Marine & Power-Plant Exhaust Gas Turbocharger Surging, Nozzle Ring Fouling & Water Washing Guide

Marine & Power-Plant Turbocharger Cleaning & Diagnostic Matrix

1. Turbocharger Surging Physics, Scavenge Air Restriction & Cylinder Imbalance Diagnostics

Diagnosing turbocharger surging falls under the general engine operation and performance competence in STCW Code tables A-III/1 and A-III/2, and it should be done before aerodynamic instability damages compressor bearings, labyrinth seals or impeller vanes. An exhaust gas turbocharger couples an exhaust-driven turbine wheel to a centrifugal air compressor on a common rotor shaft, raising scavenge or charge-air density so the engine can burn fuel efficiently. Surging occurs when the mass flow of air falls below the compressor stability limit for the prevailing pressure ratio across the scavenge air receiver. Pressurised air in the scavenge receiver momentarily reverses direction and blows backward through the diffuser and impeller until receiver pressure drops and forward flow resumes, creating a repetitive barking or coughing noise at the air intake filter.

Systematic fault isolation divides surging triggers into three physical pathways: restriction in the scavenge and charge-air path, fouling or imbalance in the exhaust gas path, and transient load or cylinder combustion disturbances. On the air side, the restriction can sit on either side of the compressor: a fouled intake filter silencer on the suction side, or a dirty charge-air cooler bundle, water carryover from the air cooler separator, or carbonised scavenge ports on the delivery side. On the exhaust side, a partially choked turbine nozzle ring, damaged turbine blades, or heavy soot build-up in the exhaust gas economiser disturbs the energy balance between turbine and compressor. Sudden helm manoeuvres in heavy weather, a misfiring cylinder, a leaking exhaust valve, or a faulty fuel injector can also trigger cyclic pressure pulses in the exhaust manifold that push the turbocharger across its surge line.

Using engine performance trends (readings corrected to ISO reference conditions), engineers should cross-check cylinder indicator diagrams, individual cylinder exhaust gas temperatures, turbocharger speed, scavenge air pressure, and air cooler differential pressure against sea-trial baselines. When surging accompanies rising exhaust gas temperatures across all cylinders, compare turbocharger speed and scavenge air pressure with the baseline and check the air filter and air cooler pressure drops before deciding where the fault lies. Use the fault table in the maker's manual for the installed model: at least one maker lists nozzle-ring contamination as charge air pressure too high with increased turbocharger speed, so a fall in scavenge air pressure on its own does not point to nozzle-ring choking. When surging coincides with a single cylinder showing abnormal peak pressure or exhaust temperature deviation, fuel injection or exhaust valve overhaul on that unit must be prioritised.

• Log scavenge air receiver pressure, charge-air cooler air-side pressure drop (manometer differential), cooling water inlet/outlet temperatures, and air cooler drain discharge rate.
• Compare individual cylinder exhaust gas outlet temperatures and maximum combustion pressures against ISO-corrected shop-trial and sea-trial reference curves.
• Inspect and clean the turbocharger air intake filter blanket or silencer segments before increasing engine load after prolonged port stays or sandstorm transits.
• Verify that scavenge air space drains are clear of sludge and unburnt cylinder oil so scavenge fire hazards and port restrictions are eliminated.
• During heavy weather pitching, apply gradual load reductions in coordination with the bridge Officer of the Watch to prevent governor hunting and repetitive turbocharger surging.

2. Compressor Water Washing, Turbine Wet Washing vs Dry Cleaning & Soot Fire Prevention

Regular in-service cleaning of both the compressor and turbine sides is essential to maintain compressor efficiency and prevent exhaust gas economiser soot fires during slow steaming or low-load operation. Compressor water washing is performed while the engine is running at the service load specified in the engine or turbocharger maker's instruction manual. A fixed volume of clean untreated fresh water (never sea water or chemical detergent unless explicitly approved by the maker) is injected over the maker's prescribed time window into the compressor intake casing. High-velocity water droplets impact the rotating impeller and stationary diffuser vanes, stripping salt deposits and oil vapour film that is then evaporated and carried through the engine.

Turbine-side cleaning addresses combustion residues from residual marine fuels or dual-fuel pilot injection. Where turbine wet washing is fitted, the engine load MUST first be reduced in collaboration with the bridge until the exhaust gas temperature at the turbocharger inlet stabilises below the equipment maker's maximum permissible washing temperature. Injecting cold water into a turbine operating at full service temperature causes severe thermal shock, warping the nozzle ring and cracking the gas inlet casing. Before opening the fresh-water supply valve, the engineer must verify that the turbocharger casing drains and exhaust uptake drains are fully open and discharging freely, and must continue running the engine at reduced load after washing until all internal moisture is dried out.

Where turbine dry cleaning is installed, a measured charge of maker-approved dry granules (such as crushed nut shells or calibrated carbon granules) is injected by compressed air into the exhaust gas stream ahead of the turbine at normal service load. Because dry cleaning relies on kinetic gas velocity to scour deposits from the nozzle ring and blade profiles, it is ineffective at manoeuvring load and cannot remove sticky deposits inside the downstream exhaust gas boiler. When vessels operate at prolonged low load (slow steaming), engineers must follow the engine maker's low-load guidance, monitor exhaust boiler gas-side differential pressure, operate sootblowers frequently, and raise engine load periodically where navigationally permitted to burn off unburnt carbon deposits.

• Confirm whether the installed turbocharger model uses turbine wet washing, dry granule cleaning, or dry-service overhaul only per the onboard maker's manual.
• For turbine wet washing, obtain bridge permission to reduce engine load, stabilise exhaust gas inlet temperature below the maker's limit, and prove all casing drains open before admitting wash water.
• Never use sea water for compressor or turbine washing, and verify fresh-water dosing vessel volume and injection duration before starting the wash cycle.
• After any wet wash, keep the engine running under load for the maker's drying period and record pre-wash and post-wash turbocharger RPM, scavenge pressure and exhaust temperatures in the Engine Room Logbook and PMS.
• Cross-check exhaust gas economiser sootblower operation and gas-side pressure drop after low-load operation to prevent uptake soot fires.

3. Emergency Rotor Locking, Overhaul Clearances & SOLAS II-2/4 Hot Surface Insulation (220 °C)

When a turbocharger develops severe high-frequency vibration, metallic rubbing, lubricating oil failure, or rotor damage at sea, immediate action is needed to protect the crew and keep propulsion available. The watchkeeping engineer must reduce engine load immediately, notify the bridge Officer of the Watch and Chief Engineer, check turbocharger lubricating oil pressure, sight-glass flow and bearing temperature, and stop the main engine as soon as the vessel is navigationally safe. If the turbocharger cannot be returned to service at sea, engineers must execute the engine maker's emergency out-of-service procedure: fitting the mechanical rotor locking device or installing the dedicated exhaust and air blanking plates, opening emergency scavenge air bypass flaps where fitted, running the electric auxiliary blowers continuously, and limiting main engine RPM and cylinder exhaust temperatures strictly to the maker's emergency operating envelope.

During scheduled overhauls in the planned maintenance system (ISM Code section 10) and at class surveys, senior engineers should verify rotor dynamic balance certificates, inspect turbine blades, lacing wires (where fitted), nozzle rings and compressor impellers for erosion, cracking or foreign-object damage, and renew gas and oil labyrinth seals. Plain bearings must be inspected for white-metal wiping or clearance growth, and rolling-element bearings must be renewed within the maker's stated running-hour limit. Before closing the casing, engineers must measure and log axial and radial rotor clearances (as designated on the maker's clearance record sheet) against the minimum and maximum tolerances in the instruction manual.

Finally, Port State Control officers walking the engine room check machinery against SOLAS Chapter II-1 (Part C, from Regulation 26) and fire prevention against SOLAS Chapter II-2 Regulation 4, and turbocharger casings and exhaust manifolds after maintenance are an obvious place to look. Under SOLAS II-2/4.2.2.6, surfaces with temperatures above 220 °C that fuel could reach after a system failure must be properly insulated, and the same regulation applies this to lubricating oil and other flammable oils; good practice is oil-impervious lagging and spray shields on oil pipe joints near hot surfaces. Any removable thermal blankets detached from the turbocharger gas inlet or outlet casing during water-wash drain maintenance or bearing inspection must be refitted and wired securely before the engine is brought back on load.

• Verify that the turbocharger emergency rotor locking tool, blanking plates, lifting gear and spare bearing/seal kit are stowed in the engine-room workshop and inventoried in the PMS critical spares list.
• Measure and record axial and radial rotor clearances, bearing running hours and vibration spectrum baselines (FFT velocity/acceleration readings) in the PMS after every overhaul.
• Inspect all thermal insulation blankets and metal cladding around the turbocharger gas inlet, outlet casing, exhaust bellows and indicator cocks to confirm that no surface above 220 °C that fuel or oil could reach after a system failure is left exposed, as SOLAS II-2/4 requires.
• Check that any insulation contaminated with fuel or lubricating oil is renewed immediately and that anti-spray tape or metal flange shields are intact on adjacent lube-oil supply and return lines.
• Ensure jacketed high-pressure fuel pipe leak alarms and turbocharger lubricating oil low-pressure / high-temperature alarms are tested and logged before departure.

Frequently Asked Questions

Related Marvel Solutionz & SeaReady Resources

Regulatory & Technical Sources

• IMO SOLAS Chapter II-1 Part C (Machinery Installations) & Chapter II-2 Regulation 4 (Probability of Ignition; Hot Surfaces above 220 °C)
• IMO STCW Convention and STCW Code Tables A-III/1 & A-III/2 (Engineer Officer Competence)
• ISM Code Section 10 (Maintenance of the Ship and Equipment, Critical Systems & Planned Maintenance)
• IACS Unified Requirements for Machinery Installations (UR M Series)