Eddy current testing recognition and evaluation method for defects of inner wall and outer wall of steel pipe under direct current magnetization

Abstract

The invention discloses an eddy current testing recognition and evaluation method for defects of the inner wall and outer wall of a steel pipe under direct current magnetization. The method comprises the steps of: carrying out non-saturated magnetization on the steel pipe by adopting a traversing direct-current magnetizing coil, picking up electromagnetic disturbance information at the defects by utilizing an eddy current detection coil, and selecting a reasonable direct-current magnetizing range according to phase contrast, thus detecting the defects of the inner wall and the outer wall and recognizing through phase difference, and realizing consistency judgment on the inner and outer wall defects of equivalent damage through respectively setting alarming thresholds of the inner and outer wall defects. A detection device comprises a phase sensitive detection module which aims at eliminating the disturbance of the defects to leakage field. The method is fast in detection speed, easily realizes automation, and can be applicable to defect detection of various ferromagnetism pipelines, thus having wide application prospects.

Description

technical field [0001] The invention relates to an eddy current detection identification and evaluation method for inner and outer wall defects of a steel pipe under direct current magnetization. Background technique [0002] Eddy current testing is suitable for non-destructive testing of conductor materials and is widely used in testing practice. Initially, it was mainly aimed at the defect detection of non-ferromagnetic materials such as aluminum and copper. There is a linear change between the defect depth and phase, but the method is extended When it is applied to flaw detection of steel pipe, the signal noise of eddy current detection is caused by the fluctuation of magnetic permeability on the surface of steel pipe, so that the defect information is submerged and it cannot be detected. Generally, the fluctuation of material permeability is suppressed by applying a saturated magnetization field to improve the signal-to-noise ratio of defects. This method is covered b...

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Problems solved by technology

This method is covered by the Chinese National Standard "Eddy Current Inspection Method for Steel Tubes" (GB / T 7735-2004) and the Machinery Industry Standard "Nondestructive Testing of Pressure Equipment Part Six: Eddy Current Testing" (GB / T 4730.6-2005), but The signal phases of defects at different depths on the outer wall of the steel pipe are basically consistent, resulting in phase failure, so only the amplitude index can be used to represent the defect equivalent

However, it is now found that when the magnetic saturation method is used, the inner wall defects of the steel pipe are also detected by the eddy current probe, and its phase is still consistent with the outer wall defects, resulting in signal aliasing, which makes the evaluation of inner and outer wall defects of steel pipes a technical problem

[0003] The Chinese patent literature discloses a "method for identification of inner and outer wall defects based on AC-DC composite magnetization", which involves a magnetic flux leakage inspection technology for distinguishing inner and outer wall defects of steel pipes, mainly applying DC and AC excitation The magnetic field magnetization steel pipe uses the outer wall defect to only respond to the DC signal component, and the inner wall defect responds to both the AC and DC signal components, so as to realize the identification of defects, but this method is inconvenient to quickly detect flaws by placing the sensor inside the pipe wall. In addition, the sensor needs electromagnetic shielding, and if the shielding effect is not good, it may cause misjudgment

The patent document "A Device for Inner and Outer Wall Defect Detection Based on Far-field Eddy Current" discloses another detection technology for inner and outer wall defects of steel pipes, which involves a far-field eddy current detection method that uses multiple magnetoresistive devices to completely cover the circumference of the pipe. direction, to realize the detection of defects within the entire circumference of the inner and outer walls of the pipe, but the detection speed of this technology is slow, and it cannot distinguish and identify the defects on the inner and outer walls of the steel pipe

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