The main source of lost revenue due to machinery downtime is commonly a direct result of some type of contamination, be it soil, water, process material, incorrect lubricant, or some mixture of these. Oil analysis results can identify these contaminants, but unless you are aware of the real problems that can arise from them, it is difficult to take the right actions.
Abrasives are at the top of the list as the problem that stands out the most in the oil analysis results, as they tend to cause the most damage. They are generally hard contaminants and their size can be in the range of dynamic clearances between machinery components, so they can cause a lot of wear.
The most common forms of abrasives are dust and dirt (probably airborne, or possibly introduced during maintenance) and process by-products (if any particles are present in the process, it is possible that this particulate enters the lubrication system and causes damage, no matter how soft or hard the particle is).
Contamination with abrasive particles results in wear on machinery, but can also lead to lubricant degradation. Abrasive wear or shear wear is generally found in systems where there is a sliding load anywhere on the unit. It most commonly occurs in plain bearings or other soft metal components, where abrasive particles can work their way into the soft metal and then cut through the hard steel surface. This is not to say that you can’t have shear wear on a copper alloy; the metal produced depends on the metallurgy of the contacting surfaces and the hardness of the contaminant.
Systems, where rotary motion is present (bearings, gears, etc.), are more prone to pitting caused by abrasive contamination. As the particles roll through the load zone, the extreme pressure exerted on the point of contact between the races and the rolling elements can pit the surfaces, causing cracks and initiating fatigue wear, and potentially spalling.
Lubricant degradation is more likely to be caused by another source, but a slight decrease in life may be seen due to particulate contamination. When a unit wears, the metal released by the abrasives can become a catalyst, and these particles increase the surface area that can come in contact with the lubricant and degradation byproducts. This should be included in the calculation in the analysis of physical assets.
To identify abrasive contaminants and the wear they cause, metal element spectrometric (AES) analysis is used. If you’ve run an analysis on particulate-contaminated oil, what you typically see is an increase in the metal concentration of items that come into direct contact with the abrasives. In gears, you will tend to find high levels of iron with low-alloy metals (chromium, nickel, manganese), and an increased level of silicon and aluminum if there is enough contamination since the silicon-to-aluminum ratio is generally low.
Another common test for monitoring contamination is the particle count. It should be noted that particle counting does not distinguish between the particles it is counting. Water, air, dirt, fibers, metals, etc. can all be counted as a “particle”, so to identify what type of contaminant is present, you will need to do some additional testing or look at the other oil analysis results.
A typical recommendation on your oil analysis report will be to first correct the entry point of the particles. This is not always possible for the end user, but machinery protection should be one of the top recommendations from an analyst. Unfortunately, it is very common that there is not a good interaction between the laboratory and the end user, so, in the absence of this knowledge, the analyst must always bet on protecting the machinery.
Afterward, they will likely suggest filtering the lubricant. Again, this is not always feasible for the user, or the plant may not have the equipment to do so, but knowing that it is physically possible to filter most lubricants and it is best not to open a system if it is not necessary, filtration should be one of the first options in most cases.
If filtration is definitely not an option, they may suggest changing the lubricant. This is not as optimal as filtration, but when you have contamination your new lube is likely to be much cleaner than the lube you have in the system, thus diluting the level of contamination and reducing abrasive wear.
The last likely recommendation is that you do some kind of exception testing. This will depend on whether there is evident wear in the system, based on the wear metals present. Analytical ferrography or membrane testing can help assess the severity of damage that has occurred to the unit, to determine if immediate action is necessary, or if the wear is not as severe as it might appear.