Time-of-Flight Diffraction (ToFD)
ToFD uses two longitudinal wave (L-Wave) angle beam transducers arranged symmetrically opposite to each other. One probe acts like a transmitter of ultrasonic energy while the other probe as receiver, in a pitch-and-catch mode. A single -axis scan with encoder recording the position of the weld enables the display of digital images in real time. ToFD detects and records signals diffracted from defect tips for both detection and sizing. The TOFD data is displayed in a grayscale B-scan view.
ToFD approach for inspection of welds has been accepted by ASME for in lieu of radiography, ASME CC 181 and CC 2235-9. ToFD has an accuracy for measurement of remaining wall loss is estimated typically as ± 0.75 mm. The accuracy of measurement of change of wa II thickness within a single scan is estimated at ± 0.50 mm.
Advantages
- Utilizing diffracted signals, detectability does not depend upon defect orientation.
- The setup is independent of weld configuration.
- No difficulty in detecting planar defects or cracks in any orientation.
- Defect height can be accurately measured.
- Inspection results are readily available
- High speed and high repeatability in performing inspection
- More economical compared to radiography for thicknesses above 25 mm
- Inspection can be performed at the range of 200 °C.
- High portability and versatility lets it to be used in difficult to access areas via rope access.
Applications
- New and existing welds with minimum wall thickness 7 mm and above.
- For service induced defects & structural damage
- Stress/ chemically assisted micro cracking – SCC, LTHA
- Components with high wall thickness
- Corrosion/ erosion profiling
- Pressure systems, vessels, tanks, spheres, pipelines etc.