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What Are The Limitations of The Crackle Test?

Evan Zabawski | Senior Technical Advisor, TestOil

In an effort to communicate the limitations of the crackle test in detecting water contamination, TestOil embarked on a lab study to uncover crackle detection limits. A total of 493 samples comprised of a variety of lubricant types were run on a 400°F hot plate. The samples were assessed for a positive or negative crackle. These same samples were then analyzed for water contamination using a Karl Fischer titration (ASTM D6304‐C). The water results were recorded in parts per million (ppm). The table below summarizes the results of the study. The table lists oil type, the number of samples in the study, the detection limit range, the lowest negative crackle value, and the highest positive crackle value.

The lowest positive values represent those samples that exhibited a positive crackle and the associated Karl Fischer result while the highest negative values represent those samples that clearly had water present according to the Karl Fischer results, yet didn’t crackle. Clearly, the study demonstrates that quite a bit of variance exists in the water detection limit of the crackle test. You really need to know your lubricant type before making assumptions on what the crackle can detect. In some cases, your water limits may fall below crackle detection and running the Karl Fischer test on every sample may be worth the cost.

Karl Fischer test | CBM CONNECT

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About the Author

Evan Zabawski Senior Technical Advisor, TestOil

Evan is a Certified Lubrication Specialist. Evan has extensive experience training tradesmen and professionals in a variety of fields including: lubrication fundamentals, contamination control, condition monitoring, RCM/FMEA and used oil analysis. Evan has been a member of STLE for over 20 years, serving as Chair of the Alberta Section for 8 years, and also as an instructor of the Condition Monitoring course at STLE Annual Meetings. Currently, Evan has Editor of TLT Magazine, and have served as the Editor for The STLE Alberta Section’s Basic Handbook of Lubrication – Third Edition, and contributed as one of the editors for STLE/CRC’s Handbook of Lubrication and Tribology, Volume II: Theory and Design, Second Edition. Evan has published several technical papers and am also a member in good standing of API and ASTM.