WO2001070597A1

WO2001070597A1 - Tank for hazardous material

Info

Publication number: WO2001070597A1
Application number: PCT/GB2000/002101
Authority: WO
Inventors: Andrew Jonathan Gaskell; Norman John Slee
Original assignee: FLEET TANKS (UK) Ltd
Current assignee: FLEET TANKS (UK) Ltd
Priority date: 2000-03-21
Filing date: 2000-06-09
Publication date: 2001-09-27
Anticipated expiration: 2002-09-21
Also published as: AU2000252315A1

Abstract

A tank (100) for storing hazardous fluids. The tank comprises a quadrilateral vessel (102) for receiving hazardous fluids and has four walls (104, 106, 108, 110), a top (114) and a bottom (116). The tank includes a reinforcing frame including a reinforcing structure (150) extending over opposed walls and at least one of the top and the bottom of the vessel.

Description

TANK FOR HAZARDOUS MATERIAL

The present invention relates to a tank, and in particular to a storage and transport tank for hazardous fluids .

Tanks for storing and transporting hazardous fluids, such as noxious, flammable, corrosive and toxic liquid chemicals, conventionally have a circular storage vessel. When required to act as a pressure vessel, they can also have curved end caps so as to help retain the hazardous materials stored under pressure. Circular tanks are preferred by the safety authorities owing to the inherent strength of circular structures and the ease with which modelling of tank performance can be carried out in circularly symmetric system.

However, circular storage tanks waste space. They occupy a circular footprint. There is a maximum packing density of' circular tanks that can be achieved, in which the gaps left between the tanks cannot be utilised.

According to the present invention there is provided, a tank for storing hazardous fluids, comprising a quadrilateral vessel for receiving hazardous fluids having four walls, a top and a bottom and a reinforcing frame including a reinforcing structure extending over opposed walls and at least one of the top and the bottom of the vessel .

The tank is suitable for storing hazardous chemicals such as noxious, flammable or corrosive liquids. The tank is specifically suitable for use in the petrochemical industries for storing hazardous chemicals and their subsequent transportation to offshore sites such as drilling and storage platforms.

The tank includes a quadrilateral vessel and a reinforcing frame extending around the vessel. The vessel can have a quadrilateral cross section in a plane substantially orthogonal to the walls of the vessel. The reinforcing frame is located around the exterior of the vessel and includes at least one reinforcing structure which encompasses a pair of opposed walls and at least one of the top and bottom of the vessel. The reinforcing structure may be either a continuous member or a number of interconnected members so as to provide a continuous reinforcing structure which extends over a pair of opposed walls and the top or bottom of the vessel.

A quadrilateral storage tank allows for close packing of storage tanks and so obviates the wastage of storage space which occurs with round storage tanks . A quadrilateral storage tank takes up a similar foot print to a circular storage tank but provides increased storage volume within the same practical foot print. Hence increased storage volume can be provided by the current invention compared to previous storage tanks .

The reinforcing frame acts to both strengthen the tank with regard to impacts and also allows the tank to act as a pressure vessel for storing volatile fluids. The ability of the quadrilateral vessel to safely store and transport hazardous, volatile fluids is a result of the reinforcing structures which extend over at least opposed walls and a top or bottom of the vessel so as to compensate for weak points introduced into the top and bottom of the vessel by- ancillary features.

The particular combination of a quadrilateral vessel and reinforcing frame provides a pressure storage and transport vessel which will safely handle hazardous fluids while meeting all safety standards of the relevant on shore and off shore authorities for static and dynamic behaviour. The particular combination of features of the tank allows the tank to store a commercially practical volume of hazardous fluids in a tank which is sufficiently light for handling, while maintaining the structural robustness of the tank to both impacts and potential explosion. It is the combination of a reinforcing frame and quadrilateral vessel that provides the substantial advantages of the present tank over prior storage or transport tanks .

In particular, the tank of the invention provides a greater amount of material to be stored or transported and having the same practical footprint as a conventional circular tank. The tank also provides for an increased packing density of tanks and so fewer tanks need to be transported in order to achieve the same total volume of transported material. Hence the tank provides increased economy, e.g. by reducing the number of barge trips required from a land base storage site to an off shore platform.

Preferably the reinforcing structure extends over opposed walls and the top and the bottom of the vessel. The reinforcing structure can form a band wholly encircling a pair of opposed walls and the top and the bottom of the vessel thereby to enhance the structural robustness of the vessel. The reinforcing structure may be a continuous member or be formed from a number of individual members fastened to provide a continuous structure around the vessel .

The reinforcing frame can include a cage around the walls of the vessel . A preferred form of the reinforcing frame is that of a cage extending around the side walls of the vessel . A cage provides structural reinforcement around the vessel thereby allowing the thickness of the walls of the vessel to be reduced so as to reduce the overall weight of the tank and enhancing the tanks dynamic performance.

Preferably the cage includes a plurality of bars extending along a longitudinal axis of the vessel . The vessel can have a longitudinal axis extending parallel to the side walls of the vessel and substantially perpendicular to the top and/or bottom of the vessel . The cage can include a plurality of bars extending parallel to the longitudinal axis of the vessel so as to reinforce the side walls of the vessel to bowing forces applied from the interior of the vessel .

Preferably a two of the plurality of bars form a part of the reinforcing structure. The reinforcing structure can include a bar on a first wall of the vessel and a bar on an opposed wall of the vessel, thereby providing members forming part of the reinforcing structure . Hence the bars provide both reinforcement against bowing of the side walls and, in co-operation with the remainder of the reinforcing structure, reinforce the wall-top and/or wall-bottom joint and reinforcement of the top and/or bottom of the vessel to bowing. Preferably the cage includes a corner post at each wall vertex. A post part of the cage can be provided at each wall-wall vertex so as to provide reinforcement of the joint at the wall vertex and also enhance the overall structural strength of the reinforcing frame . Preferably the cage includes a corner post at each wall-top/bottom vertex. The reinforcing framework can include a corner post at each joint between a respective wall and the top and/or bottom so as to reinforce the strength of the joint at that point.

Preferably a brace member extends between a corner post and a next nearest bar. The brace member acts to reinforce the corner posts with respect to impacts. Preferably the brace is located substantially at the midpoint of the corner bar so as to reduce the moment generated by an impact on the corner bar. Hence the brace member acts to reinforce the corner bar and also helps to distribute any load experienced by a corner bar throughout the rest of the framework.

Preferably the plurality of bars of the cage are equidistantly spaced along each wall. Each wall of the vessel can have a number of bars equidistantly spaced across the width of the wall. In this way the wall is uniformly reinforced with a minimum number of reinforcing members and without incurring weak spots.

Preferably the cage has five bars equidistantly spaced along each wall between the corner posts and the ends of the walls. It has been found that in practice a cage having five equidistantly spaced bars between the corner posts has provided an optimum balance of strength to weight of the tank while complying with all relevant safety regulations. It will be appreciated that the structural strength of the tank overall is the result of an interaction between the inherent vessel strength and reinforcing frame design. An increased vessel strength means that the frame strength can be decreased and vice versa. However there is a law of diminishing returns in increasing either the vessel or reinforcing frame strength to an extreme, and a five bar cage has been found to have been practically the most beneficial design.

Preferably the reinforcing structure has a rectangular hollow section. Rectangular hollow sections provide a strong lightweight structure so that the dynamic and static performance of the tank can meet the safety regulations applicable to such tanks. Preferably the bars of the cage have a square hollow section. A square hollow section for the bars has been found to provide optimum performance in terms of strength and weight for the tank.

Preferably the bottom of the tank includes a drain. More preferably, the bottom of the tank is sloped towards the drain. The drain is required in order to facilitate the removal of hazardous substances from the tank and a sloped bottom helps the gravity feed to the drain. A drain is also required for cleaning purposes so that different substances can subsequently be stored in the tanks when re-used.

Preferably the drain includes a sump. The sump can form a part of the reinforcing structure . The drain can include a sump extending downward from the bottom of the tank. The sump can provide a structural member forming part of the reinforcing structure. If no reinforcing structure around the drain part of the tank is provided, then the drain could provide a weak point of the tank which may be liable to rupture by volatile materials stored in the tank.

Preferably the tank includes a manhole in the top of the vessel. A manhole is included to allow access to the vessel for fabrication and also to allow access for inspection and cleaning and also can be used for filling the tank. A manhole includes any access port and cover allowing a person entry to the interior of the vessel and which can also be closed to re-seal the vessel.

The tank can include an annular reinforcing plate around the manhole and internal into the vessel . It will be appreciated that cutting an aperture in the top of the vessel can potentially generate a weak point in the top of the vessel . An annular reinforcing plate around the aperture of the manhole reinforced the top of the vessel around the aperture which, in co-operation with the structure of the manhole, obviates the weak spot that would be generated in the absence of the reinforcing plate .

Preferably the tank includes a manhole reinforcing structure around the manhole. The manhole reinforcing structure acts to reinforce the weak spot provided by the aperture of the manhole. The manhole reinforcing structure can provide a part of the reinforcing structure which extends around opposed walls and the top of the vessel . The manhole reinforcing structure also increases the rigidity of the top of the vessel in the proximity of the manhole aperture.

Preferably the tank includes a cover plate extending between the manhole and the manhole reinforcing structure and flush with the top of the manhole reinforcing structure to prevent accumulation of fluid. The cover plate helps to prevent the accumulation of fluid trapped between the manhole and the manhole reinforcing structure. The hazardous fluids to be stored in the tank can spill and accumulate in recesses, in the absence of a suitable cover. The accumulation of hazardous chemicals presents a health and safety risk.

Preferably the tank includes a manhole subframe fastened around the manhole to the reinforcing frame. The manhole subframe can be a separate part or an integral part of the reinforcing frame. The manhole subframe acts to reinforce the rigidity of the top of the vessel which is diminished by the aperture of the manhole. The manhole subframe can extend entirely around the manhole so as to fully reinforce the top of the vessel throughout the plane of the top of the vessel and not only in certain directions.

The tank can be made of steel. Preferably the walls of the vessel have a thickness in the range of approximately 6mm to 10mm, more preferably 7mm to 9mm and most preferably a thickness of approximately 8mm. It has been found that fabricating a vessel from steel with a wall thickness of approximately 8mm provides an optimum strength and weight of the tank overall so as to comply with safety regulations. Substantially reducing the wall thickness can result in an insufficiently robust tank for the safety regulations. Substantially increasing the wall thickness increases the weight of the vessel so that it no longer complies with dynamic safety regulation tests, e.g. a drop test.

The tank can include a base frame. Preferably the base frame has two hollow members extending across the base frame in parallel and each having open ends for receiving a part of a lifting device. The base frame can form an integral part or a separate part of the reinforcing frame and allows the tank to be safely lifted for transportation.

Preferably the tank includes a climbing means providing access for a person to the top of the vessel, in which a part of the reinforcing frame provides a part of the climbing means. A member of the reinforcing frame may be common to a climbing means by which a person can climb the tank to gain access to the top of the vessel. Preferably the climbing means is a ladder in which rungs of the ladder are provided my members extending between parts of the reinforcing frame.

The tank can store a hazardous fluid. Preferably the tank stores a hazardous liquid. More preferably the tank stores a poisonous or noxious or flammable or volatile or corrosive or hazardous liquid. The hazardous liquid can be for use in the petrol chemical industry.

A gap can be provided between the corner posts of the reinforcing frame and the vertical wall vertex of the vessel at each vertical wall vertex of the tank, so as to accommodate deformation of a corner post thereby preventing direct transfer of stresses to the vertical wall vertex joint. Hence, in this way the corner seams of the vessel are further protected thereby enhancing the safety of the tank. The gap between the corner posts and the wall vertices can be provided by an a secondary wall element bridging between adjacent main wall elements which define the quadrilateral shape of the vessel. The secondary wall elements can be straight. The vessel can have an asymmetric octagonal shape whilst remaining substantially quadrilateral .

The reinforcing frame can include a continuous brace structure adjacent the top of the vessel and extending between opposed sides of the vessel . The brace structure helps to prevent deformation of the frame under loading to prevent unwanted stresses from being experienced by the vessel. The brace structure can comprise a single member. The brace structure can comprise a plurality of aligned elements joined together. A brace structure can be provided extending across a rear side and/or a front side of the tank.

According to an aspect of the invention there is provided a method of storing a hazardous fluid comprising the step of introducing the hazardous fluid into a tank comprising a quadrilateral vessel for receiving the hazardous fluid and having four walls, a top and a bottom and a reinforcing frame including a reinforcing structure extending over opposed walls and at least one of the top and the bottom of a vessel .

According to a further aspect of the invention there is provided a method of transporting a hazardous fluid, comprising the steps of introducing the hazardous fluid into a tank comprising a quadrilateral vessel having four walls, a top and a bottom, and a reinforcing frame including a reinforcing structure extending over opposed walls and at least one of the top and the bottom of the vessel, and conveying the tank with a transporting means from a first location to a second location. Preferably the first location is onshore and the second location is offshore. The transporting means can be a ship.

A particular application of the tank is in the transportation of hazardous fluids used in the petrochemical industry from an onshore site to an offshore platform where the chemicals are stored and consumed. A preferred method of transportation of a tank filled with hazardous fluids is by barge although it would be appreciated that any transporting means capable of carrying the filled or empty tank would be suitable. A crane or fork lifting device could be used on shore for moving tanks .

The present invention will now be described in detail, by way of illustration only, with reference to the accompanying drawings, in which:

Figure 1 shows a front view of a tank according to the invention;

Figure 2 shows a side view of the tank as shown in

Figure 1 ;

Figure 3 shows a plan view of the tank shown in Figures

1 and 2 ;

Figure 4 shows a cross section along line x-x of Figure

3;

Figure 5 shows a cross section along line y-y of Figure

1;

Figure 6 shows a cross section along line z-z of Figure

1;

Figure 7 shows a front view of the tank of Figure 1 including additional features;

Figure 8 shows a side view of the tank as shown in

Figure 7 ; Figure 9 shows a plan view of the tank as shown in

Figure 7 ;

Figures 10 a, b and c respectively show plan, side and end elevations of a manhole subframe part of the tank shown in Figure 7;

Figures 11 a, b, c and d show perspective, plan, side and end elevations respectively of a base frame part of the tank as shown in the previous Figures ;

Figures 12 a, b, c and d show views corresponding to those of Figures 1, 2, 5 and 6 of a further embodiment of a tank according to the invention; and

Figures 13 a, b and c show side views of a top part of further embodiments of a tank according to the present invention.

The same items in the different Figures share common reference numerals .

With reference to the Figures there is shown a tank, designated generally by reference numeral 100, according to the present invention. The tank is particularly suited for the storage and transportation of hazardous fluids and in particular chemicals for use in the petro-chemical and associated industries.

The tank includes a vessel 102 for receiving hazardous fluids and a reinforcing frame 150 disposed about the exterior of vessel. An interior reinforcing frame could be provided but would be more difficult, and hence expensive, to fabricate.

The vessel has front 104 and back 108 walls and side walls 106, 110. The walls are arranged in a quadrilateral configuration such that the vessel is substantially square. The front and back walls are manufactured from a steel plate with dimensions 1810x1473mm and a thickness of 8mm. The vessel side walls are also made from a steel plate having dimensions 1853x1441 and a thickness of 8mm. The walls are joined at the corners with 6mm continuous fillet welds. The ends of the side walls slightly overlap the ends of the front and back walls at the corners for the welded joints. An internal and external 6mm continuous fillet weld is provided at each corner. The fabricated vessel has a substantially square cross section.

The vessel includes a top 114 and a bottom 116. The top is a steel plate with dimensions 1810x1810mm and a thickness of 8mm. The bottom is fabricated from two steel plates 118 and 120 of dimensions 1810x905mm and a thickness of 8mm, joined by an external continuous fillet weld. As an alternative the bottom may be manufactured from a single steel plate with a slight fold along a central longitudinal axis and having overall dimensions 1810x1810mm and thickness of 8mm.

The bottom of the vessel includes a drain 122 including a sump part 124. The drain is located at approximately the midpoint of the apex formed in the bottom plate. The drain includes a circular sump to which a bottom outlet valve assembly 126 is attached. The bottom valve assembly includes a 90° foot valve with an extended outlet.

The top of the vessel includes a manhole 128. The manhole includes a neck ring 130 and a six point fastening, pivotable lid 132 which includes a nitrile rubber gasket. The manhole provides access to the chamber of the vessel via an aperture 136 in the top plate. An annular reinforcing plate 138 extends around aperture 136 and is welded to the top plate 114 and to the neck ring 130 of the manhole. The reinforcing ring is made of steel and has a thickness of approximately 15mm a width of 134mm and outer diameter of 737mm. The diameter of the manhole is approximately 469mm.

The top plate of the vessel includes aperture 140 providing access for a safety valve, as will be described later, and aperture 142 allowing access for a dipstick, as will also be described later.

The reinforcing frame 150 is comprised of a number of members of rectangular and square hollow section mild steel . The reinforcing frame provides a cage extending around the walls of the vessel. The reinforcing frame provides a cage in the sense that it includes a number of bars which reinforce the vessel and which bars are held together in a particular configuration either by attaching to other bars or to other frame members .

In detail, the reinforcing frame includes a corner post 152 at each vertex of the walls of the vessel . The corner post is fabricated from 100x100mm square section of mild steel of 6.3mm thickness and length approximately 2350mm. Top side rails 154 extend between top ends of corner posts 152 on each side of the tank. The top rails are of similar construction to the corner posts but have shorter length. Side support bars 156 are provided welded to each wall of the vessel and extending in a direction substantially parallel to the longitudinal axis of the vessel. The side support bars 156 are fabricated from square hollow section of mild steel of dimensions lOOxlOOmm and 5mm thickness and a length of approximately 2050mm. Shorter side support bars 158 are provided as the central side support bar on the front and rear walls of the vessel.

Top rails 160 extend along the top of the front and rear parts of the reinforcing frame. An access gap 162 is provided in the top rail . The top rail is manuf ctured from similar dimension section to the corner posts and top side rails but in shorter lengths. Five equidistantly spaced side support bars are provided on each side wall of the vessel. A brace member 164 is provided between corner post 150 and nearest support bar 156 at each corner. The brace member is located at approximately the mid point of a corner post. The brace member is fabricated from a rectangular hollow section of dimensions lOOxlOOmm square hollow section with thickness 5mm and length 235mm. A similar brace member 166 is also provided in a top part of the reinforcing frame as will be described later.

Top support bars 168 are provided as part of a top reinforcing structure welded to the top of the vessel and extending between the rear and front of the vessel. Ends of the top support bars are welded to the side support bars and provide a reinforcing structure extending over opposed walls of the vessel and across the top of the vessel . The top support bars are fabricated from similar members to the side wall bars but with differing lengths. Shortened top support bars 170 extend between the central side support bar on the front and rear of the vessel and toward a manhole reinforcing structure 172.

Top brace members 166 extend between the central side wall reinforcing bar and the nearest adjacent top supporting bar thereby reinforcing the top wall corner of the vessel . Five equally spaced top support bars are provided extending over the width of the top plate of the vessel. A further top brace member 174 extends between the outer top support bar and a part of the manhole reinforcing structure 172 provided by intermediate top support bars. Central side wall support bars, top support braces 166, 174 and manhole reinforcing structure 172 together provide a reinforcing structure extending over opposed walls of the vessel and across the top of the vessel.

With reference to Figure 6 in particular, a bottom reinforcing structure includes bottom support bars 180 extending across the bottom plate of the vessel between the side walls. The bottom support bars are fabricated from two members of square hollow section of similar dimensions to the other support bars having a length of approximately 916mm and joined by a weld at their middle so as to accommodate the fold in the bottom plate . The bottom support bars are equidistantly spaced between the front and rear walls of the vessel. The sump 124 of the drain 122 provides a structural continuation of the central bottom support bar. The bottom support bars and side support bars 156 together form a reinforcing structure extending over opposed walls and the bottom of the vessel . The central bottom support bar 182 together with central side support bars and top bracing members and manhole reinforcing structure 172 provides a reinforcing structure extending over opposed side walls and the top and the bottom of the vessel .

Manhole reinforcing structure 172 includes brace members 184 extending between intermediate top support bars 168 and central top support bar 170. The manhole reinforcing structure 172 provides a continuous structure comprising a nu ber of separate members extending around the aperture 136 in the top plate of the vessel . The manhole reinforcing structure thereby reinforces the top plate of the vessel . Brace members 184 also form members of a reinforcing structure extending across the top plate of the vessel and over opposed side walls of the vessel.

Splash cover plates 186 are provided extending around the manhole neck ring and the manhole reinforcing structure and flush with the top of the manhole reinforcing structure to prevent the accumulation of fluids in recesses defined between the neck ring and the manhole reinforcing structure. With particular reference to Figures 4 and Figures 10 a, b and c there is shown a manhole subframe 190. The subframe 190 includes rectangular hollow section support members 192 forming a square. The subframe also includes supports 194 positioned around the frame to coincide with the manhole reinforcing structure 172. The manhole subframe also includes a pivotable access cover including a locking means to provide protection for and access to the manhole 128. The subframe both locates the cover above the manhole lid and also provides reinforcement around the aperture of the manhole so as to further rigidify the top plate of the vessel .

The front and rear of the tank includes climbing means 196 providing access to the top of the vessel in the form of a ladder. The ladder includes central support bar 158 as part of its structure and rungs 198 extended between the central support bar and neighbouring intermediate support bars 156. A central brace member 200 extends between intermediate support bars 156 and is welded to the bottom of central support bar 158. Central brace member 200 helps to rigidify the structure of the front and rear support bars with respect to forces applied to the side walls of the tank.

A lifting lug 200 is provided at each top corner of the reinforcing frame to provide an attachment point for lifting equipment. With particular reference to Figure 9 there is shown ambideck flooring 210 providing a walking surface located over the vessel top and top support bars . The ambideck flooring is supported by flooring brackets 212 secured to top rails 154. The corners of the ambideck flooring are cut away to provide access to the lifting lugs 200. A tie down lug 214 is provided towards the bottom of each corner post 152.

The tank includes a safety valve assembly 220 and a calibration gauge 224. The tank also includes a dipstick valve assembly 228 including a dust cap, securing chain and ball valve screwed to a nipple connection on the top plate of the vessel. The bottom valve assembly 230 includes a three inch bottom outlet including a 90° foot valve which is connected to the drain 122.

The tank also includes a base frame designated generally be reference numeral 240. The base frame includes side rails

241 fabricated from rectangular hollow section mild steel with dimensions 200x100mm and thickness 6.3mm and length 1830mm. The base frame also includes hollow brace members

242 extending across the base frame and penetrating through rail members 241. The brace members 242 have open ends. Longer cross brace members 243 extend between the brace members 242 and shorter cross brace members 244 extend between brace members 242 and side rails 241. An earthing boss 245 is also provided. A seal plate 246 is provided in the front rail member. The base frame 240 is located beneath the vessel and as an integral welded part of the reinforcing frame 150.

The tank as described provides a 1000 imperial gallon/4545 litre total storage volume. The design pressure of the tank is 1.76 bar G/25.5 psi and the design temperature range is between 100° and -20°C. The vessel is designed to comply with regulations ASME 8 Div 1 1997 and Appendix 13 IMOl and the frame has been designed to comply with IMOl, BS7072 and DNV 2.7-1.

A further embodiment of a tank 300 according to the present invention is illustrated in Figures 12a, b, c and d which show respective front and side views and a cross sectional views on lines X"X" and Z"Z" of Figure 12a. The tank shown in Figure 12 is substantially the same as the first embodiment described above, apart from where the corners of the vessel 310 meet the reinforcing frame 320.

In this embodiment, the vertical corners 311, 312, 313, 314 of the vessel are not joined to the corner posts 321, 322, 323, 324 of the reinforcing frame. Rather, there is a gap between the corner posts of the reinforcing frame and the vertical vertex joints of the vessel so that any impact on the corner posts of the reinforcing frame will not be directly mechanically transmitted to the corner joints of the frame, thereby further enhancing the protection afforded to the vessel. This feature helps to reduce the risk of the corner weld seam of the vessel splitting in the event of an impact on the corner posts of the reinforcing frame. It will be appreciated that the vessel still has a substantially quadrilateral cross section and that the flattened vertical vertices are merely a minor perturbation of the overall quadrilateral shape of the vessel. It will be appreciated that the top plate of the vessel 326 and bottom plate of the vessel 328 will be shaped to match the shape defined by the vessel walls. This shape may be considered an extremely asymmetric octagon.

Although flat secondary wall sections 330 are shown in Figure 12 bridging across the corners of adjacent main wall sections 332, it will be appreciated that other minor or secondary wall sections can be used to provide the separation between the corner posts and the vessel vertical corner seams. All that is required is that a sufficient gap is provided between the corner posts and the vertical corners of the vessel such that any deformation of the corner posts owing to an impact can be accommodated by that gap so as to prevent rupture of the to the corner seam of the vessel of the tank.

Figures 3a, b and c show views of a top part of further embodiments 350, 360, 370 of a tank according to the invention. Other than the differences described below the other features of the tanks shown in Figure 13 are substantially the same as in the embodiments described previously. The tanks 350, 360 and 370 all include a further continuous brace structure 355, 365, 375 extending across the front and the rear side walls of the tank. Only the front side wall is shown in Figure 13 but an identical symmetric structure is provided on the rear side wall . The continuous brace structure acts to reinforce the frame to prevent deformations caused by a load applied to the side walls, as illustrated at 352 in Figure 13a, from being transmitted to the plate (which plate? the top plate or the side wall plates?) of the tank.

In order to reduce any movement of the frame under such loading, the frame includes a continuous brace structure toward the top of the tank. In Figure 13a, the continuous brace structure is provided by a continuous top rail 355 which extends between the side walls of the vessel and across the front and rear side walls of the vessel. This rail thereby reinforces the frame against deflection under the described loading and thereby prevents unwanted stresses from being transmitted to the vessel plate.

In Figure 13b, the top rail 365 is provided with a section of rail 367 attached at one end by a pivot 368 thereby allowing the section to be pivoted into and out from the remainder of the top rail to ease access to the top of the tank. A fastener 369 is provided at the free end of the rail section 367 to allow the section to be secured in place in the brace structure during transport of the vessel or when other wise required. It will be appreciated that this embodiment provides a gate arrangement in a continuous brace extending across the tank.

Figure 13c shows a further embodiment of the tank in which the brace structure 375 is provided by a number of inline inserts 376 between the side support bars 377 and corner posts 378 of the frame. It will be appreciated that although the brace structure comprises a number of separate parts (inserts, side support bars and corner posts) , the parts are arranged so that there is a continuous mechanical structure providing a bracing effect against adverse loads applied to the frame. This brace structure provides the advantages of providing easy access to the top of the tank while still providing the reinforcement required for safety requirements .

The tank is particularly suited for storing and transporting hazardous fluids and in particular liquid chemicals and fuels used in the petro-chemical industry. The chamber of vessel can be filled through the manhole. An operative can climb the ladder, walk on the decking and lift the cover and release the manhole lid. The liquid to be stored and transported can then be introduced into the chamber of the vessel via the manhole aperture. The manhole lid can then be closed and sealed and the cover replaced. The tank can then be used either for storage or to subsequently transport the hazardous chemicals to a different site.

The tank is particularly suited for use with offshore oil storage and production platforms. Barges are typically used to transport tanks to the offshore platforms. A fork lifting device can be used to move the tank around and can take advantage of the hollow base frame brace members as a natural lifting point. The lifting lugs can also be used to hoist the storage tanks onto a barge for transportation to an offshore platform at which the tanks can then be hoisted by the lifted lugs onto the platform. The empty tanks can then be returned from the platform back to the mainland for cleaning and further re-use.

The sloped shape of the base of the vessel and the location of the drain at the low point of the base aids draining and cleaning of the vessel. Access to the interior of the vessel is provided by the manhole. Various ancillary features such as a safety valve and dipstick are also provided.

It will be appreciated that as the tank has a substantially square configuration, tanks according to the present invention can be closely packed without wasting space between the tanks as is the case with none rectangular tanks . Although the tank is described as substantially square, it would be appreciated that rectangular cross section tanks can also be provided. The stability of the tank is improved if its height is not substantially greater than its width, such that the tank is overall substantially cubic. However, it will be appreciated that tanks taller than their width are also envisaged as falling within the ambit of the invention.

As the tank is particularly for use in connection with hazardous fluids, it will be appreciated that there are strict safety regulations that need to be complied with. A tank according to the present invention can meet such safety regulations owing to a number of the design features incorporated in the tank. The overall tank design takes into account the various competing factors in assuring the structural robustness of the tank and also providing a tank which is practically handleable, provides commercially realistic volumes and can pass both static and dynamic testing requirements.

Claims

CLAIMS :

1. A tank for storing hazardous fluids, comprising: a quadrilateral vessel for receiving hazardous fluids and having four walls, a top and a bottom; and a reinforcing frame including a reinforcing structure extending over opposed walls and at least one of the top and the bottom of the vessel.

2. A tank as claimed in claim 1, in which the reinforcing structure extends over opposed walls and the top and the bottom of the vessel.

3. A tank as claimed in claim 1, in which the reinforcing frame includes a cage around the walls of the vessel .

4. A tank as claimed in claim 3 , in which the cage includes a plurality of bars extending along a longitudinal axis of the vessel .

5. A tank as claimed in claim 4 , in which a two of the plurality of bars form a part of-the reinforcing structure.

6. A tank as claimed in claim 4, in which the cage includes a corner post at each wall vertex.

7. A tank as claimed in claim 6 , and including a brace member extending between a corner post and a next nearest bar.

8. A tank as claimed in claim 6, in which the plurality of bars of the cage are equidistantly spaced along each wall .

9. A tank as claimed in claim 8, and having five bars equidistantly spaced along each wall between the corner posts at the ends of the walls.

10. A tank as claimed in claim 1, in which the reinforcing structure has a rectangular hollow section.

11. A tank as claimed in claim 4, in which each of the plurality of bars has a square hollow section.

12. A tank as claimed in claim 1, in which the bottom includes a drain and the bottom is sloped toward the drain.

13. A tank as claimed in claim 12, in which the drain includes a sump and the sump forms a part of the reinforcing structure .

14. A tank as claimed in claim 1, and including a manhole in the top of the vessel .

15. A tank as claimed in claim 14, and including an annular reinforcing plate around the manhole.

16. A tank as claimed in claim 14, and including a manhole reinforcing structure around the manhole.

17. A tank as claimed in claim 16, and including a cover plate extending between the manhole and the manhole reinforcing structure and flush with the top of the manhole reinforcing structure to prevent the accumulation of fluid.

18. A tank as claimed in claim 14, and including a manhole subframe fastened around the manhole to the reinforcing frame .

19. A tank as claimed in claim 1 and made of steel.

20. A tank as claimed in claim 1, in which the walls have a thickness in the range approximately 6mm to 10mm.

21. A tank as claimed in claim 20, in which the walls have a thickness of approximately 8mm.

22. A tank as claimed in claim 1, and including a base frame .

23. A tank as claimed in claim 22, in which the base frame has two hollow members extending across the frame in parallel and each having open ends for receiving a part of a lifting device.

24. A tank as claimed in claim 1 and including a climbing means providing access for a person to the top of the vessel, in which a part of the reinforcing frame provides a part of the climbing means.

25. A tank as claimed in claim 1 and storing a hazardous fluid.

26. A tank as claimed in claim 6, in which there is a gap between the corner post and wall vertex at each vertical wall vertex of the tank, to accommodate deformation of a corner post thereby preventing direct transfer of stresses to the vertical wall vertex joint.

27. A tank as claimed in claim 1, in which the reinforcing frame includes a continuous brace structure adjacent the top of the vessel and extending between opposed sides of the vessel.

28. A method of storing a hazardous fluid, comprising the step of introducing the hazardous fluid into a tank as claimed in claim 1.

29. A method of transporting a hazardous fluid, comprising the steps of introducing the hazardous fluid into a tank as claimed in claim 1 and conveying the tank with a transporting means from a first location to a second location.