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 Internacional de Plasticos para la Agricultura (I Congreso Argentino CAPPA – VIII Congreso Iberoamericano CIDAPA – XVII Congreso Internacional CIPA); 2006

To have water in the specific place and time is a very important feature in agriculture field. Plastic pipes have been used for this purpose in an adequate way. And their use is in expansion because of their good mechanical properties and corrosion resistance combined with their low weight and excellent quality to cost ratio. Piping made from polyethylene is a cost effective solution for a broad range of piping problems in municipal, industrial, marine, mining, landfill, duct and agricultural applications. It has been tested and proven effective for above ground, surface, buried, floating, and sub-surface marine applications. Medium density polyethylene pipe (MDPE) can carry potable water, wastewater, slurries, chemicals, hazardeous wastes, and compressed gases. In fact, polyethylene pipe has a long and distinguished history of service to the agriculture field. The joining or assembly of polymeric components is a critical manufacturing step. With the increasing demands for plastics and their composites used as components, the requirements for joining them have increased. Fusion bonding, or thermal welding, is a long established technology in the thermoplastic industry where the efficiency of the welded joints can approach the bulk properties of the adherents. The strength of the weld will depend upon the welding parameters. Static tensile testing of welded joints is one of the direct ways of joint quality assessment [Rotheiser, J. Joining of Plastics. Handbook for Designers and Engineers, 2nd Edition, Hanser Publishers, Munich, (2004); Stokes, V.K., “Experiments on the hot-tool welding of three dissimilar thermoplastics”, Polymer 39, 2469-2477 (1998); Stokes, V.K., Conway, K. R, “A phenomenological study of the hot-tool welding of thermoplastics. 4: Weld strenght data for several blends”, Polymer 42 7477-7493 (2001)]. Fracture toughness can also be used to characterize welded joints [Allen, N.S., Plamer, S.J., Marshal, G.P., Luc-Gradette, J., “Enviromental oxidation process in yellow gas pipe: implications for electrowelding”, Polymer Degradation & Stability 56, 265-274, (1997); Pfeil, M.C., Kenner, V.H., Popelar, C.H., “A fracture mechanics evaluation for the life expectancy of polyethylene butt fusion joints”, Engineering Fracture Mechanics 44, 91-107 (1993)]. In this work we have combined static uniaxial tensile tests and impact experiments with optical microcopy and thermal analysis to gain a deep characterization of the failure behavior of welded polyethylene pipes used for water transportation.