A method for production of a corrugated plastic pipe having an inner plastic wall (1a) and a corrugated outer plastic wall (1b) fused to the exterior of said inner plastic wall (1a), wherein one or more cavities are delimited between said inner (1a) and outer walls (1b).
The method comprises the extrusion of said inner plastic wall (1a) using an extruder having a die head with an inner die head (5a) part defining the interior of the inner plastic wall (1a), and also extruding and shaping said corrugated outer plastic wall (1b).
The corrugated outer wall (1b) and said inner wall (1a) are fused in the process. A mandrel (15) is positioned within said inner wall (1a), said mandrel (15) being attached to said extruder, said mandrel (15) internally supporting said inner wall (1a).