KR102245571B1 - Liquefied gas storage tank and ship having the same - Google Patents

Abstract

A liquefied gas storage tank according to an aspect of the present invention is a liquefied gas storage tank including a weldment used for welding of a low Ni base material, wherein the welded material is, by weight, manganese (Mn): 10 to 12%, Nickel (Ni): 6.5 to 9.0%, chromium (Cr): 2.5 to 4.0%, molybdenum (Mo): has a weld containing 1.5 to 2.5%.

Description

Liquefied gas storage tank and ship {LIQUEFIED GAS STORAGE TANK AND SHIP HAVING THE SAME}

The present invention relates to a liquefied gas storage tank and a ship.

With continuous industrialization and technological development, the use of storage refrigerants is increasing from -80 to -196 degrees, and accordingly, 2.25 to 9% Ni alloy steel, Invar, austenitic stainless steel, and Al are applied as the base material.

Among them, 9% Ni alloy steel has insufficient development and application status for exclusive weldments, so development is essential to increase productivity.

Typically, a Ni-based weldment is used to weld Ni alloy steel. However, in the case of a conventionally developed Ni-based weldment, a considerable amount of expensive raw materials such as Ni 50% or more, Mo, W, etc. are included, so in this case, there is a problem of high unit cost.

In addition, since most of these conventional Ni-based weldments are constructed by SMAW (Shielded Metal Arc Welding), production efficiency is extremely low and high efficiency of the welding construction is required. Is increasing throughout.

The present invention was created to solve the problems of the prior art as described above, and an object of the present invention is to provide a liquefied gas storage tank and a ship in which the alloy composition of the weldment used for welding of a low Ni base material is optimized.

A liquefied gas storage tank according to an aspect of the present invention is a liquefied gas storage tank including a weldment used for welding of a low Ni base material, wherein the welded material is, by weight, manganese (Mn): 10 to 12%, Nickel (Ni): 6.5 to 9.0%, chromium (Cr): 2.5 to 4.0%, molybdenum (Mo): has a weld containing 1.5 to 2.5%.

Specifically, the weldment may further include carbon (C): 0.35 to 0.55%.

Specifically, the welded material may further contain 0.2 to 0.7% of silicon (Si).

Specifically, the weldment may further contain boron (B): 0.1% or less.

Specifically, the weldment may further include titanium (Ti): 1% or less.

Specifically, the weldment may include a submerged arc wire, a core constituting the submerged arc wire, or a welding bead.

A ship according to another aspect of the present invention is characterized in that the liquefied gas storage tank is mounted.

Liquefied gas storage tanks and ships according to the present invention have excellent physical properties and excellent workability by optimizing the alloy composition of the welded material used for welding of low Ni base metal, and have excellent workability, and cracks while showing good weldability. There is an effect that can minimize the occurrence.

In addition, by optimizing the alloy composition of the low Ni Submerged Arc Welding weldment, it has excellent physical properties and weldability.

1 is a schematic side view of a ship having a liquefied gas storage tank according to an embodiment of the present invention.
2 is a table summarizing chemical composition ratios for weldments according to the first and second embodiments of the present invention.
3 is an experiment table for a weldment according to the first embodiment of the present invention.
4 is an experiment table for a weldment according to a second embodiment of the present invention.

Objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments in conjunction with the accompanying drawings. In adding reference numerals to elements of each drawing in the present specification, it should be noted that, even though they are indicated on different drawings, only the same elements are to have the same number as possible. In addition, in describing the present invention, when it is determined that a detailed description of a related known technology may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic side view of a ship having a liquefied gas storage tank according to an embodiment of the present invention.

Referring to FIG. 1, a ship 1 according to an embodiment of the present invention includes a liquefied gas storage tank CT, an engine room ER in which an engine system ES is located, and an engine room ER. ) It may include an engine casing (EC), a stack (F) and a deck house (DH) located on the top.

A plurality of liquefied gas storage tanks CT may be provided, and may be arranged side by side inside the hull. The liquefied gas storage tank CT of this embodiment may be arranged in a row along the longitudinal direction of the hull. However, the number, size, and shape of the liquefied gas storage tank CT may be variously modified.

For example, in the case of a container carrier other than a liquefied gas carrier, the liquefied gas storage tank CT may be formed in the form of a pressure vessel (Type C), and one or more may be provided on the deck.

The liquefied gas may be LPG, LNG, ethane, or the like, and may mean liquefied natural gas (LNG) as an example. In addition, the liquefied gas may be used as a term encompassing all of a liquid state or a gaseous state that has been naturally vaporized or forced to vaporize.

An engine room (ER) in which the engine system (ES) is placed is provided at the stern side of the ship (1), and the engine system (ES) placed in the engine room (ER) is an engine that provides the propulsion power of the ship (1). Poem). Although not specifically shown, the engine is connected to the propeller through a shaft, and consumes fuel to generate rotational force to rotate the propeller, so that the wake generated by the rotation of the propeller can advance the ship 1 .

The engine casing EC is provided above the engine room ER. The engine casing EC may have an exhaust pipe (not shown) that transmits exhaust generated from the engine system ES to the stack F.

The stack F is provided above the engine casing EC, and discharges exhaust to the outside.

The deck house (DH) is located on the upper part of the hull, and various living facilities for the crew's onboard residence and various navigational facilities for the voyage of the ship (1) are arranged. The deck house (DH) may consist of a plurality of floors, and may include a cabin, a control room, and other convenience facilities in which crew members can reside.

The ship (1) of the present invention is a gas carrier (LPGC, LNGC, etc.) equipped with a liquefied gas storage tank (CT) as a cargo tank on board, or a liquefied gas storage tank on board/offboard to use liquefied gas as fuel. It can cover ships on board, and furthermore, it can cover all offshore structures with liquefied gas storage tanks in addition to general commercial ships that transport cargo.

2 is a table summarizing the chemical composition ratio for the weldment according to the first and second embodiments of the present invention, and FIG. 3 is an experimental table for the weldment according to the first embodiment of the present invention.

First, the weldment according to the first embodiment of the present invention is a weldment used for welding of a low Ni base material, and includes a flux cored wire, a flux constituting the flux cored wire, or a welding bead. I can.

The weldment according to the first embodiment of the present invention relates to an Fe-based alloy flux cored wire weldment which is particularly used when welding 9% Ni alloy steel.

In general, the alloy flux cored wire dedicated to 9% Ni steel uses a Ni core and a Mo sheath. The flux-cored wire using Ni core and Mo sheath is too expensive to be widely applied to the entire industry due to the high price of the product itself because a large amount of expensive alloys such as Ni, Mo, and W are added.

Therefore, the present invention optimizes the alloy composition of the core and the outer shell compared to the prior art to provide a flux-cored wire weldment with minimal alloy content of expensive materials and excellent tensile strength, impact toughness, and crack resistance by using an Fe-based outer shell. can do.

Hereinafter, a flux-cored wire weldment according to a first embodiment of the present invention will be described in detail.

In the flux-cored wire weldment, the deposited metal component obtained by flux-cored wire welding is wt%, C: 0.3 to 0.5%, Si: 0.2 to 0.6%, Mn: 9 to 12%, Cr: 2.5 to 4.0% , Ni: 6 to 9%, Mo: 1.5 to 3.0%, Ti: 0.02% or less, B: 0.01% or less, the balance being Fe and inevitable impurities, these inevitable impurities are P: 0.02% or less, S : 0.02% or less, Al: 0.10% or less, W+Nb+V: 1.0% or less.

In addition, TiO2+SiO2+ZrO2 with respect to the total weight of the wire contained in either or both of the filling flux and the alloy sheath of the flux-cored wire may be 3.5 to 7.5%.

Here, the outer shell may be made of weight %, C: 0.01 to 0.3%, Si: 1.0% or less, Mn: 1.5% or less, P+S: 0.03% or less, and the remaining Fe.

In addition, the outer shell may be 50 to 80% by weight relative to the weld.

In addition, the tensile strength of the weld joint using the weldment may satisfy 650 MPa or more, and an impact toughness of 27J or more at -196 degrees.

The description of each component is as follows.

C: 0.3~0.5%

Carbon (C) is a strong austenite stabilizing element, and is a component that serves to improve strength and hardness. If the C content is less than 0.3%, austenite stabilization is unstable, and it cannot be said that the effect of improving the strength is sufficiently obtained. On the other hand, when it exceeds 0.50%, high temperature cracking resistance and toughness are deteriorated, and there is a problem that the generation of spatter increases.

In this embodiment, it is preferable to limit the content of C to 0.3 to 0.5%.

In this embodiment, the C source of the deposited metal is an Fe-based alloy forming the shell, metal carbides such as Mn-C, Cr-C, and WC contained in the flux, and C reduced from the CO2 gas and slag components in the shield gas. .

Si: 0.2~0.6%

Silicon (Si) is a component that improves deoxidation and weldability. If the content is less than 0.2%, there is a problem that the bead spreadability decreases due to insufficient deoxidation power. On the other hand, if the content exceeds 1.5%, it is segregated on the weld. There is a problem that lowers the low-temperature impact toughness by causing a problem and adversely affects the weld crack susceptibility.

In this embodiment, the Si content is preferably limited to 0.1 to 1.5%, but more preferably 0.2 to 0.6%.

In this embodiment, the Si source of the deposited metal is an Fe-based alloy forming the shell, a metal Si and an Fe-Si alloy included in the flux, or Si reduced from a slag component such as SiO.

Mn: 9-12%

Manganese (Mn) is an austenite stabilizing element, and is a component that improves the flowability of slag to improve the bead shape and maintains the proper strength and toughness of the weld. In order to obtain the above-described effect, it is necessary to contain Mn in an amount of 9% or more, but if the content exceeds 12.0%, it is not preferable because it may cause a rapid decrease in toughness.

In this embodiment, it is preferable to limit the content of Mn to 9 to 12%. More preferably, it is 11.0 to 12.0%.

On the other hand, as the Mn source of the deposited metal in this embodiment, there are Fe-based alloys forming the shell, metals Mn included in the flux, Fe-Mn alloys, MnO2 and MnCO3, etc. Quantity can be adjusted

Ni: 6~9%

Nickel (Ni) is an austenite stabilizing element, and is a component that plays a role in maintaining the proper strength and toughness of the weld. In order to obtain the above-described effect, it is necessary to contain Ni in an amount of 6% or more. However, when the content exceeds 9%, the strength decreases, which is not preferable.

Therefore, in this embodiment, it is preferable to limit the content of Ni to 6 to 9%. More preferably, it is 7.0 to 8.0%.

On the other hand, the Ni source of the deposited metal in this embodiment is a metal Ni, an Fe-Ni alloy, etc. contained in the flux, and the amount of Ni in the deposited metal can be adjusted by any addition.

At least one of P and S: less than 0.04% in total

P and S are one of the main elements that affect high-temperature cracking, and can cause high-temperature cracking by generating Ni alloys such as Ni3S7, NiS, and Ni3P, and low melting point compounds. Therefore, P and S impurity control is essential, and by controlling the total content of P and S, it is possible to reduce the occurrence of high-temperature cracking. Therefore, it is preferable that at least one of P and S is less than 0.04% in total.

Cr: 2.5~4.0%

Although chromium (Cr) is a ferrite stabilizing element, it has the effect of improving the strength of the weld metal. If it is less than 1.0%, there is no effect, and if it exceeds 4.0%, chromium carbide is excessively formed, resulting in a problem of lowering toughness.

Therefore, in this embodiment, it is preferable to limit the content of Cr to 2.5 to 4.0%. More preferably, it is 2.5 to 3.5%.

Cr sources in the deposited metal of this embodiment include metal Cr, Fe-Cr alloy, and Cr2O3 contained in the flux, and the amount of Cr in the deposited metal can be adjusted by adding any of them.

Mo: 1.5~3.0%

Molybdenum (Mo) has the effect of improving the strength and impact toughness of the deposited metal. If the Mo content is less than 1.5%, it is difficult to expect the above-described effect, whereas if it exceeds 3.0%, the toughness of the deposited metal is lowered.

Therefore, in this embodiment, it is preferable to limit the content of Mo to 1.5 to 3.0%. More preferably, it is 2.0 to 3.0%.

On the other hand, as the Mo source in the deposited metal of the present embodiment, there are metal Mo and Fe-Mo alloys contained in the flux, and the amount of Mo of the deposited metal can be adjusted by adding any of them.

Ti: 0.001~0.02%

Titanium (Ti) generates carbides or nitrides in the weld, and can act as a nucleation site when solidified at high temperatures. In addition, it serves to increase the strength of the weld by making the austenite grains smaller. Even if only 0.001% of Ti is added, it is due to the effect of improving the strength, so the minimum Ti content of the present invention is set to 0.001% or more. On the other hand, when the content exceeds 1.0%, the formation of carbides and nitrides is excessive, and the impact toughness tends to decrease rapidly and decrease.

Therefore, in this embodiment, it is preferable to limit the content of Ti to 0.001 to 0.02%. More preferably, it is 0.001 to 0.005%.

W+Nb+V: 1.0% or less

Niobium (Nb), tungsten (W), and vanadium (V) have the effect of improving the strength of the deposited metal. These alloys react with the carbon in the weld and can expect an effect of improving strength, but they cause a decrease in impact toughness. Therefore, in the present invention, it is preferable to limit the content of W+Nb+V to 1.0% or less. More preferably, it is 0.5% or less.

On the other hand, as the W+Nb+V source in the deposited metal of the present embodiment, an Fe-based alloy forming the shell, a TiO2 oxide contained in the flux, a Fe-Nb, Fe-W, Fe-V alloy, and the like.

B: 0.001~0.01% or less

Boron (B) can be expected to improve impact toughness by forming a Ti-B compound in an Fe-based alloy to refine crystal grains. However, controlling to less than 0.001% costs excessively, and even 0.001% can have a great influence on the impact toughness. On the other hand, when the content exceeds 0.01%, the impact toughness tends to decrease rapidly.

Therefore, the content of B is preferably limited to 0.001 ~ 0.005%.

TiO2+SiO2+ZrO2: 3.5~7.5%

In general, in the case of weldments, oxides such as the slag forming agents TiO2, SiO2, Al2O3, and ZrO2 are used at a level of 10 to 30% in the case of electron fine weldments. However, in the case of the welded product, it is somewhat unreasonable to subdivide the content of the total slag former to a level of less than half. Therefore, the slag composition was classified by the total content of TiO2+SiO2+ZrO2, which is a representative slag forming agent.If the content is less than 3.5%, the slag content is insufficient and the slag fluidity is poor, and if it exceeds 7.5%, the target chemical composition system is secured after welding. It's a bit difficult to do. In addition, the content of oxides in the weld zone is excessive, so that the impact toughness decreases.

The remaining component of the present invention is iron (Fe).

In addition to the above-described components, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in a typical manufacturing process, this cannot be excluded. Since these impurities are known to anyone of ordinary skill in the manufacturing process, all the contents are not specifically mentioned in the present specification.

The diameter of the flux-cored wire weldment is appropriately about 1.2 to 1.6mm, and the weight fraction of the outer shell is preferably 50 to 80% in terms of the total weight of the weldment considering the difference between the density of the outer shell and the density of the core.

This type of shell can be represented as a single shell structure surrounding the core of the alloy component.

Hereinafter, an experimental example will be described with reference to FIG. 3.

However, the composition of the outer shell and the composition of the outer shell of the flux-cored wire used in all experimental examples were the same, and only the content of the entire weld was different. The outer sheath of the weldment is composed of C: 0.01 to 0.3% by weight, Si: 1.0% or less, Mn: 1.5% or less, P+S 0.03% or less, and the remainder of Fe.

Flux Cored Arc Welding (FCAW) was performed on the weldments of each experimental example.

In the case of FCAW, welding was performed with a heat input of 17 kJ/cm under 100% CO2 conditions. The diameter of the wire for FCAW was 1.4 mm.

In the case of Experimental Examples 5 to 16 satisfying the alloy components of this example through the results of FIG. 3, excellent physical properties and welding workability were satisfied.

All position welding is possible by using the Fe-based flux cored wire that satisfies the alloy composition of the above-described weld material and the alloy composition of the outer shell surrounding the core, and the tensile strength and impact toughness of the weld joint (welded part) are great.

Hereinafter, a submerged arc wire weldment according to a second embodiment of the present invention will be described in detail.

2 is a table summarizing the chemical composition ratio for the weldment according to the first and second embodiments of the present invention, and FIG. 4 is an experimental table for the weldment according to the second embodiment of the present invention.

The weldment according to the second embodiment of the present invention is a weldment used for welding of a low Ni base material, and includes a submerged arc wire, a core constituting the submerged arc wire, or a welding bead. I can.

The weldment according to the second embodiment of the present invention relates particularly to a low Ni submerged arc wire weldment used when welding 9% Ni alloy steel.

In general, a 9% Ni steel-only submerged arc wire weldment has a large amount of alloys such as Ni, Mo, and W added, so the price of the product itself is high, making it unreasonable to be applied to the entire industry.

Accordingly, the present invention can provide a submerged arc wire weldment excellent in physical properties and weldability by applying the alloy content of an expensive material to a minimum compared to the prior art.

Hereinafter, a submerged arc wire weldment according to a second embodiment of the present invention will be described in detail.

In the submerged arc wire weldment, the deposited metal component obtained by submerged arc wire welding is in wt%, C: 0.35 to 0.55%, Si: 0.2 to 0.7%, Mn: 10.0 to 12.0%, Cr: 2.50 to 4.00%, Ni: 6.50 to 9.00%, Mo: 1.50 to 2.50%, the remaining components are Fe and inevitable impurities, and the inevitable impurities may be P: 0.015% or less, S: 0.005% or less.

The description of each component is as follows.

C: 0.35~0.55%

Carbon (C) is a strong austenite stabilizing element, and is a component that serves to improve strength and hardness. If the C content is less than 0.35%, austenite stabilization is unstable and it cannot be said that the effect of improving the strength is sufficiently obtained. On the other hand, when it exceeds 0.55%, there is a problem that high temperature cracking resistance and toughness are deteriorated. Therefore, in this embodiment, it is preferable to limit the content of C to 0.35 to 0.55%.

The C source of the deposited metal in this embodiment is C reduced from the alloy contained in the wire and the flux, the carbide contained in the flux, the CO2 gas in the atmosphere, and the slag component.

Si: 0.2~0.7%

Silicon (Si) is a component that improves deoxidation and weldability, and if its content is less than 0.2%, there is a problem that the deoxidation power is insufficient and the bead spreadability is deteriorated. There is a problem that lowers the low-temperature impact toughness by causing a problem and adversely affects the weld crack susceptibility. Therefore, in this embodiment, it is preferable to limit the content of Si to 0.2 to 0.7%.

The Si source of the deposited metal in this embodiment is Si reduced from a slag component such as metal Si and Fe-Si alloy contained in wire and flux, or SiO.

Mn: 10.0~12.0%

Manganese (Mn) is an austenite stabilizing element, and is a component that improves the flowability of slag to improve the bead shape and maintains the proper strength and toughness of the weld. In order to obtain the above-described effect, it is necessary to contain Mn in an amount of 10.0% or more, but if the content exceeds 12.0%, it is not preferable because it may cause a rapid decrease in toughness.

Therefore, in this embodiment, it is preferable to limit the content of Mn to 10.0 to 12.0%. More preferably, it is 10.0 to 12.0%.

On the other hand, as the Mn source in the deposited metal of this embodiment, there are metals Mn, Fe-Mn alloys, MnO2 and MnCO3 included in the wire and flux, and the amount of Mn of the deposited metal can be adjusted by adding any of them.

Cr: 2.50~4.00%

Although chromium (Cr) is a ferrite stabilizing element, it has the effect of improving the strength of the weld metal. If it is less than 2.50%, there is no effect, and if it exceeds 4.00%, chromium carbide is excessively formed, thereby reducing toughness.

Therefore, in this embodiment, it is preferable to limit the content of Cr to 2.50 to 4.00%.

Cr sources in the deposited metal of this embodiment include metal Cr, Fe-Cr alloy and Cr2O3 contained in wire and flux, and the amount of Cr in the deposited metal can be adjusted by adding any of them.

Ni: 6.50~9.00%,

Nickel (Ni) is an austenite stabilizing element, and is a component that plays a role in maintaining the proper strength and toughness of the weld. In order to obtain the above-described effect, it is necessary to contain Ni in an amount of 6.5% or more. However, when the content exceeds 9.00%, the strength decreases, which is not preferable.

Therefore, in this embodiment, it is preferable to limit the content of Ni to 6.5 to 9.00%. On the other hand, the Ni source in the deposited metal of this embodiment is metal Ni, Fe-Ni alloy, etc. contained in the wire and flux, and the amount of Ni in the deposited metal can be adjusted by adding any of them.

Mo: 1.50~2.50%

Molybdenum (Mo) has the effect of improving the strength and impact toughness of the deposited metal. If the Mo content is less than 1.50%, it is difficult to expect the above-described effect, whereas if it exceeds 2.50%, the toughness of the deposited metal is lowered.

Therefore, in this embodiment, it is preferable to limit the content of Mo to 1.50 to 2.50%. On the other hand, as the Mo source in the deposited metal of the present embodiment, there are metal Mo and Fe-Mo alloys contained in wire and flux, and the amount of Mo of the deposited metal can be adjusted by adding any of them.

P: less than 0.015%, S: less than 0.005%

P and S are one of the main elements that affect high-temperature cracking, and can cause high-temperature cracking by generating Ni alloys such as Ni3S7, NiS, and Ni3P, and low melting point compounds.

Therefore, P and S impurity control is essential, and by controlling the total content of P and S, it is possible to reduce the occurrence of high-temperature cracking. Therefore, it is preferable that P: less than 0.015% and S: less than 0.005%.

In addition to the above-described components, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in a typical manufacturing process, this cannot be excluded. Since these impurities are known to anyone of ordinary skill in the manufacturing process, all the contents are not specifically mentioned in the present specification.

Referring to FIG. 4, submerged arc welding was performed on the weldments of each experimental example. In the case of Experimental Examples 2 to 9 and Experimental Example 12 satisfying the alloy components of this example through the results of FIG. 4, excellent physical properties and welding workability are satisfied.

By using a low-Ni submerged arc wire weldment that satisfies the above-described alloy composition of the weldment, the physical properties and weldability of the weld joint are excellent.

In the above, the present invention has been described based on the embodiments of the present invention, but this is only an example and does not limit the present invention, and those of ordinary skill in the field to which the present invention pertains will not depart from the essential technical content of the present embodiment. It will be appreciated that various combinations or modifications and applications not illustrated in the embodiments are possible in the range. Accordingly, technical contents related to modifications and applications that can be easily derived from the embodiments of the present invention should be interpreted as being included in the present invention.

1: Ship CT: Liquefied gas storage tank
ES: Engine system ER: Engine room
EC: Engine casing F: Stack
DH: Deck House

Claims (7)

In the liquefied gas storage tank containing a weldment used for welding low Ni base materials,
The weldment is an alloy steel in which iron (Fe) is mixed with other elements,
Based on 100% by weight of the weldment, the other elements are,
Manganese (Mn): 10-12%, nickel (Ni): 6.5-9.0%, chromium (Cr): 2.5-4.0%, molybdenum (Mo): liquefaction characterized by having a weld containing 1.5-2.5% Gas storage tank. The method of claim 1,
The welded material is a liquefied gas storage tank, characterized in that it further comprises a carbon (C): 0.35 ~ 0.55%. The method of claim 1,
The welded material is silicon (Si): liquefied gas storage tank, characterized in that it further comprises 0.2 to 0.7%. The method of claim 1,
The welded material is boron (B): liquefied gas storage tank, characterized in that it further comprises 0.001% to 0.1%. The method of claim 1,
The welded material is titanium (Ti): liquefied gas storage tank, characterized in that it further comprises 0.001% to 1%. The method of claim 1,
The welding material is a liquefied gas storage tank, characterized in that it comprises a submerged arc wire (Submerged Arc Wire), a core constituting the submerged arc wire or welding beads. A ship, characterized in that the liquefied gas storage tank according to any one of claims 1 to 6 is mounted.

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