Failure Analysis Case History No. 001

Industry: Gas Treating
Specimen Description: Ball Valve Cover Capscrews
Material: ASTM A 574
Environment: Atmospheric
A 1-inch ball valve completely separated without warning, releasing a natural gas vapor cloud. Initial inspection of the failed valve showed that it separated due to failure of the two body capscrews. Both capscrews failed in a corroded thread root.
Time in Service: Unknown, but years.
Laboratory examination of the two failed capscrews showed that they had corroded with brittle appearing fracture surfaces. No secondary cracks below the fracture were observed. Hardness measurements showed the capscrews averaged HRC 44, representative of that specified in A574. SEM analysis showed that the fractures were intergranular and contained secondary cracking, typical of that caused by hydrogen embrittlement.

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