ASTM D7414 Standard Test Method for Condition Monitoring of Oxidation in In-Service Petroleum and Hydrocarbon Based Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry
4. Summary of Test Method
4.1 This test method uses FT-IR spectrometry to monitor oxidation levels in in-service petroleum and hydrocarbon based lubricants. The FT-IR spectra of in-service oil samples are collected according to the protocol for either direct trend analysis or differential trend analysis described in Practice D7418, and the levels ofoxidation are measured using the peak height or area measurements described herein.
5. Significance and Use
5.1 A large number of compounds, such as aldehydes, ketones, esters, and carboxylic acids, are produced when oils react with atmospheric oxygen. Oxidation is measured using a common FT-IR spectral feature between 1800 and 1670 cm(-1) caused by the absorption of the carbonyl group present in most oxidation compounds. These oxidation products may lead to increased viscosity (causing oil thickening problems), acidity (causing acidic corrosion), and formation of sludge and varnish (leading to filter plugging, fouling of critical oil clearances and valve friction). Monitoring of oxidation products 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 D6304), base reserve (Test Method D2896 and D4739), acid number tests (Test Methods D664 and D974) and other FT-IR oil analysis methods for nitration (Practice E2412), sulfate by-products (Test Method D7415), additive depletion (Test Method D7412), breakdown products and external contaminants (Practice E2412), which also assess elements of the oil's condition, see Refs (1-6).
6. Interferences
6.1 Various additive packages, especially those containing esters and carboxylic acids, such as some viscosity index improvers, pour point depressants, and rust inhibitors, can give false positives for oxidation. In addition, oils mixed with any synthetic ester based oil products will also give very high values for oxidation. One should trend the in-service oil against the new oil to help identify these interferences. In some oils the contributions from additive packages and synthetic ester based oils may be so high that oxidation cannot be reliably measured.
6.2 High levels of water contamination and soot will also interfere with the measurement of oxidation.
