JP2020189302A - Arc welding rod coated with low hydrogen-based coating agent for crude oil tank steel - Google Patents

Abstract

To provide an arc welding rod coated with a low hydrogen-based coating agent for a crude oil tank steel which enables a weld metal having excellent corrosion resistance and mechanical performance to be obtained, and is good in welding work efficiency, and causes no weld flaw.SOLUTION: The arc welding rod coated with a low hydrogen-based coating agent for a crude oil tank steel is provided in which the coating agent contains by mass% based on total mass of the coating agent: Si of 3.5 to 8.0%, Mn of 0.5 to 2.0% and Ti of 0.3 to 1.5%, Cu of 0.2 to 1.0%, one or two kinds of Mo of 0.05 to 0.50% and W of 0.05 to 0.50%; total of one or two or more kinds of metal carbonates of 45 to 55%; total of titanium oxide of 2 to 8% in terms of TiO2; total of silicon oxide of 3 to 10% in terms of SiO2; total of aluminum oxide of 0.5 to 5.0% in terms of Al2O3; total of one or two or more kinds of metal fluorides of 10 to 20%; total of one or more kinds of organic substances of 0.3 to 1.5%; iron sulfide of 0.05 to 0.09%; and total of sodium oxide in terms of Na2O and kalium oxide in terms of K2O of 1 to 5%.SELECTED DRAWING: None

Description

The present invention relates to a low hydrogen-based shielded metal arc welding rod of crude oil tank steel suitable for welding steel plates constituting a crude oil tank for transporting or storing crude oil, such as an oil tank of a crude oil tanker or an above-ground or underground crude oil tank.

Generally, welded structural steel with excellent strength and weldability is used for steel oil tanks that transport or store crude oil, such as oil tanks for crude oil tankers that transport crude oil and above-ground or underground crude oil tanks that store crude oil. ..

In the steel oil tank as described above, the steel plate constituting the oil tank is exposed to a corrosive environment due to the water content in the crude oil, as well as salt and corrosive gas components. In particular, on the inner surface of the oil tank of a crude oil tanker, due to volatile components in crude oil, mixed seawater, salt in oil field salt water, inert gas (exhaust gas from the engine of a ship) sent into the oil tank for explosion prevention, and temperature fluctuations during the day and night. Since a unique corrosive environment is created due to dew condensation and the like, the steel plate is corroded and thinned. When it becomes difficult to maintain the required hull strength due to such corrosion thinning of the steel plate, it is necessary to cut off the corroded member and weld-join a new member to reinforce it. , It costs a lot of money.

Further, in addition to the above-mentioned corrosion thinning, a large amount of solid sulfur content (hereinafter referred to as solid S) is generated and precipitated on the steel surface on the inner surface of the steel oil tank. It is believed that such solid S is produced by the reaction of SO ₂ and H ₂ S in the gas phase with the iron rust on the surface of the back of the corroded deck as a catalyst. At this time, the formation of new iron rust due to the corrosion of the steel sheet and the precipitation of the solid S occur alternately, so that the layered corrosion product of the iron rust and the solid S is deposited. Since the layer composed of solid S is brittle in the layered corrosion product, the product composed of solid S and iron rust easily peels off and falls off from the surface of the steel plate of the crude oil tank, and is deposited as sludge (corrosion product) on the bottom of the crude oil tank. To do.

Against this background, a corrosion-resistant steel sheet having excellent corrosion resistance as a steel sheet for a crude oil tank and producing less sludge containing solid S is required. For example, Patent Documents 1 to 3 describe crude oil tanks. And welded joints of steel for crude oil tanks are disclosed. On the other hand, since the crude oil tank generally has a welded structure, the welded portion is inevitably exposed to the crude oil tank environment unless the entire surface is painted or lined. In arc welding, which is usually performed, the welding material is melted to form the welding metal, so that the composition and structure of the welding metal are generally different from those of the steel material. In a corroded environment, when metals having significantly different chemical compositions and structures are adjacent to each other, one of the relatively electrochemically base metals is selectively corroded, and dissimilar metal corrosion is likely to occur. When such selective corrosion occurs, large local corrosion will occur.

When making a welded structure exposed to a crude oil environment using ordinary steel whose corrosion resistance has not been particularly improved, a steel material having an overwhelmingly large surface surface is electrochemically used regardless of the welding method or welding material. The problem of selective corrosion of welded joints is not so great because it is base. However, when an attempt is made to form a welded structure using a steel material having excellent corrosion resistance, the weld metal becomes more base depending on the welding method and the welding material, the weld metal is selectively corroded, and the corrosion resistance of the entire welded joint is impaired. There was a problem that there was a possibility of welding. Therefore, in order to improve the corrosion resistance of the welded structure exposed to the crude oil environment, it is necessary to consider not only the steel material but also the characteristics of the welded portion.

In response to the above problem, for example, Patent Document 4 discloses a flux-cored wire for gas shielded arc welding for welding a steel material for a crude oil tank. In particular, it is often used in full-position welding to crude oil tankers and the like, but it is difficult to move and install the welding equipment for repair welding and welding to narrow places, and it is difficult to make small turns during welding work. In addition, since it is necessary to take windproof measures at the time of welding, there is a problem that preparation for welding to a small repaired part becomes large. For this reason, there is a strong demand for a low hydrogen-based shielded metal arc welding rod that is easy to prepare for welding equipment, has a good turning radius during welding, and is more wind resistant than gas shielded metal arc welding.

On the other hand, for example, Patent Document 5 discloses a shielded metal arc welding rod having excellent corrosion resistance. However, due to its excellent sulfuric acid resistance and hydrochloric acid resistance, when it is used for crude oil tank steel, there is a difference in corrosion resistance between the welded part and the base metal, and the one with inferior corrosion resistance is selectively corroded. was there.

JP-A-2010-43342 Japanese Unexamined Patent Publication No. 2005-23421 Japanese Unexamined Patent Publication No. 2005-21981 Japanese Unexamined Patent Publication No. 2013-226757 Japanese Unexamined Patent Publication No. 2004-90044

The present invention has been devised in view of the above-mentioned problems, and is a crude oil corrosive environment of a crude oil tank for transporting or storing crude oil, such as an oil tank of a crude oil tanker formed by a welded structure or an above-ground or underground crude oil tank. Below, the welded part shows excellent corrosion resistance almost equal to that of the crude oil tank, and the weld metal with good welding workability, no welding defects, and excellent mechanical performance can be obtained. Low hydrogen coating of crude oil tank steel. It is an object of the present invention to provide an arc welding rod.

The gist of the present invention is that in a low hydrogen-based coated arc welding rod of crude oil tank steel in which a steel core wire is coated with a coating agent, the coating agent is a mass% based on the total mass of the coating agent, and Si: 3.5 to 8.0%, Mn: 0.5 to 2.0%, Ti: 0.3 to 1.5%, Cu: 0.2 to 1.0%, Mo: 0.05 to 0.50% and W : 0.05 to 0.50% of 1 or 2 types, total of 1 or 2 or more types of metal carbonates: 45 to 55%, total of TiO ₂ conversion values of Ti oxides: 2 to 8%, Total SiO ₂ conversion value of Si oxide: 3 to 10%, total Al ₂ O ₃ conversion value of Al oxide: 0.5 to 5.0%, total of one or more types of metal fluoride : 10 to 20%, total of one or more organic substances: 0.3 to 1.5%, iron sulfide: 0.05 to 0.09%, Na ₂ O conversion value of Na compound and K compound and total K ₂ O converted value: contains 1-5%, the remainder being painted agents, Fe content in the iron powder, characterized by comprising the Fe content and unavoidable impurities iron alloy.

It is also characterized by further containing Ni: 0.05 to 1.0% in mass% with respect to the total mass of the coating agent.

Further, a crude oil tank steel characterized by further containing one or two types of Sn: 0.01 to 0.30% and Sb: 0.01 to 0.30% in mass% with respect to the total mass of the coating agent. It is located in the low hydrogen shielded metal arc welding rod.

According to the low hydrogen-based shielded metal arc welding rod of the crude oil tank steel of the present invention, the crude oil corrosion environment of the steel oil tank for transporting or storing crude oil such as the oil tank of the crude oil tanker formed by the welded structure and the above-ground or underground crude oil tank. Welded metals with excellent corrosion resistance and mechanical performance are obtained, even when used under and in similar environments to the environment, with no welding defects, arc spraying, arc concentration and arc. Good stability, a small amount of spatter, no stick burning, and good welding workability such as bead shape and slag peelability can be obtained. Therefore, it can greatly contribute to the improvement of welding work efficiency and the quality of the welded portion.

In order to solve the above problems, the present inventors have prepared various low hydrogen-based shielded metal arc welding rods and examined the details.

Welded metal with excellent mechanical performance and corrosion resistance can be obtained, excellent arc stability, good arc concentration, good arc spraying, low spatter generation, no stick burning, good bead shape, slag peeling property, etc. Having welding workability is an essential condition.

First, the influence of the chemical composition of the low hydrogen-based shielded metal arc welding rod was investigated on the corrosion resistance of the weld metal in a crude oil corrosive environment. As a result, it was found that the corrosion resistance in the environment is improved by adding an appropriate amount of Mo, W, Cu, and iron sulfide as a coating agent component of the low hydrogen-based coated arc welding rod. Furthermore, it was found that the corrosion resistance can be further improved by adding appropriate amounts of Ni, Sn, and Sb.

Regarding welding workability, arc concentration, arc spraying, arc stability and reduction of spatter generation amount can be achieved by adding appropriate amounts of Si, Ti, Ti oxides, Si oxides, organic substances, Na compounds and K compounds. The stick burning resistance is good by adding an appropriate amount of metal carbonate, the slag peeling property is good by adding an appropriate amount of Si oxide, and the bead shape is good by adding an appropriate amount of Ti oxide, Al oxide, and metal fluoride. It was also found that welding defects can be prevented by adjusting the content of metal carbonate.

It was also found that the mechanical performance of the weld metal can be improved by adding appropriate amounts of Mn and Ti.

Hereinafter, the component composition in the coating agent of the low hydrogen-based shielded metal arc welding rod of the crude oil tank steel to which the present invention is applied and the reason for limiting the component composition will be described in detail. The content of each component composition shall be expressed in mass%, and when the mass% is expressed, it shall be simply described as%.

[Si: 3.5-8.0%]
Si is added from metals Si, Fe-Si, Fe-Si-Mn and the like, and is used for the purpose of deoxidizing the weld metal, but it is also necessary from the viewpoint of ensuring welding workability. If Si is less than 3.5%, blow holes are likely to occur in the weld metal due to insufficient deoxidation, and the arc becomes unstable. On the other hand, when Si exceeds 8.0%, a low melting point oxide is precipitated at the grain boundaries of the weld metal structure, so that the toughness of the weld metal is lowered. Therefore, Si is set to 3.5 to 8.0%.

[Mn: 0.5 to 2.0%]
Mn is added from metals Mn, Fe-Mn, Fe-Si-Mn, etc., and is added as a deoxidizer in the same manner as Si, and is effective in improving the strength of weld metals. If Mn is less than 0.5%, the effect cannot be sufficiently obtained and the strength of the weld metal is lowered. On the other hand, when Mn exceeds 2.0%, the strength of the weld metal becomes excessively high and the toughness becomes low. Therefore, Mn is set to 0.5 to 2.0%.

[Ti: 0.3-1.5%]
Ti is added from metals Ti, Fe-Ti, etc., is effective as an antacid, and has the effect of lowering the potential gradient of the arc and stabilizing the arc. It also has the effect of refining the microstructure of the weld metal to improve toughness. If Ti is less than 0.3%, the arc becomes unstable and the amount of spatter generated increases. Further, since the arc length is extended and oxygen in the atmosphere is easily taken in, the amount of oxygen in the weld metal is increased, the microstructure of the weld metal is not refined, and the toughness of the weld metal is lowered. On the other hand, when Ti exceeds 1.5%, the Ti oxide in the weld metal increases and the toughness of the weld metal decreases. Therefore, Ti is set to 0.3 to 1.5%.

[Cu: 0.2 to 1.0%]
Cu is added from metals such as Cu and Cu—Al, and has the effect of improving the corrosion resistance of the weld metal and suppressing the precipitation of solid S, together with 0.05% or more of Mo and 0.05% or more of iron sulfide. Incorporate. If Cu is less than 0.2%, the effect of improving the corrosion resistance of the weld metal and suppressing the precipitation of solid S cannot be sufficiently obtained. On the other hand, when Cu exceeds 1.0%, the effect of improving the corrosion resistance of the weld metal and suppressing the precipitation of solid S is saturated, and the toughness of the weld metal is lowered. Therefore, Cu is 0.2 to 1.0%.

[Mo: 0.05 to 0.50% and W: 0.05 to 0.50%, one or two types]
Mo is added from metals Mo, Fe-Mo, etc., and W is added from metals W, WC, etc., and has the effect of improving the corrosion resistance of the weld metal and suppressing the precipitation of solid S, and 0.2% or more of Cu and 0. It is contained together with 05% or more of iron sulfide. With one or two types having Mo of less than 0.05% and W of less than 0.05%, the effects of improving the corrosion resistance of the weld metal and suppressing the precipitation of solid S cannot be sufficiently obtained. On the other hand, when Mo is more than 0.50% and W is more than 0.50%, the effect of improving the corrosion resistance of the weld metal and suppressing the precipitation of solid S is saturated, and the toughness of the weld metal is lowered. Therefore, Mo is 0.05 to 0.50% and W is 0.05 to 0.50%, which is one or two kinds.

[Total of one or more metal carbonates: 45-55%]
Metallic carbonate is added from calcium carbonate, magnesium carbonate, barium carbonate, manganese carbonate, lithium carbonate, etc., and prevents stick burning due to the heat absorption effect when it decomposes in an arc to generate CO ₂ gas, and is a welded metal. Has the effect of shielding and protecting from the atmosphere. If the total of one or more of the metal carbonates is less than 45%, the shielding effect is insufficient and blow holes are likely to occur in the weld metal, and rod burning is likely to occur. On the other hand, if the total of one or more of the metal carbonates exceeds 55%, the arc becomes unstable and becomes a convex bead, and the slag peelability becomes poor. Therefore, the total of one or more metal carbonates is 45-55%.

[Total TiO ₂ conversion value of Ti oxide: 2-8%]
Ti oxide is added from rutile, titanium oxide, sodium titanate, titanium slag, etc., acts as a slag generator and an arc stabilizer, and has an effect of improving arc stability and bead shape. If the total of the TiO ₂ conversion values of the Ti oxide is less than 2%, the arc becomes unstable and the amount of spatter generated increases. In addition, the slag fluidity becomes poor and the bead shape becomes poor. On the other hand, when the total of the TiO ₂ conversion values of the Ti oxide exceeds 8%, the viscosity of the molten slag becomes high during welding, the slag fluidity deteriorates, and the bead shape becomes convex. In addition, the penetration becomes shallow and fusion defects are likely to occur in the welded portion. Therefore, the total TiO ₂ conversion value of Ti oxide is 2 to 8%.

[Total SiO ₂ conversion value of Si oxide: 3 to 10%]
The Si oxide is added from silica sand, feldspar, water glass and the like, acts as a slag generator and an arc stabilizer, and has an effect of improving arc stability and slag exfoliation property. If the total value of the Si oxides converted to SiO ₂ is less than 3%, the arc becomes weak and unstable, and the vitreous quality of the generated slag is reduced, resulting in poor slag peelability. On the other hand, when the total SiO ₂ conversion value of the Si oxide exceeds 10%, the viscosity of the slag becomes high and the bead shape becomes poor. Therefore, the total value of Si oxide in terms of SiO ₂ is set to 3 to 10%.

[Total Al ₂ O ₃ conversion value of Al oxide: 0.5 to 5.0%]
Al oxide is added from alumina or the like, acts as a slag generating agent, and has an effect of increasing the viscosity of molten slag. If the total Al ₂ O ₃ conversion value of the Al oxide is less than 0.5%, the viscosity of the slag becomes insufficient and the bead shape becomes poor. On the other hand, if the total Al ₂ O ₃ conversion value of Al oxide exceeds 5.0%, the viscosity of the molten slag becomes high during welding and the slag fluidity deteriorates, so that the shape of the bead becomes convex. , The penetration becomes shallow and fusion failure is likely to occur in the welded part. Therefore, the total Al ₂ O ₃ conversion value of Al oxide is 0.5 to 5.0%.

[Total of one or more metal fluorides: 10-20%]
The metal fluoride is added from fluorite, barium fluoride, magnesium fluoride, aluminum fluoride and the like, and has the effect of lowering the viscosity of the molten slag, improving the slag fluidity and improving the bead shape. If the total of one or more of the metal fluorides is less than 10%, the proper viscosity of the molten slag cannot be obtained and the bead shape becomes poor. On the other hand, if the total of one or more of the metal fluorides exceeds 20%, the slag peelability becomes poor. Therefore, the total of one or more types of metal fluoride is 10 to 20%.

[Total of one or more organic substances: 0.3-1.5%]
Organic substances are added from sodium alginate, wheat flour, etc. to improve the adhesion of the coating agent during welding rod manufacturing, and the surface of the coating agent can be finished uniformly and smoothly, so that the effect of increasing the concentration of arcs during welding is enhanced. Has. If the total of one or more organic substances is less than 0.3%, the surface of the coating material is likely to be cracked or the coating material is easily removed during the production of the welding rod, so that the arc concentration is deteriorated. On the other hand, if the total of one or more organic substances exceeds 1.5%, stick burning is likely to occur. Therefore, the total of one or more organic substances in the coating is 0.3 to 1.5%.

[Iron sulfide: 0.05 to 0.09%]
Iron sulfide has an effect of improving the corrosion resistance of the weld metal by retaining the contained S in the weld metal, and is contained together with 0.2% or more of Cu and 0.05% or more of Mo. If the iron sulfide content is less than 0.05%, the effect of improving the corrosion resistance of the weld metal cannot be sufficiently obtained. On the other hand, when iron sulfide exceeds 0.09%, the effect of improving the corrosion resistance of the weld metal is saturated, the fluidity of the slag is deteriorated, and the bead shape becomes poor. Therefore, iron sulfide is set to 0.05 to 0.09%.

[Total of Na ₂ O conversion value and K ₂ O conversion value of Na compound and K compound: 1 to 5%]
The Na compound and the K compound are added from sodium silicate, potassium silicate, feldspar and the like in water glass, and have an effect of stabilizing an arc by acting as an arc stabilizer. If the total of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound is less than 1%, the arc becomes unstable and the amount of spatter generated increases. Further, when the welding rod is manufactured, the surface of the coating material is liable to crack or the coating material is easily dropped off, so that the concentration of the arc is lowered. On the other hand, when the total of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound exceeds 5%, the arc spraying becomes excessively strong and the bead shape becomes poor. Therefore, the total of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound in the coating agent is 1 to 5%.

[Ni: 0.05 to 1.0%]
Ni is added from the metals Ni and Fe-Ni, and has the effect of improving the corrosion resistance of the weld metal and suppressing the precipitation of the solid S in the coexistence with the Mo, W, Cu and iron sulfide. If Ni is less than 0.05%, the effect of improving the corrosion resistance of the weld metal cannot be sufficiently obtained. On the other hand, if Ni exceeds 1.0%, high-temperature cracks are likely to occur in the weld metal. Therefore, Ni is set to 0.05 to 1.0%.

[Sn: 0.01 to 0.30% and Sb: 0.01 to 0.30%, 1 or 2]
Sn is added from the metal Sn, and Sb is added from the metals Sb, Fe-Sb, antimonyated manganese and Fe-Si-Sb. In the coexistence with the Mo, Cu and iron sulfide, the corrosion resistance of the weld metal is improved and the solid S is precipitated. Has the effect of suppressing. With one or two types having Sn of less than 0.01% and Sb of less than 0.01%, the effect of improving the corrosion resistance of the weld metal cannot be sufficiently obtained. On the other hand, when Sn is more than 0.30 or Sb is more than 0.30% of one or two, high temperature cracking is likely to occur in the weld metal. Therefore, Sn is 0.01 to 0.30% and Sb is 0.01 to 0.30%, which is one or two types. It is preferable that the upper limit of Sn is 0.10% and the upper limit of Sb is 0.10%.

The rest of the low hydrogen-based shielded metal arc welding rod of crude oil tank steel to which the present invention is applied is unavoidable as a coating agent of one or more of hectolite, mica, etc., Fe content in iron powder, Fe content of iron alloy, and so on. It is an impurity.

Further, it is preferable to use JIS G3523 SWY11 as the steel core wire to be used. Further, the coverage of the coating material on the steel core wire is preferably 25 to 40% in mass% of the coating agent with respect to the total mass of the welding rod.

The effects of the present invention will be specifically described with reference to Examples.

Various low-hydrogen-based coated arc welding rods, which were dried after coating the coating agent shown in Table 2 with a coating ratio of 25 to 35% on a steel core wire having a diameter of 4.0 mm and a length of 400 mm shown in Table 1, were prototyped.

Using these prototype welding rods, welding workability, welding defects, mechanical performance and corrosion resistance of weld metal were investigated.

Welding workability was evaluated by using a test piece made of mild steel plates with a thickness of 12 mm, width of 100 mm, and length of 450 mm assembled in a T shape, using an AC welder, and welding current of 160 to 180 A for horizontal fillets, vertical. Welding was performed using 120 to 140 A in the posture, and the presence or absence of arc spraying, arc concentration, arc stability, slag peelability, bead shape, spatter generation amount, stick burning, and high temperature cracking were visually inspected. As for the presence or absence of bar burning, it is preferable that the steel core wire generates heat when horizontal fillet welding is performed at 200A and the bar does not burn, and for high temperature cracks, the presence or absence of crater cracks in the weld bead after welding is investigated. did.

To evaluate the mechanical performance of the weld metal, a weld metal test was conducted according to JIS Z3111, the presence or absence of welding defects was investigated by an X-ray transmission test, and then a corrosion test, a tensile test, and an impact test were performed.

In the evaluation of the tensile test, the tensile strength was good at 490 to 590 MPa. The toughness was evaluated by repeating the Charpy impact test three times at a test temperature of −30 ° C., and the average value of absorbed energy was 55 J or more.

To evaluate the corrosion resistance of the weld metal, a corrosion test was conducted in an environment simulating the crude oil tank environment. A test piece having a length of 80 mm, a width of 30 mm, and a thickness of 4 mm was collected from a position of 1 mm on the surface of the steel material in the weld metal test in the direction of the weld line so that the entire surface was a welded portion. Next, the entire surface of the test piece was mechanically ground, and after a wet polishing treatment of No. 600, the end face and the back surface were covered with paint, leaving only one surface of 80 mm × 30 mm. Then, this test piece was immersed in a corrosive solution consisting of a 1% by volume HCl aqueous solution in which 20 mass% NaCl was dissolved at a pH of 0.2. As the immersion conditions at this time, the process was carried out at a liquid temperature of 30 ° C. and an immersion time of 720 hours, the maximum corrosion depth was measured, converted into a corrosion rate (mm / year), and evaluated, and the maximum corrosion rate of the test piece was determined. Those having a thickness of 0.25 mm / year or less were considered good. The composition of the above-mentioned corrosive liquid simulates the environmental conditions when local corrosion occurs in an actual steel structure, and according to the reduction in the corrosion rate in this corrosion test, the local corrosion occurs locally in the actual environment. The rate of corrosion development is reduced.

In Tables 2 and 3, the welding rod No. 1-No. 15 is an example of the present invention, welding rod No. 16-No. 32 is a comparative example.

Welding rod No. which is an example of the present invention. 1-No. 15 is the total of 1 or 2 of Si, Mn, Ti, Cu, Mo and W in the coating agent, 1 or 2 or more of metal carbonates, the total of TiO ₂ conversion values of Ti oxides, and Si. Total SiO ₂ conversion values of oxides, total Al ₂ O ₃ conversion values of Al oxides, total of one or more types of metal fluorides, total of one or more types of organic substances, iron sulfide, Since the sum of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound is appropriate, the arc spraying is appropriate, the arc concentration and arc stability are good, the amount of spatter generated is small, and the slag is peeled off. Excellent properties, good bead shape, no stick burning, and good welding workability was obtained. In addition, there were no welding defects, and the tensile strength and absorbed energy of the weld metal were also good results. Furthermore, the maximum corrosion rate was low and the results were extremely satisfactory. In addition, the welding rod No. For 3, 6, 8, 11 and 15, one or two types of Sn and Sb were added in appropriate amounts, and the welding rod No. Since an appropriate amount of Ni was added to 2, 8, 13 and 15, the maximum corrosion rate of the weld metal was very low, less than 0.20 mm / year.

Welding rod No. in the comparative example. Since 16 had a large amount of Si, the absorbed energy of the weld metal was low. Moreover, since the total of Al ₂ O ₃ conversion values of Al oxide was large, the bead shape was convex. In addition, poor fusion occurred.

Welding rod No. In No. 17, the arc was unstable because the amount of Si was small. In addition, blow holes were generated in the weld metal. Further, since the total of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound was large, the arc spraying was excessively strong and the bead shape was poor.

Welding rod No. In No. 18, since Mn was large, the tensile strength of the weld metal was high and the absorbed energy was low. Further, since the total amount of one type or two or more types of metal fluoride was large, the slag peelability was poor.

Welding rod No. In No. 19, since Mn was small, the tensile strength of the weld metal was low. Moreover, since the total amount of one or more types of metal fluoride is small, the bead shape is poor.

Welding rod No. No. 20 had a large amount of Ti, so that the absorbed energy of the weld metal was low. In addition, since the total of Al ₂ O ₃ conversion values of Al oxide was small, the bead shape was poor.

Welding rod No. In No. 21, since Ti was small, the arc was unstable and the amount of spatter generated was large. In addition, the absorbed energy of the weld metal was low.

Welding rod No. No. 22 had a large amount of Cu, so that the absorbed energy of the weld metal was low. In addition, since the total amount of one or more metal carbonates is large, the arc is unstable, the bead shape is convex, and the slag peelability is also poor.

Welding rod No. In No. 23, since the amount of Cu was small, the maximum corrosion rate of the weld metal was high. Further, since the total of one or two types of Sn and Sb was small, the effect of improving the corrosion resistance could not be obtained. Further, since the total amount of one or more organic substances is small, the arc concentration is poor.

Welding rod No. In No. 24, since there were many types 1 or 2 of Mo and W, the absorbed energy of the weld metal was low. In addition, the bead shape was poor because the total value of Si oxide converted to SiO ₂ was large.

Welding rod No. In No. 25, since one or two types of Mo and W were small, the maximum corrosion rate of the weld metal was high. Further, since the total amount of one type or two or more types of metal carbonate is small, blow holes are generated in the weld metal, and rod burning occurs.

Welding rod No. No. 26 had a poor bead shape because it contained a large amount of iron sulfide.

Welding rod No. In No. 27, since the total value of Si oxides converted to SiO ₂ was small, the arc was unstable and the slag peeling property was poor. Moreover, since the amount of iron sulfide was small, the maximum corrosion rate of the weld metal was high.

Welding rod No. No. 28 had a convex bead shape because the Ti oxide had a large TiO ₂ conversion value. In addition, poor fusion occurred.

Welding rod No. In No. 29, since the value of Ti oxide converted to TIO ₂ was small, the arc was unstable and the amount of spatter generated was large. In addition, the bead shape was poor. Furthermore, since the total amount of one or more organic substances is large, stick burning occurred.

Welding rod No. In No. 30, since the sum of the Na ₂ O conversion value and the K ₂ O conversion value of the Na compound and the K compound was small, the arc concentration was poor, the arc was unstable, and the amount of sputtering generated was large. In addition, since there are many types 1 or 2 of Sn and Sb, crater cracking occurred.

Welding rod No. In No. 31, the maximum corrosion rate of the weld metal was high because one or two types of Mo and W were small. Further, since the amount of Ni is small, the effect of improving the corrosion resistance could not be obtained.

Welding rod No. In No. 32, the total of Al ₂ O ₃ conversion values of Al oxide was small, so that the bead shape was poor. Moreover, since there is a large amount of Ni, crater cracking occurred.

Claims (3)

In a low hydrogen-based shielded metal arc welding rod of crude oil tank steel in which a coating agent is coated on the steel core wire,
The coating agent is a mass% based on the total mass of the coating agent.
Si: 3.5-8.0%,
Mn: 0.5-2.0%,
Ti: 0.3-1.5%,
Cu: 0.2-1.0%,
One or two types of Mo: 0.05 to 0.50% and W: 0.05 to 0.50%,
Total of one or more metal carbonates: 45-55%,
Total TiO ₂ conversion value of Ti oxide: 2-8%,
Total SiO ₂ conversion value of Si oxide: 3-10%,
Total Al ₂ O ₃ conversion value of Al oxide: 0.5-5.0%,
Total of one or more metal fluorides: 10-20%,
Total of one or more organic substances: 0.3-1.5%,
Iron sulfide: 0.05-0.09%,
Total of Na ₂ O conversion value and K ₂ O conversion value of Na compound and K compound: 1 to 5% is contained.
The balance is a low hydrogen-based shielded metal arc welding rod of crude oil tank steel, which is composed of a coating agent, Fe content in iron powder, Fe content of iron alloy, and unavoidable impurities. The low hydrogen-based coated arc welding rod for crude oil tank steel according to claim 1, further containing Ni: 0.05 to 1.0% in mass% with respect to the total mass of the coating agent. Claim 1 or 2 further contains one or two kinds of Sn: 0.01 to 0.30% and Sb: 0.01 to 0.30% in mass% with respect to the total mass of the coating agent. Low hydrogen-based shielded metal arc welding rod for crude oil tank steel described in.