EVALUATION AND INTERPRETATION
With the emergence of long life synthetic lubricants, oil analysis is becoming an increasingly popular tool for monitoring the serviceability of the lubricant as well as foreshadowing developing problems. With synthetic lubricants being recommended for eight to ten times the life of petroleum lubricants, a good oil analysis program is a must for assuring that there is no contamination or degradation of the lubricant and that it can continue to function for the extended drain interval.
The Petron Plus Global, Inc. Oil Analysis Program is designed to give a complete overall view of the physical and chemical characteristics of the lubricant to determine any significant lubricant deterioration as well as detect any machinery problems before they become serious and expensive to repair. These benefits can only be realized through proper evaluation and interpretation of analysis results. All the test results must be considered, along with the user’s knowledge of his compressor’s performance history, to correctly diagnose the condition of a given oil sample. Although there are given interpretations and recommendations on each lab report returned, it is very helpful for the end user to have a working knowledge of the tests involved and their significance.
VISCOSITY: The viscosity of a lubricant is monitored for significant increases or decreases from the original specification. A substantial decrease in viscosity could indicate a contamination of the lubricant causing a diluting effect. An increase in viscosity could also indicate a contamination or a degradation of the oil due to oxidation. A change of viscosity of more than 10 cSt at 100°F from the original specification usually indicates that the oil should be replaced.
TAN (TOTAL ACID NUMBER): The TAN of a lubricant measures the amount of acid and acid-acting constituents in the lubricant. This does not necessarily denote metal corroding materials as many chemicals and additives used in lubricants have an acid number.
Increase in TAN from the original specification usually indicates oil oxidation or corrosive acid contamination. A sudden increase in TAN can also indicate mechanical problems. An increase in TAN to greater than two (2) is significant in a petroleum oil; however, a gradual increase in TAN of a diester synthetic should be of no real concern until it becomes greater than ten (10).
WEAR METALS: In monitoring wear metals, it should be observed that the significant factor is not so much the amount of metal present as the rate of deposit with respect to time. A sudden increase in wear metals usually indicates an incipient wear problem and machine inspection is highly recommended. A slow, constant increase in wear metals, however, can be considered normal for most equipment and no cause for alarm or required action. These metals will usually show in the form of iron, lead, copper, aluminum, nickel, silver or tin.
ADDITIVE METALS: Additive metals tend to remain fairly stable over the life of the lubricant but can fluctuate +20 percent under normal circumstances. The emergence of an element which was not present in the original sample could indicate the addition of make-up oil whose additives differ from the original product. These metals are usually phosphorous, zinc, calcium, barium, molybdenum or antimony. Silicon is also used as an oil additive but can indicate the presence of dirt as well.
WATER CONTENT: The presence of water in a lubricant can decrease its lubricating effectiveness; therefor, a lubricant should be monitored for percent water volume. The limit for water is virtually none and can be measured to 0.05 percent (500 ppm).
POSSIBLE SOURCES OF ELEMENTS IN OIL
- ALUMINUM (Al) – Pistons, bearings, bushings, pump vanes, blower/turbos, washers, dirt, shims.
- ANTIMONY (Sb) – Babbitt bearings, grease.
- BARIUM (Ba) – New oils (dispersant/detergent), grease, water.
- BORON (B) – New oils, coolant, seals, dust, fuel dilution.
- CADMIUM (Cd) – Bearings, platings.
- CALCIUM (Ca) – New oils, (Dispersant/detergent), water, grease.
- CHROMIUM (Cr) – Plated parts (primarily piston rings), coolant, anti-friction bearings, shafts, gears, seals, bearing cages, fuel leaks gas turbines.
- COBALT (Co) – Bearings, turbine components.
- COPPER (Cu) – Bearings, bearing cushions, bushings thrust washers, valves, guides, injectors shields, oil cooler tubes, wet clutches, coolant (copper radiator) gears.
- IRON (Fe) – Rings, crankshaft, cylinder walls, calve train, pistons, anti-friction bearings, gear train, shafts, clutch plates, washers, rust, water.
- LEAD (Pb) – Babbitt or copper-lead bearings, plating, leaded gear lubes, leaded gasoline, grease, paint, seals, solder.
- MAGNESIUM (Mg) – New oils, (dispersant/detergent), bearings, superchargers, water.
- MANGANESE (Mn) – Steels, valves, valves, corrosion, blowers (exhaust & intake systems).
- MOLYBDENUM (Mo) – Additives, piston rings, electric motors.
- NICKEL (Ni) – Shafts, valves, anti-friction bearings, gears, rings, turbine components.
- PHOSPHOROUS (P) – New oils (zinc dithiophosphate) chlorinated phosphorous anti-wear additives, gears, coolant leaks.
- SILICON (Si) – Sand, dirt, dust, anti-foam, anti-freeze, gasket sealing compounds.
- SILVER (Ag) – Anti-friction bearings, silver solder, wrist pin bushings, gear teeth, shafts.
- SODIUM (Na) – Some new oils, coolant, salt water, grease.
- TIN (Sn) – Babbitt bearings, platings, solder, coolers, wrist pins, pistons, rings.
- TITANIUM (Ti) – Wear turbine engines, springs, valves, bearing hud, compressor disc, turbine blades.
- VANADIUM (V) – By products heavy fuel oil, occasionally wear metal, turbine blades, valves.
- ZINC (Zn) – Anti-oxidant, anti-corrosive, anti-wear agent, bearings, platings, gears, seals, coolant leaks, grease.