TCT 20

Common issues

• Bearing wear (journal and thrust bearings), leading to increased rotor clearances and vibration.
• Compressor fouling due to dirty intake air or oil carry-over, reducing efficiency and charge air pressure.
• Turbine fouling/deposits from exhaust gas (especially with HFO or poor combustion), causing reduced efficiency and potential imbalance.
• Nozzle ring and/or turbine blade damage (erosion, cracks, foreign object damage - FOD), impacting turbine performance.
• Oil leakage from compressor or turbine side due to worn seal rings or bearing housing issues, leading to oil contamination of air/exhaust.
• Rotor imbalance and excessive vibration, often caused by fouling, bearing wear, or mechanical damage.
• Surging, indicated by unstable operation and pressure fluctuations, often related to engine load, fouling, or control system issues.
• Cracks or distortion in casing components (e.g., exhaust gas casing) due to thermal stress or mechanical impact.

Inspection checklist

• Rotor Axial & Radial Clearances: Measure and record using a dial gauge. Compare to new and wear limits. Critical indicator of bearing health.
• Visual Inspection (External): Check for oil, exhaust gas, or water leaks from casings, connections, and drains. Look for signs of overheating, corrosion, or physical damage.
• Compressor Wheel & Casing: Inspect for fouling, erosion, foreign object damage (FOD), rubbing marks, and cracks on blades and diffuser.
• Turbine Wheel & Nozzle Ring: Inspect for heavy fouling, erosion, cracks, distortion, and FOD on blades and nozzle ring segments. Check for signs of rubbing.
• Bearing Condition (if accessible/during overhaul): Inspect bearing pads for wear, scoring, discoloration, and proper seating. Check oil supply passages.
• Lubricating Oil System: Verify correct oil pressure and temperature. Check oil filter condition and review recent oil analysis reports for contaminants or degradation.
• Air Intake & Exhaust Ducts: Ensure secure connections, no leaks, and inspect air filter elements for cleanliness and damage.
• Drainage Systems: Confirm all condensate and oil drains from compressor and turbine casings are clear and functioning correctly.
• Mounting & Fasteners: Check security of turbocharger mounting bolts, exhaust gas pipe connections, and all associated piping (oil, water, air).

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 Cartridge (or individual journal and thrust bearings, pads, and associated seals)
• Seal Rings (compressor and turbine side, including associated O-rings/gaskets)
• Gasket Set (for casing openings, oil lines, air/exhaust connections)
• O-rings (various sizes for oil, water, and air connections)
• Air Filter Elements (if specific to turbocharger intake)
• Lubricating Oil Filter Elements (if specific to turbocharger oil system)
• Nozzle Ring (especially if operating on HFO, as it's prone to erosion and fouling)
• Impeller/Turbine Wheel (less common, but critical for catastrophic damage, often supplied as part of a balanced rotor assembly)

Safety

• High Temperature Surfaces: Exhaust gas casings and turbine outlet are extremely hot during operation. Risk of severe burns. Ensure proper insulation and caution during inspection.
• High Speed Rotating Parts: The rotor operates at very high RPM. Catastrophic failure (e.g., due to imbalance or bearing failure) can result in projectile hazards. Never operate with covers removed.
• Pressurized Systems: Exhaust gas, charge air, and lubricating oil systems are under pressure. Risk of hot gas, air, or oil leaks and sprays, especially during maintenance or if seals fail.
• Noise Levels: Turbochargers generate significant noise during operation. Hearing protection is mandatory in the vicinity.
• Heavy Components: Casings, rotor assembly, and associated piping are heavy. Proper lifting gear, procedures, and personnel are essential during maintenance to prevent injury.

Class survey

During class surveys, the inspector will typically focus on: 1. Performance Verification: Review engine logbook data (turbocharger RPM, exhaust gas temperatures before/after turbine, charge air pressure/temperature) to identify any performance degradation or abnormal trends. Compare against design values and previous readings. 2. External Condition: Thorough visual inspection for oil/exhaust gas leaks, signs of overheating, corrosion, casing cracks, and secure mounting. Check insulation integrity. 3. Safety Devices: Verify functionality of any associated safety devices, such as overspeed trip (if integrated with TC or engine control), and alarm settings for high temperatures or low lubricating oil pressure. 4. Lubricating Oil System: Check oil pressure, temperature, and review recent lubricating oil analysis reports to ensure oil quality is maintained. 5. Maintenance Records: Scrutinize logbook entries for routine maintenance, cleaning, bearing replacements, rotor clearance measurements, and any reported defects or repairs. Ensure compliance with manufacturer's service intervals. 6. Rotor Clearances: Request recent axial and radial clearance measurements. If these are outside limits or trending negatively, further investigation or opening for inspection may be requested. 7. Opening for Inspection: For Special Surveys or if performance issues are suspected, the surveyor may request opening the compressor and/or turbine side for direct visual inspection of the impeller, turbine wheel, nozzle ring, and diffuser. This is particularly common for HFO-burning engines. 8. Spare Parts: Verify the presence and good condition of critical spare parts onboard, as per the vessel's Planned Maintenance System and class requirements.

Estimated lifetime: 80,000 - 100,000 running hours for main structural components (casings, shaft) with regular maintenance and replacement of wear parts (bearings, seals, nozzle ring, etc.). Major overhaul (rotor out) typically required every 16,000 - 24,000 hours.