199809_visual

The Visual Crackle

A New Twist to an Old Technique

Purpose: Moisture in hydraulic and lubricating oils is a primary contaminant that leads to degradation of lubricant base-stock and additives, corrodes component surfaces, and accelerates wear due to reduced fluid film strength. The visual crackle provides a simple field method to detect and roughly quantify the presence of moisture in these fluids.

Method: The crackle-test is a simple test to identify the presence of free and emulsified water in that is suspended oil. This is the water that is the most harmful to the machine and oil. The method is as follows:

1. Achieve surface temperature on a hot plate of 300 degrees F (135 degrees C). Always use the same temperature.

2. Violently agitate oil sample to achieve homogenous suspension of water in oil.

3. Using a clean dropper, place a drop of oil on the hot plate.

Observable Results:

1. If no crackling or vapor bubbles are produced after a few seconds, no free or emulsified water is present.

2. If very small bubbles (0.5 mm) are produced but disappear quickly; approximately 0.05-0.1% water is present.

3. If bubbles approximately 2 mm are produced, gather to center of oil spot, enlarge to about 4 mm, then disappear, approximately 0.1 to 0.2% water is present.

4. For moisture levels above 0.2%, bubbles may start out about 2-3 mm then grow to 4 mm, with the process repeating once or twice. For even higher moisture levels violent bubbling and audible crackling may result.

Limitations:
1. The method is non-quantitative.

2. Hot plate temperatures above 300 degrees F induce rapid scintillation that may be undetectable.

3. The method does not measure the presence of chemically dissolved water.

Safety Considerations:
1. Protective eyewear is suggested.

2. Long sleeves are suggested.

3. Test should be performed in a well-ventilated area.

Equipment Required:
1. Hot plate capable of achieving and maintaining 300 degrees F surface temperature.

2. Paint shaker (or equivalent) for oil agitation.

3. Oil dropper tube or lab syringe.

Applicable Standards: None

Interferences: Refrigerants and other low boiling-point suspensions may interfere. Different base stocks, viscosities, and additives will exhibit varying results. Certain synthetics, such as esters, may not produce scintillation.

1. If no crackling or vapor bubbles are produced after a few seconds, no free or emulsified water is present.
2. If very small bubbles (0.5 mm) are produced but disappear quickly; approximately 0.05-0.1% water is present.
3. If bubbles approximately 2 mm are produced, gather to center of oil spot, enlarge to about 4 mm, then disappear, approximately 0.1 to 0.2% water is present.
4. For moisture levels above 0.2%, bubbles may start out about 2-3 mm then grow to 4 mm, with the process repeating once or twice. For even higher moisture levels violent bubbling and audible crackling may result.