Maintenance policies

by • 11.09.2015 • Definitions, Maintenance management, Theory based on practical experienceComments (0)1754

This post is also available in: Russian

Maintenance Tasks and Jobs execution never starts with a wave of a magic wand. There are no such things as someone without any reason started to cut the equipment with an angle grinder. An event precedes any Maintenance activity. If the event is absent – there is no need to perform Maintenance and Repair.

One of the most interesting things is that there are only three types of Events preceding any Maintenance activity. At the same time the event type predetermines an approach to its elimination and this approach is called as MAINTENANCE POLICY.

Event:

Maintenance policy (maintenance specific type of activities)

Failure Maintenance in response to actual breakdown (operate to breakdown)
Problem identification Maintenance for technical state reasons
Coming of the planned calendar date or a certain equipment accumulated running time Preventative and predictive maintenance or routine maintenance

Any of the above mentioned policies can be applied to 80% of equipment. Moreover, application of one or another type of policy will be considered as the most well-timed and grounded, based on equipment data available.

Below you will find a detailed consideration of these policies.

  • Maintenance in response to actual breakdown, or as it referred to in foreign literature OTB (operate to breakdown).

Normally this equipment maintenance policy is mentioned as the most expensive one. In other words: something has broken and has been repaired. Repair – is an activity to be carried out in response to actual emergency breakdown and without planning stage (here to be read as «without preparation»). Elimination of some unexpected failure, which takes place for the first time, is indeed one of the most expensive things in comparison with other Maintenance activities.

     However there is a certain type of equipment, which wearing out or state degradation is impossible to detect. It has no certain failure developing period. Moreover, there is no data on clear traceable periodicity of failures occurrence for this type of equipment. This type of maintenance policy is consciously chosen exactly for this kind of equipment. The substance of such approach consists in losses decreasing at the expense of detailed preparation (the planning stage fulfillment) for emergency breakdown, taking into account the experience available (the previous emergency breakdown experience). In the course of preparation the equipment modular units are prepared, personnel is trained, repair operation sequence is scheduled and etc.

For such planned and scheduled emergency breakdown losses are expected to be minimal. Thus a very expensive 24 hours outage could turn into a planned 10-minuts PIT-STOP* emergency repair. Example: modular replacement of a damaged wheel on the road. Maintenance policy – is repair in response to actual breakdown (breakdown maintenance).

 

  • Maintenance policy for technical state reasons – it is identical to foreign term CBM (condition based maintenance).

      Classical example: the failure is revealed based on actual inspection results and certain maintenance activities are performed in consequence of the EVENT (i.e. the failure detection) to occur. Often these activities comprise adjustment and cleaning operations. But in some cases these activities comprise more severe operations dependently on the equipment state (for example, in the course of the inspection some noise was revealed). The failure developing period is assumed to be deliberately higher, than period of time by the moment of works performance.

It is assumed that at other things being equal this type of Maintenance is less expensive. But it is applicable only to such kind of equipment which technical state deterioration can be deliberately detected.

Examples: wear, imbalance, pollution and etc. In other words, the failure developing period is traceable before the breakdown to happen. This policy can be applied approximately to 80% of equipment to a greater or lesser degree.

 

  • Preventative and Predictive Maintenance** – it also has more or less similar foreign term, such as FTM (fix time maintenance).

In spite of the fact that PPM means Preventative and Predictive Maintenance** the other maintenance activities (such as Inspection and Preventive Maintenance) can be also performed upon occurrence of the event characterizing this policy.

     As to planned repair or replacement of expensive spare parts, tools and accessories it is quite speculative policy: the responsibility for taking decisions on Maintenance is shifted on Operational Procedure (which is usually established by the equipment manufacture).

Consequently all works are carried out independently on the equipment technical state. It doesn’t matter whether a gasket was worn out or not – it is a subject of replacement. It doesn’t matter whether a reduction gear oil good or not – it is a subject of change. It doesn’t matter whether a filter of 2000 000 Rub cost was worn out or not – it is a subject of replacement. Why so costly? Because it is specified and required by Operation Instructions (i.e. run time)! Thus the responsibility is taken off and shifted on Operation Instructions.

This type of policy, as a rule, is applicable on a reasonable basis for preventive and diagnostic Maintenance. Unfortunately for preventive planned replacements this policy is economically advisable for 20% of equipment, not more. In view of cost perspective it is advisable to maintain the rest 80% according its technical state or in response to actual breakdown.

Breakdowns character of this type of equipment is defined by absence of the failure developing period (or it is minimal). However the breakdowns periodicity is clearly traceable. Let’s consider for example a vehicle timing belt replacement. It is adopted to carry out replacement of the vehicle timing belt after each 90 000 km, i.e. not according to its technical state, not upon its failure, but according to its run time. The reason for this is very simple: in this case the failure developing period before breakdown is minimal, but repair in response to actual breakdown is economically inadvisable. That is such maintenance policy. Choice of one or another Maintenance Policy is as a rule depends on particular situation, but this subject will be considered in the next publication.

*PIT-STOP – is a technical stop of a racing vehicle during the race for the purpose of refueling, tires replacement, driver change, fast repair and technical state inspection. A teamwork perfected during numerous trainings is required for successful pit-stops execution. In some racing series an obligatory pit-stop is an inseparable race part (WikipediA).

** – it is the literal translatione of the Russian definitione.

 The author of the resource www.plantmaintenance.ru Fedor Belov

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