The service temperature of high pressure seamless steel pipe is below 450℃, and the domestic pipes are mainly made of SA573 Gr.70 steel specification, No.10 and No.20 carbon steel hot-rolled pipes or cold drawn pipes. High pressure seamless steel pipe is often used in high temperature and high pressure conditions. Under the action of high temperature flue gas and water vapor, the pipe will be oxidized and corroded. The steel pipe is required to have high endurance strength, high oxidation resistance and corrosion resistance, and good structure stability.
The effect of nitrogen (N) on the properties of SA573 Gr.70 steel specification and so on steel is similar to that of carbon and phosphorus. With the increase of nitrogen content, the strength of steel can be significantly improved, especially the plasticity, especially toughness, and the weldability will be decreased, and the cold brittleness will be intensified. At the same time, aging tendency, cold brittleness and hot brittleness will be increased, which will damage the weldability and cold bending property of steel. Therefore, the nitrogen content in SA573 Gr.70 steel specification and so on steel should be reduced and limited as much as possible. Generally, nitrogen content should not be higher than 0.018%.
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The selection of SA573 Gr.70 steel specification welding materials: under the condition of meeting the joint strength requirements, the welding materials with good plastic properties of deposited metal should be selected. Air protected welding wire ER50-6 is a welding material with low strength grade and low hydrogen property. The welding wire has high deposition efficiency and good plastic properties, and it is also a recognized thick plate welding material.