FIELD OF INVENTION

The present invention relates broadly to a method and staging system for constructing a floating cover for a storage tank. BACKGROUND

Storage tanks are in use for example at storage terminals or processing plants where huge stock piles of liquid raw materials are necessary for continuous operations. These storage tanks usually employ floating covers that move as the liquid levels change, and these covers provide protection against contamination to/from the external environment or weather and against evaporation losses.

The covers are typically made of steel or aluminum, mainly due to the ease of welding and their availability as construction materials. However, steel covers corrode relatively easily and are costly to maintain. For aluminum covers, the initial capital outlay is low, but the covers are typically not sufficiently robust. For example, in many instances where heavy duty mechanical mixers are deployed aluminum covers are not suitable for such heavy usage as there are typically held together by bolts and nuts. There are also disadvantages of incomparability due to lack of chemical resistance, including that the covers must be compatible with the contents stored in the tanks. Chemical corrosion will affect the longevity of the aluminum covers. The covers can also be made from laminated structures such as glass fiber reinforced structures, with pre-fabricated panels being joint by lamination processing on-site during fabrication of the cover.

These tanks are usually very large and may range from a few meters to about 100 meters in diameter. Before construction begins, a platform supported on scaffolding is erected and the cover is then formed on the platform. Due to the size of the cover, this type of construction is invariable carried out on site, i.e. the platform is constructed within the outer perimeter wall of the tank during construction.

Owing to the nature of the work, the construction of the floating covers from individual panels involves welding processes from both sides, i.e. from the top side of the cover to be constructed, and from the bottom side. In practice, the welding is thus performed in two stages, a first stage during which the welding operation is performed from the top surface, with workmen operating on top of the panels supported by the platform. The platform itself consists of an array of support panels, such as metal panels covered with plywood.

During the second stage welding and/or laminating processing, i.e. from below the platform, the platform is selectively removed, i.e. selected platform panels are removed to expose the bottom surface of the cover panels, thus enabling access for performing the welding and/or laminating processing. Because this typically involves removal of a number of supporting legs and platform panels of the platform structure, this work is typically performed only after the welding and/or laminating processing from the top has been finalized, so as to not jeopardize the structural integrity of the platform during the welding and/or laminating processing.

Additionally, as the removal of the platform structure involves removal of the platform panels, which may have a dimension of for example 4m ² , objects of that size can typically only be removed from the tank through the large roof opening of the tank structure, which in turn means that the roof of the tank structure cannot be completed until after the floating cover has been completed. This adds significantly to the overall project completion time for construction of the entire storage tank structure.

A need therefore exists to provide a construction method and components that seek to address at least one of the above mentioned problems.

SUMMARY

According to a first aspect of the present invention there is provided a method for constructing a floating cover for a storage tank, the method comprising the steps of supporting panels of the floating cover on a staging system, the staging system comprising a plurality of vertical support legs; a network of bearer beams, each bearer beam configured for releasable connection to two of the support legs; and selectively removing one or more of the bearer beams to provide access to one or more joint lines between adjacent panels for welding and/or laminating processing.

The method may further comprise selectively removing one or more of the support legs for providing access to a remaining portion of the joint lines.

The method may be performed on-site within a peripheral wall of the storage tank.

The method may further comprise removing all components of the staging system through a standard man-way cover in the peripheral wall.

The method may further comprise completing a roof structure of the storage tank prior to removal of all components of the staging system.

The method may further comprise welding and/or laminating processing of the panels substantially simultaneously on top and bottom surfaces of the panels.

According to a second aspect of the present invention there is provided a staging system for constructing a floating cover for a storage tank, the staging system comprising a plurality of vertical support legs; a network of bearer beams, each bearer beam configured for releasable connection to two of the support legs; and configured for selectively removing one or more of the bearer beams to provide access to one or more joint lines between adjacent panels for welding and/or laminating processing.

The staging system may further comprise a network of ledger rods, each ledger rod configured for releasable connection to two of the support legs.

Each bearer beam may comprise a lining on a surface facing, in use, the panels.

The lining may comprise ply wood.

Each support leg may comprise a head plate for supporting the panels in an area above the support leg.

The head plate may comprise a lining.

The lining may comprise ply wood. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

Figure 1 shows a perspective view of a staging structure according to an example embodiment.

Figure 2 shows a perspective exploded view of components of the staging structure of Figure 1.

Figures 3a) and b) show respective perspective views of components of the staging structure of Figure 1 illustrating and aspect of assembly thereof.

Figures 4a) to c) show respective perspective views of components of the staging structure of Figure 1 illustrating and another aspect of assembly thereof.

Figure 5 shows a schematic drawings of a portion of a staging system according to an example embodiment, and illustrating mounting of Internal Floating Roof (IFR) standard panels.

Figure 6 shows a flowchart 600 illustrating a method for constructing a floating cover for storage tank according to an example embodiment. DETAILED DESCRIPTION

The example embodiments described provide a staging system for construction of a floating cover for a storage tank designed to enable lamination or welding of top and bottom joints of panels of the floating cover substantially simultaneously. Furthermore, the staging system in example embodiments is designed so that all staging material can be removed from the storage tank through a standard existing "man-way" cover at the peripheral wall of the tank, thus enabling completion of the roof of the storage tank structure independent of construction of the floating cover. More particular, the roof can be fully completed simultaneously to the construction of the floating cover.

Figure 1 shows a portion of a staging system 100 according to an example embodiment. The staging system 100 comprises an array of vertical support legs in one exemplary form e.g. 102, interconnected by a network of bearer beams e.g. 104, and a network of ledger rods in one exemplary form e.g. 105. The length of the barrier beams in one exemplary form e.g. 104 is chosen to match the dimensions of individual panels of the floating cover (not shown) to be constructed, for example such that each set of 4 legs e.g. 106, 107, 107, 108, 109 together with the interconnecting bearer beams e.g. 110, 111, 112, 113 define a staging frame that supports one of the floating cover panels. The floating cover panel, when centered on the frame, is supported by substantially the inward facing half of the respective widths of the bearer beams 110 to 113.

The network of ledger rods e.g. 105 advantageously provides positional and structural integrity during the initial erection of the network of support legs e.g. 102. Additionally, in the completed staging system 100, the network of ledger rod e.g. 105 can provide additional structural integrity, in particular during removal of selected ones of the bearer beams e.g. 104.

Construction of the staging structure 100 starts in an aligned position relative to the assembly of floating cover panels for construction of the floating cover, for example starting in the center of a circular storage tank, with the bear or beams e.g. 104 aligned in an array of substantially parallel and substantially perpendicular rows relative to a diameter line of the circular storage tank and with one of the legs positioned at substantially the center point of the circular storage tank. As the staging system 100 is constructed, each group of 4 legs and bearer beams provides a support frame for one of the panels of the floating cover, and providing a working platform for workmen to perform laminating or welding processing from a top surface of the panels.

In the example embodiment, advantageously laminating and/or welding processing from a top and a bottom surface of the panels can be performed substantially simultaneously, as will now be described in more detail.

Each bearer beam e.g. 110 is designed such that it can be disengaged from its supporting legs e.g. 106, 107 without removal of the support legs e.g. 106, 107. Therefore, removal of each bearer beam e.g. 110 enables access to the joint area between two adjoining cover panels along one side of the adjoining panels, but without removal of the legs e.g. 106, 107. Therefore, advantageously the structural integrity of the staging structure with regard to support for the relevant joining cover panels is not compromised, thus enabling substantially simultaneous laminating and/or welding processing from the top and bottom of the cover panels.

While areas of the joints directly above the legs e.g. 106, 107 remain inaccessible, it will be appreciated that selective removal of individual ones of the legs e.g. 106, 107 can be readily coordinated such that the laminating and/or welding processing from the bottom can be completed. It will be appreciated that the relevant in-accessible areas of the joints are very small compared to the overall joint length between the floating cover panels, and therefore a significant time saving can advantageously be achieved since the majority of the joint length can be processed substantially simultaneously from the top and bottom surfaces of the floating cover panels.

In the example embodiment, because the staging structure 100 comprises a network of bearer beams e.g. 104 instead of platform panels as in existing platform structures, the components of the staging structure 100 are advantageously dimensioned so that they can be easily removed through a standard existing "man-way" cover at the peripheral wall of the tank structure. Thus, a roof of the storage tank structure can be completed independent of the completion of the floating cover, which can further reduce overall project completion time.

With reference to Figure 2, the components of the staging structure 100 will now be described in more detail. Each leg 102 comprises, in an exemplary form, a vertical tube 202, terminated with respective adjustable screw jacks 204, 206 being received within the vertical leg tube 202. Each screw jack 204, 206 comprises, in an exemplary form, a plate 208, 210 at the end pointing away from the vertical tube 202. For the top screw jack 204, a head plate, in an exemplary form, 212 is mounted on the plate 210. A correspondingly sized plywood plate, in an exemplary form, 214 is secured on the head plate 212, using nuts and bolts in this example embodiment, for providing a lining for preferably non-damaging contact to the floating cover panels.

With reference to Figures 3a) and 3b), the head plate 212 comprises for fastening protrusions in the form of hooks 301 to 304 as well as two securing pins 306, 307, formed at a bottom surface of the head plate 212. As shown in Figure 3b), the head plate 212 is mounted on the plate 210 of the adjustable screw jack 206 by lowering the head plate 212 onto the plate 210, whereby the hooks 301 to 304 form a substantially tight fit with respective sides of the plate 210, and the pins 306, 307 are received in corresponding holes e.g. 308 (Figure 3a)), in this example embodiment. This can advantageously provide fast assembly and disassembly, while providing sufficient mounting integrity under the applicable gravitational forces on the head plate 212 in use. Returning now to Figure 2, each bearer beam 04 comprises, in an exemplary form, a bearer base 216, and a plywood liner 218. The bearer base 216 comprises brackets 217, 219 at either end. The plywood liner 218 is connected to the bearer base 216 using nuts and bolts in the example embodiments. Each ledger rod 106 comprises, in an exemplary form, fastening elements 220, 222 for releasably securing the ledger rod 106 to the vertical tube 202 at corresponding connector elements, in an exemplary form, 224 or 226 at different heights, as desired. In this example embodiment, the fastening elements 220, 222 each comprise a slanted locking member received in respective top and bottom openings of the fastening elements 220, 222. As will be understood by a person skilled in the art, the slanted locking element is additional received and passes through corresponding slot members of the connector elements 224, 226.

In an example embodiment, materials of respective components are as follows, but it will be appreciated that the present invention is not limited to those materials. The head plate 212 and bearer base 216 may be made from galvanized steel. The plates 208, 210 may be made of mild steel. The leg tube 202, and connector elements 224, 226 may be made from galvanized steel. The ledger rod 106 and fastening elements 220 and 222 may be made from galvanized steel. The screw jacks 204, 206 may be made from mild steel.

Figures 4a) to. 4c), illustrate the connection of the bearer base 216 to the head plates 212 in an example embodiment. More particular, the hooks e.g. 301 are received in the bracket 217 of the bearer base 216. A wedge shaped locking pin 402 is inserted through a corresponding pin hole 404 of the bracket 217, and pushed/wedged so as to extend through the hook 301 and another pin hole on the opposite side of the bracket 217, for a friction/jamming securing of the locking pin 402. As will be appreciated by a person skilled in the art, a hammer may be used for locking the pin 402 into place during assembly, and for unlocking the pin during disassembly.

Figure 5 shows a portion of a staging system 500 according to an example embodiment, and illustrating mounting of IFR standard panels 502, 504. Each panel 502, 504 is centered on respective staging frames defined by a set of 4 legs of the staging system 500. The panels 502, 504, when centered on their respective frames, are supported by substantially the inward facing half of the respective width of the plywood liners, generally indicated at 510, which are mounted on bearer bases e.g. 512 using nuts and bolts in this example embodiment. Once the panels 502, 504 are in place, they can be joined together using techniques understood in the art. For example, the panels 502, 504 may be of a type as described in PCT publication no. WO 2004/067408, and may be joined as described in that document, the contents of which are hereby incorporated by cross-reference. Figure 6 shows a flowchart 600 illustrating a method for constructing a floating cover for storage tank according to an example embodiment. At step 602, panels of the floating cover are supported on a staging system. The staging system comprises a plurality of vertical support legs and a network of bearer beams, each bearer beam configured for releasable connection to two of the support legs. At step 604, one or more of the bearer beams are selectively removed to provide access to one or more joint lines between adjacent panels for welding and/or laminating processing.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.