Method and apparatus for welding pipes together

A method of j-laying a deep-sea pipeline, in which pipe sections are welded together to form the pipeline, the method including the following steps:

• holding an end of a pipeline,
• providing a pipe section for extending the pipeline,
• arranging the pipe section adjacent to said end of pipeline thereby defining a circumferential joint to be welded,
• providing a plurality of welding heads, each head having at least one welding torch, and arranging the welding heads around the circumferential joint,
• welding the pipe section to the pipeline by simultaneously
• operating the welding heads and moving said heads along the circumferential joint,
• and j-laying the pipeline underwater,
• wherein the pipe section is made of steel having a carbon content of less than 0.1% by weight, and
• during the welding step the pipes are cooled in the region of the circumferential joint by means of introducing a cooling liquid into contact with an interior surface of the pipes.

A method of j-laying a deep-sea pipeline, in which pipe sections are welded together to form the pipeline, the method including the following steps:

• holding an end of a pipeline,
• providing a pipe section for extending the pipeline,
• arranging the pipe section adjacent to said end of pipeline thereby defining a circumferential joint to be welded,
• providing a plurality of welding heads, each head having at least one welding torch, and arranging the welding heads around the circumferential joint,
• welding the pipe section to the pipeline by simultaneously operating the welding heads and moving said heads along the circumferential joint,
• and j-laying the pipeline underwater.
• wherein the pipe section is made of steel manufactured using a Thermal Mechanical Control Process and Accelerated Cooling (TMCP-AC), technique, the TMCP-AC steel having a carbon content of less than 0.1% by weight, and
• during the welding step the pipes are cooled in the region of the circumferential joint by means of introducing a cooling liquid into contact with an interior surface of the pipes.

A method of laying a pipeline underwater, in which pipe sections are welded together to form the pipeline, the method including the following steps:

• holding an end of a pipeline,
• providing a pipe section for extending the pipeline,
• arranging the pipe section adjacent to said end of pipeline thereby defining a circumferential joint to be welded,
• providing a plurality of welding heads, each head having at least one welding torch, and arranging the welding heads around the circumferential joint,
• welding the pipe section to the pipeline by simultaneously operating the welding heads and moving said heads along the circumferential joint,
• wherein the pipe section is made of steel having a carbon content of less than 0.1% by weight, and
• after the root weld has been completed cooling the pipes in the region of the circumferential joint by means of introducing a cooling gas, wherein
• the cooling gas is sprayed out of a plurality of nozzles, and after at least 3 layers of welded material have been deposited, cooling the pipes in the region of the circumferential joint by means of introducing a cooling liquid into contact with an interior surface, wherein
• the cooling liquid is sprayed out of the same plurality of nozzles out of which the cooling gas is passed, and laying the pipeline underwater.