ASTM D7412-Condition Monitoring of Phosphate Antiwear Additives in In-Service Petroleum and Hydrocarbon Based Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry
Signiﬁcance and Use
5.1 Antiwear additives are commonly used in petroleum and hydrocarbon based lubricants to prevent machinery wear by forming a chemical barrier activated by frictional heat. Anti-wear additives that are phosphate based can be measured by FT-IR spectroscopy using the phosphate absorption band. Initially, phosphate antiwear additives will decompose and form a protective ﬁlm by binding to metal surfaces and through oxidative mechanisms, and so a decrease in the level of phosphate antiwear additive relative to that in the new oil is expected during normal machinery operation. Subsequently, signiﬁcant depletion of phosphate antiwear additives due to oxidation or hydrolysis can occur when the lubricant is subjected to high temperatures and high levels of moisture. This usually occurs prior to the point where the oxidation of the lubricant begins to accelerate, making trending of phosphate antiwear additives a useful indicator of the lubricant’s remaining in-service life. Monitoring of phosphate antiwear additive depletion is therefore an important parameter in determining overall machinery health and should be considered in conjunction with data from other tests such as atomic emission (AE) and atomic absorption (AA) spectroscopy for wear metal analysis (Test Method D5185), physical property tests (Test Methods D445 and D2896) and other FT-IR oil analysis methods for oxidation (Test Method D7414), sulfate by-products (Test Method D7415), and nitration (Test Method D7624), which also assess elements of the oil’s condition.
1.1 This test method covers monitoring phosphate antiwear 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 wear. Typical phosphate antiwear additives include zinc dialkyldithiophosphates, trialkyl phosphates, and triaryl phosphates.
1.2 This test method uses Fourier Transform Infrared (FT-IR) spectrometry for monitoring of phosphate antiwear additive depletion in in-service petroleum and hydrocarbon based lubricants as a result of normal machinery operation. Monitoring the depletion of phosphate antiwear additives in in-service lubricants can indicate unusual wear or severe operating conditions of the machine. This test method is designed as a fast, simple spectroscopic check for monitoring of phosphate antiwear 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 phosphate antiwear additives in the oil.
1.3 Acquisition of FT-IR spectral data for measuring phosphate antiwear additives in in-service oil and lubricant samples is described in Practice D7418. In this test method, measurement and data interpretation parameters for phosphate antiwear 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 phosphate antiwear 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, see Ref (1).2
1.4.1 For direct trend analysis, values are recorded directly from absorption spectra and reported in units of absorbance per 0.1 mm pathlength.
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 centimeter).
1.4.3 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 phosphate antiwear additives to equipment performance.
NOTE 1—It is not the intent of this test method to establish or recommend normal, cautionary, warning, or alert limits for any machinery. Such limits should be established in conjunction with advice and guidance from the machinery manufacturer and maintenance group.
1.5 This test method is for petroleum and hydrocarbon based lubricants and is not applicable for ester based oils, including polyol esters or phosphate esters.
Extracted, with permission, from ASTM D7412-21-Condition Monitoring of Phosphate Antiwear Additives in In-Service Petroleum and Hydrocarbon Based Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be purchased from ASTM International, astm.org