Characterization of Anisotropic Mechanical Properties of X70 Spiral Welded Steel Pipes

Anisotropic tensile and compressive properties of base metals and girth welds of two API X70 spiral welded pipes have been investigated in this study. Spiral welded pipes exhibit different characteristics of anisotropy from UOE pipes, as the anisotropic property is determined by the thermo-mechanical rolling process of plates and coils produced for pipes. Spiral pipe steels have the lowest strengths in the pipe's transverse direction, contrary to UOE pipes with high strengths in the transverse direction. Yield strengths measured from tensile and compressive tests and their anisotropic characteristics are comparable, although tensile yield strengths are somewhat greater. The results of compressive tests also indicate an anisotropy in the pipe's through-thickness orientation as well as in the longitudinal orientation; yield strengths are highest in the through-thickness direction for both base metals and girth welds of the two pipes.