Crosslinked polyethylene piping systems

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. 

ISO 15875-1 2003 Plastics piping systems for hot and cold water installations - Crosslinked polyethylene (PE-X) - Part 1 General... 

ISO 15875-5 2003 Plastics piping systems for hot and cold water installations - Crosslinked polyethylene (PE-X) - Part 5 Fitness for purpose of the system ISO/TS 15875-7 2003 Plastics piping systems for hot and cold water installations - Crosslinked polyethylene (PE-X) - Part 7 Guidance for the assessment of conformity... 

For hot water systems, (i.e., in underfloor heating systems and for hot water distribution), pipes are mainly polybutylene (PB), which can be used in systems with a continuous operating temperature of 82 °C and can survive short peak temperatures of up to about 110 °C, as well as crosslinked polyethylene (XLPE) with improved creep resistances, that can withstand operating temperatures for the same range as PB. The heat dispersion is optimised by these plastic piping systems by using the heat storing capacity of the floor. 

An example system is PVC and polyethylene wire and cabling irradiated to improve stresscracking resistance, abrasion resistance, high-temperature properties and flame retardance, via controlled electron-beam crosslinking (Loan, 1977). Additionally electron-beam crosslinking is utilized to impart memory into a polymer system, such as crosslinked PE materials for heat-shrinkable films and pipe applications (Baird, 1977). The control of electron-beam processing has advanced the quality of cell size and shape of PE foams via control of crosslink distribution (Paterson, 1984). 

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