Effective Maintenance Program Development/Optimization

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Downloaded from Reliabilityweb.com on the web at http://www.reliabilityweb.comThe equipment criticality rank numbers, number range, and the rules for assigning thenumbers to systems or equipment under assessment are defined before conducting theanalysis.Criticality rank numbers are assigned to systems and/or equipment based on the rulesdeveloped. This is accomplished by comparing the equipment’s criteria consequencescores to the criticality rank number’s rules. If the equipment matches the rules, theequipment is assigned that criticality rank number. The equipment is always assigned thehighest criticality rank number it matches.5.5 Criticality and Risk AssessmentThe assessment starts by analyzing the selected system and/or equipment failureconsequences. The most serious failure consequence in each defined consequencecriterion is identified and its score recorded.System and equipment failure consequences are analyzed in terms of the resultant effectson the asset as a whole and consider the impact of the failure on safety of personnel andon the asset commercial performance. The later requires consideration of both direct andindirect failure costs.The analysis is conducted by answering a series of questions about each system orequipment item. These questions assess both the consequence of system or equipmentfailure and the frequency/probability of failure with respect to the assessment criteria.The criticality number and relative risk are calculated during the assessment fromresponses to the questions.Questions are formulated in the following form:“If the system/equipment fails, could it result in a safety consequence? If yes, howserious should the potential consequence be rated?”5.6 Results of Criticality and Risk Assessment5.6.1 Outcome of the AssessmentCriticality and risk assessment produces the results:1. Systems/equipment criticality ranks.2. Relative risk.3. Total consequence scores.4. Individual system/equipment scores.Page 6
Downloaded from Reliabilityweb.com on the web at http://www.reliabilityweb.com5.6.2 Relative RiskThe probability of failure is used in combination with the total failure consequence of asystem/equipment to determine the RR value of the system/equipment. CARA uses theconcept of the relative risk (RR) to identify system/equipment that has the greatestpotential impact on the business goals of the company.The RR of a system or equipment is the product of its Total Consequence Score (TC) andthe Frequency/Probability (F/P) Number. It is called “relative risk” because it only hasmeaning relative to the other equipment evaluated by the same method.The Total Consequence (TC) is the sum of all the scores assigned to each of the criteriaincluding: Safety (S), Environmental (E), Quality (Q), Throughput (T), Customer Service(CS) and Operating Cost (OC).TC = S + E + Q + T + CS + OCRR = TC * F/P6.0 Maintenance Tasks Development/Optimization (MTD/O)The MTD/O process described in this paper establishes a structured framework fordeveloping or assessing maintenance programs for in-service or newly commissionedassets. The process emphasizes the use of operation and maintenance experiencedocumented in a form of standard maintenance tasks (SMT).6.1 Maintenance Tasks Development/Optimization (MTD/O) OverviewThe flowchart in Figure 5 describes the steps involved in carrying out the MTD/Oprocess.The steps involved in the development/optimization of maintenance tasks are as follows:1. A system is identified for review by selecting an element from the plant technicalhierarchy. As described earlier, the selected system boundary should be clearlydefined. The selected system includes all lower level elements.2. A risk analysis is performed per section 4 of this paper. If an analysis was conductedin the past, review of failure frequencies in lieu of the current system/equipmentitems’ condition is conducted and the frequency scores changed as necessary. Thesystem/equipment items selected are then ranked by their risk ranking.3. In the case that the system under review belongs to an equipment class group that hasa Standard Maintenance Task (SMT) documented, it is only necessary to verify forlow risk systems/equipment that any specific company, standards, and regulationPage 7
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