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    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING 6340(Print), ISSN 0976 – 6359(Online) Volume 5, Issue 1, January (2014), © IAEME AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 1, January (2014), pp. 26-32 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET ©IAEME IMPLEMENTATION OF RELIABILITY CENTERED MAINTENANCE IN AIR COMPRESSOR UNIT Vivek S. Narnaware1, Ganesh D.Gosavi2, Pravin V. Jadhav3, Rahul D. Gorle4 1,2,4 (Mechanical Engg., Department, Dr. Babasaheb Ambedkar College of Engg. and Research, WanadongriHingna Road Nagpur/RTMNU Nagpur, India) 3 (Mechanical Engg., Department, Priyadarshini College of Engg., Hingna Road Nagpur/RTMNU Nagpur, India) ABSTRACT Today’s maintenance programs are suffered from many drawbacks. Some équipements get too little, while some gets too much préventive maintenance than required. Reliability centered maintenance approach is found to be successful technique for solving such complex management orientated problems regarding the maintenance. Reliability centered maintenance (RCM) is the qualitative technique for developing the optimal preventative maintenance program which ensures relability of machine opération. It focuses on the system, system function, functional failure, system failure effect, their occurrences and criticality. Failure data analysis plays an important rôle to take décision on maintenance planning. It is important to identify the occurrences of failure and probability of failure for ranking the failure paths. It gives information about area of concentration in maintenance activities. This paper includes RCM principles and methodology to understand RCM is carried out in the plant or a system. The case study has been conducted at MSEB Thermal Power Plant Khaperkheda Nagpur. An air compressor unit is selected for opération. The selection is based on the breakdown failures record of past 18 months. RCM methodology are applied an system failure analysis is done. Preventative maintenance shedule for RCM is prepared and it is compared with the plant maintenance schedule. Keywords: Functional Failure, Failure Analysis, FMEA, RCM, RTF. 1. INTRODUCTION Air compressor unit plays an important role in thermal power plant. It supplies compressed instrument air and service air to the plant. It consists of various components, proper working of which ensures the functions of the compressor unit. While studying the failure record of the 26
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 5, Issue 1, January (2014), © IAEME components, it is observed that some of them are frequently fail during the operation, some fail to work earlier than predicted. Moreover failures of such components cause the shutdown of the compressor unit and hence affect the working of the overall plant. The maintenance schedule of the company mainly focuses on the daily breaking failures and an overhauling during year. Therefore this work aims to generate proper maintenance planning and scheduling for the compressor unit that based on the RCM technique for the air compressor unit components. Reliability centered maintenance (RCM) is the qualitative technique for developing the optimal preventive maintenance program which will ensure inherit ant reliability of machine operation. RCM can be defined as a process or method used in structured way to determine the most effective approach of preventive maintenance of equipment in its operating condition after proper evaluation of failure consequence. It focuses on the system, function, functional failure, dominant failure effect, their occurrences and critically. RCM philosophy employs preventive maintenance, predictive maintenance (PDM), time directed (TD), condition directed (CD), failure finding (FF) and run-to-failure (RTF) maintenance techniques in an integrated manner to increase the probability that a machine or component will function in the required manner over its design life cycle with a minimum of maintenance. This paper contains the RCM methodology and its implementation in an air compressor unit, key points in RCM maintenance plan. 2. LITERATURE REVIEW Study made by Islam H. Afefy The results of the RCM technique applied of the plant show that the PM proposed tasks and planning are generated. Moreover, PM is consisted of on-condition and scheduled maintenance. The Run-To-Failure (RTF) frequency has been decreased. It is recommended to perform these tasks (CD, TD and FF) every yearly, six monthly and monthly. Study made by Katharina Fischer, Francois Besnard and LinaBertling A Reliability-Centred Maintenance analysis of the two wind turbine models V44-600kW and V90-2MW has been carried out. The analysis forms the basis for the development of quantitative models for maintenance strategy selection and optimization. The mathematical models for maintenance strategy selection and optimization that are being developed based on the presented RCM study aim at contributing to this process. It is concluded to be an important step in order to enhance the reliability, availability and profitability of wind turbines. Study made by Salman T. Al-Mishari, and S. M. A. Suliman The potential losses due to missing any element of the DMAIC process are very significant. Assessment of contributing factors is often based on very subjective judgment. Shifts and drifts often occur. The work reported in this paper attempts to illustrate the potential losses of missing these important elements through a real example. Study made by RizauddinRamli and Mohammad NizamArffin RCM implementation in the PM activities at automotive manufacturing plant. The RCM has been used to analyze and perform a decision making process in which maintenance strategy needs to be chosen depends on the criticality of the equipment to the organization. 3. RESEARCH METHODOLOGY This methodology will provide a comprehensive description of seven steps that have been developed to systematically delineate the required information. 27
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 5, Issue 1, January (2014), © IAEME Step 1: Step 2: Step 3: Step 4: Step 5: Step 6: Step 7: System Selection & Information Collection System boundary definition. System description & functional block diagram. System functions & functional failures. Failure mode & effect analysis (FMEA) Criticality & Probability of occurrences. Task Selection. Satisfactory completion of these seven steps will provide the preferred PM tasks. Failures in air compressor unit is selected for the RCM study and the relevant information is collected from the company. The functional block diagram for system is shown in fig.1. Failure mode and effect analysis (FMEA) for different subsystems are done then the criticality and probability of occurrences for the various failures are calculated and categorized in four groups as shown in table no. 3. RCM task is selected. In this step the preventive maintenance schedule based on reliability centered maintenance is made and compression between previous PM & RCM based maintenance is done. To Plant Power Atmospheric Supply Air Air suction & delivery system (Compress or Subsystem) Water Supply Pressurized Air Suction & Delivery Pressur I/II Pressurized Hot Air Cooling Water system Cool Oil Pressure Gauge High Pressure Air Air Receiver system Cool Air Service Air Moisture Contained Air Dry Air system Air Water Water Pressure Temp Status Status Pressure Gauge Fig. 1: Functional Block Diagram 28 Air Heating Silica Filtration Alumina Particles Heating
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 5, Issue 1, January (2014), © IAEME Table 1 and table 2 shows the predicted RCM schedule and comparison with the previous maintenance schedule. RCM Schedule: Sub assembly Effect Based task Description Moderate Cost, very high failure rate 1.Inspect chock up of valve component. 2.Inspect fracture components. 3.Periodic cleaning of a Air suction filter. 4.Replace of lapping. F.F. (Monthly) Piston ring Moderate cost, high failure rate C. D. (6 months) Guide ring Moderate Cost, high failure rate Other piston assembly parts Low failure very high cost rate 3.Unloader assembly 4.Main Bearing ‘O’ ring unloader Bearing seized low low Check during overhand T.D. (12 months) 5.Lubrication system i. Oil level trapping ii. Oil leakage gaskets iii. ‘O’ ring for oil filter Belt Low cost, failure High cost, failure Low cost, failure 1.Check for suction pressure high low 2.Check for suction pressure high, low. 3. Check for piston ring every 6 months 1.Check for suction pressure high low. 2.Check for piston ring every 6 months. 1.Keep one H.P./L.P. piston assembled with guide rings. 2.Check guide ring every 6 month Replace when fail low Check for oil level replace failure parts RTF 1.Air suction delivery valve & 2.Piston Ring Road assembly 6.Belt 7.NRV 8.Packing 9.Suction filter 10.Cooling system Component / failure mode Valve components for High cost, moderate failure NRV seat NRV plate NRV spring NRV holder 1.Oil seal (3 piece & 6 piece packing, pressure breaker) Low cost, failure 2.Thrust washer ‘O’ ring sealing ring All suction filter Low cost, low failure Moderate cost, low failure Moderate cost, Moderate failure ‘O’ ring for I/C ‘O’ ring for A/C Water leakage gasket Moderate Moderate rate low cost, failure i. C.D. (6 months) T.D. (12 months) RTF Tighting of belts ii. Keep match sets of belts Replace failure parts C.D. (3 months) Check within 3 months RTF Replace failure parts C.D. (monthly) 1.Cleaning of suction filter 2.relace 1.Acid cleaning 2.Use clean (filtered) water for cooling system 3.Use of strainer for filtration C.D. (12 months) Table 1: RCM Schedule 29 Frequency C.D.(Condition of belts) RTF
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 5, Issue 1, January (2014), © IAEME TASK COMPARISON Component / Failure mode 1.Valve Components Previous Preventive Maintenance Air suction filter cleaning Cleaning of Valves / servicing 2.Piston ring rod Piston ring, Guide ring assembly Replace 3.Connecting Check of piston rod, crosshead assembly 4.Unloader Check unloader parts 5.Bearing seized Bearing Check 6.Lub system Oil filter cleaning 7.Belt Belt tightening Frequency 12 months 12 months 3 months 3 months RTF Check RTF Replace tightening 8.NRV 9.Packing Repalce fractured part Check of packing part 12 months 3 months 10.Cooling system 11.Oil replacement All coolers Cleaning Replace 12 months RTF Check of packing parts All coolers & Jacket Cleaning Oil sample test in & 3 months 6 months 12 months Jacket 12 months RCM maintenance Air filter cleaning Frequency Piston ring guide ring Check Check 6 months Monthly 2 months ---12 months --C.D. (Condition monitory) --3 months 12 months 3 months Table 2 : Task Comparison COST ANALYSIS Ex- Salary given to the skilled labour, wages given to the semiskilled labour. In this study the Spare, Consumable and manpower costs are calculated (refer tables A1 to A13) as follows :I) Spares cost = Rs. 3,66,342 /- II) Consumables coot = Rs. 5691 /- III) Manpower cost = 25,975 X 18 = Rs. 4,67,550 /- IV) Total breakdown cost = 3,66,342 + 5691 + 4,67,550 = Rs. 8,39,583 /- RCM COST ANALYSIS In RCM cost analysis first predicted RCM failures are calculated and on this basis predicted material cost is calculated (Refer tables A14 and A15).Failures have been categorized on the basis of failure history. Prepared maintenance schedule leads to saving in maintenance cost in each category. 30
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 5, Issue 1, January (2014), © IAEME Failure Expected Rank Saving Greater than 50 A 30% Between 30 to 50 B 25% Between 15 to 29 C 20% Between 5 to 14 D 10% Less than 5 E RTF Table 3 : RCM expected saving No. of failures Results obtained from RCM cost analysis are as follows : Predicted RCM material cost = 2,99,961 /Reliability Centered Maintenance process is expected 90% savings in overtime cost. Predicted RCM manpower cost = Previous Manpower cost – overtime cost (90% of Previous) Previous Manpower cost = Rs. 4,67,550 /Overtime cost = 0.90 x 65250 = Rs. 6525 /Total Predicted RCM cost = Predicted RCM material cost + Predicted RCM manpower cost = 2,99,961 + 4,08,825 = Rs. 7,08,825 /Reduction in Preventive Maintenance Cost = Previous Pm cost – Predicted RCM cost = 8,39,583 – 7,08,825 = Rs. 1,30,797 /% Reduction in Preventive maintenance cost = (Reduction in P.M. cost / Previous P.M. cost) x 100 % = (1,30.797 / 8,39,583) x 100% = 15.57 % 4. RESULTS RCM maintenance schedule results in the overall saving of 15.57% of existing maintenance cost. Hence annual saving of Rs. 1,30,797 /- is expected. 5. CONCLUSIONS RCM Maintenance scheduled is prepared and compared with the existing Maintenance schedule. After comparison following points are observed. Air suction filter should be cleaned monthly. It will prevent the dust dirt chock up the valve parts so that failure rate will minimize. Lubrication oil sample (servo system 68) should be tested periodically in Laboratory so that the strategy for oil replacement can be made. Water strainer should be provided for filtering the raw water. It will prevent the failures in the cooling system. Valve replacement should be done instead of valve lapping. It will improve the availability of the air compressor Lapping process may be done in free time. It will minimize the labour time. RCM program typically results in short term increase in maintenance costs. This increase is 31
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 5, Issue 1, January (2014), © IAEME relatively short-lived. It will minimize the repair cost. Failures have been categorized on the basis of failure history. Prepared maintenance scheduled leads to saving in maintenance cost in each category. It is concluded that Reliability Centered Maintenance is sample & effective maintenance ensuring all through that maintenance induced failures are either eliminated or minimized. It does not required complex numerical calculation. It re-examines the validity of previous preventive maintenance schedule and develops cost effective preventive maintenance schedule. It predicts spare parts inventories & risk maintenance decision for the system or plant. 6. REFERENCES 1. Islam H. Afefy, Reliability-Centered Maintenance Methodology and Application: A Case Study, scientific research publication, Engineering, 2010, 2, 863-873. 2. Katharina Fischer, Francois Besnard, and LinaBertling, "Reliability-Centered Maintenance for Wind Turbines Based on Statistical Analysis and Practical Experience," IEEE Transactions on Energy Conversion,, vol.PP, no.99, pp.1-12. 3. Salman T. Al-Mishari, and S. M. A. Suliman, Sensitivity Analysis of Six-Sigma Applied to a, Reliability Project. International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol: 11 No: 03. 4. RizauddinRamli and Mohammad NizamArffin, Reliability Centered Maintenance in Schedule Improvement of Automotive Assembly Industry, American Journal of Applied Sciences 9 (8): 1232-1236, 2012. 5. A.Mariajayaprakash, Dr.T.Senthilvelan and K.P.Vivekananthan, “Optimisation of Shock Absorber Parameters using Failure Mode and Effect Analysis and Taguchi Method”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 328 - 345, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 6. Pravin Kumar.S, Venkatakrishnan.R and Vignesh Babu.S, “Process Failure Mode and Effect Analysis on End Milling Process- A Critical Study”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 5, 2013, pp. 191 - 199, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 7. N. Rishi Kanth, Dr.C.V.Mohan Rao and G. Yedukondalu, “New Method in Predictive Maintenance of a Machine”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 1, 2012, pp. 142 - 149, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 8. J. Arun, S. Pravin Kumar, M. Venkatesh and A.S. Giridharan, “A Detailed Study on Process Failure Mode and Effect Analysis of Punching Process”, International Journal of Industrial Engineering Research and Development (IJIERD), Volume 4, Issue 3, 2013, pp. 1 - 12, ISSN Online: 0976 - 6979, ISSN Print: 0976 – 6987, Books 1. Anthony M. Smith P.E., “Reliability –Centered Maintenance”, McGraw-Hill Publications New Delhi. 2. Richard B.Jones “Risk based management a reliability centered approach “, Jaico Publishing House New Delhi-1997. 3. P.K.Kalra, “Reliability, availability & maintainability (RAM) Engineering in Manufacturing Vol 1.” Allied publishers Ltd, New Delhi (1997). 32