Failure Analysis of an Incineration Process Thermowell

The thermowell inside the post-combustion chamber of an incineration plant failed as a result of severe high-temperature oxidation. An investigation showed that the failure was caused by deep intergranular oxidation and subsequent breakdown along the grain boundaries—in addition to gradual thinning of the component. The thermowell alloy was improper for this use because 1) there was insufficient Cr content for formation of a continuous adherent protective chromium oxide (Cr2O3) layer on the alloy surface under the operating condition and 2) the high operating temperature (950°C) approaches the upper temperature limit (1,000°C) for the alloy. The investigators recommended a silicon carbide (SiC) ceramic for replacement.