Static structures (e.g. – buildings) – Processes – Assembling exposed modules
Reexamination Certificate
1998-07-02
2001-09-04
Stephan, Beth A. (Department: 3635)
Static structures (e.g., buildings)
Processes
Assembling exposed modules
C052S747120, C052S745010, C052S745100, C052S127200, C182S036000, C182S037000, C182S128000
Reexamination Certificate
active
06282863
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to aboveground storage tanks, and more specifically to a method of constructing a tank. Unlike conventional methods, the present method does not require the use of scaffolds to provide either: (1) access to the shell plates for construction personnel; or (2) resistance to buckling damage from ambient wind during shell construction.
Aboveground storage tanks typically consist of a circular, essentially flat bottom and a vertical cylindrical shell having a lower edge that is joined to the tank bottom. The shell of a conventional storage tank consists of a stack of rings that are joined together at girth seams. Each shell ring is constructed of shell plates that are joined together at vertical seams. Tanks typically have a fixed roof that may be cone-shaped or dome-shaped and is joined to the top of the shell, or a floating roof that floats on the product stored in the tank.
During construction of the shell, it is conventional to use scaffold brackets to attach a scaffold to the outside or inside surface of the shell. The scaffold provides construction personnel with access to the shell plates during their placement in the shell rings and for fit-up and welding of vertical seams and girth seams between plates. Conventionally, a scaffold is initially mounted on the first shell ring and is consecutively “jumped” upwards as work progresses to higher shell rings.
The use of scaffolds for constructing a tank shell has a number of disadvantages. The scaffold consists of many components that must be fabricated, maintained in working order, stored in a construction equipment warehouse, shipped to the tank construction site, installed on the shell rings, moved to higher shell rings during construction of the higher shell rings, removed from the tank after tank construction, and sent back to a construction equipment warehouse for repair, maintenance, and storage until the next tank construction project. Time and effort is also required to remove the scaffold bracket straps after use, and to grind smooth any remaining weld burrs on the shell plates. The time required to successively jump a scaffold to higher shell rings alone adds significantly to the time needed to construct a tank shell. It is thus desirable to find an alternative tank construction method that does not require the use of a scaffold.
One consideration has weighed in favor of continuing the use of scaffolding. As wind flows over a cylindrical tank shell, it produces an air pressure on the upwind surface of the tank shell that is higher than the local barometric pressure at the tank site. It also produces an air pressure on the downwind surface of that same tank shell that is lower that the local barometric pressure. This differential of air pressures tends to cause the shell to deflect inwardly on the upwind side of the tank. While a tank is being constructed, the shell may lack adequate rigidity to prevent such wind-produced air pressures from causing the shell to buckle. A scaffold that completely encircles the shell during construction can, if properly designed and installed, provide the shell with resistance to such buckling. This is described, for example, in Vaughn, et al., U.S. Pat. No. 3,908,793.
SUMMARY OF THE INVENTION
According to the present invention, an aboveground storage tank can be constructed without the expense of a scaffold. A mobile manlift and carriages suspended from the top edge of the plates are used to provide the necessary access for hanging, fitting, and welding the shell plates of the upper rings.
Additional resistance to tank shell buckling, if necessary, can be provided by anchoring the tank shell to the foundation, such as through the use of individual shell anchors spaced around the lower portion of the first shell ring. If a concrete ringwall is used as part of the tank foundation, the shell anchors may be attached to the concrete Tingwall. Alternatively, shell anchors may be attached to the soil, for example with auger soil anchors. Stiffening may also be provided by guys lines or by adding stiffeners at critical heights on the sides of the tank while it is being erected.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is an elevational view of a typical aboveground fixed-roof storage tank, with a partial section view of the tank shell.
FIG. 2
is a plan view of the bottom of the tank illustrated in
FIG. 1
, showing an arrangement of bottom plates and a layout for the first ring.
FIG. 3
is an elevational section indicated by section
1
—
1
in
FIG. 2
, illustrating a method of positioning the first ring plates.
FIG. 4
is an elevational view of the outside surface of a first ring shell plate prior to its placement the first shell ring.
FIG. 5
is an isometric view of a key plate that may be used to join and fit a vertical seam between adjacent shell plates.
FIG. 6
is an isometric view of a type of shell anchor strap that may be attached to a concrete ringwall.
FIG. 7
is an isometric view of a type of shell anchor that may be attached to the soil.
FIG. 8
is an elevational view of the outside surface of a second ring shell plate prior to its placement in the shell ring.
FIG. 9
is an elevational view of the tank shell during the placement of a second ring shell plate.
FIG. 10
is an isometric view of section
2
—
2
in
FIG. 9
, illustrating the placement of a typical girth seam shim.
FIG. 11
is an elevational view of the tank shell while construction carriages are used in se fit-up automatic vertical seam welding, and automatic girth seam welding.
FIG. 12
is an isometric view of an aboveground storage tank showing placement of a top ring.
FIG. 13
shows a top angle being used as a temporary stiffener.
REFERENCES:
patent: 884813 (1908-04-01), Gordnier
patent: 1265966 (1918-05-01), Schlafly
patent: 2433335 (1947-12-01), Boardman
patent: 2852110 (1958-09-01), Dueringer
patent: 2975927 (1961-03-01), Arne
patent: 3391757 (1968-07-01), Duke et al.
patent: 3471053 (1969-10-01), Endicott et al.
patent: 3620331 (1971-11-01), Shaw
patent: 3637047 (1972-01-01), Cox
patent: 3880315 (1975-04-01), Nelson et al.
patent: 4142284 (1979-03-01), Steuber
patent: 4164268 (1979-08-01), Jones et al.
patent: 4225012 (1980-09-01), Hindle
patent: 4788803 (1988-12-01), Seitz
patent: 4828073 (1989-05-01), Friday
patent: 5009052 (1991-04-01), Welch
patent: 5148605 (1992-09-01), Julia
patent: 5271482 (1993-12-01), Walz
patent: 5590497 (1997-01-01), Moore
patent: 2 096 227 (1982-10-01), None
International search report dated Oct. 20, 2000.
Christian Harold B. (“Scott”)
Easter William R.
Chicago Bridge and Iron
Dorsey Dennis L.
Marshall O'Toole Gerstein Murray & Borun
Stephan Beth A.
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