Failure of a Boiler Feed Pump Second-Stage Impeller

Failure analysis was performed on a fractured impeller from a boiler feed pump of a fossil fuel power plant. The impeller was a 12% Cr martensitic stainless steel casting. The failure occurred near the outside diameter of the shroud in the vicinity of a section change at the shroud/vane junction. Sections cut from the impeller were examined visually and by SEM fractography. Microstructural, chemical, and surface analyses and surface hardness tests were conducted on the impeller segments. The results indicated that the impeller failed in fatigue with casting defects increasing stress and initiating fracture. In addition, the composition and hardness of the impeller did not meet specifications. Revision of the casting process and institution of quality assurance methods were recommended.