Investigation of mechanical properties and microstructure of X60 line-pipe steel

A segment of seam pipeline with an outer diameter (OD) 813 mm and wall thickness (WT) 10,6 mm, operating since 1974, was used for investigation of its mechanical properties and microstructure. The results of the tensile test show that nominal values of minimum yield point, ultimate tensile strength and ductility were reached in all specimens. Charpy V-notch test was carried out on base metal, heat affected zone and seam weld at temperatures 40, 20, 0, -20, -40 and -60 degrees C. In case of base metal, L-T orientation showed higher upper shelf energy (USE) and ductile-brittle transition temperature (DBTT) than T-L orientation than is typical for hot-rolled material. The lowest impact energy was measured in the heat affected zone and seam weld due to the presence of heterogeneous microstructure consisting of grain boundary ferrite, polygonal ferrite and Widmanstatten ferrite. (C) 2019 The Authors. Published by Elsevier B.V.