Gueugnaut Dominique
# 2012 Barcelona
(Polyethylene, Non destructive technique, Ultrasonic Phased Array, Slow Crack initiation time) Since a few years it has been proved that - among the available concepts - the Ultrasonic Phased-Array technique (PA UT) was one of the most promising candidate for Non Destructive and Non Intrusive analysis of PE and especially PE welds. In this context, in parallel to an in-depth evaluation of this technique applied to the characterization of the PE welds, GDF SUEZ’ Research & Innovation Division has decided to evaluate the capability of the PA UT in detecting and measuring the defects – either artificial or natural - located at the inner surface of the pipes. One of the major issues is to be able to detect and measure accurately the defects produced by the squeeze-off operation. The other important issue is to be able to detect the Slow Crack Initiation time in the pipe wall during its overall lifetime. The capability of the PA UT for the detection of faults in PE pipes from 20mm to 110mm was proven through a series of tests including artificial notches located at the inner surface of the pipes. Moreover the technique has proved its efficiency for the dimensioning of the defects in certain cases. Consequently it was decided to evaluate such a technique for detecting the initiation time for Slow Crack Growth (SCG) on both a notch-free and a double-notched 90mm old pipe. The preliminary tests carried out in a water/water environment failed in detecting the initiation time. The preliminary tests carried out in a water/water environment failed in detecting the initiation time. Changing the test environment (air/air) seems to be better for damage detection in terms of ultrasonic response, but at the time being the available data do not permit to detect any clear evolution with time of the dimensions of the notches machined at the inner surface of the pipe.
