Patent ID: 7086421

Claim:
A multilayer crosslinked polyethylene (“PEX”) pipe comprising: (a) an inner tubular core of high density polyethylene (“HDPE”) having a maximum wall thickness from about 28 to 100 times smaller than the nominal diameter of pipe in the range from 7 mm (0.25″) to 152 mm (6″), ratio 28 being attributable to small diameter non-SDR-9 piping, and ratio 100 being attributable to the larger diameter SDR-9 pipe, wherein the HDPE has a density in the range from 0.941 g/cc to 0.963 g/cc; and, (b) an outer tubular sheath of at least one layer of a crosslinked polyethylene contiguous with the outer surface of the inner core layer, wherein said PEX is crosslinked to a gel level of at least 65% by a silane grafting process.