KR20050108692A - Membrane metal panel for a cargo tank of lng carrier developed to increases the durability and welding productivity - Google Patents

Abstract

The present invention relates to a membrane metal panel of an insulation tank for LNG carriers with excellent durability and welding workability, the object of which is the moldability and weldability of the membrane metal panel of austenitic STS, and excellent durability and low welding cost It is to provide the shape of the membrane metal panel.

The present invention is a membrane metal having a plurality of corrugation intersections by transverse / longitudinal folds, wherein both sides of the bent portion are connected to the flat portion by the connecting portion and the trunk portion is raised in one direction, and the finishing portion is connected to the end of the trunk portion. In the panel; The corrugated intersection portion of the membrane metal panel is composed of two transverse corrugations and two longitudinal corrugations parallel to each other, and the four transverse and longitudinal corrugations are formed at an angle of 90 ° to each other and do not cross each other. Wherein each of the formed pleat ends is formed at an angle of 90 ° to face the middle of another adjacent pleat formed, while the two parallel transverse folds and the two longitudinal folds are not located in line with each other. The radius (lower curvature radius) of the connecting portion and the radius (upper curvature radius) of the bent portion (R2 / R1) are 0.25 or less, and the bent portion has a width of 30 mm to 75 mm.

Description

Membrane Metal Panel for a Cargo Tank of LNG Carrier developed to Increases the Durability and Welding Productivity}

The present invention relates to a membrane metal panel of an insulation tank for LNG carriers with excellent durability and welding workability, stress level and curved welding under operating conditions through optimization of the corrugation shape and arrangement of the membrane metal panel produced through the forming process Membrane metal panel of LNG carrier insulation tank which can reduce the production cost while improving the durability of primary barrier of insulation tank by minimizing the length.

LNG is a cryogenic liquid with a boiling point of -162 ° C under atmospheric pressure and is transported and stored in a multi-layered insulated tank. The membrane metal panel, which is the primary barrier of the multi-structured insulation tank, is made of a material having low temperature brittleness and is designed and manufactured to easily expand and contract in response to changes in temperature and load of LNG. The tank for safely transporting and storing the cryogenic LNG at minus 162 ° C. is made of an inner tank made of a membrane metal panel, and the side plate is made of carbon steel, and a heat insulating material is inserted therebetween to generate vaporized gas due to the heat of infiltration from the outside of the tank. Since the membrane metal panel is in direct contact with LNG in a cryogenic state of minus 162 ° C., low temperature brittleness such as austenitic STS, Invar, 9% nickel steel, etc. can be used to cope with the stress change due to the temperature difference. Metal of less material is used, and it is divided into forming and bending according to the manufacturing method.

Conventionally, bent membrane metal panels applied to LNG carriers have two different sizes at 340 mm intervals to facilitate expansion and contraction of rectangular unit metal panels of approximately 3000 mm × 1000 mm (width × length) as shown in FIG. 2. The corrugations of the dogs are crossed to form the entire metal panel. In this case, considering that about 40% of the insulation tank manufacturing work is used for the welding of the primary barrier of the insulation tank, that is, the metal panel, the increase of the curved welding field due to the number of corrugations decreases the welding speed and decreases the welding quality. By doing so, there is a problem such as increasing the economic burden due to the increase in manufacturing cost.

Conventional molded membrane metal panels are designed to absorb stress due to LNG thermal load by arranging a plurality of corrugations that cross or cross each other in the same way as the bent membrane metal panels as shown in FIGS. 3 to 7. However, it is very difficult to consider the shape designed in consideration of the deterioration of the mechanical properties of the base material which may occur during the shape of the appropriate wrinkles and molding process. That is, in the case of a molded-type membrane metal panel using austenitic STS, the plastic strain induced during molding should be controlled to 0.3 or less to prevent the fracture toughness and brittle fracture caused by the organic martensite transformation of the base material. to be. In addition, the maximum thermal stress acting on the metal panel by the LNG temperature difference is defined by the stress concentration effect of the corrugation intersection according to the corrugation arrangement shape and the average stress level according to the unit corrugation shape. Therefore, in order to efficiently control the thermal stress level applied to the metal panel, a wrinkle arrangement method using optimized unit wrinkles should be selected. However, in the case of the conventional molded membrane metal panel, it is difficult to apply to the LNG carrier because the above-described evaluation of the formability and the corrugated shape design for thermal stress control is not properly made.

The present invention is designed to improve the above problems, the object of which is to improve the formability, weldability and durability of the membrane metal panel made of austenitic STS, to provide a shape of the membrane metal panel which can reduce the welding cost will be.

Figure 1 shows an exemplary view showing a configuration of a membrane metal panel according to the present invention, the present invention is formed in a plurality of transverse corrugations 10 formed in parallel with each other, perpendicular to the transverse corrugations (10) In the membrane metal panel 100 consisting of a plurality of longitudinal wrinkles 20 and parallel to each other, and the planar portion 30 formed by protruding the transverse / longitudinal wrinkles in one direction, the transverse wrinkles 10 and The longitudinal pleats 20 are not intersected with each other, but are formed to form 90 ° to each other, and the ends thereof are formed to face the middle of the adjacent pleats. That is, the corrugation intersection 40 formed in the membrane metal panel 100 of the present invention is composed of two transverse corrugations and two longitudinal corrugations, and the two transverse and longitudinal corrugations are not positioned in a straight line. Formed parallel to each other, the ends of the transverse corrugations being formed toward the middle of the neighboring longitudinal corrugations (corresponding to 90 °), the ends of the longitudinal corrugations being further transverse to the adjoining (corrugated 90 °) It is formed to face the middle of the wrinkles.

The present invention formed as described above is provided with pinwheels formed by four corrugations, and when the vane shape is continuously formed, as shown in FIG. 22, it may be expressed in a pattern pattern.

The lateral and longitudinal folds 10 and 20 are formed to protrude in one direction from the planar portion 30 of the membrane metal panel, and the pleated body portions 11 and 21 are raised to a certain height, and the pleated body portion. (11,21) consists of a wrinkle finishing portion (12,22) connected to the end.

The wrinkle closing portion 12, 22 is one side is connected to the corrugated body portion (11, 21) and the other end is connected to the flat portion 30, the connection portion with the flat portion 30 when viewed in a plane, fan-shaped It has an ellipse and a radially wide shape.

As shown in FIG. 10, the corrugated body portions 11 and 21 have two connecting portions 11a and 21a having a predetermined radius of curvature (lower radius of curvature) from the flat portion, and the two connecting portions 11a and 21a. It is composed of bent portions (11b, 21b) integrally formed in the) and forming a predetermined radius of curvature (upper curvature radius). That is, the corrugated trunk portions 11 and 21 have connecting portions 11a and 21a connected to the flat portion 30 on both sides of the curved portions 11b and 21b.

In addition, the wrinkles body portion (11, 21) is selectively connected to both ends or one end of the wrinkles (12, 22). That is, when the corrugated body parts 11 and 21 are positioned in the membrane metal panel, both ends of the corrugated body parts 11 and 21 are connected to the flat part 30 by the wrinkle finishing parts 12 and 22, When one end of the corrugated body portion is connected to the side of the membrane metal panel, only one end positioned in the membrane metal panel is connected to the flat portion by the wrinkle finish portion.

In addition, the bends (11b, 21b) has a width of 30mm to 75mm, the radius of curvature of the connecting portion (hereinafter referred to as the "curvature radius", R2) and the radius of curvature of the bends (11b, 21b) (hereinafter ' The ratio of the upper curvature radius' R1) is made to be 0.25 or less. That is, when the width of the bent portion is formed to be less than 30mm, the stress acting on the unit wrinkles is large, and when the width of the bent portion exceeds 75mm, the area acting the pressure due to the weight of the cargo (LNG) As a result, the mechanical stress is increased.

In addition, as the ratio of the radius of curvature of the wrinkles increases, the size of the plastic strain also increases, and the critical plastic strain that causes the organic martensite transformation in the austenitic STS is 0.3. The fracture toughness due to the generated organic martensite transformation is lowered, thereby reducing the durability. The present invention considers such a plastic strain, limiting the ratio of the lower and upper curvature radius (R2 / R1) to 0.25 or less, due to the reduction in durability of the end of the wrinkles to the thickness reduction during the molding process and the molding organic martensite transformation It is to prevent the degradation of toughness.

Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1

Corrugated Shape Design Analysis

FIG. 8 illustrates an analysis result of stress behavior according to a change in bend width when a heat load (temperature difference = 190 ° C.) by LNG is applied to unit wrinkles of the austenitic STS membrane metal panel of FIG. 9. As the width L _C1 of the bent portion increases as shown in FIG. 8, the stress acting on the unit wrinkles decreases, and thus the bend width that optimizes thermal stress and mechanical stress can be obtained. In addition, the bend width proposed in the present invention is applicable to unit wrinkles defined by three or more different radii of curvature as shown in FIG. 11. From the above results, in order to reduce the stress acting on the unit corrugation compared with the conventional bent membrane metal panel, the width L _{C1 of the} bent portion should be designed to be at least 30 mm. In addition, as shown in FIG. 8, when the width L _C1 of the bend portion exceeds 75 mm, the thermal stress control effect, that is, the thermal stress reduction rate is drastically reduced, and the area where the pressure caused by the weight of the cargo LNG acts. This increases the mechanical stress on the pleat end. Therefore, it can be seen that the wrinkle bending portion width L _C1 of the metal panel manufactured through the molding process is designed to be at least 30 mm and at most 75 mm in terms of durability.

Example 2

Analysis of the Distribution of Thickness Reduction in Wrinkles

FIG. 12 is a graph showing an analysis result of the distribution of thickness reductions occurring in the wrinkles during the molding of the unit wrinkles having the upper radius of curvature R1 of 30 mm and the lower radius of curvature R2 of 10 mm. It can be seen that the reduction rate occurs at the wrinkle finish.

This is because the inflow of the base material into the molding portion at the end of the wrinkles is limited. However, as shown in FIG. 13, the change in the thickness reduction rate according to the unit wrinkle shape, that is, the ratio of the lower and upper radius of curvature of the wrinkles (R2 / R1) is insignificant. This means that it is possible to prevent local stress due to stress concentration or to apply a stress mitigation method by increasing the thickness of the metal panel. In the present invention, the wrinkle shape is optimized, that is, the stress through the optimization of the bend width L _C1 . The stress relief method of the concentrated part is applied.

Example 3

Distribution of Plastic Strain

FIG. 14 shows a unit having an upper curvature radius R1 of 30 mm and a lower curvature radius R2 of 10 mm in which the ratio of the radius of curvature R2 / R1 of the upper curvature radius R1 and the lower curvature radius R2 is greater than 0.25. The distribution of the plastic strain occurring in the wrinkles during the molding operation of the wrinkles is shown. As shown in FIG. 14, the maximum plastic strain during molding of the unit wrinkles is generated in an area where the unit wrinkles and the planar portion intersect, that is, the finish portion, and the maximum plastic strain is a critical plastic strain that causes organic martensite transformation in the austenitic STS. It exceeds 0.3. This can be seen that when manufacturing a metal panel having an inappropriate wrinkle shape by using the molding process can be reduced durability by the fracture toughness due to the organic martensite transformation occurs in the wrinkle portion. FIG. 15 illustrates the distribution of plastic strain according to the radius of curvature of the lower portion R2 and the upper portion R1 of the unit pleats. As shown in FIG. 15, the size of the plastic strain increases as the ratio of the radius of curvature of the pleats increases. Able to know.

Therefore, the present invention limited the upper radius of curvature (R1) of the unit wrinkles 60 to 75 mm, the ratio of R2 / R1 to 0.25 or less in consideration of the formability and the absorption capacity to the thermal stress, and by this limitation in the molding process It is possible to prevent the decrease in the durability of the wrinkle end and the toughness due to the molded organic martensitic transformation against the thickness reduction.

Example 4

Thermal stress

16 to 18 show the unit corrugation cross-sectional area of the membrane metal panel of the conventional insulation tank for LNG storage and the corrugation shape of the present invention, and FIGS. 19 to 21 are the same when the temperature difference due to LNG is 190 ° C., 16 illustrates the thermal stress distribution generated in the metal panels of FIGS. In this case, in the case of the bent membrane metal panel of FIG. 16, the interval of the wrinkle intersection is 340 mm, while the interval of the wrinkle intersection in the membrane metal panel of the present invention is about 1 times 4 times larger. However, when the thermal load due to the temperature difference of 190 ℃ acts as shown in Figs. 19 to 21, the thermal stress is the bent membrane metal panel, the T-shaped membrane metal panel known by the conventional KR1999-29326, and the membrane of the present invention. It can be seen that in order of the metal panel decreases.

This means that the ability to absorb thermal stress in the corrugated shape of the metal panel of the present invention is very excellent. In addition, when comparing the bent membrane metal panel of FIG. 16 and the metal panel of the present invention, the interval of the corrugation intersection is increased by four times or more, so that the length of the curved welding field is also reduced by four times or more, so that the primary barrier of the thermal insulation tank When welding between metal panels, the length of the curved welds is reduced, thereby reducing the manufacturing cost of the insulation tank.

Example 5

Plastic Strain Analysis According to the Number of Intersections

Figure 1 is an exemplary view showing the configuration of the membrane metal panel according to the present invention, Figure 23 shows the evaluation results for the plastic strain according to the number of each corrugation intersection, longitudinal wrinkles of the unit corrugation at the corrugation intersection The spacing Lc is 340 mm, the spacing Ls of the pleat intersection is 1345 mm, the bend radius (upper curvature radius, R1) of the unit pleats is 60 mm, the ratio of the upper and lower curvature radii, R2 / R1 is 0.25. .

As shown in FIG. 23, as the number of wrinkled intersections increases, the increase in plastic strain acting on the wrinkled intersections is very small up to four.

This is because when the number of corrugation intersections exceeds four, that is, the inflow of the base material into the corrugations during molding is limited on three sides. That is, it can be seen that the metal panel having the pleated intersection of the present invention should be manufactured so that the three sides of the intersection are not adjacent.

FIG. 24 illustrates stress levels acting on the austenitic STS membrane metal panel having two surfaces symmetrical at the intersections of the corrugations proposed through the molding process analysis when the temperature difference is 190 ° C. As shown in FIG. 24. It can be seen that the thermal stress acting on the unit metal panel is the same as the case where the number of corrugation intersections of FIG. 19 is one.

The present invention is not limited to the above-described specific preferred embodiments, and various modifications can be made by those skilled in the art without departing from the gist of the present invention as claimed in the claims. Such changes are intended to fall within the scope of the claims.

As described above, the present invention improves the safety through the control of the plastic strain and the thickness reduction rate during the fabrication of the austenitic STS membrane metal panel manufactured through the molding process, and the durability through the control of the thermal stress level due to the LNG temperature change. In the case of connecting welding between unit metal panels, it is possible to reduce the length of the curved welding field to secure the integrity of the welded part and to reduce the time and cost of manufacturing the insulation tank.

1 is an exemplary view showing a configuration of a membrane metal panel according to the present invention

2 is a perspective view of a conventional bent austenitic membrane metal panel

Figure 3 is a perspective view of the membrane metal panel of the prior art (special forces 50-21008)

Figure 4 is a perspective view of the membrane metal panel of the prior art (special forces 60-14959)

Figure 5 is a perspective view of the membrane metal panel of the prior art (special forces 60-32079)

6 is a perspective view of a membrane metal panel of the prior art (KR1994-11802)

7 is a perspective view of a conventional membrane metal panel (KR1994-11804)

8 is an exemplary view showing the thermal stress behavior according to the change in the width of the bent portion of the present invention

9 is a unit wrinkle shape diagram for thermal stress evaluation of the present invention

10 is an exemplary view showing the shape of the unit wrinkles of the present invention

11 is an exemplary view showing a pleat with three different radii of curvature in the prior art.

Figure 12 is an exemplary view showing the distribution of the thickness reduction rate during the wrinkle forming process of the present invention

13 is an exemplary view showing a change in the maximum thickness reduction rate according to the ratio of the upper curvature radius and the lower and upper curvature radius of the unit wrinkles in the wrinkle forming process of the present invention

Figure 14 is an exemplary view showing the distribution of plastic strain during the wrinkle molding process of the present invention

15 is an exemplary view showing a change in plastic strain according to the ratio of the upper curvature radius and the lower and upper curvature radius of the unit wrinkles in the wrinkle forming process

16 is a perspective view of unit wrinkles of a conventional bent membrane metal panel

17 is a perspective view of unit wrinkles of a conventional T-shaped membrane metal panel

18 is a perspective view of the unit wrinkles of the membrane metal panel of the present invention

19 is an exemplary view showing the thermal stress distribution in the unit wrinkles of the conventional bent membrane metal panel

20 is an exemplary view showing a thermal stress distribution in the unit wrinkles of conventional T-shaped membrane metal panel

21 is an exemplary view showing the thermal stress distribution in the unit wrinkles of the membrane metal panel of the present invention

22 is an exemplary view of a membrane metal panel according to another embodiment of the present invention.

23 is an exemplary view showing the behavior of the maximum plastic strain according to the number of unit wrinkles in the molding process of the present invention

24 is an exemplary view showing a thermal stress distribution when the number of corrugation intersections of the unit membrane metal panel of the present invention is four;

* Explanation of symbols for main parts of the drawings

(10): transverse wrinkles (20): longitudinal wrinkles

(11,21): wrinkled body portion (12,22): wrinkled part

(11a, 21a): Bends (11b, 21b): Connections

30: flat portion 40: corrugated cross section

(Lc): Lateral / Longer Crease Spacing (Ls): Crease Intersection Spacing

(L): Unit molded metal panel length (Ｗ): Unit molded metal panel width

(R1): radius of curvature (upper curvature) (R2): radius of coupling part (lower curvature)

(L _C1 ): Bend Width

Claims (4)

In the membrane metal panel having a plurality of corrugation intersections by the transverse / longitudinal corrugation consisting of a body portion, both sides of the bent portion is connected to the flat portion by the connecting portion and raised in one direction, and the finishing portion connected to the end of the body portion ; Wrinkle crossing portion of the membrane metal panel, Consisting of two transverse folds and two longitudinal folds parallel to each other, The four transverse / longitudinal corrugations are formed at an angle of 90 ° to each other but do not cross each other, Each of the formed wrinkle ends are formed to face the middle of another adjacent wrinkle formed at an angle of 90 °, Membrane metal panel of the insulating tank for LNG carrier, characterized in that the two parallel lateral wrinkles and two longitudinal folds are formed so as not to be in a straight line with each other. The method of claim 1; Membrane metal panel of the insulation tank for LNG carriers, characterized in that the ratio of the radius (lower curvature radius) and the radius (upper curvature radius) of the bent portion (R2 / R1) is 0.25 or less. The method of claim 1 or 2; Membrane metal panel of the insulating tank for LNG carrier, characterized in that the bent portion has a width of 30mm to 75mm. The method of any one of claims 1 to 3; Membrane metal panel of the insulation tank for LNG carriers, characterized in that the wrinkle crossing portion of the membrane metal panel does not exceed four.