1. Neglecting the optimal voltage during welding construction.

【 Phenomenon 】 When welding, whether it is bottoming, filling, covering, or regardless of the size of the groove, the same arc voltage is selected. This may not meet the required depth and width of fusion, resulting in defects such as undercutting, porosity, and splashing.
【 Measures 】 Generally, for different situations, corresponding long or short arcs should be selected separately to achieve better welding quality and work efficiency.

2. Welding does not control welding current.

Phenomenon: During welding, in order to speed up the progress, non beveling is used for the butt welds of medium and thick plates. The strength index decreases, even failing to meet the standard requirements, and cracks appear during bending tests, which can make the performance of welded joints unable to be guaranteed and pose a potential threat to structural safety.
[Measures] During welding, the welding current should be controlled according to the process evaluation, with a allowable fluctuation of 10-15%. The blunt edge size of the groove should not exceed 6mm. When docking, if the plate thickness exceeds 6mm, a groove should be made for welding.

3. Neglecting welding speed and welding current, coordinating the use of welding rod diameter.

【 Phenomenon 】 When welding, attention is not paid to controlling the welding speed and welding current, and the diameter and position of the welding rod are used in coordination.
When performing bottom welding on fully penetrated corner seams, due to the narrow size of the root, if the welding speed is too fast, the gas and slag at the root may not have enough time to be discharged, which can easily cause defects such as incomplete penetration, slag inclusion, and porosity at the root; When welding the cover, if the welding speed is too fast, it is also easy to produce pores; If the welding speed is too slow, the excess height of the weld seam will be too high and the shape will be uneven; When welding thin plates or small welds with blunt edges, the welding speed is too slow, which can easily lead to burn through and other situations.
【 Measures 】 Welding speed has a significant impact on welding quality and welding production efficiency. When selecting, it is necessary to cooperate with welding current, weld position (bottom welding, filling welding, cover welding), weld thickness, and groove size to select an appropriate welding speed. While ensuring penetration, easy discharge of gas and welding slag, no burning through, and good forming, a larger welding speed is selected to improve productivity efficiency.

4. Not paying attention to controlling the arc length during welding.

Phenomenon: During welding, the arc length is not adjusted appropriately based on the groove form, number of welding layers, welding form, and electrode model. 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 seam, short arc operation is generally used during welding, but suitable arc length can be selected according to different situations to obtain the optimal welding quality. For example, the first layer of V-shaped groove butt and corner joint should use a shorter arc to ensure welding penetration and avoid undercutting. The second layer can be slightly longer to fill the weld seam. Short arcs should be used when the gap between welds is small, and when the gap is large, the arc can be slightly longer, accelerating the welding speed.

5. Improper control of welding deformation during welding.

Phenomenon: Failure to control deformation during welding in terms of welding sequence, personnel arrangement, groove form, welding specification selection, and operation methods can lead to significant deformation after welding, difficulty in correction, and increased costs, especially for thick plates and large workpieces. Mechanical correction can easily cause cracks or layered tearing. The cost of using flame correction is high and the operation is not easy to cause overheating of the workpiece.
If effective deformation control measures are not taken for workpieces with high precision requirements, it may result in the installation size of the workpiece not meeting the usage requirements, and even cause rework or scrapping.
【 Measures 】 Adopting a reasonable welding sequence and selecting appropriate welding specifications and operating methods, as well as adopting anti deformation and rigid fixation measures.

6. Discontinuous welding of multiple layers without paying attention to controlling interlayer temperature.

【 Phenomenon 】 When welding thick plates with multiple layers, if the interlayer temperature control is not paid attention to, if the interlayer interval time is too long, welding without re preheating may easily cause cold cracks between the layers; If the interval time is too short and the interlayer temperature is too high (over 900 ℃), it will also have an impact on the performance of the weld and heat affected zone, causing coarse grains, resulting in a decrease in toughness and plasticity, and leaving potential hazards to the joint.
[Measures] When welding thick plates with multiple layers, it is necessary to strengthen the control of interlayer temperature. During the continuous welding process, the temperature of the base material should be checked to ensure that the interlayer temperature is as consistent as the preheating temperature as possible. The highest temperature between the layers should also be controlled.

7. If there are defects on the surface of multi-layer welds and welding slag is not removed, lower layer welding should be carried out.

【 Phenomenon 】 When welding thick plates in multiple layers, the welding of the lower layer is carried out without removing the welding slag and defects after each layer is completed, which can easily cause defects such as slag inclusion, porosity, and cracks in the weld seam, reduce the connection strength, and also cause splashing during the lower layer welding.
When welding thick plates in multiple layers, each layer should be continuously welded. After each layer of welding seam is completed, the welding slag, surface defects of the welding seam, and splashes should be removed in a timely manner. If any defects such as slag inclusion, porosity, and cracks that affect the welding quality are found, they should be thoroughly removed before welding.

8. Insufficient weld corner size for joint or corner joint combination welds that require penetration.

【 Phenomenon 】 For butt or corner joint combination welds that require penetration, such as T-joints, cross joints, and corner joints, the size of the weld legs is insufficient, or the weld legs of the connection weld between the web and upper flange of crane beams or similar components with fatigue calculation requirements are not enough, which will result in the strength and stiffness of the weld joints not meeting the design requirements.
[Measures] For butt joint combinations such as T-joints, cross joints, and corner joints that require penetration, sufficient welding feet must be required according to the design requirements. Generally, the size of the welding feet should not be less than 0.25t (t is the thinner plate thickness at the connection). The weld leg size of the connection weld between the web plate and the upper flange of a crane beam or similar web plate with fatigue verification requirements should be 0.5t and should not exceed 10mm. The allowable deviation for welding dimensions is 0-4 mm.

9. Welding with a welding rod or iron block inserted into the gap between the joints.

【 Phenomenon 】 Due to the difficulty in fusing the electrode head or iron block with the welded part during welding, it can cause welding defects such as incomplete fusion and incomplete penetration, reducing the connection strength. It is difficult to ensure consistency with the material of the base material if using rusted welding rod tips or iron blocks for filling; If welding rods or iron blocks with oil stains, impurities, etc. are used for filling, it will cause defects such as porosity, slag inclusion, and cracks in the weld seam.
[Measures]
(1) When the assembly gap of the workpiece is large but does not exceed the specified allowable range, and the assembly gap exceeds twice the thickness of the thin plate or exceeds 20mm, the welding method should be used to fill the concave part or reduce the assembly gap. It is strictly prohibited to use the method of filling the welding rod head or iron block for repair welding in the joint gap.
(2) When marking the machining of parts, attention should be paid to leaving sufficient cutting allowance and welding shrinkage allowance after cutting, controlling the size of the parts well, and not increasing the gap to ensure the external dimensions.