Fuel Ash and Salt Deposits

In many industrial applications, the surfaces undergoing high-temperature corrosion are far from clean and mostly covered with surface deposits of ash and/or salt form on the components. 

Chlorides Melting Point Temperature at lO atm Boiling Point 

Chemical reactions between these deposits and the protective surface oxide can lead to destruction of the oxide and rapid corrosive attack. In gas turbines, oxidized sulfur contaminants in fuel and chlorides from ingested air (marine atmospheres) tend to react to form salt deposits. The presence of sodium sulfate, potassium sulfate, and calcium sulfate together with magnesium chloride have been reported in such deposits for compressor-stage components [14]. Sodium sulfate is usually regarded as the dominant component of the salt deposits. 

Testing has indicated that in commercial nickel- and cobalt-based alloys, chromium additions play an important role in limiting this type of damage. Alloys with less than 15 percent of chromium as alloying addition are considered highly vulnerable to attack. 

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