Water is a terrible lubricant! A top priority for any maintenance program is preventing water from entering lubricating or hydraulic oil. Just as important to the health of the asset is being able to detect and remove water contamination at an early stage.
Typical Problems Associated with Water Contamination
Excessive water contamination in a lubricating or hydraulic oil may result in numerous problems, as follows:
- Corrosion – water promotes rust and acidity
- Cavitation – water is one of the leading causes of hydraulic pump cavitation
- Aeration – water encourages foaming and air entrainment
- Silting & Filter Plugging – water causes poor filterability and valve stiction
- Film Strength Loss – water causes film strength failure and hydrogen embrittlement of rolling element bearings
- Hydrolysis & Oxidation – water promotes chemical and physical changes to the base oil (i.e., acid formation, oil thickening, varnish, sludge)
- Viscosity Effects – water may lead to stable emulsions, higher viscosity, and non-Newtonian properties
- Dielectric Effects – water reduces electric insulating properties of the oil
Targets are not the same as limits
Monitoring critical oil-wetted components through oil analysis is an effective way of maintaining a contamination control program. However, it is important to know ‘how much water is too much’, and when corrective actions should be taken.
Most OEM guidelines related to water contamination specify a limit (i.e., suggested maximum). Limits are intended to prompt a corrective response, such as investigating the source of the water entry, draining off the excessive water, hooking up a filter cart, or changing the oil if needed.
Limits (or flags) will vary from one application to the next, but there are a few rules of thumb you can follow when developing your specific flagging limits:
- ASTM D4378 (1000 ppm / 0.1%)
- Saturation point (100% saturation = 400-600 ppm on most oils)
- Based on the component (i.e., expect more water in a final drive versus a hydraulic)
- Based on the oil type (i.e., PAG’s can tolerate more water than a PAO oil)
Targets, on the other hand, are generally used as a stated goal to achieve. Targets are often much lower than limits, and usually require outstanding contamination control processes. It is important to understand the difference between targets and limits to ensure response protocols are appropriate for the situation.
Sample Point Location & Procedures Will Affect Water Values
Water can co-exist with oils in three states (i.e., dissolved, emulsified, and free). Circulating oil will generally contain dissolved and emulsified water. Once the oil is fully saturated, any additional water will separate out as free water. Therefore, the expected amount of water contamination (and therefore the flagging limits) will depend on whether the sample is being collected from circulating or stagnant oil.
- Samples collected from circulating oil
- Potential Locations: After Pump, Before/After Filters, Before/ After Cooler, Return Line
- Typical range: 0 – 400 ppm (or whatever the saturation point is)
- Typical flag: 400 ppm (i.e., 100% saturation)
- Typical target: 200 ppm (i.e., 50% saturation or less)
- Samples collected from stagnant oil
- Potential Locations: From Inside Reservoir, From Drain Line
- Typical range: 0 – 2% (depending on sample procedure & flushing)
- Typical flag: 1000 ppm (i.e., positive identification of free water)
- Typical target: 400 ppm (i.e., below saturation point)
If you do find the presence of water based on a routine sample collection point, sampling from alternate collection points can provide a window the extent of the issue and where it may have occurred.
Since water contamination can significantly impact on your equipment health, it is critical to consider flagging limits, targets, and sample collection points as you develop your contamination control processes and procedures. Note, the flagging limits mentioned in this article are generic and are shown for representative purposes only. For more specific details about your application, contact Fluid Life.
by Mark Shierman, Corporate Director, Client Services