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Avoiding free water in a lubrication system

Avoiding free water in a lubrication system
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Avoiding free water in a lubrication system - 1

/ APPLICATION NOTE Avoiding free water in a lubrication system Free water in lubrication oil can cause major failures to large machinery, especially in applications where water is constantly present as in ship propulsion systems and hydro power turbines. Free water prevents oil from forming a uniform lubricating layer on metal surfaces deteriorating both the lubrication performance and the ability of the oil to protect the machine. Equipment is damaged by corrosion, cavitation, micro pitting, and spot heating. Free water also ruins polar additives of oil. In offshore applications, free water tends to be even more destructive due to the presence of salt water creating a more corrosive environment for the metals it is in contact with. In cases of sudden leaks, a free water layer can form quickly, and if only periodic oil sampling is performed, water is most likely detected too late resulting in damage. On-line monitoring enables the machinery operator to make corrective actions before any failure occurs. Formation of free water based on oil's water solubility Just like air, every fluid (e.g. lubricating oils, hydraulic fluids) has the ability to hold water in the dissolved state below the saturation point. Once the saturation point of that fluid has been reached, any additional water that enters the fluid will separate out into “free water” which can be seen as a distinct layer – usually below the oil. Oils typically have very limited water solubility. The saturation point of oil is affected not only by the base oil type, additives and anti-oxidants, but also by the fluid’s age, temperature and the chemical reactions that take place over the life of the fluid. It is also very typical that different commercial oils used for the same application, vary significantly with respect to their ability to hold dissolved water (Figure 1). A safe moisture level indicated in parts per million (ppm) for one oil may be above saturation in another. Figure 1 Water solubility of different commercial lubrication oils (2001). Tests run at 31 °C.

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Avoiding free water in a lubrication system - 2

Effects of oil temperature on the solubility In lubrication systems, the oil is typically rather warm e.g. +40…+60 °C. In situations when temperature decreases considerable, like when engines are turned off, there is a risk of free water formation, because the oil cannot anymore hold the same amount of water. While the absolute water content (ppm) has remained unchanged, the saturation point has been reached and the risk of, for example, corrosion becomes likely (see Figure 2). In case free water has formed during a shutdown, the oil should be dried first or the system has to be started...

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Avoiding free water in a lubrication system - 3

Benefits of continuous water activity (Aw) measurement versus ppm measurement Traditionally water contamination has been measured by regularly scheduled oil samples following a maintenance program using Karl Fisher titration. The output of the titration is absolute water content in ppm (parts per million). Absolute water content cannot tell the operator whether water is in dissolved or free form i.e. safe or unsafe level. When measuring the absolute water content of the oil, the operator has to know the safety limits for each specific oil type he uses. He also has to consider the ageing...

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Avoiding free water in a lubrication system - 4

Ref. B211029EN-A ©Vaisala 2010 This material is subject to copyright protection, with all copyrights retained by Vaisala and its individual partners. All rights reserved. Any logos and/or product names are trademarks of Vaisala or its individual partners. The reproduction, transfer, distribution or storage of information contained in this brochure in any form without the prior written consent of Vaisala is strictly prohibited. All specifications — technical included — are subject to change without notice. For more information, visit www.vaisala.com or contact us at sales@vaisala.com Figure...

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