Reliability-Centered Maintenance for a Merlin WR200 WROV
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- Institutt for marin teknikk 
IKM Subsea AS is an independent Remotely Operated Vehicle (ROV) company that owns and operates 20 Merlin WR200 ROV systems. In order to stay competitive on the ROV operation market IKM Subsea are seeking to reduce their downtime and operational costs, and therefore want to investigate methods to reduce these factors. IKM Subsea experience that the maintenance costs contribute to a large part of the total costs IKM (2017c). In an effort to reduce the maintenance cost IKM aims to optimize the maintenance plan to make it more efficient both regarding costs and to increase the availability of the ROV. This is of special importance as the oil and gas industry is facing a recession and the oil prices are lower than before (Norsk Olje & Gass, 2017), resultingin an increased focus on cost reductions. Many companies within several industries use maintenance plans based on the recommendationsfrom the items manufacturer. As a complete system consists of many items the proposedplan is not customized for the items as a part of a complete system. This may lead to too extensive maintenance, which subsequently result in higher-than-necessary maintenance costs. A customized maintenance plan will take the operation context and the company´sfocus area into consideration, thus resulting in a tailor-made schedule for the system. One maintenance strategy that enables to develop a tailor-made maintenance plan is the Reliability-CenteredMaintenance (RCM). The RCMstrategy s main focus is to evaluate the systems in its operationcontext. Additionally RCMfocuses on performing maintenance when needed, i.e accordingto the items condition. It is also a well-established strategy within many industries. Due to this, the author in collaboration with IKM Subsea have decided to utilize the RCM strategy in order to reach their goals. To perform a RCM analysis it is necessary to have some background knowledge regarding maintenance and technical understanding of the items to be analyzed. Therefore, the author have chosen to include a chapter regarding relevantmaintenance theory along with information concerning the ROV. In addition to these chapters the author has had good guidance from the technical department at IKM Subsea to be able to understand the ROV in detail. The development of the analysis in the thesis was based on the RCM perspective of togetherwith the RCMcriteria formed by Society of Automotive Engineers (1999). The RCManalysis consists of 7 steps where step 1-5 involves performing a Failure Mode, Effect, And Criticality analysis (FMECA). Step 6 and 7 belongs to the Maintenance Task Analysis (MTA) where suitable maintenance task are assigned, making up the maintenance plan. The analysis was performed on three subsystems of the ROVnamely the propulsion-,manipulator-, and tooling- systems. The analysis was performed by the author together with IKM Subseathrough RCM workshops at IKM Subseas office in Bryne, Norway. All input data for the analysis was obtained fromIKM Subseas ownMerlin database. As the the input data were of varying quality this can give erroneous results as the RCM analysis is dependent on input data of good quality in order to show its full potential and give good results. The results from the subsystems FMECA showed that all systems had failure modes with RiskIndex (RI) classified as unacceptable. The failure modes had especially high RI values for operational and/or cost concerns. The components of the different subsystems with the highest RI included: Sleipner Gear (Thruster), propulsion system Electric motor (Thruster), propulsion system Electric motor (HPU#2), manipulator system Hydraulic actuators (rigmaster), manipulator system Electric motor (HPU#1), tooling system The majority of the above mentioned components failure modes regarded leakage of compensatoror hydraulic fluid. This is mainly due to the fact that themajority of the ROV systems/itemsrequire pressure compensation to withstand the sea pressure at 3000 meters, which is made possible by the compensator fluid. Thus, a leakage of compensator fluid will result in a failure of the item. The data resulting from the FMECA was used to establish a tailor-made maintenance plan. Themaintenance plan consists of tasks classified as preventive and corrective maintenance actions. The tasks were chosen for each failure modes in order to reduce/prevent the probability of thefailure modes occurring. In addition to the RCM analysis the author created a Monte Carlo Next Event Simulation (MCS)script in a computer program to simulate one year of operations for a ROV. This was done to evaluate the proposed maintenance plan with regards to costs, failures, and availability of the ROV. After performing Monte Carlo Simulations of the systems together with the proposed maintenance plan the author found that maintenance for some of the failure modes did not contribute to reduce/prevent the occurrence of failure modes. Especially this is true for the components that are mentioned in the bullet points above. Taking this into consideration, the author recommend further investigation regarding other approaches that can reduce/prevent the occurrence of these failure modes. Additionally, IKM Subsea should focus on preventing/avoid all failure modes regarding leakageof compensator fluid. Since the majority of items require pressure compensating and these items often are in connectionwith each other, the probability of multiple failures caused by one leakage is highly present. The systematical approach of the RCM analysis resulted in thorough understanding and knowledgeof the analyzed systems with its additional items. The analysis was suitable to establish atailor-made maintenance plan for the analyzed systems with its additional items based on thereliability data and the items operational context. In addition, the analysis highlighted what andwhere the weakest links were in the systems, which can give IKM Subsea an overview of where toprioritize its resources.From this it is clear that RCM would be beneficial to IKM Subsea. However, it should be a longtermgoalto use RCMfor thewhole ROV system as it is a very time-consuming analysis to execute.