Description:
LFI longitudinal wave probes (TRL) are used to inspect Welds in austenitic material such as pressure vessels welds in the nuclear industry, which are often difficult to inspect with conventional angled beam probes due to the high level of dispersion noise they can generate. TRL probes (TransmitReceive-Longitudinal), as indicated by the name, use two different crystals for the transmission and the reception of the signal and generate refracted longitudinal waves. The overlapping surface
of the transmission and reception beams creates a natural focal zone in which sensitivity is maximized, whereas the longer wavelength of longitudinal waves reduces the acoustic diffusion of the graininess. Furthermore the use of different elements for transmission and reception allows to minimize unwanted noise during high-gain inspections. These probes are very sensitive to the reflectors located in the focal area. Creeping wave probes (SCR) are a special kind of dual element longitudinal waves probe, which generate compression waves in the test material at an angle between 70° and 90°. These waves, commonly called creeping waves, propagate sub-superficially to the surface of the piece under examination. Simultaneously with the creeping waves, a transverse wave beam is generated at an angle of about 32°. Creep probes are suitable for detection and the sizing of defects close to the surface such as, for example, IGSCC (intergranular stress corrosion cracking). The field being inspected is short due to the rapid decay of ultrasound energy. Usually, the most sensitive point, the so-called “Focus” is right in front of the probe itself. There focus distance varies up to 20 mm and the maximum useful range is typically 45 mm.
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