TYPES OF MAINTENANCE
When talking or writing about types of maintenance, it is in fact about classifying maintenance tasks into different categories.
Types of maintenance in accordance with the specialisation of the technician.
In the first place, maintenance can be divided into the following general types, in accordance with the specialisation of the technician who carries out the tasks:
- Operational maintenance, the one carried out by operation personnel.
- Mechanical maintenance, made by mechanic specialists.
- Electrical maintenance, carried out by electric specialists.
- Maintenance of instrumentation, executed by instrumentation specialists.
- Control maintenance, made by control specialists.
- Technical cleanings, carried out by technicians specialized in cleaning certain part of the equipment which require specific and complex procedure.
Types of maintenance in accordance with scope.
In accordance with the scope of the tasks, maintenance can be divided into the following types:
- Routine maintenance, generally carried out by production personnel.
- Underway maintenance, carried out by maintenance staff yet not needing plant, area or a whole system stoppage. Thus only implying a narrow number of equipment and subsystems which do not affect production.
- Minor revisions or inspections, when a limited amount of elements are inspected or substituted.
- Major revisions, when tasks to be accomplished imply the substitution of a great number of wearing elements, or the inspection of certain internal parts that demand great dismantling.
Types of maintenance in accordance with anticipate faults.
Lastly, according to anticipate faults, there are three major groups of maintenance tasks. In several cases, when talking about `types of maintenance´, one maybe thinking about this last category. The types of maintenance according to anticipate faults are the following:
- Corrective maintenance, gets done after the failure has been made and has as its essential goal, its own adjustment.
- Diagnosis, has as its essential goal the knowing of the machines or installation condition in order to decide if an intervention has to be done on it. Generally, an observation or measurement is related to the condition of an installation. Diagnosis tasks frequently include an estimation of its criticality, evaluating the potential severity in cases when the potential and the degradation trend of failure gets to materialise. These type of tasks used to be known as PREDICTIVE MAINTENANCE, even though nowadays this name is disused, favouring the concept of DIAGNOSIS, which is a wider concept and which defines better the wilfulness of the tasks. The diagnosis includes four types of tasks:
- Easy inspection tasks, very often generally carried out by production technician. It involves simple sensorial inspections, commonly made with the senses, without needing measure tools or additional technical means. Thus including visual inspection, observation of strange noise and vibration emissions and the recognition of abnormal odours. It also includes the reading and record of operating parameters, with instruments installed in the equipment. They require basic training and they can be carried out by any technician. Due to its simplicity these inspections can be done very often.
- Online diagnosis tasks, which are carried out basing on the readings obtained from the inline mounted instrumentation and which are received in the control system.
- Offline diagnosis tasks, which are carried out with instruments that are especially assembled for making the observation or measurements which are used to diagnose. Such an example are the analysis of vibration, thermography, the analysis of ultrasound, oils, fumes produced by combustion and so forth. These are made with offline instruments.
- Detailed inspection of tasks, carried out by specialized maintenance technicians and which may or may not require the stoppage of the equipment and systems to make these inspections. They often demand disassembly or at least, profound observation. As well as this inspections need specific education for the technician that carries them out, who has to be able to distinguish between a standard situation, a situation which requires observation in order to verify its evolution, and an appalling situation which demands immediate intervention. Among these detailed inspections, the followings stand out:
- Mechanic verification, like clearance, alignment, thickness, bolt tightening, starting, operation and stoppage measurements.
- Electrical verification, such as grounding verification, verification of the operation of emergency stop, connexion verification, and so forth.
- Verification of measuring instruments and functional check of control links. They may require an intervention in order to adjust certain parameters to default values.
- Check of certain ways of operation or the benefits of an item.
- Preventive maintenance, carried out before a failure made and which has as its main propose prevent from happening. Preventive maintenance can be further divided into four subtypes, always taking into account that it is actually about subtypes of maintenance inside the category of ‘preventive maintenance’:
- Conductive maintenance the one carried out by operation technicians and that generally refers to senses check, data samples, change in fuel and/or adjustment of parameters.
- Systematic maintenance, made from time to time or when a certain number of hours has passed.
- Hard-time maintenance, overhaul, major revision or zero hours, which is the combination of tasks made after some time of equipment, system or installation operation, and which has as its goal return the inspected ensemble to its initial state (as when it has zero hours of functioning.
- Improvement maintenance, which is the combination of tasks which are carried out in a part of the installation, and has as goal the avoidance of a certain failure to be made or made again. Although some authors doesn’t consider modifications as ‘maintenance tasks’, it is logic to consider them this way, when they have as goal the avoidance of failures. And they shouldn’t be consider ‘maintenance tasks’ when they only find improvements in security, in the environmental or production impact, without affecting failure probability.