A method for assembling pipe-in-pipe pipeline elements for transporting fluids, with each pipeline element comprising an inner pipe including a bulge at one end, and an outer pipe including a recess at one end. The method comprises the successive steps: inserting a first locking wedge axially abutting the bulge of its inner pipe and a corresponding end of its outer pipe, butt-assembling the inner pipe of a new pipeline element on the inner pipe of the pipeline, positioning the outer pipe of the new pipeline element alongside the outer pipe of the pipeline, and butt-assembling the outer pipe of the new pipeline element on the outer pipe of the pipeline by inserting a second locking wedge axially abutting against the bulge of the inner pipe of the pipeline at its free end and the recess of the outer pipe at a corresponding end thereof.