Hydrostatic pressure testing of several water pump housings for a municipal water system resulted in catastrophic brittle overload failures.

MME was engaged to perform comprehensive root cause failure analysis, including mechanical and materials engineering evaluations. Metallurgical examination on two of the failed components revealed casting imperfections associated with the failure origins.

In each case, the root cause of failure was related to the casting mold. The first incident involved an imperfection that resulted in a stress concentration that reduced the normally large critical flaw size to the microstructural level. A microstructural gradient adjacent to the fracture of the second casting was the result of an inadequate mold design that allowed for rapid cooling at a thin-walled region of the casting. Material selection was a concern of the manufacturer and was also investigated and determined to be appropriate for the intended application.