Experimental study of Fafracture Surface Characteristics of Inhomogeneous Drop Weight Tear Test Specimen Made from API X65 Steel

In this study, the fractograghy of the inhomogeneous specimen (including seam weld) of API X65 steel was performed, for the first time by the drop weight tear test. The fracture surface of the test specimen consisted of three zones of base metal, heat affected zone and weld metal. The test was performed according to API 5L standard. The crack initiated with a cleavage flat fracture from notch root and continued up to 14.7 mm from the fracture path. The cleavage fracture immediately changed to a ductile shear fracture with a 45 degree angle to the surface plane, which continued to the inverse fracture zone. SEM images of all three zone of the base metal, heat affected zone and weld metal showed signs of ductile fracture, including dimples of varying size, orientation and shape. Also, faint chevron marks with high density were observed in the root of crack in the base metal. Furthermore, in the hammer impact zone, an inverse cleavage fracture was observed, which was enclosed on both sides by shear surfaces with an angle of 45 degrees. The calculated ductile fracture surface was within the standard range and indicated the confirmed toughness of these steels for the use in gas transportation pipe lines.