Failure Analysis Case History No. 003

A hollow, fluted AISI 1040 carbon steel rotor in a downhole motor fractured while drilling a directional well. The chromium plated rotor was exposed to a corrosive, water-based drilling mud.

Laboratory failure analysis findings showed that the rotor I.D. contained many cracks at a 45^o angle to the long axis of the rotor. Metallurgical examination of a typical cracked area showed that they were torsional fatigue cracks.Craze cracks in the chromium plating did not contribute to the cracking.