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