NA397

Common issues

• Turbine fouling (soot, unburnt fuel deposits) leading to reduced efficiency and high exhaust gas temperatures.
• Compressor fouling (oil mist, dust, salt) leading to reduced air flow and potential surge.
• Bearing wear (journal and thrust bearings) due to inadequate lubrication, contamination, or excessive vibration, leading to increased clearances and potential rotor contact.
• Blade erosion (turbine and compressor) from abrasive particles in exhaust gas or intake air, or water droplets, leading to imbalance and efficiency loss.
• Oil leakage from bearing housing seals, indicating seal wear or improper oil drainage.
• Rotor imbalance due to uneven fouling or blade damage, causing excessive vibration and bearing stress.
• Casing cracks, particularly in the hot exhaust gas inlet area, due to thermal stress cycling.

Inspection checklist

• **Visual Inspection (External)**: Check casing for cracks, exhaust gas leaks, oil leaks, loose connections, and condition of insulation.
• **Performance Monitoring**: Compare current charge air pressure/temperature, exhaust gas temperatures (before/after turbine), and turbocharger RPM against baseline values. Look for deviations.
• **Vibration Analysis**: Monitor vibration levels during operation. Abnormal vibration indicates imbalance or bearing issues.
• **Bearing Clearances (Internal)**: Measure axial and radial play of the rotor shaft. Compare against OEM limits (requires opening).
• **Turbine & Compressor Inspection**: Open casing to visually inspect turbine blades, nozzle ring, compressor impeller, and diffuser for fouling, erosion, cracks, or foreign object damage (FOD).
• **Oil System Check**: Inspect oil inlet/outlet lines for blockages, check oil quality, and ensure proper oil drainage from the bearing housing.
• **Air Filter Condition**: Verify the cleanliness and integrity of the engine's air intake filters.
• **Safety Devices**: Check overspeed trip mechanism functionality and alarm settings.

Service intervals

Typical wear limits

Ranges are typical for this design class. Always confirm against the manufacturer documentation for your serial number.

Critical spares

• Bearing set (Journal bearings, thrust pads/collar).
• Sealing rings (labyrinth seals, oil seals).
• Gasket and O-ring kit for casing and connections.
• Impeller nut and locking washer.
• High-temperature bolts/studs for casing.
• Cleaning agents/kits for turbine and compressor washing.
• Complete bearing cartridge assembly (highly recommended for quick replacement).

Safety

• **High Temperatures**: Exhaust gas temperatures (up to 550°C) and hot casing surfaces pose severe burn hazards. Ensure proper insulation and PPE.
• **High Rotational Speed**: Rotor operates at extremely high RPMs (e.g., 15,000-25,000 RPM). Risk of rotor disintegration if bearings fail or imbalance is severe.
• **High Pressures**: Charge air and exhaust gas are under pressure. Ensure all connections are secure before and during operation.
• **Hot Oil**: Lubricating oil can be hot and under pressure. Exercise caution during oil system maintenance.
• **Lifting Operations**: Heavy components (casing halves, rotor) require proper lifting gear and procedures during maintenance.

Class survey

Class surveyors typically check for: 1. **Documentation Review**: Verification of maintenance records, running hours, previous inspection reports, and spare parts inventory. 2. **External Visual Inspection**: Check for any visible leaks (oil, exhaust gas), cracks in casing, condition of insulation, and security of mounting. 3. **Performance Data Review**: Scrutiny of engine room logbook entries for turbocharger performance parameters (RPM, charge air pressure/temp, exhaust gas temp) to identify trends or abnormalities. 4. **Internal Inspection Confirmation**: If an internal inspection (e.g., 8,000-hour or 16,000-hour service) has been performed, the surveyor will review reports, photos, and potentially witness reassembly or specific checks. 5. **Safety Device Check**: Confirmation of overspeed trip functionality and alarm settings. 6. **Spare Parts Verification**: Confirmation that critical spare parts are onboard as per class requirements and manufacturer recommendations.