JP2009113823A - Device for reducing stress in floating roof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the breakage of a pontoon during the sloshing of a stored liquid. <P>SOLUTION: For a floating roof 15 in a floating roof type tank, the absolute value of the uphill gradient θ provided outwardly from the inner side in the radial direction in a top surface of a pontoon 17 provided on an outer periphery of a deck 16 and the absolute value of the downhill gradient -θ provided outwardly from the inner side in the radial direction on an undersurface of the pontoon 17 are set in an angular range of 0.0-1.5°. During the sloshing of the stored liquid 14, the stress exerted to a lower end of an outer peripheral edge of the pontoon 17 is reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a floating roof type tank of a type in which a floating roof is provided on a storage liquid such as an oil tank, and the floating roof vibrates with sloshing generated in the storage liquid inside the tank. The present invention relates to a stress reducing device for a floating roof in order to reduce stress acting on the roof.

  As a large tank for storing crude oil or oil, which is a fluid with a relatively low risk of vaporization, a floating roof type storage tank is often used. FIGS. 13 (a) and 13 (b) show a general structure of a floating roof tank equipped with a single-deck type floating roof, and a bottom plate 12 installed on a foundation and standing on the upper side of the bottom plate 12 The tank body 11 is formed of a cylindrical side plate 13 that is open at the top, and further includes a floating roof 15 that floats on the liquid level of the liquid 14 stored inside the tank body 11. As a configuration. The floating roof 15 is configured such that a pontoon 17 for providing buoyancy is provided on the outer periphery of the deck 16 at the center. 18 is a sealing mechanism for filling a gap between the outer periphery of the floating roof 15 and the inner peripheral surface of the side plate 13, and 19 is a weather shield for suppressing the inflow of rainwater (for example, see Patent Document 1).

  The pontoon 17 includes a cylindrical shell-shaped inner rim 17a and an outer rim 17b arranged concentrically, an upper deck 17c that forms an upper surface, and a lower deck 7d that forms a lower surface. The outer peripheral end of the deck 16 is connected to a required height position in the vertical direction on the inner peripheral surface. Usually, an upward slope of about 3 to 4 degrees is provided on the upper surface of the pontoon 17 from the radially inner side to the outer side so that the rain water that falls on the pontoon 17 has a gradient on the upper surface of the pontoon 17. Accordingly, the rainwater that has fallen on the pontoon 17 can be prevented from flowing into the space between the outer periphery of the floating roof 15 and the side plate 13 of the tank body 11 in advance. The rainwater collected on the deck 16 from the pontoon 17 is discharged together with the rainwater that has fallen on the deck 16 through a roof drain pipe 20 connected to a required portion of the deck 16.

  On the other hand, the lower surface of the pontoon 17 is usually provided with a downward gradient of about 3 to 4 degrees outward from the inside in the radial direction, and the evaporative gas generated in the stored liquid 14 below the pontoon 17 The evaporative gas of the stored liquid 14 is provided in the gap between the outer periphery of the floating roof 15 and the inner peripheral surface of the side plate 13 by being raised along the slope of the lower surface of the steel plate and collected on the deck side. The possibility of leakage from the seal gap of the seal mechanism 18 to the outside can be prevented.

  By the way, when an earthquake occurs, when the seismic wave includes a sloshing period component of the floating roof tank, sloshing is excited in the stored liquid 14 in the floating roof tank. The sloshing of the storage liquid 14 in the floating roof type tank causes the pitching vibration of the floating roof 15, and the vibration of the floating roof 15 due to the sloshing grows greatly in resonance with the long-period component of the earthquake. A large stress is applied to 15.

  In view of this point, the present inventors in the previous application (Japanese Patent Application No. 2007-285871) use the analysis model of the floating roof tank to analyze the floating roof 15 in the floating roof tank from the variational principle. A basic equation is derived, and then a nonlinear ordinary differential equation with respect to time is derived by a mode expansion method. By solving this nonlinear ordinary differential equation, the stress acting on the floating roof 15 by the sloshing of the storage liquid 14 can be calculated. This paper proposes a method for predicting the excessive stress of floating roofs in the floating roof tank.

JP 2005-219769 A

  However, in the floating roof 15 of the conventional floating roof type tank as shown in FIGS. 13 (a) and 13 (b), the vibration of the floating roof 15 due to the sloshing of the storage liquid 14 resonates with a long-period component and greatly increases during an earthquake. When a large stress is applied to the floating roof 15 as it grows, the actual stress is that the stress generated in the pontoon 17 of the floating roof 15 is likely to increase. If the breakage acting on 17 occurs, the stored liquid 14 may enter the pontoon 17 from the damaged portion, the buoyancy may disappear, and the floating roof 15 may sink to the stored liquid 14.

  Therefore, in order to prevent a risk that the pontoon 17 is caused by a large stress in the pontoon 17 due to the stress acting on the floating roof 15 during the sloshing of the storage liquid 14 as described above, the storage liquid 14 is sloshing. Even if it occurs, it has been desired to reduce the stress generated in the pontoon 17 of the floating roof 15.

  Accordingly, as a result of repeated efforts and research to reduce the stress generated in the pontoon when the stress acts on the floating roof in association with the sloshing of the liquid stored in the floating roof type tank, The structure and storage of the floating roof using the analysis method used in the method for predicting the excessive stress of the floating roof in the floating roof tank proposed by the inventors in the previous application (Japanese Patent Application No. 2007-285871) By analyzing the relationship between the stress acting on the floating roof during liquid sloshing and finding the structure of the floating roof that can reduce the stress acting on the pontoon of the floating roof during storage liquid sloshing Invented.

  Accordingly, an object of the present invention is to provide a stress reducing device for a floating roof that can reduce the stress generated in the pontoon of the floating roof due to the sloshing of the liquid stored in the floating roof tank. .

  In order to solve the above-mentioned problem, the present invention, corresponding to claim 1, causes the radial gradient of the upper surface of the pontoon provided on the outer periphery of the floating roof of the floating roof tank to be outward from the radially inner side. An upward gradient of 0.0 to 1.5 degrees is set, and the radial gradient of the lower surface of the pontoon is a downward gradient of 0.0 to 1.5 degrees from the radially inner side to the outer side. The configuration is as described above.

  In the above configuration, a cover that covers the upper surface of the pontoon is attached at an upper position of the pontoon so as to be inclined from the inside in the radial direction so as to have an ascending slope of a required angle.

  Furthermore, in each said structure, it is set as the structure which provided the gas leakage prevention cover in the outer peripheral part of the lower surface of a pontoon so that a required dimension might protrude below.

According to the stress reducing device for a floating roof of the present invention, the following excellent effects are exhibited.
(1) The radial gradient of the upper surface of the pontoon provided on the outer periphery of the floating roof of the floating roof tank is set to be an upward gradient of 0.0 to 1.5 degrees outward from the radial inner side, In addition, since the radial gradient of the lower surface of the pontoon is configured to be a downward gradient of 0.0 to 1.5 degrees outward from the radial inner side, the sloshing of the stored liquid in the floating roof tank Sometimes the stress generated in the pontoon can be reduced. And the stress which arises in the lower end part of the outer periphery part of this pontoon which the largest stress acted conventionally can be reduced efficiently. Therefore, the effect of preventing the damage of the pontoon at the time of sloshing of the stored liquid can be expected.
(2) A cover that covers the upper surface of the pontoon is installed at a position above the pontoon so as to be inclined from the radially inner side to the outer side so as to have an ascending slope of a required angle. Rain falling from above can be received by the cover, and rainwater received on the cover can flow on the deck without depending on the gradient of the upper surface of the pontoon.
(3) The gas leakage prevention cover is provided at the outer peripheral edge of the lower surface of the pontoon so as to project the required dimension downward, so that the evaporated gas generated in the stored liquid below the pontoon Can be prevented from moving to the outer peripheral side of the floating roof. Therefore, without depending on the gradient of the lower surface of the pontoon, there is a risk that the evaporative gas generated in the stored liquid below the pontoon will leak to the outside through the seal gap of the seal mechanism provided on the outer periphery of the floating roof. Can be prevented.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 shows an embodiment of the stress reducing device for a floating roof according to the present invention. The pontoon 17 in the floating roof 15 of the floating roof tank having the same configuration as that shown in FIGS. The gradient of the upper surface and the gradient of the lower surface are made smaller than before.

  Specifically, the absolute value of the upward gradient θ provided outward from the radial inner side on the upper surface of the pontoon 17 and the absolute value of the downward gradient −θ provided outward from the radial inner side of the lower surface of the pontoon 17 are determined. The angle range is from 0.0 degrees to 1.5 degrees. As a result, it is possible to reduce the stress generated in the pontoon 17 during the sloshing of the stored liquid 14 in the floating roof tank, particularly the stress generated at the lower end of the outer peripheral edge of the pontoon 17.

  Further, a rainwater cover 21 covering the top of the pontoon 17 is attached to the upper side of the pontoon 17 so as to have a required angle and an upward slope from which rainwater flows down from the inside in the radial direction. Accordingly, rain falling from above the pontoon 17 can be received by the rainwater cover 21, and the rainwater received on the rainwater cover 21 does not depend on the gradient of the upper surface of the pontoon 17, The rainwater cover 21 can be made to flow on the deck 16 according to the gradient of the rainwater cover 21.

  Furthermore, a gas leakage prevention cover 22 is provided on the outer peripheral edge of the lower surface of the pontoon 17 so as to protrude from the lower end of the outer rim 17b so that the outer rim 17b extends a required dimension downward. Thereby, the evaporative gas generated in the stored liquid 14 below the pontoon 17 is caused by the gas leakage prevention cover 22 between the outer periphery of the floating roof 15 from the lower side of the pontoon 17 and the inner peripheral surface of the side plate 13 of the tank body 11. The movement to the gap can be prevented. Therefore, it is possible to prevent the evaporation gas generated in the stored liquid 14 below the pontoon 17 from leaking outside through the seal gap of the seal mechanism 18 without depending on the gradient of the lower surface of the pontoon 17. It is.

  Hereinafter, the reason why the angle condition of the upper surface and the lower surface of the pontoon 17 is set to the predetermined angle range will be described in detail.

  First, as shown in FIGS. 2A and 2B, a cylindrical floating roof type tank having the same configuration as shown in FIG. 13 is arranged in an xyz coordinate space with the center of the bottom plate 12 of the tank as the origin. Then, an analysis model of a floating roof tank in which a cross section at an arbitrary circumferential angle φ is shown is set.

Reference numeral 23 in FIG. 2 (a) denotes a stiffener provided for reinforcement at a required radial position on the upper surface of the deck 16 of the floating roof 15. Further, a is the radius of the cylindrical tank body 11, and h is the depth of the stored liquid 14 at the time of static equilibrium. 2B, b is the radius of the floating roof 15, b ₁ is the radius of the deck 16, H is the height of the outer rim 17b of the pontoon 17, and H ₁ is the deck 16 mounting on the inner rim 17a of the pontoon 17. vertical dimension from the position to the upper end of the inner rim 17a, H ₂ is the vertical dimension of the deck 16 mounted position on the inner rim 17a of the pontoon 17 to the lower end of the inner rim 17a. Other calculation specifications of the above-mentioned floating roof type tank are set as shown in Table 1 below assuming a general shape of an actual machine of 30,000 to 40,000 kiloliters that is generally used conventionally.

をｘ方向に作用させる条件の下で、本発明者等が先の出願（特願２００７−２８５８７１号）で提案している浮き屋根式タンクにおける浮き屋根の過大応力予測方法で用いている解析手法を適用して、貯蔵液体１４のスロッシング時に浮き屋根１５に対して作用する応力について解析した。 For the analysis model configured as described above, the excitation acceleration is determined by applying a three-wave sine wave excitation near the resonance point of the first-order sloshing mode in the circumferential direction and a radial wave number of 1.

Analysis method used in the method for predicting excessive stress of a floating roof in a floating roof tank proposed by the present inventors in a previous application (Japanese Patent Application No. 2007-285871) Was applied to analyze the stress acting on the floating roof 15 when the storage liquid 14 was sloshing.

  FIG. 3 is a diagram showing the vertical displacement at the lowest point of the outer rim 17b of the pontoon 17 due to the above-described vibration. The solid line shows the result of nonlinear analysis, and the broken line shows the result of linear analysis. This figure is a figure for observing to what extent the floating roof displacement causes the stress response described later.

について、応力の高くなる図５におけるポジション１〜１０での時刻歴応答解析を行い、該各ポジション１〜１０のそれぞれにおいて絶対値最大に達したときの値を求めた。その結果を図６に示す。 Next, local coordinates s: meridian direction coordinates ζ: thickness direction coordinates of the shell element are defined as shown in FIG.

The time history response analysis at positions 1 to 10 in FIG. 5 where the stress is high was performed, and the values when the absolute value maximum was reached at each of the positions 1 to 10 were obtained. The result is shown in FIG.

  From FIG. 6, it has been found that the largest stress as the radial out-of-plane stress is applied to the position 2 in the conventionally used floating roof tank. Moreover, since the position 2 is located at the lower end of the outer peripheral portion of the pontoon 17, if the pontoon 17 is broken at the position of the position 2, it is considered that the stored liquid 14 enters the inside of the pontoon 17 immediately. It is done.

  Therefore, the inventors of the present invention have the stress that acts on the pontoon 17 of the floating roof 15 during the sloshing of the storage liquid 14 in the floating roof tank, particularly at the position 2 that has acted as the largest stress. As means for enabling reduction of the radial out-of-plane stress, it has been considered to reduce the gradient of the upper surface and the lower surface of the pontoon 17.

Based on this idea, the absolute value of the upward gradient θ provided outward from the radial inner side on the upper surface of the pontoon 17 and the absolute value of the downward gradient −θ provided outward from the radial inner side of the lower surface of the pontoon 17 are calculated. Both of these conditions were set to 0.8 degrees. However, since the pontoon 17 may enter a person for maintenance, inspection work, etc., the inner rim 17a of the pontoon 17 from the deck 16 is secured in order to ensure a height of about 40 to 50 cm. of the distance _{H 1} to the upper end 0.27 m, are the distances of _{H 2} from the deck 16 to the lower end of the inner rim 17a of the pontoon 17 to be set to 0.22 m. Under the above conditions, time history response analysis at positions 1 to 10 was performed in the same manner as described above, and the values when the absolute value maximum was reached at each of the positions 1 to 10 were obtained. The result is shown in FIG.

  FIG. 7 is compared with FIG. 6 to reduce the absolute value of the gradient of the upper surface and the lower surface of the pontoon 17 to 0.8 degrees. Although the stress of 48.2 increased from 68.2 to 60.9, it was confirmed that the stress at position 2 where the largest stress was applied could be significantly reduced. It was also found that the stress at other positions showed a decreasing trend except for a slight increase. As for in-plane stress, an increase is seen in the circumferential stress at positions 3 and 10, but since the original value is small, it remains at a relatively small level, and the circumferential stress at positions 2 and 5 is significant. It can be seen that it has been reduced.

  Further, when the absolute values of the gradients of the upper and lower surfaces of the pontoon 17 are reduced to 0.002 degrees, time history response analysis is performed at positions 1 to 10 in the same manner as described above, The value when the absolute value reached the maximum was obtained. The result is shown in FIG. The out-of-plane stress shown in FIG. 8 is almost the same as the value shown in FIG. 7, but the in-plane stress shown in FIG. 8 is the value shown in FIG. 7 in the circumferential stress at positions 1, 3, 7, and 10. There was a tendency to become a little larger, but it remained at a small level.

Further, in order to investigate the influence of the height dimension of the pontoon 17 on the stress, the absolute value of the gradient of the upper surface and the lower surface of the pontoon 17 is kept at 0.8 degrees as in the case of FIG. for the case where the distance _{H 1} to the upper end of the inner rim 17a of the pontoon 17 was increased to 0.37 m, performs a time history analysis in positions 1 to 10, the maximum absolute value in each of the respective positions 1-10 The value when reached was obtained. The result is shown in FIG. Also in this case, the out-of-plane stress shown in FIG. 9 is comparable to the value shown in FIG. 7, and it has been found that the effect of reducing the stress from the value shown in FIG. 6 is maintained. Although the in-plane circumferential stress at positions 3, 4, 6, and 10 tends to be larger than the value shown in FIG. 7, it remains at a small level.

  As an example of seeing the stress reduction effect by the time history response, the slope of the upper surface of the pontoon 17 is 3 degrees and the slope of the lower surface is -4.4 degrees based on the calculation parameters of Table 1 as in FIG. FIG. 10A shows the result of analyzing the response of the out-of-plane stress in the radial direction at the position 2 under the above conditions. Similarly to the case of FIG. 7, the response of the out-of-plane stress in the radial direction at the position 2 was analyzed under the condition that the absolute value of the gradient of the upper and lower surfaces of the pontoon 17 was reduced to 0.8 degrees. The results are shown in FIG. In FIGS. 10 (a) and 10 (b), the solid line shows the result of nonlinear analysis, and the broken line shows the result of linear analysis. 10A and 10B, the stress of the pontoon 17 can be reduced by reducing the gradient of the upper surface and the lower surface of the pontoon 17 to 0.8 degrees from the angle condition generally employed in the past. It became clear that we could do it. Also in FIG. 10 (b), considering the non-linearity of sloshing results in a greater stress than in the case of the linear theory, it is understood that the non-linearity is important in stress evaluation.

  In FIG. 7, the absolute values of the upward gradient θ outward from the radially inner side of the upper surface of the pontoon 17 and the downward gradient −θ outward from the radially inner side of the lower surface of the pontoon are set to 0.8 degrees. It was confirmed that there was an effect of reducing the stress below, but each position when the absolute value of the gradient of the upper and lower surfaces of the pontoon 17 was changed by ± 0.2 degrees around 0.8 degrees. The change of the stress value in 1-10 was investigated. FIGS. 11A and 11B show the analysis results of the in-plane stress in the circumferential direction, FIGS. 11C and 11D show the analysis results of the out-of-plane stress in the radial direction and the axial direction, and FIGS. ) Shows the analysis results of the out-of-plane stress in the circumferential direction. The in-plane stress in the radial direction or the axial direction is omitted because the absolute value is as small as 4 MPa at the maximum. 11 (a) (b) (c) (d) (e) (f), even if the slopes of the upper and lower surfaces of the pontoon 17 are slightly changed, the stress values at positions 1 to 10 change. It was confirmed that the stress reduction effect obtained was not sensitively degraded by small fluctuations in the gradient of the upper and lower surfaces of the pontoon.

  Furthermore, as described above, in view of the object of reducing the radial out-of-plane stress at the position 2 that acted as the largest stress on the pontoon 17 of the floating roof 15 during the sloshing of the storage liquid 14 in the floating roof tank. For the out-of-plane stress in the radial direction at the position 2, the absolute values of the gradients of the upper and lower surfaces of the pontoon 17 are set to 0.002, 0.8, 2.5, and 4.4 degrees. The analysis results are shown in FIG. Based on this result, a graph plotting the correlation between the radial out-of-plane stress at position 2 and the absolute values of the gradients of the upper and lower surfaces of the pontoon 17 is shown in FIG.

  From FIG. 12 (b), the radial out-of-plane stress at position 2 where the stress is most exerted by the sloshing of the storage liquid 14 in the floating roof tank increases as the absolute value of the gradient of the upper and lower surfaces of the pontoon 17 increases. As the absolute value of stress increases and the absolute value of the gradient of the upper and lower surfaces of the pontoon 17 becomes greater than around 1.5 degrees, it has been clarified that the rate of change of stress increase with increasing gradient is considered to increase. .

  From the above, in the floating roof stress reduction apparatus of the present invention, the absolute value of the upward gradient θ outward from the radial inner side of the upper surface of the pontoon 17 and the downward gradient −θ outward from the radial inner side of the lower surface of the pontoon 17 are absolute. The quantitative range of values was set to 0.0 degrees to 1.5 degrees.

  As described above, according to the stress reducing device for a floating roof of the present invention having the above-described configuration, the calculation specifications shown in Table 1 are close to those of a typical actual floating roof tank. During the sloshing, the stress generated in the pontoon 17 can be reduced. In addition, the stress generated at the lower end of the outer peripheral edge of the pontoon 17 can be efficiently reduced. Therefore, the effect of preventing the pontoon 17 from being damaged during sloshing of the stored liquid 14 can be expected.

  The present invention is not limited to the above-described embodiment. If the tank is a floating roof type tank provided with a single deck type floating roof, the shape other than the shape of the calculation specifications shown in Table 1 is used. Needless to say, the present invention can be applied to a floating roof in a floating roof tank having the above, and various modifications can be made without departing from the scope of the present invention.

It is a general | schematic cutting side view which shows one Embodiment of the stress reduction apparatus of the floating roof of this invention. The analysis model of the floating roof type tank used for derivation | leading-out of this invention is shown, (A) is a general | schematic cutting side view, (B) is a cutting | disconnection side view which shows the detailed shape of a floating roof. It is a figure which shows the vertical direction displacement which arises in the lowest point of the outer rim of a pontoon by 3 sine wave excitation. It is a figure which shows the local coordinate of the shell element of a floating roof. It is a figure which shows the position of the positions 1-10 made into the object of the time history response analysis in a pontoon. It is a figure which shows the result of having calculated | required the value when the absolute value maximum was reached in each of each position 1-10 by performing the time history response analysis in position 1-10 under the calculation data of Table 1. . Under the condition that the absolute value of the slope of the upper and lower surfaces of the pontoon is reduced to 0.8 degrees, a time history response analysis is performed at positions 1 to 10, and the absolute value is maximized at each of the positions 1 to 10. It is a figure which shows the result of having calculated | required the value when reaching. Under the condition that the absolute value of the slope of the upper and lower surfaces of the pontoon is reduced to 0.002 degrees, a time history response analysis is performed at positions 1 to 10, and the absolute value is maximized at each of the positions 1 to 10. It is a figure which shows the result of having calculated | required the value when reaching. Under the same conditions as in FIG. 7, when the distance from the deck to the upper end of the inner rim of the pontoon is increased to 0.37 m, a time history response analysis at positions 1 to 10 is performed. It is a figure which shows the result of having calculated | required the value when the absolute value maximum is reached in each of 10. The analysis result to see the stress reduction effect in the time history response is shown. (A) shows the analysis result of the response of the out-of-plane stress in the radial direction at the position 2 under the calculation parameters of Table 1. (B) is a figure which shows the analysis result of the response of the out-of-plane stress of the radial direction in the position 2 on the conditions which reduced the absolute value of the gradient of the upper surface and lower surface of a pontoon to 0.8 degree | times, respectively. It shows the result of investigating the change of the stress value at positions 1 to 10 when the absolute value of the slope of the upper and lower surfaces of the pontoon is changed by ± 0.2 degrees around 0.8 degrees. (B) is the analysis result of the in-plane stress in the circumferential direction, (c) (d) is the analysis result of the out-of-plane stress in the radial direction or axial direction, and (e) and (f) are the out-of-plane stress in the circumferential direction. It is a figure which shows an analysis result. The result of analyzing the out-of-plane stress in the radial direction at position 2 is shown. (A) shows the stress values obtained when the absolute values of the gradients of the upper and lower surfaces of the pontoon are changed to predetermined values. (B) is a diagram showing a graph plotting the correlation between the radial out-of-plane stress at position 2 and the absolute values of the gradients of the upper and lower surfaces of the pontoon based on the result of (A). The general structure of a floating roof type tank is shown, (a) is a partially cut schematic perspective view, and (b) is a cut side view showing an enlarged floating roof portion.

Explanation of symbols

15 Floating roof 17 Pontoon 21 Rainwater cover (cover)
22 Gas leak prevention cover

Claims (3)

  A radial gradient of the upper surface of the pontoon provided on the outer peripheral portion of the floating roof of the floating roof tank is set to an upward gradient of 0.0 degree to 1.5 degrees from the radial inner side, and the pontoon A stress reducing device for a floating roof, characterized by having a configuration in which the gradient in the radial direction of the lower surface of the steel plate is a downward gradient of 0.0 degrees to 1.5 degrees outward from the radial inner side.   2. The stress reducing device for a floating roof according to claim 1, wherein a cover for covering the upper surface of the pontoon is inclined at a position above the pontoon so as to have an ascending slope of a required angle from the radially inner side to the outer side. .   The floating roof stress reduction device according to claim 1 or 2, wherein a gas leakage prevention cover is provided on the outer peripheral edge of the lower surface of the pontoon so as to project a required dimension downward.

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