Secondary shoe seal

The space between the inner wall of a petroleum or hydrocarbon tank or similar storage tank and a floating roof therein is sealed by both a primary seal and a secondary seal. The secondary seal, which has no elastomeric parts subject to rapid deterioration, includes a flexible vapor barrier fabric having a first edge coupled to the floating roof and an opposite second edge. The secondary seal further includes a plurality of plates disposed above the vapor barrier fabric and having lower ends coupled to the floating roof and opposite upper ends coupled to a metal shoe disposed against the inner tank wall and having the second edge of the vapor barrier fabric coupled thereto. The length of each metal plate between upper and lower edges thereof is adjustable by virtue of the plate being comprised of overlapping upper and lower plates joined by bolts in elongated apertures therein. The shoe is flexibly coupled to the upper edges of the plates by bolts disposed within dimpled holes in the shoe and in the upper edges of the plates.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to seals for the floating roofs of storage 
tanks for petroleum and similar products, and more particularly to an 
improved secondary seal for use in conjunction with a primary seal. 
2. History of the Prior Art 
Seals for sealing the space between a floating roof and the inner tank wall 
of a petroleum storage tank are well known and have been provided in a 
variety of different configurations. Examples of such seals are provided 
by U.S. Pat. Nos. 4,308,968, 5,078,293 and 5,103,992, all of which are 
commonly assigned with the present application. It is common practice in 
many applications to provide a tank with both a primary seal and a 
secondary seal. The primary seal is regarded as providing the primary or 
principal sealing function of the space between the floating roof and the 
inner tank wall. The secondary seal, which is often installed after the 
primary seal is in place and the tank has been in service for some time, 
provides a backup sealing function. Typically, the secondary seal is 
disposed above the primary seal in order to trap any vapors which may 
escape through the primary seal. The 1968 patent noted above provides an 
example of a secondary seal, while the '293 and '992 patents noted above 
provide examples of primary seals. 
The secondary seal described in the '968 patent noted above includes a 
plurality of overlapping metal plates which have their lower edges mounted 
on the floating roof and which extend toward the inner tank wall so as to 
terminate in upper edges disposed adjacent the inner tank wall. A 
plurality of flexible wiper blades mounted on the upper edges of the 
overlapping metal plates extend into contact with the inner tank wall. 
Depending upon whether the tank is of welded or riveted construction, the 
wiper blades may assume different configurations to accommodate the 
smoother walls of a welded tank or the irregular wall surfaces of a 
riveted tank. A vapor barrier fabric disposed beneath the overlapping 
metal plates has a first edge thereof coupled to the floating roof and an 
opposite second edge coupled to the upper edges of the overlapping metal 
plates where the wiper blades are mounted. The vapor barrier fabric seals 
the space beneath the overlapping metal plates. The overlapping metal 
plates support the wiper blade arrangement which seals the space beneath 
the overlapping metal plates at the inner tank wall. U.S. Pat. No. 
4,397,399 provides a further example of a seal having a vapor barrier 
fabric in conjunction with overlapping metal plates which support a single 
wiper blade. 
Secondary seals of the type described in the '968 patent noted above 
provide effective sealing action, particularly when compared with certain 
other seal designs including earlier roof seals. However, the elastomeric 
material typically used for the wipers is subject to relatively rapid 
deterioration which can greatly shorten the life of the seal that would be 
otherwise realized with the metal parts thereof. Most elastomers that are 
resistant to abrasion and other typical tank service conditions are 
subject to relatively rapid deterioration when exposed to certain gasoline 
additives and chemicals such as MTBE and benzene. On the other hand, the 
vapor barrier fabrics are not subject to abrasion, as are the wiper 
blades, and can be made of laminated fluoropolymers such as Teflon which 
are resistant to virtually all products stored in floating roof tanks. 
Accordingly, it would be desirable to provide an improved secondary seal 
for floating roof tanks. A more specific object would be the provision of 
a secondary seal which is free of elastomers or other materials that may 
be subject to rapid deterioration. 
BRIEF SUMMARY OF THE INVENTION 
Secondary roof seals for floating roof tanks, in accordance with the 
invention, are designed so as to avoid the use of elastomers or other 
materials normally subject to rapid deterioration. More particularly, such 
secondary seals employ a metal shoe in contact with the inner tank wall in 
conjunction with a plurality of support plates mounted on the floating 
roof. A vapor barrier fabric disposed beneath the support plates extends 
between and seals the space between the floating roof and the shoe. 
In a preferred arrangement of a secondary seal according to the invention, 
a plurality of plates have the lower ends thereof mounted on the floating 
roof and extend to opposite upper ends disposed adjacent the inner tank 
wall. The upper ends of the plates are coupled to a metal shoe having a 
major surface thereof disposed against the inner tank wall. A vapor 
barrier fabric extends between the floating roof and the shoe beneath the 
plates. A first edge of the vapor barrier fabric is coupled to the 
floating roof and an opposite second edge thereof is coupled to the shoe. 
The plates, which are spaced apart from each other, have a length between 
the lower and upper edges thereof which is adjustable to accommodate 
varying distance between the floating roof and the inner tank wall around 
the periphery of the floating roof. Adjustability is provided by 
fashioning each of the plates from upper and lower plates joined together 
by bolts disposed within elongated apertures in the plates. By loosening 
the bolts, the upper plate can be adjustably positioned relative to the 
lower plate to vary the length of the plate formed thereby. 
A flexible coupling of the shoe to the upper ends of the plates is provided 
by a coupling arrangement which utilizes dimpled holes in the shoe and in 
the upper edges of the metal plates. Bolts extend through the dimpled 
holes in the shoe and in the upper edges of the metal plates. In an 
alternative arrangement for flexibly coupling the shoe to the upper ends 
of the plates, a concave spring washer is disposed together with a flat 
washer between the plate upper end and a dimpled hole in the shoe through 
which a bolt extends to receive the spring washer and flat washer and the 
plate upper end.

DETAILED DESCRIPTION 
FIG. 1 depicts a tank 10 utilizing a secondary seal 12 in accordance with 
the invention. The tank 10 is generally cylindrical in configuration, and 
may comprise a petroleum or hydrocarbon storage tank or similar tank for 
storing a volatile liquid. The secondary seal 12 is disposed between and 
seals the space between an inner wall 14 of the tank 10 and a circular 
roof 16 which floats on the surface of the gasoline, oil or other liquid 
product in the tank 10. As described in detail hereafter, the secondary 
seal 12 is disposed above a primary seal and extends between a rim 18 at 
the outer periphery of the circular floating roof 16 and the inner wall 14 
of the tank 10. The secondary seal 12 has a flexible support structure 22 
which terminates in an upper lip 20 adjacent the inner wall 14 of the tank 
10. As also described in detail hereafter, the support structure 22 is 
comprised of metal plates which are both flexible and adjustable to 
accommodate variations in the space between the rim 18 of the floating 
roof 16 and the inner wall 14 of the tank 10. The upper lip 20 is formed 
by the upper edges of the metal plates which support a shoe and bias a 
major surface portion of the shoe against the inner tank wall 14. 
Referring to FIG. 2, the floating roof 16 has a primary seal 30 extending 
between the rim 18 thereof and the inner wall 14 of tank 10 to provide 
primary sealing of the space therebetween. In the present example, the 
primary seal 30 includes a shoe 32 disposed against the inner wall 14 of 
the tank 10 and a length of vapor barrier fabric 34. The vapor barrier 
fabric 34 has a first edge 36 thereof coupled to an upper portion of the 
shoe 32 such as by a plurality of bolts 38. The vapor barrier fabric 34 
extends across the space between the shoe 32 and the rim 18 of the 
floating roof 16, where the vapor barrier fabric 34 terminates in an 
opposite second edge 40. The second edge 40 is coupled to the rim 18. 
The primary seal 30, which is only partially illustrated in FIG. 2, can 
assume any appropriate form. As previously noted, the primary seal 30 
provides primary sealing of the space between the inner wall 14 of the 
tank 10 and the floating roof 16. However, because of the advantages of 
the secondary seal 12 in accordance with the invention, it is preferred 
that the primary seal 30 be of the type that does not utilize elastomers 
that must be resistant to abrasion. Abrasion-resistant elastomers are 
typically subject to relatively rapid deterioration when exposed to 
certain gasoline additives and chemicals such as MTBE and benzene. For 
this reason, the primary seal 30 illustrated in FIG. 2 utilizes the shoe 
32 in conjunction with the vapor barrier fabric 34. Because the vapor 
barrier fabric 34 is not subject to abrasion, the fabric 34 can be made of 
laminated fluoropolymers such as Teflon which are resistant to virtually 
all products stored in floating roof tanks. Previously referred to U.S. 
Pat. No. 5,103,992 illustrates such a primary seal in which the shoe is 
adjustably mounted on the floating roof by a series of spaced apart 
scissors hanger assemblies and in which resilient bars or plates disposed 
between the floating roof and the shoe bias the shoe into contact with the 
inner tank wall. 
In accordance with the invention, the secondary seal 12 also avoids the use 
of elastomeric materials of the type subject to relatively rapid 
deterioration. This is accomplished using a shoe 42 and the support 
structure 22 therefore in combination with a vapor barrier fabric 44. The 
vapor barrier fabric 44 has a first edge 46 thereof secured to a lower 
portion of the shoe 42 using a channel 48. As described hereafter in 
connection with FIG. 3, the channel 48 is fastened to the shoe 42 by a 
plurality of bolts, to secure the first edge 46 of the vapor barrier 
fabric 44 thereon. The vapor barrier fabric 44 extends between the shoe 42 
at the inner wall 14 of the tank 10 and the floating roof 16. The vapor 
barrier fabric 44 has a second edge 50 opposite the first edge 46 thereof 
secured to the rim 18 of the floating roof 16. 
The vapor barrier fabric 44 which extends between the shoe 42 and the 
floating roof 16 serves to trap any vapors which may escape through the 
primary seal 30. Because the vapor barrier fabric 44 is not subject to 
abrasion, it can be made of materials such as laminated fluoropolymers 
which are resistant to virtually all products stored in floating roof 
tanks, including gasoline additives and chemicals such as MTBE and 
benzene. 
As the level of the liquid product within the tank 10 varies, the shoe 32 
of the primary seal 30 and the shoe 42 of the secondary seal 12 slide 
upwardly and downwardly along the inner wall 14 of the tank 10. The shoe 
42 is supported by the support structure 22. The support structure 22 
biases the shoe 42 into contact with the inner wall 14. In addition, the 
support structure-22 has sufficient flexibility and adjustability to 
accommodate differences in the space between the outer rim 18 of the 
floating roof 16 and the inner tank wall 14 around the circumference of 
the circular floating roof 16. 
The support structure 22 is comprised of a series of spacedapart plates 52 
of resiliently flexible material such as stainless steel. Each of the 
plates 52 is comprised of an upper plate 54 and a lower plate 56. The 
upper plate 54 is joined to the corresponding lower plate 56 by a pair of 
bolts 58 which permit adjustment of the total height of the plate 52, as 
described hereafter in connection with FIGS. 6 and 7. Each upper plate 54 
has an upper edge 60 thereof which is bent at an angle relative to the 
rest of the plate 54 and which is joined to an intermediate portion of the 
shoe 42 by a bolt 62. Each lower plate 56 has a lower edge 64 thereof 
which extends beneath a channel 66 just above the outer rim 18 of the 
floating roof 16. 
The second edge 40 of the vapor barrier fabric 34 and the second edge 50 of 
the vapor barrier fabric 44 are disposed between the lower edges 64 of the 
lower plates 56 and the rim 18 of the floating roof 16, where they are 
secured together with the lower edges 64 of the lower plates 56 by the 
channel 66. The channel 66 is clamped to the rim 18 by a plurality of 
bolts 68. Although a horizontal mount configuration is shown in which the 
vapor barrier fabrics 34 and 44 and the plate lower edge 64 are joined to 
a horizontal portion of the floating roof 18, it should be understood that 
a vertical mounting arrangement can also be used. 
In the present example, the plates 52 are spaced-apart from each other 
around the rim 18 of the roof 16. For most applications, the vapor barrier 
fabric 44 is capable of exposure to the outside elements and does not have 
to be covered. However, the plates 52 can be mounted so that their side 
edges overlap to form a continuous cover for the vapor barrier fabric 44 
where desired. 
Where the plates 52 are spaced-apart as in the present example, cover 
plates may be used to cover the plates 52. The cover plates need not be 
2-piece as are the plates 52, and can be of different shape. 
Further details of the arrangement of FIG. 2 are shown in the exploded end 
view of FIG. 3. As shown therein, the second edge 40 of the vapor barrier 
fabric 34 and the second edge 50 of the vapor barrier fabric 44 are 
sandwiched between the rim 18 of the floating roof 16 and the lower edges 
64 of the lower plates 56 by the channel 66. The bolts 68 extend upwardly 
through apertures in the rim 18, the second edges 40 and 50 of the vapor 
barrier fabrics 34 and 44, the lower edges 64 of the lower plates 56 and 
the channel 66, where they receive washers 70 and nuts 72. 
The opposite first edge 46 of the vapor barrier fabric 44 is secured to a 
lower portion of the shoe 42 by the channel 48, in conjunction with a 
plurality of apertured dimples 74 in the lower portion of the shoe 42. A 
plurality of bolts 76 extend through apertures in the dimples 74, through 
apertures in the first edge 46 of the vapor barrier fabric 44, and through 
apertures in the channel 48, where they receive washers 78 and nuts 80. 
As previously noted, each upper plate 54 is joined to the lower plate 56 
associated therewith by a pair of the bolts 58. As shown in FIG. 3, the 
bolts 58 extend through apertures in the upper plate 54 and the lower 
plate 56 where they receive a nut 82. 
The upper edges 60 of the upper plates 54 are provided with apertured 
dimples 84 for interfacing with apertured dimples 86 spaced along an 
intermediate portion of the shoe 42. Each of the bolts 62 extends through 
one of the apertured dimples 86 and an associated one of the apertured 
dimples 84, where it receives a nut 88. 
The dimples 84 in the upper edges 60 of the upper plates 54 and the 
interfacing dimples 86 in the shoe 42 comprise one arrangement for 
providing the needed articulation between the upper plates 54 and the shoe 
42. This provides a relatively tight fit of the broad surface area of the 
shoe 42 against the inner wall 14 of the tank 10 under a variety of 
conditions including varying distance between the rim 18 of the floating 
roof 16 and the inner tank wall 14 around the circumference of the 
floating roof 16. The resiliently flexible nature of the upper and lower 
plates 54 and 56 combines with such articulated coupling of the upper 
edges 60 of the upper plates 54 to the shoe 42 to resiliently bias the 
shoe 42 against the inner tank wall 14 in the face of such varying 
conditions. 
The shoe 42 is shown in greater detail in FIG. 4. FIG. 4 shows a section of 
the shoe 42 which has opposite ends that overlap the ends of similar 
sections so as to form the continuous shoe 42 around the circumference of 
the inner tank wall 14. The upper and lower edges of the shoe 42 are bent 
in order to form beveled edges 90 and 92 respectively. As shown in FIG. 3, 
the upper and lower beveled edges 90 and 92 of the shoe 42 are angled away 
from the inner wall 14 of the tank 10 to facilitate sliding movement of 
the shoe 42 over the wall 14. To accommodate the slight curvature of the 
inner tank wall 14 against which the shoe 14 must reside in close-fitting 
contact, the beveled edges 90 and 92 are provided with a series of 
spaced-apart slots 94 and 96 respectively. 
As previously described, the shoe 42 is provided with the apertured dimples 
86 along an intermediate portion thereof. Such apertured dimples 86 are 
shown in FIG. 4, with one such dimple 86 being shown in detail in the 
cross-sectional view of FIG. 5. As shown in FIG. 5, the dimple 86 is of 
generally circular configuration and is raised or off-set from the plane 
of the shoe 42. An aperture 98 extends through a central portion of the 
dimple 86 to receive one of the bolts 62 shown in FIGS. 2 and 3. 
Each of the dimples 86 in the shoe 42 receives a different one of the 
apertured dimples 84 in the upper edge 60 of one of the upper plates 54. 
FIG. 6 shows one of the upper plates 54 in detail, with the apertured 
dimple 84 thereof being shown in detail in the cross-sectional view of 
FIG. 8. Like the dimple 86 in the shoe 42, the dimple 84 in the upper edge 
60 of the upper plate 54 is of generally circular configuration and is 
off-set from the plane of the upper edge 60. A central aperture 100 
therein receives one of the bolts 62. 
As shown in FIG. 6, the upper plate 54 has a tapering width which increases 
from the upper edge 60 to an opposite lower edge 102 thereof, in the 
present example. However, the upper plate 54 can be of rectangular shape, 
in which event the width thereof is uniform. The upper plate 54 has a pair 
of apertures 104 therein adjacent the lower edge 102 to receive the bolts 
58. 
One of the lower plates 56 is shown in detail in FIG. 7. Like the upper 
plate 54, the lower plate 56 has a tapering width which increases from an 
upper edge 106 thereof to the opposite lower edge 64 thereof. However, the 
lower plate 56 can be of rectangular configuration and have a uniform 
width where desired. The width of the lower plate 56 at the upper edge 106 
thereof is approximately equal to the width of the upper plate 54 at the 
lower edge 102 thereof. The lower plate 56 is provided with a pair of 
elongated apertures 108 therein adjacent the upper edge 106 thereof. The 
elongated apertures 108 receive the bolts 58 mounted within the apertures 
104 in the upper plate 54. The nuts 82 are secured on the bolts 58 outside 
of the apertures 108. The apertures 108 in the lower plate 56 are 
elongated in configuration to permit adjustment. With the nuts 82 
untightened, the bolts 58 are free to slide within the apertures 108 to 
vary the positioning of the lower edge 102 of the upper plate 54 over the 
upper edge 106 of the lower plate 56. In this manner, the combined height 
of the combined upper plate 54 and lower plate 56 can be varied or 
adjusted to compensate for variations in the distance between the rim 18 
of the floating roof 16 and the inner tank wall 14 around the 
circumference of the circular floating roof 16. 
As shown in FIG. 7, the lower edge 64 of the lower plate 56 is provided 
with a plurality of slots 110 therein for receiving the bolts 68. 
FIG. 9 shows an alternative arrangement for flexibly coupling the shoe 42 
to the upper edge 60 of the upper plate 54. As in the case of FIG. 3, the 
shoe 42 is provided with the dimple 86 through which the bolt 62 passes. 
In addition, however, a concave spring washer 112 and a flat washer 114 
are disposed between the dimple 86 and the upper edge 60 and receive the 
bolt 62. The nut 88 is then mounted on the bolt 62. As shown in the 
cross-sectional view of FIG. 10, the spring washer 112 may be of the 
Belleville type so as to be of concave configuration. This enables the 
spring washer 112 to flex to a necessary extent to provide the needed 
flexibility between the shoe 42 and the upper plate 54. 
It will be apparent to those skilled in the art that various different 
arrangements can be used to couple the shoe 42 to the overlapping plates 
52 in flexible, articulating fashion. 
It is frequently necessary or desirable to provide a floating roof seal 
with a metal shunt or other means for draining static electricity from the 
floating roof 16 to the tank wall 14. In the case of the secondary seal 
12, such shunting action is provided by the seal itself. The metal shoe 42 
which contacts the tank wall 14 is coupled by the metal bolt 62 to the 
upper edge 60 of the upper plate 54. The upper plate 54 is in direct 
contact with the lower plate 56, the lower edge 64 of which is coupled by 
the metal bolt 68 to the floating roof 16. Thus, a conductive path is 
provided between the floating roof 16 and the tank wall 14, to shunt 
static electricity. Such a shunt can also be provided by the vapor barrier 
fabric 44 which extends between the metal shoe 42 and the floating unit 
16. The vapor barrier fabric 44 may be comprised partly of carbon or other 
conductive material, so that the vapor barrier fabric 44 itself acts as a 
shunt for static electricity. 
While the invention has been particularly shown and described with 
reference to a preferred embodiment thereof, it will be understood by 
those skilled in the art that other changes in form and details may be 
made therein without departing from the spirit and scope of the invention.