Home > Technological Innovation

Common problems in steel structure welding - xlweld.com

Common problems in steel structure welding

Steel structure refers to the structure mainly composed of steel material, is one of the main building structure type. The structure is mainly composed of steel and steel plate, steel column, steel truss and other components, the components or components are usually used between the weld, bolts or rivets connected. Because of its relatively light weight, and the construction is simple, widely used in large factories, venues, high-level areas.


Steel structure in the welding process, there are many things to note, once the negligence, it may cast a big mistake.


1. Welding construction do not pay attention to choose the best voltage

【phenomenon】

When welding, whether it is primer, fill, cover, regardless of the size of the groove, select the same arc voltage. This may not meet the requirements of the depth of penetration, melting width, there are undercut, stomata, splash and other defects.

【Measures】

Generally for different situations should choose the corresponding long arc or short arc can get better welding quality and efficiency. For example, in order to get a better depth of penetration welding should be used when the short arc operation, filling or cover welding in order to get a higher efficiency and width can be appropriate to increase the arc voltage.


2. Welding does not control the welding current

【phenomenon】

Welding, in order to grab the progress, for the plate butt welds do not take the groove. Strength indicators decline, or even fail to meet the standard requirements, bending test cracks, this will make the weld joint performance can not be guaranteed, the structure of security poses a potential hazard.

【Measures】

Welding according to the process of assessment of the welding current control, allowing 10 to 15% of the float. The size of the blunt edge of the groove should not exceed 6mm. When docking, when the thickness of more than 6mm, to open the groove for welding.


3. Do not pay attention to the welding speed and welding current, electrode diameter coordinated use.

【phenomenon】

Welding does not pay attention to control the welding speed and welding current, electrode diameter, welding position coordinated use. Such as the full penetration of the corner seam for welding, due to the root size is narrow, such as welding speed too fast, the root gas, slag does not have enough time to discharge, easy to make the root does not melt, slag, porosity and other defects ; Welding, such as welding speed too fast, but also easy to produce pores; welding speed is too slow, the weld will be too high, the shape is not neat; welding sheet or blunt edge size of the weld, the welding speed too Slow, easy to burn and so on.

【Measures】

Welding speed on the welding quality and welding production efficiency has a significant impact, when selected with the welding current, weld location (primer welding, filling welding, cover welding), weld thickness, groove size to select the appropriate welding speed, To ensure that the penetration, gas, welding slag easy to discharge, do not burn, forming a good premise under the choice of a larger welding speed to improve productivity efficiency.


4. Do not pay attention to the control arc length

【phenomenon】

Welding is not based on the groove form, the number of welding layers, welding forms, electrode models and other appropriate adjustment arc length. 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, welding generally use short arc operation, but according to different circumstances to choose the appropriate arc length to obtain the best welding quality, such as V-shaped groove docking, cornering the first layer should be used Short arcs to ensure penetration, and no biting phenomenon, the second layer can be slightly longer to fill the weld. Weld gap is easy to use short arc, the gap can be slightly longer when the arc, welding speed. Arc welding arc should be the shortest to prevent the molten iron downstream; vertical welding, horizontal welding in order to control the bath temperature, but also with a small current, short arc welding. In addition, regardless of what welding, in the course of the movement should pay attention to always keep the arc length is basically unchanged, in order to ensure that the entire weld width and penetration of the same.


5. Welding does not pay attention to control welding deformation

【phenomenon】

Do not pay attention to welding from the welding sequence, personnel layout, groove form, welding specifications selection and operation methods such as control deformation, resulting in deformation after welding, correction difficulties, increase costs, especially thick and large parts, correction difficult , With mechanical correction easily lead to cracks or layered tear. With the high cost of flame correction and poor operation can easily cause the workpiece overheating. High precision requirements of the workpiece, do not take effective control deformation measures, will lead to the installation of the workpiece size does not meet the requirements, and even cause rework or scrapped.

【Measures】

Reasonable welding sequence and the use of appropriate welding specifications and methods of operation, but also the use of anti-deformation and rigid fixed measures.


6. Multi-layer welding is not continuous welding, do not pay attention to control the inter-layer temperature

【phenomenon】

Thick plate multi-layer welding, do not pay attention to the inter-layer temperature control, such as the interval between the interval is too long, do not re-preheat on the welding layer is easy to produce cold cracks; such as inter-layer interval is too short, (More than 900 ℃), the impact of the weld and heat affected area will have an impact, will cause coarse grain, resulting in toughness and plasticity of the joints will leave a potential risk.

【Measures】

Thick plate multi-layer welding, should strengthen the control of the inter-layer temperature, continuous welding process should be tested in the welding of the base metal temperature, so that the temperature between the layers as much as possible with the preheating temperature, the highest temperature between the layers To be controlled. Welding time should not be too long, in case of welding interruption should take appropriate post-heat, insulation measures, re-welding, the reheat temperature should be higher than the initial preheating temperature.


7. Multi-layer weld does not remove the welding slag and weld surface defects on the lower welding

【phenomenon】

Thick plate multi-layer welding, each layer of welding is not clear after the completion of welding slag and defects directly on the next layer of welding, easy to cause welds slag, pores, cracks and other defects, reduce the connection strength, and will cause the lower welding splash The

【Measures】

Thick plate multi-layer welding, each layer should be continuous welding. Each layer of welding after welding should be promptly removed welding slag, weld surface defects and spatter, found that the impact of welding quality slag, pores, cracks and other defects should be completely removed and then welding.


8. Require the penetration of the joint docking or angular butt joint weld weld angle size is not enough

【phenomenon】

T-shaped joints, cross fittings, corner joints, etc., shall be of insufficient size, or the web of the crane beam or similar component designed for fatigue inspection shall be connected to the upper wing edge Weld the foot size is not enough, will make the welding strength and stiffness are not meet the design requirements.

【Measures】

T-joints, cross joints, corner joints and other requirements of the penetration of the butt joint welding joints, should be in accordance with the design requirements, there must be sufficient foot requirements, the general foot size should not be less than 0.25t (t for the connection of thinner Thickness). Designed to have a fatigue check the requirements of the crane beam or similar webs and the upper flange connection weld the foot size 0.5t, and should not be greater than 10mm. The permissible deviation of the welding dimension is 0 to 4 mm.


9. Welding in the joint gap in the plug head or iron

【phenomenon】

As the welding is difficult to weld the head or iron and welded parts are welded together, will result in non-fusion, not penetration and other welding defects, reduce the connection strength. Such as the use of rusty welding head, iron filled, it is difficult to ensure consistent with the material of the base material; such as with oil, impurities and other welding head, iron filled, will make the weld hole, slag, cracks and other defects. These conditions will greatly reduce the quality of the joints of the weld, fail to design and specification of the weld quality requirements.

【Measures】

(1) When the workpiece assembly gap is large, but does not exceed the required allowable range, the assembly gap exceeds the thickness of the sheet 2 times or more than 20mm, the application of surfacing method to fill the depression or reduce the assembly gap. It is strictly forbidden to use the method of filling the welding head or iron welding in the joint gap.

(2) parts processing crossed, should pay attention to cut the remaining cutting and cutting after the welding shrinkage, control the size of parts, do not increase the gap to ensure that the size.


10. With different thickness and width of the plate docking, not smooth transition

【phenomenon】

When using different thickness and width of the plate docking, do not pay attention to whether the thickness of the plate within the standard allowable range. If it is not within the allowable range and does not do the smooth transition processing, the weld in the thickness of the sheet can easily lead to stress concentration and produce non-fusion welding defects, affecting welding quality.

【Measures】

When the relevant provisions should be exceeded when the weld should be welded into a slope, the slope of the maximum allowable value should be 1: 2.5; or one or both sides of the thickness of the weld before welding into a slope, and the slope of the maximum allowable value of 1: 2.5, when the direct The slope of the structure that is subjected to dynamic loads and requires fatigue checking shall not be greater than 1: 4. Different width of the plate docking, should be based on the factory and site conditions using thermal cutting, machining or grinding wheel grinding method to make it a smooth transition, and its maximum allowable slope of the connection point of 1: 2.5.


11. Do not pay attention to the welding sequence for components with crossed welds

【phenomenon】

For the components with cross welds, do not pay attention to the welding stress release and welding stress on the deformation of the components and reasonable arrangements for the welding sequence, but the vertical and horizontal random welding, the result will cause vertical and horizontal joints are mutually constrained, resulting in a larger temperature contraction Stress, deformation of the board, the board is uneven, and there may be cracks in the weld.

【Measures】

For components with crossed welds, a reasonable welding sequence should be established. When there are several vertical and horizontal cross welding welding, should be welded to shrink the larger deformation of the transverse joints, and then welding the longitudinal weld, so that welding the horizontal weld will not be subject to the longitudinal weld constraints, so that the transverse joint shrinkage In the case of no restraint to be released, can reduce the welding deformation, to ensure the quality of the weld, or welding the first butt weld after the weld seam.


12. Type steel bar lap joint with welding, the continuous welding at the corner

【phenomenon】

Type steel bar and continuous plate lap joint with the use of welding, the first welding on both sides of the weld, after welding the end of the weld, not continuous welding. Although this is beneficial to reduce the welding deformation, but in the corner of the bar prone to stress concentration and welding defects, affecting the quality of welded joints.

【Measures】

Type steel bar lap joint with welding, the corner should be a continuous welding to complete, do not weld to the corner and ran to the other side to welding.


13. Requires a strong butt, crane beam wings and webs at both ends without the arc plate and lead plate

【phenomenon】

In the welding butt welds, full penetration fillet welds, crane beam flange plate and web of the weld, the arc and the lead does not add the arc plate and lead plate, so that at the end of welding, the current voltage Not stable enough, the starting and ending point of the temperature is not stable enough to easily lead to the beginning of the weld has not fused, not penetration, cracks, slag, porosity and other defects, reduce the weld strength, fail to meet the design requirements.

【Measures】

In the welding butt welds, full penetration fillet welds and crane girder wings and webs of the weld, should be set at both ends of the weld plate and lead plate, its role is easy to produce defects at both ends of the part Lead to the workpiece outside, and then cut off the defect part to ensure the quality of the weld.

CONTACT US

Contact: XinLian

Phone: +86-510-6817 0282

Tel: +86-510-8657 0990

Email: sales@xinlianwelding.com

Add: No.3 Tianyuan Road, Qiaoqi, Xuxiake Town, Jiangyin City, Jiangsu Province, 214408 P.R.China

Scan the qr codeClose
the qr code