Mechanical Anisotropy in Steels for Pipelines

There has been a huge expansion in the laying of pipelines for the transmission of fossil fuels over large distances and in dire environments. Large diameter pipes can be manufactured by welding spirals of hot-rolled linepipe steels. This process has a cost advantage relative to one in which the steel is seam welded after bending into a tubular shape. However, one particular problem associated with the steels used to fabricate the pipes is that of the anisotropy of mechanical properties, especially the toughness. Even though properties such as the Charpy toughness and strength meet minimum specifications, the existence of orientation dependence can compromise, for example, the stability of the pipe to buckling. There is, therefore, a large international activity on understanding the anisotropy of pipeline steels. This review represents an attempt to critically assess the steels and the orientation dependence of their mechanical properties, with the aim of establishing a basis for further progress.