KR102297292B1 - Weldments and liquefied gas storage tank applied thereof - Google Patents

Abstract

The present invention relates to a liquefied gas storage tank and a ship, wherein the liquefied gas storage tank of the present invention is a liquefied gas storage tank including a weldment used for welding a Ni alloy steel base material, wherein the weldment is, in weight%, carbon (C): 0.025 to 0.2%, silicon (Si): 0.2 to 1%, manganese (Mn): 7% or less, nickel (Ni): 10 to 20%, chromium (Cr): 15 to 20%, molybdenum ( Mo): 2 to 5%, nitrogen (N): characterized in that it contains 0.05 to 0.17%.

Description

Weldment and liquefied gas storage tank to which it is applied

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

According to continuous industrialization and technological development, the use of storage refrigerants from -80°C to -196°C is increasing. Accordingly, 2~9% Ni alloy steel, Invar, austenitic stainless steel, Al, etc.

In particular, 9% Ni steel base material is used for LNG fuel tanks. At the current level, weldments containing more than 60% Ni are used, and 'Inconel 718' or 'Inconel 625' is mainly used. Although these materials have excellent high strength and cryogenic toughness, they have very high high temperature cracking susceptibility, and are expensive materials due to their high Ni content.

Although these materials have excellent high strength and cryogenic toughness, they have very high high temperature cracking susceptibility, and are expensive materials due to their high Ni content, so there is a problem in their limited use in the industry.

In addition, since most of these conventional Ni-based weldments are constructed by SMAW (Shielded Metal Arc Welding), there is a problem in that production efficiency is extremely low and high efficiency of welding construction is required.

In addition, high manganese steel has been developed as a new material for cryogenic steel, but there is a lot of fume and spatter, so it has excellent high strength and cryogenic toughness.

Accordingly, there is a need for research and development on Ni-based weldments having excellent economical efficiency by reducing the Ni content, and having excellent high strength, high toughness, high temperature cracking susceptibility and weldability.

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 reduce the Ni content in a weld used for welding of a Ni alloy steel base material, thereby having excellent economic efficiency, high strength, high toughness, and high temperature cracking susceptibility And to provide excellent weldability, a liquefied gas storage tank and a vessel in which the alloy composition of the Ni-based weldment is optimized.

The liquefied gas storage tank according to an aspect of the present invention is a liquefied gas storage tank comprising a weldment used for welding of a 2-9% Ni alloy steel base material, wherein the weldment is, in weight%, carbon (C): 0.025 ~0.2%, Silicon (Si): 0.2~1%, Manganese (Mn): 7% or less, Nickel (Ni): 10~20%, Chromium (Cr): 15~20%, Molybdenum (Mo): 2~ 5%, nitrogen (N): characterized in that it contains 0.05-0.17%.

Specifically, the weldment may further include tungsten (W): 1% or less.

Specifically, the weldment may further include niobium (Nb): 1% or less.

Specifically, the weldment may further include copper (Cu): 1% or less.

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

Specifically, the weldment may satisfy the relation 0.12 ≤ C + N ≤ 0.33.

Specifically, the weldment has an austenite single-phase structure, and may satisfy the relationships _{17≤Cr eq} ≤24 and 18≤Ni _{eq ≤28, where Cr eq} (Cr equivalent) = Cr+Mo+1.5Si +0.5Nb, and may be Nieq(Ni equivalent)=Ni+30C+0.5Mn+25N.

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

The liquefied gas storage tank and the ship 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 2 to 9% Ni alloy steel base material, It has the effect of minimizing the occurrence of cracks while exhibiting good weldability.

In addition, it is possible to secure price competitiveness in liquefied gas storage tanks and ships due to excellent economic feasibility by reducing the Ni content of the weldment.

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 an embodiment of the present invention.
3 is an experimental table for a weldment according to an embodiment of the present invention.
4 is a graph showing the relationship between tensile strength and impact toughness according to C and N contents of a weldment according to an embodiment of the present invention.
5 is a phase prediction Schaeffler-diagram of a weldment according to an embodiment of the present invention.

The objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and preferred embodiments taken in conjunction with the accompanying drawings. In the present specification, in adding reference numbers to the components of each drawing, it should be noted that only the same components are given the same number as possible even though they are indicated on different drawings. In addition, in describing the present invention, if 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) for accommodating liquefied gas, an engine room (ER) in which an engine system (ES) is located, and an engine room (ER). ) may include an engine casing (EC), a stack (F) and a deck house (DH) located on the.

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 line 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 where the vessel 1 is 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) for example. In addition, liquefied gas may be used as a term encompassing both a liquid state, a natural vaporized or forced vaporized state, and the like.

An engine room ER in which the engine system ES is placed is provided on the stern side of the ship 1 , and the engine system ES placed in the engine room ER is an engine (not shown) that provides propulsion power of the ship 1 . city) may be included. Although not specifically shown, the engine is connected to the propeller through the shaft, consumes fuel and generates rotational force to rotate the propeller, so that the wake generated according to the rotation of the propeller moves the ship 1 forward. .

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

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

The deck house (DH) is located in the upper part of the hull, and various living facilities for the crew's inboard residence and various navigation facilities for the navigation 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 in the ship, or a liquefied gas storage tank in/outboard to use liquefied gas as fuel. It can include ships mounted thereon, and further, it can include all offshore structures having liquefied gas storage tanks in addition to general commercial ships that transport cargo.

2 is a table summarizing the chemical composition ratio of a weldment according to an embodiment of the present invention, FIG. 3 is an experimental table for a weldment according to an embodiment of the present invention, and FIG. 4 is an embodiment of the present invention It is a graph showing the relationship between tensile strength and impact toughness according to the C and N contents of the welded material, and FIG. 5 is a Schaeffler-diagram of the phase prediction of the weldment according to an embodiment of the present invention.

A weldment according to an embodiment of the present invention is a weldment used for welding a 2-9% Ni alloy steel base material, and includes a flux-cored wire, a flux or a weld bead constituting the flux-cored wire. Or, submerged arc wire (Submerged Arc Wire), may include a core or weld bead constituting the submerged arc wire.

A weldment according to an embodiment of the present invention relates to a weldment used when welding 2 to 9% Ni alloy steel.

In general, weldments dedicated to 2-9% Ni alloy steel use a Ni core and Mo sheath. Weldings using a Ni core and Mo shell are difficult to apply widely throughout the industry because of the high price of the product itself as a large amount of expensive alloys such as Ni, Mo and W are added.

Therefore, the present invention can provide a weldment excellent in physical properties and weldability while minimizing the alloy content of expensive materials compared to the prior art.

Hereinafter, in a liquefied gas storage tank (CT) including a weld of a 2 to 9% Ni alloy steel base material according to an embodiment of the present invention, a weldment used when welding a weld of 2 to 9% Ni alloy steel alloy steel in detail Explain.

In an embodiment of the present invention, flux-cored arc welding (FCAW) was performed on the weldment, and welding was performed on a 9Ni steel base material with a heat input of 13kJ/cm under _{100% CO 2 condition, and the wire diameter} For silver, 1.2 mm was used.

As shown in FIG. 2, the weld metal component obtained by welding is C: 0.025 to 0.2%, Si: 0.2 to 1%, Mn: 7% or less, Ni: 10 to 20%, Cr: 15-20%, Mo: 2-5%, N: 0.05-0.17%.

In addition, the weldment, W: 1% or less, Nb: 1% or less, Cu: 1% or less, or Ti: 1% or less by weight % of the weld metal component obtained by welding may further include. Each of these welding metal components can be obtained through an experimental table (refer to FIG. 3) for the weld.

In addition, the weldment can optimize the tensile strength and impact toughness according to the C and N content of the weldment, and the relational expression 0.12 ≤ C + N ≤ 0.33 is satisfied. This can be seen through the experimental table of FIG. 3 and the graph showing the relationship between tensile strength and impact toughness according to the C and N contents of the welded product of FIG. 4 .

In addition, the weldment has an austenite single-phase structure and satisfies the relational expressions of _{17≤Cr eq} ≤24 and 18≤Ni _{eq ≤28.}

In the above, Cr _eq (Cr equivalent)=Cr+Mo+1.5Si+0.5Nb, and Ni _eq (Ni equivalent)=Ni+30C+0.5Mn+25N.

This can be seen through the experimental table of FIG. 3 and the phase prediction Schaeffler-diagram of the weldment of FIG. 5 .

The yield strength of the weld joint using the welded product obtained in the above composition ratio is 400 MPa or more, the tensile strength is 600 MPa or more, the elongation is 25% or more, and the impact toughness can satisfy 27J or more at -196°C.

As described above, the weldment of the present invention uses austenitic stainless steel having excellent cryogenic toughness and weldability to replace the existing Ni content of 60% or more with a Ni level of 20% or less, so that it can have excellent economic feasibility and high temperature Crack susceptibility is also significantly improved, and excellent weldability can be obtained.

In addition, while austenitic stainless steel generally has excellent cryogenic toughness, its strength is lower than 150 MPa compared to 2 to 9Ni steel, making it difficult to apply. and excellent weldability.

The description of each component constituting the weldment of the present invention is as follows.

C: 0.025~0.2%

Carbon (C) is a strong austenite stabilizing element, and is a component that improves strength and hardness. If the content of C is less than 0.025%, austenite stabilization is unstable, and the effect of improving strength cannot be sufficiently obtained. On the other hand, when it exceeds 0.2%, there is a problem in that the high-temperature cracking resistance and toughness are lowered, and the occurrence of spatter increases.

Therefore, in this embodiment, it is preferable to limit the content of C to 0.025 to 0.2%.

In this embodiment, as the C source of the deposited metal, metal carbides such as Mn-C, Cr-C, WC included in the wire and flux, CO ₂ gas in the shielding gas, and C may be reduced from the slag component.

Si: 0.2~1%

Silicon (Si) is a component that improves the deoxidation action and weldability. When the content is less than 0.2%, there is a problem in that the deoxidation power is insufficient and the bead spreadability is lowered. On the other hand, when the content exceeds 1%, segregation in the weld zone This causes low-temperature impact toughness and adversely affects welding crack susceptibility.

Therefore, in this embodiment, it is preferable to limit the Si content to 0.2 to 1%.

As the Si source of the deposited metal in this embodiment, it may be metal Si and Fe-Si alloy included in the wire and flux, or Si reduced from slag components such as SiO.

Mn: 7% or less

Manganese (Mn) is an austenite stabilizing element, and is a component that improves slag fluidity to improve a bead shape and maintains proper strength and toughness of a weld. In order to obtain the above-described effect, if it exceeds 7%, a sharp decrease in toughness may be caused, and a lot of welding fumes are generated to deteriorate weldability, which is not preferable.

Therefore, in this embodiment, it is preferable to limit the Mn content to 7% or less.

On the other hand, as the Mn source of the deposited metal in this embodiment, the metal Mn, Fe-Mn alloy, MnO ₂ and MnCO ₃ included in the wire and flux may be used, and the amount of Mn of the deposited metal can be adjusted by adding any of them. have

Ni: 10-20%

Nickel (Ni) is an austenite stabilizing element and serves to maintain proper strength and toughness of the weld zone. In order to obtain the above-described effect, it is necessary to contain Ni in an amount of 10% or more. However, when the content exceeds 20%, the strength is lowered, which is not preferable.

Therefore, in this embodiment, it is preferable to limit the content of Ni to 10 to 20%.

On the other hand, as the Ni source of the weld metal in this embodiment, it may be a metal Ni, Fe-Ni alloy, etc. included in the wire and flux, and the amount of Ni in the weld metal can be adjusted by adding any of them.

Cr: 15-20%

Chromium (Cr) as a ferrite stabilizing element has the effect of improving the strength of the weld metal. If it is less than 15%, there is no effect, and if it exceeds 20%, chromium carbide is excessively formed and there is a problem in that toughness is lowered.

Therefore, in this embodiment, it is preferable to limit the content of Cr to 15 to 20%.

On the other hand, the Cr source in the deposited metal of this embodiment may be metal Cr, Fe-Cr alloy, Cr2O3, etc. contained in wire and flux, and the amount of Cr of the deposited metal can be adjusted by adding any of them.

Mo: 2-5%

Molybdenum (Mo) has the effect of improving the strength and impact toughness of the deposited metal. If the content of Mo is less than 2%, it is difficult to expect the above-described effect, whereas if it exceeds 5%, the toughness of the deposited metal is deteriorated.

Therefore, in this embodiment, it is preferable to limit the content of Mo to 2 to 5%.

On the other hand, the Mo source in the weld metal of this embodiment may be a metal Mo and Fe-Mo alloy included in the wire and flux, and the amount of Mo in the weld metal can be adjusted by adding any of them.

N: 0.05 to 0.17%

Nitrogen (N) is a strong austenite stabilizing element, and has an effect of improving the strength of the deposited metal due to its solid solution effect. In addition, compared to other reinforcing elements, the reduction rate of impact toughness is small, so it is widely applied as a reinforcing element in the stainless alloy system.

If the nitrogen content is less than 0.05%, it is difficult to expect the above-described effects, whereas if it exceeds 0.17%, many defects such as pores are generated in the deposited metal, and the toughness of the deposited metal is reduced.

Therefore, in this embodiment, it is preferable to limit the N content to 0.05-0.17%.

W: 1% or less

Tungsten (W) has the effect of improving the strength of the deposited metal. Such W reacts with carbon at the weld and can be expected to have an effect of improving strength, but it causes a decrease in impact toughness.

Therefore, in the present invention, it is preferable to limit the content of W to 1% or less.

On the other hand, as the W source in the deposited metal of this embodiment, TiO ₂ oxide, Fe-Nb, Fe-W, Fe-V alloy, etc. contained in the wire and flux may be.

Nb: 1% or less

Niobium (Nb) has the effect of improving the strength of the deposited metal. Such Nb reacts with carbon at the weld and can be expected to have an effect of improving strength, but it causes a decrease in impact toughness and a decrease in high-temperature cracking resistance.

Therefore, in the present invention, it is preferable to limit the content of Nb to 1% or less.

Meanwhile, as the Nb source in the deposited metal of the present embodiment, TiO ₂ oxide, Fe-Nb, Fe-W, Fe-V alloy, etc. contained in the wire and flux may be used.

Cu: 1% or less

Copper (Cu) is an austenite stabilizing element and serves to maintain proper strength and toughness of the weld. In case of excessive addition, corrosion resistance and hot workability are deteriorated.

Therefore, in this embodiment, it is preferable to limit the Cu content to 1% or less.

Ti: 1% or less

Titanium (Ti) may act as a nucleation site when solidifying at a high temperature by generating carbide or nitride in the weld. It also serves to increase the strength of the weld by making the austenite grains smaller.

Therefore, in this embodiment, it is preferable to limit the content of Ti to 1%.

In addition to the above-mentioned components, since unintended impurities from raw materials or the surrounding environment may be unavoidably mixed in a typical manufacturing process, they cannot be excluded. Since these impurities are known to anyone skilled in the art of manufacturing processes, all details thereof are not specifically mentioned in the present specification.

As such, in this embodiment, by optimizing the alloy composition of the weldment used for welding of the 2 to 9% Ni alloy steel base material, it has excellent physical properties and is capable of electro-fine welding, which has an effect of excellent workability, and cracks while exhibiting good weldability. It has the effect of minimizing the occurrence.

In addition, it is possible to secure price competitiveness in liquefied gas storage tanks and ships due to excellent economic feasibility by reducing the Ni content of the weldment.

In the above, the present invention has been described focusing on the embodiments of the present invention, but this is only an example and does not limit the present invention. It will be appreciated that various combinations or modifications and applications not illustrated in the embodiments are possible within the scope. Accordingly, descriptions related to variations 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 (8)

In the weldment used for flux cored arc welding or submerged arc welding of a Ni alloy steel base material,
The weldment is one in which iron (Fe) is mixed with other elements, and has an austenite single-phase structure,
Based on 100% by weight of the weldment, the other elements are
Carbon (C): 0.025 to 0.2%, Silicon (Si): 0.2 to 1%, Manganese (Mn): 7% or less, Nickel (Ni): 10 to 20%, Chromium (Cr): 15 to 20%, Molybdenum (Mo): 2-5%, Nitrogen (N): Welding characterized in that it contains 0.05-0.17%. The method of claim 1,
The weldment further comprises tungsten (W): 1% or less. The method of claim 1,
The weldment further comprises niobium (Nb): 1% or less. The method of claim 1,
The weldment further comprises copper (Cu): 1% or less. The method of claim 1,
The weldment further comprises titanium (Ti): 1% or less. The method of claim 1,
The weldment, characterized in that it satisfies the relation 0.12 ≤ C + N ≤ 0.33. The method of claim 1,
The weldment, characterized in that 17≤Cr _eq ≤24, 18≤Ni _eq ≤28 relational expressions are satisfied.
above,
Cr _eq (Cr equivalent) = Cr+Mo+1.5Si+0.5Nb,
Ni _eq (Ni equivalent) = Ni + 30C + 0.5Mn + 25N. delete

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