Plastic Pipes Conference Association # 2006 Washington DC
Scholten, Shin
Ultrasonic detection equipment was used to investigate defective pipes and fusion joints. The following examples of its application are presented. Electro-fused joints were tested in four different 110mm PE100 and PEX pipes. The PEX pipes showed a less complete fusion between pipe and fitting in comparison to PE100 pipe, although there are also differences between the three types of PEX pipes. The slightly poorer joints showed internal surfaces at the fusion plane and hence a lower homogeneity of the fused material. These differences in joint quality correlate with the results of a new long-term testing method (the Slow Peel test) on the same four electro-fused joints. The differences noted by ultrasonic and Slow Peel testing were not seen using the traditional Peel test according to ISO 13954 at 23°C, performed in a tensile testing machine. PE pipes with many voids resulting from poor extrusion procedures were also inspected. At each of three locations in the pipe wall, more than one hundred individual voids could be counted. Butt-fused joints in these pipes also contained many voids. This correlated well with very poor tensile test results obtained on these joints. A defective jacket pipe from a district heating (hot water distribution) pipeline was investigated. Constant Tensile Load tests at 80°C according to EN 253 on strips taken from the jacket pipe showed a sub-standard long-term quality. Again, several voids were detected in the wall of the jacket pipe and these had clearly served as crack initiation sites. A further example was also from a district heating system. Jointed Polyethylene plugs to fill up holes in a shrink-sleeve were investigated. A brief comparison with other imaging techniques for defective PE pipe materials was made.
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