In general, an actual data of marine use mechanical parts is not clearly classified in the failure replacement and the periodic replacement. This main reason is that a specified period of repair is sometimes disturbed and becomes random by several reasons, for example, ship's schedule, operational conditions, judgements of a maintenance crew and so on.
In this note, the replacement data of valves of main diesel engine, i.e., the exhaust valve and the fuel oil valves, is chosen from such data which is gathered from four same type ships, and analyzed by using the Weibull chart, in which, in particular, we notice the shape parameter m.
Next, the secular change and the characteristic of valve replacement on each ship is investigated through the shape parameter m.
According to these obtained results, it is clear that m values have the range between 1.0 and 2.0, and as the time of using these parts increases, the maintenance method has a tendency to go to the specified replacement.
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