Failure Analysis Case History No. 003

Industry: Oil & Gas
Specimen Description: Downhole motor rotor
Material: AISI 1040
Environment: Corrosive drilling mud
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.
Time in Service: Unknown
Laboratory failure analysis findings showed that the rotor I.D. contained many cracks at a 45o 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.

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