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Tribologie und Schmierungstechnik HERAUSGEGEBEN VON RÜDIGER KRETHE UND MANFRED JUNGK 1 _ 23 70. JAHRGANG eOnly SONDERAUSGABE Organ der Gesellschaft für Tribologie Organ der Österreichischen Tribologischen Gesellschaft Organ der Swiss Tribology eOnly Sonderausgabe Heft 1 | Dezember 2023 70. Jahrgang Herausgeber: Dr. Manfred Jungk Tel.: +49 (0)6722 500836 eMail: manfred.jungk@mj-tribology.com www.mj-tribology.com Redaktion: Dr. rer. nat. Erich Santner Tel.: +49 (0)2289 616136 / eMail: esantner@arcor.de Ulrich Sandten-Ma Tel.: +49 (0)7071 97 556 56 / eMail: sandten@verlag.expert Beiträge, die mit vollem Namen oder auch mit Kurzzeichen des Autors gezeichnet sind, stellen die Meinung des Autors, nicht unbedingt auch die der Redaktion dar. Unverlangte Zusendungen redaktioneller Beiträge auf eigene Gefahr und ohne Gewähr für die Rücksendung. Die Einholung des Abdruckrechtes für dem Verlag eingesandte Fotos obliegt dem Einsender. 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Aktuelle Informationen über die Fachbücher zum Thema „Tribologie“ und über das Gesamtprogramm des expert verlags finden Sie im Internet unter www.expertverlag.de Ihre Mitarbeit in Tribologie und Schmierungstechnik ist uns sehr willkommen! Impressum Tribologie und Schmierungstechnik Organ der Gesellschaft für Tribologie | Organ der Österreichischen Tribologischen Gesellschaft | Organ der Swiss Tribology Editorial 1 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0025 Dear readers, in the world of industrial maintenance, the professional use of lubricants and their service and monitoring is no longer just an option, but a central element for success and sustainability. This issue is dedicated to the innovations and challenges in the field of lubricants, operating fluids and condition monitoring. Find out how modern lubricants not only extend the service life of machines, but also contribute to reducing the CO2 footprint. Be inspired by expert opinions and practical examples to meet the challenges of the future with a wealth of knowledge. Rüdiger Krethe Editorial 2 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 Eine Zeitschrift des Verband Schmierstoff-Industrie e. V. SCHMIERSTOFF SCHMIERUNG www.sus.expert Hier können Sie die Zeitschrift kostenlos abonnieren. E R S C H E I N T V I E R M A L I M J A H R Inhalt 3 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 4 Greg Livingstone, Ludger Quick, Jo Ameye Managing Turbine Oils in a Sustainable Way 10 Rüdiger Schiffer Chromium-VI formation on high alloyed screws 13 Elona Rista, Greg Livingstone Applying knowledge from accelerated turbine oil aging tests to oil management programs 19 Nicholas Lancaster, Keith Cory Schomburg Rapid identification and quantification of ethylene and propylene glycol in engine coolant by gas chromatography 25 Jo Ameye, Greg Livingstone, Cristian Soto Managing hydraulic oil deposits by using novel solubility enhancing technology 31 Jeremy Sheldon, Mark Redding Combining Oil Health, Level, and Vibration to Achieve Complete Machine Monitoring 39 Sarah Hüttner, Verena Leumann, Rachel Kling Electrical contacts - the challenge for lubricants 45 Gregory Miiller, William VanBergen, Alexei Kurchan, David Gillespie, Gunther Mueller, Rico Pelz, Timothy Newcomb, Gregory Hunt Research and Development Utilizing the Conductive Layer Deposits and Wire Corrosion Bench Test Technology for Electric Vehicle Drivetrains 1 Editorial Research Vorab Tribologie und Schmierungstechnik Organ der Gesellschaft für Tribologie Organ der Österreichischen Tribologischen Gesellschaft Organ der Swiss Tribology 70. Jahrgang, eOnly Sonderausgabe 1 Dezember 2023 Veröffentlichungen Die Autoren wissenschaftlicher Beiträge werden gebeten, ihre Manuskripte direkt an den Herausgeber, Dr. Jungk, zu senden (Checkliste und Formatvorgaben siehe Umschlagseite hinten). Authors of scientific contributions are requested to submit their manuscripts directly to the editor, Dr. Jungk (see inside back cover for formatting guidelines). IHR ONLINE-ABONNEMENT DER TuS Ab dem Jahrgang 2019 können Sie die aktuellen Hefte der Tribologie und Schmierungstechnik im Online-Abonnement beziehen. Die Hefte der vergangenen Jahrgänge werden kontinuierlich integriert. Unsere eLibrary bietet Ihnen einen qualitativ hochwertigen und benutzerfreundlichen Zugang zum digitalen Buch- und Zeitschriftenprogramm der Verlage expert, Narr Francke Attempto und UVK. Nutzen Sie mit uns die Chancen der Digitalisierung: https: / / elibrary.narr.digital/ journal/ tus Der Online-Zugang ist in Kombination mit dem Print-Abo oder als e-only-Abo erhältlich. Abo-Service: Tel: +49 (0)7071 97 97 10 Fax: +49 (0)7071 97 97 11 eMail: abo@narr.de Weitere Inhalte zu den Themen Schmierung, Reibung und Verschleiß finden Sie unter www.narr.de/ technik. product’s use and how it is treated at the End of Life. Figure 1 illustrates these stages and identifies the difference between “cradle-to-gate” and “cradle-to-grave”. The CO 2 e contribution of extracting, refining and blending the crude oil (cradle-to-gate) makes up a smaller value of greenhouse gases compared to its End of Life (cradle-to-grave). Although antioxidants have approximately twice the carbon footprint of mineral oil, they contribute a relatively small amount to the overall total since they are used at a small percentage in the formulation. Depending on what part of the world the used oil is generated, the contribution of CO 2 e at the End of Life is defined by what percentage is incinerated or re-refined. Different base oils may also contribute more CO 2 e to the overall product. For example, Polyalphaolefins (PAOs) have about twice the cradle-to-gate CO 2 e footprint as mineral oils. However, the End-of-Life of both products Research 4 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0026 1 Introduction Many companies utilizing rotating equipment have either initiated, or plan to initiate, decarbonization strategies. This is a process which reduces and compensates the emissions of carbon dioxide equivalent (CO 2 e), ultimately down to “Net 0”. Lubricants are an essential component in rotating equipment, so it makes sense to determine optimum ways of managing these fluids in the most sustainable way possible, which includes enhancing their performance. Life Cycle Assessment (LCA) is a methodology for assessing environmental impacts associated with all the stages of the life cycle of a product and is the accepted tool to analyze the potential environmental impacts of products. It is therefore the optimum tool for measuring the sustainability of a lubrication program and comparing various products and strategies. The process of performing an LCA is defined in ISO 14040 and takes a thorough inventory of all the materials and energy required to make a product, calculating a cumulative potential environmental impact. Part of this calculation involves assessing various midpoint indicators, such as stratospheric ozone depletion, acidification, eutrophication, water scarcity and toxicity potential, but for the purpose of this paper, we’ll just focus on Global Warming Potential measured in CO 2 e. LCA is a useful tool for a variety of purposes. For example, how do you know if an electric vehicle will lower emissions compared to an internal combustion vehicle? What if the electric vehicle gets its power from a coal burning power plant? Doesn’t mining lithium and manufacturing batteries produce a lot of emissions? There are a lot of complexities with this question and the answer would not be possible without performing a cradleto-grave LCA. (Incidentally, there are many studies on this, and electric vehicles greatly reduce emissions over the life of the vehicle.) 2 Cradle-to-Gate vs Cradle-to-Grave When performing an LCA on a lubricant, one can look at various stages in the life of the product. Cradle-to- Gate represents the carbon impact of a product from its inception to the moment the product is ready for sale. This is the most common LCA done on lubricants, as manufacturers do not have control over the use of the product once it is sold. Cradle-to-Grave also covers the Managing Turbine Oils in a Sustainable Way Greg Livingstone, Ludger Quick, Jo Ameye* The majority of companies using rotating machinery have implemented decarbonization strategies that systematically analyze every part of their organization to try to adopt more sustainable practices. Lubricants are an essential component in rotary equipment, so it makes sense to find optimal ways to manage these fluids in the most sustainable way, including improving their performance. Life Cycle Analysis (LCA) is the recognized tool for assessing the overall environmental impact of a product from cradle to grave and is useful to compare different liquid management strategies. This paper outlines several ways in which turbine oils can be managed more sustainably by considering the life cycle assessment of different practices. Keywords rotating machinery, decarbonization strategies, Life Cycle Analysis (LCA), lubricants, cradle to grave, turbine oils Abstract * Mr. Greg Livingstone, Fluitec, Bayonne, USA Dr. Ludger Quick, Siemens Energy, Muelheim/ Ruhr, Germany Mr. Jo Ameye, Fluitec, Dordrecht Netherlands is the same representing a larger percentage. The overall CO 2 e contribution of a mineral turbine oil versus a PAO turbine oil is illustrated in Figure 2. Therefore, effort to extend the life of in-service oil will have a significant impact on lowering the total carbon footprint of a lubricant. It is also interesting to note that transportation plays a minor role in the overall carbon footprint. This is the case as long as lubricants are not being flown around the world. 3 Comparing Lubricant Sustainability There are many factors that go into measuring the sustainability of a lubricant. Figure 3 illustrates these various factors and pathways to make the lubricant more sustainable. Using a comparison like this, it is possible to compare the sustainability of various lubricants and lubrication practices. Keep in mind that each category can be converted to kg CO 2 e, except for environmental performance, which is its own category. Biodegradability performance, bioaccumulation results and the oil’s toxicity rating are important aspects of the sustainability of the oil, but those qualities must be directly compared since they are on a different scale. Based on this spectrum, the ultimate sustainable lubricant would be one that is plant-based (oleo sourced) and Research 5 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0026 Figure 3: Factors influencing the sustainability of a lubricant Figure 2: Cradle-to-gate CO 2 e comparison between mineral and PAO turbine oils Figure 1: Stages of a Lubricant’s Life ples illustrate that the product with the highest cradleto-gate carbon footprint is not necessarily the one with the lowest carbon footprint once a cradle-to-grave analysis is completed. 4.1 Case Study 1: Avoiding a “Varnish Flush” Maintaining a turbine oil with low varnish potential has many financial benefits for a power plant. In addition to increased availability and reliability, one may avoid having to do a “varnish flush” in between oil changes. Flushes are both energy and volume intensive which accumulates to a sizeable carbon footprint. Fluitec has invented a solubility enhancing technology called DECON which decontaminates lube oil systems in between oil changes. Among other benefits, the technology allows rotating equipment users to avoid having to do a varnish flush in between oil changes. The following case examines the sustainability impact of adding 3 % DECON to an in-service turbine oil to avoid having to perform an oil flush. In this example, we use a gas turbine oil with a 5,000-gallon reservoir and an eight-year life span. The Fluitec Value Impact Calculator adds the cost and carbon footprint of adding DECON to the fluid and measures the value of not having to perform a flush during the next oil change. The results can be viewed in Figure 4. By using DECON and avoiding having to perform a lube oil system flush, this turbine can avoid generating 18 metric tons of CO 2 e per year. A calculation like this would be challenging without performing a cradle-to-grave LCA. As with most sustainable lubrication practices, avoiding a Varnish Flush also saves considerable money for the power plant as well. Research 6 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0026 made from renewable energy; one which is readily biodegradable, non-toxic and doesn’t have bioaccumulation; one which provides a long service life and improves the energy efficiency of the system it is lubricating; and finally at the end of this ideal fluid’s life, it is re-refined or re-used in another application. Also, for a sustainable lubricant to be practical, it needs to be fully compatible with the application, including materials of construction and contamination ingression. For example, an oleo-based ester may tick all the boxes but may shrink system seals and hydrolyze due to high water contamination, making it unsuitable for a specific application. 4 Lubricant Sustainability Case Studies Following are two examples of comparing the sustainability of different lubricants by using LCA. The exam- Figure 4: Example of the high carbon footprint involved in lube oil flushing and how maintaining a low varnish potential in your turbine oil reduces your carbon footprint 4.2 Case Study 2: Replenishing Turbine Oil Antioxidants instead of performing an oil change Antioxidants are sacrificial components in turbine oil formulations. The life of a turbine oil is largely dictated by the rate of antioxidant depletion, with the condemning limit by most OEMs and industry bodies stating that action needs to be taken when the antioxidants reach 25 % of their original value. The traditional approach when the life of the antioxidants has been consumed and the oil is at the end of its life is to drain, flush, and recharge the system with new turbine oil. However, this consumes outage resources and is expensive so many plants have considered simply replacing their antioxidants instead. Custom made antioxidant concentrates can be added to turbine oils in situ, provided the correct up-front, qualification tests are performed to certify compatibility. This emerging practice has been done successfully in hundreds of turbines and is a cost-saving alternative to the old model of dump and replace. It seems that this would also be environmentally beneficial, however, to quantify this, an LCA is required. Below is an example of large frame cogeneration system with single shaft configuration. Since this system is in Eastern Europe, a whole new set of assumptions are required compared to the first case study. Transportation and the percentage of oil that is rerefined versus incinerated are two examples. Figure 5 shows the results of adding an antioxidant concentrate (DE- CON AO) to the in-service oil. In this case, over 200,000 kgs CO 2 e are estimated to be saved over a 10year period, which translates to more than 75 kgs CO 2 e per day. The power plant also benefits from cost savings, waste reduction and other advantages. 5 Other Strategies to Manage Oils in a more Sustainable Way There are multiple other lubricant management strategies that can lower the carbon footprint of your lubricant program, including: • Selecting the best performing oil for your application resulting in longer drain intervals and lower maintenance costs. • Implementing an Oil Analysis Program to optimize the drain intervals of your oils. Keep in mind that not acting when oil analysis warrants it, not only increases maintenance costs but can also dramatically increase your carbon footprint. • Avoiding Varnish. In addition to failed components, deposits can create an insulating layer on bearing surfaces resulting in higher temperatures, lowering the energy efficiency of the system. Research 7 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0026 Figure 5: Value Calculator of using DECON AO instead of performing an oil change References Livingstone, G. (2023). Measuring and Attaining Sustainable Lubrication. Precision Lubrication Magazine. https: / / precisionlubrication.com/ articles/ sustainable-lubrication/ Bieker, G. (2021). A Global Comparison of the Life-Cycle Greenhouse Gas Emissions of Combustion Engie and Electric Passenger Cars. The International Council of Clean Transportation. European Climate Foundation and the Climate Imperative Foundation. Fehrenbach, H. (2005). Ecological and Energetic Assessment of re-refining used oils to base oils. Institut für Energieund Umweltforschung GmbH (IFEU), a study commissioned by GEIR-Groupement Européen de l’Industrie de la Régénération. Fluitec. (2022). Life Cycle Assessment. Bayonne, NJ: Fluitec International, LLC. Life Cycle Assessment. (kein Datum). Von Wikipedia: https: / / en.wikipedia.org/ wiki/ Life-cycle_assessment abgerufen Muralikrishna, I. a. (2017). Life cycle assessment - an overview. Science Direct Topics. Environmental Management Science and Engineering for Industry. Raimondi, A. e. (2012). LCA of Petroleum-based lubricants: state of art and inclusion of additives. The International Journal of Life Cycle Assessment, DOI: 10.1007/ s11367-012-0437-4 , 987-996. Taylor, R. e. (2005). Lubricants & Energy Efficiency: Life Cycle Analysis. Life Cycle Tribology. (2017). Tribology Opportunities for Enhancing America’s Energy Efficiency. Advanced Research Projects Agency - Energy at the US Department of Energy. Wernet, G. B.-R. (2016). The ecoinvent database version 3 (part I): overview and methodology. The International Journal of Life Cycle Assessment, 1218-1230. Young, J. E. (2020). Energy Efficient Industrial Lubricants: Reducing Energy Consumption with Industrial Lubricants. Pennsylvania Statewide Technical Reference Manual - Work Paper. Research 8 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0026 • Re-refining an Oil at the End of its Life. Creating a circular economy with your lubricant at the end of its life by re-refining instead of incinerating will reduce the carbon footprint of your lubricant program. • Minimizing Contamination Ingression. Studies have shown that contamination is responsible for as much as 70 % of premature machinery failures. Deploying a strong contamination control program not only saves significant operational costs but will also reduce associated carbon footprint. 6 Summary As the saying goes, “If it doesn’t get measured, it doesn’t get managed”. In the case of achieving sustainable lubrication, using cradle-to-grave LCA principles allows you to measure and improve the sustainability of your lubricant program. This paper illustrates how to perform these calculations, and as the case studies illustrated, the initial carbon footprint of the lubricant does not necessarily mean decreased sustainability. Performing these LCA studies allows users to easily identify areas for improvement and can quantify the benefits. These calculations can also shed some light into the practices which should be negated to assist in the decarbonization efforts, such as lube oil flushing as illustrated in Case Study 1. The carbon footprint of lubricants may seem small, especially if one does not consider “product use” in LCA equations. However, tribology in general can have a tremendous impact on lowering society’s carbon footprint. A report to ARPA-E in 2017 calculated that 24 % of energy can be saved annually through tribology efforts. Measuring these efforts start with cradle-to-grave Life Cycle Assessments. Research 9 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 Wir bilden weiter! TAE-Zerti昀katslehrgänge 24 th International Colloquium Tribology Industrial and Automotive Lubrication at TAE Join the leading event on tribology, additives and sustainable lubrication in Europe. Be part of it and save the date! Program highlights: Ost昀ldern/ Stuttgart, Germany 23. - 25. January 2024 Information and registration: www.tae.de/ go/ tribology Organizer: Technische Akademie Esslingen e.V., An der Akademie 5, 73760 Ost昀ldern/ Germany Contact: susan.ferront@tae.de, T +49 711 340 08 - 96, www.tae.de Share experiences with tribologists from all over the world! - 130 presentations in 5 parallel sessions over 3 intense days - unique mix of industry and research in the 昀eld of friction and lubrication - industrial exhibition and social program - international business networking and career development Einstieg jederzeit möglich Einstieg jederzeit möglich Oberflächen Spezialist (TAE) Lehrgang (60163) 13. Mrz. - 24. Okt. 2024 4 Module à 1 Tag Tribologie Experte (TAE) Lehrgang (60160) 07. Feb. - 28. Nov. 2024 10 Module à 1 Tag 3 Dangers of chromium VI compounds The use of chromium VI has been restricted throughout the EU since 2013 and is only possible with the appropriate approval in defined uses until September 2024. Corresponding chromium VI-free alternatives are available and have proven themselves in practice. The uncontrolled formation of chromium VI, e.g., with HT screw pastes in combination with high-alloy steels, is a significant risk for maintenance staff, especially from a health point of view. Chromium VI has a strong carcinogenic (carcinogenic) and mutagenic effect. In addition, chromium VI is very toxic, 0.6 g taken orally has a fatal effect on humans. (Figure 3) Research 10 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0027 1 Emergence of the problem High temperature (HT) screw pastes have been used successfully in almost all areas of industry for decades. Without these pastes, the correct assembly of a high-alloy screw connection is not possible. And they then facilitate their non-destructive dismantling. Over the years, the pastes have evolved: from metal-containing pastes (copper, aluminum, or nickel alloy pastes) to metal-free pastes (“ceramic pastes”) towards high-purity pastes to exclude reactions with the screw material in critical applications and to improve the function of the connection so that it cannot be influenced even under extreme conditions. (Figure 1) Chromium-VI formation on high alloyed screws Rüdiger Schiffer* HT screw pastes, high-alloy screw connection, dangers, chromium VI-free alternatives, detection Keywords * Rüdiger Schiffer OKS Spezialschmierstoffe GmbH, Germany Figure 1 Figure 3 At the end of 2020/ beginning of 2021, chrome VI was detected when high-alloy screw connections in turbines were dismantled. Subsequent investigations found that calcium hydroxide, one of the essential components of modern HT screw pastes, is the cause. 2 Formation of chromium VI in screw connections In the case of steels with a high chromium content, the calcium hydroxide acts as a catalyst and temperatures above 300 °C then promote the formation of chromate, including chromium VI. (Figure 2 right) Chromium VI is also known as a contact allergen which has a skin-irritating effect (e.g., in the past when leather was made). So, there are good reasons to prevent the uncontrolled formation of chromium VI if possible. 4 Detection of chromium VI compounds The knowledge gained about the formation of chromium VI with certain material combinations and operating conditions naturally raised the question of how the formation of chromium IV in high-alloy, chromium-containing steels can be prevented in combination with the high-temperature pastes that are currently commercially available, since most of these HT screw pastes contain calcium hydroxide. To do this, however, a methodology first had to be developed to reliably simulate the formation of chromium VI without exposing the employees in the laboratory to its dangers. Standard stainless steel balls, such as those used in roller bearings, are completely immersed in the paste and stored in an oven for a certain period of time at a temperature well in excess of 300 °C. The remains of the paste then remaining on the surface of the balls were dissolved in water. This makes it relatively easy to detect and measure chromium VI. As soon as the residues are dissolved, you can see whether little or much chromium VI has been formed. Light yellow indicates little or no chromium VI, pink or violet rather a lot. The chromium VI content of the solution is then measured. (Figure 4) 5 Solution approach Theoretically relatively simple: A - if possible white or light-colored - HT screw paste only without calcium hydroxide with largely comparable technical properties in terms of temperature range, coefficients of friction and dismantling. In addition, free of disruptive substances such as Sulphur, chlorine, etc. and - perhaps also - suitable for use in food technology. (Table 1) In practice, it wasn’t that easy after all. The coefficients of friction on V2A and V4A were initially much too high. 6 First results In the meantime, the development of an HT screw paste that does not form chromium VI in combination with high chromium steels has been largely completed. At less than 0.05 ppm, the formation of chromium VI is below the detection limit of our measuring devices. The coefficients of friction on different surfaces lie reliably in the range of µ total = 0.14 with µ thread = 0.16 and µ head = 0.12 for V2A screws. The temperature range is more than 1,000 °C. The factor for the HT breakaway torque has not yet been determined, this will take place after the final release of the formulation. The light gray paste meets the requirements for NSF H1 registration. (Table 2) 7 Outlook A new generation of HT screw pastes comes onto the market. This new HT screw paste can really be used uni- Research 11 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0027 Figure 4 Criteria Standard Condition Unit Requirement Base Oil Type Synthetic Solid Lubricants Type Colour light colored Temperatur Range minimum service Temperature °C -30 maximum service Temperature Lubrication °C > 150 maximum service Temperature Separation °C > 900 Friction value DIN EN ISO 16 047 Screw ISO 4017 M10x55-8.8 black Nut ISO 4032 M10-10 black μ 0,12 DIN EN ISO 16 047 Screw ISO 4017 A2 M10x55-70 Nut ISO 4032 A2 M10-70 μ 0,12 HT- Break Loose Torque DIN 267-27 M10 A2, 40 Nm, 400°C, 100 h Nm < 2,5 x Tightening Torque Corrosion Protection Salt spray test ISO 9227 h, μm > 500, 50 Releases Food Industry NSF H1 Listings Customs world wide REACh conform SVHC not included RoHS conform Additional Requirements PFASfree not included Chrom-VIformation OKS Standard ppm < 0,05 Table 1 other technical requirements. In addition, this paste is suitable for industrial applications as well as for applications in food technology and comparable areas. Research 12 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0027 versally. The critical formation of chromium VI in highalloy steels in combination with extreme operating temperatures is reliably minimized without reducing the Criteria Standard Condition Unit Requirement New Paste Base Oil Type Synthetic Synthetic Solid Lubricants Type Solid lubricant mixture Colour light colored light grey/ grey Temperatur Range minimum service Temperature °C -30 not determined maximum service Temperature Lubrication °C > 150 not determined maximum service Temperature Separation °C > 900 > 1.000 Friction value DIN EN ISO 16 047 Screw ISO 4017 M10x55-8.8 black Nut ISO 4032 M10-10 black μ 0,12 not determined DIN EN ISO 16 047 Screw ISO 4017 A2 M10x55-70 Nut ISO 4032 A2 M10-70 μ 0,12 0,14 (μk 0,12, μg 0,16) HT- Break Loose Torque DIN 267-27 M10 A2, 40 Nm, 400°C, 100 h Nm < 2,5 x Tightening Torque not determined Corrosion Protection Salt spray test ISO 9227 h, μm > 500, 50 not determined Releases Food Industry NSF H1 H1 eligible Listings Customs world wide world wide REACh conform conform SVHC not included not included RoHS conform conform Additional Requirements PFASfree not included not included Chrom-VIformation OKS Standard ppm < 0,05 < 0,05 Table 2 1 Introduction What turbine oil should I buy? This is a frequent question of anyone operating turbomachinery. Although there may be up to 20 physical characteristics of a turbine oil found on the product specification sheet, there is no value on this document that predicts the longevity or performance of the fluid. Virtually all the formulations available on the market meet one or more OEM specifications. A new oil’s Rotating Pressure Vessel Oxidative Test (RPVOT) value is often suggested as a proxy for oil longevity, however, as will be discussed later, there is often no real correlation between high initial RPVOT and the oil’s longevity. Far too often, a turbine oil is selected by price as purchasing agents view all products meeting the required specification as equivalent. Turbine oils are not commodity products. Nor are they consumable products. They are just as integral in the operation of a turbine as a bearing. As when purchasing other assets, considering the total cost of ownership will yield the best investment. So how do you select a turbine oil? Or rather, how do you select a good turbine oil and how can you tell when often the field performance does not live up to the marketing hype? What we proposed and undertook was simulating accelerated operating conditions to conduct stress tests for various commercially available turbine oil formulations. This approach eliminates the inevitable variabilities in machinery and operating conditions which hinder a fair comparison between different oils’ performance and longevity in the field, creating instead a controlled testing environment where the only remaining variable is the oil formulation. 2 Turbine Oil Performance Prediction (TOPP) Test There are multiple accelerated aging tests specified by ASTM, such as: • D943 - Standard Test Method for Oxidation Characteristics of Inhibited Mineral Oils • D2272 - Standard Test Method for Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel • D4310 - Standard Test Method for Determination of Sludging and Corrosion Tendencies of Inhibited Mineral Oils • D6186 - Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry (PDSC) Although there are multiple degradation pathways a turbine oil faces when subjected to operational stress, the dominant failure mode in an operating system is oxidation. While each of the above stress tests exert oxidative stress on a turbine oil, they will not necessarily predict the performance of the fluid. To evaluate the performance of turbine oils, one needs to measure both the oxidative performance and the varnishing tendencies. One ASTM test method attempts to do this: D7873 - Standard Test Method for Determination of Oxidation Stability and Insolubles Formation of Inhibited Turbine Oils at 120 °C Without the Inclusion of Water (Dry TOST Method). However, the reporting system of the test procedure uses metrics not typically used in condition monitoring, so the results are not necessarily comparative to actual turbine oil perfor- Research 13 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0028 Applying knowledge from accelerated turbine oil aging tests to oil management programs Elona Rista, Greg Livingstone* Although there are multiple degradation pathways a turbine oil faces when placed in operation, the dominant failure mode is oxidation. By analyzing a turbine oil placed under accelerated oxidation conditions in a laboratory, much can be learned about how that oil will perform when placed in service. This paper reviews the test results of over a dozen commercially available turbine oils and identifies several findings that can be applied to better managing in-service oils. The paper also proposes a benchmarking tool to predict which turbine oil will perform better in the field. Keywords in-service oils, benchmarking tool, test methods, TOPP test, RPVOT correlation, ASTM D7873 Abstract * Elona Rista Solar Turbines, San Diego, USA Greg Livingstone Fluitec, Bayonne, NJ It is often assumed that varnish formation follows the following process: Oxidation -> Antioxidant Depletion & Diminished Oxidative Stability -> Varnish formation. However, this is not necessarily the case. As can be seen in Table 1, there is not necessarily a correlation between oxidative stability and varnish formation. Turbine Oil 1 was able to retain the vast majority of its RPVOT value throughout the experiment however it generated significant MPC values. Turbine Oil 2 showed the opposite results where the RPVOT value decreased significantly, yet the MPC values were still very low. In this case, Turbine Oil 1 should be expected to outlast Turbine Oil 2 in the field, however it will generate a lot more deposits. Turbine Oil 2 will have a shorter life; however, it should provide strong resistance to varnish while in-service. Below is a radar chart illustrating the comparative performance of 14 different commercially available turbine oil formulations. In this case, Oil Life corresponds to an average of the RPVOT and RULER values at the end of the 12-week test, deposit control represents the MPC value, and varnish production is a visual assessment of the deposits on glassware from the test cell after 12-weeks. It is interesting to note how many oils show strong oxidative performance yet produce higher levels of varnish. Research 14 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0028 mance. The authors have found that by using the same accelerated oxidative process as specified in D7873 yet using standardized test methods such as the MPC, RULER and RPVOT tests to report the results, the findings can be correlated to actual field performance. The test is referred to as the Turbine Oil Performance Prediction (TOPP) test and a general overview of the test conditions are listed below. • Four (4) 350ml samples of new turbine oil are placed in glass test cells containing a steel/ copper coiled wire catalyst conforming to ASTM D5846 specification. • The test cells containing the turbine oil and catalyst coil are placed into a 120 °C (248 °F) solid-block temperature bath. • The samples are allowed to equilibrate to 120 °C (248 °F) for 20 min. After equilibration, dry atmospheric air is bubbled through the test oil at a rate of 3L/ hr to accelerate aging throughout the duration of the test. • One sample cell is removed at three (3), six (6), nine (9) and twelve (12) week intervals for testing. • After each stress period, testing includes: • Viscosity, 40C: ASTM D445 • Acid Number, mg KOH/ g: ASTM D664 • Rotating Pressure Vessel Oxidation Test, mins: ASTM D2272 • RULER, antioxidant health, ASTM D6971 • Membrane Patch Colorimetry, dE, ASTM D7843 • These results are compared to and trended against test data obtained as a baseline for the new oil (Week 0) 3 Not all turbine oils are created equally The first observation made when performing this test is that there is little change in viscosity and acid number in most formulations throughout the test period. This is consistent with what we see in the field. The difference between formulations is found in the oxidative stability and deposit control capabilities of the turbine oils, where we see significant differences in performance. Below are examples of two different turbine oils that have been stressed for 12-weeks. This example highlights the difference in values between oxidation stability and varnish control. Turbine Oil 1 Turbine Oil 2 12 - Weeks 12 - Weeks RPVOT, % 94% 40% Membrane Patch Colorimetry 56 8 Table 1: Comparison of two different turbine oil formulations after 12-weeks of stress in the TOPP accelerated aging test Figure 1: Radar Chart comparing the performance of 14 commercially available turbine oils after 12weeks in TOPP experiment. Each oil is ranked 1-14 according to its performance in each measured category (1-Best, 14-Worst) This is a common theme throughout TOPP testing. Most turbine oils tested either performed well from an oxidative stability perspective or from a deposit control perspective, but not both. The search for a turbine oil that provides long life without producing deposits has proven elusive to date, however with the rate of advancements in turbine oil formulations such products are expected to become available soon. 4 Interesting findings from TOPP testing The TOPP testing encompassed many different formulations which facilitated objective benchmarking of various turbine oils’ performances. In addition to allowing various formulations to be benchmarked, below are some other interesting findings which provide guidance on monitoring turbine oils. 4.1 Oil color is not related to oil condition It is often believed that the color of in-service oil is directly correlated to its degree of degradation or even performance. Evidence from TOPP testing however suggests that there is no such correlation. Below is an example of two different oils after 12-weeks of accelerated aging and what their corresponding MPC value is. Oil A has a color of 8, according to ASTM D1500, however the MPC rating is only an 8 ΔE. Oil B also has a color rating of 8, however its MPC value is 62 ΔE. Notating the color of in-service oil still provides value. If one observes a sudden change in color, an event has contributed to this change warranting further investigation. However, the color by itself should not be used as an indication of the health of in-service turbine oil, and should be evaluated in combination with other oil health parameters. Some oil formulations use additive components that are photosensitive and will react in the presence of light, especially UV light. If such an oil sample is exposed to sunlight, it’s not unusual to see the color of the oil change to blue, purple or black. Sufficient exposure to UV light has been known to degrade the oil causing increases in acidity and MPC values and a consumption of antioxidants. 4.2 RPVOT Correlation to Performance The Rotating Pressure Vessel Oxidation Test has been a standard method to measure the oxidative stability of inservice oils since the 1960s. Back then, the oil formulations consisted of API Group I base oils and the RPVOT value of new oil was typically below 500 mins. The precision of the test according to ASTM D2272 shows a reproducibility value of 22 % for oils with values below 1000 mins. This test has been an adequate measurement of the health of in-service turbine oils for decades. The introduction of more advanced base oils in turbine oil formulations has resulted in significantly higher starting RPVOT values. This has contributed to much lower test accuracy, especially with reproducibility. There are multiple articles purporting that high RPVOT values correspond directly to oil performance. In fact, General Electric referenced this in one of their older specification revisions (GEK 32568F) by stating, “some studies show RPVOT to be a good indicator of performance”. There were even some that stated that their new oil formulation with an RPVOT of 1500 mins had 3X the life compared to their previous formulation with an RPVOT of 500 mins. There’s no reliable and direct correlation between an oil’s initial RPVOT value and the life of the product or its varnish formation and deposition tendencies. These facts were also confirmed by the results of the TOPP test experiments. The image below shows the RPVOT trend of two different oils from TOPP testing. Turbine Oil 1 starts with an RPVOT value twice that of Turbine Oil 2. However, at the end of the 12-week test, Turbine Oil 1’s Research 15 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0028 Figure 2: Comparison of two different oils, both of which turned very dark in color, but didn’t have corresponding increases in MPC values Figure 3: Initial RPVOT results are not as indicative of oil life as RPVOT Retention during the life of the oil without any significant change to the system. TOPP testing provides one possible explanation for these puzzling field observations and illustrates why higher MPC values do not necessarily equate to higher levels of oil degradation. The image below shows the MPC results of the same oil throughout the 12-week test. The MPC value starts at 5 ΔE, peaks at a value of 66 ΔE after Week 9 and then drops precipitously to 36 ΔE at Week 12. One can also observe the glassware, where the level of visible deposits sharply increases between Week 9 and 12. From this example, one can deduce that as the oil degradation rate accelerates, so does the rate of varnish deposition which can lead to “false low” MPC results. This condition highlights a potential downfall of overreliance on MPC results to determine oil health. Additionally, it underscores the importance of building a robust trend for oil degradation parameters through frequent and consistent oil sampling and analysis, through which a “false low” can be detected. Research 16 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0028 RPVOT value is at 45 % compared to 94 % of Turbine Oil 2. ASTM D4378 suggests that a turbine oil condemning point is 25 % RPVOT value compared to new oil. Following this guidance, Turbine Oil 2 will have a significantly longer life than Turbine Oil 1, even though its initial RPVOT value is quite low by comparison. When interpreting RPVOT values, it is more important to weigh RPVOT retention instead of initial RPVOT values. There is also a misconception about oxidative stability versus varnish production. One may believe that the higher the oxidative stability, the less the oil will oxidize, and the fewer deposits will be generated. TOPP testing is consistent with in-service oil samples from the field in disproving this hypothesis. The image below shows the performance of two different oils in the TOPP test. Turbine Oil 1 had a high initial RPVOT value of 2796 mins and maintained strong oxidative stability throughout the 12-week test. At the conclusion of the test however, its MPC was 56 ΔE. Turbine Oil 2 on the other hand, had an initial RPVOT value of 1125 mins and experienced consistent depletion of oxidative stability throughout the test. However, after 12-weeks of accelerated aging under the same conditions, it only had an MPC of 8 ΔE. This data breaks the connection between RPVOT and MPC values. Figure 4: Illustration showing lack of correlation between an oil’s oxidative stability and varnish performance Figure 5: The higher the MPC doesn’t necessarily mean more oil degradation. Severe deposits are often associated with lower MPC results. Any MPC over 30 should be considered critical and justify remedial action. Figure 6: MPC values of new oils are not always low. When interpreting in-service MPC values, it is valuable to consider the MPC of the new oil baseline. 4.3 Higher MPC values don’t necessarily mean more oil degradation When monitoring in-service turbine oils, the more extreme a parameter gets, the more severe the situation. For example, the higher the particle count, the more contamination. This logical principle applies similarly to acid number, viscosity, water content and the other condition monitoring tests. It is intuitive that the same principle would apply to MPC testing. The expectation is that the higher the MPC value, the more degraded the oil and the higher its propensity to form deposits. However, many oil samples from the field do not follow this principle. It is possible to see a sharp drop in MPC values 4.4 Remember to account for Baseline MPC A worthwhile consideration when assessing MPC test results is the importance of a baseline. While it is expected that most new oils will have a negligible MPC measurement, this is not true across the board. Figure 6 below depicts the varying baseline MPC levels for three different turbine oil formulations. For example, when assessing oil analysis results for two samples both showing in-operation oil MPC levels of 30 ΔE, without consideration of the baseline MPC we would be unaware that Oil C is only experiencing an increase of 12 ΔE while for Oil A the increase of 29 ΔE is much more significant. 4.4.1 MPC is not an accurate measurement for deposited varnish It is undeniable that MPC testing has become an indispensable tool in varnish detection and treatment, however we have to acquiesce that it also only provides a partial view of the entire varnish picture within the oil system and equipment. The test evaluates the amount of varnish that is present in the liquid oil at the time of sampling. While this measurement is very valuable, it does not address two other aspects of varnish that are commonly encountered, especially in severely contaminated systems. When varnish levels surpass the oil’s carrying capacity (solubility), excess varnish drops out of the oil solution and often settles in areas of low circulation and mixability areas such as the bottom of lube oil tanks, oil coolers, low velocity piping etc. The typical oil sample is understandably extracted from regions where the oil is well mixed and thus not representative of any insoluble soft varnish that might have settled within low oil circulation areas. The conditions for varnish to drop out of the oil solution are exacerbated even more when a high temperature delta is encountered such as in the case of oil coolers, which become some of the prime varnish deposition points within the oil system. As warm oil encounters a surface of low temperature and is therefore cooled (this being the primary function of the oil cooler), its solubility point drops which allows more varnish to come out of solution. This situation creates an opportunity for varnish to plate on the metal surface, creating over time a hard and lustrous surface which is typically what we first envision as “varnish”. Among other detrimental effects on the equipment, one aspect of plated varnish is its insulating property which results in impaired heat rejection across metal surfaces. This effect results in diminishing cooler efficiency as well as excessive heat retention within the metal, the latter a detrimental condition when varnish plates on bearing surfaces. In both situations discussed above, MPC testing is “blind” to the amount of sludge or varnish that is part of the system and potentially affecting operation and equipment health, albeit also not present in the bulk liquid oil and thus not measurable. During our study however, we had a luxury seldom afforded in the field: We were able to observe the amount of varnish deposited on the glassware used for aging the oil. While an objective scale to determine deposition levels is not available, it is nonetheless possible to draw some conclusions based on the color darkness and haziness level progression of the glassware throughout the test. Figure 7 below illustrates the lack of interrelationship between MPC and deposit formation. While the oil on the right presents with a significantly higher MPC patch result, its corresponding test glassware indicates that minimal varnish deposition has occurred. By contrast, the oil on the left has deposited significantly more varnish on the glassware despite its lower MPC test results. By MPC results alone, we might conclude that the system using the oil on the right is experiencing higher levels of varnish presence and thus calls for more urgent and drastic intervention, when in reality the system using Oil A is likely at higher priority for mitigation. Research 17 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0028 Figure 7: Illustration showing that the MPC result is not always indicative of actual varnish formation Differences in an oil’s solubility point and ability to “carry” varnish could in the future become important considerations alongside the MPC test results when determining contamination severity and planning mitigation steps. 4.4.2 A Model for Benchmarking Turbine Oil Formulation After gathering oil performance data using the TOPP testing procedure, it is useful to benchmark various formulations. A useful method of benchmarking oils is by generating a Decision Matrix (often called a Pugh matrix, selection matrix, or criteria-based matrix). This is done by prioritizing which data point is of highest importance and establishing weighted criteria. This method for benchmarking is valuable because there is not an oil that is “the best” as the application plays a significant role. A Decision Matrix can be customized depending on the customer’s application. For example, in one case, Varnish Production may be the most important criteria to weigh as this is the test which most closely correlates to system reliability. In another case, Oil Life may be the most important criteria for a customer, because they already use a varnish mitigation technology and are less concerned about the oil generating deposits. way of making a purchasing decision. Nor is there a correlation between price of an oil and its field performance. The best method for selecting turbine oils is to generate comparative test data in a controlled experiment. Testing turbine oils can be done by stressing the oil following ASTM D7873’s procedure. Samples pulled after 3, 6, 9 and 12 weeks are then analyzed by standard condition monitoring tests. Throughout a 12-week aging period, the only significant changes in oil properties are its oxidation stability and varnish potential. Therefore, the tests that provide the most revealing data are the RULER (ASTM D6971), MPC (ASTM D7843) and RPVOT (ASTM D2272). Many things have been learned by performing this test, such as: • There are significant performance differences between formulations. • Formulating an oil with both long-life and low deposits has been a challenge, however the rate of improvement in both properties suggests that this elusive goal will be met soon. • The color of the oil is not related to its performance or varnish tendencies. • Initial RPVOT value doesn’t necessarily determine the life of the oil or deposit control characteristics. An oil’s RPVOT retention properties are more important to track. • A higher MPC doesn’t necessarily mean more degradation or more deposits. An MPC greater than 30 suggests that the oil is susceptible to form deposits and warrants attention. Finally, a Decision Matrix can be made from the test data and the various performance criterion weighted based on a customer’s application and needs. This allows various oil formulations to be benchmarked and provides a better selection guide for purchasing new turbine oils. Research 18 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0028 It is also important to note that an actual oil’s performance in the field is also dependent upon how it is maintained. If a customer purchases a best-in-class oil, but then doesn’t manage contamination or perform condition monitoring, the oil will likely not perform as well as an oil that benchmarked far lower but is monitored and treated as needed. Below is an example of twelve oils that have been benchmarked using the Decision Matrix tool. In this case, four different criteria are weighted, as can be seen in Table 2. Then the results of the TOPP test are evaluated and compared to each other, developing a ranking of each oil. Finally, these values are multiplied by the established criteria weight to come up with an overall rank. An example is listed below in Table 3. 4.5 Summary Selecting a turbine oil based on physical values in its product data sheet or marketing claims is not an effective Criteria Weight Meaning Deposit Control 1.5 The highest MPC rating recorded over the 12-week test Varnish Production 2.0 Visual Assessment of the 12week test cell and comparison to the other test cells Oil Life 1.0 Average of the RPVOT and Antioxidant Levels compared to New Oil at Week 12 Oil Price 0.5 Cost of the oil for the customer Table 2: Example of Measurement Criteria that could be used to help benchmark and select turbine oils Deposit Control Varnish Production Oil Life Price (Scale 1-4) Weighted Rankings Overall Rank Turbine Oil A 1 3 11 2 23.0 1 Turbine Oil B 2 2 12 4 24.0 3 Turbine Oil C 3 4 10 1 28.5 4 Turbine Oil D 4 6 1 4 29.0 5 Turbine Oil E 5 1 9 3 23.5 2 Turbine Oil F 6 7 13 2 47.0 8 Turbine Oil G 7 8 7 2 46.0 7 Turbine Oil H 8 5 6 4 39.0 6 Turbine Oil I 9 11 3 3 55.5 9 Turbine Oil J 10 13 4 2 64.0 10 Turbine Oil K 11 12 14 2 73.0 12 Turbine Oil L 12 14 2 1 68.5 11 Attribution Weight 1.5 2.0 1.0 0.5 Table 3: Decision Making Matrix to benchmark turbine oil formulations and be a criterion for oil selection 1 Introduction Aqueous based engine coolants have long been used due to the ability of water to efficiently conduct heat away from engines. However due to the relatively high freezing point of water and the extremely cold conditions engines sometimes operate in, chemical modification is necessary to ensure the coolant doesn’t freeze when exposed to low temperatures. When mixed with water, ethylene glycol and propylene glycol can alter both the freezing point and the boiling point of a coolant relative to the proportion of glycol in the mixture. [1] Hence the term ‘antifreeze’ commonly used to refer to glycol based engine coolant. ASTM standard specifications for engine coolants prescribe that a glycol concentration range of between 40 - 60 %v/ v in water of a suitable quality, will function effictively during both winter and summer to provide protection against corrosion, cavitation, freezing and boiling. [2,3] The glycol concentration of a coolant indicates the effective temperature range that a coolant will be suitable to operate in and can thus confirm whether the coolant being tested is fit for a given operating environment. Should the glycol content have been depleted during a coolant’s lifetime or if it becomes diluted by an increase in water content, the coolant can suffer from an increased freeze point or even cause increased corrosion and cavitation. Should the glycol levels be too high due to too much coolant concentrate being added, the coolant will suffer from a reduced ability to transfer heat. Commonly, glycol content is determined manually using a refractometer (ASTM D3321 [4]), either in the field or in a laboratory environment. Testing by GC allows for large sample sets to be analysed sequentially using an autosampler without the need for constant analyst attention. In high throughput testing labs, simple sample preparation procedures with the potential for automation are highly favorable. However, given the high concentrations of water and glycol in engine coolant, the sample can be quite harmful to the lifetime of the GC injection liner and column. As such two sample preparations are investigated in this paper, a 10 - fold aqueous sample dilution and a 100-fold dilution in isopropanol. The columns used for both sample preparation methods shared a common stationary phase but differed in their internal dimensions to best optimize the method for the concentration of glycol injected. 2 Methods and Materials 2.1 Instrumental A PerkinElmer Clarus 690 Gas Chromatograph was used for the analysis. The GC was configured with a liquid autosampler, programmable split/ splitless injector (PSSI), flame ionization detector (FID) and an Elite WAX ETR analytical column. Two methods were evaluated to compare the longevity of the column used. Method 1 consisted of a 10-fold dilution in deionised water Research 19 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0029 Rapid identification and quantification of ethylene and propylene glycol in engine coolant by gas chromatography Nicholas Lancaster, Keith Cory Schomburg* Determining the glycol type and concentration of an engine coolant is a useful analytical test for in-service testing laboratories to both identify the coolant type and determine whether the coolant is fit for its intended purpose. Too much glycol can result in poor heat transfer within the engine whereas too little glycol can increase the freeze point of the coolant. As such repeat testing over the lifespan of the coolant is required to avoid potential problems and ensure the overall health of the cooling system. This paper details a GC method to rapidly separate ethylene and propylene glycol in under five minutes and determine the concentration of these glycols in percentage. Two preparation methods are detailed to demonstrate a simple ‘dilute & shoot’ preparation by diluting in deionised water (10-fold dilution) or isopropanol (100-fold dilution). Keywords Glycol, Antifreeze, Engine Coolant, Condition Monitoring Abstract * Nicholas Lancaster PerkinElmer, Seer Green, United Kingdom, HP9 2FX Keith Cory Schomburg, Ph. D. PerkinElmer, Downers Grove, IL, USA, 60515 signs of column overload. For method 2 (100-fold dilution in isopropanol), a narrower bore ID and thinner df more suitable to the calibration range of 0.1 - 0.9 % ethylene and propylene glycol was selected. For both methods a 5 m long deactivated silica guard column was used with the same internal dimensions as the analytical column. 2.2 Experimental The analysis was designed to separate and quantify the glycols in the shortest possible time to allow increased sample throughput. An isothermal oven program was chosen to avoid oven cooldown times in between sample measurements. A high split ratio was necessary to deal with the large volume of water vapour formed in the injector due to the aqueous matrix of the samples. The high split ratio also helps to prevent backflash and split peaks which are common issues associated with aqueous injections. The high split ratio also contributes to improved peak shape and helps prevent column overload which is vital when measuring such high analyte concentrations. The GC parameters for both methods are shown in table 1. Both Helium and Hydrogen were tested for suitability with both showing similar results in peak retention and resolution. Hydrogen was used as carrier for the results represented in this paper. Before analysis each day the column was conditioned for an hour at 230 °C. 2.3 Standard Preparation Combined ethylene glycol and propylene glycol standards were made up in deionized water (Method 1, 10fold dilution) and Isopropanol (Method 2, 100-fold dilution). The calibration ranges for each method are show in tables 2 and 3. Research 20 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0029 and wide bore WAX column. Method 2 consisted of a 100-fold dilution in isopropanol and a narrower bore WAX column. The Elite WAX ETR column makes use of a cross bound Carbowax Polyethylene Glycol (PEG) stationary phase. The bonding mechanism of this stationary phases produces a very stable polar retention. [4] The bonding mechanism is also responsible for the column’s ability to withstand repeat water injections which is vital given the aqueous matrix of the coolant sample. The dimensions were chosen to be suitable for the concentration of glycol injected. For method 1 (10-fold aqueous dilution), the calibration ranged from 3 - 7 % of ethylene and propylene glycol. The wide bore internal diameter (ID) of 0.53 mm and dispersion film thickness (df) of 1 µm provides the most capacity for the analyte before showing GC Parameters Instrument PerkinElmer Clarus 690 Column (Method 1) Elite WAX ETR 30 m x 0.53 mm x 1 µm Column (Method 2) Elite WAX ETR 3 0 m x 0.32 mm x 0.5 µm GC Oven Parameters (Method 1) Isothermal at 150 °C for 5 minutes. GC Oven Parameters (Method 2) Isothermal at 130 °C for 5 minutes. Liquid Autosampler Parameters Syringe Size (Method 1) 5 µL Injection Vol. (Method 1) 0.5 µL Syringe Size (Method 2) 0.5 µL Injection Vol. (Method 2) 0.3 µL Injection Speed Normal Number of Plunges 6 Sample Washes 2 Pre-Injection solvent wash 1 Post-injection solvent wash 3 Wash Solvent (Method 1) Methanol: Water (50: 50) Wash Solvent (Method 2) Isopropanol Viscosity Delay 2 Injector Parameters Type Programmable Split/ Splitless Temperature 250 °C Carrier/ mode Helium/ Hydrogen flow Flow rate (mL/ min) 6 mL/ min Split Ratio 50: 1 Liner Deactivated glass liner with deactivated glass wool Detector Parameters Type FID Temperature 250°C Hydrogen 45 mL/ min Air 450 mL/ min Attenuation -3 Table 1: GC Method Parameters Table 2: Calibration range, Method 1 Table 3: Calibration range, Method 2 Ethylene and Propylene Glycol concentration (% v/ v) Standard 1 3 Standard 2 4 Standard 3 5 Standard 4 6 Standard 5 7 Ethylene and Propylene Glycol concentration (% v/ v) Standard 1 0.1 Standard 2 0.3 Standard 3 0.4 Standard 4 0.5 Standard 5 0.6 Standard 6 0.9 2.4 Sample Preparation Method 1 involves a 10-fold dilution in deionised water. 1 mL of sample is added to 5 mL of deionised water before being made up to 10 mL total volume. Method 2 involves a 100-fold dilution in isopropanol. 100 µL of sample is added to 5 mL of isopropanol before being made up to 10 mL total volume. To determine the accuracy of the method a set of ten samples with ethylene glycol concentrations determined by refractometer were used as reference. 3 Results and Discussion 3.1 Method 1: 10-fold aqueous dilution Baseline resolution was acheived in under 4 minutes with propylene glycol eluting first at 2.88 minutes and ethylene glycol eluting second at 3.19 minutes. Retention times were confirmed by injecting individual glycol standards under the same conditions. Figure 1 shows an example chromatogram of the 7 % calibration standard. Figures 2 and 3 show the linear calibration curves for the two glycols under the method 1 analysis conditions. Both curves have a coefficient of determination (R 2 ) greater than 0.99 indicating an good level of data correlation within the specified calibration range. Ten ethylene glycolbased reference sam- Research 21 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0029 Figure 4: Method 1 - example sample chromatogram y = 21275x + 751 R² = 0.994 61000 81000 101000 121000 141000 161000 3 4 5 6 7 Peak Area Concentration (%v/ v) Propylene Glycol Figure 2: Method 1 - propylene glycol calibration curve y = 18039x + 452.6 R² = 0.995 52000 62000 72000 82000 92000 102000 112000 122000 132000 3 4 5 6 7 8 Peak Area Concentration (%v/ v) Ethylene Glycol ples with known glycol concentrations (determined by refractometer reference method, ASTM D3321) were measured on the GC after method calibration. Figure 4 shows an example chromatogram clearly confirming that the sample is an ethylene glycol-based coolant with no propylene glycol present. Figure 3: Method 1 - ethylene glycol calibration curve Figure 1: Method 1 - example chromatogram (7 % propylene and ethylene glycol) 3.2 Method 2: 100-fold dilution in Isopropanol Figure 5 shows an example chromatogram using method 2. Baseline resolution is achieved for method two in under three minutes with propylene glycol eluting first at 1.99 minutes and ethylene glycol eluting second at 2.3 minutes. To further optimize method 2 an isothermal oven temperature of 130 °C was used due to the decreased retention on this column. A smaller injection volume of 0.3 µL was also used to compensate for the decreased sample capacity on the narrower bore column used for method 2. Figures 6 and 7 show the linear calibration curves of propylene and ethylene glycol collected using GC method 2. The calibration range was modified for additional accuracy given the increased dilution for method 2. The R 2 value for both analytes is greater the 0.999 indicating excellent correlation within the calibration range. The same sample set evaluated with method 1 was used with method 2 to determine the accuracy of the method. Figure 8 is an example sample chromatogram from method 2 confirming that the sample measured was an ethylene glycol-based coolant. Research 22 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0029 Table 4 shows the results for these coolant samples collected using GC method 1 with the results from the GC in the %v/ v column and the results from the reference method in the ‘Reference (%v/ v)’ column. When compared, the results collected using the two methods agreed well showing a high level of accuracy from the GC method. Table 4: Method 1 - reference sample results Propylene Glycol Ethylene Glycol Unknown Sample RT(min) %v/ v RT(min) %v/ v Reference (%v/ v) 1 2.88 ND 3.19 32.8 35 2 2.88 ND 3.19 30.1 32 3 2.88 ND 3.19 38.3 40 4 2.88 ND 3.19 46.4 45 5 2.88 ND 3.19 9.1 3 6 2.88 ND 3.19 50.4 49 7 2.88 ND 3.19 43.5 44 8 2.88 ND 3.18 40.1 42 9 2.88 ND 3.19 54.4 52 10 2.88 ND 3.19 52.4 49 Figure 6: Method 2 - propylene glycol calibration curve y = 19883x - 185.62 R² = 0.999 1700 3700 5700 7700 9700 11700 13700 15700 17700 19700 0.1 0.3 0.5 0.7 0.9 Peak Area Concentration (%v/ v) Ethylene glycol Figure 7: Method 2 - ethylene glycol calibration curve y = 24547x - 259.87 R² = 0.999 2100 7100 12100 17100 22100 27100 0.1 0.3 0.5 0.7 0.9 Peak Area Concentration (%v/ v) Propylene glycol Figure 5: Method 2 - example chromatogram (0.9 % ethylene and propylene glycol) The results of the reference sample set measured using method 2 yielded a similar level of agreement between the calculated values and reference values for the samples further indicating a high level of accuracy of the GC methods. 3.3 Method Robustness Over the course of several weeks, 500 samples were run using both methods to determine the robustness of the methods and the resilience of the column to repeat sample injections. The size of the sample set varied between 50 and 100 samples per day and the column was conditioned before measuring each set (230 °C for one hour). After the final sample set was tested a set of 10 control standards were run to evaluate the repeatability of the results. For method 1 the control standard was made up to 5 %vol/ vol of both propylene and ethylene glycol. For method 2 the standard was 0.5 %vol/ vol in isopropanol. Figure 9 shows an overlay of the ten standard chromatograms measured using method 1. Table 6 shows the retention times and calculated concentrations for both glycols after taking the dilution factor into account for each control standard (method 1). The percentage relative standard deviation (%RSD) for both propylene and ethylene glycol are below 2.5 % indicating a good degree of repeatability despite the concentration of the standards and the large volume of aqueous sample measurements that preceded the repeatability test. Retention times for both glycols showed excellent consistency. Research 23 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0029 Figure 8: Method 2 - example sample chromatogram Figure 9: Method 1 - overlaid chromatograms of ten standard replicates (5 %) after 500 aqueous injections Propylene Glycol Ethylene Glycol Unknown Sample RT(min) %v/ v RT(min) %v/ v Reference (%v/ v) 1 1.99 ND 2.30 35.2 35 2 1.99 ND 2.30 32.1 32 3 1.99 ND 2.30 38.8 40 4 1.99 ND 2.30 47.0 45 5 1.99 ND 2.30 11.0 3 6 1.99 ND 2.30 51.9 49 7 1.99 ND 2.30 44.7 44 8 1.99 ND 2.29 41.7 42 9 1.99 ND 2.29 55.9 52 10 1.99 ND 2.30 51.1 49 Table 5: Method 2 - reference sample results col by GC. The carbowax stationary phase in combination with the split injection method allow for repeat analysis of aqueous coolant samples with good accuracy and precision despite the high glycol concentration of the anlaytes present in both the samples and the standards. The repeatability of the methods tested after the injection of 500 samples display very consistent results. However the increased tailing of the glycol peaks after approximately 700 samples indicate that the methods will likely not be suitable where very high sample throughput is a requirement. Further testing is required to determine a more suitable stationary phase where sample volumes in excess of 100 per day are routine. References [1] J.D. Laukkonen, The history of antifreeze, Crankshift, March 1, 2017. http: / / www.crankshift.com/ history-of-antifreeze/ [2 ] ASTM D3306-21, “Standard Specification for Glycol Base Engine Coolant for Automobile and Light-Duty Service,” ASTM International, West Conshohocken, PA, 2021, DOI: 10.1520/ D3306-21, www.astm.org [3] ASTM D6210-2017, “Standard Specification for Fully- Formulated Glycol Base Engine Coolant for Heavy Duty Engines,” ASTM International, West Conshohocken, PA, 2017, DOI: 10.1520/ D6210-17, www.astm.org [4] ASTM D3321-19, “Standard Test Method for Use of the Refractometer for Field Test Determination of the Freezing Point of Aqueous Engine Coolants,” ASTM International, West Conshohocken, PA, 2019, DOI: 10.1520/ D3321-19, www.astm.org [5] https: / / www.perkinelmer.com/ uk/ product/ pe-wax-etr-30m-53-mm-1-0-m-n9316569 Research 24 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0029 The results from method 2 were comparable to those measured using method 1. The methods were both used to measure more samples to determine whether the methods would be suitable for large sample volumes. After approximately 700 samples both methods began to show severe peak tailing that could not be improved without both exchanging the guard column and trimming the inlet of the analytical column. 4 Conclusion This paper presents two simple and rapid methods for separating and quantifying ethylene and propylene gly- Propylene Glycol Ethylene Glycol RT %v/ v RT %v/ v 5% std 1 2.88 47.9 3.22 47.7 5% std 2 2.88 49.0 3.22 48.8 5% std 3 2.88 48.8 3.22 48.7 5% std 4 2.88 48.8 3.22 48.5 5% std 5 2.88 48.8 3.22 48.6 5% std 6 2.88 48.8 3.22 48.6 5% std 7 2.88 48.9 3.22 48.7 5% std 8 2.88 52.4 3.22 52.1 5% std 9 2.88 49.0 3.22 48.7 5% std 10 2.88 49.0 3.22 48.8 %RSD 0.00 2.42 0.00 2.38 Table 6: Method 1 - replicate analysis of ten standards (5 %) after 500 aqueous injections 1 Introduction Oil condition monitoring programs have significantly improved in the last decade, to allow the users of hydraulic oils to measure oil degradation products. Tests such as; the Membrane Patch Colorimetry and Particle Counting have allowed them to identify soft contaminants in their fluids. These are usually responsible for many mechanical issues, such as pump failures, sticking valves, decreasing cooler capacity, etc. The frequency of hydraulic oil failures as a result of deposit formation is due to a confluence of events. There has been a constant evolution in the formulation of hydraulic oils. API Group I base oils formulated with ZDDP additives are being replaced by next generation base oils and ashless antiwear technologies. Although these formulations may perform better in the field, it is essential that their degradation products are measured using a condition monitoring program. Additionally, thermal stress continues to increase in hydraulic oils as oil reservoirs shrink in size, while operating temperatures and pressures increase. Hydraulic system deposit formation needs to be addressed, in an economical and sustainable way. This paper will present the principle and use of a novel solubility enhancing technology. Case studies will illustrate how this approach can be used both reactionary; to resolve immediate mechanical issues, and proactively; to provide long-term deposit protection. Applications covered in this paper are from the automotive industry, steel manufacturing, injection moulding, mining and marine industry. 2 Lubrication requirements and developments for hydraulic applications Both lubricants and their applications continue to evolve. There has been a drive within the manufacturing and hydraulics industry towards more globalization and efficiency improvements. These have set off a chain of events, impacting all aspects of an operation. The industry is demanding faster, smaller, more efficient machines. The Original Equipment Manufacturer (OEM) responds, delivering a more compact, efficient machine however, in most cases, this results in placing higher thermal and mechanical stress on the lubricant. In the case of a hydraulic oil, the fluid is now expected to perform at higher operating pressures and temperatures, in smaller capacity systems, for longer periods of time and in the presence of many potential contaminants. Oil manufacturers have responded by reformulating their products to meet these new demanding specifications. The most consequential change to lubricant formulations over the last two decades is the use of more highly refined base stocks, such as API Group II and III. Fully formulated Group II and III lubricants have superior oxidative resistance because virtually all hydrocarbon molecules are saturated. A drawback of Group II formulated lubricants is reduced solubility. This often requires the use of a solubility enhancer, or cosolubilizer, to keep the additive package in solution. As the oil degrades, the reduced solubility properties mean a limited ability to keep oil degradation products in solution. Over the last couple of decades, the combination of the new generation of lubricants and the increased operational conditions of industrial hydraulic systems, has resulted in new oil degradation mechanisms. During maintenance overhauls, operators often report that valves or oil reservoir walls are coated with a dark brown/ amber deposit, or oil reservoirs have more problems with foaming control. These oil-derived deposits are commonly known as varnish. (Figure 1) Varnish is typically defined as a thin deposit in a lubrication system that is difficult to remove by wiping and comprised primarily of organic residue. The chemical composition of varnish can be extremely varied and classified by chemistry and degradation mechanisms. Typi- Research 25 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0030 Managing hydraulic oil deposits by using novel solubility enhancing technology Jo Ameye, Greg Livingstone, Cristian Soto* * Jo Ameye Fluitec NV, Brussels, Belgium Greg Livingstone Fluitec International, Bayonne, NJ, USA Cristian Soto Fluitec International , Bayonne, NJ, USA Condition monitoring, soft contaminants, sticking valves, decreasing cooler capacity, automotive industry, steel manufacturing, injection moulding, mining, marine industry. Keywords friction . In some control systems, the energy input of a valve is measured. Valves that are sticky due to oxidation products can be identified by the increased amount of energy required to move the valve. Besides loss of hydraulic control, valves that are coated with varnish are often considered to be malfunctioning and are prematurely replaced. Although this may immediately solve the valve sticking issue, the newly replaced valve will be quickly coated with varnish, causing reoccurring issues. (Figure 2) Research 26 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0030 cally, sludge is considered an easy to wipe, gooey substance that also contains moisture. Varnish has a more cured, shiny appearance and is not easy to wipe. Varnish is primarily caused by the continual process of oxidation which is accelerated by temperature and various metallic components as well as gaseous catalysts. Everything is susceptible to degradation due to the presence of oxygen, lubricants not excluded. Oxidation on hydraulic oils is a combination of 3 types of contaminants: dirt contamination (silt, wear metals), water, and air. Over the last 15 years significant efforts have been made in the hydraulic industry to control contamination (ISO particle counting), as well as to reduce water content (via the use of breathers, vacuum dehydradation). In parallel, significant efforts have been taken to protect the hydraulic base oils, by applying a wide range of antioxidants. Antioxidants are formulated into hydraulic oils because they are more reactive species than the base oil. The oxygen and free radicals more readily react with the antioxidants, who sacrifice themselves to protect the base oil and significantly extend the life of the oil. In addition to oxidative stress, high temperature thermal events may also be a contributing mechanism for fluid degradation. Thermal degradation is created by high temperature events without the influence of oxygen, such as Micro-dieseling (due to increased air release values) or Electrostatic Spark Discharge (ESDoften with very fine filtration). 2.1 The Impact of Deposits on Control Valves Varnish deposits are sticky in nature. This impacts the performance of proportional control valves or servo-valves, which rely on clean, deposit-free lubricants to function as designed. Often, oil flow to parts or all of the control valve is intermittent. This results in the oil cooling in temperature, allowing degradation products to come out of solution, adhering to the internals of the valve. The formation of deposits in valves has been shown to cause valve lock due to resulting high levels of static Figure1: Deposits formation on oil reservoir Figure 2: A Failed valve coated with varnish deposits 3 Condition Monitoring Programs and standards for hydraulic oils The operators of hydraulic systems are acutely aware of the need for realizing optimum reliability and availability of their assets. Monitoring the condition of the lubricant by selecting the correct tests and analysing the fluid at the right intervals helps the operator understand if the fluid is suitable for service. It is also the primary tool to identify incipient lubricant failure, allowing the operator to take proactive actions. Guidance on oil condition monitoring strategies is often provided by OEMs, international standard bodies and lube oil experts. As the formulation of hydraulic lubricants has evolved, so too have the tests required to monitor them. Traditional oil analysis methods for hydraulic oils, such as viscosity, elemental spectroscopy, acid number, particle count and water content will provide value, however they cannot be reliably used for detecting fluid failure. This is mainly for two reasons. First, the polar products formed from hydraulic oil degradation are smaller than one micron in size - which is undetectable with routine analysis. Secondly, many of today’s new lubricant formulations no longer degrade in a linear fashion thus making it more challenging to predict when the lubricant will begin to rapidly develop deposits. To achieve an optimum value for the performed oil analysis programs, the following oil analysis matrix (in complement to viscosity, particle counting (ISO 4406) and acid number), will help operators to be more proactive: 3.1 The health of a lubricant’s antioxidant system will largely determine the life of the oil. Directly monitoring individual antioxidants has demonstrated to be a very good predictive method to monitor antioxidant depletion and provides a more thorough understanding of how fluids degrade. The RULER ® is specifically engineered to measure and trend individual antioxidants. Unlike other testing methodologies that can detect antioxidant molecules, such as FTIR, the RULER is not influenced by the presence of other additive components. An example of a RULER test can be seen below (Figure 3): Once the antioxidants in a lubricant start to degrade, the first physical impact to the lubricant is the generation of extremely small, sub-micron degradation products. These contaminants may consist of degraded base oil molecules, but at the early stages of development, most often consist of the degraded antioxidants. 3.2. MPC test - The most common test method to detect oil degradation products is Membrane Patch Colorimetry (MPC), conforming to ASTM D7843. Other tests such as measuring the gravimetric weight of insolubles or ultracentrifuges have shown promise, but may also be influenced by larger contaminants. The MPC test is a relatively straight forward procedure. Fifty milliliters of sample are mixed with an equal amount of solvent (usually petroleum ether) and filtered through a 0.45-micron patch. The color of the patch is then analyzed with a spectrophotometer and the total amount of color is reported. The results are reported on the CIE LAB ∆E color scale, examples of which can be seen below. (Figure 4) Other test methods that may also be of value in a hydraulic oil analysis program are: 1. FTIR analysis - The Fourier Transform Infrared (FTIR) practice is a refined infrared spectroscopy method, which can be used to monitor molecular changes in the fluid, potentially identifying its mode of degradation or oil mixtures. 2. Air Release - Measuring the fluid’s ability to dissipate air bubbles can be of value if the lubricating oil is also expected to provide hydraulic work, such as moving a valve or lifting a bearing shaft. 3. Elemental Spectroscopy by ICP -can identify wear in various machinery components, or oil mixtures (for example to identify if zinc-containing oils are mixed into ashless hydraulic oils). In all of the above test methods, it is important to have a correct oil sampling interval. The most common sample periodicity for hydraulic oil systems is every 3 months. Oil sampling frequency shall also be adapted to the function of the condition of the oil, in order to establish a trend for the individual oil parameters. Variations from fluid condition trends may be further investigated for root cause determination. 4 A solution to remedy deposit formation on hydraulic oil systems Fluitec has developed a solution to manage deposits already formed in hydraulic and lubricating systems to prevent their further development by use of a solubility Research 27 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0030 Figure 4: Example Patches and values from the Membrane Patch Colorimetry (MPC) test. A value of 50 would be considered critical, warranting immediate action. A result of 9 would be considered acceptable Figure 3: RULER directly measures the health of individual antioxidants, revealing the health of the lubricant. The red line is the used sample and the blue line is the new oil reference sample Solvancer ® technology was developed after an exhaustive categorization of the various deposit chemistries found in hydraulic systems. Three essential properties were studied in this categorization exercise: polarity, hydrogen bonding and dispersive forces. Solvancer ® has been optimized to take these three characteristics into account to ensure that lube oil deposits are quickly dissolved back into the lubricant. Solvancer ® is typically added a treat rate between 3 and 5 % to an in-service lubricant. It has no adverse effects on the performance of the fluid and goes to work immediately dissolving deposits, and preventing further varnish from forming. The case study below shows both the immediate and long-term impact of adding Solvancer ® technology to an in-service hydraulic system. This graph shows the results from a 6-week oxidation test (120 °C), without and with adding Solvancer ® . (Table 1, Figure 5) Research 28 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0030 enhancer. This patent pending technology is referred to as Solvancer ® . (Figure 6) A solubility enhancer should only be considered under the following conditions: 1. The solution must be added to the machine while operating. 2. It must be compatible with in-service oil and other system materials. 3. It can’t affect the oil’s interaction with contaminants, inhibit corrosion, anti-wear performance and must work under intense conditions. 4. Doesn’t give into oxidative stress. 5. Usage of this solubility enhancer eliminates the need to install ANY other mitigation system. 6. Works even under extreme oxidative conditions and doesn’t produce deposits when burnt. Table 1: TOPP test results hydraulic oil with and without Solvancer treatment Figure 5: Effect of Solubility enhancer on solubility 5 Case studies hydraulic oil systems treatment 5.1 Case 1 - Injection moulding company This case study covers an injection moulding company equipped with more than 50 injection moulding machines, which have oil reservoirs from 250 to 2500 liters of hydraulic oil. In a period of 2 years, the maintenance department reported a sudden increase of sticking servovalves, shorted filter life, and failing hydraulic pumps. Through a visual inspection of one of the failed pumps, the maintenance engineers noticed light brown deposits on the pump components (Figure 6) 1. Drop of MPC values averaging an MPC of 51 d-E before treatment and MPC of 12 d-E after treatment 2. Filter life time increased to the normal lifetime of 4-6 months, without changing the retention rate of the filter (Beta 200 6 micron) 3. Over a period of 1.5 years, no problems associated with the sticking servo-valves were reported. Additionally, no hydraulic pump failures occurred. 5.2 Case 2 - Aerospace forging company For this second case study, we cover a leading aerospace component manufacturing company, which noticed a decrease in ram speed with their hydraulic radial forging press. This resulted in an inconsistent system performance which risked product quality. The Aerospace Component Manufacturer’s hydraulic radial forging press comprises of 4 x 42,000 liters reservoirs with hydraulic fluid from each reservoir powering one of four cylinders. Upon having performance-related issues, an inspection later revealed a manifold riddled with varnish deposits. Deposits were also found in pumps, valves and system internals. Further oil analysis revealed a high varnish potential (MPC >50 d-E). (Figure 8) A concentration of 3 % DECON™ was added to the in-service hydraulic oil and circulated throughout all four reservoirs. Within one week, the varnish potential was significantly lowered and DECON™ had restored system performance while simultaneously cleaning system internals. Research 29 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0030 Figure 7: MPC trend before and after DECON™ treatment Figure 6: Deposit on hydraulic pump component Figure 8: Pictures of varnish on press components Once the maintenance team added MPC analysis to their existing oil analysis program, high values of MPC were recorded for 75 % of their machines. It was also noticed from the oil analysis reports that on a few injection moulding machines, the acid number as well as the zinc-content was increasing above the expected values. After a further investigation, it was found out that the oil storage tanks for the zinc-free and zinc-containing oils had been mixed. This probably resulted in the mixing of small quantities of zinc-containing oil into the ashless oils. After consultation with the OEM, as well the oil company, the company decided to add 3 to 5 % of the solubility enhancer (DECON™ formulated with Solvancer ® ), which resulted in the following performance (Figure 7): nish deposits on valves, coolers and other lube system components. The impact of these deposits in a hydraulically controlled valve include valve sticking and locking. It is possible to monitor the health of these fluids, by optimizing the oil analysis program with methods that monitor the development of varnish such as RULER and MPC tests. One solution to the formation of deposits in hydraulic oils is the use of a solubility enhancer. Fluitec has developed its Solvancer ® technology, specifically for a wide range of industrial lubricants. It has been shown to provide immediate relief to systems suffering from varnish and long-term deposit control protection for components susceptible to failure from varnish. Research 30 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0030 DECON™ is also currently preventing the formation of additional deposits. The manufacturer is continuing to monitor the fluid on a monthly basis and has included the MPC (Membrane Patch Colorimetry) test. The manufacturer will add approximately 3 % DECON™ along with new oil whenever the system needs to be topped-up to maintain superior performance. 6 Conclusions Reliable hydraulic system operation is essential for the manufacturing industry. These fluids are under increasing levels of thermal stress and may be exposed to metallic, air and water contamination causing further acceleration to its failure. The results of hydraulic oil degradation are polar degradation products that form as var- 1 Oil Health Monitoring Oil sampling analysis has been the backbone of all oil reliability programs for the past century. From early analysis technology used by oil labs to the more modern miniaturized benchtop equipment, these have transformed the way and speed to which we make decisions around preventative maintenance. The latest of these advancements has been new in-line, real-time oil quality monitoring sensors that deliver on the earlier promises of true online monitoring capabilities. The value from oil samples is centered around oil health itself. Properties such as oxidation, TBN, TAN, additive packages, viscosity, water, fuel, soot, etc. are all used to assess the remaining-useful-life (RUL) and identify preventative, as well as corrective actions. A few notable challenges with oil sampling are the time delay between sample and results, access to remote and mobile assets, infrequency of sampling compared to reliability events, Research 31 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0031 Combining Oil Health, Level, and Vibration to Achieve Complete Machine Monitoring Jeremy Sheldon, Mark Redding* * Jeremy Sheldon Poseidon Systems LLC, Victor NY, USA Mark Redding Poseidon Systems LLC, Victor NY, USA New digital technologies are transforming the way and speed at which decisions are made for preventative maintenance. These advancements include new in-line, real-time monitoring sensors that deliver on the earlier promises of true online monitoring capabilities when compared to traditional lab-based oil analysis, visual determination of oil level, and route-based vibration data collection. Notable challenges with manual methods are the time between sample and results, access to remote and mobile assets, infrequency of sampling compared to reliability events, and elevated risk of human error. Because of these challenges, many operators are moving towards online monitoring. Industries such as energy, mining, rail, marine, etc. have all started adopting online oil monitoring programs and it is expected to become standard practice over the next few years. Recent sensor advancements are now capable of measuring a variety of oil health related parameters including oil condition, relative humidity, temperature, and others. These new sensors can detect most, if not all, key oil events and project the remaining useful life of the oil while the asset is in operation. However, oil level, the most critical measurement is typically overlooked. While oil level sensors exist, their use is not widespread due to a variety of reasons, one of the main being sensor form factors. Vibration analysis has proven to be one of the most reliable and quantitative indicators of gearbox compo- Abstract nent failures. Acquiring, analyzing, and monitoring of a machinery’s vibration can reveal much about that machine’s health. Vibration is often the preferred machinery monitoring solution. Each sensing technology and its interpretation offer varying fault detection and isolation performance. Those implementing a condition monitoring system (CMS) must evaluate the sensors, fault detection performance, cost, and various other aspects before implementing a CMS. Cost and complexity of implementing both solutions may require selection of either an oil condition sensor or vibration sensing but not both, reducing the overall CMS performance. To help address the above-mentioned challenges, the authors developed a multi-sensor device that can be used to monitor different failure modes in a single small form factor design. The developed sensor monitors the oil level, quality, water contamination, magnetic flux, and vibration in real-time. Keywords Preventative maintenance, online monitoring, condition monitoring, multi-sensor device 1.1 Oil Condition Various technologies provide the ability to measure multiple properties of a lubricant. As mentioned above, two of the more widely used methods for online oil monitoring are electrochemical impedance spectroscopy and measurement of the dielectric constant or ratio (simply referred to as dielectric) of the oil/ fluid, see Figure 1. Dielectric is a measurement of how well a material conducts electric current compared to how the same field would conduct in a perfect vacuum [1]. The relative simplicity of the sensing technology is well suited for online applications. As oil degrades contaminates and chemical changes affect the measured dielectric of the oil. Dielectric may increase or decrease depending on the change to the oil. Typically, for many important health changes, for example depletion of additives, the oil dielectric will decrease. The developed sensor incorporates a dielectric measurement for tracking oil condition. Most oil sensors are best used to determine anomalous conditions and when a sample of the lubricant should be taken and sent to a traditional oil-lab for a more traditional oil analysis before any further action is taken or the output can be used to directly determine what action should be taken when significant changes are detected. Research 32 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0031 and high risk of human error. Because of these challenges, many operators are moving towards online fluid monitoring. Typically, online sensors are electrochemical impedance, dielectric, conductivity, or permittivity measurement devices detecting degradation of the oil. Some methods and sensors can detect degradation of not only overall quality, but estimating percent soot, total base number, relative humidity, additive depletion, etc. Regardless of sensing method, effective oil condition sensors must detect most, if not all, key oil events and have an output that trends with the life of the oil while the asset is in operation. While these sensors cannot duplicate lab analysis results, they can provide the necessary insight to make preventative maintenance decisions before damage occurs. Online oil quality sensors are key enablers to shift the oil sampling paradigm from periodic to true conditionbased sampling. To completely monitor the condition of an oil, multiple parameters are required. At a minimum a combination of sensors to monitor oil level, track overall oil health, and a monitor water activity are recommended. Figure 2: Example Oil Condition Sensor Data Figure 1: Notional RH vs PPM Comparison To illustrate, a series of laboratory sub-scale testing was performed to determine the performance of a commercially available sensor at varying oil contamination levels. Two separate testing phases were performed to assess the sensor response to coolant contamination and fuel contamination. sensors at varying oil contamination levels. Coolant and fuel were used as they are common sources of contamination, however the sensor performance is expected to be similar for other fluid contaminations, for instance with incorrect fluid addition. In the first test, coolant was added incrementally. One of the measure parameters trended very well with both coolant and fuel were added, as shown in Figure 2. In addition, the parameter also responded proportionally when increasing amounts of contaminates were supplied. Consistent and proportional response to oil condition of change of interest is a critical aspect to assess when selecting an oil condition sensor. The sensed parameters must behave in a proven way to allow confidence in the resulting decisions. In addition, one must ensure the sensor is sensitive to the failure modes of the target machine. 1.2 Fluid Level When implementing a condition monitoring solution, fluid level is often overlooked. Insufficient lubrication is obviously detrimental to the machine’s mechanical components. Additionally, low oil can also cause the remaining oil to degrade more rapidly. Various studies report inadequate, or no lubrication is responsible for 30- 80 % of bearing failures[2,3]. The authors have many examples of low oil or oil out events causing massive gearbox damage. Many of these would have been avoidable had the actual oil level been actively monitored. Therefore, monitoring the level of the fluid is a critical aspect to overall machine health. An integrated level sensing mechanism is built into the developed sensor. Online real time monitoring of oil level offers many benefits over traditional manual/ visual readings. Monitoring continuously allows trending of oil level with machine operation to confirm adequate lubrication at all operating conditions. Alarms and notifications can be raised at the instant oil levels drop avoiding the time delay associated with manual readings that may occur days apart. In addition, online monitoring of level removes the need for manual checks that can be expensive and dangerous depending on the location of machinery. 1.3 Relative Humidity The developed sensor incorporates a relative humidity sensing element that uses a hydroscopic dielectric compound in a capacitive sensing element to produce an output which correlates directly to the relative saturation of moisture in the working fluid. Thus, by monitoring the change in capacitance, relative humidity can be derived. Like water is detected in the atmosphere by monitoring relative humidity, relative humidity sensors in oil provide a measure of the dissolved water present. While in the dissolved state water likely poses relatively low risk to the system; however, as the level approaches the oil’s saturation point the risk of free water and emulsion formation greatly increases. When interpreting the data and setting limits one must consider the risk the free water poses to the specific system. In most laboratory reports water content (both free and dissolved) is expressed in parts per million (PPM). The acceptable PPM levels vary greatly by oil type because the saturation points of oils are highly variable. Oil saturation points vary due to the oil chemistry, additives, age, depletion, and other influences. Saturation points also vary with oil temperatures, meaning that for fixed PPM limit the actual saturation level of the oil will change with temperature. A more relevant to machine health way to express water content in oil is as a percentage of saturation, or relative humidity. Expressing water content in relative humidity accounts for the changing saturation point and at any given time directly indicates the risk of free water without needing to know the often difficult to find oil specific saturation curve. Oils can typically absorb more water with increasing temperature. So, for a given fixed PPM limit at lower temperatures the oil could be close to or above saturation limit while at higher temperatures the oil could be relatively dry. A notional example is shown in Figure 3. In this example an assumed 1000 PPM of water is present. It should be clear that for given fixed PPM water level results in a variable risk of free water or heavily emulsified oil across changing operating temperatures, thus the risk to the asset condition is variable. When implementing a remote monitoring solution specific to water content in oil, one must consider the entire operating range of the system. Research 33 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0031 Figure 3: Notional RH vs PPM Comparison part of this analysis, shaft speeds and machine geometry are often used to calculate component-specific frequencies useful in fault isolation. Spectral (typically Fast Fourier Transform (FFT)) and time domain analysis is an important part of any vibration monitoring system. Typical systems extract condition indicators or features from the collected vibration data that are used for trending and machine health assessment. For instance, a commonly used vibration indicator, or feature, is root mean squared (RMS). RMS is a relatively easy to compute statistical feature that is indicative of the overall broad band vibration level. One of the limitations of RMS is its lack of fault isolation capabilities when compared to methods involving frequency analysis, such as FFT analysis, which will be described later in the paper. Nonetheless, RMS is an important part of many monitoring systems, including integral to accepted standards, such as ISO-10816-21 [6]. This paper will not get into the finer details of vibration analysis but will instead focus on the application and results from real world examples. 2.2 Motor Magnetic Flux Measurement of shaft speed is important for knowing the operational state of an asset. In addition, knowing the shaft speed is critical for many vibration diagnostics involving frequency domain analysis. Vibration diagnostic techniques often use shaft speeds and machine geometry to calculate component specific frequencies useful in fault isolation. Typically, shaft speed is measured using a dedicated sensor directly affixed or with direct access to the target shaft. The requirements of these types of speed sensors can make installation a challenge due to the additional complexity of adding another sensor, proximity to the rotating shaft needed by many sensors, and the difficulty of retrofitting. To overcome these challenges, the developed sensor integrates a magnetic flux measurement for detection of electrical issues and estimating shaft speed. Magnetic flux is a measurement of how much magnetic field passes through a given area, in this case the sensor element. Research 34 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0031 1.4 Temperature Although seemingly trivial, machine temperature (bearing, housing, surface, or oil temperature) is a critical part of condition and machine monitoring. Measurement of machine internal or surface temperatures can provide an overall indicator of machine health, even if the indication may be late in the fault progression. Additionally, temperature measurements can often provide insights into secondary system performance, such as cooling systems. Prolonged periods of high oil temperatures can indicate poor lubrication condition, moderate to severe mechanical damage, or other abnormal operating conditions that require remediation. Oil condition can more rapidly degrade under abnormal temperatures. In addition, some of the parameters measured by sensors are temperature dependent and a real time oil temperature reading is necessary to ensure analysis conclusions are accurate. Therefore, temperature measurements are a valuable addition to any remote monitoring system. 2 Mechanical Health Monitoring To monitor the health of mechanical components, a wide range of sensors, data acquisition devices, and processing techniques exist. In fact, there are too many sensor types to list herein. Therefore, the authors selected vibration as the sensor type for the developed multi-parameter sensor. 2.1 Vibration Vibration analysis has proven to be one of the most reliable and quantitative indicators of gearbox component failures. Acquiring, analyzing, and monitoring of a machinery’s vibration can reveal much about that machine’s health. Typically, vibration is measured via an accelerometer type sensor mounted directly to the machine. The measured raw vibration signal must first be analyzed to extract useful information form the acquired waveform [4,5]. Many analysis techniques exist, usually applying one or more signal processing techniques to process the time waveform into usable reduced-order information, sometimes called features or condition indicators. As Figure 4: Example Magnetic Flux Measurement, Shaft Speed [60 Hz] Highlighted The magnetic field is generated by the motor. The sensor measures this field and estimates the shaft speed, compensating for slippage. Additionally, the measure flux signal can be used for motor diagnostics [7]. An example of the measured signal from an operating pump motor is shown in Figure 4. 3 Multiparameter Sensor Overview To simultaneously address needs for oil and mechanical health monitoring in a single sensors, the authors have developed an integrated sensor package that combines all these parameters into a single sensor. The integrated sensing device facilitates conditioned-based maintenance practices by combining multiple sensors into a single package to enable the early indication of lubricant issues and avoiding costly downtime. The device is installed in place of an oil level sight glass, as shown in Figure 5. As mentioned above, the sensors utilize capacitive measurement to monitor oil level, a dielectric measurement to track overall oil health, and a water activity measurement to monitor for water contamination. The sensor also measures vibration at the same location. The sensor does not require any consumables or complicated installation and it is applicable to a wide range of fluid types. The technology is well suited for online applications. 4 Example Applications The following section summarizes a few use cases of the sensor highlighting each sensor parameter. 4.1 Vibration Measurement Example To assess the vibration monitoring sensor integrated into the multiparameter sensor, the authors installed the sensor’s MEMS-based wireless vibration nodes, hereafter referred to as vibration nodes, on each of three different 1.5 MW wind turbine generators. The sensors were installed radially orientated near the drive (nearest the main rotor) and non-drive end (furthest from the main rotor) generator bearings. The focus of the installation was to assess the capabilities of the sensors and integrated system. As such, the sensors were installed on three generators of known health states: healthy bearing, incipient bearing fault, and severe bearing fault. The faulted bearings were earlier identified and confirmed via borescope inspection. Data from the vibration nodes was collected over approximately eight months to assess the vibration system’s performance on each generator, focused on the bearings. The monitoring period extended beyond the bearing replacement to compare before and after repair vibration levels. The three RMS trends over time are shown in Figure 6. As expected, higher vibration levels were observed on faulted generator bearings during the first few months. The generators with faulty bearings were inoperative while repairs were in progress, the healthy turbine continued operating. Once repairs were complete, all generators exhibited similar vibration levels, except for a short duration of higher vibrations during the first start up. From the clear difference in the before and after repair vibration levels confirms the Research 35 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0031 Figure 5: Developed Multiparameter Sensor Figure 6: Generator Bearing Vibration Trend First, the multiple oil changes are clear. With each new oil change the dielectric returns to roughly the same level. The repeatability of the sensor response as the oil ages is also clear. Reliably trending data enables confidence in the conclusions drawn and knowledge derived from the data. It also simplifies the analytics, requiring simple thresholds and slope calculations. Second, there was a clearly different trend in the oil change in January, highlighted in red. The dielectric rate of increase slowed and began to plateau. This is indicative of abnormal oil health. The asset owner was notified that an oil ample should be taken. The oil sample confirmed high oxidation was occurring due engine malfunction. Once the repair was performed, the sensor data indicated the oil condition returned to normal, thus confirming the corrective maintenance action was taken. 4.4 Water Intrusion Example The sensor’s relative humidity measurement from a pump system is shown in Figure 9. During normal operation, the oil water content is relatively high, above 50 %, but normal for this type of pump application. However as noted, the sensor measured a short duration of 100 % RH indicating an issue but quickly returning to normal levels. At this point in time the operator of the pump was notified of a potential seal failure. Unfortunately, before the scheduled maintenance the seal completely failed resulting in large amounts of water contaminating the oil. The pump seal was repaired and put back into service with sensor data confirming the oil was drying out as result of the repair and top off. Without the sensor, the pump would have likely operated with the heavily contaminated oil resulting in additional damage. 4.5 Dielectric Measurement Example The final example is from a laboratory-based experiment conducted to evaluate the level sensor and vibration sensor in combination. The developed sensor was installed on a pump gearbox sump to monitor the lubrication oil level and pump itself. The sump oil level was slowly reduced over time to simulate an oil leak. Oil was refilled the following day. The level measurement during the test is shown in Figure 10. Real time alarms would have quickly indicate the reduced oil level, alerting maintenance teams to take immediate action to avoid damage due to improper lubrication. The vibration trend from the test is shown in Figure 11. There was no discernable difference in vibration when the pump was running without lubrication. The level measurement provided the first indication, and vibration may have picked up after actual damage started vs immediate response from level sensor. Although no mechanical damage occurred during the short test, a CMS based only on vibration would have missed the oil out event resulting in increased risk to secondary damage Research 36 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0031 repair adequately remedied the underlying fault state. However, from the trend, it is difficult to tell the difference between the fault severities, which is important for understanding the likely fault progression and timeline in which repairs are required. 4.2 Level Measurement Example The level of an industrial pump was measured over the course of many months. While no critical anomalies were detected over this time, an interesting response was noted. A single day of data is shown in Figure 7. The monitored asset had an automatic oil fill system that is intended to automatically replenish the sump oil when necessary. From the data, the top off events are clear. Although not indicative of an issue, the condition monitoring practitioner is able to confirm normal operation just as much as abnormal operation. 4.3 Dielectric Measurement Example An example of the measured oil dielectric from a engine application is show in Figure 8. Over the course of approximately 8 months the asset oil health was monitored using a dielectric measurement like that incorporated into the developed sensor. Two observations can be made from the data. Figure 7: Pump Gearbox Oil Level Trend Figure 8: Oil Dielectric Trend and machine failure. An example such as this highlights the need for multiple sensors to detect the variety of important machinery failure modes and the risks associated with reliance on one sensor type. 5 Summary In condition monitoring, there is no single sensor type or analysis method that will work for every component and every failure mode. Combining sensors will certainly result in the best results for any condition monitoring application. However, one must always balance cost and complexity with the required performance. In addition, certain components and machines will require specific monitoring. For instance, oil debris cannot be used on grease-lubricated components, and vibration systems cannot detect clocking bearing failure modes. Unfortunately, budgets often restrict what is possible, often requiring selection of only one monitoring approach. In that case, one must be careful in selecting the approach as there is no single sensing solution capable of detecting every failure mode. The advent of the internet of things era has helped reduce the technological and cost barriers of deploying multiple sensors on a single asset. IOTera technologies have enabled combination of sensors in reasonably priced packages for every increasing number of machines beyond the most expensive of critical assets. References [1] https: / / www.machinerylubrication.com/ Read/ 28778/ dielectric-instruments-oilanalysis [2] SKF, “Bearing damage and failure analysis,” SKF Group, June 2017. Research 37 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0031 Figure 10: Oil Level Trend During Simulated Oil Leak Figure 11: Vibration Trend During Simulated Oil Leak Figure 9: Oil Relative Humidity Trend From Pump Seal Failure Phase 1 and Phase 2 Testing,” National Renewable Energy Laboratory, 2011. [6] ISO 10816-21, “Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 21: Horizontal axis wind turbines with gearbox,” First edition, May 1, 2015. [7] Yazidi A., H. Henao, Capolino G. A., Artioli M., Filippetti F., Casadei D., “Flux Signature Analysis: an Alternative Method for the Fault Diagnosis of Induction Machines,” accessed online 12/ 01/ 2022. Research 38 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0031 [3] Booser, E. Richard, “Tribology Data Handbook: An Excellent Friction, Lubrication, and Wear Resource,” CRC Press, Boca Raton, FL 1997, pg. 900-907. [4] Sheldon, Jeremy S., Watson, Matthew J., Byington, Carl S., “Integrating Oil Health And Vibration Diagnostics For Reliable Wind Turbine Health Predictions,” Proceedings of ASME Turbo Expo 2011 GT2011 June 6-10, 2011, Vancouver, British Columbia, Canada. [5] Sheng S., H. Link, W. LaCava, J. van Dam, B. McNiff, P. Veers, and J. Keller, S. Butterfield and F. Oyague, “Wind Turbine Drivetrain Condition Monitoring During GRC 1 Introduction The most common case for breakdowns of electrical connectors is fretting corrosion. The building of an isolating oxide layer between the contact metals is caused by micro movements (oscillation, vibration, or thermal expansion).[1] A well-functioning of the connectors depends on its constructional composition as well as the friction management. Lubricants have to fulfil high-quality requirements for this complex tribosystem to ensure a long and safe lifetime of electrical contacts. The challenge for lubricants is to offer the required protection against wear, fretting corrosion and friction and thus reducing forces without hindering the electrical current to flow and ensuring a low ohmic resistance. 2 Electrical contacts 2.1 Type of electrical contacts Typically, the lubricant is responsible for ensuring a long lifetime of electrical contacts. Thinking of safety switches this is especially important and the lubricant becomes a safety relevant construction component. Special lubricants wtih characteristics against wear, corrosion, and high lubricity allow a low contact resistance, constant insertion/ operating forces, and no short circuits. This functions by a coat of lubricant on the metallic connectors and its displacement upon operating force. Electrical contacts are divided in two groups: stationary and moving. Moved electrical connections are further divided in sliding and commutating ones. The way of movement in commutating connectors is much more challenging due to the harsh conditions of the tribosystem than the one in stationary contacts. Hence, the requirement of the lubricant is much higher to protect electrical contacts e.g., brush, slider, trolley and separable contacts. All tribosystems in electrical contacts depend on the: [1] • construction  surface pressure  geometry  friction mechanism • contact materials  surface roughness  hardness  electrical conductivity  thickness of the conductive layer • installation location  ambient temperature  atmosphere  electric current and voltage Research 39 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0032 Electrical contacts - the challenge for lubricants Sarah Hüttner, Verena Leumann, Rachel Kling* Electrical contacts can be found in all industries today. In these applications lubricants are essential because they protect the metal connectors from friction and fretting corrosion, which generate wear and may lead to an isolating oxide layer and finally the destruction of the electrical connection. Measurements on customary lubricants for electrical connectors were conducted with high regard to oxidation stability, wear and friction characteristics. The selected samples also differ in the thickener systems. Besides typically non-conductive lubricants for electrical contacts, there are lubricants with high electrical conductivity required mainly for EDM bearings (electrical discharge machining) to not promote a system failure. Currently, action is taken in the industry to define standards to measure the electrical conductivity of lubricants. Keywords friction, corrosion, wear, oxide layer, oxidation stability, EDM bearings, standards Abstract * Sarah Hüttner Verena Leumann Setral Chemie GmbH, Seeshaupt, Germany Rachel Kling Sétral S.à.r.l, Romanswiller, France contacts.[2] Special antioxidant additives or base oils are necessary that lubricants withstand the development of these high temperatures. New peaks on the metal surface provide more friction or even destroy the conductive layer. Both leads to higher friction and isolating oxide layers that destroy the connection. Often, for a higher conductivity the metallic surface is coated with a very conductive metal e.g., gold, silver or copper. Since most of these metals are expensive, the layer thickness is just as thick as necessary. Typically, the interior components of electrical contacts are made out of plastics - very common are ABS and PC that are sensitive to cracking. Suited lubricants for these applications need to be compatible with the listed contact materials. Further the active protection of metallic surfaces is an essential requirement to prevent oxidation. Another important role of lubricants in an electrical environment are bearings for EDM (electrical discharge machining). Thereby, the lubricant needs to be electrically conductive to not promote a system failure. These applications are common in railway, vehicle, e-mobility technology and many more, wherever variable-speed, converter-fed electric motors and generators are used.[3] 3 Electrical conductivity 3.1 Method to measure the electrical conductivity Currently, there is no standard method to measure the electrical conductivity of lubricants nor a universally recognized definition of the value above which lubricants are considered electrically conductive. For an easy pretest for the determination of the electrical conductivity, self-constructed electric measuring cells (Figure 3.1.1) are available at setral ® - one for fluids like oils, the other for consistent lubricants like pastes or greases. The grease is spread out on the contact surface with a defined layer thickness. The electric resistance is Research 40 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0032 2.2 Functioning of the tribosystem in electrical contacts Upon closure of the electrical contact the metal peaks of the connector surfaces come into contact and allow the current to flow. The lubricant remains in the troughs together with air (see cross section in Figure 2.2.1). This application is common in stationary electrical contacts. Figure 2.2.1: orange: lubricant, white: air, arrows indicate the current flow Figure 3.1.1: electric measuring cells For the best support of the lubricant and thus the wellfunctioning of electrical contacts all parameters have to be taken into account like the general type of electrical contact, the temperature, the voltage, the amperage and the material roughness, thickness and composition. 2.2 Typical applications and requirements of the lubricant In almost all industry sectors the need of electrical contacts rises for the use in switches, controllers, printed circuit boards and many more. In the automotive industry electric contacts are ubiquitous. Here, actuartors are good example. They function by electrical contacts installed in seat height adjustments, brake boosters, control tank caps, tailgates, locking mechanism of cars etc. Not every application with electrical contact needs a lubricant with “good” electrical conductivity. The usual lubricant in moved and stationary electrical contacts is non-conductive. Other properties are much more important, because its main goal is to reduce operating and friction forces as well as wear and oxidation. Special EP/ AW additives have to be added to the lubricant to prevent the formation of abrasion particles and fretting corrosion due to micro movements.[1] As a result of insufficient lubrication an oxide layer forms on the metallic connector and the metal becomes isolated in this area and thus prevents the current from flowing. Unlubricated stationary contacts often produce arcing during opening and closing. Ionisation of the air and the associated rise in temperature causes metal transfer between the contacts, accompanying the formation of new “peaks and troughs” - a common problem in high power being measured with a high resistance measuring device by taking into account the value of the conductor area and the gap. The electrical conductivity is calculated with the reciprocal value of the electrical resistance. (Table 3.1.1) metal powders e.g., copper, graphite, graphene or carbon nano tubes (CNT). The usage of metal powders might be accompanied by other undesired effects. Therefore, lubricants filled with metal powder have to be tested thoroughly and over a long period of time in the application e.g., circuit breaker, switchgear and switches. Possible results include accelerated corrosion and remaining conductive paths, which lead to corrosion and create conductive paths, leading eventually to failures.[4] Due to their tunnel structure, CNT behave like conductor and conduct the current in one direction.[5] This technology enhances the electrical conductivity in small amounts by up to pS/ m. Using graphite increases the electrical conductivity by the factor of 1000 compared to MoS 2 . Hence, graphite is often used in electrically conductive lubricants. Ionic liquids are also a possibility for increasing the electrical conductivity. The disadvantages are the bad solubility in PAO oils of most types and that other properties of the iconic liquids have to be considered since some of them promote corrosion.[6] Additionally, the REACh restriction and the consequent limitation has to be considered. Other commonly used solid lubricants, e.g., PTFE, MoS 2 and graphite should be avoided because they are considered to increase the electrical resistance after a long period of use.[4] 4 Experiments In focus of the experimental part are electrical switches which operate at temperatures of 80 °C. Standard thickened metal soap greases are commonly used for this application. Even within this type of application the lubricant faces various challenges regarding the manifold operating conditions. This is why a lot of different formulation can be found on the market. 4.1 Data evaluation A selection of them were regarded in the following experimental part with different base oils, thickeners and some even with copper content. The samples in Table 4.1.1 were generated according to the following measurements: • Oil separation acc. to ASTM D 6184 • Worked penetration acc. to DIN ISO 2137 Research 41 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0032 Table 3.1.1 Table 3.1.2 As the first preliminary tests show, all lubricants used in electric contacts are non-conductive. Recently, there are some devices for measuring the electrical conductivity of lubricants. These devices are able to measure the conductivity at a wide temperature range from minus degrees Celsius up to high temperatures. Yet, due to its construction and the close range of the measurability of electrical conductivity it is not suited for greases but rather for electric conductive fluids. Other new methods to measure the electrical conductivity use a special adapter for the rheometer. This technology has a lot of functions and options. The strength and weakness analysis should be done carefully since a lot of knowledge and experience is required to understand the measured value and, even more important, to cover them with the actual application. 3.2 Method to improve the electrical conductivity It is important to consider that every electrical contact requires a specially designed lubricant. The commonly used lubricants in electrical contacts are non-conductive and work by other characteristics (see 2.2). Yet, sometimes there is a requirement for lubricants to be used as additional electrical contact provider to boost the electrical conductivity. This property can be enhanced by The electrical conductivity of all samples is in the range of non-conductive greases. Copper powder is added to samples B, D and G to positively influence the electrical conductivity. This leads to an increase of wear compared to identical samples without copper and for sample D increases the oxidation stability, thus copper seems to act as a catalyst.[7] Many samples reach the maximum load value of 2000 N in the SRV EP test (Chart 4.1.3). Only sample D with 1900 N, sample B with 1700 N and sample H with 1500 N Research 42 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0032 • Kinematic viscosity acc. to DIN 51562 • Copper corrosion acc. to DIN 51811 • SRV (EP) acc. to ASTM D 5706 • SRV (AW) acc. to ASTM D 5707 • RapidOxy (oxidation stability) acc. to ASTM 942 • Electrical conductivity acc. to a house method (see 3.1) (Table 4.1.1, Chart 4.1.2, Chart 4.1.3) Table 4.1.1 Chart 4.1.2 Chart 4.1.3 fall short of the values. For B this is unexpected since, the only difference to A is the copper content and copper may be used as solid lubricant. H needs more measurements for an interpretation because of the variety in differences to other samples. The lowest wear values show samples E, C and A according to the SRV AW test (Chart 4.1.2). All of the three samples reach a max. load of 2000 N in the EP test. These samples have a penetration in the range of NLGI grade 2 and an oil separation between 2-3 %. Regarding the samples E and F in combination with tests of the RapidOxy oxidation stability and the electrical conductivity, the only difference between sample E and F is, that the formulation of F contains EP additives of different types and it is one NLGI class softer. Thus, the variation in additives leads to a slightly higher value in the oxidation test. Further, this difference in additives and NLGI might lead to the increase in electrical conductivity. Sample pack four with inorganic thickened pastes shows the highest wear in the SRV AW & EP (Chart 4.1.2 and Chart 4.1.3) with sample I having exhibiting the lowest oil separation but the highest electrical conductivity. 4.2 Data analysis of the COF in the SRV EP test To evaluate the influence of the thickener in electrical contact lubricants, sample A, F and I were compared. With PAO, they all have the same base oil, but different thickeners. The SRV EP focuses on the maximum load and the coefficient of friction (COF). The running-in phase for all samples was almost 16 hours. The load was then increased in steps of 200 N up to 2000 N. Frequency (50 Hz), stroke (1 mm) and the temperature at 80 °C were constant during the measurements. Sample A The structure of calcium sulfonate complex greases is based on overbased calcium sulfonate. This is a colloidal inverse micelle disperson formed from amorphous CaCO 3 . Its micell structure is stabilized by a surfactant in the oil. The tickener with calcium carbonate initally forms a viscous caoting on the surface component. Next, calcium sulfonate creates sulfonate chains that aline vertically to the surface. At higher pressures, the sulfonates are ejected from the contact and a tribochemical film forms.[8] (Chart 4.2.1) Due to its typical thickener property, the calcium sulfonate contributes to a good extreme pressure. Thus, sample A reaches 2000 N without seizing. Further it shows a low and constant running-in phase of the COF in Chart 4.2.1. Upon increased pressure the COF decreases. Another special feature of the thickener is its micelle structur, which leads to a good oil-binding property. Calcium sulfonate greases have further special features e.g., good shear stability, a barrier to water, good anticorrosion protection, etc.. Sample F The fiber structure of lithium single soaps compared to calcium sulfonate thickeners shows a similar decreasing trend in the coefficient of friction. The running-in phase is a bit more restless compared to Chart 4.2.1. This effect might be caused by the larger particle size of single soaps. Due to the hydrogen-bonding of the hydroxyl groups, the lithium single thickener has multi-purpose properties, e.g. good shear stability, good water resistance, providing a good boundary film which causes a low coefficient of friction, etc.[9, 10] Compared to sample E, the coefficients of friction are lower. These two samples are similar but with the difference in base oil viscosity, NLGI and additional additivities. (Chart 4.2.2) Research 43 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0032 Chart 4.2.1: sample pack 1, A Chart 4.2.2: sample pack 3, F struction of the conductive layer also by preventing the formation of a non-conductive oxidation layer. All these effects work together perfectly for a long and safe lifetime of the electrical connection. References: [1] V.V. Konchits, N.K. Myshkin, Tribology of Electrical Contacts, Tribologie und Schmierungstechnik. 2017, 2, 5-12 [2] Electrolube, Contact lubricants, Switch to a superior performance, Switches and Contacts [3] B. Sauer, D. Bechev, T. Kiebach, B. Radnai, Untersuchung der Auswirkungen von leitenden und nichtleitenden Schmierfetten auf die Oberflächeneigenschaften bei spannungsbeaufschlagten Wälzlager, 2018, 3, 5-11 [4] Bella H. Chudnosky, Lubrication of Electrical Contacts, Square D, West Chester, OH 45069, USA [5] Abdullah Abdulhameed, Nur Zuraihan Abd Wahab, Mohd Nazim Mohtar, Mohd Nizar Hamidon, Suhaidi Safie, Izhal Adul Hain, Methods and Applications of Electrical Conductivity Enhancement of Materials Using Carbon Nanotubes, Springer Link, 2021 [6] C. Enekes, A.Kailer, C. Dold, T. Schubert, M. Ahrens, P. Altmann, S. Grundei, Elektrisch leitfähige Schmierstoffe für adaptive Tribosysteme - Synthese und tribologisches Verhalten unter dem Einfluss von elektrischen Potenzialen, 2016, 3, 38-44 [7] C.A. Migdal, Oxidation and the testing of turbo oils, 2008 [8] Rob Bosman and Piet M. Lugt, The microstructure of calcium sulfonate complex lubricating greases and its change in the presence of water, 2018 [9] Edit by Theo Mang, Wilfried Dresel, Lubricants and lubrication, 2007, 653 [10] Atsushi Yokouchi, Michita Hokao, Joichi Sugimura, Effects of soap fiber structure on boundary lubrication of lithium soap greases, 2011 Research 44 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0032 Sample I In comparison to sample A and F, sample I with an inorganic thickened paste shows the highest electrically conductive potential. The swelling behavior and consequently the thickening of the inorganic thickener in the base oil is well pronounced and results in the observed low oil separation. Depending on the type of inorganic thickener (e.g. silica) particles themselves have a hard and rough surface finishing. This characteristic is observed in the restless running-in phase and with the start of the applied load it comes to some high peaks in the COF. This is typically for inorganic thickeners as the particles tend to form agglomerates without well lubricity. The agglomerate disintegrates into the individual particles under continuous mechanical shear and pressure. (Chart 4.2.3) 5 Conclusion In general, soaps as calcium sulfonate or lithium soaps which form a micelle or fiber thickener structure achieve constant and low coefficients of friction. Addition of metal powder (e.g., copper) enhances the electrical conductivity with the disadvantage of higher coefficients of friction, lower oil separation and a degradation of the oxidation resistance. RapidOxy tests were run for the samples B, D, E and F and show the expected catalytic effect of copper as stated in literature.[7] A low oxidation rate is important for electrical connector applications for a long lubricant lifetime and for operating under high voltages where electrical arcing may occur. The lubricant must be able to withstand the developed high temperatures without significant degradation to further protect the metal contacts and ensure a long lifetime of the electrical switch. Depending on the application the NLGI grade and the thickener system with characteristic oil separation need to be considered. Suited lubricants reduce the friction, preventing the formation of new peaks on the metal surface and the de- Chart 4.2.3: sample pack 4, I 1 Introduction There are more components and modern technologies that cover lubricants today. The electric vehicle transmission, specifically those with the drive motor and electronic parts within the transmission fluid, has the propensity to add elements not known to standard internal combustion engines. Other technologies are critical to assist with failure analysis at a more forensic level. A property having a major effect on the utility of a lubricant, even for electric vehicles, is its resistance to oxidation and the consequences of this toward copper depletion. The probability of exposed parts, either initially or over time, truly exist in everyday scenarios. The rate of change to the copper or other metallurgical properties is important to analyse. In addition to that aspect, the formation of dendrites and the ensuing deposits in close quarters can be problematic. This type of deposit formation causing arcing between wires, conductors or circuit board traces may result in catastrophic failure of the motor or other electrical components [1]. 1.1 Oxidation and Corrosion Testing There are numerous industry oxidation and corrosion tests that exist. Collectively these tests may prove to be informative when it comes to predicting the potential failure of fluids utilized in the electric vehicle (EV) realm. Scanning Electron Microscope (SEM) and the x-ray fluorescence (XRF) are two tools that are commonly utilized to assist with evaluating corrosion products and the effects thereof. These tools alone, however, are not comprehensive enough for modern, fill-for-life applications. Several candidate test methods are used to evaluate a fluids oxidative stability. Rotating Pressure Vessel Oxidation Test ASTM D2272 [2], the Aluminium Beaker Oxidation Ford Method BJ 110-04, the JIS K 2514 Indiana Stirring Oxidation Stability Test, and the CEC L-048 Oxidation Stability (DKA) all measure similar properties such as viscosity increase, change in acid number or differential IR and a sludge rating. The Aluminium Beaker Oxidation test also looks at the total copper or lead insoluble material after the test. Visual ratings, where implemented, qualitative, and others are discrete and quantitative. Research 45 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0033 Research and Development Utilizing the Conductive Layer Deposit and Wire Corrosion Bench Test Technology for Electric Vehicle Drivetrains Gregory Miiller, William VanBergen, Alexei Kurchan, David Gillespie, Gunther Mueller, Rico Pelz, Timothy Newcomb, Gregory Hunt* The electric vehicle technology is vacillating at remarkable rates. Thus, the enhancements of the associated fluids and their associated additives are also changing. Varying conditions, depending on the EV system and usage albeit passenger car or heavy duty, can cause the formation of conductive deposits and corrosion within drivetrains. Corrosion is a wellknown entity and tools to evaluate under these conditions are imperative. However, the formation of conducting layer deposits, a corrosion product, has also been identified as a failure mechanism for current electric motor designs. Different drivetrain base stocks along with additive formulations may have inherently different corrosion rates producing conducting layer deposits in both solution and vapor phases. To help resolve these issues, a group of industry experts involving both OEM’s and lubricant experts from across the globe, have developed bench tests to better predict these conductive and corrosion deposits. The apparatus’ developed are the conductive deposit test and the wire corrosion test. This paper covers several different aspects of the EV drivetrains and fluids performing in the CDT and WCT that show both field correlation and repeatability. Keywords fluids, additives, failure mechanism, additive formulation, CDT, WCT Abstract * Gregory Miiller, William VanBergen Savant Group Alexei Kurchan, David Gillespie Cargill Incorporated Gunther Mueller, Rico Pelz APL Landau Timothy Newcomb, Gregory Hunt The Lubrizol Corporation 2 Transmission Fluids with Electric Vehicles The performance requirements are changing for transmission fluids. The EV motors are more elegant in design and demanding because of the ability to have tight tolerances and the need for high torque and quick acceleration [5]. This is the opportunity to re-write requirements and develop new testing. Unlike internal combustion engines where engine testing and bench testing combined provide protection for the engines and enhance engine oil development, the EV technology lends itself more to strictly bench tests as the conditions are more readily reproduced in the laboratory. Understanding the conditions of each EV, BEV or other is important when developing these tests. Components, therefore, can be monitored individually as to performance characteristics such as foam, aeration, viscosity, thermal transfer, and electrical conductivity. However, it may be necessary in these cases to understand oxidation characteristics when testing various facets of the fluid. The results may be impacted in ways that could seriously modify the outcome thus more accurately depicting the actual outcome of the EV application. Oxidation properties can be recreated synthetically and in several diverse ways. Heating, airflow, oxygen flow, water, pressure and agitation are all methods to create the required conditions. Corrosion tests and deposit tests also have the potential to create predictive oxidation conditions. 2.1 Corrosion Testing Needs Corrosion testing has been shown necessary in both ICE and EV technologies. The degradation of metal surfaces through corrosion is a destructive process wherein the metal is electrochemically oxidized through interaction with its environment. Copper corrodes when exposed to a variety of aggressive agents including acids, salts, phosphates, oxygen, and sulphur compounds. When the environment is a formulated hydrocarbon solution, such as fuels and lubricants, the main concern is corrosion by sulphur compounds. The wire corrosion test (WCT) was developed specifically for the electric vehicle industry. With fluid materials in contact with various metals products, especially copper, this type of testing has become critical as these destructive conditions have been problematic globally [6]. This test was designed not to look at the level of corrosion that occurs such as the ASTM D130 copper corrosion test but was developed to analyze the rate of corrosion at a given temperature. This analysis is intrinsic for the industry with motors, motor windings, electrical connectors, electrical components, and circuitry all potentially exposed in the EV application. Research 46 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0033 The ASTM D5704 L-60 Engine Oxidation test takes another perspective for evaluation. Not only are the analytes from the other tests monitored, but the added gear carbon and varnish analyses are added to the dossier. This is valuable within the EV realm because of the agitation caused in the areas of concern. Final ratings for varnish are combined with a sludge rating from the pentane insoluble analysis and parts per million soluble copper measurement. However, none these tests were truly developed for the EV industry. Because of that they lack the depth for such an analysis needed for this sophisticated technology. How do actual corrosion tests such as the copper strip corrosion test ASTM D130 perform for these motors? 1.2 Limitations of ASTM D130 - Copper Strip Corrosion Test Despite being simple and straight-forward, it is clear the ASTM D130 method [3], is limited in precision due to the subjective color rating of the copper strip at the end of the test. However, that is not the only definitive factor of the limitations involved with this test. The method was first published in 1930 to analyze the free sulphur and corrosive compounds in gasoline. It was not until 1949 when the test was expanded to include the analysis of other petroleum products, including lubricating oils [4]. Since that time, the method has been utilized extensively by the petroleum industry, included several specifications. What has not changed is the variability that comes with the analysis. It is completely subjective, not including the exceptions where the tests are a definitive pass or fail. The concern is that fluids may become improperly tainted as being problematic when they may perform satisfactorily. However, electrification of the transportation industry, the incorporation of electronics and electric motors, has resulted in failure modes that require an understanding of corrosion that occurs under the actual operating temperatures, as well as potential damage from corrosion products on the application hardware [4]. There are two concerns in the end; one is that the test really is not definitive in nature. There are debates that can be argued in either direction. The other is that the test is subjective. Either way, the test is rooted in history. That means the tendency to remove such a test is difficult, because of the data history. That is not to mention the chemistries that have been formulated in conjunction with such a test and the history thereof. Modern technologies, however, should not have to be imperilled by such an antiquated test. surfaces require proper tribological performance causing an increase in rotational forces, surface wear and movement. However, conductive deposits create a destructive element that can be unpredictable. Therefore, a test has been developed to assist the industry with conductive deposit formation. This is the conductive deposit test, known as the CDT. The CDT was developed as a methodology to measure and monitor the formation of conductive deposits over time. The level of conductive deposits can be monitored by the reduction of resistance between traces on a circuit board with an applied voltage. The test utilizes circuit boards with conductive copper traces not to duplicate the failure of circuit boards, but to provide a small anulus Research 47 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0033 Figure 3: Motor winding destroyed The WCT test simulation takes place with a small diameter wire that is lowered into the test cell with one half in the fluid and the other in the vapor while being maintained at temperatures anywhere from 80 °C to 150 °C. With the introduction of a low voltage and amperage, the change in potential across the wire can be denoted as corrosion takes place. The corrosion can be destructive enough that the wire is eventually severed. The actual diameter change can be measured in angstroms over time. See Figure 1 for the test application and Figure 2 for the rate of change. As important monitoring corrosion has become within the industry, it cannot predict all types of oxidation failure modes or methodologies. One critical area is deposition. 2.2 Deposit Formation Concerns Exposure of various metals and other materials is inevitable in new EV systems. With moderately elevated temperatures, temperature cycling, aeration, mixing, water, and other contamination can cause oxidation deposit formation. When adding the corrosion of materials, it enhances the possibility of chemical reactions occurring thus forming carbonaceous and sludge conditions. Other products may also form from the additives or base stocks utilized in the fluid’s formula. There is evidence that a correlation may exist between the level of oxidative stress a lubricant endures and its propensity to create conductive deposits, but it has been observed that some lubricants can form conductive deposits well before any obvious oxidative indicators are evident. Components such as sulphur may initiate the corrosion, removal and even buildup of copper and other metal by-products. Potentially these deposits may prove to be conductive in nature within the confines of the electrical and mechanical areas of the EV transmission. There have been cases sited where the conductive deposits have become detrimental to the overall performance of field vehicles. Catastrophic failure has been documented [6]. Figure 3 depicts the failure of a motor stator. The hairpin, located at the top of the stator, was destroyed due to arcing caused by conductive deposit formation. 3 Conductive Deposit Test (CDT) Overview Corrosion and the ensuing by-products are synonymous in nature. However, it is the type of corrosion by-product or subsequent deposition that can be concerning. Not all deposit formations are created equal. Deposits may limit performance due to the destructive nature of moving Figure 1: WCT Diagram Figure 2: Wire diameter rate of change measured by a transformation equation measuring the summation of the areas between the expected passing result and the breakdown that may actually occur. The changes in resistance limits to failing fluids are determined based on the EV application. The summation, therefore, is recommended as it depicts the rate of change in Figure 6 which assists with the determination of a failure point. It has been shown that some known failing fluids have a conductive deposit factor, CDF, of over 2 CDF within the 500-hour testing period. However, the failure limit may be modified and set by specification groups based on the equipment being protected. As shown, there are poor field performing that fluids tran- Research 48 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0033 duplicating constricted areas in the EV where conductive deposits are formed as shown in Figure 4. Part of the circuit is in the test sample and the other is in the vapor phase. The fluid is maintained at 150 °C but may be modified to other desired temperatures. As these destructive deposits are formed, the resistance decreases between copper traces increases the potential for arcing. Propagation of these deposits over time form conductive bridges between copper traces and the resulting decrease in resistance is monitored as a function of time. Once arcing occurs, the traces may fail completely causing an open circuit. The test was originally designed to run out to 1000 hours. However, failures correlating to field failures have shown to occur far less than 500 hours. Even though the testing in this paper is 1000 hours, testing beyond 500 hours has been determined not to be critical in most cases. Figure 4: CDT Test Board in Fluid 4 Testing and Analysis The data collection involves monitoring the change in resistance of traces on the board in the liquid and vapor phase over time. As conductive deposits are formed in each phase, liquid and vapor, the total resistance of the decreases. The resulting graph is shown in Figure 5. A proven good fluid may run the entire 500 hours. Some failing fluids will come to the end of the test within 100 hours. Variability in resistance is expected as the conductive deposits form, copper is depleted through plating or solubility occurs. To exculpate data from these excursions, the data are filtered. It was still desirable to have a result that can be utilized as an indicator when the culmination of the reaction process is at a reasonable conversion of progression. This is ! ! " ! "" ! """ ! """" ! """"" ! """""" ! """"""" " ! "" #"" $"" %"" &"" '"" ("" )"" *"" ! """ ! "#$%&'(%)")*+#,%'-./ 0)1 2"0%'-345&)1 ! "#$%&'(&)*)+",-&'./ "$0' +,-./ 011,12.342 5367/ ./ 011,12.342 Figure 6: rate of change of deposits Figure 5 spire within the first 250 hours of the test. The conductive deposit factor will be referenced in this paper throughout. 5 Research Analysis using the CDT - Transmission Fluids used in EV The precision has been proven dependable for this test over the past few years of development. Because of the consistency of the test researchers have been active to investigate potential improvements to fluids performance. A study was conducted with existing EV transmission fluids. The transmission oils are in-industry fluids with known performance results. These fluids were first evaluated utilizing the CDT and kinematic analysis at 100 °C. The CDT results for ATF A and ATF B are shown below evaluating the resistance change over time. It is evident that these two transmission fluids have failure mechanisms, but in different capacities. The potential reasoning will be discussed later in this document. ATF A, Figure 7, had a propensity to fail in the vapor phase while leaving the oil phase stable over the entire 1000-hour period. Alternatively, ATF B in Figure 8, failed the oil phase with the vapor phase remaining unscathed from deposit. Thus, having two finished and marketed products with distinctively opposing failures was optimum for this study. 5.1 Material Reactions - Base Stock and Ester Dilution The goal for this experimental process was to determine the chemical relationships between these fluids and the dilution effects of various base stocks and additives. The first target was a wellknown group II base stock. The goal was to see if 20 % of this base stock or an ester would extend the result in hours. Understanding the relationships with enhanced materials is important. Esters are known for their excellent dielectric capabilities, and they are sulphur free. That make the EV application more inviting. Research 49 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0033 Figure 7: ATF A fresh ! ! " ! "" ! """ ! """" ! """"" ! """""" ! """"""" " #"" $"" %"" &"" ! """ ! #"" '()*+,-.+/ (/ 01)2+-3456/ 7 8(6+-39: ; ,/ 7 ! "#$ %&&'()*)+,-.(&/ 0,12) ! "#$%&''"'($)*( +),-%$%&''"'($)*( Figure 8: ATF B fresh ! " # $ % & ' ( ) * "! ! "! ! #! ! $! ! %! ! &! ! '! ! (! ! )! ! *! ! "! ! ! +,-./ 012345647,82159: 01,; 5<+69= >2? 45<@,/ ; 8= ! "#$ ! %%&'()%*+%,*-./ 0(12)%3)4*51(%,6'-7) A2B5C/ ? 5" D: 7,; 5C/ ? 5" ATF B is shown in Figure 11. The traction fluid had a significant impact on this fluid in the liquid phase, putting into the passing category. The interest here was the overall reaction to both materials. The traction reduction additive, in each case, extended the life of the transmission fluid significantly, see Figure 11. Both fluids went from failing early, or borderline failing, to easily passing at the solid performance level. From 200 hours to 800 and 1000 hours is significant as shown in Figure 12. Research 50 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0033 The reactions for the two original transmission fluids were more interesting than expected. Results are shown in Figure 9. ATF A, which had a failing oil phase failure at 268 hours remained unchanged. It was anticipated that if the interaction of the additives were causing the oil phase failures, then diluting it with 20 % of the group II base stock or the ester would improve the result. These tests were repeated to verify the accuracy of the results. The tests, not shown, were within a percent of one another. The reactivity of the vapor, created with without the dilution, was significant enough to not only destroy the copper but create significant levels of dendrites for conductive deposits. Vapor materials can be extremely destructive to metallic part [7, 8, 9]. ATF B, which failed the liquid phase at 506 hours, yielded some interesting results in both phases. Dilution using both the ester and group II base stocks did lead to improving the resistance to conductive deposit formation in the liquid phase, but had the opposite effect in the vapor phase. Instead of an oil failure of less than 200 hours the fluid did not have conductive deposit issues until beyond 700 hours, see Figure 10. However, there was enough of a mechanism change due to the base stock to cause the vapor to have conductive deposit issues, but only beyond 700 hours. Since the test will be anticipated to last only 500 hours to predict failures the 700 hours would not necessarily be concerning. To know that this change increased the probability of oil phase failure is interesting, nonetheless. The main take away is that ATF A, which failed in the vapor state, was unaffected by the dilution. The additives in the oil may be diluted or masked. 5.2 Materials - Traction reduction additive A traction reduction additive was selected that is a hydrocarbon synthetic based material that provides slip reduction in transmissions. The material is slightly higher in viscosity, to note, than the transmission fluid or ester utilized in this study. That is a fact to note for future reference. Once again, the traction reduction additive was added to the original EV driveline fluids. The purpose of this experiment was to investigate the level of reaction from the dilution of this material. The interesting result of ! " # $ % & ' ( ) * "! ! "! ! #! ! $! ! %! ! &! ! '! ! (! ! )! ! *! ! "! ! ! +,-./ 012345647,82159: 01,; 5<+69= >2? 45<@,/ ; 8= ! "#$%& '()*$+,-$./ 012$33$& 405617)(89$: 920; ()$<=)9$0>$4*=5? 9 ! "#$%&'$( )*+,-$%&'$( Figure 10: ATF B with 20 % base stock dilution ! " # $ % & ' ( ) * "! ! "! ! #! ! $! ! %! ! &! ! '! ! (! ! )! ! *! ! "! ! ! +,-./ 012345647,82159: 01,; 5<+69= >2? 45<@,/ ; 8= ! "#$%$&'()$*+,$"-./ ('01$#23'4$.14$ $*+,$5677$8 6.(9$0: $; ).1<9$5-.=) ! "#$%&'$( )*+,-$%&'$( Figure 11 Figure 9: Dilution table and response To evaluate this response, the viscosity of all the fluids, as mentioned above, were taken at 100 °C. The relative kinematic response was higher for the traction reduction additive. This led to an investigation of the boards. For in-fluid responses, the viscosity should not necessarily play a role in the improvement of the response. At least not from the authors’ perspective. Dilution, of course, is always a possibility but the rate of enhancement was significantly more than 20 %. However, for the vapor phase improvements there was noticeable changes on the actual board as well. There was a distinct line where the conductive deposits were formed. A capillary action is occurring for the lower viscosity fluids. For example, the transmission fluid had a KV100 at 7.33 cP with a capillary movement up the board of 6 mm. The fluid dilution of traction reduction additive had a KV100 of 10.74 cP and capillary movement of 0.3 mm. Thus, the board had an increase in conductive deposits on the upper portion of the board potentially from the capillary movement. The higher viscosity fluids did not have the capillary action. Not to mention the volatility level, potentially lower, could also play a part in the improvement. So, the level of deposits in the vapor phase area of the board were lower because of it, at least in this situation [10]. Further studies of these effects will be analysed for the next paper. 6 Conclusions Conductive deposits have proven to be problematic in the EV industry. Failures have occurred and resolutions are in place to help rectify the situation. The performance of the fluids utilized in the transmission have varying levels of quality. The conductive deposit test was developed to evaluate this attribute. The conductive deposit test has an electrified and nonelectrified circuit board with a tightly controlled space between them. At 150 °C the test will evaluate the resistance response in the oil and vapor phase simultaneously. As conductive deposits are formed, the resistance drops until potentially complete failure occurs. The test aligns with passing and failing field performing fluids. This paper evaluated the response of base stock, ester and traction reduction additives added to a driveline fluid that were poor performing. One in the vapor and the other in the oil phase. The base stock dilution had negligible effect where the ester had moderate improvement characteristics notably from the oxidation protection and polar responses. The largest improvement was from the dilution with the traction reduction additive. This synthetic fluid improved the propensity of both driveline fluids to form conductive deposits. 7 Future Work Continuing work in this area is important. Evaluation of the conductive deposit dendrites that are formed is necessary. Determination of appearance and composition of these deposits in various areas of the failures and the interaction of elements such as sulphur, oxygen and copper will be critical. Each of the documented scenarios from this paper will be evaluated. Scanning electron microscopy and inductively coupled plasma spectroscopy will be utilized for this process. Other additives will also be evaluated. 8 References [1] Han, Ji-Hung, “Over-limiting Current and Control of Dendritic Growth by Surface Conduction in Nanopores” [2] ASTM Method of Test D2272-02, Oxidative Stability of Steam Turbine Oils by Rotating Pressure Vessel (Reapproved 2011). ASTM 5 vol., pp. 846-864, 2010 and IP Method of Test 142/ 85 (92) [3] ASTM Method of Test D130-19: Standard Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test. ASTM Digital Volume D130 Section [4] Accepted for publication. Hunt, G., Choo, L., and Newcomb, T., “100 Years of Corrosion Testing—Is It Time to Move beyond the ASTM D130? The Wire Corrosion and Conductive Deposit Tests,” SAE Int. J. Fuels Lubr.17(1): 2024, doi: 10.4271/ 04-17-01-0002. [5] Chauhan, Saurabh “Motor Torque Calculations for Electric Vehicles” International Journal of Scientific & Technology Research Volume 4, Issue 8, August 2015. [6] Hunt, G., Javaid, R., Simon, J., Peplow, M. et al., “Understanding Conductive Layer Deposits: Test Method Development for Lubricant Performance Testing for Hybrid and Electric Vehicle Applications,” SAE Int. J. Elec. Veh. 12(2): 263-277, 2023, https: / / doi.org/ 10.4271/ 14-12-02- 0014. Research 51 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0033 Figure 12 rate. Journal of the Electrochemical Society 1988, 135 (8), 2027. https: / / doi.org/ 10.1149/ 1.2096201. [7] Hunt , G. New Perspectives on the Temperature Dependence of Lubricant Additives on Copper Corrosion SAE Int. J. Fuels Lubr. 10 2 2017 521 527 https: / / doi.org/ 10.4271/ 2017-01-0891 [8] Hunt , G.J. , Gahagan , M.P. , and Peplow , M.A. Wire Resistance Method for Measuring the Corrosion of Copper by Lubricating Fluids Lubrication Science 29 4 2017 279 290 https: / / doi.org/ 10.1002/ ls.1368 [9] Hunt, G. and Prengaman, C., “Understanding Vapor and Solution Phase Corrosion of Lubricants Used in Electrified Transmissions,” SAE Technical Paper 2020-01-0561, 2020, doi: 10.4271/ 2020-01-0561 [10] Forslund, M., “E-Mobility Fluid Testing for Heavy Truck Transmissions”, presented at the STLE EV Conference, San Antonio, TX, 2021. Research 52 Tribologie + Schmierungstechnik · 70. Jahrgang · eOnly Sonderausgabe 1/ 2023 DOI 10.24053/ TuS-2023-0033 [A] Barcroft, F.T., “A Technique for Investigating Reactions between E.P. Additives and Metal Surfaces at High Temperatures,” Wear 3, no. 6 (1960): 440-453 [B] Gahagan, M. and Hunt, G., “New Insights on the Impact of Automatic Transmission Fluid (ATF) Additives on Corrosion of Copper—The Application of a Wire Electrical Resistance Method,” International Journal of Automotive Engineering 7 (2016): 115-120. [C] Savant Group, USA and APL, Germany Zou, L. C.; Hunt, C., A new approach to investigate conductive anodic filament (CAF) formation. Soldering & Surface Mount Technology 2015. https: / / doi.org/ 10.1108/ SSMT-02-2014-0002. Vaughen, B.; Roth, J.; Steppan, J.; Hall, L.; Major, C., Electrolytic Copper Migration in Accelerated Tests: I. 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ISSN 0724-3472 Aus Wissenschaft und Forschung Science and Research www.expertverlag.de Greg Livingstone, Ludger Quick, Jo Ameye Managing Turbine Oils in a Sustainable Way Rüdiger Schiffer Chromium-VI formation on high alloyed screws Elona Rista, Greg Livingstone Applying knowledge from accelerated turbine oil aging tests to oil management programs Nicholas Lancaster, Keith Cory Schomburg Rapid identification and quantification of ethylene and propylene glycol in engine coolant by gas chromatography Jo Ameye, Greg Livingstone, Cristian Soto Managing hydraulic oil deposits by using novel solubility enhancing technology Jeremy Sheldon, Mark Redding Combining Oil Health, Level, and Vibration to Achieve Complete Machine Monitoring Sarah Hüttner, Verena Leumann, Rachel Kling Electrical contacts - the challenge for lubricants Gregory Miiller, William VanBergen, Alexei Kurchan, David Gillespie, Gunther Mueller, Rico Pelz, Timothy Newcomb, Gregory Hunt Research and Development Utilizing the Conductive Layer Deposits and Wire Corrosion Bench Test Technology for Electric Vehicle Drivetrains