Oil Analysis in Industrial Equipment: Indicators of Wear Metals, Contamination and Degradation of Lubricants

1. Introduction: The Challenge of Industrial Reliability

The reliability of industrial equipment is an essential pillar for productivity and operational sustainability. Unexpected machine failures can generate significant production losses, high repair costs and safety risks. In this scenario, oil analysis emerges as a critical engineering tool, offering in-depth diagnostic insight into the internal health of vital components such as engines, reducers, compressors and hydraulic systems. Its proactive application allows early detection of anomalies, optimizing maintenance cycles and extending the useful life of assets.

UNITEC-D, with its vast experience in high-performance industrial components, recognizes the fundamental importance of oil analysis. Understanding the data generated by this technique not only prevents catastrophic failures, but also guides the correct selection and application of lubricants and spare parts, ensuring that Brazilian manufacturing plants operate at their peak efficiency, in compliance with strict standards such as NR-12, which establishes minimum requirements for the prevention of accidents and occupational illnesses in machinery and equipment.

2. Fundamental Principles of Oil Analysis

Oil analysis is based on the systematic evaluation of the physicochemical properties of the lubricant and the identification of materials suspended in it. The oil, in addition to lubricating, acts as the "blood" of the system, carrying vital information about the internal wear of the components, the presence of contaminants and its own degradation condition.

2.1. Lubricant Functions

• Reduction of Friction and Wear: Creation of a film between moving surfaces.
• Heat Removal: Dissipation of thermal energy generated by friction.
• Cleaning: Transport of wear particles and contaminants to the filter.
• Sealing: Aid in sealing gaps.
• Corrosion Protection: Formulations with anti-corrosive additives.

2.2. Wear Mechanisms

Wear is the progressive removal of material from the surface of a component. The main types identified via oil analysis include:

• Abrasive Wear: Caused by hard particles trapped between surfaces (e.g., sand, dirt). Metals such as Aluminum (Al), Silicon (Si - from dirt) are indicators.
• Adhesive Wear (Galling): Transfer of material between surfaces in direct contact under load (failure of the lubricating film). Iron (Fe), Copper (Cu) and Lead (Pb) are common.
• Corrosive Wear: Chemical attack of the metal surface by acids or water. Elevated levels of Iron, Chromium (Cr) and Nickel (Ni) may indicate corrosion.
• Fatigue Wear: Formation of cracks and detachment of particles due to cyclic stresses. Larger particles of Iron or Chromium.

2.3. Sources of Contamination

External and internal contaminants directly affect the useful life of the oil and components:

• Solid Particles: Dust, sand, welding residue, fibers (indicated by Silicon, Aluminum, etc.).
• Water: Can come from condensation, leaks or processes. Causes corrosion, degradation of additives and loss of viscosity.
• Fuel: In internal combustion engines, it indicates injection or sealing problems. Reduces oil viscosity.
• Coolant/Glycol: Cooling system leaks. Forms sludge and attacks additives.

2.4. Oil Degradation

The oil is not eternal and degrades over time of use due to:

• Oxidation: Reaction of oil with oxygen, accelerated by heat and metal catalysts. Increases viscosity and forms acids and varnishes.
• Nitration: Reaction with nitrogen oxides, common in combustion engines. Increases viscosity and forms sludge.
• Additive Depletion: Natural consumption of additives (anti-wear, antioxidants, dispersants) over time.
• Shear: Loss of viscosity due to the breakdown of polymer molecules in multigrade oils under high shear stress.

3. Technical Specifications and Standards

Interpreting oil analysis results requires knowledge of typical lubricant properties and applicable technical standards, which define test methods and acceptable limits.

3.1. Key Properties of Oil and Its Norms

• Viscosity (cSt): Measure of the oil's resistance to flow. It is the most critical property for the formation of the lubricating film. Significant variations (±10% of new viscosity) may indicate fuel/solvent contamination (decrease) or oxidation/water/glycol (increase). Standard: ABNT NBR 10441 (similar to ASTM D445).
• Total Acid Number (NAT/TAN - mg KOH/g): Measures the total content of acid constituents in the oil, resulting from oxidation or additives. Increases indicate oil degradation. Standard: ABNT NBR 14459 (similar to ASTM D664).
• Total Basic Number (NBT/TBN - mg KOH/g): Measures the alkaline reserve of the oil, important for neutralizing acids in combustion engines. Its decrease below 50% of the initial value indicates depletion of the additive. Standard: ABNT NBR 14458 (similar to ASTM D2896 or ASTM D4739).
• Flash Point (ºC): Minimum temperature at which oil vapor momentarily ignites. Reduction indicates contamination by fuel or solvents. Standard: ABNT NBR 11341 (similar to ASTM D93).
• Particle Count (ISO 4406): Indicates the cleanliness of the oil in terms of contamination by solid particles. The code ISO 4406 (e.g., 18/16/13) represents the number of particles per milliliter in sizes >4 µm, >6 µm, and >14 µm, respectively. Contamination limits are critical to component life, especially in high-precision hydraulic systems.
• Fourier Transform Infrared Spectroscopy (FTIR): Analysis of the oil's molecular "fingerprint" to monitor oxidation, nitration, sulfation, water presence and additive depletion. Standard: ASTM D7412.

4. Corrective Action Selection and Sizing Guide

Interpreting an oil analysis report requires technical knowledge and experience. Below is a simplified matrix to aid decision making based on common wear metal levels.

4.1. Interpretation of Wear Metals (ICP-OES)

Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES) quantifies the concentration of various elements in oil in parts per million (ppm). The table below presents generic alert thresholds. It is crucial to consult the base values (new oil) and establish specific trends for each equipment, according to manufacturers' recommendations and standards such as ISO 14838.

5. Sampling and Data Collection Best Practices

The quality of the oil analysis directly depends on the representativeness of the sample. Inadequate collection can lead to erroneous diagnoses and poor maintenance decisions.

5.1. Sampling Procedure (ABNT NBR ISO 55512)

1. Sampling Point: Always use a dedicated point, located in an area of ​​turbulent and active flow, before the filter and away from return lines or dead spots.
2. Frequency: Define based on equipment criticality, operating hours, manufacturer recommendations and failure histories. For critical equipment, a monthly frequency or every 250-500 hours of operation is common.
3. Collection Material: Use sterilized, specific bottles for oil analysis, avoiding external contamination.
4. Collection Technique: Purge the sampling point (discard 5-10 times the tube volume) before collecting the "live" sample, with the equipment at normal operating temperature.
5. Identification: Label the bottle immediately with accurate data: date, time, type of equipment, hours of oil use, hours of equipment use, type of oil and sampling point.

6. Failure Modes and Root Cause Analysis

Oil analysis is a valuable tool in identifying specific failure modes and conducting an effective root cause analysis. Wear and contamination indicators provide crucial clues.

6.1. Correlation between Anomalies and Failures

• High iron (Fe) + high Silicon (Si): Strong indication of abrasive wear. Potential root cause: compromised air filter, poor sealing, dirt entering the system.
• High Copper (Cu) and Lead (Pb): Wear of bearings and bushings. Potential root cause: overload, misalignment, lack of lubrication, water contamination.
• Água (H2O) > 0.2% + Aumento de Viscosidade: Degradação do óleo. Cause Potential root: internal condensation, cooling water leak.
• Drastic decrease in NBT: Depletion of additives in diesel engines. Cause Potential root: excessive oil change interval, poor quality fuel.
• Sudden increase in large particles (ferrography): Severe wear imminent. Cause Potential root: bearing failure, gear misalignment.

Visual identification of varnishes, sludge or emulsions in the oil also complements the diagnosis, confirming thermal degradation or water/glycol contamination.

7. Predictive Maintenance and Condition Monitoring

Oil analysis is a central component of Predictive Maintenance and Condition Monitoring (PdM/CM) strategies, enabling intervention before failure and optimizing maintenance scheduling.

7.1. Main Analytical Techniques

• Elemental Analysis (ICP-OES): Quantifies wear metals, additives (Zn, P, Ca, Mg, Ba, Mo) and contaminants (Si, Na, K). Essential for monitoring lubricant wear and health.
• Viscosimetry: Monitors the viscosity of the oil at controlled temperatures (e.g., 40°C and 100°C). Changes indicate oxidation, fuel dilution, or shear.
• Particle Count (ISO 4406): Evaluates the cleanliness of the hydraulic system and lubricants. Fundamental to the useful life of pumps, valves and actuators.
• FTIR analysis: Detects oxidation, nitration, sulfation, water and glycol. Crucial for evaluating oil degradation.
• Karl Fischer (ASTM D6304): Accurate method for determining water content in oils, even at very low concentrations.
• Ferrography: Morphologically analyzes and quantifies large wear particles (>5 µm), identifying the type and severity of wear (abrasive, adhesive, fatigue).
• Fuel Contamination Analysis: Via gas chromatography (ASTM D7593) or flash point.

The integration of these techniques with other PdM strategies, such as vibration analysis and thermography, offers complete coverage for machine health, aligned with the requirements of the NR-10 standard for safety in electrical installations and services, where equipment failure can have serious electrical consequences.

8. Oil Analysis Techniques Comparison Matrix

The choice of analysis technique depends on the type of equipment, criticality, cost and information desired. The table below compares some of the most used methodologies.

9. Conclusion: The Strategic Value of Oil Analysis

Oil analysis goes beyond merely detecting problems; is an asset optimization strategy that directly impacts industrial performance and safety. By providing accurate data on the state of wear, presence of contaminants and lubricant degradation, it empowers maintenance teams to make data-driven decisions, reduce unplanned downtime and maximize return on equipment investment. Adherence to technical standards, such as those established by ABNT and ISO, is essential for the reliability of results.

UNITEC-D positions itself as a strategic partner for Brazilian industries, providing components and engineering solutions that complement a robust oil analysis program. Our products are selected to guarantee the durability and performance required in the most challenging industrial environments, contributing to maintaining compliance with NBR standards and operational excellence.

To explore our full line of products and solutions that support the health and longevity of your equipment, visit our e-catalog: https://www.unitecd.com/e-catalog/

10. References

1. BRAZILIAN ASSOCIATION OF TECHNICAL STANDARDS (ABNT). Various NBR standards for lubricants and hydraulic fluids.
2. ISO 4406:1999. Hydraulic fluid power -- Fluids -- Method for coding level of contamination by solid particles.
3. ASTM International. Technical publications on test methods for lubricants (e.g., ASTM D445, ASTM D93, ASTM D664).
4. Noria Corporation. Machinery Lubrication Magazine and technical whitepapers.
5. SKF. Machine Health Assessment for Industrial Lubricants.