US3106309A

US3106309A - Secondary seal for floating tank roof

Info

Publication number: US3106309A
Application number: US61260A
Authority: US
Inventors: William R Nelson; Marshall U Bagwell
Original assignee: Texas Pipe Line Co
Current assignee: Texas Pipe Line Co
Priority date: 1960-10-07
Filing date: 1960-10-07
Publication date: 1963-10-08
Anticipated expiration: 1980-10-08

Description

Oct. 8, 1963 w. R. NELSON ETAL SECONDARY SEAL FOR FLOATING TANK ROOF Filed 001,- 7, 1960 United States Patent 01 This invention relates generally to liquid storage tanks having floating roofs and particularly to the secondary seal for the space between the floating roof and the tank wall.

Many oil storage tanks require a floating roof cover of the pontoon type which is capable of moving up and down within the tank in accordance with changes in the volume of the tank contents.

Sealing structures to close the annular area between the wall of the tank and the floating roof usually include a primary seal comprising a plurality of shoes supported by the floating roof itself, with the open space between the primary seal and the floating roof being closed by a continuous flexible fabric seal usually.

Even though the shoes are held against the inside wall surface of the tank with pressure, it is not always possible to hold them in a seal-tight condition in order that water and other contaminants will not seep into the tank through the space between the shoes and the wall and become admixed with the stored product. Furthermore, there is a problem of corrosion arising in the areas contacted by the shoes of the primary seal and in case of severe weather, liquids may freeze between the primary seal shoes and the tank wall.

Accordingly, it is an object of the invention to provide an improved floating roof seal which will prevent or minimize the flow of contaminants across the seal contact area into the tank.

Another object of the invention is to provide a simple floating roof seal which is economical with respect to the cost of material and the labor for its installation.

Still another object of the invention is to provide a secondary seal for a floating tank roof which is simple and inexpensive to make and without a requirement for separate and special support therefor.

Another object of this invention is to provide a novel secondary seal for a floating tank roof which is in contact with the tank wall at all times.

These and other objects, [features and advantages of the present invention will become apparent from the following description and claims of the present invention when read in the light of the drawings in which:

FIG. 1 is a perspective view of a cross section of a floating tank roof showing the primary and secondary seals; and

FIG. 2 is an enlarged, partial perspective, cross sectional view of the secondary seal shown diagrammatically in operative position.

The objects of the present invention are achieved by the application of a flexible seal directly to the primary seal of a floating tank roof without the requirement of a special support for the secondary seal which will be held at all times in sealing position against the tank Wall.

Referring to the drawing, part of a cylindrical, open end storage tank, indicated generally at '10, is shown, includingthe upstanding side wall 11 and the floating pontoon type cover or roof 12. The floating roof -12 comprises the top deck 13, the bottom deck 14, interconnected by the rim plate at 15 and bulk heads, one of which is shown at 15a.

The primary seal 16 comprises a number of shoes, indicated at 16a, each of which is supported by and interconnected with the floating roof by means of the counterof the secondary seal.

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weight hanger structure indicated generally at 17. By an appropriate balance of the counterweight, the shoes of the primary seal are held in contact with the tank side Wall as the floating roof rises and falls in accordance with changes in the amount of the contents stored in the tank.

To close the annular area between the floating roof and the shoes of the primary seal, a continuous flexible seal, 18, for example fabric, is fastened to the roof and the primary seal at 18a and '18b respectively, by means of a backing strip and bolts. Conventional grounding straps between the floating roof and the primary seal are indicated at 19. Seals and interconnections between each of the shoes are in a manner well known in the art and are not described here. i V

Withrespect to the edge structure of each of the shoes of the primary seal, there is disclosed at 20 an inwardly turned edge or flange portion angled approximately at 45 and about /2 inch in extent. On this inwardly turned flange or break, a secondary seal 21 is positioned with a slot therein for fitting over the break in the shoe for support thereby.

Referring in detail to FIG. 2, there is shown a cross section of the resilient secondary seal of flexible plastic, e.g.

synthetic rubber resistant to hydrocarbon attack and tendency to set, comprising the tapered contact portion 21a, and an offset end or support portion 21b at the wider end This offset end is defined by a smooth curved surface continuing from the outer exposed surface of the tapered portion and a pair of straight surfaces continuing therefrom and from the inner contact surface of the tapered portion which intersect to define a right angle (in projection), as at 21c. From this projected line of intersection at 210, a notch at 22' 'is formed so that the axis of this notch and the axis of the tapered portion intersect at an obtuse angle as disclosed at 22a. Thus, when such a secondary seal is positioned over the 45 angle of the break of the primary seal, because of this obtuse angle, a good portion, approximately half of the tapered portion of a secondary seal, makes contact with the side wall of the tank and is deformed into an ogee or reverse S shape as shown in dotted outline in FIG. 2 and more distinctly in FIG. 1. This intimate contact with the side wall not only provides an effective seal to minimize or prevent the flow of contaminants across the seal into the tank itself, but the configuration of the downwardly directed shape of the secondary seal is such that the rain water runs off toward the center of the tank roof whence it is removed in a manner well known in the art.

In use, it has been found most expedient to prepare for the application of the improved secondary seal by cleaning the upper edges or breaks of the shoes of the primary seal by scraping and wire brushing, followed by scrubhing with a suitable solvent to remove paraflin or oil deposits. A thin film of a rubber cement or other rubber adhesive is applied to both sides and the edge of each break for use as a lubricant in forcing on a secondary seal and for bonding the seal to the shoe. To complete the joint between individual sections of the secondary seal, tapes well known in the art are used and span the joint adequately.

Since the secondary seal will be made of rubber and most likely from synthetic resilient materials which are not subject to deterioration either by contact with hydrocarbon vapors or to abrasion and excessive wear as the seal rubs against the inner tank wall, and even though the shoes of the primary seal may be deflected from the shell by weld scams or deformations of the tank wall, the secondary seal has sufficient flexibility and elasticity to bridge the maximum observed deflection of the shoes I from the tank wall. The close contact of the secondary seal with the tank wall surface prevents the escape of oil or other volatile product vapors from the storage tank while preventing contaminants from entering the tank across the face of the primary seal. As an example of the economy in time, it has been found that a ten foot section of our improved secondary seal can be applied in approximately one half hour including the time for cleaning and preparation of the edges for the seal fitting.

Thus there has been shown that the secondary seal of the type shown herein can be used to augment etfectively the primary seal of a floating roof of a storage tank in order to retain vapors from the liquid contents thereof while preventing the entrance of contaminants thereinto.

We claim:

1. A secondary seal for use with a floating roof in an open end tank by afiixture on the inwardly extending top edges of a plurality of shoes of the primary seal thereof comprising a flexible member having two angularly disposed sections, one of said sections being elongated and tapered for contact at its thinned outer edge with an inside tank wall, the other of said sections being thickened for support on said top edges and having a slot extending inwardly from the outer edge thereof at an angle so that in cross section the center line of said slot and the center line of the elongated tapered section intersect at an obtuse angle facing said inside tank wall whereby said elongated tapered section forms an ogee in cross section when in contact with said inside tank wall, said slot having dimensions for a tight fit on said top edges of said shoes and being shallow enough to avoid contact of the thickened section with said inside tank wall yet deep enough for adequate support engagement thereon.

2. In combination with an open end container for holding fluid, a cover therefor adapted to move upwardly and downwardly in said container corresponding to changes in the volume of the fluid held in said container comprising a floating roof, a primary seal having a plurality of shoes supported in contact position with the inside wall surface of said container by said floating roof and being spaced annularly therefrom, flexible interconnecting means for closing the annular opening between said primary seal and said floating roof, and a secondary seal atfixed on the inwardly extending top edges of said plurality of shoes of said primary seal and contacting said inside wall sunface, said secondary seal comprising a flexible, angular member formed by a first section in the shape of an elongated, outwardly thinned contact portion and a second section in the shape of a thickened support portion having a slot at its outer end with dimensions for a tight fit on said top edges of said shoes, the axis of said slot in said support portion and the axis of said contact portion intersecting at an obtuse angle facing said inside wall surface, said slot in said support portion being deep enough for adequate engagement with said top edges of said shoes and shallow enough to prevent contact of said support portion with said inside wall surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,568,728 Goldsby et a1 Sept. 25, 1951 2,588,628 Higbie et al Mar. 11, 1952 2,722,978 Frisk Nov. 8, 1955 2,897,998 Ulm Aug. 4, 1959

Claims

1. A SECONDARY SEAL FOR USE WITH A FLOATING ROOF IN AN OPEN END TANK BY AFFIXTURE ON THE INWARDLY EXTENDING TOP EDGES OF A PLURALITY OF SHOES OF THE PRIMARY SEAL THEREOF COMPRISING A FLEXIBLE MEMBER HAVING TWO ANGULARLY DISPOSED SECTIONS, ONE OF SAID SECTIONS BEING ELONGATED AND TAPERED FOR CONTACT AT ITS THINNED OUTER EDGE WITH AN INSIDE TANK WALL, THE OTHER OF SAID SECTIONS BEING THICKENED FOR SUPPORT ON SAID TOP EDGES AND HAVING A SLOT EXTENDING INWARDLY FROM THE OUTER EDGE THEREOF AT AN ANGLE SO THAT IN CROSS SECTION THE CENTER LINE OF SAID SLOT AND THE CENTER LINE OF THE ELONGATED TAPERED SECTION INTERSECT AT AN OBTUSE ANGLE FACING SAID INSIDE TANK WALL WHEREBY SAID ELONGATED TAPERED SECTION FORMS AND OGEE IN CROSS SECTION WHEN IN CONTACT WITH SAID INSIDE TANK WALL, SAID SLOT HAVING DIMENSIONS FOR A TIGHT FIT ON SAID TOP EDGES OF SAID SHOES AND BEING SHALLOW ENOUGH TO AVOID CONTACT OF THE THICKENED SECTION WITH SAID INSIDE TANK WALL YET DEEP ENOUGH FOR ADEQUATE SUPPORT ENGAGEMENT THEREON.