said corrugations, said concave portions adjacent thereto, and said intermediate flat portions being located sequentially along {HEAD ~ the axis} of {TAIL ~ the pipe} 
of
said corrugations , said concave portions adjacent thereto , and said intermediate flat portions being located sequentially along { HEAD ~ the axis } of { TAIL ~ the pipe }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL