An investigation on the corrosion of flue gas sensor in boiler stack

• Failure of sulfur containing flue gas sensor in a boiler stack.
• Acid dew point corrosion.
• Galvanic coupling between titanium and stainless steel.
• Hydrogen attack of titanium.

A commercial gas velocity sensor used for flue gases monitoring was subject to severe corrosion failure. An investigation was conducted based on visual inspection, microstructural study and SEM observation coupled to EDX analysis. A combination of mechanisms was proposed including a dominating severe dew point corrosion for both transducer and its covering, galvanic attack and an eventual hydrogen attack for the transducer side part. Recommendations were proposed to avoid a future severe damage to such type of sensor including an insulation between transducer and covering metals and an up-grade of the titanium alloy used.