Dye-penetrant inspection of the impeller revealed many areas of random,
PT indications over much of the impeller blade and hub. Visual examination of
blade fractures revealed thumbnail areas where the fracture was a different color from that of the overload fracture. Fractures initiated from the
"loaded" side of the impeller blade.
SEM examination of a fracture revealed fatigue striations at the initiation edge of the blades. Microstructural examination of a blade at a fracture revealed that
dealuminification had occurred in service,. reducing the strength of the blade material in the dealuminified areas. The impeller blades had suffered fatigue at weak, dealuminified areas near the blade hub. The dealuminification was due to exposure to the filtered water environment.