Benchmarks #7

Service Accuracy

The ability to complete oil changes, oil filter changes and greasing (collectively known as routine lubrication service) at intervals close to what the equipment manufacture specifies, is important. Oils and their additives wear out and filters have finite capacity. If routine service exceeds recommended intervals, abnormal and accelerated wear and damage takes place. Component lives are shortened and costs and downtime will be driven upward over time.

Keeping track of the ability to complete lubrication service at close to expected intervals is important. A factor for this is call Service Accuracy or SA.

Graph #5 (above) is a scatter diagram used to track adherence to a target service interval. In this example the mine is planning to complete services every 400 hours. The scatter diagram has “management lines” (upper and lower “limits”) at 10% above and below the target. As can be seen, in the early part of the period, a high percentage of the services fell within the limits. Later in the period, the ability to come close to the target interval became much worse. Collecting data and producing a scatter diagram is no more difficult than completing the calculation methods that follow. The scatter diagram is, however, easier to analyze and is more informative than finding SA through any calculations.

Some mines calculate an average service interval. This is deceptive. In the above example the average interval is close to the target. The scatter diagram shows that a calculated average is meaningless. The numbers can “average”. The component wear does not. Metal worn away during extended service intervals does not get replaced when a short service interval occurs.

A more acceptable mathematical calculation is to calculate a standard deviation for a computed average. Another method is to find the percentage of services that fall with the upper and lower limits. The following method can be used:

SA = [Number of Scheduled Services with +/- 5% Limits / Total Number of Services ] X 100

The benchmarks discussed above; mechanical availability (MA), mean time to repair (MTTR), mean time between stoppages (MTBS), maintenance ratio (MR), percent scheduled service (SS) and service accuracy (SA) are certainly not the only benchmarks that a maintenance organization should use. However, the experience gained from studying maintenance systems and organizations over the past 20 years has shown that they should be the core benchmarks in any system.