Condition Monitoring - Oil Sampling Analysis in Construction & Mining Machines

Bhaskarudu Peddakotla, Consultant – Construction and Mining Machinery, suggests that machine owners should implement condition monitoring and thereby become self-reliant in maintaining their assets and enhancing their operational/productive life.

Oil sampling in machines involves testing the oil from various compartments such as the engine, transmission, hydraulics, differential and final drives, swing devices, etc. at regular intervals to find out wear metals, contaminants, and physical properties.

Oil sampling is necessary to get the maximum life from the machine with consistent availability and healthy utilization, so that its overall operating cost will be under control. There is scope to extend oil change intervals, particularly hydraulic and gear oils, without affecting the life of the components.

Operating cost mainly depends upon asset utilization and productivity. Utilization can be healthy only when the machine is available consistently, which, in turn, is possible only when we undertake a thorough monitoring of the machine, which includes oil sampling.

Oil sampling for maintaining consistent machine availability
Oil sampling in a machine is much like the health check-up one takes to help prevent the onset of any major health issue. Similarly, lube oil sampling at regular intervals will help us know the condition of major assemblies like engine, torque convertor, transmission, hydraulics, differential, final drives, steering system, etc. In case of any problem, it can be addressed right away and thereby prevent the machine from a major failure.

Furthermore, through oil sampling, we can improve the operational and maintenance practices by fine tuning operator skills, preventing dust entry inside the components, maintaining oil storage and transfer system cleanly, and doing oil and filter changes as per the schedule. All these actions help maintain machine’s availability.


Tests carried on oil during sampling
Oil analysis and tests depend on the various compartments of the machine such as the Engine, Transmission, Differential, Final Drive, Swing Device, etc. Some of the oil analysis tests are as follows:

Viscosity: It is necessary to maintain the required oil film thickness between moving components. It is important that the viscosity be measured at 100 degree Celsius, as working temperature of most of the oils will be around 100 degree Celsius. There is no use of measuring viscosity at room temperature.

Viscosity Index: This is the change of viscosity relative to change in temperature. But as long the viscosity at 100 degree Celsius is monitored, the Viscosity Index doesn’t carry much significance in used oils.

Oxidation: This normally happens with age, high temperature, water entry, etc. Oxidation leads to increase in viscosity (oil is unable to flow in narrow places of moving parts), depleting additives due to acid formation, etc.

Soot: Soot formation happens in the engine oil due to incomplete burning of fuel. Excess soot formation leads to rapid wear of engine parts.

Sulfation: This happens mainly in the engine oil due to excess sulphur in the fuel, and due to fuel particles mixing with water during combustion (improper functioning injector, poor compression pressure etc). Even though engine oils contain neutralizing agents, exceeding of sulfation beyond a certain limit causes corrosion of internal parts.

Other chemical parameters: TAN, TBN, ZDDP (additive depletion)
Fuel Dilution: Due to fuel dilution in engine oil, the viscosity drops, and oil cannot maintain the required film thickness between moving parts which leads to direct contact between parts, resulting in rapid wear,

Coolant: Coolant is mixed with oil due to cylinder head cracks, head gasket failure, cooler internal leakage etc. Coolant contamination leads to sludge formation and faster wear. Coolant can mix with other oils where the cooler or heat exchanger is provided in the system.

Water: Water dilution occurs due to condensation, pressure washing, etc. If water mixes with any oil, it leads to corrosion.

Silica: Silica normally enters due to poor intake piping, improper seating of air filter elements, loose/missing caps, poor maintenance of oil storage and oil transfer system. If silica mixes with any oil, it will lead to rapid wear of the components.

Wear Metals: The presence of metals like copper, iron, chromium, aluminium, lead, tin, manganese, nickel etc., can be traced in used oil. Excessive finding of any metal or combination of metals will give a clue to trouble in the component(s).

In addition to the above tests, other tests like particle count, patch microscope test, etc., are also carried out. Experts in the field and machine manufacturers can guide customers with the proper solutions as per their machine types.

Benefits of oil sampling

• Consistency in machine availability
• Healthy utilization
• Longer machine life
• Lower operating cost
• Higher productivity
• Better resale value

Saving on lubricants cost
It is proved that regular monitoring of hydraulic oils and final drive oils, the change interval can be extended to the extent of 200% of the standard recommendation. Normally, oil cost accounts for 5 to 6% of the machine’s total operating cost (excluding fuel but including all repairs and overhauls). So, any additional life obtained beyond the standard recommended period is a saving for the owner, and that too without affecting the machine’s life.

There are many incidences of saving engines, transmissions, differentials, final drives, and hydraulic components by identifying wear metal and contaminants at the initial stage and preventing major failures. The cost incurred for oil testing will be much less than the amount spent on account of premature and sudden breakdowns. Sudden, unexpected breakdowns can adversely affect the entire production chain, and sometimes, the situation may even demand engaging a rental machine to meet production target, which would increase costs for the machine owner.

Value-added services by service providers & equipment manufacturers
To get the real benefit, oil sampling has to be looked at as a preventive maintenance activity and should be done at regular intervals. Inconsistency and improper sample collection, delay in testing and report submission, and ignorance or delay in acting on abnormal findings, will not only dilute the purpose of this condition monitoring activity, but will also waste the time and money spent. Further, any oil sampling test done post breakdown of the machine will be considered as a part of the post-mortem.

It is the moral responsibility of the service provider to support and guide the customer for effective implementation of condition monitoring that includes oil sampling and analysis. Their services should include the following:

• Educating customer maintenance team on each and every process from sample collection and report analysis, to troubleshooting and fixing the issue identified.
• Ensuring that sampling is done at regular intervals, as decided mutually.
• Interpretation of oil sample report and advise for proper troubleshooting and fixing the identified problem, if any.
• Undertaking testing and providing the report in the shortest time possible (preferably within a week of sample collection), as delay in the sampling report can aggravate the problem, since the machine will be in running condition and the purpose of oil sampling will be lost.
• Supporting customer in extending oil change intervals through regular monitoring as this will help in minimizing maintenance cost.
• Training operators to fine tune their operating skills.