Failure analysis of brace bolt

Fractographic and metallographic studies showed that the brace bolt has failed by hydrogen embrittlement. Evidences suggest that the bolt had two pre-existing cracks at the fillet of the change of cross section. The cracked bolt was held together by a thin ridge of metal separating the two cracks at two different planes. During the functional check, this thin ridge of material got fractured leading to the separation of the bolt. From the analysis, it appears most probable that the brace bolt had picked up hydrogen at the time of surface reconditioning processes during the last overhaul. No metallurgical abnormalities in the material were found responsible for the failure. The hardness in the threaded region of the bolt was found to be higher than that of the specification and it is believed that this has further aggravated the situation. A detailed analysis of the failure is presented in this report