FR2735847A1 - Internal wall membrane plate for LPG storage tank construction - Google Patents

Abstract

The membrane is formed by a series of modular rectangular plates, each including a projecting rounded channel section (20) extending from each edge (21) towards a central hole (9) which receives a fastening bolt. The inner end (31) of each channel section is rounded. The hole is surrounded by an annular projection (25) with coaxial inner and outer surfaces which form a continuous surface with the body of the plate. The dimensions and location of the annular projection, and its distance from the inner ends of the edge channels, are predetermined as a function of the strength of the plate. The channels and the annular projection are of a similar semicircular or part-elliptical cross-section.

Description

MEMBRANE FOR LIQUEFIED NATURAL GAS STORAGE TANK
The present invention relates to an improvement to the membrane structure for liquefied natural gas (LNG) storage tanks, and, more particularly, to an annular nodule membrane and integrally formed grooves, and to a nodule membrane. annular and separately formed grooves, both comprising the combination of an annular nodule and grooves on portions of a unitary membrane plate.

 In general, LNG is a cryogenic liquid having a boiling point of -162 ° C at atmospheric pressure. Typically, such LNG is stored in a large tank, having a double cylindrical structure, extending vertically. The reservoir comprises an internal reservoir, having a membrane made of a material having a high resistance to brittleness at low temperatures, and an outer plate, as an external reservoir, made of prestressed concrete or carbon steel. An insulating material is interposed between the inner and outer tanks to minimize evaporation loss gas production due to heat from outside the tank.

 The membrane disposed at the cryogenic storage tank means a specific plate member, configured and constructed so that it expands and contracts freely when subjected to a change in temperature or charge. The membrane is disposed at the side and bottom surfaces of the inner reservoir and has a sealing function to prevent the cryogenic liquid contained in the inner reservoir from leaking. The membrane also serves not only to withstand a cyclic load of fatigue caused by the thermal load, but also to absorb a load caused by the pressure or the weight of the liquid contained in the inner tank and to transfer the absorbed load to the insulation board .

 Various membrane structures are known, some of which are illustrated in FIGS. 1 to 5.

 Referring to FIGURE 1, it can be seen that a spline plate is shown as described in Japanese Patent Publication No. Sho 50-21008.

As shown in FIGURE 1, the spline plate has a splined structure having a plurality of continuous hexagonal (honeycomb) grooves, adapted to absorb expansion and contraction of the plate caused by a change in temperature. Adjacent grooves form a Y intersection, defining an intersection angle between them of 120-. . However, this membrane with honeycomb splines having the same shape causes difficulty in analyzing the stresses on it and a difficulty in making it by compression. This structure also has the disadvantage of the presence of residual stresses.

 FIG. 2 illustrates a cryogenic reservoir without curvature, which is described in Japanese Patent Publication No. Sho 60-14959. As shown in FIGURE 2, the non-curvature cryogenic reservoir comprises a shaped plate having a unitary structure comprising a triangular groove having a triangular cross-section and a trapezoidal groove orthogonal to the triangular groove. At the intersection between the triangular groove and the trapezoidal groove, is disposed a pair of opposed triangular faces and four quadrilateral faces, each having the shape of a parallelogram. The quadrilateral faces are formed by folding without excess or lack of area to connect the triangular faces to the triangular groove.However, this membrane structure, constituted by the combination of a triangular groove and a quadrilateral groove, causes a difficulty for analyze the constraints on it and a difficulty in shaping and finishing. In addition, there are the disadvantages of the presence of residual stresses and a high manufacturing cost.

FIGURE 3 illustrates a membrane having a flexible structure as described in Japanese Patent Publication No. Sho 60-32079. As shown on the
FIG. 3, this membrane structure comprises a plurality of splines protruding from the surface of the membrane disposed at a cryogenic liquefied gas reservoir. The flutes are arranged to branch off from at least one concentration zone. The concentration zone is curved upward from a flat plate area of the membrane, to have a projecting portion upwardly. Each of the splines is coupled to the upwardly projecting portion by a pair of curved faces interposed therebetween. Coupling grooves is obtained by welding.However, this membrane structure causes difficulty to analyze the constraints on it and a difficulty of manufacture.

In addition, there are the problems of a phenomenon of stress concentration and the presence of residual stresses.

 Referring to FIGURE 4, it can be seen that there is shown a one-piece triangular flute type membrane as disclosed in Japanese Patent Publication No. Sho 62-12439. This membrane comprises grooves coupled together at an annular nodule in various forms, as shown in FIG. 4. However, this membrane structure causes difficulty in analyzing the stresses on it and a difficulty of manufacture. In addition, there are the problems of a phenomenon of stress concentration and the presence of residual stresses.

Furthermore, FIGURE 5 illustrates a unitary membrane structure as described in Japanese Patent Publication No. Sho 62-46759. As shown on the
FIGURE 5, this unitary membrane structure comprises a plurality of unitary flutes, each having a pair of flutes. Each spline of each unit groove has a cross section having a gently curved, corrugated shape and forms, at the opposite longitudinal ends thereof, smooth curvature surfaces for contact with a planar plate area of the membrane. In other words, each groove has a three-dimensional surface shape, projecting smoothly from the flat plate area. Unit membranes each having the above structure are welded together.

However, this membrane structure causes the problems of a phenomenon of stress concentration and the presence of residual stresses. In addition, a rotational contraction due to heat occurs.

 Although various membrane structures are known as mentioned above, all have a number of problems. The problems encountered in conventional membrane structures will now be described in more detail.

 The membrane structure comprising triangular and quadrilateral grooves, orthogonal to each other (this structure is referred to as "the first fluted membrane") raises the problem that a significant concentration of stress occurs at a corner zone where the lower portion of the membrane is in contact with the wall of each groove and at a portion of each groove having a strongly curved shape.

 Furthermore, a rotational contraction behavior occurs in the membrane structure including a plurality of stainless steel plates each having two pairs of parallel flutes orthogonal to each other (this structure is referred to as "the second double-splined membrane"). "). This rotational contraction is caused by the effect of parallel double-line splines absorbing thermal stress. This membrane structure is configured such that a balanced stress of the splines is generated by subjecting the splines to rotational contraction in opposite directions and in a symmetrical manner. Consequently, the deformation of the grooves does not reveal any significant problem. When the equilibrium of the thermal stress is no longer expected due to the external conditions, a serious local concentration of the thermal stresses can occur. Such a local concentration of thermal stresses can reveal a significant problem. It goes without saying that the second double line spline membrane is easier to weld, shape and fabricate than the first splined membrane, and that stress analysis is also easier. Since the curvature at the wedge area is relatively large and smooth, this second double line spline membrane has less potential for local stress concentration than the first splined membrane.

 The membrane, which comprises plates each having a flange shape bent at each end thereof and butt welded at the upper portion thereof to the top of another plate adjacent thereto, allows easy manufacturing because it can be made by simply welding the plates (this membrane is referred to as "the third fluted membrane"). However, in this third fluted membrane, stable and good quality is assured only when the shaping and welding techniques used are much higher.

 Meanwhile, the membrane having no groove at its membrane plates (this membrane is designated as "the fourth membrane without groove") is mainly used for LNG vessels. The plates of the fourth non-corrugated membrane are made of Invar having a very low coefficient of thermal expansion. Although Invar has a very high rate of thermal contraction at a cryogenic temperature, it is expensive and difficult to obtain.

 Therefore, an object of the invention is to eliminate the aforementioned problems encountered in the prior art and, therefore, to provide a membrane for LNG storage tanks having a simple structure, including the combination of an annular nodule and grooves, thus allowing easy manufacture.

 Another object of the invention is to provide a membrane for LNG storage tanks having a very useful and stable structure, capable of reducing the height of the grooves when subjected to a pressure or temperature load, even if the curvature of the grooves is slightly increased.

 Another object of the invention is to provide a membrane for LNG storage tanks, capable of achieving a uniform distribution of stresses and a low level of stress when subjected to pressure.

In accordance with one of its aspects, the present invention provides a membrane for a liquefied natural gas storage tank including a plurality of unitary membrane plates, characterized in that it comprises
- four grooves extending linearly from
respective external borders of each plate of
unitary membrane in the direction of a bolt hole
Anchor, formed in the center of the membrane plate
unitary, the grooves having together the shape of a
cross; and an annular nodule connected to the inner ends of the
splines, the annular nodule having a surface
outer ring and inner annular surface
formed in one piece with, and symmetrically to, the
outer annular surface.

According to another aspect, the present invention provides a membrane for a liquefied natural gas storage tank including a plurality of unitary membrane plates, characterized in that it comprises: - four linearly extending curved grooves
from the respective outer edges of each
unitary membrane plate towards a hole for
anchor bolt, formed in the center of the plate
unitary membrane, each of the grooves having a
curved inner end; and an annular nodule spaced a predetermined distance apart
relative to the curved inner ends of the
splines, the annular nodule having a surface
outer ring and inner annular surface
formed in one piece with, and symmetrically to, the
outer annular surface.

 The grooves and the nodule advantageously have the same height protruding from the unitary membrane plate. On the other hand, the splines and the annular nodule may have a semicircular or ellipsoidal cross section having a smaller transverse diameter than its longitudinal diameter.

Other objects and aspects of the invention will become apparent upon reading the following description of embodiments thereof, with reference to the accompanying drawings. In these drawings - FIGURES 1-5 are views each illustrating a
classical membrane structure, where
FIGURE 1 is a perspective view of a
fluted membrane structure in nests
bee in one piece
FIGURE 2 is a perspective view of a
membrane structure comprising the combination
a triangular groove and a groove
quadrilateral - FIGURE 3 is a plan view of a structure of
triangular flute membrane of a single
FIGURE 4 shows perspective views of
various variants of the membrane structure to
triangular grooves in one piece; and FIGURE 5 represents plan views and
side of a double splined membrane
FIGURE 6 is a perspective view illustrating an annular nodule membrane and integrally formed grooves, in accordance with a first embodiment of the present invention. FIGURE 7 is a plan view of the diaphragm shown in FIG. FIGURE 8 is a side view of the diaphragm shown in FIGURE 6 FIGURE 9 is a schematic view illustrating a finite element array for a membrane of FIG.
TECHNIGAS FIGURE 10 is a schematic view illustrating a finite element array for a Kawasaki membrane FIGURE 11 is a schematic view illustrating a finite element array for the annular nodular membrane and integrally formed grooves, in accordance with FIG. FIG. 12 is a diagrammatic view illustrating boundary conditions for the annular nodular membrane and integrally formed grooves, in accordance with the present invention. FIG. 13 is a diagram illustrating an equivalent von Mises stress distribution on FIG. 14 is a diagram illustrating an equivalent von Mises stress distribution on the Kawasaki membrane FIGURE 15 is a diagram illustrating an equivalent von Mises stress distribution on the annular nodule membrane and flutes formed from a single according to the present invention FIGURE 16 is a perspective view Fig. 17 is a plan view of the diaphragm shown in Fig. 16. FIGURE 18 is a diagram illustrating a distribution showing a diaphragm with an annular nodule and splines formed separately in accordance with a second embodiment of the present invention. equivalent von Mises stress on the upper layer of the first type of the annular nodule membrane and separately formed splines, in accordance with the present invention FIGURE 19 is a diagram illustrating an equivalent von Mises stress distribution on the intermediate layer of the first The type of the annular nodule membrane and splines formed separately, in accordance with the present invention. FIGURE 20 is a diagram illustrating an equivalent von Mises stress distribution on the upper layer of the second type of annular nodule membrane and grooves formed of separately, in accordance with this FIGURE 21 is a diagram illustrating an equivalent von Mises stress distribution on the intermediate layer of the second type of annular nodule membrane and separately formed splines, in accordance with the present invention; FIGURE 22 is a diagram illustrating a distribution of equivalent von Mises stress on the upper layer of the third type of the annular nodule membrane and separately formed splines, in accordance with the present invention FIGURE 23 is a diagram illustrating an equivalent von Mises stress distribution on the intermediate layer of the third type of the annular nodule membrane and separately formed splines, in accordance with the present invention FIGURE 24 is a diagram illustrating an equivalent von Mises stress distribution on the top layer of the fourth type of annular nodule membrane and shaped corrugations. separate In accordance with the present invention, FIGURE 25 is a diagram illustrating an equivalent von Mises stress distribution on the intermediate layer of the fourth type of the annular nodule membrane and separately formed splines, in accordance with the present invention. FIG. plan views of the membranes according to the first and second embodiments of the present invention FIGURE 27 is a diagram illustrating a stress distribution in the annular nodular membrane and integrally formed grooves of the present invention, along line AB of FIGURE 26; FIGURE 28 is a diagram illustrating a stress distribution in the first type of the separately formed annular nodular membrane and splines of the present invention along line AB of FIGURE 26 FIGURE 29 is a diagram illustrating a distribution Stresses in the second type of the separately formed annular nodule membrane and splines of the present invention along line AB of FIGURE 26 FIGURE 30 is a diagram illustrating a stress distribution in the third type of membrane with annular nodule and separately formed grooves of the present invention according to the line
AB of FIGURE 26 FIGURE 31 is a diagram illustrating a stress distribution in the fourth type of
the annular nodule membrane and grooves formed of
separately, of the present invention, according to the
line AB of FIGURE 26 - FIGURE 32 is a diagram illustrating a
stress distribution in the nodule membrane
ring and grooves formed integrally, of the
present invention, according to the AC line of the
FIGURE 26 - FIGURE 33 is a diagram illustrating a
distribution of constraints in the first type of the
annular nodule membrane and flutes formed of
separately, of the present invention, according to the
line AC of FIGURE 26 - FIGURE 34 is a diagram illustrating a
constraint distribution in the second type of the
annular nodule membrane and flutes formed of
separately, of the present invention, according to the
line AC of FIGURE 26 - FIGURE 35 is a diagram illustrating a
constraint distribution in the third type of
the annular nodule membrane and grooves formed of
separate way of the present invention, according to the line
AC of FIGURE 26; and FIGURE 36 is a diagram illustrating a
distribution of constraints in the fourth type of
the annular nodule membrane and grooves formed of
separately, of the present invention, according to the line
AC of FIGURE 26.

A membrane for storage tanks
LNG according to a first embodiment of the present invention is illustrated in FIGURES 6 to 8. The membrane comprises a plurality of unitary membrane plates having a quadrilateral shape. In FIGURES 6 to 8, only one of the unitary membrane plates is shown and designated by the reference numeral A. Although the unitary membrane plate A is illustrated and described as having a quadrilateral shape for convenience of the explanation, it has a circular shape in most cases.As the membranes are used in cryogenic conditions and subjected to a pulsating hydraulic pressure, the analysis of a stress-strain behavior occurring at a membrane is very important in terms of the choice of the material composing the membrane and the configuration of the membrane. Typically, the membranes are made of stainless steel, aluminum alloy, Invar or 9% nickel steel. In the case of SUS stainless steel, an austenitic stainless steel plate having a thickness of 1.2 to 2.0 mm is the most used.

 The unitary membrane plate A is provided with four flutes 10 extending respectively from the outer edges 1 to a hole 9 for anchor bolt, formed in the center of the unitary membrane plate A. The flutes 10 have together the shape of a cross. The flutes 10 have the same cross section and the same curvature. Each of the flutes 10 has a left side surface 12 and a right side surface 13 integral with the left side surface. The left and right side surfaces of each flute 10 have the same curvature. Since the unitary membrane plate A is provided with four flutes 10 having a predetermined curvature, it may have a cross-sectional, flexible, neutral axis capable of preventing the occurrence of stress. Although the four splines 10 are cross-shaped, they do not intersect each other directly at a circular zone extending radially from the anchor bolt hole 9 on a predetermined radius. The unitary membrane plate A is also provided with an annular nodule 2 disposed around the anchor bolt hole 9.

This annular nodule 2 has an outer diameter corresponding to the diameter of the circular zone and an inner diameter smaller than the outer diameter. The annular nodule 2 serves as a crossing element on which the four flutes 10 intersect. The annular nodule 2 has an inner annular surface 4 and an outer annular surface 5 integral with the inner surface 4. The inner and outer surfaces outer 4 and 5 of the annular nodule 2 have the same curvature. It is preferred that the annular nodule 2 and the flutes 10 have the same height projecting from the surface of the plate. In other words, it is preferred that the height of the ridge of each groove 10 from the flat plate A be the same as the height of the ridge of the annular nodule 2 from the plate A. The transverse sections of the nodule annular and grooves may have a substantially semicircular shape or an ellipsoidal shape having a transverse diameter less than its longitudinal diameter. The above description clearly shows that the unitary membrane plate A of the present invention has a symmetrical structure, allowing it to be manufactured easily.

 It is preferred that the unitary membrane plate A is formed by compression, so as to form at the same time the flutes and the annular nodule. To obtain the membrane, several unitary membrane plates A are mounted on a support panel (not shown). Desirably, the support panel has a thickness less than that of the unitary membrane plates A, so as to reduce the cost of these plates. For example, a 2 mm stainless steel plate is used for unitary membrane plates A, while a 1.2 mm stainless steel plate is used for the support panel requiring bending.

 Due to a complex three-dimensional configuration of membrane nodules, it is very difficult to theoretically analyze the stress behavior presented in a membrane structure. For this purpose, the analysis of such a constraint behavior has been carried out experimentally.

 The present invention aims not only to overcome the problems encountered in conventional models, but also to obtain the development of a new type of membrane model and the optimal configuration of this model by analyzing the stress-strain behavior of the membrane. , which is the most important element of cryogenic tanks, using a finite element method, and comparing and examining the new model and existing models, based on the results of the analysis. In accordance with the present invention, a three-dimensional behavioral analysis is performed under conditions in which each model is divided into quadrant portions, taking into consideration the geometric symmetry of each membrane plate. Since the membrane plate is subjected to either at a uniformly distributed load, applied vertically, on the splines, due to the pressure of the stored liquid, or to thermal expansion and contraction effects of the cryogenic liquid at -162 C, the finite element analysis is carried out, taking the influences of both the uniformly distributed load and the effects of thermal expansion and contraction are considered.

FIGS. 9 to 11 each show a finite element array used for analysis of finite element membranes. As shown in FIGURES 9 to 11, the finite element array consists of 1100 to 1300 quadrilateral elements, each having axial symmetry and 1200 to 1400 crossing points of the elements. Since the membranes have a very complex configuration because of their functions, the quadrilateral mesh configuration of the finite element array is rearranged so that it can conform to the configuration characteristic of each membrane. In particular, the quadrilateral elements corresponding to the ends of the splines, to the annular nodules and to the junctions between the splines and the annular nodules, are divided into finer elements. In this case, MARC, available from "MARC User's Manual", 1993, Version K.5, MARC Analysis
Research Co., is used as a program for finite element analysis. For the program, boundary conditions are substituted which are very close to the actual loading conditions applied to the membrane plates.

 Table 1 shows simulation data values on the material characteristics and boundary conditions used for a numerical analysis.

Furthermore, FIGURE 12 shows boundary conditions for modeling the membrane assay according to the present invention.

TABLE 1

<tb><SEP> Material <SEP> | <SEP> SUS <SEP> 304 <SEP> | <SEP> Temperature <SEP> in <SEP> C <SEP> | <SEP> -162
<tb> Thickness <SEP> Coefficient <SEP> of
<tb> in <SEP> mm <SEP> 1,2 <SEP> - <SEP> 2,0 <SEP> dilation <SEP> linear <SEP> 1,4 <SEP> x
<tb><SEP> in <SEP> mm / mm <SEP> C <SEP>
<tb> Coefficient
<tb> elastic <SEP> Density <SEP> 7.85
<tb> in <SEP> N / mm2 <SEP> 3,14 <SEP> x <SEP> 103
<tb> (kg / mm2) <SEP> (0.32 <SEP> x <SEP> 1 <SEP>
<tb> Report <SEP> of <SEP> Pressure <SEP> in <SEP> N / mm2 <SEP> 0.98
<tb> Fish <SEP> 0.475 <SEP> (kg / mm2) <SEP> (O, l) <SEP>
<Tb>
In the case of FIGURE 12, the first limit is assumed to involve neither a displacement in the direction of the X axis, nor a rotational movement in the directions of the Y axis and the axis. The second limit is also assumed to involve a displacement in the direction of the X axis or a displacement in rotation in the directions of the Y axis and the Z axis. parts of the membrane plate, except the annular nodules and grooves, are analyzed under conditions not involving displacement in the Z-axis direction. The boundary conditions for annular nodules of the membrane conforming to this The invention is applied equally to the comparative membrane models (FIGURES 9 and 10).

Are used as models subjected to computer simulation, a membrane available from the company Technigaz, France, and corresponding to the first splined membrane shown in FIGURE 2, a membrane available from the Kawasaki Company Company
Ltd., Japan, and corresponding to the second double line spline membrane shown in FIGURE 5, and the annular nodule membrane and integrally formed grooves, in accordance with the present invention. The membrane of Technigaz can be the membrane representative of existing membranes. In order to more precisely analyze the membranes, the numerical results of the analysis are obtained under conditions according to which the thickness of each membrane plate is divided into three parts. parts in thickness, namely the upper layer (the first layer), the intermediate layer (the second layer) and the lower layer (the third layer).

 FIGURES 13 to 15 each represent the equivalent von Mises stress distribution on the three membrane plates. By the analysis performed for the three models, the equivalent von Mises stress occurring at the upper membrane layer was analyzed as being 1030 N (105 kg) for the 765 N (78 kg) Technigaz membrane. for the Kawasaki membrane, and 314 N (32 kg) for the present membrane, as shown in FIGURES 13a, 14a and 15a, respectively.

The von Mises-equivalent stresses at the intermediate membrane layer were analyzed as being respectively 598 N (61 kg) for the Technigaz membrane, 343 N (35 kg) for the Kawasaki membrane, and 206 K N (21 kg) for this membrane.

The maximum equivalent von Mises stress has been shown in the case of the Technigaz membrane, whereas the minimal equivalent von Mises stress has been shown in the case of the present membrane.

 The Technigaz membrane was analyzed as having a relatively uniform stress distribution, even though a high concentration of stresses occurred locally. The Kawasaki membrane exhibited unstable rotational deformation behavior because a slightly non-uniform stress distribution occurred despite relatively low stress concentration. In addition, the integrally formed annular nodule membrane and flutes of the present invention exhibited a symmetrically uniform stress distribution.

In particular, the present annular nodule membrane has shown a very superior performance compared to the two conventional membrane models, in that it has manifested about 65.6% of the concentration of the constraints of the membrane of Technigaz, and about 40% of the concentration of Kawasaki membrane stresses.

Also, the three membrane models were compared with each other for the crossing areas of the ring nodule and the grooves considered to be the weakest membrane part. As a result of the comparison, the model of the present invention of annular nodule membrane and integrally formed flutes was analyzed as the most stable in that its equivalent von Mises stress was 206 to 314 N (21). at 32 kg).

FIGURE 13a shows the distribution of stress or compression stresses in the upper layer of the Technigaz membrane. A maximum compressive stress of approximately 824 N (84 kg) was observed at the flat plate area and the nodule area where the splines intersect. However, at the splines of the intermediate layer, no stress has been shown because the compression stress generated at the upper layer is shifted by the stress stress generated at the lower layer, as shown on the
FIGURE 13b. The weight of the liquid acting on the Technigaz membrane plate serves as a uniform pressure load applied to the splines. In this respect, the peak of each groove is subjected to an effect of the pressure load which is greater compared to the side surfaces of the groove. As a result, the groove generates a small displacement along which its ridge is deformed into a convex shape. In other words, the spline plate is subjected to compressive deformation, thereby causing the membrane in the reservoir to be contracted as a result of a temperature load acting in the reservoir. Since the unitary membrane plates are in the welded state while being fixed by anchor bolts, a change in temperature leads to a sliding phenomenon taking place at the membrane. As a result of the slip phenomenon, a tension deformation behavior is manifested.

FIGURE 14a shows the distribution of tension stresses in the upper layer of the Kawasaki membrane. The maximum tension stress of about 765 N (78 kg) has been manifested at areas where the ends of the flutes are respectively disposed. In the middle layer of the membrane of
In Kawasaki, tensile and compressive stresses of about 343 N (35 kg) were unevenly manifested at the end regions of the flutes, as shown in FIG. 14b. The Kawasaki membrane exhibited a different deformation behavior than that of the Technigaz membrane. In particular, the deformation behavior at the groove areas was manifested as a decrease in the height of the crest of the groove under a uniform pressure load. As a result, a high concentration of stresses was observed. has been manifested at the corners where the grooves are in contact with the flat plate. This means that the Kawasaki membrane involves increased deformation and decreased stress at its flute zones compared to the Technigaz membrane.

 Furthermore, FIGURE 15a shows the distribution of stress stresses in the annular nodule membrane and integrally formed grooves of the present invention. In this membrane, the maximum stress stress of about 314 N (32 kg) has been manifested at the areas where the flutes intersect with the flat plate. The ridge of each annular nodule was subjected to a compressive stress of approximately 255 N (26 kg). As shown in FIGURE 15b, the pressure distribution in the intermediate layer of the present membrane is completely symmetrical and uniform.

A compressive stress of approximately 206 N (21 kg) has been observed in the areas where the ridges of the nodule meet the flutes respectively.

 The above numerical analysis shows that the integrally formed annular nodule membrane and grooves of the present invention exhibit a completely symmetrical stress distribution and a very small difference in stress between the annular nodules and the flutes, by comparison with both classic models. In the case of the present membrane, the deformation behavior at the annular nodules manifests itself in the shape of a deformation at the level of the lower layer, under the conditions under which a uniform pressure load is applied.

In other words, the concentration of the stresses at the level of the nodules is greatly reduced even if the deformation at the same zones is increased. As a result, the cause of the fatigue failure can be greatly eliminated. Decreased production of stresses at the nodule areas in the annular nodule membrane and integrally formed grooves of the present invention can provide a very significant advantage in terms of the stability of the membrane structures. In the present annular nodule membrane and integrally formed grooves, the contraction deformation caused by temperature variation leads to a deformation behavior manifesting in the same manner as in the Technigaz membrane. Overall behavior can be obtained by analyzing the combination of behavior caused by pressure and behavior caused by temperature variation.

 The result of the numerical analysis using the finite element program shows that the present membrane exhibits a very superior performance. Although the Technigaz membrane and the Kawasaki membrane are analyzed as being under high stress, there is no problem of resistance due to such high stress.

 In the above description, strain-strain behavior was analyzed for the membrane model of the present invention and two typical membrane models widely used for cryogenic storage tanks, using the analysis method. by finite elements.

 Based on the behavioral analysis, all three membranes exhibited the phenomenon that a high concentration of stresses occurs in the areas where the splines are in contact with the flat membrane plate and the groove nodule areas. The stress concentration at the intermediate layer of the membrane plate was 598 N (61 kg) for the Technigaz membrane, 343 N (35 kg) for the Kawasaki membrane, and 206 N (21 kg) for annular nodule membrane and integrally formed grooves. Moreover, the concentration of the stresses at the level of the upper layer in contact with a cryogenic liquid was analyzed as being 1030 N (105 kg) for the membrane of Technigaz, 765 N (78 kg) for the membrane of Kawasaki, and 314 N (32 kg) for the annular nodule membrane and integrally formed grooves.

 The integrally formed annular nodule membrane and grooves of the present invention was analyzed as the most stable because it exhibited a symmetrical and uniform stress distribution and a low stress concentration, distinguished from those other models. As a result, the present annular nodule membrane and integrally formed corrugations greatly lengthens the fatigue strength which can be shortened by a change in the load caused by the change in liquid pressure occurring in the membranes of the reservoirs. storage for boats.

 FIGURES 16 and 17 illustrate a membrane according to a second embodiment of the present invention. The membrane comprises a plurality of unitary membrane plates B having a quadrilateral shape. The membrane is made of the same material as that of the first embodiment.

 As shown in FIGS. 16 and 17, the unitary membrane plate B is provided with four splines 20, extending linearly from the respective central portions of the outer edges 21 towards a hole 9 for anchor bolt formed at the center of the unitary membrane plate B. The flutes 20 have the same cross section and the same curvature. Each of the flutes 20 has a left side surface 23 and a right side surface 24 integral with the left side surface 23. The left and right side surfaces 23 and 24 of each flute 20 have the same curvature. Since the unitary membrane plate B is provided with the four splines 20 having a predetermined curvature, it may have a neutral cross-sectional axis, flexible, capable of preventing the occurrence of stresses.

The flutes 20 have curved inner ends 31, respectively spaced radially by a predetermined distance from an anchor bolt hole 9, formed in the center of the unitary membrane plate B, so that they do not intersect. not directly. The unitary membrane plate B is also provided with an annular nodule 25 disposed around the hole 9 for the anchor bolt. This annular nodule 25 has an inner annular surface 27, spaced a predetermined distance from the anchor bolt hole 9, and an outer annular surface 28 formed integrally and symmetrically with the inner annular surface 27. At the same time as the splines 20, the annular nodule 25 is formed by compression. In the second embodiment of the present invention, it is important to space the annular nodule 25 from the four splines 20. The inner and outer annular surfaces 27 and 28 of the annular nodule 25 have the same curvature. It is preferred that the annular nodule 25 and the splines 20 have the same height protruding from the surface of the membrane plate. In other words, it is preferred that the height of the ridge of each groove 20 from the flat plate B be the same as the height of the ridge of the annular nodule 25 from the plate B. The cross sections of the nodule annular and grooves may have a substantially semicircular shape or an ellipsoidal shape having a transverse diameter less than its longitudinal diameter. The above description clearly shows that the unitary membrane plate B of the present invention has a symmetrical structure, making it easy to manufacture.

 In this embodiment, a computer simulation was also performed in the same environment as in the first embodiment. In order to analyze the membranes more precisely, the numerical results of the analysis were obtained under conditions under which the thickness of each membrane plate to be analyzed was divided into three parts in thickness, namely, the upper layer (the first layer), the intermediate layer (the second layer) and the lower layer (the third layer).

 As mentioned above, FIGURE 15 shows an equivalent von Mises stress distribution on the annular nodule membrane plate and integrally formed grooves in accordance with the first embodiment of the present invention. By the aforementioned analysis, the equivalent von Mises stress occurring at the top layer of the annular nodule membrane and integrally formed grooves was analyzed as 314 N (32 kg), as shown on FIG. FIGURE 15a. The equivalent von Mises stress occurring at the intermediate membrane layer was analyzed as 206 N (21 kg). These numerical results show that the annular nodule membrane and integrally formed grooves show a distribution of symmetrically uniform stresses and superior performance in terms of stress concentration. In the annular nodule membrane and integrally formed grooves, a stress of 206 to 314 N (21 to 32 kg) was exhibited at the annular nodule areas and grooves considered to be the portion of the membrane. weaker.

 As mentioned above, a compressive stress of about 206 N (21 kg) is manifested at the areas where the nodule ridges meet respectively with the grooves, in the annular nodule membrane and integrally formed grooves. To prevent the production of compression stress at the areas where the ridges of the nodule meet the grooves, it is necessary to separate the grooves of the annular nodule associated with them. this requirement is satisfied by the configuration and analysis of the separately formed annular and spline membrane in accordance with the second embodiment of the present invention.

 According to the second embodiment of the present invention, the basic structure of the integrally formed annular nodule membrane and grooves according to the first embodiment is modified so that the splines are spaced a predetermined distance apart. relative to the annular nodule associated therewith, to reduce the stress concentration and lower the stress level.Analysis of the annular nodule membrane and separately formed grooves according to the second embodiment of the present invention has been performed. while varying the main configuration parameters of the membrane, ie the distance a between the anchor bolt hole and the top of the annular nodule, and the distance b between the top of the annular nodule and the top of the separate groove of the annular nodule, as shown in Table 2 and FIGURE 17.

TABLE 2

<tb><SEP><SEP>Templates><SEP> Membrane <SEP><SEP><SEP> Parameter <SEP> Parameter
<tb><SEP> configuration <SEP> configuration
<tb><SEP> a <SEP> b
<tb> Membrane <SEP> to <SEP> Annular nodule <SEP>
<tb> and <SEP> splines <SEP> formed <SEP> of a <SEP> 62 <SEP> mm <SEP> 0 <SEP> mm
<tb> alone <SEP> holding
<tb> First <SEP> type <SEP> of <SEP> membrane <SEP> to
<tb> nodule <SEP> annular <SEP> and <SEP> 120 <SEP> mm <SEP> 100 <SEP> mm
<tb> splines <SEP> formed <SEP> of <SEP> way
<tb> separated
<tb> Second <SEP> type <SEP> of <SEP> membrane <SEP> to
<tb> nodule <SEP> annular <SEP> and <SEP> 100 <SEP> mm <SEP> 140 <SEP> mm
<tb> splines <SEP> formed <SEP> of <SEP> way
<tb> separated
<tb> Third <SEP> type <SEP> of <SEP> membrane <SEP> to
<tb> nodule <SEP> annular <SEP> and <SEP> 100 <SEP> mm <SEP> 120 <SEP> mm
<tb> splines <SEP> formed <SEP> of <SEP> way
<tb> separates
<tb> Fourth <SEP> type <SEP> of <SEP> membrane <SEP> to
<tb> nodule <SEP> annular <SEP> and <SEP> 100 <SEP> mm <SEP> 105 <SEP> mm
<tb> splines <SEP> formed <SEP> of <SEP> way
<tb> separated
<Tb>
The boundary conditions applied to the annular nodule membrane and separately formed grooves are the same as those used for analyzing conventional membranes and annular nodule membrane and integrally formed grooves according to the first embodiment of the present invention. invention. The data on the properties of the membrane material and the thickness of the membrane used in the second embodiment were the same as those used in the first embodiment. The results of the simulation for the membrane models presented in FIG. Table 2 are shown in FIGURES 18 to 25 in the form of equivalent von Mises stresses, manifested in the upper membrane layer (the first layer) being in contact with the liquid layer and the intermediate membrane layer (the second layer). ).

 Referring to FIGURES 18 to 25, it can be found that the annular nodule membrane and separately formed grooves of the second embodiment exhibit a generally lowered stress level, as compared to the annular nodule membrane and integrally formed grooves of the first embodiment. It is also found that the concentration of the stresses can be decreased as a function of the variations of the configuration parameters.

 Referring to FIGURES 27 to 31, it can be found that the annular nodule membrane and separately formed groove model, having a small value of configuration parameter a, exhibits a relatively high stress at the level of an area disposed within the annular nodule, because the radius of curvature of the annular nodule is too small. It can also be found that although the annular nodule membrane and separately formed groove pattern having a significant value of the configuration parameter has, for example, that of the fourth type of Table 2, it does not exhibit stress concentration because the area defined inside the annular nodule is increased, its rigidity is decreased, thereby causing the level of constraints to become higher.By the analysis performed while varying the configuration parameter has, it It can be found that the optimal stress level and the optimal stress distribution were manifested when the configuration parameter was 100 mm. Therefore, for second to fourth type membrane models, the analysis was performed by varying only the configuration parameter b, while setting configuration parameter a to 100 mm.

 Referring to FIGURE 27 and FIGURES 29-31, a variation of the stress depending on a variation of the configuration parameter b can be found.

In other words, it could be found that the stress level is lowered while the configuration parameter b is increased. A strongly reduced concentration of stress has also been shown in areas where ring nodules meet the flutes. However, if the configuration parameter b is too large, a non-uniform distribution of constraints will be shown. In this case, the decrease in the stress level will also be very low. It is expected that a desirable result will be obtained in terms of stress level and stress concentration when the configuration parameter b, which indicates the distance between the vertex of the annular nodule and the vertex of the spline separated from the annular nodule, is 120-140 mm. Based on this expectation, the analysis was performed for a configuration parameter b of 120-140 mm.

FIGURES 32 to 36 respectively illustrate the stress distributions in the membrane models of the
Table 2, according to the AC line of FIG. 26. For all models, similar stress distributions are shown respectively. Although the variation of the stress level depending on the variation of the configuration parameter b is not constant, the stress level is gradually increased as the configuration parameter b increases to 120 mm, and then gradually decreases. as configuration parameter b increases further from 120 mm.

 From the analysis above, it can be understood that the configuration parameters should not be too large or small. In other words, it is important to find optimal configuration settings. Although the configuration parameter b provides the advantage of lowering the stress level as it is increased, an excessive increase of the configuration parameter b may rather lead to disadvantages, such as non-compliance. uniformity of the stress distribution and increased manufacturing cost, due to an increased area subjected to compression.Therefore, it is possible to improve the stability of the membrane, in particular the resistance to fatigue by optimizing the parameters of configuration a and b, to obtain a lowered stress level and a uniform distribution of stresses in the entire membrane.

 The welding of the membranes will now be described.

Since the membranes used to store a cryogenic liquid in a storage tank are mounted on the inner wall and the bottom of the storage tank, the welding areas thereof can be classified as follows (1) Welding area where membrane plates get
overlap each other (2) Welding area where each membrane plate comes into
contact with a corner corner associated with it (3) Welding area where each membrane plate comes into
contact with a corner piece associated with it; and (4) Welding area where each membrane plate comes into
contact with a corner point associated with it.

 When welding a membrane, the cleaned membrane plates are welded together at their opposite edges, so that they are partially assembled as a membrane panel. After verification, all membrane panels are transported to a storage tank construction site, so that they can be assembled completely at the site.

 As welding used to install membrane plates in a storage tank, there are two welding methods, namely peripheral welding for anchor points and lap welding for the overlapping portions of the membrane plates. For both the annular nodule membrane and integrally formed grooves and the separately formed spline and annular nodule membrane in accordance with the present invention, conventional lap welding and conventional plug welding are used. for welding the steel plates of the membrane. Overlap welding is also used to weld parts in contact with individual plates and panels.

Since overlay welding is used to couple unit plates and panels together, the unit plates can be formed by compression.

In this case, the panels can be formed by bending.

The membranes, manufactured using the method of assembly taking advantage of the two types of operation mentioned above, have the following characteristics: (1) Since the panels are formed by bending,
it is possible to greatly reduce the production of
residual stresses and the phenomenon of
concentration of constraints. If a compression is
performed to obtain a desired panel shape, a
heat treatment, such as annealing, is necessary
because residual stresses are produced
as a result of a non-uniform variation in thickness
of the panel to be shaped. However, bending
eliminates such additional heat treatment (2) The matrices used for compression can
have a simple and compact structure. Given
that compression is used only for
single membrane plates according to the method
assembly, it can be easily performed. Yes
compression is still used for panels,
complicated matrices for the global membrane are
required ; and (3) The possibility of saving the material of the plate is
obtained because a 2 mm stainless steel plate
can be used for membrane plates
units to be compressed, then
that a 1.2 mm stainless steel plate can be
used for signs to be submitted to
bending.

 The above description clearly demonstrates that the present invention provides a membrane having a very simple structure, capable of exhibiting a uniform stress distribution and a low stress level corresponding only 23 to 29% of those manifested in conventional membranes. . The membrane of the present invention is very useful and stable because, when subjected to a pressure and temperature load, the height of the flutes is reduced even though the curvature of the flutes is slightly increased.

 Although preferred embodiments of the invention have been described for purposes of illustration, those skilled in the art will understand that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention. invention, as described in the appended claims.

Claims (5)

 1 - Membrane for a liquefied natural gas storage tank including a plurality of unitary membrane plates, characterized in that it comprises  - four curved flutes (20), extending so  linear from the outer edges  respective ones (21) of each unitary membrane plate  in the direction of a hole (9) for anchor bolt, formed  in the center of the unitary membrane plate, each  splines (20) having an inner end  curve (31); and - an annular nodule (25) spaced a distance  predetermined with respect to the inner ends  curves (31) of the grooves (20), the nodule  ring (25) having an outer annular surface (28)  and an inner annular surface (27) formed of a single  holding with, and symmetrically to, the annular surface  external (28).  2 - membrane according to claim 1, characterized in that the grooves and the annular nodule have the same height projecting from the unitary membrane plate.  3 - membrane according to one of claims 1 or 2, characterized in that the grooves and the annular nodule have a substantially semicircular cross section.  4 - membrane according to one of claims 1 or 2, characterized in that the grooves and the annular nodule have an ellipsoidal cross section having a transverse diameter smaller than its longitudinal diameter.  Membrane for a liquefied natural gas storage tank including a plurality of unitary membrane plates, characterized in that it comprises four flutes (10) extending linearly from respective outer edges (1) of each unitary membrane plate in the direction of a hole (9) for anchor bolt, formed in the center of the unitary membrane plate, the flutes (10) being in the form of a cross; and an annular nodule (2) connected to the inner ends of the splines (10), the annular nodule (2) having an outer annular surface (5) and an inner annular surface (4) formed integrally with, and symmetrically to the outer annular surface (5).