ULTRASONIC NON-DESTRUCTIVE TESTING

• US 20100058869A1
• Filed: 09/14/2006
• Published: 03/11/2010
• Est. Priority Date: 11/04/2005
• Status: Active Grant

• Current Assignee: Permasense Limited (Emerson Process Management Limited)
• Original Assignee: Imperial Innovations Limited (Imperial College London)
• Inventors: Cawley, Peter, Cegla, Frederick Bert
• Granted Patent: US 8,381,592 B2
• Time in Patent Office: Days
• US Class Current: 73/596
• CPC Class Codes: G01N 2291/0234 Metals, e.g. steel
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 29/069 Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
• CPC Class Codes: G01N 29/2412 using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]; investigating the presence of flaws using eddy currents G01N27/90, magnetostrictive transducers B06B1/08, measuring magnetostrictive properties G01R33/18
• CPC Class Codes: G01N 29/28 providing acoustic coupling , e.g. water impedance matching G10K11/02
• CPC Class Codes: G01N 29/34 Generating the ultrasonic, sonic or infrasonic waves , e.g. electronic circuits specially adapted therefor
• CPC Class Codes: G10K 11/24 for conducting sound through solid bodies, e.g. wires

Abstract

An apparatus and method for ultrasonic non-destructive testing provides an elongate strip of ultrasound transmissive material coupled at a proximal end to an object under test. The elongate strip has a transverse cross-section with a width and thickness giving an aspect ratio greater than unity and matched to the ultrasonic transducer such that excitation induces a substantially non-dispersive ultrasonic signal to propagate along the elongate strip to the proximal end and to enter the object under test. These non-dispersive pulses are particularly suited for time-of-flight measurements, thickness measurements, crack measurements and the like. The elongate strip helps to separate the transducer from a potentially hostile environment associated with the object under test. The elongate strip also has a large area of contact with the object under test allowing efficient transmission of energy into the object under test.

Claims

1. Apparatus for ultrasonic non-destructive testing for an object under test, said apparatus comprising:

an elongate strip of ultrasound transmissive material, said elongate strip having a proximal end for coupling to said object under test and a distal end; and

an ultrasonic transducer coupled to said elongate strip;

wherein

said elongate strip has a transverse cross-section with a width and a thickness giving an aspect ratio greater than unity and matched with said ultrasonic transducer such that excitation of said ultrasonic transducer induces substantially non-dispersive ultrasonic signals to propagate along said elongate strip to said proximal end and to enter said object under test.

2. Apparatus as claimed in claim 1, wherein said elongate strip is formed of a material having a shear velocity C_s and a shear wavelength λ

_B, where λ

_B=C_s/F and F is the frequency corresponding to λ

_B, and said substantially non-dispersive ultrasonic signals are formed of components of different frequencies and having shear wavelengths extending from λ

_short to λ

_long.

3. Apparatus as claimed in claim 2, wherein said thickness is less than 2.5 λ

_short.

4. Apparatus as claimed in claim 2, wherein said thickness is less than λ

_short.

5. Apparatus as claimed in claim 2, wherein said width is greater than 3.5 λ

_long.

6. Apparatus as claimed in claim 2, wherein said width is greater than 5 λ

_long.

7. Apparatus as claimed in claim 2, wherein said thickness is less than λ

_long.

8. Apparatus is claimed in claim 1, wherein said substantially non-dispersive ultrasonic signals comprises lowest order shear mode vibrations with a polarisation perpendicular to propagation direction and parallel to said width.

9. Apparatus as claimed in claim 1, wherein said elongate strip is formed of a material having a bar velocity C_bar and a bar wavelength λ

_bar where λ

_bar=C_bar/F and F is the frequency corresponding to λ

_bar, and said substantially non-dispersive ultrasonic signals are formed of components of different frequencies and having bar wavelengths extending from λ

_short to λ

_long.

10. Apparatus as claimed in claim 9, wherein said thickness is less than 2.5 λ

_short.

11. Apparatus as claimed in claim 9, wherein said thickness is less than λ

_short.

12. Apparatus as claimed in claim 9, wherein said width is greater than 3.5 λ

_long.

13. Apparatus as claimed in claim 9, wherein said width is greater than λ

_long.

14. Apparatus as claimed in claim 9, wherein said substantially non-dispersive ultrasonic signals comprise lowest order compression mode vibrations with polarisation parallel to the propagation direction.

15. Apparatus as claimed in claim 1, wherein said ultrasonic transducer excites substantially only a single mode of propagating guided wave.

16. Apparatus as claimed in claim 15, wherein said ultrasonic transducer is apodised to excite substantially only said single mode of propagating guided wave to induce said substantially non-dispersive ultrasonic signals.

17. Apparatus as claimed in claim 1, wherein, said substantially non-dispersive ultrasonic signals spread substantially cylindrically from said proximal end to said object under test.

18. Apparatus as claimed in claim 1, wherein said ultrasonic transducer is coupled to said distal end.

19. Apparatus as claimed in claim 18, wherein said ultrasonic transducer is coupled to said distal end by one of:

(iv) a bonded connection;

(v) a mechanical fixing and ultrasound transmissive couplant; and

(vi) a mechanical fixing and variable force.

20. Apparatus as claimed in claim 1, wherein said ultrasonic transducer comprises a transducer coupled to at least one longitudinal side of said elongate strip.

21. Apparatus as claimed in claim 1, wherein said ultrasonic transducer comprises a coil operable to provide electromagnetic ultrasound transduction.

22. Apparatus as claimed in claim 1, wherein said elongate strip is bent around an axis that is substantially parallel to said width of said elongate strip and substantially perpendicular to the propagation direction.

23. Apparatus as claimed in claim 1, wherein said elongate strip is bent around an axis substantially parallel to the propagation direction.

24. Apparatus as claimed in claim 1, comprising an ultrasound receiver operable to receive reflected ultrasound from said object under test resulting from said substantially non-dispersive ultrasonic signals entering said object under test.

25. Apparatus as claimed in claim 24, wherein said ultrasound receiver comprises one or more further elongate strips each coupled to said object under test at a respective position to receive said reflected ultrasound and having a receiving ultrasonic transducer to detect said reflected ultrasound.

26. Apparatus as claimed in claim 24, wherein said elongate strip and said ultrasonic transducer also form said ultrasonic receiver.

27. Apparatus as claimed in claim 24, wherein said reflected ultrasound comprises at least one reflected signals and said ultrasound receiver measures a time difference between said reflected signals.

28. Apparatus as claimed in claim 1, wherein said proximal end is fixed to said object under test by one of:

(i) welding;

(ii) brazing;

(iii) soldering; and

(iv) bonding.

29. Apparatus as claimed in claim 1, wherein said proximal end is clamped to said object under test.

30. Apparatus as claimed in claim 29, wherein ultrasound transmissive couplant is disposed between said proximal end and said object under test.

31. Apparatus as claimed in claim 29, wherein a clamp clamps said elongate strip to said object under test with an adjustable force.

32. Apparatus as claimed in claim 31, wherein said clamp is coupled to said object under test by studs welded to said object under test.

33. Apparatus as claimed in claim 1, wherein said proximal end is coupled to a surface of said object under test such that said propagation direction is not normal to said surface such that said ultrasonic signals enter said object under test at a non-normal angle.

34. Apparatus as claimed in claim 1, wherein said ultrasonic non-destructive testing is thickness measurement.

35. Apparatus as claimed in claim 1, wherein said ultrasonic non-destructive testing is crack monitoring.

36. Apparatus as claimed in claim 1, wherein said object under test is:

(i) at a temperature greater than 200°

C.; and

(ii) subject to above background levels of ionising radiation.

37. A method of ultrasonic non-destructive testing of an object under test, said method comprising:

coupling a proximal end of an elongate strip to an object under test;

exciting substantially non-dispersive ultrasonic signals within said elongate strip to propagate along said elongate strip and to enter said object under test.

38. A method as claimed in claim 37, wherein said elongate strip is formed of a material having a shear velocity C_s and a shear wavelength λ

_B, where λ

_B=C_s/F and F is the frequency corresponding to λ

_B, and said substantially non-dispersive ultrasonic pulses are formed of components of different frequencies and having shear wavelengths extending from λ

_short to λ

_long.

39. A method as claimed in claim 38, wherein said elongate strip has a transverse cross-section with a thickness less than 2.5 λ

_short.

40. A method as claimed in claim 38, wherein said elongate strip has a transverse cross-section with a thickness less than λ

_short.

41. A method as claimed in claim 38, wherein said elongate strip has a transverse cross-section with a width greater than 3.5 λ

_long.

42. A method as claimed in claim 38, wherein said elongate strip has a transverse cross-section with a width greater than 5 λ

_long.

43. A method as claimed in claim 38, wherein said elongate strip has a transverse cross-section with a thickness less than λ

_long.

44. A method as claimed in claim 37, wherein said substantially non-dispersive ultrasonic signals comprises lowest order shear mode vibrations with a polarisation perpendicular to propagation direction and parallel to a width of said elongate strip.

45. A method as claimed in claim 37, wherein said elongate strip is formed of a material having a bar velocity C_bar and a bar wavelength λ

_bar, where λ

_bar=C_bar/F and F is the frequency corresponding to λ

_bar, and said substantially non-dispersive ultrasonic signals are formed of components of different frequencies and having bar wavelengths extending from λ

_short to λ

_long.

46. A method as claimed in claim 45, wherein said thickness is less than 2.5 λ

_short.

47. A method as claimed in claim 45, wherein said thickness is less than λ

_short.

48. A method as claimed in claim 45, wherein said width is greater than 3.5 λ

_long.

50. A method as claimed in claim 45, wherein said thickness is less than 5 λ

_long.

51. A method as claimed in claim 45, wherein said substantially non-dispersive ultrasonic signals comprise lowest order compression mode vibrations with polarisation parallel to the propagation direction.

52. A method as claimed in claim 37, wherein substantially only a single mode of propagated guided wave is excited in said elongate waveguide.

53. A method as claimed in claim 37, wherein said ultrasonic non-destructive testing is thickness measurement.

54. A method as claimed in claim 37, wherein said ultrasonic non-destructive testing is crack monitoring.

55. A method as claimed in claim 37, wherein said object under test is:

(i) at a temperature greater than 200°

C.; and

(ii) subject to above background levels of ionising radiation.

49. A method as claimed in wherein said width is greater than 5 λ

_long.