Can industrial lubricating oil still be used after filtering?

Whether industrial lubricating oil can continue to be used after filtration depends on the filtration effect, the degree of oil deterioration and the equipment requirements. The following are specific judgment criteria and precautions:

1. Conditions for the reuse of lubricating oil after filtration

Key indicators meet the standards:

- Cleanliness: The particle level meets ISO 4406 or NAS standards (such as hydraulic oil needs to be ≤ISO 15/12/9).

- Moisture content: ≤100ppm (precision equipment requires ≤50ppm).

- Acid value: No significant increase (such as increment ≤0.1mg KOH/g).

- Viscosity: Change range <±10% (consistent with the crude oil grade).

No additive loss:

- Filtration temperature ≤65℃ to avoid high temperature damage to antioxidants, extreme pressure agents, etc. (such as ZDDP).

Equipment compatibility:

- The filtered oil must meet the requirements of the equipment manufacturer (such as the oil standards for turbines and gearboxes).

2. Non-reusable situations

❌ The oil has been seriously deteriorated:

- Acid value > 2.0mg KOH/g, or sludge and coking appear.

- Base oil oxidation (carbonyl peak exceeds the standard through FTIR detection).

❌ Key additives are exhausted:

- Such as anti-wear agents (zinc and phosphorus content drops sharply through elemental analysis).

❌ Irreversible pollution:

- Mixed with chemical solvents, fuel oil, or metal wear particles > 25μm.

3. Mandatory inspection items before reuse

| Inspection items | Method standards | Qualified threshold |

|------------------|-----------------------|----------------------------|

| Particle contamination | ISO 4406 | According to equipment level (such as NAS level 7) |

| Moisture | ASTM D6304 | ≤100ppm (precision equipment ≤50ppm) |

| Kinematic viscosity (40℃) | ASTM D445 | Deviation from crude oil <±10% |

| Acid value | ASTM D664 | Increment <0.1mg KOH/g |

| Antioxidant content | HPLC/RULER test | Residue >70% of initial value |

4. Recommendations for extending oil life

- Use an online filtration system: remove particles and moisture in real time (such as an electrostatic oil filter).

- Regular monitoring: test moisture, acid value, and particle size every 3 months.

- Avoid cross-contamination: Dedicated oil filter equipment is used according to the type of oil.

5. Economic judgment

- When the filtration cost is less than 30% of the new oil cost, reuse is more cost-effective (labor, energy consumption, and filter material consumption need to be calculated).

Conclusion: Industrial lubricating oil can be reused if the indicators are qualified after filtration, but strict testing is required. For high-value equipment (such as gas turbines and precision hydraulic systems), it is recommended to change the oil directly to reduce risks.