means for providing {HEAD ~ a smooth transition} between {TAIL ~ a said corrugation} and adjacent intermediate flat portions comprising a pair of spaced portions, concave as viewed from the exterior of said pipe, each said concave portion being tangent to a said intermediate flat portion and joined to said convex corrugation, 
means for providing { HEAD ~ a smooth transition } between { TAIL ~ a said corrugation } and adjacent intermediate flat portions comprising a pair of spaced portions , concave as viewed from the exterior of said pipe , each said concave portion being tangent to a said intermediate flat portion and joined to said convex corrugation ,
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH