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Detecting and Controlling Moisture in Oils

Thursday, January 14, 2016 | AMETEK Brookfield
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Doug Elliott, National Account Representative at Arizona Instrument LLC talks about how their equipment can be used to measure water contamination in oil-based lubricants and the ASTM approval of their moisture analysis method.


From’s insights from industry interview on 1/14/16 with Doug Elliott, National Account Representative at Arizona Instrument LLC. Read the interview on or below.

WS: Could you provide our readers with an update on the major developments which have been going on at Arizona Instrument LLC since our previous interview?
DE: We are proud to announce that the US Department of Defense has approved the Computrac® Vapor Pro® (ASTM D7546) instrument and method for moisture content as an alternative to ASTM D6304 (Karl Fischer) in MIL-PRF-17331K. They are also adding it to their QPL (Qualified Products List) requirements.

The ASTM method D-7546-09 Procedure B (using the Vapor Pro® L) has been balloted and passed. We are in the midst of the repeatability and reproducibility testing on Procedure A. The plan is to have that data returned and balloted by the summer.

WS: Why is moisture considered a chemical contaminant when suspended or mixed with lubricating oils?

DE: For oil-based lubricants, the presence of water is of significant concern, as it can decrease the efficiency or the lubricant and cause early wear of the parts. This, in turn, increases maintenance cost as well as down-time while the equipment is being repaired. Water reacts with additives to create sediment, hydrogen sulfide and other compounds while it also reduces additive effectiveness and shortens additive life.

It has been reported that a 10% reduction in maintenance cost in the average plant creates a bottom-line effect equivalent to a 40% increase in sales. Moisture contamination is the second most common cause of lubrication-based equipment failure, directly after particle contamination.

WS: Could you explain to our readers the effects which water has on equipment and lubricants?

DE: Water gives the acid in oil its greatest destructive potential. It causes film strength failure and hydrogen embrittlement of metal parts.

WS: What are the other factors which affect the corrosion of mechanical machinery such as engines?
DE: Water promotes changes in chemical and physical properties in mineral oils as well as in some synthetics, which can lead to acid formation, viscosity change, varnish creation and sludge. Water contamination also contributes to foaming and air entrapment.

WS: How does the effect of moisture contamination vary depending on whether the water in oil is Dissolved, Emulsified or Free Moisture?
DE: The water saturation point is the maximum amount of dissolved water that an oil will hold at a given temperature. This could be in the range of low ppm to over 2,000 ppm, depending on the type of oil. Above that level, microscopic globules of water are dispersed in a stable suspension, like fog, called an emulsion.

While all states of water in oil can cause damage to both the oil and the machine, emulsified water is considered to be the most destructive. Above that concentration level, the suspended water will settle-out as free water.

WS: Could you outline the main techniques which can be used to detect moisture in oils and explain the advantages and disadvantages associated with each of these methods?
DE: The simplest technique to determine moisture in oils is the Crackle Test. A couple of drops of oil are placed on a 160ºC hot plate. Free or emulsified water will form bubbles of various sizes and quantities depending on the concentration. Developed in 1935, the classic laboratory technique to measure the amount of water in oil is named after its developer, Karl Fischer. For higher concentrations of water, over 1%, the current preference is volumetric titration. For lower concentrations, coulometric titration by electrolysis provides more sensitivity, where the amount of charge required to reach the endpoint is used to calculate the amount of water in the sample.

Although many chemistry modifications have been recommended, the Karl Fischer technique is prone to interferences from detergents, functional additives, oxidation products, free alkali, and sulphur/nitrogen/phosphate-based substances. Karl Fischer results should be considered relative rather than absolute due to the numerous interferences.

Other techniques developed over the years include:

  • Co-distillation with toluene or Dean Stark
  • Percent water saturation sensors
  • Calcium Hydride hydrogen gas generation

WS: How can Arizona Instrument’s Computrac® Vapor Pro® series be used as a cost-effective alternative to Karl Fischer titration methods?

DE: Our Vapor Pro® series of moisture analyzers warm the sample like a crackle test and sweeps the sample bottle headspace with a dry carrier, such as air or nitrogen. The evolved vapors of water and light organics are transported to the Relative Humidity (RH) sensor.

The face of the sensor is coated with a thermoplastic layer to protect the platinum electrodes from external dust, dirt and condensed organics. The porous platinum layer has a pore structure just large enough for water to diffuse through to the dielectric capacitance layer and still small enough that molecules larger than water are rejected and leave the analyzer via the exhaust. Typical interferences are blocked from the sensor and do not bias the data.

There are no titration or electrolysis chemicals to purchase, to interfere, or to dispose, no specialty glassware to buy or to replace and no special operator training. The sample bottles for the Vapor Pro are often cleaned and reused many times. The Teflon-faced silicone rubber septa can be punctured a few times in low-level, high accuracy tests or 10 to 20 times for higher concentration, trending tests.

WS: Why is setting appropriate moisture content level targets important?
DE: Since every lubricant and every machine type has a different critical target point, it is important to work with your suppliers to get their recommendation. As a general rule, it is best to keep the water concentration below the saturation point at all in-service temperatures. If not, always strive to keep the water concentration as low as is reasonably achievable.

WS: How can the amount of moisture in oil be controlled?
DE: The selection of the proper oil, which is based on the equipment and application, controlled handling and filling, desiccant breathers and regular PM inspections with an oil analysis test slate all help to monitor and control the amount of moisture contamination in a specific oil.

WS: Where can our readers find out more information on how Arizona Instruments can help them to detect and control moisture in oils?
DE: People interested in performing water concentration testing on petroleum samples are encouraged to contact us online or give us a call at (800) 528-7411. Thank you for this opportunity to reach out to your readers who are interested in performing water content testing and looking for an alternative to the classic Karl Fischer wet chemical method.

About Doug Elliott

In January 2016 Doug celebrated his 10th anniversary at Arizona Instrument LLC as a National Account Representative in the Computrac moisture analysis division. During that time he has worked with customers in the Chemicals, Battery, Petroleum, Catalyst and Gypsum application areas. His objective is and has always been to help customers get the best data and performance possible from their Computrac moisture analyzers. He relocated from Pennsylvania where he worked in R&D analytical services and in laboratory essential performance supplies. He says the best thing about living in Arizona is that that “the skies are not cloudy all day!”

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