JPS59433B2 - Method for forming tank bottom corners of field-assembled cylindrical tanks - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a tank bottom corner of a field-assembled tank.

Conventionally, for example, at the bottom corner of a large capacity cylindrical tank such as a crude oil tank, a foundation block b is placed in an annular shape on foundation ground a, and the top surface of this foundation block is connected to the foundation, as shown in Figure 1. An annular plate c is installed on the foundation block b and the ground a, and the first stage tank side plate d is installed above the position corresponding to the center of the width of the foundation block b. is welded to an annular plate c, and a tank bottom plate e is welded to the inner peripheral edge of the annular plate c.

Therefore, the extra length f of the annular plate c appears on the bottom outer periphery of the field-assembled cylindrical tank. The main cause of leakage accidents in large cylindrical tanks is that an overload external force is applied to the tank body due to uneven settlement of the foundation ground, etc. It is said that this is caused by excessive stress occurring at the joint B.

We have conducted extensive experiments and experiments to understand the mechanism by which such excessive stress occurs.
As a result of repeated research, it was confirmed that the cause of this problem lies in the above-mentioned method of forming the corner joint between the side plate d and the annular plate c, and in particular, the existence of the extra length f of the annular plate. That is, when liquid enters the tank having the tank bottom corner shown in FIG. 1, the first stage side plate d as shown in FIG.
tries to move horizontally from the position A to the position A' due to the internal pressure g, but the lower end of the side plate d, as shown in FIG.
Since it is connected to the bottom plate e via the annular plate c, as shown in FIG. 3, if only the side plate d is taken out, a horizontal force Q acts on the lower end, and the horizontal movement is prevented. The base of the side plate d attempts to rotate by a rotation angle θ with respect to the vertical direction.

Now, if we examine the situation in a little more detail, as shown in Figure 2, the lower end of the side plate d is mounted on something like a base plate, in other words, something with extremely high rigidity, so that it can rotate freely around an axis i. Assuming that, in this case, the side plate d can freely rotate around the axis i, so the angle θ corresponds to the internal pressure acting on the side plate d. rotation, and restrains this rotation, in other words, a rotational restraint moment Mr.
(Therefore, the direction is clockwise) does not occur. Therefore, if we express the rotation angle of the side plate d by θ, in the case of the opening in Figure 2, θ =
θ0, rotational restraint moment Mr=O. Also, if
As shown in FIG. 2C, if the lower end of the 1111 plate d is restrained to something like the base plate so that it cannot rotate freely, in other words, it is fixed so that it cannot rotate, The lower end of the side plate d cannot rotate, and the fact that it cannot rotate is considered to mean that the rotational restraint moment Mr, which tries to prevent the rotation angle θ from occurring, is acting in the direction of the arrow (clockwise).

In this case, the rotational angle θ about the point B1 where the center line m of the side plate d intersects with the base plate has an O rotation restraining moment Mr, which is large, and if the magnitude is MF, Mr=MF. However, as shown in Figure 1, the side plate d of the tank has its lower end fixed to an annular plate c that can be deformed by external force, and is less rigid than the base plate described above. ,
Since the side plate d deforms upward when subjected to internal pressure, the state shown in Fig. 4 occurs, and the restraining moment Mr
Even if MF occurs, it is not as large as the MF in case C of FIG.

Let M be the rotational restraint moment Mr in the case of FIG. 4, and let θ1 be the rotation angle θ. By the way, as shown in Fig. 1, when the side plate d is fixed to the annular plate c with an extra length f left behind, if the side plate d is deformed as shown in Fig. 4, the extra length f becomes the foundation. This pushes the ground or the foundation block b, and prevents the side plate d from rotating in the counterclockwise direction. (This obstructive effect is called a leverage effect). This means that the extra length f
When the reaction force p of the force pushing the foundation ground or foundation block b becomes a moment, a restraint occurs at the intersection B' of the center line m of the side plate d and the center line n of the annular plate c, as shown in Fig. 2. This will further add to the moment Mr. The relationship between the rotation angle θ and the restraining moment Mr in the cases of Figures 2 and 4 is as shown in Figure 2 E. Then, M
is between O and MF, and the rotation angle θ in the case of Fig. 4 is θ
1, θ, is θ than O. It's between. This rotational restraint moment M generates a large local stress close to the yield stress of the base material at the joint B between the side plate and the annular plate, and furthermore, an overload external force due to the uneven settlement mentioned above is generated. When added, this local stress exceeds the yield stress,
Fatigue failure or cracking of the material was expected to occur, and it was found that this had a significant impact on the safety of the tank bottom corners. Note that this local stress becomes even greater when the base block b is located below the extra length part f. To summarize the facts found as a result of analysis of the conventional side plate one bottom plate joining method regarding this rotational restraint moment M and stress distribution state, 1) In Fig. 4,
The intersection B' between the first stage side plate d and the annular plate c
The more that is prevented from rotating counterclockwise about the end h of the extra length f, the larger the rotation restraint moment M at the intersection B' becomes.

2) The longer the extra length molecule of the annular plate c becomes, the greater the lever action becomes, and therefore the rotational restraint moment M also becomes greater.

3) Most of the resistance local stress (80% or more) due to the generated rotational restraint moment M occurs on the bottom plate side of the intersection B' in the annular plate C, and almost no stress occurs on the extra length part f.

What can be concluded from this fact is: 1) If the intersection B' between the side plate d and the annular plate c is allowed to rotate freely in the counterclockwise direction in FIG. 4, the rotational restraint moment M can be reduced. The occurrence can be reduced.

2) The extra length f of the annular plate c does not contribute to reducing local stress at all, but only increases the generated rotational restraint moment M.

3) When the lower end of the side plate d is fixed to the annular plate c and the side plate d rotates counterclockwise around the intersection B', the rotation is different from that shown in the opening of FIG. The rotation is as shown in Figure 2C, that is, the lower end of the side plate d has a rotation angle θ-0, but as it goes upwards the side plate d gradually curves to a curve with a radius r1, and then reverses at a radius R2. Turn and rotate in such a way that a curved conversion point S is created in the middle of the side plate d.

Therefore, since the local stress distribution with respect to the rotational restraint moment becomes opposite around this conversion point S, the stress becomes O at the conversion point S. Furthermore, if the first stage side plate d is welded near the conversion point S, no particular problem will occur in welding.
It was hot.

When we examine the stress state of the tank bottom corner formed by the conventional method of forming the tank bottom corner of the field-assembled cylindrical tank shown in Figure 1, we find that the liquid inside the tank is as shown in Figure 5. As shown in the bending stress distribution curve D in the direction of the center line of each thickness of the measured plate, the annular plate, and the extra length of the annular plate, the local stress when the side plate d and the annular plate c The maximum value is reached at the intersection point BI of the center line of the thickness.

The reason why the local stress distribution with respect to the rotation restraint moment of the side plate d in FIG. 5 is reversed at point S midway is due to the reason explained in 3) above. The method of forming the tank bottom corner of a field-assembled cylindrical tank according to the present invention was conceived in view of the above facts, and when the present invention is explained based on the drawings, for example, as shown in FIG. , an annular plate 2 having a rising edge 1 on the outer periphery and an L-shaped longitudinal section is laid, and an annular plate 2 having a rising edge 1 on the outer periphery is laid, and an annular plate 2 is placed at a location avoiding the location where the local stress of the rising edge 1 is maximum (for example, at point S). ) Weld the lower end of the first stage tank side plate 3, and weld the tank bottom plate 4 to the inner peripheral edge of the annular plate, avoiding the inner corner of the L-shaped cross section of the annular plate. It is characterized by this.

Note that 6 indicates the basic block and 5 indicates the receiving plate. The tank bottom corner formed by the method of this invention has the structure as described above, and as shown in Figure 6, the center of the thickness of the steel plate and annular plate when liquid is poured into the tank. As is clear from the bending stress distribution curve in the linear direction, the hot spot F where the maximum local stress occurs is strong because the rising edge 1 and the annular plate 2 are made integrally. The welding point 7 between the step side plate 3 and the rising portion 1 of the annular plate 2 is located near the lowest local stress point, or at least in a location that avoids the highest local stress point, thereby increasing the safety of the entire tank. The quality is extremely high. Note that an annular plate having an L-shaped vertical cross section with a rising edge has a bent portion that does not have an angular shape, as shown in FIG. 6, but has an arc shape, as shown in FIG. It's okay. In that case, a support ring 13 may be provided to support the weight of the side plate as shown in FIG. The method of this invention and the conventional method were implemented on a crude oil tank with a capacity of 150,000 KL, and the resulting stress distribution situation obtained from drawings and calculations was 7 times higher than that of the conventional method.
0% or less, there is no need to use special steel even for large-capacity tanks, and general structural rolled steel can be used.Since the rising edge 1 and the annular plate 2 are made as one piece, the maximum local It can have sufficient resistance against the generation of stress, and the first stage side plate can be welded avoiding the area where the maximum local stress occurs in the rising edge 1, making welding easier. have

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the method of forming the tank bottom corner of a conventional field-assembled cylindrical tank, and Figure 2 A, C, and C are explanatory diagrams of the relationship between various installation situations of the lower end of the side plate and rotational restraint moment generation situations. Figure 2, Figure 2, is an explanatory diagram of the intersection B', Figure 2, E is the second
Figure 3 is a diagram showing the relationship between the rotation angle and the rotational restraint moment of the side plate in the case of Figure 4 and the case of Figure 4. Figure 3 is an explanatory diagram showing the force acting on the side plate when only the side plate is taken out. The figure is an explanatory diagram of the lever action and rotational restraint moment when an annular plate with an extra length f is joined to a side plate, and Figure 5 shows the local stress generated at the corner of the tank bottom formed by the above conventional method. An explanatory diagram of the distribution, FIG. 6 is an explanatory diagram of the method of forming the tank bottom corner of the field-assembled cylindrical tank according to the present invention, and FIG. 7 is an explanatory diagram of another embodiment.
2 indicates a rising edge, 2 indicates an annular plate, 3 indicates a tank side plate, and 4 indicates a tank bottom plate.

Claims (1)

[Claims] 1. An annular plate 2 having a rising edge 1 on the outer periphery and an L-shaped longitudinal section is laid, and a first stage is placed on the rising edge 1 at a location avoiding the area where the local stress is maximum. A field-assembled cylinder characterized in that the lower end of the tank side plate 3 is welded, and the tank bottom plate 4 is welded to the inner peripheral edge of the annular plate, avoiding the inner corner of the L-shaped cross section of the annular plate. How to form the bottom corner of a shaped tank.