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Certain contaminants get special status. Take dirt and water for example. Everybody knows all about them, the damage they cause and the fact that they are bad. Yet other contaminants are out there that are perhaps equally as damaging - such as air, heat and in some cases engine coolants - yet seldom receive the attention that they should.
Why is that? The answer is simple: visibility. Dirt and water are the bad actors in the front row of the oil analysis stage. Other contaminants, like the latter ones mentioned, are the phantoms of the stage - they are difficult or even impossible to detect directly.
Sometimes you must resort to special tests to detect their presence; other times their presence is not detectable at all, and you have to look for evidence of their passing, like a flickering candle when a ghost walks past.
Dirt and Water
Dirt is typically easy to detect. The signature elements of dirt are silicon and aluminum, in varying ratios, the most common ratio of 4:1. The trace elements associated with dirt are likely a function of the process environment. These may include iron, manganese, titanium, calcium and many others. Knowing possible elemental contaminants in a plant makes dirt detection a cinch.
Water is another easy contaminant to detect. Many tests, like the crackle test, calcium-hydride and various Karl Fischer titrations, can be used to recognize and quantify this element.
Let's look at some of the more common phantoms and how you can go about detecting their presence.
Air is a damaging contaminant. It is the primary source of lubricant oxidation, and causes other damage including cavitation in pumps, micro-dieseling and varnish. The reason this element is difficult to detect is that by the time the sample arrives at the laboratory, the air has mostly vacated the oil. So how can we detect it?
Begin with basic in-machine testing: visual analysis of oil level indicators and tank inspections. Are there signs of cloudiness and foaming? These may be due to water contamination, but that factor is easy to eliminate.
Visually inspect the oil sample.
If air contamination is still suspected, utilize air entrainment and foam stability tests.
In hydraulic samples, high nitration (FTIR) provides a clear indication of aeration. High nitration indicates damaging micro-dieseling is taking place.
Heat is a real phantom. It is an extremely damaging contaminant and, like air, is impossible to directly detect at the laboratory. (Obviously the oil sample has cooled down by the time it gets to the lab.) Heat is a primary pro-oxidant - for every 10°C increase in temperature, the oil life is cut in half.
So how can heat contamination be detected? As far as lab oil analysis goes, heat contamination cannot be directly detected. You must resort to looking for symptoms such as premature acid number increase, and even this is not diagnostic because acid number increase can be caused by multiple factors.
The definitive solution is to install thermometers, either stand-alone or wired into the control system (the latter option may be an expensive alternative).
Internal Coolant Leaks
Some engine coolants are easy to detect. They have inorganic elements, such as sodium, boron and potassium, which are readily measurable with elemental analysis. It is always a good idea to have a coolant elementally analyzed; therefore, you will know the components of the coolant.
Unfortunately, some coolants have no readily detectable elements, and identifying them can be difficult. Looking for water to indicate a coolant leak is unreliable due to the operating temperatures of the oil because water flashes off quickly. If a coolant-detection test is not performed on every engine sample, then the trick is to look for elements that are associated with coolant leaks. These include:
Iron. This could come from the coolant system (water pump) or wear in the engine (liners, crankshaft).
Copper. From the oil-cooler piping.
Silver. From the silver-solder used in the coolant piping, or possibly from journal bearings.
Babbitt Metals (lead, tin, antimony). These are indicators of journal bearing wear. With internal coolant leaks, the journal bearings are usually the first machine components to start wearing due to water flashing in the hydrodynamic contact zone.
Treat any increase in these elements with suspicion, and carry out further testing to confirm the coolant leak immediately.
Just because there is no apparent contamination, it doesn't mean it's not there. Keep looking for the flickering candles, and an expensive repair might be avoided.