A low-stress crack prevention repair welding process for a carbon steel composite 2205 duplex steel tube plate corrosion tube bundle

Abstract

The application relates to the technical field of metal material repair welding process, and discloses a carbon steel composite 2205 duplex steel pipe plate corrosion pipe bundle low-stress anti-cracking repair welding process. In view of the problem that the durability of a carbon steel composite 2205 duplex steel pipe plate structure is insufficient under acid and alkali corrosion working conditions, through integration of high-temperature oscillation cleaning, groove shaping, gradient low-temperature preheating, nickel-based transition and duplex surface layer segmented pulse argon arc welding, and low-temperature slow cooling and ultrasonic impact stress relief process procedures, long-term anti-cracking repair of the material is realized from the multiple angles of impurity removal, thermal expansion stress relief, realization of heterogeneous metal metallurgical grade transition and residual stress elimination.

Description

Technical Field

[0001] This invention relates to the field of metal material repair welding technology, and discloses a low-stress anti-cracking repair welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets. Background Technology

[0002] With the rapid development of the petrochemical, bio-fermentation, and fine chemical industries, shell-and-tube heat exchangers are widely used as core heat exchange equipment. To balance the overall pressure resistance and resistance to strong acids, alkalis, and chloride ion corrosion, composite tube sheets with a carbon steel matrix and 2205 duplex stainless steel are widely used in industry. However, under long-term harsh conditions with acidic and alkaline media, localized corrosion, cracking, and leakage are highly likely to occur at the connection between the heat exchanger tube bundle and the tube sheet. Traditional repair techniques for carbon steel matrix and 2205 duplex stainless steel composite tube sheets suffer from the following five major drawbacks, resulting in extremely poor repair outcomes: First, incomplete removal of corrosion residue disrupts the balance of steel properties: acids, alkalis, salts, and chloride ions easily accumulate in pipe openings and composite layer gaps, and simple surface wiping cannot completely remove them. High welding temperatures cause impurities to decompose and leach out, resulting in brittle phases in the weld and heat-affected zone. This disrupts the austenite-ferrite balance structure of 2205 duplex steel, significantly reducing the equipment's resistance to acids and alkalis and stress corrosion, leading to renewed cracking and leakage shortly after repair.

[0003] Secondly, the difference in properties between dissimilar materials can easily lead to interlayer peeling and cracking: the thermal expansion coefficient and thermal conductivity of carbon steel matrix and 2205 duplex steel are quite different. Traditional welding does not have precise temperature control and gradient preheating process. The welding thermal stress is concentrated at the composite interface, which can easily cause the composite layer to peel and delaminate, exacerbating the tube bundle leakage problem.

[0004] Third, the welding materials are not compatible enough, resulting in weak weld performance: the nickel and nitrogen content of conventional ER2594 welding wire is too low, and the weld's resistance to chloride ion acid and alkali corrosion is weaker than that of 2205 base material; at the same time, it cannot adapt to the dissimilar metal welding transition requirements of carbon steel and duplex steel, resulting in poor fusion between the weld and the carbon steel base material, which easily leads to cold cracking.

[0005] Fourth, the lack of stress relief process leads to residual stress inducing cracks: Traditional repair lacks standardized preheating, slow cooling, and stress relief procedures, leaving a large amount of welding stress at the composite interface. Under the synergistic effect of acid and alkali corrosive media, stress corrosion cracks quickly occur at the pipe weld and the edge of the composite layer, resulting in an overall repair rate of over 65%.

[0006] Fifth, there is serious waste in overall production costs: simple repairs have short failure cycles and high rework rates, requiring workshops to purchase new equipment in bulk every year. Combined with maintenance consumables, labor, and downtime losses, the total annual loss is nearly 2 million yuan, resulting in a huge waste of production costs.

[0007] Therefore, it is necessary to design a repair welding process based on the comprehensive engineering needs of thoroughly removing corrosion residues, overcoming the thermal stress differences of dissimilar materials, optimizing the matching of dissimilar metal welding materials, and eliminating welding residual stress, so as to fundamentally solve the pain points of composite layer peeling and weld cracking, significantly extend the equipment repair life, and reduce the overall operation and maintenance costs. Summary of the Invention

[0008] To address the problem of insufficient durability of carbon steel composite 2205 duplex steel tube sheets under acid and alkali corrosion conditions in existing technologies, this invention provides a low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets.

[0009] To achieve the above objectives, this application adopts the following technical solution: This invention provides a low-stress anti-cracking welding process for corrosion-resistant tube bundles made of carbon steel composite 2205 duplex steel tube sheets, comprising the following steps: S1: Corrosion-affected tube bundles of carbon steel composite 2205 duplex steel tube sheet are pretreated by high-temperature vibration cleaning and grinding; S2: Shape the pipe opening; S3: Layered gradient low-temperature preheating of the tube sheet; S4: The pipe ends are repaired by segmented pulsed argon arc welding using dissimilar metal matching. S5: Low-temperature ultrasonic composite stress relief treatment of the tube sheet; S6: After inspecting and accepting the tube ends and tube sheet, the low-stress anti-cracking repair welding process for corrosion-damped carbon steel composite 2205 duplex steel tube sheet is completed.

[0010] Preferably, the specific process of step S1 is as follows: using a neutral flame, uniformly heating the area around the corroded tube bundle of carbon steel composite 2205 duplex steel tube sheet within 180-220mm, holding at 80-100℃ for 15-20min, and simultaneously performing high-frequency vibration grinding until the tube sheet and tube openings reveal a metallic luster, then wiping with anhydrous ethanol and drying with hot air to complete the pretreatment; The neutral flame is selected from one of the following: an oxyacetylene neutral flame, an oxypropane neutral flame, or an oxynatural gas neutral flame.

[0011] This invention uses high temperature to decompose and volatilize acid, alkali, salt, chlorosilane, and chloride ion deposits in the gaps. At the same time, high-frequency vibration grinding thoroughly removes penetrating corrosion interlayers. After wiping with anhydrous ethanol and drying with hot air, chloride ion residue is prevented from entering the molten pool, thus avoiding the imbalance of the two-phase structure of 2205 duplex steel.

[0012] Preferably, the specific process of step S2 is as follows: the pipe opening is ground and shaped to a narrow bevel with a single-sided angle of 12-18°, the grinding depth exceeds the bottom of the corrosion defect by at least 2mm, and a 2.5-3.5mm sealing platform is reserved on the outer edge of the bevel.

[0013] Preferably, the specific process of step S3 is as follows: using a neutral flame for layered gradient low-temperature preheating, the heating range covers an area with a diameter of 150-200 mm centered on the damaged tube bundle; During the layered gradient low-temperature preheating, the temperature of the 2205 duplex steel surface layer of the tube sheet is controlled to be ≤100℃, and the carbon steel substrate below the tube sheet is heated synchronously, with the temperature difference between the two controlled to be 1-5℃. After the heating is completed, the overall temperature is controlled to be constant at 80-100℃ and held for 4-8 minutes. The neutral flame is selected from one of the following: an oxyacetylene neutral flame, an oxypropane neutral flame, or an oxynatural gas neutral flame.

[0014] The surface layer of 2205 duplex steel is heated to ≤100℃, and the lower carbon steel substrate of the tube sheet is heated synchronously. The temperature difference between the two is controlled to be 1-5℃, which can reduce the thermal stress at the composite interface and prevent the composite layer from delamination. At the same time, low-temperature preheating avoids the precipitation of σ brittle phase in 2205 duplex steel due to high temperature.

[0015] Preferably, when the total thickness of the tube sheet is 50-80 mm, the heat preservation time is 4-7 min; When the total thickness of the tube sheet is 80-100 mm, the heat preservation time is 5-7 min; When the total thickness of the tube sheet is 100-120mm, the heat preservation time is 6-8min.

[0016] Preferably, the specific process of step S4 is as follows: under the protection of a mixed protective gas, a DC positive pulse argon arc welding machine is used to diagonally divide the pipe opening area and then stagger the welding, and two layers of surfacing welding are performed for the root transition layer and the surface corrosion-resistant layer to form a weld. The welding wire for the underlay transition layer is ERNiCrMo-4 nickel-based welding wire, and the welding wire for the surface corrosion-resistant layer is ER2209 duplex stainless steel welding wire. The ratio of austenite to ferrite in the weld is 40%-60%.

[0017] ERNiCrMo-4 nickel-based welding wire can achieve a smooth transition between carbon steel matrix and 2205 duplex steel dissimilar metals, avoiding cold cracking at the fusion line; ER2209 duplex stainless steel special welding wire can ensure that the ratio of austenite and ferrite in the weld is 40%-60%.

[0018] Preferably, the process parameters for the dissimilar metal matching segmented pulse argon arc welding are: welding current of 60-70A, voltage of 15-20V, and welding speed of 7-8cm / min. The protective gas mixture is a mixture of 95-98% argon and 2-5% nitrogen, with a gas flow rate of 5-8 L / min; The width of a single weld bead is ≤7mm, and the thickness of a single weld layer is 1.8-2.2mm.

[0019] Preferably, in step S4, the diameter of the ERNiCrMo-4 nickel-based welding wire is 1.0-1.6 mm; The ERNiCrMo-4 nickel-based welding wire, by mass fraction, includes C≤0.02%, Mn≤1.00%, Si≤0.08%, P≤0.020%, S≤0.010%, Cr: 14.50-16.50%, Mo: 15.00-17.00%, Fe: 4.00-7.00%, W: 3.00-4.50%, Co≤2.50%, with the balance being Ni and unavoidable impurities; The diameter of the ER2209 duplex stainless steel welding wire is 1.0-1.6mm; The ER2209 duplex stainless steel welding wire, by mass fraction, includes C≤0.03%, Mn: 0.50-2.00%, P≤0.03%, S≤0.03%, Si≤0.90%, Ni: 7.50-9.50%, Cr: 21.50-23.50%, Mo: 2.50-3.50%, N: 0.08-0.20%, Cu≤0.75%, with the balance being Fe and unavoidable impurities.

[0020] Preferably, the specific process of step S5 is as follows: heating the area with a diameter of 150-200mm centered on the weld bead to 145-155℃ and holding it at that temperature for 1-2 hours, then cooling it to 20-25℃ at a rate of 28-32℃ / h, and then performing ultrasonic impact treatment on the weld and the composite interface area.

[0021] High-temperature annealing at 600-900℃ not only causes the precipitation of σ-embrittled phase in 2205 duplex steel, but also causes thermal expansion difference at the composite interface, leading to delamination. Ultrasonic impact treatment of the weld and composite interface area can form a compressive stress layer on the material surface, which greatly improves the resistance to acid and alkali stress corrosion cracking.

[0022] Preferably, the testing items in step S6 include penetrant testing, hydrostatic pressure holding test, and working condition durability verification.

[0023] The technical effects and advantages of this invention are as follows: (1) The low-stress anti-cracking welding process for carbon steel composite 2205 duplex steel tube sheet corrosion tube bundle provided by the present invention addresses the problem of insufficient durability of carbon steel composite 2205 duplex steel tube sheet structure under acid and alkali corrosion conditions. By integrating high-temperature vibration cleaning, beveling, gradient low-temperature preheating, nickel-based transition and duplex surface layer segmented pulse argon arc welding, as well as low-temperature slow cooling and ultrasonic impact stress relief process, the long-term anti-cracking repair of the material is achieved from multiple angles, such as removing impurities, relieving thermal expansion stress, realizing metallurgical-grade transition of dissimilar metals and eliminating residual stress.

[0024] (2) The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheet provided by the present invention can reduce the thermal stress difference between carbon steel and duplex steel by using a gradient low-temperature preheating, nickel-based underlay transition welding wire, and low-temperature slow cooling stress relief scheme. This eliminates the problem of peeling and delamination of the composite interface after welding and solves the problem of easy detachment and failure of the traditional repair composite layer.

[0025] (3) The carbon steel composite 2205 duplex steel tube sheet corrosion corrosion tube bundle low stress anti-cracking welding process provided by the present invention thoroughly removes chloride ions, acid and alkali residues by high temperature vibration cleaning in the pre-treatment. Combined with ER2209 surface corrosion resistant layer welding wire and nitrogen-argon mixed protective gas, it can effectively stabilize the two-phase structure of duplex steel. After repair, the equipment can run continuously and stably for 12 months without repeated leakage. It has the ability to resist acid, alkali and chloride ion stress corrosion for a long time and greatly improves the repair life.

[0026] (4) The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheet provided by the present invention is applicable to various types of shell-and-tube heat exchangers with carbon steel surfacing 2205 duplex stainless steel and acid and alkali corrosive media, and is not limited by tube sheet thickness, tube bundle aperture, or number of leaking pipes, and has strong process versatility. Attached Figure Description

[0027] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0028] Figure 1 This is a flowchart of the low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheet according to the present invention. Detailed Implementation

[0029] It is readily understood that, based on the technical solutions of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without departing from the spirit or scope of this invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solutions of this invention and should not be considered as the entirety of this invention or as limitations or restrictions on the technical solutions of this invention.

[0030] The raw materials and equipment used in the following embodiments of the present invention are described below (unless otherwise specified, they are all commercially available products in the art): The root pass transition layer welding wire is ERNiCrMo-4 nickel-based welding wire conforming to international standards, namely Hastelloy C-276 welding wire. Its mass fraction includes C≤0.02%, Mn≤1.00%, Si≤0.08%, P≤0.020%, S≤0.010%, Cr: 14.50-16.50%, Mo: 15.00-17.00%, Fe: 4.00-7.00%, W: 3.00-4.50%, Co≤2.50%, with the balance being Ni and unavoidable impurities.

[0031] Surface corrosion-resistant layer welding wire: ER2209 duplex stainless steel special welding wire conforming to standards is used. Its mass fraction includes C≤0.03%, Mn: 0.50-2.00%, P≤0.03%, S≤0.03%, Si≤0.90%, Ni: 7.50-9.50%, Cr: 21.50-23.50%, Mo: 2.50-3.50%, N: 0.08-0.20%, Cu≤0.75%, with the balance being Fe and unavoidable impurities.

[0032] Protective gas: A mixture of 98% high-purity argon and 2% nitrogen is used.

[0033] Ultrasonic impact equipment: A handheld ultrasonic impact gun with a working frequency of 20kHz is used.

[0034] Example 1 S1: Using an oxyacetylene neutral flame, uniformly heat the area around the corrosion tube bundle of the carbon steel composite 2205 duplex steel tube sheet within 200 mm, hold at 90℃ for 20 min, and simultaneously perform high-frequency vibration grinding until the tube sheet and tube openings reveal a metallic luster. Then wipe with anhydrous ethanol and dry with hot air to complete the pretreatment. S2: Grind and shape the pipe opening to a narrow bevel with a single-sided angle of 15°. The grinding depth exceeds the bottom of the corrosion defect by 3mm. A 3mm sealing platform is reserved on the outer edge of the bevel. After grinding, PT penetrant testing is used to confirm that there are no hidden microcracks or corrosion layers. S3: Use an oxyacetylene neutral flame for layered gradient low-temperature preheating, covering an area with a diameter of 200mm centered on the damaged tube bundle. Control the temperature of the 2205 duplex steel surface layer of the tube sheet to ≤100℃, and simultaneously heat the carbon steel substrate below the tube sheet, controlling the temperature difference between the two to be 3℃. After the heating is completed, control the overall constant temperature at 90℃ and hold for 7 minutes. S4: Under the protection of a mixed gas with a flow rate of 6.5 L / min, a DC positive pulse TIG welding machine is used to perform diagonal partitioning welding of the pipe nozzle area in the pattern 1→3→2→4. Two layers of welding are performed, namely the root pass transition layer and the top pass corrosion-resistant layer, to form a weld. The welding wire for the root pass transition layer is ERNiCrMo-4 nickel-based welding wire with a diameter of 1.6 mm, and the welding wire for the top pass corrosion-resistant layer is ER2209 duplex stainless steel welding wire with a diameter of 1.6 mm. The width of a single weld pass is 6 mm, and the thickness of a single weld layer is 2 mm. After each pass, the weld is lightly tapped with a small hammer. The ratio of austenite to ferrite in the weld is 50%. The process parameters for segmented pulsed argon arc welding of dissimilar metals are: welding current of 65A, voltage of 18V, and welding speed of 8cm / min. S5: Heat the area within a 200mm diameter zone centered on the weld bead to 150℃ and hold for 1 hour, then cool it to 25℃ at a rate of 30℃ / h, and then perform ultrasonic impact treatment on the weld and composite interface area. S6: After inspecting and accepting the tube ends and tube sheet, the low-stress anti-cracking repair welding process for corrosion-damped carbon steel composite 2205 duplex steel tube sheet is completed.

[0035] Comparative Example 1 The process is basically the same as in Example 1, except that in step S4, ordinary stainless steel welding wire is used and a high-current continuous welding method is adopted to perform one-time filling welding on the pipe opening from bottom to top.

[0036] Comparative Example 2 The process is basically the same as in Example 1, except that in step S4, the 1.6mm diameter ERNiCrMo-4 nickel-based welding wire and the 1.6mm diameter ER2209 duplex stainless steel special welding wire are replaced with 1.6mm diameter ERNiCrMo-4 nickel-based welding wire.

[0037] Comparative Example 3 The process is basically the same as in Example 1, except that in step S4, the 1.6mm diameter ERNiCrMo-4 nickel-based welding wire and the 1.6mm diameter ER2209 duplex stainless steel special welding wire are replaced with the 1.6mm diameter ER2209 duplex stainless steel special welding wire.

[0038] Comparative Example 4 Basically the same as Example 1, except that the staggered welding method of diagonal partition 1→3→2→4 is replaced by continuous circumferential welding in a single direction for the pipe opening.

[0039] Performance testing 1. Constant load stress corrosion test Test method: According to the test standard of GB / T 15970, a constant tensile stress equivalent to 75% of the specified plastic elongation strength of the material is applied to the specimen, and then it is immersed in an acidic chloride aqueous solution simulating the real environment of the workshop. The specimen is continuously observed and recorded to see if it breaks within 1000 hours.

[0040] 2. PT Penetrant Testing Test method: According to the test standard of GB / T 18851.1-2005, remove the stains on the weld surface, spray penetrant on the area to be inspected and keep it for 10-30 minutes, remove the excess penetrant and dry it, spray white developer and keep it for 7-10 minutes, then observe whether there are red stripes or dots on the development layer to determine whether there are porosity, slag inclusions or microcracks in the weld.

[0041] 3. Hydraulic pressure resistance Test method: According to the test standard of GB / T 151, use a test pump to increase the pressure until the test pressure reaches 1.5 times the design working pressure, maintain the pressure for 30 minutes, observe the change of pressure gauge reading, and check for water leakage, wetting or obvious pressure drop.

[0042] 4. Durability under long-term operating conditions Test method: After repair, the heat exchanger was continuously and stably operated under acid and alkaline media conditions in the workshop for 12 months to check for secondary leaks and peeling of the composite layer. The test results are shown in Table 1 below: Table 1 Test Results

[0043] Comparing the test results of Example 1 and Comparative Example 1, it can be seen that the present invention uses graded welding material selection with dissimilar metal matching and pulse staggered segmented welding process to replace the conventional high-current continuous welding method and ordinary stainless steel welding wire. Example 1 did not break during the 1000-hour constant load stress corrosion test, had no defects in PT penetrant testing, achieved a pressure drop of 0 MPa and no leakage in hydraulic pressure resistance, and achieved no secondary leakage and no peeling in working condition durability. In contrast, Comparative Example 1 broke after about 320 hours of operation, accompanied by micropores, microcracks and hydraulic leakage. This shows that the dissimilar metal matching and segmented pulsed argon arc welding process of the present invention can significantly improve the stress corrosion resistance, density, load-bearing capacity and long service life of the weld while avoiding local heat accumulation.

[0044] Comparing the test results of Example 1 and Comparative Example 2, it can be seen that the present invention uses a graded welding material combination of ERNiCrMo-4 nickel-based welding wire and ER2209 duplex stainless steel special welding wire to replace the use of ERNiCrMo-4 nickel-based welding wire alone. Although Comparative Example 2 did not break and remained hydraulically stable in the constant load stress corrosion test, it experienced pitting corrosion in the later stage and failed after 5 months of operation due to the surface corrosion-resistant layer being corroded and perforated by acid and alkali media. In contrast, Example 1 achieved excellent working condition durability of more than 12 months without secondary leakage through the synergistic effect of the two-grade welding materials. This shows that the graded welding material formula of the present invention greatly improves the surface acid and alkali resistance and pitting corrosion resistance while ensuring crack resistance.

[0045] Comparing the test results of Example 1 and Comparative Example 3, it can be seen that the present invention uses a graded welding material combination of ERNiCrMo-4 nickel-based welding wire and ER2209 duplex stainless steel special welding wire to replace the single use of ER2209 duplex stainless steel special welding wire for the entire layer. Due to the lack of flexible buffer and stress absorption of the intermediate nickel base layer, Comparative Example 3 fractured after only about 180 hours in the constant load stress corrosion test, with a large number of cold cracks at the fusion line. Significant pressure drop and leakage occurred after 15 minutes of pressure holding. However, all indicators of Example 1 met the standards perfectly. This shows that the present invention successfully eliminated the thermal stress of dissimilar metal welding by using nickel-based welding wire as the base layer, ensuring the high crack resistance and high sealing performance of the structure.

[0046] Comparing the test results of Example 1 and Comparative Example 4, it can be seen that the present invention uses a diagonal staggered welding method (1→3→2→4) to replace the continuous circumferential welding in a single direction. Due to the concentrated accumulation of heat along a single direction, Comparative Example 4 fractured after running for about 650 hours in the constant load stress corrosion test, and peeling cracks appeared at the interface edge. After running for 6 months, peeling and flaking appeared at the edge of the composite interface. However, after ultrasonic composite stress relief, Example 1 showed extremely strong bonding and no peeling occurred. This indicates that the diagonal staggered segmented welding of the present invention can effectively balance the thermal field and release residual stress, playing a decisive role in preventing peeling and flaking of the carbon steel-2205 composite layer and improving the stress corrosion resistance life.

[0047] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A low-stress anti-cracking welding process for corrosion-resistant tube bundles made of carbon steel composite 2205 duplex steel tube sheet, characterized in that, Includes the following steps: S1: Corrosion-affected tube bundles of carbon steel composite 2205 duplex steel tube sheet are pretreated by high-temperature vibration cleaning and grinding; S2: Shape the pipe opening; S3: Layered gradient low-temperature preheating of the tube sheet; S4: The pipe ends are repaired by segmented pulsed argon arc welding using dissimilar metal matching. S5: Low-temperature ultrasonic composite stress relief treatment of the tube sheet; S6: After inspecting and accepting the tube ends and tube sheet, the low-stress anti-cracking repair welding process for corrosion-damped carbon steel composite 2205 duplex steel tube sheet is completed.

2. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 1, characterized in that, The specific process of step S1 is as follows: using a neutral flame, uniformly heating the area around the corrosion tube bundle of carbon steel composite 2205 duplex steel tube sheet within 180-220mm, holding at 80-100℃ for 15-20min, and simultaneously performing high-frequency vibration grinding until the tube sheet and tube openings reveal a metallic luster, then wiping with anhydrous ethanol and drying with hot air to complete the pretreatment. The neutral flame is selected from one of the following: an oxyacetylene neutral flame, an oxypropane neutral flame, or an oxynatural gas neutral flame.

3. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 1, characterized in that, The specific process of step S2 is as follows: the pipe opening is ground and shaped to a narrow bevel with a single-sided angle of 12-18°, the grinding depth exceeds the bottom of the corrosion defect by at least 2mm, and a 2.5-3.5mm sealing platform is reserved on the outer edge of the bevel.

4. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 1, characterized in that, The specific process of step S3 is as follows: use a neutral flame for layered gradient low-temperature preheating, and the heating range covers an area with a diameter of 150-200 mm centered on the damaged tube bundle; During the layered gradient low-temperature preheating, the temperature of the 2205 duplex steel surface layer of the tube sheet is controlled to be ≤100℃, and the carbon steel substrate below the tube sheet is heated synchronously, with the temperature difference between the two controlled to be 1-5℃. After the heating is completed, the overall temperature is controlled to be constant at 80-100℃ and held for 4-8 minutes. The neutral flame is selected from one of the following: an oxyacetylene neutral flame, an oxypropane neutral flame, or an oxynatural gas neutral flame.

5. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 4, is characterized in that, When the total thickness of the tube sheet is 50-80mm, the heat preservation time is 4-7min; When the total thickness of the tube sheet is 80-100 mm, the heat preservation time is 5-7 min; When the total thickness of the tube sheet is 100-120mm, the heat preservation time is 6-8min.

6. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 1, characterized in that, The specific process of step S4 is as follows: under the protection of mixed protective gas, the pipe opening area is divided into diagonal sections by a DC positive pulse argon arc welding machine and then welded alternately. Two layers of surfacing are performed, namely the root transition layer and the surface corrosion-resistant layer, to form a weld. The welding wire for the underlay transition layer is ERNiCrMo-4 nickel-based welding wire, and the welding wire for the surface corrosion-resistant layer is ER2209 duplex stainless steel welding wire. The ratio of austenite to ferrite in the weld is 40%-60%.

7. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 6, is characterized in that, The process parameters for the segmented pulsed argon arc welding of dissimilar metals are: welding current of 60-70A, voltage of 15-20V, and welding speed of 7-8cm / min. The protective gas mixture is a mixture of 95-98% argon and 2-5% nitrogen, with a gas flow rate of 5-8 L / min; The width of a single weld bead is ≤7mm, and the thickness of a single weld layer is 1.8-2.2mm.

8. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 6, is characterized in that, In step S4, the diameter of the ERNiCrMo-4 nickel-based welding wire is 1.0-1.6 mm; The ERNiCrMo-4 nickel-based welding wire, by mass fraction, includes C≤0.02%, Mn≤1.00%, Si≤0.08%, P≤0.020%, S≤0.010%, Cr: 14.50-16.50%, Mo: 15.00-17.00%, Fe: 4.00-7.00%, W: 3.00-4.50%, Co≤2.50%, with the balance being Ni and unavoidable impurities; The diameter of the ER2209 duplex stainless steel welding wire is 1.0-1.6mm; The ER2209 duplex stainless steel welding wire, by mass fraction, includes C≤0.03%, Mn: 0.50-2.00%, P≤0.03%, S≤0.03%, Si≤0.90%, Ni: 7.50-9.50%, Cr: 21.50-23.50%, Mo: 2.50-3.50%, N: 0.08-0.20%, Cu≤0.75%, with the balance being Fe and unavoidable impurities.

9. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 1, characterized in that, The specific process of step S5 is as follows: heat the area with a diameter of 150-200mm centered on the weld bead to 145-155℃ and hold it for 1-2 hours, then cool it to 20-25℃ at a rate of 28-32℃ / h, and then perform ultrasonic impact treatment on the weld and composite interface area.

10. The low-stress anti-cracking welding process for corrosion-resistant tube bundles of carbon steel composite 2205 duplex steel tube sheets according to claim 1, characterized in that, The testing items in step S6 include penetrant testing, hydrostatic pressure holding test, and working condition durability verification.

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