On large two-stroke engines, the turbocharger is among the components with the highest failure impact. A turbocharger failure means at best a significant power reduction, at worst a total loss of main propulsion. On vessels with only one turbocharger per engine – typical for engines up to approximately 40,000 kW – there is no redundancy.
Operating conditions are extreme: turbine inlet temperatures of 400–650°C, speeds of 8,000–18,000 rpm depending on design, all under constant exposure to exhaust gas particulates, particularly when operating on heavy fuel oil (HFO) or VLSFO. The combination of thermal loading, high speed and aggressive exhaust gas constituents makes the turbocharger one of the most demanding components on board.
The two dominant manufacturers in the two-stroke segment – ABB and MAN Energy Solutions (formerly MAN Diesel & Turbo) – have different maintenance philosophies and interval recommendations. ABB favours modular overhaul concepts for its A100 and A200 series, while MAN places greater emphasis on condition-based extensions for the TCA series. Both approaches require disciplined trend monitoring as a foundation.
Early warning signs include elevated bearing or exhaust gas temperatures, changed speed ratios and unstable scavenge air pressures. The most important signal is the turbocharger speed ratio (TC RPM to engine RPM) at comparable load. A decline in this ratio over weeks indicates fouling of the turbine or compressor side.
Turbocharger bearing temperatures should be read and documented during every watch round. An increase of more than 5°C above the reference value at the same load requires closer investigation. Causes may include bearing wear, insufficient oil supply or contamination of the oil system.
Scavenge air pressure is another key parameter. At a constant load profile, scavenge air pressure should remain stable. A gradual decline – even by just 0.05–0.1 bar over several weeks – indicates reduced compressor performance, often attributable to compressor-side fouling. Anyone who systematically records these parameters and evaluates them weekly typically detects problems 4–8 weeks before a critical condition is reached.
Online and offline washing can be effective when applied in accordance with manufacturer guidelines. Online washing (turbine side) is performed during operation by injecting water into the exhaust gas stream upstream of the turbine. It removes loose deposits but cannot dissolve hard encrustations. Frequency depends on fuel quality and load profile – typically every 48–72 hours when operating on HFO.
Compressor-side washing is also performed online by injecting water or specialist cleaning agent into the air intake. Compliance with manufacturer specifications regarding water temperature, quantity and pressure is decisive. Too much water can damage the compressor; too little is ineffective.
Offline washing requires the engine to be stopped and provides more thorough cleaning. It should be combined with a visual inspection via the borescope access. For planning a turbocharger overhaul, the following orientation values apply: ABB recommends a major overhaul for the A100 series after 16,000–24,000 running hours (depending on operating conditions), MAN for the TCA series after 12,000–18,000 hours. These are guideline values – the actual decision should be condition-based.
During overhaul, rotor dynamics (balance protocol), bearing clearances, seal condition and blade geometry are the central inspection points. Manufacturer-specific service bulletins – such as ABB’s TI Notices or MAN’s SB documents – must be checked for currency before every overhaul. It regularly occurs that service engineers are unaware of changes issued since the last revision.
Turbocharger maintenance should be closely linked to spare parts strategy, port windows and load profiles. The superintendent must ensure that critical spare parts – particularly bearing sets, seal rings and potentially an exchange rotor – are available before an intervention is planned. Lead times for turbocharger spare parts are typically 8–16 weeks, for complete rotor cartridges up to 6 months.
A frequent mistake is postponing a detected fouling issue with the argument “we can make it to the next docking.” Reality shows: what begins as light fouling can, through thermal layering, become a hard encrustation within a few weeks that can only be removed by mechanical cleaning during overhaul. Costs then increase by a factor of 5–10.
Proactive superintendents maintain a turbocharger condition table per vessel, documenting TC RPM ratio, scavenge air pressure, bearing temperature and washing frequency weekly. This table forms the basis for the decision: continue operation, intensify washing, or plan intervention.
The main wear mechanisms in maritime turbochargers are fouling, erosion, corrosion and bearing wear. Turbine-side fouling is caused by unburnt fuel constituents and ash deposits, exacerbated when operating on vanadium-containing HFO. Compressor-side fouling results from oil mist in the engine room, sea salt and moisture deposits.
Erosion primarily affects turbine blades and is caused by hard particles in the exhaust gas stream – particularly when using fuel contaminated with catalyst fines. Detection is via borescope inspection and performance loss analysis. IMO MEPC.1/Circ.642 provides recommendations on fuel quality that directly influences turbocharger fouling.
For diagnostics, the following procedure has proven effective: weekly recording of key parameters (TC RPM, scavenge air pressure, bearing temperature, exhaust gas temperature before and after turbine), monthly borescope inspection of the compressor side, and quarterly borescope inspection of the turbine side. This programme requires approximately 30 minutes per week per vessel and delivers a reliable condition assessment.
Vibration measurements on the turbocharger complement the picture. The characteristic frequencies of the turbocharger – rotational frequency and blade passing frequency – are easily identifiable. An increase in rotational frequency amplitude indicates imbalance (fouling, erosion or mechanical damage), while an increase in blade passing frequency points to blade problems.
A bulk carrier with MAN 6S60MC-C and ABB A175-L turbocharger showed a 4% decline in TC RPM ratio over four weeks. The crew performed online washes, which brought short-term slight improvement but did not reverse the long-term trend. The decision was made to postpone an offline wash to the next available port – still three weeks away.
Two weeks later, an abrupt performance drop occurred. Borescope inspection revealed massive deposits on the turbine blades with incipient cracking on two blades. The consequence: emergency port call, turbocharger cartridge exchange, 5 days off-hire. Total cost: over EUR 180,000. A timely offline wash would have cost less than EUR 5,000.
The decision on intervention timing should be based on three criteria: first, the trend of key parameters – if TC RPM ratio or scavenge air pressure decline over two consecutive weeks, intensified washing and borescope inspection are due. Second, the effectiveness of online washing – if it no longer shows a measurable effect, an offline measure is necessary. Third, the availability of port windows and spare parts – a planned intervention requires 4–6 hours in port.
As a rule of thumb: better an offline wash too early than an overhaul too late. The costs differ by a factor of 20–30.
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