The extension of hydrogen blister-crack array in linepipe steels

Abstract

Hydrogen induced fracture in linepipe steels is characterized by the formation of internal blisters caused by hydrogen precipitation at an inclusion-matrix interface, followed by the formation of blister-crack array by cracking the region connecting the blisters through the action of internal hydrogen pressure and external stress. The manner of extension of the hydrogen induced fracture of this type is considerably influenced by the presence of external stress: in the absence of the external stress fracture develops by linking the blisters which are formed in stacked arrays out of a plane approximately perpendicular to the external stress axis. Shear stress distribution induced around the blister is sensi-tively influenced by the external stress applied parallel to the blister plane; therefore, it is expected that the manner of extension of the blister-crack array should be influenced by the external stress. In the present paper the above mentioned influence of the external stress on the manner of extension of the hydrogen induced fracture is explained based on stress analysis around a hydrogen gas pressurized crack-like cavity under stress.