On August 11, 2022, a containership working within the North Pacific Ocean skilled a lack of propulsion as a result of a controllable pitch propeller (CPP) system failure. The Nationwide Transportation Security Board (NTSB) investigated the incident involving important mechanical harm, although no accidents have been reported.
What Occurred
Whereas en route from Tacoma, Washington, to Anchorage, Alaska, the vessel’s engine crew detected a hydraulic oil leak from the CPP hub lubricating system. In response, the crew diminished the propeller pitch. It replenished the oil within the CPP hub head tank to take care of propulsion. Suspecting a blade seal failure, they continued the voyage to Anchorage, the place shore-based technicians beneficial emergency drydocking. The vessel then proceeded towards a shipyard in Oregon.
In the course of the transit, the hydraulic oil loss worsened, prompting the crew to make use of contemporary water to complement the fluid. The state of affairs deteriorated additional as water started contaminating the strict tube lubricating system. To stop full propulsion failure and potential seawater ingress into the equipment area, the primary engine was shut down, and the vessel was towed the remaining distance to the shipyard.
Subsequent underwater inspection revealed fractures in two CPP blades. One blade had a big fracture that prolonged by way of the hub space and was confirmed to be the supply of the hydraulic oil leak. Put up-incident testing verified that potable water used in the course of the voyage had leaked from this broken blade.
Why It Occurred
Put up-incident evaluation decided that the lack of propulsion was brought on by a crack in one of many CPP blades that developed into an entire fracture as a result of high-cycle fatigue. The blade didn’t meet a number of of the producer’s design specs, together with the required counterbore radius on the bolt gap, materials impression toughness, tensile and yield energy, and chemical composition. These deficiencies made the blade extra liable to fatigue and cracking. The failure originated on the bolt gap counterbore, an space crucial to structural integrity.
Actions Taken
In response to the findings, the CPP blade producer revised the interior radius necessities for all seven bolt gap counterbores to reinforce fatigue resistance. A finite aspect evaluation of comparable CPP programs didn’t establish comparable points, suggesting the incident was an remoted manufacturing defect.
Classes Discovered
Important parts akin to CPP blades should conform strictly to engineering and materials specs to make sure fatigue resistance and operational reliability.
Early identification and monitoring of fluid loss in propulsion programs are important for managing danger throughout a voyage.
Substituting incompatible fluids, akin to water for hydraulic oil, can result in additional system degradation and may solely be thought of in excessive circumstances with clear contingency plans.
Efficient coordination between crew, shore-based engineers, and producers is important in managing emergent technical failures at sea.
Did you subscribe to our Every day publication?
It’s Free! Click on right here to Subscribe!
Supply: NTSB
Source link
