A Novel Measurement Method of Nonferromagnetic Metal Pipe Thickness Based on the Tilt Angle Intersection

The measured thickness of the pipe is the basis for judging pipe quality and ensuring safe operation. The existing pipe thickness measurement methods based on the tilt angle intersection require the known pipe conductivity. The intersection point refers to the intersection point of multiple coil relative impedance curves corresponding to different tilt angles, which varies with the scanning frequencies. This article proposes a novel method to accurately measure the nonferromagnetic metal pipe thickness to overcome this shortcoming. Based on the theoretical analysis, it is found that there is a linear relationship between the logarithm of tilt angle intersection frequency and the liftoff, and the pipe thickness is determined by the slope of this line. The outstanding advantages of this method are that it is independent of the conductivity of pipes; it can avoid the influence of coil deflection. Experimental results verified that the presented method had a low error of 6% by measuring the metal pipe with a thickness of 1.5 mm. In addition, the results showed that the method had good anti-interference ability to the tilt angle error. This method can provide a new direction for accurately measuring the thickness of nonferromagnetic pipes.