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  • Reliability Centered

    Maintenance (RCM)

  • Evolution of Maintenance

    At the very beginning, Maintenance was an appendix to Operations / Production:

    It existed only to fix failures, when they happened. These were the days of absolute

    Corrective Maintenance

    http://www.supertrafego.com/cliparts_graficos_mostra.asp?interno=profissoes_i&numarq=0026&cat=Profiss%C3%B5es&pagina=3&subcat=Profissoes%20I&internopos=Profissoes%20I

  • As times went by, it was detected that many failures have an almost regular pattern, failing after an

    average period. Therefore, one could choose regular intervals to fix the equipment BEFORE the failure:

    Preventive Maintenance Also know as Time Based Maintenance.

    Evolution of Maintenance

    http://www.supertrafego.com/cliparts_graficos_mostra.asp?interno=profissoes_i&numarq=0039&cat=Profiss%C3%B5es&pagina=4&subcat=Profissoes%20I&internopos=Profissoes%20I

  • However, very often these failures happen in irregular periods. To avoid an unwanted failure, the periods of Preventive Maintenance are shortened. If equipment

    conditions were known, the maintenance could be later. Technology development enabled to identify failure

    symptoms: Predictive Maintenance

    Also know as Condition Based Maintenance.

    Evolution of Maintenance

  • Many pieces of equipment have sporadic activity (alarms, stand-by equipments, etc.). However, we must be sure that they are ready to run. These are "hidden faults“. Detect and

    prevent hidden failure is called: Detective Maintenance

    Evolution of Maintenance

  • Evolution of Maintenance The different failure modes mean that there’s not one only approach, about Corrective, Preventive or Predictive Maintenance Programs.

    The correct balance will give in return better equipment reliability, thus the name:

    Reliability Centered Maintenance

    Remember, my kid, Prevention is better than

    Cure....

    Take it easy, grandma, not

    always!

  • Reliability Centered Maintenance (RCM)

    John Moubray 1949-2004

    After graduating as a mechanical engineer in 1971, John Moubray worked for two years as a maintenance planner in a packaging plant and for one year as a commercial field engineer for a major oil company.

    In 1974, he joined a large multi-disciplinary management consulting company. He worked for this company for twelve years, specializing in the development and implementation of manual and computerized maintenance management systems for a wide variety of clients in the mining, manufacturing and electric utility sectors.

    He began working on RCM in 1981, and since 1986 was full time dedicated to RCM, founding Aladon LCC, which he led until his premature death in 2004.

    John Moubray is today considered a synonym of RCM.

  • Reliability Centered Maintenance (RCM) Its origins

    What about a failure rate of 0.00006/event? Quite good, no?

    This was the average failure rate in commercial flights takeoffs, in the 50’s. Two thirds of them caused by equipment failures.

    Today, this would mean 2 accidents per day, with planes with more than 100 passengers!!!

    That’s why Reliability Centered Maintenance has begun in the Aeronautical Engineering. Pretty soon, Nuclear activities, Military, Oil & Gas industries also began to use RCM concepts and implement them in their facilities.

  • Reliability Centered Maintenance (RCM) Reliability and Availability

    Bibliography: Kardec, Alan y Nascif, Julio - Manutenção- Função Estratégica, Editora Qualitymark

    Reliability

    Reliability is a broad term that focuses on the ability of a product to perform its intended function. Mathematically speaking, reliability can be defined as the probability that an item will continue to perform its intended function without failure for a specified period of time under stated conditions.

    Reliability is a performance expectation. It’s usually defined at design.

    Availability Depends upon Operation uptime and Operating cycle.

    Availability is a performance result. Equipment history will tell us the availability.

  • Reliability Centered Maintenance (RCM) Reliability and Availability

    Bibliography: Kardec, Alan y Nascif, Julio - Manutenção- Função Estratégica, Editora Qualitymark

    Availabil i ty = MTBF

    MTBF + MTTR

    MTBF = Mean Time Between Failures

    MTTR = Mean Time To Repair

    A first definition:

  • Reliability Centered Maintenance (RCM) Availability definitions

    Inherent Availabi l i ty = MTBF

    MTBF + MTTR

    MTBF = Mean Time Between Failures

    MTTR = Mean Time To Repair

    MTBM = Mean Time Between Maintenance actions

    M = Maintenance Mean Downtime (including preventive and planned corrective downtime)

    Inherent Availability: consider only corrective downtime

    Achieved Availability: consider corrective and preventive maintenance

    Operational Availability: ratio of the system uptime and total time

    Achieved Availabil i ty = MTBM

    MTBM + M

    Operational Availabil i ty = Uptime

    Operation Cycle

  • Reliability Centered Maintenance (RCM) Reliability and Availability

    MTBF = (250 + 360 + 200 + 120) / 4 = 232.5 days

    MTTR = (9 + 6 + 2) / 3 = 5.67 days

    Availability = 232.5 / (232.5 + 5.67) = 97.62 %

    250 days 360 days

    9 d

    200 days

    6 2

    120 days

    Downtime 

    180 days 400 days

    7

    120 days

    4 3

    233 days

    Downtime 

    MTBF = (180 + 400 + 120 + 233) / 4 = 233.25 days

    MTTR = (7 + 4 + 3) / 3 = 4.67 days

    Availability = 233.25 / (233.25 + 4.67) = 98.04 %

    = 947 days

    = 947 days

  • Reliability Centered Maintenance (RCM) Reliability and Availability

    Bibliography: Kardec, Alan y Nascif, Julio - Manutenção- Função Estratégica, Editora Qualitymark

    To improve Availability: Improve MTBM: •Reduce Preventive Programs to a minimum, or, have Preventive intervals as well defined as possible.

    •Using Predictive techniques whenever possible

    •Implementing Maintenance Engineering (RCM, TPM...)

    Minimize M: •Implementing Maintenance Engineering (Planning, Logistics...)

    •Improving personnel technical skills (training)

    •Developing Integrated Planning (Mntce+Ops+HSE+Inspection+...)

    Achieved Availability↑ = MTBM↑/ (MTBM+M↓)

  • Reliability Centered Maintenance (RCM) Improving Productivity

    Bibliography: Kardec, Alan y Nascif, Julio - Manutenção- Função Estratégica, Editora Qualitymark

    Productivity Improvement Factors: Detailed work planning Delivering equipments to Maintenance as clean as possible Check-list at the end of Maintenance activities Complete and comprehensive Equipment data available Supplies available on job site Skilled personnel

  • Reliability Centered Maintenance (RCM) Availability benchmark

  • Reliability Centered Maintenance (RCM) Translating percents to daily routine...

    Availability % Downtime per year Downtime per month* Downtime per week

    90% 36.5 days 72 hours 16.8 hours

    95% 18.25 days 36 hours 8.4 hours

    98% 7.30 days 14.4 hours 3.36 hours

    99% 3.65 days 7.20 hours 1.68 hours

    99.5% 1.83 days 3.60 hours 50.4 min

    99.8% 17.52 hours 86.23 min 20.16 min

    99.9% ("three nines") 8.76 hours 43.2 min 10.1 min

    99.95% 4.38 hours 21.56 min 5.04 min

    99.99% ("four nines") 52.6 min 4.32 min 1.01 min

    99.999% ("five nines") 5.26 min 25.9 s 6.05 s

    99.9999% ("six nines") 31.5 s 2.59 s 0.605 s

  • Reliability Centered Maintenance (RCM) Maintenance Programs costs

    Maintenance Program Cost US$/HP/year

    Corrective (unplanned) 17 to 18

    Preventive 11 to 13

    Predictive / Planned Corrective 7 to 9

    NMW Chicago 1998

  • Reliability Centered Maintenance (RCM) Benchmarking balance between Mtce programs

    NMW Chicago 1998

    Maintenance activities %

    Corrective actions 28

    Preventive actions 36

    Predictive actions 19

    Maintenance studies 17

  • Reliability Centered Maintenance (RCM) Definitions

    Bibliography: Lafraia, João Ricardo - Manual de Confiabilidade, Mantenabilidade e Disponibilidade, Editora Qualitymark

    Failure rate (λ) Failure rate (λ) is defined as the reciprocal of MTBF:

    Reliability: R(t) Let P(t) be the probability of failure between 0 and t; reliability is defined as:

    R(t) = 1 – P(t)

    MTBF t 1)( =λ

  • Reliability Centered Maintenance (RCM) Some math...

    Considering rate failure (λ) constant, it is proven (check at www.weibull.com), that R(t), meaning the probability of having operated until instant t, is given by:

    tetR λ−=)( This reinforces the idea that Reliability is function of time, it isn’t a definite number. So, it’s incorrect to affirm: “This equipment has a 0.97 reliability factor...”. We should rather say: “This equipment has 97% reliability for running, let’s say, 240 days...”

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