Predictive maintenance (PdM) is analogous to a physician taking a patient’s blood pressure. The blood pressure test gives the physician information about the patient’s condition and is helpful for assessing overall health. Facilities and plants use predictive maintenance to assess the condition of equipment. PdM can indicate which equipment is operating in a degraded state and at risk of failure, thus giving the maintenance staff time to plan and schedule corrective action to prevent the failure and its consequences. To make this possible, one needs to know about certain key areas of the technology:
- PdM program implementation
- Integrating PdM with the preventive maintenance (PM) and work order systems
- Measuring, reporting and communicating results
- Gaining additional benefits of PdM.
Design your PdM program
The first step is to gain management support for the PdM concept. When you present the ideas to your management team, do it in a simple manner using terms they’re familiar with. Use simple everyday examples relevant to your site's experience to explain why PdM can improve the long-term financial picture. Be prepared to discuss and quantify the goals of the proposed PdM program, which could include improving the reliability in a critical area or system, reducing failures and trouble calls, reducing maintenance expenditures, eliminating recurring failures or introducing PdM to optimize your PM program. Don’t bother investing time and effort in developing your PdM program before you’ve gained management support.
Then define which equipment to target for PdM. Look closely at equipment failure histories and the root causes of those failures. This information is generally available from your CMMS or work order system. The equipment that fails the most provides the greatest potential for cost savings and improvements. It’s essential to target the equipment whose downtime affects production and reliability.
Also, target the areas where your PM program is excessive or ineffective. Replacing PM with PdM might provide better results and more useful indications of equipment health. For example, using a strobe for a PdM inspection of a belt drive can be done while the equipment is on-line and can detect excessive belt slip, which might not be found by visually inspecting the belt during a PM shutdown.
Compare the costs of PdM against the costs of equipment breakdowns. Equipment that doesn’t break down often or that has small effect on the operation might not be good candidates for a PdM program. It might be cheaper to run the equipment to failure and perform breakdown maintenance. Using good business sense is critical to determining which equipment should be considered for PdM.
Select PdM technologies
The next step in the implementation process is to decide which PdM technologies to use. The four most common technologies:
Vibration analysis: Use this to detect excessive vibration in rotating equipment — fans, pumps, motors, compressors and generators. Excessive vibration can be an early warning sign for bearing failure, misalignment, looseness, soft foot or an out-of-balance condition. Figure 1 shows an example of a vibration spectrum on a belt-driven fan that has high vibration caused by looseness and misalignment.
Figure 1. This is a vibration spectrum for a belt-driven fan suffering from looseness and misalignment. The red arrow indicates the peak vibration frequency.
Figure 2: Electrical contactor showing a loose, overheated connection.
Infrared thermography: This non-destructive method uses an infrared camera to detect thermal patterns and measure operating temperatures. It’s useful for detecting loose or improperly terminated electrical connections, overloading, defective contacts, phase imbalances and other electrical problems. In mechanical applications, it’s useful for detecting overheated bearings; misalignment in belts, sheaves and couplings; faulty steam traps; and other anomalies that exhibit a thermal change as components degrade. Figure 2 shows a typical thermal image of a loose connection in an MCC contactor/starter.
Ultrasonic inspection: This technology is used for leak detection in pressurized systems (such as steam and air) to detect problems such as faulty steam traps, air leaks and leaking drain valves. Ultrasound also is used to monitor bearing condition and ensure proper lubrication, and to monitor high-voltage electrical equipment for tracking, corona and abnormal electrical discharges.
Oil analysis: This provides useful information about lubricant condition, machine condition and contamination levels in bearings, compressors, gearboxes and engines. By sampling and analyzing oil, users can detect degradation in lubricant properties, excessive wear in lubricated components, a build-up of contaminants and moisture, improper use of the wrong lubricant and other conditions that affect reliable equipment operation.
The next step in the implementation process is deciding which resources you need to implement the PdM program. A key factor is determining whether PdM will be performed by in-house personnel or outsourced to a qualified service provider. The use of in-house personnel for PdM must:
- Assign the PdM activities to individuals in the group
- Allocate enough time to perform periodic field data collection, data analysis, reporting and tracking
- Train technicians in PdM theory, technology, practices and future certifications to develop expertise
- Provide funds to purchase data collection equipment.
Outsourcing PdM to a qualified service provider often is a feasible option if internal resources aren’t available or the cost of developing the in-house expertise is greater than the cost of using a service provider. However, even if an outsourced approach is determined to be the most cost-effective strategy, recognize that you must still assign internal resources for managing and administering the PdM program and for following up on the results.
Integrate PdM into existing systems
Predictive maintenance can be effective only if results are integrated into the work processes and the work order system. If PdM data-collection activities aren’t performed on schedule, or PdM results aren’t followed up with corrective actions, then you’re wasting time and money. To ensure the PdM program is integrated into the existing work processes properly, ensure that PdM activities are scheduled through the CMMS or work order system. This captures cost, work order history and corrective actions. Also, introduce a simple “Data » Information » Action” model to ensure follow-through on information coming from the PdM effort and to facilitate a condition-based maintenance approach (Figure 3).
Figure 3. The work flow for condition-based maintenance provides a continuous stream of feedback that improves the overall work process.
PdM can detect equipment problems at the earliest stages of failure, which leads to less costly corrective actions and avoidance of unanticipated failures. However, the benefits and savings can be realized only if results are acted upon and properly documented.
For example, a routine predictive maintenance activity detects that a critical HVAC fan has excessive vibration, caused by imminent bearing failure. This triggers a new work order to acquire spare parts and schedule the repair to be performed between production runs. If the faulty bearing hadn’t been detected, the HVAC unit could have failed during production, causing loss of product and downtime.
Coordinate PM and PdM activities
The PdM program doesn’t negate the need for a strong preventive maintenance program. The two should complement each other. In setting up your PdM program, decide which PM activities will continue and which will be replaced by PdM. The streamlined PM program should reduce the scope of PM activities, extend PM intervals and introduce new PdM activities to more proactively monitor the health and condition of critical equipment. Examples of where introducing PdM can optimize the PM program and lead to an overall strategy that has a lower cost and higher level of reliability include:
- Monitoring belt/sheave condition with strobe and vibration instead of periodic time-based belt replacement
- Performing an in-service infrared and visual inspection of electrical panels and air-ventilated transformers instead of shutting the equipment down, inspecting, cleaning and tightening connections (which might itself introduce problems)
- Monitoring filter differential pressures via building automation system gauges to determine when filters need to be replaced instead of using time-based filter change-outs
- Sampling and analyzing oil-lubricated bearings and gearboxes instead of using periodic time-based oil changes.
Report results and metrics
Publicizing your PdM program’s results and metrics is an important element that helps ensure continued management support. Also, communicate these results to the people responsible for operating and maintaining the equipment. Because some personnel might initially be skeptical about the benefits of PdM, sharing results and case studies helps demonstrate the successes being achieved and reinforces the wisdom of the decision to invest in PdM. Results can be communicated in several ways, including:
- Periodic training programs and seminars
- Electronic media and Webcasts
- Posting metrics on bulletin boards in the plant.
Keep the results simple and easy to understand. Avoid acronyms when possible. Your message must be easy to understand by people who might not have a technical background or who might not be involved in the day-to-day PdM activities. Communicate the PdM program’s financial aspects. It’s a challenge to show cost savings, especially if there’s been no adverse financial impact. In many cases, cost avoidance rather than cost savings is the appropriate measure.
Provide ongoing communications to technicians and solicit their input. Foster a sense of ownership among technicians. They often will have useful suggestions on PdM technologies, training needs and equipment that should be included in the program. Reward and recognize the technicians who help to develop and improve the PdM program. Technicians who are committed and see the value of the PdM program will help to sell it to others in the organization.
Enjoy additional benefits
PdM also can be effective in other areas besides routine equipment monitoring. PdM can be used during the commissioning or acceptance testing phase of new construction to identify design or installation problems before the equipment is turned over to the site. Used in this manner, it can provide quantifiable performance data to substantiate warranty claims.
PdM also can help you reduce energy consumption. Leaks in steam or compressed air systems can cost thousands of dollars per year and are easily identified using ultrasound and IR technologies. Vibration analysis of rotating equipment can detect alignment problems, which can cost thousands of dollars per year in additional energy consumption. These are just two of many examples of how PdM can reduce the facility’s carbon footprint.
Managing a successful predictive maintenance program is much more than introducing new technology and fancy measuring equipment. It’s about changing the way people think and how they make decisions about maintenance. It’s strategic and depends on dedicated people to make it work. Focusing on the programmatic and process issues is just as important as the technology itself, and critical to implementing a successful PdM program for your facility.
Dean Wallace is owner of Applied Facility Solutions in Jeffersonville, Pennsylvania. Contact him at firstname.lastname@example.org and (610) 630-7414.
Jeff Evans is vice president of Maintenance Strategies, Inc. in King of Prussia, Pennsylvania. Contact him at email@example.com and (800)-676-6565.