Preventative maintenance

 
 

Preventative Maintenance

Preventative maintenance (PM) is and remains the dominant maintenance strategy across a number of industries. Preventative maintenance gained popularity due to its reduction of costs and equipment downtime when compared to reactive or run-to-failure maintenance, which repairs machinery only after failure has occurred.

Today, in addition to PM, a much wider variety of maintenance strategies exist, such as predictive or condition-based monitoring, which has advanced rapidly due to technological advancements in cost-effective data collection, developed by companies such as ProAxion®. As a result, maintenance methods have been changing. However, preventative maintenance still has a number of uses, especially when applied in conjunction with other maintenance strategies.

What Is Preventative Maintenance?

Preventative maintenance is a strategy which relies on regular, highly scheduled inspection and repair to address failures in equipment and machinery before they occur. It is traditionally either time-based, with inspections and upkeep scheduled at regular intervals of several weeks to several years depending on the nature of the equipment, or use-based, with maintenance occurring after the machine has run for a certain number of hours or miles. Time-based preventive maintenance is more common, with use-based strategies usually applied to manufacturing equipment, automobiles, construction machinery and occasionally aircraft.

When a preventative technique is employed, the equipment is inspected and then any number of maintenance tasks are performed which can ultimately prevent failure from occurring. Upkeep tasks which often occur during a preventative inspection include cleaning, lubrication, oil change, and the repair or replacement of individual parts. If failure is judged as being particularly likely to occur soon, partial or complete overhaul of the system may also be carried out.

Accurate records must be kept of every inspection to create a complete picture of the equipment’s performance throughout its life cycle. Traditionally, these records were created in the form of handwritten documents, but recently many companies have made the switch to digital records.

The key tenet behind preventative maintenance is the idea that a piece of equipment becomes more and more likely to fail as it ages. Usually, the intervals between scheduled inspections decrease as a machine becomes older. Additionally, preventative maintenance also takes into account the periods of time when equipment sees most frequent use when determining a schedule. For example, an air conditioning system might be inspected once per year in May or June, at the beginning of summer, while a heating system is instead inspected in October or November as winter begins. Today, a number of software products exist which can help manufacturers efficiently schedule inspections depending on the age and use of the equipment.

As preventative maintenance increased in popularity, many manufacturers began including recommended inspection times, usually in the owner’s manual which accompanies the equipment. For example, a manufacturer of a small personal vehicle might recommend that it undergo inspection and/or oil change after every 5,000 miles of driving.

Four Questions - Should I Use Preventative Maintenance

There are four questions which can be asked regarding a piece of equipment when determining whether or not preventative maintenance is the proper strategy to employ.

These questions are:

1.     Does the equipment perform a critical function? What does the equipment do, and how important is this function to the overall productivity of the facility or company?

2.     Does failure of the equipment come with safety risks? Is the equipment regularly operated by human workers? Would those human workers be in danger of injury, illness or death were the equipment to fail? Alternately, could failure cause major property or environmental damage?

3.     Is the equipment expensive to repair? How much does the equipment cost when only reactive / run-to-failure maintenance is used? Would regular inspection be ultimately cheaper?

4.     Does the equipment being down disrupt business? Can the facility or company still be productive without the equipment, or not? Would the equipment being down force employees to work overtime or create unnecessary, unproductive downtime?

If the answer to any one of these four questions is “Yes,” the equipment is probably a good candidate for preventive maintenance. However, if the answer to all four is “No” – it does not perform a critical function, has no safety risk, is inexpensive to repair, and does not disrupt business when down – reactive or run-to-fail maintenance may be the lowest cost option to be used.

Advantages of Preventative Maintenance

Preventative maintenance has proven to possess a number of advantages, especially when compared with run-to-failure strategies. It is, in most cases, less expensive than reactive maintenance, and does not cause unplanned equipment or employee downtimes (and the resulting loss of production) as failures are addressed before they occur. Prior to the advent of ProAxion Tactix, preventative maintenance could even be considered more cost-effective than condition based or predictive maintenance, which had required constant or scheduled manual measurement or observation of the equipment.

In addition, preventative maintenance has been found to improve the life cycle of many types of machinery, as well as decreasing the risk of injury for equipment which is operated by human workers. It also produces significantly less paperwork than reactive maintenance, as the documentation of equipment failure requires an extensive and time-consuming process. Lastly, sticking to a preventative maintenance schedule means that equipment is far more likely to pass external audits (safety, quality, etc) and inspections at any time during its operation.

Disadvantages of Preventative Maintenance

However, preventative maintenance is not without its disadvantages. Foremost among these is the time and resources required in implementing such a strategy. Employees must be trained in inspection techniques (or a professional inspector hired, which can be quite costly), inspections must be scheduled, and of course all upkeep tasks performed must be carefully documented in minute detail.

In addition, while unplanned downtime is prevented, this sort of maintenance must still occur while the equipment is not functioning – so unplanned downtime is merely replaced in many cases with planned downtime. Contrast this with condition-based, predictive maintenance, which is capable of testing and collecting data on the machinery while it is still running, and the inefficiency of preventative maintenance can be seen.

Lastly, preventative maintenance runs the high risk of carrying out either too much or too little maintenance on any given piece of equipment. Too-frequent inspections are a waste of time, labor, resources and money, while too-infrequent ones can lead to failure and force the company to resort to reactive maintenance instead.

In recent years, the theory that an equipment’s rate of failure decreases steadily as it ages has been discounted and disproved (particularly by the 1978 Nowlan-Heap Report, which introduces the non-age based reliability-centered maintenance strategy). Some types of equipment experience a consistent failure rate over time, while others actually possess greater risk of failure shortly after installation (a concept referred to as “infant mortality”). Increasingly, preventative maintenance’s age-based scheduling techniques have become seen as outdated and inefficient.

Additionally, technological advancements in the field of predictive maintenance (aka condition-based maintenance) have increasingly left more traditional preventative maintenance in the dust. Predictive maintenance allows for the real-time monitoring of equipment to detect failures before they occur, allowing maintenance to occur only when-needed. For example, ProAxion®’s signature vibration and temperature monitoring technology, Tactix™, is simple and cost-efficient to install and uses vibration and temperature to predict failures in advance. This saves industry leaders a significant amount of money in the long run as unnecessary maintenance is never performed.

When to Use Preventive Maintenance

Despite its disadvantages, preventive maintenance still sees use today. It should be applied when equipment experiences a regularly consistent failure rate or one which increases with age, or in situations when either predictive or reactive maintenance are not cost-effective.

Preventive maintenance is best used in conjunction with other maintenance strategies including predictive and reactive. The reliability-centered maintenance (RCM) approach analyzes equipment failure modes and consequences and then implements the most time-, labor- and cost-efficient strategy. When preventive maintenance is recommended by RCM, it has been determined to be effective and should be used.

Contact ProAxion® today to learn more about both the advantages and drawbacks of preventive maintenance and its role as a possible solution within the overall RCM process.