(1) welding methods: due to the majority of stainless steel pipes and sizes, according to the welding characteristics of stainless steel, as far as possible, reduce the amount of heat input, the manual electric arc welding, argon arc welding is adopted two kinds of methods, d > 159 mm Φ adopts argon arc welding, manual arc welding covering. D ≦ Φ 159 mm all use argon arc welding. The welding machine adopts the manual arc welding/argon arc welding of the WS7-400 inverter arc welding machine.
(2) the welding material: austenitic stainless steel is special steel, to meet the joint with the same performance, should follow the principle of “the composition such as” to choose the welding material, at the same time to strengthen the joint between the thermal crack and corrosion ability, make a small amount of ferrite appear in the joint, choose HooCr19Ni12Mo2 argon arc welding with welding wire, hand arc welding with electrode CHSO22 as filling material, its composition is shown in table 1 and table 2.
Table 1 chemical composition of welding wire HOOCr19Ni12Mo2 (%)
Table 2 chemical composition of welding rod CHS022 (%)
(3) welding parameter. The outstanding feature of austenitic stainless steel is that it is sensitive to overheating, so it is necessary to control the interlayer temperature strictly under the condition of small current and fast welding, and the interlayer temperature is less than 60 degrees.
(4) Groove form and assembly position welding. Using V groove, groove form with lower welding current, penetration is small, thus groove blunt edge is smaller than carbon steel, approximately 0-0.5 mm, groove Angle is bigger than carbon steel, which is about 65 ° to 700 °. Due to the large thermal expansion coefficient of stainless steel, the welding stress can be produced when welding, and strict positioning welding is required. For d ≦ Φ 89 mm tube adopts two positioning, d = Φ 89 – Φ 219 mm USES three positioning, d ≧ 219 mm by four o ‘clock positioning; Position weld length 6-8 mm.
(5) Welding technical requirements:
1. The welding machine adopts dc inverse when manual arc welding, and dc is used when argon arc welding.
2. Before welding, the wire should be brushed with stainless steel wire to remove the oxide skin of the surface and clean with acetone. Electrode should be in 200-250 ℃ drying 1 h, as you take;
3. Before welding, clean the oil on both sides of the slope of the workpiece by 25 mm, and wash the sides of the slope with acetone.
4. Argon arc welding, the nozzle Φ 2 mm in diameter, extremely rich tungsten tungsten electrode, specifications Φ 2.5 mm;
5. When the argon arc welding stainless steel, the back must be protected by argon gas to guarantee the back forming. The flow rate is 5-14l/min, and the positive argon flow rate is 1213l/min.
The seam thickness should be as thin as possible at the bottom of the bottom welding, and it should be in good shape with the root, and the arc should be formed in a gentle slope. If the arc is retracted, the grinding machine will be worn out. The arc must be filled in the groove and the arc crater should be filled to prevent the cracks.
Due to the stainless steel to austenitic stainless steel, to prevent the carbide precipitation sensitization and intercrystalline corrosion, should strictly control the interpass temperature and cooling rate after welding, the welding interlayer temperature control under 60 ℃, must immediately after welding water-cooled, by subsection welding at the same time. The specific section method is shown in figure 1. This symmetrical dispersion welding sequence can increase the cooling speed of the connector and reduce the welding stress.
Figure 1. Welding schematic of different pipe diameters
2 the results
(1) the appearance inspection has no porosity, welding tumor, sag and biting edge etc., forming well.
(2) to stretch and bend test pieces, all mechanical property indexes meet the requirements, and no defects such as fusion and cracks are found.
(3) macroscopic metallographic examination, found that the weld bead was well fused, and the penetration was 1-1.5mm. Microscopic metallographic examination, parent material and the heat affected zone is all austenitic organization, weld metal for ten ferrite austenite (4%) of the organization, fully meet the requirements of intergranular corrosion resistance and resistance to brittle, after incoalation company site construction to ensure the welding quality.
Source: China 316L Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)