Failure Analysis Case History No. 004

Industry: Chemical Process
Specimen Description: Agitator Motor Bolts
Material: J429 Gr. 8
Environment: Atmospheric
J429 hex-head bolts attaching an output shaft to the top motor thrust plate of a chemical agitator failed, causing damage to the bottom steady bearing.
Time in Service: Unknown
Laboratory failure analysis of the bolts showed that the bolt fracture surfaces exhibited features attributed to rotating fatigue. No significant corrosion was observed. It was suspected that the bolts became loose, allowing the thrust plate to rock back and forth while turning. Gross non-metallic inclusions were observed in one of the failed bolts. The hardness of all failed bolts met J429 Gr. 8 specification requirements.


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