US 8,552,718 B2Granted

Method for the nondestructive testing of pipes

AssigneeV & M Deutschland GmbH

InventorsAndreas Groos, Stefan Nitsche

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Abstract

In a method for the nondestructive testing of pipes made of ferromagnetic steel for flaws by means of stray flux, the pipe is magnetized by a constant field and the discontinuities in the near-surface region of the outer or inner surface of the pipe cause magnetic stray fluxes, which exit the pipe surface and are detected by probes of a test unit, 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 external or internal flaw via defined flaw thresholds respectively. For this, prior to associating the detected amplitude signals to 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 via a previously determined correction factor for amplitudes and/or frequencies of a perpendicular angular position.

Claims4

Dependent claims

A method for the nondestructive testing of pipes of ferromagnetic steel for flaws by means of stray flux, comprising the steps of:

magnetizing the pipe with a constant magnetic field having a direction,
detecting with probes of a test unit for longitudinal and/or transversal flaw testing, amplitudes or frequencies or both of magnetic stray fluxes caused by a test flaw oriented perpendicular relative to the magnetic field direction;
determining a correction factor as a function of the amplitudes or frequencies or both of the magnetic stray fluxes caused by the test flaw;
determining an angular orientation of another flaw relative to the magnetic field direction;
determining amplitudes or frequencies, or both, of magnetic stray fluxes caused by the other flaw,
correcting the amplitudes or frequencies, or both, of the magnetic stray fluxes caused by the other flaw with the determined correction factor, and
associating the corrected amplitudes or frequencies, or both of the magnetic stray fluxes with an external or internal flaw based on an amplitude height or a frequency spectrum, or both, via defined flaw thresholds.

4 more elements

Dependencies are inferred from the claim text.