Preventive & Predictive Maintenance

by Ken Staller, Senior Maintenance Consultant

If you ask ten people what their definition of Preventive Maintenance is, you will get ten different answers. The tasks range from very simple to fairly complex. What's more, the manner in which they are performed and the depths to which they are carried out vary considerably. For the purpose of this guide to Preventive Maintenance (PM) and Predictive Maintenance (PDM), I will use the following definition: PM and PDM are a series of tasks and company policies that, if followed, improve and keep business profits as high as possible. This is achieved by adhering to three general guidelines.

		Maintain the production equipment and plant utility systems equipment as close to brand new condition as possible and have all equipment ready to start up and run with no unplanned shutdowns.
		Maintain the production equipment and plant utility systems equipment in the best possible operating condition for the purpose of producing quality manufactured goods while the machines are in service.
		Complete all PM and PDM work on a regularly scheduled basis without exceeding the "Point of Diminishing Returns on Investment" for the labor, tools and materials required to perform the work.

The difference between Preventive and Predictive Maintenance is that Preventive Maintenance tasks are completed when the machines are shut down and Predictive Maintenance activities are carried out as the machines are running in their normal production modes.

With PM and PDM systems – as in all systems and processes of work – there are the Who, What, When, Where and Why questions to answer before any actual work begins. With the above three guidelines we have already defined the "Why" question.

The "Who" question relates to several different types of members of the PM and PDM team.

A.		Someone who has an abundance of maintenance and plant engineering experience should write the individual tasks. To receive the expected results from the investments made in the PM and PDM protocol, the person writing the details of what needs to be done must have a deep understanding of the many aspects of machines. Aging, wear, component material fatigue patterns, effects of dirt and other contaminants, heat/cold, humidity, effects of chemical contact, vibration, lubrication practices, measurement processes, maximum safety methods, work efficiency standards, work scheduling, people skills, and plant processes are all factors that must be carefully considered.
B.		The mechanics and electricians that perform the PM and PDM work must be of high caliber and possess the skill levels of a maintenance department. On average, 85% to 90% of PM and PDM work orders call for machine inspection work and only 10% to15% lubrication work. The people performing these tasks must fully understand machine and machine component operations before they can effectively inspect for specific problems and negative operating trends.
C.		The management person directly responsible for the people performing the PM and PDM work must understand the work to be accomplished and set the performance standards, goals and expectations. They must be able to monitor the quality and quantity of work completed as well as measure the results. Also, they should be able to make on going changes and improvements to the individual PM tasks as part of an overall continuous improvement effort. These changes are dictated by the results of measurements and changes in the plant processes and equipment. Finally, the management person should also be able to complete component failure analyses. Determining why and how a component failed is the first step in determining how to prevent subsequent failure.
D.		The plant upper management must view the PM and PDM work system as required constant work practices that are just as important to the production process as any other function. This will require a minimal planned downtime of equipment to accomplish all PM and PDM work.
E.		Production employees also are a significant part of PM systems. They can be, and many times are, the first to see changes in the equipment they operate. Total Productive Maintenance (TPM) represents the active participation of all production employees in various machine set-ups, inspections and, in some cases, the lubrications of machinery. The amount of participation in TPM varies with the complexity of the equipment, the types of processes involved and the overall skill levels of the work force. Training the work force and the setting its expectations varies with the philosophies of the plant management of each facility.
F.		Contractors should be included in some PM work, especially the PDM work involved. Many contractors can supply cost effective services in some of the more specialized inspections and tests required. For example, many plants do not have trained refrigeration mechanics and they hire contractors to do the scheduled PM on Heating Ventilation and Air Conditioning (HVAC) units for the plant systems. Other contractor applications may be for air compressor and air dryer PM. In addition, vibration and ultra sonic analyzing is highly specialized aspect of PDM and requires extensive training and high test equipment purchase and upkeep costs.

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