A coupling for pipe-in-pipe pipeline tubing formed of an assembly of sections each incorporating an inner pipe and an outer pipe butt welded to the inner pipe, two successive sections being joined together by the welding of respective inner pipes delimiting a segment of inner pipe, wherein it is formed by a sleeve arranged perpendicularly to the segment and a filler material constituted by a quick-set mortar based on aluminous cement and sand, said filler material being arranged in the free space delimited by the sleeve, said segment and the outer pipes of two successive sections.