Welding of duplex stainless steel

The TIG welding material corresponding to duplex stainless steel SAF2205 (S31803) is 2209 wire (AWS ER2209)

Thank you, floor 1. But what are the differences in welding this duplex steel compared to welding austenitic stainless steel? Are there any things to keep in mind?

3.4 Welding of duplex stainless steel (1) Duplex stainless steel has good weldability; no preheating or post-weld heat treatment is required. However, for thicker composite plate structures, preheating and post-weld heat treatment should be carried out in accordance with relevant standards and specifications, depending on the thickness of the base material. Welding of duplex stainless steel can be carried out using methods such as manual arc welding, submerged arc automatic welding, and TIG welding. When the design specifications require low-temperature impact toughness for the material and welding of duplex stainless steel, TIG welding should be used, with care taken to control the heat input and interpass temperature in order to ensure the weld microstructure and corrosion resistance. (2) Welding procedure qualification and welder skill assessment: Before welding duplex stainless steel equipment, welding procedure qualification and welder skill assessment must be carried out in accordance with standard requirements to ensure the viability of the welding process and the recognition of the welders’ qualifications. Relevant inspections can also be carried out on the welding procedure qualification test plates, including surface inspection of the welds, radiographic testing and dye penetrant testing, as well as tests for chemical composition and mechanical properties, microstructural examination, ferrite determination, and corrosion testing, in accordance with the design requirements and specifications in the drawings. (3) Selection of welding materials: Welding materials are determined through welding procedure qualification. The general principle for selection is to use materials similar to those of the base metal; taking into account welding-induced loss, the Cr and Ni content in the welding materials is slightly higher than that in the base metal. In special cases where higher requirements are imposed on the weld metal, welding materials of a higher grade can also be chosen. For 2205, ultra-low carbon welding materials of the 22Cr-8Ni-3Mo or 22Cr-9Ni-3Mo type are generally chosen. There are many suppliers of welding materials abroad, with well-known companies including Sandvik, Svesta, Metrode, FILAC, ESAB, and others. (4) TIG welding is recommended for the welding of pipes and tube sheets. The welding of tubes to tube sheets falls into the following 4 categories: 1) Both the tube and the tube sheet are made of duplex stainless steel, usually of the same grade; the selection of welding materials is as described above. For duplex stainless steels of different grades, welding materials can be selected based on the higher Cr and Ni contents. 2) For heat exchangers designed with similar thermal expansion coefficients between duplex stainless steel and carbon steel or low-alloy steel, the tubes are made of duplex stainless steel, the tube sheet adopts a surfacing welding structure, and austenitic stainless steel can be used as the welding material. For low-alloy steel, the transition layer of the tube sheet can be surfaced with 309L, while the surface layer can be surfaced with 308L; for the welding of the surfacing layers on the tubes and tube sheet, 316L can be used ； 3) Heat exchangers designed for stress corrosion resistance, with tubes made of duplex stainless steel, and tube sheets made of composite steel plates or forged composite duplex steel. After the tube sheet is compounded, stress relief treatment is carried out. Taking into account the stresses resulting from the compounding process, the temperature limits associated with the heat treatment of the duplex steel, and the mechanical properties of the base material, it is appropriate to use the lower temperature used in the solution treatment for stress relief. The welding of the tubes and the tube sheet involves welding between duplex steels, and preheating as well as post-weld heat treatment may not be necessary ； 4) For heat exchangers designed to resist stress corrosion, the tubes are made of duplex stainless steel, while the tube sheets have a surfacing structure. Choosing the temperature for stress relief after the first layer of surfacing on the duplex stainless steel is somewhat complicated; it is necessary to take into account both the temperature limits of the duplex stainless steel and the mechanical properties of the base material. Generally, this temperature is kept between 550 and 690°C, depending on the type of base material used. The surfacing and heat treatment of the tube sheet must pass welding procedure qualification; otherwise, problems are likely to occur.