Evaluation of an unusual superheated steam pipe failure

An examination has been made of a steam generator outlet pipe that failed locally after some 100,000 h of operation. Failure took place by cracking along preferentially formed lines (or planes) of graphite nodules. Grain boundary decohesion and void formation ahead of the crack tips were very local in nature, voids being formed very close to the propagating cracks only. The graphitization is concluded to have occurred locally because of inhomogeneity in carbon content.