Design of double-wire submerged arc welding process for S355NL straight seam welded pipe used in offshore wind turbine foundation

S355NL fine-grained structural steel has been widely used in offshore wind power, oil platforms, welded steel pipes, etc. due to its excellent performance.

In order to further improve the production efficiency of welded steel pipes and obtain steel pipe welded joints with excellent performance for the foundation of offshore wind turbines, the welding process research of S355NL longitudinal seam welded pipes was carried out.

The double-wire buried solitary flat method and the low-nickel alloy welding material can not only refine the grain of the weld structure, but also reduce the hardening tendency and improve the low-temperature impact toughness of the weld of S355NL longitudinal seam welded pipe.

In the welding process, multi-layer and multi-pass welding is used to control the heat input ≤ 5.0kJ/mm, reduce the residence time of the fusion zone and the heat-affected zone in the high-temperature area, and ensure the impact performance of the fusion line and the heat-affected zone.

The test results show that the mechanical properties of the test plate and finished welded pipe produced by this process are qualified, and can meet the requirements of the Charpy impact test at -40°C. The production application shows that the formulation of the welding process and the selection of welding consumables are correct and appropriate, which can improve the welding production efficiency.

The welding process is applied to the actual production of the tube mill equipment, and the production efficiency of the welded pipe is increased by about 15% compared with the previous period, and all the properties of the welded pipe meet the standards and project requirements.