Pressure vessels are different from other welded structures. This is a special all-welded structure. Its welded joint bears the same various loads, temperatures, and physical and chemical effects of the working medium as the container shell. The butt weld metal not only requires its static load strength to be basically equal to the static load strength of the shell material, but also requires sufficient plasticity and toughness to prevent the welding joints of the compression parts from being subjected to various stresses during processing and during processing. surgery. Under the combined action of temperature, premature failure or brittle fracture will occur. In addition, in some applications, the weld metal is also required to have the ability to resist corrosion by the working medium. Therefore, the performance requirements of pressure vessel weld metal should follow the principles of equal strength, equal plasticity, equal toughness and equal corrosion resistance.

1. The principle of equal strength: the equal strength of the welded joint of a pressure vessel should be understood as its strength performance is not lower than the lower limit specified by the parent metal standard. Strength characteristics include normal temperature, high temperature short-term strength. In fact, it is impossible and unnecessary for the strength value of the welded joint to be absolutely equal to the corresponding strength value of the base metal. In addition, because the metallographic structure of the base metal and the weld metal are different, the yield ratio is also different. It is difficult to simultaneously make the tensile strength and yield strength of the weld metal reach the specified value of the base metal standard. For high-temperature pressure vessels, the strength index of the welded joint should be the high-temperature short-term tensile strength at the highest working temperature, and it is not necessary to reach the specified normal temperature strength index at the same time.

2. The principle of equal plasticity and equal toughness: The equal plasticity and equal toughness of pressure vessel welded joints refer to those whose plasticity and toughness are not lower than the lower limit of the plasticity and toughness index specified by the parent material standard. Lower than the specified value of shipbuilding technical conditions. According to the current relevant standards, the impact toughness of welded joints or weld metals of pressure vessels is usually measured by Charpy V-notch impact test, and is characterized by impact absorption energy (J). When inspecting welding materials and product witness test boards, the notch of the impact sample is opened in the center of the welding metal. In the weldability test, welding process test and welding process qualification test of the new steel grade, the notches of the impact specimen were opened in the weld metal, fusion zone and heat-affected zone respectively. The notched impact toughness of each area should not be lower than the lower limit specified by the standard.

3. Principle of corrosion resistance: The corrosion resistance of pressure vessel welded joints should be understood as corrosion resistance, hydrogen resistance and oxidation resistance not lower than the index specified by the parent material standard or the corresponding specified value. Product manufacturing technical conditions. In order to meet this requirement, the alloy composition of the weld metal shall not be lower than the value specified in the base metal standard. Considering that welding heat treatment may adversely affect the corrosion resistance of the joint, the main alloy composition should be selected slightly higher than the main alloy composition of the base metal. Welding materials with lower carbon content than the base metal.