Spectrometric Oil Analysis Program (SOAP)

Spectrometric Oil Analysis Program (SOAP) is a powerful analytical tool/technique for elemental analysis of structural metal & other material particles (up to approximately 5 micron in size) entrained in machinery Oil Samples. Generation of Wear metals & other particles in an ‘Engine-Oil’ system can indicate the changing conditions of its various parts, like Oil Pump, Gears, Bearings, & other metallic parts. The various elements (Metals & Non-Metals) present in the base oil are identified & measured in parts per million (ppm) by weight. This term is specifically used in the Aviation industry, & the corresponding term in the Military sector (especially US Armed Forces) is Jet Oil Analysis Program (JOAP). Spectrometric or Spectrochemical Oil analysis was first used on an industrial scale in 1960. Analysis is done by the use of Atomic Spectroscopic methods like Atomic Absorption & Atomic Emission Spectrometry.
SOAP is a Proactive Condition Monitoring/Maintenance tool/technique which helps to assess the relative wear conditions of the lubricated/Oil-wetted parts on the basis of the concentration of the Wear particles in the Used Oil. Besides, it can also indicate the rate of Wear & its source. Hence, it can provide an early warning of Abnormal Wear occurring (Wear Anomaly), & also about Failure of any engine component. By carrying out analysis of Used Oil (for a particular machine/engine) at periodical intervals, which is also called ‘Trend Analysis’, Baseline Data can be recorded which can be used for addressing problems related to specific internal engine components based on the knowledge about the metals used for the construction of the engine. Such an analysis can also be used for comparison purposes & also to predict ‘Failure’ of a machine.
The main advantages of a well-planned SOAP are: (1) Prevention of Catastrophic Failures which endangers Safety of personnel,
(2) Reduction/Prevention of non-scheduled Downtime,
(3) Reduction of expenditure due to repairs,
(4) Prolonged Machinery Life,
(5) Increase in Efficiency of Machines.
The basic limitation of a SOAP analysis is its inability to detect larger particles, especially larger than 10 μm. For analysis of larger particles, other methods like ‘Ferrography’ have to be used.

The analyzed elements in Lubricating Oil can be categorized into 3 categories:

  • Wear Metals: These originate from Friction & Corrosion of the engine components, like pistons & bearings. Examples include Iron, Chromium, Nickel, Aluminium etc. Iron is the most prominent of all analyzed elements.
  • Contamination: Contaminants can come from external sources, like dirt, leaks, or residual metal pieces. Examples include Silicon (from Sand) etc.
  • Additives: These are added in order to reduce engine wear, & can be used as detergents, anti-oxidants, & anti-wear agents. Examples include Phosphorus, Calcium, & Zinc.

Possible Sources of the elements found in Used Oil analysis:

Element/Elements Possible Source/Sources
Iron (Fe) Shafts, Gears, Piston Rings, Cylinder Walls
Chromium (Cr) Piston Rings, Roller Bearings, Cylinder Walls
Copper (Cu) Bearings, Bushings, Thrust Washers
Aluminium (Al) Pistons, Pumps, Bearings, Thrust Washers
Nickel (Ni) Pumps, Gear Platings, Valves
Tin (Sn) Journal Bearings, Bearing Cages, Solder
Lead (Pb) Anti-Wear Gears, Bearings
Silicon (Si) Dirt, Airborne Dust, Defoamant Additive
Boron (B) Anti-Corrosion in Coolants
Zinc (Zn) Anti-Wear Additive
Calcium (Ca) Detergent Additive, Dispersant Additive
Magnesium (Mg) Coolant Additive
Phosphorus (P) Anti-Wear Additive, Extreme Pressure Gear Additive
Molybdenum (Mo) Extreme Pressure Additive
Sodium (Na) Detergent Additive, Coolant Additive
Titanium (Ti) Alloy in high quality Steel for Gears & Bearings