New underwater welding with super-wager-repellent material

摘要

Economical and reliable mechanized wet welding is desired for practical fabrication and maintenance technique of offshore structures. Wet welding with the local dry cavity by water jet curtain is the useful method for this purpose, but this method was applicable to the offshore construction only with the backing steel strip, because of the poor accuracy of the joints. In this case, the problems are fatigue strength and crevice corrosion at backing strip. To solve this problem, the underwater full penetration welding method with ceramic backing coated by a super- water-repellent material was developed. This material had two special features, the super-water-repellent property and the ability of formation of air membrane on the surface. The combined material of the hydrophobic silica fine particles and silicone resin was selected as the most suitable material for underwater welding use. Coating this material to the ceramic backing and the weld zone could easily form the stable local dry cavity on the surfaces and made underwater full penetration welding possible. CO{sub}2 and MAG welding could be applied for the 13mm thickness plates under water with good full penetration beads by using the special water curtain nozzle and the ceramic backing. Bead appearances and macro sections of the underwater welded beads were good enough up to the 10mm of root gap width and 3mm height misalignment. The Vickers hardness of the weld joint was slightly increased and Charpy impact values of the underwater welds were 10% less than those of the welds in air, but results of tensile test and bending test showed good quality.