Ultrasonic Testing (UT)

Ultrasonic Testing (UT) is a specialist NDT discipline that can be used to identify surface and sub-surface discontinuities in many materials but typically metals. It is particularly useful during the integrity assessment of welds and plate materials at fabrication stage, but is also an important technique for in-service condition monitoring of pipework and structural welds.

The key advantages of UT are:

– It can provide accurate real time information on remaining wall thickness and can determine the rate of corrosion or erosion if such mechanisms are in existence.
– It can also show the size, orientation and shape of any defects deep within a weld / material.
– It can be used through coatings, eliminating the need for removal prior to inspection.

UT Theory

High frequency vibrations in the ultrasonic range (typically 5mHz) are produced within a probe unit and are transmitted into the test material. These waves travel through the test material until they are reflected back by a ‘reflector’ – this could be a crack, weld porosity, lamination or simply the physical edge of the test piece specimen. Any reflected ultrasound is detected by a receiver in the probe. As ultrasound travels at a fixed speed in any given material, and the angle of travel (incidence) is fixed by the choice of probe used, the distance the ultrasound has travelled to its reflector can be calculated (known as the beam path distance). Ultrasound therefore enables the location and physical dimensions of any defect to be calculated to a high degree of accuracy.