ASTM D7624 Standard Test Method for Condition Monitoring of Nitration 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 nitration 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 of nitration are measured using the peak height measurements described herein.
5. Significance and Use
5.1 There is a wide variety of nitration compounds that may be produced and accumulate when oils react with gaseous nitrates formed during the engine combustion process. These nitration products may increase the viscosity, acidity and insolubles in the oil, which may lead to ring sticking and filter plugging. Monitoring of nitration 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, D6304, and D2896), and other FT-IR oil analysis methods for oxidation (Test Method D7414), sulfate by-products (Test Method D7415), additive depletion (Test Method D7412), and breakdown products and external contaminants (Practice E2412), which also assess elements of the oil's condition.
6. Interferences
6.1 Very high water levels can interfere with the nitration measurement.
6.2 Conjugated ketones, quinones, unsaturated carboxylic acids and carboxylic acid salts (formed due to the reaction of acids with overbased oil additives) are also sources of interference.
6.3 Some aromatic compounds may interfere as well.
