Spectrographic Analysis

Spectrographic Analysis

The spectrometer operates with a very intense plasma arc which burns the sample at approximately 13 000 deg C. The light emissions from each element are then measured in intensity and their concentrations calculated in parts per million (PPM) of the element monitored.

The Spectro analysis results give us an indication of the elemental composition of the wear metals present in a sample. However the Spectrometer is limited, due to its ability to read only particles smaller than 5um; Hence it is not a good failure forecasting tool because of its inability to accurately measure true element levels represented by the larger particles.

In the early stages of failure, larger particles will be generated which pass through undetected by the spectrometer. These particles will not be read until they have been in the system for long enough to be ground into fine particles bypassing through the bearings, gears and other components of the system, often destroying perfectly good equipment as they operate. Hence an entire system is now damaged in all component areas by the time the spectrometer picks it up.

Coupled with the microscopic analysis, which looks at all particle size and shapes, but cannot identify elements, and with the spectrometer identifying the elements but ignorant of size, we are able to monitor wear trends and forecast potential failures early with a very high degree of accuracy. Providing regular samples are taken from the trend, we can identify a potential failure before it becomes a major catastrophe causing severe damage and unplanned shutdowns.

In cases when it may be necessary to identify the predominant wear elements in large particles, we are able to digest the particles in a strong acid solution. This method is called Acid Digestion and is the method by which the spectro analysis results become very accurate. However, it is not a preferred practice due to the slow preparation time and consequently high labour cost per sample resulting in higher sample charges.

Acid digestion is however, a very effective means of measuring and monitoring wear levels in grease samples. The entire contents of the grease sample are digested into solution and all elements fully measured.

The spectrometer also allows us to accurately monitor contamination levels such as dust through Silicon and coolant through Sodium or in marine applications saltwater ingression.

We also look at oil additive levels with the spectrometer, which allows us to trend additive levels, or if the compartment has been topped up with the wrong oil as different types of oil have different element levels in their additives.

Remember regular scheduled sampling allows early failure detection and facilitates shutdown planning which equates to continued production which equal profits.

One of the most commonly asked questions regarding wear metal analysis is: “What do the spectrographic analysis numbers mean”?

This is a course subject on its own and will vary in every different type of unit. Mostly the concentrations of the elements are expressed in Parts Per Million (PPM) or occasionally as percentages. These elements will give us a guide to the origin of the wear metals. Very briefly, they go roughly like this:

Wear Metals
  • Iron. Cylinders, crank, gears, roller bearings, camshafts, gears, rings and valves.
  • Lead. Bearings (white metal), additives, bushing or petrol.
  • Tin. Bearings (white metal), bushing and piston skirts.
  • Copper. Bearings, bushes, thrusts washers, gears, brasses, bronzes and additives.
  • Aluminium. Pistons, washers, housings, bushing and clay dust.
  • Chromium. Hardening material from cams, rings, rollers, valves and shafts.
  • Nickel. Hardened or stainless steel shafts, valves and roller bearings.
  • Vanadium. Used with chrome coating and on valve stems etc.
  • Titanium. Aircraft components and lightweight, high strength parts.
  • Silver. Bearings, ring coating in some early engines and solder.
  • Silicon. Dust, sealant and gasket material, coolant and anti-foam additive.
  • Sodium. Coolant additive, salt water contaminant or detergent additive.

Additives are added to base oil to enhance the properties of the oil for different uses, hence are a helpful identifier to check for cross contamination and in some cases contamination levels.

  • Calcium. Usually high in engine oils as TBN, detergent or dispersant additives.
  • Magnesium. Detergent, dispersant additives (higher in engines).
  • Boron. EP and coolant additive.
  • Manganese. Detergent additive and lightweight metal.
  • Phosphorous. Anti-wear additive.
  • Molybdenum. Anti-wear additive with extremely low co-efficient of friction.
  • Zinc. Anti-wear, EP and anti-rust additive.
  • Sulphur. Naturally occurring in base oil, anti-wear additive, extreme pressure additive and combustion by-product.

Remember when interpreting spectrographic results, it is important to monitor the trend of the elements rather than the actual elemental levels. Check and stay below the manufacturer’s recommended limit but be alerted of a pending problem whenever wear trends move by more than 10% over similar oil hours…. always sample on a consistent and regular basis to maintain accurate trends – the key to a successful program.