Gas-tight coating

Abstract

A method for waterproofing a liquefied gas tank (1), the tank (1) having a wall (2), the method comprising installing a multilayer coating (A, B) on an external surface of the wall (2), the installation of the multilayer coating comprising the deposition of an inner layer (A) having an open-cell network and the deposition on the inner layer (A) of an airtight outer layer (B). Abstract figure: Figure 6

Description

Title of the invention: Gas-tight coating technical field

[0001] This disclosure relates to the field of fluid product storage tanks, and more specifically to liquefied natural gas (LNG) storage tanks. This disclosure addresses the issue of waterproofing such tanks. Prior art

[0002] It is known to employ above-ground or semi-buried structures made of reinforced or prestressed concrete for the storage of liquefied natural gas (LNG), such as methane, ethane, butane or propane.

[0003] The walls of certain structures may have defects (cracks, porosity, local or penetrating defects) that can lead to gas leaks through the tank wall. The gas is maintained in a liquid phase at very low temperatures (typically -160°C) within the tank and coexists with its gaseous phase in the upper part of the tank. The equilibrium overpressure of the gaseous phase can induce leaks through the tank wall or the tank roof. In order to limit gas losses and protect the environment, the tank wall must be sealed.

[0004] Among the known solutions, one involves depositing a sealing layer in the form of a resin on the external surface of the tank wall. This sealing layer is often ineffective because the overpressure of the leaking gas through the wall can cause bubbling (or blistering) during or after the resin application, which can weaken or perforate the sealing layer. Furthermore, such a resin applied to the tank wall is prone to perforation and poor adhesion. Therefore, for this technique to be reliable, it requires a shutdown of operations (emptying the tank) to carry out the tank sealing. Shutting down such a tank, which often contains several hundred thousand liters of LNG, entails significant costs and logistical constraints.There is therefore a need for a more reliable and cost-effective tank waterproofing process and device, which can consequently effectively protect the environment. Summary.

[0005] This disclosure improves the situation.

[0006] A method for waterproofing a liquefied gas tank is proposed, the tank having a wall, the method comprising the installation of a multilayer coating on an external surface of the wall, the installation of the coating multilayer comprising the deposition of an inner layer having an open cell network and the deposition on the inner layer of an airtight outer layer.

[0007] Applying a sealing coating composed of two distinct layers allows this coating to be applied even while the tank is in operation, that is, while overpressure is causing gas to escape through the wall. The outer impermeable coating does not present any adhesion or bubbling problems since it is applied to the inner layer placed on the wall and not to the wall itself. Furthermore, the open-cell network allows for the possibility of channeling the gases to a gas recovery device.

[0008] In this application, the terms "inner" and "outer" are used in relation to the tank wall, with the "inner" side facing the outer surface of the tank wall and the "outer" side being exposed to the environment. In other words, the inner layer is closer to the tank wall than the outer layer.

[0009] The concept of airtightness is understood in a broad sense, that is to say, impermeability to all types of gas and in particular natural gases of the type CxHy with x between 1 and 8 and y between 4 and 18.

[0010] According to another aspect, the inner layer comprises a three-dimensional matrix and a resin, the process comprising impregnating the three-dimensional matrix with the liquid resin and then solidifying the resin. The matrix can be flexible before the resin that impregnates it hardens. The matrix can thus partially absorb the mechanical energy of the pressurized gas.

[0011] According to another aspect, the outer layer is applied to the inner layer after the resin has solidified. This prevents the outer layer from being damaged by deformation of the inner layer: after solidification, the inner layer is mechanically and chemically stable.

[0012] According to another aspect, during the installation of the multilayer coating, the tank is in operation and at least partially filled with liquefied gas. Indeed, one of the advantages of the proposed coating is that it allows the coating to be applied without having to empty the tank, since the coating can be reliably applied even if there are gas leaks through the wall. It goes without saying that it is not mandatory for the tank to contain gas for the multilayer coating to be reliably applied.

[0013] According to another aspect, the waterproofing process comprises manufacturing the multilayer coating and then installing the multilayer coating on the external surface of the liquefied gas tank wall. Indeed, in this embodiment, the multilayer coating can be prefabricated and then installed on the tank wall. This technique can be advantageous in certain situations, particularly when the on-site access time is too short compared to the setting and drying times of the inner layer.

[0014] According to another aspect, the inner layer is permeable to air. The overpressure of the gas escaping from the reservoir can be both dampened (and contained) by the flexibility of the three-dimensional matrix and the open cells, but also by the porosity or permeability of the material constituting the matrix and the residual permeability of the resin once polymerized. This permeability further reduces the risk of bubbles appearing on the inner layer or adhesion defects in the inner layer.

[0015] According to another aspect, the waterproofing process includes the installation of means for recovering gases present in the inner layer. Indeed, the gases trapped in the network of open cells of the inner layer can be directed, drawn in, channeled and / or pressurized to flow towards gas recovery means. They can then be stored, treated and / or reinjected into the tank in liquid or gaseous form.

[0016] The invention also relates to a multilayer coating for waterproofing a liquefied gas tank, the multilayer coating comprising: an inner layer comprising an open cell network; and an airtight outer layer, affixed to the inner layer.

[0017] According to another aspect, the inner layer comprises a three-dimensional matrix and a resin.

[0018] According to another aspect, the three-dimensional matrix is ​​composed of at least one of the following elements: glass fibers, carbon fibers, aramid fibers, basalt fibers, polyethylene fibers, and / or natural fibers.

[0019] According to another aspect, the three-dimensional matrix comprises two substantially parallel layers and junction elements connecting the two layers to each other, the junction elements and the layers delimiting the open cells. In a variant, more than two parallel layers may be provided.

[0020] According to another aspect, the resin is an epoxy resin or a polyester resin.

[0021] According to another aspect, the outer layer comprises a two-dimensional tissue and a epoxy resin.

[0022] The invention also relates to a liquefied gas tank made waterproof by the process according to one of the embodiments described above.

[0023] According to another aspect, the tank contains a liquefied gas and has an external surface on which is applied a coating comprising an internal layer comprising an open cell network and an airtight external layer, the coating preferably conforming to one of the embodiments described above.

[0024] According to another aspect, the reservoir includes means for recovering gases present in the inner layer. Brief description of the drawings

[0025] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the accompanying drawings, on which:

[0026] [Fig-1] shows an existing solution for sealing a tank.

[0027] [Fig.2] shows a first step in the installation of a waterproofing coating according to this disclosure.

[0028] [Fig.3] shows a second stage of the installation of a coating waterproofing according to this disclosure.

[0029] [Fig.4] shows a third stage in the installation of a coating waterproofing according to this disclosure.

[0030] [Fig.5] shows a fourth step in the installation of a coating waterproofing according to this disclosure.

[0031] [Fig.6] shows a fifth step in the installation of a coating waterproofing according to this disclosure.

[0032] [Fig.7] shows a sixth step in the installation of a waterproofing coating according to this disclosure. Description of the implementation methods

[0033] Figure 1 shows a partial cross-sectional view of a tank 1. The tank comprises a wall 2 which has an internal surface 3 that delimits an enclosure 4. The enclosure 4 receives a liquefied gas to be stored. An external surface 5 of the wall 2 faces the environment.

[0034] The wall 2 can be made of reinforced concrete. An additional metallic wall (not shown), for example made of nickel-based steel, can also be used to cover the internal surface 3. The wall 2 is shown as being horizontal, but the invention relates to any type of wall, i.e., both horizontal tank walls and those that are vertical, oblique, curved, etc.

[0035] The tank 1 can have a capacity of several hundred or several thousand cubic meters, for example 120,000 m3. The gas can be kept liquid in the enclosure 4 by a negative temperature for example -160°C and under an overpressure of 200 to 400 mbar.

[0036] The wall 2 may have defects 8 (for example, cracks or porosity) and the overpressure, illustrated by the arrows 10, tends to create a leakage gas flow. In some cases, the leakage can reach 4 liters per minute per square meter of wall, which represents a loss of operation and adverse environmental consequences.

[0037] It is therefore necessary to attempt to seal the wall 2. In the known example illustrated in [Fig. 1], a coating 12 attempting to waterproof the wall 2 was applied to the external surface 5. However, the gas flow 10 tends to cause bubbling and deterioration of the coating 12. This means that depositing a liquid coating 12 on an operating tank 1 generates structural defects and adhesion defects of the coating 12. Sealing is therefore not guaranteed. Applying a coating 12 to the external surface 5 is therefore not suitable for waterproofing an operating tank.

[0038] Among the known unsuccessful trials of coatings 12 are an epoxy resin with or without glass fiber fabric, a sprayed methacrylate reinforced with glass fibers, or a thick polyurea resin membrane, applied by roller or sprayed.

[0039] Figures 2 to 7 illustrate successive states of a process for waterproofing the tank 1 according to the present disclosure.

[0040] In a first step illustrated in [Fig.2], a resin 14 is applied to the external surface of the wall 2. Unlike the resin 12 of [Fig.1], the resin 14 is not intended to seal the wall 2. It can be applied only to certain areas of the wall 2, or in smaller proportions than the resin 12.

[0041] A bonding primer (not shown) can be applied to the substrate before depositing the resin 14.

[0042] The resin 14 can be chosen from epoxy resins or polyester-based resins.

[0043] While the resin 14 is still in a liquid (viscous) state, a three-dimensional matrix 16, illustrated in [Fig. 3], is applied to the external surface of the wall 2. The three-dimensional matrix 16 is dry and flexible upon application. The three-dimensional matrix 16 may comprise at least two substantially parallel layers 18, 20, and joining elements 22 connecting the layers 18, 20. The matrix 16 may be made of glass fiber fabrics. Alternatively or in addition, the matrix 16 may comprise carbon, aramid, basalt, polyethylene, and / or natural fibers. The basis weight of the matrix 16 may be between 100 and 1000 g / m², preferably between 250 and 900 g / m².

[0044] As illustrated in [Fig.4], the three-dimensional matrix 16 can, by spring effect, or under the pressure of leakage gas (arrow 10) expand in volume.

[0045] The matrix 16 comprises open cells 24 forming a network. The matrix 16 may be porous and / or permeable to air and / or may comprise openings between two adjacent cells 24.

[0046] Thus, unlike the solution presented in [Fig. 1], the gas pressure has no effect on the quality of the resin 14 or the matrix 16, since these are permeable to gas.

[0047] Figure 4 also shows the impregnation of the matrix 16 by the resin 14, particularly by capillary action or by smearing. In a first variant, the volume of resin 14 applied to the wall 2 is intended to be sufficient for the complete impregnation of the matrix 16. In a second variant, a first volume of resin 14 is deposited before the application of the matrix 16 (for example, a resin layer between 200 and 600 g / m²), and a second volume of resin 14 (for example, a more heavily loaded resin layer, between 400 and 800 g / m²) is applied to the matrix 16 placed against the wall 2. The objective of these steps is to ensure the saturation of the matrix 16 with resin 14.

[0048] Figure 5 shows the matrix completely soaked (saturated with resin), thus forming an inner layer A. This layer is permeable to gas, as indicated by the arrows. The inner layer A is allowed to dry (resin polymerization) for a sufficient period (for example, at least 24 hours). After drying, the inner layer A can have a thickness of between 2 and 10 mm.

[0049] Figure 6 illustrates that after the inner layer A has dried, an outer, waterproof layer B can be applied over the inner layer A. An optional sandblasting step can be carried out on the inner layer A before the application of the outer layer B, in order to deposit a layer of silica (for example between 300 and 500 g / m2) promoting the adhesion of the outer layer B to the inner layer A.

[0050] The outer layer B may consist of a two-dimensional matrix (for example, a fiber fabric) impregnated with resin 26, in particular epoxy resin. The application of the outer layer B may consist of applying the two-dimensional matrix already impregnated with resin. In one embodiment, the application of the outer layer B may consist of applying a layer of resin (for example, with a thickness between 300 and 900 microns, and a basis weight between 600 and 1400 g / m2) and then placing a two-dimensional matrix of glass fibers on the resin (for example, 200 to 800 g / m2, preferably 400 to 500 g / m2), and saturating the two-dimensional matrix with resin (for example, with a thinner layer than the previous one, between 300 and 700 microns, between 400 and 800 g / m2).

[0051] After the outer layer B has dried, one or more finishing layers can be applied to the outer layer B, for example a UV and / or weather-resistant layer, or an electrically conductive layer allowing monitoring of the coating's integrity.

[0052] Sealant joints 28 can be arranged at certain ends of the multilayer coating A, B as illustrated in [Fig.6].

[0053] The outer layer B is impermeable to gas, which allows the gases (see arrow 10) to be contained in the inner layer A.

[0054] The internal layer A and external layer B, together with the optional tack coat, sanding and finishing coats, form a multi-layer coating A, B.

[0055] As shown in [Fig. 7], one or more openings arranged in suitable locations allow the gases to be channeled to gas recovery means 30. These means may include one or more pumps, one or more filters, and circuits for recycling and / or reintroducing the gas into the tank, either in gaseous form or in liquid form after the gas has cooled. The gas recovery means 30 may have a recovery capacity of between 0.5 and 5 liters / min / m².

[0056] In one variant, the gas recovery means 30 can be installed before the permeable outer layer B is deposited.

[0057] Optionally, the fluidic connection between the recovery means 30 and the open cells 24 can be established even while the resin 14 is solidifying.

[0058] The waterproofing process may include additional steps for preparing the external surface 5 of the wall, for example cleaning or repairing surface defects.

[0059] In one embodiment, instead of successively depositing the different layers onto the external surface 5 of the wall, it is possible to prefabricate the multilayer coating A, B, for example in the form of rolls or sheets, and apply it to the external surface 5 of the wall. The roll or sheets can be cut to adapt the multilayer coating to the dimensions of the tank wall.

[0060] Whether the coating is formed on the wall 2 or prefabricated, the permeability of the inner layer A and the impermeability of the outer layer B allow the coating to be installed even when the tank is at least partially filled with liquefied gas, the gaseous phase of which may leak through the tank walls or the tank roof. This gaseous phase appears mainly in the upper part of the tank, due to thermal infiltration through the walls, despite their thermal insulation, the external surface 5 of the tank being at ambient temperature, while the internal surface 3 is at a negative temperature, for example close to -160°C when the tank contains a light natural gas.

[0061] The permeability of the inner layer A can be between 10 and 100,000 cm3 / day / m2.

[0062] The outer layer B is considered impermeable in comparison, its permeability being less than 5 cm3 / day / m2, advantageously less than 1 cm3 / day / m2.

[0063] These values ​​are understood according to ASTM D1434: a sample is prepared in the form of a 10cm x 0cm strip, conditioned at 23°C + / - 2°C and 50% humidity for 24 hours. The sample is placed between two chambers, a manometer and an air source ensuring a constant pressure difference of 1 atm between the two chambers, and a flow meter measuring the air flow rate that has passed through the sample over a given period, for example a few hours.

Claims

Demands

1. Method for waterproofing a liquefied gas tank (1), the tank (1) having a wall (2), the method comprising the installation of a multilayer coating (A, B) on an external surface (5) of the wall (2), the installation of the multilayer coating comprising the deposition of an inner layer (A) having an open cell network (24) and the deposition on the inner layer (A) of an airtight outer layer (B).

2. A method according to claim 1, wherein the inner layer (A) comprises a three-dimensional matrix (16) and a resin (14), the method comprising impregnating the three-dimensional matrix (16) with the liquid resin (14) and then solidifying the resin (14).

3. Method according to claim 2, wherein the outer layer (B) is applied to the inner layer (A) after the resin has solidified.

4. A method according to any one of claims 1 to 3, wherein during the installation of the multilayer coating (A, B), the tank (1) is in operation and at least partially filled with liquefied gas.

5. A method according to any one of claims 1 to 3, comprising manufacturing the multilayer coating (A, B), then installing the multilayer coating (A, B) on the external surface (5) of the wall (2) of the liquefied gas tank (1).

6. A method according to any one of claims 1 to 5, wherein the inner layer (A) is permeable to air.

7. A method according to any one of claims 1 to 6, further comprising the installation of means (30) for recovering gases present in the inner layer (A).

8. Multilayer coating (A, B) for waterproofing a liquefied gas tank, the coating (A, B) comprising: - an inner layer (A) comprising an open cell network (24); and - an airtight outer layer (B) affixed to the inner layer (A).

9. Multilayer coating (A, B) according to claim 8, wherein the inner layer (A) comprises a three-dimensional matrix (16) and a resin (14).

10. Multilayer coating (A, B) according to claim 9, wherein the three-dimensional matrix (16) is composed of at least one of the following: glass fibers, carbon fibers, aramid fibers, basalt fibers, polyethylene fibers, and / or natural fibers.

11. Multilayer coating (A, B) according to claim 9 or 10, wherein the three-dimensional matrix (16) comprises two substantially parallel sheets (18, 20) and junction elements (22) connecting the two sheets (18, 20) to each other, the junction elements (22) and the sheets (18, 20) delimiting the open cells (24).

12. Multilayer coating (A, B) according to any one of claims 9 to 11, wherein the resin (14) is an epoxy resin or a polyester resin.

13. Multilayer coating (A, B) according to any one of claims 8 to 12, wherein the outer layer (B) comprises a two-dimensional fabric and an epoxy resin.

14. Liquefied gas tank (1) made impermeable by the process according to any one of claims 1 to 7.

15. Tank (1) containing a liquefied gas and having an external surface (5) on which is applied a multilayer coating (A, B) comprising an inner layer (A) comprising an open cell network (24) and an airtight outer layer (B), the multilayer coating (A, B) preferably conforming to one of claims 8 to 13.

16. Reservoir (1) according to claim 14 or 15, comprising means (30) for recovering gases present in the inner layer (A).

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