METHOD AND DEVICE FOR CHECKING A FERROMAGNETIC TESTED PRODUCT BASED ON SCATTERING FLUX WITH SIGNAL NORMALIZATION

Claims

1. A method for testing a ferromagnetic test item, in particular ferromagnetic pipes, based on leakage flux for recording defects, including: magnetization of the tested volume of the tested product by means of an external magnetic field to create a state of magnetization of the tested volume, characterized by magnetization; scanning the surface of the product being tested by means of a probe structure comprising at least one magnetic field-sensitive leakage flux probe for recording magnetic leakage fields caused by defects, wherein the leakage flux probe is held during scanning at a final inspection distance from the surface of the product being tested and generates electrical probe signals which represent a measure of the leakage field strength; characterized in that it includes: determining the magnetization state of the tested volume in the region of the leakage flux probe using at least one magnetic field probe to generate magnetization signals that represent a measure of the magnetization state of the tested article in the region of the leakage flux probe; normalization of probe signals by means of corresponding magnetization signals to find normalized probe signals; processing of normalized probe signals for the purpose of qualitative assessment of defects.

2. The method according to paragraph 1, characterized in that a magnetic field sensitive probe is used as a magnetic field probe, separate from the leakage flux probe and provided in addition to the leakage flux probe.

3. The method according to paragraph 1 or 2, characterized in that in order to determine the state of magnetization, the parallel component of the magnetic field is measured, directed essentially parallel to the surface of the product being tested and parallel to the main direction of magnetization, in the near region around the leakage flux probe.

4. A method according to any of the preceding claims, characterized in that the product being tested is a ferromagnetic tube, and in order to determine the state of magnetization, preferably, a component of the magnetic field directed substantially tangentially to the surface of the product being tested is measured.

5. A method according to any of the preceding paragraphs, characterized in that, in order to normalize the probe signal, a component of the constant field of the magnetization signal is found and used.

6. A method according to any of the preceding claims, characterized in that the probe signal of the leakage flux probe has a signal amplitude, and in that, in order to normalize the probe signal, the signal amplitude is multiplied by a compensating coefficient that at least partially compensates for the dependence of the sensitivity of the test on the magnetization, wherein the compensating coefficient is preferably inversely proportional to the degree of magnetization of the volume being tested, scanned by the leakage flux probe.

7. A method according to any of the preceding paragraphs, characterized in that it includes: performing calibration measurements on a tuning section of the product being tested, wherein said tuning section has at least one tuning flaw, to find a compensation curve that describes the functional relationship between the magnetization state of the product being tested in the case of external magnetic fields of different strengths, the corresponding magnetization signals of the magnetic field probe and the amplitude of the probe signal generated by the standard flaw; and obtaining compensating coefficients for normalizing probe signals according to the compensation curve during probe signal processing.

8. The method according to paragraph 7, characterized in that it includes: taking into account the change in the magnetization state depending on the axial position of the test section to be tested, when finding a correction factor to be applied to the test section, by a procedure in which, when finding the correction factor, the axial shift between the calibration section and the test section is determined and the correction factor is modified depending on the shift.

9. The method according to claim 7 or 8, characterized in that the correction coefficient for the axial position in the section being tested is found on the basis of a shifted compensation curve, wherein the shifted compensation curve has the form of a compensation curve found in the calibration section, and this compensation curve is shifted by a shift value corresponding to the axial shift, relative to the compensation curve found in the calibration section.

10. A method according to any one of the preceding claims, characterized in that the probe structure has a probe array comprising a plurality of leakage flux probes arranged adjacent to each other in a first direction, and, preferably, two or more magnetic field probes are provided for recording the magnetization state, arranged at a distance from each other in the first direction, wherein the number of magnetic field probes is preferably less than the number of leakage flux probes.

11. A device for testing a ferromagnetic test item, in particular ferromagnetic pipes, based on leakage flux for recording defects, comprising: magnetizing device for magnetizing the tested volume of the tested product (PR); a probe structure (SA) comprising at least one leakage flux probe (SO) for recording magnetic leakage fields caused by defects, wherein the leakage flux probe (SO) is designed with the possibility of being held during scanning at a final inspection distance (AB) from the surface of the product being inspected and generating electrical probe signals with a defect signal amplitude dependent on the leakage flux, wherein said probe signals represent a measure of the leakage field strength; a processing device (AW) for processing probe signals for the purpose of qualitative assessment of defects, characterized in that the device is provided with at least one magnetic field probe (SM) for generating magnetization signals which represent a measure of the magnetization state of the tested article (PR) in the region of the leakage flux probe (SO); and the processing device is designed with the possibility of normalizing the probe signals by means of corresponding magnetization signals in order to find normalized probe signals and process the normalized probe signals for the purpose of qualitatively assessing defects.

12. The device according to claim 11, characterized in that the magnetic field probe (SM) is a magnetic field-sensitive probe, separate from the scattering flux probe (SO) and provided in addition to the scattering flux probe (SO).

13. The device according to claim 11 or 12, characterized in that the device has at least one test head (TH) in which a probe structure (SA) is located in a fixed spatial relationship to one another, containing at least one leakage flux probe (SO), as well as at least one magnetic field probe (SM).

14. A device according to any one of paragraphs 11-13, characterized in that the leakage flux probe (SO) is designed with the possibility of recording the normal component of the leakage field, oriented essentially perpendicular to the surface of the sample being tested, and / or in that the magnetic field probe (SM) is designed with the possibility of recording the parallel component of the magnetic field, oriented essentially parallel to the surface of the product being tested and parallel to the main direction of magnetization.

15. A device according to any one of claims 11-14, characterized in that the probe structure has a probe matrix comprising a plurality of leakage flux probes (SO) arranged next to each other in direct sequence in the first direction, and, preferably, two or more magnetic field probes (SM) are provided for recording the magnetization state, arranged at a distance from each other in direct sequence in the first direction.

16. The device according to any one of claims 11-15, characterized in that the number of magnetic field probes (SM) is less than the number of leakage flux probes (SO), wherein, preferably, the number of leakage flux probes (SO) is at least five times greater, preferably, at least one order of magnitude greater than the number of magnetic field probes (SM), and / or in that the leakage flux probes are located at equal distances from each other, and in that the magnetic field probes are located at unequal distances from each other, wherein the density of magnetic field probes is preferably greater in the end regions of the probe structure than in the middle region of the probe structure.

17. A device according to any one of paragraphs 11-16, characterized in that the probes (SO) of the scattering flux are located on the side of the test head (RK) facing the tested sample (PR), and the probes (SM) of the magnetic field are located at a distance behind the probes of the scattering flux.