Assessing key reliability and criticality aspects of ship systems for improved energy efficiency

Research output: Contribution to conferencePaperpeer-review


The maintenance of the global fleet has always been a key challenge in ship operation and the shipping industry in general, as the condition of the global fleet is closely tied with the prosperity of international trade. It is the scope of this paper to assess the reliability and criticality of Liquefied Natural Gas (LNG) carriers’ ship systems in terms of energy efficiency, a subject of no previous research. In the first part of the study, a database of LNG carrier ship systems, failure rates and drawings is compiled. From the available systems the steam generating plant is studied, as according to service experience it is a system that is prone to failure. The assessment is carried out using Fault Tree Analysis (FTA) with dynamic gates in a dedicated reliability assessment software. The exact calculation method is used to quantify the reliability of the steam generating plant, as represented with its fault tree. Similarly, the Criticality Importance Measure (IM) is employed to identify the critical components of the system. Based on the above results additional spare parts, inspection, and maintenance are suggested. It is important to mention that by using a total of 12 additional spare parts and maintaining 4 additional sub-systems, the reliability of the steam generating plant can increase by as much as 40%. The viability of this proposal is then assessed in terms of the ship’s operation. It is seen that when the LNG carrier operates in gas fuel mode and in unfavourable economic conditions (low chartering rate, and high fuel prices) the above suggestion can yield an increase in profit.
Original languageEnglish
Publication statusPublished - 2015


  • ship systems
  • ship reliability
  • energy efficiencey

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