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Preventive Maintenance



1. Definitions

  • Preventive maintenance is the work activity that has been programmed on a regular basis to inspect a system,
    to uncover potential problems, and to make whatever repairs are necessary to ensure that the system does not
    fail during normal operation. Studies have indicated that if good preventive maintenance management practices are applied, and integrated with other operations activities, cost reductions of 35% or moreare possible.

  • "Maintenance (including inspection, cleaning, and repair) of equipment on a regular basis that is sufficient to prevent unplanned failure."

    "It is a daily maintenance (cleaning, inspection, oiling and re-tightening), designed to retain the healthy condition of equipment and prevent failure through the prevention of deterioration, periodic inspection or equipment condition diagnosis, to measure deterioration."

    It is further divided into:

Periodic Maintenance (Time Based Maintenance - TBM)

  • "Time based maintenance consists of periodically inspecting, servicing and cleaning equipment and replacing parts to prevent sudden failure and process problems."

Predictive Maintenance (Condition Based Maintenance)

  • "This is a method in which the service life of important part is predicted based on inspection or diagnosis, in order to use the parts to the limit of their service life." It manages trend values, by measuring and analyzing data about deterioration and employs a surveillance system, designed to monitor conditions through an on-line system.

  • "An equipment maintenance strategy based on measuring the condition of equipment in order to assess whether it will fail during some future period, and then taking appropriate action to avoid the consequences of that failure. The condition of equipment could be monitored using Condition Monitoring, Statistical Process Control techniques, by monitoring equipment performance, or through the use of the Human Senses. ... KeyTerms.htm

2. Level of preventive maintenance

  • Maintenance is a cost and to a customer really adds no value to a product.

  • Maintenance Costs include:

    •  the salaries maintenance staff,

    • cost of inventories kept for the maintenance procedures such as spares for machines, tools & equipment and

    • Cost of outsourced maintenance activities

  • On the other hand Failure Costs include:

    • cost of idle production employees during the lost time when equipment is down for repairs.

    • production losses during breakdown taking into consideration upstream  and bottleneck equipment  can be costly if it means the shutdown of the whole plant.

    • cost of penalties or damages claimed by the customer

  • The frequency of maintenance must be balanced with the cost if a failure should occur.

  • In some instances, it might be less costly to run a machine until it breaks down, and then to perform the necessary emergency repairs.

  • The relationship between the maintenance costs and the cost of failures is illustrated in the figure below.

  • The curve illustrates that there is an optimum level when preventive maintenance programs should be carried out when Cost of Maintenance and Cost of Breakdown are equal.