Vanadium enhanced corrosion

Alumina, iron, nickel, silica, sodium, and vanadium are examples of compounds which can be found in residual fuel ash. If the vanadium content of residual fuel is high, severe corrosion of turbine blades can occur and exhaust system deposit formation can be enhanced. Vanadium-enhanced corrosion can occur at temperatures above 1200°F (648.9°C). 

Vanadium/sodium enhanced corrosion of metal occurs when molten slag containing vanadium compounds forms on metal system parts. The steps in the corrosion sequence are listed below ... 

The most important undesired metallic impurities are nickel and vanadium, present in porphyrinic structures that originate from plants and are predominantly found in the heavy residues. In addition, iron may be present due to corrosion in storage tanks. These metals deposit on catalysts and give rise to enhanced carbon deposition (nickel in particular). Vanadium has a deleterious effect on the lattice structure of zeolites used in fluid catalytic cracking. A host of other elements may also be present. Hydrodemetallization is strictly speaking not a catalytic process, because the metallic elements remain in the form of sulfides on the catalyst. Decomposition of the porphyrinic structures is a relatively rapid reaction and as a result it occurs mainly in the front end of the catalyst bed, and at the outside of the catalyst particles. 

Some heavy fuel oils cause severe corrosion that is attributed to the presence of vanadium compounds. In most examples of high corrosion rates these have been considered to be due to the ash composition or to a less favourable ratio of vanadium to sodium in the ash. Corrosion is very much a function of temperature (see Chapter 10). Naturally occurring contaminants other than sodium and vanadium present in the ash of heavy fiiel oil tend to act as corrosion inhibitors by shifting the reaction toward the formation of the relatively non-corrosive metavanadate [Niles and Sanders 1962]. The relatively low melting points of the vanadium compounds enhance the corrosion effects. 

Alloy steel pipe composition has various elements, with total concentration between 1.0% and 50% by weight, which enhances the mechanical properties and corrosion resistance. These steels can be grouped under low-alloy steels. Along with economic growth, the demand of alloy steel pipes and tubes for industrial use has increased enormously. The most common alloying elements are nickel, chromium, silicon, vanadium, and molybdeniun. Special pipe steels also contain very small amounts of aluminum, cobalt, tungsten, titanium, and zirconium. Alloy steel has different properties on the basis of its composition. Alloy steel tubes cater to domestic and industrial requirements, such as gas drilling, offshore projects, refineries, and petrochemical plants. 

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