Investigation On Tube To Tube All Position TIG Inner Butt Welding Technology

One nuclear pressure vessel safety end uses89mmdiameter,4mm thick stainlesssteel pipe all position connect main heat exchanger. Because of a89mmdiameter obstacletube which outside the connect tube, conventional TIG weldingequipment operating space is limited, therefore only can use the method of TIG innerwelding. Besides, the welding space is limited, so the welding head can’t oscillate. Onthis base, making use of flat linear welding to verify the effect of each pulsewelding parameters on the weld penetration, weld width. Then, basing on TIG allposition inner welding machine, use U type groove, V type groove, I type groove andargon and helium as protective gases to research its welding technology.All position TIG inner butt welding experiment indicates that when use U typegroove argon arc welding, root welding can realize a good formation. Due to thewelding head can’t oscillate, it can’t Solve side wall lack of fusion and overheadwelding seam collapse which caused by cumulative heat during filling welding, Sothis method is not feasible. When use V type groove argon arc welding, due to this typegroove’s welding technology is sensitive to undercut, it is not stable even underlaboratory conditions, so it is not possible on actual production conditions. when use Itype groove helium arc one-side welding with back formation, overhead welding seamhas collapse trend. By Increasing the welding speed, reducing welding current and arcvoltage to reduce this trend, but it can’t avoid, the thickness of overheadwelding seam collapse about0.2mm. Besides, molten pool on downhill welding positionhas down flow trend which resulting in increased the actual welding thickness causingdifficult penetration. It found that increasing welding current, reducing welding speedand arc voltage can solve this problem. In a word, I type groove helium arc welding isfeasible.Right now, all position TIG inner butt welding belongs to the domestic first time,according to welding groove form and welding position, U type groove and I grooveroot welding are divided into four zones. Then compare its welding technology’sdifferences between conventional TIG all position U type groove root welding.Finally, by NDT test, mechanical performance test, microstructure analysis,intergranular corrosion test, welding seam ferrite content test, it proved that the heliumarc welding joint which under optimal technology meet weld quality inspectionrequirements. This experiment shows that when welding head can’t oscillate,4mm thickness stainless steel tube to tube all position inner butt welding use I groove heliumarc welding can realize one-side welding with back formation. Right now, this weldingtechnology is pre-accepted by one Nuclear Research Institute and plan to be used on theactual products.