Thick-wall steel tube internal crack detection method based on surface magnetic conductivity differential measurement

Abstract

The invention relates to a thick-wall steel tube internal crack detection method based on surface magnetic conductivity differential measurement. The method includes the following steps that a detected steel tube is magnetized to be saturated through a magnetizer, and maximum local magnetic induction strength distortion is generated in the steel tube or around inner wall cracks; the center line of an eddy excitation coil and the center lines of two detection coils are respectively distributed on the outer surface of the steel tube in the normal direction, the eddy excitation coil generates eddies on the surface layer of the steel tube, the detection coils are distributed in a spatial staggered mode in the direction of a magnetic field and conduct differential output, and differential change of surface magnetic conductivity of the steel tube in the magnetizing direction is detected; the steel tube moves relative to the magnetizer and a detection probe, output signals change, and whether cracks exist in the steel tube or not and the size of the cracks are analyzed according to the output signals. The method achieves high-precision detection of lift-off thick-wall steel tube inner wall micro cracks, has the advantages of being simple in system structure and high in universality and interchangeability, can achieve non-contact quick automatic detection, and is high in signal-no-noise ratio and sensitivity.

Description

technical field [0001] The invention relates to an electromagnetic non-destructive detection technology, in particular to a method for detecting internal cracks in thick-walled steel pipes based on differential measurement of surface magnetic permeability. Background technique [0002] The quantitative detection of internal cracks in pipelines is very important, but the detection of internal cracks in thick-walled steel pipes has certain difficulties and limitations. Commonly used ultrasonic testing methods generally require a suitable coupling method, and steel pipes with a thickness-to-diameter ratio exceeding 0.2 cannot detect flaws in principle. As a common steel pipe inspection method, magnetic flux leakage inspection has a fast flaw detection speed. However, when using the magnetic flux leakage detection method to detect the inner wall cracks of thick-walled steel pipes, the leakage magnetic field generated by the inner wall cracks in the steel pipe is shielded from t...

AI Technical Summary

Problems solved by technology

With the increase of wall thickness and the improvement of inner wall flaw detection requirements, it becomes more and more difficult to detect the cracks on the inner wall by measuring the leakage magnetic field on the outer wall of the pipe, and even the tiny cracks on the inner wall cannot be detected.

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