STEAM GENERATOR NONDESTRUCTIVE EXAMINATION METHOD

• US 20070125175A1
• Filed: 11/22/2006
• Published: 06/07/2007
• Est. Priority Date: 11/28/2005
• Status: Active Grant

• Current Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Lareau, John, Junker, Warren
• Granted Patent: US 7,647,829 B2
• Time in Patent Office: Days
• US Class Current: 73/592
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 2291/0427 Flexural waves, plate waves, e.g. Lamb waves, tuning fork, cantilever
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/2634 cylindrical from outside
• CPC Class Codes: G01N 29/041 on the surface of the material, e.g. using Lamb, Rayleigh or shear waves
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00

Abstract

A method of examining a steam generator heat exchange tube from the outside surface employing ultrasonic nondestructive inspection techniques. An ultrasonic transducer contacts the outside surface of the tube and transmits a pseudo helical Lamb wave into the wall of the tube chosen to have a mode that does not significantly interact with water in the tube. The reflected waves are then analyzed for changes in modes to identify defects in the wall of the tube.

Claims

1. A method of examining a steam generator heat exchanger tube having an elongated axial dimension which is substantially filled with a fluid, comprising the steps of:

contacting an outer surface of a wall of the tube with an ultrasonic transducer;

establishing a predetermined Lamb wave mode that when transmitted into the wall of the tube is not substantially attenuated by the water in the tube;

transmitting a pseudo helical Lamb wave of the predetermined Lamb wave mode into the wall of the tube from the ultrasonic transducer; and

analyzing reflected or modified waves for wear scar defects in the wall of the tube.

2. The method of claim 1 wherein the transmitting step transmits a pseudo helical Lamb wave from the contacting location of the ultrasonic transducer on the wall of the tube in opposite directions along the axial length of the wall of the tube.

3. The method of claim 1 wherein the helical Lamb wave travels a first axial dimension while making a 360 degree rotation around the wall of the tube including the step of moving the ultrasonic transducer axially along the outer surface of the tube a distance equal to at least the first axial dimension while transmitting intermittent Lamb waves.

4. The method of claim 3 including the step of receiving reflected waves in a pulse-echo mode.

5. The method of claim 3 wherein the ultrasonic transducer is moved axially in increments and the helical Lamb wave is transmitted substantially at each increment.

6. The method of claim 1 wherein the tube is anchored at a first end in a tube sheet and the contacting step is performed on the tube just above the tube sheet.

7. The method of claim 1 including the step of tuning the frequency of the Lamb wave to sweep across a given band of frequencies.

8. The method of claim 7 wherein the given band of frequencies extends approximately five percent on either side of a primary frequency.

9. The method of claim 8 wherein the primary frequency is chosen within the range of 700 KHz and 2 MHz.

10. The method of claim 7 wherein the given band of frequencies extends approximately one percent on either side of a primary frequency.

11. The method of claim 1 wherein the steam generator tube is a “

U”

tube and the ultrasonic transducer contacts the wall of the tube in the region of the “

U”

bend.

12. The method of claim 11 wherein the ultrasonic transducer transmits Lamb waves in opposite axial directions along the wall of the tube.

13. The method of claim 1 wherein the ultrasonic transducer is a phased array transducer.

14. The method of claim 1 wherein the ultrasonic transducer is an EMAT transducer.

15. The method of claim 1 wherein the establishing step determines the predetermined Lamb wave mode through experimentation by varying the transducer'"'"'s frequency and angle of introduction of the ultrasonic signal into the tube wall until a mode is identified that results in a response that is least affected by the fluid in the tube and best characterizes a wear scar defect'"'"'s penetration through the tube wall.

16. The method of claim 15 including the step of performing a visual inspection of the tube to determine a location and shape of the wear scar defect on the outer surface of the tube prior to performing the contacting step.

17. The method of claim 16 wherein the predetermined Lamb wave mode is stored in a library classified by the shape of the wear scar so that the establishing step for subsequently detected wear scars searches the library for the same or similar shaped wear scars on tubes having the same dimensions.

18. The method of claim 15 wherein the experimentation is conducted on a laboratory mockup of the steam generator heat exchanger tube filled with the fluid and having a simulated wear scar defect similar in location and shape to the wear scar defect observed on the steam generator heat exchanger tube.

19. The method of claim 1 wherein the steam generator heat exchanger tube is part of a tube bundle having approximately 3 mm tube lane clearance between tubes wherein the contacting step includes inserting the ultrasonic transducer in the tube lane between tubes.

20. A method of determining the existence of defects in the walls of an elongated “

U”

shaped heat exchange tube from the secondary side of a steam generator while a primary side of the steam generator is water solid, comprising the steps of;

contacting an outer surface of a wall of the tube with an ultrasonic transducer in an area of a “

U”

-bend of the tube;

establishing a predetermined Lamb wave mode that when transmitted into the wall of the tube is not substantially attenuated by the water in the tube;

transmitting a pseudo helical Lamb wave into the wall of the tube from the ultrasonic transducer in opposite directions along the elongated dimension of the tube; and

analyzing reflected waves for defects in the wall of the tube.

21. The method of claim 20 wherein the helical Lamb wave travels a first distance along the elongated dimension of the tube while making a 360 degree rotation around the wall of the tube including the step of moving the ultrasonic transducer along the elongated dimension of the outer surface of the tube a distance equal to at least the first distance while transmitting intermittent Lamb waves.

22. The method of claim 21 wherein the ultrasonic transducer is moved in increments along the elongated dimension of the tube and the Lamb wave is transmitted substantially at each increment.

23. An ultrasonic transducer having a profile that can navigate a clearance in lanes between heat exchange tubes in a secondary side of a nuclear steam generator wherein the clearance is approximately 3 mm.

24. The ultrasonic transducer of claim 23 including a biasing mechanism that can leverage off of adjacent heat exchange tubes to positively press the ultrasonic transducer into firm contact with a heat exchange tube to be interrogated for wear scars.

25. The ultrasonic transducer of claim 24 wherein the biasing mechanism is a spring pack.

26. The ultrasonic transducer of claim 24 wherein the biasing mechanism is an inflatable bladder.