Confirmation of hydrogen damage in boiler tubes by refracted shear waves

• US 5,243,862 A
• Filed: 06/04/1991
• Issued: 09/14/1993
• Est. Priority Date: 06/04/1991
• Status: Expired due to Fees

• Current Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Original Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Inventors: Latimer, Paul J.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): MILLER, ROSE MARY
• Application Number:
  US07/710,271
• Time in Patent Office: 833 Days
• Field of Search: 73/600, 73/599, 73/592, 73/637, 73/638, 73/596, 73/622, 73/634
• US Class Current: 73/600
• 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 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 29/043 in the interior, e.g. by shear waves
• CPC Class Codes: G01N 29/11 by measuring attenuation of acoustic waves

Abstract

A method and apparatus for distinguishing between hydrogen damage in the wall of a boiler tube, and surface damage on the inside surface of the tube, comprises a pair of transducers which are spaced on the outer surface of the tube and which apply a refracted shear ultrasonic wave through a chord of the tube with a beam angle that is calculated from the outside radius and wall thickness of the tube. The transducers are first applied to an undamaged tube and an instrument connected to the transducers is adjusted to 80% of full screen height. The same transducers are then, applied to a suspected boiler tube. Any attenuation of the initially high amplitude below 12 dB indicates hydrogen damage as opposed to inner surface damage which has been found to produce a far lower attenuation.

Claims

1. A method for distinguishing between hydrogen damage in a wall of a boiler tube, and other surface conditions which can give false indications of hydrogen damage on an inside surface of the tube, the tube having an outside radius r and a wall thickness t, the method comprising the steps of:

placing a pair of ultrasonic transducers on an outside surface of an undamaged tube for sending a refracted shear wave through a chord in the wall thickness of the undamaged tube, the undamaged tube having the same outside radius and wall thickness as the boiler tube, the chord determining a spacing between the transducers and being calculated as a function of a beam angle φ

, which is the angle between a tangent to the outer surface of the tube and the chord through the wall thickness between the transducers, where the chord length is equal to two times the outside tube radius r, times sin φ

;

adjusting an amplitude of the wave between the transducers to be about 80% full screen height;

placing the transducers on an outside surface of the boiler tube at positions corresponding to the positions of the transducers of the undamaged tube;

passing a refracted shear wave at the same adjusted amplitude through a chord of the boiler tue corresponding to the chord of the undamaged tube; and

measuring an attenuation of the shear wave between the transducers, a relatively large attenuation being indicative of hydrogen damage and a relatively small attenuation being indicative of other surface conditions inside the boiler tube.

2. A method according to claim 1, including utilizing an instrument having a screen display to display signal amplitude, to generate and measure the ultrasonic waves, the adjusted amplitude corresponding to approximately 80% of a full screen height for the display.

3. A method according to claim 2, wherein the attenuation which is indicative of hydrogen damages is at least 12 db.

4. An apparatus for distinguishing between hydrogen damage in a wall of boiler tube and other surface conditions which can give false indications of hydrogen damage on an inside surface of the boiler tube, the boiler tube having an outside radius r and a wall thickness t, the apparatus comprising:

a pair of ultrasonic transducers spaced from each other by a chord which is calculated as a function of a beam angle φ

between a tangent to an outside surface of the tube and the chord, wherein the chord length equals two items the outside radius r, times sin φ

, one of said transducers sending a refracted shear wave through the chord of the boiler tube to be received by the other transducers;

a fixture to which the transducers are fixed, the fixture having a tube contact surface and which matches a contour of the outside surface of the tube; and

means for measuring attenuation of an amplitude for the refracted shear wave for distinguishing between hydrogen damage in the boiler tube and other surface conditions on the inside surface of the boiler tube which can give false indications of hydrogen damage.