US Patent 7484535 Corrugated pipe with outer layer

A pipe having an axially extending bore is defined by a pipe wall including a corrugated outer wall having axially adjacent annular outwardly-extending crests separated by valleys. The pipe wall also includes a non-linear outer layer having adjacent concave portions and convex portions. The concave portions are aligned with the corrugation crests of the outer wall so that the convex portion of the outer layer extends outwardly between at least two corrugation crests to provide improved resistance to deformation.