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Napier Turbochargers

NA397

Turbocharger · Turbochargers

Technical data from manufacturer or class sources · not yet verified by a person​​‍‌​​‍‌⁠​‍‍⁠⁠⁠‍‌⁠‍‍
Per manufacturer datasheetCapacity
Exhaust gas / charge airMedium

On large ships equipped with medium-speed diesel engines, the Napier NA397 turbocharger plays a crucial role in enhancing engine performance by utilizing exhaust gases and charge air. This turbocharger is designed specifically for 4-stroke engines, ensuring efficient operation in demanding marine environments. Common issues that can arise include turbine and compressor fouling, as well as wear in bearings and thrust parts, and blade erosion. To maintain optimal performance, it is essential to follow the manufacturer’s guidelines and classification society requirements during servicing. Additionally, rotor and wheel parts must be properly balanced and documented according to OEM specifications. Regular annual inspections at class survey intervals are recommended to ensure compliance and safety standards are met. Stocking spare parts as specified by the manufacturer helps in reducing downtime and maintaining operational readiness.

Specifications

Technical data.

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Engine Type4-stroke
Service

Service notes.

What our service work and the manufacturer documentation say about keeping this model running.

Servicing per the manufacturer's manual and classification society requirements. Annual inspection at class survey. Stock spare parts as specified by the manufacturer.

Inspection

Common failures & inspection points

Inspection

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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

Minor Inspection (Visual/Performance)2,000 - 4,000 operating hours or every 3-6 months.
Intermediate Inspection (Bearing Check/Cleaning)8,000 - 12,000 operating hours. Includes opening for bearing inspection, cleaning of turbine/compressor.
Major Overhaul (Rotor Balancing/Component Replacement)16,000 - 24,000 operating hours. Full disassembly, inspection, balancing, and replacement of worn components.
Class Survey InspectionAnnually, typically coinciding with an intermediate or major inspection.

Typical wear limits

Axial Bearing PlayNew: 0.15 - 0.30 mm. Max allowable: 0.50 - 0.65 mm (refer to OEM manual for exact model limits).
Radial Bearing PlayNew: 0.20 - 0.35 mm. Max allowable: 0.60 - 0.75 mm (refer to OEM manual for exact model limits).
Blade Erosion/DamageMax 10-15% material loss on blade leading/trailing edges or specified depth/area as per OEM manual. Any crack formation is critical.
Shaft Run-outMax 0.02 - 0.03 mm (at bearing journals).

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.

Estimated lifetime: Rotor Assembly (with intermediate overhauls): 48,000 - 72,000 operating hours. Casing/Major Components: 100,000+ operating hours with proper maintenance and repair.

Spares

Replacement Parts

Spare parts notes

NA397 rotor and wheel parts require proper balancing and OEM-compatible service documentation.

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