Study on the enhancement effect of weak magnetic excitation on stress-induced magnetic signals in ferromagnetic pipeline weld joint

Abstract Weak magnetic testing (WMT) is suitable for evaluating the girth weld stress due to its advantages in non-contact detection. However, the stress-induced magnetic signal collected by WMT is prone to interference from external noise signals. Therefore, weak magnetic excitation is proposed to enhance the strength of stress-induced magnetic signals. In this paper, the enhancement mechanism of the weak magnetic excitation on the stress-induced magnetic signal is revealed from the perspective of magnetic domain energy. Then, a tensile experiment is carried out to analyze the stress-induced magnetic signal variation law of cover welding, filler welding, and root welding layers under different excitation magnetic fields. Finally, the stress-magnetic coupling model of weak magnetic excitation at the pipe three-dimensional stress state is established, which is validated by a full-scale pressurized pipe test. The results illustrate that the excitation magnetic field will modify the strength and variation features of stress-induced magnetic signals of weld joints. The strengthening effect of the excitation magnetic field is to first increase and then decrease. There is an optimal magnetic field that can make the stress-induced magnetic signal of different welding layers change synchronously. In addition, the optimal magnetic field value at a three-dimensional stress state is greater than that under single axial stress.