said convex corrugations each having an arcuate crest at a greater radius from {TAIL ~ the axis} of {HEAD ~ the pipe} than said intermediate flat portions, 
said convex corrugations each having an arcuate crest at a greater radius from { TAIL ~ the axis } of { HEAD ~ the pipe } than said intermediate flat portions ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH