ASTM D7155 for evaluating compatibility of mixtures of turbine lubricating oils
ASTM D7155 Standard Practice for Evaluating Compatibility of Mixtures of Turbine Lubricating Oils
4. Summary of Practice
4.1 Option 1 - Prepare a 50:50 mixture of two oils to be evaluated for compatibility. This mixture and the two neat, constituent oils are tested using the primary compatibility tests. Depending on the performance of the mixture, relative to those of the constituent oils, 10:90 and 90:10 mixtures may need to be tested in addition.
4.2 Option 2 - Instead of testing mixtures in sequential order, 10:90 and 90:10 mixtures are tested at the same time the 50:50 mixture is evaluated. If all mixtures pass the primary compatibility tests, or if the application requires the evaluation of specific properties, secondary compatibility tests can be employed for further evaluation. Such tests can be run concurrently, if desired.
5. Significance and Use
5.1 The compatibility of oils can be important for users of oil-lubricated equipment. It is well known that the mixing of two oils can produce a substance markedly inferior to either of its constituent materials. One or more of the following can occur:
5.1.1 A mixture of incompatible oils most often forms a precipitate.
5.1.2 The precipitate will form unwanted deposits in the lubrication system, plug filters and oil passageways.
5.1.3 Such events can lead to catastrophic equipment failures.
5.2 Because of such occurrences, lubricant suppliers recommend evaluating compatibility of lubricating oil of different formulations and sources prior to mixing. Equipment users most often do not have the resources to evaluate oil compatibility and must rely on their suppliers. Mixing of oils is a highly imprudent practice without first determining the compatibility.
5.3 Although new turbine oils may be compatible, in-service oil of the same type may be degraded or contaminated to such an extent that the new oil added may not be compatible with the system oil. In-service oil compatibility with new oil additions should be evaluated on a case by case basis.
5.4 The oxidation resistance of different oils of the same type can vary widely, and compatibility does not imply equivalent performance.
