• • • •
Not amplitude base method Diffracted signals Matched angle probes Longitudinal wave
• LW and BW have a opposite phase • A=C • B=DProbe Configuration
Highly damped broad band High frequency 10-15MHz Small diameter 1/4”, 5/8”
Wall Thickness (mm) 32 Probe Parameters 5/8” x 15 MHz ¼” x 10MHz 2-sets ¼” x 10MHzCodes and Specifications
• BS 7704 -Guide to calibration and setting up of the ultrasonic time of flight diffraction technique • ENV 583-6 - Defines the general principles for theapplication of TOFD technique for both detection and sizing of discontinuities
The advantages of TOFD
1. TOFD defect detection does not depend on the defect orientation, in contrast to the pulse echotechnique. Safety net. 2. Defect height can be determined. 3. The inspection results are immediately available, as is a permanent record. 4. High-test speed. It possible to perform scans with a speed ofhundreds of millimeter per second. 5. High probability of defect detection. 6. Most efficient for inspection of thick-wall. 7. TOFD can be used in high temperature environment. 8. The entire volume canbe inspected using a single pass. 9. TOFD can detect the lamination. 10.TOFD is safe and environmental friendly method.
The disadvantages of TOFD
1. Sensitivity level: If the instrumentsensitivity (gain) is set on very low level, the TOFD image would display no diffracted echo. If the instrument sensitivity is set just above electronic noise level, the TOFD image will display a lot ofdiffracted echoes, which are caused by very small indications. 2. Flaw size determination: In practice, diffracted echoes at flaw tips are not so clear. That can make sizing with the TOFD techniquedifficult. A TOFD image inspector needs to perform depiction decisions similar to that used in radiography. 3. Detection of small flaws at backside: Close to the back wall the flaw tip echo amplitude is...