Corrosion studies with a new laboratory-scale system simulating large-scale diesel engines operating with residual fuels - Part I: Corrosion of Nimonic 80 A samples

A new laboratory-scale deposition–corrosion apparatus (DCA) has been designed to study the corrosion of Nimonic 80 A samples. The apparatus simulates conditions in a large-scale diesel engine operated with high sulphur- and ash-content heavy fuel oils. The fuel composition and ash particle formation were simulated with synthetic ash particles (SAP) generated by aerosol methods. The deteriorated areas, i.e. the zones under the deposits, ranged from 0 μm at 700 °C with no synthetic ash particle feed to 135 μm at 750 °C with synthetic ash particle and SO₂(g) feeds. A zone of “black islands” (thickness 30 μm), i.e. internal precipitates, rich in S, Cr and Ti indicating internal sulphidation of the base material was observed at the bottom of the regions under the deposits. A comparison between a Nimonic 80 A exhaust valve from a field endurance test and material studied with this laboratory system indicated similar internal sulphidation mechanisms. Corrosion propagation for Nimonic 80 A is also discussed.