Special welding process and NDT requirements for duplex stainless steel
Duplex stainless steel is a kind of stainless steel with dual phase microstructure of ferrite and austenite. The proportion of ferrite and austenite in solution structure is about 50%, and the content of less phase is more than 30%. The metallographic structure determines that the performance of the Ferritic Austenitic duplex stainless steel is between ferritic stainless steel and austenitic stainless steel. It has the advantages of both stainless steels. It not only has good plasticity, toughness, corrosion resistance and weldability, but also has stronger intergranular corrosion resistance than other kinds of stainless steel. Duplex stainless steel has good resistance to pitting corrosion, stress corrosion, intergranular corrosion, high strength and low linear expansion coefficient. It is mainly used in places with strong corrosiveness below 270 ℃.(Difference between duplex stainless steel and ferritic stainless steel)
The joint performance of duplex stainless steel is mainly in the welding heat affected zone, which is greatly affected by the welding heat cycle. The metallographic structure is good or bad, that is, the proportion of ferrite and austenite in this zone and the size of ferrite grains determine the performance of duplex stainless steel.
Therefore, it has many advantages in the fields of energy, chemical industry, pharmaceutical industry, papermaking, seawater desalination, etc It is widely used. Faced with the high standards and strict requirements of the owner Aramco, the Saudi Jizan project of China Power Construction Nuclear Power Co., Ltd. applies duplex stainless steel to the public water and fire water systems, so that the pipeline system can work for a long time under the conditions of poor service environment and high corrosion resistance requirements.