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The selection of welding electrodes must be carried out on the premise of ensuring the safety and feasible use of the welded structure. It involves a comprehensive evaluation of factors such as the chemical composition and mechanical properties of the material to be welded, the plate thickness and joint type, the characteristics of the welded structure, the stress conditions, the requirements for weld performance based on the structural usage conditions, as well as the welding procedures and technical-economic considerations. Accordingly, the appropriate welding electrode should be chosen; when necessary, welding feasibility tests are also required. (1) Key points for selecting electrodes when welding the same type of steel: ① Consider the mechanical properties and chemical composition of the weld metal. For ordinary structural steel, it is generally required that the weld metal have the same strength as the base material; therefore, electrodes whose tensile strength of the deposited metal is equal to or slightly higher than that of the base material should be used. For alloy structural steel, it is sometimes also required that the alloy composition be the same as or similar to that of the base material. In situations where welded structures have high rigidity, high stress at the joints, and a tendency for cracks to form in the welds, it is advisable to consider using electrodes with a strength lower than that of the base material. When the contents of elements such as carbon, sulfur, and phosphorus in the base metal are high, cracks are likely to occur in the weld; therefore, alkaline low-hydrogen electrodes with good crack resistance should be used. ②Considering the service performance and operating conditions of welded components, for weldments subjected to loads and impact forces, in addition to meeting strength requirements, it is essential to ensure that the weld metal possesses high impact toughness and ductility; therefore, low-hydrogen electrodes with high ductility and toughness values can be used. For weldments exposed to corrosive media, stainless steel electrodes or other corrosion-resistant electrodes should be selected based on the properties of the medium and its corrosion characteristics. For welded components that operate under high-temperature, low-temperature, wear-resistant, or other special conditions, corresponding heat-resistant steels, low-temperature steels, cladding materials, or welding electrodes for special purposes should be used. ③Taking into account the characteristics of welded structures and their stress conditions, for thick welded components with complex shapes and high rigidity, large internal stresses are generated during welding, which can easily lead to cracks in the welds; therefore, alkaline low-hydrogen electrodes with good crack resistance should be used. For weldments that are not subject to heavy stress and whose welding areas are difficult to clean thoroughly, acidic electrodes that are not sensitive to rust, scale, and oil should be used. For weldments that cannot be flipped due to constraints, electrodes suitable for all-position welding should be used. ④Taking into account construction conditions and economic benefits, acid welding electrodes with good workability should be selected as long as the product’s performance requirements are met. In confined or poorly ventilated areas, acidic electrodes or low-dust electrodes should be used. For structures that require a large amount of welding work, high-efficiency electrodes should be used whenever possible, such as iron powder electrodes and high-efficiency gravity electrodes, or specialized electrodes like root pass electrodes and vertical welding electrodes, in order to improve welding productivity. (2) Key points for selecting welding electrodes when welding dissimilar steels: ① For carbon steel + low-alloy steel (or low-alloy steel + high-strength low-alloy steel) with different strength grades, it is generally required that the strength of the weld metal or joint be no less than the lowest strength of the two metals being welded. The strength of the weld metal produced by the selected electrode should ensure that the strength of the weld and joint is at least as high as that of the material with the lower strength; meanwhile, the plasticity and impact toughness of the weld metal should be no less than those of the material with higher strength but poorer plasticity. Therefore, the electrode can be selected based on the steel with the lower strength level of the two. However, to prevent welding cracks, the welding procedure must be determined based on the steel grade with a higher strength level and poorer weldability, including the welding specifications, preheating temperature, and post-weld heat treatment. ②For low-alloy steel + austenitic stainless steel, electrodes should be selected in accordance with the specified limits for the chemical composition of the deposited metal. Generally, Cr25-Ni13 type austenitic steel electrodes with high chromium and nickel contents, as well as good plasticity and crack resistance, are chosen to prevent cracks resulting from the formation of brittle hardened structures. However, the welding process and specifications should be determined based on the stainless steel with poor weldability. ③For stainless steel composite plates, three welding electrodes with different properties should be selected to meet the welding requirements of the base layer, overlay layer, and transition layer. For welding base metals (carbon steel or low-alloy steel), use structural steel electrodes of the appropriate strength grade ； Since the cladding is in direct contact with the corrosive medium, welding electrodes made of austenitic stainless steel with appropriate compositions should be used. The key lies in the welding of the transition layer (i.e., the interface between the clad layer and the base layer); the dilution effect of the base material must be taken into account, and Cr25-Ni13 type austenitic steel electrodes with high chromium and nickel contents, as well as good plasticity and crack resistance, should be used.