ToFD (Time of Flight Diffraction) is a type of non-destructive testing (NDT) that is used to detect and size defects in welds. ToFD uses ultrasonic waves to inspect the weld and determine the presence and size of any defects, without causing any damage to the material.

ToFD is based on the principle of time of flight diffraction, which states that the time it takes for a sound wave to travel between two points is affected by the presence of defects. ToFD uses two sets of transducers, one to transmit a pulse of ultrasonic energy and the other to receive the reflected signal. The time it takes for the sound wave to travel between the transducers and reflect off a flaw is measured and used to calculate the size and location of any defects in the weld.

ToFD is considered to be a highly accurate and reliable method for detecting and sizing defects in welds, and it is often used in the construction and maintenance of pipelines, pressure vessels, and other critical structures. ToFD inspection is also faster and more efficient than other NDT methods, such as radiography, because it allows the inspector to scan a larger area in a shorter amount of time.

ToFD inspection is performed by trained and certified NDT technicians who use specialized equipment to generate and detect the ultrasonic waves. The equipment consists of a control unit, a pulser/receiver, and a pair of transducers. The control unit is used to generate and control the ultrasonic pulses, while the pulser/receiver is used to amplify and measure the reflected signal. The transducers are used to generate and detect the ultrasonic waves, and they are typically mounted on a scanning device that allows them to be moved across the weld.

ToFD inspection is typically performed in two steps: setup and data acquisition. During the setup phase, the technician selects the appropriate parameters for the inspection, such as the type and frequency of the ultrasonic pulse, the angle of incidence, and the sensitivity of the receiver. The technician also positions the transducers and calibrates the equipment to ensure that it is properly set up for the inspection.

During the data acquisition phase, the technician uses the scanning device to move the transducers across the weld, while the control unit generates and receives the ultrasonic pulses. The reflected signal is then processed by the control unit and displayed on a screen, where the technician can analyze it to identify and size any defects in the weld.

ToFD inspection provides a number of advantages over other NDT methods. It is highly accurate and reliable, and it is capable of detecting and sizing small defects that may be missed by other methods. It is also faster and more efficient, allowing the technician to scan a larger area in a shorter amount of time. Additionally, ToFD inspection is non-destructive, meaning it does not cause any damage to the material being inspected. Overall, ToFD inspection is an important tool for ensuring the integrity and safety of welded structures.