DNV: Deepwater Horizon Blowout Preventer Design Flawed, May Affect Other BOPs

March 2011, Vol. 238 No. 3

Det Norske Veritas has completed its eight-month forensic examination of the Deepwater Horizon blowout preventer (BOP), made at the request of the U.S. Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE), and determined that the primary cause of trouble was that the blind shear rams intended to cut through the drill pipe were unable to sever a bent pipe. The report is publicly available as of March 23, in two PDF volumes, Vol. I and Vol. II.

The report theorizes that the position of a drill pipe tool joint led to a pipe buckle just above the position of the blind shear rams from the moment the well began flowing–long before the explosion. The buckle meant the pipe was held in an off-center position in respect to the blind shear rams, so when the shear rams closed, part of the pipe was not in contact with the cutting surface. This part of the pipe wedged between the joining surfaces of the ram block faces, which were intended to seal off the flow of the pipe, and therefore prevented the flow from sealing.


A section of the bent drill pipe, as recovered.

An Associated Press summary of the findings quoted Philip Johnson, a University of Alabama civil engineering professor, on the possible ramifications of the discovery: “My reaction is, `Holy smokes, every set of blind shear rams out there may have this problem.'”

The blowout preventer, a 50-foot, 300-ton assembly was raised and taken to NASA’s secure facility in Michoud, Lousiana in August for forensic examination. (View video of the transport.)

BOEMRE/U.S. Coast Guard (USCG) Joint Investigation Team announced that it will hold a seventh session of public hearings the week of April 4, 2011. The hearings, which will focus specifically on the forensic examination of the Deepwater Horizon blowout preventer, are scheduled to take place at the Holiday Inn Metairie, New Orleans Airport, 2261 North Causeway Blvd., Metairie, La.

The forensic examination is one aspect of the much broader comprehensive investigation into the causes of the Deepwater Horizon explosion, loss of life, casualty loss, and the subsequent oil spill. Although the full investigation report is not expected to be released until sometime this summer, a report on the BOP and other matters is scheduled to be issued within the next month.


The fault tree from the report.