Spectrometric Metals Analysis (SM) - usually Off-Site

Virtually all analyses for metals in oil, with the exception of iron (Fe -  see also Wear Particle section), involve ultra-violet (UV) spectrometric oil analysis or x-ray fluorescence, with UV easily the most dominant for a variety of reasons, most notably being speedier and less expensive.



The UV-SM process involves the vaporization of a small sample of oil (or solvent-diluted oil) and the subsequent measurement of UV radiation unique to each element of interest. This discreet UV frequency for each relevant element of interest is measured or absorbed, dependent on the instrumentation utilized. The amount of UV measured/absorbed at each wavelength is proportionate to the elemental concentration for each respective element.

Reporting Units: Values are almost always reported in parts-per-million (ppm) by weight for each element analyzed.

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Note that the latest generation of On-Line sensors will now both quantify and differentiate between ferrous and none ferrous metalic particle contamination to laboratory accuracy.  A gross indication of contaminant level for ferrous can be achieved down to sub micron sized particles (Kittiwake Total Ferrous sensor)  but speciation requires particle sizes above about 40 micron (Kittiwake metallic article sensor).



Above: Failure due to metallic wear particles

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General Application Information: Often considered the ‘heart’ of an oil analysis program, SM offers an array of as many as 20 or more elements that can reveal, dependent on the machine, its metallurgy, its environment and the lubricant it uses. If combustion is involved, the fuel may contribute metals (as contamination) in the circulating lube. Likewise, when coolants seep into a sump. The elements detected can be divided into three primary categories:

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Wear metals

• Iron (Fe), aluminum (Al), copper (Cu) and lead (Pb) are most prevalent with some exception, such as titanium (Ti) in aircraft components. These “Big 4” wear elements are usually the only ones to show concentrations greater than 10ppm, and are usually the only metals that are practical to trend in terms of percentage movement from sample to sample. Other, minor wear metals, e.g., tin (Sn) or chromium (Cr), are considered ancillary and possibly helpful in isolating abnormal wear of a specific part within the component. Because they are usually below 10 ppm in concentration, limits are more dependable flagging points for maintenance action

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Contaminant metals

• Silicon (Si) is most often representative of abrasives (“dirt”) but can also reside in Wear (gasket and o-ring) and Additive (anti-foamant) chemistry form
• Sodium* (Na), potassium (K) and boron (B) are often found in antifreeze additive packages. This provides highly sensitive indications of coolant leakage into the oil sump of a diesel. All three of these metals can also be employed in additive packages and, thus, become members of the Additive metals group, as well as the Contaminants group

*If a component is in an offshore environment, seawater (salt water) must also be considered when Na is abnormal.

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Additive metals

• Magnesium (Mg), calcium (Ca) and barium (Ba) are detergent-type additives, also providing some alkalinity to help neutralize acids formed from diesel fuel combustion
• Phosphorus (P) and zinc (Zn) are frequently seen in anti-wear (AW) oils for industrial gears and hydraulics, as well as diesel and gasoline motor oils as an anti-wear/anti-oxidant additive
• There are a variety of specialized additives, some featuring molybdenum (Mo), or even copper (Cu) in a soluble form. Clearly it is imperative to obtain and analyze a reference new lube before attempting to evaluate the presence of metals of any nature, i.e., to be aware of the possibilities

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Things to Note about SM

SM is not able to discern the molecular aspect of a metal, only its atomic presence. Thus one would not be able to ‘see’ the difference between Si as an additive or an abrasive. However, one might use the presence of Fe, e.g., to corroborate the likelihood that Si is abrasive if both are in lock step in terms of increasing concentrations.

Similarly, analyzing for any of the additive metals doesn’t provide any assurance that the additive is a ‘working’ chemical. It may be depleted or partially so, yet still showing its metallic constituency in atomic form. The primary benefit of measuring additive metals is to have some assurance that the product intended for the component resides in its sump or crankcase. Thus one gets a metal ‘signature’, but measuring remaining active additive is not included in this process and must be accomplished by other means.