Floating roof for liquid storage tanks with inclined surface

Abstract

The present invention refers to a fire-resistant chamfered (sloped) floating roof (200) having a continuously inclined sloped surface (203) with an inclination of the slope in the range of 0.5 to 5° for tanks, used e.g. for the storage of flammable liquids, having a fire retardant coating (209).

Description

[0001] The present invention refers to a chamfered floating roof for external storage tanks, used e.g. for flammable liquids like crude oil, fuel, kerosene etc., having a fire retardant coating and a fireproof laminate layup with polypropylene honeycombs.

[0002] External large storage tanks used to store flammable liquids like gasoline, naphtha, kerosene, diesel, and crude oil with floating roof tops are already known in the prior art e.g. WO 91 / 15418 and WO 90 / 08076 and are commercially available, e.g. HMT ®< Deckmaster ™< .

[0003] Floating roofs are required for safety, either prevent evaporative losses of flammable gases and to prevent pollution. Floating roofs must be able to rise and fall depending on the liquid level inside the tank, to make sure that vapor space inside is limited and the roof top remains contact with the liquid. Another required property is that the roof shall not have too much weight, since low weight reduces immersion depth which leads to more filling capacity.

[0004] Typical floating roofs are made of metal or glass-fibre reinforced plastics (GRP). These floating roofs are swimming on the liquid which is stored in the tank, it can move up and down corresponding to the amount of liquid that is stored in the tank and they are sealed with a rim gap seal so that neither gas or liquid can escape through the contact region of the floating roof and the tank. The problems for metal floating roofs are increased internal stresses due to changes of temperature in case of solar radiation. This could lead to cracks and damages on the roof, which can result in a certain loss of the stored liquid

[0005] These cracks might lead also to a distribution of flammable liquids out of the tank onto the roof, and evaporative losses can ignite and may result in fire. When non-flammable or flammable liquids are spilled onto the plain metal or GRP roofs due to cracks or nature effects, if the liquids stay on the roof, the surface material will become brittle due to corrosion effects. This can lead to additional cracks and evaporative loss or a pass through of liquids.

[0006] To ensure that in case of droplets either of flammable liquids, or water, wet the surface of the external floating roof, different shapes and structures are already known and used. A currently commercially available composite external roof design is a low weight flat roof with a step-like inclined surface. The disadvantage of those steps is the accumulation of water or a flammable product on the deck, thus increasing the risk of potential ignition of the petrochemical or chemical liquids that might have accumulated. Furthermore, the accumulation of water in the steps leads to visible pollution of the deck. Another disadvantage of a step-like structure are the stress concentrations in the corners which may lead to cracks and therefore to water ingress into the system.

[0007] Further issues might arise if the flammable liquids are assembled in the roof drain and not transported away.

[0008] The object of the present invention was therefore the provision of a fire retardant floating roof for storage tanks, which are usually circular. More specifically, for tanks comprising flammable liquids which provide increased safety by inhibiting the event of fire. The present invention overcomes and avoids the disadvantages known by the prior art, by optimizing the external roof design.

[0009] The object of the present invention is therefore solved by a chamfered floating roof with a continuously inclined surface, having an inclination angle in the range of 0.5 to 5°. In an especially preferred embodiment, the angle is between 0,5 and 1.5°, preferably 1° + / - 0,5°. In a further specific preferred embodiment, the angle is 1° + / - 0,1°. This angle is from a safety point very advantageous as the non-flammable and flammable liquids are guided from the surface of the roof to a roof drain which is typically arranged in the centre of the roof.

[0010] By the provision of the continuously inclined surface of 0.5 to 5°of the roof, any flammable and non-flammable liquids are directly diverted to a centrally arranged roof drain, thus leading liquids away from the roof top and the rim gap area. Therefore, an event of a rim gap fire is very unlikely, as no rest of any flammable or non-flammable liquid remains on the roof itself. Preferably the roof according to the invention is of the GRP (glass fibre reinforced plastic) type. Of course, any other suitable materials, like metals, plastics, material composites (metal and plastics) can be used as well, either in from of layered structures or as a single body structure.

[0011] The continuously inclined surface structure ensures that there is no flash flooding e.g. due to heavy rain or high amounts of flammable liquid on the roof. Due to the chamfered roof, the liquid is quickly drained away while the end of the roof slows down the speed of the liquids.

[0012] In one embodiment of the invention, the chamfered roof has a layered structure, for example comprising a fire proof coating, a fire-retardant honeycomb core material and a fire protection laminate. Of course it is understood that several layers of the above-mentioned type may be present as well as other functional layers.

[0013] The advantage of the chamfered roof according to the present invention shows best results in relation of the speed of the liquids flowing down the roof into the roof centre. Therefore, the inclined surface leads efficiently any non-inflammable or flammable liquids spilled onto the roof continuously into drainage system e.g., at heavy rain.

[0014] The chamfered roof avoids any accumulation of the liquid, maximizing efficiency and increasing the fire safety and durability properties of the external floating roof, as no liquids remain on the surface or in the corners.

[0015] The advantages of the present invention are therefore an increase in safety of a storage tank using the roof according to the present invention as it prevents the risk of cracks of the surface material due to the continuously inclined surface and therefore prevents the risk of any fire caused by flammable liquids or the gaseous flammable substances.

[0016] According to another embodiment of the present invention, the chamfered, preferably GRP (glass fibre reinforced plastic) floating roof, comprises a fire proof coating, a fire-retardant honeycomb core material, a fire protection laminate and a roof drain system. The honeycomb structure of fire-retardant material may be replaced entirely or partially in another preferred embodiment by a foam structure.

[0017] The chamfered GRP floating roof is preferably entirely, in other embodiments only partially coated with a fire proof coating, the so-called top-laminate layer. If the roof is only partially coated, the coating is preferably applied to the edge area (i.e. the outer rim) and in the center of the roof. The fireproof coating is for example made of a special resin available for example from BÜFA under the trademark Firestop ®< .

[0018] Furthermore, in another embodiment of the present invention, the lay-up comprises several layers of glass fibres laminated with a fireproof resin, available for example from BÜFA under the trademark Firestop ®< . The fireproof polypropylene material for the honeycomb or foam structure is for example nidaplast 8FR ®< . These fireproof resins, can withstand a direct fire exposure of a minimum of 45 minutes.

[0019] The chamfered floating roof according to the invention contains further a fire-retardant core material, having a honeycomb structure which is typically made of polypropylene, preferably halogen free polypropylene, like for example nidaplast 8FR ®< from Nidaplast France. The complete layup of the sandwich structure could contain several layers of polypropylene honeycombs (or foams), preferably halogen free polypropylene as well.

[0020] The core material of the slope may also consist of or comprise fire-retardant materials, e.g. a halogen-free, flame retardant polypropylene compound. The laminated and fire-retardant top laminate layers of the slopes are made of a firestop resin with higher fire-retardant properties than the core material. The core material is for example cut by CNC to achieve this gradient. The key benefits of this new GRP roof design are an increased fire safety, durability and no more water or liquid accumulation on the external GRP floating roof surface, which extends the lifecycle of the roof according to the present invention.

[0021] The chamfered floating roof according to the present invention, comprises a drain system or in another words a roof drain, for example in the roof centre but it can be arranged at any other suitable position. The roof centre with the drain system according to the present invention has preferably a circular or rectangular shape. But according to the inventive idea underlying the present invention, any shape might be applied, unless it provides collection of liquids flowing down the roof into the drain system.

[0022] Typically, the drain system may be equipped with a pipe system beneath the surface so that liquids can be led off the drain system in the roof centre. This arrangement provides that no liquids are kept on the roofs surface which increases safety from flammation of flammable liquids and prevents that the roof is damaged due to collection of non-flammable liquids.

[0023] The invention is further described in the figures which are not meant to limit the scope of the present invention and are provided to better illustrate further details of the present invention. Figure 1 shows a cross-section through one half of a tank with a fireproof external floating roof according to the state of the art Figure 2 shows a cross-section through one half of a tank with a fireproof external floating roof according to the present invention Figure 3 shows a cross-section through an entire tank with a floating chamfered roof according to the present invention Figure 1 shows a cross-sectional view of one half of a floating roof 100 according to the prior art. The roof 100 is mainly made of a composite material of a base layer 107 and a second layer in the form of steps 103. They are made from materials described below in more detail.

[0024] The roof 100 is floating on a flammable liquid 104, for example crude oil, refined oil products like fuel or diesel and covers the entire surface of the tank which is shown only in form of a cross-sectional view through the tank shell 106. The roof 100 is connected to the tank shell 106 by two sealings, a primary sealing 101 and a secondary sealing 102 which are typically made of stainless steel several types of membranes, e.g. PVC or PTFE. The secondary sealing 102 increases the security of the overall roof 100 by protecting first sealing 101 against rainwater, pollutions like dirt, snow, rust etc.

[0025] The surface 103 of the roof 100 is formed as a step-inclined surface 103 with steps 103a, 103b, 103c, 103d and 103e. It is understood that in other embodiments more or less steps have been also realized. The material of the surface 103 is typically made of glass-fibre reinforced plastic as for example disclosed in EP 3931241 A1. The last step 103e of the surface is made from a different material and is formed as the base layer 107 of the composite structure of the roof 100. The base layer 107 is made of polypropylene, for example obtainable from Nidaplast France as nidaplast 8 ®< and has a honeycomb structure.

[0026] Water or any other liquid is finally collected via the (centrally) arranged roof drain 105, made for example from GFK laminate with for example 2 drainage lines which are not shown in figure 1. Water from rain or snow and the like can be collected on top of the floating roof and if the water accumulates to a certain level, it may cause the roof to sink or cause structural damage to the roof. Usually, such floating roofs provide a drain connection with a closable valve, whereby the valve may be manually opened to drain excess water from the surface of the roof and thereby prevent sinking or damage to the roof.

[0027] The disadvantage of the step-like surface 103 of the roof 100 is the accumulation of water or a flammable product on the deck, therefore increasing the risk of potential ignition of the petrochemical liquids which might have been accumulated. Furthermore, the accumulation of water in the steps leads to visible pollution of the deck.

[0028] Another disadvantage of a step-like structure of the surface 103 are the stress concentrations in the corners which may lead to cracks and therefore to water ingress into the tank system.

[0029] Figure 2 shows a cross-sectional view of one half of a floating roof 200 according to the invention. The exact geometric dimensions may vary according to specific needs and requirements. The width of the one half of the roof from the tank shell 206 to the centre of the roof drain 210 is adjustable.

[0030] As in the prior art, the roof 200 is floating on a flammable liquid 204, for example crude oil, refined oil products like fuel or diesel and covers the entire surface of the tank which is shown only in form of a cross-sectional view through the tank shell 206. The roof 200 is connected to the tank shell 206 by two sealings, a primary sealing 201 and a secondary sealing 202 which are typically made of stainless steel and different types of membranes, e.g. made of PVC or PTFE. The second sealing 202 increases the security of the overall roof 200 by protecting the primary sealing 201 against rain water and pollutions like dirt, snow, rust etc.

[0031] Water or any other liquid is finally collected via the centrally arranged roof drain 205 with for example 2 drainage lines which are not shown in figure 2. Furthermore, the drain system may be equipped with a pipe system beneath the surface so that liquids can be led off the drain system in the roof centre. This arrangement provides that no liquids are kept on the roofs surface which increases safety from flammation of flammable liquids and prevents that the roof is damaged due to collection of non-flammable liquids. The roof centre with the drain system according to the present invention has preferably a circular or rectangular shape. But according to the inventive idea underlying the present invention, any shape might be used, unless it provides a fast collection of liquids flowing down the roof 200 into the roof drain 205 and the drain system.

[0032] The surface of the roof 200 is entirely laminated with a firestop resin coated with a fire proof coating 209 available for example from BÜFA under the trademark Firestop ®< . The fireproof polypropylene like nidaplast 8FR ®< is used for layer 203. Furthermore in one embodiment of the present invention the coating 209 comprises several layers of glass fibres and the firestop, available for example from BÜFA under the trademark Firestop ®< . These coated laminate can withstand a direct fire exposure of a minimum of 45 minutes.

[0033] The roof 200 has a core material 207 in the form of a honeycomb structure, alternatively with a foam structure, which is typically made of polypropylene, like for example nidaplast 8 ®< from Nidaplast France. This core material 207 is completely sheathed to its surface by a second honey-comb structure 208 and 203 made of flame retardant polypropylene, preferably halogen free polypropylene as well, but has better fire retardant properties, like for example nidaplast 8FR ®< obtainable from Nidaplast France-

[0034] The surface 203 of the roof 200 according to the present invention has a continuously inclined surface with an angle of 0.5 -5° of the slope. In an especially preferred embodiment, the angle is between 0,5 and 1.5°, preferably 1° + / - 0,5°. In the specific embodiment of figure 2, the angle is 1° + / - 0,1°. This angle is from a safety point very advantageous as the non-flammable and flammable liquids are directed from the surface 203 of the roof 200 to the roof drain 210 even faster.

[0035] The slope material may consist of fire-retardant materials, e.g. of a halogen-free flame retardant honeycombs, and flame retardant firestop resin as already described in more detail above.

[0036] Through the continuously inclined surface 203 of the roof 200, any flammable and non-flammable liquid(s) will be directly diverted to the centrally arranged roof drain 210, thus leading liquids away from the rim gap area. Therefore, an event of a rim gap fire is very unlikely. Furthermore, a full-surface roof fire will be impossible with this design of the roof 200 according to the invention as the liquid cannot remain on the chamfered surface and is flowing immediately to the centre.

[0037] The key benefits of the roof according to the invention are an increased fire safety, durability and no more water or liquid accumulation on the external roof surface, which extends the lifecycle of the roof according to the present invention.

[0038] Figure 3 shows a cross-section through an entire tank 300 with a floating roof 301 according to the invention.

[0039] As already explained in figure 2, the roof 301 is floating on a flammable liquid 304, for example crude oil, refined oil products like fuel or diesel and covers the entire surface of the tank which is shown in form of a cross-sectional view through the tank shell 306. The roof 300 is connected to the tank shell 306 by two sealings, a primary sealing 303 and a secondary sealing 304 which are typically made of stainless-steel and different types of membranes, e.g. made of PVC or PTFE.. The secondary sealing 304 increases the security of the overall roof 300 by protecting the primary sealing 303 against rain water and pollutions like dirt, snow, rust etc., Water or any other liquid is finally collected via the centrally arranged roof drain 305 with drainage lines 311. Furthermore, the drain system is equipped with a pipe system 312 beneath the surface so that liquids can be led off the drain system from the roof drain 305 in the roof centre. This arrangement provides as already described before that no liquids are kept on the roofs surface which increases safety from flammation of flammable liquids and prevents that the roof is damaged due to collection of non-flammable liquids. The roof centre with the drain system including the roof drain 305 according to the present invention has preferably a circular shape. But according to the inventive idea underlying the present invention, any shape might be used, unless it provides a fast collection of liquids flowing down the roof 301 into the roof drain 305 and the drain system.

[0040] The surface of the roof 300 is entirely laminated with a firestop resin coated with a fire proof coating 309 available for example from BÜFA under the trademark Firestop ®< . The fireproof honeycomb structure is made of polypropylene like for example nidaplast 8FR ®< which is used for layer 303. Furthermore, in one embodiment of the present invention the coating 309 comprises several layers of glass-fibres and the firestop resin. These coated laminate can withstand a direct fire exposure of a minimum of 45 minutes.

[0041] The roof 300 has a core material 307 in the form of a honeycomb structure which is typically made of polypropylene like for example nidaplast 8 ®< from Nidaplast France. This core material 307 is completely sheathed or coated by a second honey-comb structure 308 made of flame retardant polypropylene, preferably halogen free polypropylene as well, but has better fire-retardant properties, like for example nidaplast 8FR ®< obtainable from Nidaplast France.

[0042] The surface 312 of the roof 300 according to the present invention has a continuously inclined surface with an angle of 0.5 -5° of the slope. In an especially preferred embodiment, the angle is between 0,5 and 1.5°, preferably 1° + / - 0,5°. In the specific embodiment of figure 3, the angle is 1° + / - 0,1°. This angle is from a safety point very advantageous as the non-flammable and flammable liquids are directed from the surface 303 of the roof 300 to the roof drain 305 even faster.

[0043] The slope material may consist of fire-retardant materials, e.g. of a halogen-free, flame retardant polypropylene compound as described above.

[0044] Through the continuously inclined surface 312 of the roof 300, any flammable and non-flammable liquid(s) will be directly diverted to the centrally arranged roof drain 305 thus leading liquids away from the rim gap area. Therefore, an event of a rim gap fire is very unlikely. Furthermore, a full-surface roof fire will be impossible with this design of the roof 300 according to the invention as the liquid cannot remain on the chamfered surface and is flowing immediately to the centre.

Claims

1. Chamfered floating roof (200) with a continuously inclined surface (203), having an inclination angle of the slope in the range of 0.5 to 5°.

2. Chamfered floating roof (200) according to claim 1, wherein the continuously inclined surface (203) is directed towards the centre of the roof or towards the drainage system.

3. Chamfered floating roof (200) according to claim 1 or 2 wherein the chamfered floating roof (200) comprises a fire proof coating with fire proof laminate (209), a fire-retardant core material (208), a core material (207) and a roof centre with a roof drain (210).

4. Chamfered floating roof (200) according to one of the preceding claims, wherein the continuously inclined surface (203) has an inclination angle of the slope of 1° ± 0,5°.

5. Chamfered floating roof (200) according to one of the preceding claims, wherein the roof surface (203) has fire-retardant coating (209).

6. Chamfered floating roof (200), according to one of the preceding claims, wherein the fire-retardant core material (208) has a honeycomb structure.

7. Chamfered floating roof (200) according to one of the preceding claims, wherein the core material (208) is covered by a flame retardant fire proof coating (209).

8. Chamfered floating roof (200) according to one of the preceding claims, wherein the fire-retardant properties of the fire-proof coating (209) are higher than the fire-retardant properties of the fire-retardant core material (208).

9. Chamfered floating roof (200) according to one of the preceding claims, wherein the material of the fire-proof coating (209) comprises a halogen-free, resin system10. Chamfered floating roof (200) according to one of the preceding claims, wherein the fire-proof coating (209) of the roof (200) withstands a direct fire exposure during a minimum period of 45 minutes.

11. Chamfered floating roof (200) according to one of the preceding claims, wherein the fire-retardant coating (209) is formed from a fibre-reinforced material comprising an organic resin, such as a vinyl ester resin, a polyester resin or an epoxy resin.

12. Storage Tank comprising a chamfered floating roof (200) according to any one of the preceding claims.

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