Equipment Failure - Main Engine
- USA.
- Official Report No. 9806.
I am indebted to the Washington State Office of Marine Safety for sending the following prevention bulletin #95 ñ01. Further information can be obtained from Marine Investigations, PO BOX42407, Olympia WA 98504-2407. Telephone (360) 664-9116.
On October 11, 1994 at about 0410, the DONA V, a Liberian flagged bulkcargo vessel, was forced to shut down her main diesel engine because ofmechanical failure. The vessel was completing an 18 day trip from Chinato Tacoma and was to load bulk grain. When the Captain stopped the engine,the DONA V was approximately 2880 yards north east of Foulweather Bluffin Admiralty inlet Washington, in the inbound traffic lane. The vessel thendrifted in a south easterly direction at approximately 0.5 knots acrossthe traffic lanes and anchored near Double Bluff. She was later towed withoutfurther incident into the harbour anchorage. The Office of Marine Safetydetermined that the probable cause of the main engine casualty was a holein the piston crown of #2 cylinder. It is likely that the piston crown hadnot been removed or cleaned for many years, allowing the accumulation ofsludge on the crownís cooling surfaces. The loss of lube oil pressurecaused the main engine to shut down to avoid further damage to the engine.
During the investigation the Chief Engineer was asked to explain theprocedures used to inspect pistons and piston crowns. He stated that itis company policy that pistons are inspected during routine piston overhaulsevery 7/8,000 hours of operation. It is neither the Chief Engineerísnot the companyís policy to routinely remove the piston crown fromthe piston body for examination, testing or cleaning during a piston overhaul.If the piston crown is not removed during the overhaul period, it is notpossible to ascertain the amount of carbon that may have built up on theoil side of the piston crown. Carbon build up on the oil side of pistoncrowns reduces heat transfer and can lead to thermal corrosion and failureof the piston crown.
From the information collected during the investigation, it is probablethat the piston crown had not been removed from the piston body for manyyears, allowing carbon to accumulate and adhere to the cooling surface ofthe piston crown. It is presumed that the collected carbon considerablyreduced the effects of the cooling oil, causing the piston crown to crack.
During the course of the investigation, the Chief Engineer stated thathe was not aware of any engine manufacturerís preventative maintenanceprocedures for the piston crown. The Chief Engineer reviewed the vesselísengine manuals during the investigation and could not find any requirementsto gauge the surface of the piston crowns or any guidance on when to replacepiston crowns. Based upon experience, the Chief Engineer believed that pistoncrown failures are routine casualties. He had experienced two or three otherpiston crown failures during his sailing career and he also discussed thesefailures with other engineers. In his opinion, piston crown failures couldnot be prevented.
The Chief Engineer stated that the main engine maintenance was difficultto schedule because of the vesselís short stays in port (a grainship can load in 18 ñ 30 hours, making engine maintenance difficultto accomplish). He indicated that he had to maintain the vesselísmachinery within the scheduled port times to load cargo. He did not feelcomfortable in requesting additional port time to perform routine maintenanceof machinery. This dilemma is an indication of maritime industry culture.In some instances, vessel operators are emphasising vessel schedules atthe expense of maintenance and safety.
Mitsubishi, the engine manufacturers, have recommended the followingpreventative measures:
Thermal corrosion will cause the piston crown to fail if carbon is allowed to build up and adhere to the cooling surface of the piston crown.
They have developed procedures to improve the performance of the piston crown. The procedures will prevent thermal corrosion and wear on the flame side of the piston crown.
They have published a recommended inspection and cleaning schedule to prevent thermal corrosion of piston crowns.
They have also developed a process to address flame impingement and corrosion to the surfaces of the flame side of piston crowns by building up the crown surface with a special steel alloy. The steel alloy can be applied to new pistons and pistons in service. In addition, a jet cooling system has been developed by Mitsubishi to enhance the cooling of the piston crown.
Mitsubishiís maintenance procedures demonstrate a commitment to improving engine operations and educating the maritime industry to reduce engine failures.
Source article nautinst.
