Failure analysis of welded joints of polyethylene pipes for water transportation

SILVINA DE MICCO; LEANDRO LUDUEÑA; VALERIA PETTARIN; PATRICIA FRONTINI

Buenos Aires, Argentina

Congreso; Congreso Plasticultura; 2006

CAPPA, Comité Argentino de Plásticos para la Producción Agropecuaria

In this work a mechanical characterization of but fusion welded joints of polyethylene pipes was assessed. Quasi static tensile and high-speed Charpy impact tests were conducted on welded specimens in order to evaluate the difference in properties of a medium-density polyethylene pipe substrate and fusion joint. Calorimetric results showed that a variation of the degree of cristallinity was generated by the welding process, exhibiting a lower value in the welded joint and its surroundings. Features of quasi static tensile curves were similar for welded and non-welded specimens. Tensile apparent strength was slightly lower for welded samples but a noticeable detriment in their elongation capability was detected. Regarding impact tests, in all cases the impact energy of the fusion joints were much (almost 40%) lower than that of the substrate. Microstructure of fusion zones, such as degree of crystallinity and orientation, is different from that of the pipe substrate. Sufficient plastic deformation before fracture does not seem to be able to occur when joints are subjected to impact loading. This phenomenon may be caused either by the change in supermolecular structure induced by the thermal treatment supported by parent material during welding, or by the lack of chain interdiffusion at the interface.