Although originally developed as an accurate defect sizing and characterization tool, Time of Flight Diffraction (TOFD) is now universally accepted as a fast and reliable method of detection.

More importantly it generates an immediate dimensionally proportionate image of the integrity-critical through wall elevation, showing embodied defects in true size and location, whilst simultaneously providing an accurate profile of the back wall - making the technique also suitable for corrosion and erosion assessment.

Unlike pulse echo ultrasonic methods (including Phased Array) and radiographic techniques which measure the recorded change in captured energy (which can be influenced by many factors, other than defect size) TOFD uses the measurement of time (and therefore distance) to establish the presence, position and extent of defects.

Today the technique is prescribed in all major inspection codes but, as with all inspection techniques, TOFD has its limitations - most notably near surface resolution due to the presence of a lateral wave. However, the benefits of this method of testing massively out way the drawbacks.


The benefits include -

 Non-invasive - requires access to one side only

 Can be used on stream - remotely & at elevated temperature

 Effective on thick wall material - above 6mm

 Non-comparative - enables absolute size measurement

 Proven POD and repeatability - with low FCR

 High resolution - can be accurate to within +/- 0.1mm

 Relatively insensitive to defect orientation and surface condition

 Sensitive to integrity critical defects - cracks, LOF, structural damage

 Fast (full) volumetric coverage - up to 10m/hr

 Couplant status automatically monitoring

 Immediate presentation of 'through wall' image - incl. back wall & clad interface

 All 'raw data' captured & stored electronically

 Code compliant and accepted by most certification bodies

 Safe and non-disruptive



Specialized Inspections Co. Ltd & Testing Services has a considerable amount of experience in the use of TOFD in a wide variety of applications across many industrial sectors. This ranges from very sophisticated applications involving the detection, sizing and characterization of micro-structural anomalies on metallurgically and geometrically complex components to routine weld quality testing and back wall profiling on process pipe work, pressure vessels and storage spheres.

This knowledge may be of particular value in those situations where the logistics, cost or productivity implications demand careful consideration and applications where accurate and repeatable condition monitoring is called for.

Specialized Inspections Co. Ltd. provides AUT services on vessels and pipings.

NDT Inspection and Testing > TOFD

Time Of Flight Diffraction (TOFD)