1. Overview of the horizontal fixed argon electric joint welding process for stainless steel pipe butt joints.
Stainless steel pipe butt joints have the characteristics of horizontally fixed tungsten arc welding base, electrode arc welding cover surface, and single-sided welding and double-sided forming.
During the horizontal butt welding process, the weldment seam is divided into two semicircles according to the position of the clock face. The starting point of the welding seam is at 6 o’clock on the clock face and the endpoint is at 12 o’clock on the clock face. It is divided into left semicircles. And the right semicircle, when welding, the two semicircle welds should overlap by about 10mm at the starting point and end point. The welding gun and welding wire move in all positions around the welding seam, that is, welding is carried out in the upward welding, vertical welding, and flat welding positions. When welding, care should be taken to prevent the occurrence of undercut defects.
2. Preparation before welding
(1) Welding machine: 1 WS-400 welding machine.
(2) Welding wire: H10Cr19Ni9 welding wire, 2mm.
(3) Welding rod: Use E308-15 (A107) welding rod, 3.2mm, dried at 350-400℃ for 1~2 hours before welding. The dried welding rod should be placed in the welding rod insulation cylinder for ready use. The welding rod should not stay outside the furnace for more than 4 hours. Otherwise, the welding rod must be placed in the furnace to be re-dried. The number of times the welding rod should be re-dried should not be more than 3 times.
(4) Tungsten electrode: WCe-5 type cerium tungsten electrode, diameter 2.5mm.
(5) Argon gas: purity (volume fraction) is above 99.96%.
(6) Weldment: The weldment material is 12Cr18Ni9 stainless steel pipe, the specification size (diameter x wall thickness) is 168mm × 6mm, the weldment assembly, welding level, and weld arc ignition and end position.
(7) Auxiliary tools and measuring tools: angle grinder, welding rod insulation barrel, slag hammer, steel ruler, wire brush, bench vise, weld universal energy gauge, etc.
3. Weldment assembly positioning
(1) Cleaning before welding: Use an angle grinder to grind the groove of the weldment within 20mm on both sides of the edge of the groove to give it a metallic luster, and remove oil, rust, and scale. The welding wire must also be cleaned. Do the same.
(2) Assembly of weldments: Assemble the polished weldments so that the misalignment is less than 0.5mm.
(3) Position welding: The cleaned weldment must be tack welded before welding. There are 3 tack welds. Each of the 3 tack welds is 120° apart. The weld length is 5~8mm and the weld thickness is 3 ~4mm, the quality of positioning welds should be the same as that of formal welds.
4. Welding operation
The welding layer is divided into two layers: the base layer and the cover layer.
(1) Bottom welding: During bottom welding, divide the weldment into two semicircles, left and right, from 6 o’clock to 12 o’clock on the clock face. That is, the left semicircle is 6 o’clock → 7 o’clock → 8 o’clock → 9 o’clock → 10 o’clock → 11 o’clock → 12 o’clock; the right semicircle is 6 o’clock → 5 o’clock 4 o’clock → 3 o’clock → 2 o’clock → 1 o’clock → 12 o’clock. There are two semicircles on the left and right, whichever semicircle you start welding first can be used. The semicircle welded first is the front half, and the one welded last is the rear semicircle. The arc starting point of the left semicircle is at 6 to 7 o’clock; the arc starting point of the right semicircle is at 5 to 6 o’clock. Where the two semicircles intersect at 6 o’clock and 12 o’clock, they must overlap by 15~25mm. For bottom welding, you can weld the front semicircle first. Move the arc from 6 o’clock to 7 o’clock on the clock face by 5 to 10 mm, and try to keep the arc as low as possible. When the first molten hole appears at the root, fill in a drop of molten metal in each of the left and right places. drop, so that the two droplets fuse. The welding wire should be close to the root of the groove. When both sides of the groove are well fused, the welding speed should be as fast as possible to prevent the weld pool in the overhead welding part from being damaged due to excessive temperature. Falling occurs, forming a concave inside the weld.
During the welding process, the welding wire is welded within the protection range of argon gas, using an intermittent wire feeding method of one advance and one retreat, and the molten droplets are fed into the molten pool drop by drop. During the welding process, in addition to always paying attention to controlling the shape of the molten pool, we must always keep the size of the molten pool consistent and the arc penetration uniform to prevent defects such as weld nodules, concavities, or concavities in the weld. In addition, it is also important to note that before welding the rear semicircular weld, use an angle grinder or saw blade to grind it into a sloped shape at the joint with the front semicircular weld to prepare for the weld joint.
(2) Cover welding: Start the arc on the base layer and start welding at 6 o’clock on the clock face. The welding arc swings in a crescent or zigzag shape. Stop for a moment on both sides of the groove and add a drop of molten droplet to each side. Make the deposited metal blend well with the base metal. There should be less molten metal filling in the overhead welding part to prevent the deposited metal from falling. In the vertical welding part, the angle of the welding rod must be controlled to prevent the metal in the molten pool from falling. In the flat welding position, the temperature of the weldment is already high at this time, so it is necessary to ensure that the weld seam in the flat welding position is full. When stainless steel pipes are butt-joined with horizontal fixed electrode arc welding and cover welding, the angle between the electrode and the pipe is 75~80°.
5. Post-weld treatment
After the welding seam is welded, use a wire brush to clean away the spatter produced during the welding process, so that the welding seam is in a clean state and should be properly ground. Welding quality inspection: the radiographic testing technology is not lower than the AB level, and the welding seam quality grade is not lower than the AB level. Those below level II are considered qualified.
Post time: Jan-22-2024