Mp Anantharaman

Using reliability block diagrams and fault tree circuits to develop a condition based maintenance model for a vessel's main propulsion system and related subsystems

Merchant shipping has undergone a great transformation over the past three decades. The shipping market is highly competitive which, coupled with high crewing and fuel costs, leads to high operational costs. One of the paramount factors involved in vessel operation is the maintenance cost, and there is a dire need to keep this cost to a minimum. Fortunately, the earlier policy of repair- only maintenance in commercial shipping has been done away with, replaced by the policy of preventive maintenance. The Planned Maintenance System was introduced by ship management companies in the early 1990s. Planned Maintenance offered benefits over the repair-only policy, but has its own demerits. Often machinery equipment is opened up for routine maintenance after a specified time interval, irrespective of the need. This can lead to potential failures, which is explained by the fact that preventive maintenance results in meddling of a well set piece of machinery equipment, leading to its subsequent failure. This is where condition-based maintenance (CBM) steps into prominence. CBM monitors the health of the machinery equipment, analyses the condition and helps in decision making. The main propulsion system forms the heart of a vessel and its reliability needs to be ensured, together with the reliability of its associated sub-systems. The entire system can be represented by reliability block diagrams, to show the interdependence of various components comprising the system. This helps in the decision making process of CBM whereby a ship’s engineer may decide to stop the running machinery equipment, open and overhaul the same, or postpone the overhaul for a later safe date.

A step-by-step approach for evaluating the reliability of the main engine lube oil system for a ship's propulsion system

Effective and efficient maintenance is essential to ensure reliability of a ships main propulsion system, which in turn is interdependent on the reliability of a number of associated sub-systems. A primary step in evaluating the reliability of the ships propulsion system will be to evaluate the reliability of each of the sub- system. This paper discusses the methodology adopted to quantify reliability of one of the vital sub-system viz. the lubricating oil system, and development of a model, based on Markov analysis thereof. Having developed the model, means to improve reliability of the system should be considered. The cost of the incremental reliability should be measured to evaluate cost benefits. A maintenance plan can then be devised to achieve the higher level of reliability. Similar approach could be considered to evaluate the reliability of all other sub-systems. This will finally lead to development of a model to evaluate and improve the reliability of the main propulsion system.

Reliability assessment of main engine subsystems considering turbocharger failure as a case study

Safe operation of a merchant vessel is dependent on the reliability of the vessel’s main propulsion engine. Reliability of the main propulsion engine is interdependent on the reliability of several subsystems including lubricating oil system, fuel oil system, cooling water system and scavenge air system. Turbochargers form part of the scavenge sub system and play a vital role in the operation of the main engine. Failure of turbochargers can lead to disastrous consequences and immobilisation of the main engine. Hence due consideration need to be given to the reliability assessment of the scavenge system while assessing the reliability of the main engine. This paper presents integration of Markov model (for constant failure components) and Weibull failure model (for wearing out components) to estimate the reliability of the main propulsion engine. This integrated model will provide more realistic and practical analysis. It will serve as a useful tool to estimate the reliability of the vessel’s main propulsion engine and make efficient and effective maintenance decisions. A case study of turbocharger failure and its impact on the main engine is also discussed.

Reliability assessment of vessel’s main engine by combining Markov analysis integrated with time dependent failures

Safe operation of a merchant vessel is dependent on the reliability of the vessel’s main propulsion engine. Overall reliability of the main propulsion engine is interdependent on the reliability of a number of subsystems including lubricating oil system, fuel oil system, cooling water system and scavenge air system. The reliability of various components of certain system such as gear pumps in a fuel oil system or filters in a lubricating oil system, which exhibit constant failure rate (random failure) independent of their history of operation, therefore could be analysed using Markov modelling. Other vital component such as turbochargers exhibits time dependent failure rate (wearing out). The wearing out failure rate (increasing failure rates) can be analysed using Weibull analysis. This paper presents integration of Markov model (for constant failure components) and Weibull failure model (for wearing out components) to estimate the reliability of the main propulsion engine. This integrated model will provide more realistic and practical analysis. It will serve as a useful tool to estimate the reliability of the vessel’s main propulsion engine and make efficient and effective maintenance decisions.