Spare Parts Provisioning by MikeJenny

VIEWS: 14 PAGES: 21

									Overview and Case Studies


SMS – Spares Management
Software




                          1
  Spares Management Software (SMS)

                 Optimization criteria

                     Interval Stock
Non-Repairable         Reliability
Spares
                     Instant. Stock      Optimal
                       Reliability
                                         Spares
                         Cost            Requirement
Repairable           Minimization
Spares

                      Availability

                                         Stock
                     Supportability      Remaining
                                         Life
                                                     2
# items in
service
                 Repairable Spares

                     Failures

                                                    time




                                            stock
  failed units


                           repaired units

       Repair
       shop




                                                           3
Criteria for Decision Making

1.Instant reliability
2.Interval reliability
3.Cost minimization
4.(Process) Availability


                               4
                             Scenario
• Plant has 62 electric motors on their conveyor systems (Mining company)
• MTBReplacements of motors is 3000 days (8 years)
• Planning horizon is 1825 days (5 years)
• Cost of spare motor is 15,000 $
• Value of unused spare is 10,000 $
• Cost of emergency spare is 75,000 $
• MTTRepair a motor is 80 days
• Cost of plant downtime for a single motor is 1000 $ per day
• Holding cost of a spare is 4.11 $ per day (10% of value of part/annum)


QUESTION: HOW MANY SPARE PARTS TO STOCK?

                                                                            5
          Results: Repairable Parts
Electric motors

   • Interval reliability: 95% reliability requires 7 spares
   • Instant reliability: 95% reliability requires 4 spares
   • Cost minimization: requires 6 spares. Associated plant
   availability is 100.00%
   • Availability of 95%: requires 0 spares. Associated
   electric motor availability is 97.4% [Note: If availability of
   99% was required (rather than the specified 95%) then
   spares required would be 2]


                                                                6
           Reference Case
Population         100 transformers

Failure Rate       0.005
                   failures/transformer/yr
Repair Time        1 yr

Replacement Time   0.001yr

Interval           1 yr


                                             7
Repairable Instantaneous Reliability

                                 Vary Spares
                    1

                  0.99

                  0.98

                  0.97
    Reliability




                  0.96

                  0.95

                  0.94

                  0.93

                  0.92

                  0.91

                   0.9
                         1   2     3      4    5

                                 Spares
                                                   8
                Additional Cases


Case studies:

1.   Fume fan shaft, blast furnace in a steel operation: non-
     repairable part, decision support

2.   Power train component, haul trucks: repairable parts, multiple
     criteria

3.   Frigate control system: supportability interval




                                                                  9
    1. Fume fan shaft – steel mill

      Spares provisioning optimization project

         •   Part: fume fan shaft used in a Blast Furnace
         •   Decision: should there be 0 or 1 spares?
         •   Complication:
             •  Part has long lifespan (25-40 years).
             •  Long lead time (22 weeks).
             •  If part fails, results are catastrophic (loss of almost $6 million
                per week).
             •  Inventories are trying to be minimized.



    SMS was used to quantify the risk involved in not having a spare

                              Decision support                                 10
  How many spares – Fume fan shaft?

                                   MTBF Vs Reliability with 22 week LT

              100.5

               100

               99.5
Reliability




                99                                                                 0 spares
                                                                                   1 spare
               98.5                                                                2 spares
                98

               97.5

                97
                      0   5   10       15     20     25      30    35    40   45
                                      Mean time between failures

                                                                                              11
2. Repairable components – haul trucks


                        Open pit mining operation in
                       South America
                        Haul truck power train
                       component: COMPONENT X




                                                    12
      Repairable components - Data / 1

General
     6,600 operating hours per truck per year (average fleet utilization)

     Preventive replacement policy at 9,000 operating hours in place


Time to replacement
     Two parameter Weibull distribution, fitted using Weibull++

       • 171 events: 86 failures, 85 suspensions (preventive
         replacements)

       • Beta = 0.8565

       • Eta = 14,650 operating hours

       • Mean time to replacement = 6,420.3 operating hours              13
       Repairable components - Data / 2

Time to repair
      Based on estimations provided by maintenance personnel

      Estimated at MTTR = 452 operating hours




Cost of downtime and holding costs

      Downtime: estimated using operational indicators (value of lost
       production, $2,173.3 / op. hour)

      Holding: 25% of the value of the part per annum ($1.51/ op. hour)



                                                                         14
 Repairable components - Data Summary

Parameter                                       Value

Number of components in operation               78

MTBReplacements (μ)                             6420.3 (op. hours)

Planning horizon (T)                            6600 (op. hours)

MTTRepair (μR)                                  452 (op. hours)

Holding cost for one spare                      $1.51 per op. hour (25% of
                                                    value of part/annum)


Cost of plant downtime for a single component   $2173.3 per op. hour




         SMS can perform the optimization based on four criteria

                                                                        15
     Repairable components - Results

Case & Optimization criteria   Optimal Stock        Associated Values
                                   level
Interval Reliability                15               Reliability = 98.05%
(goal = 95%)                                    (for stock=14, Rel.=94.99%)
Instantaneous Reliability           10              Reliability = 97.53%
(goal = 95%)                                    (for stock=9, Rel.=94.75%)
Availability                        6              Availability = 99.14 %
(goal = 99%)
Cost minimization                   14         Total cost per unit time = $23
                                                  Inst. Reliability = 99.94%




                                                                             16
    4. Frigate control system – supportability
    intervals (S.I.)

      Determination of supportability intervals

         •   Several electronic components – control system
         •   Parts no longer available - discontinued
         •   Decision: how long can we support the operation of the
             system using only the current stock? (achieving the
             desired reliability of the stock)




                                                                17
    Case Study – Supportability Interval (S.I.)

       Summary of Data
    Part       # Parts in      Rate of Replacements            Stock Level
               Operation           
                                   replacem en
                                             ts
                                                           
                                                  part year
            (complete fleet)
    V             12                   0.0556                       6
    W             12                   0.4259                       8
    X             12                   0.3241                      16
    Y             12                   0.3796                      19
    Z             36                   0.0432                      11



        Supportability interval (RUL of current stock) can be rapidly
             calculated using SMS – NEWLY ADDED FEATURE


                                                                             18
                       Case Study (S.I.) / 2

      Results

Part     Stock Level                 Supportability Interval T* (years)
                         Reliability=90%     Reliability=95%       Reliability=99%
V            6                5.84                  4.92                3.49
W            8                1.06                  0.92                0.69
X            16               3.08                  2.79                2.28
Y            19               3.19                  2.91                2.43
Z            11               5.03                  4.45                3.49



       Supportability for the system is influenced by the (shortest)
               supportability for any of its critical parts




                                                                               19
               Case Study (S.I.) / 3

   Informed decisions for:

      •   Adequate timing for replacement of current
          system
      •   Placement of final orders for discontinued
          parts
      •   Maximum supportability interval for current
          stock – procurement planning




                                                        20
Thank you




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