The pre-finished welding production process of submerged arc welded spiral welded pipes (SSAW/SAWH) has become the development trend of spiral welded pipe production technology due to its high production efficiency and good weld quality. However, due to factors such as operation and welding process constraints, welding defects occur in precision welding seams, which affects the quality of welds. So what are the preventive measures for common defects in precision welding seams such as undercuts and pores?
1. Cracks occur in the weld seam
If cracks occur during precision welding of steel pipes, they are crystallization cracks caused by excessive welding line energy. The reason for the cracks in the weld is generally that the size of the external welding groove is too large, more filler metal is required, and the welding current is too large, resulting in excessive welding line energy and crystallization cracks.
Preventive measures:
When a crack is found, pickling samples or repair welding gouging must be taken to confirm whether it is an internal welding crack or an external welding crack. Cracks that appear in precision welding are generally external welding cracks. The prevention method is to reduce the welding line energy, that is, reduce the welding current and arc voltage of the external welding wire, reduce the eccentricity of the external welding, and increase the dry elongation of the external welding wire.
2. Undercut defect
The main cause of undercut defects is the fluctuation of welding current and arc voltage caused by unstable wire feeding; in addition, inappropriate selected welding specifications and welding head parameters can also cause undercut defects.
Preventive measures:
When there is undercutting in the weld, you should first check the stability of the wire feeding system, including whether the wire spool, wire spool, wire feeding drive wheel, steering wheel, contact tip, etc. are normal. If no abnormality is found, you can consider whether there is a problem with the feedback line and wire feed motor. After the above problems are solved, readjust the welding process parameters and conduct trial welding.
3. Porosity and slag inclusion defects
The main reasons for the occurrence of pores and slag inclusions in precision welding seams: ① The welding wire or flux is contaminated; ② The pre-welding weld is dirty (iron oxide powder); ③ The pre-welding weld itself has pores or slag inclusions. In this case, Porosity or slag inclusions can easily occur during precision welding.
Preventive measures:
Generally speaking, weld pores and slag inclusion defects caused by contamination of the welding wire or flux are continuous. When the imaging system finds that the entire weld has pores or slag inclusions, the welding wire and flux should be considered first. Check the purity of the welding wire, replace the flux, and check whether there is oil stains or rust on the surface of the welding wire. Another situation is that the pre-welded weld itself has a honeycomb-shaped gas connection. To ensure that the internal welding is not in the coal kiln, the current of wire 1 and wire 2 needs to be increased, or the welding speed must be reduced to make the pores in the melt. There is plenty of time to emerge from the pool.
4. Incomplete welding defects
The main reasons for incomplete penetration of precision welding seams: ① Insufficient energy of the internal and external welding wires; ② Incomplete penetration caused by welding deviation.
Preventive measures:
Under normal circumstances, the welding parameters set through process qualification should be reasonable, but the blunt edge, pre-weld height, and groove size of each steel pipe vary. These differences sometimes lead to incomplete welding. Phenomenon. This requires welding operators to pay attention to changes in pre-weld seam height and groove size at all times, and appropriately adjust welding parameters to prevent the occurrence of incomplete welding defects. However, it should be noted that the adjustment of welding parameters is fine-tuning, which mainly adjusts the welding current of the inner and outer welding wires. The other parameters should remain unchanged and the adjustment range is within 100A.
For incomplete welding defects caused by welding deviation, you should take samples to observe whether the molten pool is tilted or branched, and make adjustments after determining it. The adjustment method is to re-align the lamp, ensure that the welding wire is on the same straight line, and adjust the position of the lamp point and laser tracking head. After arc starting, pay attention to the relative position of the inner welding red line and the weld seam. The outer welding should also be marked in time and marked outside. After arc welding, observe whether the red line of the external welding is in the normal position.
5. Irregular defects of weld bead
The main reasons for irregular weld beads in precision welding seams: ① The internal welding machine head vibrates; ② The instability of the orthogonal rollers causes the steel pipe to move; ③The instability of forming pre-welding causes the steel pipe to shake during the precision welding process, resulting in irregular weld beads.
Preventive measures:
The cause of vibration of the internal welding machine head is generally the contact and friction between the internal welding cantilever and the inner wall of the steel pipe. At this time, you should mainly check whether the flux shoe, flux recovery nozzle, welding line and control line are in contact with the inner wall of the steel pipe.
The cause of the movement of the orthogonal rollers is that the end cover screws of the bearings of individual orthogonal rollers are loose, which requires the center and equipment of the orthogonal rollers to be inspected. Especially when the steel pipe shakes, the orthogonal rollers at that location should be checked. , check for problems and handle them accordingly.
The main reason for the irregularity of the weld bead due to problems with the pre-welded seam is the sudden shaking of the steel pipe during fine welding. This requires the operator to inspect the pre-welded steel pipe, mainly checking the diameter and straightness of the steel pipe. Specifically, the diameter and straightness of the steel pipe at different positions of the pipe end and pipe body should be measured, and then the cause of the shaking of the steel pipe should be analyzed. The problematic pipe ends (mainly the head end) that cause the steel pipe to shake should be removed. After the removal, the empty carriage will be used to observe whether the steel pipe still "sways", and welding will be carried out after confirmation.
Read more: How to Choose the Appropriate Spiral Steel Pipe Specifications according to your Needs?
