Abstract: A method of rotationally molding a large-diameter pipe fitting, the wall structure of which is characterized as having a generally smooth interior surface and an exterior surface that is defined by a plurality of axially-spaced circumferentially extending ribs which are monolithically formed and homogeneous with the smooth interior surface of the fitting. The fitting is seamless and modularly designed with integral coupling elements at each terminal end, and with a ribbed wall structure profile capable of withstanding the loads typically found in buried applications with watertight performance requirements, where such ribbed wall structure meets the following dimensions and dimensional ratios: Rib Sidewall Angle (95-105 degrees); Bottom/Top Rib Thickness Ratio (1.80-2.80); Pitch/Rib Height Ratio (1.50-1.95); Rib Height/Fitting Diameter Ratio (0.04-0.09); and Avg. Rib Thickness/Rib Height Ratio (0.28-0.40).

Abstract: High flow capacity corrugated coilable dual wall plastic pipe having improved longitudinal flexibility and a bend radius sufficient to permit coiling and plowing of such pipe into the ground using automated installation equipment. The coilable dual wall pipe has an outer corrugated wall formed of a thermoplastic material such as high density polyethylene, and an inner smooth wall formed of a different more flexible and resilient thermo-bondable material that has an enhanced strain capacity and lower modulus of elasticity. The inner wall material also has enhanced mechanical properties which generally improve processing and help prevent excessive drag and tearing of the liner material during the manufacturing process.

Abstract: High flow capacity corrugated coilable dual wall plastic pipe having improved longitudinal flexibility and a bend radius sufficient to permit coiling and plowing of such pipe into the ground using automated installation equipment. The coilable dual wall pipe has an outer corrugated wall formed of a thermoplastic material such as high density polyethylene, and an inner smooth wall formed of a different more flexible and resilient thermo-bondable material that has an enhanced strain capacity and lower modulus of elasticity. The inner wall material also has enhanced mechanical properties which generally improve processing and help prevent excessive drag and tearing of the liner material during the manufacturing process.

Abstract: A method of rotationally molding a large-diameter pipe fitting, the wall structure of which is characterized as having a generally smooth interior surface and an exterior surface that is defined by a plurality of axially-spaced circumferentially extending ribs which are monolithically formed and homogeneous with the smooth interior surface of the fitting. The fitting is seamless and modularly designed with integral coupling elements at each terminal end, and with a ribbed wall structure profile capable of withstanding the loads typically found in buried applications with watertight performance requirements, where such ribbed wall structure meets the following dimensions and dimensional ratios: Rib Sidewall Angle (95-105 degrees); Bottom/Top Rib Thickness Ratio (1.80-2.80); Pitch/Rib Height Ratio (1.50-1.95); Rib Height/Fitting Diameter Ratio (0.04-0.09); and Avg. Rib Thickness/Rib Height Ratio (0.28-0.40).