Definition - What does Gaseous Corrosion mean?
Gaseous corrosion is a type of high-temperature corrosion that occurs in diesel engines, furnaces, gas turbines and other machinery that interacts with hot gas surrounded by contaminants.
Almost all alloys, materials and metals of technological importance will undergo oxidation and corrosion at high temperatures, resulting in gaseous corrosion. The rate, mechanism and corrosion nature differ broadly according to the existing temperatures and environments.
Corrosionpedia explains Gaseous Corrosion
By far, oxidation is the most typical type of gaseous corrosion. Almost all beneficial alloys and metals will go through oxidation at certain temperatures. This leads to:
- Loss of matter
- Physical property changes
Gaseous corrosion is not restricted only to oxygen. With gases bearing sulfur, halogens, carbon oxides and other substances, the attack may occur in a distinct matter. Fuels, at times, contain compounds called sulfates or vanadium that can create compounds throughout combustion, producing a low melting point. Such salts melted by liquid are extremely corrosive to stainless steel as well as other alloys that are typically static against high temperatures and corrosion. Thus, gaseous corrosion may involve oxidation in high temperatures, carbonization and sulfidation.
Vanadium that is found in petroleum in porphyrine complex structures can get too concentrated when exposed to high boiling fractions. This serves as the base of fuel oils with heavy residuals. Also, sodium residues and treatment chemicals are contributory to gaseous corrosion. In fact, over 100 ppm of vanadium and sodium is capable of producing gaseous corrosion, more specifically fuel ash deterioration. Almost all fuels being used in the industry today contain small amounts of vanadium. This can be oxidized to various vanadates, which can hasten oxygen diffusion into the salt layer into the metal. Vanadates can be ionic or semiconducting. Of these two, the latter can tremendously lead to more serious corrosion since the oxygen travels through oxygen vacancies. The ionic form, on the other hand, transports oxygen through vanadate diffusion, which can produce a slower rate of corrosion.
The damage caused by vanadates can be reduced by decreasing the levels of excess air used for combustion or by using alloys high in chromium as well as application of refractory coatings.