Preventive maintenance: setting intervals and actually keeping them

Time, usage or condition as the trigger

A calendar interval is simple to administer and appropriate where deterioration follows elapsed time, such as lubricant ageing or seasonal effects. A usage trigger based on running hours, cycles or units produced fits wear-driven failure and avoids servicing equipment that has barely run, but it requires reliable counting. Where the failure gives warning as it develops, a condition trigger is usually better than either. The common error is putting everything on a calendar because it is administratively convenient, which over-maintains lightly used assets while under-maintaining heavily used ones on the same interval.

Task content is where most programmes are weakest

Many routines were copied from an equipment manual, inherited from a previous plant or written before the asset was modified, and they instruct the technician to check items that have never failed while omitting the failure that recurs. Review the task list against the actual failure history of that asset, remove tasks that address nothing, and add checks for the modes that have caused real stoppages. Write instructions specific enough to be repeatable, including what constitutes a pass, because a task recorded as inspected without a criterion produces a record rather than an inspection.

Getting the equipment time and keeping it

Preventive work needs production to release equipment, and that release is the first thing sacrificed when the plant is behind. Schedule routines into the production plan as visible events rather than requesting access at short notice, and prefer to align them with changeovers, planned shutdowns or the quieter shift. Where a routine keeps being deferred, the resolution is either to move it to a window production can actually give, to reduce its duration, or to accept the risk explicitly. Silent repeated deferral is how a well-designed programme becomes a fiction while still appearing in the plan.

Compliance measured honestly, including whether the work was done properly

The standard measure is the share of routines completed within their due window, and it is worth tracking by asset criticality rather than as one plant total, since a high overall figure often conceals repeated deferral of the few tasks that matter. Guard against the second failure mode, which is completion recorded without the work being performed. Spot-check by inspecting the asset afterwards, by looking at whether the expected parts were consumed, and by asking whether findings were ever recorded. A routine that never generates a finding is either unnecessary or not being done.

Pruning routines that are not earning their place

Programmes grow: every incident adds a task, and nothing is ever removed. Periodically review each routine against evidence — has this task ever found anything, has the failure it targets occurred, is the interval supported by the history — and delete or extend those that cannot justify themselves. Be careful with the reasoning, since a failure that has not occurred may be absent precisely because the task is being done. The test is whether the task addresses a plausible mode for that asset, not merely whether stoppages have been recorded recently.

Frequently asked questions

Can you do too much preventive maintenance?

Yes, in two ways. Intervening on equipment that is running well consumes technician hours and production time that could go elsewhere, and every intervention carries a risk of introducing a fault through incorrect reassembly, contamination or disturbed settings. For components whose failure is random rather than age-related, scheduled replacement adds cost without reducing failures. Where the history shows problems clustering shortly after servicing, over-maintenance is the likely explanation and the interval should be reconsidered.

Who should perform routine preventive tasks, operators or technicians?

Split them by skill and risk. Simple checks, cleaning, lubrication and visual inspection can sit with operators, who are present continuously and notice change early, provided they are trained, the task is documented and any isolation requirement is respected. Work involving guarding removal, stored energy, calibration or dismantling belongs with qualified technicians. Getting the boundary wrong in either direction wastes technician capacity or creates a safety exposure.

How do we set an interval when we have no failure history?

Start from the manufacturer's recommendation adjusted for your actual duty, since published intervals usually assume moderate use and clean conditions. Then treat the interval as provisional and gather evidence: record findings at each service, note whether components were near the end of their life or barely worn, and adjust. Assets in harsh conditions typically need shorter intervals than the manual suggests, and lightly loaded assets longer, so a single inherited figure rarely suits both.