TOFD Technique

The TOFD technique was first applied in 1985 at the Harwell Center (UK) in response to insistent requests to size cracks in nuclear reactor welds. The TOFD technique is a fully computerized system able to scan, store, and evaluate indications in terms of height, length, scan, store, and evaluate indications in terms of height, length, and position with a grade of coverage, accuracy and speed not achieved by other ultrasonic techniques. The TOFD technique is based on diffraction of ultrasonic energy from tips of discontinuities, instead of geometrical reflection on the interface of the discontinuities.

This phenomena makes TOFD effective for identifying cracks and lack of fusion located along the vertical axis of the weld (in particular for narrow gap preparation) or with any other orientations, because defect detection is not affected by unfavourable orientation to the primary sound energy angle. unfavourable orientation to the primary sound energy angle. These features have extended the use of TOFD to replace Radiography and complex Ultrasonic inspection by tandem technique wherever planar defects (cracks, lack of fusion) are the main object of examination.