- Buyer's Guide
Pro-Seal Service Group, a distributor for Royal Purple synthetic lubricants, encounters numerous lubrication-related failures and is thereby challenged to improve reliability on all machinery.
This case study discusses a common lubrication delivery method used throughout industry that, in this case, led to an early bearing failure.
A chemical plant in Michigan approached Pro-Seal concerning a frequent bearing failure that did not relate to a typical bearing lifespan. The maintenance engineer explained that several large-service water pumps were failing due to sludge building up in the bearing housing. He believed the sludge buildup was a result of early oxidation and the breakdown of oil.
After questioning the customer further, the author discovered the plant was using constant-level oilers and was experiencing plugged supply lines from the bottle oiler reservoir, thus cutting off the oil supply to the bearing housing. As part of routine maintenance, the plant cleaned out these bottle oilers weekly to prevent plugging.
Root Cause Analysis
The first step in root cause analysis is to ask questions that are pertinent to the application, determining what initiated the failure. What type of pump was involved? Was the bearing running hot? Was there any notable vibration or noise? What type of bearing was used and was the bearing or oil sample saved for inspection?
The maintenance staff had indeed saved the bearing, and they were able to provide an oil sample for analysis. Overwhelming evidence indicated contaminants in both the bearing and oil sample, which were obviously water and particulates.
Sludge is created from water, ingressed particulates and the contaminants reacting with the oil. Because these pumps were located in a coal-fired power plant, coal dust or fly ash is visible in the air.
After viewing the pumps, the author noticed all three had a high flow of air directed toward the pumps and the bearing housing from electric drive motor cooling fans.
The bearing housing had a typical vent cap with no filtering capability. When asked if the bottle oiler was vented, the response was "no." Upon inspection of a new bottle oiler, it was obviously ventilated to seek the same pressure in the bottle as the bearing housing to allow proper oil flow.
At this point, two vent ports were discovered with water and dirt entering and mixing with the oil to formulate sludge, essentially plugging off the oil supply to the bearings. This was not an oil failure issue, but rather a contamination problem.
To rectify this problem, after studying a manufacturer's catalog, personnel decided to switch to a closed-loop system that eliminates the oil from being vented to atmosphere and impedes the contamination ingress.
While evaluating this project, an interesting question was asked by one of the mechanics. "If this is what led to the sludge buildup, why wasn't the same problem experienced 30 feet away on the two boiler feed pumps that also used these bottle oilers?"
These particular pumps used steam turbines as drivers and, unlike the other pumps, had no electric motors or fans to create the air flow. In addition, the steam turbines leaked a fair amount of steam that settled over the pump area and in effect shrouded the air with moisture, which kept the air particulates (dust) to a minimum. Finally, these pumps run continuously, reducing the chance of air expansion and contraction within the bearing housing.
The lesson learned here is that sometimes a third-party evaluation can help reduce maintenance problems, thereby increasing the mean time between failure of equipment. In addition, some resourceful information can be obtained from your lubricant supplier.