FINA Lubricants - Cake Analysis

Centrifugal Cake Analysis

Some stationary engines (natural gas) or diesel fleets (with high soot generation) use centrifugal units to keep the oil clean and extend the life of the engine and/or oil. These devices are efficient and do remove all materials more dense than the engine oil. Materials removed include soot, dirt, water, coolant (from leaks or trace contaminant) and wear particles.

The centrifuge creates a solid cake that can be up to one-inch thick. These “cakes” are removed periodically (typical interval is 1 to 3 months). If used oil analysis is performed on the oil the oil will appear to be clean with low soot, metals and no water or coolant metals. The only items that will be seen will be viscosity increase/decrease, fuel dilution and the TAN/TBN change. Hence, coolant leaks and wear problems in the engine can be hidden by the use of centrifugal “filters”. Hence to detect these problems will require an additional “cake analysis”.

How is the test performed? The cake analysis test is a 2-sample process. First is a dilution of the early layer of the cake material that receives a spectrochemical analysis. The second sample is a dilution of the last layer of the cake material that also receives a spectrochemical analysis. The two test results, plus the evaluation are reported. The results will give the user an early warning of mechanical problems with his engine (or unit).

Reporting units. Same as spectrochemical (metals content)

Interpretation. Same as for spectrochemical except that a time frame element is added. The cake sample is similar to rings of a tree. The outer edge represents the first level or a point in time. The inner edge represents the last level of deposit and the last point in time. This can show a coolant leak that develops with time, or was a one-time occurrence.

By properly testing of the sample we can trend across time the levels of metallic elements (corrosion/wear, abrasives and coolant intrusion) in a single cake sample (note each time a sample is taken the clock starts over, so no trend is possible from one cake sample to another.) If the contamination levels are going down then the system is cleaning up. If not then the contamination level is consistent, but not normal. If the contamination levels are increasing, then a possible critical condition may exist.

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