What are the general conditions for which preventive maintenance is appropriate ?

What are the general conditions for which preventive maintenance is appropriate ?


Maintenance work can be either planned or unplanned! Let us now discuss the different types of maintenance systems.
Emergency Maintenance: An un planned maintenance which is necessary to put in hand immediately to avoid serious consequences, for instance loss of production, extensive damage to assets or for safety reasons. Emergencies should remain exceptions rather than the rule. To ensure such a possibility, it is better to have planned maintenance systems.
Planned Maintenance: Maintenance Organised and carried out with forethought, control and records to a predetermined plan. Planned maintenance can be split up into essentially two main activities namely preventive and corrective.
Preventive Maintenance: Also termed ' Diagnostic or Predictive Maintenance' is maintenance carried out at pre determined intervals, or to other prescribed criteria and is intended to reduce the likelihood of an equipment's condition falling below a required level of acceptability. You try to anticipate failure and then attempt to prevent its occurrence by taking preventive actions. The proverbial saying ' Prevention is better than cure' or 'A stitch in time saves nine' is the basic philosophy of Preventive Maintenance. Preventive maintenance can be done on machines either when running or during shut down.
Running Maintenance: Maintenance, which can be carried out when the item is in service.


Shut down Maintenance: Maintenance, which can only be carried out when the item is out of service. Further preventive maintenance can be time- based or condition- based.
A Time -Based Preventive Maintenance: This policy is effective when the failure of any item of an equipment is time dependent and the item is expected to wear out within the life of the equipment . Moreover the total costs of replacement of the item should be-substantially less than those of failure replacement repair.
Condition-based Maintenance : is carried out in response to a significant deterioration in unit as indicated by a change in a monitored parameter of the unit condition or performance. It is here that one can make use of predictive maintenance by using a technique called SIGNATURE ANALYSIS which is intended to continually monitor the health of the equipment by recording systematically signals or information derived from the form of mechanical vibrations, noise signals, acoustic and thermal emissions, change in chemical compositions, smell, pressure, relative displacement and so on. Scientific collection of these informative signals or signatures, diagnosis and detection of the faults, if any, present by a thorough analysis of these signatures based on the knowledge hitherto acquired in the field , and judging the severity of the faults for decision-making , all put together , is called ' Signature Analysis'. The technique involves the use of electronic instrumentation specially designed for the purpose of varied capacities, modes of application and design features. Vibration and noise signals are the most versatile parameters in machine condition monitoring techniques. Periodic vibration signature analysis is somewhat similar to vibration analysis. A stock pulse meter is used o monitor the condition of roller bearings.
Condition-based maintenance thus reduces injuries and fatal accidents caused by machinery as the condition of machinery are indicated well before hand. It enables the plant to be stopped safely when instant shutdown is not permissible. Moreover, it permits advanced planning to reduce the effect of impending breakdowns and be in time to have necessary spare parts available. However, condition monitoring is not always used because it involves high manpower and monitoring costs and , further more, it is difficult to monitor some parameters.
Corrective Maintenance : Maintenance carried out to restore an item which has ceased to meet an acceptable condition. It involves minor repairs that may crop up between inspections.
Design- out Maintenance is yet another policy, which is practiced frequently in, developed countries. This is discussed in greater detail later on in this unit. The policy here aims at minimising the effect of failure and at eliminating the cause of maintenance . In essence, an attempt is made to pinpoint the defects in the design of the equipment. Poor design of many equipment leads to frequent breakdowns.
Also an appropriate choice of terminological materials might eliminate the needs fro subsequent lubrication frequencies.

Total maintenance planning embraces all activities necessary to plan, control and record all work done in connection with keeping an installation to the acceptable standard by devising appropriate maintenance systems. In a fully controlled situation, the time spent on emergency work, viz, the 'unplanned' portion, could well be less than ten per cent of the available man-hours in the maintenance department. The administrative control of maintenance work is very significantly altered when changing from emergency maintenance methods to a policy of planned maintenance. This brings in some increased amount of paperwork.
Maintenance Request
The most important single document in the organisation of maintenance we shall henceforth call the 'maintenance request', which is alternatively termed as work order, work requisition, job card or work ticket etc. As prerequisite for planning the maintenance function, it is necessary to know exactly what the labour force is doing, and how long each task takes.
The maintenance request by the production staff details the defect or work believed to be required. Hopefully, the 'cause' should have been identified ' before' or' after' rectifying the fault so as to help planners for conducting subsequently studies for critical analysis and the all important function of 'designing-out' maintenance .The maintenance request provides all the information necessary as regards the type of labour employed, and the time labour has taken to do the job.
Assets/Facility Register
The first step of a planned maintenance procedure is to establish what is to be maintained. This requires the need to establish an Asset/ Facility Register. Each asset must be identified I terms of name and code; description; 'reference numbers pertaining to manufacturers, suppliers, users, location with provision for changes if item is interchangeable or mobile and supplier's details. When the items are recorded either in a register or in a card- index form, they could be classified and sub-divided in terms of asset usage / availability, technical groups or maintenance methods. Sometimes certain items may be subject to statutory inspections. The assets-register is the information centre of the planned maintenance system.

Maintenance Schedules

Next we must decide how these assets or facilities are to be maintained .A' maintenance schedule' must be prepared fro every item listed in the asset/ facility register. A typical maintenance schedule card indicates grade of labour required, frequency of the work to be done, details of the work to be done and estimated time for the execution of the work. A mistake so often made is when companies setting up a planned maintenance scheme for first time prepare the maintenance schedule fro all the plant first, and then endeavour to apply these to a maintenance programme on a specific starting date. In the absence of plant- history records, this method of approach is doomed to failure, since it is just not


possible to switch from emergency maintenance methods to planned preventive maintenance overnight.


Work/ Job Specifications

Having prepared our maintenance schedules we must prepare the work/ job specifications, which are compiled from the maintenance schedules and are a means of communication between the engineer and the tradesman. Precise specifications for the activities on the maintenance schedule vary in depth and presentation for according to the system, the local labour requirements, the complexity of the items to be maintained etc. It should define specific items on the machine requiring attention and clearly indicate the required action e.g. inspect, check, gauge. It should give guidance in respect of method, however appropriate it might be. The objective is it maintain to a required standard without forgetting on the safety aspect concerning both the tradesman and operators.
Programming Annual and Weekly Planned Maintenance Programmes
Having prepared our maintenance schedules and build up a workload from our job specifications, we are now in a position to commence the preparation of an annual maintenance programme to decide when the planned productive maintenance jobs shall be carried out. Over a period of time, planned maintenance significantly reduces the demands on the during annual shutdown periods. The weekly planning maintenance programme can be derived from the annual planned maintenance programme. However, tactical planning is required at the weekly level by interacting with the production planning and control section especially. Unforeseen circumstances sometimes arise, however careful the forward planning, which make it impossible to release a machine /asset according to the weekly programme charted out. It is important to communicate the weekly planning programme, at least a week a head, to all concerned.

Inspection Report
One of the important forms of maintenance is to carry out inspection at the right time and duly record the data so as to produce an inspection report. This form/document is used only for reporting the results of planned productive maintenance inspections, as set out in the job/ work specifications. The in specification report closely resembles the maintenance request, discussed earlier on. It is imperative that inspection reports must be used by and for maintenance supervision and planned maintenance controller and his prior to filling the history records.


History Records
The last operation in our planned maintenance procedure is to build up a detailed historical records of the results of maintenance on every machine receiving it . Plant history records should be properly updated so that they can be referred to and made use of more meaningfully. Traditionally, history records have been 'written up' by records clerks from timesheets or work orders.



The operations of an effective maintenance records system provides information about: (1) the percentage of planned work achieved in the period, (ii) ratio of planned to unplanned work, (iii) down time for the period, (iv) maintenance requirement assets, 9vO indicators for reliability of the products of particular manufacturers, (viO trends in spare-parts consumption, (viiO equipment failure patterns, (viii) performance details fro personnel, by individual or by trade group.
Records are kept in many different ways ranging from card files to computerized devices. Planned Lubrication
Some form of lubrication routine is rightly considered to be an essential part of plant maintenance by most firms, yet this is a responsibility which is frequently relegated to an oiler greaser gun and a dubious supply of lubricants .: Lubrication schedules are usually provided by the planning engineers of oil companies. The schedules include information about the number of application points, frequency of each application, method to be used e.g. grease gun, oil can etc, the amount and type of lubricant required. Planned lubrication should be an integral part of planned maintenance, and , because of its utmost importance , daily and weekly lubrication tasks should usually be carried out separately from the mechanical and electrical schedules. Monthly lubrication tasks and oil changing should be usually fully integrated with the maintenance schedules.

To ensure a smooth implementation of planned lubrication techniques, you could adopt a3- phase procedure. In the first_phase, a survey of all plant that requires lubrication is carried out to establish WHAT has to be lubricated. The second phase establishes WHEN lubrication has to be done and the third phase is to conduct the OPERATION by establishing HOWLUBRICATION IS TO BE CARRIED OUT.

Work Priority
Most of us, at some time to a greater or lesser degree, come up against the problems of deciding job priority. Obviously maintenance work of an n emergency nature required to keep production going or to reduce downtime, once incurred, should be given the first or topmost priority. However, with planned maintenance, hopefully, emergency cases are reduced to just about 10% of all cases. But still some method of priority fixing must be established preferably. After 'emergency', a 'machine running' priority could be thought of. In this case the machine is running, but attention is required to maintain efficient operation or for safety reasons. Yet the least priority could be labeled 'not applicable' if the request for maintenance work is not relevant to a machine stoppage, and also for most work involving civil and building trades. It is usually found that these three priority levels are found to be adequate and acceptable in most instances. If however, the problem persists, it becomes necessary to devise a PRIORITY INDEX based on two important group factors, namely.

a) Work priority factors where all work done by maintenance department personnel is separated into 10 classes, most important being class 1.


Emergency Maintenance-1,1 land 111, Modification, Capital, Sundry and Special Maintenance, and Housekeeping are respectively ranked from 10 down to 1.
b) Facility priority factor in which each facility, plant, building etc. is placed in one of 10 classes, most important being class 1. key services, key production plant, flow line or process plant, multi-production machines, standby services, mobile transport, buildings and roads, machines ,building, roads, offices and furniture fittings re respectively ranked from 10 down to 1.
c) To obtain the priority index for any job, multiply ' work priority' class by the 'facility/ machine priority' class. You can note that 10 classes have been chosen so that the priority index for each job can be expressed as a percentage priority.
d) For example, emergency maintenance for a key service sub-station equipment, the priority index would be (10*10) = 100%. For an emergency repair to a leaking roof (building) over a production machine, the priority index would be (10*4) = 40%.
Safety
The observance of safety ay work is essential at all times. The general rule is always ' 'safety first'. Some of the main safety considerations when carrying out a maintenance management task are the following:
a) Guards are supplied by plant manufactures or subsequently fitted by the company. Safety steps should be taken to ensure that these are not tampered with resulting in potential hazards. In fact, condition and security of easily accessible guards fnust always be included in job specification as items fro-regular checks at planned preventive -maintenance inspections.
b) Protective Clothing such as helmets, gloves, goggles gasmasks etc. must be given full consideration especially in chemical and allied industries. You must preferably include the need for wearing protective clothing in the maintenance request or the work/job specification.
c) Power isolation by the use of appropriate fuses might be necessary while effecting certain types of maintenance tasks. Water and compressed air supplies can usually be isolated and locked off where necessary. Gas lines may have to be purged before any welding is permitted.
d) Pressure vessels, piped power, lifting appliance should have some type of a 'permit' system to open and / or blank off.
e) Permit to work for carrying out maintenance tasks should remain valid for a specific appropriate period only. A copy of the certificate should be posted or affixed in such a place that it is not possible for anyone to start up or machine before referring to it.