NR-S NR26/S

Common issues

• Bearing failure (journal and thrust) due to oil contamination, insufficient lubrication, or excessive vibration, leading to rotor imbalance and potential rubbing.
• Fouling of compressor and turbine sides, reducing efficiency, increasing exhaust back pressure, lowering boost pressure, and potentially causing surging.
• Oil leakage from bearing housings (compressor/turbine side) into charge air or exhaust gas, or externally, indicating worn oil seals or damaged bearings.
• Surging, characterized by unstable operation, rapid fluctuations in boost pressure, and a distinct 'barking' sound, often caused by fouling or engine load changes.
• Excessive vibration, indicative of rotor imbalance (fouling, damage), bearing wear, or foundation issues, leading to structural fatigue.
• Exhaust gas leakage from turbine casing joints, exhaust manifold connections, or nozzle ring area, reducing efficiency and posing a safety hazard.

Inspection checklist

• Visual inspection for oil, exhaust gas, and charge air leaks from casings, flanges, and connections.
• Measurement of rotor free play (axial and radial) with a dial gauge during planned maintenance, comparing against manufacturer's limits (e.g., axial 0.15-0.30mm new).
• Inspection of journal and thrust bearings for signs of wear, scoring, discoloration, or pitting during overhaul.
• Examination of compressor wheel and turbine blades for erosion, foreign object damage (FOD), cracks, and fouling.
• Inspection of nozzle ring and diffuser for fouling, erosion, cracks, and distortion, ensuring free movement if variable geometry.
• Verification of lube oil system integrity, including oil pressure, temperature, and filter condition.
• Checking tightness of mounting and foundation bolts for signs of fatigue or corrosion.
• Monitoring operational parameters: boost pressure, exhaust gas temperatures (in/out), turbocharger RPM, and vibration levels during engine operation.
• Functional check of the overspeed trip mechanism (if accessible for testing or via records).

Service intervals

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 (Journal bearings, thrust bearing segments, thrust collar)
• Oil Seals / Labyrinth Seals (Compressor and turbine side)
• Gasket & O-ring Kit (For casing joints, oil lines, and inspection covers)
• Lube Oil Filter Elements (If dedicated turbocharger oil filter)
• Nozzle Ring (Prone to erosion and fouling, crucial for performance)
• Rotor Cartridge (Highly recommended for quick repair, includes rotor shaft, compressor & turbine wheels, and often bearings pre-assembled)

Safety

• High Temperature Surfaces: Exhaust gas inlet/outlet and turbine casing operate at very high temperatures (300-600°C), posing severe burn risks.
• High Rotational Speed: Rotor operates at extremely high RPM (e.g., 30,000 - 60,000 RPM). Catastrophic failure due to imbalance or material fatigue can cause severe injury or damage.
• Pressurized Systems: Exhaust gas, charge air, and lube oil are under pressure. Improper disassembly or leaks can be hazardous.
• Noise Levels: Turbochargers generate significant noise; hearing protection is mandatory in the vicinity.
• Hot Oil/Exhaust Gas Leaks: Can ignite on hot surfaces, leading to fires.

Class survey

Class surveyors typically focus on the external integrity and operational safety. They will check for: absence of oil, exhaust gas, or charge air leaks; secure mounting and foundation; verification of overspeed trip functionality (if testable or records available); presence of guarding for rotating parts; integrity of exhaust gas piping, insulation, and connections; condition and cleanliness of the charge air cooler; adequate lube oil supply pressure and temperature; and review of maintenance records, running hours, previous survey reports, and critical spare parts inventory. Operational performance (boost pressure, exhaust temperatures) may also be observed.