Abstract: Based on the construction requirements of an offshore windfarm jacket fabrication project, the structural steel of EN10025-3 S355N/NL and EN10025-4 S355M/ML shall meet the low temperature impact requirements of minimum impact energy 34 J at-40 ℃, and the welding process qualification and construction shall meet the requirements of DNVGL-OS-C401—2018 and DNVGL-ST-0126—2018.In this study, compositions and properties of the parent materials, welding groove design, selection of consumable materials, welding process sequence and parameters were introduced in detail.The measured results showed that macro morphology, stretching, bending, low-temperature impact energy at-40 ℃, and microhardness of the welding joints obtained by JCOE pipe process fulfil the project specifications and standards, which have good strength and low-temperature impact toughness, and can ensure the welding quality and mechanical properties.JCOE pipe process developed in this study can be applied to the offshore windfarm jacket fabrication project to greatly improve the welding efficiency.It is also suitable for the fabrication of other pipe bodies, and has broad application prospect.Highlights:(1)According to the base materials, EN10025-3 S355N/NL and EN10025-4 S355M/ML plates, a pipe welding process scheme based on JCOE forming process was developed, and excellent welded joints were obtained.(2)According to the welding process and construction requirements given in DNVGL-OS-C401—2018 and DNVGL-ST-0126—2018, the mechanical properties of the welded joints were tested.The tensile fracture occurred in the base materials, and no open crack occurred at 180 side bending specimens, the minimum impact energy at-40 ℃ was greater than 46 J, and the maximum hardness was lower than 325HV10, which fulfil the specifications of the standards.