Failure Analysis: Sootblower nozzle tip B-12 failed due to thermal fatigue, likely from repeated quenching when the high temperature sootblower nozzle tip was exposed to the relatively cold steam/condensate in the blowing media. Higher operating temperatures were likely due to the location of the sootblower and/or poor shielding/retractable mechanism. The amount of carbon detected was higher than the specified maximum. Higher carbon content likely played a role in the failure, causing the cracks to propagate at a faster rate. The cracks may have followed the inter-dendrites due to lack of ductility. Higher carbon in the steel likely diminished the fatigue strength due to lack of ductility. The observed hardness was higher than the expected range.       

     

Material Verification: The samples did not meet the chemical requirements for UNS N08330 (RA330) heat-and corrosion-resistant alloy (Ni-Fe-Cr alloy). Higher carbon was detected, perhaps due to diffusion of carbon into the steel during operation. However, away from the nozzle tip where it was not exposed to high radiant heat, the carbon content was also measured at 0.41%. This suggests that the nozzle may have contained higher carbon when it was new. Higher carbon content than the specified maximum is detrimental in oxidation and corrosion resistance. Over a period of time, the higher carbon in the steel may have combined with chromium and reduced its ductility, resulting in reduced fatigue strength.