Quantitative study on internal detection signal of weak magnetic stress in oil and gas pipelines based on force-magnetic noncoaxial effect

Abstract

The weak magnetic stress internal detection technology is globally an important technical challenge in pipeline inspection. However, the stress concentration area in the in-service pipeline is very complex, and the influence of the stress direction on the magnetic signal is worthy of further assessment. To improve the accuracy of the magnetic signal analysis of ferromagnetic materials under stress, the angle compensation of classical model is carried out, and a finite element model of non-coaxial force and magnetic was proposed. Compared with the existing model, the improved model improves the detection accuracy within the weak magnetic stress, can more effectively assess the stress state of the pipeline, and timely repair of the pipeline according to the stress state can effectively reduce the possibility of serious accidents in the pipeline. According to the results, in the angle compensated model, the accuracy of the magnetic signal was elevated by 61%, respectively, leading to accurately predict the variation trend of magnetic signal. Gradient total characteristic parameter Stotal increased linearly with the elevation of internal pressure. With the increase of stress angle with the magnetic field, the axial amplitude parameter Rx varied 33% more than the radial amplitude parameter Ry, and the axial angle factor fx decreases at a 50% higher rate than the radial angle factor fy. It indicated that the axial component of the magnetic signal was more sensitive to the change of stress direction.