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 |