Sintered flux for submerged arc welding of hydrogen transport pipe

Abstract

The application belongs to the technical field of pipeline welding, and particularly relates to a sintered flux suitable for hydrogen delivery submerged arc welding steel pipe. The sintered flux comprises the following components in percentage by weight: HJ431 welding powder: 40-50%, MgO: 10-15%, CaF2: 15-20%, BaCO3: 5-10%, TiO2: 2-5%, Al powder deoxidizer: 1-3%, Mn-Fe alloying agent: 5-10%, P: less than 0.02%, and S: less than 0.018%. The sintered flux of the application is used in combination with H08MnNi2A welding wire for high-speed submerged arc welding of hydrogen-resistant pipeline steel at 1.6 m / min, and the weld has moderate tensile strength, excellent impact toughness, low diffusible hydrogen content, and good HIC and SSCC corrosion resistance consistent with the corresponding hydrogen-resistant base material, which can effectively solve the problems of high-efficiency welding of pipeline steel, strength and toughness, and safe delivery of hydrogen energy pipeline.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of pipeline welding, and particularly relates to a sintered flux suitable for hydrogen delivery submerged arc welding steel pipes. BACKGROUND

[0002] Pipeline transportation is an indispensable way for large-scale and long-distance transportation of hydrogen. Compared with the economic radius of 150km of long pipe trailer, pipeline transportation of hydrogen can easily realize hydrogen transportation of more than 200km, and the hydrogen transportation capacity of liquid hydrogen transportation is also much smaller than that of pipeline transportation. Generally, pure hydrogen pipeline can realize hydrogen transportation capacity of 100 tons / day, which can efficiently and quickly meet the application of downstream hydrogen end industry. As a gas molecule, hydrogen is extremely small, colorless and odorless, and has the characteristics of small density and large diffusion coefficient compared with natural gas. For general pipe materials, long-term contact with hydrogen will enter the internal defects of metal materials structure and cannot diffuse out, which is easy to cause the reduction of plasticity and strength of metal materials, leading to material cracking and serious degradation of mechanical properties and causing brittle fracture phenomenon, i.e. "hydrogen embrittlement" phenomenon. For the welding of hydrogen transportation pipeline steel pipes, the internal organization state, structure and free state diffusion hydrogen of the weld will have a great influence on the hydrogen embrittlement sensitivity, especially the number, shape, size and distribution of internal inclusions, which are particularly significant for inducing hydrogen embrittlement fracture. At the same time, C, Mn, Si, S, P and other elements which are easy to harden and contaminate the weld will also increase the probability of "hydrogen embrittlement" of the weld after pipe welding. Under high pressure, the hydrogen embrittlement and hydrogen-induced cracking phenomenon of high-strength material welds will be more obvious, so the pipe material for hydrogen medium transportation is preferentially selected as low-grade steel pipe, and higher requirements are put forward for the purity, organization form and internal hydrogen ion content of the weld.

[0003] Most of the high-pressure hydrogen energy pipeline pipes are produced by submerged arc welding process, and the main means for controlling [H] in the weld is the reasonable selection and matching of welding materials during welding. As an auxiliary material in the submerged arc welding process, sintered flux plays a role in preventing harmful gases in the outside air from entering and in the metallurgical chemical reaction of slag and weld pool. A large number of production practices and related researches at home and abroad have proved that the main source of the increase of free hydrogen ions and inclusions in the flux is the flux material. Therefore, the most effective measure to reduce the hydrogen damage hidden danger in the pipe from the source is to optimize the related components in the sintered flux to achieve the dissolution and control of residual [H] in the weld during the metallurgical chemical reaction of the flux. The content of Mn, Si and C in the commonly used SJ101 and SJ301 fluxes is often too high, and the control requirement of P and S content is too loose, and there is no strict requirement for diffusible hydrogen. If it is directly applied to the welding of hydrogen-resistant pipeline steel, it is easy to cause segregation and inclusions in the weld, which increases the hydrogen embrittlement sensitivity of the steel pipe weld, and finally causes great safety hidden danger to the hydrogen pipeline steel pipe. The commonly used special low-hydrogen sintered flux on the market is mainly produced by improving the quality of raw materials, reducing the crystalline hydrate in the flux, optimizing the sintering temperature and protection measures in the preparation process, etc. on the basis of the conventional fluoride-alkali slag system. It often has problems such as high cost of raw materials and production, inability to effectively control the diffusible hydrogen of the weld, and low welding speed, which seriously restricts the large-scale production and application of hydrogen energy pipeline pipes. Therefore, a low-cost high-speed sintered flux suitable for hydrogen transmission submerged arc welding steel pipe for hydrogen-resistant pipeline steel needs to be developed. At present, there are many patents about low-hydrogen sintered flux in the existing technology. Among them, the search patents are: an ultra-low diffusible hydrogen sintered flux for low-temperature steel welding and preparation and application (publication number: CN 108581273A), which mainly uses fluoride-alkali slag system to achieve the purpose of dehydrogenation and performance improvement by matching different components. The raw materials added in the flux are complex and expensive. High-alkali high-toughness low-hydrogen sintered flux and its preparation method (publication number: CN 102601544A), which controls the P and S inclusions in the flux more widely, which is not conducive to the safety requirements of pipeline hydrogen transmission. Sintered flux for hydrogen-resistant steel and its preparation method, and deposited metal (publication number: CN 112496596A), which adds a certain amount of HJ431 smelting flux slag after welding and a large amount of chemical components to achieve low hydrogen requirements. The complex formed by the combination of MnO and SiO2 in the HJ431 smelting slag and FeO, and S and P compounds are easy to form inclusions in the weld, which can easily cause the purity of the weld to decrease and cause safety hazards to the pipeline hydrogen transmission. SUMMARY

[0004] In view of the above problems, the present application aims to provide a sintered flux suitable for hydrogen delivery submerged arc welding steel pipe, which, when used in combination with H08MnNi2A submerged arc welding wire for high-speed submerged arc welding of hydrogen-resistant pipeline steel at 1.6 m / min, can provide a weld with moderate tensile strength, excellent impact toughness, low diffusible hydrogen content, and good HIC and SSCC corrosion resistance consistent with the corresponding hydrogen-resistant base material, thereby effectively solving the problems of high-efficiency welding of pipeline steel, strength and toughness, and safe delivery of hydrogen energy pipelines.

[0005] The technical solution of the present application is a sintered flux suitable for hydrogen delivery submerged arc welding steel pipe, wherein the chemical components of the sintered flux are as follows in terms of weight percentage: HJ431 welding powder: 40-50%, MgO: 10-15%, CaF2: 15-20%, BaCO3: 5-10%, TiO2: 2-5%, Al powder deoxidizer: 1-3%, Mn-Fe alloying agent: 5-10%, P: <0.02%, S: <0.018%.

[0006] The particle size of the HJ431 welding powder is 80-100 mesh, and the MnO content in the HJ431 welding powder is more than 40%; the CaF2 is added in the form of fluorite mineral powder, the particle size of the fluorite mineral powder is more than 100 mesh, and the CaF2 content of the fluorite mineral powder is 98%; the MgO is added in the form of fused magnesite, the particle size of the fused magnesite is 80-100 mesh, and the MgO content of the fused magnesite is 99%; the TiO2 is added in the form of natural rutile, the particle size of the natural rutile is 80-100 mesh, and the TiO2 content of the natural rutile is 93%; the BaCO3 is added in the form of barium carbonate, the particle size of the barium carbonate is 100-120 mesh, and the BaCO3 content of the barium carbonate is 99.2%; the particle size of the Al powder deoxidizer is 60-80 mesh, and the Al content of the Al powder deoxidizer is 99%; the particle size of the Mn-Fe alloying agent is 60-80 mesh, and the Mn content of the Mn-Fe alloying agent is 99%.

[0007] When the HJ431 welding powder, fluorite mineral powder, fused magnesite, natural rutile, barium carbonate, Al powder deoxidizer, and Mn-Fe alloying agent are added to the sintered flux in the form of chemical components required by the sintered flux, the weight percentage of the mineral components and the alloy in the sintered flux is as follows: HJ431 welding powder: 40-50%, fluorite mineral powder: 12-24%, fused magnesite: 12-18%, barium carbonate: 7-12%, natural rutile: 2-5%, Al powder deoxidizer: 3-5%, and Mn-Fe alloying agent: 5-10%.

[0008] The Mn-Fe alloying agent is an electrolytic Mn-Fe alloying agent.

[0009] The moisture content in the sintering flux is less than 0.1%, the mechanical inclusion in the sintering flux is less than 0.3%, the tensile strength of the weld after welding is 485-517 MPa, the ring weld impact energy at-10 DEG C is greater than or equal to 100 J, the toughness transition temperature is below-40 DEG C, the-10 DEG C CTOD fracture toughness m is greater than or equal to 0.254 mm, and the diffusible hydrogen content is less than or equal to 4 ml / 100 g.

[0010] The selection of the chemical components of the sintering flux for hydrogen delivery submerged arc welding steel pipe is based on:

[0011] (1) BaCO3 is used as an alkaline oxide. After adding BaCO3 to HJ431, CO2 generated after decomposition forms a gas slag combined protection in the weld pool during welding, reduces the hydrogen partial pressure in the arc atmosphere, inhibits the diffusible hydrogen content in the deposited metal, greatly increases the basicity of the slag, improves the impact toughness of the deposited metal, and enhances the crack resistance of the weld. When the content of BaCO3 is less than 5%, gas protection cannot be formed, and the effect of BaCO3 on the weld is not obvious. However, when the content of BaCO3 exceeds 10%, too much BaCO3 is added, which releases too much gas during submerged arc welding, easily produces too much smoke, reduces the protection effect of the slag, and the generated CO bubbles are easily formed into pits on the surface of the weld, and too much smoke is not conducive to environmental protection. Therefore, the content of BaCO3 needs to be controlled at 5-10%;

[0012] (2) MgO is an alkaline oxide and a high-melting-point oxide with a melting point of 2800 DEG C. The addition of MgO to the HJ welding powder composition increases the basicity of the slag, reduces the viscosity of the acidic slag, increases the gas permeability of the slag, and reduces the diffusible hydrogen content. At the same time, during welding, the melting temperature of the flux slag is increased, the melting speed is reduced, the amount of slag is reduced, and the process performance of the weld is well adjusted. When the content of MgO is less than 10%, the total content of MgO in the flux is too low, the effect of increasing the melting point of the slag is not obvious, too much slag is produced during welding, which easily causes the edge of the weld to be irregular and not beautiful. When the content of MgO is less than 15%, the total content of high-melting-point components in the slag is too high, the reaction in the weld metal cannot be fully carried out during welding, which easily causes weld pits and cannot achieve free spreading. Therefore, the content of MgO needs to be controlled at 10-15%;

[0013] (3) CaF2 is a kind of alkaline salt, as an important component of dehydrogenation in welding flux, it has smaller surface tension and lower melting point, and can effectively dilute the flux melt in the welding process;Under high temperature arc, CaF2 is relatively active, can react with SiO2 to generate SiF4 gas, which can remove hydrogen in the arc area, thereby preventing hydrogen from dissolving in the metal, thereby reducing the hydrogen content in the weld. CaF2 also has good effect on metal desulfurization, and can also reduce the oxygen content of the weld metal, improve the plasticity and impact toughness of the weld. However, too much CaF2 will damage the potassium and sodium ions in the arc cavity atmosphere, causing the submerged arc welding arc to be unstable, in addition, it will also excessively dilute the slag, thereby affecting the weld forming and deslagging, at the same time, the fluoride gas generated during welding will cause great harm to the human body, therefore, the content of CaF2 needs to be controlled at 15-20%.

[0014] (4) TiO2 is added to improve the weld appearance and improve the arc stability, and at the same time, the Ti element is transferred to the weld. TiO2 can reduce the surface tension in liquid state, and can rapidly increase the surface tension during cooling process. However, if the amount of TiO2 is too large, the slag will be greatly diluted, the slag shell will be hard, and the permeability of the slag will be reduced. Since the HJ welding powder contains more than 5% TiO2, the content of TiO2 in the flux is more than 5%, therefore, the surface tension of the slag will be too large, the slag will be too dilute, and the deslagging performance after welding will be deteriorated, and the protective effect on the weld will not be as expected. However, if TiO2 is not added, the addition of single MgO will make the melting point of the slag too high, and the coverage of the slag on the weld metal will be reduced. Therefore, the content of TiO2 in the flux should be limited to 2-5%.

[0015] (5) Al powder deoxidizer and Mn-Fe alloying agent, Al has a strong affinity for oxygen, which can reduce the hydrogen overcoefficient in iron, and can also improve the corrosion resistance of the weld. Al is easily oxidized, and when combined with Mn, it can combine with O2 in front of the arc during welding to promote the transition of Mn elements to the weld metal, thereby improving the weld structure, refining the pearlite grains, improving the strength and hardness of the weld, and reducing the brittle transition temperature. In order to obtain high strength and low temperature toughness, the content of Al powder deoxidizer and Mn-Fe alloying agent in the flux of the present application is controlled at 1-3% and 5-10%.

[0016] (6) P and S as impurity elements, S and iron can be infinitely soluble in liquid, easy to generate distribution in austenite Fe+FeS fusible eutectic, causing weld hot brittle, resulting in plastic, toughness of weld sharply decreased; P in the form of phosphide generally exist, promote the hydrogen evolution corrosion intensified, but at the same time, phosphorus can improve the corrosion resistance of steel. Too much phosphorus will produce cold brittle, deteriorate the toughness of steel, so the content is controlled in P≤0.015%; S≤0.010%;

[0017] A preparation method of sintered flux for hydrogen delivery submerged arc welding steel pipe as described above, comprising the following steps:

[0018] S1: by weight parts, 40~50 parts of HJ431 welding powder, 12~18 parts of fused magnesite, 7~12 parts of barium carbonate, 18~24 parts of fluorite mineral powder, 2~5 parts of natural rutile, 3~5 parts of Al powder deoxidizer, 5~10 parts of Mn-Fe alloying agent are uniformly mixed;

[0019] S2: adding 15.48~31.5 parts of binder to the mixture obtained in step S1, and vibrating or shaking the wet material with a dustpan or a granulator to form granules;

[0020] S3: during the granulation process, the particle size of the granulated flux is controlled between 10~60 meshes by passing through a 10~20 mesh sieve;

[0021] S4: the formed flux is dried by a high temperature furnace at a temperature range of 200~350℃;

[0022] S5: the dried flux is sintered by a sintering furnace at a temperature range of 800~900℃;

[0023] S6: the sintered flux is packaged after being sieved by 10~60 mesh.

[0024] The binder in step S2 is potassium sodium water glass, and the specific gravity of the potassium sodium water glass as the binder is 41.9~43.9, and the modulus is 2.5~2.7.

[0025] The technical effect of the present application is that: 1. The present application introduces CaF2 in the chemical composition of the sintered flux, which can effectively dilute the flux melt during welding; under high-temperature arc, CaF2 is relatively active and can react with SiO2 to generate SiF4 gas, which can remove hydrogen in the arc area, thereby preventing hydrogen from dissolving in the metal, thereby reducing the hydrogen content in the weld. 2. The present application introduces the corresponding Al powder deoxidizer and Mn-Fe alloying agent by adding them in the flux, thereby reducing the oxidation ability of the slag, reducing harmful gases and impurities in the slag, and the flux auxiliary transition Mn alloy plays a good fine-grained role during welding, promoting a large amount of fine and uniform acicular ferrite structure in the weld metal, ensuring that the weld has high strength and toughness and stable quality, and the weld has excellent process and mechanical properties and HIC and SSCC corrosion resistance, thereby improving the purity of the weld. 3. The tensile strength of the weld after welding using the sintered flux of the present application is 485-517 MPa, the-10℃ circumferential weld impact energy is ≥100J, the toughness transition temperature is below-40℃, the-10℃ CTOD fracture toughness m is ≥0.254mm, and the diffusible hydrogen content is ≤4ml / 100g. DETAILED DESCRIPTION

[0026] Example 1

[0027] A sintered flux suitable for hydrogen delivery submerged arc welding steel pipe, the chemical composition of the sintered flux is as follows in terms of weight percentage: HJ431 welding powder: 40-50%, MgO: 10-15%, CaF2: 15-20%, BaCO3: 5-10%, TiO2: 2-5%, Al powder deoxidizer: 1-3%, Mn-Fe alloying agent: 5-10%, P <0.02%, S <0.018%.

[0028] The particle size of the HJ431 welding powder is 80-100 mesh, and the MnO content in the HJ431 welding powder is more than 40%; the CaF2 is added in the form of fluorite mineral powder, the particle size of the fluorite mineral powder is more than 100 mesh, and the CaF2 content of the fluorite mineral powder is 98%; the MgO is added in the form of fused magnesia, the particle size of the fused magnesia is 80-100 mesh, and the MgO content of the fused magnesia is 99%; the TiO2 is added in the form of natural rutile, the particle size of the natural rutile is 80-100 mesh, and the TiO2 content of the natural rutile is 93%; the BaCO3 is added in the form of barium carbonate, the particle size of the barium carbonate is 100-120 mesh, and the BaCO3 content of the barium carbonate is 99.2%; the particle size of the Al powder deoxidizer is 60-80 mesh, and the Al content of the Al powder deoxidizer is 99%; the particle size of the Mn-Fe alloying agent is 60-80 mesh, and the Mn content of the Mn-Fe alloying agent is 99%.

[0029] The mineral components and alloy weight percentage in the sintering flux are as follows: HJ431 welding powder: 40-50%, fluorite mineral powder: 12-24%, fused magnesite: 12-18%, barium carbonate: 7-12%, natural rutile: 2-5%, Al powder deoxidizer: 3-5%, and Mn-Fe alloying agent: 5-10%.

[0030] The Mn-Fe alloying agent is an electrolytic Mn-Fe alloying agent.

[0031] The moisture content in the sintering flux is less than 0.1%, the mechanical inclusions in the sintering flux are less than 0.3%, the tensile strength of the weld joint after welding is 485-517 MPa, the-10 ℃ ring weld impact energy is greater than or equal to 100 J, the toughness transition temperature is below-40 ℃, the-10 ℃ CTOD fracture toughness m is greater than or equal to 0.254 mm, and the diffusible hydrogen content is less than or equal to 4 ml / 100 g.

[0032] Embodiment 2

[0033] A preparation method of the sintering flux suitable for hydrogen delivery submerged arc welding steel pipes as described above, comprising the following steps:

[0034] S1: uniformly mixing 40-50 parts of HJ431 welding powder, 12-18 parts of fused magnesite, 7-12 parts of barium carbonate, 18-24 parts of fluorite mineral powder, 2-5 parts of natural rutile, 3-5 parts of Al powder deoxidizer, and 5-10 parts of Mn-Fe alloying agent by weight;

[0035] S2: adding 15.48-31.5 parts of a binder to the mixture obtained in step S1, and vibrating and shaking the wet material bonded into a shape with a dustpan or a granulator to perform granulation;

[0036] S3: controlling the particle size of the sintering flux granulated into a shape to be between 10-60 meshes through a 10-20 mesh sieve during the granulation process;

[0037] S4: drying the sintered flux at a temperature in the range of 200-350 ℃ through a high-temperature furnace;

[0038] S5: sintering the dried flux at a temperature in the range of 800-900 ℃ through a sintering furnace;

[0039] S6: packaging the sintered flux after screening through a 10-60 mesh sieve.

[0040] The binder in step S2 is potassium-sodium water glass, and the specific gravity of the potassium-sodium water glass as the binder is 41.9-43.9, and the modulus is 2.5-2.7.

[0041] Example 3

[0042] A sintered flux for hydrogen transfer submerged arc welding steel pipe according to the above-mentioned example 1 is prepared by using the preparation method of a sintered flux for hydrogen transfer submerged arc welding steel pipe according to the above-mentioned example 2. The specific process is as follows:

[0043] (1) Flux components

[0044] When the chemical components required by the sintered flux are added in the form of HJ431 welding powder, fused magnesia, barium carbonate, fluorite, rutile, aluminum iron, and electrolytic manganese iron, the weight percentage of the mineral components and the alloy in the sintered flux is as follows: HJ431 smelting welding powder: 47.6%; fluorite mineral powder: 18.8%; fused magnesia: 12.4%; barium carbonate: 7%; natural rutile: 6%; aluminum powder deoxidizer: 2%; electrolytic Mn-Fe alloying agent: 6.2%.

[0045] (2) Preparation of sintered flux

[0046] After the above-mentioned mineral components and alloys are mixed and stirred uniformly, a bonding agent, potassium sodium water glass, is added for wet mixing, and then a sieve or a granulator is used for granulation, the particle size of the flux is controlled between 10-60 meshes, and then low-temperature drying at 200-250°C is carried out, followed by high-temperature sintering at 800-900°C, and then screening through a 10-60 mesh sieve, and then packed into a moisture-proof packaging bag.

[0047] (3) The flux of the present application is matched with the corresponding H08MnNi2A submerged arc welding wire for deposited metal welding, according to the relevant welding material standard requirements, the test plate is Q235, the thickness is 25mm, the bevel 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℃, and the mechanical properties of the welded metal are shown in Table A.

[0048] Table A Mechanical properties of deposited metal

[0049]

[0050] As can be seen from Table A, the flux of the present application is matched with the corresponding submerged arc welding wire for deposited metal welding, compared with the standard requirements, the weld has higher strength and toughness, and at the same time, has lower diffusible hydrogen content.

[0051] (4) The welding flux is matched with the H08MnNi2A submerged arc welding wire to perform welding on the hydrogen medium conveying steel pipe, wherein the steel pipe steel grade is L360 / X52, the specification is Φ457x8.8mm, the chemical components are C: 0.05, Si: 0.25, Mn: 1.18, P: 0.011, S: 0.0016, Nb: 0.07, Ni: 0.05, Cr: 0.02, Mo: 0.05, V: 0.05, Al: 0.03, and the rest is iron. The adopted process is as follows: Y type groove form, the lower groove angle is 80°, the root gap is 2mm, and the blunt edge is 5-6mm; the welding sequence is as follows: the double-wire submerged arc welding mode is adopted to perform welding from the inside first, and then the single-wire submerged arc welding mode is adopted to perform welding from the outside of the steel pipe. In the process, the inner welding is double-wire, the outer welding is single-wire, the outer welding current is 850A, and the voltage is 30V; the front wire current is 680A, the voltage is 31.5V, the rear wire welding current is 480A, the voltage is 35V, the welding speed is 1.6m / min, and the mechanical properties of the welded joint metal after welding are shown in Table B.

[0052] Table B Mechanical properties of the welded joint metal of the steel pipe

[0053]

[0054] As shown in Table B, after the welding flux is matched with the H08MnNi2A submerged arc welding wire to perform submerged arc welding on the hydrogen medium conveying pipe line steel pipe, the welded joint has high strength and toughness, the welding slag does not flow away during the welding process, the welding bead is regular, the welded joint surface is smooth, the metal luster is obvious, the welding slag is easy to fall off, the tensile strength of the welded joint metal meets the requirements of the standard specification, after the steel pipe is welded by the welding flux and the H08MnNi2A submerged arc welding wire, and then is subjected to nondestructive testing according to the natural gas conveying pipe welding standard, no cracks, excessive pores and slag inclusions are found in the welded joint, which meets the standard requirements, and the welded joint has excellent fracture toughness.

[0055] According to the sintered flux suitable for hydrogen conveying submerged arc welding steel pipe in Embodiment 1, the sintered flux for hydrogen conveying submerged arc welding steel pipe in Embodiment 2 is prepared by the sintered flux preparation method, and the same flux using process in Embodiment 3 is used, and the specific conditions are shown in Embodiments 5, 6, 7 and 8, and the comparative examples are Comparative Examples 1, 2, 3 and 4.

[0056] The chemical element components of the sintered flux in Embodiments 4-7 and Comparative Examples 1-4 are shown in Table C in terms of weight percentage.

[0057] Table C Chemical element components of the sintered flux in Embodiments 4-7 and Comparative Examples 1-4 in terms of weight percentage (wt%)

[0058]

[0059] The mechanical property results of the girth welds welded by the sintered fluxes of Examples 4-7 and Comparative Examples 1-4 are shown in Table D.

[0060] Table D Test results of the sintered fluxes of Examples 4-7 and Comparative Examples 1-4 and the mechanical and process property results of the girth welds

[0061]

[0062] As shown in Table C, the weight percentages of some components in the fluxes of Comparative Examples 1-4 exceed the range involved in the technical solution of the present application, for example, in Comparative Example 1, the weight percentage of the HJ431 flux added in the flux is lower than the weight percentage determined in the flux of the present application, in Comparative Example 2, no Mn ferroalloy agent is added, in Comparative Example 3, the amount of the HJ431 flux added is higher than the weight percentage determined in the present application, and no Al deoxidizing agent is added, and in Comparative Example 4, no TiO2 substance and Al deoxidizing agent is added in the flux. As shown in Table D, at least one of the performance indicators of the fluxes in Comparative Examples 1-4 is lower than the standard design requirement, and the process performance of the welds obviously decreases. For example, in Comparative Example 1, the impact toughness does not meet the standard requirement, and the process performance of the weld after welding cannot meet the requirement, in Comparative Examples 2, 3 and 4, the impact toughness value, CTOD fracture toughness value and inclusions all exceed the standard, and cannot meet the standard requirement, therefore, the fluxes in Comparative Examples 1-4 are not suitable for the application requirement of the pipe for hydrogen medium.

[0063] As shown in Table D, compared with Comparative Examples 1-4, the tensile strength of the welds after welding by the submerged arc sintered fluxes in Examples 4-7 is 485-517 MPa, the water content in the flux is <0.1%, the mechanical inclusions in the flux are <0.3%, the impact energy of the girth weld at -10℃ is ≥100 J, the toughness transition temperature is below -40℃, the CTOD fracture toughness σm at -10℃ is ≥0.254 mm, and the diffused hydrogen content is obviously lower than 4 ml / 100 g. At the same time, the slag shell can automatically fall off after welding by the several fluxes, and the surface of the weld bead is smooth and beautiful, therefore, the pipe for hydrogen medium after welding by the fluxes in Examples 4-7 has high strength, high toughness and excellent anti-fracture performance, especially the weld bead appearance after welding is obviously improved compared with the ordinary flux, and the performance is much better than the current similar products, and the present application can meet the requirement of the pipe for hydrogen medium.

[0064] The above description is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this, any change or replacement within the technical range disclosed in the present application can be easily thought by the person skilled in the art, and should be covered in the protection scope of the present application.

Claims

1. A sintered flux suitable for hydrogen transport submerged arc welding of steel pipes, characterized by: The chemical composition of the sintered flux is as follows by weight: HJ431 welding powder: 40-50%, MgO: 10-15%, CaF2: 15-20%, BaCO3: 5-10%, TiO2: 2-5%, Al powder deoxidizer: 1-3%, Mn-Fe alloying agent: 5-10%, P<0.02%, S<0.018%, the moisture content of the sintered flux is less than 0.1%, and the mechanical inclusions in the sintered flux are less than 0.3%. When the sintered flux is combined with H08MnNi2A submerged arc welding wire for high-speed submerged arc welding of hydrogen-resistant pipeline steel at a speed of 1.6 m / min, the weld has a tensile strength of 485-517 MPa, an impact energy of a girth weld at -10°C of ≥100 J, and a CTOD fracture toughness σ at -10°C. m ≥0.254mm, diffusible hydrogen content ≤4ml / 100g.

2. The sintered flux for hydrogen transport submerged arc welding of steel pipes according to claim 1, characterized in that: The Mn-Fe alloying agent is an electrolytic Mn-Fe alloying agent.

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