ASTM D7155 for evaluating compatibility of mixtures of turbine lubricating oils
ASTM D7155 Standard Practice for Evaluating Compatibility of Mixtures of Turbine Lubricating Oils
6. Apparatus
6.1 The equipment and materials required for this practice shall be those required by the test methods used to evaluate compatibility.

6.1.1 Laboratory Oven, static-air or stirred-air type, capable of maintaining the test temperature within +/-3°C and equipped with one or more grill-type wire shelves.

6.1.2 Laboratory Cooler, capable of maintaining the test temperature within +/-3°C.

6.1.3 Reflector Flood Lamp, 150 watt.

7. Procedure
7.1 Testing is conducted using either of two options (see Section 5.4) for mixture proportions as agreed upon with the test requestor or user and dependent on the available sample volumes supplied. Either the sequential testing protocol described in Option 1 or the concurrent testing protocol described in Option 2 can be used. Using Option 1, a 50:50 mixture and the two constituent oils are tested. If this mixture is found compatible, 10:90 and 90:10 mixtures which reflect drain-and fill conversion or make up proportions may be tested. Using Option 2, all mixtures (10:90, 50:50, and 90:10) and the two constituent oils are tested concurrently. At the discretion of the interested parties, the testing may be continued even after an incompatible test result is observed.

7.2 Preparation of Mixtures (Tier 1 and Tier 2) - Prepare mixtures similarly, regardless of whether one or three mixtures of differing ratios will be tested sequentially or concurrently.

7.2.1 Prepare a fresh 50:50 mixture of the two oils to be evaluated for compatibility. (neat, constituent oils are designated A and B.) Determine the amounts to be mixed from the amount of oil required by the tests. Prepare at least 10 % more mixture than is actually needed for the tests. Do not prepare more than can be used immediately. No more than 30 days should elapse between mixture preparation and the start of any test.

7.2.2 Add equal amounts +/-1% of all oils, A and B neat oils, and the 50:50 mixture into separate clean, dry, glass beakers, and mix thoroughly

7.2.3 Heat the beaker and mixtures in the oven at 65 +/- 3°C (149 +/- 5.4°F) for a minimum of 168 h (+/- 1 h) for Tier 1 or Tier 2 testing. Samples may be removed after a minimum of 24 h (+/- 0.5 h) to conduct the Tier 2 primary tests, if requested.

NOTE 2 - Longer oven storage times may be employed with agreement between the parties involved.

7.2.4 Remove the beakers from the oven, and allow them to cool to room temperature before evaluating appearance.

7.2.5 Observe the oil in accordance with Appendix X1. If the oils display an incompatible result, further testing is not required. Conclude the test, and report in accordance with Section 8. If the results are satisfactory, proceed to 7.2.6.

7.2.6 Cool the beaker containing the oil mixtures to 0°C (32°F) for 24 h (+/-0.5 h). Longer times may be employed with agreement between the parties involved. Remove from the cooler and bring to room temperature.

7.2.7 Observe the oil in accordance with Appendix X1. If the oils display an incompatible result, conclude the test, and report in accordance with Section 8. If the results are satisfactory and Tier 2 level testing is to be conducted, proceed to 7.3. If Tier 1 testing was requested the testing can be concluded and reported.

NOTE 3 - Use great care when preparing the contents of the beaker for some tests. Semi-solid material not visible to the unaided eye may have settled to the bottom of the vessel. This material needs to be thoroughly mixed back into the sample prior to Tier 2 testing for insolubles and the like.

7.3 Tier 2 Testing - If resources permit, the specified tests can be performed concurrently. Otherwise, any sequence of these tests can be used.

7.3.1 Viscosity - Determine and record the viscosity as described in Test Method D445.

7.3.1.1 The mixture is considered to be compatible, and its results shall be recorded as compatible or pass if the viscosity is that of either constituent oil or if it is between them. If the viscosity of the mixture is less than the lower viscosity oil or greater than higher viscosity oil by an amount greater than repeatability of the test method, record as incompatible or fail. The temperature at which the viscosity is performed to determine the ISO Viscosity Grade is 40°C. To obtain the viscosity index, in accordance with Practice D2270, an additional viscosity must be performed at 100°C.

7.3.2 Acid Number - Determine and record the acid number as described in Test Methods D664 or D974.

7.3.2.1 The mixture is considered to be compatible if the acid number of the mixture is between or equal to either constituent oil. Record as compatible or pass. If the acid number of the mixture is less than or greater than the constituent oils by an amount greater than repeatability of the test method, record as incompatible or fail.

7.3.3 Pentane Insolubles - Determine the pentane insoluble content using Test Method D893. The mixture is considered to be compatible if the pentane insoluble content of the mixture is equal to either constituent oil. Record as compatible or pass. If the insoluble content of the mixture is greater than the constituent oils by an amount greater than repeatability of the test method, record as incompatible or fail.

7.3.3.1 Foaming Characteristics - Determine and record the foaming characteristic as described in Test Method D892. The mixture is considered to be compatible if the foaming characteristic of the mixture is equal to or less than either constituent oil. Record as compatible or pass. If the foaming characteristic of the mixture is greater than the constituent oils by an amount greater than repeatability of the test method, record as incompatible or fail.

7.3.4 Air Release Properties - Determine and record the air mixture as described in Test Methods D3247.

7.3.4.1 The mixture is considered to be compatible if the air release properties of the mixture is equal to or less than either constituent oil. Record as compatible or pass. If the air release properties of the mixture is greater than the constituent oils by an amount greater than repeatability of the test method, record as incompatible or fail.

7.3.5 Water Separability - Determine and record the water separability results as described in Test Method D1401. The mixture is considered to be compatible if the water separability of the mixture is equal to or better than either constituent oil. Record as compatible or pass. If the water separability of the mixture is worse than the constituent oils by an amount greater than repeatability of the test method, record as incompatible or fail.

7.3.6 Oxidation Stability - Select the appropriate oxidation stability test based on the type of lubricant being investigated. Determine and record the oxidation stability as described in the selected test method. The mixture is considered to be compatible if the oxidation stability of the mixture is equal to or higher than either constituent oil. Record as compatible or pass. If the oxidation stability of the mixture is lower than the constituent oils by an amount greater than repeatability of the test method, record as incompatible or fail.

7.3.7 Rust Prevention - Determine and record the rust prevention results as described in Test Method D665. The mixture is considered to be compatible if the rust prevention characteristics test is a pass. Record as compatible or pass. If the rust prevention characteristics of the mixture is a fail, record as incompatible or fail.

7.3.8 Copper Corrosion - Determine and record the copper corrosion results as described in Test Method D130. The mixture is considered to be compatible if the copper corrosion characteristics test is equal to or better than either of the constituent oil alone. Record as compatible or pass. If the copper corrosion characteristics of the mixture is a fail, record as incompatible or fail.

7.4 For oils determined to be compatible in primary testing, the user, or by agreement, the user and supplier, should determine whether additional testing is required. Depending on the criticality of the specification requirements, selection should be made from the secondary compatibility tests listed in Appendix X2.

7.4.1 If all of the mixtures pass all primary tests and the selected secondary tests, the oils shall be reported as compatible. If any mixture passes all primary tests but fails one or more secondary tests, the oils shall be reported as generally compatible but incompatible in certain applications. The failed tests shall be reported as well as the applications suggested by these tests.