On paper, Preventive maintenance and reliability centred maintenance may seem to be at odds with each other, but they do share almost as many similarities as they do differences and may actually work well as a mixed solution, depending upon the solution that fits your company.
What Is Preventive Maintenance?
As we have seen in previous posts, a Preventive Maintenance (PM) schedule is regarded as a program of work which is planned and routinely carried out on facilities and equipment to minimise the possibility of equipment suffering an unanticipated and potentially costly failure. This routine program of work is intensive and usually requires CMMS software to run it effectively, such is the intensity of a such a work system.
Preventive maintenance has a number of advantages, including increased equipment life, reduced energy wastage on machines that are properly maintained, and, of course, less unexpected failures. However, it is seen as a highly intensive and fairly costly means of ensuring that all machines and facilities are always in their best condition and requires extensive planning and reporting input. PM, isn’t selective, and demands that all facilities and equipment are maintained to the highest standard, rather than be assessed for their need to be in a PM program.
What Is Reliability Centred Maintenance?
On the other hand, a Reliability-Centred Maintenance (RCM) program grades facilities and equipment on certain criteria and establishes a plan that is suitable for each item, thereby prioritising their maintenance needs separately. The plan needs to be based on the need to preserve the systems function by identifying and prioritizing the failure modes and applying suitable controls to deal with the potential of them happening. In order to assess equipment, each piece needs to be subject to seven questions, being:
- What are the functions and desired standards of performance for the equipment?
- What is needed for each asset to fulfil its required functions?
- What are the recognised failure mode for each potential failure?
- What are the root cause failure modes?
- What are the consequences of the failure modes?
- What can be done to guard against each failure mode?
- What alternative actions can be done if there is not a suitable proactive task?
In this way a detailed picture of the company equipment can be built up and a measurement of the worth – in terms of its importance to the company rather than financial value – it represents to the business and the consequences of it failing. The process then examines failure modes and protection against them – if any are deemed possible – to create an overall plan that dictates your actual level of maintenance.
One of the main criticisms of RCM is that the initial sorting a\n planning stage can be long, intensive, and highly protracted. Akin to carrying out a Failure Modes and Effects Analysis (FMEA) on a large and complex product and requires extensive discussion to ensure that all the information for the seven questions is correct and up to date. This may mean carrying the review out as a series of multi-discipline meetings to hammer out the correct information and to formulate an effective action plan.
The major advantages of RCM include a reduction in maintenance costs – you apply more effort to equipment that needs or warrants it – and increased equipment availability through fewer unexpected downtimes. Conversely, RCM has the disadvantages of not considering the total cost of ownership, and much effort and resource may be applied to a piece of equipment that is of low value simply because it is important to the operation. RCM is also very time-consuming in its initial planning stages.
Melding the Two?
There has been increased interest of late in the possibility of running a hybrid system that takes the best parts from both PM and RCS and runs them to in parallel, to create a system that ensures that the best maintenance is applied only where it needs to be, but than also considers other options rather than just blindly maintain. This brings the cost of equipment into the equation, along with a planned approach to each piece of equipment to ensure that the process that it supports receives the greatest amount of uptime. The total availability of the equipment – thereby defining the amount of useful work that it can do for the company, which equates directly to profit – becomes the overriding factor and the resulting plan determines the best way for that to be achieved. Consider these the examples:
- A large, complex, and expensive piece of machinery is shown to have a very low failure rate and may cause delays if certain problems arose. By using a combination of PM and RCM, it can be deduced that certain parts need to be replaced at defined intervals and the machine will continue to perform as expected. Maintenance is minimal but effective.
- A small, cheap, yet production-critical device that can be maintained but may fail unexpectedly. PM says continue to maintain it, while RCM says replace it periodically, regardless of whether it has failed or not. The cost of the failure is way beyond the cost of the device, so simply don’t bother with preventive maintenance in this case.
In this way, more options are added to the maintenance program and each piece of equipment receives the level of intervention appropriate to its cost as well as its worth, which are different.
Of course, a key feature to implementing a program such as this is the amount of initial planning needed and the ongoing commitment to deal with each piece of equipment, and this is where CMMS really comes into its own. To try and run such a program manually would be disastrous, with all the work planning, the ordering of parts, the interaction with sub-contractors, and the overall cost analysis of the program. However, using a recognised program such as UpKeep means that, once the information is on the system, it runs itself and will give a breakdown of what needs maintaining – or replacing even – before the event occurs, making the maintenance program seamless as well as ensuring maximum production time for the company.