HOUSTON (AP) -- A critical device at the center of an investigation into the Gulf oil rig explosion didn't undergo a rigorous recertification process in 2005 as required by federal regulators, a worker responsible for maintaining the equipment told investigators Wednesday.Mark Hay of rig-owner Transocean said the blowout preventer -- designed to prevent a spill in the case of an explosion -- was not recertified because it was being constantly maintained.