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in the new oil interact with oxidised oil, potentially improving formulations to reduce sludge and varnish formation. The benefit is enhanced predictive capability and optimised additive packages to improve the stability and cleanliness of turbine oils. This test offers a more realistic assessment of the oil’s performance over time.
Example of test results
The graph below illustrates the determination of oxidation lifetime based on a 25% RPVOT ratio and the impact of replacing 50% of the oil:
extended parameters at different oxidation states for 12 weeks when the test is carried out at 120°C and including tests like Viscosity, TAN, RPVOT, RULER and MPC.
By using the same accelerated oxidative process specified in ASTM D7873, alongside standardised test methods such as FTIR, MPC, RULER, RPVOT, insoluble material content, TAN, viscosity, metals, and deposit evaluation, the results and findings can be correlated to actual field performance.
Ammonia TOST
Ammonia has a Global Warming Potential (GWP) and Ozone Depletion Potential (ODP) of zero. It is commercially available worldwide, can be produced in a greenway and has an acceptable energy density, making it an environmentally friendly choice.
Oxidation tests using ammonia in combination with air have been developed primarily for two purposes:
Inertness to ammonia for compressor oils (ammonia compressors)
The following graph illustrates the impact of top-ups on the increase of insoluble materials:
The aim of this test is: • To ensure that lubricants do not react chemically with ammonia, which can lead to the formation of harmful deposits and reduce the efficiency of the compressor.
• To confirm that the lubricant maintains its properties and performance in the presence of ammonia.
Based on the information provided by these graphs, we can conclude that regular top-ups combined with oil monitoring can significantly extend the oil’s life. However, precautions should be taken to avoid the accumulation of insoluble materials. If regular top-ups are performed, it is advisable to combine them with efficient oil filtration.
TOPP (Turbine Oxidation Performance Prediction) TOPP has been developed by Fluitec to assess the physical and chemical alterations of turbine oil. This test is an alternative to the Dry-TOST, evaluating
44 LUBE MAGAZINE NO.187 JUNE 2025
In this test, a mixture of air (8.6 l/h) and ammonia (1.4 l/h) bubbles through 300 ml of oil in the presence of a copper coil. Water (0.1%; 0.3 ml) is added at the beginning of the test and every 24 hours. The test runs for 150 hours at 125°C, and the oil is analysed at the end of the test based on the following criteria: • Total Acid Number (mg KOH/g) • Organic Insolubles (wt%) • Soluble Copper (ppm)
Ammonia contamination can lead to rapid oxidation of the oil. This occurs when aqueous ammonia in the oil reacts with copper alloy components, producing oil-soluble copper complexes that act as powerful catalysts. The consequences are overheating, deposit formation, and sticking.
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