Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/359954
8 | July - August 2014 | www.machinerylubrication.com and contamination. Every test performed on an oil sample can be categorized in at least one of these areas. Sensory Analysis While some visual or audible observations require interpreta- tion, many are intuitive and only involve a system to manage and act on the information. Most operators and technicians are familiar with the machinery they maintain or operate, and consequently are aware of the "normal" sounds of that machine, making them qual- ified to identify unusual conditions. Part of any strong PdM program is the ability to verify a fault with more than one technology. This not only ensures the validity of the fault but also helps make a more accurate and precise repair recommendation. The importance of verification with a second technology is never more evident than on a critical piece of equip- ment that requires plant outages for repair. For instance, consider the following scenarios: infrared Thermography and Vibration While making a routine inspection of an electrical panel located on a mezzanine catwalk, a technician noticed a tiny, but clearly anomalous heat signature below in the direction of a smaller component on the ground. Upon further inspection at ground level, the tech discovered an anomaly in the coupler between a small motor and pump. He was able to spot the issue from a quick scan at more than 30 feet away. The apparent temperature at the coupler was not very high, but it was enough relative to the surface temperatures of the motor and the pump to make the technician suspicious. He performed a slow-mo- tion study using a strobe light, setting its frequency to the shaft's revolutions per minute. This essentially "froze" the shaft for inspec- tion. The two halves of the coupler, which were joined by a flexible insert, appeared to be contacting one another. At this point, vibration analysis detected both mechanical looseness and misalignment. During scheduled downtime, the pump was shut down, and the entire assembly was disassembled and inspected. Four of the insert's eight legs were seriously damaged, allowing the coupler halves to make contact and produce vibration and excessive heat. A new coupler and insert were installed, and the pump was put back into service. In this case, infrared thermography was used as a screening tool, while a strobe light, sensory inspections and vibration analysis were employed to validate the potential failure, which would have gone unnoticed if only thermography had been used. Thermography, Vibration and Oil Analysis During a routine thermography route, the drive-end bearing of a large, oiled electric motor was found to be running 15 degrees hotter than any of the prior samples. Vibration testing showed nothing out of the ordinary based on the previous six months of data. An oil sample was taken, which revealed a viscosity increase of more than 100 percent. The analysis also indicated signs of cross-contamination between lubricant types based on elemental analysis. It was determined that the wrong oil had been added to the motor during the last top-up. To correct the issue, the motor was drained, flushed and refilled with the proper lubricant. Thermography, Vibration and Motor Current Analysis During a routine infrared PdM inspection, a technician deter- mined that a motor was operating at an excessively high temperature. The 7.5-horsepower motor powered a coolant pump in the machining center responsible for critical machining of a key component in the assembly plant. Failure of this seemingly insignif- icant cooling pump could cause the entire plant to shut down. The PdM program at the plant included a broad spectrum of predictive/preventive maintenance technology options. A work order for additional analysis was generated to determine if the root cause of the fault was electrical or mechanical. Initially, motor current analysis confirmed that the motor and cabling tested electrically sound. Follow-up vibration analysis iden- tified a bearing fault in the motor. Close monitoring allowed the motor to be run until the scheduled downtime, when it was replaced. A post-installation infrared scan confirmed that the new motor was operating within normal parameters. Subsequent cost analysis of this one incident showed a 100-percent return on invest- ment for all the instruments used. Ultrasound, Thermography and Vibration When used in conjunction, these technologies can be employed in a wide variety of applications, including leak detection in pres- sure and vacuum systems, bearing inspections, detection of valve blow-by, steam trap inspections, detection of corona, tracking and arcing in electrical gear, detection of cavitation in pumps, checking the integrity of seals and gaskets in transformers, etc. Technicians can easily use infrared thermography and ultra- sound analysis to inspect steam valves. First, touch the upstream and downstream sides of the valve with an ultrasonic sensor's contact probe. Steam passing through a leaking valve producing turbulence can be heard through headphones as a gurgling or rushing sound. A blockage will emit no sound. Since valve blow-by in steam systems will generate a higher temperature reading down- stream, infrared thermography can be used to detect the thermal anomaly along the pipe run and confirm the analysis. Heat can be a good indicator of a leaking hydraulic valve. The frictional forces of fluid moving through a leak can produce heat From the FIeld By applying and integrating the results of different inspection options, PdM professionals can make better and more informed decisions.