Pipeline crack far-field vortex checking method

Abstract

The invention discloses a pipeline crack far field vortex test method, belonging to the nondestructive testing technique field. The online test technique of the pipeline crack far field vortex in axial direction based on a circumferential magnetization principle is concretely realized in two different configuration methods of exciting coils: using a coil in radial direction with low frequency AC current as an exciting coil to produce a circumferential magnetic field, or using two coils which are placed crossly and the plane normals of which are vertical to each other as the exciting coil. The two coils are respectively electrified with low frequency AC current of the same amplitude but a phase difference of 90 degrees to produce a rotating magnetic field in a circumferential cross section of the pipeline, and the rotating magnetic field produces the circumferential magnetic field. The measurement of the test coils in circumferential layout in the far field area is indirectly coupled with magnetic field signals and the amplitude of signals and the change of signals relative to the phase difference of the exciting current show the existence of the defects of the cracks. The far field vortex technique based on the circumferential magnetization principle has the advantages of more intense function of the circumferential magnetic field and cracks of the pipeline wall in axial direction, which leading the test of cracks in axial direction to be easily realized.

Description

technical field [0001] The invention relates to a far-field eddy current nondestructive detection method for axial cracks in ferromagnetic material pipelines, and belongs to the technical field of nondestructive detection. Background technique [0002] On-line detection of pipeline axial cracks has always been a difficult point in the field of non-destructive testing. For volumetric corrosion defects with dimensions in three directions: axial length, circumferential width and radial depth, the magnetic flux leakage detection method using permanent magnets to generate axial magnetic field leakage is a simple and effective method; cracks are generally only in two The extension in the third direction is very small, and it is generally difficult to excite enough leakage flux to be detected by the detection element. For example, the most harmful and most common on natural gas pipelines is the stress corrosion crack (SCC) extending axially along the pipeline. This crack has a lar...

AI Technical Summary

Problems solved by technology

These improvement measures make up for some shortcomings of the original far-field eddy current technology and reduce the application difficulty of far-field eddy current. However, this patent does not make further analysis and discussion on the special requirement of ferromagnetic material pipeline axial crack detection.

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