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US 5,526,691 AGranted
Detection of corrosion fatigue cracks in membrane boiler tubes
AssigneeThe Babcock & Wilcox Company
InventorsPaul J. Latimer, Daniel T. Maclauchlan
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Abstract
A method for detecting corrosion fatigue cracks in membraned boiler tubes in a membrane tube panel employs at least one EMAT coil generating ultrasonic SH shear waves at a predetermined beam angle. The method of the present invention provides better signal-to-noise ratios than conventional ultrasonic techniques as well as not requiring any couplant.
Claims5
A method for detecting corrosion fatigue cracks in boiler tubes, comprising the steps of:
- positioning two electromagnetic acoustic transducers externally on a boiler tube of a boiler tube membrane tube panel, one electromagnetic acoustic transducer being positioned at approximately 120.degree. and the other at approximately 170.degree. adjacent the boiler tube;
- generating ultrasonic SH shear waves with at least one of said electromagnetic acoustic transducers;
- propagating the ultrasonic SH shear waves into the boiler tube at a predetermined beam angle with an adjustable frequency with the ultrasonic SH shear waves undergoing no mode conversion upon successive bounces as the ultrasonic SH shear waves propagate around the boiler tube;
- measuring the returned ultrasonic SH shear waves from the boiler tube with at least one of said electromagnetic acoustic transducers;
- and
- determining from the returned ultrasonic SH shear waves any corrosion fatigue cracks with data acquisition means.
3 more elements
Dependencies are inferred from the claim text.