Microstructure and Mechanical Properties of Butt Welding Joint of GT90 Coiled Tubing

Welding procedure test is conducted on the GT90 coiled tubing to analyze the structure and mechnical properties of its weld joint.It is concluded that the weld joint is of granular bainite structure;and due to the effect of welding thermal cycle,the butt welding weld joint HAZ shows softening that will result in decreased hardness and strength.During the process of fatigue bending deformation,strain will concentrate at the soften area and lead to fracture,which will make the fatigue life of the joint lower than that of the parent metal.So,in order to reduce softening phenomenon,improve mechanical properties and increase fatigue life of a weld joint,it is recommended to use smaller linear energy input to weld a coiled tubing.