NAxx/S

Common issues

• Bearing wear (thrust and journal) due to high rotational speeds, inadequate lubrication, or oil contamination, leading to increased vibration and potential rotor contact.
• Nozzle ring and turbine blade fouling/erosion from exhaust gas impurities (e.g., heavy fuel oil combustion byproducts, ash), reducing efficiency and increasing exhaust back pressure.
• Compressor wheel fouling/erosion from intake air impurities (e.g., salt, dust, oil mist), leading to reduced boost pressure and potential surging.
• Rotor unbalance caused by uneven deposits, blade damage, or bearing wear, resulting in excessive vibration and risk of catastrophic failure.
• Oil leakage from bearing housings or sealing air labyrinths, indicating worn seals or incorrect pressure differentials.
• Control system or sensor malfunction (e.g., speed sensor, temperature/pressure transmitters) due to moisture ingress, vibration, or electrical faults, affecting performance monitoring and safety.
• Air filter clogging or damage, restricting intake air flow, causing reduced engine power and potential compressor surging.
• Corrosion of casing components, particularly on the exhaust gas side, due to high temperatures and corrosive elements in the exhaust gas.

Inspection checklist

• Monitor turbocharger RPM, boost pressure, and exhaust gas temperatures (before/after turbine) against manufacturer's specified operating parameters and historical trends.
• Perform visual inspection of the compressor and turbine sides for fouling, erosion, foreign object damage (FOD), or blade tip rubbing marks (requires opening casing or using boroscope).
• Check lubrication oil pressure and temperature at the turbocharger inlet/outlet; inspect for any oil leaks from bearing housings or connections.
• Inspect the condition and cleanliness of the intake air filter elements and the exhaust gas silencer/spark arrester.
• Verify the integrity of the turbocharger casing, mounting bolts, and insulation for cracks, deformation, loose connections, or signs of overheating.
• Check for abnormal noise or vibration during operation using a stethoscope or vibration meter; investigate any deviations from baseline.
• Inspect the cooling water system (if applicable for bearing cooling) for proper flow, temperature, and signs of leakage or corrosion.
• Confirm the proper function and calibration of safety devices, including the overspeed trip mechanism and pressure relief valves.
• Check all drainage points for blockages and ensure proper functioning of any washing systems (water washing, grit blasting).

Service intervals

Typical intervals for this design class, not the manufacturer’s figures for your model. The manufacturer’s manual is binding.

Typical wear limits

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

Critical spares

• Complete bearing set (thrust and journal bearings)
• Gasket and O-ring kit for overhaul
• Air filter elements
• Sealing air labyrinth rings
• Temperature and pressure sensors (e.g., exhaust gas temperature, boost pressure, turbocharger speed)
• Lubricating oil filter elements (if separate from main engine system)
• Nozzle ring segments (if modular design and prone to wear/fouling)

Safety

• High-speed rotating machinery: Risk of catastrophic failure (e.g., rotor disintegration) due to unbalance or bearing failure, leading to projectile hazards and severe damage.
• Extreme temperatures: Exhaust gas temperatures can exceed 500-600°C; inadequate insulation or leaks pose severe burn risks and fire hazards.
• Pressurized systems: Air and oil lines are under high pressure; sudden leaks can cause injury or create an explosive atmosphere with oil mist.
• Noise levels: High noise levels during operation necessitate hearing protection for personnel in the vicinity.
• Hot work: Any welding or cutting near the turbocharger requires strict fire precautions due to residual oil and high operating temperatures.

Class survey

Class surveyors typically verify compliance with manufacturer's service schedules and maintenance records. They perform an external visual inspection for leaks, damage, and security of fastenings. Performance parameters (boost pressure, exhaust gas temperatures) are checked against design values. Functionality of safety devices (e.g., overspeed trip, emergency shutdown) is confirmed. Depending on the survey cycle or observed condition, an internal inspection of the compressor and turbine sides (e.g., for fouling, erosion, damage) may be required, often necessitating opening of the casing. Insulation integrity and fire-fighting arrangements in the vicinity are also checked.

Estimated lifetime: 24,000 - 36,000 hours (before major overhaul, with proper maintenance the unit's total service life can exceed 100,000 hours)