13 Major and Most Easily Overlooked Problems in Steel Structure Welding

Steel structure is a construction structural form primarily composed of steel materials, assembled from components such as steel beams, steel columns, and steel trusses. These components are mainly made of section steel and steel plates, and are fixed to each other through welding, bolting, or riveting. Due to its advantages like light dead weight and convenient construction, it is widely utilized in fields such as large-scale industrial plants, stadiums, and super high-rise buildings. In the process of steel structure welding, there are numerous technical essentials that must be strictly controlled, as a slight oversight can lead to severe consequences.

1. Improper Selection of Welding Voltage

• Manifestation of the Problem: During welding operations, the same arc voltage is used regardless of whether it is backing welding, filler welding, or cosmetic welding, and without considering differences in groove dimensions. This practice makes it difficult to obtain the ideal penetration depth and width, and easily produces quality defects such as undercut, porosity, and spatter.
• Corrective Measures: Appropriate arc lengths should be selected based on different welding stages. A short arc should be used for backing welding to obtain good penetration depth. For filler welding and cosmetic welding, the arc voltage can be appropriately increased to improve efficiency and increase penetration width, ensuring a balance between welding quality and production efficiency.

2. Improper Control of Welding Current

• Manifestation of the Problem: To rush the schedule, butt welds of medium and thick plates are welded directly without cutting grooves as required. This results in a decrease in weld strength, sometimes failing to meet standard requirements. Cracks easily appear during bending tests, meaning joint performance cannot be guaranteed, which poses hazards to structural safety.
• Corrective Measures: Operate strictly in accordance with the welding current determined by the welding procedure qualification (WPQ), allowing a fluctuation range of 10% to 15%. The root face size should not exceed 6 mm. When the plate thickness exceeds 6 mm, appropriate grooves must be cut before performing butt welding.

3. Welding Speed Does Not Match Related Parameters

• Manifestation of the Problem: During welding, the welding speed is not reasonably adjusted according to the welding current, electrode diameter, and welding position. For example, during the backing of a full-penetration fillet weld, the root gap is small; if the welding speed is too fast, gas and slag cannot escape fully, making it easy to produce defects like lack of penetration, slag inclusion, and porosity. Too fast a speed during cosmetic welding also easily causes porosity. If the speed is too slow, it causes excessive weld reinforcement and an uneven appearance. If the speed is too slow when welding thin plates, burn-through is highly likely to occur.
• Corrective Measures: Comprehensively consider factors such as welding current, weld position, plate thickness, and groove dimensions to select an appropriate welding speed. On the premise of ensuring full penetration, sufficient slag and gas discharge, no burn-through, and good weld formation, a faster welding speed should be adopted as much as possible to improve production efficiency.

4. Improper Control of Arc Length

• Manifestation of the Problem: During welding, the arc length is not flexibly adjusted according to factors like groove form, welding layer, joint type, and electrode brand, making weld quality difficult to guarantee.
• Corrective Measures: Under normal circumstances, short-arc welding is advisable, but the arc length can be optimized based on specific situations. For the first layer of V-groove butt joints and fillet joints, a short arc should be used to ensure root penetration and prevent undercut. The second layer can be appropriately elongated to fill the groove. Use a short arc for small gaps, and a slightly longer arc for large gaps. Overhead welding must use the shortest arc to prevent molten steel from sagging. Vertical and horizontal welding should also use low current and a short arc to control the molten pool temperature. The arc length should be kept basically stable throughout the welding process to ensure uniform weld width and penetration depth.

5. Insufficient Control Measures for Welding Deformation

• Manifestation of the Problem: Failure to systematically control deformation from aspects such as welding sequence, personnel allocation, groove form, welding parameters, and operation methods leads to severe post-weld deformation, which makes rectification difficult and increases costs. Especially for thick plates and large components, rectification is highly difficult; mechanical rectification may induce cracks, while flame rectification is costly and easily causes overheating of the workpiece. For components with high precision requirements, if effective deformation control measures are not taken, it may result in installation dimensions failing to meet requirements, or even rework and scrapping.
• Corrective Measures: Arrange the welding sequence reasonably, select appropriate welding specifications and operation methods, and simultaneously adopt technical measures such as counter-deformation and rigid fixing to effectively control welding deformation.

6. Improper Interpass Temperature Control

• Manifestation of the Problem: During multi-layer welding of thick plates, interpass temperature control is ignored. If the interpass interval is too long and welding continues without re-preheating, cold cracks are easily generated between layers. If the interval is too short, resulting in an excessively high interpass temperature, the grains in the weld and heat-affected zone (HAZ) will become coarse, and toughness and ductility will decrease, leaving hidden quality hazards in the joint.
• Corrective Measures: Strengthen interpass temperature monitoring. During continuous welding, the temperature of the base metal should be measured, and efforts should be made to keep the interpass temperature consistent with the preheating temperature, while controlling the maximum interpass temperature. When welding is interrupted, appropriate post-heating and insulation measures should be taken; when re-welding, the preheating temperature should be appropriately higher than the initial preheating temperature.

7. Incomplete Interpass Cleaning

• Manifestation of the Problem: During multi-layer welding of thick plates, the next layer is welded directly after completing each layer without removing welding slag and surface defects. This easily causes defects like slag inclusion, porosity, and cracks, reduces joint strength, and causes spatter during the welding of the subsequent layer.
• Corrective Measures: Multi-layer welding of thick plates should be performed continuously. After each layer is welded, welding slag, surface defects, and spatter must be cleaned up in a timely manner. If quality problems such as slag inclusion, porosity, or cracks are found, they must be thoroughly removed before welding the next layer.

8. Insufficient Weld Leg Size of Penetration Joints

• Manifestation of the Problem: For full-penetration butt joints or combined butt-fillet welds requiring penetration, such as T-joints, cross joints, and corner joints, the weld leg size fails to meet design requirements. For crane beams or similar structures with fatigue calculation requirements, the weld leg size connecting the web and the top flange plate is insufficient, resulting in the strength and stiffness of the welded joint failing to meet design requirements.
• Corrective Measures: Strictly control the weld leg size of combined penetration welds according to design requirements; generally, it should not be less than 0.25 times the plate thickness. For structures like crane beams that require fatigue calculation, the weld leg size connecting the web and top flange should be 0.5 times the plate thickness and not greater than 10 mm. The permissible deviation for the weld leg size is 0 to 4 mm.

9. Foreign Matter Filled in Joint Gaps

• Manifestation of the Problem: To fill an excessively large assembly gap, welding rod ends or iron blocks are stuffed into the joint for welding. It is difficult for these foreign objects to fuse thoroughly with the base metal, which easily causes defects like lack of fusion and lack of penetration. If rusted or greasy welding rod ends or iron blocks are used for filling, it can also lead to problems like porosity, slag inclusion, and cracks, severely degrading joint quality and failing to meet design and specification requirements.

• Corrective Measures: When the assembly gap exceeds 2 times the thickness of a thin plate or is greater than 20 mm, surfacing (overlay welding) should be used to fill the recessed areas or reduce the gap. It is strictly prohibited to stuff welding rod ends or iron blocks into joint gaps. When marking out parts during processing, sufficient cutting allowance and weld shrinkage allowance should be reserved, and part dimensions must be strictly controlled to avoid relying on expanding gaps to guarantee overall external dimensions.

10. Abrupt/Uneven Transition in Butt Joints of Unequal Thickness (Width)

• Manifestation of the Problem: When plate materials of different thicknesses or widths are butt-jointed, there is a failure to check whether the thickness difference is within the permissible range. If it exceeds the permissible range and a smooth transition treatment is not made, the weld is prone to stress concentration and lack of fusion defects on the thin plate side, affecting welding quality.

• Corrective Measures: When the thickness difference exceeds regulations, the weld should be machined into a slope with a maximum slope not exceeding 1:2.5; alternatively, one or both sides of the thick plate should be machined into a slope before welding, also with a maximum slope of 1:2.5. For structures directly bearing dynamic loads and requiring fatigue calculation, the slope should not be greater than 1:4. When plates of different widths are butt-jointed, methods such as thermal cutting, mechanical machining, or grinding should be used according to on-site conditions to make the transition smooth, and the maximum permissible slope value at the connection is 1:2.5.

11. Unreasonable Welding Sequence for Intersecting Welds

• Manifestation of the Problem: For components with longitudinal and transverse intersecting welds, the welding sequence is determined arbitrarily without analyzing the impact of welding stress release on deformation. Welding in a crosswise, haphazard sequence results in the welds constraining each other and generating substantial thermal contraction stress, causing uneven deformation of the plate surface and even generating welding cracks.
• Corrective Measures: Formulate a reasonable welding sequence: generally, transverse welds with larger shrinkage deformation should be welded first, followed by longitudinal welds, so that the contraction of transverse welds is not constrained by longitudinal welds and stress can be released. Alternatively, weld butt welds first and then fillet welds to effectively control welding deformation and ensure weld quality.

12. Improper Welding at Corners during Wrap-Around Welding of Section Steel Lap Joints

• Manifestation of the Problem: When section steel members and continuous plates are lapped using wrap-around welding, the welds on both sides of the member are welded first, followed by the end weld, without continuous welding. Although this method helps reduce welding deformation, it easily causes stress concentration and welding defects at the corners of the member, affecting joint quality.
• Corrective Measures: During wrap-around welding of section steel lap joints, the corners should be welded continuously in one pass, avoiding interrupting the weld upon reaching a corner and moving to the other side to continue welding.

13. Failure to Set Run-on and Run-off Tabs at Both Ends of Critical Welds

• Manifestation of the Problem: When welding butt welds, full-penetration fillet welds, and connection welds between the flange plate and web of crane beams, run-on and run-off tabs are not set at both ends of the weld. Because the current and voltage are unstable and the temperature field is non-uniform at the starting and ending points, defects like lack of fusion, lack of penetration, cracks, slag inclusion, and porosity are easily generated. This reduces weld strength and fails to meet design requirements.

• Corrective Measures: When welding the aforementioned critical welds, run-on and run-off tabs must be set at both ends of the weld to lead the parts prone to defects at both ends out of the workpiece. These parts are then cut off after welding, ensuring that the weld quality complies with requirements across its entire length.