US3167206A

US3167206A - Secondary seal for floating tank roof

Info

Publication number: US3167206A
Application number: US224028A
Authority: US
Inventors: William R Nelson
Original assignee: Texas Pipe Line Co
Current assignee: Texas Pipe Line Co
Priority date: 1962-09-17
Filing date: 1962-09-17
Publication date: 1965-01-26
Anticipated expiration: 1982-01-26

Description

Jan. 26, 1965 w. R NELSON SECONDARY SEAL FOR FLOATING TANK ROOF Filed Sept. 17, 1962 United States Patent 3,167 ,206 SECONDARY SEAL FOR FLOATING TANK ROOF I William R. Nelson, Houston, Tex., assignor to The Texas Pipe Line Company, Houston, Tex., a corporation of 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 inner 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 fluid level as the volume of the tank contents varies.

Sealing structures to close the annular area between the inner wall surface 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 inner wall surface of the tank with pressure, it is not always possible to hold them in a seal-tight condition so that water and other contaminants will not seep into the tank through the clearance 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 claim of the present invention when read in the light of the drawing in which:

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

FIG. 2 is a cross sectional view of the improved secondary seal;

FIG. 3 is a partial, cross sectional view of the secondary seal shown in operative position; and

FIG. 4 is a fragmentary view showing an alternate means of fastening the secondary seal to the edge of the primary seal.

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, and 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, including the 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 "ice 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, such as indicated at 16a, each of which is supported by and interconnected with the floating roof by means of the hanger structure indicated generally at 17. By an appropriate balance of the hanger, 17a, the shoes of the primary seal are held in contact with the inner surface of 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 space 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 to the primary seal at 18a and 18b respectively, by means of backing strips 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.

With respect to the edge structure of each of the shoes of the primary seal, there is disclosed at 16b an inwardly turned edge or flange portion angled approximately at 45 and about /2 inch in extent. On this inwardly turned flange portion or break, a secondary seal 20 is positioned, the seal having a slot or recess for fitting over the break in the shoe for support thereby.

Refering in detail to FIG. 2, there is shown a cross section of the resilient secondary seal of a flexible plastic material, e.g. synthetic rubber resistant to hydrocarbon attack and tendency to set, comprising the offset contact end portion at 21, the enlarged olfset support portion at 22, and the planar intermediate interconnecting portion at 23. The contact end portion is shown slightly offset and projecting out of the plane of the back or inner surface of the intermediate portion and having a sharp contact edge, but other configurations can be used for this contact end portion to compensate for wear, and to insure suflicient pressure against the inner tank wall surface.

The offset support portion 22 is shown as ending in a substantially hemispherical cross section, as indicated at 22a, with a recess 22b extending from the edge of the hemispherical surface inwardly at an angle such that the axis of this recess intersects the axis of the straight uniform section of the intermediate portion 23 at an obtuse angle X of slightly less than so that when the secondary seal is placed on the 45 break of the upper edge of the shoes of the primary seal at 1612, the divergence in angularities will allow adequate contact surface between the contact end portion of the secondary seal and the inner wall surface. 1

To provide a more positive contact with and to insure pressure on the inner wall surface, use is made of external positioned metallic stiffeners or inserts. On the outer exposed surface 24 of the intermediate portion 23, there are provided tongue-

like members

25, 26, projecting toward each other to define

grooves

25a, 26a, facing each other. Into these grooves, metallic stiifeners or inserts 27 are cupped and seated, the length of each stiffener in the radial direction being slightly greater than the distance between the bottoms of the facing

grooves

25a, 26a, so that the force exerted by the spring action of the stifleners in a radial direction provides pressure and results in more positive contact with the inner wall surface of the tank. These external positioned inserts are flat sheet metal, e.g. spring bronze strips, about 6 in width, and are spaced circumferentially about A2" apart in the grooves to act as radial springs. In view of the substantially large diameter of the storage tank in which the secondary seal is to be used, and with the flexibility of the -not only provides an effective seal to minimize or prevent theflow of"c'ontaminants' 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't'oward' thecenter of the tank roof, whence it' is removed in a manner well known in the art.

In use, it'hasbeen found most expedient to prepare for 'the application of theimproved' secondary seal by cleaning theupperedgesor' breaks of the shoesof the primary seal by' scraping and wire brushing, followed 'by scrubbing 'witha s'iiitable'solvent' to remove 'paraflin or oil, deposits.

A thin film of a rubber. cement or other rubber adhesive 'is' applied to'bo'th sides and the edge of'ea ch' break for use as a lubricant in forcing'on the secondary seal and for'bonding the seal to the shoe. To complete the joint between individual SO'Lsections of 'the-:secor1dary seal,

tapes Well known in the art are useda'n'd span the joint adequately; In addition, when conditions require I to secure the secondary seal positively, fastening pins or self tapping screws, appropriately spaced, -'are used as indicated at 40, FIG. 4. f V 7 "Since the secondary seal will'be .made'of rubber and "most likely from synthetic resilie'nt materials which are "not subject to deterioration'either by contact withhydrocarbon vapors orto abrasion and excessive wear as the seal rubs against the'innerjtank fwall, andfeven though the shoes of the. primary seal rnay'be deflected from the shell by weld seams or deformations of the tankwall, the secondary seal has 'sufiicient flexibility and elasticity to bridge the maximum observed deflection of the shoes from thetank wall. The close contact "of' the secondaryseal with the tank 'wall surface preventsfthe escape of'oil or other volatile product vapors from the storage tank while preventing contaminants' from 'f'entering thetank across,

the face of the primary seal. Thus there'hasb'een shown'that the secondary seal of "the type shown herein can be used to aument etf'ective- 1y 'the'prirnar'y seal of a'fioating roof'of a" storage tank 7 in order to retain vaporsfr'o'm'the liquid contents thereof while preventing the entrance of contaminants thereinto.

' .Qther modifications and variations of" the invention,

as hereinbefo're setforth, may'be made without departing fronithe spirit and scope thereof, and therefore only 'suchllimitiations should be imposed as are indicated in the appended claim, I

I claim:

, a wardly and downwardly in said container corresponding f to changes in'the' volume of the fiuidihel'd in said container comprising a fioating'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, each ofsaid. plurality of shoes having its top edge projecting angulary away from said inside wall surface, "flexible interconnecting means for closing the annular opening between said 10 primary seal andrsaidfloating roofpand a secondary seal aliixed 'on the top edges of said plurality of shoes of said primary seal and contacting said inside wall surface on its inner protected face with respect thereto, comprising aiflexiblefangular member having an inside tank Wall "surface contact portion at one; end thereof and" an offset 7 support portion at the other end thereofwith a recess therein, and arr-intermediate portion interconnecting said contact portionwith said support portionjthe axis of said "recess-in said oifet portion and the axis of said intermediate portion intersecting at 'an' 'obtuse-angle' facing said -in- 'side wall surface-said" recess insaidsupport portion hav- "mg-dimensions for-atightfit-onsaid top edges of said shoes, *deep. enough for adequate engagement with said topedges-bf said shoesand shallow enough to prevent contact' be said support portion with said inside wall surface, said", intermediate portion having *tongue-like'mem- "bers projecting toward each other thereby'defining a pair of grooves-facing each other 'onthe outerexposed face thereof with respecttosaid inside wall surface, said tongue like members extending longitudinally of said "secondary"-seal adjacent the support and contact portions "thereof, and a plurality or resilient metallic inserts seated 'in' closely spaced circumferential relationship in said pair of grooves; said -inserts having a transverse dimension "greater than'the-fdistance between the'bottoms of said pair of grooves whereby a spring action of the inserts in 'a'radial direction isprovided ar'oun'd sai'doffset support portion-to maintain" said contact portion of said secondary seal-in positivecontact-withsaid inside tankv Wall 40 surface.

R'efei-en'ces Cit'ed inthe file of this patent 5 UNITED :STATES PATENTS 2,259,185 Swedman Oct. 14, 1941 2,287,211 'Wiggins June 23, 1942 2,348,379 Gouloo ze -May 9, 1944 2,568,728 Goldsby etal. ..Sept. 25, 1951 ;-2,'897,998 Ulm n. Aug. 4, 1959 0 2,973,113 Fino Feb. '28, 1961