TIME OF FLIGHT DIFFRACTION (TOFD)
Time-of-Flight Diffraction (TOFD) is an advanced non-destructive testing (NDT) technique that utilizes ultrasonic waves to detect, locate, and accurately size defects in welded joints. Recognized for its high precision, TOFD employs longitudinal ultrasonic waves, which provide more reliable flaw sizing than conventional shear-wave ultrasonic testing methods.
The TOFD technique uses two ultrasonic transducers positioned on opposite sides of the weld. One transducer transmits ultrasonic pulses through the material, while the other receives the diffracted signals generated by the tips of any discontinuities or defects. By measuring the time of flight of these signals, TOFD can accurately determine the location, depth, and size of flaws, even when the defects are not directly aligned with the ultrasonic beam.
TOFD offers several significant advantages, including rapid inspection speed, full volumetric weld coverage, high sizing accuracy, and excellent repeatability. The technique is also highly adaptable to a wide range of weld configurations and component geometries, making it suitable for both fabrication and in-service inspections.
TOFD is widely applied in the inspection of critical welded structures, including pressure vessels, power plant piping, process pipelines, and other safety-critical components. It is also highly effective for monitoring fatigue cracks, stress corrosion cracking (SCC), and creep damage, enabling condition assessment and supporting safe operation until scheduled maintenance can be performed.
With its exceptional accuracy, speed, and reliability, TOFD has become an indispensable inspection method for ensuring the structural integrity and operational safety of critical assets across industries such as oil and gas, power generation, petrochemical, and manufacturing.
