Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an improvement in floating
roof tanks used for the storage of petroleum products or other
volatile liquid materials, and in particular relates to an
improved seal for a floating roof.
In a conventional floating roof tank, with which
the seal of the invention is particularly useful, there is
provided a clearance space or rim space between the tank side
wall and the vertical rim of the roof. It is necessary to
provide clearance space to permit unrestrained vertical travel
of the roof within the tank. The clearance space is of suffi-
cient si~e that local dimensional variations in the circularity
of the tank side~all or shell, commonly called out-of-roundness,
which can result from uneven foundation settlement, imprecise
fabrication or erection or unusual live loads such as high
winds and the like, do not hamper vertical travel of the roof.
A conventional system for centering a floating roof
in a tank and simultaneously sealing the space between the
roof rim and the tank inner side wall employs as a sealing
means a yieldable annulus suspended by the roof and extending
from contact with the roof rim into contac~ with the tank
wall. The annulus can be made of flexible sheet material
and can contain a fluid, i.e. liquid or gas, such as water
or nitrogen, or a resilient material such as a polymeric foamed
material. U~S. Pat. Nos. 3,136,444; 3,120,320; 3,075,668;
3,055,533; 2,973,113 and 2,968,420 illustrate seals of those
types.
Other apparatus to maintain the roof centered in
the tank and to effect a seal against evaporation loss uses
a plurality of vertical shoes adapted to slidably contact
the entire circular inner side wall of the tank and means
supported by the roof for pressing the shoes against the inner
side wall, as well as to support the shoes. Vapor loss between
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the roof and shoes is prevented by a flexible nonpermeable
fabric barrier which extends from the upper part of the shoes
to the floating roof top edge. Such apparatus is disclosed sin many U.S. Pat. Nos. including 2,587,508; 2,630,937; 2,649,985
and 2,696,930.
Although such types of seals function quite well
in commercial installations some product vap~r may still escape
past the seal. This possibility is substantially increased
on windy days since air flow over the floating roof creates
a negative pressure over part of the circumference at the seal,
and positive pressure over the other part. The positive wind
pressure will usually be located in the semicircular rim clear-
ance space downwind form the center of the roof and the negative
pressure upwind. When the negative pressure is created the
higher vapor pressure leads to flow of vapor, from beneath
the sealing means, between the seal and the tank inner wall
into the atmosphere. Similarly, the positive pressure causes
air to flow into the vapor space, thereby setting up a ~low
around the vapor space and out the negative side carrying vapor
~ith the flow. This results in undesirable air pollution~
There is accordingly a need for improvements in such liquid
storage tank floating roof seals and materials used in such
seals.
Wiper type seals are also disclosed in the prior
art and are used alone as a primary seal, or as a secondary
seal in conjunction with a primary seal such as those already
described. See U.SO Pat. Nos. 2,190,476; 1,698,158; 2,873,042;
2,973,113; and 3,372,831. U.S. Pat. No. 2,973,113 discloses
a secondary wiper seal made of rubber with a reduced thickness
hinge portion reinforced ~ith embedded nylon. U.S. Pat. No.
2,190,476 discloses a primary seal in the form of a pear-shaped
loop of sheet material with resilient metal strips embedded
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therein in spaced relation to each other. It is believed
that such wiper seals will not produce the vapor seals now
needed to prevent vapor emissions adequately to meet present
day environmental air purity standards.
United States Patent No. 4,138,032 discloses a second-
ary seal made of an elastomeric strip impermeable to petroleum
vapor comprising a plurality of flexible resilient elongated
stiffeners laterally positioned and embedded in elastomeric
material. The patent discloses that as the roof is displaced
up and down, the elastomeric strip can be flexed from an upward-
ly curved arch to a downwardly curved arch and vice versa.
This is largely due to the relatively high coefficient of
friction between the rubber strip used for the seal and the
metal tank wall. In many tanks, it is undesirable for the
sealing strip to flip-flop, as indicated, with vertical displace-
ment of the roof. A better, more continuous seal is quite
often obtained when the sealing strip stays continuously in
an upwardly or downwardly arched condition during and after
vertical displacement of the roof, whether the movement is
up or down.
According to one aspect of the present invention,
there is provided an improved elastomeric strip, impermeable
to petroleum vapor, and useful as a seal in a floating roof
tank, characterized by having a slick face adapted to at all
times contact a surface with which it has slidable contact,
such as a tank wall, with little, if any, sticking. The slick
Face is achieved by applying, on a removable or nonremovable
basis, a layer of antifriction material having a lower coeffi-
cient of friction than the material otherwise comprising the
surface of the elastomeric strip. The slick face prevents
the strip, when used as a seal, from sticking and flip-flopping
with vertical movement of a floating roofO
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The antifriction can comprise a woven or nonwoven
fabric or cloth, or a flexible sheet of polymeric material
fastened to the elastomeric strip by any suitable means, such
as by vulcanizing or by an adhesive, clips, stitching, riveting,
or by some other mechanical fas-tening means. The woven fabric
or cloth, and the nonwoven fabric or cloth, such as a web
of random fibers matted together as a felt, can be applied
to the surface of, or be at least partially embedded in, the
elastomeric strip so as to be nonremovably attached thereto
when the rubber o~ which the elastomeric strip is ma~e is
vulcanized.
It is generally desirable to install the woven or
nonwoven fabric or cloth in separate pieces, each piece being
about 2 inches (5.08 cm.) wide and arranged in closely spaced,
side-by-side relation on the elastomeric strip face so that
a portion of each piece of fabric is carried on each of the
opposite surfaces of the elastomeric strip and extends around
one of the side edges thereof. Consequently, the fabric at
all times contacts the tan~ wall surface and, by using narrow
width pieces, stretching of the elastomeric strip is readily
acco~modated as the composite strip moves close to and then
away from the tank wall. The slick face can also comprise
a polymeric material applied as a thermoplastic or thermosetting
coating or layer and bonded directly to the face of the strip.
Some of the polymeric materials which can be used
to provide the slick face are nylon, polyethylene~ a polyEluoro-
ethylene such as Teflon, or a polychlorofluoroethyleneO
According to a further aspect of the invention there
is provided an improvement in a vertical cylindrical liquid
storage tank of imprecise circularity having a circular 10ating
roof of smaller cliameter than the tank thereby defining a
vapor space between the roof edge and the tank wall, and an
elastomeric strip impermeable to vapor connected at its inner
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l3~
edge by an essentially vapor tight joint to the roof edge
and extending as an annulus arched outward:Ly, upwardly or
downwardly., to the tank inner side wall, for substantially
preventing flow of vapor from a liquid product stored in the
tank through the vapor space to the atmosphere, with the improve-
ment comprising a layer of woven or nonwoven polymeric fabric
or cloth on that portion of the fac-e of the elastomeric strip
which is adapted to substantially at all times make contact
with the tank inner side wall, said polymeric fabric having
a substantially lower coefficient of friction than that of
the elastomeric strip to thereby provide a slick face slidably
movable against the side tank wall to thereby negate reverse
arching of the strip with vertical movement of the floating
roof relative to the tank wall.
The invention will be described further in conjunction
with the attached drawings., in which:
Figure 1 is a vertical sectional view through a
tank and the edge of a floating roof having a primary seal
and a secondary seal strip;
Figure 2 is an enlarged partial view in perspective
of the secondary sealing strip shown in Figure l;
Figure 3 is a plan view, partially in section and
partially broken away, of the secondary seal oE Figures 1
and 2 laying flat;
Eigure 4 is a view like Figure 2 except that the
sealing strip is arched downwardly instead of upwardly;
Figure 5 is an enlarged, fragmentary perspective
view, similar to Figure 2, of the portion of the secondary
sealing strip that engages the inner side wall of the tank
and showing a layer of polymeric fabric or cloth partially
embedded in the opposite surfaces of the strip;
Figure 6 is a fragmentary plan view of a pcrtion
of the radially inner surface of the secondary seal strip,
and the partially embedded layer of polymeric fabric illustrated
in Figure 5, both of which do not normally en~age the tank
inner side wall;
Figure 7 is a fragmentary plan view of a portion
of the radially outer surface of the secondary seal strip
and the partially embedded layer of polymeric fabric illustrated
in Figure 5, only a part of the outer surface of the polymeric
fabric normally engaging the tank inner side wall;
Figures 8 and 9 are fragmentary plan views, similar
to Figures 6 and 7, respectively, but show.ing an alternate
construction of the layer of polymeric fabric or cloth that
is partially embedded in the radially inner and outer surfaces
of the secondary seal strip; and
Figure lO is an enlarged, fra~mentary perspective
view, similar to Figure.5, of the radially outer edge portion
of the secondary seal strip that engages the inner side wall
of the tank, a layer Oc polymeric felt being shown partially
embedded in the edge portion of the strip.
So far as is practical, the same parts or elements
which appear in the various views of the drawings will be
identified by the same numbers.
With reference to Figure 1., the tank 10 has a vertical
circular cylindrical wall 11 in which floating roof 12 is
located. The floating roof 12 has a top 13, bottom 14 and
a vertical side 15 having an upper portion 16 which extends
above top 13.
Mounted around the periphery of the floating roof
are primary seal 20 and secondary seal 30. The primary seal
20 is of known construction and comprises a polymeric flexible
and resilient foam annulus 21 bonded to a vertical circular
metal plate 22. Vapor and liquid impervious fabric envelope
23 loosely surrounds the foam annulus 21. The ends of the
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fabric envelope 23 are brought together in contact with the
top edge of metal plate 22 and fastened by bolts 24 to the
upper portion 16 of the floating roof.
To further guard against escape of vapor between
the edge of the roof and the tank wall, the primary seal 20
is supplemented by secondary seal 30 which comprises elastomeric
composite strip 31, impermeable to vapor, having its radially
inner edge connected to the roof edge flange 32 by metal band
33 and bolts 34. The composite strip 31, as shown in Figs.
1 and 2, is normally flat but after installation on a floating
roof it arches upwardly since its width is always greater than
the maximum distance between its place of connection to the
floating roof and the tank wall. A curved support 35 helps
to hold strip 31 and to keep it from reversing the direction
in which it is arched. Due to its flexible, spring-like in-
herent properties, which continually seek to return it to
its natural flat state in which it is manufactured, the radially
outer or peripheral-edge of the strip 31 is urged towards
the tank wall.
The specific strip 31 as shown in Fig. 3 has a plural-
ity of flexible resilient elongated stiffeners 3~ laterally
positioned and embedded in elastomeric material, which can
be synthetic rubber, such as neoprene. The sti~eners may
be roughened or otherwise prepared to improve bonding with
the elastomeric material. The stiffeners 36 as shown in Fig.
3 are integrally joined to a band portion 37 along the strip
edge. Spaced apart bolt holes 38 may exten~ entirely through
strip 31 and receive bolts 34 when the strip is joined to
the floating roof~
The stiffeners 36, as shown in Fig. 3, are flat
fingers which are tapered and narrower at the edge of the
strip 31 which contacts the tank wall than at the edge which
is joined to the floating roof. This form of stiffener is
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particularly useful since the tapering fingers provide wide
areas 39 of elastomeri~ material which provide excellent and
necessary circumferential elasticity in strip 31 to press
against the tank wall with increase in the radial space between
the roof edge and the tank wall. Also, by using tapered stif-
feners progressively greater stiffness of the total seal is
achieved, i.e. it is stiffer at the roof rim and decreasingly
stiff as it extends closer to the tank shell.
The flexible resilient elongated stiffeners can
be made of metal, such as spring steel or spring aluminum,
or they can be made of a solid polymeric sheet material having
the necessary physical properties, such as nylon, polypropylene,
or even a ~lass fiber impregnated polymeric material as for
example polymethacrylate.
To prevent the secondary sealing strip 31 from stick-
ing, or resisting slidable movement, against the tank wall
surfacè during up and down vertical displacement of the floating
roof in the tank when a liquid product is supplied to or removed
from the tank, a sheet 50 of polymeric material is placed
on the strip 30. The sheet 50 has a front 51, and end 52
and a flange 53 spaced outwardly from, but parallel to, front
51 thereby defining a groove into which nests the outer edge
portion of the strip 31. This mechanical attachment in itself
can often be enough to hold sheet 50 in place.
Sheet 50 is made of a polymeric material which pro-
vides a slick surface which facilitates slidable movement against
the tank wall. Materials such as those described and identified
previously herein can be used.
Sheet 50 can be made from sheet polymeric material
shaped into the described form or it can be molded or extruded
into the desired shape. Regardless of the particular shape,
or the specific polymeric material used, it is desirable for
the outer edge of the strip 31 to be covered so that it will
always be able to slide freely against the tank wall.
In an exemplary embodiment, the sheet 50 is made
of a closely woven nylon fabric about 0.025 inch thick and
bonded to the strip 31. The front 51 is about 3 inches, end
52 is about 0.25 inch and flange 53 is about 1.0 inch wide~
Figure 4 illustrates the embodiment of Figure 2 but
with the secondary seal arched in a downwardly direction.
In all other respects the construction is the same in both
instances except that in Figure 4 the suport 35 is above the
strip 31 rather than below it as in Figure 2.
In Fig. 5, a portion of another elastomeric composite
strip 61, embodying the features of the present invention,
is illustrated. The strip 61 may be mounted in the same manner
as the strip 31, i.e. the radially inner edge thereof (not
shown) may be connected to the upper pvrtion (Figs. 1 and 2)
of the floating roof 12 by a metal band 33 and bolts 34.
The composite strip 61 is also similar to the composite
strip 31 in that the strip 61 is normally flat but, after instal-
lation on a floating roof, it arches upwardly since its widthis always greater than the maximum distance between its place
of connection to the floating roof and thè tank wall. A curved
support (not shown) may also be provided to help hold the strip
61 and to keep it from reversing the direction in which it
is arched. Because of the flexible, spring-like inherent proper-
ties of the material of the strip 61, the radially outer edge
portion thereof, indicated at 62, continually seeks to return
to the natural flat state in which it was manufactured~ Thus,
the radially outer or peripheral edge portion 62 of the strip
61 is urged toward the inner surface of the tank wall 11 at
all times when the secondary seal is installed on the roof
12.
The strlp 61 also preferably includes a plurality
of elongated flexible, resilient stiffener~ (not shown), such
as the stiffeners 36 of the strip 31. Thus, the sti~feners
in the strip 61 may extend laterally of the strip and may be
embedded in the elastomeric material thereof. The stiffeners
are preferably tapered and narrower at the radially outer edge
portion 62 of the strip 61 so that the seal is stiffest at
the roof rim and decreasingly stiff as it extends closer to
the inner surface of the tank wall 11.
Referring now to Figs. 6 and 7 in conjunction with
Fig. 5, it will be seen that a woven layer of polymeric fabric
or cloth, indicated generally at 70, is carried on the radially
outer edge indicated at 63, and portions of the radially inner
and outer surfaces, indicated at 67 and 68, respectively, of
the strip 61 to provide a slick face which prevents the secondary
sealing strip 61 from sticking or resisting sliding movement
against the inner surface of the tank wall 11 during up and
down vertical displacement of the floating roo 12. According
to the present invention., the layer of polymeric fabric 70
is formed from woven filaments of polymeric material such as
nylon, polyethylene, a polyfluoroethylene such as Teflon, or
a polychlorofluoroethylene. Thus, the layer of woven polymeric
fabric or cloth 70 has a portion 72 carried on the radially
inner surface 67 of the elastomeric strip 61, another portion
73 carried on the radially outer surface 68 of the elastomeric
strip 61, and a portion 74 which extends around the radially
outer edge 63 of the elastomeric strip 61 and connects the
portions 72 and 73.
According to the present invention the layer of woven
polymeric fabrlc or cloth 70 is at least partially embedded
in the radially inner and outer surfaces 67 and 68 of the elasto-
meric strip 61, rather than being bonded onto or otherwise
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secured t~ these surfaces. ThiS construction is illus~rated
in Fig. 5 and exaggerated for clarity. As a result of such
partial embedding, the outer surface of the portion 72 of the
woven polymeric fabric layer 70 is substantially flush with
the radially inner surface 67 of the strip 61 and the outer
surface of the portion 73 is substantially flush with the radial-
ly outer surface 68 (Fig. 7) of the strip~ Partial embedding
of the layer of woven polymeric fabric 70 in the elastomeric
strip 61 may be accomplished when the elastomeric material
61 is vulcanized.
Referring now to Figs. 8 and 9l an alternate construc-
tion, indicated generally at 80, of the layer of woven polymeric
fabric or cloth of the previous embodiment is illustrated.
The layer of polymeric fabric 80 may be of the same proportions
and material as the layer 70, and likewise may be secured to
the radially inner and outer surfaces 67 and 68, respectively,
of the strip 61 in the same manner as the polymeric fabric
layer 70. The layer 80 differs, however, from the layer 70
in that the layer 80 is formed in separate pieces, some of
which are indicated at 80a-80d, respectively, in Figs. 8 and
9. The pieces of woven fabric which make up the layer 80 are
preferably about 2 inches (5.08 cm.) wide and are separated
by slits or gaps, indicated at 82, which extend perpendicularly
or radially with respect to the outer edge 63 of the elastomeric
strip 61. Consequently~ the pieces of polymeric fabric which
make up the layer 80 likewise extend perpendicularly or radially
with respect to the radially outer edge 63 of the elastomeric
strip. Because the strips 80a-80d are separated by the gaps
or slits 82, the material of the radially outer edge portion
62 of the strip 61 is free to expand or stretch when out-of-
round areas in the tank sidewall or shell are encountered during
movement of the roof 12.
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Referring now to Fig. 10, another alternate construc-
tion, indicated generally at 90, of the layer of polymeric
fabric that i5 carried on the radially inner and outer surfaces
67 and 68, and edge 63 of the elastomeric strip 61 is illus-
trated, the layer 90 differing from the layers 70 and 80 in
that the layer 90 is formed from nonwoven random fibers, matted
together as a felt. Otherwise, the layer of polymeric fabric
90 is applied to portions of the radially iner and outer sur-
faces 67 and 68 of the strip 61, and the radially outer edge
portion 62 thereof in the same manner as either the layer
70 or the layer 80 of polymeric fabric. In addition, the
layer of polymeric fabric 90 is also preferably at least par-
tially embedded in the elastomeric strip 61, rather than being
bonded or otherwise secured to the radially inner and outer
surfaces 67 and 68 of the strip 61.
While several embodiments of the invention have
been herein illustrated and described, it will be understood
that modifications and variations thereof may become apparent
to those skilled in the art without departing from the spirit
of the invention and the scope of the appended claims.
The foregoing detailed description has been given
for clearness of understanding only, and no unnecessary limita-
tions should be understood therefrom, as modifications will
be obvious to those skilled in the art.
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