CO2 welding general welding technique
2022-02-25
Butt weld——Flat butt welding 1/1
2022-03-12
Tube sheet welding technology 1
Tube sheet welding joint is one of the welding joint forms of boiler pressure vessel, pressure pipeline welding mechanism and metal welding structure. Connect the two situations. Insertion type tube sheet welding is easier, as long as the welding root has a certain penetration depth and welding foot size, and the internal defects of the welding seam are within the allowable range, it can be qualified. In the welding of saddle-type tube sheet, in addition to the formation of the back of the welding root, the size of the welding leg must be ensured, and there are no defects outside the allowable range in the weld to be qualified.
The biggest difficulty in welding tube-to-sheet joints is that the operator must turn the wrist in time and continuously according to the curvature of the tube circumference at the welding place, and constantly adjust the inclination angle of the welding torch and the arc centering position to ensure that the back is well formed and there is no internal defect. , Welding seam with no external undercut and qualified welding foot size requires repeated practice and continuous summarization of experience in order to master it.
Plug-in tube sheet butt welding
CO2 plug-in tube sheet butt welding is a basic welding method for welding plug-in tube sheets, and it is a relatively easy welding technique to master. Solder feet. In order to save welding materials, the inserting tube sheet welding training can be assembled in the way shown in Figure Tube sheet welding technology-1, and two welds can be welded by using a block orifice plate.
Preparation before welding
The pre-welding preparation for inserting tube sheet mainly includes the preparation of workpiece, welding wire, CO2 gas, welding machine and auxiliary tools.
The workpiece is made of low-carbon steel pipes and plates suitable for welding. The size standard is pipe φ60mmx100mmx6mm (tube thickness). If there is no steel pipe with a thickness of 6mm, a seamless steel pipe with a thickness of about 4mm can be selected instead. Training; the plate is 100mm X100mmx12mm, first machine the insertion hole of φ61 on the plate, if there is no 12mm thick steel plate, it can also be replaced with a steel plate of about 10mm, as shown in Figure Tube sheet welding technology-2.
Welding wire and CO2 gas.
When welding, choose H08Mn2SiA welding wire, the diameter of the welding wire is 1.0 mm, and the surface of the welding wire should be cleaned before use; the purity of CO2 gas should reach 99.5%.
Welders and Auxiliary Tools
Welding was carried out with a semi-automatic CO2 gas shielded welding machine. The main auxiliary tools include wire brushes for cleaning weldments, chisels, files, grinders and slag hammers used during welding.
Operation process
Welding parameters
The welding parameters of CO2 gas shielded insertion tube sheet welding are very important, and the data in Table Tube sheet welding-1 can be selected as a reference during operation.
Welding essentials
- Torch angle and welding method. The left-hand welding method is adopted for the insertion type tube sheet welding, and the single-layer and single-pass welding is used. The angle of the welding torch and the centering position of the arc are shown in Figure Tube sheet welding-3.
Welding location placement.
Adjust the height of the welding frame and place the tube sheet vertically on the welding frame. Ensure that the operator is standing and welding.
The gun can be moved easily along the to-be-welded area, and a tack weld is located on the right side where the arc is to be struck.
Welding steps
① Start the arc on the positioning weld on the right side of the weldment, and weld along the outer circle of the pipe from the stone to the left. After welding 1/4~1/3 of the circumference, stop the arc, and grind the arc stop according to the requirements of Figure Tube sheet welding technology-4. beveled.
② Quickly turn the arc crater to the starting point of welding to start the arc, and immediately re-weld 1/4~1/3 of the circumference of the pipe while taking advantage of the residual heat of the joint. Repeat this until the last remaining closed weld is left.
③Before welding the closed seam, both ends of the welded seam shall be welded and ground into a bevel, as shown in Figure Tube sheet welding technology-5.
④ Turn the polished weldment to a suitable position and finish welding the last section of the weld. At the end of the welding, the arc crater must be filled and the joint should not be too high.
⑤ Remove the welding slag and spatter on the surface of the weld bead, especially the welding slag on both sides of the weld bead. Use an angle grinder to grind the local bulge on the front of the weld bead that is too high.
Welding Requirements and Standards
See Table 5-12 for the welding requirements and standards of CO2 gas shielded insertion tube-sheet welding.
Saddle tube sheet butt welding
The welding of the saddle-type tube sheet is more difficult. During the practice, the operator must master the movement of turning the wrist, the angle of the welding torch and the centering position of the arc, and can skillfully control the formation of the back weld bead according to the size of the melting hole. Solder well-proportioned and beautiful legs.
The flat welding of the saddle-type tube sheet is the basic skill of welding the saddle-type tube sheet, and it is difficult to master, because the welding seam is on the circumference, the angle of the welding torch and the centering position of the arc need to be changed at any time, not only to ensure the welding feet of the T-joint Symmetric, but also to master single-sided welding double-sided forming technology.
Preparation before welding
The preparation before butt welding of saddle tube sheet mainly includes the preparation of workpiece, welding wire CO2 gas, welding machine and auxiliary tools.
The workpiece is made of low-carbon steel pipes and plates suitable for welding. The size standard is pipe φ60mmx100x6mm (pipe thickness). If there is no steel pipe with a thickness of 6m, a seamless steel pipe with a thickness of about 4m can also be selected instead for training. : board is 100 mm x 100 mm x 12 mm, first machine a hole with a diameter of φ52 and the same diameter as the tube. If there is no steel plate with a thickness of 12 mm, it can be replaced with a steel plate with a thickness of about 10 mm, as shown in Figure Tube sheet welding-6.
Welding wire and CO2 gas When welding, choose H08Mn2SiA welding wire, the diameter of the welding wire is 1.0 mm, and the surface of the welding wire should be cleaned before use; CO, gas purity requirements reach 99.5%.
The welding machine and auxiliary tools are semi-automatic CO2 gas shielded welding machine for welding. The main auxiliary tools include wire brushes for cleaning weldments, chisels, files, grinders and slag hammers used during welding.
Operation process
Welding parameters.
The welding parameters of CO2 gas shielded saddle-type tube-sheet welding are very important, and the data in Table Tube sheet welding-2 can be selected as a reference during operation.
Welding essentials
- Welding torch angle and welding method. The CO2 gas shielded saddle-type tube sheet welding adopts the left welding method, two layers and two passes, and the angle of the welding torch and the centering position of the arc are shown in Figure Tube sheet welding-3.
The position of the weldment is placed. Adjust the height of the welding frame and place the tube sheet vertically on the test plate frame to ensure that the welding gun can smoothly rotate along the outer circle of the tube when the operator stands, and a positioning weld is located on the right side where the arc is to be struck.
Bottom welding. After adjusting the welding parameters of the bottom bead, follow the steps below to weld the bottom bead:
①Start the arc on the tack weld to form the fusion hole, weld along the outer circle of the pipe from right to left, swing the welding torch up and down slightly to ensure good fusion, and adjust the welding speed according to the gap to keep the diameter of the fusion hole as consistent as possible; During the process, the operator’s upper body should preferably lean forward along the moving direction of the welding torch, so as to clearly observe the welding pool, until it is difficult to observe the arc breaking at the molten pool. Usually, 1/4~1/3 of the circumference can be welded. Be sure to ensure that the weld bead is well fused with the original tack weld, and the arc can also be broken in front of the tack weld.
②Use a thin grinding wheel to grind the arc end into a bevel, and grind off the tack weld. Be careful not to widen the gap when grinding.
③Turn the tube sheet to be welded at an angle so that the polished slope is at the arc strike. Start the arc at the top of the slope, and continue to weld along the outer circle of the pipe until the arc is broken at the appropriate position.
④Before welding the last section of the closed bead, grind both ends of the bead into a bevel, and do not expand the gap.
⑤ Grind off the protruding welding meat at the joint of the bottom welding pass to ensure the consistent size of the welding leg as much as possible.
cover welding
After debugging the welding parameters of the cover layer bead, follow the steps of welding the bottom layer bead to finish the cover layer bead, and pay special attention to the following points during welding:
① Ensure that both sides of the weld are well fused, and the size of the weld feet is symmetrical.
②The horizontal swing amplitude of the welding torch and the welding speed should be kept as uniform as possible to ensure the appearance of the welding bead is beautiful and the joints are flat.
③ Remove the welding slag and spatter on the surface of the weld bead, especially the welding slag on both sides of the weld bead. Use an angle grinder to grind the local bulge on the front of the weld bead that is too high.
Welding Requirements and Standards
See Table Tube sheet welding-3 for welding requirements and standards for CO2 gas shielded saddle-type tube-sheet welding.
