First, introduction
The horizontal fixed tungsten inert gas hydrogen arc welding for base welding and arc welding for cover welding for stainless steel pipe butt welding has the characteristics of single-sided welding and double-sided forming. In the horizontal butt welding process, the weld of the weldment is divided into two semicircles according to the position of the clock face. The starting point of the weld is at 6 o’clock on the clock face, and the endpoint is at 12 o’clock on the clock face, which is divided into the left semicircle and the right semicircle. When welding, the two semicircular welds should overlap about 10mm at the starting point and the endpoint. The welding gun and welding wire are all moved around the weld in all positions, that is, welding is carried out in the overhead welding, vertical welding, and flat welding positions. When welding, pay attention to prevent the occurrence of undercut defects.
Second, 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, and dry it at 350-400℃ for 1~2h before welding. The dried welding rod is placed in the welding rod insulation tube for use at any time. The welding rod should not stay outside the furnace for more than 4 hours, otherwise, the welding rod must be placed in the furnace for re-drying, and the welding rod should not be dried more than 3 times.
(4) Tungsten electrode: WCe-5 cerium tungsten electrode, diameter 2.5mm.
(5) Argon: 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 layer and weld arc starting and end position are shown in Figure 1.
(7) Auxiliary tools and measuring tools: angle grinder, welding rod insulation tube, slag hammer, steel ruler, wire brush, bench vise, weld universal gauge, etc.
Third, weldment assembly and positioning
(1) Cleaning before welding: Grind the weldment groove and the groove edge within 20mm on both sides with an angle grinder to make it present a metallic luster, and remove oil, rust and dirt. The welding wire should also be treated in the same way.
(2) Assembly of weldment: Assemble the weldment after grinding, and the misalignment should be less than 0.5mm.
(3) Positioning welding: After cleaning the weldment, positioning welding should be performed before welding. There are 3 positioning welds, each of which is 120° apart. The weld length is 5~8mm and the weld thickness is 3~4mm. The quality of the positioning weld should be the same as that of the formal weld.
Fourth, welding operation
The welding layer is divided into two layers: the base layer and the cover layer.
(1) Base welding: When base welding, the weldment is divided into two semicircles, the left and right semicircles, from the 6 o’clock to 12 o’clock position 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. You can start welding from either semicircle. The semicircle to be welded first is the front half, and the semicircle to be welded later is the back half. The arc starting point of the left semicircle is at 6~7 o’clock; the arc starting point of the right semicircle is at 5~6 o’clock. The two semicircles must overlap 15~25mm at the intersection of 6 o’clock and 12 o’clock.
For the base welding, the front half circle can be welded first. The arc is started by moving 5~10mm from 6 o’clock to 7 o’clock on the clock face. The arc is pressed down as much as possible. When the first molten hole appears at the root, a drop of molten drop is filled at the left and right places to fuse the two drops of molten droplets together. The welding wire should be close to the root of the groove. When the two 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 falling due to excessive temperature and forming a concave inside the weld. During the welding process, the welding wire is in the protection range of argon gas, and the intermittent wire feeding method of advancing and retreating is adopted to weld, and the molten droplets are fed into the molten pool drop by drop. In addition to paying attention to controlling the shape of the molten pool at all times, the welding process should always keep the size of the molten pool consistent, and the arc penetration should be uniform to prevent defects such as weld nodules, concave or concave in the weld. In addition, it should be noted that before welding the rear semicircular weld, the angle grinder or saw blade should be used 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 stays on both sides of the groove for a while and adds a drop of molten metal to each side to make the deposited metal blend well with the base material. Fill less molten metal in the overhead welding area to prevent the deposited metal from falling. In the vertical welding area, the electrode angle should be controlled to prevent the molten pool metal from falling. In the flat welding position, the temperature of the weldment is already high at this time, and the weld seam in the flat welding area must be full. When the stainless steel pipe is butt-jointed with a horizontal fixed electrode arc welding cover welding, the angle between the electrode and the pipe is 75~80°.
Fifth, post-weld treatment
After the weld is welded, use a wire brush to clean the spatter generated during the welding process, keep the weld in a clean state, and perform appropriate grinding. Welding quality inspection: The radiographic detection technology is not lower than AB level, and the weld quality level is not lower than Level II to be qualified.
Post time: Apr-08-2025