Detection of gas pipe wall thickness based on electromagnetic flux leakage

Abstract

Based on electromagnetic flux leakage (EMFL), a nondestructive testing (NDT) technique for the detection of gas pipe wall thickness is presented, and its principle and feasibility is evaluated by means of equivalent magnetic circuit analysis and finite element analysis. An online NDT device adopting this technique is developed, and its structure and working principle are introduced in detail. This device is composed of a detector array with 32 pipe wall thickness sensors that employ a Hall element as the element for sensing the magnetic flux density, and it can be adapted to pipe diameters from O400mm to O650 mm. On the basis of the experimental investigation for this device, the influences of some factors on thickness measurement, namely the excitation current, excitation coil turns, gap distance, concentrator of the magnetic field, magnetization time, and number of sensors in the detector array, are revealed and the optimal excitation voltage for the sensors of the detector array is selected. The measuring calibration is given to establish the relationship between the pipe wall thickness and the output voltage of the sensors. The results show that the proposed EMFL for measuring the wall thickness of ferromagnetic pipe is feasible, the technical parameters of the sensor are important for improvement of measurement precision and resolution, and the developed device has precision, resolution, and a linear output curve. Carried by the developed gas pipeline inspection robot through a universal joint, this NDT device can move inside the gas pipeline and monitor the state of the pipe wall.