Method of determining if deterioration in structural integrity of a pressure vessel, a pressure vessel, and a structural integrity testing apparatus therefor

• US 20040010382A1
• Filed: 06/13/2003
• Published: 01/15/2004
• Est. Priority Date: 07/15/2002
• Status: Active Grant

• Current Assignee: Saskatchewan Research Council
• Original Assignee: Saskatchewan Research Council
• Inventors: Lung, Bryan, Wong, Joe Y.
• Granted Patent: US 6,785,616 B2
• Time in Patent Office: Days
• US Class Current: 702/34
• CPC Class Codes: G01H 1/00 Measuring characteristics of vibrations in solids by using direct conduction to the detector G01H9/00, G01H11/00 take precedence

Abstract

A method for determining if deterioration in structural integrity of a pressure vessel, having both sensor means and oscillator means affixed to or embedded in said exterior surface thereof. An electrical current is provided to the oscillator means so as to cause said oscillator means to oscillate and produce a mechanical disturbance to the exterior surface and cause a detectable natural frequency response of said pressure vessel. The resultant natural frequency response is detected and recorded. After a period of elapsed time, the natural frequency response is again obtained. It is compared with the recorded natural frequency response first obtained, and if there be a difference therebetween, such as a shift in the frequencies at which the natural resonances occur, or a decrease or increase in the amplitude of one or more of the natural frequency resonances, then a flag is raised. An apparatus for determining if deterioration in structural integrity of a pressure vessel, and a pressure vessel, is further disclosed.

Claims

1. A method for determining if there may be deterioration in structural integrity of a pressure vessel having an exterior surface comprised of a composite material having both sensor means and oscillator means affixed to or embedded in said exterior surface, comprising:

(a) providing an electrical current to said oscillator means so as to cause said oscillator means to oscillate so as to produce a mechanical disturbance to said exterior surface and cause a detectable natural frequency response of said pressure vessel;

(b) detecting, using said sensor means, said natural frequency response;

(c) recording said natural frequency response;

(d) after a period of elapsed time, repeating steps a) and b); and

(e) comparing said recorded natural frequency response first obtained with said natural frequency response last obtained, and determining if there be a difference therebetween.

2. The method as claimed in claim 1, wherein said mechanical disturbance in step a) occurs when said pressure vessel is subject to no internal pressure or a selected internal pressure, and said steps a) and b) are repeated as per step d) when said pressure vessel is subjected to said same no pressure or said selected pressure.

3. The method as claimed in claim 1, wherein said mechanical disturbance in step a) occurs when said pressure vessel is subject to a particular temperature, and said steps a) and b) are repeated as per step d) when said pressure vessel is subjected to said same particular temperature.

4. The method as claimed in claim 1, wherein said mechanical disturbance in step a) occurs when said pressure vessel is subject to a particular pressure and/or temperature, and steps a) and b) are repeated as per step d) when said pressure vessel is subjected to a different pressure and/or temperature, and prior to step e), applying a correction to said natural frequency response last obtained to correct for said different pressure and/or temperature so as to be able to compare said frequency response first obtained with said frequency response last obtained.

5. The method as claimed in claim 1 wherein said sensor means comprises piezoelectric sensor means.

6. The method as claimed in claim 1, and said oscillator means comprises piezo-electric oscillator means.

7. The method as claimed in claim 1, wherein said step of detecting using sensor means and providing an electrical impulse to said oscillator means comprises utilizing at least two individual piezo-electric materials, one of which is provided with said electrical impulse and the other or others detect said resultant natural frequency response.

8. The method as claimed in claim 5, wherein said steps of detecting using sensor means and providing an electrical impulse to said oscillator means comprises utilizing a single piezo-electric material, whereby said piezo-electric material is provided with said electrical impulse and also subsequently thereafter detects said resultant natural frequency response.

9. The method as claimed in claim 5, wherein said step of comparing said natural frequency response first obtained with said natural frequency response last obtained comprises obtaining a voltage response from said piezo-electric sensor means as a function of time and comparing said voltage response with a later obtained voltage response as a function of time, and determining if there be any differences.

10. The method as claimed in claim 5 wherein said step of comparing said resultant natural frequency response first obtained with said natural frequency response last obtained comprises:

i) calculating a power spectrum density as a function of frequency from said resultant natural frequency response of said piezo-electric sensor means first obtained, and

ii) calculating a power spectrum density as a function of frequency from said natural frequency response of said piezo-electric sensor means last obtained; and

iii) comparing said power spectrum density obtained from step ii) above with that obtained from step i) above, and determining if there are differences.

11. The method as claimed in claim 1, wherein the step of determining if there be any differences comprises comparing the first obtained natural frequency response and the later-obtained natural frequency response, and determining if there has been a shift in the frequencies at which the natural resonances occur.

12. The method as claimed in claim 1, wherein the step of determining if there be any differences comprises comparing the first obtained natural frequency response and the later-obtained natural frequency response, and determining if there has been a a decrease or increase in the amplitude of one or more of the natural frequency resonances.

13. A structural integrity testing apparatus for a composite-reinforced pressure vessel having an exterior surface comprised of a composite material, comprising:

(i) sensor means and oscillator means affixed to or embedded in said exterior surface;

(ii) means for applying ng an electrical current to said oscillator means so as to cause said oscillator means to oscillate so as to produce a mechanical disturbance to said exterior surface and cause a detectable natural frequency response of said pressure vessel;

(iii) means for recording said natural frequency response of said pressure vessel; and

(iv) means for comparing said recorded resultant natural frequency response with a later-obtained natural frequency response, and determining if there be any difference therebetween

14. The structural integrity testing apparatus as claimed in claim 13, further comprising:

means for indicating lack of pressure vessel integrity to an operator if said means for comparing indicates differences were detected.

15. The structural integrity testing apparatus as claimed in claim 14, further comprising:

means for applying a correction to said later-obtained natural frequency response to adjust for any differences in temperature and/or pressure to which said pressure vessel may be then subject as compared to temperature and/or pressures which it was subject at the time of first recording said resultant natural frequency response.

16. The structural integrity testing apparatus as claimed in claim 14, wherein said sensor means comprises piezo-electric sensor means.

17. The structural integrity testing apparatus as claimed in claim 14, wherein said oscillator means comprises piezo-electric oscillator means.

18. The structural integrity testing apparatus as claimed in claim 13, wherein said sensor means and said oscillator means each comprise piezo-electric materials.

19. The structural integrity testing apparatus as claimed in claim 13, wherein

said sensor means and said oscillator means each comprise a single piezoelectric material, and said single piezo-electric material is first provided with said electrical impulse and subsequently thereafter detects said resultant natural frequency response.

20. The structural integrity testing apparatus as claimed in claim 13, wherein

said means for recording said natural frequency response comprises means for detecting a voltage response from said sensor means and recording said voltage response from said sensor means as a function of time.

21. The structural integrity testing apparatus as claimed in claim 13, wherein

said means for recording said natural frequency response comprises means for calculating a power spectrum density from an output signal received from said sensor means as a function of frequency.

22. A pressure vessel, comprising:

an inner vessel;

a reinforced material surrounding said inner vessel and forming an exterior surface;

both sensor means and oscillator means affixed to or embedded in said exterior surface; and

,

means for storing a resultant natural frequency response as received from said sensor means, after a mechanical disturbance has been provided to said exterior surface of said pressure vessel by said oscillator means.

23. The pressure vessel as claimed in claim 22, wherein said oscillator means comprises piezo-electric material which receives an electrical impulse so as be caused to oscillate and produce said mechanical disturbance.

24. The pressure vessel as claimed in claim 22, wherein said sensor means is a piezoelectric material which senses said mechanical disturbance.

25. The pressure vessel as claimed in claim 22, wherein said sensor means and said oscillation means each comprise piezo-electric materials.

26. The pressure vessel as claimed in claim 22, wherein said sensor means and oscillation means comprise a single piezo-electric material, and said piezo-electric material is provided with said electrical impulse and subsequently thereafter also detects said resultant natural frequency response.