Ask the Experts

"Is there a recommended test to determine the vapor-phase corrosion-inhibiting properties of lubricants?"

The standard test method for measuring vapor-phase corrosion inhibition is ASTM D-5534. In this test, a steel specimen is attached to the top of an ASTM D-3603 test apparatus that contains the fluid to be tested at 60 degrees C (140 degrees F). The specimen is then exposed to water and oil vapors for a period of six hours. At the end of the test, the specimen is examined for evidence of corrosion. If corrosion is present, the lubricant is scored as a fail. Obviously, if there is no sign of corrosion, the lubricant is given a pass.

While it is important to have a lubricant that can protect against water ingression and the eventual humidity created by the water and hot machine oil, what is more important is taking a proactive approach to reduce water ingression in the frst place. There are many viable solutions, which tend to be application-dependent, including desiccant breathers, headspace purging, expansion chambers, etc. One of the easiest, cheapest and most fundamental ways to reduce ingression is to simply seal the system as best you can. This would include not leaving tank hatches open, not relying on OEM breathers to stop moisture and not running water across the top of a sump to cool it.

If water does enter the system, you must be able to recognize its presence, analyze its state and concentration, and remove it as quickly as possible. Water can exist in oil in three states or phases. The frst state, known as dissolved water, is characterized by individual water molecules dispersed throughout the oil. Most industrial oils such as hydraulic fluids, turbine oils, etc., can hold as much as 200 to 600 parts per million of water (0.02 to 0.06 percent) in the dissolved state, depending on the oil’s temperature and age, with aged oils capable of holding three to four times more water in the dissolved state than new oil.

Once the amount of water has exceeded the maximum level for it to remain dissolved, the oil is saturated. At this point, the water is suspended in the oil in microscopic droplets known as an emulsion. In a lubricating oil, this condition is often referred to as haze, with the oil said to be cloudy or hazy.

The addition of more water to an emulsifed oil/water mixture will lead to a separation of the two phases, producing a layer of free water as well as free and/or emulsifed oil. For mineral oils and polyalphaolefn (PAO) synthetics with a specifc gravity of less than 1.0, this free water layer is found on the bottom of tanks and sumps.

Recognizing the states and analyzing the concentration can help you make a decision on how to best remove the water, but as stated earlier, stopping the ingression in the frst place should be the ultimate goal.

"What percentage of total life-cycle costs do lubricants account for in a pump, motor, conveyor or blower/fan?"

When estimating the lifecycle costs of machinery, you must take into account several factors. Of course, there is the initial purchase and installation of the equipment, as well as any aftermarket accessories attached to the machine. There is also the cost of ownership, including all the maintenance procedures that are performed routinely to ensure the pump, motor, conveyor, fan, gearbox, etc. is running correctly.

Properly maintaining a piece of equipment is much easier said than done. When a simple oil change is required, several costs are incurred. Not only is there the cost of the lubricant but also an expense for the labor associated with changing the oil. In larger-capacity reservoirs, it may take hours if not days to complete the oil change. This is referred to as the “hidden cost of an oil change.” If you are using premium formulated oils, especially synthetic fluids, the cost of the lubricant alone can be more than $50 dollars per gallon.

Perhaps the best way to answer this question is to explain the benefts of properly lubricating and maintaining equipment. An equipment failure can occur for a variety of reasons, yet in a recent study it was determined that as much as 43 percent of equipment failures are directly attributed to the incorrect choice and usage of lubricants.

A common mistake that can lead to premature failure is the selection of the wrong viscosity based upon the operating conditions (load, speed, surface roughness, etc.), which can greatly increase the amount of wear a machine experiences. While the cost of a lubricant can be very low, the beneft of using it correctly can be very high.

Aside from using the incorrect viscosity, the cleanliness of the lubricant makes a big difference in how well and how long a machine can operate. By keeping the lubricant clean, you can extend the life of the machine in which it is operating. A study by Ernest Rabinowicz has shown that 70 percent of machines lose their usefulness due to surface degradation of internal parts. Proper lubricant conditioning can lessen this occurrence and thus extend machine life.

So while it is diffcult to put a dollars and cents value on the cost of a lubricant throughout the life cycle of a piece of equipment, the effects the lubricant has on the machine are limitless. In order to get the most from your machines and cut down on the mean time between failures (MTBF), you must properly maintain the lubricant.

If you have a question for one of Noria’s experts, email it to editor@noria.com