Take A Look At These 8 Most Easily Overlooked Problems In Welding. Do You Have Any Of Them?

1. Not paying attention to the selection of the best voltage during welding construction

[Phenomenon] When welding, regardless of the size of the groove, the same arc voltage is selected for base, filling, or capping. This may fail to achieve the required depth of penetration and width of weld, resulting in defects such as undercut, pores, and spatter.

[Measures] Generally, the corresponding long arc or short arc should be selected for different situations to obtain better welding quality and work efficiency.

For example, in order to obtain better depth of penetration during base welding, short arc operation should be used. In order to obtain higher efficiency and width of weld during filling welding or capping welding, the arc voltage can be appropriately increased.

2. Not paying attention to the coordinated use of welding speed, welding current, and electrode diameter

[Phenomenon] When welding, do not pay attention to controlling the welding speed and welding current, and use the electrode diameter and welding position in coordination.

For example, when performing the base welding of the fully penetrated corner seam, due to the narrow root size, if the welding speed is too fast, the root gas and slag inclusions do not have enough time to be discharged, which may easily cause defects such as incomplete penetration, slag inclusions, and pores at the root; when performing the cover welding, if the welding speed is too fast, pores may also be easily generated; if the welding speed is too slow, the weld height will increase and the shape will be uneven; when welding thin plates or welds with small blunt edges, the welding speed is too slow, which may easily cause burn-through.

[Measures] The welding speed has a significant impact on the welding quality and welding production efficiency. When selecting, select the appropriate welding speed in combination with the welding current, weld position (base welding, filling welding, cover welding), weld thickness, and groove size. Select a larger welding speed to improve production efficiency while ensuring full penetration, easy discharge of gas and welding slag, no burn-through, and good forming.

3. Welding current is not controlled during welding

[Phenomenon] During welding, in order to speed up the progress, the butt weld of medium and thick plates is not grooved. The strength index decreases, and even fails to meet the standard requirements. Cracks appear during the bending test, which makes the performance of the weld joint unguaranteed and poses a potential hazard to the safety of the structure.

[Measures] During welding, the welding current should be controlled according to the process assessment, and a 10-15% fluctuation is allowed. The blunt edge size of the groove should not exceed 6mm. When butt welding, if the plate thickness exceeds 6mm, a groove should be opened for welding.

4. Failure to control welding deformation during welding

[Phenomenon] Failure to control deformation in terms of welding sequence, personnel arrangement, groove form, welding specification selection and operation method during welding leads to large deformation after welding, difficulty in correction and increased costs, especially for thick plates and large workpieces, which are difficult to correct and can easily cause cracks or layered tearing by mechanical correction. The cost of flame correction is high and poor operation can easily cause overheating of the workpiece.

For workpieces with high precision requirements, failure to take effective measures to control deformation will result in the installation size of the workpiece not meeting the use requirements, and even cause rework or scrapping.

[Measures] Adopt a reasonable welding sequence and select appropriate welding specifications and operation methods, and also adopt anti-deformation and rigid fixation measures.

5.Multi-layer welding is not continuous, and the temperature between layers is not controlled.

 [Phenomenon] When welding thick plates in multiple layers, the temperature between layers is not controlled. If the interval between layers is too long, cold cracks are easily generated between layers if welding is performed without re-preheating. If the interval is too short and the temperature between layers is too high (over 900°C), the performance of the weld and the heat-affected zone will also be affected, resulting in coarse grains, reduced toughness and plasticity, and potential hidden dangers for the joints. [Measures] When welding thick plates in multiple layers, the temperature between layers should be controlled. During continuous welding, the temperature of the base material to be welded should be checked to keep the temperature between layers consistent with the preheating temperature as much as possible, and the maximum temperature between layers should also be controlled. The welding time should not be too long. If welding is interrupted, appropriate post-heating and insulation measures should be taken. When welding again, the re-preheating temperature should be appropriately higher than the initial preheating temperature.

6. Failure to control arc length during welding

[Phenomenon] When welding, the arc length is not properly adjusted according to the groove form, number of welding layers, welding form, electrode model, etc. Due to improper use of welding arc length, it is difficult to obtain high-quality welds.

[Measures] In order to ensure the quality of the weld, short arc operation is generally used during welding, but the appropriate arc length can be selected according to different situations to obtain the best welding quality. For example, the first layer of V-shaped groove butt joint and corner joint should use a shorter arc to ensure penetration and no undercutting. The second layer can be slightly longer to fill the weld. When the gap between the welds is small, a short arc should be used. When the gap is large, the arc can be slightly longer, and the welding speed is accelerated. The arc for overhead welding should be the shortest to prevent molten iron from flowing down; in order to control the temperature of the molten pool during vertical welding and horizontal welding, low current and short arc welding should also be used.

In addition, no matter what welding is adopted, it is important to keep the arc length basically unchanged during the movement to ensure that the molten width and depth of the entire weld are consistent.

7. The weld angle size of the joint butt or corner butt combination welds that require full penetration is not enough

[Phenomenon] The weld leg size of the butt or corner butt combination welds that require full penetration, such as T-joints, cross joints, corner joints, etc., is not enough, or the weld leg size of the web and upper wing edge connection welds of crane beams or similar components designed with fatigue verification requirements is not enough, which will make the strength and stiffness of the welding fail to meet the design requirements.

[Measures] T-joints, cross joints, corner joints, etc., which require full penetration, must have sufficient weld leg requirements according to design requirements. Generally, the weld leg size should not be less than 0.25t (t is the thickness of the thinner plate at the connection). The weld leg size of the crane beam or similar web and upper flange connection welds designed with fatigue verification requirements is 0.5t, and should not be greater than 10mm. The allowable deviation of welding size is 0~4 mm.

8. The next layer is welded without removing the welding slag and defects on the weld surface during multi-layer welding of thick plates

[Phenomenon] When welding thick plates in multiple layers, the next layer is welded directly without removing the welding slag and defects after each layer is welded, which can easily cause defects such as slag inclusion, pores, cracks, etc. in the weld, reduce the connection strength, and cause spatter during the welding of the lower layer.

[Measures] When welding thick plates in multiple layers, each layer should be welded continuously. After each layer of weld is welded, the welding slag, weld surface defects and spatter should be removed in time. If there are defects such as slag inclusion, pores, cracks, etc. that affect the welding quality, they should be thoroughly removed before welding.

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