Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1378657
40 | May - June 2021 | www . machinerylubrication.com CONTAMINATION CONTROL & LUBRICANT RECONDITIONING into the oil. Dissolved water is what causes any part not coated in oil to start rusting, promoting further oxidation and contamina- tion down the road. As the concentration or saturation of dissolved water builds, it will turn into free water or emulsify with the oil. You can have both free and emulsified water in the same sump. Free Water We all know water and oil do not mix well together. Water is usually heavier than oil and will sometimes settle out in the bottom of the sump. is is what we refer to as free water. Free water is usually in high concentration because of a shaft seal leak or some other source of outside water ingression. Free water is also hard to identify in small concentrations unless we have a window or some way to see the oil inside the sump. If caught early enough, free water is the easiest form to remove from a sump or reser- voir. Installing a bottom sediment and water bowl or column sight glass on the drain port is a good way to keep a constant eye on water contamination. Free water buildup can cause serious problems, with oil levels eventually filling up and either overflowing or causing the gears to now operate with water and oil causing emulsification. If water is allowed to mix around in the oil, it can cause foam and become suspended within the oil, emulsifying and causing serious viscosity changes which then results in boundary conditions and even- tual machine failure. Emulsified Water Water/oil emulsification occurs when free water and hot oil are agitated together. e oil and water become mixed, leading to increased viscosity, loss of film strength, additive washout and lubricant failure. Viscosity is the most important physical characteristic of an oil. When free water is allowed to become emul- sified, the viscosity will go up and machines will start working harder, become hotter and machine parts will fail. Emulsified water is almost impossible to fight with filtration. It is important to catch the problem during the free state to prevent emul- sification. Failure due to water contamination may be catastrophic, but it may not be imme- diate. Many failures blamed on lubrication are truly caused by excess water contamination. Some of the effects of water on gearboxes: • Shorter component life due to rust and corrosion (gears and bearings). • Water etching caused by the generation of hydrogen sulfide and sulfuric acid from water. • Erosion caused by free water flashing onto hot metal surfaces and causing pitting. • Hydrogen embrittlement happens when water invades microscopic cracks in the metal surfaces. Under extreme pressure, water decomposes into its components and releases hydrogen. is explosion forces the crack to become wider and deeper, leading to spalling. • Film strength loss — the pitch line of a gear tooth is protected because oil viscosity increases as pressure increases due to the oil's pressure/viscosity coeffi- cient. Water does not possess this property. Its viscosity remains constant (or drops slightly) as pressure increases. As a result, water contamination increases the likeli- hood of contact fatigue (spalling failure). Some of the effects of water on gearbox oil: • Water accelerates oxidation of the oil. • Water depletes additives like oxidation inhibitors and demulsifiers. • Water causes ZDDP anti-wear additives to destabilize over 180°F. • Competes with polar additives for metal surfaces. Water can lead to soot agglomeration, wax curd and even sludge by mopping polar impurities. Chemically, it can cause additive depletion and oxidation of the lubricant while also forming acid and rust. Physically, it can alter the viscosity of the lubricant. Now that we know all about how water affects gearboxes and the damage it can cause, let's talk about how to solve the problem and keep it from happening again. e most common cause of water ingres- sion or contamination is through open ports/ hatches, shaft seals, flange fittings and cooling systems. Water is used in every industry and is therefore the leading cause of machine failures. Water contamination is a silent killer. It can take a long time to cause noticeable damage, but when the signs do appear, it is usually too late. However, all oils will have a traceable amount of water in them. It is important to test new oil coming in, so you have a baseline or starting point — something to use as a refer- ence if a problem does arise. Some of the ways to monitor water in oil are: • e use of sight glasses (column sight glass & BS&W bowl) for a quick visual indica- tion. Moisture sensors attached to the oil reservoir. • Moisture sensors can be installed to measure the moisture in the headspace of the reservoir as well as moisture in the oil. • Oil analysis is another way to monitor the amount of water in the oil. For the most accurate results, I recommend using an oil analysis lab. • A convenient way to determine water concentration in the field is by using a calcium hydride test kit. Water reacts with solid calcium hydride to produce hydrogen gas, which is directly proportional to the amount of water present in the sample. e water content of the sample is meas- ured by the increase in pressure in a sealed container. ese test kits are reported to be accurate down to 50 ppm free or emul- sified water. e calcium hydride test is a great starting point, letting you know immediately that a water problem exists. • Another way to monitor for water contam- ination is by suspending a metal rod inside the reser-voir's headspace. Over time, if water is present, the metal rod starting to rust will let you know that water contam- ination is an issue. Controlling water contamination can be accomplished in a variety of different ways: • A simple desiccant breather mounted on the headspace. Desiccant breathers allow the air entering equipment to flow through the desiccant media, stripping out any moisture and trapping it in the desiccant media before entering equipment. • On medium size reservoirs, you can attach