How Water Causes Bearing Failure?
- Water is THE SCOURGE OF OUR MACHINES. Please do not underestimate the attack potential of water.
- There is no contaminant more complex, intense and confounding than water.
- Damage both oil and machines, operational failure of bearing
- Will cause cascading or chain reaction failure.
- Premature oxidation of the base oil; when oxides combine with more water, a corrosive acidic fluid environment exists.
- Oxidation can throw-off sludgy insoluble and increase oil viscosity ; impede oil flow
There are 9 most FAILURE MODALITIES:
- Hydrogen-Induced Fractures
Called as hydrogen embrittlement or blistering. The sources of the hydrogen can be water, but also electrolysis and corrosion (aided by water). Once in contact with the free metal within the fissure, the water breaks down and liberates atomic hydrogen. Sulfur from additives (extreme pressure (EP), antiwear (AW), etc.), mineral oils and environmental hydrogen sulfide may accelerate the progress of the fracture
Soluble and free water can contribute to rust formation. Water gives acids their greatest corrosive potential. Etched and pitted surfaces from corrosion on bearing raceways and rolling elements disrupt the formation of critical elastohydrodynamic (EHD).
High temperatures flanked by metal particles and water can consume the antioxidants rapidly and rid the lubricant from the needed oxidative protective environment.
- Additive Depletion
Cripples or diminishes the performance of a host of other additives include AW, EP, rust inhibitors, dispersants, detergents and demulsifying agents. Sulfur-phosphorous EP additives in the presence of water can transform into sulfuric and phosphoric acids, increasing oil’s acid number (AN).
- Oil Flow Restrictions
Water is highly polar, and as such, has the interesting ability to mop up oil impurities that are also polar. Filters are short-lived in oil systems loaded with suspended sludge. In subfreezing conditions, free water can form ice crystals which can interfere with oil flow as well
- Aeration and Foam
Water lowers oil’s interfacial tension (IFT), which can cripple its air-handling ability, leading to aeration and foam. Aeration and foam can also incapacitate the effectiveness of oil slingers/flingers, ring oilers and collar oilers.
- Impaired Film Strength
If the loads are too great, speeds are too low or the viscosity is too thin, then the fatigue life of the bearing is shortened. When small globules of water are pulled into the load zone the clearance is often lost, resulting in bumping or rubbing of the opposing surfaces (rolling element and raceway). Water can also flash or explode into superheated steam in bearing load zones, which can sharply disrupt oil films and potentially fracture surfaces.
- Microbial Contamination
Water is a known promoter of microorganisms such as fungi and bacteria, these can form thick biomass suspensions that can plug filters and interfere with oil flow. Microbial contamination is also corrosive.
- Water Washing
When grease is contaminated with water, it can soften and flow out of the bearing. Water sprays can also wash the grease directly from the bearing, depending on the grease thickener and conditions.
Source from Machinery Lubrication