Time Of Flight Diffraction
The Time of Flight Diffraction is nowadays widely used in the welding examination and has universally been recognized as the technique that allows to obtain the highest POD (Probability of Detection) index among the ultrasonic methods, as it does not depend on the defect orientation (planar and/or three-dimensional).
The detection is performed by the diffraction at the apices of a crack and/or along the cylindrical walls of a hole or a volumetric defect.
The TOFD technique can investigate a significant volumetric portion of the weld with a parallel-to-seam simple scanning line, so that the testing times are significantly reduced.
On the other hand:
- the detection and discrimination of discontinuities located in the sub-surface area from the inspection side is uncertain;
- with reference to the seam, the lateral position of the indication cannot be estimated;
- it is necessary to discriminate very low amplitude signals because of the use of small transducers;
- by increasing the material thickness, more scans or more simultaneous configurations are needed.
Metalprove S.r.l. puts into practice an innovative method with two Phased Array probes arranged in a TOFD configuration, so as to generate in sequence different focal laws to ensure the entire volumetric inspection required by the codes (ISO EN 16828, CEN/TS 14751, ASME Sec. V, ASME Sec. VIII, etc.).