Failure Analysis Case History No. 009

Industry: Petrochemical
Specimen Description: Hex Head Capscrews
Material: Unknown low alloy steel
Environment: Atmospheric
Hex head capscrews that attached valves to vertical piping unexpectedly failed. No inspection or maintenance history was known.
Time in Service: 7 years
Laboratory analysis showed that the capscrews most probably failed due to pre existing quench cracks. Non-metallic inclusions, believed to be aluminum oxide dross particles from the steelmaking killing operation, are thought to have contributed to quench cracking. Static load and vibrational stresses are believed to have caused total separation of the capscrews over time. The hardness of the capscrews measured 44 HRC.


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