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.