Medium-density polyethylene piping

With a satisfactory performance from the 38 mm CTM, a 120 mm unit was fitted as a replacement for the toothed plates of an existing turbine mixer attached to the production extruder producing LDPE and medium-density polyethylene pipes to British Standards (Figure 9.13). The unit ran satisfactorily in all respects and very significantly reduced... 

Viebke, J., Bible, E. et al. Degradation of Unstabilized Medium-density Polyethylene Pipes in Hot Water Applications, Polymer Engineering and Science, 34 (1994) 17, p. 1354- 1361... 

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. 

Another 140,000 tonnes of medium density polyethylene was used in Europe s gas pipes in 2002. 

For applications up to 1400 kPa (200 psi), high-density polyethylene pipes are available for a number of low to medium abrasive slurries. 

Excavations following the accident uncovered, at a depth of about 3 feet, a 4-inch steel main. Welded to the top of the main was a steel tapping tee manufactured by Continental Industries, Inc. (Continental). Connected to the steel tee was a 1/2-inch plastic service pipe, (see Figure 13.2.) Markings on the plastic pipe indicated that it was a medium-density polyethylene material manufactured on June 11, 1970, in accordance with American Society for Testing and Materials (ASTM) standard D2513. The pipe had been marketed by Century Utility Products, Inc. (Century). The plastic pipe was found cracked at the end of the tee s internal stiffener and beyond the coupling nut. 

Mruk, S. A., Validating the Hydrostatic Design Basis of PE Piping Materials, and Bragaw, C. G., Eracture Modes in Medium-Density Polyethylene Gas Piping Systems, Plastics and Rubber Materials and Applications, pp. 145-148, November 1979. 

Ethene MDPE, medium-density polyethylene ZIegler-Natta, metallocene catalysis Gas pipes, refuse sacks, plastic bags... 

The development of medium and high density polyethylene pressure pipes over the last thirty years has led to an extensive database on their stress-rupture behaviour, with associated standards for their testing and the interpretation of results [1, 2], Various forms of PVC are also used. The accelerated testing of gas and water pipes is introduced as an example of a field where there is a large database of pressure testing on which current regulations are based, the number of polymers is limited and accelerated tests are widely used (unusually, with two accelerating parameters). 

Medium Density High Density Polyethylene MDPE (or MDHDPE) is produced by copolymerization of ethylene with a-olefins using Ziegler-Natta, supported chromium or single site catalysts. MDPE cannot be produced by free radical polymerization. MDPE has a linear structure similar to LLDPE, but comonomer content is lower. Density is typically 0.93-0.94 g/cm. MDPE is used in geomembrane and pipe applications. 

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