A welding process for nuclear grade carbon steel pipe

Abstract

The application belongs to the field of welding process, and discloses a kind of welding process for nuclear-grade pipeline carbon steel coiled pipe, comprising S1: double chemical treatment is carried out on the carbon steel coiled material to be welded part, S2: the carbon steel coiled material after chemical treatment is preheated in vacuum environment, S3: alternating welding is adopted, S4: after each layer of welding is completed, compressed air is immediately used for rapid cooling, S5: passivation treatment is carried out after welding, S6: the welding joint is comprehensively detected by adopting the mode that magnetic powder detection and liquid penetration detection are combined;The purpose of the application is to provide a kind of welding process for nuclear-grade pipeline carbon steel coiled pipe, by optimizing welding pretreatment, welding process and postwelding treatment etc. links, improve the quality of welded joint, enhance the reliability and safety of nuclear-grade pipeline.

Description

Technical Field

[0001] This invention relates to the field of welding technology, specifically to a welding process for nuclear-grade carbon steel coiled welded pipes. Background Technology

[0002] Nuclear-grade pipelines play a crucial role in nuclear power plant systems by transporting various media, and their quality directly affects the safe and stable operation of the plant. Carbon steel welded pipes are widely used in nuclear-grade pipeline manufacturing due to their cost advantages and excellent overall performance. However, existing welding processes for nuclear-grade carbon steel welded pipes have several problems. For example, insufficient pre-welding treatment leads to residual impurities at the weld joint, affecting weld quality; during welding, a single welding method cannot simultaneously guarantee the strength, toughness, and corrosion resistance of the weld; and post-weld treatment does not completely eliminate welding stress, easily causing defects such as cracks, reducing the reliability and service life of nuclear-grade pipelines. Therefore, a new welding process is urgently needed to improve the welding quality of nuclear-grade carbon steel welded pipes. Summary of the Invention

[0003] The purpose of this invention is to provide a welding process for carbon steel coiled welded pipes for nuclear-grade pipelines. By optimizing pre-welding treatment, welding process and post-weld treatment, the quality of welded joints is improved, thereby enhancing the reliability and safety of nuclear-grade pipelines.

[0004] To achieve the above objectives, the present invention provides the following technical solution: The technical solution provided by this invention is: a welding process for nuclear-grade carbon steel coiled welded pipes, specifically including the following steps: S1: Pre-welding treatment: The carbon steel coil to be welded undergoes a double chemical treatment. First, it is pickled with a 15%-20% hydrochloric acid solution for 10-15 minutes to remove surface rust. Hydrochloric acid is a strong acid that can chemically react with rust, dissolving and removing it. Then, it is alkaline washed with a 5%-8% sodium hydroxide solution for 8-12 minutes to neutralize residual acid and further remove oil. Sodium hydroxide solution can neutralize hydrochloric acid, and its alkalinity emulsifies the oil, causing it to detach from the metal surface. To reduce the corrosion of carbon steel coil substrate by hydrochloric acid, a corrosion inhibitor with a mass fraction of 0.5%-1% is added to the hydrochloric acid solution during the pickling process. The corrosion inhibitor added during the pickling process is an organic corrosion inhibitor containing alkynyl alcohol compounds, which, by mass fraction, contains 10%-15% propargyl alcohol, 5%-8% thiourea, 3%-5% alkylamine hydrochloride, and the balance is water. This corrosion inhibitor forms a protective film by adsorption on the metal surface, inhibiting the uniform corrosion of the carbon steel substrate by hydrochloric acid, while not affecting the dissolution efficiency of rust and leaving no harmful impurities that affect the welding quality.

[0005] S2: After chemical treatment, the carbon steel coil is preheated in a vacuum environment, maintaining a vacuum level of 1×10⁻⁶. -2 -1×10 -3 Pa, the preheating temperature is 150-200℃, and the preheating time is 30-40 minutes. Preheating in a vacuum environment can prevent oxygen, moisture and other substances in the air from reacting with the metal surface, while also ensuring uniform internal temperature of the metal and reducing thermal stress during welding.

[0006] S3: Welding Process: Alternating welding is employed. The first layer uses shielded metal arc welding (SMAW) with a 3.2mm diameter electrode, a welding current of 110-130A, an arc voltage of 22-26V, and a welding speed of 60-80mm / min. SMAW offers high flexibility and is suitable for root pass welding, ensuring the fusion quality at the weld root. The second layer uses submerged arc welding (SAW) with a 4.0mm diameter wire, a welding current of 500-600A, an arc voltage of 30-34V, and a welding speed of 30-40mm / min. Subsequent layers repeat the alternating SMAW and SAW process. SAW offers high welding efficiency and deep penetration, improving the strength of the weld joint. Alternating welding combines the advantages of both methods, resulting in better weld strength, toughness, and shape. Furthermore, in alternating welding, the overlap between SMAW and SAW is 40%-60% of the weld width, ensuring the continuity and density of the weld joint.

[0007] The welding electrodes used in this process, by mass percentage, contain: C: 0.08-0.12%, Si: 0.4-0.7%, Mn: 1.3-1.7%, P≤0.025%, S≤0.025%, Cr: 0.9-1.1%, Ni: 0.6-0.8%, Mo: 0.45-0.55%, V: 0.08-0.12%, Nb: 0.02-0.05%, Ti: 0.03-0.06%, with the balance being Fe. Carbon (C) can improve the strength of the weld, but excessive content will reduce toughness and crack resistance. This invention strictly controls the carbon content within a suitable range. Silicon (Si) and manganese (Mn) are commonly used deoxidizers and alloying elements that can improve the strength and toughness of the weld. Phosphorus (P) and sulfur (S) are harmful elements, and strictly limiting their content can reduce the tendency of hot and cold cracking in the weld. Alloying elements such as chromium (Cr), nickel (Ni), and molybdenum (Mo) can improve the corrosion resistance and high-temperature strength of the weld. Elements such as vanadium (V), niobium (Nb), and titanium (Ti) can refine the grains and improve the overall performance of the weld.

[0008] The electrode coating, by weight percentage, contains: calcium fluoride 18-23%, rutile 12-16%, ferromanganese 6-9%, ferrosilicon 4-7%, ferromolybdenum 3-5%, ferrotitanium 2-4%, rare earth oxides 1.5-2.5%, soda ash 1.2-2.2%, cellulose 2.5-4.5%, with the balance being marble. Calcium fluoride and marble form an alkaline slag system, effectively removing impurities from the weld and improving its resistance to porosity and cracking. Rutile stabilizes the arc and improves welding process performance. Various ferroalloys supplement the alloying elements in the weld, ensuring its chemical composition and properties. Rare earth oxides purify the weld metal, further improving weld quality.

[0009] S4: Post-weld treatment: After each layer of welding is completed, rapid cooling is immediately performed using compressed air at a pressure of 0.5-0.8 MPa. After cooling to 60-80℃, the welded area is mechanically rolled at a pressure of 2-5 MPa. Rapid cooling reduces the residence time of the weld joint at high temperatures, preventing grain growth and improving the strength and toughness of the weld. Mechanical rolling makes the weld surface denser, eliminates surface defects, and further reduces welding stress. During mechanical rolling, the surface roughness of the rolling wheel is Ra0.8-Ra1.6; a suitable surface roughness helps ensure the rolling effect.

[0010] S5: After welding, the welded nuclear-grade carbon steel coiled pipe is immersed in a 10%-15% sodium silicate solution at 80-90℃ for passivation treatment for 20-30 minutes. The sodium silicate solution forms a dense passivation film on the metal surface, improving the metal's corrosion resistance. After passivation, the welded nuclear-grade carbon steel coiled pipe is rinsed with clean water and dried at 120-150℃ for 1-2 hours to remove residual solution and prevent corrosion.

[0011] S6: Finally, a comprehensive inspection of the welded joint is conducted using a combination of magnetic particle testing and liquid penetrant testing. Magnetic particle testing can detect surface and near-surface defects, while liquid penetrant testing can detect open defects. The combination of these two methods ensures that the welded joint is defect-free.

[0012] The beneficial effects of this technical solution are: (1) The present invention can thoroughly remove impurities from the carbon steel coil to be welded by means of dual chemical treatment and vacuum preheating, avoid the influence of impurities on the welding quality, and reduce the thermal stress during welding, thus laying the foundation for high-quality welding.

[0013] (2) Alternating welding combines the advantages of shielded metal arc welding and submerged arc welding, resulting in better weld strength, toughness and form. Furthermore, the specific composition of the welding rod and the coating design further improve the overall performance of the weld and meet the strict requirements of nuclear-grade pipelines for the quality of welded joints.

[0014] (3) The improved post-weld treatment process, including rapid cooling, mechanical rolling, passivation treatment and comprehensive testing, effectively eliminates welding stress, improves the corrosion resistance of welded joints, ensures the quality of welded joints, enhances the reliability and safety of nuclear-grade pipelines, and extends the service life of nuclear-grade pipelines. Attached Figure Description

[0015] Figure 1 This is a data table for Example 1 of the welding process for nuclear-grade carbon steel coiled welded pipe proposed in this invention; Figure 2 This is a data table for Example 2 of the welding process for a nuclear-grade carbon steel coiled welded pipe proposed in this invention; Figure 3 This is a comparison table of the differences between embodiments of the welding process for nuclear-grade carbon steel coiled welded pipe proposed in this invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The specific implementation process is as follows: Example 1: Please see Figure 1-3 The present invention provides a technical solution: a welding process for nuclear-grade carbon steel coiled welded pipe, comprising the following steps: S1: Select carbon steel coils of suitable specifications and perform double chemical treatment on the parts to be welded. Prepare a 15% hydrochloric acid solution and immerse the parts of the carbon steel coil to be welded in it for pickling for 10 minutes to remove surface rust. Then prepare a 5% sodium hydroxide solution and perform alkaline washing for 8 minutes to neutralize residual acid and remove oil stains. During the pickling process, add 0.5% corrosion inhibitor to the hydrochloric acid solution. The corrosion inhibitor added during the pickling process is a mixed solution of 12% propargyl alcohol, 6% thiourea, 4% alkylamine hydrochloride (CH3CH2CH2CH2NH2·HCl), and the remainder is water.

[0018] S2: The chemically treated carbon steel coil is placed in a vacuum environment for preheating. A vacuum furnace is used for preheating, and the heating rate and holding time are precisely controlled by a temperature control system, maintaining a vacuum level of 1×10⁻⁶. -2 Pa, preheating temperature is 150℃, preheating time is 30 minutes.

[0019] S3: Alternating welding is used. The first layer uses shielded metal arc welding (SMAW) with a 3.2mm diameter electrode, a 110A welding current, a 22V arc voltage, and a welding speed of 60mm / min. The second layer uses submerged arc welding (SAW) with a 4.0mm diameter wire, a 500A welding current, a 30V arc voltage, and a welding speed of 30mm / min. Subsequent layers repeat the alternation of SMAW and SAW, with the weld overlap being 40% of the weld width.

[0020] The welding electrode composition, by mass percentage, is as follows: C: 0.08%, Si: 0.4%, Mn: 1.3%, P: 0.02%, S: 0.02%, Cr: 0.9%, Ni: 0.6%, Mo: 0.45%, V: 0.08%, Nb: 0.02%, Ti: 0.03%, with the balance being Fe; the electrode coating composition, by mass percentage, is as follows: calcium fluoride 18%, rutile 12%, ferromanganese 6%, ferrosilicon 4%, ferromolybdenum 3%, ferrotitanium 2%, rare earth oxides 1.5%, soda ash 1.2%, cellulose 2.5%, with the balance being marble.

[0021] S4: After each layer of welding is completed, the welded parts are immediately cooled rapidly with compressed air at a pressure of 0.5MPa. After cooling to 60℃, the welded parts are mechanically rolled. Roller rolling equipment is used to roll the parts unidirectionally along the weld seam to ensure uniform force on the surface. The rolling pressure is 2MPa and the surface roughness of the rolling wheel is Ra0.8.

[0022] S5: After welding, the welded nuclear-grade carbon steel coiled pipe is immersed in a 10% sodium silicate solution at 80°C for passivation treatment for 20 minutes. Afterwards, it is rinsed with clean water and dried at 120°C for 1 hour.

[0023] S6: A combination of magnetic particle testing and liquid penetrant testing is used to conduct a comprehensive inspection of the welded joint. The inspection results show that the welded joint is free of defects. The magnetic particle testing is performed in accordance with the GB / T26951-2011 standard "Magnetic Particle Testing for Non-destructive Testing of Welds" and the liquid penetrant testing is performed in accordance with the GB / T5616-2017 standard "Guidelines for Application of Non-destructive Testing". The absence of defects exceeding the standard in the inspection results is used as the basis for judging the welded joint as qualified.

[0024] In Example 1, the pre-welding treatment, involving pickling with low-concentration hydrochloric acid and appropriate alkaline washing, combined with a corrosion inhibitor, effectively removed impurities from the surface of the carbon steel coil. This, combined with 1×10... -2 A vacuum level of 180 Pa and preheating at 150℃ reduced welding thermal stress, ensuring welding quality. During welding, alternating shielded metal arc welding (SMAW) for the root pass and submerged arc welding for the fill pass, combined with specific electrode compositions and flux coatings, ensured good root fusion and high overall strength. Testing showed significant improvements in weld tensile strength, yield strength, and impact toughness compared to traditional processes, validating the advantages of this welding process. Post-weld treatment, rapid cooling and mechanical compaction refined the weld microstructure, increasing surface hardness by approximately 12% and reducing roughness; sodium silicate solution passivation enhanced the corrosion resistance of the weld joint; and a combination of magnetic particle testing and liquid penetrant testing ensured defect detection, ultimately achieving a defect-free weld joint and a 96% first-pass yield. This fully demonstrates the comprehensive benefits of synergistic optimization across all stages of the process, reducing scrap losses and rework costs.

[0025] Example 2: Please see Figure 1-3 The present invention provides a technical solution: a welding process for nuclear-grade carbon steel coiled welded pipe, comprising the following steps: S1: Similarly, carbon steel coils are selected, and the parts to be welded are subjected to double chemical treatment. A 20% hydrochloric acid solution is prepared and pickled for 15 minutes; an 8% sodium hydroxide solution is prepared and alkaline pickled for 12 minutes. During pickling, a corrosion inhibitor with a mass fraction of 1% is added to the hydrochloric acid solution. The corrosion inhibitor added during the pickling process is a mixed solution of 15% propargyl alcohol, 8% thiourea, 5% alkylamine hydrochloride (CH3CH2CH2NH2·HCl), and the remainder is water.

[0026] S2: The carbon steel coil is preheated in a vacuum furnace, with the heating rate and holding time precisely controlled by a temperature control system. The vacuum level is 1×10⁻⁶. -3 Pa, preheat for 40 minutes at a preheating temperature of 200℃.

[0027] S3: During the alternating welding process, the parameters for the first layer of shielded metal arc welding are: electrode diameter 3.2mm, welding current 130A, arc voltage 26V, and welding speed 80mm / min; the parameters for the second layer of submerged arc welding are: wire diameter 4.0mm, welding current 600A, arc voltage 34V, and welding speed 40mm / min. Subsequent layers are performed alternately, with the overlap of weld beads being 60% of the weld bead width. The electrode composition by mass percentage is: C: 0.12%, Si: 0.7%, Mn: 1.7%, P: 0.025%, S: 0.025%, Cr: 1.1%, Ni: 0.8%, Mo: 0.55%, V: 0.12%, Nb: 0.05%, Ti: 0.06%, with the balance being Fe; the electrode coating composition by mass percentage is: calcium fluoride 23%, rutile 16%, ferromanganese 9%, ferrosilicon 7%, ferromolybdenum 5%, ferrotitanium 4%, rare earth oxides 2.5%, soda ash 2.2%, cellulose 4.5%, with the balance being marble.

[0028] S4: After each layer is welded, it is rapidly cooled to 80°C with compressed air at a pressure of 0.8MPa, and then mechanically rolled. Roller rolling equipment is used to roll in one direction along the weld seam to ensure uniform force on the surface. The rolling pressure is 5MPa and the surface roughness of the rolling wheel is Ra1.6.

[0029] S5: After welding, immerse the welded pipe in a 15% sodium silicate solution at 90°C for 30 minutes to passivate it, then rinse it with water and dry it at 150°C for 2 hours.

[0030] S6: The welded joint is of good quality and free of defects after magnetic particle testing and liquid penetrant testing. The magnetic particle testing was carried out in accordance with GB / T26951-2011 "Magnetic Particle Testing for Non-destructive Testing of Welds" and the liquid penetrant testing was carried out in accordance with GB / T5616-2017 "Guidelines for Application of Non-destructive Testing". The absence of defects exceeding the standard in the test results is used as the basis for judging the welded joint as qualified.

[0031] In Example 2, higher concentration hydrochloric acid pickling and longer alkaline washing, combined with 1% corrosion inhibitor and preheating at higher vacuum and temperature, further improved the pretreatment effect, resulting in higher cleanliness of the weld area and better control of thermal deformation. During welding, larger welding current, voltage, and speed parameters, along with 60% weld overlap and more optimized electrode and coating composition, further improved weld strength and toughness, increasing tensile strength by approximately 18%, yield strength by approximately 16%, and impact toughness by approximately 28%, while also significantly improving welding efficiency. In the post-weld treatment stage, rapid cooling with high-intensity compressed air and high-pressure mechanical compaction increased the surface hardness of the weld by approximately 14%, making the surface denser and significantly reducing fluid transport resistance; passivation treatment with high-temperature, high-concentration sodium silicate solution improved the corrosion resistance of the weld joint by approximately 4 times in a simulated nuclear power plant environment; comprehensive testing ensured the quality of the weld joint. The final product achieved a 97% first-pass yield, which not only reduced production costs but also enhanced the reliability and safety of nuclear-grade pipelines, extended their service life, and further verified the significant beneficial effects and reliability of this welding process in practical applications. The above descriptions are merely embodiments of the present invention; common knowledge regarding specific technical solutions or characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solution of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A welding process for nuclear-grade carbon steel coiled welded pipe, characterized in that, Includes the following steps: S1: Perform double chemical treatment on the carbon steel coil to be welded. First, use a 15%-20% hydrochloric acid solution for pickling for 10-15 minutes to remove surface rust. Then, use a 5%-8% sodium hydroxide solution for alkaline washing for 8-12 minutes to neutralize residual acid and further remove oil stains. During the pickling process, a corrosion inhibitor with a mass fraction of 0.5%-1% is added to the hydrochloric acid solution. The corrosion inhibitor is an organic amine corrosion inhibitor. S2: Preheat the chemically treated carbon steel coil in a vacuum environment, maintaining a vacuum level of 1×10⁻⁶. -2 -1×10 -3 Pa, the preheating temperature is 150-200℃, and the preheating time is 30-40 minutes; S3: Alternating welding is used. The first layer uses shielded metal arc welding (SMAW) with a 3.2mm diameter electrode, a welding current of 110-130A, an arc voltage of 22-26V, and a welding speed of 60-80mm / min. The second layer uses submerged arc welding (SAW) with a 4.0mm diameter wire, a welding current of 500-600A, an arc voltage of 30-34V, and a welding speed of 30-40mm / min. Subsequent layers repeat the alternation of SMAW and SAW. S4: After each layer of welding is completed, compressed air is used for rapid cooling. The compressed air pressure is 0.5-0.8MPa. After cooling to 60-80℃, the welded parts are mechanically rolled with a rolling pressure of 2-5MPa. S5: After welding, the welded nuclear-grade carbon steel coiled pipe is immersed in a sodium silicate solution with a temperature of 80-90℃ and a concentration of 10%-15% for passivation treatment for 20-30 minutes. S6: A combination of magnetic particle testing and liquid penetrant testing is used to conduct comprehensive testing on welded joints.

2. The welding process for nuclear-grade carbon steel coiled welded pipe according to claim 1, characterized in that, In the alternating welding, the overlap between the shielded metal arc welding and submerged arc welding is 40%-60% of the weld width.

3. The welding process for nuclear-grade carbon steel coiled welded pipe according to claim 1, characterized in that, During the mechanical compaction process, the surface roughness of the compaction wheel is Ra0.8-Ra1.

6.

4. The welding process for nuclear-grade carbon steel coiled welded pipe according to claim 1, characterized in that, After the passivation treatment, the welded nuclear-grade pipeline carbon steel coiled pipe is rinsed with clean water and dried at 120-150℃ for 1-2 hours.

5. The welding process for nuclear-grade carbon steel coiled welded pipe according to claim 1, characterized in that, The welding rods used in the alternating welding process, by mass percentage, contain: C: 0.08-0.12%, Si: 0.4-0.7%, Mn: 1.3-1.7%, P≤0.025%, S≤0.025%, Cr: 0.9-1.1%, Ni: 0.6-0.8%, Mo: 0.45-0.55%, V: 0.08-0.12%, Nb: 0.02-0.05%, Ti: 0.03-0.06%, with the balance being Fe; the coating of the welding rods, by mass percentage, contains: calcium fluoride 18-23%, rutile 12-16%, ferromanganese 6-9%, ferrosilicon 4-7%, ferromolybdenum 3-5%, ferrotitanium 2-4%, rare earth oxides 1.5-2.5%, soda ash 1.2-2.2%, cellulose 2.5-4.5%, with the balance being marble.

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