The Elemental Test
R. David Whitby | TLT Worldwide July 2016
When analyzing oil, you must know which indicators are calls to corrective action.
Contaminants can act as catalysts for wear or oxidation, leading to premature oil and equipment degradation.
© Can Stock Photo Inc. / michaeljung
ONCE A SAMPLE OF OIL HAS BEEN ANALYZED, it is crucial to understand what the results mean and what, if any, action(s) should be taken as a consequence.
If the oil has been analyzed in your own analytical laboratory, the report will have all the information about when the sample was taken and from which piece of equipment. If the sample has been analyzed in a contractor’s laboratory, the report may only have a sample number, which will need to be correlated with the time, date and place of sampling.
In all cases, the report should also list maxima and minima for each of the tests done on the sample. These will provide a guide as to whether or not the oil is in satisfactory condition and, therefore, whether or not some type of corrective action needs to be taken.
Viscosity is the most commonly run test for oils; it is regarded as an oil’s most important property. If an oil’s viscosity is too low for the applied load, an oil film cannot be established at the contact point(s), which may lead to higher wear or even seizure.
An oil with a viscosity that is too high can lead to overheating, accelerated oxidation and ultimately failure of the equipment. An oil’s viscosity is satisfactory if it is within plus or minus 10% of its ISO viscosity grade. Corrective action needs to be taken if it is outside this range, and if it is plus or minus 20% of its viscosity grade, the situation should be considered critical.
Elemental content is the next most commonly run test. The elements tested for—iron, copper, lead, sulphur, phosphorous and/or several others—will depend on the type of oil and the equipment in which it is used. Some elements can present in additives in the oil; others are likely to be contaminants. These can arise through wear, servicing, faulty seals or open tanks, but they are likely to cause significant damage to the equipment.
When looking at elements in oils that contain additives, any significant differences between a new oil and the test sample may indicate the need for an oil change. For wear metals, it is wise to analyze trends over time, from one sample to the next, to look for any sudden increases. These may indicate that one or more components in the equipment is wearing faster than normal. The load or operating temperature may have increased. The oil’s viscosity may also give you a clue.
Contaminants can be water, dust, sand, metals or rubber. If they are present in the oil, you need to find out where they came from and how to prevent further ingress. Contaminants can act as catalysts for wear or oxidation, leading to premature oil and equipment degradation. Free water in an oil is a serious threat, as water is a poor lubricant and promotes rust (corrosion) of ferrous (iron and steel) surfaces. Dissolved water can degrade some oil additives and can cause accelerated wear, higher friction, higher operating temperatures and accelerated oxidation.
Another commonly run test is Total Acid Number (TAN), also described as Acid Number (AN). Oxidation of oils results in increases in acid content, high levels of which can indicate excessive oxidation and can lead to unwanted corrosion. Results for TAN tests need to be considered in conjunction with other factors, particularly water content and additive elements. When the TAN value reaches a predetermined value, the oil needs to be changed.
The concentration and type of wear particles in an oil can be determined using particle counting and analytical ferrography respectively. The particle count test provides the amount and sizes of the particles in the oil. If the results are too high, this may be indicative that one or more filters is blocked (and bypassing) or damaged. In either case, replacement is required. Analytical ferrography, although relatively expensive, is one of the most powerful tools available currently. When used correctly it can be very helpful with identifying an active wear problem. The results should include a photomicrograph of the wear particles and a description of their likely source.
Lubrication engineers need to be able to interpret oil analysis test results to determine whether they are abnormal or not.
David Whitby is chief executive of Pathmaster Marketing Ltd. in Surrey, England. You can contact him at pathmaster.marketing@yahoo.co.uk.