A sintered flux for double pipe submerged arc welding and a preparation method thereof

Abstract

The present application relates to oil and gas pipeline welding technical field, especially relates to a kind of sintered flux for double pipe submerged arc ring welding and preparation method thereof.A kind of sintered flux for double pipe submerged arc ring welding, the chemical composition of the sintered flux is as follows in percentage by mass:CaF2:5~15%, MgO:15~20%, Al2O3:15~20%, CaO:2~5%, MnO:3~10%, BaCO3:5~10%, TiO2:3~10%, Ni:1~5%, B:0.8~1.5%, Re:1~0.05%, SiO2:15~20%, iron powder:10~30%, S≤0.015%, P≤0.020%.The present application adds the chemical composition required by sintered flux in the form of fluorite, fused magnesite, bauxite, marble, barium carbonate, manganese ore, rutile, rare earth ferrosilicon, nickel iron, boron iron, iron powder, in the process of the present application in 20mm or above large wall thickness X80 submerged arc steel pipe submerged arc welding, weld slag does not lose, deslagging is easy, weld is flat, regular.

Description

Technical Field

[0001] This invention relates to the field of oil and gas pipeline welding technology, and in particular to a sintering flux for submerged arc circumferential welding of twin pipes and its preparation method. Background Technology

[0002] Twin-pipe construction involves welding two steel pipes together on-site using a prefabrication method. This twin-pipe approach significantly reduces pipeline construction time, greatly meeting the project's goals of speed, efficiency, and cost-effectiveness. Submerged arc welding (SAW) offers high production efficiency, good process stability, uniform weld microstructure, and excellent weld joint performance, making it the primary welding process for twin-pipe construction and widely used in long-distance pipeline construction both domestically and internationally.

[0003] Unlike conventional spiral and straight-seam submerged arc welding in horizontal positions, double-pipe welding is circumferential. This process involves a smaller welding plane for both the inner and outer welds, significantly limiting the variation in weld point positions. Furthermore, it primarily employs low heat input submerged arc welding, with welding speeds less than 1 m / min, often using multi-layer welding, and heat input typically not exceeding 15 KJ / cm. Conventional fluxes prioritize welding speed and efficiency, resulting in high welding speeds, sometimes exceeding 1.8 m / min. They are typically single-layer, one-time welds. However, the slag has a short melting range of 1000-1300℃, leading to a high crystallization rate and excessive cooling. This prevents the effective removal of inclusions and gases from the weld, resulting in poor weld cleanliness, insufficient reaction of effective components, and hindering the free flow of weld metal and the effective transition of beneficial alloys. Consequently, excellent weld joint microstructure cannot be achieved. Especially when used for low-speed welding, the weld metal is limited, easily leading to poor transition and inadequate filling, severely impacting the quality and performance of double-ring welds in X70 and higher grade steels. In particular, the fracture toughness of the weld cannot be guaranteed, often adversely affecting pipeline safety on-site. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this invention is to provide a sintered flux for submerged arc welding of twin tubes and its preparation method. This sintered flux is suitable for submerged arc welding of twin tubes of X70 steel grade and above. It enables the weld slag to have a large melting range within 1000~1300℃ and a low crystallization rate, ensuring the purity of the weld during welding, allowing effective components to fully react, facilitating the free flow of weld metal and the effective transition of beneficial alloys, thereby obtaining an excellent weld joint microstructure that possesses both high strength and toughness, as well as excellent CTOD fracture toughness.

[0005] The technical solution of the present invention is: a sintered flux for submerged arc welding of twin tubes, wherein the chemical composition of the sintered flux by mass percentage is: CaF2: 5~15%, MgO: 15~20%, Al2O3: 15~20%, CaO: 2~5%, MnO: 3~10%, BaCO3: 5~10%, TiO2: 3~10%, Ni: 1~5%, B: 0.8~1.5%, Re: 1~0.05%, SiO2: 15~20%, iron powder: 10~30%, S≤0.015%, P≤0.020%.

[0006] The CaF2 is added in the form of fluorite mineral powder, with a CaF2 content of not less than 95% and P ≤ 0.003%; the MgO is added in the form of fused magnesia, with an MgO content of not less than 97%, S ≤ 0.003%, and P ≤ 0.05%; the Al2O3 is added in the form of bauxite, with an Al2O3 content of not less than 84%, and S and P ≤ 0.03%; the CaO is added in the form of marble, with a CaO content of not less than 40%; the MnO is added in the form of manganese-rich ore after roasting, air drying, and water leaching, with an MnO content of not less than 30%, S ≤ 0.05%, and P ≤ 0.05%; the BaCO3 is added in the form of barium carbonate, with a content of not less than 70%; the SiO2 is introduced through manganese ore, bauxite, fluorite, fused magnesia, rare earth ferrosilicon, and water glass as a binder, with the total SiO2 content controlled below 20%, and S and P ≤ 0.03%; the TiO2 is added in the form of natural rutile, with a TiO2 content of ≥58%; the Re and Si alloy is added in the form of rare earth ferrosilicon, with a Re content of ≥30% and a Si content of ≥45%; the Ni alloy is added in the form of electrolytic ferronickel, with a Ni content of ≥90% and P and S ≤0.03%; the B ferroalloy is added in the form of electrolytic ferronickel, with a B content of ≥20%, P ≤0.03%, and S ≤0.03%; the iron powder is atomized reduced iron powder with an oxygen content of ≤0.5%, and the Fe content is ≥40% relative to the total iron powder.

[0007] The fluorite mineral powder has a particle size of 100 mesh or larger; the fused magnesia has a particle size of 80-100 mesh; the bauxite has a particle size of 80-100 mesh; the SiO2 has a particle size of 80-100 mesh; the natural rutile has a particle size of 100 mesh or larger; the rare earth ferrosilicon has a particle size of 80-120 mesh; the nickel-iron has a particle size of 80-120 mesh; and the atomized reduced iron powder has a particle size of less than 200 mesh.

[0008] The selection criteria for the chemical composition of the sintered flux used in submerged arc welding of twin tubes are as follows:

[0009] (1) CaF2, as a slag-forming agent, reacts with SiO2 and H2O on the surface of liquid metal to generate HF gas, which is insoluble in molten steel. This reduces the partial pressure of hydrogen in the arc and decreases the solubility of hydrogen in the metal. However, this gas is toxic to the human body. At the same time, CaF2 dilutes the molten slag, improves its fluidity, reduces its viscosity, and facilitates rapid solidification. However, excessive CaF2 content will severely reduce the stability of the arc, affect the weld formation, and increase the toxicity to operators. Insufficient CaF2 content will not achieve the desired effect. Based on the above, the CaF2 content should be controlled between 5% and 15%.

[0010] (2) MgO is an alkaline material. Together with CaO, it plays a role in regulating the alkalinity of the flux and has a significant effect on improving the melting point and melting temperature of the slag. It can regulate the melting point and existence time of the weld metal and ensure the effective precipitation of harmful substances. In order to ensure the fluidity and spreadability of the weld metal, its content should not be greater than 20%. If the content is too high, the melting point of the slag will increase, resulting in poor fluidity of the slag, poor weld formation, and serious problems such as undercut and difficulty in slag removal. Based on the above, the content of MgO should be controlled at 15~20%.

[0011] (3) Al2O3, as the main slag-forming agent, has good stability at high temperatures. Together with MgO, it plays a good role in regulating the melting point, viscosity, and melting temperature range of the slag, thereby improving and adjusting the weld morphology. At a certain content, it can make the fish-scale pattern of the weld finer and the weld surface smoother. In this invention, when the Al2O3 content exceeds 25%, the melting point of the slag is too high and the viscosity increases, which will significantly reduce the fluidity of the slag and thus seriously deteriorate the appearance of the weld. Accordingly, the content of Al2O3 is set at 15-20%.

[0012] (4) CaO, as a major component of alkaline slag systems, has the characteristics of small linear expansion coefficient and low crystallization phase transformation temperature. It can increase the surface tension of slag and the interfacial tension between slag and metal, improve slag removal ability, and greatly improve the process performance of weld. It can increase the basicity of slag and increase the desulfurization and dephosphorization ability of slag. If the content is too high, the slag will form a 3CaO.SiO2 complex, which increases the melting point of slag and has an adverse effect on the fluidity of weld metal. Based on this, the content of Al2O3 is controlled at 2~5%.

[0013] (5) BaCO3 has the functions of stabilizing the arc and forming slag. It can replace part of SiO2, and play a role in adjusting the melting point, viscosity, surface tension and fluidity of the slag, thereby improving the arc stability, reducing weld undercut and improving weld formation. At the same time, a certain amount of BaCO3 is needed, but if the content is too high, it is easy to decompose and combine with TiO2 to form BaO.TiO2, which will worsen the slag removal performance. Based on this, the content of BaCO3 is controlled at 5~10%.

[0014] (6) TiO2 has the functions of stabilizing the arc and slag formation. It can adjust the melting point, viscosity, surface tension and fluidity of the slag, and is particularly suitable for circumferential welding, improving the weld morphology and reducing undercut. At the same time, in the Ti transition weld, during the weld crystallization and cooling process, second phase particles such as carbides, nitrides and intermetallic compounds are precipitated, which can refine the austenite grains, thereby refining the transformed ferrite grains and ensuring that the weld has good strength and toughness. Generally, it is necessary to exceed 10% to achieve the desired effect. However, if it is greater than 10%, it will reduce the solidification temperature range of the slag and be detrimental to the fluidity of the flux slag. Therefore, the content of TiO2 is determined to be 3~10%.

[0015] (7) MnO is added in the form of manganese ore in this project, which can reduce the surface tension of the slag, improve fluidity, and facilitate weld formation. It also has the ability to increase the welding current carrying capacity. However, since manganese ore contains a lot of impurities such as S and P, this invention uses manganese-rich ore and reduces the P and S content in the manganese ore to below 0.05% through high-temperature roasting, air drying and water leaching. Therefore, the MnO content is controlled at about 5~10%.

[0016] (8) SiO2 exists as a deoxidizer and can play a certain role in regulating the basicity, viscosity, and softening temperature of the slag. It can combine with most of the alkaline oxides in the slag to form a complex, which can increase the viscosity of the slag, ensure that the steel pipe does not drip slag during high-speed rotation, and prevent the loss of weld metal solution, so that the weld has a good appearance. In addition to the main components, the raw materials used, such as wollastonite, bauxite, fluorite and fused magnesia, also contain a large amount of SiO2. Therefore, SiO2 is not directly added in this project, but is controlled to 15~20% through the adjustment of other raw materials.

[0017] (9) Rare earth is an alloy made by melting silicon, rare earth, etc. It is a good spheroidizing agent, which significantly improves the quantity and morphology of banded sulfide inclusions, and has a significant effect on reducing the sulfur content in the weld, improving the cleanliness of the weld, and ensuring the overall quality stability and uniformity of the weld. Since the amount of rare earth added is extremely small, the flux preparation is very difficult. Therefore, this project selects an alloy component made by melting silicon alloy and rare earth. The effect of rare earth on the weld is to improve the weld performance by changing the microstructure through the flux entering the weld. Too little content will not play the due role, and too much content will contaminate the grain boundaries and lose the expected effect. At the same time, too much silicon element will easily increase the viscosity of the slag. Therefore, the rare earth content in this project is determined to be 0.05~1%.

[0018] (10) Ni and B alloys have a high transition coefficient and strong activity. In this project, they are added in the form of ferronickel, ferromanganese, and rare earth ferrosilicon. During the welding process, they play a role in reducing the oxygen activity of the slag and can compensate for the Ni and B lost in the weld metal during the welding process. At the same time, they protect the beneficial alloying elements in the weld from being burned off, effectively play a role in forming and stabilizing austenite, and increase the undercooling degree of the austenite to ferrite transformation, improve the nucleation rate, reduce the grain growth time, and achieve a good grain refinement effect. At the same time, they can also effectively control the inclusions in the weld pool, which plays a crucial role in obtaining high toughness welded joints at low temperatures, resulting in fine and uniform weld structure and ensuring excellent low-temperature fracture toughness of the weld. Therefore, the content of added Ni alloy is determined to be about 1~5%, and the content of added B is determined to be 0.8~1.5%.

[0019] (11) Iron powder is an essential additive in high-speed welding to increase the deposition rate of welding wire and in high-efficiency submerged arc welding. Adding iron powder can improve and enhance the welding process performance, such as improving arc stability, improving slag removal performance, and making the weld bead smooth and beautiful. When the iron powder content is less than 10%, it will not improve the welding efficiency. If the iron powder content exceeds 30%, the iron powder will easily agglomerate in the flux during molten / solidified processes. Excessive iron powder will easily adhere to the weld surface, reducing the spreadability of the weld bead. For low-hydrogen fluxes, excessive oxygen content in the iron powder will make the welding slag thinner, affecting the protective effect of the flux and hindering the transition of alloying elements. In this invention, the oxygen content in the iron powder must be strictly limited to less than 0.5%. Therefore, the iron powder content is determined to be between 10% and 30%.

[0020] The above-mentioned method for preparing sintered flux for submerged arc welding of twin tubes includes the following steps:

[0021] S1: By weight, mix 8-18 parts fluorite, 18-22 parts fused magnesia, 20-25 parts bauxite, 5-10 parts marble, 7-15 parts barium carbonate, 8-15 parts manganese ore, 8-15 parts rutile, 0.2-1 parts rare earth ferrosilicon, 1-5 parts nickel iron, 0.8-1.5 parts boron iron, and 10-30 parts iron powder evenly.

[0022] S2: Add 15.48~31.5 parts of binder to the mixture obtained in step S1, and granulate the bonded wet material by vibrating and shaking it with a sieve or granulator.

[0023] S3: During the granulation process, the particle size of the granulated flux is controlled between 10 and 60 mesh by passing it through a 10-20 mesh sieve;

[0024] S4: The formed flux is dried in a high-temperature furnace at a temperature range of 200~350℃.

[0025] S5: The dried flux is sintered in a sintering furnace at a temperature range of 800~900℃;

[0026] S6: The sintered flux is packaged after being screened through a 10-60 mesh.

[0027] The binder in step S2 is sodium silicate, which has a Baumé degree of 41.9 to 43.9 and a modulus of 2.5 to 2.7.

[0028] In the actual preparation process, the sodium silicate used as a binder has a Baume degree of 41.9~43.9 and a modulus of 2.5~2.7, which can effectively reduce the moisture and hydrogen content in the flux and increase the alkalinity of the flux, ensuring that the flux particles have good strength.

[0029] In step S5, an inert gas with a flow rate of 0.1 to 1 liter / minute is introduced during sintering to protect the flux.

[0030] In the actual preparation process, inert gas is used to protect the flux, which can effectively prevent the flux from oxidizing under high temperature conditions.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. This invention introduces TiO2 and BaCO3 into the chemical composition of the sintering flux to ensure that the slag has a large melting range and a low crystallization rate within 1000~1300℃, thereby ensuring the purity and process performance of the weld during the welding process.

[0033] 2. This invention introduces acidic and alkaline substances MgO and CaO into the chemical composition of the sintering flux. Compared with ordinary flux, this invention ensures that the flux has a higher alkalinity value, reduces the oxidation capacity of the slag, reduces harmful gases and impurities in the slag, and ensures a more effective transition of beneficial alloys.

[0034] 3. The present invention introduces iron powder into the chemical composition of the sintering flux, which can further improve the metal deposition rate during welding with low heat input, ensure the amount of weld metal filling, and simultaneously reduce the number of welding passes to improve welding efficiency.

[0035] 4. This invention introduces B, Ni alloys and rare earth microalloying substances into the chemical composition of the sintering flux, which refines and homogenizes the weld grains while ensuring a greater amount of acicular ferrite structure. This ensures that the weld has excellent CTOD fracture toughness while possessing high strength and toughness.

[0036] 5. Using the flux of this invention and the corresponding welding wire, circumferential submerged arc welding was performed on the steel pipe. The heat input was greater than 15 KJ / cm, the weld slag did not flow out, the weld bead was regular, the weld surface was smooth, the metallic luster was obvious, and the slag was easy to remove.

[0037] 6. After welding using the flux of this invention matched with the corresponding welding wire, the circumferential weld metal R m =695-750MPa, X80 Φ1422×21.4mm steel pipe after welding can be applied to a wide range of welding process parameters. Using this invention, in the submerged arc welding process of X80 submerged arc steel pipe with a wall thickness of more than 20mm, the weld slag does not flow out, the slag removal is easy, and the weld bead is flat and regular.

[0038] 7. After circumferential welding of two X80 grade steel pipes using the flux of this invention and the corresponding welding wire, non-destructive testing was performed according to the welding standards for natural gas transmission pipelines. No cracks or excessive porosity were found in the weld, and the slag inclusions met the standard requirements. At the same time, the weld has excellent fracture toughness. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to embodiments:

[0040] Example 1

[0041] A sintered flux for submerged arc welding of twin tubes, wherein the chemical composition of the sintered flux by mass percentage is: CaF2: 5~15%, MgO: 15~20%, Al2O3: 15~20%, CaO: 2~5%, MnO: 3~10%, BaCO3: 5~10%, TiO2: 3~10%, Ni: 1~5%, B: 0.8~1.5%, Re: 1~0.05%, SiO2: 15~20%, iron powder: 10~30%, S≤0.015%, P≤0.020%.

[0042] The CaF2 is added in the form of fluorite mineral powder, with a CaF2 content of not less than 95% and P ≤ 0.003%; the MgO is added in the form of fused magnesia, with an MgO content of not less than 97%, S ≤ 0.003%, and P ≤ 0.05%; the Al2O3 is added in the form of bauxite, with an Al2O3 content of not less than 84%, and S and P ≤ 0.03%; the CaO is added in the form of marble, with a CaO content of not less than 40%; the MnO is added in the form of manganese-rich ore after roasting, air drying, and water leaching, with an MnO content of not less than 30%, S ≤ 0.05%, and P ≤ 0.05%; the BaCO3 is added in the form of barium carbonate, with a content of not less than 70%; the SiO2 is introduced through manganese ore, bauxite, fluorite, fused magnesia, rare earth ferrosilicon, and water glass as a binder, and is not specifically added, with the total SiO2 content controlled below 20%, and S and P ≤ 0.03%; the TiO2 is added in the form of natural rutile, with a TiO2 content of ≥58%; the Re and Si alloy is added in the form of rare earth ferrosilicon, with a Re content of ≥30% and a Si content of ≥45%; the Ni alloy is added in the form of electrolytic ferronickel, with a Ni content of ≥90% and P and S ≤0.03%; the B ferroalloy is added in the form of electrolytic ferronickel, with a B content of ≥20%, P ≤0.03%, and S ≤0.03%; the iron powder is atomized reduced iron powder with an oxygen content of ≤0.5%, and the Fe content is ≥40% relative to the total iron powder.

[0043] The fluorite mineral powder has a particle size of 100 mesh or larger; the fused magnesia has a particle size of 80-100 mesh; the bauxite has a particle size of 80-100 mesh; the SiO2 has a particle size of 80-100 mesh; the natural rutile has a particle size of 100 mesh or larger; the rare earth ferrosilicon has a particle size of 80-120 mesh; the nickel-iron has a particle size of 80-120 mesh; and the atomized reduced iron powder has a particle size of less than 200 mesh.

[0044] Example 2

[0045] A method for preparing a sintered flux for submerged arc welding of twin tubes includes the following steps:

[0046] S1: By weight, mix 8-18 parts fluorite, 18-22 parts fused magnesia, 20-25 parts bauxite, 5-10 parts marble, 7-15 parts barium carbonate, 8-15 parts manganese ore, 8-15 parts rutile, 0.2-1 parts rare earth ferrosilicon, 1-5 parts nickel iron, 0.8-1.5 parts boron iron, and 10-30 parts iron powder evenly.

[0047] S2: Add 15.48~31.5 parts of binder to the mixture obtained in step S1, and granulate the bonded wet material by vibrating and shaking it with a sieve or granulator.

[0048] S3: During the granulation process, the particle size of the granulated flux is controlled between 10 and 60 mesh by passing it through a 10-20 mesh sieve;

[0049] S4: The formed flux is dried in a high-temperature furnace at a temperature range of 200~350℃.

[0050] S5: The dried flux is sintered in a sintering furnace at a temperature range of 800~900℃;

[0051] S6: The sintered flux is packaged after being screened through a 10-60 mesh.

[0052] The binder in step S2 is sodium silicate, which has a Baumé degree of 41.9 to 43.9 and a modulus of 2.5 to 2.7.

[0053] In step S5, an inert gas with a flow rate of 0.1 to 1 liter / minute is introduced during sintering to protect the flux.

[0054] Example 3

[0055] According to the sintered flux for submerged arc welding of twin tubes described in Example 1 above, the sintered flux is prepared using the preparation method for the sintered flux for submerged arc welding of twin tubes described in Example 2. The specific process is as follows:

[0056] (1) Flux composition (wt%)

[0057] When the required chemical composition of the sintering flux is added in the form of fluorite, fused magnesia, bauxite, marble, barium carbonate, manganese ore, rutile, rare earth ferrosilicon, nickel ferrophosphate, ferroboron, and iron powder, the mineral composition and alloy weight percentage in the sintering flux are as follows: fluorite 10, fused magnesia 18.5, bauxite 21.5, marble 6, barium carbonate 8.5, manganese ore 12, rutile 6, rare earth ferrosilicon 0.2, nickel ferrophosphate 3, ferroboron 1, and iron powder 12.

[0058] (2) Preparation of sintering flux

[0059] After mixing and stirring the above mineral components and alloys evenly, add potassium sodium water glass binder for wet mixing, then granulate using a winnowing basket or granulator to control the flux particle size between 10 and 60 mesh. After drying at a low temperature of 200 to 250°C, sinter at a high temperature of 800 to 900°C, and then package it in moisture-proof packaging bags after screening through a 10 to 60 mesh screen.

[0060] (3) The flux of the present invention was matched with the corresponding low-temperature welding wire for fusion metal welding. According to the relevant welding material standards, the test plate was Q235 with a thickness of 25mm, a bevel angle of 20°, and a root gap of 15mm. The welding specifications were 480A current, 30V voltage, 26m / h welding speed, and 150±15℃ interpass temperature. The mechanical properties of the fusion metal after welding are shown in Table 1.

[0061] As can be seen from Table 1, when the flux of this invention is matched with the corresponding low-temperature welding wire for fusion metal welding, compared with the standard requirements, the weld not only has high strength and toughness, but also excellent CTOD fracture toughness.

[0062] (4) The flux of this invention is matched with the corresponding low-temperature welding wire to perform circumferential welding of two steel pipes. The steel pipe grade is X80, the steel pipe specification is Φ1422×21.4mm, and the chemical composition is C: 0.05, Si: 0.25, Mn: 1.68, P: 0.011, S: 0.0016, Cu: 0.17, Ni: 0.37, Cr: 0.22, Mo: 0.22, Ti: 0.018, V: 0.05, Al: 0.03, B: 0.0004, and the remainder is iron. The process adopted is as follows: the bevel angle of the circumferential position is 60° on the inner surface and 80° on the inner surface, the root gap is 2mm, and the blunt edge is 6~8mm; the welding sequence is to first use an internal alignment tool to assemble the two steel pipes, and then use CO2 gas shielded automatic welding for pre-welding, and then use submerged arc welding to complete the internal and external welding of the assembled steel pipes in sequence. The submerged arc welding process uses a combination of internal single-wire welding, external single-wire welding for root pass and filler / cover pass. The internal welding current is 850A and the voltage is 30V. The external welding root pass specifications are: welding current 680A, voltage 31.5V, and welding speed 0.7m / min. The filler and cover pass welding wire current is 700A and voltage 30V, welding speed is 1m / min, and the interpass temperature is 150±15℃. The mechanical properties of the welded metal are shown in Table 2.

[0063]

[0064] As can be seen from Table 2, when the flux of this invention is matched with the corresponding low-temperature welding wire to perform circumferential welding of two steel pipes, the weld has high strength and toughness. During the welding process, the weld slag does not flow out, the weld bead is regular, the weld surface is smooth, the metallic luster is obvious, the slag is easy to fall off, and the tensile strength of the circumferential weld metal is much higher than the standard value. After circumferential welding of two X80 grade steel pipes using the flux of this invention and the corresponding welding wire, after non-destructive testing according to the welding standard for natural gas transmission pipelines, no cracks or excessive porosity and slag inclusions were found in the weld, which met the standard requirements. At the same time, the weld has excellent fracture toughness.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A sintered flux for submerged arc welding of twin tubes, characterized in that: The chemical composition of the sintering flux, by mass percentage, is as follows: CaF2: 5~15%, MgO: 15~20%, Al2O3: 15~20%, CaO: 2~5%, MnO: 3~10%, BaCO3: 5~10%, TiO2: 3~10%, Ni: 1~5%, B: 0.8~1.5%, Re: 1~0.05%, SiO2: 15~20%, iron powder: 10~30%, S≤0.015%, P≤0.020%. CaF2 is added in the form of fluorite mineral powder, with a CaF2 content of not less than 95% and P≤0.003%. MgO is added in the form of fused magnesia, with a MgO content of... The content of the following materials is not less than 97%, with S ≤ 0.003% and P ≤ 0.05%; Al2O3 is added in the form of bauxite, with Al2O3 not less than 84%, and S and P ≤ 0.03%; CaO is added in the form of marble, with CaO content not less than 40%; MnO is added in the form of manganese-rich ore after roasting, air drying, and water leaching, with MnO content not less than 30%, S ≤ 0.05%, and P ≤ 0.05%; BaCO3 is added in the form of barium carbonate, with a content not less than 70%; SiO2 is introduced through manganese ore, bauxite, fluorite, fused magnesia, rare earth ferrosilicon, and binder water glass, with the total SiO2 content controlled below 20%, and S and P ≤ 0.05%. 0.03%; TiO2 is added in the form of natural rutile, with a TiO2 content of over 58%; Re is added in the form of rare earth ferrosilicon, with a Re content of over 30% and a Si content of over 45%; Ni is added in the form of electrolytic nickel-iron, with a Ni content of over 90%, and P and S ≤0.03%; the iron powder is atomized reduced iron powder with an oxygen content of less than 0.5%, and the Fe content is over 40% relative to the total iron powder.

2. The sintering flux for submerged arc welding of twin tubes according to claim 1, characterized in that: The fluorite mineral powder has a particle size of 100 mesh or larger; the fused magnesia has a particle size of 80-100 mesh; the bauxite has a particle size of 80-100 mesh; the SiO2 has a particle size of 80-100 mesh; the natural rutile has a particle size of 100 mesh or larger; the rare earth ferrosilicon has a particle size of 80-120 mesh; the nickel-iron has a particle size of 80-120 mesh; and the atomized reduced iron powder has a particle size of less than 200 mesh.

3. A method for preparing the sintered flux for submerged arc welding of twin tubes as described in claim 1, characterized in that: Includes the following steps: S1: By weight, mix 8-18 parts fluorite, 18-22 parts fused magnesia, 20-25 parts bauxite, 5-10 parts marble, 7-15 parts barium carbonate, 8-15 parts manganese ore, 8-15 parts rutile, 0.2-1 parts rare earth ferrosilicon, 1-5 parts nickel iron, 0.8-1.5 parts boron iron, and 10-30 parts iron powder evenly. S2: Add 15.48~31.5 parts of binder to the mixture obtained in step S1, and granulate the bonded wet material by vibrating and shaking it with a sieve or granulator. S3: During the granulation process, the particle size of the granulated flux is controlled between 10 and 60 mesh by passing it through a 10-20 mesh sieve; S4: The formed flux is dried in a high-temperature furnace at a temperature range of 200~350℃. S5: The dried flux is sintered in a sintering furnace at a temperature range of 800~900℃; S6: The sintered flux is packaged after being screened through a 10-60 mesh.

4. The method for preparing a sintered flux for submerged arc welding of twin tubes according to claim 3, characterized in that: The binder in step S2 is sodium silicate, which has a Baumé degree of 41.9 to 43.9 and a modulus of 2.5 to 2.

7.

5. The method for preparing a sintered flux for submerged arc welding of twin tubes according to claim 3, characterized in that: In step S5, an inert gas with a flow rate of 0.1 to 1 liter / minute is introduced during sintering to protect the flux.

Images