CN116275699A - A kind of sintering flux for submerged arc girth welding of duplex pipes and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of welding of oil and gas pipelines, in particular to a sintered flux for submerged arc girth welding of duplex pipes and a preparation method thereof. A kind of sintering flux for submerged arc welding of duplex pipes, the chemical composition of said sintering flux is: CaF ₂ : 5-15%, MgO: 15-20%, Al ₂ O ₃ : 15-20% %, CaO:2~5%, MnO:3~10%, BaCO ₃ :5~10%, TiO ₂ :3~10%, Ni:1~5%, B:0.8~1.5%, Re:1~ 0.05%, SiO ₂ : 15~20%, Iron powder: 10~30%, S≤0.015%, P≤0.020%. In the present invention, the chemical components required for sintering flux are added in the form of fluorite, fused magnesia, bauxite, marble, barium carbonate, manganese ore, rutile, rare earth ferrosilicon, ferronickel, ferroboron, and iron powder. During the submerged arc welding process of X80 submerged arc steel pipe with a wall thickness of more than 20mm, the weld slag will not be lost, the slag is easy to remove, and the weld bead is smooth and regular.

Description

A kind of sintering flux for submerged arc girth welding of duplex pipes and preparation method thereof

technical field

The invention relates to the technical field of welding of oil and gas pipelines, in particular to a sintered flux for submerged arc girth welding of duplex pipes and a preparation method thereof.

Background technique

The double-connected pipe is a steel pipe in which two steel pipes are assembled and welded together by on-site prefabrication. Through the method of "double-connected pipes", the construction time of pipeline construction can be fully and effectively shortened, and the project's expected goal of "short, flat and fast" can be greatly met. The submerged arc welding process has high production efficiency, good process stability, uniform weld structure and excellent performance of welded joints. It has become the main process for double-connected pipe welding and has been widely used in long-distance pipeline construction at home and abroad for a long time.

Unlike the conventional spiral and LSAW helical and horizontal position welding, the duplex pipe is welded in a circumferential direction. The internal and external welding welding plane of this process is small, and the position of the welding point is greatly limited, and most of them adopt the small heat input submerged arc welding process, and the welding speed is less than 1m/min. Multi-layer welding is mostly used, and the heat input generally does not exceed 15KJ /cm. The conventional flux pays more attention to the welding speed and efficiency, the welding speed is relatively high, the maximum can reach more than 1.8m/min, and it is single-layer one-time welding, and the melting range of the slag at 1000-1300℃ is too short. The crystallization rate is high, and the cooling rate is too high, so that the inclusions and gas cannot be effectively discharged from the weld in time, which can easily cause poor cleanliness of the weld, and the effective components cannot fully react, which is not conducive to the weld deposited metal The free flow of the alloy and the effective transition of the beneficial alloy cannot obtain an excellent structure of the welded joint; especially when it is used for low-speed welding, the welding deposited metal is relatively limited, and it is very easy to have poor transition and unfavorable filling quality defects, which are serious. It affects the quality and performance of the double pipe girth weld above X70 steel grade, especially the fracture toughness of the weld cannot be guaranteed, which often has an adverse impact on the safety of the pipeline site.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a sintered flux for submerged arc welding of double pipes and a preparation method thereof. The sintered flux of the present invention is suitable for submerged arc welding of double pipes above X70 steel grade, and can realize welding melting The slag has a large melting range and a low crystallization rate at 1000-1300 ° C, which ensures the purity of the weld during the welding process, and the effective components react fully, which is conducive to the free flow of weld deposit metal and the formation of beneficial alloys. Effective transition, so as to obtain excellent welded joint structure, which not only has high strength and toughness, but also has excellent CTOD fracture toughness.

The technical solution of the present invention is: a kind of sintered flux used for submerged arc girth welding of duplex pipes, the chemical composition of said sintered flux is: CaF ₂ : 5-15%, MgO: 15-20%, Al ₂ O ₃ : 15-20%, CaO: 2-5%, MnO: 3-10%, BaCO ₃ : 5-10%, TiO ₂ : 3-10%, Ni: 1-5%, B: 0.8- 1.5%, Re: 1-0.05%, SiO ₂ : 15-20%, iron powder: 10-30%, S≤0.015%, P≤0.020%.

The _CaF2 is added in the form of fluorite mineral powder, the _CaF2 content is not less than 95%, P≤0.003%; the MgO is added in the form of fused magnesia, the MgO content is not less than 97%, S≤0.003% , P≤0.05%; the Al ₂ O ₃ is added in the form of bauxite, and the Al ₂ O ₃ is not less than 84%, and S, P≤0.03%; the CaO is added in the form of marble, and the CaO content is not less than 40%; the MnO is added in the form of manganese-rich ore after roasting, air-drying and water immersion treatment, the MnO content is not less than 30%, S≤0.05%, P≤0.05%; the BaCO ₃ is in the form of barium carbonate Added, the content is not less than 70%; the SiO ₂ is brought in through manganese ore, bauxite, fluorite, fused magnesia, rare earth ferrosilicon and binder water glass, the total content of SiO ₂ is controlled below 20%, S , P≤0.03%; the TiO ₂ is added in the form of natural rutile, and the TiO ₂ content is more than 58%; the Re and Si alloys are added in the form of rare earth ferrosilicon, and the Re content is more than 30%, and the Si content is more than 45%; The Ni alloy is added in the form of electrolytic nickel iron, the Ni content is more than 90%, P and S≤0.03%; the B iron alloy is added in the form of electrolytic nickel iron, the B content is more than 20%, P≤0.03%, S≤0.03%; The iron powder is an atomized reduced iron powder with an oxygen content of less than 0.5%, and an Fe content of more than 40% relative to the total iron powder.

The particle size of the fluorite mineral powder is above 100 mesh; the particle size of the fused magnesia is 80-100 mesh; the particle size of the bauxite is 80-100 mesh; the particle size of the _SiO2 is 80-100 mesh. 100 mesh; the particle size of the natural rutile is above 100 mesh; the particle size of the rare earth ferrosilicon is 80-120 mesh; the particle size of the ferronickel: 80-120 mesh; the particle size of the ferronickel: 80-120 mesh ; The particle size of the atomized reduced iron powder is below 200 mesh.

When the chemical components required for sintering flux are added in the form of fluorite, fused magnesia, bauxite, marble, barium carbonate, manganese ore, rutile, rare earth ferrosilicon, ferronickel, ferroboron, and iron powder, the minerals in the sintering flux Material components and alloy weight percentages are: fluorite: 8-18%, fused magnesia: 18-22%, bauxite: 20-25%, marble: 5-10%, barium carbonate: 7-15% , Manganese ore: 8-15%, rutile: 8-15%, rare earth ferrosilicon: 0.2-1%, nickel-iron: 1-5%, boron iron: 0.8-1.5%, iron powder: 10-30%.

The basis for the selection of the chemical composition of the above-mentioned sintered flux for submerged arc girth welding of duplex pipes is as follows:

(1) As a slagging agent, CaF ₂ reacts with SiO ₂ and H ₂ O on the surface of liquid metal to generate HF gas insoluble in molten steel, which can reduce the partial pressure of hydrogen in the arc and reduce the solubility of hydrogen in the metal. However, this gas has a poisonous effect on the human body; at the same time, CaF ₂ has a dilution effect on the liquid slag, which improves the fluidity of the slag, reduces the viscosity of the slag, and is conducive to the rapid solidification of the slag. If the CaF ₂ is too high, it will seriously reduce The stability of the arc affects the formability of the weld, and at the same time increases the poisonous effect on the operator, if it is too low, the desired effect cannot be achieved. According to the above, the content of CaF ₂ is controlled at 5-15%.

(2) MgO is an alkaline material, which together with CaO can regulate the alkalinity of the flux, and has a significant effect on improving the melting point of slag and the temperature of the melting range, and can adjust the melting point and existence time of the weld metal to ensure the effective removal of harmful substances. Precipitation, 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 and poor weld formability. For the problems of undercutting and difficult slag removal, according to the above, the content of MgO should be controlled at 15-20%.

(3) As the main slagging agent, Al ₂ O ₃ has good stability at high temperature. Together with MgO, it plays a very good role in regulating the melting point, viscosity and melting temperature of slag, thus playing a role in Improvement and adjustment of weld seam morphology. At a certain content, the fish scale pattern of the weld seam can be made finer and denser, and the weld seam surface is smoother. In the present invention, when the _Al2O3 content exceeds ₂₅ %, the melting point of the molten slag is too high and the viscosity increases, which will make the The fluidity of the slag is obviously weakened, which seriously deteriorates the appearance of the weld bead. According to this, the content of Al ₂ O ₃ is 15-20%.

(4) As a main component of alkaline slag system, CaO has the characteristics of small linear expansion coefficient and low crystallization phase transition temperature, which can increase the surface tension of slag and the interfacial tension between slag and metal, and improve the slag removal ability , can greatly improve the process performance of the weld. It can increase the basicity of slag, and can increase the desulfurization and dephosphorization ability of slag; if the content is too high, slag will form 3CaO.SiO ₂ compound, increase the melting point of slag, and adversely affect the fluidity of weld metal According to this, the content of Al ₂ O ₃ is controlled at 2-5%.

(5) BaCO ₃ has the functions of arc stabilization and slag formation, and can replace part of SiO ₂ , adjust the melting point, viscosity, surface tension and fluidity of slag, improve arc stability, reduce weld undercut, and improve weld seam Formability; at the same time, a certain content of BaCO ₃ , but when the content is too high, it is easy to decompose and combine with TiO ₂ to form BaO.TiO ₂ , which deteriorates the deslagging property. According to this, the content of BaCO ₃ is controlled at 5-10%.

(6) TiO ₂ has the functions of arc stabilization and slagging. The melting point, viscosity, surface tension and fluidity of the slag can be adjusted, especially suitable for circumferential welding, improving the shape of the weld bead and reducing undercut; at the same time, in the Ti transition bead weld, in the process of weld crystallization and cooling Precipitation of second phase particles such as carbides, nitrides and intermetallic compounds can refine the austenite grains, so that the transformed ferrite grains can be refined, ensuring that the weld has good strength and toughness. If it exceeds 10%, it will reduce the solidification temperature range of slag, which is unfavorable to the fluidity of flux slag. Therefore, the content of TiO ₂ is determined at 3-10%.

(7) MnO is added in the form of manganese ore in this project, which can reduce the surface tension of slag, improve fluidity, and be beneficial to weld formation, and at the same time, it can increase the carrying capacity of welding current. However, since the manganese ore contains many impurities such as S and P, the present 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 treatment and water immersion, so the MnO content is roughly controlled. In 5 ~ 10%.

(8) SiO ₂ exists as a deoxidizer, which can regulate the alkalinity, viscosity, and softening temperature of the slag to a certain extent. It can combine with most of the basic oxides in the slag to form a compound, which can Increase the viscosity of slag to ensure that the steel pipe does not flow slag during high-speed rotation, and the weld metal solution does not lose, so that the weld bead has a good appearance. The raw materials of wollastonite, bauxite, fluorite and fused magnesia all contain a large amount of SiO ₂ in addition to the main components. Therefore, in this project, SiO ₂ is not directly added. Deploy and control it at 15-20%;

(9) Rare earth is an alloy formed by melting silicon, rare earth, etc. It is a good nodularizer, which can significantly improve the number and shape of sulfide inclusions distributed in strips, and can significantly reduce the welding seam. The effect of the sulfur content in the solder can improve the cleanliness of the weld and ensure the overall quality stability and uniformity of the weld. Due to the extremely small amount of single rare earth added, it is very difficult to prepare the flux. Therefore, this project uses silicon alloy and rare earth fusion. alloy components. The effect of rare earth on the weld is to improve the performance of the weld through the transition of flux into the weld to change the microstructure. If the content is too small, it will not have the desired effect, and if the content is too large, it will pollute the grain boundary and lose the expected effect. , At the same time too much silicon is easy to increase the viscosity of slag, therefore, this project will determine the content of rare earth as 0.05 ~ 1%.

(10) Ni and B alloys have high transition coefficients and strong activity. This project is added in the form of ferronickel, ferromanganese, and rare earth ferrosilicon, which plays a role in reducing the oxygen activity of slag during the welding process, and can Make up for the Ni and B burned in the weld metal during the welding process, and at the same time protect the beneficial alloying elements in the weld from being burned, effectively play the role of forming and stabilizing austenite, and achieve the increase of austenite to iron The supercooling degree of element body transformation improves the nucleation rate, reduces the grain growth time, and has a good grain refinement effect; at the same time, it can also effectively control the inclusions in the welding pool, which is suitable for obtaining at low temperature. The high-toughness welded joint plays a vital role, and the fine and uniform weld structure ensures excellent low-temperature fracture toughness of the weld. Therefore, the Ni alloy content is determined to be about 1-5%, and the B content is determined to be 0.8-1.5%.

(11) Iron powder is an essential additive in high-speed welding to increase welding wire deposition rate and high-efficiency submerged arc welding. Adding iron powder can improve and improve welding process performance, such as improving arc stability, improving slag removal performance, and using The welding seam is smooth and beautiful. When the iron powder content is less than 10%, the effect of improving the welding efficiency cannot be achieved. If the iron powder content exceeds 30%, the iron powder is easy to agglomerate in the melting/solidifying flux, and too much iron powder is easy to adhere On the surface of the weld bead, the spreadability of the weld bead is reduced. For low-hydrogen type flux, the excessive oxygen content in the iron powder will thin the welding slag, affect the protective effect of the flux, and be unfavorable for the transition of alloying elements. In the present invention, the oxygen content in the iron powder must be strictly limited to less than 0.5% or less, therefore, the content of iron powder is determined at 10-30%.

Above-mentioned a kind of preparation method of the sintered flux that is used for submerged arc girth welding of duplex pipe, comprises the following steps:

S1: By weight, 8-18 parts of fluorite, 18-22 parts of fused magnesia, 20-25 parts of bauxite, 5-10 parts of marble, 7-15 parts of barium carbonate, 8-15 parts of manganese ore, 8-15 parts of rutile, 0.2-1 part of rare earth ferrosilicon, 1-5 parts of ferronickel, 0.8-1.5 parts of ferroboron, 10-30 parts of iron powder, and mix evenly;

S2: Add 15.48 to 31.5 parts of binder to the mixture obtained in step S1, vibrate and shake the bonded wet material with a dustpan or a granulator to granulate;

S3: During the granulation process, the particle size of the granulated flux is controlled between 10-60 mesh through a 10-20 mesh sieve;

S4: drying the molded flux in a temperature range of 200-350°C in a high-temperature furnace;

S5: sintering the dried flux through a sintering furnace at a temperature range of 800-900°C;

S6: Packaging the sintered flux after passing through 10-60 mesh screening.

The binder in the step S2 is sodium silicate, and the Baume degree of the sodium silicate as binder is 41.9-43.9, and the modulus is 2.5-2.7.

In the actual preparation process, the Baume degree of the sodium silicate as a binder is 41.9-43.9, and the modulus is 2.5-2.7, which can effectively reduce the moisture content and hydrogen content in the flux, and increase the alkalinity of the flux to ensure The flux particle size has good strength.

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

In the actual preparation process, inert gas is used to protect the flux, which can effectively prevent the flux from being oxidized under high temperature conditions.

The beneficial effects of the present invention are:

1. The present invention introduces TiO ₂ and BaCO ₃ into the chemical composition of the sintered flux to ensure that the slag has a larger melting range and a lower crystallization rate within 1000-1300 °C, ensuring the purity and purity of the weld seam during the welding process. weld process performance.

2. The present invention introduces acid-base substances MgO and CaO into the chemical composition of the sintered flux, which ensures that the flux of the present invention has a higher alkalinity value, reduces the oxidation ability of the molten slag, and reduces the harmful gas in the molten slag compared with the ordinary flux and impurities, ensuring a more efficient transition of beneficial alloys.

3. The present invention introduces iron powder into the chemical composition of the sintered flux, which can further increase the metal deposition rate during the welding process with small heat input, ensure the filling amount of weld metal, and simultaneously reduce the number of welding passes to achieve the purpose of improving welding efficiency .

4. The present invention introduces B, Ni alloys and rare earth microalloys into the chemical composition of the sintered flux to refine and uniformize the weld grains while ensuring more acicular ferrite Organization, in order to ensure that the weld has excellent CTOD fracture toughness on the basis of high strength and toughness.

5. Using the flux of the present invention and the corresponding welding wire to carry out submerged arc welding on the steel pipe in the circumferential position, the line energy is greater than 15KJ/cm, the weld slag does not flow, the weld bead is regular, the weld surface is smooth, the metal luster is obvious, and the slag Easy to fall off.

6. After using the flux of the present invention to match the corresponding welding wire for welding, the girth weld metal R _m =695-750MPa, after welding the X80Φ1422×21.4mm steel pipe, can be applied to a wider range of welding process parameters. Using the present invention, the welding process is more than 20mm During the submerged arc welding process of X80 submerged arc steel pipe with large wall thickness, the weld slag will not be lost, the slag is easy to remove, and the weld bead is smooth and regular.

7. After using the flux of the present invention and the corresponding welding wire to carry out circumferential welding of two X80 steel grade steel pipes, after carrying out non-destructive testing according to the welding standards of natural gas transmission pipelines, no cracks and excessive pores and slag inclusions in the welds meet the standard requirements, and at the same time The weld has excellent fracture toughness.

Detailed ways

Below in conjunction with embodiment the present invention is described in further detail:

Example 1

A sintered flux for submerged arc welding of double pipes, the chemical composition of the sintered flux is: CaF ₂ : 5-15%, MgO: 15-20%, Al ₂ O ₃ : 15-20 %, CaO: 2~5%, MnO: 3~10%, BaCO ₃ : 5~10%, TiO ₂ : 3~10%, Ni: 1~5%, B: 0.8~1.5%, Re: 1~ 0.05%, SiO ₂ : 15-20%, iron powder: 10-30%, S≤0.015%, P≤0.020%.

The _CaF2 is added in the form of fluorite mineral powder, the _CaF2 content is not less than 95%, P≤0.003%; the MgO is added in the form of fused magnesia, the MgO content is not less than 97%, S≤0.003% , P≤0.05%; the Al ₂ O ₃ is added in the form of bauxite, and the Al ₂ O ₃ is not less than 84%, and S, P≤0.03%; the CaO is added in the form of marble, and the CaO content is not less than 40%; the MnO is added in the form of manganese-rich ore after roasting, air-drying and water immersion treatment, the MnO content is not less than 30%, S≤0.05%, P≤0.05%; the BaCO ₃ is in the form of barium carbonate Added, the content is not less than 70%; the SiO ₂ is brought in through manganese ore, bauxite, fluorite, fused magnesia, rare earth ferrosilicon and binder water glass, not specially added, and the total content of SiO ₂ is controlled 20% or less, S, P≤0.03%; the TiO ₂ is added in the form of natural rutile, and the TiO ₂ content is above 58%; the Re and Si alloy is added in the form of rare earth ferrosilicon, the Re content is more than 30%, and the Si content More than 45%; the Ni alloy is added in the form of electrolytic nickel-iron, the Ni content is more than 90%, P, S≤0.03%; the B iron alloy is added in the form of electrolytic nickel-iron, the B content is more than 20%, P≤0.03%, S≤0.03%; the iron powder is an atomized reduced iron powder with an oxygen content of less than 0.5%, and the Fe content is more than 40% relative to the total iron powder.

The particle size of the fluorite mineral powder is above 100 mesh; the particle size of the fused magnesia is 80-100 mesh; the particle size of the bauxite is 80-100 mesh; the particle size of the _SiO2 is 80-100 mesh. 100 mesh; the particle size of the natural rutile is above 100 mesh; the particle size of the rare earth ferrosilicon is 80-120 mesh; the particle size of the ferronickel: 80-120 mesh; the particle size of the ferronickel: 80-120 mesh ; The particle size of the atomized reduced iron powder is below 200 mesh.

When the chemical components required for sintering flux are added in the form of fluorite, fused magnesia, bauxite, marble, barium carbonate, manganese ore, rutile, rare earth ferrosilicon, ferronickel, ferroboron, and iron powder, the minerals in the sintering flux Material components and alloy weight percentages are: fluorite: 8-18%, fused magnesia: 18-22%, bauxite: 20-25%, marble: 5-10%, barium carbonate: 7-15% , Manganese ore: 8-15%, rutile: 8-15%, rare earth ferrosilicon: 0.2-1%, nickel-iron: 1-5%, boron iron: 0.8-1.5%, iron powder: 10-30%.

Example 2

A preparation method for sintered flux for submerged arc girth welding of duplex pipes, comprising the following steps:

S1: By weight, 8-18 parts of fluorite, 18-22 parts of fused magnesia, 20-25 parts of bauxite, 5-10 parts of marble, 7-15 parts of barium carbonate, 8-15 parts of manganese ore, 8-15 parts of rutile, 0.2-1 part of rare earth ferrosilicon, 1-5 parts of ferronickel, 0.8-1.5 parts of ferroboron, 10-30 parts of iron powder, and mix evenly;

S2: Add 15.48 to 31.5 parts of binder to the mixture obtained in step S1, vibrate and shake the bonded wet material with a dustpan or a granulator to granulate;

S3: During the granulation process, the particle size of the granulated flux is controlled between 10-60 mesh through a 10-20 mesh sieve;

S4: drying the molded flux in a temperature range of 200-350°C in a high-temperature furnace;

S5: sintering the dried flux through a sintering furnace at a temperature range of 800-900°C;

S6: Packaging the sintered flux after passing through 10-60 mesh screening.

The binder in the step S2 is sodium silicate, and the Baume degree of the sodium silicate as binder is 41.9-43.9, and the modulus is 2.5-2.7.

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

Example 3

According to a kind of sintering flux for double pipe submerged arc welding described in above-mentioned embodiment 1, adopt the preparation method of a kind of sintering flux for double pipe submerged arc welding described in embodiment 2, carry out sintering Flux preparation. The specific process is as follows:

(1) Flux components (wt%)

When the chemical components required for sintering flux are added in the form of fluorite, fused magnesia, bauxite, marble, barium carbonate, manganese ore, rutile, rare earth ferrosilicon, ferronickel, ferroboron, and iron powder, the minerals in the sintering flux Material components and alloy weight percentages are: 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 iron 3, boron iron 1, iron powder12.

(2) Preparation of sintered flux

After the above mineral components and alloys are mixed and stirred evenly, the binder potassium sodium water glass is added for wet mixing, and then granulated with a dustpan or a granulator to control the particle size of the flux between 10 and 60 mesh, and then carry out Low-temperature drying at 200-250°C, high-temperature sintering at 800-900°C, screening of 10-60 meshes, and packaging in moisture-proof packaging bags.

(3) The flux of the present invention is matched with the corresponding low-temperature welding wire to carry out deposited metal welding. According to the relevant welding material standard requirements, the test plate adopts Q235, the thickness is 25mm, the groove angle is 20°, and the root gap is 15mm. The welding specification is current 480A, voltage 30V, welding speed 26m/h, interpass temperature 150±15°C, and the mechanical properties of the deposited metal after welding are shown in Table 1.

Table 1 Mechanical properties of deposited metal

It can be seen from Table 1 that when the flux of the present invention is matched with the corresponding low-temperature welding wire for deposited metal welding, compared with the standard requirements, the weld seam has excellent CTOD fracture toughness on the basis of higher strength and toughness.

(4) The flux of the present invention is matched with the corresponding low-temperature welding wire to carry out welding in the circumferential position of two steel pipes. The steel pipe steel grade is X80, the steel pipe specification is Φ1422×21.4mm, and the chemical composition 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 rest are iron. The process used is: the groove angle at the circumferential position is 60° on the inner surface, 80° on the inner surface, the root gap is 2mm, and the blunt edge is 6-8mm; And use CO ₂ gas shielded automatic welding for pre-welding, and then use submerged arc welding to complete the internal and external welding of the paired steel pipes in sequence. Among them, the submerged arc welding process adopts the combination process of internal welding single wire, external welding single wire bottoming and filling cover, internal welding current 850A, voltage 30V; external welding bottoming specification: bottoming welding current 680A, voltage 31.5V, The welding speed is 0.7m/min; the current of the welding wire before covering and filling is 700A, the voltage is 30V, the welding speed is 1m/min, and the interpass temperature is 150±15°C. The mechanical properties of the metal after welding are shown in Table 2.

Table 2 Mechanical properties of girth weld metal

As can be seen from Table 2, the weld flux of the present invention is matched with the corresponding low-temperature welding wire to carry out the circumferential position welding of two steel pipes. The surface is smooth, the metallic luster is obvious, the slag is easy to fall off, and the tensile strength of the girth weld metal is much higher than the standard value. After the non-destructive testing of welding standards, there are no cracks, excessive pores, and slag inclusions in the welds to meet the standard requirements, and the welds have excellent fracture toughness.

According to a kind of sintering flux for double pipe submerged arc welding described in above-mentioned embodiment 1, adopt the preparation method of a kind of sintering flux for double pipe submerged arc welding described in embodiment 2, carry out sintering Flux preparation, and adopt the same flux use process in embodiment 3, specific situation is as described in embodiment 4, embodiment 5, embodiment 6, embodiment 7, comparative example is comparative example 1, comparative example 2, comparative example 3 , comparative example 4.

The chemical element components of the sintered flux in Examples 4-7 and Comparative Examples 1-4 are shown in Table 3 by weight percentage.

The chemical element composition of sintered flux in table 3 embodiment 4～7, comparative example 1～4 is by weight percentage (wt %)

serial number CaF ₂ MgO Al ₂ O ₃ CaO MnO BaCO ₃ TiO ₂ Ni B Re Fe P S Example 4 15 16 18 4 9 5 10 1 1.3 1 10 0.01 0.01 Example 5 13 18 19 5 5 9 7 3 0.9 0.08 15 0.009 0.018 Example 6 14 20 18 4 8 9 6 4 0.8 0.08 12 0.017 0.018 Example 7 12 15 19 3 6 10 3 5 0.8 0.05 30 0.015 0.018 Comparative example 1 13 20 19 3 5 -- 11 5 -- 0.09 15 0.01 0.013 Comparative example 2 15 18 20 5 7 7 2 -- 1.0 -- -- 0.08 0.01 Comparative example 3 13 17 16 5 10 11 5 3 1.5 1.2 31 0.12 0.05 Comparative example 4 15 20 16 3 5 7 5 6 0.9 0.02 9 0.05 0.015

The preparation parameters of the sintered flux in Examples 4-7 and Comparative Examples 1-4 are shown in Table 4.

The preparation parameters of sintered flux in table 4 embodiment 4～7, comparative example 1～4

Table 5 shows the mechanical property results of the sintered flux welded girth welds of Examples 4-7 and Comparative Examples 1-4.

Table 5 Examples 4 to 7, comparative examples 1 to 4 sintered flux detection and the mechanical and process performance results of the girth weld

In conjunction with Table 3 and Table 4, the percentage by weight (wt %) of some components in comparative examples 1～4 bushing exceeds the scope involved in the technical solution of the present invention, for example: in comparative example ₁ , the TiO wherein The weight percent The percentage by weight of TiO ₂ in the flux of the present invention is higher than that of TiO 2 in the flux of the present invention. In Comparative Example 3, the percentage by weight of BaCO ₃ , Fe powder and Re is higher than that of TiO ₂ , Fe and Re in the flux of the present invention; Comparative Example 1 Some preparation process parameters of the sintered flux in ~ 4 exceed the range involved in the technical solution of the present invention, for example, the drying temperature of the flux in the comparative example 1 is lower than the drying temperature of the technical solution of the present invention; as can be seen from Table 5, the comparative example 1 ~ For flux 4, at least one of the performance indicators is lower than the standard design requirements. For example, the CTOD performance in Comparative Example 1 does not meet the standard requirements, and the process performance after welding cannot meet the requirements. The impact toughness value and CTOD in Comparative Example 2 are both Can not meet the standard requirements, therefore, the flux in Comparative Examples 1 to 4 is not suitable for the application requirements of the submerged arc double pipe.

As can be seen from Table 5, compared with Comparative Examples 1 to 4, the tensile strength of the weld seam after submerged arc sintering flux welding in Examples 4 to 7 is 695 to 715 MPa, the moisture content in the flux is <0.1%, and the mechanical strength in the flux is Inclusions <0.3%, -10°C girth weld impact energy ≥150J, and ductile transition temperature below -40°C, -10°C CTOD fracture toughness σm≥0.254mm. At the same time, several kinds of fluxes can realize the automatic shedding of the slag crust after welding, and ensure the smooth and beautiful appearance of the weld bead surface. Therefore, the fluxes in Examples 4 to 7 are used for double pipe girth welding to have high strength and high toughness And excellent fracture resistance performance, especially the weld bead morphology after ring welding has been significantly improved compared with ordinary flux, and the performance is much better than the current similar products. The present invention can meet the performance of submerged arc welding double pipe ring welding requirements.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention.

Claims (7)

1. A sintered flux for submerged arc welding of double pipes, characterized in that: the chemical composition of the sintered flux is by mass percentage: CaF ₂ : 5 ~ 15%, MgO: 15 ~ 20%, Al ₂ O ₃ :15~20%, CaO:2~5%, MnO:3~10%, BaCO ₃ :5~10%, TiO ₂ :3~10%, Ni:1~5%, B:0.8~1.5 %, Re: 1~0.05%, SiO ₂ : 15~20%, Iron powder: 10~30%, S≤0.015%, P≤0.020%. 2. According to claim 1, a kind of sintered flux for double tube submerged arc welding is characterized in that: said CaF ₂ is added in the form of fluorite mineral powder, and the content of CaF ₂ is not less than 95%, P ≤0.003%; the MgO is added in the form of fused magnesia, the MgO content is not less than 97%, S≤0.003%, P≤0.05%; the Al ₂ O ₃ is added in the form of bauxite, and the Al ₂ O ₃ Not less than 84%, S, P≤0.03%; the CaO is added in the form of marble, and the CaO content is not less than 40%; the MnO is added in the form of manganese-rich ore after roasting, air-drying and water immersion treatment, The MnO content is not less than 30%, S≤0.05%, P≤0.05%; the BaCO ₃ is added in the form of barium carbonate, and the content is not less than 70%; the SiO ₂ is passed through manganese ore, bauxite, fluorite, Fused magnesia, rare earth ferrosilicon and binder water glass are brought in, the total content of SiO ₂ is controlled below 20%, S, P≤ 0.03%; the TiO ₂ is added in the form of natural rutile, and the content of TiO ₂ is above 58% The Re and Si alloys are added in the form of rare earth ferrosilicon, with a Re content of more than 30% and a Si content of more than 45%; the Ni alloy is added in the form of electrolytic nickel iron, with a Ni content of more than 90%, and P and S ≤ 0.03%; The B iron alloy is added in the form of electrolytic ferronickel, with a B content of more than 20%, P ≤ 0.03%, and S ≤ 0.03%; the iron powder is an atomized reduced iron powder with an oxygen content of less than 0.5%. amount, the Fe content is above 40%. 3. according to claim 2, a kind of sintered flux for submerged arc welding of duplex pipes is characterized in that: the granularity of the fluorite mineral powder is more than 100 mesh; the granularity of the fused magnesia is 80~100 mesh; the particle size of the bauxite is 80~100 mesh; the particle size of the _SiO2 is 80~100 mesh; the particle size of the natural rutile is more than 100 mesh; the particle size of the rare earth ferrosilicon is 80 ~120 mesh; the particle size of the ferronickel: 80~120 mesh; the particle size of the ferronickel: 80~120 mesh; the particle size of the atomized reduced iron powder is below 200 mesh. 4. According to claim 2, a kind of sintered flux for double tube submerged arc welding is characterized in that: through fluorite, fused magnesia, bauxite, marble, barium carbonate, manganese ore, rutile, rare earth When the chemical components required for sintering flux are added in the form of ferrosilicon, ferronickel, ferroboron, and iron powder, the mineral components and alloy weight percentages in the sintering flux are: fluorite: 8~18%, fused magnesia: 18% ~22%, bauxite: 20~25%, marble: 5~10%, barium carbonate: 7~15%, manganese ore: 8~15%, rutile: 8~15%, rare earth ferrosilicon: 0.2~1% , Ferronickel: 1~5%; Ferroboron: 0.8~1.5%, Iron powder: 10~30%. 5. a method for preparing the sintered flux for submerged arc welding of duplex pipes as claimed in claim 1, characterized in that: comprising the following steps: S1: In parts by weight, mix 8~18 parts of fluorite, 18~22 parts of fused magnesia, 20~25 parts of bauxite, 5~10 parts of marble, 7~15 parts of barium carbonate, 8~15 parts of manganese ore, 8~15 parts of rutile, 0.2~1 part of rare earth ferrosilicon, 1~5 parts of ferronickel, 0.8~1.5 parts of ferroboron, 10~30 parts of iron powder, mix evenly; S2: Add 15.48 to 31.5 parts of binder to the mixture obtained in step S1, vibrate and shake the bonded wet material with a dustpan or a granulator to granulate; S3: During the granulation process, the particle size of the granulated flux is controlled between 10-60 mesh through a 10-20 mesh sieve; S4: Dry the formed flux in the temperature range of 200~350°C through a high temperature furnace; S5: sintering the dried flux through a sintering furnace at a temperature range of 800-900°C; S6: Packaging the sintered flux after passing through 10-60 mesh screening. 6. A kind of preparation method for the sintered flux that is used for submerged arc girth welding of duplex pipe according to claim 5, is characterized in that: the binding agent in the described step S2 is sodium water glass, and described sodium water glass is used as The Baume degree of the binder is 41.9~43.9, and the modulus is 2.5~2.7. 7. A method for preparing a sintered flux for submerged arc welding of double pipes according to claim 5, characterized in that: in the step S5, the inert flux whose flow rate is 0.1 to 1 liter/min during sintering is The gas shields the flux.