Abstract: A pipeline includes a plurality of units each consisting of a pipe section, a netting of longitudinal inserts about the pipe section and a slotted primary outer jacket the edges of which are folded down into an outer groove of one of the inserts which is then filled with a hardenable material providing fluid-tight closure. The jacket section is shorter than the inserts, which are shorter than the pipe section whereby each unit has stepped ends. The ends of the pipe sections of adjacent units are welded together with the grooved inserts aligned, and joining sections of the netting are wrapped about the pipe ends. Secondary sections of the slotted jacket, previously placed over the primary jacket sections of the units, are then slid between the primary jacket sections and secured by folding down the edges thereof into the aligned grooves of the grooved inserts.