM EDT
Updated: Mar 23, 2011 2:42 PM EDT

NEW ORLEANS (AP) — A federal probe has found that a trapped piece of drill pipe prevented a blowout preventer from properly sealing to stop last year's massive Gulf oil spill.

A report released Wednesday identified the primary cause of the blowout preventer's failure as the blind shear rams failing to close completely and seal the well due to a portion of drill pipe becoming trapped.

Shear rams are components in a blowout preventer that cut, or shear, through drill pipe and form a seal against well pressure.

Blowout preventers sit at the wellhead of exploratory wells and are supposed to lock in place to prevent a spill in case of an explosion.

The 300-ton device that was used with BP's Macondo well was raised from the seafloor