Application Note

Sources of Wear Metals in Oil Analysis

The following tables are a guide to the sources of wears metals detected by oil analysis. Also consult your equipment manufacturer for specific guidelines.

Iron

Iron is the most common of the wear metals. Present in some form in virtually all equipment. Its widespread presence means that there are many sources of the wear particles. Because of this knowledge, the metallurgy of the component allows the analyst to distinguish the source of the wear debris, e.g. cast iron bolts vs. stainless steel lube oil piping.

Equipment Wear Metal Source
Engines Most common of the wear metals. Engines: Cylinder Liners, Piston Rings, Valve train, Crankshaft, rocker arms, spring gears, lock washers, nuts, pins, connecting rods, Engine Blocks, Oil pump,
Bearings Rolling element Bearings: rollers (tungsten alloyed steel), raceways and cages, Journal Bearings: Journal shaft, bearing Shoe backing. Locking keys
Gears Bull gears, pinions, case hardened teeth, locking pins
Transmissions Gears, bearings, Brake bands, clutch, shift spools, pumps, power take off (PTO)
Hydraulic Systems Pump, motor, vanes, pump housing, cylinder bores and rods, servo valves, pistons
Compressors Rotary Screw, lobes, vanes, connecting rods, rocker arm, bearings, cylinders, housing, shafts, roller bearings (see above) oil pump, piston rings
Turbines Reduction gear, shaft, bearings, piping, case

Copper

Widely used as an alloying element, copper is prized because of its materials properties - very ductile, and excellent thermal and electrical conductivity. It is heavily used in bearing systems, as well as heat exchangers.

Equipment Wear Metal Source
Engines Valve train bushing, Wrist pin bushing, Cam bushings, Oil Cooler core, Thrust washers, governor, connecting rods bearings, valve gear train thrust buttons,
Bearings Rolling element Bearings: alloyed element in cages, Journal Bearings: journal bearing pads, slinger rings, Locking keys
Gears Bushings, thrust washers
Transmissions Clutches, steering discs, bearings
Hydraulic Systems Pump thrust plates, bushings, cylinder gland guides, pump pistons, oil coolers
Heat Exchangers Cooler tubes, baffles, plates.
Compressors bearings, cylinder guides, wear plates, thrust washers, bearings (see above) oil pump, oil coolers, thermostats, separator filters
Turbines Bearings (see above) piping, coolers

Tin (Sn)

Tin is used as an alloying element with copper and lead for sacrificial bearing liners.

Equipment Wear Metal Source
Engines Valve train bushing, Wrist pin bushing, Cam bushings, Oil Cooler core, Thrust washers, governor, connecting rods bearings, valve gear train thrust buttons,
Bearings Rolling element Bearings: alloyed element in cages, Journal Bearings: journal bearing pads (babbited)
Gears Bushings
Transmissions Clutches, steering discs, bearings
Hydraulic Systems Pump thrust plates, bushings, Can be a residue from catalyst in some oils (Quintolubric series)
Compressors bearings, separator filters
Turbines Bearings (see above) piping, coolers

Aluminum (Al)

Aluminum is valued in equipment because of it high strength to weight ratio, and excellent corrosion resistance. Alloyed with other elements improves its wear and temperature resistance. It is widely specified for equipment manufacture nowadays.

Equipment Wear Metal Source
Engines Engine blocks, pistons, blowers, Oil pump bushings, bearings (some) Cam bushings (some), Oil coolers (some)
Bearings Rolling element Bearings: alloyed element in cages, Locking keys
Gears Bushings, thrust washers, grease contamination
Transmissions Bushings, clutches
Hydraulic Systems Cylinder gland (some) pump, motor pistons, oil coolers. Aluminum complex grease contaminant
Heat Exchangers Cooler tubes, baffles, plates
Compressors Housing, bearings, cylinder guides, wear plates, thrust washers, bearings (see above), oil pump, oil coolers
Turbines Bearings (see above) piping, coolers EHC Systems: Residue from synthetic media (alumina) filters

Chrome (Cr)

Chrome is used as an engineering material for its great hardness and corrosion resistance. It is found in many systems operating under harsh conditions.

Equipment Wear Metal Source
Engines Rings, Liners, exhaust valves, zinc chromate from cooling system inhibitor
Bearings Rolling element Bearings: alloyed /coated element in rollers, tapers
Gears Bearings (some), shaft coatings, some special gears are chrome plated
Transmissions Bearings, water treatment
Hydraulic Systems Cylinder liners, rods, spools
Heat Exchangers Cooler tubes, baffles, plates
Compressors Housing, bearings, cylinder guides, wear plates, thrust washers, bearings (see above), oil pump, oil coolers
Turbines Shaft coating (some) bearings,

Lead (Pb)

A soft metal used for sacrificial wear surfaces such as journal bearings. Lead based babbitts are widely used .

Equipment Wear Metal Source
Engines Main Bearings, connecting rod bearings. Lead can be present as a contaminant from Gasoline (Leaded gas) (Octane improver, anti-knock compound)
Bearings Rolling element Bearings: alloyed element in cages, Journal Bearings: Major alloying element in Babbitt bearings, alloying elements
Gears Bearings, can also be red lead paint flakes from gear case walls
Hydraulic Systems Bearings
Compressors Bearings
Turbines Bearings

Silicon (Si)

Silicon is the most common contaminant found in lube oil analysis. Abundant in all areas, sand is a very hard crystalline material, and very abrasive to metal components.

Equipment Wear Metal Source
Engines Engine blocks (alloying element with aluminum parts), ingested dirt from breathers, external sources. Can also be from defoamant additive in lubricant
Bearings Rolling element Bearings: alloyed element with aluminum in cages
Gears Bushings, thrust washer, silicone sealant, defoamant additive
Transmissions Brake shoes, clutch plates, ingested dirt
Hydraulic Systems Elastomeric seals (some) pump, motor pistons, oil coolers
Heat Exchangers Cooler tubes, baffles, plates
Compressors Ingested dirt, silicone sealant, bearings, cooler (alloyed with aluminum)
Turbines Ingested dirt, silicone sealant, defoamant additive

Silver (Ag)

Silver has exceptional thermal conductivity, and is an excellent bearing plate material, providing minimum friction. It is susceptible to corrosive attack by zinc-based additives, and so railroads ensure that they receive zinc free oils if they run EMD locomotives. Silver is used more outside of the US in general industrial equipment.

Equipment Wear Metal Source
Engines Valves, Valve guides, Cylinder liners, Bearings. Can also be from heavy
Bearings Rolling element Bearings: alloyed element in rollers, races
Gears Alloying element for tool steel gears
Hydraulic Systems Bearings, servo valve plating pumps, pistons
Compressors Bearings
Turbines Bearings, shaft, reduction gears

Metallic additives

Several other elements are detected with oil analysis. The major elements found are listed here:

Element Possible Sources
Sodium Corrosion inhibitor additive, also indicates coolant leak into oil, can also be road Salt, Sea water, Ingested Dirt
Boron Corrosion Inhibitor additive, Antiwear/Antioxidant additive, can indicate coolant leak, grease contamination
Magnesium Detergent/dispersive additive, can also be alloying element in steels
Calcium Detergent/dispersant additive, Alkaline reserve additive for high sulfur fueled engines, can be grease contamination,
Molybdenum Solid/liquid antiwear additive, alloy in bearing and piston rings
Barium Corrosion inhibitors, Detergents, Rust inhibitors
Zinc Antiwear, Corrosion inhibitors, Anti-oxidants, alloying element for bearings, thrust washers, galvanized cases
Phosphorus Antiwear, Corrosion inhibitors, Anti-oxidants additives, EP additives

Other Wear Metals

Several other elements are detected with oil analysis. The major elements found are listed here:

Element Possible Sources
Titanium Wear metal for aircraft engines, bearings, Can also be contaminant from paint (titanium dioxide)
Vanadium Fuel Contaminant, can also be alloying element for steel

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