PREVENTABLE INCIDENT
NTSB: Wrong Bearing Led to Engine Fire on OSV
The NTSB has released its investigation into a catastrophic engine failure aboard the OSV Ocean Guardian during sea trials off Seattle last year, and has determined that service technicians had installed an improperly-sized main bearing in one of the engines.
In late 2021, Ocean Guardian arrived at a yard in Seattle to begin an overhaul for a new, unspecified mission in the Western Pacific. She received a shelter deck over her aft deck, two cranes, an A-frame and extra accommodations spaces. In January and February 2022, local technicians overhauled the top ends of all four of her diesel-electric main engines and replaced bearings as needed on the bottom ends.
In May, with modifications and repairs completed, the vessel conducted a sea trial to prepare for departure. On May 27, two tugs brought Ocean Guardian out through the Ballard Locks to Shilshole Bay. At about 1400, the crew began to test the ship's propulsion. At 1435, with the No. 3 engine at 30 percent load, the engineers in the control room heard a loud bang and saw smoke in the engine room.
Flames burst out next to the No. 3 engine, and the chief engineer activated an emergency stop to shut it down. The engineering crew evacuated the engine room and the captain remotely shut down ventilation, closed dampers, shut off fuel supply valves and closed the watertight doors to the compartment. Shortly after, the chief engineer activated the fixed firefighting system and effectively put out most of the blaze. The crew mopped up a few small residual fires on and under the engine room deckplates, and two tugs brought the stricken vessel back to port. (The captain did not report the incident to VTS or the local fire department, according to NTSB, as he believed it was under control.)
The damage to the No. 3 main engine was not repairable. A conn rod had gone through the side of the block, and there was extensive damage throughout the inside of the engine. The No. 3 had to be pulled out and replaced with a spare.
A forensic analysis determined that something had gone wrong during the maintenance period on the main engines.
During the overhaul, a service tech had pulled the No. 6 main bearing on the No. 3 main engine for an inspection. The bearing was within tolerances, so the rest of the main bearings on the engine did not have to be replaced. However, it was company policy to replace any bearing removed during inspection with a new one, no matter its condition, in order to prevent any alignment or torque issues with reinstalling a used part. The conn rod bearings were all standard size on inspection, so the tech believed that the main bearing journals were also standard size, as would be normal practice. He did not record the part number printed on the main bearing he removed, and he ordered a replacement in standard size. Another technician installed it.
Unfortunately, the crankshaft main bearing journals on the No. 3 engine had been ground undersized by 0.025 inches at some point in the past. No record had been kept of this service, which was nonstandard: normally all the conn rod journals and main bearing journals would be milled down at the same time during a repair.
When the No. 3 engine started up, the wrong-sized bearing shell on the No. 6 main bearing leaked out so much oil that the oil supply to the adjacent No. 9 and 10 conn rod journal bearings fell by about 80 percent. Without lubrication, the No. 9 and 10 conn rod bearings overheated until the cap bolts fractured, sending the rods, bearing caps and bolts flying about the inside of the engine.
"Vessel crews and equipment manufacturer technicians should carefully identify and document part numbers of all components removed from shipboard equipment. Tracking systems are an effective form of recordkeeping that can be used to ensure proper replacement part selection for reinstallation," advised NTSB.
After repairs, in August 2022, Ocean Guardian departed for the Western Pacific on an unspecified charter. AIS data provided by Pole Star shows that she spent long periods in strategic locations like the Strait of Luzon near Dalupiri Island; South China Sea near Manila; and East China Sea off Okinawa, where the U.S. maintains a naval base. She carried out several survey trackline patterns, one off Okinawa and another south of Chuuk, in Micronesia.
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