Hot corrosion is a form of accelerated oxidation that is produced by the chemical reaction between a component and molten salts deposited on its surface. Hot corrosion comprises a complex series of chemical reactions, making corrosion rates very difficult to predict. Sodium sulfate (Na2SO4) is usually the primary component of the deposit; and degradation becomes more severe with increasing concentration levels of contaminants such as sodium, potassium, vanadium, sulfur, chlorine, fluorine, and lead. The rate and mechanism of hot corrosion attack are influenced by temperature.
Hot Corrosion Damage Mechanism
•Caused by Formation of Molten Salts in Turbine Hot Section
•Sodium Sulfate (Na2SO4) Most Common Molten Salt
•Breaks Down Protective Oxide on Blade Alloys
•End Result Accelerated Oxidation Damage
There are two types of hot corrosion:
• Type I, or high temperature, hot corrosion occurs at a temperature range of 730 to 950°C (1,350 to 1,750 °F).
• Type II, or low temperature, hot corrosion occurs at a temperature range of 540 to 700°C (1,000 to 1,300 °F).
Damages experienced after blade separation.
The Primary Source is Fuel and air, secondary is water for compressor washing.
Typically salt is carried in the air, offshore issues
Recommendations to minimize Hot Corrosion.
Evaluate gas fuel heater performance in order to High-risk sulfur presence.
Evaluate the air inlet filtration.
Evaluate the first and second stages of material (alloys/ superalloy).
Perform a borescope inspection routinely to identify any blade or nozzle distress.
Include deionized water to perform engine water wash.
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