Planned Maintenance
INTRODUCTION
All Consultants will be aware of the importance of planned maintenance in respect of plant and services and its major impact on the control of fire and liability risks.
This Technical Bulletin summarises the main recognised disciplines normally employed for the purposes of planned maintenance, together with RSG survey expectations.
PREVENTATIVE MAINTENANCE
Preventative maintenance is maintenance that is regularly performed on a piece of equipment to lessen the likelihood of it failing. Preventative maintenance is performed while the equipment is still working, so that it does not break down unexpectedly.
Preventative maintenance is planned so that any required resources are available.
The maintenance is scheduled based on a time or usage trigger. A typical example of an asset with a time based preventative maintenance schedule is an air-conditioning unit which is serviced every year, before summer. A typical example of an asset with a usage based preventative maintenance schedule is a motor vehicle which might be scheduled for service every 12,000 miles.
Preventative maintenance is more complex to coordinate than run-to-failure maintenance (detailed later) because the maintenance schedule must be planned. Preventative maintenance is less complex to coordinate than predictive maintenance (detailed later) owing to the fact that monitoring strategies do not have to be planned nor the results interpreted.
Applications suitable for preventative maintenance include those that:
Have a critical operational and/or safety function;
Have failure modes that can be prevented with regular maintenance;
Have a likelihood of failure that increases with time or use.
Unsuitable applications for preventative maintenance include those that:
Have random failures that are unrelated to maintenance (such as circuit boards);
Do not have a critical operational and/or safety function.
PREDICTIVE MAINTENANCE
The aim of predictive maintenance is two-fold. Firstly, to predict when equipment failure might occur and, secondly, to prevent occurrence of the failure by performing any required maintenance. The task of monitoring for future failure allows maintenance to be planned before the failure occurs. Ideally, predictive maintenance allows the maintenance frequency to be as low as possible to prevent unplanned reactive maintenance, without incurring costs associated with doing too much preventative maintenance.
Predicting failure can be done with one of many techniques. The chosen technique must be effective at predicting failure and also provide sufficient warning time for maintenance to be planned and executed. The techniques include vibration analysis, oil analysis, thermal imaging and equipment observation. Thermal imaging, as well as being applied to electrical systems, has the ability to detect problems associated with rotating equipment, such as bearing failure, and can also be employed to check many other items such as boiler tubes and refractory materials. Choosing the correct technique for performing condition monitoring is an important consideration that is best accomplished in consultation with equipment manufacturers and condition monitoring experts.
When predictive maintenance is working effectively as a maintenance strategy, maintenance is only performed on machines when it is required. That is, just before failure is likely to occur. This brings several cost savings:
Minimizing the time the equipment is being maintained;
Minimizing the production hours lost to maintenance;
Minimizing the cost of spare parts and supplies.
However, these cost savings come at a price. Some condition monitoring techniques are expensive and require specialist and experienced personnel for data analysis to be effective.
Applications suitable for predictive maintenance include those that:
Have a critical operational and/or safety function;
Have failure modes that can be cost-effectively predicted with regular monitoring.
CONDITION BASED MAINTENANCE (CBM)
CBM is a maintenance strategy that uses the actual condition of the asset to decide what maintenance needs to be done. CBM dictates that maintenance should only be performed when certain indicators show signs of decreasing performance or upcoming failure.
Checking a machine for these indicators may include non-invasive measurements, visual inspection, performance data and scheduled tests. Condition data can be gathered at certain intervals, or continuously (as is done when a machine has internal sensors). CBM can be applied to critical and non-critical assets.
Unlike in planned scheduled maintenance, where maintenance is performed based upon predefined scheduled intervals, condition based maintenance is performed only when it is triggered by asset conditions. Compared with preventative maintenance, this will normally increase the time between maintenance tasks, because maintenance is done on an as-needed basis.
The goal of CBM is to spot upcoming equipment failure so maintenance can be proactively scheduled when it is needed, and not before. Asset conditions need to trigger maintenance within a long enough period before failure, so work can be finished before the asset fails or performance falls below the optimal level.
REACTIVE MAINTENANCE
Reactive maintenance (also known as "breakdown maintenance") relates to repairs that are done when equipment has already broken down. Reactive maintenance focuses on restoring the equipment to its normal operating condition. The broken-down equipment is returned to working within service specifications by replacing or repairing faulty parts and components. Emergency repairs cost considerably more than planned repairs; as a result, maintenance plans that rely on reactive maintenance are generally the most expensive.
Breakdown maintenance can be extremely costly on account that shutdowns happen during production runs (instead of pre-scheduled maintenance shutdowns during downtimes); also, expedited shipping for spare parts can cost much more than regular shipping, and maintenance staff may be required to work overtime to repair machinery.
Reactive maintenance should only be performed on components that are inexpensive, easy to replace, where the failure does not cause collateral damage in the system or where they are not safety critical.
Reactive maintenance is to some extent present in all maintenance strategies on account that equipment failure is unable to be perfectly predicted.
RUN TO FAILURE
The simplest intentional maintenance strategy to execute is "Run to Failure" (also known as "Run to Fail"). In this strategy, assets are deliberately allowed to operate until they break down, at which point reactive maintenance is performed. No maintenance, including preventative maintenance, is performed on the asset up until the failure event.
Importantly, a plan is in place ahead of the failure, so that the asset can be fixed without causing production issues.
Under run-to-fail, it is important to have spare parts and staff on hand to replace the failed part and to keep availability above organisational requirements. This strategy should not be confused with reactive maintenance because of the active plan to allow the asset to run to failure. This strategy is useful for assets that, on breakdown, pose no safety risks and have minimal effect on production.
The most familiar example of run to failure maintenance is the maintenance plan for general purpose light bulbs. Bulbs are allowed to run until they fail, at which time a new light bulb is obtained from stocks and replaced when convenient.
PLANNED MAINTENANCE STANDARDS
Whist reactive and run to failure maintenance strategies may be planned, they will have little impact on controlling fire and liability risks for which an appropriate programme of preventative, predictive and condition based maintenance strategies should be implemented, tailored to the specific needs of the business/facility.
Small businesses will often lack the required investment to mount an effective planned maintenance programme and in these circumstances little more than reactive maintenance may be encountered. However, when moving up the scale within the SME sector and beyond, planned maintenance starts to become the norm as businesses realise that investment in effective planned maintenance has the potential to increase efficiency and, more importantly, profitability.
Consultants should enquire as the nature of any planned maintenance arrangements in place in respect of equipment and services, brief details of which are to be included in the survey report.
In cases where planned maintenance is seriously lacking, resulting in an increase in risk, a suitable risk improvement is to be raised. Apart from Consultants with specialist skills, risk improvements shall be worded in a generic fashion calling for the implementation of a planned maintenance programme consisting, in the main, of preventative, predictive and condition based maintenance strategies commensurate with the facilities and the risk exposure.