{HEAD ~ The corrugation} 22, concave arc portion 32 and {TAIL ~ horizontal flat portion} 24 are located sequentially along the axis of pipe 20 
{ HEAD ~ The corrugation } 22 , concave arc portion 32 and { TAIL ~ horizontal flat portion } 24 are located sequentially along the axis of pipe 20
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH