High-strength and slow-speed-stress-cracking-resistance polyethylene pipe and preparation method thereof

The invention discloses a high-strength and slow-speed-stress-cracking-resistance polyethylene pipe; and 95-99.9 weight parts of conventional polyethylene and 0.1-5 weight parts ultrahigh molecular polyethylene with molecular weight not smaller than 1000000 g/mol are fully mixed, and are put in a polymer pipe rotation extruding device for melting, rotating, extruding, cooling and sizing with the rotating speed of 1-24 rpm/min, the temperature of a melting section of 180-260 DEG C and the temperature of a mouth mold section of 170-220 DEG C by using any one mode of single rotation of a core rod, single rotation of a mouth mold, synchronous rotation of the core rod and the mouth mold in the same direction or synchronous rotation of the core rod and the mouth mold in opposite directions. The annular strength of the obtained pipe under the testing conditions of 80 DEG C and static hydraulic pressure is 5.69-7.28 MPa; and under the standard pressure of 120%, the damage time exceeds 1000 hours. As the relaxation time of polyethylene molecules in a molten state can be prolonged, the formation of serial crystals and the arrange directions thereof in polymer pipes are effectively controlled to form and construct orientation structures deviated from the axial direction, and the annular strength and the slow-speed stress cracking resistance of the polyethylene pipe are greatly improved.