US3533531A

US3533531A - Liquid storage tanks

Info

Publication number: US3533531A
Authority: US
Inventors: John F Delahunt
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1968-09-12
Filing date: 1968-09-12
Publication date: 1970-10-13
Anticipated expiration: 1987-10-13

Description

0d. 13, i970 J. F. DELAHUNT 3,533,533

LIQUID STORAGE TANKS Filed sept. 12,.y 1968 ya@ .Eek/M Inventor AfOfney United States Patent O LIQUID STORAGE TANKS John F. Delahnnt, Florham Park, NJ., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Sept. 12, 1968, Ser. No. 759,428 Int. Cl. B65d 7/42 U.S. Cl. 220-68 6 Claims ABSTRACT OF THE DISCLOSURE Nonmetallic bottoms are used in the construction or repair of metallic tanks by adhesively securing the nonmetallic material only at its periphery.

BACKGROUND OF THE INVENTION This invention relates to liquid storage tanks. More particularly, it relates to the use of nonmetallic bottoms in storage tanks having metallic shells. The invention relates also to methods of making new tanks or repairing corroded metallic tanks by the installation of nonmetallic bottoms.

The use of liquid storage tanks is common in many industries. Generally, liquid storage tanks involve a metallic shell secured or attached to a horizontal bottom which is ordinarily flat or shaped convex downwardly. A frequent difficulty encountered in the use of liquid storage tanks is the uneven rate of corrosion which usually occurs. In general, the bottom of the tanks corrode much more rapidly than the sides or shell of the tank. The bottom is subject to corrosion both internally and externally. In the chemicals and petroleum industries, many relatively stable and noncorrosive hydrocarbons, fuels, or other liquids may at times contain water, acids, wax, sludge and the like which tend to internally corrode tank bottoms at a rate significantly more rapidly than the sides of the tank. Simultaneously, external bottom corrosion may be hastened by water, salt, poor foundation designs, etc. To overcome these difficulties, it has been necessary to repair the bottoms or install new bottoms unless special metals or metals of increased thickness were used in the bottom of the tank when originally manufactured.

It has thus long been felt desirable to develop a technique for manufacturing tanks which are suitable for liquid storage and yet are economical to maintain. Similarly, it has been considered desirable to develop a method for repairing metallic tanks Whose bottoms have become corroded until they are unsafe or uneconomical to use due to the threat of leakage of the liquid contents.

SUMMARY OF THE INVENTION This invention contemplates a tank for storing liquids which has a metallic shell resting upon a horizontal support means, c g., a foundation or bottom, and having at` tached to the inner walls of the shell and the support means a nonmetallic corrosion-resistant bottom secured only at its periphery. The invention also contemplates the repair of tanks having corroded bottoms by installing a nonmetallic corrosion-resistant bottom inside the tank sealed adhesively only at the periphery of said bottom and the lower portions of the inner walls of the shell.

The invention is based on the discovery that excellent strengths can be achieved in attaching the nonmetallic bottom to the support means and shell by adhesively securing the nonmetallic bottom only to a small strip or portion around the periphery of the bottom and extending up the sides of the wall a short distance. Preferably, the nonmetallic bottom is adhesively secured in a zone of the periphery of the support means not greater 3,533,531 Patented Oct. 13, 1970 than about 1A the diameter of the bottom. Similarly, the edges of the nonmetallic bottom extend upwardly inside the shell and are adhesively secured thereto only a short distance, generally less than 1A the height of the tank. Although the precise dimensions of the adhesively secured portion of the nonmetallic bottom depends upon the dimensions of the tank, it is ordinarily unnecessary to secure more than about a 1 foot wide portion around the periphery of the bottom and about a 1 foot high portion along the vertical walls of the shell.

Among the outstanding advantages which can be obtained by using unique peripherally secured nonmetallic bottoms is that a major portion of the preparation which is ordinarily required for repairing a metallic bottom is eliminated. For example, ordinarily it is essential to clean, sandblast, and prime a metallic bottom before attempting to adhesively secure a nonmetallic material to it. Eliminating much of this work results in substantial savings, particularly where large tanks are involved. Also, by leaving the major portion of the non-metallic bottom unattached or free of the support means or metallic bottom, a certain degree of freedom or flexibility, with corresponding resistance or adaptability to strains, can be achieved.

A wide variety of nonmetallic materials can be used for the tank bottom in this invention. For example, many plastic materials, such as polyethylene, polypropylene, and the like, glass-resin laminates, including epoxies, polyesters, and the like, can be used. Similarly, elastomers, including butyl rubber, neoprene, ethylene-propylene rubber, and the like, are satisfactory. It is also possible to use many other types of nonmetallic materials, including composites that may contain some metals such as stainless steel with the nonmetallic material.

The nonmetallic bottom is sealed to the tank shell or walls and to the bottom support means using adhesive bonding or heat bonding. Mechanical bonds, or bonding devices of various types, may also be used in combination with the adhesive.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows, in cross section, a cylindrical metallic storage tank having a nonmetallic bottom installed to protect an existing corroded metal bottom.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawing there is shown a metallic cylindrical tank having a cylindrical shell 10 and a metallic support or bottom 11 attached thereto. Inside the shell is shown a fillet 15 placed at the joint between the tank shell and the shell support to give relief from exural stresses at the junction between the shell and bottom.

Over the center portion of the tank there is shown a thin sheet of plastic 16, such as polyethylene, which is used to cover the uncleaned portion of the tank bottom which has not been sandblasted and primed. The purpose of the thin plastic sheet 16 is merely to keep contaminants, i.e., the sludge or other impurities, which are present in the tank from previous use, from polluting the nonmetallic bottom which is to be applied and thus the sheet may be only a few mils in thickness.

Sections A and B of the inner Walls of the shell and the metallic support or bottom are carefully cleaned and sandblasted to insure good adhesion with the nonmetallic bottom. In this example, A and B are each only 12 inches, which, in a tank feet in diameter and 40 feet high, represent only a very small percentage of the surface which would have to be sandblasted and primed under normal repair procedures.

After the surfaces A and B are sandblasted and primed, a glass/resin laminate is applied in liquid form to the tank bottom by conventional techniques, eg., hand layup, or using glass/resin spray equipment, etc. The glass/ resin laminate, after curing, forms a corrosion-resistant layer 17 which protects the entire original bottom 11. The layer 17 is xed, or adhesively secured at the tank periphery due to its own adhesiveness in curing and does not require a separate or different adhesive. The glass/ resin laminate is, however, free of the bottom over the entire center portion covered by the thin plastic sheet 16.

The thin plastic sheet 16 may serve to prevent liquid bottom-forming material from seeping into pits, holes, etc. in the corroded metallic bottom before curing as well as to keep oil, dirt or other contaminants out of the liquid mixture.

The type of nonmetallic bottom material, e.g., laminate, which is useful for corrosion-resistant bottoms depends, of course, upon the nature of the liquid to be stored in the tank. In general, however, it is desired to employ a glass mat, cloth, weave, etc., with a phenolic, epoxy, or polyester type resin, since these produce excellent physical strength and have excellent resistance to many corrosive materials.

Although the tank shown in the drawing has a cylindrical cross section, the invention is not to be limited to use with only those types of tanks. It may be used in rigid or semirigid or even collapsible tanks of any shape, including cylinders, spheres, hemispheres, and the like.

The invention can be used with new tanks where the support 11 is not attached to the cylindrical shell, or when it is attached but not sealed thereto. Thus, for example, a metallic shell may be positioned over any xed support which is susceptible to adhesion to the nonmetallic corrosion-resistant material.

The nonmetallic bottom material can be applied as a solid sheet, rather than a liquid, in which event a separate adhesive material, such as an epoxy resin is used at the sandblasted and primed zones of the shell walls and support area. Thus, the invention has utility in any liquid storage tanks susceptible to adhesion at a peripheral area of the bottom and lower edge of the sides without any adhesion to the center of the support means. Thus, although the invention has been described with particularity with respect to a preferred embodiment in which it is employed for repairing a corroded existing tank, it will be appreciated by those skilled in the art that many other uses and variations are within the scope of the instant invention.

What is claimed is:

1. A tank for storing liquid comprising:

an upwardly extending metallic shell having an inner surface and an outer surface;

a nonmetallic bottom having edges extending upwardly overlapping said inner surface;

horizontal support means beneath said shell and bottom; and

sealant adhesively securing the upwardly extending edges of said bottom to said inner surface adjacent its lower end and securing to said support means only the outer peripheral portion of said bottom, said sealed outer peripheral portion having a sealed width along any one inner surface of less than onefourth of the total width of the bottom diameter, whereby the center portion of said bottom is in unattached relation to said support means.

2. The tank of claim 1 wherein said upwardly extending edges of the bottom extend upwardly less than onefourth the height of said inner surface.

3. The tank of claim 1 wherein said nonmetallic bottom comprises glass/plastic laminate.

4. The tank of claim 1 wherein said support means comprises a metallic bottom attached to said metallic shell.

5. The tank of claim 4 wherein said metallic bottom is substantially corroded.

6. A method for sealing a tank having an upwardly extending metallic shell and horizontal support means beneath same which comprises sealantly securing a nonmetallic bottom to a lower portion of the inner surfaces of said shell and to only a peripheral portion of the said support means of less than one-fourth the diameter of said support means, immediately adjacent the inner surfaces of said shell, whereby the center portion of said bottom is in unattached relation to said support means.

References Cited UNITED STATES PATENTS 211,813 1/1879 Watt 220-68 1,941,922 1/1934 Worth 220-63 X 2,113,728 4/ 1938 Harrison. 2,131,855 10/1938 Hummel 220-63 X 2,173,585 9/1939 Harrison 229-31 2,798,636 7/1957 Ketchledge 220-63 3,391,823 7/1968 Tijms 220-64 FOREIGN PATENTS 151,790 10/1920` Great Britain.

JOSEPH R. LECLAIR, Primary Examiner I. R. GARRETT, Assistant Examiner Us. c1. XR. 29M4o1; 113-120