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Availability Modeling of Cooling Water Pumps to Assess if a Replacement Option is Economically Feasible. Dr. Salman Mishari. Presenter. Dr. Salman Mishari Affiliation Reliability Engineer in S. Aramco 20 years postgraduate experience Vibration Rotating equipment Reliability. Presenter.

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  1. Availability Modeling of Cooling Water Pumps to Assess if a Replacement Option is Economically Feasible. Dr. Salman Mishari

  2. Presenter • Dr. Salman Mishari • Affiliation • Reliability Engineer in S. Aramco • 20 years postgraduate experience • Vibration • Rotating equipment • Reliability

  3. Presenter • Education • B.S. in ME (USA) • M.S in Engineering. Mgt (KFUPM) • PhD in Reliability (UOB)

  4. Presentation Outline • Some background on the problem: • Availability concern on a group of low lift pumps. • How availability was modeled and estimated for both: • The current situation • The replacement alternative • How availability and other factors were used in the replacement analysis. • The Results of the Assessment. • Lessons Learned

  5. Inlet Canal Excess Capacity Excess Capacity 4 X 60,000 GPM pumps 3 X 35,000 GPM pumps Sea Background • Seven low left pumps running in parallel are used to pump sea water to inlet canal

  6. Inlet Canal Excess Capacity Excess Capacity 4 X 60,000 GPM pumps 3 X 35,000 GPM pumps Sea Background • Water in inlet canal is picked up by high lift pumps to provide cooling for the whole plant

  7. Inlet Canal Excess Capacity Excess Capacity 4 X 60,000 GPM pumps 3 X 35,000 GPM pumps Sea Background • Three have a flow rate of 35,000 GPM. Four are rated at 60,000 GPM.

  8. Inlet Canal Excess Capacity Excess Capacity 4 X 60,000 GPM pumps 3 X 35,000 GPM pumps Sea Background • Two or three pumps are normally needed depending on the capacities of the available pumps.

  9. Inlet Canal Excess Capacity Excess Capacity 4 X 60,000 GPM pumps 3 X 35,000 GPM pumps Sea Background • The normal mode of operation is one low and one high capacity pumps giving a combined flow rate of 95,000 GPM. • .

  10. Inlet Canal Excess Capacity Excess Capacity 4 X 60,000 GPM pumps 3 X 35,000 GPM pumps Sea Background • The flow requirement is only about 80,000 GPM so the excess amount is diverted to the outlet canal, and it is considered a waste of energy.

  11. Background • Background • The pumps are very old with some being over 50 years of age. • Time spent to repair has been very long due to major component failures and waiting for custom-made spare parts. • All of this raised concerns about their future capability to sustain the required level of availability.

  12. Data Gathering • Data Gathering And Analysis • Six-year worth of failure data history was collected from the Company computerized maintenance management system (CMMS). • They all averaged about five-year MTBF and one-year MDT. • The current MTBF value of five years was considered acceptable. • The MDT of one year was, however, considered to be on the high side.

  13. Alternative • Alternative • As per Company design practice, the replacement alternative, if found necessary, is three 50% pumps

  14. Analysis • Analysis • One of the big-capacity pumps is not in operation so it’s not included in the analysis. • The required flow rate is 80,000 GPM so any scenario that is capable of providing the required flow is considered a success state.

  15. Analysis • Analysis • Success states, • All pumps being operable is an obvious success state. • Two small pumps being operable is a failure state they can provide only 70,000 GPM (2X35,000) when the requirement is 80,000 GPM.

  16. Success Scenarios • Success Scenarios • There are 16 possible scenarios • 12 of which are success states and • 4 are failed states.

  17. Success States

  18. State Probability • The probability of being at any state depends on • Failure rate • Repair rates. • Failure and repair rates are reciprocals MTBF and MDT • FR = 0.2 per year , • RR = 1 year

  19. Availability Solution • Problem can not be easily solved for availability using simple engineering reliability methods. • An approach usually reserved for complex systems is the Markov model.

  20. Markov Solution 03 0.2 , 3 13 02 0.2 , 2 0.2 , 3 01 23 12 0.2 , 1 0.2 , 2 0.2 , 3 33 22 11 00 0.2 , 1 0.2 , 2 0.2 , 1 32 21 10 0.2 , 1 0.2 , 2 31 20 0.2 , 3 30

  21. Markov Solution P33 P32 P31 P30 P23 P22 P21 P20 P13 P12 P11 P10 P03 P02 P01 P00 -1 = =

  22. Availability Solution • Solution of current system • Availability is the sum of the success states and it was equal to 99.98% for the subject system. • Solution of alternative • Similar availability analysis was done for the replacement alternative; i.e., the 3X50% pumps.

  23. Feasibility Assessment • The result was a similar level of availability (99.98%). • It was, therefore, concluded that replacement on the basis of availability was not economically feasible

  24. Economic Replacement Analysis So, Availability is not a feasible basis for replacement What about other factors • Unnecessary Extra Capacity • Maintaining 3 pumps instead of 7 All this savings need to be assessed against Capital investment. The engineering economic approach is used to evaluate the economic feasibility.

  25. Economic Replacement Analysis • Estimated replacement capital investment • This cost was estimated to be $1000,000 • Return on investment • Return on investment is realized through savings of: • Unnecessary Extra Capacity • Maintaining 3 pumps instead of 7

  26. Unnecessary extra capacity • The current mode of operation is • One small and one big giving a combined flow rate of 95,000 GPM • Requirement is only about 80,000 GPM. • Excess Energy: PSI X GPM 7.58 psi X 15,000 GPM HP = ------------------ = -------------------------------- = 77 hp = 58KW 1714 X eff. 1714 X 0.86 • This translates to an annual cost savings of about • Annual Cost = 58 X 24 hrs X 365 days X $.026 =$13,000

  27. Difference in maintenance costs • The replacement alternative is three pumps while the current set up is seven. • Maintaining three pumps should be cheaper than maintaining seven. • Maintenance history indicates that the average maintenance cost per pump has been about $1000,000 for seven pumps over 18 years. Therefore,

  28. Difference in maintenance costs • Annual maintenance cost = ($1,000,000 ÷ 7 pumps) ÷ 18 years = $8,000/pump • Alternative is four pumps less, Maintenance savings = 4 X $8,000 = $32,000 • Total return on investment = $13,000 + 32,000 = $45,000 What do you think? Is this attractive?

  29. The Minimum Attractive Return • The estimated return is compared to the minimum attractive return • This is calculated using Compound Interested Tables. • Project life window of 20 years • Minimum attractive rate of return of 9%, • This corresponds to 0.11282.

  30. Interest Table

  31. The Minimum Attractive Return For an investment capital of $1,000,000, The minimum attractive return = $1,000,000 X 0.11282 = $112,820 Estimated is less than attractive Replacement of current system is not economically feasible.

  32. Lessons Learned • Many lessons can be learned from this case study. • However, I would like to focus on the area of assessing the maturity of an organization from a Reliability Management Perspective.

  33. Lessons Learned • There are many reliability improvement opportunities. • Maturity is needed, however, to be able to capture these opportunities. • I suggest the following questions should be emphasized if you conduct a self assessment at your facility.

  34. Lessons Learned • Does your facility keep good failure and maintenance records: • Bad data  badly estimated parameters  bad model  bad analysis  wrong decision

  35. Lessons Learned • What triggers your reliability assessment and studies? • strictly SME judgment? Like in the example. • Certain level of loss? • Is it a Bad Actor Program? • Is it KPI’s? if yes, • Is it accurate data? (for example MTBF <> MTBWO) • Is it accurate and consistent calculation methodologies?

  36. Lessons Learned • Who does your reliability and replacement analysis? • Do you have qualified reliability engineers • Are they well trained in reliability modeling? • Do they have knowledge in sampling and Statistics (estimating model parameters)? • Are they qualified in using Engineering Economics principles?

  37. Lessons Learned • How good is your root cause analysis program? • What triggers an RCA study? • Who facilities the study? Is he trained in RCA? • Who participates in the study? • Where do you document the results and how easy can you retrieve them?

  38. Lessons Learned • How good is your PM program? • How often do you review your PM program? • How do you set the PM tasks and their frequencies? • What methodology do you use? RCM; PMO?

  39. Lessons Learned • How is your recommendation tracking system? • Who ensures that all recommendations are implemented? • Who ensures the credibility of the implemented recommendations?

  40. Any Questions

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