13 TIPS to be noted in welding of steel structure

Steel structure refers to a structure mainly composed of steel materials and is one of the main types of building structures. The metal structure is mainly composed of steel beams, steel columns, and other components made of section steel and steel plates. The components or components are usually connected by welds, bolts, or rivets. Because of its lightweight and easy construction, it is widely used in large factories, stadiums, super high-rises, and other fields.

In the welding process of steel structure, there are many things that need to be paid attention to. If it is negligent, it may be cast into a big mistake.

1. Don't pay attention to choose voltage during welding construction

【phenomenon】

The same arc voltage is selected regardless of the priming, filling, and cover surface, regardless of the size of the groove. In this way, the required penetration depth and width may not be achieved, and defects such as undercuts, blowholes, and splashes may occur.

【Measures】

Generally, the corresponding long arc or short arc should be selected for different situations to get better welding quality and working efficiency. For example, in order to obtain better penetration in short welding, short arc operation should be used. In order to obtain higher efficiency and melting width in filling welding or cover welding, the arc voltage can be increased appropriately.

2. Welding does not control the welding current

【phenomenon】

During welding, in order to speed up the progress, the grooves for butt welds of medium and heavy plates are not opened. The strength index drops, which does not even meet the standard requirements, and cracks appear during the bending test, which will make the performance of the welded joint impossible and pose a potential hazard to structural safety.

【Measures】

Welding should be controlled according to the welding current in the process evaluation, allowing 10 to 15% to float. The blunt edge size of the groove should not exceed 6mm. When docking, when the thickness of the board exceeds 6mm, the groove must be opened for welding.

3. Don't pay attention to the welding speed and welding current, the diameter of the electrode is used in coordination

【phenomenon】

When welding, care is not taken to control the welding speed and welding current, and the electrode diameter and welding position are used in coordination. For example, when performing bottom welding on a 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 is easy to cause defects such as unpenetrated, slag inclusions, pores, etc. ; When welding the cover surface, if the welding speed is too fast, it is easy to produce blowholes; the welding speed is too slow, the excess weld seam will be too high, and the shape is not regular; when welding thin plates or welds with small blunt edge sizes, the welding speed is too high Slow, easy to burn through.

【Measures】

The welding speed has a great influence on the welding quality and welding production efficiency. When selecting the welding current, the position of the welding seam (priming welding, filling welding, cover welding), the thickness of the welding seam, and the size of the groove, the appropriate welding speed is selected. Penetration, gas, and welding slag are easy to be discharged without burning through. On the premise of good forming, select a larger welding speed to improve production efficiency.

4. Do not pay attention to control the arc length when welding

【phenomenon】

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

【Measures】

For welding quality, short arc operation is generally used in welding, but the appropriate arc length can be selected according to different situations to obtain the welding quality, such as V-groove butt joint, corner joint layer should use a shorter arc, To weld through without undercutting, the layer can be slightly longer to fill the weld. It is better to use a short arc when the weld gap is small. When the gap is large, the arc can be slightly longer, and the welding speed is accelerated. The arc of the back welding should be short to prevent the molten iron from flowing; in order to control the temperature of the molten pool during vertical welding and horizontal welding, small current and short arc welding should also be used. In addition, no matter what kind of welding is adopted, it is necessary to keep the arc length basically unchanged during the movement to ensure that the weld width and penetration depth of the entire weld is consistent.

5. Welding does not pay attention to control welding deformation

【phenomenon】

When welding, care is not taken to control the deformation in terms of welding sequence, personnel arrangement, bevel form, welding specification selection, and operation method, etc., resulting in large deformation after welding, difficult to correct, and increased costs, especially for thick plates and large workpieces, which is difficult to correct, Mechanical correction is easy to cause cracks or lamellar tears. Using flame to correct the cost is high and the operation is not easy to cause the workpiece to overheat. For workpieces with high accuracy requirements, effective deformation control measures will not be taken, which will cause the installation size of the workpiece to fail to meet the requirements for use, and even cause rework or scrap.

【Measures】

Adopting a reasonable welding sequence and selecting appropriate welding specifications and operating methods, it is necessary to adopt anti-deformation and rigid fixing measures.

6. Multi-layer welding is not applied continuously, and the temperature between layers is not controlled.

【phenomenon】

When welding thick plates in multiple layers, do not pay attention to the temperature control between the layers. If the interval between the layers is too long, welding without reheating will easily cause cold cracks between the layers; if the interval is too short, the temperature between the layers is too high ( (More than 900℃), it will also affect the performance of the weld and the heat-affected zone, causing coarse grains, resulting in a decrease in toughness and plasticity, and leaving potential hidden dangers to the joint.

【Measures】

When thick plates are welded in multiple layers, the temperature control between the layers should be strengthened. During the continuous welding process, the temperature of the welded base metal should be checked to ensure that the temperature between the layers is as consistent as possible with the preheating temperature. Be controlled. The welding time should not be too long. In the case of welding interruption, appropriate post-heating and heat preservation measures should be taken. When re-welding, the reheating temperature should be higher than the initial preheating temperature.

7. The multi-layer welding seam does the lower layer welding without removing the welding slag and the surface of the welding seam.

【phenomenon】

In multi-layer welding of thick plates, the welding of the lower layer is carried out without removing the welding slag and defects after each layer is welded, which is easy to cause defects such as slag inclusions, pores, cracks, etc. in the weld, reducing the connection strength and causing splashing during the welding of the lower layer.

【Measures】

When thick plates are welded in multiple layers, each layer shall be continuously welded. Welding slag, weld surface defects and spatters should be removed in time after welding of each layer. Welding, slag inclusions, cracks, and other defects that affect the welding quality should be thoroughly removed before welding.

8. Welding corner size of welded joints or corner butt joints that require penetration is not enough

【phenomenon】

T-joints, cross joints, corner joints, etc. require welded butt joints or corner butt joint welds, the welding leg size is not enough, or the web of the crane beam or similar member designed with fatigue check requirements is connected to the upper wing plate edge If the size of the welding leg is insufficient, the strength and rigidity of the welding will not meet the design requirements.

【Measures】

T-joints, cross joints, corner joints and other welded joints that require penetration should be in accordance with the design requirements, and there must be sufficient welding feet. The general welding foot size should not be less than 0.25t (t is the thinner joint) Plate thickness). The welding leg size of the welding seam of the crane beam or similar web and upper flange designed with fatigue check requirements is 0.5t, and should not be greater than 10mm. The allowable deviation of the welding size is 0 ~ 4 mm.

9. Welding the tip or iron block in the joint gap

【phenomenon】

Because it is difficult to fuse the electrode head or iron block with the welded part during welding, it will cause welding defects such as unmelted and unmelted, which reduces the connection strength. If it is filled with rusty electrode heads and iron blocks, it is difficult to be consistent with the material of the base material; if it is filled with electrode heads and iron blocks with oil stains and impurities, it will cause defects such as porosity, slag inclusions and cracks in the weld. These conditions will greatly reduce the quality of the weld seam of the joint and fail to meet the quality requirements of the weld seam in the design and specifications.

【Measures】

(1) When the assembly gap of the workpiece is large, but it does not exceed the range allowed for use, and the assembly gap exceeds the thickness of the thin plate 2 times or greater than 20mm, the surfacing method is used to fill the recessed part or reduce the assembly gap. It is strictly forbidden to use the method of plug welding electrode head or iron block repair welding in the joint gap.

(2) When processing the parts, you should pay attention to the cutting allowance and the welding shrinkage allowance after cutting, control the size of the parts, and do not increase the gap to the external dimensions.

10. Uneven transition when using plates with different thickness and width

【phenomenon】

When using plates with different thicknesses and widths, but do not pay attention to whether the thickness difference of the plates is within the standard allowable range. If it is not within the allowable range and no gentle transition treatment is performed, the weld seam is likely to cause stress concentration and unwelded welding defects at a position above the thickness of the thin plate, which affects the welding quality.

【Measures】

When exceeding the relevant regulations, the welding seam should be welded into a slope, the allowable value of the slope should be 1:2.5; or one or both sides of the thickness should be processed into a slope before welding, and the allowable value of the slope should be 1:2.5. The slope of the structural slope under load and requiring fatigue check shall not be greater than 1:4. When the boards of different widths are connected, thermal cutting, mechanical processing or grinding wheel grinding should be used to make a smooth transition according to the conditions of the factory and the construction site, and the allowable slope value of the connection is 1:2.5.

11. No attention is paid to the welding sequence for components with cross welds

【phenomenon】

For components with cross welds, care is not taken to analyze the welding stress release and the effect of welding stress on the deformation of the components, and the welding sequence is reasonably arranged. Instead, the welding is performed longitudinally and horizontally. The stress deforms the board, the surface of the board is uneven, and may cause cracks in the weld.

【Measures】

For components with cross welds, a reasonable welding sequence should be established. When there are several kinds of vertical and horizontal cross welds, the horizontal joints with larger shrinkage deformation should be welded first, and then the longitudinal welds should be welded so that the transverse welds will not be constrained by the longitudinal welds, so that the shrinkage stress of the transverse joints Released without restraint, can reduce welding deformation, weld quality, or weld butt welds first and then fillet welds.

12. When the lap joints of profiled steel rods are welded, continuous welding is performed at the corners

【phenomenon】

When surrounding welding is adopted for the lap joint of the steel rod and the continuous plate, the welding seams on both sides of the rod are welded first, and then the welding seams at the end are welded discontinuously. Although it is beneficial to reduce welding deformation, it is easy to produce stress concentration and welding defects at the corner of the rod, which affects the quality of the welded joint.

【Measures】

When surrounding welding is adopted for the lap joints of profiled steel rods, continuous welding should be completed at the corner once, and do not weld to the corner and run to the other side to weld.

13. The equal strength joint is required, and the arc beam and the lead plate are not provided at both ends of the crane beam wing plate and the web plate

【phenomenon】

When welding butt welds, full penetration fillet welds, crane beam flange plates, and webs, no arc plates and lead plates are added at the arc starting point and lead-out point. It is not stable enough, and the temperature at the start and endpoints is not stable enough, which may lead to defects such as unfused, unpenetrated, cracked, slag inclusions, porosity, etc. at the start and end ends, reducing the strength of the weld and failing to meet the design requirements.

【Measures】

When welding butt welds, full penetration fillet welds and the welds of crane beam wing plates and webs, arc-leading plates and lead-out plates shall be provided at both ends of the welds. After being led out of the workpiece, the defective part is divided to obtain the quality of the weld.