Sheath for protecting against fire

Abstract

The invention relates to a protective sheath (50) for covering a fluid-transporting pipeline, comprising a flame-proof, non-inflammable layer (52) and a heat insulation layer (54) arranged beneath the non-inflammable layer, the non-inflammable layer consisting only of carbon and the heat insulation layer comprising a knitted fabric, the knitted fabric comprising a plurality of stitches and air trapped within the plurality of stitches such that the heat insulation layer comprises at least 70 vol. % of air. Furthermore, the non-inflammable layer comprises carbon fibers providing 100% coverage in order to protect the heat insulation layer from contact with flames.

Claims

1. A protection sheath, intended to cover a fluid transporting pipe, the sheath comprising a flame-proof non-flammable layer and a heat insulation layer arranged beneath the non-flammable layer, the non-flammable layer comprising only carbon and the heat insulation layer comprising a knitted fabric, the knitted fabric comprising a plurality of stitches and air trapped within the plurality of stitches, the heat insulation layer comprising at least 70 vol. % of air, and wherein the non-flammable layer comprises carbon fibers providing a 100% fiber coverage rate without spaces between the carbon fibers in order to protect the heat insulation layer from contact with flames.

2. The sheath according to claim 1, wherein the sheath comprises, over the non-flammable layer, a sealing anti-fire-starter layer intended for preventing, prior to a fire, combustibles from the outside environment from penetrating through the sheath.

3. The sheath according to claim 2, wherein the sealing anti-fire-starter layer comprises a fluoropolymer.

4. The sheath according to claim 3, wherein the sealing anti-fire-starter layer is made of polytetrafluoroethylene (PTFE).

5. The sheath according to claim 1, wherein the knitted fabric corresponds to a glass fiber knitted fabric.

6. The sheath according to claim 1, wherein the non-flammable layer corresponds to a carbon fiber braid.

7. The sheath according to claim 1, wherein the heat insulation layer is constituted of two superimposed knitted fabric layers.

8. A method of producing a pipe comprising an upper layer, the method comprising a step of depositing, on the upper layer of the pipe, a protection sheath according to claim 1.

9. The method according to claim 8, wherein the step of depositing the sheath on the upper layer comprises a step of knitting the heat insulation layer onto the upper layer of the pipe in order to obtain a heat insulation layer of an external diameter such that the heat insulation layer comprises 70% vol. of air, and a step of depositing the non-flammable layer comprising carbon and of an internal diameter substantially equal to the external diameter of the heat insulation layer.

10. The method according to claim 8, wherein the step of depositing the non-flammable carbon layer corresponds to braiding carbon fibers.

11. A composite pipe intended for transporting a fluid in an aircraft, comprising an internal tubular layer forming a chemical barrier within which a fluid is intended to flow, at least one reinforcing layer covering the internal tubular layer and being intended to resist pressure inside the pipe, at least one fire resistance layer covering said at least one reinforcing layer, wherein said at least one fire resistance layer includes carbon and is intended for protecting the pipe from fire, and a protection sheath according to claim 1, wherein said at least one fire resistance layer corresponds to the non-flammable layer.

12. The pipe according to claim 11, wherein the internal tubular layer forming chemical barrier is made of polytetrafluoroethylene (PTFE).

13. An aircraft, in particular an airplane, comprising a pipe according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will become apparent from the following description of an embodiment, given by way of non limiting example, with reference to the accompanying drawings in which:

(2) FIG. 1 is a side view showing the successive layers of a sheath equipping a pipe, according to an embodiment of the invention,

(3) FIG. 2 is a side view showing different layers of a pipe, with the aim of illustrating comparative tests,

(4) FIG. 3 is a side view showing the successive layers of a pipe according to an embodiment of the invention.

DETAILED DESCRIPTION

(5) FIG. 1 shows a composite pipe 1 equipped with a protection sheath 50 according to an embodiment of the invention. This pipe 1 may more particularly correspond to a flexible composite pipe, intended for transporting fluid, such as lubricating or fuel fluid, in an aircraft, in particular for an aircraft engine.

(6) The sheath 50 comprises a non-flammable layer 52.

(7) The non-flammable layer 52 is flame-proof. The non-flammable layer 52 is composed of carbon only.

(8) The sheath 50 also comprises a heat insulation layer 54, arranged beneath the non-flammable layer 52.

(9) The heat insulation layer 54 corresponds to a knitted fabric.

(10) The knitted fabric comprises a plurality of stitches and air trapped in the plurality of stitches, in such a manner that the heat insulation layer 54 comprises at least by volume 70% of air.

(11) The volume of air in the knitted fabric is measured by calculating the section of the knitted fabric layer on the basis of the difference between the external diameter and the internal diameter, then by weighing the knitted fabric, then, knowing the mass density proper to the material in which the knitted fabric layer is made, by calculating the apparent density, thus allowing to deduce the volume of air.

(12) According to the invention, the non-flammable layer 52 comprises carbon fibers providing a 100% coverage rate for integrally protecting the heat insulation layer 54 from direct contact with the flames. Thus, the flames cannot cross the non-flammable layer 52.

(13) The air-carbon combination and coverage rate of 100%-70% volume of air according to the invention allows producing a light dual-function dual-layer flame proof-heat insulation sheath providing a substantially improved protection against fire.

(14) Preferably, the heat insulation layer 54 corresponds to a glass fiber knitted fabric which offers the advantage of lightness and contributes to heat insulation. It may alternatively correspond to a basalt fiber knitted fabric, to a mica fiber knitted fabric, a metal fiber knitted fabric such as titanium, or even a ceramic fiber knitted fabric.

(15) The heat insulation layer 54 may be constituted of two superimposed knitted fabric layers.

(16) The non-flammable layer 52 may advantageously comprise a carbon fiber braid.

(17) As it can be seen on FIG. 1, the sheath 50 advantageously comprises, over the non-flammable layer 52, a sealing anti-fire-starter layer 56.

(18) The sealing anti-fire-starter layer 56 is intended to prevent, prior to a fire, combustibles from the outside environment from penetrating through the sheath 50.

(19) This sealing anti-fire-starter layer 56 is in fact sealing with respect to combustibles from the outside environment, such as greases or oils.

(20) It is worth noting that the sealing anti-fire-starter layer 56 may advantageously comprise a fluoropolymer. Preferably, the sealing anti-fire-starter layer 56 comprises of polytetrafluoroethylene (PTFE). It can also be composed of polyvinylidene fluoride (PVDF), or perfluoroalkoxy (PFA), or fluorinated ethylene propylene (FEP).

(21) The greater the thickness of the non-flammable layer 52 and the heat insulation layer 54, the longer the sheath 50 is resistant to a fire. However, according to a possibility, the thickness of the non-flammable layer 52 may be of the order of 1 mm and the thickness of the heat insulation layer 54 may be of the order of 1 mm, thus allowing to lighten the sheath 50 without causing prejudice to the barrier performance with regard to flames and heat insulation.

(22) By way of example, the numbering of the fiber forming the knitted fabric is in the range of 60 to 80 decitex, and the numbering of the carbon fiber forming the non-flammable layer is in the range of 1200 tex.

(23) The method of producing the pipe 1 is described hereinafter. It comprises a step of depositing the protection sheath 50 on an upper layer 4 of the pipe 1, this layer 4 able to correspond to a reinforcing layer for example of aramid material.

(24) The step of depositing the sheath 50 on the upper layer 4 comprises a step of knitting the heat insulation layer 54 onto the upper layer 4 of the pipe 1 in order to obtain a heat insulation layer 54 with an external diameter such that the heat insulation layer 54 comprises 70 vol. % of air, and a step of depositing the non-flammable layer 52 constituted only of carbon and having an internal diameter substantially equal to the external diameter of the heat insulation layer 54, so as not to compress the air contained in the knitted fabric.

(25) The step of depositing the non-flammable carbon layer 52 is advantageously carried out by crossing carbon fibers, in particular by braiding, coiling, filament winding, reaming, taping, knitting, flat weaving or circular weaving the carbon fibers.

(26) The flexible composite pipe 1 of FIG. 3 here comprises an internal tubular layer 2 forming chemical barrier, one or several reinforcing layers 4, for example in braids of aramid material, covering the internal tubular, layer 2, possibly one or several layers 6 made of refractory material covering the reinforcing layer or layers 4, at least one fire resistant layer 8 made of carbon, optionally covering the layer or layers 6 made of refractory material or the reinforcing layer or layers 4, and for example an external layer 10 forming sealing barrier covering the fire resistant layer or layers 8 made of carbon.

(27) The internal tubular layer 2 forming chemical barrier is intended for the flow of a fluid, such as a lubricating or fuel fluid. This internal tubular layer 2 may correspond to a fluorinated, single or dual layer, flexible convolute or smooth duct, or to any suitable duct having the chemical barriers and compatibilities required for the flow of a lubricating or fuel fluid. By way of example, the internal tubular layer 2 may be made of polytetrafluoroethylene (PTFE). It may comprise carbon serving for electrical conductivity, in order to resolve the issues of static electricity.

(28) The reinforcing layer or layers 4, by the number of two according to the example of FIG. 3, ensure the mechanical hold and structure of the pipe 1. These reinforcing layers 4, here in braids of aramid material, are suitable for resisting to pressure in the pipe 1. They may comprise for example of Kevlar. They can be produced by any yarn crossing technique, in particular by braiding, coiling, filament winding, reaming, taping, knitting, flat weaving or circular weaving of aramid fibers.

(29) Still according to the example of FIG. 3, the pipe 1 here comprises one single layer 6 made of refractory material, resistant to high temperatures, for protecting the pipe 1 from fire. The layer 6 for example is made of glass fiber. It may comprise basalt, mica or silicone. The layer 6 may also be composed of glass fiber and basalt, glass fiber and mica, or glass fiber and silicone.

(30) The layer 8 is intended to ensure the fire resistance of the pipe 1. This layer 8 is made of carbon. Thus, it allows keeping the structural entirety of the pipe in the event of fire. It may be produced by any yarn crossing technique, in particular by braiding, coiling, filament winding, reaming, taping, knitting, flat weaving or circular weaving the carbon fibers.

(31) It may comprise carbon fibers of all moduli, in particular of high modulus, standard modulus or intermediate modulus.

(32) The layer 10 forming sealing barrier is added to the surface of the underlying, carbon, fire stability layer (or layers) 8. This layer 10 is intended to seal the pipe 1. The layer 10 may be obtained by any polymerization method of liquid and hydrocarbon resistant material. The layer 10 may be obtained by extrusion, molding, coating, injecting, forming or sintering. By way of example, it can be constituted by PTFE, PVDF or PFA fluorines.

(33) The layer 10 forming sealing barrier may comprise fluorinated ethylene propylene (FEP).

(34) The aforementioned sheath 50 may form an integral part of the pipe 1. Optionally, the layer 6 may correspond to the heat insulation layer 54, the carbon layer 8 may correspond to the non-flammable layer 52, and the external layer 10 may correspond to the sealing anti-fire-starter layer 56. Optionally, the layer 6, the layer 8 and the layer 10 comprise all or part of the aforementioned features respectively of the heat insulation layer 54, the non-flammable layer 52 and the sealing anti-fire-starter layer 56.

(35) The pipe 1 is intended for use in the aeronautics field. In this respect, the invention also relates to an aircraft, such as an airplane, comprising the pipe 1.

(36) The pipe 1 fully meets the expectations, and goes beyond the requirements of the ISO 2685 aeronautics standard.

(37) Tests were conducted. These tests comprised applying the standard flame defined by the ISO 2685 standard to test the fire resistance.

(38) Thus, during the exposure to the standard flame according to the ISO 2685 standard, samples are exposed to the following constraints: circulation of a hydraulic fluid having a fluid temperature over 93 C., a fluid pressure of 10 bars and a fluid output of 4 L/min, and exposed to a vibration of 33 Hz with a 1.6 mm amplitude. The samples are exposed to the standard flame until the test specimen ruptures. The duration of tests has been set to 30 minutes maximum, corresponding to twice the maximum duration set by the ISO 2685 standard, for this demonstration.

(39) In reference to FIG. 2, the samples submitted for testing are flexible ducts 100 having the following configurations:

(40) TABLE-US-00001 Reference Composition Configuration 1 101 = PTFE 102 = Aramid 103 = Glass Configuration 2 101 = PTFE 102 = Aramid 104 = Carbon Configuration 3 101 = PTFE 102 = Aramid 103 = Glass 104 = Carbon

(41) Layers 101 and 102 are identical in dimensions and features in the three configuration cases. The layer 104 is lower in weight than layer 103. Layers 103 of configuration 1 and configuration 3 are the same in dimensions and features.

(42) The following results are obtained:

(43) TABLE-US-00002 Sample reference and comparative results Test conditions Requirements Configuration 1 Configuration 2 Configuration 3 Sample length >600 mm >600 mm >600 mm >600 mm Oil >93 C. >93 C. >93 C. >93 C. temperature inlet Flame >1020 C. >1020 C. >1020 C. >1020 C. temperature Density of heat >106 kW/m.sup.2 >106 kW/m.sup.2 >106 kW/m.sup.2 >106 kW/m.sup.2 flow rate of the burner Output 4 l/min 4 l/min 4 l/min 4 l/min Pressure 10 bars 10 bars 10 bars 10 bars Distance 75 mm 10% 75 mm 75 mm 75 mm between the surface of the burner and the surface of the sample Test duration 30 minutes Rupture at 8 min. Rupture at 19 min. 30 min. (test 25 s 6 s stopped without rupture)

(44) These tests show that, with an identical diameter, a pipe (configuration 1) comprising an internal PTFE layer 101, a layer 102 made of aramid material covered by a glass fiber braid layer 103 resists for 8 minutes to the fire, whereas when the glass fiber layer 103 is replaced by a lighter carbon layer 104, the pipe (configuration 2) resists at least for nineteen minutes to the fire. Furthermore, when in addition to a glass fiber layer 103, a carbon layer 104 (configuration 3) is added, the pipe resists for more than thirty minutes (test stopped after thirty minutes).

(45) It is to be understood that the obtained results in terms of resistance to fire using a carbon layer go beyond the anticipated results.

(46) These results are all the more interesting since the use of a carbon layer simultaneously allows attaining a reduction of the pipe mass between 30% to 50%, in particular with respect to conventional flexible pipes comprising stainless steel and silicone layers, for identical internal tube dimensions and identical use performance requirements.

(47) This gain in mass is significant in an airplane equipped with pipes 1 according to the invention, considering the important number of pipes that can equip such an airplane.

(48) The use of a fire resistant casing obtained by crossing carbon fibers, in particular by braiding, coiling, filament winding, reaming, taping, knitting, flat weaving or circular weaving the carbon fibers, allows protecting an object contained in the casing from the fire, in particular a duct, a cable, a mechanical longitudinal part, such as a revolution part.

(49) Of course, the invention is in no way limited to the aforementioned embodiment, this embodiment having been given by way of example. Modifications remain possible, in particular from the point of view of the constitution of the various components or by the substitution of technical equivalents without however departing from the scope of the invention.

(50) Thus, the pipe 1 may comprise a unique reinforcing layer 4.

(51) Furthermore, the pipe 1 could comprise more than one layer 6 of refractory material.