WO2011145741A1 - 耐食性に優れる溶接継手および原油タンク - Google Patents
耐食性に優れる溶接継手および原油タンク Download PDFInfo
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- WO2011145741A1 WO2011145741A1 PCT/JP2011/061700 JP2011061700W WO2011145741A1 WO 2011145741 A1 WO2011145741 A1 WO 2011145741A1 JP 2011061700 W JP2011061700 W JP 2011061700W WO 2011145741 A1 WO2011145741 A1 WO 2011145741A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/24—Selection of soldering or welding materials proper
- B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
- B23K35/3053—Fe as the principal constituent
- B23K35/3073—Fe as the principal constituent with Mn as next major constituent
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/24—Selection of soldering or welding materials proper
- B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
- B23K35/3053—Fe as the principal constituent
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
Definitions
- the present invention relates to a crude oil tanker oil tank (oil tank) formed by welding steel materials or a tank for transporting or storing crude oil (hereinafter referred to as a crude oil tank).
- a crude oil tank formed by welding steel materials or a tank for transporting or storing crude oil (hereinafter referred to as a crude oil tank).
- the steel materials used in the crude oil tank of the present invention include thick steel plate, thin steel sheet, and shaped steel.
- the most effective method for preventing the above-described general corrosion and local corrosion is to apply a heavy coating to the surface of the steel material to shield the steel material from the corrosive environment.
- the painting operation of crude oil tanks requires an enormous area to be applied, and the paint film must be repainted once every 10 years due to the deterioration of the coating film. To do.
- corrosion is promoted on the damaged part of the heavy-painted coating film in the corrosive environment of the crude oil tank.
- Patent Document 1 For the corrosion problem as described above, several techniques for improving the corrosion resistance of the steel material itself in the corrosive environment of the crude oil tank have been proposed. For example, in Patent Document 1, in mass%, C: 0.001 to 0.2%, Si: 0.01 to 2.5%, Mn: 0.1 to 2%, P: 0.03% or less, S: 0.02% or less, Cu: 0.01 to 1.5%, Al: 0.001 to 0.3%, N: 0.001 to 0.01%, and Mo: 0.001%.
- Patent Document 2 in mass%, C: 0.001 to 0.2%, Si: 0.01 to 2.5%, Mn: 0.1 to 2%, P: 0.03% or less , S: 0.02% or less, Cu: 0.01 to 1.5%, Al: 0.001 to 0.3%, N: 0.001 to 0.01%, and Mo: 0
- C 0.001 to 0.2%
- Si 0.01 to 2.5%
- Mn 0.1 to 2%
- P 0.03% or less
- S 0.02% or less
- Cu 0.01 to 1.5%
- Al 0.001 to 0.3%
- N 0.001 to 0.01%
- Mo 0
- Patent Document 1 and Patent Document 2 described above contain Cu as an essential element for improving corrosion resistance
- the addition of Cu causes surface cracks during hot rolling, so that production stability is improved. Have the problem of harming.
- an object of the present invention is to provide a welded joint having excellent local corrosion resistance in a tanker oil tank formed by welding a steel material excellent in manufacturability without causing problems such as cracking during hot rolling. And providing a crude oil tank having the welded joint.
- the inventors have intensively studied to solve the above problems. As a result, when forming a crude oil tank by welding steel materials with improved corrosion resistance by controlling the component composition of steel, the content of Cu, Mo and W contained in the weld metal of the welded joint is within the proper range. As a result, it was found that the local corrosion generated in the welded joint of the crude oil tank can be remarkably reduced, and the present invention has been completed.
- the steel material used for the welded joint of the present invention is characterized by further containing at least one component of the following groups A to D in addition to the above component composition.
- Group A Ni: 0.005 to 0.4 mass% and Co: 0.01 to 0.4 mass% or one selected from Group B; Nb: 0.001 to 0.1 mass%, Ti : 0.001 to 0.1 mass%, Zr: 0.001 to 0.1 mass%, and V: 0.002 to 0.2 mass%, one or more C groups; Ca: 0.0002 ⁇ 0.01 mass%, REM: 0.0002 to 0.015 mass%, and Y: 0.0001 to 0.1 mass%, one or more D groups; B: 0.0002 to 0.003 mass %
- the present invention is a crude oil tank having the above-mentioned weld joint.
- C 0.03-0.16 mass%
- C is an element that enhances the strength of steel.
- 0.03 mass% or more is added in order to secure a desired strength.
- addition exceeding 0.16 mass% lowers the weldability and the toughness of the welded heat affected zone. Therefore, C is set to a range of 0.03 to 0.16 mass%. A range of 0.06 to 0.16 mass% is more preferable.
- Si 0.05-1.50 mass%
- Si is an element added as a deoxidizer, but is also an effective element for increasing the strength of steel. Therefore, in the present invention, 0.05 mass% or more is added in order to ensure a desired strength. However, addition exceeding 1.50 mass% reduces the toughness of steel. Therefore, Si is set to a range of 0.05 to 1.50 mass%. A range of 0.15 to 0.50 mass% is more preferable.
- Mn 0.1 to 2.0 mass%
- Mn is an element that increases the strength of steel, and in the present invention, 0.1 mass% or more is added in order to obtain a desired strength. On the other hand, addition exceeding 2.0 mass% reduces the toughness and weldability of steel. Therefore, Mn is in the range of 0.1 to 2.0 mass%. From the viewpoint of maintaining high strength and suppressing the formation of inclusions that deteriorate the corrosion resistance, a range of 0.5 to 1.6 mass% is preferable, and a range of 0.7 to 1.4 mass% is more preferable. preferable.
- P 0.025 mass% or less
- P is a harmful element that segregates at the grain boundaries and lowers the toughness of the steel, and is desirably reduced as much as possible. In particular, if added over 0.025 mass%, the toughness is greatly reduced. Moreover, when P is added exceeding 0.025 mass%, it will also have a bad influence on the corrosion resistance in a tank oil tank. Therefore, P is set to 0.025 mass% or less. Preferably it is 0.015 mass% or less.
- S 0.010 mass% or less
- S is a harmful element that forms MnS, which is a non-metal inclusion, and becomes a starting point of local corrosion, and reduces local corrosion resistance. Is desirable. In particular, addition exceeding 0.010 mass% leads to a significant decrease in local corrosion resistance. Therefore, the upper limit of S is 0.010 mass%. Preferably, it is 0.005 mass% or less.
- Al 0.005 to 0.10 mass%
- Al is an element added as a deoxidizer, and 0.005 mass% or more is added in the present invention. However, if added in excess of 0.10 mass%, the toughness of the steel decreases, so the upper limit of Al is 0.10 mass%. Preferably, it is in the range of 0.01 to 0.05 mass%. A range of 0.02 to 0.04 mass% is more preferable.
- N 0.008 mass% or less
- N is a harmful element that lowers toughness, and is desirably reduced as much as possible.
- the toughness is greatly lowered, so the upper limit is made 0.008 mass%.
- it is 0.006 mass% or less, More preferably, it is 0.004 mass% or less.
- the above-mentioned effect is particularly remarkable in a portion that comes into contact with a liquid containing a high concentration of salt separated from a crude oil component, such as a bottom plate portion of a tanker oil tank, and a Zn-containing primer treatment is applied to the steel material in the above-mentioned portion containing Cr.
- a Zn-containing primer treatment is applied to the steel material in the above-mentioned portion containing Cr.
- the corrosion resistance can be remarkably improved as compared with a steel material not containing Cr.
- addition of 0.1 mass% or less is not sufficient, while addition exceeding 0.5 mass% deteriorates the toughness of the weld. Therefore, Cr is in the range of more than 0.1 mass% and less than 0.5 mass%. A range of 0.11 to 0.3 mass% is more preferable. The range of 0.12 to 0.2 mass% is more preferable.
- Cu 0.03-0.4 mass%
- Cu is an element that increases the strength of the steel, and also exists in the rust generated by the corrosion of the steel and has the effect of increasing the corrosion resistance. These effects cannot be sufficiently obtained with addition of less than 0.03 mass%.
- addition over 0.4 mass% saturates the effect of improving corrosion resistance and causes problems such as surface cracking during hot working. . Therefore, from the viewpoint of stably producing the steel material of the present invention, Cu needs to be added in the range of 0.03 to 0.4 mass%.
- the range of 0.008 to 0.15 mass% is preferable from the viewpoint of cost effectiveness. A range of 0.01 to 0.14 mass% is more preferable.
- the steel material of this invention needs to contain 1 type, or 2 or more types chosen from W, Mo, Sn, and Sb other than the said component in the following range.
- W: 0.01 to 1.0 mass% W has the effect of suppressing pitting corrosion at the tanker tank bottom plate and the effect of suppressing overall corrosion of the tanker upper deck. The above effect is manifested by addition of 0.01 mass% or more. However, if it exceeds 1.0 mass%, the effect is saturated. Therefore, W is added in the range of 0.01 to 1.0 mass%. The range is preferably 0.01 to 0.5 mass%, more preferably 0.02 to 0.3 mass%.
- W has the above-described effect of improving corrosion resistance
- WO 4 2 ⁇ is generated in the rust generated as the steel sheet corrodes, and the presence of this WO 4 2 ⁇ causes chloride ions ( chloride ion) can be suppressed from entering the surface of the steel sheet, further, in the site where pH is lowered such anode portion of the steel sheet surface (anode), generated by FeWO 4, the chloride ions by the presence of this FeWO 4 It is because the penetration
- Mo 0.01 to 0.5 mass% Mo not only suppresses pitting corrosion on the bottom plate of the tanker oil tank, but also after the coating in a corrosive environment that repeats salt water immersion and high humidity like the ballast tank, as well as the overall corrosion resistance of the tanker backside. There is an effect of improving the corrosion resistance of.
- the effect of Mo is manifested by addition of 0.01 mass% or more, but the effect is saturated when it exceeds 0.5 mass%. Therefore, Mo is in the range of 0.01 to 0.5 mass%. The range is preferably 0.02 to 0.5 mass%, more preferably 0.03 to 0.4 mass%.
- Mo has the above-described effect of improving corrosion resistance is that, like W, MoO 4 2 ⁇ is generated in the rust generated along with corrosion of the steel sheet, and the presence of MoO 4 2 ⁇ causes chloride ions. This is thought to be because the penetration of steel into the steel sheet surface is suppressed.
- Sn: 0.001 to 0.2 mass%, Sb: 0.001 to 0.4 mass% Sn and Sb have the effect of suppressing pitting corrosion on the tanker tank bottom plate and the effect of suppressing the overall corrosion of the tanker upper deck.
- the above effects are manifested by the addition of Sn: 0.001 mass% or more and Sb: 0.001 mass% or more.
- Sn: more than 0.2 mass% and Sb: more than 0.4 mass% are added, the effect is saturated.
- Sn and Sb are preferably added in the above ranges.
- the steel material of this invention contains 1 type or 2 types chosen from Ni and Co other than the said essential component in the following range.
- Ni and Co have the effect of refining the generated rust particles to improve the corrosion resistance in the bare state and the corrosion resistance in the state where the epoxy primer is applied to the zinc primer. . Therefore, these elements are preferably added in an auxiliary manner when it is desired to further improve the corrosion resistance.
- the above effects are manifested by adding Ni: 0.005 mass% or more and Co: 0.01 mass% or more.
- Ni has an effect of suppressing surface cracks during hot working that occur in steel containing Cu or Sn. Therefore, Ni and Co are preferably added within the above ranges.
- the element symbol in the above formula indicates the content (mass%) of the element, and the element not contained is calculated as 0 (zero). It is necessary to contain so that the X value defined by may satisfy 0.5 or less.
- the above equation (1) is an equation for evaluating the influence of each component on the corrosion in the tanker oil tank, and the coefficient of the component that improves the corrosion resistance is expressed as negative, and the coefficient of the component that deteriorates the corrosion resistance is expressed as positive. Yes. Therefore, the steel material having a smaller value of X has better corrosion resistance.
- the inventors have found that if X is 0.5 or less, the corrosion resistance in the corrosive environment in the tanker oil tank is reduced. Although it is excellent, it discovered that the said corrosion resistance deteriorated when X exceeded 0.5. Therefore, in determining the content of P, S, Cr, Cu, W, Mo, Sn, Sb, Ni and Co, the steel material of the present invention is designed so that the X value is 0.5 or less. There is a need.
- the element symbol in the above formula indicates the content (mass%) of the element, and the element not contained is calculated as 0 (zero). It is necessary to contain so that the Z value defined by (1) may be 0.15 or less.
- Cu is an element that causes surface cracking during hot working
- Sn is an element that promotes cracking due to Cu.
- Ni is an effective element for preventing the harmful effects of the above elements, but in order to exhibit the above effects of Ni, it is necessary to satisfy the above formula (2) and to add Ni. .
- the steel material of the present invention may further contain one or more selected from Nb, Ti, V and Zr in the following range in addition to the above components. it can.
- Nb 0.001 to 0.1 mass%
- Ti 0.001 to 0.1 mass%
- Zr 0.001 to 0.1 mass%
- V 0.002 to 0.2 mass%
- Nb, Ti, Zr and V are all elements that increase the strength of the steel material, and can be appropriately selected and added according to the required strength.
- Nb, Ti, and Zr each 0.001 mass% or more, and V to add 0.002 mass% or more.
- the toughness decreases, so Nb, Ti, Zr, V are added within the above ranges, respectively. Is preferred.
- the steel material of the present invention further includes one or more selected from Ca, REM and Y in the following range in addition to the above components.
- Ca 0.0002 to 0.01 mass%
- REM 0.0002 to 0.015 mass%
- Y 0.0001 to 0.1 mass%
- Ca, REM, and Y are all effective in improving the toughness of the weld heat affected zone, and can be added as necessary.
- the above effect can be obtained by adding Ca: 0.0002 mass% or more, REM: 0.0002 mass% or more, Y: 0.0001 mass% or more, but Ca: 0.01 mass%, REM: 0.015 mass%, Y: If added in excess of 0.1 mass%, the toughness is reduced, so Ca, REM, and Y are preferably added in the above ranges.
- the steel material of this invention can contain B in the following range in addition to the said component.
- B 0.0002 to 0.003 mass%
- B is an element that increases the strength of the steel material, and can be added as necessary. In order to acquire the said effect, adding 0.0002 mass% or more is preferable. However, when it exceeds 0.003 mass%, toughness will fall. Therefore, B is preferably added in the range of 0.0002 to 0.003 mass%.
- the steel material of the present invention is obtained by converting a steel adjusted to a component composition suitable for the present invention into a known refining process (steel converter, electric furnace, vacuum degassing equipment) or the like. It is melted using a refinery process and made into a steel material (slab slab) by continuous casting process or ingot-bundling rolling process. It is preferable that the steel material is rolled (hot rolled) to be a steel material such as a thick steel plate, a thin steel plate and a shaped steel.
- the reheating temperature before the hot rolling is preferably 900 to 1200 ° C. If heating temperature is less than 900 degreeC, a deformation resistance is large and it will become difficult to hot-roll. On the other hand, when the heating temperature exceeds 1200 ° C., austenite grains are coarsened, resulting in a decrease in toughness, and a scale loss due to oxidation becomes significant, resulting in a decrease in yield ratio. It is. A more preferable heating temperature is 1000 to 1150 ° C.
- the finish rolling finish temperature is preferably 750 ° C. or higher. If the temperature is lower than 750 ° C., the deformation resistance of the steel increases, the rolling load increases, it becomes difficult to roll, and a waiting time occurs until the rolled material reaches a predetermined rolling temperature, so the rolling efficiency decreases. It is because.
- the steel material after hot rolling may be cooled by either air cooling or accelerated cooling, but accelerated cooling is preferred when higher strength is desired.
- the cooling rate is 2 to 80 ° C./sec and the cooling stop temperature is 650 to 300 ° C.
- the cooling rate is less than 2 ° C./sec and the cooling stop temperature exceeds 650 ° C.
- the effect of accelerated cooling is small and sufficient strength cannot be achieved.
- the cooling rate exceeds 80 ° C./sec and the cooling stop temperature is less than 300 ° C., the toughness of the obtained steel material may be reduced, or the shape of the steel material may be distorted.
- a welded joint of a crude oil tank formed by welding steel plates manufactured by adjusting to the above-mentioned appropriate components must contain Cu, Mo and W in the weld metal in the following ranges.
- Cu 0.05 to 0.5 mass%
- Mo + W 0.03 to 1.0 mass%
- the inventors have determined that the influence of the alloy content in the weld metal on the corrosion resistance of the welded joint is dominated by the total content of Cu and Mo and W, and Cu and Mo and / or W are combined. It has been found that when added, the corrosion resistance of the welded joint is greatly improved by the synergistic effect of these elements.
- Cu content in a weld metal and the total content of Mo and W are restrict
- content of Mo and W does not need to include any one of Mo and W.
- the welding material used for welding is used depending on the component composition of the steel (base material) and the welding conditions. )) Is preferably selected as appropriate.
- a welding wire having a composition obtained by dividing the target composition of Cu, Mo, and W in the weld metal by the dilution ratio of the base material is produced and welded using this.
- the welding method used for welding the crude oil tank of the present invention is a high heat input welding (high welding such as FAB welding, FCB welding, RF welding, which is a one-sided submerged arc welding method (one-side submerged arc welding)).
- high welding such as FAB welding, FCB welding, RF welding
- -heat input welding or carbonate gas arc welding (CO 2 welding (CO 2 arc welding)
- CO 2 welding CO 2 arc welding
- small heat input welding such as) (small-heat input welding) or the like
- the chemical composition of the weld metal From the viewpoint of controlling to an appropriate range, it is necessary that the welding method uses a welding wire.
- FAB welding is a registered trademark related to the welding method at Kobe Steel, Ltd., and a back bead is formed by one-pass welding by directly applying a backing material composed of glass tape, solid flux, etc. to the back surface of the steel plate.
- FCB welding is a registered trademark related to the welding method of Kobe Steel, Ltd., and spraying a backing flux on a copper plate and pressing it against the back of the steel plate to form a back bead by one-pass welding.
- the RF method is a registered trademark related to the welding method of Kobe Steel, Ltd., and a jig frame with an underlay flux piled under a backing flux containing a welding thermosetting resin is applied to the back of the steel plate. A method of forming a back bead by one-pass welding by pressing the flux.
- the weld joint of the crude oil tank of the present invention has a corrosion potential (corrosion potential) in a corrosion test solution of a steel material (matrix) alone and a weld metal alone.
- the difference from the corrosion potential in the corrosion test solution must be 60 mV or less. If the corrosion potential of steel is higher than the corrosion potential of the weld metal by more than 60 mV, corrosion is concentrated on the weld metal, and conversely, the corrosion potential of the weld metal exceeds 60 mV from the corrosion potential of the steel. When it is high, corrosion is concentrated on the steel material. Therefore, the difference between the corrosion potential of the steel material and the corrosion potential of the weld metal in the corrosion test solution is limited to 60 mV or less.
- the corrosion potential is determined by immersing each test piece cut out from the base metal portion and the weld metal portion at the position of the plate thickness 1/4 in a predetermined test solution, and the corrosion potential after 10 minutes from the start of immersion. It is a value measured using an Ag / AgCl standard electrode (standard reference electrode).
- the test solution used for measuring the corrosion potential is preferably one that simulates the corrosive environment of the tanker bottom plate of an actual ship.
- an aqueous solution having a mass of 2.0 mass% or more simulates a corrosive liquid inside pitting corrosion generated on a tanker bottom plate
- an acidic aqueous solution having a pH of 2.0 or less is preferably used.
- the acidic aqueous solution may contain Cl.
- each steel plate of 1 to 36 was welded by the welding method shown in Table 2 to produce a welded joint.
- the heat input of each welding method was 146 kJ / cm for FCB welding, 180 kJ / cm for FAB welding, and 1.5 kJ / cm for CO 2 welding. All the grooves were V grooves.
- the composition control of Cu, Mo, and W in the weld metal of each welded joint is performed by setting the target composition of Cu, Mo, and W to the base material dilution ratio (about 11% for CO 2 welding, about 47% for FAB welding, FCB welding). A welding wire having a composition obtained by rebating by about 67% was produced, and welding was performed using this.
- FCB welding For FCB welding, a flux (PF-I55E / manufactured by Kobe Steel) and a back flux (PF-I50R / manufactured by Kobe Steel), and for FAB welding, a flux (PF-I52E / ( Kobe Steel, Ltd.), filler (RR-2 / Kobe Steel) and backing material (FA-B1 / Kobe) were used.
- FCB welding refers to a method in which a backing flux is spread on a copper plate and pressed against the back surface of the steel plate to form a back bead by one-pass welding.
- FAB welding refers to a method in which a backing material composed of glass tape, solid flux or the like is directly applied to the back surface of a steel plate to form a back bead by one pass welding.
- the contents of Cu, Mo and W in the weld metal were measured using atomic absorption spectrometry. Furthermore, using a Ag / AgCl standard electrode and potentiostat, the corrosion potential of the base metal alone and the corrosion potential of the weld metal alone of the welded joint in a 10 mass% NaCl (pH 0.85) corrosion test solution were measured. The potential difference (potential difference) was determined.
- a local corrosion test was performed that simulated the tanker bottom plate environment as follows. First, the above-mentioned No. A rectangular piece of width 25 mm ⁇ length 60 mm ⁇ thickness 4 mm is placed so that the weld metal is positioned in parallel with the width direction of the test piece from the position of the plate thickness 1 ⁇ 4 of the thick steel plate welded joints 1 to 36. It was cut out and the entire surface was polished with 600th emery paper.
- a test solution prepared by adjusting a 10 mass% NaCl aqueous solution to a Cl ion concentration of 10 mass% and a pH of 0.85 using concentrated hydrochloric acid was prepared, and a thread was formed in a 3 mm ⁇ hole opened at the top of the test piece.
- a corrosion test was performed in which the test piece was immersed in 2 L of the test solution for 168 hours.
- the test solution was preheated and maintained at 30 ° C. and replaced with a new test solution every 24 hours.
- the apparatus used for the corrosion test is shown in FIG.
- This corrosion test apparatus is a double-type apparatus comprising a corrosion test tank 2 and a thermostat 3, and the above-mentioned test solution 4 is placed in the corrosion test bath 2, and the test piece 1 is a test piece 5. It is hung and immersed. The temperature of the test solution 4 is maintained by adjusting the temperature of the water 6 placed in a constant-temperature bath 3. After removing the rust generated on the surface of the test piece after the above corrosion test, measure the mass, divide the mass difference before and after the test by the total surface area, and calculate the reduction in thickness (corrosion rate on both sides) per year. It was.
- the local corrosion resistance is good ( ⁇ ), and the corrosion rate is over 1.0 mm / year.
- the local corrosion resistance was evaluated as poor (x) when local corrosion was visually observed in either the base metal part or the welded part.
- the results of the magnetic particle testing, the analysis results of the weld metal, the measurement results of the corrosion potential difference, and the results of the corrosion resistance test are shown in Table 2 together with the X value and the Z value obtained from the component composition of each steel plate. .
- Table 2 shows that the base metal and the weld metal satisfy the composition of the present invention, satisfy the X value and Z value conditions, and the corrosion potential difference satisfies the conditions of the present invention.
- the thick steel plates 1 to 4, 6, 7 and 10 to 29 are free from cracking during rolling and exhibit good corrosion resistance in a corrosion resistance test simulating a tanker bottom plate environment. No.
- the thick steel plates of 5, 8, 9 and 30 to 36 are cracked during rolling and / or have not obtained good corrosion resistance.
- Test piece 2 Corrosion test tank 3: Constant temperature bath 4: Test liquid 5: Tegus 6: Water
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Abstract
Description
(1)塩化ナトリウム(sodium chloride)を代表とする塩類が高濃度に溶解した凝集水(brine)の存在、
(2)過剰な洗浄によるオイルコートの離脱、
(3)原油中に含まれる硫化物(sulfide)の高濃度化、
(4)結露水に溶け込んだ、原油タンク防爆用に封入されたイナートガス(inert gases)中のO2、CO2、SO2等の高濃度化、
などの項目が挙げられている。実際、実船のドック検査時に、原油タンク内に滞留した水を分析した結果では、高濃度の塩化物イオンと硫酸イオンが検出されている。
3≧溶接金属のCu含有量(質量%)/鋼材のCu含有量(質量%)≧0.15
3≧(溶接金属のMo含有量+W含有量(質量%))/(鋼材のMo含有量+W含有量(質量%))≧0.15
−0.3≦(溶接金属のCu含有量(質量%)−鋼材のCu含有量(質量%))≦0.5
3≧溶接金属のCu含有量(質量%)/鋼材のCu含有量(質量%)≧0.15
3≧(溶接金属のMo含有量+W含有量(質量%))/(鋼材のMo含有量+W含有量(質量%))≧0.15
X値=(1−0.8×Cu0.5)×{1−(0.8×W+0.4×Mo)0.3}×{1−(Sn+0.4×Sb)0.3}×{1−(0.05×Cr+0.03×Ni+0.03×Co)0.3}×{1+2×(S/0.01+P/0.025)} ・・・(1)
で定義されるX値が0.5以下、下記(2)式;
Z値=(1+10×Sn)×(Cu−0.7×Ni) ・・・(2)
で定義されるZ値が0.15以下となるよう含有し、残部がFeおよび不可避的不純物からなる鋼材同士を溶接して形成される原油タンクの溶接継手において、溶接継手の溶接金属がCu:0.05~0.5mass%および(Mo+W):0.03~1.0mass%を含有し、鋼材の腐食電位と溶接金属の腐食電位との差が60mV以下であることを特徴とする耐食性に優れる溶接継手である。ここで、上記各式中の元素記号は、その元素の含有量(mass%)を示す。
記
A群;Ni:0.005~0.4mass%およびCo:0.01~0.4mass%のうちから選ばれる1種または2種
B群;Nb:0.001~0.1mass%、Ti:0.001~0.1mass%、Zr:0.001~0.1mass%およびV:0.002~0.2mass%のうちから選ばれる1種または2種以上
C群;Ca:0.0002~0.01mass%、REM:0.0002~0.015mass%およびY:0.0001~0.1mass%のうちから選ばれる1種または2種以上
D群;B:0.0002~0.003mass%
C:0.03~0.16mass%
Cは、鋼の強度を高める元素であり、本発明では、所望の強度を確保するため、0.03mass%以上添加する。一方、0.16mass%を超える添加は、溶接性(weldability)および溶接熱影響部(welded heat affected zone)の靭性(toughness)を低下させる。よって、Cは0.03~0.16mass%の範囲とする。0.06~0.16mass%の範囲がより好ましい。
Siは、脱酸剤として添加される元素であるが、鋼の強度を高めるのに有効な元素でもある。そこで、本発明では、所望の強度を確保するため、0.05mass%以上添加する。しかし、1.50mass%を超える添加は、鋼の靭性を低下させる。よって、Siは0.05~1.50mass%の範囲とする。0.15~0.50mass%の範囲がより好ましい。
Mnは、鋼の強度を高める元素であり、本発明では、所望の強度を得るため、0.1mass%以上添加する。一方、2.0mass%を超える添加は、鋼の靭性および溶接性を低下させる。よって、Mnは0.1~2.0mass%の範囲とする。なお、高強度を維持し、かつ、耐食性を劣化させる介在物の形成を抑制する観点からは、0.5~1.6mass%の範囲が好ましく、0.7~1.4mass%の範囲がより好ましい。
Pは、粒界に偏析して鋼の靭性を低下させる有害な元素であり、できる限り低減するのが望ましい。特に、0.025mass%を超えて添加すると、靭性が大きく低下する。また、Pは0.025mass%を超えて添加すると、タンク油槽内の耐食性にも悪影響を及ぼす。よって、Pは0.025mass%以下とする。好ましくは0.015mass%以下である。
Sは、非金属介在物(non−metal inclusion)であるMnSを形成して局部腐食の起点となり、耐局部腐食性を低下させる有害な元素であり、できる限り低減するのが望ましい。特に、0.010mass%を超える添加は、耐局部腐食性の顕著な低下を招く。よって、Sの上限は0.010mass%とする。好ましくは、0.005mass%以下である。
Alは、脱酸剤として添加される元素であり、本発明では0.005mass%以上添加する。しかし、0.10mass%を超えて添加すると、鋼の靭性が低下するので、Alの上限は0.10mass%とする。好ましくは、0.01~0.05mass%の範囲である。0.02~0.04mass%の範囲がより好ましい。
Nは、靭性を低下させる有害な元素であり、できる限り低減するのが望ましい。特に、0.008mass%を超えて添加すると、靭性の低下が大きくなるので、上限は0.008mass%とする。好ましくは0.006mass%以下、より好ましくは0.004mass%以下である。
Crは、腐食の進行に伴って錆層中に移行し、Cl−の錆層への侵入を遮断することによって、錆層と地鉄の界面へのCl−の濃縮を抑制する。また、Zn含有プライマー(primer)を塗布したときには、Feを中心としたCrやZnの複合酸化物を形成して、長期間にわたり鋼板表面にZnを存続させることができるため、飛躍的に耐食性を向上することができる。上記効果は、特に、タンカー油槽の底板部のように、原油油分から分離された高濃度の塩分を含む液と接触する部分において顕著であり、Crを含有した上記部分の鋼材にZn含有プライマー処理を施すことにより、Crを含有しない鋼材と比較して、格段に耐食性を向上することができる。上記Crの効果は、0.1mass%以下の添加では十分ではなく、一方、0.5mass%を超える添加は、溶接部の靭性を劣化させる。よって、Crは0.1mass%超0.5mass%以下の範囲とする。0.11~0.3mass%の範囲がより好ましい。0.12~0.2mass%の範囲がさらに好ましい。
Cuは、鋼の強度を高める元素であるとともに、鋼の腐食によって生成した錆中に存在して耐食性を高める効果がある。これらの効果は、0.03mass%未満の添加では十分に得られず、一方、0.4mass%を超えて添加すると、耐食性向上効果が飽和するほか、熱間加工時に表面割れなどの問題を引き起こす。よって、本発明の鋼材を安定して製造する観点から、Cuは0.03~0.4mass%の範囲で添加する必要がある。なお、Cu添加の効果は、添加量の増加にともない飽和していくため、費用対効果の点からは、0.008~0.15mass%の範囲が好ましい。0.01~0.14mass%の範囲がより好ましい。
W:0.01~1.0mass%
Wは、タンカー油槽部底板における孔食を抑制する効果があるほか、タンカー上甲板部の全面腐食を抑制する効果がある。上記効果は、0.01mass%以上の添加で発現する。しかし、1.0mass%を超えると、その効果が飽和する。よって、Wは0.01~1.0mass%の範囲で添加する。好ましくは0.01~0.5mass%、より好ましくは0.02~0.3mass%の範囲である。
Moは、タンカー油槽部底板における孔食を抑制するだけでなく、タンカー上甲板裏面部の耐全面腐食性や、バラストタンク(ballast tank)のように塩水浸漬と高湿潤を繰り返す腐食環境における塗装後の耐食性を向上させる効果がある。上記Moの効果は0.01mass%以上の添加で発現するが、0.5mass%を超えると、その効果は飽和する。よって、Moは0.01~0.5mass%の範囲とする。好ましくは0.02~0.5mass%、より好ましくは0.03~0.4mass%の範囲である。
なお、Moが上記のような耐食性向上効果を有する理由は、Wと同様、鋼板の腐食に伴い生成する錆中にMoO4 2−が生成し、このMoO4 2−の存在によって、塩化物イオンの鋼板表面への侵入が抑制されるからと考えられる。
SnおよびSbは、タンカー油槽部底板における孔食を抑制する効果を有する他、タンカー上甲板部の全面腐食を抑制する効果がある。上記効果は、Sn:0.001mass%以上、Sb:0.001mass%以上の添加で発現する。一方、Sn:0.2mass%超えおよびSb:0.4mass%超え添加しても、その効果は飽和する。さらに、Snの多量の添加は、Cuによる熱間加工時の表面割れを助長する。よって、SnおよびSbは、それぞれ上記範囲で添加するのが好ましい。
Ni:0.005~0.4mass%、Co:0.01~0.4mass%
NiおよびCoは、生成した錆粒子を微細化して、裸状態での耐食性およびジンクプライマー(zinc primer)にエポキシ系塗装(epoxy coating)が施された状態での耐食性を少なからず向上する効果を有する。したがって、これらの元素は、耐食性をより向上したい場合に、補助的に添加するのが好ましい。上記効果は、Ni:0.005mass%以上、Co:0.01mass%以上の添加で発現する。一方、Ni:0.4mass%超え、Co:0.4mass%超え添加しても、その効果が飽和する。また、Niは、CuやSnを含有する鋼において発生する熱間加工時の表面割れを抑制する効果がある。よって、NiおよびCoは、それぞれ上記範囲で添加するのが好ましい。
X値=(1−0.8×Cu0.5)×{1−(0.8×W+0.4×Mo)0.3}×{1−(Sn+0.4×Sb)0.3}×{1−(0.05×Cr+0.03×Ni+0.03×Co)0.3}×{1+2×(S/0.01+P/0.025)} ・・・(1)
ここで、上記式中の元素記号は、その元素の含有量(mass%)を示しており、含有していない元素は0(ゼロ)として計算する。
で定義されるX値が0.5以下を満たすよう含有している必要がある。
Z値=(1+10×Sn)×(Cu−0.7×Ni) ・・・(2)
ここで、上記式中の元素記号は、その元素の含有量(mass%)を示しており、含有していない元素は0(ゼロ)として計算する。
で定義されるZ値が0.15以下となるように含有していることが必要である。その理由は、Cuは、熱間加工時の表面割れを引き起こす元素であり、また、Snは、上記Cuによる割れを助長する元素である。一方、Niは、上記元素による弊害を防止するのに有効な元素であるが、Niの上記効果を発現させるためには、上記(2)式を満たしてNiを添加する必要があるからである。
Nb:0.001~0.1mass%、Ti:0.001~0.1mass%、Zr:0.001~0.1mass%およびV:0.002~0.2mass%
Nb,Ti,ZrおよびVは、いずれも鋼材強度を高める元素であり、必要とする強度に応じて適宜選択して添加することができる。上記効果を得るためには、Nb,Ti,Zrはそれぞれ0.001mass%以上、Vは0.002mass%以上添加するのが好ましい。しかし、Nb,Ti,Zrはそれぞれ0.1mass%を超えて、Vは0.2mass%を超えて添加すると、靭性が低下するため、Nb,Ti,Zr,Vは、それぞれ上記範囲で添加するのが好ましい。
Ca:0.0002~0.01mass%、REM:0.0002~0.015mass%およびY:0.0001~0.1mass%
Ca,REMおよびYは、いずれも、溶接熱影響部の靭性向上に効果があり、必要に応じて添加することができる。上記効果は、Ca:0.0002mass%以上、REM:0.0002mass%以上、Y:0.0001mass%以上の添加で得られるが、Ca:0.01mass%、REM:0.015mass%、Y:0.1mass%を超えて添加すると、却って靭性の低下を招くので、Ca,REM,Yは、それぞれ上記範囲で添加するのが好ましい。
B:0.0002~0.003mass%
Bは、鋼材の強度を高める元素であり、必要に応じて添加することができる。上記効果を得るためには、0.0002mass%以上添加するのが好ましい。しかし、0.003mass%を超えて添加すると、靭性が低下する。よって、Bは0.0002~0.003mass%の範囲で添加するのが好ましい。
すなわち、本発明の鋼材は、本発明に適合する成分組成に調整した鋼を、転炉(steel converter)や電気炉(electric furnace)、真空脱ガス(vacuum degassing equipment)等、公知の精錬プロセス(refinery process)を用いて溶製し、連続鋳造法(continuous casting process)あるいは造塊−分塊圧延法で鋼素材(スラブ(steel slab))とし、次いで、この素材を再加熱してから熱間圧延(hot rolling)し、厚鋼板、薄鋼板および形鋼等の鋼材とするのが好ましい。
上記適正成分に調整して製造した鋼板同士を溶接して形成した原油タンクの溶接継手は、溶接金属中のCu,MoおよびWが下記の範囲で含有していることが必要である。
Cu:0.05~0.5mass%、(Mo+W):0.03~1.0mass%
発明者らは、溶接継手の耐食性に及ぼす溶接金属中の合金成分の影響は、CuおよびMoとWの合計含有量の影響が支配的であり、Cuと、Moおよび/またはWを複合して添加した場合には、これらの元素の相乗効果によって、溶接継手の耐食性が大幅に向上することを見出した。しかし、溶接継手の溶接金属中のCuが0.05mass%未満、あるいは、溶接金属中のMoとWとの合計量が0.03mass%未満の場合には、上記の相乗効果が期待できず、溶接継手の耐食性が低下する。一方、溶接金属中のCuが0.5mass%超え、あるいは、溶接金属中のMoとWとの合計量が1.0mass%超えの場合には、母材(鋼材)部に比して溶接金属の耐食性が格段に向上するが故に、母材部に集中して腐食が発生するようになる。また、溶接継手の低温靭性が低下するという弊害もある。よって、本発明においては、溶接金属中のCu含有量およびMoとWの合計含有量をそれぞれ上記の範囲に制限する。なお、MoとWの含有量は、その合計量が上記範囲内にあれば、MoおよびWのうちいずれか一方を含まなくてもよい。
なお、ここでFAB溶接とは、(株)神戸製鋼所の溶接方法に関する登録商標で、ガラステープ、固形フラックス等で構成した裏当て材を鋼板裏面に直接当てて、1パス溶接で裏波ビードを形成する方法を言う。また、FCB溶接とは、(株)神戸製鋼所の溶接方法に関する登録商標で、銅板の上に裏当てフラックスを散布して、鋼板裏面に押し当てて、1パス溶接で裏波ビードを形成する方法を言う。また、RF法とは、(株)神戸製鋼所の溶接方法に関する登録商標で、溶接熱硬化性樹脂を含んだ裏当てフラックスの下に下敷きフラックスを重ねた冶具枠を鋼板裏面に当て、枠中のフラックスを押し当てて、1パス溶接で裏波ビードを形成する方法を言う。
かくして得られたNo.1~36の厚鋼板について、磁粉探傷試験で鋼板表面の割れの有無を調査し、割れが検出されなかったものを○、割れが検出されたものを×と判定した。
なお、前述したようにFCB溶接とは、銅板の上に裏当てフラックスを散布して、鋼板裏面に押し当てて、1パス溶接で裏波ビードを形成する方法を言う。また、FAB溶接とは、ガラステープ、固形フラックス等で構成した裏当て材を鋼板裏面に直接当てて、1パス溶接で裏波ビードを形成する方法を言う。
さらに、Ag/AgCl標準電極とポテンショスタット(potentiostatically)を用いて10mass%NaCl(pH0.85)腐食試験液中における母材単独の腐食電位と溶接継手の溶接金属単独の腐食電位を測定し、その電位差(difference in potential)を求めた。
次いで、10mass%NaCl水溶液を、濃塩酸(concentrated hydrochloric acid)を用いてClイオン濃度10mass%、pH0.85に調製した試験溶液を作製し、試験片の上部に開けた3mmφの孔にテグス(thread)を通して吊るし、1試験片につき2Lの試験溶液に168時間浸漬する腐食試験を行った。なお、試験溶液は、予め30℃に加温・保持し、24時間毎に新しい試験溶液と交換した。
上記腐食試験に用いた装置を図1に示す。この腐食試験装置は、腐食試験槽2、恒温槽3の二重型の装置で、腐食試験槽(corrosion test bath)2には上記試験溶液4が入れられ、その中に試験片1がテグス5で吊るされて浸漬されている。試験液4の温度は、恒温槽(constant−temperature bath)3に入れた水6の温度を調整することで保持している。
上記腐食試験後、試験片表面に生成した錆を除去した後、質量を測定し、試験前後の質量差を全表面積で割り戻し、1年当たりの板厚減少量(両面の腐食速度)を求めた。その結果、腐食速度が1.0mm/year以下でかつ母材部および溶接部に局部腐食が目視で認められない場合を耐局部腐食性が良好(○)、腐食速度が1.0mm/year超、あるいは、母材部か溶接部のいずれか一方にでも局部腐食が目視で認められる場合を耐局部腐食性が不良(×)と評価した。
2:腐食試験槽
3:恒温槽
4:試験液
5:テグス
6:水
Claims (6)
- C:0.03~0.16mass%、
Si:0.05~1.50mass%、
Mn:0.1~2.0mass%、
P:0.025mass%以下、
S:0.010mass%以下、
Al:0.005~0.10mass%、
N:0.008mass%以下、
Cr:0.1mass%超0.5mass%以下、
Cu:0.03~0.4mass%を含有し、かつ、
W:0.01~1.0mass%、Mo:0.01~0.5mass%、Sn:0.001~0.2mass%およびSb:0.001~0.4mass%のうちから選ばれる1種または2種以上を含有し、さらに上記成分が、下記(1)式で定義されるX値が0.5以下、下記(2)式で定義されるZ値が0.15以下となるよう含有し、残部がFeおよび不可避的不純物からなる鋼材同士を溶接して形成される原油タンクの溶接継手において、
上記溶接継手の溶接金属がCu:0.05~0.5mass%および(Mo+W):0.03~1.0mass%を含有し、鋼材の腐食電位と溶接金属の腐食電位との差が60mV以下である溶接継手。
記
X値=(1−0.8×Cu0.5)×{1−(0.8×W+0.4×Mo)0.3}×{1−(Sn+0.4×Sb)0.3}×{1−(0.05×Cr+0.03×Ni+0.03×Co)0.3}×{1+2×(S/0.01+P/0.025)} ・・・(1)
Z値=(1+10×Sn)×(Cu−0.7×Ni) ・・・(2)
ここで、上記式中の元素記号は、その元素の含有量(mass%)を示す。 - 上記鋼材は、上記成分組成に加えてさらに、Ni:0.005~0.4mass%およびCo:0.01~0.4mass%のうちから選ばれる1種または2種を含有する請求項1に記載の溶接継手。
- 上記鋼材は、上記成分組成に加えてさらに、Nb:0.001~0.1mass%、Ti:0.001~0.1mass%、Zr:0.001~0.1mass%およびV:0.002~0.2mass%のうちから選ばれる1種または2種以上を含有する請求項1または2に記載の溶接継手。
- 上記鋼材は、上記成分組成に加えてさらに、Ca:0.0002~0.01mass%、REM:0.0002~0.015mass%およびY:0.0001~0.1mass%のうちから選ばれる1種または2種以上を含有する請求項1~3のいずれか1項に記載の溶接継手。
- 上記鋼材は、上記成分組成に加えてさらに、B:0.0002~0.003mass%を含有する請求項1~4のいずれか1項に記載の溶接継手。
- 請求項1~5のいずれか1項に記載の溶接継手を有する原油タンク。
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