Electrofusion welding

FT-IR spectroscopy has been used in the investigation of welding crosslinked polyethylene pipes [23]. Three types of crosslinking systems were used namely, peroxide (PEXa), silane (PEXb) and electron beam (PEXc). Scholten and co-workers [23] observed that only PEXa pipes have a satisfactory electrofusion quality. The strength of electrofusion welds of PEXb and PEXc pipes is not acceptable. The most likely explanation for the differences in weld quality is related to the adhesion theory and more specifically to differences in composition. Figure 5.6 shows the infrared spectra of medium density polyethylene (MDPE), PEXa, PEXb and PEXc. 

Techniques, used by the gas and water industries to join and repair pipelines, include butt fusion, electrofusion socket welding and socket jointing (309). The study of bond strength testing for solvent joints in piping systems has noted extreme sensitivity to minor variations in sample preparation (259). 

Section through a car bumper Three mouldings have been joined with electrofusion welds, to form a hollow beam, with high torsional and bending stiffness. 

The other popular type of electrofusion joint is the service saddle joint. This is used to make tee connections between a small diameter service and a larger diameter main pipe. These were also originally heated tool type welds but electrofusion reduces operative involvement and provides a greater level of control in fusion conditions. The technology has also been extended to larger size saddle connections that produce pipe branches that can be made whilst the main pipe is still under pressure. 

Electrofusion technology for PE joint connections is essentially common to gas, water and industrial applications of MDPE and HOPE pipes and, because the coupler does not require direct pipe to pipe welding, the method can be used to join PE pipes with dissimilar melt flow characteristics. Where pipework of mixed history may occur this is a considerable advantage over butt welding. Similarly pipes of the same outer diameter but differing thickness, which cannot be securely butt welded, may be electrofused. Electrofusion couplers have also been made for PP and PB industrial and heating pipe systems. 

Joining of plastic pipes is shown to be done more effectively, economically and in a much shorter time on-site by linear vibration welding , rather than the conventional hot plate welding or electrofusion welding techniques. 

New pipe concepts with multilayer structures, or so-called functional layers, have helped to expand the applications of HOPE. Pipes with special protective layers (on the outside and/or inside) can be laid without a sand bed under some circumstances. This significantly reduces the pipe laying costs. There have also been new developments in joining technology. For example, electric welding fittings up to 700 mm are now available. Electrofusion jointing of PE pipes for gas distribution is also applied. 

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