1. Scope

1.1 This test method covers monitoring phenol antioxidant additives in in-service petroleum and hydrocarbon-based lubricants such as various types of engine oils, hydraulic oils, and other lubricants that are formulated for protection against oxidation. Typical phenol antioxidant additives include sterically hindered, alkyl-substituted phenols such as 2,4,6-Tri-tert-butylphenol (2,4,6-TTBP), 2,6-Di-tert-butylphenol (2,6-DTBP), or 2,6-Di-tert-butyl-p-cresol. 1.2 This test method uses Fourier transform infrared (FTIR) spectrometry for monitoring of phenol antioxidant additive depletion in in-service petroleum and hydrocarbon-based lubricants as a result of normal oil aging. Monitoring the phenol antioxidant in in-service lubricants can indicate severe operating conditions before a degradation of the base oil itself. This test method is designed as a fast, simple spectroscopic check for monitoring of phenol antioxidant additives in in-service petroleum and hydrocarbon-based lubricants with the objective of helping diagnose the operational condition of the machine based on measuring the level of phenolic compounds in the oil. 1.3 Acquisition of FT-IR spectral data for measuring phenol antioxidant additives in in-service oil and lubricant samples is described in Practice D7418. In this test method, measurement and data interpretation parameters for phenol antioxidant additives using both direct trend analysis and differential (spectral subtraction) trend analysis are presented. 1.4 This test method is based on trending of spectral changes associated with phenol antioxidant additives in in-service petroleum and hydrocarbon-based lubricants. Warnings or alarm limits can be set on the basis of a fixed minimum value for a single measurement or, alternatively, can be based on a rate of change of the response measured. 1.4.1 For direct trend analysis, values are recorded directly from absorption spectra and reported in units of absorbance per 0.1 mm path length. 1.4.2 For differential trend analysis, values are recorded from the differential spectra (spectrum obtained by subtraction of the absorption spectrum of the reference oil from that of the in-service oil) and reported in units of 100*absorbance per 0.1 mm pathlength (or equivalently absorbance units per centimetre). 1.4.3 For the calculation of remaining phenolic antioxidant, values are recorded directly from absorption spectra of both, the new oil and the in-service oil in units of absorbance per 0.1 mm pathlength. Remaining antioxidant concentration is calculated as the peak height in the in-service oil relatively to the peak height in the new oil. 1.4.4 In either case, maintenance action limits should be determined through statistical analysis, history of the same or similar equipment, round robin tests, or other methods in conjunction with the correlation of changes in the level of phenolic antioxidant additives to equipment performance. 1.5 Units--The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard. 1.5.1 ExceptionThe unit for wave numbers is cm-1. 1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Keywords

condition monitoring; differential trend analysis; direct trend analysis; Fourier transform infrared; FT-IR; hydrocarbon-based lubricants; in-service petroleum lubricants; infrared; IR; lubricants; oils; phenol antioxidant

Rationale

This new standard provides a fast but reliable spectroscopic method for the determination of phenolic compounds in lubricating oils. phenolic compounds are widely used in engine, hydraulic, and many other oils to protect against oxidation. Knowledge of the remaining antioxidant can help machinery operators recognizing severe operating conditions before base oil degradation and machinery failure.

The title and scope are in draft form and are under development within this ASTM Committee.