23rd International Colloquium Tribology - January 2022 391 Improved Oil Condition Monitoring of Industrial Gear Oils Dipl.-Ing. Rüdiger Krethe OilDoc GmbH, Kerschelweg 28, 83098 Brannenburg, OELCHECK GmbH, Kerschelweg 28, 83098 Brannenburg Dr. Thomas Fischer OilDoc GmbH, Kerschelweg 28, 83098 Brannenburg, OELCHECK GmbH, Kerschelweg 28, 83098 Brannenburg Summary Oil oxidation is the most important process in oil aging for almost all industrial lubricants. New application areas and requirements for much longer oil drain intervals lead to a strong increase in the use of synthetic gear oils. Typical test patterns like viscosity, acid content and IR oxidation are not sufficient for a reliable oil condition monitoring of synthetic gear oils particularly in large industrial gearboxes. The paper demonstrates the principle and application of new methods in oil condition monitoring. It includes a number of field examples from different applications to demonstrate the value of the new methods and to give a basic evaluation guide for application. 1. New lab methods of Oil Condition Monitoring 1.1 Oxidation Index FT-IR based methods are used to detect oxidation in mineral oils for decades. In Europe this method is standardised in DIN 51543 / 6/ . The oxidation level in industrial applications like gearboxes is appr. 10 - 20 times lower than in combustion engines. Therefore, a single wave-number based oxidation test methods like standardised in DIN 51453 is not able to detect oxidation in industrial applications reliable and on an early stage. The Oxidation Index is based on the monitoring of an area instead of a single wavenumber, like shown in figure 1. Figure 1: Oxidation detection using FT-IR. Single wavenumber based versus area-based. The oxidation process generates different species of products. Especially when ongoing on a low level, a single wave-number based methods becomes unreliable. This way, the area-based method produces much more reliable results. It allows the oxidation detection on an early stage and a trend evaluation when sampling on regular basis. 1.2 Additive depletion Much more stable synthetic base oils move the focus from the oxidation detection more to the additional monitoring of additive condition to provide a reliable forecast for scheduling the oil drain interval. For the detection of additive condition are different methods suitable, for example: • Infrared spectroscopy (FT-IR, antioxidants, antiwear, EP) / 7/ • Linear voltammetry (RULER, antioxidants) / 4/ • High-pressure liquid chromatography (HPLC) for the thiazoles (anti-corrosion) / 8/ In order not to go beyond the scope of this publication, we refer in this respect to the literature references 1.3 Deposit potential testing The MPC (Membrane Patch Colorimetry) was initially developed to monitor the tendency of deposit generation of turbine oils / 9/ . A special membrane patch is generated. The deposits on the membrane patch are evaluated by colorimetry (reflected light). The MPC test result is calculated by luminance and special color distribution. This test was adopted to detect the tendency of deposit generation for other applications like hydraulic systems, gear boxes or other XXL lubrication systems with success. 392 23rd International Colloquium Tribology - January 2022 Improved Oil Condition Monitoring of Industrial Gear Oils 2. Conclusion The reliable oil condition monitoring of modern industrial gear oils needs more detailed analysis methods and evaluation rules. Typical test patterns like viscosity, acid content and IR oxidation are not sufficient for a reliable oil condition monitoring of synthetic gear oils particularly in large industrial gearboxes. Oil oxidation is the most important process in oil aging for almost all industrial lubricants. Due to the higher saturation level of modern mineral oil based, but much more synthetic base oils the ongoing of oil oxidation is harder to detect reliable. The Oxidation Index, a new area-based IR-method provides more reliable results, even when measuring PAO based, ester containing oils. Additive depletion is not only a sign of reduced useful life of the oil filling, but often the cause of significant deposit generation in gearboxes and higher effort to clean up the gearbox during oil change. Considering the increased use of synthetic base oils the monitoring of additive depletion becomes much more important. References [1] Krethe, R., Handbuch Ölanalysen (Manual of oil analysis, German), expert-Verlag, Tübingen, 2020, ISBN 978-3816934998 [2] Jensen et al, Initiation in hydrocarbon autooxidation at elevated temperatures. International Journal of Chemical Kinetics 22, (1990) [3] Krethe, Fischer, New Method for oxidation detection in industrial lubricants, International Colloquium of Industrial and Automotive Lubrication, Ostfildern, 2020 [4] Ameye, Jo, Krethe Rüdiger: Linear Sweep Voltammetry (RULER©) - An innovative approach for Looking Forward to Lubricant Oxidation. Part I: Fundamentals, Part II: Determination of Remaining Useful Lifetime of Lubricating Oils, Application and Examples. 15th International Colloquium Tribology, Ostfildern, 2006 [5] OELCHECK: Oil analysis reports (internal). www. oelcheck.de. [6] DIN 51453: 2004-10. Testing of lubricants - Determination of oxidation and nitration of used motor oils - Infrared spectrometric method (Prüfung von Schmierstoffen - Bestimmung der Oxidation und Nitration von gebrauchten Motorenölen - Infrarotspektrometrisches Verfahren). Beuth-Verlag. www.beuth.de [7] OilDoc GmbH: Additives in lubricating oils and their condition monitoring. 2020, online-training in 2 modules. www.oildoc.com or https: / / elopage. com/ s/ oildoc [8] Monitoring of nonferrous metal passivators in gear oils - Proactive copper wear detection in wind turbine. (part I and II), Dr. T. Fischer, Dipl.-Ing. S. Mitterer, OilDoc Conference, Rosenheim, 2019 [9] ASTM D7843-18. Standard Test Method for Measurement of Lubricant Generated Insoluble Color Bodies in In-Service Turbine Oils using Membrane Patch Colorimetry [10] Krethe, Rüdiger; Bots, Steffen: Particle Counting of In-service lubricants: Lab analysis meets reality. Reliable Plant Conference, Louisville, April 5 - 7, 2016