High-temperature corrosion vanadium attack

Vanadium in a fuel forms various metal compounds with low melting points, and causes molten-salt corrosion of steel called vanadium attack. Another example of high temperature corrosion is sulfidation. Carbon monoxide, carbon dioxide, and hydrocarbons form metal carbides at high temperatures and this is called carburization. Nitriding involves chemical reaction of nitrogen with metal. 

The elements of Group 5 are in many ways similar to their predecessors in Group 4. They react with most non-metals, giving products which are frequently interstitial and nonstoichiometric, but they require high temperatures to do so. Their general resistance to corrosion is largely due to the formation of surface films of oxides which are particularly effective in the case of tantalum. Unless heated, tantalum is appreciably attacked only by oleum, hydrofluoric acid or, more particularly, a hydrofluoric/nitric acid mixture. Fused alkalis will also attack it. In addition to these reagents, vanadium and niobium are attacked by other hot concentrated mineral acids but are resistant to fused alkali. 

Ash Maximum amount usually present is 0.2%. The content is important. High vanadium ashes have reduced melting temperature and can build up as deposits and attack refractory lining. Vanadium/Sodium These compounds in ash cause eutectic compounds with very low melting points (as low as 600°C). This results in a liquid, sticky ash that congeals onto the heat exchanger surfaces resulting in faster build up, corrosion, and problems. 

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