Ultrasonic non-destructive testing

• US 8,381,592 B2
• Filed: 09/14/2006
• Issued: 02/26/2013
• 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
• Primary Examiner(s): Macchiarolo, Peter
• Assistant Examiner(s): MILLER, ROSE MARY
• Application Number:
  US12/092,630
• Publication Number:
  US 20100058869A1
• Time in Patent Office: 2,357 Days
• Field of Search: 736/17, 736/44, 735/96
• US Class Current: 73/617
• 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 of a solid object, the apparatus comprising:

a solid object under test, the solid object having studs welded thereto;

an elongate strip of ultrasound transmissive material, said elongate strip having a transverse cross-section with a width and a thickness giving an aspect ratio greater than unity, a proximal end and a distal end;

an ultrasonic transducer coupled to said elongate strip and matched thereto such that excitation of said ultrasonic transducer induces non-dispersive ultrasonic signals to propagate along said elongate strip to said proximal end, said signals being formed of components of different frequencies having wavelengths extending from λ

_short to λ

_long; and

a clamp clamping with an adjustable force said proximal end to the studs welded to the solid object, wherein said non-dispersive signals are coupled into the solid object;

wherein said thickness is less than 2.5 λ

_short and said width is greater than 3.5 λ

_long.

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.

3. Apparatus as claimed in claim 1, wherein said thickness is less than λ

_short.

4. Apparatus as claimed in claim 1, wherein said width is greater than 5 λ

_long.

5. Apparatus as claimed in claim 1, wherein said non-dispersive ultrasonic signals comprise lowest order shear mode vibrations with a polarisation perpendicular to their propagation direction and parallel to said width.

6. Apparatus as claimed in claim 1, wherein said non-dispersive ultrasonic signals comprise lowest order compression mode vibrations with polarisation parallel to the propagation direction.

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

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

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

10. 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 perpendicular to the propagation direction.

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

12. Apparatus as claimed in claim 11, 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 an ultrasonic transducer to detect said reflected ultrasound.

13. Apparatus as claimed in claim 12, wherein said one or more elongate strips and said ultrasonic transducer also form said ultrasound receiver.

14. Apparatus as claimed in claim 1, wherein said solid object is:

(i) at a temperature greater than 200°

C.; and

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

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

_bar where λ

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

_bar.