CA2241354C

CA2241354C - Double wall tank

Info

Publication number: CA2241354C
Application number: CA002241354A
Authority: CA
Inventors: Roger J. Baron; R.W. Mitchell (Rick); Robert W. Hoffman
Original assignee: Nusco Manufacturing & Supply Ltd
Current assignee: Nusco Manufacturing & Supply Ltd
Priority date: 1998-06-19
Filing date: 1998-06-19
Publication date: 2005-05-24
Anticipated expiration: 2018-06-19
Also published as: CA2241354A1

Abstract

A double walled tank for above ground use includes a circular base defined by an upper primary floor and a slightly larger lower, secondary floor connected to the primary floor by a peripheral weld seam; a cylindrical side wall defined by an inner primary shell and an outer secondary shell, the bottom end of the secondary shell being above the bottom end of the primary shell, such bottom end being connected to the primary floor and to the primary shell by weld seams and a continuous sealing ring; and a conical roof connected to the top end of the primary shell by a weld seam.

Description

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, 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.

2 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.

3 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.

4 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 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 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 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.

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 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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. A double wall 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.

2. The double walled tank of claim 1 including a lower compression ring extending around the bottom end of said secondary shell, said lower ring being connected to said secondary shell and to said primary floor.

3. The double walled tank of claim 2, including an upper compression ring extending around a top end of said secondary shell for reinforcing the top end of the tank.

4. The double walled tank of claim 1, 2 or 3, including a first opening in said primary floor outside of said bottom ring permitting the creation of a vacuum between said primary and secondary floors; and a second opening in said outer shell above said lower ring permitting the creation of a vacuum between said inner and outer shells, whereby the integrity of the primary floor and the inner shell can be monitored.

5. The double walled tank of any one of claims 1 to 4, wherein said inner shell includes a plurality of first metal sheets butt joined along the edges thereof; and said outer shell includes a plurality of second sheets lap joined along edges thereof.

6. The double walled tank of claim 3, wherein said inner and outer shells are cylindrical, and said upper and lower compression rings have an inverted L-shaped cross-section.

7. The double walled tank of any one of claims 1 to 6 including a notch in the top end of said outer shell, and a lifting lug in said notch inside of said upper compression ring, said lug being connected to said primary and secondary shells and to said upper compression ring.

8. The double walled tank of any one of claims 4 to 7, including a pressure release device connected to the space between said primary and secondary shells for limiting the build up of gas pressure between said shells.