ASTM D7155 for evaluating compatibility of mixtures of turbine lubricating oils
ASTM D7155 Standard Practice for Evaluating Compatibility of Mixtures of Turbine Lubricating Oils
1. Scope
1.1 This practice covers the compatibility of mixtures of turbine lubricating oils of the same ISO VG grade and type as defined by Specification D4304. The Tier 1 method compares the visual appearances of specific mixtures with those of the neat oils after storage at specified conditions.

1.2 If the current in-service oil is causing problems or if circumstances indicate the need for additional testing, a Tier 2 method compares selected performance properties of the mixture and its constituent oils.

1.3 The Tier 1 and Tier 2 methods can be used to evaluate new (unused) lubricant compatibility or the effects of adding new (unused) lubricant to in-service lubricant in the system.

1.4 This method does not evaluate the wear prevention characteristics, load carrying capacity, or the mechanical shear stability of lubricants mixtures while in service. If anti-wear (AW), extreme pressure (EP), or shear stability are to be evaluated, further testing of these parameters may be required.

1.4.1 Tier 1 - Mixtures of the two constituent oils to be evaluated are prepared at specified proportions, stored in an oven at 65°C for 168 h, and then evaluated for changes in physical appearance.

1.4.2 Tier 1 - Mixtures of the two constituent oils to be evaluated are prepared at specified proportions, stored in an oven at 65°C for 168 h, and then evaluated for changes physical appearance and parameters detailed in 7.3.

1.5 Mixtures of the two constituent oils are evaluated in a primary testing protocol using the following standards:
Appearance (Tier 1 and Tier 2): Appendix X1
Kinematic Viscosity: Test Method D445
Acidity: Test Methods D664 and D974
Pentane Insoluble: Test Method D893
Copper Corrosion: Test Method D130
Rust Prevention: Test Method D665
Foaming Characteristics: Test Method D892
Air Release Properties: Test Method D3427
Water Separability: Test Method D1401
Oxidation Stability Test: Test Method Note 1

1.5.1 For compatible mixtures, a supplemental (nonmandatory) testing scheme is suggested when circumstances indicate the need for additional testing the beyond Tier 2 primary recommended tests.

NOTE 1 - The oxidation stability test method should be selected based on the product type and in agreement with the lubricant supplier (see Appendix X2 for options). Unlike other tests described in this practice, the impact on oxidation stability may not be easily interpreted with a pass/fail rating. The user is encouraged to contact the lubricant supplier for assistance in the evaluation of the data.

1.6 Sequential or concurrent testing is continued until the test requestor or user is satisfied that the intent of this practice has been met. If any mixture fails the Tier 1 visual appearance method or any of the Tier 2 primary tests, when requested, the oils are incompatible. If all mixtures pass the Tier 1 or Tier 2 tests, the oils are considered compatible by those methods.

1.7 This practice applies only to lubricating oils having characteristics suitable for evaluation by the suggested test methods. If the scope of a specific test method limits testing to those oils within a specified range of properties, oils outside that range cannot be tested for compatibility by that test method.

1.8 This practice may be used to evaluate the compatibility of different types and grades of oil. However, it is not intended to evaluate such mixtures. The user is advised to consult with suppliers in these situations.

1.9 This practice does not purport to cover all test methods that could be employed.

1.10 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.11 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents
2.1 ASTM Standards:
D130 Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test
D445 Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and Calculation of Dynamic Viscosity)
D611 Test Methods for Aniline Point and Mixed Aniline Point of Petroleum Products and Hydrocarbon Solvents
D664 Test Method for Acid Number of Petroleum Products by Potentiometric Titration
D665 Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water
D892 Test Method for Foaming Characteristics of Lubricating Oils
D893 Test Method for Insolubles in Used Lubricating Oils
D974 Test Method for Acid and Base Number by Color-Indicator Titration
D1401 Test Method for Water Separability of Petroleum Oils and Synthetic Fluids
D1500 Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
D2270 Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 and 100°C
D2272 Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel
D3120 Test Method for Trace Quantities of Sulfur in Light Liquid Petroleum Hydrocarbons by Oxidative Microcoulometry
D3427 Test Method for Air Release Properties of Petroleum Oils
D4304 Specification for Mineral Lubricating Oil Used in Steam or Gas Turbines
D4310 Test Method for Determination of Sludging and Corrosion Tendencies of Inhibited Mineral Oils
D5185 Test Method for Determination of Additive Elements, Wear Metals, and Contaminants in Used Lubricating Oils and Determination of Selected Elements in Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES)
D5846 Test Method for Universal Oxidation Test for Hydraulic and Turbine Oils Using the Universal Oxidation Test Apparatus
D6186 Test Method for Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry (PDSC)
D6304 Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration
D6514 Test Method for High Temperature Universal Oxidation Test for Turbine Oils

3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 compatibility, n - of lubricating oils, the ability of lubricating oils to mix together without significant degradation of properties or performance.

3.1.1.1 Discussion - When a mixture of two oils has properties or performance significantly inferior to both of the constituent oils, then the two oils are incompatible. If the properties are inferior to those of one neat oil but not inferior to those of the other, then such is not necessarily considered an indication of incompatibility. To be considered significantly inferior, the property of the mixture would be worse than the poorer of the two neat oils by an amount exceeding the repeatability (or in the case of third party verification testing, the reproducibility) of the test method used to evaluate the property. (See fail and pass.)

3.1.2 fail, n - in compatibility testing of oil mixtures, a test result that is inferior to that of the poorer of the two constituent oils by an amount exceeding the repeatability of the test method used for the evaluation.

3.1.3 pass, n - in compatibility testing of oil mixtures, a test result that is equal to or better than that of the poorer of the two constituent oils.

3.1.4 primary compatibility tests, n - of lubricating oils, those test methods employed in the Tier 2 method to evaluate the impact on performance properties when circumstances indicate the need for additional testing.

3.1.4.1 Discussion - The test methods considered the most relevant in the evaluation of turbine oils, insofar as they provide the most information with the least expenditure of testing resources.

3.1.5 secondary compatibility tests, n - of lubricating oils, those test methods used to evaluate compatibility when the primary compatibility tests are insufficient or inconclusive.

3.1.5.1 Discussion - Such tests are driven by the critical features of a given application. For example, if the application subjects the oil to extraordinary high temperature an evaluation of the onset of oxidation at various temperatures using differential scanning calorimetry to construct an Arrhenius plot may be warranted. Aniline Point might be added to evaluate the relative difference in solvency characteristics. Secondary compatibility tests are suggested, but not required, by this practice.

3.1.6 type and grade, n - Type and grade refer to lubricants of the same general type such as Rust and Oxidation Inhibited turbine oil (R) and ISO Viscosity grades

3.1.7 10:90 mixture, n - a uniform blend of 10 % by volume of one oil with 90 % by volume of a second oil.

3.1.8 50:50 mixture, n - a uniform blend of 50 % by volume of each of two component oils.

3.1.9 90:10 mixture, n - a uniform blend of 90 % by volume of one oil with 10 % by volume of a second oil.