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