A lot has been written and continues to be written over the classification of Types of Maintenance. It is also seen the maintenance types being unnecessarily classified in too many categories, even 7 or 8 at times. This creates unwarranted confusion in the minds of many readers.

This article is intended to simplify the method of classification of maintenance types by focusing on the actual definition and what each of the types mean. This should help eliminate ambiguities in the minds of some of the readers if any.

All the maintenance activities in reality have only three main types and these are,

• Corrective Maintenance-CM
• Preventive Maintenance-PM
• Predictive Maintenance & Condition Monitoring-PdM/CdM

Corrective Maintenance -CM

Any repair work undertaken to rectify a fault or defect on an equipment is corrective maintenance. It can be a small or a major repair work, planned or unplanned. Thus, Breakdown Maintenance too which is Corrective maintenance.

Preventive Maintenance-PM

Also defined as Scheduled Restoration and Scheduled Discard is a proactive time or cycle based scheduled maintenance undertaken on any equipment to prevent unexpected failures regardless the condition of the equipment at that time.

Predictive Maintenance & Condition Monitoring- PdM/CdM

Certain maintenance tasks are carried out on an equipment to detect potential failure so that necessary corrective maintenance actions be taken up to prevent these failures. While Predictive maintenance focusses on early detection of potential failures, condition monitoring encompasses real time detection of potential failures.

Risk Based Maintenance -. Inspection of certain critical assets is carried out on regular basis based on knowledge of risk of failures and preventive action is subsequently taken to arrest these potential failures. Thus, RBM too is a subclass of Predictive Maintenance and Condition Monitoring though it is classified differently.

Similarly Prescriptive Maintenance too falls under Predictive Maintenance and Condition Monitoring by definition.

Failure Finding tasks :- The maintenance involves  making certain checks on an equipment to find out whether it has  failed or not. It is commonly followed on safety critical elements. This type of maintenance doesn’t fall under the definition of Preventive Maintenance or On Condition Maintenance or even Corrective Maintenance. It’s definition doesn’t fit into any of the above mentioned maintenance types. However, this particular maintenance is generally undertaken under Preventive Maintenance Tasks as the maintenance is time based.

Similarly General Inspections undertaken to identify defects is covered under Preventive Maintenance though in reality it is Condition Monitoring in true sense.

It is also common to see Reactive Maintenance being termed as a type of maintenance. Reactive maintenance is a maintenance culture. In reactive maintenance, repair is taken once equipment is malfunctioning or broken down. It is the opposite of Planned Maintenance.

All maintenance work carried out by proper planning of resources, safety, support services etc. in advance is Planned Maintenance.

Proactive Maintenance– Tasks undertaken to prevent failures fall under Proactive maintenance. Thus Preventive and Predictive maintenance is Proactive Maintenance. Identifying and eliminating defects also falls under Proactive Maintenance as these actions are undertaken to prevent failures.

Conclusion :- Thus any maintenance activity taken up on an equipment invariably comes under three main types namely Corrective Maintenance, Preventive Maintenance and  Predictive Maintenance & Condition Monitoring.