WO2010097766A1

WO2010097766A1 - Joining device including a shield

Info

Publication number: WO2010097766A1
Application number: PCT/IB2010/050812
Authority: WO
Inventors: Christian His; Franceline Villermaux; Guillaume Belly
Original assignee: Saint-Gobain Centre De Recherches Et D'etudes Europeen
Priority date: 2009-02-24
Filing date: 2010-02-24
Publication date: 2010-09-02
Also published as: FR2942519B1; FR2942519A1

Abstract

The invention relates to a device including a first part (22) made from a ceramic material and banded by a first band (42), wherein at least one portion of the first band is protected by means of a shield (40) covering which, together with the first band, defines an annular chamber (62).

Description

Shield assembly device Technical area

The invention relates in particular to an apparatus selected from an oven, a boiler, a superheater, a steam generator, a chemical reactor and a heat exchanger, in particular for the production of ethylene. In particular, it relates to means for providing or improving an end-to-end connection between a ceramic tube (in particular silicon carbide) and a metal tube, with or without direct contact between the two tubes.

State of the art

The production of ethylene is typically a steam cracking, from ethane or naphtha. For this purpose, an ethylene production unit 5, as shown diagrammatically in FIG. 1, conventionally comprises an oven 10 comprising an enclosure 11 through which a bundle of tubes 12 passes and heated by means of a burner 13.

The tubes 12, of circular section, have an outer diameter of between 50 and 250 mm and a wall with a thickness of between 5 and 25 mm. These tubes, folded hairpin, have a length inside the enclosure of the oven several meters. They are made of alloy of iron, nickel and chromium. To produce ethylene, feed means 14 feed an upstream end of the tubes 12 with a reactive mixture M of hydrocarbons and steam, a temperature above 1000 ⁰ C being maintained in the chamber 11. The flow rate of this mixture is adapted so that the reaction mixture M can reach a temperature above 750 ⁰ C and react to lead to the production of ethylene. Ethylene production results in coke deposition on the inner surfaces of the tubes 12, lowering productivity.

In particular, it has been discovered that the nickel of the alloy constituting the tubes catalyzes the production of coke. The researchers therefore considered replacing metal tubes with nickel-free tubes, particularly ceramic tubes. Ceramic tubes must be connectable to the rest of the installation, and in particular to metal tubes used to bring the reactive mixture or to evacuate the products of the reaction. Research has therefore been conducted to find suitable connecting devices, in particular capable of withstanding thermal cycles, typically of an amplitude of more than 700 ⁰ C, which result from the furnace shutdowns.

In particular, ceramic tubes and metal tubes have very different expansion coefficients, typically about 4.10 ^-6 K- ¹ and about 18 -10 ^-6 K- ¹ , respectively. In the targeted applications, the connections tested lead to leakage or even disconnection of the tubes. For example, FR 2 645 941 discloses a connection device between a metal support and a ceramic tubular element in which a ring is fixed on the support and surrounds the ceramic tube with a functional clearance. The seal is obtained by a coke seal resulting from the operation of the production unit. This functional game however leads, at the start of the production unit, to oil leaks. In addition, the connection is not mechanically reliable, especially at room temperature. It is therefore not suitable for an environment such as that of an ethylene production furnace.

In addition, the decoking can not be carried out with water vapor, but must necessarily result from mechanical abrasion.

Finally, the connecting device described in FR 2 645 941 can only be applied in installations generating coke.

Summary of the invention

There is therefore a need for a new connecting device, particularly adapted to the connection of a ceramic tube with a metal tube in an environment such as that of an ethylene production furnace, but without being limited thereto.

An object of the invention is therefore to respond, at least partially, to this need. First aspect of the invention

According to a first aspect of the invention, this object is attained by means of a device comprising a first coin hooped by means of a first hoop, the first hoop being itself hooped by means of a second hoop having a coefficient of expansion less than the coefficient of expansion of the first hoop, at least between 20 ⁰ C and 1000 ⁰ C.

At room temperature, the frets provide a reliable mechanical connection and a good seal. During a rise in temperature, the second hoop expands less than the first hoop. It thus exerts on the latter a compressive force avoiding its separation from the first piece or a loss of tightness between the first piece and the first hoop.

As will be seen in more detail in the following description, when the first piece is a ceramic tube, it thus becomes possible, by fixing a metal tube on the first hoop, to obtain a particularly reliable mechanical connection between the ceramic tube. and the metal tube. This connection may advantageously be sufficiently tight, in particular for the intended applications, not only at room temperature but also over a range of several hundred degree temperatures, typically over 700 ⁰ C, of more than 800 ⁰ C, or even more than 900 ⁰ C.

A device according to the invention may also include one or more of the following optional features:

The first piece is made of a material having a coefficient of expansion less than

10.10 ^"6 K ^{" 1} , less than 8.10 ^"6 K ^{" 1} , less than 6.10 ^"6 K ^{" 1} , or even less than 5.10 ⁶ K ^"1 , between 20 ^° C. and 1000 ^° C.

The first piece is made of a material having a modulus of elasticity (MOE) greater than 150 GPa.

The first part is made of a ceramic material, carbide, nitride or oxide, capable of withstanding temperatures reaching 1400 ^° C., or even 1500 ^° C. - The first part comprises a ceramic or glass-ceramic material. This material may in particular be selected from silicon carbide, alumina, mullite, silicon nitride, zirconia, cordierite, aluminum titanate and mixtures thereof.

The mass quantity of silicon carbide in the material of the first part is greater than 80%, preferably greater than 90%. Preferably said material is made of silicon carbide. Silicon carbide has particularly useful properties in the intended application. In particular, it makes it possible to limit coke formation and has a high thermal conductivity allowing efficient transfer of heat from the furnace to the reactive mixture circulating in the tubes. The energy efficiency is thus higher than that obtained with a corresponding metal tube. Finally, silicon carbide, whose maximum temperature of use is greater than 2000 ⁰ C, retains its mechanical properties, even at very high temperatures. Advantageously, it therefore becomes possible to increase the temperature inside the oven and, simultaneously, to increase the flow rate of the reagent mixture circulating in the tubes. The productivity of the oven can thus be considerably increased. The material of the first part has a total porosity of less than 5%, preferably less than 2%, or even less than 1%. Advantageously, the permeability of the first part is reduced.

The first hoop has a metal. Preferably the first hoop is made of one or more metals. In one embodiment, it comprises a ferrous metal.

The first hoop is of a material having an expansion coefficient of less than 25.10 ⁶ K ^-1 , less than 20 10 ⁶ K ^-1 and / or greater than 10 10 ⁶ K ^-1 , or greater than 15 10 ⁶ K ^-1 , between 20 ⁰ C to 1000 ⁰ C. the first hoop is of a material having a higher melting temperature to 1200 ⁰ C. Advantageously, the first hoop can thus be heated to very high temperatures to be mounted on the first part and / or during its The material of the first hoop is selected from cobalt-based alloys, such as Stellit, austenitic, ferritic, or titanium-based alloys, In one embodiment, the first hoop does not include copper. and / or does not have tin.

The first hoop is made of a single material.

The first band has the shape of a ring or a sleeve whose radial expansion is not impeded. In particular, the first hoop is not inserted into a room that would hinder its radial outward expansion. The assembly of the first fret is simplified.

The ratio of the coefficient of expansion of the material of the first hoop to the coefficient of expansion of the material of the first part, measured at a temperature between 20 ° C. and 1000 ^° C., is greater than 2.5, greater than 3, greater than 4 and / or less than 6, or even less than 5.

The second ferrule is of a material having a coefficient of expansion lower than 15.10 ^-6 K ^"1, or even less than 10.10 ^-6 K ^'1 and / or greater than 4.10 ⁶ ^{K" 1,} or even greater than 6.10 ^"6 ^{K" 1} 20 ⁰ C and 1000 ⁰ C. The material of the second hoop may in particular have a coefficient of thermal expansion of 8.10 ^"6 K ^{" 1} between 20 ⁰ C and 1000 ⁰ C. The second hoop is a material having a melting temperature greater than 1200 ⁰ C. Advantageously, the second hoop can be heated to very high temperature to be mounted on the first hoop, which provides a particularly tight connection.

The ratio of the coefficient of expansion of the material of the first hoop to the coefficient of expansion of the material of the second hoop, between 20 ^° C. and 1000 ^° C., is greater than 1.2, greater than 1.5, greater than 1, 8 and / or less than 3.5, less than 3, or even less than 2.5. The second hoop is made of a material having a modulus of elasticity (Young's modulus) at 20 ^° C. of less than 110 GPa, preferably less than 100 GPa. The material of the second hoop may in particular have a modulus of elasticity (Young's modulus) of 90 GPa at 20 ^° C. The material of the second hoop has a mass content of niobium and / or Dilver PI greater than 80% preferably greater than 85% and / or less than 95%, preferably less than 93%. Advantageously, the presence of niobium makes it possible to obtain a particularly suitable dilatometric behavior when the device is used for the production of ethylene. The Dilver P1 can advantageously be used when the device according to the invention is not subjected to temperatures higher than 600 ^° C. in use. Under these temperature conditions, the niobium is preferably completely replaced by the Dilver Pl. The modification of the niobium content and / or Dilver P1 also makes it possible to precisely adjust the coefficient of thermal expansion to the intended application. The material of the second hoop has a mass content of hafnium, in metallic form, of greater than 5%, preferably greater than 8% and / or less than

15%, preferably less than 12%. Advantageously, the presence of hafnium improves the mechanical strength when hot. The material of the second ring has a mass content of titanium, in metallic form, greater than 0.5%, preferably greater than 0.8% and / or less than 1.5%, preferably less than 1.2%. . Advantageously, the presence of titanium improves the ductility and the resistance to oxidation. - The material of the second hoop is made of niobium and / or Dilver P1, hafnium and titanium, the complement to 100% being impurities representing less than 2%, preferably less than 1%, in percentages by weight. The second hoop is made of a single material. The second band is in the form of a ring or a sleeve whose radial expansion is not impeded. In particular, the second fret is not inserted into a room that would hinder its radial outward expansion. The mounting of the second fret is simplified.

The first hoop and / or the second hoop extends over a length greater than 40 mm and / or less than 150 mm. - The first hoop has a thickness, preferably substantially constant, greater than 1 mm, preferably greater than 3 mm, more preferably greater than 3.5 mm and / or less than 5 mm and / or the second hoop has a thickness , preferably substantially constant, greater than 3 mm, preferably greater than 5 mm, preferably greater than 8 mm, and / or less than 15 mm, preferably less than 13 mm. These lengths and thicknesses have proved optimal to ensure a good seal of the connection. A second piece is fixed on the first fret.

The second piece is of a material having an expansion coefficient of less than 25.10 ⁶ K ^-1 , less than 20 10 ⁶ K ^-1 and / or greater than 10 10 ⁶ K ^-1 , or greater than 15 10 ⁶ K ^-1 , between 20 ⁰ C and 1000 ⁰ C. A device according to the invention is particularly suitable for connecting first and second parts having very different expansion coefficients.

The material of the second piece is metallic. In particular, this material may be chosen from cobalt-based alloys, such as Stellit, austenitic, ferritic or even ferrous steels or titanium-based alloys.

The second piece is a material having a coefficient of expansion and / or a chemical composition substantially identical to that or that of the first hoop. The second piece is welded or brazed on the first fret. The implementation of a weld or solder advantageously allows a reliable attachment, even at high temperature. It is particularly well suited when the materials of the second part and the first band are of similar compositions, or even identical. - The openings of the first hoop and / or the second hoop is (are) cylindrical circular section. In other words, the first part externally has a circular cylindrical portion on which the first hoop is mounted and / or the first hoop externally has a circular cylindrical portion on which the second hoop is mounted. The first and second frets can in particular have the general shape of rings.

The interior of the first piece and / or the second piece is solid, hollow or partially solid. The hollow interior volume may be of any shape. The first part and / or, where appropriate, the second part are chosen from a tube and a solid bar. - The tube and / or bar has (s) a length greater than 1 m, preferably greater than 3 m.

The largest external transverse dimension of said tube or bar (i.e. the outer diameter in the case of a circular section), upstream and / or downstream of the connecting device, is greater than 10 mm. , preferably greater than 20 mm, greater than 30 mm, greater than 40 mm and / or less than 150 mm, less than 100 mm, less than 75 mm.

In a cross section of said tube, upstream or downstream and / or at the connecting device, the contour of the inner surface is of the same or different shape of the contour of the outer surface of said tube. For example the inner surface may have grooves or asperities or be polygonal, for example square, and the outer surface be circular.

In a cross section of the first hoop, the contour of the inner surface of the first hoop is identical in shape or different from the contour of its outer surface. - A third piece is fixed on said second piece.

The device has no screws or bolts. These pieces are indeed likely to break under the effect of an incrustation of coke in their nets. The first piece is a ceramic tube or a solid ceramic bar and / or, where appropriate, the second piece is a metal tube or a solid metal bar. In one embodiment, the first and second parts are first and second axially aligned tubes. Preferably, they are mounted end to end, preferably without contact with each other.

In one embodiment, the first hoop projects from the first piece, i.e., in the case where the first piece is a tube or bar, extends beyond the axial end of the first piece. the first piece on which it is mounted, and the second piece does not protrude from the first piece, or is mounted flush on the first piece.

In one embodiment, said first and second tubes have the same internal diameter.

Preferably, said first and second tubes are spaced axially from each other by less than 5 mm, less than 3 mm, or less than 1 mm. - The first and / or second pieces are tubes which preferably extend over a length (along the axis of the tube) greater than 10 cm, greater than 50 cm, or even greater than Im beyond the axial end of the first hoop extending in said transverse plane. The first piece is a ceramic tube, preferably extending about an axis substantially vertically, and the second piece is a metal tube. The ceramic tube may in particular have a length greater than 1 meter, greater than 5 meters, or even greater than 8 meters. The metal tube may in particular have a rectilinear axis and be arranged coaxially in the extension of the ceramic tube. Alternatively, the metal tube can be bent or even be shaped "U". In one embodiment, the two branches of the "U" are connected to ceramic tubes, each time by means of a connecting device according to the invention.

The conformation of the first and second pieces can be arbitrary. However, at the connecting device, the dimensions of the second part must allow its attachment to the first hoop, itself attached to the outside of the first part. In an embodiment in which the first and second parts are tubes having, over their entire length, including at the level of the connecting device, a substantially constant external diameter and wall thickness, this requirement therefore leads to a reduction in the transition section to the transition between the second room and the first room.

Therefore, preferably, the first and second parts are tubes (or bars) having, over their entire length, a constant outside diameter, except, as regards the second part, at the connecting device. In this embodiment, such as that represented in FIG. 3, the second part is thus a tube having an enlarged axial end, for example in the form of a cylindrical skirt, the dimensions of which are adapted so that it can serve to the fixation on the first fret.

The enlarged axial end may be integral with the rest of the tube. The practical realization of a second piece having such a conformation can however be tricky. In one embodiment, said enlarged axial end is thus attached to a conventional tube (of constant diameter over its entire length) in the form of a junction piece. For example, a skirt having an inside diameter greater than the inside diameter of such a tube may be welded to one end of said tube.

Advantageously, the passage section can thus be kept constant regardless of the axial position considered (upstream, downstream or at the level of the connecting device).

The use of a junction piece is particularly effective when the second piece is a solid bar.

The above features as well as those of the other aspects of the invention which are described hereinafter are advantageously incorporated together in the same device to obtain an optimal bond, although in some cases the advantages which result from these characteristics may be used separately from others, in different devices.

The invention also relates to a method of assembling a first part made of a material having a first expansion coefficient and a second part made of a material having a second coefficient of expansion greater than said first coefficient of expansion, said method comprising the following steps : 1) hooping a first hoop on the first piece;

2) hooping a second hoop on the first hoop, said second hoop being made of a material having a coefficient of expansion less than the coefficient of expansion of the first hoop; 3) independently of step 1) or step 2), preferably after step 2), fixing the second piece on the first hoop.

Preferably, the first piece, the second piece, the first hoop and the second hoop are chosen so as to obtain, after step 3), a device according to the invention, according to any one of its aspects.

The invention also relates to a method for adapting a hoop to an environment having a determined thermal variability, for example of an amplitude greater than 200 ^° C., greater than 400 ^° C., greater than 700 ^° C., or even greater than 900 ^° C. C, said method of modifying the composition of said hoop, in particular by modifying the niobium content and / or Dilver P 1.

The hoop may in particular have one or more characteristics, optionally optional, of a second hoop according to any aspect of the invention. The material of the hoop may in particular have a mass content of niobium and / or Dilver PI greater than 80%, preferably greater than 85% and / or less than 95%, preferably less than 93%.

Second aspect of the invention

Mounting a first hoop on a first part conventionally consists of axially aligning the first hoop heated at high temperature and a corresponding cylindrical portion of the first piece, and then axially displacing the first hoop relative to the first piece in order to grip the first fret on the first piece.

The axial alignment of the first part and the first hoop must be sufficiently precise and the first part and the first hoop must be dimensioned with the smallest possible tolerance. The physical proximity of the first hoop and the first piece during assembly can lead to the occurrence of thermal shocks. In particular, the low clearance can lead to rapid heat transfer, especially in case of contact between the first hoop and the first part, and in particular when the first part has a high thermal conductivity, for example because it is carbide of silicon.

These heat transfers can degrade the first part. In addition, they can lead to an expansion of the first part and a contraction of the first band leading to a locking position of the first hoop before it could reach the desired final position. There is therefore a need for a hooping process to solve, at least partially this problem.

An object of the invention is to respond, at least partially to this need.

According to a second aspect of the invention, this object is achieved by coating the first piece and / or the first hoop with a coating made of a material having a thermal conductivity lower than that of the material of the first piece.

This coating thus limits the heat exchange between the first part and the first hoop and thus reduces the risk of thermal shock and locking in the intermediate position, especially in case of contact during assembly.

Preferably, the coating material has a thermal conductivity of less than 10 ° C, and preferably the ratio of the thermal conductivity of the material of the first part to the thermal conductivity of the coating material is greater than 10.

The coating material is preferably a refractory material. In particular, the coating material may be selected from zirconia, doped zirconia, cordierite, alumina, mullite, aluminum titanate, yttrium oxide, magnesium oxide, oxide hafnium and a mixture of these materials. A coating comprising more than 80% by weight of zirconia has been particularly effective.

The coating material could also be metal.

The first piece and / or the first hoop may or may not be a first piece and / or a first hoop of a device according to one or more other aspects of the invention. Third, fourth and fifth aspects of the invention

The inventors have found that when a first hoop is mounted on the first piece, material can migrate from the first hoop to the first piece. In particular, they found that the nickel of the first hoop can migrate to the silicon carbide of the first part, leading to stress zones in the first part, which can lead to breaks during temperature changes.

There is therefore a need for a device comprising a first hoop mounted on a first piece and having improved mechanical strength.

Moreover, when the first piece is made of a material based on a silicon compound (that is to say comprises more than 50% by mass of said silicon compound), and in particular when the first piece is made of carbide In silicon, a ceramic oxide coating may be difficult to adhere to the surface of the first piece.

This adhesion is particularly delicate when the material of the first part has a total porosity of less than 5%. There is therefore a need for a process for coating a substrate based on a silicon compound by means of a coating comprising at least one ceramic oxide, which method makes it possible to fix said coating in a reliable and durable manner.

An object of the invention is to provide a technical solution for solving, at least partially, the aforementioned problems. According to a third aspect of the invention, this object is achieved by means of a method for coating a substrate based on a silicon compound by means of a coating comprising at least one ceramic oxide, said process comprising the successive steps following: al) application on said substrate, preferably at room temperature, of particles comprising, preferably, said at least one ceramic oxide; bl) heat treating said substrate under conditions adapted to react said at least one ceramic oxide with silicon of the substrate to form a coating of said at least one ceramic oxide and a transition layer comprising silica at the transition between said substrate and said coating; cl) optionally, applying a layer of a compliant material to the outer surface of said coating, said compliant material being in accordance with the eleventh aspect of the invention described hereinafter; dl) optionally, mounting a first hoop so that said first hoop covers, at least partially, preferably completely, said coating.

Alternatively, according to a fourth aspect of the invention, this goal is achieved by means of a method for coating a substrate based on a silicon compound by means of a coating comprising at least one ceramic oxide, said process comprising the successive successive steps: a2) oxidation, at least on the surface of said substrate, of said silicon compound, for example by a heat treatment in an oxidizing atmosphere, so as to form silica on said surface, b2) application to said substrate, preferably at room temperature, particles comprising, preferably, said at least one ceramic oxide; c2) heat treating said substrate under conditions adapted to react said at least one ceramic oxide with said silica so as to form a coating of said at least one ceramic oxide and a transition layer comprising silica at the transition between said substrate and said coating; d2) optionally, applying a layer of a compliant material to the outer surface of said coating, said compliant material being in accordance with the eleventh aspect of the invention described hereinafter; e2) optionally, mounting a first hoop so that said first hoop covers, at least partially, preferably completely, said coating.

Alternatively, according to a fifth aspect of the invention, this object is achieved by means of a method for coating a substrate, in particular based on a silicon compound, for example based on SiC, S13N4 silicon nitride. or SiAlON, using a coating comprising at least one ceramic oxide, said process comprising the following successive steps: a3) deposition of a silicon layer on the surface of the substrate, preferably by plasma spraying; b3) applying to said silicon layer, preferably at room temperature, particles preferably comprising said at least one ceramic oxide; c3) optionally, heat treating said substrate to react said at least one ceramic oxide with silicon of the substrate so as to form a coating of said at least one ceramic oxide and a transition layer comprising silica at the transition between said substrate and said coating; d3) optionally, applying a layer of a compliant material to the outer surface of said coating, said compliant material being in accordance with the eleventh aspect of the invention described hereinafter; e3) optionally, mounting a first hoop so that said first hoop covers, at least partially, preferably completely, said coating.

Step c3) can be performed as step b1). However, in this process, advantageously, no heat treatment is necessary if, in step b3) the particles are applied by thermal spraying. The process is advantageously simplified.

Whatever the method according to the invention for coating a substrate based on a silicon compound, the nature of the coating and the silicon compound of the substrate are not limiting. In particular, the coating and / or the substrate may comprise one or more characteristics of the coating and the substrate defined in the sixth aspect of the invention.

The above methods may still have one or more of the following optional features:

The silicon compound is a non-oxide compound. The methods are indeed particularly well suited to this type of silicon compounds. In step a1) or b2), the particles of the at least one ceramic oxide are applied by spraying, painting or dipping. For this purpose a slip is prepared which is applied to the substrate. Preferably, the slip does not comprise silica, preferably does not comprise silicon compound. In step b1) or c2) or c3), the substrate is subjected to baking at a temperature of between 1000 ^° C. and 1400 ^° C., preferably for a duration greater than 1 hour.

Step b1) or c2) or c3) is performed in situ, that is to say after the coated substrate has been installed in its operating position. Advantageously, the process is simplified and at a reduced cost. For example, when the substrate is a first part of a connecting device according to the invention, this step can be carried out after final fixing of said device, for example after interposition between two tubes arranged in an ethylene production furnace or within a heat exchanger. The cooking thus results from the first use of the connecting device. The invention also relates to a part comprising a substrate coated according to a method according to any one of the third, fourth and fifth aspects of the invention.

Sixth aspect of the invention According to a sixth aspect, the invention also relates to a "coated part" comprising a substrate made of a material based on a silicon compound and a coating made of a coating material comprising at least one ceramic oxide, a transition layer comprising silica extending between the substrate and the coating.

This coated part may have one or more of the following optional features:

The transition layer has a thickness greater than 0.1 μm and / or less than

20 μm.

The thickness of the transition layer is less than 10 μm, preferably less than 8 μm, preferably less than 6 μm. - The transition layer consists of a silica layer continuously adhered to the substrate. The thickness of the coating is less than 300 μm, preferably less than 250 μm. The thickness of the coating, preferably substantially constant, is greater than 10 μm, preferably greater than 30 μm.

The coating material has a lower thermal conductivity and / or emissivity and / or effusivity than the substrate.

The ratio of the thermal conductivity of the substrate material to the thermal conductivity of the coating material is greater than 10 and / or less than 150. The coating material has a thermal conductivity of less than 10 W m. ⁰ C, preferably is a refractory material. - The silicon compound is a non-oxide compound.

The coating material comprises more than 50%, preferably more than 80%, preferably more than 90%, more preferably substantially 100% of said at least one ceramic oxide, in weight percent. The coating material is selected from the group consisting of zirconia, optionally doped, especially in magnesia or yttrium oxide; cordierite; alumina; mullite; alumina-magnesia spinel; aluminum titanate; yttrium oxide; magnesium oxide; hafnium oxide and mixtures of these materials. Advantageously, the coated part then has good anti-adhesion and anti-scratch properties, is resistant to corrosion and has a low exudation temperature.

The coating material comprises more than 80% zirconia. The coating material may in particular be zirconia or a doped zirconia. Preferably, the coating material comprises less than 5%, less than 1%, less than 0.1%, or no silicon metal alloy compound, and in particular silica. - The coating is covered, at least in part, preferably completely, by a layer of a compliant material according to the eleventh aspect of the invention, and / or by a first hoop, in particular as described in the first aspect of the invention. 'invention. Advantageously, the coating effectively acts as an anti-diffusion barrier improving the resistance to thermal shocks. - Preferably, the coating is covered, at least in part, preferably completely, by a layer of a compliant material according to the eleventh aspect of the invention, itself covered by a first hoop, in particular as described according to the first aspect of the invention.

The substrate comprises a ceramic material.

The mass quantity of silicon carbide in the substrate is greater than 80%, preferably greater than 90%. Preferably, said substrate material is made of silicon carbide.

The substrate has a total porosity less than 5%, less than 2%, or even less than 1%.

The coated part is a piece intended to serve as a cooking support, especially for cooking ceramic pieces. In particular, the coating may be applied to a flat surface of a cooking medium.

The coated part is manufactured according to a process according to any one of the third, fourth and fifth aspects of the invention.

The substrate and said at least one ceramic oxide are selected to manufacture a "first piece" of a device according to one or more other aspects of the invention. A coated part according to the sixth aspect of the invention may thus also comprise one or more optional features of a

"First piece" of a device according to one or more other aspects of the invention.

The invention also relates to a coated part according to the invention in the form of a cooking support or a shrink piece or a hoop.

As explained above, the coating can in fact be used to coat a first part to prevent too rapid heat transfer with a first band when mounting the latter.

The inventors have also discovered that when a first hoop is mounted on a coated part according to the invention, the coating very effectively limits the chemical reactions between the materials of the first part and the first hoop. The coating thus acts as a barrier limiting the diffusion of material between the first piece and the first hoop. This results in improved thermal cycling resistance.

In particular to limit these thermal transfers and / or these chemical reactions, but without being limited thereto, the following optional features are preferred: The first band is itself fretted by means of a second band. The coating at least partially covers a cylindrical surface, in particular of circular cross section, of the first piece and / or the first hoop and / or, where appropriate, the second hoop. The coating surrounds said cylindrical surface. - The coating defines at least a portion, preferably the whole of the contact zone between said first hoop and said first part and / or, where appropriate between said second hoop and said first hoop.

The coating is disposed at least at least 50%, preferably at least 80%, more preferably substantially 100% of said contact area. - Preferably, the coating extends from the edge of the first part or the first hoop through which the first piece enters the first hoop during assembly. A second piece is fixed on the first fret.

The first piece and / or the second piece and / or the first hoop and / or the second hoop may or may not be a first piece and / or a second piece and / or a first hoop and / or a second hoop. a device according to one or more other aspects of the invention, respectively. A device according to the sixth aspect of the invention may thus further comprise one or more optionally optional characteristics of a device according to one or more other aspects of the invention. In general, the invention relates to an assembly comprising a coated part as described above and a hoop mounted on said coated part, said coated part comprising a substrate made of a material based on a silicon compound and a coating made of a coating material containing at least one ceramic oxide, a transition layer comprising silica extending between the substrate and the coating, said coating defining at least a portion of the contact area between said hoop and said coated part.

The invention also relates to the application of a coating as defined above between a first part and a first hoop mounted on the first part as "diffusion barrier", that is to say to limit the migration of material between said first piece and first fret. Seventh aspect of the invention

Thus, according to a seventh aspect, the invention also relates to a method of shrinking a first piece, in particular a ceramic material, by means of a first hoop, in which process, before assembly of the first hoop on the first part, is applied to the first part and / or on the first hoop a coating of a material having a lower thermal conductivity and / or an effusivity greater than that of the first part.

The coating is preferably applied to the first piece when the first hoop is heated to allow mounting. The coating is preferably applied by a method for coating a substrate according to the invention.

Preferably, this method is adapted so that the first part is a coated part according to the invention.

Eighth aspect of the invention

During their tests, the inventors have also found that the assembly of a ceramic tube to a metal tube by means of one or more frets, as described according to the first aspect of the invention, can lead to breaks in the ceramic tube.

There is therefore a need for a solution to limit the deterioration of a ceramic part when it is fretted by means of a first hoop.

An object of the invention is to meet this need.

According to an eighth aspect of the invention, this objective is achieved by means of a device comprising a first piece of ceramic material hooped by means of a first hoop, a device in which the edges of the axial ends of the cylindrical portion of said first piece and first fret by which the first fret was mounted on the first piece belong to the same transverse plane.

In other words, the first band extends to the edge of the cylindrical portion of said first piece on which it was mounted, but without protruding axially. By For the sake of clarity, it is said that the first hoop is mounted "flush" on the first piece.

In the case of an end-to-end connection of two tubes or two bars, this type of assembly is original, the search for a rigid attachment of these tubes or bars naturally encouraging that at least the first fret is mounted straddling these two tubes or bars. The inventors have however found that a "flush" assembly very significantly limits the deterioration of the first part during assembly of the first hoop.

It is said that two edges "belong to the same transverse plane" when their axial offset is less than 1 mm. Preferably according to the invention, this offset is less than

0.8 mm, preferably less than 0.5 mm, more preferably less than 0.3 mm, more preferably less than 0.1 mm. In the case where one or two of said edges will not be included in a transverse plane, it is considered that both edges

'Belong to the same transverse plane' where, irrespective of the point of an edge considered, the distance to the other edge is less than 1 mm, preferably less than

0.8 mm, preferably less than 0.5 mm, more preferably less than 0.3 mm, more preferably less than 0.1 mm.

The term "transverse plane" is a plane perpendicular to the axis of the first hoop.

A device according to the eighth aspect of the invention may optionally further comprise one or more of the following features:

A second piece is fixed, preferably welded or brazed, on the first hoop.

The first hoop itself is preferably hooped by means of a second hoop.

The second fret is flush mounted on the first fret. In other words, the edges of the axial ends of the first hoop, the second hoop and the first piece belong to the same transverse plane.

A second piece is fixed on the first hoop, preferably so as to define, in cooperation with the first hoop, a chamber, preferably sealed, in which the second hoop is housed. The first piece and / or the second piece and / or the first hoop and / or the second hoop may or may not be a first piece and / or a second piece and / or a first hoop and / or a second hoop. a device according to one or more other aspects of the invention, respectively. A device according to the eighth aspect of the invention may thus further comprise one or more optional features of a device according to one or more other aspects of the invention.

Ninth aspect of the invention In one embodiment of a device according to the first aspect of the invention, the second part is fixed on the first band by welding or brazing. This type of connection is indeed advantageously mechanically resistant and durable. The inventors have however found that when the first piece is made of ceramic material, it can break when the second piece is fastened. There is therefore a need for a solution that makes it possible to limit this risk of breakage. An object of the invention is to meet this need.

According to a ninth aspect of the invention, this objective is achieved by means of a device comprising a first piece of ceramic material hooped by means of a first hoop and a second part fixed on said first hoop, for example by a method of heating, the junction region between the first hoop and the second piece being at all points spaced at least 1 mm from said first piece. For example, in the embodiment of FIG. 3, this spacing of at least 0.8 mm or even at least 1 mm corresponds to the radial spacing δ between the outer surface of the ceramic tube and the weld bead. to bind the metal tube to the first hoop. As will be seen in more detail in the following description, the spacing of the junction area limits the interactions with the first part when fixing the second part on the first hoop. Especially when the second piece is welded or brazed to the first hoop, this gap reduces the thermal gradients within the first piece. A device according to the ninth aspect of the invention may optionally further comprise one or more of the following features:

The junction region extends to the right of the first piece. In particular, when the first piece is a tube, said spacing is a radial spacing, measured along a line included in a transverse plane and passing through the axis of the tube.

Said spacing, in particular when it is radial, is greater than 0.8 mm, greater than

1 mm, preferably greater than 3 mm, greater than 5 mm, more preferably greater than 10 mm, or even greater than 15 mm.

The second piece is welded or brazed on the first fret. - The first hoop has a flange, continuous or discontinuous, preferably continuous, on the edge of which the second piece is fixed.

The collar is continuous and belt said first hoop.

The flange is formed at an axial end of said first hoop.

The flange is disposed at the axial end of the first ferrule by which the first ferrule has been mounted (that is to say inserted axially) on the first part.

The first fret is itself fretted by means of a second fret.

In a particularly advantageous embodiment, the first hoop is not mounted flush on the first piece, but in fact protrudes axially, and the second piece is fixed on the portion of the first hoop protruding, preferably at the end the first fret opposed to the end by which it was strung on the first piece.

Advantageously, this embodiment does not require the care of a flange, which simplifies the manufacture of the first hoop. It also allows minimal space.

Preferably, however, the second hoop is flush mounted on the first piece, that is to say it extends to the edge of the cylindrical portion of said first piece on which it was mounted.

The first piece and / or the second piece and / or the first hoop and / or the second hoop may or may not be a first piece and / or a second piece and / or a first hoop and / or a second hoop, respectively of a device according to one or more other aspects of the invention. A device according to the ninth aspect of the invention may thus also comprise one or more of the characteristics, optionally, a device according to one or more other aspects of the invention.

Tenth aspect of the invention The inventors have again sought to increase the life of a device according to the first aspect of the invention.

According to a tenth aspect of the invention, they thus discovered a device comprising a first piece made of a ceramic material hooped by means of a first hoop, in which at least a part of the first hoop, preferably at least the part of the first hoop in contact with the first piece, or even the entire first hoop, is protected by covering by means of a shield.

Preferably, the first hoop is itself hooped by means of a second hoop and at least a portion of the second hoop, preferably at least the portion of the second hoop in contact with the first hoop, or even the entire hoop. second fret, is protected by recovery by means of a shield.

As will be seen in more detail in the following description, the establishment of a protective shield covering at least partially a hoop, allows to limit its deterioration, including mechanical aggression, and therefore to increase the duration of the device. A device according to the tenth aspect of the invention may optionally further comprise one or more of the following features:

The shield seals the first fret and / or the second fret.

The shield is not in contact with the portion of the first hoop in contact with the first piece. - The shield is not in contact with the second hoop.

The shield, preferably in cooperation with the first hoop, defines a chamber, preferably annular.

The second hoop is housed in said chamber.

The room is airtight. The chamber may have any section. It may extend over all or part of the periphery of the part of the first part on which the first hoop is fixed.

The chamber contains a cooling or cooling fluid or thermally insulating or thermally insulating or chemically insulating and / or measuring means, in particular means for measuring the pressure and / or temperature and / or detection means and / or or means for analyzing the environment.

A second piece is fixed, preferably welded, to the first hoop, preferably via said shield. - The shield is part of the second piece and, preferably, came from material with the second piece.

The shield, or even the second part, is fixed, preferably welded, on a flange of the first hoop, preferably on the free edge of said flange, said flange preferably being integral with the first hoop. - The flange is disposed at the end of the first hoop by which the first hoop was mounted on the first piece. Where appropriate, the flange is preferably arranged on the opposite side of the first hoop, relative to the second hoop, at the axial end of the cylindrical portion of the first piece by which the first hoop has been mounted on the first piece. . - The second hoop is disposed axially between the flange and the edge of the axial end of the first piece by which the first hoop was mounted on the first piece.

The mass quantity of silicon carbide in the material of the first part is greater than 80%. The first piece and / or the second piece and / or the first hoop and / or the second hoop may or may not be a first piece and / or a second piece and / or a first hoop and / or a second hoop, respectively of a device according to one or more other aspects of the invention. A device according to the tenth aspect of the invention may thus also comprise one or more optional features of a device according to one or more other aspects of the invention. Eleventh aspect of the invention

During cleaning operations, the pressure inside the tubes of an ethylene production unit can be increased considerably and typically reaches several bars. During thermal cycling, the sealing of the connection by the hoop can also be called into question by the pressure of the reactive mixture, typically greater than 2.5 bar, at temperatures above 900 ^° C., or even above 1000 ^° C. .

The inventors have therefore sought complementary solutions to improve the sealing of the connection between two parts subjected to such stresses, and in particular between two parts having very different expansion coefficients. According to an eleventh aspect of the invention, they have thus discovered a device comprising a first member assembled to a second member preferably having a coefficient of expansion greater than the first member, the assembly being effected by means of a compliant material. consisting of an alloy comprising at least two materials among silver, gold, and palladium. The inventors have found that said compliant material is very resistant to an environment subject to large temperature variations, ensuring good cohesion of the assembled members and sealing of the connection.

A device according to the eleventh aspect of the invention may optionally further comprise one or more of the following features:

The alloy comprises, if not consists of - silver and / or gold and

- palladium.

The alloy comprises more than 0.5% or even more than 3% of palladium, in percentage by weight.

The alloy comprises less than 50% palladium, in percentage by weight. - The alloy has less than 30% palladium, in percent by weight. The alloy comprises less than 5% of glass frit.

The thickness of compliant material between the two members is less than 1 mm and / or greater than 5 μm, preferably greater than 10 μm. The second organ is a fret of the first organ. - The second organ is itself fretted by means of a third member. The material of the third member has a mass content of niobium and / or

Dilver Pl greater than 80%.

The assembly of the third member on the second member is performed by means of a layer of said compliant material. - The material of the second member has a coefficient of expansion greater than the material of the first member and, where appropriate, the third member has a coefficient of expansion less than the coefficient of expansion of the second member, between 20 ⁰ C and 1000 ⁰ C.

The mass quantity of silicon carbide in the material of the first member is greater than 80%.

A fourth member is attached to the second member.

The first member is coated with a coating of a refractory material.

The refractory material is preferably chosen from zirconia, a doped zirconia, cordierite, alumina, mullite, aluminum titanate, yttrium oxide, magnesium oxide and hafnium oxide. and a mixture of these materials.

The first member is coated with a coating of a material having a lower thermal conductivity than the material of the first member.

The coating is in accordance with that described according to the second aspect of the invention.

The invention also relates to a method of assembling a first member and a second member by means of a compliant material interposed between a first surface of the first member and a second surface of the second member, in which method a ) at least one of the first and second surfaces is coated with a precursor of a compliant material as defined above; b) pressing the first surface on the second surface with a pressure greater than 5 MPa, and c) preferably simultaneously with step b) is heated to a temperature above 150 ⁰ C said first and second surfaces in contact.

Preferably, in step a), the precursor of compliant material is coated at the same time with the first surface and the second surface. More preferably, in step b), the pressure is exerted by fretting the first member by means of the second member. The precursor of compiling material may in particular be a suspension of silver powders and / or gold and palladium.

The first member and the second member may in particular be a first piece and a first hoop, respectively, or a first hoop and a second hoop, respectively, of a device according to one or more other aspects of the invention. In the presence of a first piece and two frets, the precursor of compiling material may in particular be arranged so that the compiling material extends between the first piece and the first hoop and between the first hoop and the second hoop. The third organ can also be a second fret. A device according to the eleventh aspect of the invention may further comprise one or more optional features of a device according to one or more other aspects of the invention.

The invention also relates to an apparatus selected from an oven, a boiler, a superheater, a steam generator, a chemical reactor and a heat exchanger, in particular intended for the production of ethylene, said apparatus comprising a device according to any one of aspects of the invention. In particular, said apparatus may comprise at least one tube made of a material based on a silicon compound, in particular silicon carbide, fixed by at least one of its ends to a metal tube, the tube made of a material based on of a silicon compound and the metal tube respectively constituting a first part and a second part of a device according to any aspect of the invention and / or the tube made of a material based on a silicon compound constituting a coated part according to the sixth aspect of the invention and / or the tube made of a material based on a silicon compound or a first hoop mounted on the tube made of a material based on a silicon compound constituting a first organ of a device according to the eleventh aspect of the invention and / or the tube made of a material based on a silicon compound, the first hoop mounted on the tube made of a material based on a silicon compound, the second mounted fret e on the first band and the metal tube constituting a first member, a second member, a third member and a fourth member, respectively, of a device according to the eleventh aspect of the invention. Twelfth aspect of the invention

The inventors have also sought to improve the quality of the connection of a ceramic tube with a metal tube of a connecting device according to the invention, especially in an environment such as that of an ethylene production furnace. They thus discovered particularly advantageous adjustments.

If we designate

DE: the outer diameter of the assembly formed by the ceramic tube, optionally the coating made of a material having a thermal conductivity lower than that of the material of the ceramic tube (according to the second aspect of the invention), optionally the layer of material comp Binder between the ceramic tube and the first hoop (according to the eleventh aspect of the invention), DE ₄₂ : the outer diameter of the first hoop, DI42: the inner diameter of the first hoop, DI42: the inner diameter of the second fret, - Δi: the ratio 100 * (DE-DI ₄₂ ) / DE, and

- A ₂ : the ratio 100 ^ DE ₄₂ -DI ₄₄ VDE ₄₂ . all the measurements being carried out at 20 ^° C.,

Δi and / or Δ ₂ , preferably Δi and Δ ₂ are greater than or equal to 0.00 and / or less than 0.25, or even less than or equal to 0.20. Preferably, Δi is greater than or equal to 0.05.

Brief description of the figures

Other features and advantages of the invention will become apparent upon reading the following detailed description and the accompanying drawing in which: - Figure 1 shows, schematically, an ethylene production unit;

- Figure 2 shows, in cross section, a hoop and a fretted part before and after assembly;

- Figure 3 shows, in perspective and cut by a median longitudinal plane, a device according to a preferred embodiment of the invention; - Figures 4 to 6 illustrate the different steps of a method used to assemble the device shown in Figure 3; and FIG. 7 represents a variant of a device according to the invention.

In the various figures, identical references are used to designate identical or similar members.

detailed description

Figure 1 has been described in the preamble of the description.

The hooping is a technique of axial mounting of an outer part on an inner part exploiting a difference in dilatometric behavior between these two parts. The outer part is conventionally called "frette", in English "flange". The inner part is called "fretted".

More specifically, the hoop is made of a material having a coefficient of thermal expansion greater than that of the inner part. As shown in Figure 2, the band F has an orifice O, defined by an inner surface, whose dimensions make it difficult or impossible to mount on the inner part P by hand or even, conventionally, the press. When the ferrule F is cylindrical with a circular cross-section, its inside diameter ID is thus smaller than the outside diameter OD of the inner part P in the range of temperatures intended for use of the assembly. In this range, the mounting of the hoop is impossible. For this, the band F must be brought to a temperature higher than that of the inner part P. This temperature difference can be obtained by heating the band F and / or cooling the inner part P, for example with nitrogen liquid or with dry ice. The temperature difference must be determined so that the dimensions of the orifice 0 of the hoop F then allow its introduction on the inner part. Once the ferrule F has been introduced on the inner part P, the assembly is brought to the same temperature, for example at the initial ambient temperature, which causes the band F to compress the inner part and ensures the cohesion between the band F and the inner part P.

This cohesion can however be questioned if the temperature of the environment of the assembly increases. Indeed, the hoop will then expand faster than the inner room. An increase in temperature can therefore lead to a loss of sealing, or even an involuntary separation of parts.

In particular, under the conditions of temperature variation of a furnace of an ethylene production unit, the inventors have found that an assembly of a metal tube by hooping on a ceramic tube is unsatisfactory. The coefficients of thermal expansion of the materials of these tubes are indeed too different for the shrinking can ensure a reliable connection over a temperature range of an amplitude of more than 1000 ⁰ C.

US 4,624,484 discloses a connection device for assembling a ceramic piece by means of a hoop. Before assembly of the hoop, a layer of a nonferrous metal is applied to the inner surface of the hoop intended to be brought into contact with the ceramic part. After assembly, this layer is deformed so as to compensate for the differences in expansion between the ceramic tube and the hoop. Such a layer, or generally a coating, are not frets. The inventors then imagined ensuring the connection between the ceramic tube and the metal tube by means of several intermediate frets having gradually increasing coefficients of expansion: A first band having a coefficient of thermal expansion slightly greater than that of the ceramic tube was mounted on this ceramic tube, a second hoop having a coefficient of thermal expansion slightly higher than that of the first hoop was mounted on this first hoop, this type of assembly being reproduced until a hoop having a coefficient of thermal expansion similar to that metal tube. The metal tube was then fixed on this last hoop. However, tests have shown that, under the conditions of temperature variation of a furnace of an ethylene production unit, this technical solution leads to the application of high stresses on the ceramic tube and can lead to its rupture.

The inventors then imagined and realized a connection device of quite different design.

In one embodiment, this connecting device comprises a first hoop mounted on the ceramic tube and a second hoop mounted on the first hoop, the second hoop having a coefficient of expansion less than that of the first hoop. In case temperature increase, the second hoop therefore opposes the expansion of the first hoop, and thus prevents a loss of seal or a separation of the first hoop. In addition, this type of assembly has proved particularly reliable under the conditions of an ethylene production furnace. FIG. 3 represents an example of assembly by means of a connection device according to a preferred, non-limiting embodiment of the invention.

For the sake of clarity, it is considered that the tubes shown in FIG. 3 are positioned along a vertical axis V. In a nonlimiting manner, the words "high", "low", "upper" and "lower" are used to qualify organs or organ parts according to their position relative to this axis.

FIG. 3 represents the lower part 20 of an X-axis ceramic tube 22 connected coaxially with the upper part 24 of a metal tube 26 by means of a connecting device 30.

The ceramic tubes 22 and metal 26 have, except at the connecting device, identical annular cross-sections. The outer diameter of the tubes 22 and 26 is preferably greater than 50 mm and / or less than 100 mm. The inside diameter of the tubes 22 and 26 is preferably greater than 40 mm and / or less than 50 mm.

The ceramic tube 22 is made of a non-oxide material, preferably of silicon carbide, and preferably has a porosity of less than 1%, this porosity being closed. The lower portion 20 of the ceramic tube 22 is coated with a thermally insulating coating 32, for example made of zirconia. The coating 32 extends along an annular surface intended to serve as a support for a first hoop which will be described below. It has a thickness of about 30 microns.

Clichés show, at the interface between the silicon carbide of the ceramic tube 22 and the zirconia of the coating 32, the presence of a transition layer of a substantially constant thickness of about 5 microns. The transition layer consists of a silica layer continuously adhered to the ceramic tube 32.

Except in its upper part 24, the metal tube 26 is a tube similar to the tubes used in the interior technique upstream or downstream of the furnaces used for the production of ethylene. The upper part 24 of the metal tube 26 has a wall 34 whose thickness gradually widens to be maximum in a transverse plane P ₁ . In this plane, the metal tube 26 has a planar annular surface 36, on which a lower edge 38 of the ceramic tube 22 and / or the lower edge of the first hoop described below come, in the non-limiting embodiment of the invention. figure 3, take support. A circular cylindrical peripheral skirt 40 of X axis extends upwards from the periphery of the annular surface 36.

The connecting device 30 comprises a first band 42 and a second band 44.

The first fret 42 is made of a material having a coefficient of expansion lower than 25.10 ^-6 K ^"1 and greater than 10 x ^{10" 6} K ^"1 between 20 and 1000 ⁰ C, preferably consists of the same material as the tube metal 26, for example HP40 steel or FeNiCr alloy The use of the same material to manufacture the metal tube 26 and the first hoop 42 advantageously facilitates their welding to one another.

The first hoop 42 has a total length L ₄₂ of approximately 60 mm and a thickness Q42 of substantially constant wall, preferably between 1 and 5 mm, preferably about 2 mm. The actions of the second hoop on the first hoop and the first hoop on the ceramic tube 22 are then optimal in the event of an increase in temperature from 20 ^° C. to 900 ^° C.

In one embodiment, the first ferrule 42 has a thickness e ₄ 2 substantially constant wall greater than 3 mm, or even greater than 3.5 mm, or substantially equal to 4 mm. The inventors have discovered that the thickness of the first fret changes the quality of the sealing of the connection at room temperature, the best results have been obtained with a thickness e ₄₂ of about 4 mm.

The first band 42 has the shape of a cylindrical sleeve 46 of circular section and a length L ₄₆ of about 50 mm, extended, upwards, by a flange 48.

Throughout its length, the cylindrical sleeve 46 is in contact with the coating 32 of the ceramic tube 22, via a layer 50 of a compliant material improving the seal between the ceramic tube and the first hoop. The layer 50 has a substantially constant thickness of approximately 30 μm. The compiling material comprises on the one hand silver and / or gold, and on the other hand palladium. The inventors have discovered that such a material is particularly reliable. In particular, this material has a very good refracting and a very high melting temperature which makes it compatible with the stresses encountered in a furnace of an ethylene production unit.

For example, the compiling material comprises about 30% palladium, the balance being silver.

The cylindrical sleeve 46 defines a lower edge 52 of the first ferrule 42. The lower edge 52 of the cylindrical sleeve 46 is coplanar with the lower edge 38 of the ceramic tube 22 and may be in contact with the annular surface 36. The inventors have in fact discovered that this configuration limits the risk of rupture of the ceramic tube 22.

The flange 48 results from a gradual flaring until the wall of the first hoop extends substantially perpendicularly to the axis X. This gradual flaring limits the risk of breakage of the ceramic tube during assembly of the first hoop 42 and facilitates the introduction of the ceramic tube 22 in the first ferrule 22. The flange 48 defines a "top edge" 56, circular, of the first ferrule 42.

The upper edge 58 of the peripheral skirt 40 is fixed on the upper edge 56 of the flange 48 by means of a weld bead 60. The radial spacing δ between the outer surface 61 of the ceramic tube 22 and the weld bead 60 is for example about 5 mm.

The annular surface 36, the peripheral skirt 40 and the first hoop 42 thus define a chamber 62. The weld bead 60 is preferably continuous so that the chamber 62 is substantially sealed. Optionally, the chamber 62 is also isolated from the interior of the ceramic tubes 22 and metal tubes 26. The internal volume of the chamber 62 is a few tens of cm ³ , preferably more than 20 cm ³ , more than 50 cm ³ , and / or preferably less than 100 cm ³ , less than 80 cm ³ , preferably about 70 cm ³ . Advantageously, the possible accumulation of coke is thus limited.

The second hoop 44 is made of a material having a coefficient of expansion less than that of the first hoop. The difference of the coefficients of dilation between the first fret and the second fret is determined according to the application. When the connecting device is intended to undergo temperature variations such as those encountered inside the enclosure of an ethylene production unit furnace or immediately upstream or downstream of such an enclosure, the second band may in particular be made of an alloy comprising more than 70% niobium and / or Dilver P1. Such a niobium and / or Dilver P1 alloy advantageously has a low coefficient of thermal expansion, a low Young's modulus (module elasticity), and good resistance to heat and corrosion at high temperature, the latter can be further improved by the presence of a coating. For example, the material of the second hoop comprises 89% niobium, 10% hafnium and 1% titanium. The corrosion resistance can be further improved by coating the second fret with a protective coating, or "coating" type "coating 32". The second hoop 44 has the shape of a cylindrical sleeve of circular section and is mounted on the first hoop by hooping via a layer 63 of compliant material, for example identical to that extending between the ceramic tube and the first fret.

The length L ₄₄ of the second hoop 44 is substantially identical to that of the cylindrical sleeve 46 of the first hoop 42. The thickness Q44 is between 3 and 15 mm, preferably between 5 and 13 mm. The action of the second fret on the first fret is then optimal in case of increase in temperature. Furthermore, the second hoop 44 is housed inside the chamber 62. Advantageously, the second hoop 44 is thus protected from the outside. The peripheral skirt 40 thus acts as a shield for protecting the second hoop 44, but also the first hoop 42.

The lower edge 64 of the second hoop 44 is substantially coplanar with the lower edge 38 of the ceramic tube 22 and the lower edge 52 of the first hoop 42. This configuration has indeed proved optimal to limit the risk of breakage of the ceramic tube when mounting the second fret.

The upper edge 65 of the second ferrule 26 is beveled inwardly and outwardly. The embodiment of a connecting device such as that shown in FIG. 3 can be carried out as follows:

The lower part of the ceramic tube 22 is first covered with the insulating coating 32. The adhesion of a ceramic oxide coating to a tube made of a non-oxide material is however difficult, particularly when the non-oxide material is not or only slightly porous.

In particular, conventional techniques for direct projection of very fine particles of said ceramic oxide by means of a plasma torch have proved to be ineffective in the case of projection onto a first non-oxide ceramic part.

The inventors, however, have discovered several new methods for coating a substrate based on a silicon compound by means of a coating comprising at least one ceramic oxide. In particular, they have discovered a process for coating a substrate based on a silicon compound by means of a coating comprising at least one ceramic oxide, comprising the following successive stages: (al) application to said substrate, preferably at a temperature ambient, particles comprising, preferably consisting of, said at least one ceramic oxide; bl) heat treatment of said substrate under conditions adapted to react said at least one ceramic oxide with silicon of the substrate so as to form silica. Preferably, the particles of said at least one ceramic oxide are applied directly to the substrate, without an intermediate layer. In particular, no intermediate layer of silicon or silica is placed on the substrate before step a1). The thickness of the transition layer formed during step b1) is then advantageously very small, typically less than 10 μm, or even less than 8 μm or even less than 6 μm.

In a preferred embodiment, a method according to the invention does not comprise a step for forming silica before step a1).

In step a1), all conventional techniques can be used to apply the particles. In particular, the particles of said ceramic oxide can be applied by spraying, painting or dipping. For this purpose a slip is prepared which is applied on the substrate. The slip typically comprises a solvent, preferably water, an organic dispersant, and said particles.

Preferably, the slip does not comprise silica, preferably does not comprise silicon compound. After firing, the silica will therefore be present only in the transition layer, a coating devoid of silica being exposed to the outside. The absence of silica can modify the permeability of the coating, but in the embodiment shown, this modification has no practical effect, the coating being itself covered with a layer of compliant material and / or a first hoop . In addition, the manufacturing process is simplified. The application can be carried out at ambient temperature, for example in the open air. The amount of particles is adapted according to the desired coating thickness.

More preferably, the method does not include any step between steps a1) and b1).

In step bl), the substrate is preferably subjected to baking at a temperature of 1000 ⁰ C to 1400 ⁰ C, preferably for a period greater than 1 hour, for example in air.

Surprisingly, the heat treatment results in the formation in the substrate of a transition layer in which a portion of the silicon compound has reacted to form a silica layer within the substrate material. Without being able to explain it theoretically, the inventors have found that the silica layer considerably improves the quality of the adhesion of the ceramic oxide.

In a preferred embodiment, a method according to the invention comprises only steps a1) and b1). The silica of the transition layer thus results exclusively from the execution of step b1. The process is then particularly easy to implement.

The inventors have also developed variants of this process. In particular, they have discovered a process for coating a substrate based on a silicon compound by means of a coating comprising at least one ceramic oxide, this process comprising the following successive steps: a2) oxidation, at least on the surface of said substrate, said silicon compound, for example by a heat treatment in an oxidizing atmosphere, so as to form silica, b2) applying to said substrate, preferably at room temperature, particles comprising, preferably, said at least one ceramic oxide; c2) heat treatment of said substrate under conditions adapted to react said at least one ceramic oxide with said silica.

In step a2), the oxidation thermal treatment can be carried out, for example, by heating the surface of the substrate at a temperature of 1250 ^° C. for 3 hours, for example in air, for example at atmospheric pressure.

In one embodiment, only a portion of the substrate, particularly only its surface, or only the portion of its surface for receiving the coating, is heated. For example, in the case of a ceramic tube, it is not always necessary to introduce the entire tube into the oven.

Preferably, only a surface layer of the substrate is oxidized. More preferably, the substrate is oxidized only to a depth of less than 20 μm. In step b2), the particles of said at least one ceramic oxide may be applied as in step a1).

In step c2), the substrate is preferably subjected to firing at a temperature of between 1000 ^° C. and 1400 ^° C., preferably for a duration greater than 1 hour, for example in air.

The inventors have also invented a process for coating a substrate based on a silicon compound by means of a coating comprising at least one ceramic oxide, this process comprising the following successive steps: a3) deposition of a layer of silicon in substrate surface, preferably by plasma spraying; b3) applying to said silicon layer, preferably at room temperature, particles preferably comprising said at least one ceramic oxide; c3) optionally, heat treating said substrate to react said at least one ceramic oxide with silicon of the substrate so as to form silica. In step a3), a conventional plasma torch can be implemented.

In step b3), the particles of the at least one ceramic oxide may be applied as in step a1).

It is possible to adhere the coating 32 of zirconia on the substrate formed by the lower portion of the ceramic tube 22, following one of the three processes just described.

Before putting in place the first hoop 42 on the first piece, a compliant material precursor layer is applied to the outer surface of the lower portion 20 of the ceramic tube 22 and / or to the inner surface (intended to come into contact with the the lower part 20) of the first hoop 42. The precursor of compliant material can be prepared in the form of an organic solvent suspension. This suspension is then applied, for example by spraying, painting or soaking. The solvent is then removed, for example by drying.

The particle size of the suspension powder, the amount and the nature of the solvent are adapted according to the nature of the surfaces and the thickness of compliant material desired.

Mounting of the first hoop 42 on the lower part 20 of the ceramic tube 22 is then effected, preferably by expanding the first hoop by heating, then introducing it axially, by its axial end provided with the flange 48, on the ceramic tube 22. Preferably, the first hoop is mounted "flush" on the lower portion 20 of the ceramic tube 22. In other words, it is immobilized in a position in which its lower edge 52 is aligned, in the same transverse plane, with the lower edge 38 of the ceramic tube. The inventors have found that this arrangement advantageously limits the risk of rupture of the ceramic tube. As explained above, the silicon carbide is very thermally conductive and any contact between the first ferrule 42 and the ceramic tube 22 would result, in the absence of coating 32, a sudden contraction of the first ferrule leading to its axial locking before that she could reach the desired final position. The presence of the coating 32 limits the heat exchange between the first hoop 42 and the ceramic tube 22, especially in case of contact. During the introduction of the first hoop 42 on the ceramic tube 22, the insulating coating is advantageously a thermal barrier limiting the heat transfer between the first hoop 42 at high temperature and the ceramic tube 22 thermally conductive. The difference between the inside diameter of the first ferrule 42 and the outside diameter of the ceramic tube 22 is called "clearance." At the moment of the introduction of the first ferrule 42 on the ceramic tube 22, the clearance J is positive and allows the fitting by fitting of the first band on the ceramic tube 22. Due to the presence of the coating, the clearance J can be advantageously considerably reduced and / or the temperature of the first hoop decreased, without risk of improper axial locking.

The return to ambient temperature leads to a contraction of the first hoop stronger than that of the ceramic tube, which results in a cancellation of the clearance J and then a pressure of the first hoop on the ceramic tube 22 (Figure 4). Advantageously, this compression also contributes to the effectiveness of the compliant material. Before setting up the second band 44 on the first band 42, a precursor layer of compliant material is also applied on the outer surface of the first band 42 and / or on the inner surface of the second band 44, at least on the areas of these surfaces intended to be in contact after hooping.

The second hoop 44 can then be mounted on the first hoop 42 by conventional hooping (Figure 5). The inward beveled shape of the upper edge 65 of the second hoop 44 facilitates the fitting on the first hoop.

As for mounting the first hoop on the ceramic tube 22, a thermal barrier coating can also be applied to the outer surface of the first hoop to limit the clearance required during the hooping operation. Preferably, the second hoop is mounted "flush" on the first hoop. In other words, it is immobilized in a position in which its lower edge 64 is aligned, in the same transverse plane P ₁ , with the lower edge 52 of the first hoop. The inventors have found that this position advantageously limits the risk of rupture of the ceramic tube.

The outwardly beveled shape of the upper edge 65 of the second ferrule 44 also advantageously limits the stresses applied to the ceramic tube 22.

The ceramic tube 22 is then brought closer coaxially to the metal tube 26 to abut on the annular surface 36. The first ferrule 42 and the second ferrule 44 being mounted flush with the lower edge 38 of the ceramic tube 22, it is also possible that the support on the annular surface 36 is achieved through the lower edge 52 of the first hoop 42 and / or the lower edge 64 of the second hoop.

In this stop position, as shown in Figure 6, the upper edge 58 of the peripheral skirt 40 is opposite the upper edge 56 of the flange 48. These edges are then unified by welding or brazing.

The production of the weld bead 60 conventionally involves temperatures of approximately 1500 ^° C. Advantageously, the junction zone (weld bead 60) between the upper edge 56 of the flange 48 and the upper edge 58 of the peripheral skirt 40 is remote from the outer surface 61 of the ceramic tube 22. Advantageously, the risk of a thermal shock likely to break the ceramic tube is limited.

In this position, the first hoop 42 and the metal tube 26 define the chamber 62. The second hoop is disposed in the chamber 62. Advantageously, it is thus protected from aggression, particularly physical.

Preferably, the weld bead 60 is substantially continuous, so that the chamber 62 is sealed, thus also protecting the second band from chemical attack.

The ceramic tube 22 is then reliably fastened to the metal tube 26. FIG. 7 shows a device according to the invention according to a variant in which the first hoop 42 has the shape of a sleeve which protrudes beyond the axial end of the ceramic tube 22. The metal tube is attached to the free end of the first ferrule 42 by means of a weld bead 60, remote from the ceramic tube. The second hoop 44 is flush mounted on the ceramic tube 22. Variations of the embodiment shown in Fig. 7 are possible. For example, the metal tube 26 may be welded end to end of the first ferrule 42, the edges of the first ferrule and the metal tube being in contact. The inner diameter and / or outer diameter of the first ferrule 42 may be constant or variable along the X axis. The metal tube 26 may also be attached to the outer surface of the first ferrule 42.

Tests have been carried out with a connecting device of the type shown in FIG. 3.

DE: the outside diameter of the assembly formed by the ceramic tube 22, the coating

32 and the layer 50 of compliant material, DE ₄₂ : the outer diameter of the first hoop 42, DI42: the inner diameter of the first hoop 42, DI42: the inner diameter of the second hoop 44,

Δi: the ratio 100 * (DE-DI ₄₂ ) / DE, and

A ₂ : the ratio 100 ° (DE ₄₂ -DI ₄₄ VDE _42), all the measurements being carried out at 20 ^° C., the combinations of the following values of A ₁ and Δ ₂ led to particularly reliable assemblies:

Table 1

Tests were again carried out, with the device of Example 6, to measure the interest of a coating 32 on the surface of the ceramic tube and a layer 50 of compliant material interposed between the coating 32 and the first hoop 42.

The compliant material was an Ag / Pd alloy. The following table 2 summarizes the results obtained:

Table 2

These results show that the coating 32 and the layer 50 have not only an effect on the seal, but also on the resistance to thermal cycling.

Of course, the invention is not limited to an embodiment described and shown.

In particular, a hoop does not require that the shrunk piece has, in a cross section, a circular outer contour. In one embodiment, the first piece and / or the first hoop does not have a circular outline. Advantageously, any rotation of the first hoop and / or the second hoop, respectively, around the axis of the first hoop and / or the second hoop, respectively, is then prevented. The first piece and / or the first hoop may in particular have, in cross section, an oblong contour, or a contour having a plurality of points, preferably equiangularly distributed around the axis, for example a star shape.

Claims

1. Device comprising a first piece (22) of a ceramic material hooped by means of a first hoop (42), wherein at least a portion of the first hoop is protected by covering by means of a shield (40) defining in cooperation with the first hoop, an annular chamber (62).

2. Device according to the preceding claim, wherein the first hoop is itself fretted by means of a second hoop (44) and wherein at least a portion of the second hoop is protected by recovery by means of said shield.

3. Device according to any one of the preceding claims, wherein at least the portion of the first hoop in contact with the first piece and / or, where appropriate, at least the portion of the second hoop in contact with the first hoop. , is (are) protected by recovery by means of said shield.

4. Device according to any one of the preceding claims, wherein the shield surrounds the first hoop and / or, where appropriate, the second hoop.

5. Device according to any one of the preceding claims, wherein the second hoop is housed in said chamber.

6. Device according to any one of the preceding claims, wherein the chamber is airtight.

7. Device according to any one of the preceding claims, wherein the chamber contains a cooling fluid or cooling or heat transfer or thermally insulating or chemically insulating or measuring means, in particular pressure measuring means and / or temperature and / or detection means and / or means for analyzing the environment.

8. Device according to any one of the preceding claims, wherein a second part (26) is fixed on the first hoop via said shield.

9. Device according to any one of the preceding claims, wherein the shield is fixed on a flange (48) of the first hoop.

10. Device according to any one of the preceding claims, wherein the flange is disposed at the axial end of the first hoop by which the first hoop has been mounted on the first piece.

11. Device according to any one of the two immediately preceding claims, wherein a second hoop (44) frettant said first hoop, is disposed axially between the flange and the edge (38) of the axial end of the first part by which the first fret was mounted on the first piece.

12. Device according to any one of claims 2 to 11, wherein the second hoop has a coefficient of expansion less than the coefficient of expansion of the first hoop between 20 ⁰ C and 1000 ⁰ C.

13. Device according to any one of claims 2 to 12, wherein the material of the second band has a niobium mass content greater than 80%.

14. Device according to any one of claims 2 to 13, wherein the first hoop has a thickness greater than 1 mm and less than 5 mm and the second hoop has a thickness greater than 3 mm and less than 15 mm.

15. Device according to any one of the preceding claims, wherein the mass quantity of silicon carbide in the material of the first part is greater than 80%.

16. Apparatus selected from an oven, a boiler, a superheater, a steam generator, a chemical reactor and a heat exchanger, said apparatus comprising at least one silicon carbide tube fixed by at least one of its ends to a metal tube , the silicon carbide tube and the metal tube respectively constituting a first part and a second part of a device according to any one of claims 9 to 15.

17. Use of an apparatus according to the preceding claim in a steam-cracking unit.

18. Use of an apparatus according to claim 16 in a waste recovery unit, in particular a household waste incinerator.