The Connection between Reducers of Heat Exchangers & Dissimilar Steel Pipes
Posted: 05/23/2022 08:46:28 Hits: 3
Formulating the construction plan
1. Principles of welding carbon steel 20 and stainless steel 304 dissimilar steel
According to the analysis of the weldability of austenitic stainless steel 304 and ferritic carbon steel 20 dissimilar steel, hot cracks easily happen when the two are welded, and the migration of carbon and residual stress also have adverse effects on the quality of welded joints. Keep the welding part clean in the process and use filler metal of welding seams with high nickel content to reduce welding stress. Surfacing transition layer on the carbon steel 20 first; control fusion ratio to reduce the influence of the migration of carbon, and welding heat input. The generation of welding hot cracks can be prevented; the migration of carbon and welding stress can be reduced through the above measures.
1. Principles of welding carbon steel 20 and stainless steel 304 dissimilar steel
According to the analysis of the weldability of austenitic stainless steel 304 and ferritic carbon steel 20 dissimilar steel, hot cracks easily happen when the two are welded, and the migration of carbon and residual stress also have adverse effects on the quality of welded joints. Keep the welding part clean in the process and use filler metal of welding seams with high nickel content to reduce welding stress. Surfacing transition layer on the carbon steel 20 first; control fusion ratio to reduce the influence of the migration of carbon, and welding heat input. The generation of welding hot cracks can be prevented; the migration of carbon and welding stress can be reduced through the above measures.
2. The selection of welding materials
According to NB/T47015-2011 Welding Regulations for Pressure Vessels, and HG/T20581-2011 The Selection of Materials for Steel Chemical Vessels Chapter 8.8 The Selection of Welding Materials for Dissimilar Metals stipulates that When the temperature of the welding material of austenitic stainless steel and ferrite is lower than 450℃, A302 electrode or H13Cr24Ni13 welding wire should generally be used. According to the working conditions of this equipment, use H12Cr24Ni13 argon arc welding wire as bottom welding, A302 electrode the transition layer and other layers. Considering that the back of the welded structure cannot be filled with argon protection, and the stainless steel welded joint will be oxidized and fail, we choose TGF309 type self-protected argon arc welding wires with Cr24Nil3, A302 electrodes ( Model E309-16) electrode for welding.
3. Carrying out the welding plan
3.1 Cleaning before welding
When welding austenitic stainless steel 304 and ferritic carbon steel 20 dissimilar steel, strictly clean the welding groove surface and welding materials and remove the stuff and rust in the original pipe fittings, preventing sulfur, phosphorus and other impurities from melting into the welding seam and reducing the generation of gas holes and hot cracks.
3.2 Groove preparation
To ensure that there is enough welding space for the transition layer and to reduce the effect of the fusion ratio and the migration of carbon in the welding process of the transition layer, the groove angle is larger than that of the ordinary butt joint.
3.3 Welding sequence
Use TGF309 self-protection welding wire to make the bottom bead 1 by argon arc welding, and use A302 electrode to surface the transition layer weld on the groove side of carbon steel 20. Then, use the A302 electrode to weld 3 to 6 welding seams between the stainless steel 304 base metal. The welding sequence is shown in Figure 1.
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Figure 1 Welding sequence of welding grooves between stainless steel 304 and carbon steel 20
3.4 Welding specification parameters
To control the fusion ratio, the current as small as possible is selected, and the welding is performed at the lower limit of the qualified welding line energy to reduce the tendency of thermal cracking.
4. The effect of repair
The carbon steel 20 reducer at the inlet and outlet of the heat exchanger is welded with the 304 stainless steel pipeline. By optimizing the welding structure, the dissimilar steel welded joint is located at the horizontal welding position, which is conducive to controlling the welding heat input. Self-shielded argon arc welding wire is used for bottom welding. Use A302 electrodes to weld the transition layer and other technological measures, ensuring the quality of the welding of dissimilar steel, and the equipment has been running smoothly for one year after installation.
3. Carrying out the welding plan
3.1 Cleaning before welding
When welding austenitic stainless steel 304 and ferritic carbon steel 20 dissimilar steel, strictly clean the welding groove surface and welding materials and remove the stuff and rust in the original pipe fittings, preventing sulfur, phosphorus and other impurities from melting into the welding seam and reducing the generation of gas holes and hot cracks.
3.2 Groove preparation
To ensure that there is enough welding space for the transition layer and to reduce the effect of the fusion ratio and the migration of carbon in the welding process of the transition layer, the groove angle is larger than that of the ordinary butt joint.
3.3 Welding sequence
Use TGF309 self-protection welding wire to make the bottom bead 1 by argon arc welding, and use A302 electrode to surface the transition layer weld on the groove side of carbon steel 20. Then, use the A302 electrode to weld 3 to 6 welding seams between the stainless steel 304 base metal. The welding sequence is shown in Figure 1.
Figure 1 Welding sequence of welding grooves between stainless steel 304 and carbon steel 20
3.4 Welding specification parameters
To control the fusion ratio, the current as small as possible is selected, and the welding is performed at the lower limit of the qualified welding line energy to reduce the tendency of thermal cracking.
4. The effect of repair
The carbon steel 20 reducer at the inlet and outlet of the heat exchanger is welded with the 304 stainless steel pipeline. By optimizing the welding structure, the dissimilar steel welded joint is located at the horizontal welding position, which is conducive to controlling the welding heat input. Self-shielded argon arc welding wire is used for bottom welding. Use A302 electrodes to weld the transition layer and other technological measures, ensuring the quality of the welding of dissimilar steel, and the equipment has been running smoothly for one year after installation.
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