Choose the welding process in the steel pipe
1. Root welding
Pre-heating before welding: X70 steel grade is higher and has a strong tendency to crack. It must be pre-heated before root welding, and the groove and its surroundings must be heated to 80-120°C before root welding.
2. Root welding: E6010 cellulose downward welding is adopted, and the double combination is welded from the top of the tube. Start welding from the point where the apex is 5mm-8mm beyond the centerline, start the arc from the surface of the groove, and then lead the arc to the root of the groove. After the blunt edge is penetrated, it is dragged straight down along the weld.
Short arc operation is adopted to prevent the generation of air holes, which is beneficial to the penetration of the root of the groove and prevents the generation of incomplete penetration and fusion. At the same time, it is necessary to prevent the generation of recesses and collapses, and the joints should be full when the electrode is replaced.
After the root welding is completed, the surface slag and spatter should be completely removed, especially the junction of the weld, and the groove surface should be cleaned to avoid slag inclusion during the welding of the lower weld bead.
3. Filling welding:
The filling layer is made of Lincoln E81T8-G φ2.0 flux-cored self-protected welding wire, which adopts manual and semi-automatic welding.
X70 steel has a certain tendency to crack. To prevent cracks, the interlayer temperature must be above 80℃, and proper heating measures must be taken during winter welding.
After the root welding is completed, the weld layer should be cleaned immediately, followed by the welding of the hot weld layer and the filler layer; the welding defects of the filler layer are mainly porosity, slag inclusion, and infusion. Keep short arc welding during filling welding; use a straight line or slightly swing; continuously adjust the inclination of the welding gun from top to bottom,
Keep the welding wire at a certain angle; after each layer is welded, the slag must be cleaned up with a polisher or electric wire brush before welding the next layer; when the filling layer is wide, row welding can be used, and the next row must be rowed first. Arrange the top lanes and go up in turn, as shown in Figure 3. The weld bead is required to be uniform and full, with good fusion on both sides. Particular attention should be paid to not destroy the edge of the groove during the last layer of fill welding, to ensure that the groove of the cover layer is well-defined, and to provide a reference for controlling the melt width of the cover welding.
4. Cover the surface
Cover welding should be of qualified weld appearance size, no welding defects, and a beautiful appearance. It is the last process of the weld and is also a key process.
The oblique 45℃ pipe mouth cover welding has outstanding difficulties. The appearance is prone to defects such as undercut and super high weld seam. Grooves are easy to appear between weld beads. Appropriate process methods must be adopted: strictly per the requirements of process parameters. Swing the strip in a straight line slightly, the swing amplitude should be appropriate,
It is advisable to melt the edges of the grooves on both sides by 1.5mm~2mm. The swinging conveyor is used to facilitate gas precipitation and slag floating, which can prevent the generation of pores and slag inclusions; when welding, it is better to arrange the upper channel first and then the lower channel.
This can not only appropriately reduce the number of rows of welds, but it is also easy to control weld undercuts, ultra-high welds, and grooves between welds. The transition between welds is smooth and the shape is beautiful, which is beneficial to improve the quality and efficiency of welds.