Protection against high temperature corrosion with laser welded claddings - Applied and tested on exhaust valve discs of large diesel engines burning heavy fuel oil

In close co-operation between Wartsila Switzerland and BIAS, exhaust valves of two-stroke diesel engines were clad by laser welding with functional coatings to improve the corrosion behaviour and extend the life cycle of these exhaust valves. The coatings consisted of different nickel-based alloys. The investigations were carried out in a period of three years. The cladding tests and experimental investigations were carried out at BIAS, whereas Wartsila Switzerland organised the suitable valves and a seagoing ship for the testing. The inspections of the coatings on board and the evaluations of the results after valve dismounting were carried out jointly. In the preliminary stages of the study, the process window of various corrosion-resistant materials were determined and the most promising ones were applied on Nimonic 80A valve discs. The laser-clad valves were installed for test runs in a modern container ship. Depending on the process parameters and the corrosion resistant materials used the laser generated coatings were inspected after every 1000 h of service and evaluated comparatively. The results of this study are presented.