A study on the slow crack growth resistance in PE 100 pipes

Slow crack growth (SCG) resistance was studied in pipes made from three grades of PE 100 produced by leading European manufactures (Table 1). The PE pipe material was characterized in terms of melt flow rate (MFR) (Table 2), degree of crystallinity (Table 5), oxygen induction time (OIT) (Table 4), IR spectra (Figs. 4-7, Table 3), tensile yield, elongation at break (Table 6), and Char-py's notched impact strength (Table 7). Samples were cut out from pipes before and after the pipes had been submitted to the pressure test. The test was to determine the period of time required for a pipe heated at a temperature of 80 degrees C to break after a pressure of 4.6 MPa had been applied to the wall of the pipe The studies showed the pipes to differ essentially in the SCG resistance. The best PE pipe required a period of time five times as long as that required by the worst PE pipe to break (Fig. 2). These difference are not reflected in the fundamental mechanical property data nor in the features of molecular and supramolecular structures of the polyethylenes.