| 摘要 |
A method of laying a pipeline (6) underwater includes the steps of holding a n end of a pipeline (6), providing a pipe section (5) for extending the pipeli ne (6), arranging the pipe section (5) adjacent to said 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 (9) move along the circumferential joint (7) and are operated simultaneously to weld the pipes together. The pipes (5, 6) are made of TMCP-AC steel (steel manufactured usi ng a thermal mechanical control process with accelerated cooling and having a carbon content of less than 0.1% by weight). 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, fr om nozzles (2) onto an interior surface of the pipes (5, 6) in the region of th e circumferential joint (7), thereby cooling the pipes (5, 6).
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