Thermography Scan Prevents Gearbox Failures

During a routine thermography scan of rotating equipment at Harrison Power Station, it was noted that the 3B recycle pump gearbox was operating at elevated temperatures.

The other five pumps (two pumps per unit were in operation at the time), all of which have 30-gallon capacity oil reservoirs and use ISO 220 lubricant, had gearbox temperatures between 140°F and 150°F. The gearbox on the 3B pump was operating at almost 200°F.

Figure 1. 3B Pump Gearbox

Figure 1 shows an infrared image of the backside of the 3B gearbox. The hottest areas were the pinion bearings, with the entire casing heating up as the oil in the gearbox operated at elevated temperatures. For comparison, Figure 2 shows an infrared image acquired on the 3D gearbox.

Figure 2. 3D Pump Gearbox

These images also show the cause of the overheating gearbox. The oil pump on the drive shaft of the 3B gearbox had failed. The infrared image shows the pump inlet and outlet lines at about 98°F, which was significantly lower in temperature than the oil temperature in the gearbox.

A properly operating gearbox oil pump is shown in Figure 2. Figure 3 shows the 3B gearbox oil sight glass at the time the infrared images were acquired.

Figure 3. Oil Sight Glass
on the 3B Pump Gearbox

Operations was notified of the problem and this pump was shut down until repairs could be made to the gearbox oil pump. An oil sample was pulled to confirm that no damage was done to the oil or gearbox components.

Figure 4. The 3B Pump Gearbox

The point to remember here is that while routine thermography scans need to be done on electrical equipment; critical rotating equipment should also be included in the thermography route. All lubrication reservoirs and their associated heat exchangers should be scanned.

The detection of this fault prevented us from running elevated oil temperatures on this gearbox that would have accelerated wear.

Submitted by Joe Dominick, Allegheny Energy Supply

Editor’s Comment
This case study perfectly exemplifies the need to separate the condition monitoring tool from the maintenance objective. Historically, thermography has been viewed primarily as a tool for evaluating electrical circuits.

However, it is also a useful tool for finding and/or clarifying a range of lubricant and lubrication management problems. Likewise, oil analysis, to the casual participant, is a tool that indicates when the oil should be changed. Our typical reader, however, knows that the oil contains critical information about the machine and the machine’s relationship with its operating environment.

It’s time to quit “pigeon holing” condition-monitoring technologies into certain activities and focus their capabilities on the full range of machine reliability and maintenance problems and opportunities about which they can shed light and provide clarity.

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