1. Not paying attention to selecting the optimal voltage during welding
[Phenomenon]
Regardless of whether it is root, filling, or cover passes, the same arc voltage is chosen for all welds, regardless of the size of the groove. This may result in insufficient penetration and width, leading to defects such as undercut, porosity, and spatter.
[Measure]
In general, choosing the appropriate long or short arc for different situations can yield better welding quality and work efficiency.
2. Not controlling welding current during welding
[Phenomenon]
To expedite the welding process, some welders avoid beveling the joints of medium and thick plates.
This can result in reduced strength, failure to meet standard requirements, and cracks during bend testing, compromising the integrity of the welded joint and posing potential safety hazards to the structure.
[Measure]
Welding current should be controlled according to the process evaluation, allowing a 10-15% fluctuation.
The size of the blunt edge of the bevel should not exceed 6mm. For plate thicknesses exceeding 6mm, beveling is required for welding.
3. Not paying attention to the coordination of welding speed, welding current, and electrode diameter
[Phenomenon]
When welding, it’s essential to control the welding speed, welding current, electrode diameter, and welding position.
For instance, during root pass welding of a full penetration fillet weld, inadequate welding speed can lead to defects such as incomplete fusion, slag inclusion, and porosity at the root due to insufficient time for gas and slag expulsion.
When welding the cover pass, too fast a speed can also lead to porosity, while too slow a speed can result in an excessively high weld bead and an uneven appearance.
When welding thin plates or welds with small blunt edge sizes, slow welding speed can cause burn-through.
[Measure]
Welding speed has a significant impact on welding quality and production efficiency. By coordinating the welding current, weld position (root pass, fill pass, cover pass), thickness of the weld, and bevel size, an appropriate welding speed can be selected.
Aim for a faster welding speed that ensures complete penetration, easy expulsion of gas and slag, no burn-through, and good formation to improve production efficiency.
4. Not paying attention to controlling arc length during welding
[Phenomenon]
While welding, the arc length is not properly adjusted according to factors such as groove type, welding layers, welding style, and electrode model. Due to the improper use of welding arc length, it is difficult to achieve high-quality welds.
[Measure]
To ensure weld quality, short arc operation is generally used during welding. However, the appropriate arc length can be chosen according to different situations to achieve optimal welding quality.
For example, use a shorter arc for the first layer of V-groove butt welds and fillet welds to ensure penetration and prevent undercut.
The second layer can have a slightly longer arc to fill the weld. Use a short arc when the weld gap is small, and a slightly longer arc with increased welding speed when the gap is large.
5. Not paying attention to controlling welding deformation
[Phenomenon]
Not paying attention to controlling deformation from aspects such as welding sequence, personnel arrangement, groove type, welding specification selection, and operation method can result in significant post-welding deformation, making correction difficult and increasing costs.
This is especially true for thick plates and large workpieces, where mechanical correction can cause cracks or lamellar tearing, and flame correction is expensive and can easily cause overheating if not operated properly.
For workpieces with high precision requirements, not taking effective measures to control deformation can result in installation dimensions not meeting usage requirements, and even rework or scrapping.
[Measure]
Adopt a reasonable welding sequence, select appropriate welding specifications and operation methods, and use counter-deformation and rigid fixing measures.
6. Not paying attention to controlling interpass temperature during multi-layer welding
[Phenomenon]
When performing multi-layer welding on thick plates, not paying attention to controlling the interpass temperature can cause issues.
If the interval between layers is too long, cold cracking may occur without reheating before welding; if the interval is too short and the interpass temperature is too high (exceeding 900°C), the properties of the weld and heat-affected zone can be affected, resulting in coarse grains, reduced toughness and plasticity, and potential hidden dangers in the joint.
[Measure]
During multi-layer welding of thick plates, the control of interpass temperature should be strengthened. Inspect the base material temperature during continuous welding to keep the interpass temperature as close to the preheat temperature as possible, and control the maximum interpass temperature.
7. Proceeding to the next layer of multi-layer welds without removing slag and surface defects
[Phenomenon]
During multi-layer welding of thick plates, welders may proceed to the next layer without removing slag and defects, which can result in slag inclusions, porosity, cracks, and other defects in the weld, reducing joint strength and causing spatter in subsequent layers.
[Measure]
For multi-layer welding of thick plates, continuous welding should be performed for each layer. After each layer is welded, promptly remove slag, surface defects, and spatter. If slag inclusions, porosity, or cracks that affect welding quality are found, they should be thoroughly removed before continuing welding.
8. Insufficient weld size for required penetration in butt and fillet joint combinations
[Phenomenon]
For T-joints, cross-joints, and fillet joints requiring full penetration, the weld size may be insufficient, or the weld size of the web-to-upper flange connection in crane beams or similar components with fatigue calculation requirements may be inadequate. This can result in the strength and stiffness of the weld not meeting design requirements.
[Measure]
For T-joints, cross-joints, and fillet joints requiring full penetration in butt joint combinations, the weld size should meet design requirements, and
