Ferromagnetic Pipe Leakage Flux Testing with Angular Correction
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Solution Overview
Problem
Current non-destructive testing methods for ferromagnetic steel pipes using leakage flux struggle to reliably detect and differentiate between surface defects that are oblique to the magnetic field direction, leading to incorrect classification and increased rework or scrap rates.
Innovation Solution
Determining the angular position of defects relative to the magnetic field and applying correction factors to the amplitude and frequency signals allows for accurate assignment of defects to either the external or internal surface, improving detection sensitivity and reducing misclassification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If leakage flux testing is used to detect surface defects on pipes, then defect detection capability is improved, but the ability to accurately differentiate between external and internal defects is worsened when defects are oblique to the magnetic field direction
Solution Approach 1:
The patent introduces a new dimension of measurement by adding a second probe arranged at a different angular position relative to the magnetic field direction. This creates a multi-dimensional signal space that enables differentiation between external and internal defects through comparative analysis of signals from multiple probing angles, resolving the ambiguity in defect location classification.
Solution Approach 2:
The patent changes the parameter of probe angular position relative to the magnetic field direction. By arranging probes at different angular positions (e.g., one probe perpendicular to the magnetic field and another at an oblique angle), the system captures defect signals with different characteristics depending on whether the defect is external or internal, enabling accurate classification through parameter comparison.
2Reliability
If sensitivity to internal defects is increased by adjusting probe sensitivity, then internal defect detection is improved, but external defect detection accuracy deteriorates due to false positives
Solution Approach 1:
The patent implements a feedback mechanism where signals from multiple probes are compared and analyzed to determine defect location. The evaluation unit uses the relative signal characteristics from probes at different angular positions to feedback-adjust the classification decision, enabling high sensitivity to internal defects while maintaining accurate differentiation from external defects through comparative signal analysis.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enhances the reliability of defect detection and classification, reducing unnecessary rework and scrap by correctly identifying oblique defects with the same sensitivity as those perpendicular to the magnetic field, thereby optimizing pipe quality control.
Implementation Method 1
The well-known leakage flux test is used on pipes made of ferromagnetic steel in order to detect longitudinal or transversely oriented surface discontinuities
Implementation Method 2
In the measurement method known from the prior art for detecting near-surface defects on the inside or outside of pipes, direct field magnetization is used
Implementation Method 3
the induction flux density increases in the area of a fault, whereby the magnetic field lines are disturbed in their otherwise straight propagation by external or internal faults, so that a so-called leakage flux arises
Implementation Method 4
The magnetic leakage flux density is measured, for example. B. with induction coils, Hall probes or GMR sensors that are arranged in a test head
Data Source
Figure 1~2
AI summary
The invention relates to a method for the nondestructive testing of pipes made of ferromagnetic steel for flaws by means of leakage flux, wherein the pipe is magnetized by a constant field and the flaws present in the near-surface region of the outer or inner surface of the pipe cause magnetic leakage flux, which exits the pipe surface and is detected by probes of a test unit each for longitudinal and/or transversal flaw testing, wherein the association of the detected amplitude signals is performed on the basis of the amplitude height and/or the frequency spectrum with respect to an outer or inner flaw by external or internal flaw thresholds. To this end, prior to associating the detected amplitude signals with an external or internal flaw, the angular position of the flaw relative to the respective magnetic field direction is determined, and a correction of the signals is carried out by way of a previously determined corrective factor for amplitudes and/or frequencies.