Improvements in fully austenitic stainless steel tubes, a method of preparing such tubes for union by welded joints and a method of butt weld uniting such tubes

摘要

769,256. Welding by fusion. BABCOCK & WILCOX, Ltd. April 5, 1955 [April 5, 1954], No. 9927/55. Class 83 (4). A fully-austenitic nickel-chromium alloy steel tube is formed for butt-welding to a similar tube with an extension comprising an annular weld deposit of partially ferritic nickel-chromium alloy steel. A thin walled tube 101 of a fully-austenitic stainless steel containing 18 per cent chromium, 8 per cent nickel and columbium is formed with a 2.5 degrees taper 11 to receive the tapered end 21 of a cylindrical plug 20 having a central bore 24 and an annular recess 25. The plug 20 is cast from an alloy steel and then machined and consists of less than 0.08 per cent carbon, 19-21 per cent chromium, 7.5-8.5 per cent nickel, 1.25-1.75 per cent manganese, ten times as much columbium as carbon, less than 0.5 per cent silicon, 0.03 per cent sulphur and 0.03 per cent phosphorus, and the remainder iron. The recess 25 is filled by welds 31 ... 34 in succession deposited by arc welding with reverse polarity from a coated electrode 35. The welds 31 ... 34 and the electrode 35 consist of a partially ferritic stainless steel containing 17-19 per cent chromium, 9-12 per cent nickel, up to 0.08 per cent carbon, up to 2 per cent manganese and columbium up to ten times the carbon content. The plug and weld deposits are machined to form an extension 30, Fig. 5. To form a butt weld, two tubes 10 are provided with extensions 30 and a ring 40 of the same composition as the electrode 35 and cleaned in hydrochloric acid is tack-welded to the extension. Argon or helium under a manometer pressure equivalent to 1.25 inches of water is passed through the tubes which are welded using an argon or helium shielded tungsten electrode 55, straight polarity, and a stainless steel filler rod 58 of composition similar to that of the ring 40 and which deposits weld metal having a ferrite content of 3-8 per cent. The weld is made in four runs, each passing upwards from the horizontal centre line to the vertical centre line of the joint section. After each run the weld is water cooled and after two runs have been made the tubes are turned through 180 degrees.