When engaged by a client to review their maintenance data, a common finding in the mine plan is the disconnect between the equipment availability forecast and the scheduled maintenance downtime forecast. Quite often the equipment availability forecasts are based on historical performance. While this is common practice and an easy way to produce the forecast for the mine plan, the disconnect comes in when planned equipment maintenance outages are added.
What we see time and time again is an under-represented scheduled outage plan that does not align to either the site equipment management strategy or to the maintenance KPI for overall proportion of scheduled maintenance downtime.
For well-maintained equipment, approximately 70% of the total maintenance downtime should be scheduled. To represent the implications of 70% scheduled maintenance, the table below shows the target scheduled and unscheduled maintenance hours for ranges of availability from 85% to 90%.
However, in many of the forecasts we see, the scheduled downtimes are typically well below the numbers represented above. To give an example, a site may set an equipment availability target of 86%. However scheduled equipment downtime allowances only include regular scheduled servicing of the equipment, resulting in scheduled downtime forecasts of 200 to 300 hrs per year, barely 25% of total maintenance downtime. Thus, the remaining 900+ hours of maintenance allowance to reach the 86% availability has been allocated to equipment breakdowns.
This raises the question – what is wrong with this forecasting approach? One of the perceptions that we often encounter when we work with clients is that the best way to maximise availability is by minimising scheduled downtime. This is typically done by either extending shutdown/service intervals, or by reducing the duration of outages. In practice, what then happens is that tasks are removed from the plan in order to fit the reduced outage windows, and either PM tasks, or corrective work to repair defects, is not performed when needed. The result is normally an increase in downtime because these defects turn into breakdowns.
So, how do you fix this disconnect? As a first step you need to ensure the scheduled downtime allowance is reflective of your site maintenance strategy – does it cover all the tasks you need to perform, or is the scheduled downtime allowance inadequate because that’s all production will let you have? The maintenance strategy can vary greatly depending on the equipment, its age, current operating context and general utilisation.
Once the maintenance strategy aligns with the scheduled downtime allowance, the next step is to review against the availability and scheduled work percentage targets. If the scheduled work percentage target is still low, consideration should be given to adjusting the target availability by reducing unscheduled maintenance allowances so that the percentage of scheduled work increases.
Reducing unscheduled maintenance allowances and increasing availability by optimising (and even increasing) scheduled maintenance is often easier than sites realise, even if it can seem counter-intuitive. By allowing more scheduled downtime to perform PM tasks and correct defects in a controlled manner, tasks are performed faster and with higher quality than if they were done as breakdown work, and the equipment normally responds by operating more reliability.
We recently observed one site that brought in a short pit-stop shutdown in between the main shutdowns as a trial. The pit-stop shutdown let them perform some basic PM tasks such as lubricating and adjusting the equipment, cleaning it, and correcting small defects. The result was that for every percentage point increase in scheduled maintenance, there was a two-percentage point decrease in unscheduled maintenance downtime, leaving them better off overall.
In some cases, availability has been generated from historical performance, your strategy is aligned, and the resulting scheduled maintenance percentage is still low due to excessive unscheduled downtime that you don’t seem to be able to reduce. You may then need to review the maintenance practices that may be contributing to this unscheduled downtime.
Bluefield have written several blogs that can help you focus your attentions in the right areas.