RESISTANCE OF PIPE GRADE POLYETHYLENES TO HIGH SPEED CRACK PROPAGATION

RCsud- Les polykthyEnes (PE) de moyenne B forte densite pour tubes pressurisks sont caractkrisCs par une grande ductilitk et une haute rksistance aux faibles vitesses de propagation des fissures, mais les tubes extrudCs de PE testks sous pression de gaz peuvent supporter la propagation B haute vitesse (100-300 ms-I) des fissures axiales fragiles. La mCthode du test de Double Torsion B Haute Vitesse (HSDT) a CtC dCvelopCe pour mesurer la rksistance aux fissures aux conditions d'ktat stationnaire B haute vitesse stable. Comme l'indique le test des tubes, la rksistance aux fissures B grande vitesse dans les polyCthylknes est meme plus faible que celle suggCrCe par les tests conventionnels des impacts de Charpy. Abstract- Medium to high-density polyethylenes (PE) for pressure pipe service are characterised by high ductility and high resistance to low speed crack growth, but extruded PE pipelines tested under gas pressurisation can sustain axial "brittle " crack propagation at high speeds (100-300 ms-I). The High Speed Double Torsion test method has been developed to measure crack resistance under stable, high speed, steady state conditions. As the pipe tests indicate, resistance to a high speed crack in PE is even lower than conventional Charpy impact tests would suggest