LUBE OILS >>WATER CONTAMINATION

 
 
Water contamination or moisture contamination is a adultrant for the oil, and it is wisely said, oil and water do not mix. Hence when mixed, it poses a combination of chemical and physical relating problems to the lubricant and the machinery.

The problems and effects due to water contamination may not be immediate but non the less they are going to catastrophic. The effects of contamination of water or moisture on the machinery are :
  • Rusting and corrosion resulting in lowering the life of the component

  • Vaporous cavitation due to water etching and erosion

  • Hydrogen embrittlement

  • Oxidation of bearings

  • Machinery wear due to loss of oil film and lubricity

Rusting and Corrosion

Water attacks iron and steel surfaces to produce iron oxides. Water teams up with acid in the oil and corrodes ferrous and nonferrous metals. Rust particles are abrasive. Abrasion exposes fresh metal which corrodes more easily in the presence of water and acid.

Water Etching

Water etching can be found on bearing surfaces and raceways. It is primarily caused by generation of hydrogen sulfide and sulfuric acid from water-induced lubricant degradation.

Erosion

Erosion occurs when free water flashes onto hot metal surfaces and causes pitting.

Vaporous Cavitation

If the vapor pressure of water is reached in the low-pressure regions of a machine, such as the suction line of a pump or the pre-load region of a journal bearing, the vapor bubbles expand. Should the vapor bubble be subsequently exposed to sudden high pressure, such as in a pump or the load zone of a journal bearing, the water vapor bubbles quickly contract (implode) and simultaneously condense back to the liquid phase. The water droplet impacts a small area of the machineís surface with great force in the form of a needle-like micro-jet, which causes localized surface fatigue and erosion. Water contamination also increases the oilís ability to entrain air, thus increasing gaseous cavitation.

Hydrogen Embrittlement

Hydrogen embrittlement occurs when water invades microscopic cracks in metal surfaces. Under extreme pressure, water decomposes into its components and releases hydrogen. This explosive force forces the cracks to become wider and deeper, leading to spalling.

Film Strength Loss

Rolling element bearings and the pitch line of a gear tooth are protected because oil viscosity increases as pressure increases. Water does not possess this property. Its viscosity remains constant (or drops slightly) as pressure increases. As a result, water contamination increases the likelihood of contact fatigue (spalling failure).

The effects on lubricating oil can be equally harmful:

  • Water accelerates oxidation of the oil

  • Depletes oxidation inhibitors and demulsifiers

  • May cause some additives to precipitate

  • Causes ZDDP antiwear additive to destabilize over 180įF

  • Competes with polar additives for metal surfaces

TESTS FOR WATER IN OIL

The guidelines in the Table below help only if it is known how much water is in the oil. There are several qualitative and quantitative tests to determine water content. The easiest one to perform is a simple visual test. An ISO 68 turbine lubricant was observed at room temperature with controlled amounts of water. The Table shows the results of the test.

Coulometric Karl Fischer 
Titration Analyzer

Bear in mind that several factors can affect the cloudy or hazy appearance of the oil. First, as the oil sits, it will clear up and the oil may become supersaturated. Second, dye and dark-color oil can mask cloudiness.

Visual Crackle Test

A test that can be performed on-site is the crackle test. It is a quick control test that is performed by heating the oil in a small metal pan using a Bunsen burner or hot plate. It is heated rapidly to 100įC and the technician listens carefully for the number of pops or crackles. It is not run on hazy oil unless there is a doubt as to whether the haziness is caused by water or some other substance.

Karl Fischer Test

Quantitative tests for water include Karl Fischer, water by distillation and FTIR. Karl Fischer is accurate from 1 ppm to 100 percent and is relatively quick and inexpensive. The oil sample is titrated with a standard Karl Fischer reagent until an end-point is reached. The difference in test methods is based on the amount of sample used for the test and the method used to determine the titration end-point.

Coulometric Karl Fischer Titration Analyzer

ASTM D1744

A volumetric method, is reliable and precise, but there can be reproducibility problems at low water concentrations (200 ppm or less). Soaps, salts from wear debris and sulfur-based additives react with the Karl Fischer and can give a false positive. In fact, a new, clean, dry antiwear (AW) or extreme pressure (EP) oil may give a reading of as much as 200 to 300 ppm.

ASTM D6304

A coulometric titration method is more reliable than D1744 at low water concentrations and is less prone to interference effects, although again, AW and EP additized oils can show as much as 100 ppm of water.

The most reliable method is ASTM D6304. The oil sample is heated under a vacuum so that any water present in the sample evaporates. Water vapors are condensed and dissolved into toluene, which is then titrated. Because the additives and other interfering contaminants remain in the oil, the condensed water in the toluene is a true indication of water present in the sample.

   
Glycol
Viscosity
Nitration
Oxidation
Sulfation
Total Acid Number
Total Base Number
Water Contamination
Fuel Dilution
Wear-Metals
Petroleum
 
 
Viscosity | Viscosity is a measure of a fluidís resistance to flow (Kinematic viscosity)
 
Viscosity | Viscosity is a measure of a fluidís resistance to flow (Kinematic viscosity)
 
Viscosity | Viscosity is a measure of a fluidís resistance to flow (Kinematic viscosity)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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