The longitudinal sides 21, 22 comprise grooves and tongues for joining the longitudinal sides 21, 22 to form the pipeline according to {HEAD ~ the invention} by rolling up {TAIL ~ the portion} of material 19, which longitudinal sides are formed in accordance with the illustration in FIGS 1 and 2 
by rolling up
The longitudinal sides 21 , 22 comprise grooves and tongues for joining the longitudinal sides 21 , 22 to form the pipeline according to { HEAD ~ the invention } by rolling up { TAIL ~ the portion } of material 19 , which longitudinal sides are formed in accordance with the illustration in FIGS 1 and 2
OTH OTH OTH OTH OTH OTH 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 REL REL 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