Water contamination of grease is a problem that is generally not well understood. It has a major impact on bearing life. Other than the obvious issue of bearings being in wet conditions, hot and dry conditions can also affect bearings.
Many people often overlook water contamination as a cause of bearing failure. Especially when bearings are not in direct proximity to wet areas or obvious sources of water contamination. One might think that water contamination won’t be an issue unless the bearing operates in wet conditions or sits near liquids in surrounding equipment. This is not so.
Condensation inside the housing is a cause of water contamination of grease. Condensation will occur as hot conditions during the day become cool, or with cold conditions at night, and the water in the air trapped in the housing becomes a condensate. Humidity will also cause degradation of the grease through water contamination.
Processes such as wash downs with high pressure hoses are likely to force water back into the housing through the seals. This is unless the seals are in good condition and continuously and fully grease purged.
The Impact of Water Contamination on Lubrication and Bearing Performance
The limit for the absolute water content in mineral oil – the lubrication component of most greases – above which problems will occur, is 200 ppm. Water contamination higher than this will cause a number of lubrication problems and failures of the grease’s lubrication and protection properties. Clearly the higher the water contamination the worse the result but it is most important to understand that lubrication failures can start to occur with an extremely small amount of water contamination in the grease.
One can expect a breakdown in the oil film strength, reducing the oil’s ability to separate rolling elements under load. Damaged surfaces is one result of this. The roughness prevents hydro-dynamic oil film separation of the rolling surfaces. In turn, this causes accelerated wear and surface damage leading to bearing failure.
The performance of the oils and additives in the grease is critical to lubrication outcomes. Water not only causes corrosion, it also aids in the formation of acids as a result of the lubricant breakdown. This is due to sulphurs released from the oil and the EP and anti-wear additives in the grease. Corrosion isn’t the only result of these acid formations. Not only does corrosion follow from the formation of acids but the grease is additive-depleted and unable to perform the required lubrication as it originally did.
The presence of water causes hydrogen-induced embrittlement and cracking. Acceleration of the hydrogen-induced fracture process, started with the water contamination and advanced by corrosion and electrolysis, causes the rolling elements and raceways to become etched and pitted.
This surface damage then causes high temperatures at the point of load as a result of the loss of oil film separation between the damaged surfaces, resulting in further oxidation of the oils in the grease, in turn adding to corrosion and bearing damage.
Methods of preventing water contamination:
- You can maintiain the seals in good condition to prevent water ingress. If you are using labyrinth seals, you can ensure that you continuously fully grease-purge them.
- You can maintain continuous re-lubrication of the bearings to ensure that there is a progressive and continuous replacement of lubricant. You can also purge any contaminated grease from the bearing.
GreaseMAx Lubricators provide an effective and proven solution to the problems of contamination and bearing damage caused by water ingress and from condensation. This low-cost improvement can provide considerable maintenance and productivity benefits.
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