In this article information is given on need for maintenance and types of maintenance practices followed in an industry.
Why Maintenance?
Every part of a machine/equipment undergoes a certain wear and tear during operation. The wear can be due to abrasion, corrosion, erosion, aging, contamination, damage, operating error, etc. In order to counter this, every machine has limited wear reserves. Beyond certain limit, it may function at a lower efficiency or reach damage limit resulting in break down. Maintenance is required to correct this condition. The task of maintenance is to keep the wear reserves always so large that the plant is fully operative for the desired duration of time. In a continuous process industry, maintenance becomes critical because a break in the process is quite costly as it takes considerable time to reestablish the process cycle. In many cases during reestablishment, it consumes raw material with out producing anything (Example – though fuel is consumed by steam generator during start up operation, a power plant is not generating power till required quality of steam is generated by the steam generator).
Aims of Maintenance
- Ensure availability of equipment in good service worthy condition.
- To correct lost efficiency to lower production cost.
- Ensure safety of operating equipment and safety of working personnel.
- To meet statutory regulation (Example – as per Indian Boiler Regulation act, boiler of a power plant shall be hydraulically tested in the presence of an IBR inspector once in two years provided the boiler has been operated safely and normally).
Types of Maintenance
There are two types of maintenance.
Breakdown Maintenance
In this type of maintenance, no care is taken for the machine/equipment until it fails. Repair is taken up after breakdown. This type of maintenance could be used when the failure does not significantly affect the operation or production or generate any significant loss other than repair cost (Example – allowing a light bulb to fuse before its replacement). However, the failure of a component from a big machine may be injurious to the operator. In such cases, breakdown maintenance shall be avoided.
Preventive Maintenance
In this type of maintenance repair is taken up before breakdown of machine/equipment. Here work is taken up to retain the healthy condition of equipment and prevent failure through the prevention of deterioration, periodic inspection or equipment condition monitoring. It is further divided into three types – daily maintenance, periodic maintenance and predictive maintenance.
Daily Maintenance
Small and routine types of works like inspection, cleaning, oiling, re-tightening, etc. are carried out in daily maintenance. These are small jobs like leaks, filter cleaning, etc. They generally do not develop as an urgency but if neglected can lead to serious troubles, even a breakdown.
Periodic Maintenance (Time Based Maintenance – TBM)
Time based maintenance consists of periodically inspecting, servicing and cleaning equipment and replacing parts to restore efficiency and prevent sudden failure / process problems. If equipment is taken out of service for maintenance, it is called overhaul of that equipment (Example – overhaul of cooling water pump in a thermal power plant). If the full plant is taken out for inspection and maintenance, it is called plant outage / shut down / annual overhaul (Example – shut down of steam generator, turbine and associated equipment in a power plant).
Predictive Maintenance
This is a method in which the service life of important part is predicted based on inspection or diagnosis. Compared to periodic maintenance, predictive maintenance is condition-based maintenance. It involves measuring and analyzing data about deterioration and generally employs an on-line surveillance system (Example – vibration measurement of turbine bearings).
To highlight type of work carried out, some times special names are given to maintenance activities. Two of them are:
Corrective Maintenance
It improves equipment and its components so that preventive maintenance can be carried out reliably. Here equipment with design weakness is redesigned to improve reliability or improving maintainability. This happens at the equipment user level. (Example – installing a breather with filter instead of normal breather on lubrication oil tank to prevent contamination of lubricating oil by atmospheric dust in dusty environment).
Maintenance Prevention
Here weakness of current machines is sufficiently studied (on site information leading to failure prevention, easier maintenance, safety, ease of manufacturing, etc.). The observations and the study made are shared with the equipment manufacturer and necessary changes are made in the design of new machine.
Total Productive Maintenance (TPM)
Total Productive Maintenance (TPM) is a maintenance program, which involves a newly defined concept for maintaining plants and equipment. The goal of the TPM program is to increase production, reduce cost and at the same time increase employee morale and job satisfaction. TPM brings maintenance into focus as a necessary and vitally important part of the business. More information about TPM will be covered in future by an article on TPM.
