Industrial Equipment Maintenance and Repair

Organising maintenance and repair

Equipment does not run reliably unless it is maintained and repaired on time, to the right scope and quality. To keep it serviceable for a long time, to spend less on upkeep and to lose less main production to downtime, operation has to be organised sensibly and all the maintenance work done without gaps. A planned preventive maintenance (PPM) system covers: the types of repair work and how they are described; planning of preventive operations (adjustment, tightening bolted joints) and monitoring that they are done; the length of repair cycles and periods between repairs; repair complexity categories; the service that carries out repairs; methods of repair and restoring worn parts; buying and recording spare parts; lubrication; material supply to the repair service; and quality control of repair and care of equipment.

At the end of each year the head of the repair service draws up the PPM schedule for the following year, month by month. Inspections and all kinds of repair are done by the service’s repair fitters and electricians. Each item of equipment is assigned to the operating staff of the section, and their names are shown on plates on the equipment. Maintenance instructions must be kept at the workplaces.

Maintenance and repair of process equipment come in these forms: in-shift maintenance (running repair), inspection, minor repair, medium repair and major repair. In-shift maintenance is done by operating, duty and repair staff during process downtime. It is based on the shift handover log, which records malfunctions, stoppages and downtime. An inspection checks the condition of the equipment, fixes mechanical and electrical faults and determines what preparatory work is needed before the next maintenance or planned repair.

A minor repair is a planned one: worn parts are replaced or restored and mechanisms adjusted, so that the equipment runs normally until the next planned repair. A medium repair means partial dismantling, major repair of individual assemblies, replacement or restoration of the main worn parts, then assembly, adjustment and testing under load; the equipment is also checked for process accuracy. A major repair is complete dismantling, replacement of all worn assemblies and parts, repair of base parts and assemblies, then assembly, adjustment and testing under load. It restores the geometric accuracy of the equipment provided for in the documents. The results are entered in the unit log.

Equipment is taken out of service for repair according to the PPM plan. A repair may be postponed or cancelled only with the permission of the head of the enterprise. Before work starts, the customer (the head of the production section) must hand the equipment over clean, clear the area of foreign objects and disconnect it from all kinds of energy.

Types of industrial equipment maintenance

EN 13306, the European standard on maintenance terminology (2017 edition), divides maintenance into preventive and corrective. Preventive maintenance is done before a failure, to make it less likely and to slow down wear; corrective maintenance is done once a fault has been detected, to bring the equipment back to working condition. Within these two groups the types are distinguished by what triggers the work: a schedule, the actual condition of the unit, or the fault itself.

This is a general classification: the intervals and scope of work are set by the equipment manufacturer’s documentation and the enterprise’s own rules.

Planned and unplanned maintenance and repair: what is the difference

Two separate divisions overlap here, which is where the confusion comes from. Preventive or corrective depends on the purpose of the work: to prevent a failure or to eliminate a fault that has already been found. Planned or unplanned depends only on whether the work was entered in the schedule in advance; this is a practical distinction.

Vibration diagnostics followed by balancing or alignment is condition-based, that is, preventive maintenance, and it is usually put into the plan for a convenient stop, so it counts as planned. While the unit is running and the readings only show vibration creeping up, no fault has been recorded yet.

Once a fault is found that cannot wait, the work becomes immediate corrective maintenance. That is unplanned work: it pushes the schedule aside. A fault with no immediate consequences is dealt with during the next planned shutdown (deferred corrective), so in terms of timing that work is planned.

Repairs follow the same logic. In the broad sense a repair is part of maintenance, since it restores a function lost through failure or wear, and the planned/unplanned division applies to it too. The scope of a repair and the time it is ordered are different characteristics: minor, medium and major repairs under the PPM system are entered in the schedule in advance, while a repair after a sudden failure may be of the same scope but is unplanned. What each of them includes is described above, in the section on organising maintenance and repair.

Maintenance and repair of industrial equipment: how to choose the type of work

There is no single right choice for every unit, so the type of maintenance is chosen unit by unit. What it depends on:

• The price of a sudden failure: downtime, safety risks. The higher it is, the less sense there is in waiting for a breakdown.
• Fans, induced draft fans, pumps and electric motors can be run on condition-based maintenance because their vibration can be measured (see vibration diagnostics). Units whose condition cannot be measured stay on a schedule.
• The interval and scope of planned work are taken from the data sheet and the manufacturer’s documentation, not from universal tables.
• The unit log shows which assemblies fail most often, and the schedule is adjusted to match.

The method and the consequences of late balancing are covered in the articles Dynamic Rotor Balancing: Method and Stages and Consequences of Late Fan Impeller Balancing; how vibration diagnostics is done and how accuracy is checked is described in Vibration Diagnostics and Process Accuracy Checks of Industrial Equipment.