High Temperature Corrosion Mechanisms by Combustion Products of Heavy High Sulfur Fuel Oils: An Extension of the Wilson Model

Metallic dissolution caused by molten vanadates has been classically considered the main corrosion procesS involved in the degradation of alloys exposed to the combustion products of heavy fuel oils. However, residual oils used today have higher sulfur contents, and field and laboratory studies have shown that alloys exposed at elevated temperatures to their combustion products experience a more complex corrosion process. High temperature oil ash corrosion involves, besides the occurrence of vanadium corrosion, accelerated oxidation, sulfidation and carburization, depending on temperature, local atmosphere and ash composition. Wilson O) proposed a model for the transport, through the corrosion product scale, of species leading to metallic dissolution by molten vanadates. An extension to this model is proposed in order to include the transport of sulfur and oxygen through the scale and into the metal for including internal oxidation and sulfidation. This proposal has been validated by previously published results of a comprehensive corrosion testing of different alloys using real oil ashes and analytical results of corroded specimens carried out by the authors.