18H46DF

Common issues

• Gas Admission Valve (GAV) operational issues, leakage, or sticking, leading to unstable gas combustion or gas slip.
• Cylinder liner scuffing, particularly during transient operations, fuel changeovers, or due to inadequate lubrication in DF mode.
• HFO pilot fuel injector nozzle coking and wear, impacting combustion efficiency and increasing maintenance frequency.
• Exhaust valve burning and seat wear, exacerbated by varying combustion temperatures and fuel quality in dual-fuel operation.
• Turbocharger fouling (compressor and turbine side) and bearing wear, affecting engine efficiency and increasing exhaust back pressure.
• Control system (ECS/PMS) sensor failures or software glitches, critical for stable dual-fuel operation and safety interlocks.
• Crankshaft main and connecting rod bearing wear, often indicated by increased oil consumption or metal particles in lube oil analysis.
• Methane slip and associated exhaust system component fouling (e.g., waste heat recovery boiler).

Inspection checklist

• Gas System Integrity: Conduct visual inspection for gas leaks (soap test/sniffer), check condition of gas valve unit (GVU), double-wall piping, and ventilation in gas-safe areas. Verify gas detection system calibration.
• Cylinder Unit Condition: Perform endoscopic inspection of combustion chambers (piston crown, cylinder liner, exhaust valves) for signs of wear, scuffing, carbon deposits, or burning.
• Fuel Injection Equipment: Inspect HFO pilot fuel injectors for coking and leakage. Check gas admission valves (GAVs) for proper operation and sealing.
• Turbocharger Inspection: Check axial and radial play of the rotor shaft. Inspect compressor and turbine blades for fouling, damage, or erosion. Verify air cooler cleanliness and condition.
• Crankcase & Bearings: Check crankcase breather for excessive blow-by. Listen for abnormal bearing noises. Review oil mist detector readings and recent lube oil analysis reports for wear metals.
• Performance Parameter Review: Analyze engine logbook data (exhaust gas temperatures per cylinder, cylinder pressures, fuel consumption for both HFO/LNG, turbocharger speeds, charge air pressure) for deviations or trends.
• Safety Devices & Alarms: Verify functionality of overspeed trip, low lube oil pressure shutdown, high cooling water temperature shutdown, emergency stops, and gas supply shutdown systems.
• Crankcase Inspection: Check for cleanliness, excessive carbon deposits, and proper drainage, which can indicate poor combustion or oil carry-over.

Service intervals

Typical wear limits

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

Critical spares

• HFO Fuel Injector assembly (complete unit or nozzle/valve needle set)
• Exhaust Valve spindle and seat ring (at least one set per cylinder type)
• Piston ring sets (complete for at least one cylinder)
• Gas Admission Valve (GAV) assembly or critical repair kit (e.g., seals, springs)
• Cylinder head gasket set (complete for at least one cylinder)
• Turbocharger bearing cartridge or complete repair kit
• Main and Connecting Rod bearing shells (at least one set of each type)
• Assorted sensors (pressure, temperature, speed, gas detection) for critical engine parameters

Safety

• LNG Leakage: High risk of fire, explosion, and asphyxiation in enclosed spaces (engine room, gas valve unit room) due to methane's flammability and displacement of oxygen. Strict adherence to gas-safe procedures is paramount.
• High-Pressure HFO Fuel Spray: Potential for spray fires from leaking high-pressure fuel lines, especially on hot surfaces. Ensure proper shielding and leak detection.
• Crankcase Explosion: Risk from overheating bearings or piston seizure leading to ignition of oil mist. Regular oil analysis, oil mist detector functionality, and proper crankcase relief valve maintenance are vital.
• Hot Surfaces & Exhaust System: Severe burn hazards and potential for fire if insulation is damaged or fuel/oil leaks onto hot components.
• Emergency Shutdown Systems: Critical for preventing catastrophic failures. Regular testing and verification of overspeed, low LO pressure, high CW temp, and gas supply shutdown systems are mandatory.

Class survey

Class surveyors will pay particular attention to: - Gas System Integrity: Verification of gas detection system calibration, functionality of gas supply shutdown valves, ventilation in gas-safe areas, and leak testing of gas piping (e.g., soap test, sniff test). - Engine Performance Records: Thorough review of logbooks for consistent operation, fuel changeover stability, exhaust gas temperature deviations, and any alarms or shutdowns related to dual-fuel operation. - Safety Devices: Functionality testing of overspeed trip, low lubricating oil pressure shutdown, high cooling water temperature shutdown, and emergency stop buttons. - Crankcase Protection: Inspection of crankcase relief valves, flame traps, and oil mist detector functionality. - Fire Prevention: Inspection of high-pressure fuel oil pipe shielding, quick-closing valves for fuel lines, and fire dampers in engine room ventilation. - Cylinder Unit Condition: Request for endoscopic inspection reports or visual inspection of cylinder heads (if accessible) for exhaust valve condition and piston crown deposits. - Maintenance Documentation: Review of planned maintenance system records, oil analysis reports, spare parts inventory, and previous survey recommendations.

Estimated lifetime: 80,000 - 100,000+ hours before major engine block/crankshaft reconditioning is typically considered.