Metal pipeline defect detection technology based on variable-frequency alternating-current potential fall method

Abstract

The invention discloses metal pipeline defect detection technology based on a variable-frequency alternating-current potential fall method and belongs to the technical field of nondestructive detection. Excitation current electrodes (1) are mounted at two ends of a to-be-detected area of a detected metal pipeline (3), measuring electrodes (2) are mounted in the to-be-detected area, and alternating-current excitation currents different in frequency are applied to the detected pipeline (3) through the excitation current electrodes (1); due to existence of skin effect, when the excitation currents are high in frequency, a skin current (4) only exists in a shallow layer close to the outer wall of the metal pipeline and will exist in the whole wall of the metal pipeline along with frequency lowering; existence of a defect (5) may influence distribution of the skin current (4), and influences amplitude of voltage among the measuring electrodes (2) in other words, and depth information of the detect can be acquired through differential deviation of the voltage. By the technology, measuring of original voltage, reference voltage and original wall thickness is not needed, and influence on measuring caused by system drift and errors in measuring the original wall thickness can be effectively overcome.

Description

technical field [0001] The present invention is mainly used for measuring the defect depth of metal pipelines, specifically, it relates to a method of applying AC excitation currents of different frequencies to the measured pipelines, and performing differential derivation on a series of voltage values ​​obtained from the measurement, and using the extreme points of the derivatives to obtain Method to solve for flaw depth. Both the traditional field fingerprint method based on the DC potential drop method and the single frequency AC potential drop method need to accurately measure the original wall thickness information of the tested pipeline, and then calculate the wall thickness loss according to the voltage value, that is, the two In essence, the technology cannot directly measure the absolute thickness of the pipe under test, and can only calculate the relative wall thickness based on the original wall thickness value, so the measurement error of the original wall thicknes...

AI Technical Summary

Problems solved by technology

[0014] The present invention mainly aims at the current situation that the current traditional field fingerprint method based on the DC potential drop method and the traditional single frequency AC potential drop method are easily disturbed by system drift, and proposes a metal pipeline defect detection method based on the variable frequency AC potential drop method Detection technology, specifically, applies a series of AC excitation currents of different frequencies to the pipeline under test, uses the skin effect to control the distribution of the current in the pipeline under test, and measures the voltage sequence corresponding to the excitation current of different frequencies. The sequence is differentially derived, and the depth of the corrosion defect is finally solved by using the extreme value of the derivative curve;

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