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Where There’s Condensation, There’s Probably Water

While collecting oil samples on a 1,200 HP oiled, sleeve bearing motor, I noted an unusual amount of condensation on the inside of the outboard bearing reservoir slinger ring sight glass. For those unfamiliar with oiled electric motors, they generally get oil to the bearings via an oil ring or slinger ring that rotates on the shaft. The slinger ring is larger than the shaft and hangs down into an oil reservoir that is .750” to 1.5” below the level of the shaft and bearing contact area (see Figure 1). Generally, there is a larger sized sight glass located on the top half of the bearing cavity which allows a visual inspection of the slinger ring as it carries oil to the shaft and lubricates the bearing (see Figure 3).

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Figure 1: Motor bearing reservoir with top cap removed

When oil samples were pulled from the inboard and outboard bearing cavities, the outboard sample was not emulsified, but it was not bright and clear like the inboard sample (see Figure 2).

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Figure 2: Oil samples from inboard and outboard bearing reservoirs

One of the positive advantages of industrial oils is their ability to demulsify water. Since this reservoir is not aggressively circulated to emulsify the oil, a small volume of free water above the saturation point will separate under normal running conditions. The outboard reservoir drain valve was opened, which yielded about two tablespoons of free water before pure oil started flowing out. The original design of these motors had a drain plug directly in the bottom of the bearing reservoir. During the years before condition-based oil changes were implemented, the drain plug was replaced with a section of pipe, a valve and a cap or plug. This made yearly oil changes much easier and less messy than the previous plug removal. Currently, this set up serves as a low leg for water coming out of the reservoir area to collect in (see Figure 3).

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Figure 3: Outboard end of motor

Neither sample crackle tested positive in-house or at the lab. A Karl Fischer water test was requested even when crackle was negative to see what the water ppm was in the samples. The inboard tested at 25.3 ppm and the outboard at 32.3 ppm. Since the inboard bearing reservoir did not have visible condensation in the sight glass or free water from the drain when it was checked as the outboard did, this illustrates the close range of saturation to free water in this oil type. Another interesting note is once the free water had been drained from the outboard bearing reservoir, the condensation in the slinger ring sight glass was gone by the next day.

Most people are aware that water can be a very detrimental contaminant. When we think about water contamination, we generally think about gross water contamination, not necessarily the damage that can occur from low levels of water contamination. Water not only reduces the load carrying ability of a lubricant that can increase wear, but also promotes oxidation and corrosion and can cause additives to precipitate or drop out, thus degrading the lubricant’s properties. Another serious problem with water in bearings, sleeve, or anti-friction is hydrogen embrittlement. If the water is forced into micro cracks of the babbitt or steel, it releases hydrogen under extreme force or loading and heat, which can create mini explosions that make larger cracks. These cracks sometimes loosen the bond between the babbitt and underlay, or can lead to spalling in anti-friction bearings. With a weakened bond or spalling, it is only a matter of time before the bearing fails.

The next obvious question would be, Where did the water come from? There are a couple of possibilities here. The wash down and cleaning frequency has been increased recently. The two holes shown in Figure 3 are open to atmosphere and come into an area in the middle of the labyrinth seal on the inboard of the bearing housing. A misdirected water spray could possibly get into the bearing cavity, thus causing water to enter the oil reservoir. In case this was the cause, some educational material with internal pictures of these reservoirs showing the possible path of ingress for water was passed along to those responsible for wash downs. A picture of the slinger ring sight glass was included with condensation on the inside and a comment to check the drain for free water and to contact PdM for oil analysis. In the future, a rag will be placed in the holes or a piece of tape over the openings during wash downs.

The other possibility is condensation while passing through dew points when the equipment is shut down based on reduced load requirements. Load reductions are more frequent during spring and fall with moderate temperatures and reduced electricity consumption. The easy fix for condensation would be a desiccant breather on the reservoir. The problem with this is when the reservoir has more than one opening to the atmosphere, as evident in Figure 3. The desiccant would remove moisture from the headspace in the reservoir, but with the housing open to the atmosphere, the path for exchange air would not be exclusively through the breather, thus causing the desiccant to rapidly deplete in high humidity areas.

In conclusion, whatever the cause for the water intrusion, two of the best defenses are training and education. An observant operator should be able to identify gross water contamination by the coloration of the oil in the sight glass, or recognize slight water contamination by condensation in a sight glass above the oil level. When the problem is identified and dealt with in a timely manner, the possibility of damage can be greatly reduced.

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