Claims
- 1. 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.
- 2. A method as recited in claim 1, further comprising the step of scanning the boiler tube for corrosion fatigue cracks.
- 3. A method as recited in claim 1, wherein the ultrasonic SH shear waves are generated in a frequency ranging from 1 MHz to 4 MHz depending upon the tube diameter and wall thickness.
- 4. A method as recited in claim 3, wherein the frequency of the ultrasonic SH shear waves is adjustable with a range of 1 MHz to 4 MHz as required.
- 5. A method as recited in claim 4, wherein the predetermined beam angle is determined by the tube size and obtained by adjusting the frequency to obtain the desired beam angle by a relationship of sin .crclbar.=c/2Df
- where:
- f=frequency
- c=shear wave velocity
- D=separation between adjacent conductors in an EMAT coil.
Parent Case Info
This is a continuation of application Ser. No. 08/089,881 filed Jul. 12, 1993 now abandoned.
US Referenced Citations (4)
Non-Patent Literature Citations (1)
Entry |
Power Engineering, May 1992, "A Vision for Reducing Boiler Tube Failures: Part II", Barry Dooly, Electric Power Research Institute. |
Continuations (1)
|
Number |
Date |
Country |
Parent |
89881 |
Jul 1993 |
|