ASTM D6186 Standard Test Method for Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry (PDSC)

Get Certified ASTM D6186 Testing for Reliable Lubricant Oxidation Stability Data 

Lubricating oils are more prone to oxidation once it begins, which causes the formation of sludge, varnish, and other acidic by-products that can affect the performance of engines and other equipment. ASTM D6186 offers the chemical analyzer a rapid pressure differential scanning calorimetry method for estimation of oxidation stability of lubricants in considerably less time than other oxidation test methods. Chemists use ASTM D6186 results for research and development, quality control, and specification testing of an extensive range of lubricating oils.

• Determines the oxidation induction time of lubricating oils under oxygen pressure of 3.5 MPa (500 psig).
• Applies to test temperatures within the range of 130 °C to 210 °C.
• Expresses values in SI units (MPa) as primary; the psig (pounds per square inch gauge) are included for information purposes only.
• Requires only a very small oil sample compared with longer-running oxidation stability tests.
• States that there has not been an established correlation between oxidation induction time results and service performance in actual operating conditions.

What are the Uses of ASTM D6186 Testing? 

ASTM D6186 testing allows chemists to determine the oxidation stability of a lubricating oil through a rapid, low-sample-consumption procedure. Formulators then use the results to compare additive packages and screen new oil blends quickly. This standard-

• Determines the relative oxidation stability of different lubricating oil formulations.
• Supports research and development work on new lubricant additive packages.
• Assists manufacturers in using oxidation induction time as an internal quality control checkpoint.
• Provides a faster alternative to longer oxidation stability tests when screening many samples.
• Assists in specification testing for lubricating oils intended for demanding service conditions.

Which Materials Can Be Tested Under ASTM D6186? 

ASTM D6186 specifies that this test method applies to lubricating oils designed for use in engines, industrial, turbine, or other mechanical equipment where oxidation resistance is important. The test method applies to small liquid oil samples placed directly into a cell of the pressure differential scanning calorimeter. Before testing, a chemist selects a representative oil sample and sets the target isothermal temperature between 130 and 210 degrees Celsius, based on the oil’s anticipated service temperature.

Why is ASTM D6186 Important? 

ASTM D6186 gives lubricant formulators and users a rapid primary screening test in order to avoid the need for a longer and more resource-intensive oxidation test. As oxidation is normally the primary reaction that leads to lubricant degradation to sludge, varnish, and acidic byproducts, an oil with a low induction period may be more susceptible to these lubricant problems. Due to the short analysis time and reduced sample size needed for this test method, it can be used for rapidly comparing numerous candidate lubricant formulations or additive packages during lubricant development, though the standard is clear that the results of this testing do not show a direct correlation to service performance.

ASTM D6186 Testing Process and Data Collection 

A chemist weighs a small oil sample into an open pan and transfers it into a pressure differential scanning calorimeter cell. The chemist seals the cell and pressurizes it with oxygen to 3.5 MPa, then heats the sample to the selected isothermal temperature in the range of 130°C and 210°C. The calorimeter observes the flow of heat from the sample throughout the isothermal hold, and the chemist identifies the point at which a sharp exothermic reaction signifies the initiation of oxidation. The analyst records the elapsed time as the oxidation induction time for the respective sample.

Common Challenges and Troubleshooting 

Accurate ASTM D6186 relies upon a properly calibrated calorimeter with consistent sample masses and stable oxygen pressure throughout the test, as trace metal contamination or irregular sample pan material facilitates catalysis of oxidation with unpredictable consequences for induction time. Chemists use clean sample pans, verify pressure and temperature calibration regularly, and prepare each sample consistently to keep results comparable.

• The analyst provides oxidation induction time in minutes from initiation of the isothermal step to the onset of the exothermic oxidation reaction
• The report provides the temperature and pressure at which the measurement was taken, as these variables directly impact the oxidation induction time
• The analyst compares the induction time to a reference oil or a target specification, rather than providing pass/fail criteria
• The report notes that a longer induction time indicates greater apparent oxidation resistance under test conditions, but no relationship to actual service life is implied

Link to ASTM D6186