Failure Analysis Case History No. 016

Industry: Oil & Gas
Specimen Description: Offshore Platform Drilling Riser Bolt Insert
Material: AISI 4340 Quenched and Tempered Low Alloy Steel
Environment: Seawater
Background:
AISI 4340 drilling riser bolt inserts were cracking after exposure to seawater and cathodic protection currents.
Time in Service: Unknown
Findings:
Visual examination of the as-received insert showed circumferantial cracking at the body to flange radius. The fracture face was brittle appearing with a single cracking initiation site. SEM imaging of the fracture revealed a deposit high in calcium obscuring the fracture features. After removing the deposit with inhibited hydrochloric acid, the true, intergranular fracture could be observed. The integranular fracture and knowledge of the service environment suggested failure from hydrogen embrittlemnt.

 

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