Abstract: A multi-layer bell is formed from the outer shell of a multi-layer pipe in a secondary process, thereby allowing the extrusion process to be conducted at normal speeds. The bell may include a strain limiting membrane fused or mechanically secured between the outer shell extrusion layer and the inner liner extrusion layer, increased hoop or circumferential stiffness. This invention allows the extrusion process to be in its simplest form, with no adjustments to the corrugator or extruder speeds.

Abstract: A multi-layer bell is formed from the outer shell of a multi-layer pipe in a secondary process, thereby allowing the extrusion process to be conducted at normal speeds. The bell may include a strain limiting membrane fused or mechanically secured between the outer shell extrusion layer and the inner liner extrusion layer, increased hoop or circumferential stiffness. This invention allows the extrusion process to be in its simplest form, with no adjustments to the corrugator or extruder speeds.

Abstract: A corrugated pipe 2 has a plurality of corrugation structures 10, 12 positioned adjacent one another. The corrugation structures 10, 12 comprise an inner cylindrical wall 22, two annular wall portions 28, 32 that extend outwardly from the inner cylindrical wall 22, and a bowed annular wall portion 40 that is connected to the outer ends 36, 38 of the two annular wall portions 28, 32. The corrugation structure 10, 12 includes a centroid 48, 49 and at least a portion of the inner surface 50 of the bowed wall portion 40 has a radius R1 centered on the centroid 48, 49 and at least a portion of the outer surface 52 of the bowed wall portion 40 has a radius R2 centered on the centroid 48, 49. The cavity 56 defined by the corrugation structure 10, 12 has an inner surface with an inner radius R1, R3 that is equal to or greater than one half the thickness T1 of the inner cylindrical wall 22.