Stepwise cracking in a longitudinally welded steel linepipe

Degradation by hydrogen of steel linepipes takes the form of stepwise cracking in the absence of stress in sour environments. These cracks have an intimate relation with the banded microstructure often observed in linepipes. In this article the relative susceptibilities of the near weld region and the parent material of a steel linepipe are compared. After a study of the hydrogen effusion kinetics and the microstructure, it was felt that weld induced residual stresses were possibly responsible for the higher susceptibility of near weld regions. The residual stress effect could be an implicit effect of altering the kinetics of hydrogen trapping which was found to be much enhanced near welds.