Water Contamination in Lubricants: What You Need to Know

Whenever I have the opportunity to discuss water contamination in lube oils — whether at tech conferences, during training sessions, or in casual conversations with colleagues — I always ask two main questions: Where in your oil system can water be found, and how do you get rid of it? More than 80% will say that water accumulates at the bottom of the oil tank and that most of it can be removed by opening the drain valve. While there is some truth to that statement, I can’t help but assume that most are unaware of the three forms of water contamination in oil: dissolved, emulsified, and free. Each of these can cause both direct and indirect effects on your machine’s performance. Let’s delve deeper to understand why water contamination is considered the second most destructive form of contamination in your machineries, next only to particle contamination.?

Dissolved Water

It turns out that oil and water do mix. Over time, the natural attraction and interaction of the lubricant to the ambient air humidity increases the dissolved water in the oil. Oil, along with its additives, is hygroscopic, meaning it tends to attract moisture. A higher concentration of additives tends to attract more moisture. This characteristic of the oil is one of the reasons why you can’t have too much additives on your lubricants, especially on critical applications like turbines.

Most industrial oils can contain between 100 to 600 ppm of water, with acceptable levels typically ranging from 50 to 300 ppm, depending on the oil’s age and operating temperature. As temperature increases, the saturation point of any oil decreases. It is also important to note that as the oil ages, its capacity to dissolve water generally increases.

Why is this a problem? Although dissolved water is less damaging compared to other forms of water contamination in oil, it still requires attention. Water molecules are polar, which means they tend to adhere to other polar surfaces, including metal components in your machinery. This adhesion can lead to corrosion of metal parts such as gears and bearings, resulting in premature failure. Additionally, dissolved water can react with the oil’s additives, causing them to lose their effectiveness and ultimately leading to significant equipment problems.

Analogy: Dissolved water is like the moisture you feel in the air: It’s not visible to the naked eye, but you know it’s there.

Emulsified Water

Oil can only absorb dissolved water up to a certain saturation point. Once this limit is reached, any additional water introduced into the system forms suspended micro-droplets within the oil, known as an emulsion. Emulsified water causes the oil to appear foggy or hazy and moves freely throughout the system with the oil. This is one reason why it is considered by many in the industry to be the most damaging type of water contamination in oil.

How does it damage your equipment? Emulsified water can have multiple effects that directly or indirectly cause issues in your equipment. The primary concern is the impact on the oil’s compressibility. The presence of suspended water in the oil results in a significant increase in bulk modulus, which makes the oil more difficult to compress and can lead to premature wear of machine components. An example of this is the loss of hydrodynamic oil film in the journal bearing of the turbine leading to excessive wear.

Like dissolved water, emulsified water can also cause rusting of metal parts. However, a more complex issue arises when rust particles combine with the emulsified water, creating what is known as sludge. This sludge can cause further abrasion of metal parts, generating additional particulates, and the cycle continues until corrective measures are taken.

Other effects of emulsified water in the system include the clogging of filters and the formation of acid.

Analogy: Fog formation

Free Water

As additional water enters the system, the two phases will separate. Depending on the specific gravity of the oil, free water may either settle at the bottom of the sump if the specific gravity is less than 1.0, or float on top of the tank if the specific gravity exceeds 1.0.

What impact does it have on your machinery? Free moisture causes significant rusting of the metal parts and has a direct effect in increasing the aging rate of the oil.

Analogy: Rainfall due to excessive amount of moisture in the air.

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What you need to do?

You cannot effectively manage what you cannot measure. Therefore, the first step is to conduct periodic monitoring of your oil’s moisture content. Several testing methods are available, including the Crackle Test, Fourier Transform Infrared Spectroscopy (FTIR), Karl Fischer Titration (KFT), and Relative Humidity Sensor Technology. Each method has its own advantages and limitations, so it is important to select the one that is most suitable for your specific application.

The next step is to investigate the root cause of water contamination. As with any issue, early detection is crucial for preserving both the integrity of your equipment and the quality of the oil. Oil analysis will determine whether the oil remains usable despite water contamination. Once confirmed, several methods are available for removing water from the oil. The most common techniques are outlined below:

Settling: This method typically employs a bottom sediment and water bowl (BS&W) to remove free water. However, it is not effective in removing dissolved or emulsified water.

Centrifugal Separation: This device operates on the principle of centrifugal force to separate oil and water. By rapidly rotating a mixture within a bowl or chamber, the machine creates a strong centrifugal force that causes the denser water to move outward, towards the outer walls of the chamber, while the less dense oil remains closer to the center. In a centrifuge, both free and emulsified water can be removed.

Vacuum Distillation: This process operates by creating a vacuum to lower the boiling point of water. The oil is then heated to a temperature that is sufficiently low to prevent significant damage to the base oil or its additives. This method effectively removes free, emulsified, and dissolved water from the oil.

Polymeric Filters: These filters are designed for the removal of water from oil. It utilizes advanced materials and filtration technology to enhance the separation process. These filters are composed of specialized polymeric membranes or substrates that selectively capture water droplets while allowing oil to pass through.

In conclusion, understanding and managing water contamination in lubricants is vital for the optimal performance and longevity of machinery. By employing appropriate monitoring and remediation techniques, you can mitigate the adverse effects of water contamination and maintain the reliability of your equipment.

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