Welding process of duplex stainless steel pipe

According to many years of experience in welding duplex stainless steel in the factory, the welding technology and methods of duplex steel are summarized as follows. Then, let's learn about it together.duplex steel stainless steel pipeThe welding process method and operation steps!

Weldability of 1. duplex stainless steel tubes

Dual-phase stainless steel pipes have good welding performance. Preheating is not required before welding, heat treatment is not required after welding, cold and hot crack sensitivity is low, embrittlement tendency is lower than ferrite, and metallographic structure contains about 50% ferrite. Generally, the working temperature of duplex stainless steel is below 250. At the same time, the welded joint of duplex stainless steel may precipitate intermetallic compound phase of chromium and iron and embrittlement, and the formation temperature of phase is about 750~950. The formation of the phase takes a certain period of time, generally occurs within 10 to 20 minutes, and grows after 10 to 20 minutes. Therefore, it is preferable to use a relatively low linear energy during welding, rapid cooling, and a low temperature of 550 to 600 during stress relief treatment.

Selection of 2. welding methods

1. Electron beam welding and plasma arc welding are generally not used because of the high line energy, the welding metal and HTHAZ have coarse grains and reduced toughness. On the other hand, electroslag welding, melting electrode arc welding (GMAW, MIG), submerged arc welding) SAW), the use is also limited.

2. The general welding methods for duplex steel and stainless steel pipes are manual arc welding (SMAW) and tungsten arc welding) GTAW). Manual arc welding is suitable for all-round welding and is a versatile, flexible, simple and widely used method. Tungsten arc welding is usually used for automatic welding of pipe joint root bead or pipe, and is also commonly used for welding of sheet or pipe to tubesheet joints. This method can ensure good mechanical properties of weldments, especially low temperature toughness. However, even if it is automatically welded, the deposition of nerves is not efficient. Pure Ar or 98% Ar 2% N2 is usually used as the protective gas, but when welding on one side and welding on both sides, no matter what kind of joint form is used, the protective gas (root gas) on the back side is required, usually pure Ar or 98% Ar 2% N2. Multi-layer welding, multi-pass and low deposition rate welding methods are habitually used.

Selection of 3. welding materials

Generally speaking, the welding of dual-phase steel and stainless steel pipes generally uses welding rods in manual arc welding, and welding lines are used in tungsten arc welding. At the time of welding, in order to obtain the same/phase ratio as that of the base material, nickel is usually added to the wire at a level of 2% to 4% higher than that of the base material to obtain the same phase ratio as that of the base material. Chemical composition and cooling rate will affect the ratio of medium/phase in the welded joint, but if nickel is added to the welding, the phase transition temperature will rise, and the transition from to will be more complete, so the influence of chemical composition is greater; in terms of welding rod, The weldability of titanium type (rutile type) clad composite electrode is better than that of alkaline electrode. The former has good slag removal, especially beneficial to the slag removal of the weld bead at the pipe end, however, in the case of low-temperature mechanical properties of the electrode, special consideration is given to the use of alkaline electrodes. In order to prevent the generation of voids, the electrodes before welding must be used for 250 to 350 hours, 2 hours of firing or super moisture resistant electrodes.

Control of 4. welding heat input and post-weld cooling rate

In order to ensure the excellent comprehensive properties of duplex stainless steel, it is very important to maintain the balance of ferrite/austenite, but due to the rapid cooling rate in the welding thermal cycle, this balance is unstable in welding. This is because the ferrite content in the weld metal is far more than 50%. In order to restore the balance, in addition to the nickel content in the welding wire by 2% to 4%, the welding heat input is also controlled, and the latter is used to control the cooling rate, thereby producing diffusive ferrite.

The above introduction is the welding process and operation steps of duplex steel stainless steel pipe. If you need to know more, please feel free to contact us!