What an in-service oil analysis measures
A complete in-service oil analysis measures four categories of parameters, each providing different information about the state of the system:
- Lubricant properties: kinematic viscosity at 40°C and 100°C, viscosity index, flash point, acidity (TAN), and basicity (TBN). These values detect base oil degradation and additive depletion.
- Contamination: water content (Karl Fischer), particle count (ISO 4406), soot, glycol (indication of coolant leak), and unburnt fuel (in engines). A contaminated oil lubricates less and accelerates wear.
- Wear metals: elemental analysis (ICP) of iron, copper, aluminium, chromium, lead, tin, nickel. Each metal corresponds to a specific equipment component: iron indicates wear of liners or gears, copper points to bronze bearings, aluminium to pistons.
- Additives: phosphorus, zinc, boron, magnesium, calcium. Depletion of anti-corrosion or anti-wear additives without elevated wear indicates the lubricant is at the end of its service life even if its visual appearance is acceptable.
How to interpret the results
The values of an oil analysis are not interpreted in absolute terms, but as a trend. An elevated iron value is concerning if it has risen 300% compared to the previous analysis; it is irrelevant if it is consistent with the equipment's history.
The laboratory issues a report with a traffic light (green / amber / red) per parameter. Amber is the attention signal: it is not necessary to stop the equipment, but a review should be scheduled or analysis frequency increased. Red implies immediate intervention.
Without an analysis history, the first analysis only gives a snapshot. The value lies in the trend. At least 3 consecutive analyses of the same equipment are needed to establish equipment-specific reference values.
Signals that justify an urgent analysis
- Change in oil colour or appearance (cloudy, milky, intense black).
- Abnormally high operating temperature without apparent cause.
- Unusual noise in bearings or gears.
- Vibrations above normal (confirmed by measurement).
- Suspected water or external contaminant ingress.
- Before changing lubricant or supplier.
In which equipment it is most cost-effective
Oil analysis is especially cost-effective in equipment with high repair or replacement costs, extended downtime, difficult access for visual inspection, or systems critical to production.
- Large reducers and multipliers (>50 kW).
- High-capacity screw and piston compressors.
- High-pressure hydraulic systems in process machinery.
- Steam and gas turbines.
- Power electrical transformers.
- Marine engines and generator sets.
How to implement an analysis programme
An in-service oil analysis programme does not require investment in an in-house laboratory. Specialist laboratories offer sampling kits, courier collection, and results within 48–72 hours. The cost per complete analysis is between €30 and €80 depending on the test battery.
Sampling is critical: it must be done with the equipment in operation (or immediately after shutdown), from the representative point of the system (not from the bottom of the reservoir or the clean return zone) and in a clean, dry container. A poorly taken sample generates incorrect results.
- Recommended frequency: quarterly for critical equipment, semi-annual for important equipment, annual for secondary equipment.
- Always document: date, equipment, extraction point, oil hours, equipment hours, and any anomaly observed.
- Do not change the oil just before analysing: new oil analysis provides no wear information.
- Establish equipment-specific alarm limits based on the first three analyses, not on generic table values.
Cost of analysis vs cost of not doing it
A quarterly analysis of a critical reducer costs €320/year. A large reducer repair, including production downtime, can cost €15,000–€50,000 or more. An analysis that detects the problem four weeks in advance allows the repair to be scheduled for a weekend, with spare parts prepared and without production downtime.
The cost/benefit ratio of oil analysis for critical equipment is among the highest of any predictive maintenance practice. It is not a tool exclusive to large plants: any workshop or industry with process equipment can implement it.
In-service oil analysis transforms corrective maintenance into predictive maintenance without the need for expensive sensors or real-time monitoring systems. It is accessible, reliable, and delivers immediate returns in any installation with process equipment lubricated by oil. At LUBESOLUT, we can advise you on how to implement an analysis programme in your plant and which parameters are priorities for your type of equipment.
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