Method and apparatus for magnetic crack depth prediction

• US 9,599,592 B2
• Filed: 03/10/2011
• Issued: 03/21/2017
• Est. Priority Date: 03/10/2010
• Status: Active Grant

• Current Assignee: ROBEL Holding GmbH (Plasser & Theurer Beteiligungs & Finanzierungs AG)
• Original Assignee: Ian Stewart Blair, Lloyd Lissiman, Stephanie Klecha
• Inventors: Klecha, Stephanie, Blair, Ian Stewart, Lissiman, Lloyd
• Primary Examiner(s): Hollington, Jermele M
• Assistant Examiner(s): CURTIS, SEAN M
• Application Number:
  US13/583,624
• Publication Number:
  US 20130113472A1
• Time in Patent Office: 2,203 Days
• Field of Search: 324216-217, 324220-221, 324/228, 324/235, 324237-238, 324/242, 324/251, 324/260, 324262-263, 702/35, 702/38
• US Class Current: 1/1
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws
• CPC Class Codes: G01N 27/83 by investigating stray magnetic fields

Abstract

A method of magnetic crack depth prediction for a magnetisable component of a first geometry comprising determining a measure of remnant magnetic flux leakage for a section of the component and, converting the remnant magnetic flux leakage to a predicted crack depth for that section of the component using an empirically determined relationship between remnant magnetic flux leakage and crack depth for a previously tested in service component of the first geometry.

Claims

1. A method of maintaining a magnetisable component in which cracks are induced due to fatigue, the method comprising:

subjecting the magnetisable component to a magnetic field;

after application of the magnetic field, determining a measure of remnant magnetic flux leakage for a section of the component;

using the determined remnant magnetic flux leakage to calculate a damage index representative of a predicted crack depth for that section of the component; and

dependent on the damage index, determining a maintenance action for that section of the component wherein the maintenance action is one of;

taking no action;

removing surface material from the section; and

replacement of that section.

2. The method according to claim 1 further comprising:

empirically determining a relationship between damage index and crack depth and utilising this relationship to predict crack depth for a calculated damage index.

3. The method according to claim 1 wherein determining remnant magnetic flux leakage comprises:

obtaining at least one signal representative of remnant magnetic flux leakage at multiple sampling points along the section of the component and processing the at least one signal to determine remnant magnetic flux leakage.

4. The method according to claim 3 comprising applying a magnetic field in one direction along the section of the component to produce the remnant magnetic field in the section of the component and wherein the at least one signal is representative of magnetic flux leakage from the remnant magnetic field.

5. The method according to claim 4 wherein obtaining the at least one signal comprises obtaining respective signals for each of a plurality of mutually adjacent strips of the section of the component at each sampling point where the strips extend transverse to the direction of application of the magnetic field.

6. The method according to claim 3 wherein processing the at least one signal comprises filtering the at least one signal.

7. The method according to claim 6 wherein filtering the at least one signal comprises filtering the at least one signal through a high pass filter to remove signal components having a wavelength greater than a first wave length.

8. The method according to claim 7 wherein filtering the at least one signal comprises passing the at least one signal through a digital high pass filter in opposite directions.

9. The method according to claim 6 wherein the filtering comprises passing the at least one signal through a low pass filter to remove signals of a wavelength less than a second wave length.

10. The method according to claim 9 wherein the at least one signal is passed through the low pass filter prior to passing through the high pass filter.

11. The method according to claim 3 wherein processing the at least one signal comprises conditioning the signals on the basis of distance between each sensor and an underlying surface of the component for each of the sampling points.

12. The method according to claim 11 wherein conditioning the signal comprises multiplying each signal by a factor:

13. The method according to claim 12 wherein processing comprises analysing the one or more signals and providing an indication of major damage to the section of the component when the signals have a characteristic of low frequency and high amplitude.

14. The method according to claim 13, wherein providing an indication of major damage comprises subsequent to the high pass filtering, calculating respective sums of data points from the high pass filtered signals above and below respective positive and negative thresholds for all of the sensors, comparing the sums with a pre-calculated severe damage indicator, and reporting the existence of major damage when either sum exceeds the pre-calculated severe damage indicator.

15. The method according to claim 6 wherein processing further comprises calculating a maximum peak to peak amplitude for each filtered signal for the section of the component.

16. The method according to claim 15 wherein processing further comprises integrating the peak to peak amplitude for each signal for the section of the component to provide the measure of remnant magnetic flux leakage for the section of the component.

17. A method of maintaining a magnetisable component of a first geometry in which cracks are induced due to fatigue, the method comprising:

subjecting the magnetisable component to a magnetic field;

after application of the magnetic field, determining a measure of remnant magnetic flux leakage for a section of the component;

converting the remnant magnetic flux leakage to a predicted crack depth for that section of the component using an empirically determined relationship between remnant magnetic flux leakage and crack depth for a previously tested in service component of the first geometry; and

dependent on the damage index, determining a maintenance action for that section of the component wherein the maintenance action is one of;

taking no action;

removing surface material from the section; and

replacement of that section.

18. The method according to claim 17 wherein determining remnant magnetic flux leakage comprises:

obtaining at least one signal representative of remnant magnetic flux leakage at multiple sampling points along the section of the component and processing the at least one signal to determine remnant magnetic flux leakage.

19. The method according to claim 18 comprising applying a magnetic field in one direction along the section of the component to produce the remnant magnetic field in the section of the component and wherein the at least one signal is representative of magnetic flux leakage from the remnant magnetic field.

20. The method according to claim 19 wherein obtaining the at least one signal comprises obtaining respective signals for each of a plurality of mutually adjacent strips of the section of the component at each sampling point where the strips extend transverse to the direction of application of the magnetic field.

21. A method of magnetic crack depth prediction for a magnetisable component comprising:

determining a measure of remnant magnetic flux leakage for a section of the component by obtaining at least one signal representative of remnant magnetic flux leakage at multiple sampling points along the section of the component and processing the at least one signal to determine remnant magnetic flux leakage;

wherein processing the at least one signal comprises conditioning the at least one signals on the basis of distance between each sensor and an underlying surface of the component for each of the sampling points;

wherein conditioning the signal comprises multiplying the or each signal by a factor;

22. The method according to claim 21 wherein processing comprises analysing the one or more signals and providing an indication of major damage to the section of the component when the signals have a characteristic of low frequency and high amplitude.

23. The method according to claim 22, wherein providing an indication of major damage comprises subsequent to the high pass filtering, calculating respective sums of data points from the high pass filtered signals above and below respective positive and negative thresholds for all of the sensors, comparing the sums with a pre-calculated severe damage indicator, and reporting the existence of major damage when either sum exceeds the pre-calculated severe damage indicator.

24. The method according to claim 21 wherein processing further comprises calculating a maximum peak to peak amplitude for each filtered signal for the section of the component.

25. The method according to claim 24 wherein processing further comprises integrating the peak to peak amplitude for each signal for the section of the component to provide the measure of remnant magnetic flux leakage for the section of the component.