Plastic Pipes Conference Association # 2004 Milan
Istituto Italiano dei Plastici (I.I.P., Italian Institute of Plastic Materials) sponsored and supported a research work to investigate and define the remaining life time of PE pipes which were in operation for several years to convey potable water in municipal waterworks. Specifically the investigation has been carried out on four samples of PE pipes, which have been in continuous operation for 8 to 14 years at pressure ranging from 3.5 to 10 bar in different Italian municipal waterworks. The samples of PE pipes, which have been subjected to investigation have been originally produced by different Italian pipe manufacturers using as raw material PE type 63 of different producers and have been originally certified by I.I.P. as conforming to the norm UNI 7611 : 1976 and, on this base, had the mark IIP-UNI. The four recovered samples aged in operation were characterized as it concerns physical mechanical features, thermal stability and type of fracture. The comparison of the experimental data of resistance to the stress of the aged pipes at 80 and 60°c with the corresponding data of the original pipes (with life time zero) evidences a significant decrease; specifically the resistance to the stress of the aged pipes is similar to that of pipes manufactured from a raw material PE type 40 and apparently the original PE-63 degradated with the time in exercise to PE 40. Furthermore the inner surface of the aged pipes were found to show a continuous oxidized layer (few micrometer of thickness) containing carbonyl groups and the fractures, which initiated from morphological discontinuities and defects, were brittle. In spite of the apparent degradation of PE raw material from 63 to 40, the evaluation of the residual life time of the aged pipes (done following the methodology ISO/TR 9080 and assuming the timetemperature proportionality factor of the original PE material) results to be well above the overall life time of 50 years with the pipes continuing to work in operation at pressures ranging from 3.5 to 10 bar.