A ST27-A

Common issues

• Bearing wear (journal and thrust bearings) leading to increased rotor clearances, vibration, and potential contact between rotor and casing.
• Fouling of compressor impeller and turbine nozzle ring/blades due to combustion residues (turbine side) or intake air contamination (compressor side), resulting in reduced efficiency and boost pressure.
• Oil leakage from bearing housing seals, often visible as oil stains on the casing or entering the exhaust gas stream (blue smoke) or compressor side (oil in charge air cooler).
• Exhaust gas leakage from casing joints, turbine inlet/outlet connections, or exhaust manifold connections, reducing turbine efficiency and posing a fire hazard.
• Rotor imbalance or blade damage (erosion, corrosion, foreign object damage) causing excessive vibration, noise, and potential catastrophic failure.
• Surging, indicated by unstable boost pressure, characteristic 'whooshing' sound, and rapid fluctuations in turbocharger RPM, often due to engine load changes, compressor fouling, or issues with the air system.
• Cracks in turbine casing or exhaust gas manifold connections due to thermal stress and fatigue, leading to gas leaks and reduced performance.

Inspection checklist

• Visual Inspection: Check for oil leaks (bearing housing, oil lines), exhaust gas leaks (casing joints, manifold connections), cracks on casings, loose fastenings, and general cleanliness. Pay attention to insulation integrity on hot parts.
• Rotor Free Play: Measure axial and radial clearances (free play) of the rotor using a dial gauge. Compare measured values against OEM limits to assess bearing wear.
• Bearing Condition: If accessible (e.g., during scheduled maintenance), inspect journal and thrust bearings for signs of wear, scoring, pitting, or overheating. Check for correct lubrication.
• Fouling Check: Inspect compressor impeller and turbine blades for deposits (fouling) and erosion/corrosion. Note any signs of foreign object damage (FOD) on blades.
• Lubricating Oil System: Verify oil pressure and temperature at the turbocharger inlet, check oil filter condition, and inspect oil lines for leaks or damage. Ensure oil quality is maintained.
• Air Filter/Silencer: Inspect intake air filter for cleanliness and integrity. A clogged filter restricts airflow and can cause surging.
• Performance Monitoring: Review engine room logbook data for boost pressure, exhaust gas temperatures (inlet/outlet), turbocharger RPM, and compare against normal operating parameters. Look for trends indicating performance degradation (e.g., decreasing boost, increasing exhaust temp spread).
• Vibration Analysis: Check for excessive vibration during operation, which could indicate rotor imbalance, bearing issues, or blade damage. Use portable vibration analysis equipment if available.
• Safety Devices: Verify the functionality of the overspeed trip device (if fitted and testable) and ensure alarms for high temperature/low oil pressure are operational and correctly set.
• Drainage: Ensure water drain points (e.g., from charge air cooler) are clear and functional to prevent water ingress to the compressor, which can cause erosion.

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 set of journal and thrust bearings (including bearing bushes, thrust pads, and associated hardware).
• Bearing housing sealing rings (oil and gas side) and associated O-rings/gaskets.
• Full gasket and O-ring set for complete overhaul.
• Lubricating oil filter elements (if specific to TC lubrication system).
• High-temperature fasteners (nuts, bolts, studs) for casing joints and connections.
• Overspeed trip sensor or complete overspeed trip mechanism (if mechanical type).
• Small repair kit for minor blade damage (e.g., grinding stones for minor nicks, if approved by OEM).

Safety

• High Temperatures: The turbine casing and exhaust gas piping operate at extremely high temperatures (300-600°C), posing severe burn risks. Ensure all thermal insulation is intact and well-maintained.
• High Rotational Speeds: The rotor operates at very high RPMs (e.g., 20,000 - 40,000 RPM for this frame size). Rotor disintegration due to bearing failure or foreign object damage is a catastrophic risk, potentially causing severe injury or structural damage.
• Pressurized Systems: Compressed air (up to 4-5 bar) and hot lubricating oil (up to 5 bar) are under pressure. Leaks can cause injury, fire (especially hot oil on hot surfaces), or environmental pollution.
• Noise Hazard: High noise levels (typically 100-120 dB) during operation necessitate the use of hearing protection in the vicinity of the turbocharger.
• Hot Oil/Exhaust Gas Leaks: Can lead to engine room fires, particularly if hot oil sprays onto hot surfaces. Regular inspection for leaks is crucial.

Class survey

During class surveys (annual, intermediate, special), the surveyor will typically focus on the following: 1. General Condition: Visual inspection for overall integrity, absence of oil or exhaust gas leaks, loose fastenings, and excessive corrosion. Proper securing to the engine structure is checked. 2. Safety Devices: Verification of the overspeed trip device functionality (if testable without engine shutdown) and proper operation of associated alarms (e.g., low lubricating oil pressure, high exhaust gas temperature). Alarm set points may be checked. 3. Performance Records: Review of engine room logbooks to check turbocharger performance parameters (boost pressure, RPM, exhaust gas temperatures) against design values and identify any adverse trends that could indicate a deteriorating condition. 4. Maintenance Records: Examination of maintenance records for scheduled services, overhauls, bearing replacements, and any repairs carried out. Compliance with the Planned Maintenance System (PMS) is verified. 5. Insulation Integrity: Check that thermal insulation on hot parts (turbine casing, exhaust piping) is intact and effective to prevent fire hazards and personnel burns. 6. Drainage: Ensure condensate drains from the charge air cooler are clear and functional to prevent water ingress to the compressor. 7. Compliance: Verify that any modifications or repairs have been carried out in accordance with approved procedures and class requirements, with relevant documentation available.

Estimated lifetime: 24,000 - 36,000 running hours before a major workshop overhaul is typically required, assuming regular maintenance, adherence to OEM service schedules, and good operating conditions. Some units may exceed 40,000 hours with meticulous care and favorable operating profiles.