Welding electrode for 5.5 Ni steel LNG storage tank

Abstract

The invention discloses an electric welding rod for a 5.5 Ni steel LNG (Liquefied Natural Gas) storage tank, which consists of a welding core and a coating, the welding core is coated with the coating, and the coating accounts for 0.5-0.7 of the total weight coefficient of the welding rod. Through the reasonable composition design of the core wire and the coating wrapping the surface of the core wire, deposited metal of the welding rod has high strength and high toughness matching, the all-position weldability is excellent, the deposition rate is high, and the porosity resistance and the crack resistance are excellent. Compared with ENiCrMo-6 and ENiCrFe-9 welding rods matched with a traditional 9% Ni steel LNG storage tank, the welding rod has the higher strength advantage, and the performance of the welding rod can be matched with that of 5.5% Ni steel for a newly developed economical and economical LNG storage tank in the market.

Description

Technical Field

[0001] The invention belongs to the field of welding materials, and particularly relates to an electric welding rod for a 5.5% Ni steel LNG storage tank. Background Art

[0002] As a clean energy, natural gas has the characteristics of high calorific value, low sulfur content and low CO2 emissions, and is actively developed and utilized by countries around the world.

[0003] Due to the flammability and ultra-low temperature properties of LNG, LNG tank materials are required to have high strength and good low-temperature toughness. At present, 9% Ni steel with high strength, good low-temperature toughness and low cost is generally used as the liner structure material for building LNG storage and transportation equipment internationally. On the basis of ensuring product quality, it is urgent to reduce the construction cost of LNG tanks, improve the comprehensive competitiveness of tank design and construction, and develop low-cost nickel-saving LNG tank steel and supporting welding materials.

[0004] As a new type of low-temperature material for LNG storage tanks, nickel-saving 7% Ni steel has an excellent combination of strength and plasticity and outstanding ultra-low temperature toughness. It can reach the same level as 9% Ni steel and can be used as ultra-low temperature structural steel, which significantly reduces the material and manufacturing costs of LNG storage tank construction. Furthermore, reducing the Ni content to 5.5% is the development direction for further cost reduction and efficiency improvement of LNG storage tanks. ASTM A645 has included 5.5% Ni steel plates, and Jiangyin Xingcheng Special Steel disclosed "A 5.5% Ni steel plate for ultra-low temperature environment and its manufacturing method" in September 2023, producing a 5.5% Ni steel plate with a strength equivalent to that of 9Ni steel plate and an impact absorption energy of ≥100J at -196℃. However, the research and development of welding materials matching 5.5% Ni steel has not yet been reported in the literature.

[0005] ENiMo-9 is a nickel-based alloy welding rod that can be used for the construction of ultra-low temperature LNG storage tanks. There are few relevant materials and reports available at present. Its deposited metal composition is relatively complex, mainly composed of Ni and Mo alloy elements, and also contains Fe, Mn, Si, W, Cu, etc., and has high requirements for impurity elements such as C, P, and S. At present, most of the welding rods used for welding large LNG storage tanks are ENiCrMo type, most of which are monopolized by ESAB ENiCrMo-6, and a few use Kobelco's ENiCrFe-9 type. Jingqun has been promoting the localization of ENiCrMo-6 welding rods since 2016, and has also achieved remarkable results in the construction of 9% Ni steel LNG ship tanks and large LN land tanks. It is the first in China to promote the application of 7% Ni steel matching welding rods in the construction of 7% Ni steel LNG storage tanks. In order to match the performance of the economical and economical 5.5% Ni storage tank steel that is expected to be promoted and applied in the future, it is urgent to develop and design alloy welding rods that match 5.5% Ni storage tank steel. Summary of the invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide an economical 5.5% Ni steel LNG storage tank supporting electric welding rod, which has good adaptability with the economical 5.5% Ni steel for LNG storage tanks. The welding rod of the present invention has the advantages of matching high strength and high toughness, excellent all-position weldability, high deposition rate, excellent porosity resistance and crack resistance. Compared with the traditional 9% Ni steel LNG storage tank supporting ENiCrMo-6 and ENiCrFe-9 welding rods, it has a higher strength advantage and can match the performance of the newly developed economical 5.5% Ni steel for LNG storage tanks in the market.

[0007] To achieve the above technical purpose, the technical solution of the present invention is a 5.5Ni steel LNG storage tank welding rod, which is composed of a welding core and a coating, the coating is coated on the outside of the welding core, and the coating accounts for 0.5-0.7 of the total weight coefficient of the welding rod. Based on the total weight of the welding core, the chemical composition and weight percentage content of the welding core are as follows: C < 0.01%, Mn < 0.10%, Si < 0.10%, P ≤ 0.005%, S ≤ 0.003%, P + S ≤ 0.006%; Ni ≥ 99.0%, Al: 0.020-0.060, Ti: 0.030-0.100%, O < 100ppm;

[0008] Based on the total weight of the coating, the components of the coating are calculated by weight percentage: calcium carbonate: 16-24%, strontium carbonate: 5-12%, barium fluoride: 2-5%, calcium fluoride: 10-13%, cryolite: 2-4%, sodium carbonate: 0.5-1.0%, electrolytic manganese: 0.8-1.8%, rare earth ferrosilicon: 2-5%, molybdenum powder 24-28%, pure titanium: 4-6%, copper powder: 1.5-3.2%, aluminum-magnesium alloy: 1.6-2.8%, tungsten powder: 2.5-4.0%, quartz powder: 3-6%, rutile: 3-5%, zirconium oxide 2-4%, and alginate: 0.8%-2.5%.

[0009] Among them, the components of the deposited metal of the 5.5Ni steel LNG storage tank welding rod are, by weight percentage: C: 0.026-0.048%, Mn: 0.3-0.6%, Si: 0.2-0.6%, P≤0.008%, S≤0.005%, P+S≤0.012%, Ni: 68.0-78.0%, Mo: 16.0-20.0%, Fe≤4.0%, Cu: 0.6-1.2%, W: 2.0-3.5%, Al: 0.018-0.042%, Ti: 0.10-0.24%, O≤300ppm (i.e. 0.030%), and other impurity elements ≤0.50%.

[0010] The present invention also provides a method for preparing the 5.5Ni steel welding rod for LNG storage tanks, and the preparation method is carried out according to the following steps:

[0011] 1) preparing a welding core according to the proportion;

[0012] 2) The components of the coating are mixed evenly according to the proportion, wherein the quartz powder, rutile and zirconium oxide are first dried at 800-850°C;

[0013] 3) Add 16-28% of the weight of the binder to the coating, stir and mix evenly, and then use a hydraulic coating machine to evenly coat the coating on the welding core;

[0014] 4) The binder is a mixture of potassium silicate and sodium silicate and 2-5% lithium silicate water glass, with a modulus of 2.6-3.2 and a concentration of 36-43Be;

[0015] 5) It is made by high and low temperature baking, the low temperature baking temperature is 80-120℃×2h, and the high temperature baking temperature is 300-400℃×1h.

[0016] The present invention develops and smelts a low-C-low-impurity-Al and Ti pure nickel welding core, the coating is designed as a CaCO3-SrCO3-CaF2-BaF2 slag system, the alloy adopts a coating + welding core mixed transition mode, and manganese and silicon are combined with aluminum, magnesium, titanium and the like for deoxidation. The composition of the deposited metal is designed to be a NiMo type Hastelloy type. The welding rod for the 5.5% Ni steel LNG storage tank of the present invention has excellent all-position welding process performance and fire resistance; the high proportion of 0.5-0.7 coating weight coefficient makes the welding rod of the present invention have a higher deposition efficiency; the unique Hastelloy type composition design has a higher strength advantage than the conventional 9% Ni steel LNG storage tank matching ENiCrMo-6 and ENiCrFe-9 welding rods. While having comparable mechanical properties to the conventional 9% Ni steel matching ENiCrMo-6 welding rod, it can match the performance of the newly developed economical and economical 5.5% Ni steel for LNG storage tanks on the market.

[0017] The present invention adopts an extremely low C-low impurity-Al and Ti pure nickel welding core, and the coating is designed to be a CaCO3-SrCO3-CaF2-BaF2 slag system with a certain proportion of cryolite and acidic oxides (quartz powder, rutile, zirconium oxide, etc.). Firstly, it can effectively improve the welding characteristics of nickel-based welding rods that are prone to red tail, and significantly optimize the refractoriness of the welding rods; secondly, a certain proportion of cryolite and acidic oxides can effectively stabilize the arc, adjust the surface tension and fluidity of welding slag and molten iron, so that the welding rod of the present invention has excellent all-position weldability, and can allow the gas generated during the welding process to escape smoothly, avoiding the formation of welding pores.

[0018] The present invention designs a deoxidation system that combines electrolytic manganese with aluminum-magnesium alloy, pure titanium and rare earth ferrosilicon for joint deoxidation, which fully deoxidizes, removes hydrogen, purifies and removes impurities from the metallurgical point of view; and transitions alloy elements such as Mo, W, and Cu from the coating to the weld to achieve a perfect combination of high-purity welds and excellent weld metal properties, so that the O content of the weld is ≤300ppm, and the structure is uniform, and the porosity resistance and crack resistance are better.

[0019] The main functions of the electrode coating of the present invention are gasification, slag formation, improvement of all-position welding processability, deoxidation and alloy transition to the weld, etc. The following specifically analyzes the functions of the main components of the coating in the electrode of the present invention.

[0020] The main functions of carbonate in welding rods are slag formation and gasification. The alkaline oxides produced by decomposition can increase the basicity of slag, refine the molten droplets, remove S and P, improve the crack resistance of weld metal, and adjust the melting point, viscosity, surface and interfacial tension of slag. The use of multi-component mixed carbonates and different decomposition temperatures can enable the welding rod coating to maintain a good protective atmosphere throughout the welding process. The precise combination of minerals with different melting points can enable the welding rod coating to maintain good fire resistance. When the carbonate content is low, the gasification and slag-forming capabilities of the coating decrease, and the protective effect on the weld is reduced, making it difficult to ensure the quality of the weld; if the carbonate content is too high, the coating gasification is too large, the spatter increases, and the weld is rough. The carbonate content in the present invention is controlled at 21-36%.

[0021] The fluoride in the present invention is mainly CaF2, BaF2 and cryolite, which can adjust the melting point of the slag, and play a key role in adjusting the melting speed of the coating, maintaining the stiffness of the sleeve, reducing the porosity of the weld, and improving the weld formation. The difficulty in the design of nickel-based welding materials lies in the viscosity of the molten iron of nickel-based welding rods, the large surface tension of the liquid metal, the poor fluidity, and the difficulty of gas escaping from the weld. Fluoride, cryolite, etc. can significantly reduce the surface tension of the liquid metal, adjust the viscosity of the molten welding slag, improve the coverage of the welding slag, and make the weld beautiful and low in porosity. In addition, the K produced by the decomposition of cryolite + / Na + It can also significantly improve the arc stability of the welding rod, but cryolite contains Al. Excessive aluminum oxide and acidic oxides such as SiO2 and TiO2 can easily form hard and brittle spinel compounds and affect the slag removal performance. Therefore, the welding rod of the present invention strictly controls the ratio of cryolite and fluoride, and controls the total amount of fluoride to 16-22%.

[0022] TiO2, SiO2 and zirconium sand can adjust the melting point of the slag, balance the melting rate of the coating, adjust the shape of the molten pool and the surface tension, and improve slag removal.

[0023] The main functions of metal powders such as electrolytic manganese, rare earth ferrosilicon, pure titanium, magnesium aluminum alloy, molybdenum powder, tungsten powder, etc. are deoxidation and alloying, ensuring the alloy element composition in the weld, ensuring the weld strength and achieving the best toughness, porosity resistance and crack resistance matching through reasonable element design. The alloy system of the present invention ensures that the molten pool is fully deoxidized, dehydrogenated, purified, and impurities are removed from the molten pool metallurgy, and alloy elements are transitioned to the weld, ensuring that the O content of the weld is ≤300ppm, and excellent crack resistance and porosity resistance are obtained while achieving excellent weld metal properties.

[0024] The adhesive of the present invention adopts potassium sodium mixed water glass plus (2-5%) lithium silicate water glass with alginate. In addition to coating and bonding welding rods, water glass also has the functions of slag making and adjusting the slag state. While taking into account the manufacturability, coating performance and maintaining the coating strength, the K generated by ionization during arc welding + 、Na + , Li + Can effectively stabilize the arc.

[0025] Different from the conventional 9% Ni steel tank welding rods which generally adopt Ni-Cr-Mo alloy design, the welding rod of the present invention is designed as NiMo Hastelloy alloy. Develop a very low C, low impurity, Al / Ti pure nickel welding core; use CaCO3-SrCO3-CaF2-BaF2 slag system with a certain proportion of cryolite and acidic oxides (quartz powder, rutile, zirconium oxide, etc.); electrolytic manganese with aluminum-magnesium alloy, pure titanium and rare earth ferrosilicon combined deoxidation system, and transition manganese, Mo, W, Cu and other alloy elements from the coating to the weld.

[0026] The welding rod of the present invention has high strength and high toughness matching, excellent all-position weldability, high deposition rate, excellent porosity resistance and crack resistance through the precise design of the welding core and coating, composition and proportion. Compared with the traditional 9% Ni steel LNG storage tank ENiCrMo-6 and ENiCrFe-9 welding rods, they have higher strength advantages and can match the performance of the newly developed economical 5.5% Ni steel for LNG storage tanks.

[0027] The beneficial effects of the present invention are:

[0028] 1. Develop and smelt extremely low C-low impurity-containing Al and Ti pure nickel welding core. Accurate and strict control of alloy elements is the basic guarantee for the safety and reliability of joint quality.

[0029] 2. The alloy adopts a mixed transition mode of flux coating + welding core, which can flexibly design and adjust the welding material composition to better match the performance of the parent material; the welding rod has better fire resistance than pure welding core transition. The Hastelloy alloy composition design has higher strength advantages than the traditional 9% Ni steel LNG storage tank matching ENiCrMo-6 and ENiCrFe-9 welding rods, and can match the performance of the newly developed economical LNG storage tank 5.5% Ni steel.

[0030] 3. The CaCO3-SrCO3-CaF2-BaF2 slag system, with a certain proportion of cryolite and acidic oxides (quartz powder, rutile, zirconium oxide, etc.), can firstly effectively improve the welding characteristics of nickel-based welding rods that are prone to red tailing, and significantly optimize the refractoriness of the welding rods; secondly, a certain proportion of cryolite and acidic oxides can effectively stabilize the arc, adjust the surface tension and fluidity of welding slag and molten iron, so that the welding rod of the present invention has excellent all-position weldability, and can make the gas generated during the welding process escape smoothly, avoiding the formation of welding pores.

[0031] 4. The deoxidation system combines electrolytic manganese with aluminum-magnesium alloy, pure titanium and rare earth ferrosilicon to fully deoxidize, dehydrogenate, purify and remove impurities from the metallurgical point of view; the alloy elements such as Mo, W, Cu are transferred from the coating to the weld to achieve a perfect combination of high-purity welds and excellent weld metal properties. The O content of the weld is ≤300ppm, and the structure is uniform, and the porosity and crack resistance are better.

[0032] 5. The binder is potassium sodium mixed water glass plus (2-5%) lithium silicate water glass with alginate. In addition to coating and bonding welding rods, water glass also has the functions of dehydrogenation, slag formation, and adjustment of slag state. While taking into account the manufacturability, coating performance, and maintaining the strength of the coating, the K generated by ionization during arc welding + 、Na + , Li + It can also effectively stabilize the arc.

[0033] The economical and economical 5.5% Ni steel LNG storage tank supporting electric welding rod of the present invention has excellent all-position welding process performance and fire resistance, and high deposition efficiency; the unique Hastelloy alloy composition design has a higher strength advantage than the traditional 9% Ni steel LNG storage tank supporting ENiCrMo-6 and ENiCrFe-9 welding rods. The mechanical properties of the deposited metal are excellent and stable, with a tensile strength of ≥720MPa, excellent low-temperature impact toughness, an average impact energy of ≥90J at -196℃, and no pores in high-definition radiographic TOFD films, which can meet the welding needs of economical and economical 5.5% Ni steel LNG storage tanks and is expected to greatly reduce the construction cost of large LNG storage tanks.

[0034] The present invention is designed based on the consideration of all-position weldability, mechanical properties, anti-porosity and deposition efficiency, and is a nickel-molybdenum alloy electrode with a pure nickel core and a coating mixed transition. The present invention is applied to the welding of economical 5.5% Ni steel LNG storage tanks, which can match the performance of the parent material, support and promote the application of nickel-saving steel, has strong practical significance and long-term social value, and is expected to produce huge social and economic benefits. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these embodiments.

[0036] The present invention is composed of a welding core and a coating, wherein the coating is coated on the outside of the welding core, and the coating accounts for 0.5 to 0.7 of the total weight coefficient of the welding rod. A low-C, low-impurity, Al- and Ti-containing pure nickel welding core is developed and smelted, and the welding core component requirements (weight percentage %) are shown in Table 1.

[0037] Table 1: Solder core component requirements (wt%)

[0038]

[0039] The actual core compositions of Examples 1 to 5 are shown in Table 2.

[0040] Table 2: Composition of solder cores of Examples 1 to 5 (weight percentage %)

[0041]

[0042] The coating of the present invention is designed as a CaCO3-SrCO3-CaF2-BaF2 slag system, with a certain proportion of cryolite and acidic oxides (quartz powder, rutile, zirconium oxide, etc.), and a deoxidation system of electrolytic manganese combined with aluminum-magnesium alloy, pure titanium and rare earth ferrosilicon. The core wire diameter is 2.6mm and 3.2mm.

[0043] The coating components of Examples 1-5 are shown in Table 3.

[0044] Table 3: Examples of coating components (weight percentage)

[0045]

[0046]

[0047] The test results of the chemical composition of the deposited metal corresponding to each implementation case are shown in Table 4.

[0048] Table 4: Chemical composition of deposited metal in various implementation cases (wt%)

[0049]

[0050] The test results of mechanical properties and porosity resistance of the weld metal corresponding to each embodiment are shown in Table 5.

[0051] Table 5: Performance of each embodiment

[0052]

[0053] As can be seen from Table 5, the deposited metal of the welding rod of the present invention has excellent mechanical properties, tensile strength ≥ 720 MPa, excellent low-temperature impact toughness, and an average impact energy of ≥ 90 J at -196°C. The weld metal has excellent crack resistance and good porosity resistance, and there is no porosity in the high-definition radiographic TOFD film.

[0054] It can be seen that the economical 5.5% Ni steel LNG storage tank supporting welding rod of the present invention has excellent all-position welding process performance and fire resistance, and high deposition efficiency; the unique Hastelloy alloy composition design has higher strength advantages than the traditional 9% Ni steel LNG storage tank supporting ENiCrMo-6 and ENiCrFe-9 welding rods. The weld has high purity, excellent porosity resistance and crack resistance, and the mechanical properties of the deposited metal are excellent and stable. Its tensile strength is ≥720MPa, and its low-temperature impact toughness is excellent. The average impact energy at -196℃ is ≥90J. There is no porosity in the high-definition radiographic TOFD film. It can meet the welding needs of economical 5.5% Ni steel LNG storage tanks and is expected to greatly reduce the construction cost of large LNG storage tanks.

[0055] The present invention is applied to the welding of economical 5.5% Ni steel LNG storage tanks, can match the performance of the base material, has strong practical significance and long-term social value, and is expected to produce huge social and economic benefits.

[0056] The above-described embodiments are only preferred implementations of the present invention. It should be pointed out that a person skilled in the art may make several modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements all belong to the protection scope of the present invention.

Claims

1. A 5.5Ni steel welding rod for LNG storage tanks, comprising a welding core and a coating, wherein the coating is coated on the outside of the welding core, and the coating accounts for 0.5 to 0.7 of the total weight coefficient of the welding rod, characterized in that: Based on the total weight of the welding core, the chemical composition and weight percentage of the welding core are as follows: C < 0.01%, Mn < 0.10%, Si < 0.10%, P ≤ 0.005%, S ≤ 0.003%, P + S ≤ 0.006%; Ni ≥ 99.0%, Al: 0.020-0.060, Ti: 0.030-0.100%, O < 100ppm; Based on the total weight of the drug coating, the components of the drug coating are as follows: calcium carbonate: 16-24%; strontium carbonate: 5-12%; barium fluoride: 2-5%; Calcium fluoride: 10-13%, cryolite: 2-4%; Sodium carbonate: 0.5-1.0%; Electrolytic manganese: 0.8-1.8%; rare earth ferrosilicon: 2-5%, molybdenum powder 24-28%, pure titanium: 4-6%; copper powder: 1.5-3.2%, aluminum-magnesium alloy: 1.6-2.8%; tungsten powder: 2.5-4.0%; quartz powder: 3-6%; Rutile: 3-5%; Zirconia 2-4%, Alginate: 0.8%-2.5%.

2. The 5.5Ni steel welding rod for LNG storage tank according to claim 1, characterized in that: In terms of weight percentage, the components of the deposited metal of the welding rod are: C: 0.026-0.048%, Mn: 0.3-0.6%, Si: 0.2-0.6%, P≤0.008%, S≤0.005%, P+S≤0.012%, Ni: 68.0-78.0%, Mo: 16.0-20.0%, Fe≤4.0%, Cu: 0.6-1.2%, W: 2.0-3.5%, Al: 0.018-0.042%, Ti: 0.10-0.24%, O≤300ppm, and other impurity elements ≤0.50%.

3. The 5.5Ni steel welding rod for LNG storage tank according to claim 1, characterized in that: The coating is evenly coated on the welding core with a binder whose weight is 16-28% of the coating weight; the binder is a mixture of potassium silicate and sodium silicate and water glass with 2-5% lithium silicate water glass, with a modulus of 2.6-3.2 and a concentration of 36-43Be.

4. The 5.5Ni steel welding rod for LNG storage tank according to claim 1, characterized in that: The 5.5Ni steel LNG storage tank welding rod is composed of a welding core and a coating wrapped on the surface of the welding core, and is prepared according to the following steps: 1) preparing a welding core according to the proportion; 2) Mix the various components of the coating evenly according to the proportion, wherein the quartz powder, rutile and zirconium oxide are first dried at 800-850°C; 3) Add 16-28% of the weight of the binder to the coating, stir and mix evenly, and then use a hydraulic coating machine to evenly coat the coating on the welding core; The binder is a mixture of potassium silicate and sodium silicate and 2-5% lithium silicate water glass, with a modulus of 2.6-3.2 and a concentration of 36-43Be; 4) It is made by high and low temperature baking, the low temperature baking temperature is 80-120°C×2h, and the high temperature baking temperature is 300-400°C×1h.

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