Qualified requirements for turbine oil filtration effect

The cleanliness level of turbine oil after filtration needs to be comprehensively determined based on the equipment type, operating requirements and international standards. The following are specific classification standards and applicability guidelines:

Turbine oil cleanliness grade standard

1. ISO 4406 particle contamination grade (most commonly used)

| ISO code | Number of particles per milliliter (≥4/6/14μm) | Applicable scenarios |

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

| 12/10/8 | ≤2,000/400/50 | Nuclear power turbine, precision servo system |

| 14/12/10 | ≤4,000/1,000/200 | Gas turbine, supercritical turbine |

| 15/13/11 | ≤8,000/2,000/400 | Conventional steam turbine, industrial turbine |

| 16/14/12 | ≤16,000/4,000/800 | Old equipment or short-term emergency operation |

2. NAS 1638 level (US standard)

| NAS level | Particle count (in 100mL) | ISO 4406 equivalent |

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

| Level 5 | ≤9,600 (5~15μm) | 13/11/9 |

| Level 6 | ≤19,200 (5~15μm) | 14/12/10 |

| Level 7 | ≤38,400 (5~15μm) | 15/13/11 |

Permissible use levels for different equipment

1. Gas turbine (combined cycle)

- Requirement: ISO 14/12/10 or NAS level 6

- Reason: Particle wear will significantly shorten blade life in high-temperature and high-pressure environments.

2. Conventional steam turbines

- Requirements: ISO 15/13/11 or NAS level 7

- Exception: The speed control system oil circuit needs to be upgraded to ISO 14/12/10 (due to the sensitivity of the servo valve).

3. Nuclear power steam turbines

- Requirements: ISO 12/10/8 or NAS level 5

- Based on: IAEA TS-R-1 Nuclear Safety Guidelines.

4. Industrial drive steam turbines (non-power generation)

- Requirements: ISO 16/14/12 or NAS level 8

- Note: If the bearing clearance is large (>100μm), it can be relaxed to NAS level 9.

Oil cleanliness detection method

1. Automatic particle counter (ISO 4406)

- Equipment: PSS AccuSizer, HIAC 9703

- Sampling point: main oil pump outlet or oil tank return pipe.

2. Microscope method (NAS 1638)

- A 100 mL oil sample needs to be filtered and counted manually under a microscope.

3. Online monitoring

- Recommended: Pall Ultipor sensor (displays ISO code in real time).

Key measures to meet filtration standards

| Type of pollution | Target value | Filtration technology | Equipment example |

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

| Particles | ISO 14/12/10 | β≥1000 (1μm) filter | Donaldson Ultra-Web filter element |

| Moisture | ≤100ppm | Vacuum dehydration (-95kPa) | Alfa Laval MAB 104 |

| Colloid | Transmittance ≥80% | Electrostatic oil purifier | Nikkiso ESU-100 |

Operation specifications

1. Before injecting new oil:

- Must be filtered to ISO 15/13/11 (even if the new oil meets the standards when leaving the factory, transportation may introduce contamination).

2. Maintenance during operation:

- Check cleanliness monthly, and start bypass filtration when it exceeds the standard (flow ≥ 10% of the system oil volume).

3. Startup after overhaul:

- ISO 14/12/10 must be achieved to prevent residual impurities from damaging the equipment during installation.

Recommendations from authoritative organizations

- GE Power: Gas turbine lubricating oil must maintain ISO 14/12/10, otherwise the warranty will be invalid.

- Siemens: The TFA manual stipulates that the steam turbine NAS ≤ 6.

- National standard GB/T 14541: NAS ≤ 8 in operation (equivalent to ISO 16/14/12).

Conclusion:

- Minimum allowable level: ISO 16/14/12 (NAS level 8), emergency only.

- Recommended level: gas turbine/nuclear power requires ISO 14/12/10 or above, conventional steam turbine ISO 15/13/11.

Regular monitoring + high β value filtration is the core means to ensure the long-term operation of steam turbines.