CTOA levels of welded joint in API X70 pipe steel

The CTOA toughness and fracture morphology of growing crack in spirally welded steel pipe of grade API X70 were investigated. An optical test procedure based on modified double cantilever beam was used which produced a measure of the steady-state ductile fracture toughness for test material. From this, CTOA value of 8.2° and 7.5° were obtained for base and weld metal, respectively. The specimens fracture surfaces were examined next, which demonstrated dimple-typed shear mode fracture. Discussion on the difficulties in establishing measures of fracture resistance in pipeline steels and potential advantages and limitations of the applied test technique conclude the paper.

► The paper presents CTOA data on spiral seam weld for the first time (not reported previously in the literature).
► Besides, it demonstrates detailed features of the fracture surface from modified DCB specimen.
► It also shows the validity of an experimental technique (optical imaging used with reference grid) for CTOA measurement in ductile materials.