A method of welding together the ends of outer pipe sections (16A, 16B) of pipe-in-pipe pipeline to be laid on a seabed employs an annular member (5) interposed between adjacent lengths of pipe. The annular member comprises a first axial part (11) which fits within the end of the first outer pipe section, and a flange part (12) which is interposed between the adjacent ends of the two lengths of outer pipe sections (16A, 16B) to be joined. The flange part (12) of the annular member (5) projects radially outwardly beyond the inside of the outer pipe sections (16A, 16B) and terminates radially inwardly of the outside of the outer pipe sections (16A, 16B), and provides some of the welding material for the joint.