Condition Monitoring on a Budget
Maintenance strategies can be reactive, preventative, or predictive. Each strategy has its place, but predictive maintenance often provides substantial benefits, such as catching problems before they reduce efficiency or lead to failure.
Category: Blogs, PSM Newsletter, Standards June 15, 2021
Saving money over the long and short haul doesn’t have to be expensive.
Maintenance strategies can be reactive, preventative, or predictive, as outlined in Figure 1. Each strategy has its place, but predictive maintenance often provides substantial benefits, such as catching problems before they reduce efficiency or lead to failure.
While there are many complex and expensive predictive condition monitoring systems, owners, and maintenance and reliability professionals can also implement low-cost monitoring to keep their systems up and running efficiently.
Condition monitoring enables savvy maintenance and reliability professionals to increase uptime and save on maintenance, expensive repairs, and lost facility runtime. One way to do this is to use predictive techniques instead of time (preventative) to schedule repairs (like bearing overhauls) to coincide with low-demand periods or facility shutdowns. Periodic or continuous monitoring also reduces the likelihood of surprise breakdowns and catastrophic failures.
So, what are some of the ways operators can monitor pump conditions? The Hydraulic Institute guideline ANSI/HI 9.6.5 Rotodynamic Pumps for Condition Monitoring identifies 13 strategies for monitoring the condition and heath of pumping equipment. Let’s look at a few.
Temperature. Measuring the absolute temperature or temperature rise within a pump or lubrication system is relatively simple and can provide valuable information about process fluid properties and if the lubricant risks vaporization. In fact, some pumps come with thermowells that allow the use of a thermocouple or resistant temperature device (RTD). Similarly, manufacturers may install thermocouples in bearings or seals used in critical equipment. A rise in temperature might signal a problem with loading, coolant flow, vaporization, or degraded lubricant.
Electrical input power. Another simple measurement involves observing how electrical input power to the pump motor changes over time. This is often done by setting control limits. If the power drops too far, it could mean a lack of flow through in a pump, a clogged impeller or piping, insufficient suction pressure, or air locking. If the power increases, it might signal too much flow or head, higher operating speeds, reduced efficiency or mechanical binding and contact.
Pressure. Simply understanding the pump’s differential pressure (head) can indicate the pumps operating point or condition. This can be done by inserting a pressure gauge or pressure transducer into the piping at the pump inlet and outlet. Monitoring head periodically at a consistent flow rate and speed and/or under varying conditions and comparing the data to the OEM pump curve, will indicate when pump hydraulics are wearing, the pump is becoming less efficient, and when repairs make financial sense.
By collecting data on both electrical input power and pressure simultaneously, it is possible to calculate and trend the pumps wire to water efficiency.
Vibration monitoring. Vibration monitoring of pumps, motors and drive trains is the most common condition monitoring technology used for rotating equipment. It is typically done with accelerometers mounted on the bearing housings. By trending these measurements, it is possible to identify machinery faults that are present or progressing, such as imbalance, misalignment, binding, bent shafts, bearing wear, and much more.
Vibration monitoring has evolved rapidly over the past 20 years due to lower cost measurement devices and improved data and communication systems. Therefore, monitoring can range from “simple” periodic monitoring and analysis of overall vibration levels to more “advanced” continuous monitoring that transmits data to cloud-based storage, where artificial intelligence systems analyze it and send an alert if there is a problem.
The field of vibration analysis has also advanced due to standardized training and certification for vibration analysist. The Vibration Institute (a partner of the Hydraulic Institute) offers four levels of certification in vibration analysis. These courses and certification progress from teaching the analysist the basics of taking measurements and understanding the data and trends, to understanding the equipment dynamics and techniques to diagnose and solve problem vibration.
Shaft position monitoring. Another form of vibration monitoring uses proximity probes to measure shaft position in bearing housings. This is most often done with journal bearings, where fluid is forced into the gap between the shaft and a cylindrical bearing to keep the shaft suspended as it rotates. The proximity probes are mounted 90 degrees apart and provide the shaft orbit in the bearing. On some critical equipment, control systems automatically shut down to prevent damage and ensure safety if the proximity probes detect the centerline of the shaft is moving more than the bearing clearance.
If you are interested in condition monitoring and predictive maintenance, check out the Hydraulic Institute publication ANSI/HI 9.6.5 Rotodynamic Pumps for Condition Monitoring
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