What are the technical points for quality control of steel structure welding?

Recently, with the transformation of China's construction industry towards green and industrialization, steel structures have been widely used in various projects such as large venues, high-rise buildings, bridge engineering, industrial parks, etc. due to their advantages of lightweight and high strength, convenient construction, energy conservation and environmental protection. Welding, as the core process of steel structure connection, has a direct impact on the overall integrity, bearing capacity, and durability of the steel structure. Poor welding quality can easily lead to safety hazards such as weld cracking and structural deformation, seriously affecting the service life and operational safety of the project.
The quality control of steel structure welding follows the core principles of "pre prevention, in-process control, and post inspection", which runs through the entire welding construction process. The core goal is to ensure that the weld seam is well formed, meets performance standards, and has no quality defects such as cracks, slag inclusions, and porosity. Industry experts suggest that the quality control of steel structure welding should take into account process standardization, personnel professionalism, and scientific testing. Based on the type of engineering structure, welding difficulty, and on-site environment, targeted control measures should be developed to ensure that welding quality meets design and industry standards, laying a solid foundation for the safety of steel structure engineering.

Quality control before welding is the foundation for preventing welding defects and the primary link of the entire welding quality control system, mainly covering core points such as welding material control, construction personnel control, welding process preparation, and welding environment inspection. The quality of welding materials directly determines the strength and toughness of the weld seam, and is the first line of defense for welding quality control.

Before construction, it is necessary to strictly inspect the welding rods, welding wires, fluxes, protective gases and other materials used for welding, verify the specifications, models, quality certificates and qualification certificates of the materials, and ensure that the materials are consistent with the design requirements. For welding materials of important structures, sampling and re inspection are also required to test the chemical composition, mechanical properties and other indicators of the materials. Unqualified materials are strictly prohibited from being put into use. At the same time, the storage and preservation of welding materials should also be standardized. Welding rods and fluxes should be stored in dry and ventilated warehouses, with temperature and humidity controlled to prevent materials from getting damp or deteriorating; The welding wire needs to be treated with rust prevention, and the protective gas needs to ensure purity to avoid welding defects caused by material problems. In the construction of a large steel structure factory, the construction unit established a special management ledger for welding materials, which controlled the entire process of material entry, storage, and requisition, effectively avoiding the flow of unqualified materials into the construction process.

The control of construction personnel is the key to welding quality control. Welding operations, especially special welding, require high professional skills and operational norms from construction personnel. Welding personnel must possess corresponding professional qualifications, and special operation personnel must hold valid work permits before they can work. Construction units need to regularly provide professional training and skill assessments to welding personnel to enhance their mastery of welding processes, operating standards, and quality control points. At the same time, technical disclosure should be conducted to the construction personnel before welding, clarifying welding process parameters, weld quality requirements, defect prevention measures, etc., to ensure that the construction personnel strictly follow the specifications and disclosure requirements, and avoid welding defects caused by improper operation.

Welding process preparation is an important step before welding. Before construction, a special welding process document should be prepared based on the requirements of steel structure design, component materials, and welding difficulty. The document should clarify the core contents such as welding methods, welding parameters, preheating temperature, interlayer temperature, and post weld heat treatment. For complex structures, thick plate welding, or welding of special materials, it is necessary to conduct welding process evaluation in advance, determine reasonable welding process parameters through experiments, verify the mechanical properties of the welded joints, and ensure the feasibility and reliability of the welding process. Welding equipment also needs to be inspected and debugged in advance, with a focus on checking the current and voltage regulation functions, cooling system, and grounding protection devices of the welding machine to ensure stable equipment performance and normal operation, providing equipment guarantee for welding quality.

The inspection of welding environment cannot be ignored, as poor welding environment can directly affect the formation of weld seams and welding quality, which can easily lead to defects such as porosity and cracks. Welding operations should avoid rainy, snowy, and windy weather, and outdoor welding should be covered with rainproof and windproof shelters; The welding environment temperature should be controlled within the allowable range of the specifications. Preheating measures should be taken for welding in low-temperature environments to prevent cold cracks from forming in the weld seam; The welding area needs to be kept clean, removing rust, oil stains, oxide scales, and other debris from the welding parts of the components to ensure a tight fit of the welding joints and avoid impurities affecting the welding quality.

Quality control during the welding process is the core link that directly determines the final quality of the weld seam, mainly covering key points such as welding parameter control, welding operation specifications, and interlayer quality control. The rationality of welding parameters is the key to ensuring welding quality. During the construction process, it is necessary to strictly follow the parameters specified in the welding process documents, with a focus on controlling parameters such as welding current, voltage, welding speed, and the extension length of welding rods (wires).

Excessive welding current can easily lead to defects such as burn through and undercutting of the weld seam, while insufficient current can cause incomplete penetration and fusion; The welding voltage and welding speed need to be matched. Excessive voltage can easily cause porosity, while excessive speed can affect the formation and penetration of the weld seam. During the construction process, welding personnel need to observe the formation of the weld seam in real time, adjust the parameters according to the actual situation, and ensure that the width and height of the weld seam meet the design requirements, and the formation is uniform and smooth. Welding operations must comply with regulatory requirements, and manual arc welding requires controlling the angle of the welding rod and the speed of the wire transport to ensure a uniform molten pool; Gas shielded welding requires sufficient flow of shielding gas to prevent air from entering the molten pool and causing porosity.

Interlayer quality control mainly targets multi-layer welding of thick plates. After each layer of welding is completed, welding slag and spatter should be removed in a timely manner, and the quality of interlayer welds should be inspected. If defects such as incomplete penetration and slag inclusion are found, they should be repaired in a timely manner before proceeding to the next layer of welding to avoid the accumulation of defects. At the same time, it is necessary to control the interlayer temperature to prevent excessive or insufficient temperature from affecting the performance of the weld seam. The interlayer temperature should be controlled within the range specified in the welding process document, and insulation measures should be taken if necessary.

The quality control after welding is the last line of defense for welding quality, mainly including key points such as weld appearance inspection, non-destructive testing, and defect repair. The appearance inspection of the weld seam should be carried out in a timely manner after the welding is completed, with a focus on checking the shape, size, surface defects, etc. of the weld seam. The surface of the weld seam should be free of defects such as cracks, slag inclusions, pores, undercutting, and incomplete penetration. The width and height of the weld seam should meet the design requirements, and the surface should be smooth and uniform. For welds that fail the appearance inspection, they need to be repaired in a timely manner, with clear repair processes and parameters. After repair, a new appearance inspection is required.

Non destructive testing is the core means of verifying the internal quality of welding, suitable for quality inspection of important structures and concealed welds. Common testing methods include ultrasonic testing, radiographic testing, magnetic particle testing, penetrant testing, etc. The construction unit shall select appropriate non-destructive testing methods based on the type, thickness, and design requirements of the weld seam, and the testing ratio shall comply with industry standards. Important welds shall undergo 100% non-destructive testing. During the testing process, it is necessary to have professional testing personnel operate to ensure accurate and reliable testing results. For internal defects found during testing, the cause of the defect should be analyzed, and a special repair plan should be developed. After repair, non-destructive testing should be carried out again until the testing is qualified. It is strictly prohibited to put unqualified welds into use.

The reporter learned that with the development of large-scale and complex steel structure engineering construction, welding quality control technology is constantly upgrading. The application of intelligent welding equipment and new detection technology has further improved the accuracy and efficiency of welding quality control. Industry experts remind that quality control of steel structure welding is a systematic project that needs to run through the entire construction process. Construction units need to strictly implement the quality responsibility system, strengthen control at all stages, standardize construction processes and testing standards. In the future, we will further promote the refinement and intelligence of welding technology, strengthen the research and application of new welding materials and processes, improve the quality control system, provide strong support for the high-quality construction of steel structure engineering, and help create a safe, durable, and efficient building structure system.