Failure Analysis Case History No. 008

Industry: Oil & Gas
Specimen Description: Downhole Motor Transmission Coupling
Material: AISI 9310
Environment: Drilling Mud
A downhole motor failed while drilling at 3300 meters. Inspection revealed that two female AISI 9310 case hardened couplings in the ball drive shaft had fractured. Corrosion was evident on the coupling and the fracture.
Time in Service: Hours
Laboratory analysis showed that the couplings had experienced several types of damage, including pitting corrosion, fatigue and hydrogen embrittlement cracking. The maximum case hardness measured 675 HK, while the core hardness was 29 HRC.


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