Toughness degradation during fabrication of API X42 and X60 grade pipeline

Two fabrication steps in the manufacture of pipelines, namely cold bending and welding are identified for the significant deterioration of the steel p lates used. In X60 grade around 57% and 40% loss in CTOD toughness are acco unted for welding and bending respectively. However, a combined effect of t he two results in 80% loss. In X42 grade, the toughness is measured by impa ct energy which is reduced significantly from 78.5 J (unweld) to 35 J due t o welding. Microstructural and microfractographic results are used to justi fy the various toughness values in the parent mental, weld zone and heat af fected zone in X42 grade. The orientation of pearlite banding as observed o n fracture plane with respect to notch front and applied loading direction appears to have strong influence on the shape, size and morphology of the d imples and the corresponding toughness values.