NDTnet 1998 Aug, Vol.3 No.8

Abstract

Some defects are very difficult to detect by means of ultrasonic soundness inspection because of their rounded and lied appearance. An other method permits to detect this kind of defect in laboratory investigation; this is the method of the thickness measurements. We suggest a different type of detection suitable for industrial use. This is the "Detection Vallourec" method internally called the "D.V" method. The Vallourec Detection method pitch-catch method which uses two transducers, one of which transmits and the receives. The inspection area is parallel to the generating of the tube. The transducers be held at an angle of 11° in order to generate a sufficiently long series of reflections in the tube being inspected. Using this incidence angle, numerous echoes are generated in the part. These echoes are generated by transverse waves, longitudinal waves and converted wawes which are reflected off the internal and external tube walls. In the configuration shown in figure 1, the receiver is positioned in such a way to detect the maximum energy from transverse waves. According to the features of the receiver (surface area, frequency), it also detect longitudinal waves and converted waves. In the presence of a defect, part of the ultrasonic beam is deviated by the defect and is therefore not detected by the receiver. In the configuration shown in the figure 2, the maximum energy of the transverse waves is no longer detected. The receiver receives a series of waves of much lower amplitude. important to note that this technique also enables similar defects on the external wall detected. For this type of defect the ultrasonic beam is also deviated and the amplitude of the echoes detected by the receiver is much weaker than if there was no defect. The disadvantage of this method is that it generates a lot of background noise. To reduct noise, the signal analysis is applied on the echodynamic of the signal in real time. The filtering parameters have to be calibrated using an external artificial defect ground to minimum depth required by the A.P.I (12,5% of the tube) in real time. This method gives good results in industrial conditions of control.

Figure 1 ; Figure 2

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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