Time of Flight Diffraction (TOFD)
Time of Flight Diffraction (TOFD) is an automated, highly reliable ultrasonic non-destructive examination technique developed for rapid weld screening and unmatched flaw sizing accuracy in thick-walled pressure vessels, storage tanks, and critical structural components.
Whilst conventional ultrasonic testing relies principally on the amplitude of reflected acoustic waves (which inherently varies with defect orientation and surface roughness), TOFD measures the precise time of flight of diffracted waves emitted from the extremities and tips of discontinuities. A transmitter probe and receiver probe are positioned symmetrically astride the weld seam; the transmitter emits a wide longitudinal beam, whilst the receiver detects the lateral wave along the near surface, backwall reflections, and diffracted signals from flaw tips.
Because TOFD measures arrival times rather than amplitude, it achieves exceptional through-wall crack height and depth measurement precision (within ±0.5 mm), regardless of defect orientation. When deployed in tandem with PAUT, TOFD provides comprehensive volumetric coverage fulfilling ASME Code Case 2235, BS EN 10863, and stringent EPC engineering specifications.
Key Technical Highlights & Capabilities
Sub-Millimetre Flaw Sizing Accuracy
Diffracted wave physics yields through-wall flaw depth and height precision within ±0.5 mm.
Flaw Orientation Independence
Detects mid-wall planar flaws, lack of sidewall fusion, and vertical cracks with uniform sensitivity.
High-Speed Automated Scanning
Encoder-synchronised scanners evaluate linear metres of heavy-wall weld seams rapidly in a single continuous pass.
Synergistic PAUT & ASME Code Compliance
Synergistic PAUT and TOFD methodology fulfills ASME Code Case 2235 and API 620/650 vessel validation criteria.
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