What is the recommended frequency of preventive maintenance?

It is key to specify the frequency of preventive maintenance required. The first thing to do is to specify which equipment needs to be part of the preventive maintenance programme. To do this, it is important to use tools and programmes that can help determine the probability of failure of industrial assets and its consequences.

For example, the plant's historical records are a good place to start to determine which equipment needs preventive maintenance. Reviewing past equipment performance, including corrective maintenance work performed, along with preventive maintenance documentation, helps to establish the number for the probability of failure and worst case consequences.

Other ways of determining the frequency of preventive maintenance and the machines that need to be included in such a programme are:

The company's industrial machinery registers.
Industry standards and operational experience.
The individual experience of plant personnel.

The percentages of the management of maintenance hours in industrial plants are the main indicators for the overall maintenance programme. Maintenance executives following this percentage guideline can expect corrective maintenance work hours to be 40% of the total weekly hours if 60% of the hours are used in preventive maintenance. If any percentage falls outside the predetermined tolerance parameters, the maintenance programme should be put under review.

Once it has been determined which equipment needs to be part of the preventive maintenance programme and the frequency of preventive maintenance is established, it is necessary to determine the type of preventive maintenance to be performed. Most maintenance activities fall into the categories of intrusive maintenance or non-intrusive maintenance.

By intrusive means there could be a high possibility of problems being introduced when servicing. Some types of electrical checks could cause the insulation of electrical wiring to break if not carried out carefully.

While we need to have confidence in the technicians when performing maintenance, we also need to help eliminate potential problems that could result from performing maintenance. It would be necessary to perform the electrical check based on a previously conducted investigation, this could be an alternative that would bring the maintenance activity into the non-intrusive category. Industrial predictive maintenance normally falls into the non-intrusive category.

It is advisable to use as many tools as necessary to ensure that the industrial asset maintenance programme is good enough to achieve the goals set by management. No one tool provides all the information needed to establish a quality maintenance programme. Programmes need to be reviewed at least annually.

A quality maintenance programme integrates each step outlined above. Understanding management's expectations regarding the balance between corrective maintenance and preventive maintenance is a starting point. The expectation or philosophy of maintenance management may include a basic approach to developing the critical equipment list. This usually includes some variant of the probability and consequent curve.

The preparation of the critical equipment list is necessary to place the equipment in its appropriate maintenance category. The equipment can then be incorporated into a frequency management work activity taking into account the degree of maintenance it needs. If you can synchronise the steps outlined above, you can have a quality maintenance programme.

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