A welding rod for welding inner bottom plate of crude oil storage tank steel with yield strength not less than 370 MPa

Abstract

The application discloses a welding rod for welding an inner bottom plate of a crude oil storage tank steel with a yield strength of not less than 370 MPa, and belongs to the technical field of welding materials.The welding rod comprises a welding core and a coating covering the welding core, and the composition of the welding core comprises the following components in percentage by mass: C 0-0.05%, Si 0.2-0.4%, Mn 1.0-1.4%, S≤0.005%, P≤0.005%, Cr≤0.03%, Ni 0.3-1.3%, Mo 0.05-0.60%, Cu 0.15-0.80%, Ti 0.02-0.04%, Sn 0.01-0.05%, Ce 0.1-0.5%, Mg≤0.005%, Zr 0.01-0.03%, and the balance of Fe and inevitable impurities.In addition, the application further provides a preparation method of the welding rod.The welding rod has excellent welding process performance and mechanical properties, and when the welding rod is used for welding a new type of corrosion-resistant storage tank steel, according to the IMO 'Guidelines for the Inspection of Corrosion Resistant Steel for Cargo Oil Tanks of Crude Oil Tankers', the annual average corrosion rate (CR) of the weld metal in a typical corrosion-resistant crude oil storage tank steel corrosion environment is less than or equal to 0.9 mm, and the technical index of the corrosion-resistant crude oil storage tank welding can be met.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, specifically relating to a special welding electrode for welding the inner bottom plate of crude oil storage tanks with a yield strength of not less than 370MPa, which can be used for welding crude oil storage tanks, oil tankers, and oil pipelines. Background Technology

[0002] Since the reform and opening up, my country's economy has developed rapidly, especially in the industrial sector, leading to a surge in demand for oil. my country's imported oil mainly comes from the Middle East, transported primarily by tankers and stored in major coastal refineries. As of 2020, China's oil imports reached 540 million tons, with a foreign dependence rate of 73.6%. The safety of crude oil transportation and storage is a key concern for crude oil security. Most existing crude oil storage tanks use traditional high-strength ship steel, which meets the strength, toughness, and welding performance requirements during construction and use. However, this ship steel has poor corrosion resistance during service, resulting in difficult and costly maintenance. In particular, the large-scale import and transportation of high-sulfur, high-acid crude oil from the Middle East in recent years has exacerbated corrosion problems in crude oil tanks and storage tanks, significantly shortening the lifespan of oil tankers and storage tanks. Crude oil storage tanks are subject to both hydrogen sulfide corrosion and coastal environmental corrosion; therefore, the development of corrosion-resistant steel for crude oil storage tanks fills a gap in the field of steel for crude oil storage. As an important welding material for steel plate welding, welding electrodes, when used in conjunction with corrosion-resistant steel welding, require weld metals that not only possess high strength and high toughness, but also excellent resistance to hydrogen sulfide corrosion and coastal environmental corrosion. Existing welding electrodes for welding corrosion-resistant crude oil storage tanks cannot meet the corrosion resistance requirements of production and construction; therefore, the development and application of new welding electrodes is urgently needed.

[0003] In the prior art, for example, Chinese invention patent CN1415452 discloses a matching welding electrode for steel resistant to hydrogen sulfide corrosion. The core composition of the electrode is C≤0.12%, Si:0.2~0.5%, Mn:0.3~0.9%, Cr:1.0~3.5%, Al:0.3~0.7%, Mo:0.3~1.2%, RE≤0.15%, S≤0.015%, P≤0.02%. The core composition of this invention patent contains 1.0~3.5% Cr element. Under the condition of storing high acid crude oil, Cr element is prone to pitting corrosion due to the acidic storage environment, which increases the self-corrosion potential difference and is not conducive to the corrosion resistance of crude oil storage tank steel. In addition, the large amount of aluminum element is not conducive to welding processability. Aluminum element is prone to absorbing gas during welding, forming porosity defects, reducing the strength and sealing performance of the welded joint. The large coefficient of thermal expansion and thermal conductivity make the thermal stress generated during welding prone to hot cracking. The addition of aluminum element also increases the tendency of cold cracking in welding.

[0004] Chinese invention patent CN105033503A discloses a welding electrode for welding corrosion-resistant steel, with a core composition of: C: 0.06~0.07%, Mn: 0.4~0.6%, Si: 0.2~0.35%, S≤0.005%, P≤0.005%, Ni: 1.2~1.5%, Cr: 0.2~0.4%, Mo: 0.08~0.11%, Cu: 0.15~0.3%, Ti: 0.02~0.22%, Sb: 0.02~0.04%, and the balance being iron. This invention patent contains 0.2~0.4% Cr, which is detrimental to the pitting corrosion resistance of crude oil storage tanks in acidic environments; simultaneously, the core does not contain Sn, making it prone to pitting corrosion in acidic environments.

[0005] Chinese invention patent CN102794579A discloses a corrosion-resistant welding electrode for constructing cargo oil tankers on oil tankers. The electrode's deposited metal contains the following components: C: 0.03~0.15%, Si: 0.05~1.0%, Mn: 0.1~2.0%, P≤0.025%, S≤0.012%, Ni: 0.05~1.5%, Cu: 0.05~1.0%, Ti: 0.005~0.5%, Cr: 0~1.0%, Mo: 0~1.0%, W: 0~1.0%; B: 0~0.1%, RE: 0~0.1%, Al: 0~0.1%, with the balance being iron and unavoidable impurities. This invention patent adds elements such as Al and W, which can reduce weldability, easily cause welding defects, and lead to a decrease in weld mechanical properties.

[0006] Therefore, developing a corrosion-resistant welding electrode that improves the corrosion resistance and extends the service life of crude oil storage tanks, while meeting the requirements for the mechanical properties of welded joints in relevant standards and specifications, is of great significance for promoting my country's oil and gas construction. Summary of the Invention

[0007] The problem this invention aims to solve is to provide a welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa, wherein the weld metal deposited by this electrode meets the R... eL ≥370MPa, R m The weld has a strength of ≥500MPa, an A% of ≥17%, and a KV2 of ≥60J at -20℃. Furthermore, the average annual corrosion rate (CR) of the weld metal in a typical corrosion-resistant crude oil storage tank steel environment is ≤0.9mm; the relative corrosion rate between the weld metal and the base metal is ≤10%. Metallographic microscopy at 100x magnification shows no obvious corrosion steps between the base metal and the weld, and the corrosion depth difference is less than 30µm, which meets the welding requirements for large crude oil storage tanks.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a welding electrode for welding the inner bottom plate of crude oil storage tanks with a yield strength of not less than 370 MPa. The welding electrode includes a core and a coating covering the core. The composition of the core, by mass percentage, includes: C 0~0.05%, Si 0.2~0.4%, Mn 1.0~1.4%, S≤0.005%, P≤0.005%, Cr≤0.03%, Ni 0.3~1.3%, Mo 0.05~0.60%, Cu 0.15~0.80%, Ti 0.02~0.04%, Sn 0.01~0.05%, Ce 0.1~0.5%, Mg≤0.005%, Zr 0.01~0.03%, with the balance being Fe and unavoidable impurities.

[0009] The alloy element content in the welding core conforms to the relationship of 0.040≤Φ≤0.10, where Φ is the corrosion factor, Φ=(5×C+0.3×Mn+S+5×Cr) / (5×Ni+3×Mo+15×Cu+10×Sn+5×Ce+15×Ni×Sn).

[0010] Furthermore, the diameter of the welding core is 3.2~4.0mm.

[0011] Furthermore, the coating quality coefficient of the welding electrode is 0.35≤K b ≤0.4.

[0012] Furthermore, the coating comprises a coating powder and a binder, wherein the binder accounts for 15-20% of the coating mass, and the coating powder comprises, by mass percentage: marble 30-40%, fluorite 10-18%, one or two types of silica powder or quartz 6-17%, rutile 6-17%, potassium titanate 6-10%, sodium carbonate 0.5-1.5%, phlogopite 0.5-2%, medium-carbon ferromanganese 3-7%, ferrosilicon 3-7%, carboxymethyl cellulose 0-2%, rare earth oxides 0-3%, and rare earth fluorides 0-3%.

[0013] Furthermore, the basicity of the coating is 1.5≤B≤2.5, where B is the basicity of the electrode coating, B=(1.68×CaCO3+CaF2) / (3×SiO2+TiO2).

[0014] Furthermore, the binder is potassium sodium silicate with a modulus of 3.

[0015] Furthermore, the weld metal deposited by the welding electrode satisfies R eL ≥370MPa, R m ≥500MPa, A%≥17%, -20℃KV2≥60J.

[0016] Furthermore, the annual average corrosion rate (CR) of the weld metal deposited by the welding electrode in a typical corrosion environment of corrosion-resistant crude oil storage tank steel is ≤0.9mm, and the relative corrosion rate between the weld metal and the base metal is ≤10%.

[0017] The present invention also provides a method for preparing a welding electrode, which includes the following steps:

[0018] (1) Mix the raw materials in the powder component of the medicine skin evenly according to the proportion to make a mixed powder;

[0019] (2) Then add the binder to the mixed powder and stir evenly;

[0020] (3) The well-stirred coating is evenly coated onto the surface of the core electrode on a welding electrode coating machine, and the finished welding electrode is obtained after drying and baking.

[0021] Furthermore, in step (3), the coated welding rod is allowed to air dry naturally, and then placed in a drying oven and dried at 70°C for 1 hour, 100°C for 1 hour, 150°C for 1 hour, and 360°C for 2 hours.

[0022] The beneficial effects of the present invention are: (1) The welding electrode has excellent welding process performance and mechanical properties, and the weld deposited metal meets R eL ≥370MPa, R m ≥500MPa, A%≥17%, -20℃KV2≥60J; at the same time, it has good corrosion resistance. When welding with new corrosion-resistant storage tank steel, referring to the IMO "Guidelines for Inspection of Corrosion-Resistant Steels for Cargo Tanks of Crude Oil Tankers", the average annual corrosion rate (CR) of the weld metal in the typical corrosion environment of corrosion-resistant crude oil storage tank steel is ≤0.9mm; at the same time, using the base material as a comparison, under a 100x metallographic microscope, no obvious corrosion steps were observed between the base material and the weld, and the difference in corrosion depth was less than 30um. It can meet the technical indicators for welding corrosion-resistant crude oil storage tanks. (2) The composition of the welding core was designed through reasonable alloy composition; a reasonable coating composition was prepared for the welding core, and rare earth elements were transferred to the weld by adding rare oxides or rare earth fluorides to the welding electrode coating, which can effectively refine the weld metal, improve the weld strength and low-temperature impact toughness; adding corrosion-resistant elements such as Ni, Mo, Cu, and Sn can improve the corrosion resistance of the weld metal. (3) The coating composition is reasonable, and it has the advantages of less spatter, easy slag removal and good weld formation.

[0023] The present invention will now be described in detail with reference to the accompanying drawings. Attached Figure Description

[0024] Figure 1 The microstructure of the weld metal in Embodiment 1 of the present invention is shown at 200x magnification.

[0025] Figure 2The microstructure of the weld metal in Embodiment 1 of the present invention is shown at 500x magnification.

[0026] Figure 3 This is the morphology of the deposited metal after corrosion in Example 2 of the welding wire of the present invention;

[0027] Figure 4 The image shows the morphology of the weld metal after corrosion in Comparative Example 1. Detailed Implementation

[0028] This invention provides a welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa, comprising a core and a coating covering the surface of the core, wherein the coating quality coefficient is 0.35 ≤ K. b ≤0.4, the diameter of the welding core is 3.2~4.0mm.

[0029] The composition of the aforementioned core material, by mass percentage, includes: C 0~0.05%, Si 0.2~0.4%, Mn 1.0~1.4%, S≤0.005%, P≤0.005%, Cr≤0.03%, Ni 0.3~1.3%, Mo 0.05~0.60%, Cu 0.15~0.80%, Ti 0.02~0.04%, Sn 0.01~0.05%, Ce 0.1~0.5%, Mg≤0.005%, Zr 0.01~0.03%, with the balance being Fe and unavoidable impurities.

[0030] The alloy element content in the welding core conforms to the relationship 0.040≤Φ≤0.10, where Φ is the corrosion factor.

[0031] Φ=(5×C+0.3×Mn+S+5×Cr) / (5×Ni+3×Mo+15×Cu+10×Sn+5×Ce+15×Ni×Sn).

[0032] The roles and mechanisms of each element in the welding core are as follows.

[0033] C: Carbon can expand the austenite phase region, improve the strength and hardness of materials, and also improve the hardenability of steel. However, it is prone to causing welding cracks during welding, reducing the toughness and plasticity of materials. Therefore, the carbon content should not be too high. Thus, the C content is 0~0.05%, preferably 0.01~0.04%, and more preferably 0.031~0.039%.

[0034] Silicon (Si): Silicon is an effective deoxidizing element during welding. When silicon and manganese work together, they form oxide complexes, which facilitate flotation from the molten pool, resulting in a significant deoxidation effect. However, excessive silicon content in the weld metal significantly reduces its toughness. Therefore, the Si content is 0.2-0.4%, preferably 0.25-0.35%, and more preferably 0.31-0.39%.

[0035] Mn: Manganese can expand the austenite phase region and lower the bainite transformation temperature. At the same time, Mn can also improve hardenability, refine the microstructure, and improve the strength of weld metal through solid solution strengthening. Therefore, the Mn content is 1.0~1.4%, preferably 1.05~1.3%, and more preferably 1.06~1.15%.

[0036] S: It has a detrimental effect on the toughness of weld metal. Excessive content can easily cause cracks in the weld. Its content should be reduced as much as possible, and the content of S element should not exceed 0.005%.

[0037] P: It has a detrimental effect on the toughness of weld metal. Excessive content can easily cause cracks in the weld. Its content should be reduced as much as possible, and the content of P element should not exceed 0.005%.

[0038] Ni: Nickel is an austenite stabilizing element that can exist in austenite and ferrite in a miscible form with Fe, improving strength and low-temperature impact toughness. Ni can also refine grains and inhibit the precipitation of ferrite at grain boundaries. Ni is also a good corrosion-resistant element. Therefore, the Ni content is 0.3~1.3%, preferably 0.5~1.1%, and more preferably 0.87~0.94%.

[0039] Mo: Molybdenum is a carbide-forming element that plays a significant role in improving strength and refining grain size, and its loss during welding is minimal. Therefore, the Mo content is 0.05~0.60%, preferably 0.2~0.5%, and more preferably 0.34~0.42%.

[0040] Cu: Copper has good corrosion resistance, but it increases the size of austenite grains, which can easily lead to coarsening of the weld structure. Therefore, the Cu content is 0.15~0.80%, preferably 0.2~0.65%, and more preferably 0.21~0.27%.

[0041] Ti: When Ti is added to submerged arc welding wire, it can form dispersed oxides and nitrides. These fine, dispersed inclusions can promote the nucleation of acicular ferrite within the grains, inhibit grain boundary ferrite, effectively refine the grains, and improve the low-temperature toughness of the weld. Therefore, the Ti content is 0.02~0.04%, preferably 0.025~0.035%, and more preferably 0.023~0.03%.

[0042] Cr: The presence of Cr in the weld can inhibit the precipitation of proeutectoid ferrite, refine the ferrite structure, and improve the strength, toughness, and corrosion resistance of the weld metal. However, research suggests that the improved corrosion resistance of Cr is due to the formation of a passivation film. This passivation film exhibits good corrosion resistance in alkaline and neutral environments. The internal environment of crude oil storage tanks is acidic, making them susceptible to pitting corrosion that damages the passivation film formed by Cr, increasing the self-corrosion potential difference and thus reducing corrosion resistance. Therefore, the Cr content should be controlled to no more than 0.03%.

[0043] Sn: A certain amount of Sn in the weld metal provides good corrosion resistance. The corrosion resistance of steel plates containing an appropriate amount of Sn is 3 to 4 times that of steel plates without Sn. In the early stages of corrosion, Sn forms SnO2, which accumulates at austenite grain boundaries or within high-energy [1,1,1] grains. Over time, it expands into the ferrite region, effectively covering the corroded area. SnO2 can also form denser composite products with chloride ions, further improving the corrosion resistance of the weld. However, an increase in Sn content increases proeutectoid ferrite, severely affecting the mechanical properties of the joint. Therefore, the Sn content is 0.01~0.05%, preferably 0.023~0.031%, and more preferably 0.023~0.027%.

[0044] Ce: Ce can play a role in deoxidation and desulfurization, forming non-metallic inclusions. These inclusions have a lattice constant close to that of α-Fe, and have a good heterogeneous nucleation effect on acicular ferrite, thereby improving the strength and toughness of the weld metal. Therefore, the Ce content is 0.1~0.5%, preferably 0.21~0.28%.

[0045] Mg: Mg is a pre-deoxidizing element that protects the transition of alloying elements to the weld. However, high magnesium content increases the tendency for hot cracking in the weld, which is detrimental to the welding process. Therefore, the Mg content should be controlled to no more than 0.005%, preferably 0.002~0.004%.

[0046] Zr: Zr can promote the formation of acicular ferrite in weld metal and improve the low-temperature impact toughness of weld metal. Therefore, the Zr content is 0.01~0.03%, preferably 0.011~0.016%, and more preferably 0.013~0.015%.

[0047] The weld seam of a corrosion-resistant crude oil storage tank welded with welding rods must not only have good corrosion resistance, but its corrosion resistance must also match that of the base material. Therefore, the alloy element ratio of the welding rod core wire should meet the requirement of 0.040≤Φ≤0.10. Φ is the corrosion factor and Φ=(5×C+0.3×Mn+S+5×Cr) / (5×Ni+3×Mo+15×Cu+10×Sn+5×Ce+15×Ni×Sn). C (carbon) in weld metal easily leads to corrosion of the metal matrix; Mn (magnesium) is a weak carbide-forming element, which reduces the metal's oxidation resistance; S (sulfur) and P (phosphorus) impurities easily cause intergranular corrosion; since crude oil storage tanks are often in high-salt, high-humidity environments, Cl- in them will react with Cr (chromium), causing pitting corrosion; Ni (ni), Mo (mo), and Cu (cubic copper) are all corrosion-resistant elements and are widely used in corrosion-resistant steels; an appropriate amount of Sn can form Sn-containing complexes, which can exist stably in acidic Cl- ion environments, isolating chloride ions to protect the matrix, reducing the corrosion rate, increasing the self-corrosion potential, and reducing the self-corrosion current density. At the same time, Sn and Ni have a synergistic effect in corrosion resistance; an appropriate amount of Ce (cerium) can increase the corrosion resistance of the matrix and improve the uniformity of matrix corrosion.

[0048] The coating consists of coating powder and a binder. The binder accounts for 15-20% of the coating weight. The coating powder, by weight percentage, includes: marble 30-40%, fluorite 10-18%, one or two types of silica powder or quartz 6-17%, rutile 6-17%, potassium titanate 6-10%, sodium carbonate 0.5-1.5%, phlogopite 0.5-2%, medium-carbon ferromanganese 3-7%, ferrosilicon 3-7%, carboxymethyl cellulose 0-2%, rare earth oxides 0-3%, and rare earth fluorides 0-3%. The binder is potassium-sodium silicate with a modulus of 3. The basicity B of the coating is 1.5 ≤ B ≤ 2.5, where B = (1.68 × CaCO3 + CaF2) / (3 × SiO2 + TiO2).

[0049] The effects and mechanisms of the various components in the drug coating are as follows.

[0050] Marble: The main component of marble is calcium carbonate, which acts as a gas generator and slag former. During welding, marble decomposes at high temperatures, producing a large amount of carbon dioxide gas. This carbon dioxide gas covers the molten pool, isolating it from the air and protecting it. Marble also desulfurizes, thus cleaning the weld metal. Therefore, marble accounts for 30-40% of the weld metal.

[0051] Fluorite: The main component of fluorite is calcium fluoride, and its main function is slag formation. It can increase the basicity of the welding electrode, lower the melting point and surface tension of the slag, and increase the fluidity of the slag. In addition, fluorite reduces the oxygen content of the weld metal, which is beneficial for the transition of alloying elements. It can also reduce the diffusible hydrogen content of the weld metal and improve the impact toughness of the weld metal. Therefore, the fluorite content is 10-18%.

[0052] Silica powder: Its main component is silicon dioxide. Its main functions are slag formation, adjusting slag viscosity, refining droplets, and improving forming. In addition, it can also improve the coating properties of welding electrodes.

[0053] Quartz: Its main component is silicon dioxide. Quartz can adjust the viscosity of molten slag, refine the molten droplets, and improve the weld formation. An appropriate amount of quartz can make the slag shell brittle, which is beneficial for slag removal.

[0054] In this invention, one or both of silicon micropowder or quartz can be selected, with a content of 6-17%, preferably 6-16%.

[0055] Rutile: The main component of rutile is titanium dioxide. Its primary function is slag formation. It can also adjust the melting point of the slag, improve weld bead formation, refine molten droplets, and enhance welding process performance. The rutile content is 6-17%, preferably 6-15%.

[0056] Potassium titanate: Potassium titanate can reduce arc voltage, stabilize the arc, and reduce spatter, exhibiting good usability. The content of potassium titanate is 6~10%.

[0057] Sodium carbonate: Sodium carbonate can improve the coating properties of welding electrodes and is beneficial to the forming of the electrodes. The sodium carbonate content is 0.5~1.5%.

[0058] Phlogopite: Phlogopite has a slag-forming effect and can also improve the coating performance of welding electrodes. The content of phlogopite is 0.5%~2%.

[0059] Carboxymethyl cellulose: Carboxymethyl cellulose is an organic compound with a certain viscosity. Adding it to the electrode coating increases the coating's viscosity, which is beneficial for the electrode's pressing and forming process. The content of carboxymethyl cellulose is 0-2%.

[0060] Medium-carbon ferromanganese: an alloy powder that can transfer carbon and manganese elements to the weld, improving weld strength. The content of medium-carbon ferromanganese is 3-7%.

[0061] Ferrosilicon: An alloy powder that can transition carbon and silicon elements into the weld. Silicon is a precipitating deoxidizer, and in synergy with manganese, it has a good deoxidizing effect. The ferrosilicon content is 3-7%.

[0062] Rare earth oxides: mainly oxides of rare earth cerium. The addition of rare earth oxides is beneficial for deoxidation of the weld, and rare earth elements also have the effect of desulfurization and phosphorus removal. The content of rare earth oxides is 0~3%.

[0063] Rare earth fluorides: Rare earth fluorides can reduce the diffusion of hydrogen and refine the grain size. The content of rare earth fluorides is 0-3%.

[0064] Basicity is an important indicator of welding electrodes. Theoretically, when B > 1, it is an alkaline slag; when B < 1, it is an acidic slag; and when B = 1, it is a neutral slag. Weld metal is a product of the physicochemical reactions of the base metal, the electrode core, and the electrode coating. Low basicity and high acidity result in high dissolved oxygen content in the slag system, leading to severe loss of alloying elements and hindering the improvement of weld mechanical properties. Conversely, while excessively high basicity reduces dissolved oxygen and alloying element loss, the increased alkaline oxides increase the viscosity and melting point of the coating, causing significant spatter and negatively impacting weld formation. Therefore, the basicity of the welding electrode has a significant impact on weld performance. This invention's welding electrode controls basicity to 1.5 ≤ B ≤ 2.5 by adding different amounts of alkaline and acidic substances.

[0065] CaCO3 is mainly added in the form of marble, and its function is to generate gas and slag. During the welding process, CaCO3 decomposes at high temperatures, producing a large amount of carbon dioxide gas. The carbon dioxide gas covers the molten pool and isolates it from the air, thus protecting the molten pool. Its decomposition product, CaO, is alkaline. Under the action of the electric arc, the decomposition product CaO of CaCO3 undergoes the following reaction:

[0066] 3CaO + 2[P] + 5[O] = 3CaO·P₂O₅(s)

[0067] CaO + [S] = CaS(s) + [O].

[0068] This achieves good desulfurization and dephosphorization effects, resulting in cleaner weld metal. CaF2 is a strong alkaline oxide and plays an important role in the electrode coating. It can lower the melting point of the electrode coating, giving the electrode better melting characteristics. It can also reduce the viscosity of the molten pool, allowing bubbles and slag to float to the surface in time, preventing defects. Furthermore, under the action of the arc, CaF2 reacts with [H] to form HF gas, which is insoluble in the molten pool. Therefore, CaF2 can reduce the [H] content of the weld and improve the impact toughness of the weld metal. Na2CO3 is an alkaline substance that decomposes into carbon dioxide gas at high temperatures. Its decomposition product, sodium oxide, has a low ionization energy, thus exhibiting good arc stabilization performance. In addition, Na2CO3 is a good binder, improving the pressure coating properties of the electrode. SiO2 is an acidic oxide that introduces oxygen into the weld during welding, causing severe loss of alloying elements. However, SiO2 will form SiO4. 2+ Adjusting the viscosity of the molten pool in the weld pool prevents slag runoff. Furthermore, appropriate amounts of SiO2 increase the stress in the slag shell during the slag cooling stage due to phase transformation, which facilitates slag removal from the weld. TiO2 is an acidic oxide, and titanium dioxide helps regulate viscosity and refines the molten droplets. K2TiO3 is also an acidic oxide, and potassium titanate has good arc stabilization properties, improving the arc stabilization performance of the welding electrode.

[0069] The welding electrode of this invention conforms to the IMO "Guideline for the Inspection of Corrosion-Resistant Steels for Cargo Tanks of Crude Oil Tankers." The weld metal deposited in a typical corrosion-resistant crude oil storage tank steel environment exhibits an average annual corrosion rate (CR) ≤ 0.9 mm, and the relative corrosion rate between the weld metal and the base metal is ≤ 10%. Metallographic microscopy at 100x magnification reveals no obvious corrosion steps between the base metal and the weld, with a corrosion depth difference of less than 30 μm. The weld metal deposited by the electrode meets the R... eL ≥370MPa, R m ≥500MPa, A%≥17%, -20℃KV2≥60J.

[0070] The present invention also provides a method for preparing the above-mentioned welding electrode, comprising the following steps: (1) mixing each raw material in the coating powder component in proportion to form a mixed powder; (2) adding a binder to the mixed powder and stirring evenly; (3) uniformly coating the stirred coating material onto the surface of the welding core on a welding electrode coating machine, and obtaining the finished welding electrode after drying and baking.

[0071] In step (3), the coated welding rod is allowed to air dry naturally, and then placed in a drying oven and dried at 70℃ for 1 hour, 100℃ for 1 hour, 150℃ for 1 hour, and 360℃ for 2 hours.

[0072] The present invention will now be described in detail with reference to specific embodiments.

[0073] The composition of the electrode coatings of Examples 1-10 and Comparative Examples 1-3 in this invention is shown in Table 1; the bevel form and welding parameters of the fusion welding test are shown in Table 2.

[0074] Table 1. Composition ratio of electrode coating in the examples and comparative examples

[0075] .

[0076] Table 2. Groove type and welding parameters for fusion welding test

[0077] .

[0078] The composition of the weld metal in the examples and comparative examples is shown in Table 3 below (balance is Fe and unavoidable impurities):

[0079] .

[0080] The mechanical properties and corrosion resistance of the weld seam in the embodiment are shown in Table 4 below:

[0081] .

[0082] like Figure 1 and Figure 2As shown, in Embodiment 1 of the present invention, the weld metal contains a high proportion of fine acicular ferrite, exceeding 80%. Acicular ferrite has a closed structure, which can effectively hinder crack propagation. Therefore, the present invention exhibits high impact toughness, indicating that the alloy elements and coating composition of the electrode core wire are rationally combined.

[0083] like Figure 3 As shown, the morphology of the weld metal after corrosion in Example 2 of the present invention is shown. After a periodic accelerated corrosion test, the test surface of Example 2 showed no corrosion pits and the sample surface was smooth and flat, indicating that the weld metal of the welding electrode of the present invention has good corrosion resistance.

[0084] like Figure 4 As shown, after a periodic accelerated corrosion test, corrosion pits were clearly visible on the surface of the weld metal of Comparative Example 1, indicating that the weld metal of Comparative Example 1 has poor corrosion resistance.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa, comprising a core and a flux coating on the surface of the core, characterized in that, The composition of the welding core, by mass percentage, includes: C 0~0.05%, Si 0.2~0.4%, Mn 1.0~1.4%, S≤0.005%, P≤0.005%, Cr≤0.03%, Ni 0.3~1.3%, Mo 0.05~0.60%, Cu 0.15~0.80%, Ti 0.02~0.04%, Sn 0.01~0.05%, Ce 0.1~0.5%, Mg 0.002~0.004%, Zr 0.01~0.03%, with the balance being Fe and unavoidable impurities. The alloy element content in the welding core conforms to the relationship of 0.04≤Φ≤0.10, where Φ is the corrosion factor, Φ=(5×C+0.3×Mn+S+5×Cr) / (5×Ni+3×Mo+15×Cu+10×Sn+5×Ce+15×Ni×Sn). The coating comprises a coating powder and a binder. The binder accounts for 15-20% of the coating mass. The coating powder comprises, by mass percentage: marble 30-40%, fluorite 10-18%, one or two types of silica powder or quartz 6-17%, rutile 6-17%, potassium titanate 6-10%, sodium carbonate 0.5-1.5%, phlogopite 0.5-2%, medium-carbon ferromanganese 3-7%, ferrosilicon 3-7%, carboxymethyl cellulose 0-2%, rare earth oxides 0-3%, and rare earth fluorides 0-3%. The basicity of the coating is 1.5≤B≤2.5, where B is the basicity of the electrode coating, B=(1.68×CaCO3+CaF2) / (3×SiO2+TiO2).

2. The welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa as described in claim 1, characterized in that, The diameter of the welding core is 3.2~4.0mm.

3. The welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa as described in claim 1, characterized in that, The coating quality coefficient of the welding electrode is 0.35≤K b ≤0.

4.

4. The welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa as described in claim 1, characterized in that, The binder is potassium-sodium silicate with a modulus of 3.

5. A welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa, as described in any one of claims 1-4, characterized in that... The weld metal deposited by the welding electrode satisfies R eL ≥370MPa, R m ≥500MPa, A%≥17%, -20℃KV2≥60J.

6. The welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa, as described in any one of claims 1-4, is characterized in that... The weld metal of the electrode has an annual average corrosion rate (CR) ≤0.9 mm in a typical corrosion environment of corrosion-resistant crude oil storage tank steel, and the relative corrosion rate between the weld metal and the base metal is ≤10%.

7. A method for preparing a welding electrode for welding the inner bottom plate of a crude oil storage tank with a yield strength of not less than 370 MPa, used to prepare the welding electrode as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Mix the raw materials in the powder component of the medicine skin evenly according to the proportion to make a mixed powder; (2) Then add the binder to the mixed powder and stir evenly; (3) The well-stirred coating is evenly coated onto the surface of the core electrode on a welding electrode coating machine, and the finished welding electrode is obtained after drying and baking.

8. The preparation method according to claim 7, characterized in that, In step (3), the coated welding rod is allowed to air dry naturally, and then placed in a drying oven and dried at 70℃ for 1 hour, 100℃ for 1 hour, 150℃ for 1 hour, and 360℃ for 2 hours.

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