Ultrasonic Tests (UT)
Ultrasonic Tests (UT) are generally termed as a volumetric method of non destructive testing.
Ultrasonic Tests are primarily used to find internal imperfections in welds or other product forms such as forgings, plate sections etc. As one of the most common and popular non destructive weld testing methods, UT weld inspection is primarily concerned with testing the thickness of a material to check for imperfections to the material such as erosion/corrosion and also laminations. The main principle of ultrasonic inspection is to transmit a sound wave into a structure, using the same transducer to pick up ultrasonic reflections of the original wave, which it then examines to create a picture of the structure and its thickness.
Ultrasonic inspection can sometimes be specified to ensure no laminations are present in materials that are to be subsequently welded in highly stressed joint configurations or, even after welding has taken place, to ensure imperfections such as lamellar tearing have not occurred during the welding operation.
How Does Ultrasonic Inspection Work?
During an ultrasonic test of welds, a strong specular reflection is required to resolve a flaw response from the background noise level with pulse-echo ultrasonics. For planar flaws (cracks, lack of fusion, etc.) a specular reflection will only result if the ultrasonic beam is normal (or near normal) to the plane of the flaw. Angled beam shear wave probes are commonly used for manual ultrasonic inspection in ferritic steels, as these provide the only way of directing ultrasound into the weld body when the cap reinforcement is still present. Where a weld cap restricts probe movement, the sound can be reflected off the bottom surface and directed into the weld body under the cap.
Where sound is angled directly at the area of interest, this is referred to as “half skip testing”. “Full skip” testing occurs when the bottom surface is used to reflect the sound before it enters the weld.
For a typical girth weld, a 45° probe is used for inspecting the root region, and 60°/70° probes for the sidewall fusion faces and weld body. The behavior of the echo-dynamic pattern and shape of the flaw response (with respect to probe movement) can be used to identify the type of flaw, estimate the length, and, in some cases, the through-wall height of the flaw.
What will Ultrasonic Inspection find?
What gives ut weld inspection an advantage over weld testing methods is that it will detect most manufacturing flaws (lack of sidewall fusion, lack of root fusion, lack of root penetration, porosity, solidification cracking, etc.) and in-service flaws (fatigue cracking, stress corrosion cracking, etc.).
Where Is Ultrasonic Non Destructive Testing used?
The ultrasonic method is used for the inspection of welds made in both ferritic and non-ferritic metals in pressure vessels, pipework, storage tanks, bridge structures etc.
Our UT weld inspection services can be offered on or off-site to suit our customers’ needs. Contact us to enquire.