A method of laying a pipeline (6) underwater includes the steps of holding an end of a pipeline (6), providing a pipe section (5) for extending the pipeline (6), arranging the pipe section (5) adjacent to the end of pipeline (6) thereby defining a circumferential joint (7) to be welded, and welding the pipes (5, 6) together. A plurality of welding torches (8) move along the circumferential joint (7) and are operated simultaneously to weld the pipes together. The pipes (5, 6) are made of TMCP-SC steel. After the root weld is laid, a cooling ring (1) mounted on an internal clamp inside the pipes (5, 6) sprays cooling liquid, for example a fluid spray of atomised water (10) and air, from nozzles (2) onto an interior surface of the pipes (5, 6) in the region of the circumferential joint (7), thereby cooling the pipes (5, 6).