Note: Descriptions are shown in the official language in which they were submitted.
CA 02241354 2004-09-21
DOUBLE WALL TANK
This invention relates to a double walled tank.
Double walled tanks are commonty used to store hydrocarbons
such as crude ar refined oil or produced water, i.e. water from an oil well.
Examples of double walled tanks are described in United States Patents Nos.
3,848,765, issued to Hermann Durkop on November 19, 1974; 3,902,356,
issued to ~tto Rupf-Bolz on September 2, 1875; 4,685,327, Issued to Bruce R,
Sharp on August 11, 1987; 4,805,445 issued to Jacques Grappe an February
21, 1989; 5,265,465, issued to Horace F. Thomas on November 30, 1993 and
5,400,846 issued to Donal A. Draus et al on March 28, 1995. In general,
double walled tanks are used in the ground with the longitudinal axis of t>~e
tank in a horizontal plane. ~ .
The ease of a double walied tank above ground with a vertical
longitudinal axis would obviate the need for a bean surrounding the tank. For
the most part, the tanks discloses! by the above reference patents do not lend
themselves to above ground use.
Often a vacuum is maintained between the walls of the tank, and
the vacuum is monitored to provide an indication of whether any leakage has
occurred, i.e. 1f a leak develops in the inner wall, the pressure between the
walls will change. In general, double walled tanks can be expensive to
manufacture, and it can be difficult to eff~t proper sealing between the wails
and/or floors of the tank for maintaining a vacuum.
The obj~ct of the present invention is to provide a solution to the
above identified problems in the form of a reiativelysimple double walled
tank,
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which is easy to produce, and which has effective sealing between the layers
of
the tank.
Accordingly, this invention relates to a double walled tank
comprising:
(a) a base including
(i) a primary floor,
(ii) a secondary floor beneath and spaced apart from said
primary floor, said secondary floor extending outwardly
beyond said primary floor, and
(iii) a first seam sealing the gap between the periphery of
said primary floor and said secondary floor;
(b) a side wall including
(i) a primary, inner shell,
(ii) a secondary, outer shell spaced apart from and
extending around said inner shell, said secondary shell having
a bottom end above the bottom end of said primary shell,
(iii) a second seam sealing the gap between the bottom end
of the secondary shell and the primary shell, and
(iv) a third seam sealing the gap between the top end of the
primary and secondary shells; and
(c) a roof sealed on the top end of said primary shell.
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The invention is described below in greater detail with reference to
the accompanying drawings, which illustrate a preferred embodiment of the
invention, and wherein:
Figure 1 is a side view of a double walled tank on accordance
with the present invention;
Figure 2 is a top view of the tank of Fig. 1;
Figure 3 is a cross section of vertical weld seams in the side wall
of the tank of Figs. 1 and 2;
Figure 4 is a cross section of a cross section taken generally
along line 4-4 of Fig. I;
Figure 5 is an isometric, cross-sectional view of an area of a base
and side wall of the tank of Figs. 1 and 2;
Figure 6 is a cross-section of an area of the base and side wall of
the tank of Figs. 1 and 2 containing vacuum openings;
Figure 7 is an isometric cross section of an area of a side wall
and roof of the tank of Figs. 1 and 2;
Figure 8 is an isometric view of a lifting lug used on the tank of
Figs. 1 and 2;
Figure 9 is a cross section taken generally along 9-9 of Fig. 8;
Figure 10 is an isometric view of a nozzle used in the tank of Figs.
1 and 2;
Figure 11 is a longitudinal section of the nozzle of Fig. 10; and
Figure 12 is a side view of a pressure release device used in the
tank of Figs. 1 and 2.
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It should be noted that the drawings are not to scale, being
intended for the purpose of illustration of the preferred embodiment.
With reference to Figs. 1 and 2, the basic elements of the double
walled storage tank include a base 1, a cylindrical side wall 2 and a conical
top
wall or roof 3. A variety of fittings and accessories, which are off-the-shelf
hardware are provided on or in the tank. Such fittings and accessories include
an inlet 5 and an outlet 6 for introducing and discharging liquid from the
tank,
drain 7 in the bottom of the tank, a standard clean-out 8 near the bottom of
the
side wall 2, normally closed by a cover 9, nozzles 10 and 11 near the top of
the
side wall 2 for receiving high level shut down devices (not shown), and a
central vent 12, a level indicator opening 13 and a so-called thief hatch 14
in
the roof 3. The thief hatch 14 is merely a spring loaded cover or valve which
opens when gas pressure in the tank build up above a predetermined level.
Four lugs 15 (one shown - Fig. 1) are provided at the top of the side wall 2
for
lifting the tank. A ladder 17 with a safety cage 18 is mounted on the side
wall
2 of the tank.
Referring to Figs. 5 and 6, the base 1 of the tank is formed of a
pair of circular steel plates defining a primary or upper floor 19 and a
secondary or lower floor 20. The secondary floor 20 has a slightly larger
diameter than the primary floor 19. The floors 19 and 20 are spaced a minimal
distance apart, and are welded together around the entire periphery of the
primary floor 19, i.e. a weld seam 21 extends between the floors around the
outer edge of the floor 19.
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The cylindrical side wall 2 is defined by a primary or inner shell 23
and a secondary or outer shell 24. The primary shell 23 is formed of sheets 25
of steel (Fig. 3) which are butt joined by vertical weld seams 27. The
secondary
shell 24 is formed of sheets of steel which are lap joined to each other by
vertical
seams 30. In a high tank, a plurality of sheets 31 and 31' are used. As best
shown in Fig. 4, the bottom end of the uppermost sheet 31 is connected to the
inner shell 23 by a horizontal weld seam 32. The top end of the subjacent
sheet
31' is lap joined to the upper sheet by a horizontal weld seam 33. The bottom
end 34 of the primary shell 23 is connected to the primary floor 19 by a pair
of
weld seams 36 and 37 extending around the entire bottom end 34 of the shell
23.
Referring to Figs. 5 and 6, the secondary shell 24 is spaced a short
distance from the primary shell 23. The bottom end 38 of the secondary shell
24
is located a short distance above the bottom end 34 of the primary shell 23.
The
gap between the bottom end of the secondary shelf 24 and the shell 23 is
connected by a stitch weld seam 39. The spacing of the bottom end 38 of the
secondary shell 24 from the primary floor 19 facilitates assembly of the tank,
avoiding the difficulty of welding the bottom of both shells directly to the
floor of
the tank. A lower sealing ring 40 of inverted L-shaped cross section extends
around the bottom of the tank. The ring 40 is connected to the primary floor
19
by a weld seam 41, and to the bottom end 38 of the secondary shell 24 by a
weld
seam 42.
The top ends 44 and 45 (Figs. 7 and 8 ) of the primary and
secondary shells 23 and 24, respectively are joined by a weld seam 46
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extending around the entire periphery of the tank to seal the gap bEtween the
top ends of the shells Another weld seam 47 connects the outer edge 48 of
the roof 3 to the top end 44 of the primary shell 23. A upper compression or
reinforcing ring 49 of inverted L-shaped cross section is provided at the top
end of the secondary shell 24. The ring 4a9 is connected to the secondary
shell
24 by a pair of weld seams 51 and 52.
With reference to Figs. a and 9, the lifting lug 15 includes an
elongated body 54, with a semicircular top end 55. A hole 56 is provided near
the top end'55 of the body for receiving a lifting cable (not shown) or the
like.
The lug body 54 is mounted in a rectangular notch (not shown) in the top end
of the secondary shell 24. The sides and bottom ends of~the body 54 are
connected to the top end 44 of the primary shell 23 by a weld seam 57 (Fig.
9).
Another weld seam 58 connects the sides and bottom of the notch to the
primary shell 23. The weld seam 47 in the area of the inner surface of the lug
i5 is bigger to fill the gap between the roof 3 and the lug. The upper
compression ring 49 extends across the outer surface of the lug 15.
Referring to Figs. 10 and j1, in all cases where a fitting or nozzle,
60 (e.g. the inlet 5 and the outlet 6) 'extends through the secondary shell
'24 to
the primary shell 23, the nozzle is welded to the inside and outside of the
primary shell 23 by weld seams 6i and 62. The nozzle 60 extends outwardly
through an opening 64 In the secondary shell 24. The opening B4 is closed by
a circular plate 65, which is connected to the secondary shell 24 by a weld
seam 6E, and to the nozzle 64 by a weld seam 67. A flange 69 on.the outer
end of the nozzle 60 is used to connect the latter to an appropriate pipe.
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As mentioned above, the tank is used to store hydrocarbons or
produced water. The high level shut down device mounted in the nozzle 10 is
used to ensure that the tank is not filled beyond the level of the lower
device.
Many jurisdictions require that tanks of this type have an additional 10%
capacity, i.e. space for 10% more liquid than the level at which the tank is
considered to be full. Accordingly, the high level shut down device is a
considerable distance beneath the top of the tank. A second shut down
device, referred to as a high, high level shut down device is mounted in the
nozzle 11 for shutting down liquid flow to the tank in the event that the tank
is
overfilled.
The integrity of the inner or primary shell 23 is monitored by
subjecting the space between the shells 23 and 24 to a vacuum. For such
purpose openings 71 and 72 (Fig. 6) are provided in the primary floor 19
outside of the lower ring 40 and in the secondary shell 24 above the ring 40,
respectively. Internally threaded fittings 75 and 76 are provided around the
openings for receiving vacuum lines (not shown). The vacuum lines are
connected to an off-the-shelf pump and vacuum gauges. If a leak occurs in
the primary floor 19 or shell 23, the pressure in the space between the floors
or
shells changes to indicate the presence of the leak.
With reference to Fig. 12, as an added safety feature, a pressure
release or interstitial space relief device is provided at the upper end of
the side
wall of the tank. The device includes a tube 76 extending through the outer
shell 24. A check valve 77 is connected to the tube 76. An inverted J-shaped
exhaust tube 78 is mounted on the top end of the check valve 77. If there is a
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leak in the primary shell 23 and an accumulation of gas in the space between
the shells above a predetermined limit, the check valve 77 opens to discharge
gas from between the shells 23 and 24.
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