Lean Maintenance. Joel Levitt

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      The economics of this choice are clear, but what are the other consequences? There are several kinds of consequences. For one, the customer (operations) is disturbed 4 times a year for over one shift each time, amounting to 52 hours of chargeable downtime a year. This problem is not too bad if you have only one such pump, but imagine if you had 100 pumps, each failing for over one shift, 4 times a year. Of course the pumps would break at the least convenient times, and probably the failures would bunch up (lengthening the time to respond and the downtime).

      Running in breakdown mode requires 40 hours of maintenance worker time. Another consequence would be the cost of $35,600 per year (in both above- and below-the-waterline costs). On the plus side, this situation requires little management and no capital expenditures. Although safety and environmental considerations are beyond the scope of this model, it is intuitively obvious that unscheduled and random events such as breakdowns are the least safe choice.

       Economic model for hot swapping

      Another breakdown alternative is to replace the pump after failure with a rebuilt pump and rebuild the faulty unit off-line. In the computer field, this approach might be called hot-swapping. Components (such as circuit boards) are swapped with the computer running. We can’t actually swap the pump while it is running but we still call the method hot-swapping (maybe we could call it warm swapping). To set up the method we would have to purchase a second full-pump unit and adapt it for quick changes.

      The second pump will cost $15,000. After engineering the quick change, swapping to the second pump will take 2 hours. Downtime is down to 6 hours (2 hours to respond, 2 hours to swap and 2 hours to fill the system). The rebuild will cost the same amount as the breakdown model above, $2000 for parts and 10 hours off-line. Only 1 pump core is needed to rotate with the installed pump so we have to be sure to charge for only 1 pump core. The purchased pump is a capital expenditure.

      Management needs to ensure that when the damaged pump is removed from service it is rebuilt reliably within 2–4 weeks. That element of management is in addition to a simple stocking strategy like the one described above. If the pump is not rebuilt in time, you run the risk of spending money for the spare and still having the downtime of the breakdown option. Having a breakdown on top of not having the pump rebuilt is the worst of both worlds (and is fat maintenance not Lean Maintenance).

       Economics of hot swapping

      What are the consequences of this choice? Once again there are several kinds of consequences. The Operations or production process is disturbed 4 times a year but this time it is for less than one shift. Chargeable downtime drops by 24 hours per year, or better than a 50% reduction, which is an improvement. There is no difference in the cost of maintenance labor or parts for this scenario. Annual costs have improved to $19,600 because of the reduction in downtime. The costs above the water line are the same. Each incident will still need 40 hours of maintenance labor and $2000 of parts. There is a capital cost, but it gets paid off within the year. More management is needed than with the previous example, to insure that the pump is rebuilt in a timely way. Safety is not affected because the failure mode is still random and unscheduled.

       PM

      PM is a common strategy. In fact, it might be tough to run a breakdown-only scenario because most firms do some PM (even if it is only a shot of grease). Frequently we notice that the greatest returns come from the most basic PM activity. There is a diminishing return to increased PM expenditure. Of course, if the subject is a fuel pump on a jet engine, the added benefit is worth while. The effectiveness of the PM is always at issue and is discussed in another section. An ineffective PM will consume resources without providing an adequate Return on Investment. It is important to look deeply at different strategies because the best way to take care of an asset might depend on the downtime cost, not just the breakdown cost.

      The PM routine was designed by the mechanics, will take 1 hour a week, and requires downtime to accomplish (but that hour of downtime is free). We will assume that the PM routine as designed is effective. Additional corrective repairs (resulting from the PM inspector finding deterioration and fixing it before failure) take 5 hours per incident (3 incidents per year on average) and $1700 worth of materials per incident. With the new PM program, the system becomes significantly more reliable, and breakdowns will drop to 1 every other year (each breakdown costing the same as the original breakdown mode. that is: 10 labor hours + $2000 worth of parts and 14 hours of downtime).

       Economics of PM

      What are the consequences of a PM strategy? The customer is disturbed 3½ times a year. The significant difference is that 3 of the interruptions are scheduled. Operations can choose when to go down for the corrective work. Overall, the chargeable downtime is about the same as with the hot-swap example, СКАЧАТЬ