Improving Machinery Reliability 3 Episode 15 doc

604 Iniproviizg Machinery Reliability In spite of relatively high maintenance costs, the Society of Maintenance and Reli- ability (SMRP) Professionals reported in 1996 that more than 56% of U.S. industries do not have a comprehensive maintenance and reliability program. Modern Power Systems, July 1994, reported results from an EPRI study, which was independently collaborated by Chevron, that showed the execution of a predictive maintenance pro- gram on electric motors could reduce the cost of maintenance by more than 50%. Comparative Cost of Maintenance Strategies Run to Failure EPRI Study $1 7-$19 Chevron Preventative Maintenance $1 1 -$13 $1 3 Predictive Maintenance $749 $8 Figure A-3. Predictive maintenance practices for electric motors can reduce mainte- nance costs by 50%) Current Maintenance Methods Differ Significantly from Best Practice SMRP surveyed their membership in the Spring 1996 and reported that only 44% of their membership have integrated reliability and maintenance programs. Surpris- ingly, 17% of the companies surveyed reported the absence of any reliability or pre- dictive maintenance program. Maintainability No Reliability or Maintainabilit Reliability and Maintainability Figure A-4. Do you have a reliability and maintainability process?' Appendix A: Useful and Interesting Statistic 605 Deloitte and Touche in their study, “Maintenance Practices and Technologies,” report that management recognizes the importance of maintenance. Diagnostics and predictive maintenance practice rank as high as traditional cost reduction programs. Min. Plant Down Time Skill Training PM Program Employee Motivation Cost Reduction Diagnostics Predictive Maintenance I I I I 0 20 40 60 80 Figure A-5. Maintenance programs recognized to be of importance.’ The same Deloitte and Touche study shows that the majority of companies sur- veyed employed reactive maintenance strategies versus the preferred predictive and proactive capability with a high degree of automation. C. L. Hays, in his paper entitled, “Plant Maintenance and Diagnostics, Current Practice and Future Trends” at the P/PM conference in late 1996 summarized the disadvantage of a strict preventive maintenance policy based on a time-based overall of a mechanical component. Figure A-6 shows the traditional “bathtub curve” that represents the probability of a failure versus time for a random system. Traditional preventative maintenance practice is based on “guessing” the appropriate time to replace a critical component to avoid the expected downtime from a failure. The premature replacement of a criti- cal component under the preventive maintenance strategy does not always result in improved uptime because the system may experience an untimely failure of the new component. Condition-based maintenance strategies (CBM) are key to improving the uptime of a mechanical system. CBM is based on the ability to proactively identify the root cause of failures, eliminate the source of failures, and to provide for predictive main- tenance methods. These methods provide early detection of impending failures and thus provide for maximum system life without prematurely introducing an overall cycle as is shown in Figure A-6. Plant-wide Asset Management Provides Platform for Integrating Assets The second Offshore Reliability Data Survey (OREDA) of ten large offshore petroleum producers in the North Sea provides an interesting view of the failure rates of major plant assets used for offshore oil production. 606 Improving Machinery Reliability E 3 ([I U 0 E B ([I P ,o (L - Y- - Condition-Based Maintenance Premature Random Wearout Failures Fai I u res Fai I u res Predictive maintenance assures early detection of failures I '\,> \ Proactive maintenance \ * Time Figure A-6. Proactive maintenance reduces the probability of failure and extends the MTBR. Figure A-7 is based on the failure rate data provided in the OREDA report and confirms the premise that rotating equipment affords the most significant opportuni- ty for increased reliability and reduction of maintenance costs. Figure A-7. OREDA failure data. Appendix A: Useful and Interesting Statistic 607 75% 7 Maintenance Repair Results 68% OK Adjust Repair in Pull Place Figure A-8. Rotating equipment maintenance costs can be reduced by condition moni- toring.' The Innovation Management Group shows that the implementation of condition monitoring strategies for rotating equipment can reduce maintenance costs by 32% as a result of the opportunity to detect impending failures provided for in situ main- tenance versus the traditional pull and replace method used. 41 Early adopters of asset management maintenance strategies showing significant savings Regulatory Advanced P/PM Control Control Strategies Figure A-9. Early adopters measuring savings from asset management? 608 Improving Machinery Reliability The December 1995 P/PM Journal chronicles a study of varied pump mainte- nance practices and the value of using predictive maintenance strategies versus run to fail. An overall savings of 40 times the initial purchase price of the pump is reported. Plantwide asset management provides the platform for integrating emerging main- tenance technologies built on the foundation of field device diagnostics. Adoption of open communication networks and planning with equipment suppliers will permit realization of the vision of a plantwide asset management system that will reduce maintenance costs by up to 70%. Early adopters of asset management strategies are already reporting benefits. One early adopter of the “islands of automation” approach has measured savings of 1.75% versus 3.2% for regulatory control with less than 20% of the assets being monitored. References 1. Boynton, B. and Lenz, G., “Plant Asset Management: An Integrated Maintenance Vision,” presented at 6th International Process Plant Reliability Conference, Houston, Texas, October 1997. Appendix B h 0 W Common Sense Reliabilitv Models A Heuristic Approach Contributed by: Paul Barringer, P.E. Barringer & Associates, Inc. Manufacturing, Engineering, and Reliability Consultants P.O. Box 3985 Humble, TX 77347-3985 Phone: 281-852-6810 FAX: 281-852-3749 hpaul@barringerl.com http://www. barringerl.com Reliability measures the capacity of equipment or processes to operate without failure for a specified interval when put into service and used correctly. Reliability Definitions Reliability Is Probability of failure-free interval Performing the intended function Working for specified time intervals Working under stated conditions Reliability Is Not Certainty of no failures Performing any possible functions Functioning forever Working under all possible conditions Primary Measures Of Reliability Mean time between failure is a primary yardstick for measuring reliability - If MTTF is Iasge compared to the missisn->aeliable - If MTTF is short cornpared to the mission->unreliable!! - Do you know your MTTF for rotating equipment? - Do you know your MTTF for non-rotating equipment? - Which cost you the most money for failures? b b a 3 The business measure for reliability is the cost of k' k 2 E' w UNreliability (lost gross margin + maintenance $'s) !? - How much UNreliability can you afford? - How much UNreliabiIity can you correct? - What's your Pareto list of the top 10 ten cost items? F 5 g - Where do you start the corrections and how much can you afford? Reliability Problems = Business Problems B Y 2 h) 0.5 1.0 Reliability Sensitivity to MTTF 0.135 0.368 High Reliability Requires Long MTTF 5.0 10.0 15.0 20.0 30.0 40.0 1 0.8 0.6 0.4 0.2 I A I I I I 0 10 20 30 40 50 MTTF As Multiples Of Mission Time 0.819 0.905 0.936 0.967 a f. 5 % The graph shows MTTF as !% 3 i? multiples of the mission time Long MTTFs, compared to the mission time, give high reliability 5 c1 The results: t*MTTF Reliability I’ a 13: 3 Failures: Roots Of eiia bility Problems Early Plant Life Frequency % Design Error Fabrication Error Random Component Failure Operator Error Procedure Error & Unknowns Maintenance Error 35 1 18 12 10 12 Unknown 12 e Design e People Corn onent failures - 100 Mature Plants People 38 0 Procedures + Processes 0 Equipment Machines 100 [...]... Inherent Component Reliability 100 hp pump: 8" discharge * IO" suction 14" case I 1 beta I eta 1 EffectsOf I I :or Installation Good Practice 1 MlTF(yrs) * eta From = I 0.9726 0.8547 n 9717 0.9712 -.- .0.9677 0.9712 0.9801 1.oooo 1.oooo nnnn -1.oooo i 2.50 I 1 .30 I 1 .30 1.40 1.20 2.00 1 .30 1.00 1 DO 1 38 9,045 34 1,882 38 8.476 38 7,090 38 8,476 294, 030 150 ,000 150 ,000 30 0.000 30 0 000 39 .40 36 .05 40.96 40.27... Alignment Practice IEffects Inherent LSt Component Reliability I I Practices Except For 100 hp pump: 8" discharge l!Y' suction 14" case Better Rotational Alignment Practices beta I Pump beta Multiplier eta Of Practices o n Component Life eta 2.50 1 .30 1 .30 1.40 1.20 2.00 1 .30 1 oo 1 oo 1.20 36 9,5 93 324,788 33 9,917 34 8 .38 1 33 9,917 267 ,30 0 140,250 150 ,000 280.500 30 0.000 Good Practice Replacements Life Multiplier... 8498 0.8910 0. 935 0 1 oooo 0. 935 0 1.0000 - =-Mea 26.209 hc 37 . 43 34.24 35 .84 36 .25 36 .50 27.04 14.79 17.12 32 .02 32 .21 For Ail Mech.s Items For All Elect.-> Items 2.75 time between system failures= or= loss= 24,060 2,148 hours hours Best Practices For Installation And Use Except For Better Rotational Alignment Achieves 92% of Inherent System Life Better Rotational Alignment Practices = 50.0 03 inches or...s P Basic Serial Reliability Models &=Chi = h, + h2+ h3 Many Components In Series Destroys Systems Reliability S Y t e m e i a b i I i t Y 1 0.9 0.8 0.7 0.6 0.5 0.4 0 .3 0.2 0.1 0 0.95 4 0.96 0.97 0.98 Individual Component Reliability 0.99 1 M a ch ch 2 The Re1iabiIity Hierarchy The Issue Reliability Engineering Principles New Enaineerina Tools To Solve... Good LID Practices Achieves 76% of Inherent System Life Good Intake U D Practices = I to 3 LID Suction Straight Run Effects On Reliability & Cost Intake Piping Practice L/D Ratio Effects 100% 98% 130 % 80% 120% 60% 40% 110% 20% 100% 0% Best Prsctices Better Practices G O QPractices ~ U D = 10 t 12 o U D = 6t 8 o UD=lto3 System Life Includes Pump And Motor-All Other Features Use Best Practices Except AS... & Geitner’s Machimry Reliability Assessment b ~ ~ k Simple serial models are used to assimilate the data b g sR F? b (D 2 P 3 5 B 4 Pump Curve Characteristics I Pump Curve Sensitivity For Pump Reliability I rhis is the correct point for ichieving the greatest inherent ife for the pump System Resistance Curve Desired Poor Example Of System Resistance Curve Desired * Intrinsic reliability- is achieved... by engineering Bumps operating off the curve are a major reason for short life of bearings and seals 0 Reliability & Costs Effects Pump Curve Sensitivity Effects 60% , c u) 0 ~- 150 % 0 40% 20% 0% -~ - 100% 7 Best Practices -10% to +5% Of BEP Better Practices Good Practices -20% to +lo% -30 % to +15% O BEP f O BEP f System Life Includes Pump And Motor-All Other Features Use Best Practices Except As... 00 Problems Causing Short Pump Life I Pump Curve Sensitivity For Pump Reliability Operational problems noted on the pump curve decrease the intrinsic system reliability- so long life is obtained only for a small portion of the pump curve Best Efficiency Poin I % Flow 8 Usable Portion Of Pump Curves Pump Curve Sensitivity For Pump Reliability Recirculation & BeannglSeal Problems Best Practices->Long... System Life Good Rotational Alignment Practices = kO.009 inches or k0.229 mm Q\ w o \ Rotational Alignment Effects On Costs & Reliability Rotational Shaft Alignment Error Effects 98% 150 % u) CI u) 125% o 0 100% Best Practices iO.001inch or i0.025mm Better Practices Good Practices f0.003inch or t0.076mm t0.009inch or 20.229mm System Life Includes Pump And Motor-All Other Features Use Best Practices Except... Component Chakxteristic Life -MTTF Impeller life Mtr Starter life Mtr Winding life Coupling life -best Practices = Good Practices = -inferior Practices = * -40% io 5% Of BEP -20% to + I O % Of BEP -30 % to *15% Of BEP Straight Runs Of Suction Piping Long runs of pipe are required to smooth flow and create equal mechanical loads on pumps Short runs of pipe produce unequal impeller loads and cause undesirable . 2.50 I 38 9,045 39 .40 0.8547 1 .30 I 34 1,882 36 .05 n 9717 1 .30 1 38 8.476 40.96 I 0.9726 2.50 38 9,045 39 .40 0.8547 1 .30 34 1,882 36 .05 0.9712 1 .30 38 8.476 40.96 0.9677 1.40 38 7,090. loss= 0.9677 1.40 38 7,090 40.27 0.9712 1.20 38 8,476 41.71 0.9801 2.00 294, 030 29.75 1 .oooo 1 .30 150 ,000 15. 81 1 .oooo 1.00 150 ,000 17.12 i nnnn 1 DO 30 0.000 34 .25 For All Items. 1.40 38 7,090 40.27 0.9712 1.20 38 8,476 41.71 0.9801 2.00 294, 030 29.75 1 .oooo 1 .30 150 ,000 15. 81 1 .oooo 1.00 150 ,000 17.12 i nnnn 1 DO 30 0 000 34 .25 1 .oooo =-Mean time