Headquartered in Charleston, S.C., Allied Reliability Group specializes in implementing condition monitoring techniques including oil analysis, vibration analysis, infrared thermography, motor circuit analysis and ultrasonic analysis to understand the current state of machinery.
Oil analysis ranks high on the list of these tools. It can identify changes in lubricant chemistry, wear particles that indicate component defects, and contaminants coming from outside the lubrication system. It enables maintenance professionals to uncover what is happening inside their rotating machinery, including pumps, motors, compressors, gearboxes, air handlers, transmissions and more.
This article describes a number of examples where oil analysis was used to reduce repair costs and improve throughput. A common thread throughout was the application of ASTM D7416, Standard practice for analysis of in-service lubricants. D7416 outlines a rigorous, five-part integrated test practice that is intended for use by maintenance personnel doing on-site oil analysis to detect common lubrication problems.
The device Allied Reliability Group used in each of these cases was a minilab from Spectro Scientific, which includes the Spectro 5200 Trivector Analyzer, digital viscometer and Oilview software. Requiring an oil sample size of only 2 oz. (50 ml), the analyzer can determine water content, viscosity, laser particle counts, ferrous index, microscopic debris analysis, dielectric permittivity and chemical index (important for spotting soot and changes in the oils base number).
The Spectro 5200 Trivector Analyzer has proven its ability to identify principle root causes of equipment failure such as unseen corrosion, contaminants, improper lubrication and water intrusion, said Niels Maes, asset health analyst for Allied Reliability Group. Early identification of these problems enables preventive intervention prior to catastrophic failure.
Case 1: Water Intrusion
A canning line fills up to 50,000 cans per hour, and then seams the filled cans. The filling machines have an automated clean-in-place program that flushes the equipment with large volumes of water and chemicals. Allied Reliability Group monitors the main oil reservoirs with oil analysis.
Over a period of five months, the main drive showed recurring problems with water intruding into the gearbox and oil tanks, as shown by oil analysis. Although the oil was changed frequently and the seals were inspected and replaced, this did not solve the problem. Allied Reliability Group suggested supplying dry air to the oil reservoirs. The overpressure was limited to a small level to avoid blowing out the seals. This approach eliminated the water intrusion problems.
Case 2: Bearing Damage
The same factory uses a bottle washing machine that rinses bottles before they are filled. Gearboxes drive the translation chain which moves bottles through the washing machine. Vibration measurements have been successfully used for condition monitoring of the ingoing shaft, which operates at 55 rpm. Comparatively, the outgoing shaft operates at only 1 rpm – much too slow for accurate vibration measurements. Therefore, oil analysis is performed every three months on the shaft lubrication reservoir.
A recent measurement using the Spectro 5200 showed a sudden increase of wear particles in the oil. The first step was to change the oil and rerun the oil analysis, but the level of wear particles was also high in the new analysis. The number and size of wear particles continued to increase, revealing particles larger than 40 microns. The machine was shut down and inspected at the first planned stop. The inspection revealed a severely damaged bearing on the outgoing shaft.
The problem was solved by overhauling the reduction gearbox. If the problem had not been detected by oil analysis, the gearbox would have crashed and caused other parts to fail. Production would have been lost because the line could not operate the rinsing machine until the repairs were complete.
Case 3: Glue in the Gearbox
A labeling machine in the same factory has the ability to run at 60,000 bottles per hour. The high complexity and structural limitations of this machine means that certain parts can only be monitored by oil analysis. Oil analysis of the gearbox reservoir revealed an increased viscosity, a large increase in the dielectric constant, and a water intrusion.
An inspection of the gearbox showed a large amount of glue intruded into the oil reservoir because a seal failed. If the problem had not been identified by oil analysis, the gearbox would eventually have stopped, resulting in high repair costs and production losses. Accurate oil analysis enabled the plant to make relatively inexpensive corrections that fixed the problem during the next scheduled production stop.
Case 4: Rising Ferrous Index
A steel mill uses a cold-rolling process in which metal stock passes through one or more pairs of rolls to reduce its thickness and thickness variations. The skin pass is the final cold-rolling pass, and involves the least amount of thickness reduction, typically just 0.5 percent to 1 percent. The skin pass also produces a smooth, uniform surface on the rolled steel plate. The numerous reducers which drive the skin pass are lubricated from a shared oil reservoir containing 6,000 liters (1,585 gallons) of Shell Omala 220 oil.
Recently, an oil sample from this reservoir showed an increased ferrous index, increased number of particles, and a drop in viscosity from 220 cSt to 82 cSt. Allied Reliability Group advised the steel mill to urgently inspect the oil reservoir. The inspection showed that several heating elements had failed, which caused the particle count and ferrous index to increase. The inspection also revealed a failure in the circulation pump which caused the oil to overheat and reach high local temperatures.
The steel plant was able to replace the broken heating elements, repair the circulation pumps, and replace the oil during a scheduled outage. A new oil sample taken from the same point revealed that the problem was solved. If the company had continued to operate the machine with bad oil, the gearboxes would have been damaged, resulting in increased repair expenses and lost production due to an unplanned outage.
Case 5: Slow-moving Woes
In this same steel plant, the vibrations of faster-moving shafts are monitored using vibration measurements. But a shaft that drives a gearbox at 9 rpm moves too slow for vibration measurement to be effective. Instead, an oil sample is analyzed every three months.
The most recent oil sample showed an increase in particle count and ferrous particles, although vibration analysis on other shafts driven by the same gearbox did not uncover any anomalies. The gearbox was opened up and inspected at the next planned stop.
Inside, the rolling elements of the slow-moving axle showed clear signs of grinding. The outer ring of the bearing was black from the extreme heat generated by the grinding. The bearing obviously would have crashed if it had not been replaced. Once again, oil analysis saved a considerable amount of money in reduced repair costs and by avoiding a production outage.
Case 6: A Balancing Act
A steel-producing plant uses a fan 3 meters in diameter that turns at 1,000 rpm to remove gases from steel converters. The gases are so hot that the fan blades need to be cooled with water. This causes steel dust to adhere to the fan blades and throw them out of balance. To compensate for this imbalance, four oil chambers are integrated into the fan, arrayed at 90 degrees from each other around the diameter of the fan. Oil is pumped between the chambers in order to balance the fan, and oil analysis is performed on a regular basis to monitor the health of this balancing system.
At a certain point a large increase in the water and contaminant level was detected in the oil. The problem was immediately reported to the maintenance team, which planned an inspection at the first scheduled stop. A couple of days after the analysis was performed – but before the inspection could be performed – the oil pump crashed due to the high level of water. An inspection showed a problem with one of the seals, which permitted cooling water from the fan blades to enter the balancing system.
Our final example involves an oil sample retrieved from a piston compressor. In this case, the analysis revealed a high level of water and the presence of ferrous particles.
Based on these results, the compressor was overhauled. During this inspection, the camshafts indicated high levels of wear. The wear was presumably caused by reducing the lubricating properties of the oil caused by the water intrusion. The water intrusion was in turn traced back to a failure of the water separator. Once again, oil analysis reduced repair costs and prevented a production outage.
These applications are typical of the savings in repair costs and lost production that can be provided by oil analysis, Maes concluded. Asset health monitoring finds defects early to prevent unexpected failures and help the organization plan and schedule maintenance. The Spectro 5200 provides clear indications of metal wear, lubricant chemistry and contamination.
Maes notes that the instrument also generates machinery health trend analysis to support data-driven predictive and preventive maintenance decisions. Lubricant condition monitoring also conserves oil and reduces oil disposal costs by driving maintenance on an as-needed basis.
Yuegang Zhao is vice president of global sales and service at Spectro Scientific, which specializes in instruments and software that support condition-based maintenance decisions. He joined the Chelmsford, Mass., company in 2011, with responsibility for worldwide sales, product management and customer support. E-mail him at yzhao@spectrosci.com, or phone (978) 431-1121. Web: www.spectrosci.com