With ultrasonic inspection, material defects are detected by means of ultrasound. This way; even components that are already installed can be tested. First, a coupling aid is applied to the surface of the material, such as glue paste, gel, water or oil. This way, the sound from the probe can spread into the material. Subsequently, the surface is scanned with an ultrasonic probe. If a cavity or a crack is detected, either within the material or in a spot close to the surface, the sound pulse is reflected. The depth and position of the discontinuity can then be derived from the time that elapsed between sending and receiving the ultrasonic signal. Even the size, which is referred to as the discontinuity, is assessable. For this, a replacement reflector is used as a reference.
The ultrasonic inspection can be applied to all sound-conductive materials and is also used for the measurement of wall thickness, e.g. in power plants.
In the through-transmission method, Selenium probes are used. Their primary function is to measure doubling, or else, scan near-surface areas for which the reflection sound process is unsuited. It is applied in the HAZ (heat affected zone) in welding seam preparation, to ensure a top quality welding seam. The selection of probes is based on material thickness, attenuation and the standard requirements that have to be met.