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Proper material selection: The choice of welding materials for dissimilar steels in pressure vessels is crucial for welding; the quality and performance of the welded joints are closely related to the welding materials used. In line with the principles of rational, scientific, and effective material selection, the following guidelines should be followed: (1) When welding carbon steel and low-alloy steel, 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 electrode used should be no less than that of the base metal with the lower strength. At the same time, the plasticity and impact toughness of the weld metal should be inferior to those of the base metal with the higher strength but poorer plasticity. Therefore, the welding material with the lower strength between the two can be selected. At the same time, to prevent welding cracks, the welding process should be determined based on the steel grade, which has high strength but poor weldability, including welding specifications, preheating temperature, and post-weld heat treatment. (2) When welding low-alloy steel and austenitic stainless steel, electrodes should be selected in accordance with the specified limits for the chemical composition of the deposited metal. Generally, austenitic steel electrodes with high chromium and nickel contents, as well as good plasticity and crack resistance, are chosen; the welding process and specifications are determined based on the relatively poor weldability of the stainless steel. (3) For welding stainless steel composite plates, different types of electrodes should be selected according to the requirements for the base layer, transition layer, and overlay layer. For welding of base materials (carbon steel or low-alloy steel), use corresponding structural steel electrodes ； Appropriate austenitic steel electrodes should be used for the cladding ； The transition layer must take into account the dilution effect of the base material, and austenitic steel electrodes with high chromium and nickel content, as well as good plasticity and crack resistance, should be selected. Appropriate groove shape: For welding of dissimilar steels, the groove shape should be chosen in such a way as to reduce the dilution rate of the weld metal; butt joints should be preferred whenever possible, with no sharp corners or gaps. Increasing the groove angle can increase the amount of welding wire that melts into the weld, thereby reducing the fusion ratio. The groove shape is usually selected from those specified in GB/T 985; for composite plate materials, the shapes listed in NB/T 47015-2011 \"Welding Procedures for Pressure Vessels\" are used. These include V-shaped grooves, combined V and U-shaped grooves, and X-shaped grooves. Furthermore, when welding composite steel plates, the base metal on the joint side can be thinned through machining, which ensures that during the welding of the clad layer and the transition layer, the weld metal of the transition layer merges into the base metal, thereby guaranteeing the quality of the clad layer welding and the performance of the final product. Welding process parameters: The setting of welding process parameters for dissimilar steels is closely related to the fusion ratio. The required fusion for welding dissimilar steels is relatively small; therefore, welding should be carried out with low wire energy, typically using a lower current, a higher welding speed, and multi-layer multi-pass welding. The preheating temperature should be selected based on the principle of using the highest possible value; for steels with poor weldability, preheating is necessary to prevent the occurrence of cold cracks. One of the two steels requires preheating, while the other does not; preheating measures should be taken during welding. For example, since pearlitic heat-resistant steel requires preheating while low-carbon steel does not, it should be preheated at the preheating temperature specified for pearlitic heat-resistant steel. If one type of steel requires a higher preheating temperature while another requires a lower one, welding should be carried out with preheating at the higher temperature. The welding procedure specification must be followed correctly. The welding procedure specification for welding dissimilar steels in pressure vessels serves as a reference document for weldment processing and practical operations; it ensures quality consistency when carried out by skilled welders, and it also acts as a standard for welding technicians to conduct quality inspections on the products. For the specific welds of certain products, it is necessary to utilize theoretical and practical expertise to develop reasonable and scientific welding procedures. These procedures must be provided to the welders, who are required to follow the parameters specified in them strictly; they must not rely on their habitual working methods in order to ensure the quality of the welds.