water contamination in oil

Water contamination in oil can cause severe damage to machinery by accelerating corrosion, promoting oil degradation, and destroying lubricating film strength. Water can exist in oil in three phases—dissolved, emulsified, and free—with emulsified and free water being the most destructive. 

Three phases of water in oil

• Dissolved water: Individual water molecules are dispersed throughout the oil below the saturation point. It is invisible and causes long-term damage, such as oxidation, but is less harmful than the other phases.

• Emulsified water: When the water content exceeds the saturation point, it is suspended in the oil as microscopic droplets, giving the oil a milky or cloudy appearance. Emulsions are highly destructive and severely reduce the oil's lubricating properties.

• Free water: When the oil can no longer hold water in an emulsified state, the water separates and settles at the bottom of the tank or sump (in most mineral oils, which are lighter than water). 

Common causes

• Leaks: Coolant or process water can leak into the lubrication system through faulty heat exchangers, coolers, or seals.

• Condensation: Changes in temperature, such as a cold engine in a humid environment, cause water vapor to condense inside the system. This is a common source of moisture, especially in intermittently operated machinery.

• Poor storage: Storing drums or other containers outside or in high-humidity areas can allow water to seep in through seals or bungs.

• Ingression during operation: Water can enter through damaged or poor-quality seals, vents, and breathers, especially during machine washdowns. 

Destructive effects

• Oil degradation: Water promotes oxidation of the oil's base stock, which accelerates aging and leads to the formation of harmful acids and sludge.

• Additive depletion: Water chemically attacks or "washes out" important additives, such as rust inhibitors and anti-wear agents, compromising the oil's performance.

• Increased corrosion and wear: Free water causes rust on metal surfaces. Emulsified and dissolved water can reduce the lubricating film strength, leading to accelerated wear and fatigue. In rolling-element bearings, high pressure can cause trapped water to flash-vaporize and create erosive pitting.

• Cavitation: In hydraulic pumps, water droplets can vaporize under low pressure and implode when exposed to high pressure, causing pitting and erosion of metal surfaces.

• Microbial growth: In systems with free water, microbes can proliferate and further degrade the oil and its additives. 

Prevention and removal

To combat water contamination, use a combination of proactive prevention and reactive removal methods. 

Prevention

• Use desiccant breathers to absorb moisture from the air entering the reservoir.

• Properly seal and store new oil drums indoors to protect them from environmental exposure.

• Maintain and upgrade seals to prevent water from entering the system.

• Check and replace oil caps, especially in vehicles, to ensure a proper seal.

• Regularly analyze oil samples for water content using a lab test like Karl Fischer titration, which is highly accurate. 

Removal

• Gravity separation: For free water, draining from the bottom of a sump or reservoir is the simplest method.

• Vacuum dehydration: This method removes free, emulsified, and dissolved water by boiling it off under a vacuum and at a moderate temperature.

• Centrifugal separation: A centrifuge uses centrifugal force to separate denser water from oil. It effectively removes free water and some emulsified water.

• Water-absorbing filters: Filters with super-absorbent polymers can trap free and emulsified water.

• Headspace dehumidification: A dehumidifier can remove moisture from the air in the reservoir's headspace, drawing water out of the oil.