HT-C HT-71C

Common issues

• Bearing wear (journal and thrust bearings) leading to increased axial/radial clearances and vibration.
• Compressor fouling due to intake air contamination or oil carry-over, reducing efficiency and air flow.
• Turbine fouling (soot deposition) on nozzle ring and turbine blades, impacting engine performance and increasing exhaust back pressure.
• Oil leakage from bearing housing seals, often visible externally or indicated by oil in the compressor/turbine discharge.
• Foreign Object Damage (FOD) to compressor or turbine blades, causing imbalance and potential catastrophic failure.
• Surging, often indicated by fluctuating boost pressure and unusual noises, potentially due to engine load changes, fouling, or turbocharger malfunction.
• Cracks or erosion on nozzle ring and turbine blades due to high temperatures and corrosive exhaust gases.
• Vibration due to rotor imbalance, bearing wear, or structural issues, detectable through monitoring or unusual noise.

Inspection checklist

• Check axial and radial clearances of the rotor shaft using a dial gauge (refer to manufacturer's manual for specific limits).
• Inspect compressor wheel for fouling, erosion, or damage to blades. Ensure air filter is clean and intact.
• Inspect turbine wheel and nozzle ring for fouling, erosion, cracks, or foreign object damage (requires opening gas casing).
• Verify lubricating oil pressure and temperature at turbocharger inlet/outlet are within specified ranges.
• Check for any oil or gas leaks from casing joints, bearing housing, or drain lines.
• Assess overall vibration levels and listen for unusual noises (e.g., grinding, whistling, rubbing).
• Inspect security of mounting bolts, insulation, and connections for air, exhaust, and oil lines.
• Ensure drain lines from bearing housing are clear and free-flowing.
• Check condition of turbocharger washing nozzles and ensure they are not clogged.

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 assembly (journal and thrust bearings).
• Oil seals and O-ring sets for bearing housing.
• Gasket sets for casing joints (gas inlet/outlet, air outlet).
• Lubricating oil filters (if external to engine system).
• Nozzle ring (especially if operating in challenging fuel conditions or if previous damage history).
• Compressor/Turbine cleaning agents and washing nozzles.
• Special tools for dismantling and assembly (e.g., rotor lifting tools, bearing pullers).

Safety

• High temperatures: Exhaust gas casing and turbine components operate at extremely high temperatures; severe burn hazard.
• High rotational speeds: Rotor operates at tens of thousands of RPM; risk of catastrophic failure (rotor burst) if severely imbalanced or damaged.
• High pressure: Compressor discharge air and exhaust gas are under high pressure; potential for injury during maintenance if not depressurized.
• Hot oil: Lubricating oil can be hot and under pressure; risk of burns and slips.
• Heavy lifting: Turbocharger components (e.g., casings, rotor assembly) are heavy and require proper lifting gear and procedures during maintenance.

Class survey

Class surveyors typically focus on: 1. Review of maintenance records, running hours, and spare parts certificates. 2. Visual inspection for external leaks, damage, and security of mounting. 3. Verification of operational parameters (RPM, boost pressure, exhaust temperatures) against design values. 4. If due for an overhaul or if performance issues are reported, an opening inspection of the compressor and turbine sides may be required to assess fouling, wear, and damage. 5. Confirmation of overspeed trip functionality and alarm settings. 6. Integrity of the lubricating oil supply and drainage system.