US3300986A - Method of constructing storage tank - Google Patents

Description

Jan. 31, 1967 HlRoSl-n HIRATA 3,300,986

METHOD OF CONSTRUCTING STORAGE TANK Filed April 6, 1964 lll United States zuPatent titice iiid Patented Jan. 31, 1967 3,300,986 METHOD F CNSTRUCTING STRAGE TANK Hiroshi Hirata, Meguro-ku, Tokyo, Japan, assigner to Chiyoda Kako Kensetsu llahushiki Keisha, Tokyo, Japan, a corporation of Japan Fiied Apr. 6, 1964, Ser. No. 357,379 Claims priority, application `lapan, Mar. 17, 1964, 35i/14.590 3 Claims. (Cl. 61--5) The present invention relates to la method of constructing a cylindrical storage tank, more particularly to a method of construction a cylindrical storage tank in which the ground immediately below the tank is completely, or almost completely, compacted beforehand as `a foundation by means of a simple p-rocess. Thereafter, the permanent bottom plates and the tank itself are assembled and the tank serves to receive liquid such as oil, water and the like, pulverized subs-tance such as cement, grain and the like or granular matter such as soybean, wheat and so on.

There have been many instances of serious accident or inoperativeness such as an upsetting or tilting of the tank, cracks or deformations of a bottom plate, a column or roof, various troubles of the heating coils, cracks and damage of the st-ructure during a hydrostatic testing caused by uneven sinking o-f the ground after the installation of the tank, such as la petroleum storage tank, on the soft ground. A technique such as using various kinds of pilings, or replacing soft soil with sand has been heretofore use-d to remedy the situation as described hereinabove, but provided most of the time to be unsatisfactory because of incomplete .resolution of the problem and the labor consumption and cost involved. While serious troubles will occur as a result `of neglecting the design of the foundation, a great deal of money has been meaninglessly investe-d in some instances by overdesigning the foundation or being too sensitive and cautious in connection with this problem.

An object of the present invent-ion is to provide a novel method for construction tanks thereby overcoming the dili-culties encountered in the conventional technique as described hereinabove. That is, in order to prevent a tank from being involved in serious troubles of various kinds caused by a sinking of the soft ground, the ground immediately below the tank is to sink beforehand suiciently until a safe sinking of the ground is attained and firmly hardened to the extent that substantially no more sinking will occur, prior to assembling the inner bottom portion of said tank. For this purpose, a temporary bottom of exible water impervious film will be provided on the sketch plate (the bottom plate upon which the shell rests), which tank is not yet provided with its proper inner bottom member, and the water is lled into this tank. The ground immediately below the tank will sink sufiiciently by weight of the water. An object of the present invention is to reduce a time required 'for attaining required sinking by providing sand piles in the grou-nd and to fit the temporary bottom `member simply and securely by providing particular reinforcing members and protection sheets (precautionary flexible sheets) over the connection between the flexible water impervious film and the sketch plates which are connected to the side wall in the lowest part thereof, and by meohanizing a jointing and inspecting process of the flexible water impe-rvious lm.

Now, a preferable embodiment according to the present invention will Kbe Ihereinafter described in detail with reference to the accompanying drawings in which:

FIG. 1 is a vertical longitudinal sectional view showing a tank and its foundation in a condition prior to uneven sinking;

FIG. 2 is a vertical longitudinal sectional view showing a condition after uneven sinking by means of water ballast;

FIG. 3 is a vertical longitudinal sectional view showing a complete condition `of the predetermined configuration by levelling an uneven surface;

FIGS. 4- =and 5 are plan views showing the bottom plating of t-he different arrangement;

FIG. 6 is a detailed sectional View show-ing a part A in FIG. l, in an enlarged scale;

FIG. 7 is` a vertical sectional view showing a process of welding together the water impervious film;

FIG. 8 is a vertical sectional view showing an inspecting process of the Water impervious film to detect a flaw such as a pin hole by means of la hole detector; and

FIG. 9 is a cross sectional View showing a reinforcing member.

Like reference numerals have been provided to denote the like members in each of above drawings.

The -following brief description gives the designation of t-he parts wherein 1 is the surface of the ground on which the foundation for the tank is placed; 1 that portion of the surface of the ground to be sunk and compacted by a water ballast; 2 a sand yfoundation prior to water ballasting (FIG. l); 2 a sand foundation sunken by the water .ballast (FIGS. 2 and 3); 3 a support member for a side wall of the tank, for instance, of concrete, brick or steel plate, designed for preventing a sketch plate 4 immediately below the side wall from deforming due to the weight of the side wall of the tank and `for easy assembly work of the side plates of the tank; 4 the skitch plates constituting peripheral parts of the bottom; 5 side plates of the tank; 6 a temporary bottom member of flexible water impervious lm; 6 a iiexible wate-r impervious lm brought into the tank separately; 7 an overlapped joint lof the temporary bottom 6 with the sketch plate 4; 8 a nozzle and valve mounted on the tank in the lower part thereof intended for filling or discharging water or liquid; 9 the water ballast; 10 a piece of soft ground; 11 sand piles; 12 bottom plates of the tank located inwardly of the sketch plates; 13 a soft resilient reinforcing member fitted annularly over the inner edge of the sketch plates designed Ifor preventing the temporary bottom 6 lfrom damage when in a ballasted condition; 14 a precautionary exible protecting sheet adhered to the sketch plate covering the upper part of the reinforcing member 13; 15 an electrical welding unit of high frequency for the flexible film, and 22 an electrical hole detector adapted to give an alarm when a circuit therefor is closed.

At the time of construction of a tank, necessary data will be collected for computing van amount of sinking of the ground caused by the weight of the sand banking for the foundation, the tank itself and the content therein and for working out a time required for producing the amount of sinking. This amount of sinking will be cornputed using those data from a soil survey. The size and spacing of the sand piles 11 will be determined in such a manner as to produce majority of the Iamount of sinking in a time suited for the construction schedule of the tank. The sand pile will act as a draining passage for the water contained in a soft `ground and is very effective for strengthening the found-ation.

Now, as described in FIG. 1, sand piles having the aforementioned diameter and spacing will be provided in a soft ground 10 and a sand banking 2 will be built on the ground 1 while compacting it, Furthermore, a support member 3 for the side wall is provided annularly in a location immediately below the side wall 5 of the tank. The sketch plates 4 and the tank side wall S are placed thereupon with necessary parts being welded together in a tight manner. The configuration and number of the sketch plates 4 and the inner bottom plating 12 as illustrated in FIGS. 4 and 5 are intended to show merely an embodiment according to the present invention and may be designed in any other way. A soft resilient reinforcing member 13 is fitted annularly over said sketch plates 4 along its inner edge in order to prevent the fiexible water impervious lm from damage as illustrated in FIG. 6. Further, a protection film 14 is adhered annularly on the sketch plate 4 covering the reinforcing member 13. And then, a temporary bottom 6 of flexible water impervious film is laid out on the sand banking within a tank and adhered to the upper surface of the sketch plate along its periphery using suitable adhesive. As the bottom area of the tank becomes larger, a coverage of flexible water impervious film 6 will also become bigger, rendering a transportation and laying out thereof difficult. Therefore, the film may be divided into any suitable size and then brought into the tank. In this case, said flexible water impervious film will be welded together in place by a process as illustrated in FIG. 7. That is, a welding is carried out -by means of a high frequency electric welding process.

When fiexible water impervious films of suitable size are fitted all over the bottom area of the tank, the surface of the sand pile is moistened with appropriate spray. In fitting the films on the surface of the moistened sand pile, respective end portions of the film must overlap one above the other. Then as shown in FIG. 7, a conductive metal plate 19 is disposed under overlapping end portions and welding electrodes 18 and 18 mounted on a portable high frequency electrical welding unit 15 are disposed on the overlapping end portions. When a high frequency electric current is applied to the welding electrodes 18 and 18 through circuits 16 and 17, the overlapping end portions will be fused and welded together. In the device shown in FIG. 7, for the purpose of increasing adhesion, a positive electrode 18 and a negative electrode 18 are disposed adjacent to each other in such a manner as to weld in two portions, By moving the conductive metal plate 19 under the overlapping end portions and the welding electrodes 18 and 18', a weld is made in the form of two continuous seams.

By thus welding respective overlapping end portions one after the other, a continuous watertight temporary bottom is obtained all over the bottom area of the tank. The inspection of defects such as pin holes causing a leakage in such temporary bottom will naturally cost much labor and time due to a large area of examination. As shown in FIG. 8, means have been successfully provided by this invention for efiicient detection of flaws in a reduced period of time. Namely, a pinhole detector comprising a collector 4brush 26 attached at the end of handle 25 of insulating material is used. The collector brush is connected at one end with a high voltage generator 22 by means of a circuit 23. The high voltage generator 22 is a stepup transformer, connected with a high voltage circuit in the secondary side, having a collector brush 26 at one end, and grounded at the other end in a sand pile outside the tank through a ground bar 24. Further, the sand pile, previously moistened by sprinkling as described hereinabove, will become electrically conductive so that a high voltage circuit will be formed as follows: 22 23 26 6- 2 24 22 (see FIG. 8). If film 6 has no defect, such as a pin hole, the film will be a perfect insulating material permitting no high voltage circuit to be formed with no current flowing.

If there is any defect, such as a pin hole in the film, the collector brush '26 will come into contact with the moistened sand pile 2 through the defective spot to form a high voltage circuit in which electric current flows. The detection of this electric currentl will locate a defective spot and then sound a buzzer.

Sweeping of the temporary bottom by means of a pin hole detector comprising such a collector brush will permit a large area of the temporary bottom to be inspected in a short time. A leaking part may be adhered together and mended -by using the same material as the flexible water impervious film 6.

The water impervious film 6 is fitted merely as a temporary bottom member and an examination and mending of defective parts will be completed in this manner. And then water will be directed into the tank through a valve 8. Actually, water is gradually filled therein in such a manner to avoid a shearing type flow.

When the tank is filled up, it is left alone in that condition until the sinking operation is almost completed. The period during which the tank is maintained in a full condition will substantially agree with that period computed as described hereinabove, because the size and spacing of the sand pile is determined as a result of the soil survey in such a manner that a majority of sinking of the ground will take place in a relatively short time. The water will be discharged through the valve 8 after a sinking operation is almost completed as described hereinabove. As a result, each part of the ground will be sunk unevenly dependent upon the non-uniformity of the ground as illustrated in FIG. 2. Accordingly, the temporary bottom 6 will be removed and then the sand banking 2 and uneven sinking under the side plates of the tank will be corrected to a predetermined configuration as illustrated in FIG. 3. Thereafter, many bottom plates 12 constituting an inner portion of the tank bottom are laid out in a close contact with each other and welded together tightly among themselves and to the sketch plates 4 thereby completing a construction of the tank main body. And then a roof and other annexed equipments will be mounted thereon, thus finishing the construction of the whole tank. According to the present invention, in cases of soft ground including loose sand or alternate layers of sand and clay or silt, the sand pile 11 can be eliminated thereby reducing a construction period and assuring an economical construction of the tank. According to the present technique, a water load is applied on a soft ground by filling the tank to the full prior to fitting and welding of the permanent bottom structure of the proper design. Therefore, sinking and compacting of the ground will be effected to a considerable depth where the load of the tank is transmitted. Uneven sinking of the ground is effected beforehand and a foundation of the sand banking is corrected to a predetermined conguration and then the bottom platings of proper design are laid out and welded together thereby entirely safe-guarding against sinking in the future. Since water ballast is used as a temporary load instead of a conventional load including soil and sand, the loading operation is facilitated and construction Will be carried out in a reduced period of time and hence be very economical.

It will be understood that although the present invention has been described in a preferable embodiment, various modifications and alterations can be made by those skilled in the art in connection with design, technique as well as material without departing from the spirit of the present invention. For instance, reinforced plastics, fiber reinforced plastics, concrete, aluminum and so on may be used as an alternative for conventional steel material.

What is claimed is:

1. A method of constructing storage tanks wherein a foundation of sand banking is built on soft ground intended to support the tank, placing a support member, upon said foundation to form the peripheral foundation of the tank, mounting a sketch plate which extends about the inner periphery of the support member on said support member and sealingly engaging the sketch plate with the side walls of said tank, placing a temporary bottom member of a flexible water impervious film over the bottom portion of said tank to cover the entire surface area thereof with its peripheral portion being sealingly attached to said sketch plate, filling said tank with water to effect a sinking and settling of said soft ground and sand foundation, draining said tank, removing said temporary bottom member, correcting said ground surface and seal- References Cited by the Examiner ingly fitting a permanent bottom into said tank fastened about its periphery to said sketch plate. UNITED STATES PATENTS 2. A method of constructing a storage tank as described 1,049,221 12/ 1912 Franignoul 61-50 in claim 1 in which a reinforcing member and a protec- 5 2,301,061 11/1942 Logeman 220-18 tion film are applied to said `sketch plate and said temporary bottom member is .attached to said protection lm. OTHER REFERENCES 3. A method of constructing a storage tank as de- Engineering NeWs Rec0rd (published) Ann 28I 1955,

scribed in claim 1 in which said temporary bottom memp 41.

ber of flexible water impervious lm is welded together 10 -by means of high frequency Welding after wetting said y banking and simultaneously subjecting said lm to an CHARLES E' OCONNELLP'lma'y Exammer' examination for defects. JACOB SHAPIRO, Examiner.

Claims (1)

1. A METHOD OF CONSTRUCTING STORAGE TANKS WHEREIN A FOUNDATION OF SAND BANKING IS BUILT ON SOFT GROUND INTENDED TO SUPPORT THE TANK, PLACING A SUPPORT MEMBER, UPON SAID FOUNDATION TO FORM THE PERIPHERAL FOUNDATION OF THE TANK, MOUNTING A SKETCH PLATE WHICH EXTENDS ABOUT THE INNER PERIPHERY OF THE SUPPORT MEMBER ON SAID SUPPORT MEMBER AND SEALINGLY ENGAGING THE SKETCH PLATE WITH THE SIDE WALLS OF SAID TANK, PLACING A TEMPORARY BOTTOM MEMBER OF A FLEXIBLE WATER IMPERVIOUS FILM OVER THE BOTTOM PORTION OF SAID TANK TO COVER THE ENTIRE SURFACE AREA THEREOF WITH ITS PERIPHERAL PORTION BEING SEALINGLY AT-

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