Abstract
By adjusting the maintenance approach towards the significant components of ship’s engines and equipment, through the use of operational data from the ship machinery’s daily reports, higher operability and navigation safety can be achieved. The proposed maintenance adjustment model consists of an operation data analysis and risk analysis. The risk analysis comprises the definition of the upper and the lower risk criterion, as well as the definition of a risk index. If the risk index is higher than the lower risk criterion, the component is significant, while it is not significant and has an acceptable risk index if the risk index is lower than the lower risk criterion. For each significant component with a risk index found to be “unacceptable” or “undesirable”, an efficient maintenance policy needs to be adopted. The assessment of the proposed model is based on data regarding the power engine original operation throughout a 13-year period. The results of engine failure examinations reveal that the exhaust valve is the most vulnerable component with the highest rate of failure. For this reason the proposed model of adjusting the maintenance approach has been tested on the exhaust valve sample. It is suggested that the efforts to achieve higher ship operability and navigation safety should go in the direction of periodical adjustments of the maintenance approach i.e. choosing an efficient maintenance policy by reducing the risk indices of the significant engine components. KEY WORDS: maintenance adjustment approach, risk analysis, risk index, lower risk criterion, upper risk criterion, significant components, ship navigation
Highlights
The ships that are designed and built to satisfy the classification rules and the IMO regulations have an acceptable level of reliability for safe navigation
Longer and safer navigation is achieved with the adjustment of maintenance approach for the significant components, i.e. by choosing an efficient maintenance policy by reducing the failure frequency in the component lifetime or by a modification: decrease of significance of the failure effect on safety and operation
The results of the analysis of the propulsion engine failures have shown that most failures occurred on the injection valve and the exhaust valve
Summary
The ships that are designed and built to satisfy the classification rules and the IMO regulations have an acceptable level of reliability for safe navigation. Since occasional failures occur during the whole work cycle of the system, and the experts’ answers are mostly uncertain, it is safe to conclude that in the case of older machinery t0 = 0 In such a case, the Weibull distribution has two parameters (W^h, bh) and the ratio’s parameter represents the preventive maintenance interval (h = mean life). In the significant component there is at least one failure combination of mode/cause, whose safety or operation risk index is higher than LRC. For the failure modes effects having the risk index in an unacceptable zone, preventive maintenance (PM) could be required to reduce the risk. If the time of reaction is zero or very short (totally unexpected or almost totally unexpected failure) the “on-condition PM” option will be rejected
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