CSB finds design flaw in Blowout Preventer used in Deepwater Horizon

Industrial Accidents

June 5, 2014- Houston– The US Chemical Safety Board has found a design flaw in the Blow Out Preventer (BOP) mechanism used in the BP Deepwater Horizon rig, that most likely led to the accident that became on of the world’s biggest oil spills in history. The worrying fact is that existing BOPs on existing offshore rigs may also be having this same flaw, that can cause yet another disaster!

For an animation of what went wrong, the CSB has released a video (below) that details the sequence of events on the night of the disaster and these should be noted by everybody working in the offshore oil and gas industry.

The buckling of the drill pipe under similar conditions is easily possible in other offshore installations and should be noted with care by Oil and Gas companies that operate similar rigs.

The blowout caused explosions and a fire on the Deepwater Horizon rig, leading to the deaths of 11 personnel onboard and serious injuries to 17 others.  Nearly 100 others escaped from the burning rig, which sank two days later, leaving the Macondo well spewing oil and gas into Gulf waters for a total of 87 days. By that time the resulting oil spill was the largest in offshore history.  The failure of the BOP directly led to the oil spill and contributed to the severity of the incident on the rig.

The CSB report concluded that the pipe buckling likely occurred during the first minutes of the blowout, as crews desperately sought to regain control of oil and gas surging up from the Macondo well.  Although other investigations had previously noted that the Macondo drill pipe was found in a bent or buckled state, this was assumed to have occurred days later, after the blowout was well underway.

After testing individual components of the blowout preventer (BOP) and analyzing all the data from post-accident examinations, the CSB draft report concluded that the BOP’s blind shear ram – an emergency hydraulic device with two sharp cutting blades, intended to seal an out-of-control well – likely did activate on the night of the accident, days earlier than other investigations found.  However, the pipe buckling that likely occurred on the night of April 20 prevented the blind shear ram from functioning properly.  Instead of cleanly cutting and sealing the well’s drill pipe, the shear ram actually punctured the buckled, off-center pipe, sending huge additional volumes of oil and gas surging toward the surface and initiating the 87-day-long oil and gas release into the Gulf that defied multiple efforts to bring it under control.

The identification of the new buckling mechanism for the drill pipe ­– called “effective compression” – was a central technical finding of the draft report.  The report concludes that under certain conditions, the “effective compression” phenomenon could compromise the proper functioning of other blowout preventers still deployed around the world at offshore wells.  The complete BOP failure scenario is detailed in  the above video and also in a report that the CSB released (in draft form).

The CSB draft report also revealed for the first time that there were two instances of miswiring and two backup battery failures affecting the electronic and hydraulic controls for the BOP’s blind shear ram.  One miswiring, which led to a battery failure, disabled the BOP’s “blue pod” – a control system designed to activate the blind shear ram in an emergency.  The BOP’s “yellow pod” – an identical, redundant system that could also activate the blind shear ram – had a different miswiring and a different battery failure.  In the case of the yellow pod, however, the two failures fortuitously cancelled each other out, and the pod was likely able to operate the blind shear ram on the night of April 20.

“Although both regulators and the industry itself have made significant progress since the 2010 calamity, more must be done to ensure the correct functioning of blowout preventers and other safety-critical elements that protect workers and the environment from major offshore accidents,” said Dr. Rafael Moure-Eraso, the CSB chairperson. “The two-volume report we are releasing today makes clear why the current offshore safety framework needs to be further strengthened.”

The incident shows that in addition to the design flaw, there were also maintenance and supervision issues on the rig, otherwise the wrong wiring should never have taken place and even if it did take place, should have been detected in inspections at a later date. It is not clear if such inspections are carried out regularly (which they should).

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