Ultrasonic Testing, also called Ultrasonic Flaw Testing or simply UT, uses high frequency ultrasonic waves to detect surface breaking and internal imperfections, measure material thickness and determine acceptance or rejection of a test object based on a reference code or standard. Flaw detection is a fast and accurate inspection method to evaluate internal product integrity. Ultrasound penetrates deeply into materials searching for defects, cracks, delamination, lack of bonding and other discontinuities.

Shear wave Ultrasonic Testing or A-scan testing transmits an ultrasonic wave at a predetermined angle into the test material. Surfaces normal to the beam path and cornertraps reflect the wave energy back to the transducer. The display shows the distance the wave travelled to the imperfection and the relative strength of the energy.

Ultrasonic Testing is mostly used to guarantee the integrity of critical welds in process equipment or structures but can also be used to detect and/or quantify defects occurring in other locations. The testing is often applied directly after the welding process. If welds are identified to be out of specifications, the weld will be grinded down and re-welded. Ultrasonic Flaw Testing has big advantages over RT as there are no radiation risks and it does not interfere with work in surrounding areas.

There are many different advanced Ultrasonic Testing techniques and variations of the technology such as Phased Array and Time of Flight Diffraction (TOFD) and Dacon is well qualified in all UT techniques from thickness gauging through to corrosion under support testing.

Some of the advantages and disadvantages of Ultrasonic Testing are:
Internal defects can be detected and sized
Same time frame needed for measuring thick or thin test pieces
Only need to access one side of the test piece
No radiation hazard
Planar defects of any orientation can be detected
Operator skill and experience is essential
No permanent record of the inspection as there is in radiography
Misreading of signals, can result in unnecessary repairs