NTSB: Incorrect bearing led to OSV fire near Seattle

(WASHINGTON) — An incorrectly sized bearing led to an engine failure and fire last year on board an offshore supply vessel near Seattle, the National Transportation Safety Board (NTSB) said Wednesday.

On May 27, 2022, the supply vessel Ocean Guardian was conducting a sea trial in Shilshole Bay when its No. 3 diesel generator engine suffered a mechanical failure, resulting in an engine room fire that caused $1.1 million in damage. No injuries or pollution were reported.

​After maintenance was completed on all four main diesel generator engines in January and February 2022, full-function tests of vessel systems were conducted in open waters. During the sea trial, the engineering crew heard a “large bang” and observed flames near the No. 3 main engine. The crew extinguished the fire using the vessel’s carbon dioxide fixed fire-extinguishing system.

The walkway between the No. 3 and No. 4 main engines on Ocean Guardian after the engine failure (looking forward). NTSB photo
Ocean Guardian before the casualty. Stabbert Maritime Group photo

Investigators found that the No. 3 main engine’s main bearing journals had been machined down to a smaller diameter, and undersized bearings were installed at some point prior to the 2022 maintenance.

During the 2022 maintenance, Caterpillar service technicians did not identify the bearing’s part number on the service report and replaced it with a standard-sized one. The bearing’s incorrect size allowed lube oil to leak from the larger clearances of the bearing. The decreased lube oil supply pressure resulted in a rapid temperature increase of the connecting rod bearings and multiple engine components breaking free while the engine was running.

The NTSB determined the probable cause of the mechanical failure of the No. 3 main engine and resulting fire aboard Ocean Guardian was the replacement of a crankshaft main bearing with an incorrectly sized bearing during an engine overhaul due to the engine service technicians not identifying the removed bearing’s part number, which resulted in the loss of lube oil pressure in adjacent connecting rod bearings.

“When maintenance is performed, correct replacement of machinery components is critical to ensuring safe and reliable vessel operation,” the report said. “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 record-keeping that can be used to ensure proper replacement part selection for reinstallation.”

Following the engine failure and fire, the local Caterpillar service company switched to a new service tracking system that allows technicians to upload pictures and reports on their cellphones to improve documentation and information sharing between technicians.

Marine Investigation Report 23-08​ is available here.​ ​​​​

– National Transportation Safety Board

By Rich Miller