A flux-cored gas shielded welding wire for high-strength liquid carbon dioxide storage tank and application thereof

Abstract

This invention discloses a high-strength flux-cored gas-shielded welding wire for liquid carbon dioxide storage tanks and its application; belonging to the field of welding technology, it comprises 65-70 wt% steel strip and 30-35 wt% flux powder; the steel strip is rolled into a U-shaped tube, the flux powder is added into the U-shaped tube, the seam is closed, the wire is drawn and reduced in diameter, the wire is wound, surface treated, and layered to obtain the high-strength flux-cored gas-shielded welding wire for liquid carbon dioxide storage tanks; its application method is mainly for vertical and overhead welding positions of liquid carbon dioxide storage tanks; in the actual use of EOR technology, CO2 is usually required to be stored in cryogenic liquefaction, which requires the material, the welding material itself, and the post-weld joint strength to reach above 770 MPa and withstand -60℃ impact; in addition, the composition of flux-cored gas-shielded welding wire is easy to adjust, the welding operation requirements are low, and long-distance continuous welding is possible, which can replace welding rods in vertical and overhead welding positions of liquid carbon dioxide storage tanks, improving work efficiency.

Description

Technical Field

[0001] This invention belongs to the field of welding technology and relates to a flux-cored gas-shielded welding wire for high-strength liquid carbon dioxide storage tank steel and its application. Background Technology

[0002] Currently, EOR (Extractable Orifice) technology improves oil well recovery by encapsulating CO2 underground, while simultaneously preserving significant CO2 resources. The storage and transportation of liquid CO2 requires tank materials with a strength exceeding 770 MPa and the ability to withstand operating temperatures as low as -60°C.

[0003] In the manufacturing process of high-strength and high-toughness steels, submerged arc welding and manual welding are mainly used. However, submerged arc welding is limited by the equipment itself and welding materials, and is mainly used for flat and circumferential welds. Manual welding is mainly used for vertical and overhead welding of tank assembly, but the electrode length is limited, and the welding process requires frequent replacement of new electrodes, resulting in low welding efficiency. In addition, the actual number of weld joints is large, increasing the probability of welding defects. Currently, there is still no mature, large-scale application of flux-cored welding wire for liquid carbon dioxide steel. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a high-strength flux-cored gas-shielded welding wire for liquid carbon dioxide storage tanks and its application. This welding wire and its application method can meet the requirements for vertical welding and overhead welding of other parts of liquid carbon dioxide storage tanks, with low operation requirements and high work efficiency.

[0005] The technical solution of the present invention is as follows: The present invention provides a flux-cored gas-shielded welding wire for high-strength liquid carbon dioxide storage tank steel, wherein the flux-cored gas-shielded welding wire for high-strength liquid carbon dioxide storage tank steel is composed of 65-70 wt% pure steel strip and 30-35 wt% flux powder.

[0006] Furthermore, the steel strip is made of ultrapure steel strip, with the following requirements: C≤0.05wt%, P≤0.002wt%, S≤0.001wt%, and the balance being Fe and unavoidable impurities.

[0007] Furthermore, the chemical composition of the powder is as follows: rutile 30-32 wt%, low-carbon ferromanganese 1.5-2.5 wt%, 75# ferrosilicon 0.3-0.4 wt%, nickel powder 2-3 wt%, chromium powder 0.01-0.03 wt%, molybdenum powder 0.4-0.5 wt%, arc stabilizer is a mixture of sodium oxide, potassium oxide, and potassium titanate 0.2 wt%-0.3 wt%, and the balance is iron powder and unavoidable impurities.

[0008] Furthermore, the rutile has a purity of ≥99% and a particle size of ≤0.3mm.

[0009] Furthermore, the purity of the low-carbon ferromanganese is ≥99%, and the particle size of the low-carbon ferromanganese is ≤0.3mm.

[0010] Furthermore, the purity of the 75# ferrosilicon is ≥99%, and the particle size of the 75# ferrosilicon is ≤0.3mm.

[0011] Furthermore, the purity of the nickel powder is ≥99%, and the particle size of the nickel powder is ≤0.3mm.

[0012] Furthermore, the purity of the chromium powder is ≥99%, and the particle size of the chromium powder is ≤0.3mm.

[0013] Furthermore, the purity of the molybdenum powder is ≥99%, and the particle size of the molybdenum powder is ≤0.3mm.

[0014] Furthermore, the arc stabilizer is a mixture of sodium oxide, potassium oxide, and potassium titanate.

[0015] Furthermore, the preparation method is as follows: using conventional flux-cored welding wire preparation method, the steel strip is rolled into a U-shaped tube, the flux powder is added into the U-shaped tube, then the seam is closed, the wire is drawn to reduce the diameter, the wire is wound, the surface is treated, and the wire is layered to obtain a high-strength flux-cored gas shielded welding wire for liquid carbon dioxide storage tank steel with a diameter of 1.2mm.

[0016] Furthermore, its application (usage method) is as follows: It is mainly used for vertical and overhead welding of liquid carbon dioxide storage tanks, using 100% CO2 gas protection at a flow rate of 18–25 L / min. Before welding, preheating should be performed at a temperature not lower than 140℃ according to the requirements of the liquid carbon dioxide storage tank steel. During welding, the layer temperature should be maintained between 140–180℃. For the root pass, the welding current is 220–240A, the voltage is 24–26V, and the welding speed is 35–40 cm / min; for the fill pass, the welding current is 260–280A, the voltage is 28–30V, and the welding speed is 25–35 cm / min; for the top pass, the welding current is 240–260A, the voltage is 26–28V, and the welding speed is 25–35 cm / min.

[0017] In this invention, EOR technology typically requires the cryogenic liquefaction and storage of CO2 during practical use. This necessitates that the materials, welding consumables themselves, and the post-weld joint strength reach over 770 MPa and withstand impacts of -60°C. Furthermore, the composition of flux-cored gas-shielded welding wire is easily adjustable, the welding operation requirements are low, and it can be used for continuous welding over long distances. It can replace welding rods in vertical and overhead welding positions in liquid carbon dioxide storage tanks, thereby improving work efficiency.

[0018] The beneficial effects of this invention are as follows: 1. The rutile in the powder of this invention is 30-32 wt%. Rutile plays a role in regulating the melting point of the slag and the viscosity of the molten pool. A thin protective slag layer is formed during the welding process, reducing the porosity sensitivity of the weld metal and ensuring the quality of weld inspection. At the same time, it reduces welding spatter and is beneficial to weld formation. The amount added must meet the design value; otherwise, the effect will be insignificant or the weld metal formability will be deteriorated. 2. The low-carbon ferromanganese in the powder of this invention is 1.5-2.5 wt%. The low-carbon design ensures the low-temperature impact toughness of the weld joint. The Mn element has the effect of solid solution strengthening, stabilizing austenite, and inhibiting the formation of ε-martensite, while ensuring the weld... 1. Joint tensile strength; the amount added must meet the design value, otherwise it will affect the joint strength or deteriorate the weld metal properties and increase the crack rate; 2. The 75# ferrosilicon in the powder of this invention is 0.3-0.4 wt%, which slightly improves the strength of the welded joint, but adding too much will easily cause Si to segregate at the grain boundaries, weakening the grain boundaries, reducing plasticity and low-temperature toughness. The amount added must meet the design value; 3. The nickel powder in the powder of this invention is 2-3 wt%. Under the premise of ensuring the impact toughness requirement at -60℃, considering its high price, adding a large amount would be too costly. Therefore, the above-mentioned addition amount is controlled; 4. In this invention, the P of the steel strip is ≤0.002 wt% and S is ≤0.001 wt%, and the impurities are... Elements phosphorus (P) and sulfur (S) easily cause liquefaction cracks and reheat cracks in weld metal. Therefore, it is necessary to purify the molten steel to minimize the P and S content in the steel strip, avoiding the tendency for hot cracking due to P and S segregation, and ensuring good weld metal quality. 6. In this invention, the welding method is crucial for the use of welding materials. Using 100% CO2 gas as the shielding gas results in better welding processability, while using a mixture of, for example, 80% Ar + 20% CO2 increases spatter and affects weld formation. The welding preheating temperature should be ensured to be no less than 140℃ to prevent cracking during the root pass of high-strength steel. During the welding process, the layer temperature should be maintained between 140 and 180℃ to prevent metal element... Overheating and slow cooling rates cause elemental misalignment to the grain boundaries, degrading the impact toughness at -60℃. Welding parameters directly affect weld formation and impact toughness. During welding, the welding current for the root pass is 220–240A, the voltage is 24–26V, and the welding speed is 35–40cm / min; the welding current for the filler pass is 260–280A, the voltage is 28–30V, and the welding speed is 25–35cm / min; and the welding current for the cap coat is 240–260A, the voltage is 26–28V, and the welding speed is 25–35cm / min. Using the above welding process effectively controls the fusion ratio of the weld joint, reduces the width of the heat-affected zone of the base material, and ensures the joint performance. Detailed Implementation

[0019] The specific technical solution of the present invention will be further described in detail below with reference to specific examples.

[0020] Example 1

[0021] A high-strength flux-cored gas-shielded welding wire for liquid carbon dioxide storage tank steel is composed of 65 wt% pure steel strip and 35 wt% flux powder.

[0022] The steel strip is made of ultrapure steel strip, with the following requirements: C≤0.05wt%, P≤0.002wt%, S≤0.001wt%, and the balance being Fe and unavoidable impurities.

[0023] The chemical composition of the powder is as follows: 30 wt% rutile, 1.5 wt% low-carbon ferromanganese, 0.3 wt% 75# ferrosilicon, 2 wt% nickel powder, 0.01 wt% chromium powder, 0.4 wt% molybdenum powder, 0.2 wt% arc stabilizer (a mixture of sodium oxide, potassium oxide, and potassium titanate), and the remainder being iron powder and unavoidable impurities.

[0024] The rutile has a purity of ≥99% and a grain size of ≤0.3mm.

[0025] The purity of the low-carbon ferromanganese is ≥99%, and the particle size of the low-carbon ferromanganese is ≤0.3mm.

[0026] The purity of the 75# ferrosilicon is ≥99%, and the particle size of the 75# ferrosilicon is ≤0.3mm.

[0027] The purity of the nickel powder is ≥99%, and the particle size of the nickel powder is ≤0.3mm.

[0028] The purity of the chromium powder is ≥99%, and the particle size of the chromium powder is ≤0.3mm.

[0029] The molybdenum powder has a purity of ≥99% and a particle size of ≤0.3mm.

[0030] The arc stabilizer is a mixture of sodium oxide, potassium oxide, and potassium titanate.

[0031] The preparation method is as follows: using conventional flux-cored welding wire preparation method, the steel strip is rolled into a U-shaped tube, the flux powder is added into the U-shaped tube, then the seam is closed, the wire is drawn to reduce the diameter, the wire is wound, the surface is treated, and the wire is layered to obtain a high-strength flux-cored gas shielded welding wire for liquid carbon dioxide storage tank steel with a diameter of 1.2mm.

[0032] For vertical and overhead welding of 50mm thick tank bodies, a 100% CO2 mixture is used for gas protection at a flow rate of 18–25 L / min. Preheating is 140℃, and the layer temperature is maintained between 140–180℃ during welding. For the root pass, the welding current is 220–240A, voltage is 24–26V, and welding speed is 35–40 cm / min; for the fill pass, the welding current is 260–280A, voltage is 28–30V, and welding speed is 25–35 cm / min; for the top pass, the welding current is 240–260A, voltage is 26–28V, and welding speed is 25–35 cm / min.

[0033] The joint requires Rm≥770MPa, no cracks upon bending, and AKv≥47J at -60℃. Mechanical property testing was performed on the joint, with tensile strengths of 801MPa and 799MPa, D=4a, no cracks upon 180° bending, and AKv values ​​at various locations at -60℃ as shown in Table 1.

[0034] Table 1. Results of the joint impact test in Example 1

[0035]

[0036] The flux-cored gas-shielded welding wire and its application method meet the requirements.

[0037] Example 2

[0038] A high-strength flux-cored gas-shielded welding wire for liquid carbon dioxide storage tank steel is composed of 70 wt% pure steel strip and 30 wt% flux powder.

[0039] The steel strip is made of ultrapure steel strip, with the following requirements: C≤0.05wt%, P≤0.002wt%, S≤0.001wt%, and the balance being Fe and unavoidable impurities.

[0040] The chemical composition of the powder is as follows: 32 wt% rutile, 2.5 wt% low-carbon ferromanganese, 0.4 wt% 75# ferrosilicon, 3 wt% nickel powder, 0.03 wt% chromium powder, 0.5 wt% molybdenum powder, 0.3 wt% arc stabilizer (a mixture of sodium oxide, potassium oxide, and potassium titanate), and the remainder being iron powder and unavoidable impurities.

[0041] The rutile has a purity of ≥99% and a grain size of ≤0.3mm.

[0042] The purity of the low-carbon ferromanganese is ≥99%, and the particle size of the low-carbon ferromanganese is ≤0.3mm.

[0043] The purity of the 75# ferrosilicon is ≥99%, and the particle size of the 75# ferrosilicon is ≤0.3mm.

[0044] The purity of the nickel powder is ≥99%, and the particle size of the nickel powder is ≤0.3mm.

[0045] The purity of the chromium powder is ≥99%, and the particle size of the chromium powder is ≤0.3mm.

[0046] The molybdenum powder has a purity of ≥99% and a particle size of ≤0.3mm.

[0047] The arc stabilizer is a mixture of sodium oxide, potassium oxide, and potassium titanate.

[0048] The preparation method is as follows: using conventional flux-cored welding wire preparation method, the steel strip is rolled into a U-shaped tube, the flux powder is added into the U-shaped tube, then the seam is closed, the wire is drawn to reduce the diameter, the wire is wound, the surface is treated, and the wire is layered to obtain a high-strength flux-cored gas shielded welding wire for liquid carbon dioxide storage tank steel with a diameter of 1.2mm.

[0049] For vertical and overhead welding of 50mm thick tank bodies, a 100% CO2 mixture is used for gas protection at a flow rate of 18–25 L / min. Preheating is 140℃, and the layer temperature is maintained between 140–180℃ during welding. For the root pass, the welding current is 220–240A, voltage is 24–26V, and welding speed is 35–40 cm / min; for the fill pass, the welding current is 260–280A, voltage is 28–30V, and welding speed is 25–35 cm / min; for the top pass, the welding current is 240–260A, voltage is 26–28V, and welding speed is 25–35 cm / min.

[0050] The joint requires Rm≥770MPa, no cracks upon bending, and AKv≥47J at -60℃. Mechanical property testing was performed on the joint, with tensile strengths of 801MPa and 805MPa, D=4a, no cracks upon 180° bending, and AKv values ​​at various locations at -60℃ as shown in Table 1.

[0051] Table 2 Results of Joint Impact Test in Example 2

[0052]

[0053] The flux-cored gas-shielded welding wire and its application method meet the requirements.

[0054] The present invention aims to propose a flux-cored gas-shielded welding wire for high-strength liquid carbon dioxide storage tank steel and its application method, so as to provide basic support for the storage of liquid carbon dioxide and the promotion and application of this type of steel.

Claims

1. A flux-cored gas-shielded welding wire for high-strength liquid carbon dioxide storage tank steel, characterized in that, The high-strength liquid carbon dioxide storage tank steel flux-cored gas shielded welding wire comprises 65-70 wt% steel strip and 30-35 wt% flux powder. The steel strip is made of ultra-pure steel strip, and its chemical composition by weight percentage is: C≤0.05wt%, P≤0.002wt%, S≤0.001wt%, with the balance being Fe and unavoidable impurities; The chemical components of the powder, by weight percentage, are as follows: rutile: 30~32wt%, low-carbon ferromanganese: 1.5~2.5wt%, 75# ferrosilicon: 0.3~0.4wt%, nickel powder: 2~3wt%, chromium powder: 0.01~0.03wt%, molybdenum powder: 0.4~0.5wt%, arc stabilizer: 0.2wt%~0.3wt%, with the balance being iron powder and unavoidable impurities; The rutile has a purity of ≥99% and a particle size of ≤0.3mm. The purity of the low-carbon ferromanganese is ≥99%, and the particle size of the low-carbon ferromanganese is ≤0.3mm; The purity of the 75# ferrosilicon is ≥99%, and the particle size of the 75# ferrosilicon is ≤0.3mm; The purity of the nickel powder is ≥99%, and the particle size of the nickel powder is ≤0.3mm; The purity of the chromium powder is ≥99%, and the particle size of the chromium powder is ≤0.3mm; The molybdenum powder has a purity of ≥99% and a particle size of ≤0.3mm; The arc stabilizer is a mixture of sodium oxide, potassium oxide and potassium titanate; The preparation steps are as follows: The prepared steel strip is rolled into a U-shaped tube, and then the powder is added into the U-shaped tube. Then the seam is closed, the wire is drawn and the diameter is reduced, the wire is wound, the surface is treated, and the wire is layered to obtain a high-strength liquid carbon dioxide storage tank steel flux-cored gas shielded welding wire. The diameter of the high-strength liquid carbon dioxide storage tank steel flux-cored gas-shielded welding wire prepared therefrom is 1.2 mm.

2. The application of the flux-cored gas-shielded welding wire for high-strength liquid carbon dioxide storage tanks as described in claim 1 in the vertical and overhead welding positions of high-strength liquid carbon dioxide storage tanks; The specific usage method is as follows: use 100% CO2 for gas protection; Preheating to at least 140℃ is required before welding, in accordance with the requirements for steel used in liquid carbon dioxide storage tanks. During welding, the welding current for the root pass is 220~240A, the voltage is 24~26V, and the welding speed is 35~40cm / min; the welding current for the fill pass is 260~280A, the voltage is 28~30V, and the welding speed is 25~35cm / min; the welding current for the cover pass is 240~260A, the voltage is 26~28V, and the welding speed is 25~35cm / min. The gas flow rate in the aforementioned gas protection system is 18~25 L / min; Furthermore, ensure that the layer temperature is between 140 and 180°C during the welding process.

Images