Application of high current density submerged arc welding on 9%Ni steel.

概要

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To improve welding quality and welding efficiency of submerged arc welding, the authors developed HCD (High Current Density) SAW methods using DC of drooping characteristics for horizontal position and AC for flat position with twin wires with high deposition rate and high speed with current density of 100-200A/mm2.In this study, applicability of the HCD-SAW method to 9% Ni steel was investigated in horizontal and flat position. Effect of current density on deposition rate, workability, arc stability with current density and the properties of the welded joints were investigated with using 70% nickel alloy type welding material of 1.6mm dia. New methods were actually applied to the aboveground LNG storage tanks of 80, 000kl capacity successfully.Results obtained are as follows;1) Appropriate current density of the methods was 100-140A/mm2 for horizontal position and 160-180A/mm2 for flat position, which gave the deposition rate of 150-210g /min and 240-290g/min respectively, 1.3-2 times larger than that of the conventional methods.2) Properties of the welded joints were the same or superior than those of the joints by conventional methods.3) Welding was done successfully at site and shop, and exellent welding quality was confirmed by radiographic test.
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