Analysis of delaminations occurring during different rupture tests of X70 pipeline steels

The delamination phenomenon occurring during the different rupture tests of X70 pipeline steels was systematically investigated using the experimental and finite element method in the present study. It is shown that the anisotropic microstructures or weak interfaces, which were oriented to the rolling direction (RD), and the triaxial state of stress are the basic cause of the delaminations. The amount or size of delaminations decreases with decreasing the temperature and the rate of curve at notch root in a notched plate. When the notch planes are longitudinal-short transverse (L-S) orientation, the amount or size of delaminations increases with increasing the thickness of specimens. When the notch planes are longitudinal-transverse (L-T) orientation, the delaminations are independent on the thickness of specimens.