FR3100571A1 - Pipe for an aircraft turbomachine - Google Patents

Abstract

The invention relates to, on an aircraft turbomachine, a pipe (1) having a flexible part (7) comprising a tubular metal braid (9) and a fluoropolymer tubing (11) to be maintained via crimping fittings. The flexible part (7) comprises at least one electrically conductive wire (13) which is in contact with the tubing (11) and with the crimping fittings, and which is arranged so as to be able to be also in contact with the fuel to be circulated in the tubing (11). Figure to be published with the abstract: Figure 3.

Description

Pipeline for an aircraft turbine engine

Technical field of the invention

The invention comprises a pipe for use in a turbomachine for an aircraft, in particular an airplane.

State of the prior art

An aircraft conventionally comprises one or more propulsion systems each comprising a turbomachine, such as for example a turbojet or a turboprop.

In a turbomachine, pipes are used to interconnect two pieces of equipment. These pipes allow a fluid to circulate from one point to another.

There are two families of pipes: "flexible pipes" or "semi-rigid pipes" and "rigid pipes".

The so-called "rigid" pipes include a simple metal tube and flanges at the ends. So-called “flexible” or “semi-rigid” pipes include different elements and materials. They are typically used to make the interconnection between two pieces of equipment or two fixing points which may have significant relative displacements. A flexible pipe is typically connected to a portion of rigid tube via a crimping tail.

As a "flexible" or "semi-rigid" pipe for an aircraft turbomachine, where the pipe is to be fitted between a first and a second piece of equipment of the turbomachine so that (liquid) fuel intended for the turbomachine can flow therein, a pipe is known having an intermediate section having:

- a flexible part suitable for the fuel to circulate in it, and

- a first and second ends where the pipe respectively comprises first and second crimping ends, hollow, electrically conductive, at least one of which is to be connected to ground.

By flowing inside the pipe, the fuel creates an electrical (electrostatic) charge on or in the surface with which it is in contact. This charge is normally evacuated to the crimp fitting(s) of the hose line, allowing discharge to engine ground, typically via equipment. However, the fuel supply devices, known as "fuel systems" used to supply turbomachinery, implement increasingly high flow rates. Beyond a certain flow velocity, the rate of electrical charge accumulation becomes greater than the electrical discharge capacity, thus causing an increase in electrical (electrostatic) charge. An electric arc can then be created, with the potential perforation of the pipe, mainly in its flexible part. A fuel leak may then occur.

A widespread and benchmark fuel for civil aviation is Jet A-1. Its properties are defined by the international standard A.S.T.M. D1655.

The invention aims to remedy these drawbacks in a simple, reliable and inexpensive manner.

Presentation of the invention

To this end, the invention proposes a pipe for an aircraft turbomachine, the pipe therefore being to be fitted between a first and a second piece of equipment of the turbomachine so that fuel intended for the turbomachine can circulate therein, the pipe having an intermediate section having :
- a flexible part comprising, radially from the outside inwards:
-- a tubular metal braid,
-- a fluoropolymer tubing suitable for fuel to flow through, and
- a first and second ends where the pipe comprises respectively first and second crimping ends, hollow, electrically conductive, each comprising a crimping sleeve surrounding a crimping shank clamping together the flexible part, at least one of the first and second crimping end pieces to be connected to ground,
characterized in that the flexible part further comprises at least one electrically conductive wire in contact with the fluoropolymer tubing and with the first and second crimping end pieces, and arranged so as to be able to also be in contact with the fuel to flow in the said tubing in fluoropolymer.

The use of electrically conductive wire(s), typically metallic (such as stainless steel) will improve the conductivity of the pipe via the presence of a highly electrically conductive material, without disturbing significantly the flow of fuel, while benefiting from properties of flexibility and pressure resistance, due to the constitution of the pipe. This must limit the phenomena of electrostatic charge and therefore the risks of perforations by electrical breakdown.

Among the aims targeted by the invention, it will also be noted:
- be able to use the pipeline without any real pressure limit with regard to the pressure ranges in question, ranging from a few bars to several hundred and more particularly from 1 to 300 bars (1bar=10 ⁵ Pa),
- limit the dynamic response to vibration of the pipeline, without risk of rupture, including, if they exist, rigid parts (tubes) located upstream and downstream of the flexible part (see below).

To secure the maintenance of said at least one electrically conductive wire and the circulation of electrical energy, it is proposed that this (these) electrical wire(s) be (are) partially embedded in the tubing in fluoropolymer and held tight between the crimp sleeve and the crimp shank.

In order to facilitate the implementation of the solution and its mass production, it is also proposed that said at least one electrically conductive wire comprises:
- a wire wound in a helix, or
- several wires extending along the fluoropolymer tubing.

To avoid shape accidents on the flow surface and/or efficient positioning in the wall of the flexible part, it is proposed to use electric wire(s):
- of small diameter, less than about ten mm, and more particularly from 0.1 to 5 mm,
- can be placed in the direction of fluid flow (the wire wound in a helix will have an axial component),
- at weak squared moment, this one depending on the diameter of the wire ), from almost 0 to 62mm ⁴ ,
- and therefore partially embedded in fluoropolymer tubing.

The terms axial, radial and circumferential are defined with respect to the longitudinal axis (X) of the pipe, along which the tubes extend: metal braid and fluoropolymer tubing.

Electrically conductive means: having an electrical conductivity greater than 20 µA under a voltage of 1000V.

Furthermore, it is proposed that said fluoropolymer tubing comprises polytetrafluoroethylene (called PTFE), with the advantages of excellent properties: fuel glide in the pipe, dielectric, chemical resistance to fuel, thermal resistance.

Such a solution makes it possible to integrate the electrical wire(s) directly during the PTFE extrusion process, which is a well-mastered technique.

It is also proposed that the fluoropolymer tubing have radially from the inside out:
- an inner part charged with carbon, in contact with the first or the second crimping end pieces and surrounded by
- an outer part not or less loaded with carbon.

Such "carbonaceous fluoropolymer" or even "carbonaceous PTFE" is not a very good electrical conductor, which can always lead to electrostatic discharges piercing the pipe. On the other hand, associating such a double part with one or more electrical wire(s) arranged on the internal face of the fluoropolymer tubing and embedded with it must ensure the desired advantages and in particular a high electrical conductivity, greater than 1000 µA under a voltage of 1000V.

As already indicated, provision is also made for the pipe to further comprise first and second rigid tubes to which the first and second crimping end pieces will then be connected by welds respectively and via which the pipe may be mounted between the first and second equipment of the turbomachine.

Also concerned is a turbine engine for an aircraft comprising a pipe having all or part of the above characteristics.

Brief description of figures

is a perspective view of a possible embodiment of the pipeline of the invention, with its fittings;

is a diagrammatic half-view in axial section of zone II of FIG. 1;

is a schematic internal view, in perspective, of zone III of FIG. 1, according to a first embodiment;

is a schematic internal view, in perspective, of zone III of FIG. 1, according to a second embodiment; And

is a partially internal schematic view of area V in Figure 1.

Detailed description of the invention

A pipe 1 for an aircraft turbomachine can be seen in particular in FIG. 1 and is intended to be mounted between a first and a second piece of equipment 3a, 3b of the turbomachine so that fuel F intended for the turbomachine can circulate therein.

Pipe 1 has a longitudinal axis X.

Along this axis and as the section of FIG. 2 illustrates in more detail, the pipe 1 has an intermediate section 5 extending between the upstream longitudinal ends (or first end 5a, through which the fluid F will enter) and downstream 5b (or second end, through which the fluid F will exit).

The intermediate section 5 also has a flexible part 7 comprising, radially from the outside inwards (see also figures 3,4):
- a tubular metal braid 9,
- a tubing 11 in fluoropolymer adapted so that the fuel F circulates inside, and
- at least one electrically conductive wire 13 in contact with the pipe 11 and arranged so as to also be able to be in contact with the fuel F to circulate in the pipe 11.

The pipe 11 seals the pipe 1 with respect to the fuel F.

To be a good electrical conductor, said at least one wire 13 may be metallic, in particular stainless steel and of diameter < Ø20mm.

Having to be in contact with the fuel F flowing in the central axial orifice 10a of the pipe 1, the internal surface 10b of the pipe 11 will preferably be smooth, therefore not convoluted.

At the first and second ends 5a, 5b (only the first end 5a is shown in FIG. 2), the pipe further comprises respectively first and second crimping ends 15a, 15b, hollow, electrically conductive.

Each first and second crimping end pieces, the central orifice of which communicates with the orifice 10a, comprises a crimping sleeve 15 surrounding a crimping tail 17, the two clamping together the flexible part 7.

Said (at least one) electrically conductive wire 13 is in contact with the first and second crimping ends 15a, 15b.

At least one of the first and second crimping ends 15a, 15b is connected to ground 19.

Figures 3.4 illustrate two embodiments of the flexible part 7, for example in zone III of figure 1.

These embodiments differ in the way in which said at least one electrically conductive wire 13 is made:
- in the first embodiment (figure 3), there are several wires 13 extending along the tubing 11, therefore with a mainly axial component, here parallel to the axis X,
- In the second embodiment (Figure 4), there is a single wire 13 wound helically around the X axis.

Any wire 13 is partially embedded in the fluoropolymer tubing 11, while being able to be in contact with the fuel F when it flows in line 1.

Any wire 13 is also preferably held mechanically by at least one of the crimping end pieces 15a, 15b up to which it extends so as to ensure that the electrostatic charge created by the fuel F on the internal surface 10b of the pipe 1 is evacuated by the wire(s) 13 as far as at least one of the crimping end pieces 15a, 15b, thus allowing the discharge to ground 19, a priori via the equipment(s) 3a and/or 3b.

For this, any wire 13 will be favorably clamped between the (each) crimping sleeve 15 and the (each) crimping shank 17, each of which may be metallic.

A layer (smooth or convoluted) of carbonaceous PTFE in contact with the fluid F could additionally ensure an even greater improvement in the electrical conductivity.

It is therefore proposed that the fluoropolymer tubing 11 present radially, from the inside out, as shown schematically in Figure 2:
- an inner part 11a loaded with carbon, in contact with the first or the second crimping end pieces and which can be surrounded by
- an outer part 11b not or less charged with carbon.

As a carbon-filled PTFE, a minimum 10% carbon charge can be chosen.

There are many references on the market.

Furthermore, in particular for (if necessary) fire resistance, an outer layer of silicone 21 may cover the metal braid 9.

In this case, it may be considered that the flexible part 7 comprises the aforementioned layers or elements (9, 11 and 21).

Regarding the crimping and as shown schematically in Figures 2.5, at the end(s), of the flexible part 7 with the crimping end pieces 15a, 15b, the different layers can (see Figure 2):
- longitudinally and axially towards the inside of the flexible part 7, for the tubing 11 with integrated wire(s) 13, be in abutment against a radial circumferential rib 171 of the (each) crimping shank 15,
- Radially, including for the tubing 11 with integrated wire(s) 13, be clamped between the crimping sleeve 15 and the crimping tail 17 which surrounds it.

The metal braid 9 can extend up to the crimp sleeve 15.

A radial rim 151 of the crimping sleeve 15 can for this purpose be blocked, by fitting, in the narrow circumferential slot 23 defined between a radial rim 173 of the crimping shank 17 and the radial circumferential rib 171.

The outer layer of silicone 21 may come level with the axial tubular part 153 of the crimping sleeve 15. It may be lined with a layer of varnish 24.

By means of a tubular connection, or flange, 175 projecting axially outwards (relative to the flexible part 7), the (each) crimping sleeve 15 can be fixed in a sealed manner (typically welded) to one of the first and second rigid tubes 25a, 25b, also metal a priori (see Figure 1).

These first and second crimping end pieces 25a, 25b are typically used to mount the pipe 1 between the first and second equipment items 3a, 3b of the turbomachine, and therefore to connect it to them.

The solution of the invention should make it possible to eliminate almost any electrical breakdown situation.

A gas turbine engine 30 for an aircraft will therefore advantageously comprise such a pipe.

Claims (8)

Pipe (1) for an aircraft turbine engine, the pipe being to be fitted between a first and a second piece of equipment of the turbine engine so that fuel intended for the turbine engine can flow therein, the pipe having an intermediate section having:
- a flexible part (7) comprising, radially from the outside inwards:
-- a tubular metal braid (9),
-- a tube (11) made of fluoropolymer suitable for the fuel (F) to circulate in it, and
- a first and second ends where the pipe comprises respectively first and second crimping endpieces (15a, 15b), hollow, electrically conductive, each comprising a crimping sleeve (15) surrounding a crimping shank (17) clamping between them the flexible part (7), at least one of the first and second crimping ends being connected to ground,
characterized in that the flexible part (7) further comprises at least one electrically conductive wire (13):
- in contact with the tubing (11) made of fluoropolymer and with the first and second crimping end pieces (15a, 15b), and
- Arranged to also be in contact with the fuel (F) to flow in said fluoropolymer tubing. Pipe (1) according to claim 1, wherein said at least one electrically conductive wire (13) is partially embedded in the fluoropolymer tubing (11) and held tight between the crimp sleeve (15) and the crimp shank (17 ). A conduit (1) according to claim 1 or 2, wherein said at least one electrically conductive wire (13) comprises helically wound wire. Line (1) according to claim 1 or 2, wherein said at least one electrically conductive wire (13) comprises several wires extending along the fluoropolymer tubing. A line (2) according to any preceding claim, wherein said fluoropolymer tubing (11) comprises polytetrafluoroethylene. Pipe (2) according to any one of the preceding claims, in which the said tubing (11) in fluoropolymer has radially from the inside outwards:
- an inner part (11a) filled with carbon, in contact with the first or the second crimping end pieces and surrounded by
- an outer part (11b) not or less charged with carbon. Pipe (2) according to any one of the preceding claims, which further comprises first and second rigid tubes (25a, 25b) to which the first and second crimping end pieces (15a, 15b) are connected by welds respectively and by the through which the pipe (1) can be mounted between the first and second equipment (3a, 3b) of the turbine engine. Turbomachine comprising a pipe (1) according to any one of the preceding claims.