Effect of axial surface scores on rapid crack propagation in polyethylene pipe

Above a critical pressure and below a critical temperature, an internally pressurised plastic pipe can fail by sustained, axial, Rapid Crack Propagation (RCP). The fracture resistance of ductile pipe-grade polyethylenes is greater under plane stress than under plane strain – a fact which has important implications for large, thick-walled pipes. Previous small scale ISO 13477 ‘S4' tests on pipe have shown that a sharp, axial score on the inside pipe surface can suppress plane stress deformation during RCP, significantly reducing the critical pressure and increasing the critical temperature. This paper reports further results from S4 tests on specimens with sharp internal and external notches of controlled depth. The results are discussed in terms of ability of surface scores and notches to attract and guide cracks under different modes of pipe wall deformation, as well as their effect of reducing the resistance of the material to them.