Case 3 Fractured Piston Ring Type of Vessel Principle Machinery Place of Damage Bulk Carrier Year of Build 1994 2004 48 hours Slow speed 2 stroke Diesel Engine (7 Year of Accident cylinders, Bore: 520mm) Piston rings, cylinder liners, etc Down time Summary if accident:
While a vessel was under way, an alarm sounded concerning a high scavenging temperature in the No.6 cylinder of the main engine. After avoiding stormy weather, the main engine was stopped for inspection. The inspection revealed that the piston rings for all the cylinders were either broken or abnormally worn.
State of accident:
(1). The top and second piston rings of No.2,3,4,5 and 6 cylinder units had fractured.
(2). The other piston rings were found to be abnormally worn, but the cylinder liners were only
slightly affected.
Repair work:
The damaged piston rings in the No.2,3,4,5 and 6 cylinders were renewed and later replaced those in the No.1 and No.7 cylinders when the necessary parts were delivered.
Cause of accident:
The cause of the accident is not identified. < The result of the fuel oil analysis>
The result of fuel oil analysis by laboratory was as follows: Al + Si (Aluminum Silicon) 69 mg/kg
* ISO 8217 recommendation: Max 80 mg/kg, Manufacture: 30mg/kg
Importance information:
(1). Fuel oil pretreatment system
Marine fuel oil is supplied on the assumptions that bunker fuel oil is used for the engine after the fuel oil is properly treated by the shipboard pretreatment system and marine fuel oil is vary in quality. Various problems are expected when using degraded fuel oil or fuel oil that has unstable properties. Therefore, proper pretreatment of fuel oil, along with various measures for the main engine, are extremely important for supplying optimum fuel oil to the main engine. In particular, give careful consideration to high viscosity and contained impurities. For high viscosity, adjust heating temperatures, paying attention to heat stability. Meanwhile, for contained impurities, remove sludge, water, and impurities as much as possible through pretreatment systems. (2). Al + Si (Aluminum-Silicon)
Aluminum-Silicon, also referred to as catalyst fines, is small particles arising from the catalytic cracking process in the refinery or the mixture of sand. Under microscope
observation of 50 to100 magnifications, FCC catalyst fines are usually globular in shape, while particles in the form of sand are irregular in shape. These catalyst fines are very abrasive and cause accelerated wear to lubricating surfaces and contact surfaces. Engine manufactures recommended that the value of Al+ Si in fuel oil at engine inlets be 7 to 15 PPM. For fuel oil with a high Al + Si content, respond with the pretreatment system.
(1). Throttle the flow rate as little as possible and set the purifiers in parallel operation.
(2). When Al + Si content exceeds 50 to 60 PPM, sufficient removal results may not be obtained
in single-stage purification performed by one centrifugal separator. In such case, set two or more separators in series, or store the treated fuel oil in tanks for a while and have it pass through the separator again before supplying to the engine.
(3). FCC fines tend to accumulate at the bottom of tanks, so it is desirable that tank cleaning or
tank dredging be carried out accordingly.
(4). Separation efficiency varies with type of equipment, and the operational and maintenance conditions of the pretreatment system. It is desirable that actual separation efficiency be checked by comparing with a retained sample and a sample at engine inlet beforehand.
