In compliance with Tier II NOx regulations and Energy Efficiency Design Index (EEDI) guidelines, engine cylinders must operate under increased pressures and reduced operating temperatures. These regulations have led to an increase in cold corrosion.
The increased pressure and reduced temperatures within the engine cylinder create conditions below the dew point, allowing water to condense on the cylinder liner walls. That condensate combines with sulphur, forming sulphuric acid – corroding the liner surface and creating excessive wear of the liner material.
Cold corrosion is the most serious in modern engine designs and earlier engine designs that have been modified for part-load or low-load operation (known as “slow steaming,” where vessels may operate as low as 10 percent load). These modifications may include:
- Turbocharger cut-out
- Variable turbo charger nozzle rings fitted
- Exhaust gas bypass valve fitted
- Engine tuning changes
Avoiding cold corrosion is difficult, but here are some steps you can take to help mitigate the effects:
First, identify how serious the problem is. MAN recommends using a Sweep Test and Winterthur Gas and Diesel (formerly Wärtsilä) has a similar Quick Test. You can contact ExxonMobil for help from our field engineers who can advise you on how to conduct these tests.
Second, implement a condition monitoring programme to monitor the performance of the engine and cylinder oil. This programme should monitor the parameters of iron wear and the residual Total Base Number (TBN) in scrape down oil, and will help you to:
- Select the correct cylinder oil. ExxonMobil offer two cylinder oils to help address cold corrosion: Mobilgard™ 570 and Mobilgard™ 5100
- Optimise the feed rate to suit the engine, operating conditions and cylinder oil in use
Find out more about our Cylinder Condition Monitoring programme or contact an ExxonMobil representative for more information.