Armin Sabetghadam-Isfahani - Mechanical Engineering Department, Petroleum University of Technology, Ahvaz, Khozestan, Iran.

Monthly maintenance reports include different maintenance categories such as Machinery, Hydraulic, HVAC, Electrical, Instrument and etc. Finding out which maintenance category data has the most importance and effect on the performance, time consuming, and cost of the done activities in the operational site, is a great challenge for all the decision makers. So presenting some fundamental and mathematical criteria for weighting the maintenance data of each category and then ranking them according to their performance, time and cost consuming based on their obtained weights, is essential. All mathematical calculations gust can have digits and numbers as their inputs, hence, making all maintenance data dimensionless is necessary. In this paper, two different criteria for data weighting have been investigated one is Multi-Criteria Decision Making (MCDM) and another Logarithmic Mean Difference (LMD). MCDM is well known but LMD is a new method that has been presented in this paper for the first time. MCDM surveys the maintenance data based on the time and cost consuming but LMD based on the performance. The effectiveness of these two methods has been examined in the Preventive Maintenance (PM) department of Persian Gulf Star Oil Company (PGSOC). According to the investigations by focusing on the category with the greatest MCDM to decrease its number, a significant change was observed in time and cost consuming and by concentrating on the category with the least LMD, the performance of personnel, physical assets and etc. was promoted and therefore suitable changes were observed in time and cost consuming. Eventually and according to operational experiences, it can be said that focusing on LMD and MCDM simultaneously, can have great effects on decrees of the consumed time and cost for the maintenance activities in the site

Logarithmic Mean Difference (LMD), MCDM, Data Weighting, Maintenance