Self-calibration system for ultrasonic inspection apparatus

• US 4,567,747 A
• Filed: 01/16/1984
• Issued: 02/04/1986
• Est. Priority Date: 01/16/1984
• Status: Expired due to Fees

• Current Assignee: TRW Incorporated Cleveland Oh An Corporation
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: Matay, Istvan M.
• Primary Examiner(s): Bashore, S. Leon
• Assistant Examiner(s): Anderson, Andrew J.
• Application Number:
  US06/571,317
• Time in Patent Office: 750 Days
• Field of Search: 73/1 DV, 73/597, 73/598, 73/622, 367/13
• US Class Current: 73/597
• CPC Class Codes: G01N 29/30 Arrangements for calibrating or comparing, e.g. with standard objects

Abstract

A tubular workpiece (10) undergoes axial and rotational movement relative to a collar (12) filled with an acoustically coupling medium (14). Longitudinal waves are emitted into the coupling medium and the workpiece from a first transducer (22) and acoustic echoes are received thereby. From the coupling medium travel times between the transducer and the surface of the workpiece, a contour reconstruction apparatus (58) reconstructs the peripheral contour of the workpiece. The workpiece travel times are stored in a memory (92) until the longitudinal velocity of the acoustic wave in the workpiece is determined. Transducers (24, 26) emit and detect a Rayleigh wave which travels around the workpiece circumference. A divider (80) divides the workpiece circumference as determined by the contour reconstruction apparatus by the Rayleigh wave travel time to determine the Rayleigh wave acoustic velocity. A multiplier (82) multiplies the Rayleigh wave velocity by a preselected Rayleigh wave to longitudinal wave ratio to determine the velocity of the longitudinal wave in the workpiece. A second multiplier (100) multiplies the stored longitudinal wave travel times by the longitudinal wave velocity to determine the thickness of the workpiece and the depth of any acoustically reflective flaws.

Claims

1. A method of acoustically inspecting a workpiece comprising:

(a) determining a preselected physical calibration distance along a workpiece being inspected;

(b) measuring a first travel time in which a first acoustic wave travels said calibration distance, said calibration distance being determined acoustically by measuring the travel times of acoustic waves through an acoustic coupling medium that contacts the workpiece along the calibration distance;

(c) adjusting the determined distance for variations in the temperature and pressure of the coupling medium;

(d) determining a calibration acoustic velocity from the calibration distance and the first travel time;

(e) measuring a second workpiece travel time in which a second acoustic wave travels through a portion of the workpiece to be inspected; and

,

(f) determining an inspection distance through the workpiece traveled by the second acoustic wave from the calibration acoustic velocity and the second travel time.

2. The method as set forth in claim 1 further including repeating steps (a) through (f) to inspect another portion of the workpiece, whereby the calibration acoustic velocity is redetermined for each inspected workpiece portion.

3. The method as set forth in claim 1 wherein the calibration distance is determined along a first surface of the workpiece and the first acoustic wave comprises a Rayleigh wave which travels the calibration distance along the workpiece first surface.

4. The method as set forth in claim 3 wherein the second acoustic wave comprises a longitudinal wave which travels into the workpiece and produces at least one acoustic echo from at least one workpiece interface, such as a flaw and a second surface of the workpiece, said longitudinal wave traveling in the workpiece with a longitudinal wave velocity;

and,

wherein in the step of determining the calibration acoustic velocity, the longitudinal wave velocity is determined, whereby the inspection distance is indicative of at least one of the depth of a flaw in the workpiece and the thickness of the workpiece between the first and second surfaces.

5. The method as set forth in claim 4 wherein the step of determining the calibration acoustic velocity includes dividing the calibration distance by the first travel time to determine the acoustic velocity of the Rayleigh wave and multiplying the Rayleigh wave velocity by a preselected velocity constant which represents the ratio of the longitudinal wave velocity to the Rayleigh wave velocity, whereby the longitudinal wave acoustic velocity is determined.

6. The method as set forth in claim 4 wherein the step of determining the calibration distance includes:

transmitting the longitudinal wave from an ultrasonic transducer through an acoustic coupling medium to the workpiece, the longitudinal wave being in part reflected from the workpiece first surface producing a first longitudinal acoustic wave echo, the acoustic velocity of the longitudinal wave and echo in the coupling medium being predetermined;

measuring a plurality of coupling medium travel times, each coupling medium travel time being indicative of the time in which at least one of the longitudinal wave and echo travels through the acoustic coupling medium between a preselected surface and the workpiece first surface along the calibration distance; and

,

determining the calibration distance from the coupling medium travel times.

7. The method as set forth in claim 6 wherein the step of determining the calibration distance further includes determining the contour of the workpiece first surface at least along the calibration distance from the plurality of coupling medium travel times.

8. The method as set forth in claim 7 further including the step of comparing the determined first surface contour with a preselected contour, whereby conformity of the workpiece first surface contour to a preselected contour is determined.

9. The method as set forth in claim 8 wherein the step of measuring the plurality of coupling medium travel times further includes moving the workpiece and an ultrasonic transducer relative to each other as a plurality of longitudinal waves are generated and longitudinal echoes are received, measuring the second and coupling medium travel times, and storing the second travel times at least until sufficient coupling medium travel times are measured to determine the calibration distance and the longitudinal wave acoustic velocity.

10. An acoustic workpiece inspection system comprising:

a calibration distance determining means for determining a preselected physical calibration distance along a workpiece being inspected;

a first travel time measuring means for measuring a first travel time in which a first acoustic wave travels said calibration distance;

calibration acoustic velocity determining means for determining a calibration acoustic velocity from the calibration distance and the first travel time, the calibration acoustic velocity determining means being operatively connected with the calibration distance determining means and the first travel time measuring means;

a second travel time measuring means for measuring a second travel time in which a second acoustic wave travels through a portion of the workpiece to be inspected; and

,

inspection distance determining means for determining from the second travel time and the calibration acoustic velocity an inspection distance through the workpiece traveled by the second acoustic wave, the inspection distance determining means being operatively connected with the calibration acoustic velocity determining means and the second travel time measuring means.

11. The inspection system as set forth in claim 10 wherein the calibration distance determining means determines the calibration distance without mechanical contact with the workpiece.

12. The inspection system as set forth in claim 10 wherein the calibration distance determining means measures the calibration distance along a first surface of the workpiece and the first acoustic wave comprises a Rayleigh wave which travels the calibration distance along the first surface.

13. The inspection system as set forth in claim 12 wherein the second acoustic wave comprises a longitudinal wave which travels into the workpieces and produces at least one acoustic echo from at least one interface in the workpiece;

and,

wherein the calibration acoustic velocity determining means determines an acoustic velocity of the longitudinal wave.

14. The inspection system as set forth in claim 13 wherein the calibration acoustic velocity determining means includes a divider means for dividing the determined calibration distance by the first travel time to determine the Rayleigh wave velocity and first multiplying means for multiplying the Rayleigh wave velocity by a ratio of the longitudinal wave velocity to the Rayleigh wave velocity of the inspected workpiece.

15. The inspection system as set forth in claim 13 further including:

an acoustic coupling medium contacting at least a portion of the workpiece first surface including the calibration distance, the acoustic coupling medium transmitting acoustic waves with a known coupling medium velocity; and

,

wherein the calibration distance determining means includes;

a coupling medium travel time measuring means for measuring a plurality of coupling medium travel times, each coupling medium travel time representing travel time of the longitudinal wave through the acoustic coupling medium between a preselected surface and the workpiece first surface along the calibration distance; and

,

wherein the calibration distance determining means determines the calibration distance from the coupling medium travel times.

16. The inspection system as set forth in claim 15 wherein the calibration distance determining means further includes means for determining the contour of the workpiece first surface at least along the calibration distance.

17. The inspection system as set forth in claim 16 further including contour comparing means for comparing the determined contour with a preselected contour.

18. The inspection system as set forth in claim 16 wherein the second and coupling medium travel time measuring means include at least one common ultrasonic transducer generating the longitudinal wave which travels through the coupling medium to the workpiece, echoes in part from the workpiece first surface and returns to the common ultrasonic transducer, in part enters and travels through the workpiece, and echoes in part from at least one interface, said echoes returning to the workpiece first surface and travel from the workpiece first surface through the coupling medium to the common ultrasonic transducer;

said system further including means for moving the workpiece and the common ultrasonic transducer relative to each other such that a plurality of second and coupling travel times are measured, each travel time corresponding to a predetermined position along the workpiece first surface; and

,

travel time storage means for storing at least the second travel times at least until sufficient coupling medium travel times are measured to determine the calibration distance and the calibration acoustic velocity.

19. An acoustic inspection apparatus for inspecting tubular workpieces in which velocities of ultrasonic inspection waves are unknown, the inspection apparatus comprising:

supporting means for supporting a tubular workpiece to be inspected;

an acoustic coupling medium operatively connected with the supporting means to be supported in contact with a first surface of the inspected workpiece, the acoustic coupling medium transmitting longitudinal ultrasonic waves with a predetermined coupling medium velocity;

at least one ultrasonic longitudinal wave transducer means for producing ultrasonic longitudinal waves and receiving ultrasonic longitudinal wave echoes, the transducer means being operatively connected with the supporting means in contact with the acoustic coupling medium and oriented to direct ultrasonic longitudinal waves radially toward the workpiece;

rotation means for causing relative rotational movement between the workpiece and the transducer means about a central axis of the workpiece, the rotation means producing a rotational position signal indicative of the relative angular orientation of the longitudinal wave transducer means and the workpiece;

a coupling medium travel time measuring means for measuring travel time of the ultrasonic longitudinal waves traveling between the transducer means and the workpiece first surface at a plurality of relative angular orientations between the workpiece and the longitudinal wave transducer means;

contour determining means for determining a contour of the workpiece first surface, the contour means being operatively connected with the rotation means to receive the rotational position signal therefrom and with the coupling medium travel time measuring means for receiving the measured coupling medium travel times therefrom;

calibration distance calculating means for calculating a calibration distance along the workpiece first surface from the contour, the calibration distance calculating means being operatively connected with the contour determining means;

at least one surface wave transducer means for producing ultrasonic Rayleigh waves traveling circumferentially along the workpiece first surface over the calibration distance, the surface wave transducer means being operatively connected with the supporting means in cotact with the acoustic coupling medium;

a surface wave travel time measuring means for measuring a surface wave travel time in which the Rayleigh wave traverses the calibration distance;

an acoustic velocity determining means for determining a longitudinal wave acoustic velocity in the workpiece, the acoustic velocity means being operatively connected with the calibration distance calculating means and the surface wave travel time measuring means;

a workpiece travel time measuring means for measuring workpiece travel times in which the longitudinal waves travel between the workpiece first surface and at least one workpiece interface such as an inner workpiece surface and a flaw, the workpiece travel time measuring means being operatively connected with the longitudinal wave transducer means; and

,

inspection distance determining means for determining a distance between the workpiece first surface and each interface, the inspection distance determining means being operatively connected with the acoustic velocity determining means and the workpiece travel time means.