Apparatus and method of discriminating flaw depths in the inspection of tubular products

• US 5,085,082 A
• Filed: 10/24/1990
• Issued: 02/04/1992
• Est. Priority Date: 10/24/1990
• Status: Expired due to Term

• Current Assignee: MAST Automatic
• Original Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Inventors: Cantor, Barry I., Flora, John H., Latimer, Paul J.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): MILLER, ROSE MARY
• Application Number:
  US07/603,334
• Time in Patent Office: 468 Days
• Field of Search: 73/592, 73/597, 73/598, 73/620, 73/622, 73/627, 73/629, 73/643, 340/540, 340/679, 340/683
• US Class Current: 73/622
• CPC Class Codes: G01N 2291/0234 Metals, e.g. steel
• 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 2291/102 one emitter, one receiver
• 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 29/0618 synchronised with scanning, e.g. in real-time
• CPC Class Codes: G01N 29/11 by measuring attenuation of acoustic waves
• 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 29/27 by moving the material relative to a stationary sensor
• CPC Class Codes: G01N 29/30 Arrangements for calibrating or comparing, e.g. with standard objects
• CPC Class Codes: G01N 29/40 by amplitude filtering, e.g. by applying a threshold or by gain control
• CPC Class Codes: G01N 29/4445 Classification of defects

Abstract

An apparatus and method for discriminating between flaw depths of 5% and 10% of the tube wall thickness of electric resistance welds are disclosed. At least two electromagnetic acoustic transducers (EMATs) are employed to generate ultrasonic surface and shear waves. A logic circuit discriminating means selectively activates an alarm for flaw depths of about 10% or greater, but does not activate the alarm for flaw depths of about 5% or less, thereby avoiding waste in time and materials.

Claims

1. A method of discriminating between inner and outer diameter flaws for rapidly detecting a flaw having a throughwall depth greater than or equal to a preset depth in a tube formed with a weld line, comprising the steps of:

positioning externally on the tube at least two electromagnetic acoustic transducers substantially adjacent the weld line;

generating ultrasonic surface waves with said first electromagnetic acoustic transducer and propagating the ultrasonic surface waves along a surface of the weld line;

generating ultrasonic shear waves with said second electromagnetic acoustic transducer and propagating the ultrasonic surface waves through the weld line;

measuring reflected ultrasonic surface and shear waves and establishing signals indicative thereof for identifying flaws in and around the weld line;

determining from the ultrasonic wave signals whether an identified flaw is an outer diameter flaw or an inner diameter flaw, the outer diameter flaw being determined from both the ultrasonic surface and shear wave signals exceeding a preset level for each of the ultrasonic signals, the inner diameter flaw being determined from the ultrasonic shear wave signal exceeding its preset level with the ultrasonic surface wave signal being below a noise threshold level; and

providing an alarm for a flaw with a throughwall depth greater than or equal to a preset depth.

2. A method as recited in claim 1, wherein the preset depth is a depth of about 10% or greater of tube wall thickness.

3. A method as recited in claim 1, further comprising the step of providing an audio alarm for a throughwall defect having a depth of about 10% or greater of tube wall thickness.

4. A method as recited in claim 1, wherein the determining step identifies outer diameter flaws having a throughwall depth of about 5% of tube wall thickness.

5. An apparatus for discriminating between inner and outer diameter flaws for rapidly detecting a flaw having a throughwall depth greater than a preset depth in a tube formed with a weld line, comprising:

electromagnetic acoustic transducer means for generating both ultrasonic surface and shear waves, said electromagnetic acoustic transducer means being situated externally on the tube substantially adjacent the weld line and propagating the ultrasonic waves across and through an area of the weld line;

means for measuring the reflected ultrasonic surface and shear waves and establishing signals indicative thereof, said measuring means identifying flaws in and around the weld line from the ultrasonic surface and shear wave signals;

logic circuit means for discriminating between inner and outer diameter flaws from the ultrasonic wave signals, an outer diameter flaw being determined by ultrasonic surface and shear wave signals exceeding preset levels, an inner diameter flaw being determined by the ultrasonic shear wave signal exceeding its preset level with the ultrasonic surface wave signal being below a noise threshold level; and

an alarm responsive to said logic discriminating means for signalling a flaw with a throughwall depth greater than or equal to the preset depth.

6. An apparatus as recited in claim 5, wherein the preset depth is a throughwall depth of about 10% or greater of tube wall thickness.

7. An apparatus as recited in claim 5, wherein said logic circuit discriminating means identifies outer diameter flaws having a throughwall depth of about 5% of tube wall thickness.

8. An apparatus as recited in claim 5, further comprising a carriage for holding at least two electromagnetic acoustic transducers.

9. An apparatus as recited in claim 8, wherein said carriage orients at least two electromagnetic acoustic transducers in a superimposed position.