Pipe connection for end-face connection of pipe elements

Abstract

The invention relates to a pipe connection for the end-face connection of pipe elements, comprising a first pipe element (1) made of a metal material, a second pipe element (2) made of a ceramic material, and a reinforcement layer (4) which completely surrounds the first pipe element (1) and the second pipe element (2) in the circumferential direction and at least partially surrounds same in the longitudinal direction and which is connected to both the outer lateral face of the first pipe element (1) and the outer lateral face of the second pipe element (2), wherein the reinforcement layer (4) is made of a ceramic fibre composite material which has a fibre structure which comprises metal fibres and ceramic fibres, wherein the proportion of metal fibres at the end of the reinforcement layer (4) resting against the first pipe element (1) is greater than the proportion of ceramic fibres, the proportion of ceramic fibres at the end of the reinforcement layer (4) resting against the second pipe element (2) is greater than the proportion of metal fibres, and the fibre structure is embedded in an oxide-ceramic matrix.

Description

[0001] Pipe connection for the frontal connection of pipe elements

[0002] Description

[0003] The invention relates to a pipe connection for the end-face connection of pipe elements comprising a first pipe element made of a metallic material, a second pipe element made of a ceramic material and a reinforcing layer which completely surrounds the first pipe element and the second pipe element in the circumferential direction and at least partially in the longitudinal direction.

[0004] Generic pipe connections are known from the state of the art for a variety of applications. A problem with regard to permanent tightness often arises with pipe connections in which the pipe elements to be connected are made of different materials, especially when the pipe elements differ in their thermal expansion coefficients. If such pipe elements are subjected to thermal stress or thermal cycling, the pipe elements experience different linear expansions due to their material properties, which can lead to leaks at the pipe connection or damage to the pipe elements, such as cracks.

[0005] However, the use of pipe elements made of different materials is desirable or necessary in some applications, for example, in power plant technology or chemical process engineering. For example, in high-temperature processes, the use of pipe elements made of ceramic materials has proven to be effective, as they offer advantages over metallic materials. However, the use of ceramic pipes usually requires a connection between a metal pipe element and a ceramic pipe element – ​​with the aforementioned problems regarding the permanent sealing effect and mechanical integrity of the connection.

[0006] Pipe connections that address the problem of differential expansion under thermal stress are known from the prior art. For example, patent application US 2012 / 0003128 A1 discloses a device for connecting a ceramic pipe to a metal pipe. A first, inner shrink ring is shrunk onto the ceramic pipe and connected to the metal pipe. A second, outer shrink ring is mounted on the first shrink ring. This second shrink ring is made of a material with a lower thermal expansion coefficient than the first shrink ring. When thermal stress is applied due to heating of the pipe connection, the expansion of the first shrink ring is limited by the second shrink ring.

[0007] Even though this type of connection technology is suitable for a specific temperature range and material combinations, it does have some disadvantages. Firstly, under severe thermal stress, the inner shrink ring can expand so much, despite its external limitations, that an annular gap forms between the ceramic tube and the inner shrink ring, causing the connection to leak. Secondly, installing the inner shrink ring on the ceramic tube requires the shrink ring to be heated to a high temperature. Applying the hot shrink ring to the cool ceramic tube can cause thermal shock to the ceramic material, resulting in damage or destruction.

[0008] A similar approach for connecting a ceramic pipe to a metal pipe is disclosed in EP 1 795 794 A1. A hose made of an elastomeric material is pushed over the junction of the two pipes. This hose is fully enclosed by a band spring that exerts inward pressure on the elastomer. Even with this type of connection technology, sufficiently high thermal stress, particularly severe thermal cycling, can lead to leaks, e.g., due to plastic deformation of the elastomeric material. Furthermore, the application of this pipe connection is limited to a relatively low temperature range, since the elastomeric material is damaged or destroyed at high temperatures.

[0009] The task was to further develop generic pipe connections in such a way that they are, on the one hand, easy to manufacture and, on the other hand, can be used for a wide range of thermal loads without spontaneous or permanent leaks occurring.

[0010] This object is achieved according to the invention by a device according to claim 1 and a method according to claim 11. Advantageous embodiments of the device are specified in claims 2 to 10.

[0011] In the following, the terms "have", "have", "comprise" or "include" or any grammatical variations thereof are used in a non-exclusive manner. Accordingly, these terms can refer both to situations in which, apart from the feature introduced by these terms, no other features are present, or to situations in which one or more other features are present. For example, the expression "A has B", "A has B", "A comprises B" or "A includes B" can refer both to the situation in which, apart from B, no other element is present in A (i.e., a situation in which A consists exclusively of B), and to the situation in which, in addition to B, one or more other elements are present in A, for example, element C, elements C and D, or other elements.

[0012] Furthermore, it should be noted that the terms "at least one" and "one or more," as well as grammatical variations of these terms or similar terms, when used in connection with one or more elements or features and intended to express that the element or feature may be provided once or multiple times, are generally used only once, for example when the feature or element is first introduced. When the feature or element is subsequently mentioned again, the corresponding term "at least one" or "one or more" is generally no longer used, without limiting the possibility that the feature or element may be provided once or multiple times.

[0013] Furthermore, the terms “preferably”, “in particular”, “for example” or similar terms are used hereinafter in connection with optional features, without limiting alternative embodiments. Thus, features introduced by these terms are optional features, and these features are not intended to limit the scope of the claims, and in particular the independent claims. Thus, as those skilled in the art will recognize, the invention can also be carried out using other embodiments. Similarly, features introduced by “in one embodiment of the invention” or by “in an embodiment of the invention” are understood as optional features, without limiting alternative embodiments or the scope of the independent claims.Furthermore, these introductory expressions are intended to leave untouched all possibilities of combining the features introduced thereby with other features, whether optional or non-optional.

[0014] Measurements are referred to below with their usual abbreviations. In particular, the units meter are abbreviated to "m", millimeter to "mm", micrometer to "pm", degrees Celsius to "°C", pascal to "Pa", gigapascal to "GPa", and percent to "%". One aspect of the invention relates to a pipe connection for the end-face connection of pipe elements, comprising a first pipe element made of a metallic material, a second pipe element made of a ceramic material, and a reinforcement layer that completely surrounds the first pipe element and the second pipe element in the circumferential direction and at least partially in the longitudinal direction and is connected to both the outer surface of the first pipe element and the outer surface of the second pipe element. The reinforcement layer is made of a ceramic fiber composite material having a fiber framework comprising metallic fibers and ceramic fibers.wherein the proportion of metallic fibers at the end of the reinforcement layer adjacent to the first pipe element is greater than the proportion of ceramic fibers, the proportion of ceramic fibers at the end of the reinforcement layer adjacent to the second pipe element is greater than the proportion of metallic fibers, and the fiber framework is embedded in an oxide-ceramic matrix.

[0015] A further aspect of the invention relates to a method for producing a front-end connection of pipe elements, comprising the steps of a) providing a first pipe element made of a metallic material and a second pipe element made of a ceramic material, b) applying a reinforcement layer made of a ceramic fiber composite material to the outer surface of the first pipe element and the outer surface of the second pipe element, wherein the ceramic fiber composite material has a fiber framework comprising metallic fibers and ceramic fibers, wherein the proportion of metallic fibers at the end of the reinforcement layer adjacent to the first pipe element is greater than the proportion of ceramic fibers, the proportion of ceramic fibers at the end of the reinforcement layer adjacent to the second pipe element is greater than the proportion of metallic fibers, and the fiber framework is embedded in an oxide-ceramic matrix,and c) connecting the reinforcement layer to the outer surface of the first pipe element and to the outer surface of the second pipe element.

[0016] The term "tubular element" as used herein is a broad term which should be given its ordinary and current meaning as understood by one skilled in the art. The term is not limited to any specific or adapted meaning. The term can, without limitation, refer in particular to a hollow component through which a fluid medium can be conducted. This can be, for example, a tube, a tube segment or an end piece of a straight or bent tube. Further examples are tubular sections of other components, e.g. a flange, valve or tube sheet of a reactor or heat exchanger. The first tubular element can be any tubular element which is suitable for being connected to the second tubular element, for example a tube, a tube segment, an end piece of a straight or bent tube or a tubular section of another component.

[0017] The outer diameter of the first tubular element at its end intended for connection to the second tubular element is preferably from 6 mm to 300 mm, particularly preferably from 10 mm to 200 mm, in particular from 15 mm to 150 mm.

[0018] The outer diameter of the first pipe element at its end facing away from the connection to the second pipe element is preferably from 6 mm to 300 mm, particularly preferably from 10 mm to 200 mm, in particular from 15 mm to 150 mm.

[0019] The difference between the largest outer diameter and the smallest outer diameter of the first tubular element is preferably from 0 mm to 50 mm, particularly preferably from 0 mm to 40 mm, in particular from 0 mm to 30 mm. The ratio of this diameter difference to the nominal diameter of the first tubular element is preferably from 0 to 0.05, particularly preferably from 0 to 0.02, in particular from 0 to 0.01.

[0020] The length of the first tubular element is preferably from 20 mm to 2000 mm, particularly preferably from 30 mm to 1500 mm, in particular from 50 mm to 500 mm.

[0021] The wall thickness of the first tubular element is preferably from 0.5 mm to 20 mm, particularly preferably from 1 mm to 15 mm, in particular from 1 mm to 10 mm. The difference between the largest wall thickness and the smallest wall thickness of the first tubular element is preferably less than 10 mm, particularly preferably less than 7 mm, in particular less than 5 mm.

[0022] The roughness of the outer surface of the first tubular element is preferably from 2 pm to 100 pm, particularly preferably from 10 pm to 50 pm. The roughness of the inner surface of the first tubular element is preferably from 2 pm to 100 pm, particularly preferably from 10 pm to 50 pm. The roughness values ​​are determined using a method as described in DIN EN ISO 4287:1997.

[0023] The first tubular element is made of a metallic material. Preferably, the metallic material is selected from the group consisting of high-temperature-resistant stainless steels, nickel-based alloys, copper-based alloys, austenitic iron-based alloys, and ferritic iron-based alloys. Furthermore, the metallic material is preferably selected from the group of alloys with a material number n1 .m1m2m3m4 according to DIN EN 10027-2:2015-07, where n1 corresponds to the number 1, 2 or 3, preferably to the number 1 or 2, m1 corresponds to the number 0, 1, 3, 4 or 8, preferably to the number 3 or 4, particularly preferably to the number 4, m2 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, preferably to the number 4, 5, 6, 7, 8 or 9, m3 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and m4 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9.

[0024] In one embodiment, the metallic material can be selected from the group of alloys with the material number 1.4m2m3m4, 2.08m3m4 and 2.4m2m3m4, where in this case m2 corresponds to the number 4, 5, 6, 7, 8 or 9, m3 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and m4 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9.

[0025] In a further embodiment, the metallic material can be selected from the group of alloys with the material number 1.4767, 2.4633, 1.48m3m4 and 2.48m3m4, where in this case m3 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and m4 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, for example 1.4841, 1.4852, 1.4876.

[0026] The metallic material can, for example, be a ferritic iron-chromium-aluminum alloy (FeCrAl alloy). FeCrAl alloys include, for example, products sold under the trade names Kanthai® AF, Kanthai® A-1, and Kanthai® D.

[0027] In one embodiment, the first tubular element has a widened portion, with the inner diameter of the first tubular element increasing toward the front end. Preferably, the outer surface of the first tubular element is at least partially covered by the reinforcement layer in the area of ​​the widened portion. It has been found that, in a first tubular element with a widened portion at least partially covered by the reinforcement layer, the reinforcement layer adheres better to the outer surface of the first tubular element.

[0028] The term "expansion" as used herein is a broad term which should be given its ordinary and customary meaning as understood by one skilled in the art. The term is not limited to any specific or adapted meaning. The term can, without limitation, refer in particular to any type of enlargement of the inner diameter towards the end of the first tubular element. The transition from the smallest inner diameter to the largest inner diameter of the expansion can be continuous or discontinuous. Preferably, the transition is continuous, so that the inner diameter increases steadily towards the end of the first tubular element. Preferably, the inner diameter in the expansion increases linearly, so that the interior of the expansion has the shape of a cone or truncated cone.In this case, the half opening angle of the cone is preferably less than 45°, particularly preferably less than 30°, in particular less than 15°.

[0029] The outer diameter of the first tubular element can remain constant or vary in the area of ​​the expansion. Preferably, the outer diameter of the first tubular element is constant in the area of ​​the expansion. The wall thickness of the first tubular element decreases toward the end of the first tubular element in the area of ​​the expansion.

[0030] The length of the widened portion is preferably from 5 mm to 200 mm, particularly preferably from 10 mm to 150 mm, in particular from 20 mm to 100 mm. The length of the widened portion is understood to be the axial extension of the section of the first tubular element in which the inner diameter increases.

[0031] In one embodiment, the widened portion extends to the end of the first tubular element, so that the end of the widened portion also forms the tubular end. In another embodiment, the widened portion forms a transition section between two regions of the first tubular element with different inner diameters. In this embodiment, the end of the widened portion with the larger inner diameter preferably transitions into a region with a constant inner diameter that extends to the tubular end of the first tubular element.

[0032] In one embodiment, the first pipe element has a section with a reduced and / or enlarged outer diameter in an area covered by the reinforcement layer. The change in the outer contour creates a positive connection between the first pipe element and the reinforcement layer covering the outer surface, which has a beneficial effect on the durability of the pipe connection.

[0033] In one configuration of this embodiment, the section has at least one notch, at least one bulge, or both at least one notch and at least one bulge. The term "notch" as used herein is a broad term to be given its ordinary and common meaning as understood by those skilled in the art. The term is not limited to any specific or adapted meaning. The term may, without limitation, refer in particular to a portion of the first tubular element in which the outer diameter is reduced relative to other regions.

[0034] The notch can be of various shapes. Viewed longitudinally, the notch can be, for example, a hemisphere, a semi-ellipse, a sinusoid, a triangle, a quadrilateral, a trapezoid, a polygon, or combinations thereof. The shape can be symmetrical or asymmetrical when viewed longitudinally. The transitions from the non-reduced outer surface to the notch can be angular or rounded.

[0035] Viewed in the circumferential direction, the notch can be a circumferential structure whose shape is constant or variable in the longitudinal direction. However, it can also be individual elements distributed over the circumference of the outer surface of the first tubular element, for example, symmetrically or asymmetrically.

[0036] The notch can also have multiple recesses or sub-elements viewed longitudinally. These can be identical or different. For example, an external thread on the lateral surface that extends radially into the outer lateral surface can also serve as a notch.

[0037] The difference between the non-reduced outer diameter of the first tubular element and the smallest diameter of the notch is preferably from 0.25 mm to 10 mm, particularly preferably from 0.5 mm to 5 mm, in particular from 1 mm to 3 mm.

[0038] The pitch angle of the shorter flank in the longitudinal direction of the tubular element of the transition from the non-reduced outer diameter of the first tubular element to the smallest outer diameter in the section of the notch is preferably from 5° to 60°, particularly preferably from 10° to 45°.

[0039] The term "bulge," as used herein, is a broad term that should be given its ordinary and common meaning as understood by those skilled in the art. The term is not limited to any specific or adapted meaning. The term may refer, without limitation, specifically to a portion of the first tubular element in which the outer diameter is enlarged relative to other areas.

[0040] The bulge can have different shapes. Viewed longitudinally, the bulge can, for example, be shaped like a hemisphere, a semi-ellipse, a sinusoid, a triangle, a quadrilateral, a trapezoid, a polygon, or combinations thereof. Viewed longitudinally, the shape can be symmetrical or asymmetrical. The transitions from the non-enlarged outer surface to the bulge can be angular or rounded.

[0041] Viewed in the circumferential direction, the bulge can be a circumferential structure whose shape is constant or variable in the longitudinal direction. However, it can also be individual elements distributed over the circumference of the outer surface of the first tubular element, for example, symmetrically or asymmetrically.

[0042] The bulge can also have several elevations or sub-elements viewed longitudinally. These can be identical or different. For example, an external thread on the lateral surface that protrudes radially beyond the outer lateral surface can also serve as a bulge.

[0043] The difference between the largest diameter of the bulge and the non-enlarged outer diameter of the first tubular element is preferably from 0.25 mm to 50 mm, particularly preferably from 0.5 mm to 30 mm, in particular from 1 mm to 20 mm.

[0044] The pitch angle of the shorter flank in the longitudinal direction of the tubular element of the transition from the non-enlarged outer diameter of the first tubular element to the largest outer diameter in the section of the bulge is preferably from 5° to 60°, particularly preferably from 10° to 45°.

[0045] The second tubular element may be any tubular element suitable for being connected to the first tubular element, for example a tube, a tube segment, an end piece of a straight or bent tube or a tubular section of another component.

[0046] The outer diameter of the second tubular element at its end intended for connection to the first tubular element is preferably from 6 mm to 300 mm, particularly preferably from 10 mm to 200 mm, in particular from 15 mm to 150 mm. The wall thickness of the second tubular element is preferably from 0.5 mm to 20 mm, particularly preferably from 1 mm to 15 mm, in particular from 1 mm to 10 mm. The difference between the largest wall thickness and the smallest wall thickness of the second tubular element is preferably less than 10 mm, particularly preferably less than 7 mm, in particular less than 5 mm.

[0047] The second tube element is made of a ceramic material. Preferably, the ceramic material is selected from the group consisting of at least one of the following components: a binary oxide (MxOz), a mixed oxide (M1yM2vOz), a meta II carbide (M3vCw), a metal nitride (M3vNw), mixtures of binary oxides (M1yOz / M2v0w, MxOz / M1yOz / M2v0w), mixtures of mixed oxides (MxM1yOz / MuM2vOw), mixtures of binary oxides and metal carbides (MxOz / M3vCw), and / or mixtures of binary oxides and metal nitrides (MxOz / M3vNw). Where O refers to the chemical element oxygen, C to the chemical element carbon, and N to the chemical element nitrogen.

[0048] M can, for example, be an element selected from the group consisting of: aluminum (Al), zirconium (Zr), silicon (Si), calcium (Ca), magnesium (Mg), beryllium (Be), yttrium (Y), lanthanum (La), iron (Fe), nickel (Ni), chromium (Cr), tungsten (W), hafnium (Hf), strontium (Sr), scandium (Sc), cerium (Ce), ytterbium (Yb). Preferably, M can be an element selected from the group consisting of: aluminum, zirconium, silicon, yttrium, lanthanum, hafnium, strontium. More preferably, M is aluminum, zirconium or yttrium.

[0049] M1 can, for example, be an element selected from the group consisting of: aluminum (Al), zirconium (Zr), yttrium (Y), magnesium (Mg), and silicon (Si). M1 can preferably be aluminum.

[0050] M2 can, for example, be an element selected from the group consisting of: zirconium (Zr), silicon (Si), magnesium (Mg), yttrium (Y), titanium (Ti).

[0051] M3 can, for example, be an element selected from the group consisting of: aluminum (Al), silicon (Si), boron (B), tungsten (W). x, y, z, u, v and w can each independently be between 1 and 10, preferably between 1 and 7 and particularly preferably between 1 and 5. For example, the ceramic material can comprise at least one mixture selected from the group consisting of: binary and ternary mixtures of aluminum oxide (Al2O3), zirconium oxide (ZrCh) and yttrium oxide (Y2O3) (e.g.Zirconium oxide-reinforced aluminum oxide); mixtures of silicon carbide (SiC) and aluminum oxide; mixtures of aluminum oxide and magnesium oxide (MgO spinel); mixtures of aluminum oxide and silicon oxide (mullite); mixtures of aluminum silicates and magnesium silicates, ternary mixtures of aluminum oxide, silicon oxide and magnesium oxide (cordierite); steatite (magnesium silicate); zirconium oxide-reinforced aluminum oxide; stabilized zirconium oxide: stabilizers in the form of magnesium oxide (MgO), calcium oxide (CaO) or yttrium oxide, optionally cerium oxide (CeO2), scandium oxide (ScOs) or ytterbium oxide (YbO3) are also used as stabilizers; also aluminum titanate (stoichiometric mixture of aluminum oxide and titanium oxide, Al2O3 / TiO2); silicon nitride and aluminum oxide (silicon aluminum oxynitrides).

[0052] As zirconium oxide-reinforced aluminum oxide, Al2O3 with 10 to 20 mol% ZrO2 is advantageously used. To stabilize ZrO2, 10 to 20 mol%, preferably 16 mol% CaO, 10 to 20 mol%, preferably 16 mol% MgO, or 5 to 10 mol% Y2O3, preferably 8 mol% Y2O3 ("fully stabilized zirconium oxide") or 1 to 5 mol% Y2O3, preferably 4 mol% ("partially stabilized zirconium oxide") can advantageously be used. For example, 80% Al2O3, 18.4% ZrO2, and 1.6% Y2O3 are advantageous as a ternary mixture.

[0053] For example, the ceramic material can be selected from the group consisting of quartz glass (SiO2), silicon carbide (SiC), silicon nitride (SiO2), aluminum nitride (AlN), corundum (AlO3), zirconia (ZrO2), mullite or fiber composite materials based on these components.

[0054] The ceramic material may also comprise a composite material, for example a composite material made up of several layers of monolithic ceramic and / or oxide fiber composite ceramic, as described, for example, in documents WO 2016 / 184776 A1 or EP 3 835 639 A1.

[0055] In one embodiment, a sleeve made of a metallic material is completely connected to the first tubular element and to the second tubular element in the circumferential direction.

[0056] Preferably, the metallic material of the sleeve is selected from the group comprising high-temperature-resistant stainless steels, nickel-based alloys, copper-based alloys, austenitic iron-based alloys, ferritic iron-based alloys, platinum group metals (PGMs), refractory metals, gold, and silver. PGMs include the elements platinum, palladium, iridium, rhodium, osmium, ruthenium, and their alloys. Refractory metals include the elements titanium (Ti), zirconium (Zr), hafnium (Hf), and vanadium (V). i Niobium (Nb), Tantalum (Ta), Chromium (Cr) x Molybdenum (Mo), tungsten (W) and alloys containing these elements as main components.

[0057] Preferably, the metallic material of the sleeve is selected from the group of alloys with a material number n1.m1 m2m3m4 according to DIN EN 10027-2:2015-07, where n1 corresponds to the number 1, 2, or 3, preferably the number 1 or 2, m1 corresponds to the number 0, 1, 3, 4, or 8, preferably the number 3 or 4, particularly preferably the number 4, m2 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9, preferably the number 4, 5, 6, 7, 8 or 9, m3 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and m4 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9 corresponds.

[0058] In one embodiment, the metallic material of the sleeve can be selected from the group of alloys with the material number 1 .4m2m3m4, 2.4m2m3m4 and 2.08m3m4, where in this case m2 corresponds to the number 4, 5, 6, 7, or 8, m3 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and m4 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9.

[0059] In a further embodiment, the metallic material of the sleeve can be selected from the group of alloys with the material number 1.4767, 2.4633, 1.48m3m4 and 2.48m3m4, where in this case m3 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and m4 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, for example 1.4841, 1.4852, 1.4876.

[0060] The metallic material of the sleeve can be, for example, a ferritic iron-chromium-aluminum alloy (FeCrAl alloy). FeCrAl alloys include, for example, products sold under the trade names Kanthai® AF, Kanthai® A-1, and Kanthai® D.

[0061] The metallic material of the sleeve and the metallic material of the first tubular element may be the same or different materials.

[0062] In one embodiment, the sleeve is connected to the first tubular element at its end face. The sleeve can be a separate component, preferably a tubular component, which is connected to the end of the first tubular element at its end face, for example by welding or soldering. The sleeve can also be an integral part of the first tubular element. In an advantageous embodiment, the sleeve forms the end section of the first tubular element. In this embodiment, the sleeve can be produced, for example, by enlarging the inner diameter of the first tubular element in the region of the sleeve compared to the region of the first tubular element behind it, for example by mechanically milling or turning the tubular end of the first tubular element.

[0063] In a further embodiment, the sleeve is a separate component that rests completely in the circumferential direction on the outer surface of the first tubular element at its end intended for connection and at least partially in the longitudinal direction, preferably encompassing the outer surface. The sleeve can be a prefabricated component that is closed in the circumferential direction, for example a hollow cylinder, which is pushed onto the end of the first tubular element. The sleeve can also be formed as a component by joining a flat element such as a strip or a film. For example, the sleeve can be produced by wrapping a strip of metallic material around the outer surface of the end of the first tubular element and fastening it. The sleeve and the outer surface of the first tubular element are preferably connected in a sealing manner.A sealed connection can be created, for example, by shrinking the sleeve onto the end of the first tubular element, or by joining the two components firmly, for example by welding or soldering. Preferably, the sleeve is welded circumferentially to the outer surface of the first tubular element. The length of the overlap of the outer surface of the first tubular element in the longitudinal direction is preferably from 3 mm to 300 mm, particularly preferably from 5 mm to 200 mm, in particular from 10 mm to 100 mm.

[0064] In a further embodiment, the sleeve is a separate component that rests completely in the circumferential direction and at least partially in the longitudinal direction on the inner surface of the first tubular element at its end intended for connection. The sleeve can be a prefabricated component that is closed in the circumferential direction, for example a hollow cylinder, which is inserted into the end of the first tubular element. The sleeve can also be formed as a component by joining a flat element such as a strip or a film. For example, the sleeve can be produced by applying and fastening a strip made of a metallic material to the inner surface of the end of the first tubular element. The sleeve and the inner surface of the first tubular element are preferably connected in a sealing manner.A sealed connection can be created, for example, by joining the two components in a materially bonded manner, for example by welding or soldering. Preferably, the sleeve is welded circumferentially to the inner surface of the first tubular element. The length of the overlap of the inner surface of the first tubular element in the longitudinal direction is preferably from 3 mm to 300 mm, particularly preferably from 5 mm to 200 mm, in particular from 10 mm to 100 mm.

[0065] In one embodiment, the sleeve is connected to the second tubular element at its end face. The connection is preferably made by a material fit, in particular by soldering or gluing. The sleeve can also be an integral component of the second tubular element. In an advantageous embodiment, the sleeve is embedded in the end face of the second tubular element. In this embodiment, the sleeve can be produced, for example, by being incorporated into the ceramic material during the manufacture of the second tubular element and being completely enclosed by it at one end. When the ceramic material is fired, the sleeve is permanently bonded to the second tubular element.

[0066] In a further embodiment, the sleeve is a separate component that rests completely in the circumferential direction on the outer surface of the second tubular element at its end intended for connection and at least partially in the longitudinal direction, preferably enclosing the outer surface. The sleeve can be a prefabricated component that is closed in the circumferential direction, for example a hollow cylinder, which is pushed onto the end of the second tubular element. The sleeve can also be formed as a component by joining a flat element such as a strip or a film. For example, the sleeve can be produced by wrapping a strip of metallic material around the outer surface of the end of the second tubular element and fastening it. The sleeve and the outer surface of the second tubular element are preferably connected in a sealing manner.A sealed connection can be created, for example, by shrinking the sleeve onto the end of the second tubular element, or by bonding the two components together, for example by soldering or gluing. The sleeve is preferably soldered to the outer surface of the second tubular element all the way around in the circumferential direction. The length of the overlap of the outer surface of the second tubular element in the longitudinal direction is preferably from 3 mm to 300 mm, particularly preferably from 5 mm to 200 mm, in particular from 10 mm to 100 mm. The outer surface of the second tubular element can have a reduced outer diameter in the area covered by the sleeve. In one embodiment, the outer diameter of the outer surface of the second tubular element is reduced by the value of the material thickness of the sleeve, so that after the sleeve has been applied, a flat surface without edges or offset is produced when viewed in the longitudinal direction.

[0067] In a further embodiment, the sleeve is a separate component that rests completely in the circumferential direction and at least partially in the longitudinal direction on the inner surface of the second tubular element at its end intended for connection. The sleeve can be a prefabricated component that is closed in the circumferential direction, for example a hollow cylinder, which is inserted into the end of the second tubular element. The sleeve can also be formed as a component by joining a flat element such as a strip or a film. For example, the sleeve can be produced by applying and fastening a strip made of a metallic material to the inner surface of the end of the second tubular element. The sleeve and the inner surface of the second tubular element are preferably connected in a sealing manner.A sealed connection can be created, for example, by joining the two components in a materially bonded manner, for example by soldering or gluing. Preferably, the sleeve is soldered circumferentially to the inner surface of the second tubular element. The length of the overlap of the inner surface of the second tubular element in the longitudinal direction is preferably from 3 mm to 300 mm, particularly preferably from 5 mm to 200 mm, in particular from 10 mm to 100 mm.

[0068] The outer surface of the second tubular element can have a reduced outer diameter in the area where the sleeve is attached. In one embodiment, the outer diameter of the outer surface of the second tubular element is reduced by the value of the material thickness of the sleeve, so that after the sleeve has been applied, a flat surface without edges or offset is produced in the longitudinal direction. In this case, a force-fitting or material-fitting connection can preferably be achieved between the inside of the sleeve and the outside of the second tubular element. The temperature resistance of the connecting elements is preferably greater than 1200°C, the HT strength of the metal sleeve is preferably less than 100 MPa, the HT elastic modulus of the metal sleeve is preferably less than 100 GPa, and the fit between the sleeve and the second tubular element is preferably a sliding fit, in which the sleeve and the second tubular element can slide against one another.

[0069] The material, shape, and dimensions of the sleeve can be selected according to specific requirements. For example, the sleeve can be shaped like a hollow cylinder or a cone. It can also have an angled shape, with the transition area of ​​the angled section being rounded or angular. The sleeve can also have an irregular shape, for example, similar to a bellows. Especially when manufacturing the sleeve from a flat structure such as a film or strip, there are virtually no limits to the shape of the sleeve.

[0070] The wall thickness of the sleeve is preferably from 0.03 mm to 0.7 mm, particularly preferably from 0.1 mm to 0.5 mm. The inner diameter of the sleeve in the attached state is preferably from 6 mm to 300 mm, particularly preferably from 10 mm to 200 mm, in particular from 20 mm to 150 mm.

[0071] The dimensional tolerance in the diameter of the sleeve is preferably from 0 pm to 150 pm, particularly preferably from 0 pm to 90 pm, in particular from 0 pm to 60 pm, whereby the dimensional tolerance is understood to mean the deviation of the dimension of a component from the target dimension (nominal dimension). The ratio of the dimensional tolerance of the sleeve to its inner diameter is preferably from 0 to 0.006, particularly preferably from 0 to 0.004, in particular from 0 to 0.003.

[0072] The roundness tolerance of the sleeve is preferably from 0 pm to 150 pm, particularly preferably from 0 pm to 90 pm, in particular from 0 pm to 60 pm, wherein the roundness tolerance is understood to be the deviation between the two concentric circles in the plane perpendicular to the axis of the sleeve, between which the circumferential lines of all cross sections of the sleeve lie.

[0073] The cylindricity tolerance of the sleeve is preferably from 0 pm to 150 pm, particularly preferably from 0 pm to 90 pm, in particular from 0 pm to 60 pm, wherein the cylindricity tolerance is understood to mean the deviation between the two coaxial cylinders between which the outer surface of the sleeve lies.

[0074] The roughness of the sleeve on its inside, determined according to the specifications of the standard DIN EN ISO 4287:1997, is preferably from 0.025 pm to 3.2 pm, particularly preferably from 0.1 pm to 1.6 pm.

[0075] In the area covered by the sleeve, the dimensional tolerance of the outer surface of the second tubular element is preferably from -60 pm to 60 pm, particularly preferably from -40 pm to 40 pm, whereby the dimensional tolerance is understood to be the deviation of the dimension of a component from the target dimension (nominal dimension). The roundness tolerance of the outer surface of the second tubular element in the area covered by the sleeve is preferably from -60 pm to 60 pm, particularly preferably from -40 pm to 40 pm, whereby the roundness tolerance is understood to be the deviation between the two concentric circles in the plane perpendicular to the axis of the outer surface of the second tubular element, between which the circumferential lines of all cross sections of the outer surface of the second tubular element lie.

[0076] The cylindricity tolerance of the outer surface of the second tubular element in the region of the coverage by the sleeve is preferably from -60 pm to 60 pm, particularly preferably from -40 pm to 40 pm, wherein the cylindricity tolerance is understood to mean the deviation between the two coaxial cylinders between which the outer surface of the second tubular element lies.

[0077] The roughness of the outer surface of the second pipe element in the area of ​​coverage by the sleeve, determined according to the specifications of the standard DIN EN ISO 4287:1997, is preferably from 0.025 pm to 3.2 pm, particularly preferably from 0.1 pm to 1.6 pm.

[0078] An adhesive can be used to firmly bond the sleeve to the second pipe element.

[0079] An adhesive can be, for example:

[0080] • A ceramic adhesive, for example the products of the manufacturer Cotronics Corporation with the trade names Resbond™ 904 or Resbond™ 989

[0081] • A glass adhesive or glass solder, for example the products of the manufacturer Schott with the trade names G018-346, G018-358, G018-385.

[0082] • One or more fillers and pastes, for example the products of the manufacturer Nohtec GmbH with the trade names ZYROBOND® INOX GARD or ZYROBOND® HTW PASTE, of the manufacturer INTERFLON with the trade name HT 1200 or of the manufacturer Adolf Würth GmbH with the trade name HSP 1400.

[0083] In the processing state, the viscosity of the adhesive is in the range of 10 2 mPa*s to 10 8 mPa*s, preferably in the range of 10 3 up to 10 7 mPa*s, particularly preferably in the range of 10 4 up to 10 6 mPa*s.

[0084] Furthermore, in the processed state, the proportion of organic components is in the range of 0 to 5 wt.%, preferably in the range of 0 to 2 wt.%, particularly preferably in the range of 0 to 1 wt.%.

[0085] In the final state, the adhesive bonds preferably have the following properties: • The maximum application temperature is in the range from 600 to 1800 °C, preferably in the range from 800 to 1600 °C, particularly preferably in the range from 1000 to 1400 °C.

[0086] • Corrosion resistance is given in oxidizing atmosphere and in reducing atmosphere.

[0087] • The permeability is in the range of 0 to 10 Darcy, preferably in the range of 0 to 1 Darcy, particularly preferably in the range of 0 to 0.1 Darcy.

[0088] Furthermore, a solder can be used to firmly bond the sleeve to the second tubular element. The term "solder," as used herein, is a broad term to which its usual and common meaning should be given, as understood by those skilled in the art. The term is not limited to any specific or adapted meaning. The term can, without limitation, refer in particular to a material suitable for improving the adhesion between a metallic material and a ceramic material.

[0089] Preferably, the material of the solder is selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd) and alloys of at least two of the elements gold, silver (Ag), palladium, nickel (Ni), cobalt (Co), copper (Cu), manganese (Mn).

[0090] The material of the solder is particularly preferably selected from the group consisting of gold, platinum, palladium and alloys of silver and palladium (Ag / Pd); gold, copper and nickel (Au / Cu / Ni); gold and palladium (Au / Pd); gold, palladium and manganese (Au / Pd / Mn); gold, palladium and nickel (Au / Pd / Ni); gold, nickel, palladium, manganese and copper (Au / Ni / Pd / Mn / Cu); palladium and cobalt (Pd / Co); palladium and nickel (Pd / Ni); palladium, nickel, copper and silver (Pd / Ni / Cu / Ag); whereby the alloys may each contain traces of further elements.

[0091] The material of the solder is particularly preferably selected from the group consisting of gold and alloys of gold and palladium (Au / Pd); gold, palladium and nickel (Au / Pd / Ni); palladium and cobalt (Pd / Co); palladium and nickel (Pd / Ni); palladium, nickel, copper and silver (Pd / Ni / Cu / Ag); whereby the alloys may each contain traces of further elements.

[0092] Such precious metal-containing brazing alloys are commercially available, for example, as products of Morgan Advanced Materials plc (www.morganbrazealloys.com) under the product or brand names Nicoro (Au / Cu / Ni), Palco (Pd / Co), Palmansil5 (Au / Pd / Mn), Palni (Pd / Ni), Palnicurom25 (Au / Ni / Pd / Mn / Cu), Palnicusil (Pd / Ni / Cu / Ag), Palnirol (Au / Pd / Ni), Palniro4 (Au / Pd / Ni), Palniro7 (Au / Pd / Ni), Paloro (Au / Pd), Palsill 0 (Ag / Pd).

[0093] The melting temperature of the solder is preferably from 1120°C to 1350°C, particularly preferably from 1150°C to 1300°C, in particular from 1160°C to 1240°C. The solidification temperature of the solder is preferably from 1100°C to 1300°C, particularly preferably from 1120°C to 1280°C, in particular from 1150°C to 1250°C.

[0094] A reinforcement layer completely surrounds the first pipe element and the second pipe element in the circumferential direction and at least partially in the longitudinal direction and is connected to both the outer surface of the first pipe element and the outer surface of the second pipe element.

[0095] The term "reinforcing layer," as used herein, is a broad term to which its ordinary and customary meaning should be given, as understood by those skilled in the art. The term is not limited to any specific or adapted meaning. The term may, without limitation, refer in particular to a layer of a material suitable for permanently bonding the two pipe elements of the pipe joint and increasing the strength of the pipe joint.

[0096] The reinforcement layer can comprise several individual layers or be a continuous layer as a flat structure. For example, the reinforcement layer can comprise several individual layers running in the longitudinal direction of the pipe connection, each of which is connected to both the outer surface of the first pipe element and the outer surface of the second pipe element. Preferably, the reinforcement layer is formed as a continuous flat layer that completely encloses the ends of the two pipe elements in the longitudinal and circumferential directions.

[0097] The reinforcement layer can be connected to the first pipe element and to the second pipe element in different ways, for example by frictional connection, form closure, material connection or combinations thereof.

[0098] A frictional connection can be achieved, for example, by making the cross-section of the reinforcement layer smaller after completion than during application. This cross-section reduction forces the reinforcement layer onto the areas of the two pipe elements it covers, creating a frictional connection. This is the case, for example, if the ceramic fiber composite material of the reinforcement layer is first applied and the pipe connection is then fired.

[0099] A positive-lock connection can be achieved, for example, by the reinforcement layer covering regions of the first pipe element and / or the second pipe element that have a geometry designed to prevent slippage or loosening of the connection. This is the case, for example, in embodiments in which the first pipe element has a section with a reduced and / or enlarged outer diameter in an area covered by the reinforcement layer.

[0100] A bonded connection can be created, for example, by soldering, welding, gluing, or combinations thereof. Bonded connections between the reinforcement layer and the first pipe element are preferably created by soldering or welding, in particular by welding. Bonded connections between the reinforcement layer and the second pipe element are preferably created by gluing.

[0101] The thickness of the reinforcement layer in the radial direction can preferably be from 0.25 mm to 8 mm, particularly preferably from 0.5 mm to 6 mm, in particular from 1 mm to 5 mm. In embodiments that have a sleeve, the ratio of the thickness of the reinforcement layer to the wall thickness of the sleeve can preferably be from 2 to 100, particularly preferably from 4 to 50.

[0102] The length of the coverage of the outer surface of the first pipe element by the reinforcement layer in the longitudinal direction can preferably be from 3 mm to 300 mm, particularly preferably from 5 mm to 200 mm, in particular from 10 mm to 100 mm.

[0103] The length of the reinforcement layer covering the outer surface of the second pipe element in the longitudinal direction can preferably be at least 3 mm, particularly preferably at least 5 mm, in particular at least 10 mm. The reinforcement layer preferably covers the outer surface of the second pipe element by at least 50%, preferably at least 75%, particularly preferably 100%.

[0104] The reinforcement layer is made of a ceramic fiber composite material. The terms "composite" and "fiber composite material," as used herein, are broad terms that should be given their ordinary and customary meaning as understood by those skilled in the art. The terms are not limited to any specific or adapted meaning. The term "composite" can refer, without limitation, to any material made from two or more constituents. These constituents may have significantly different chemical or physical properties and can be fused into a single material with properties distinct from those of the individual materials. Within the composite material, the individual materials may remain separate.

[0105] The term "fiber-reinforced composite" can, without limitation, refer in particular to any material that generally comprises at least two main components: reinforcing fibers and an embedding matrix that can serve as a filler and / or adhesive between the fibers. Mutual interactions between the two components can impart superior properties to the overall material than either component alone. The fiber-reinforced composite can, in particular, comprise the fibers as a discontinuous or dispersed phase, the matrix as a continuous phase, and an interphase region, which can also be referred to as an interface.

[0106] The term "ceramic matrix composite" ("CMC"), as used herein, is a broad term to which its ordinary and common meaning should be given, as understood by those skilled in the art. The term is not limited to any specific or adapted meaning. The term may refer, without limitation, to any composite material, in particular to any fiber-reinforced composite comprising a plurality of ceramic fibers embedded in a ceramic matrix. In this context, carbon and carbon fibers may also be considered ceramic materials.

[0107] The term “oxide ceramic matrix composite” (“OCMC”), as used herein, is a broad term to which its ordinary and customary meaning should be given, as understood by one skilled in the art. The term is not limited to any specific or adapted meaning. The term may, without limitation, refer in particular to any ceramic matrix composite comprising an oxide ceramic matrix reinforced by oxide ceramic reinforcing fibers. OCMCs may be fiber-reinforced composites comprising a fiber scaffold embedded in a porous oxide ceramic matrix. The term “OCMC” may refer to structures with a purely ceramic fiber scaffold or to structures whose fiber scaffold comprises, in addition to ceramic fibers, further fibers of at least one other material, e.g., metal fibers.Advantages of such OCMCs include high temperature resistance up to 1300 °C or more in oxidizing or reducing atmospheres, high thermal shock resistance, and quasi-ductile deformation and fracture behavior. The open porosity £ of fiber-reinforced ceramics can typically range between 5% and 50%. The fracture toughness of OCMCs can reach values ​​of KIC = 10 - 50 MPa / m. Due to their porous structure, fiber-reinforced ceramics can exhibit a lower density, a lower elastic modulus, and a lower thermal conductivity coefficient compared to monolithic ceramics with the same chemical composition.

[0108] The following table provides a list of the relevant standards for the determination of these parameters, in particular a list of the relevant standards for the determination of the structural, mechanical and thermophysical parameters for monolithic ceramics and for OCMC.

[0109] The thermal conductivity coefficient is defined by the following relationship: Thermal conductivity coefficient = density x (specific heat capacity) x thermal diffusion coefficient.

[0110] The following table compares the properties of monolithic ceramics and OCMC based on alumina.

[0111] The fiber framework, also referred to as a "fiber fabric," is a hybrid fiber framework comprising at least two different types of fibers. The fiber framework comprises both fibers made of a ceramic material, preferably an oxide-ceramic material, and fibers made of a metallic material. The fibers made of a ceramic material are referred to below as "ceramic fibers" or "ceramic fibers," and the fibers made of a metallic material are referred to as "metallic fibers" or "metal fibers."

[0112] Metallic fibers can be made of at least one material. The material is preferably selected from the group consisting of iron-based alloys, nickel-based alloys, platinum group metals (PGMs), and refractory metals.

[0113] In one embodiment, the material is selected from the group of alloys with a material number n1.m1 m2m3m4 according to DIN EN 10027-2:2015-07, where n1 corresponds to the number 1, 2 or 3, preferably to the number 1 or 2, m1 corresponds to the number 0, 1, 3, 4 or 8, preferably to the number 3 or 4, particularly preferably to the number 4, m2 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, preferably to the number 4, 5, 6, 7, 8 or 9, m3 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and m4 corresponds to the number 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9.

[0114] In one embodiment, the material is a ferritic iron-chromium-aluminum alloy (FeCrAl alloy). FeCrAl alloys include, for example, products sold under the trade names Kanthai® AF, Kanthai® A-1, and Kanthai® D.

[0115] The metal fibers can be made from several individual strands. Such a metal fiber can, for example, comprise from 4 to 100 strands, preferably from 6 to 50 strands, particularly preferably from 10 to 30 strands. The thickness of the individual strands is preferably from 10 μm to 150 μm, preferably from 15 μm to 100 μm. The metal fibers can preferably have a modulus of elasticity of from 40 GPa to 400 GPa, preferably from 80 GPa to 200 GPa.

[0116] Ceramic fibers can be made from at least one material. The material is preferably selected from the group consisting of at least one of the following components: a binary oxide (MxOz), a mixed oxide of the formula M1xM2yOz, a mixed oxide of the formula M1xM2yM3wOz, mixtures of binary oxides (M1yOz / M2v0w), mixtures of mixed oxides (MxM1yOz / MuM2vOw), and / or a metal carbide (MxCy). Where O refers to the chemical element oxygen, and C to the chemical element carbon.

[0117] M can, for example, be an element selected from the group consisting of: aluminum (Al), zirconium (Zr), silicon (Si), calcium (Ca), magnesium (Mg), beryllium (Be), yttrium (Y), lanthanum (La), iron (Fe), nickel (Ni), chromium (Cr), tungsten (W), hafnium (Hf), strontium (Sr), scandium (Sc), cerium (Ce), ytterbium (Yb). Preferably, M can be an element selected from the group consisting of: aluminum, zirconium, silicon, yttrium, lanthanum, strontium.

[0118] M1 can, for example, be an element selected from the group consisting of: aluminum (Al), zirconium (Zr), yttrium (Y). M1 can preferably be aluminum. M2 can, for example, be an element selected from the group consisting of: zirconium (Zr), silicon (Si), magnesium (Mg), yttrium (Y). M3 can, for example, be cobalt (Co). x, y, u, v and w can each, independently of one another, be between 1 and 10, preferably between 1 and 7 and particularly preferably between 1 and 5, z can be between 1 and 30, preferably between 1 and 20 and particularly preferably between 1 and 10.

[0119] In one embodiment, the ceramic fibers are selected from the group consisting of mullite, alumina (Al2O3), a mixture of mullite and alumina.

[0120] The fiber framework can be manufactured, for example, as a film, mat, especially as a continuous mat, or as continuous filaments. The fiber framework can be manufactured using known techniques, for example, by weaving, knitting, braiding, or sewing.

[0121] The fiber scaffold can be manufactured in a two-dimensional or three-dimensional orientation. In the two-dimensional orientation, the fibers are essentially aligned only along a single plane in the x-direction and y-direction of the material. In the three-dimensional orientation, the fibers are aligned in the x-direction, y-direction, and z-direction. The fiber scaffold can also be referred to as a fiber preform, fiber skeleton, or fiber fabric.

[0122] The fiber fabric can be woven in a specific weave pattern selected from the group consisting of: unidirectional, plain weave, twill K1 / 2, twill K2 / 2, twill K1 / 3, twill 4 / 4, atlas A1 / 4, atlas A1 / 7. Preferred weave patterns can be twill 2 / 2, twill 4 / 4, atlas 1 / 4, atlas 1 / 7, and especially twill 4 / 4, atlas 1 / 4, and atlas 1 / 7. The fiber fabric can be laminated, in particular, at an angle of 0 / 90° or at an angle of 45°, preferably at an angle of 0 / 90°. In this context, the term "lamination" refers to the process during the manufacture of OCMC components in which fabric layers are impregnated with slurry and stacked on top of one another.

[0123] The proportion and distribution of the metallic fibers and the ceramic fibers can vary depending on the requirements of the pipe connection. For example, the ratio of metallic fibers to ceramic fibers can be from 0.001 to 1000, preferably from 0.01 to 100, and particularly preferably from 0.02 to 50.

[0124] In a hybrid fiber fabric comprising warp and weft threads, the metal fibers can be warp threads, weft threads, or both warp and weft threads. The ceramic fibers can also be warp threads, weft threads, or both warp and weft threads. Metal fibers are preferably used as weft threads. The arrangement and distribution of metal fibers and ceramic fibers in the hybrid fiber fabric can be uniform or irregular.

[0125] The proportion of metallic fibers at the end of the reinforcement layer adjacent to the first pipe element is greater than the proportion of ceramic fibers, whereas the proportion of ceramic fibers at the end of the reinforcement layer adjacent to the second pipe element is greater than the proportion of metallic fibers. In the part of the reinforcement layer adjacent to the first pipe element, the proportion of metal fibers is thus higher than in the part of the reinforcement layer adjacent to the second pipe element. Preferably, the proportion of metal fibers decreases approximately continuously from one side of the reinforcement layer to the other side of the reinforcement layer. The design with an uneven distribution of metal fibers has several advantageous effects. The varying proportion of metal fibers in the longitudinal direction of the reinforcement layer means that the reinforcement layer has different thermal expansion coefficients along its length.This prevents stress fractures or detachment of the reinforcement layer from the remaining components. Furthermore, a proportion of metal fibers in the end region of the reinforcement layer on the side of the first pipe element enables a material bond between the metal fibers of the reinforcement layer and the outer surface of the first pipe element, for example, by soldering or welding.

[0126] In one embodiment, the ceramic fiber composite material of the reinforcement layer comprises metallic fibers that are at least partially accessible at the surface of the reinforcement layer and are integrally connected, preferably welded, to the outer surface of the first pipe element.

[0127] The reinforcement layer may comprise multiple layers of fiber fabrics, preferably arranged one above the other. Such a multi-layer reinforcement layer can be produced, for example, by successively wrapping multiple layers of fiber fabrics around the ends of the two pipe elements.

[0128] In multi-layer reinforcement layers, similar or different fiber fabrics can be layered on top of one another. In one embodiment, exclusively homogeneous fiber fabrics can be arranged in multiple layers. In another embodiment, exclusively hybrid fiber fabrics can be arranged in multiple layers. In a further embodiment, homogeneous fiber fabrics and hybrid fiber fabrics can be arranged in multiple layers. A “homogeneous fiber fabric” is understood to mean a fiber fabric that contains exclusively fibers of the same type, for example, with regard to the material from which the fibers are made. The homogeneous fiber fabrics preferably comprise ceramic fibers, while the hybrid fiber fabrics comprise ceramic fibers and metal fibers. Layers of hybrid fiber fabrics preferably alternate with layers of homogeneous fiber fabrics, resulting in a sandwich arrangement of the different fabric types.

[0129] The number of reinforcement layers comprising hybrid fiber fabrics can preferably be from 1 to 30, particularly preferably from 1 to 25, in particular from 1 to 20. In embodiments with different types of fabrics, the proportion of hybrid fiber fabric layers relative to the total number of layers is preferably from 10% to 100%, particularly preferably from 20% to 75%. The ceramic matrix in which the fibers are embedded can be made of at least one material. Preferably, the material is selected from the group consisting of at least one of the following components: a binary oxide (MxOz), a mixed oxide of the formula M1xM2yOz, a mixed oxide of the formula M1xM2yM3wOz, mixtures of binary oxides (M1yOz / M2v0w) and / or mixtures of mixed oxides (MxM1yOz / MuM2v0w). Where O refers to the chemical element oxygen and C to the chemical element carbon.

[0130] M can, for example, be an element selected from the group consisting of: aluminum (Al), zirconium (Zr), silicon (Si), calcium (Ca), magnesium (Mg), beryllium (Be), yttrium (Y), lanthanum (La), iron (Fe), nickel (Ni), chromium (Cr), tungsten (W), hafnium (Hf), strontium (Sr), scandium (Sc), cerium (Ce), ytterbium (Yb). Preferably, M can be an element selected from the group consisting of: aluminum, zirconium, silicon, yttrium, lanthanum, strontium.

[0131] M1 can, for example, be an element selected from the group consisting of: aluminum (Al), zirconium (Zr), yttrium (Y). M1 can preferably be aluminum. M2 can, for example, be an element selected from the group consisting of: zirconium (Zr), silicon (Si), magnesium (Mg), yttrium (Y). M2 can preferably be silicon. M3 can, for example, be cobalt (Co). x, y, u, v and w can each, independently of one another, be between 1 and 10, preferably between 1 and 7 and particularly preferably between 1 and 5, z can be between 1 and 30, preferably between 1 and 20 and particularly preferably between 1 and 10.

[0132] In one embodiment, the material of the ceramic matrix is ​​selected from the group consisting of at least one of the following components: silicon-containing mixed oxides of the formulas SixMyOz, SixM1yM2wOz, and / or SixByNzCw, aluminum nitride (AlN), and aluminum-containing binary oxides (AlxOz). Where O refers to the chemical element oxygen, B to the chemical element boron, N to the chemical element nitrogen, and C to the chemical element carbon.

[0133] In one embodiment, the material of the ceramic matrix comprises a mixture of aluminum oxide (Al2O3) and zirconium dioxide (ZrO2). The weight fraction of Al2O3 in the total mixture is preferably from 50% to 100%, particularly preferably from 70% to 95%, in particular from 80% to 90%. The weight fraction of ZrO2 in the total mixture is preferably from 0% to 50%, particularly preferably from 5% to 30%, in particular from 10% to 20%. The ratio of the weight fraction of ZrO2 to the weight fraction of Al2O3 is preferably from 0 to 0.5, particularly preferably from 0.1 to 0.25.

[0134] It has been found that a pipe connection according to the invention, in which a reinforcing layer made of a ceramic fiber composite material is bonded to both the outer surface of the first pipe element and the outer surface of the second pipe element, is both mechanically stable and gas-tight. The pipe connection can withstand even large, rapid temperature changes without damage and without leakage.

[0135] A separate measure to seal the components against each other is not mandatory, but possible. The term "seal" or "sealing," as used here, is a broad term that should be given its usual and common meaning, as understood by a person skilled in the art. The term is not limited to any specific or adapted meaning.

[0136] Examples of seals include flat seals or stuffing box seals made of graphite or mica, as well as lens seals or O-ring seals made of metal. Seals can also be manufactured by connecting components such as the ends of the pipe elements and / or a sleeve in a form-fitting and / or material-fitting manner.

[0137] Seals can be present, for example, between the first pipe element and the sleeve, between the first pipe element and the reinforcement layer, between the second pipe element and the sleeve, or between the second pipe element and the reinforcement layer. In a preferred embodiment, a circumferential seal is applied between the outer surface of the second pipe element and the inner surface of the sleeve.

[0138] Further details and features of the invention will become apparent from the following description of preferred embodiments, particularly in conjunction with the subclaims. The respective features can be implemented individually or in combination with one another. The invention is not limited to the embodiments. The embodiments are illustrated schematically in the drawings. The drawings are to be understood as schematic representations. They do not represent a limitation of the invention, for example, with regard to specific dimensions or design variants. The same reference numerals in the individual drawings designate identical or functionally equivalent elements, or elements corresponding to one another in terms of their functions. In detail:

[0139] Fig. 1 Longitudinal section through a pipe connection according to a first embodiment of the invention;

[0140] Fig. 2 Longitudinal section through a pipe connection according to a second embodiment of the invention;

[0141] Fig. 3 Longitudinal section through a pipe connection according to a third embodiment of the invention;

[0142] Fig. 4 Longitudinal section through a pipe connection according to a fourth embodiment of the invention;

[0143] Fig. 5 Longitudinal section through a section of a first tubular element with enlarged outer diameter;

[0144] Fig. 6 Longitudinal section through a pipe connection according to a fifth embodiment of the invention;

[0145] Fig. 7 Detailed view of the joint between the sleeve and the pipe element 2 with the sleeve shrunk on;

[0146] Fig. 8 Detailed view of the joint with a material-tight connection between the sleeve and the pipe element 2.

[0147] Examples of implementation

[0148] Fig. 1 schematically shows a longitudinal section through a pipe connection according to a first embodiment of the invention. The pipe connection is rotationally symmetrical; the dashed line in Fig. 1 indicates the axis of symmetry. A first pipe element 1 and a second pipe element 2 are connected to each other at their end faces.

[0149] The first tubular element 1 is made of a metallic material, for example, Centralloy® G 4852 Micro (trade name of Schmidt + Clemens GmbH + Co. KG, Lindlar, Germany). Its inner diameter is, for example, 42 mm, and its outer diameter is 50 mm.

[0150] The sleeve 3 is made of a flexible metallic material, for example, as a strip or foil. The material of the sleeve 3 is, for example, Alloy 800 H (material number 1.4876 according to DIN EN 10027-2). The wall thickness of the sleeve 3 can be, for example, 0.25 mm to 0.3 mm. The sleeve 3 is completely connected to the first tubular element 1 in the circumferential direction. In the example shown, the sleeve 3 is integrally connected to the outer surface of the first tubular element 1 by a circumferential weld seam 8.

[0151] The second tube element 2 is made of a ceramic material, for example, Alsint 99.7 (trade name of Morgan Advanced Materials Haldenwanger GmbH, Waldkraiburg, Germany). Its inner diameter is, for example, 42 mm, and its outer diameter is 50 mm.

[0152] A reinforcement layer 4 is applied to the outer surface of the end of the first pipe element 1 and the outer surface of the end of the second pipe element 2, completely enclosing the ends of both pipe elements in the circumferential direction and at least partially enclosing them in the longitudinal direction. The reinforcement layer 4 is bonded to both the outer surface of the first pipe element 1 and the outer surface of the second pipe element 2.

[0153] Reinforcing layer 4 is made of a ceramic fiber composite material. The ceramic fiber composite material comprises a hybrid fiber fabric made of ceramic fibers and metallic fibers. The weave pattern is, for example, 4 / 4 twill. For the warp threads of the fabric, a yarn of the type NEXTEL 610-1500 denier (trade name of 3M Deutschland GmbH, Neuss, Germany) can be used, for example. Ceramic yarns of the type NEXTEL 610-1500 denier and metallic strands made of an FeCrAl alloy with, for example, five cores, each with a diameter of 100 μm, can be used as weft threads. The fabric can, for example, comprise predominantly ceramic fibers. In a 100 mm long edge section of the fabric web, for example, ceramic yarns and metallic strands are used alternately as weft threads.

[0154] The proportion of metallic fibers 10 at the end of the reinforcement layer 4 adjacent to the first tubular element 1 is greater than the proportion of ceramic fibers. In the part of the reinforcement layer 4 adjacent to the second tubular element 2, the proportion of ceramic fibers is greater than the proportion of metallic fibers. The sequence of the weft threads in the edge region of the fabric web and in the direction of the end adjacent to the first tubular element 1 can be, for example, as follows: 10K-1M-6K-1M-4K-1M-3(3K-1M)-4(2K-1M)-8(1K-1M)-4(1K-2M)-3(1K-3M)-1K-4M-1K-6M-1K-10M-1K-10M. Where iK denotes the number i of consecutive ceramic weft threads, jM denotes the number j of consecutive metallic weft threads and n in the specification n(iK-jM) denotes the number of repetitions of the pattern (iK-jM).

[0155] Preferably, the proportion of metal fibers 10 decreases approximately continuously from the end of the reinforcement layer 4 that rests against the first pipe element 1 to the area of ​​the reinforcement layer 4 that rests against the second pipe element 2. In one variant, the reinforcement layer 4 completely surrounds the outer surface of the second pipe element 2. The design with an uneven distribution of the metal fibers has several advantageous effects. The metal fibers 10 can be firmly bonded to the outer surface of the first pipe element 1, e.g., by soldering or welding. Furthermore, the varying proportion of metal fibers in the longitudinal direction of the reinforcement layer means that the reinforcement layer has different thermal expansion coefficients along its length. This prevents stress fracture or detachment of the reinforcement layer from the other components.

[0156] The oxide-ceramic matrix of the ceramic fiber composite material can, for example, be a mixture of 85% aluminum oxide and 15% zirconium dioxide, such as that commercially offered under the name WPS FW12 by Walter EC Pritzkow Spezialkeramik (70794 Filderstadt-Sielmingen, Germany). The thickness of the reinforcement layer 4 in the radial direction is, for example, 2.5 mm.

[0157] To complete the pipe connection, after the ceramic fiber composite material has been applied as a reinforcement layer 4, the component is dried in a drying oven, for example at a temperature of 80°C for a period of 12 hours. The component is then fired in a furnace, for example at a temperature of 1200°C. During the firing process, the diameter of the reinforcement layer 4 is reduced, so that it is pressed firmly against the outer surfaces of the two pipe elements. It has been found that this contact force is sufficient to create a gas-tight connection between the metallic first pipe element 1 and the ceramic second pipe element 2. Fig. 7 and Fig. 8 show in detail two embodiments for sealing the joint between the pipe element 2 and the sleeve 3. Fig. 7 shows a detailed view of the joint between the pipe element 2 and the shrunk-on sleeve 3.The sealing effect is achieved both through the combination of hermetic contact between the outer surface of the tubular element 2 and the inner surface of the sleeve 3 and through a labyrinth effect, which is achieved by reducing the gap width in the gap 13 when the sleeve 3 is shrink-fitted onto the tubular element 2. The advantage of this embodiment is that it requires no auxiliary materials. Fig. 8 shows a detailed view of the joint with a material-to-material connection between the tubular element 2 and the sleeve 3. The adhesive, filler, or solder fills the gap 14 between the outer surface of the tubular element 2 and the inner surface of the sleeve 3 and thus seals the joint. The advantage of this embodiment is that it tolerates a coarser fit between the tubular element 2 and the sleeve 3, which facilitates assembly and reduces manufacturing costs.

[0158] To increase the mechanical stability, the metal fibers 10 at the end of the reinforcement layer 4 can be integrally connected to the outer surface of the first pipe element 1 via a weld seam 9.

[0159] Fig. 2 schematically shows a longitudinal section through a pipe connection according to a second embodiment of the invention. The pipe connection is rotationally symmetrical; the dashed line in Fig. 2 indicates the axis of symmetry. A first pipe element 1 and a second pipe element 2 are connected to each other at their end faces via a sleeve made of a metallic material s.

[0160] The first tube element 1 is made of a metallic material, for example, Centralloy® G 4852 Micro. Its inner diameter is 50 mm, and its outer diameter is 60 mm.

[0161] The sleeve 3 is made of a flexible metallic material, for example, as a strip or foil. The material of the sleeve 3 is, for example, Alloy 800 H (material number 1.4876 according to DIN EN 10027-2). The wall thickness of the sleeve 3 can be, for example, 0.25 mm to 0.3 mm. The sleeve 3 is completely connected to the first tubular element 1 in the circumferential direction. In the example shown, the sleeve 3 is integrally connected to the inner surface of the first tubular element 1 by a circumferential weld seam 8.

[0162] The second tubular element 2 is made of a ceramic material, for example Alsint 99.7. Its inner diameter is, for example, 42 mm, and its outer diameter 50 mm. In this example, the end face of the second tubular element 2 is conically beveled, with the inner diameter of the second tubular element 2 increasing towards its end. In an advantageous variant, the conical end of the second tubular element 2 is metallized by coating its surface with a layer of molybdenum. The molybdenum layer serves as an adhesive base for a material-to-material connection, for example by soldering. The sleeve 3 is materially bonded to the second tubular element 2 at the conical end face and is completely connected in the circumferential direction, for example by soldering. The material of the solder is, for example, Palniro®-4 (trade name of Morgan Advanced Materials plc, United Kingdom).

[0163] A reinforcement layer 4 is applied to the outer surface of the end of the first tubular element 1, the outer surface of the sleeve 3, and the outer surface of the end of the second tubular element 2. The reinforcement layer 4 completely surrounds the ends of both tubular elements in the circumferential direction and at least partially in the longitudinal direction. The reinforcement layer 4 is bonded to both the outer surface of the first tubular element 1 and the outer surface of the second tubular element 2.

[0164] Reinforcing layer 4 is made of a ceramic fiber composite material. The ceramic fiber composite material comprises a hybrid fiber fabric made of ceramic fibers and metallic fibers. The weave pattern is, for example, 4 / 4 twill. For the warp threads of the fabric, a NEXTEL 610-1500 denier yarn can be used, for example. For the weft threads, ceramic yarns of the NEXTEL 610-1500 denier type and metallic strands made of an FeCrAl alloy with, for example, five strands, each with a diameter of 100 μm, can be used. The fabric can, for example, comprise predominantly ceramic fibers. In a 100 mm long edge section of the fabric web, for example, ceramic yarns and metallic strands are used alternately as weft threads.

[0165] The proportion of metallic fibers 10 at the end of the reinforcement layer 4 adjacent to the first tubular element 1 is greater than the proportion of ceramic fibers. In the part of the reinforcement layer 4 adjacent to the second tubular element 2, the proportion of ceramic fibers is greater than the proportion of metallic fibers. The sequence of the weft threads in the edge region of the fabric web and in the direction of the end adjacent to the first tubular element 1 can be, for example, as follows: 10K-1M-6K-1M-4K-1M-3(3K-1M)-4(2K-1M)-8(1K-1M)-4(1K-2M)-3(1K-3M)-1K-4M-1K-6M-1K-10M-1K-10M. Where iK denotes the number i of consecutive ceramic weft threads, jM denotes the number j of consecutive metallic weft threads and n in the specification n(iK-jM) denotes the number of repetitions of the pattern (iK-jM).

[0166] Preferably, the proportion of metal fibers 10 decreases almost continuously from one side of the reinforcement layer 4 to the other side of the reinforcement layer 4. The design with an uneven distribution of the metal fibers has several advantageous effects. The varying proportion of metal fibers in the longitudinal direction of the reinforcement layer results in the reinforcement layer having different thermal expansion coefficients along its length. This prevents stress fracture or detachment of the reinforcement layer from the remaining components.

[0167] The oxide-ceramic matrix of the ceramic fiber composite material can, for example, be a mixture of 85% aluminum oxide and 15% zirconium dioxide, such as that commercially offered under the name WPS FW12 by Walter EC Pritzkow Spezialkeramik (70794 Filderstadt-Sielmingen, Germany). The thickness of the reinforcement layer 4 in the radial direction is, for example, 2.5 mm.

[0168] The reinforcement layer 4 covers both the sleeve 3 and sections of the outer surface of the first pipe element 1 and the second pipe element 2 completely in the circumferential direction and partially in the axial direction.

[0169] To complete the pipe connection, the component is fired in a furnace after the ceramic fiber composite material has been applied as a reinforcement layer 4, for example, at a temperature of 1250°C. During the firing process, the diameter of the reinforcement layer 4 is reduced, so that it is pressed firmly against the outer surfaces of the two pipe elements. It has been found that this contact force is sufficient to create a gas-tight connection between the metallic first pipe element 1 and the ceramic second pipe element 2.

[0170] To increase the mechanical stability, the metal fibers 10 at the end of the reinforcement layer 4 are integrally connected to the outer surface of the first pipe element 1 via a weld seam 9.

[0171] Fig. 3 schematically shows a longitudinal section through a pipe connection according to a third embodiment of the invention. A first pipe element 1 and a second pipe element 2 are connected to each other at their end faces via a sleeve made of a metallic material 3.

[0172] The first tubular element 1 is made of a metallic material, for example Centralloy® G 4852 Micro. Its inner diameter is 42 mm, for example, and its outer diameter is 55 mm. The sleeve 3 is made of a flexible metallic material, for example as a strip or foil. The material of the sleeve 3 is platinum, for example. The wall thickness of the sleeve 3 can be 0.25 mm to 0.3 mm, for example. The sleeve 3 is completely connected to the first tubular element 1 in the circumferential direction. In the example shown, the sleeve 3 is materially connected to the outer surface of the first tubular element 1 by a circumferential solder joint 8. The material of the solder joint 8 can be Palniro®-4, for example.

[0173] The second tubular element 2 is made of a ceramic material, for example, Alsint 99.7. Its inner diameter is, for example, 42 mm, and its outer diameter is 50 to 55 mm. In this example, the outer diameter of the second tubular element 2 increases toward its end. The sleeve 3 is recessed into the end face of the second tubular element 2 and is thus completely connected to the second tubular element 2 in the circumferential direction.

[0174] A reinforcement layer 4 is applied to the outer surface of the end of the first pipe element 1 and the outer surface of the end of the second pipe element 2, completely encompassing the ends of both pipe elements in the circumferential direction and at least partially in the longitudinal direction. The reinforcement layer 4 also completely covers the sleeve 3. The reinforcement layer 4 is bonded to both the outer surface of the first pipe element 1 and the outer surface of the second pipe element 2.

[0175] Reinforcing layer 4 is made of a ceramic fiber composite material. The ceramic fiber composite material comprises a hybrid fiber fabric made of ceramic fibers and metallic fibers. The weave pattern is, for example, 4 / 4 twill. For the warp threads of the fabric, a NEXTEL 610-1500 denier yarn can be used, for example. For the weft threads, ceramic yarns of the NEXTEL 610-1500 denier type and metallic strands made of an FeCrAl alloy with, for example, five cores, each with a diameter of 100 μm, can be used. The fabric can, for example, comprise predominantly ceramic fibers. In a 100 mm long edge section of the fabric web, for example, ceramic yarns and metallic strands are used alternately as weft threads.

[0176] The proportion of metallic fibers 10 at the end of the reinforcement layer 4 adjacent to the first pipe element 1 is greater than the proportion of ceramic fibers. In the part of the reinforcement layer 4 adjacent to the second pipe element 2, the proportion of ceramic fibers is greater than the proportion of metallic fibers. The oxide-ceramic matrix of the ceramic fiber composite material can, for example, be a mixture of 85% aluminum oxide and 15% zirconium dioxide, as is commercially available under the name WPS FW12 from Walter EC Pritzkow Spezialkeramik (70794 Filderstadt-Sielmingen, Germany). The thickness of the reinforcement layer 4 in the radial direction is, for example, 2.5 mm.

[0177] To complete the pipe connection, the component is fired in a furnace after the ceramic fiber composite material has been applied as a reinforcement layer 4, for example, at a temperature of 1200°C. During the firing process, the diameter of the reinforcement layer 4 is reduced, so that it is pressed firmly against the outer surfaces of the two pipe elements. It has been found that this contact force is sufficient to create a gas-tight connection between the metallic first pipe element 1 and the ceramic second pipe element 2.

[0178] In addition to the force-locking connection due to the shrinkage process of the reinforcement layer 4, the overlap of the outer surface of the second pipe element 2, which increases in its outer diameter towards its end, causes a positive connection between the second pipe element 2 and the reinforcement layer 4, which has a beneficial effect on the durability of the pipe connection and reliably prevents the components from slipping apart in the axial direction.

[0179] To further increase the mechanical stability, the metal fibers 10 at the end of the reinforcement layer 4 are integrally connected to the outer surface of the first pipe element 1 via a weld seam 9.

[0180] Fig. 4 schematically shows a longitudinal section through a pipe connection according to a fourth embodiment of the invention. The pipe connection is rotationally symmetrical; the dashed line in Fig. 4 indicates the axis of symmetry. A first pipe element 1 and a second pipe element 2 are connected to each other at their end faces via a sleeve made of a metallic material s.

[0181] The first pipe element 1 is made of a metallic material, for example, Alloy 800 H (material number 1.4876 according to DIN EN 10027-2). Its inner diameter is, for example, 42 mm, and its outer diameter is 50 mm.

[0182] The first tubular element 1 has a widened portion 5, where the inner diameter of the first tubular element 1 increases toward the front end. The transition from the smallest inner diameter of the first tubular element 1 before the widened portion 5 to the largest inner diameter at the end of the widened portion 5 is linear in this example. The resulting cone of the widened portion 5 has, for example, an axial length of 30 mm, and the half-opening angle of the cone is 7.5°.

[0183] The sleeve 3 forms the front end section of the first tubular element 1 and is thus integrally and completely connected to it in the circumferential direction. The wall thickness of the sleeve 3 can be, for example, 0.25 mm to 0.3 mm. The outer diameter of the first tubular element 1 is constant over its entire length. The sleeve 3 and the widened portion 5 can be manufactured, for example, by bringing a milling tool or a turning tool to the front end of the original first tubular element and creating the enlarged inner cross-section of the sleeve 3 and the cone of the widened portion 5 by machining material.

[0184] The first pipe element 1 has, in an area intended to be covered by the reinforcement layer 4, a section with an enlarged outer diameter in the form of a bulge 6. In longitudinal section, the bulge 6 has a sinusoidal shape, with the transitions from the non-enlarged outer surface to the bulge 6 each starting at the minimum of the sinusoidal shape. The sinusoidal bulge 6 has, for example, an amplitude of 5 mm, measured from the non-enlarged outer surface of the first pipe element 1. The sinusoidal bulge 6 has a wavelength of 40 mm, which corresponds to the distance between the two transition points to the non-enlarged outer surface of the first pipe element 1. In the example shown, the shape of the bulge 6 is symmetrical in the longitudinal direction. The bulge 6 is designed to run continuously in the circumferential direction.

[0185] The second tubular element 2 is made of a ceramic material, for example Alsint 99.7. Its inner diameter is 42 mm, for example, and its outer diameter 50 mm. In this example, the outer surface of the second tubular element 2 has a reduced outer diameter in the area covered by the sleeve 3. The end of the second tubular element 2 can be designed over a length of, for example, 20 mm to 50 mm with a diameter of 49 mm and a fit f7, h7 or h8. The reduction in diameter in the area of ​​the fit can, for example, serve to compensate for dimensional deviations or shape deviations of the second tubular element after firing. In the area of ​​the fit, the outer wall of the second tubular element can have a mean roughness Ra according to DIN EN ISO 4287 of less than 1.6 pm. The wall thickness of the sleeve 3 can, for example, be 0.25 mm to 0.3 mm. The length of the sleeve can, for example, be 30 mm to 50 mm.To fasten the sleeve 3 to the outer surface of the second tubular element 2, the inner diameter of the sleeve 3 can be matched to the outer diameter of the outer surface of the second tubular element 2 without any play, so that the sleeve 3 can be pushed precisely onto the end face of the second tubular element 2. The inner diameter of the sleeve 3 can be 49 mm, for example. The inner diameter of the sleeve 3 can be designed with an H7 fit or an H8 fit, for example. In the area of ​​the fit, the inner wall of the sleeve 3 can have a mean roughness Ra according to DIN EN ISO 4287 of less than 1.6 pm.

[0186] In an alternative fastening variant, the sleeve 3 is heated so that it expands, and then, in the heated state, is pushed onto the end face of the second tubular element 2. Optionally, a solder in the form of a foil or paste can be applied to the outer surface of the second tubular element 2 before the sleeve 3 is mounted. After the sleeve 3 has cooled, its inner diameter decreases so that it is shrunk onto the outer surface of the second tubular element 2. The sleeve 3 thus completely surrounds the second tubular element 2 in the circumferential direction and partially in the longitudinal direction.

[0187] Arranged on the outer surface of the sleeve 3 is a reinforcement layer 4 made of a ceramic fiber composite material. The ceramic fiber composite material comprises a hybrid fiber fabric made of ceramic fibers and metallic fibers. The weave pattern is, for example, 4 / 4 twill. For the warp threads of the fabric, a yarn of the type NEXTEL 610-1500 denier can be used, for example. As weft threads, ceramic yarns of the type NEXTEL 610-1500 denier and metallic strands made of an FeCrAl alloy with, for example, five cores, each with a diameter of 100 μm, can be used. The fabric can, for example, comprise predominantly ceramic fibers. In an edge section of the fabric web that is, for example, 100 mm long, ceramic yarns and metallic strands are used alternately as weft threads.

[0188] The proportion of metallic fibers 10 at the end of the reinforcement layer 4 adjacent to the first tubular element 1 is greater than the proportion of ceramic fibers. In the part of the reinforcement layer 4 adjacent to the second tubular element 2, the proportion of ceramic fibers is greater than the proportion of metallic fibers. The sequence of the weft threads in the edge region of the fabric web and in the direction of the end adjacent to the first tubular element 1 can be, for example, as follows: 10K-1M-6K-1M-4K-1M-3(3K-1M)-4(2K-1M)-8(1K-1M)-4(1K-2M)-3(1K-3M)-1K-4M-1K-6M-1K-10M-1K-10M. Where iK denotes the number i of consecutive ceramic weft threads, jM denotes the number j of consecutive metallic weft threads and n in the specification n(iK-jM) denotes the number of repetitions of the pattern (iK-jM).

[0189] The varying proportion of metal fibers along the length of the reinforcement layer results in the reinforcement layer exhibiting different thermal expansion coefficients along its length. This prevents stress fracture or detachment of the reinforcement layer from the remaining components.

[0190] The ceramic matrix of the ceramic fiber composite material can, for example, be a mixture of 85% aluminum oxide and 15% zirconium dioxide, such as that commercially offered under the name WPS FW12 by Walter EC Pritzkow Spezialkeramik (70794 Filderstadt-Sielmingen, Germany). The thickness of the reinforcement layer 4 in the radial direction is, for example, 2.5 mm.

[0191] The reinforcement layer 4 covers both the sleeve 3 and sections of the outer surface of the first pipe element 1 including the bulge 6 and the second pipe element 2 completely in the circumferential direction and partially in the axial direction.

[0192] In the area of ​​the bulge 6, the reinforcement layer 4 can be slit longitudinally, for example, by three, four, five, or six slits evenly or unevenly distributed around the circumference. In such a slitted design, the reinforcement layer 4 thus comprises several individual layers running in the longitudinal direction of the pipe connection. The positive connection between the OCMC reinforcement and the pipe element 1 allows axial forces to be transmitted over a large area. At the same time, the connection is flexible in the radial direction, so that differences in thermal expansion between the pipe element 1 and the OCMC reinforcement can be compensated for without stress.

[0193] After the reinforcement layer 4 has been applied, the component is dried in a drying oven, for example at a temperature of 80°C for a period of 12 hours. To complete the pipe connection, the component is fired in a furnace, for example at a temperature of 1200°C, after the ceramic fiber composite material has been applied and dried as the reinforcement layer 4. During the firing process, the diameter of the reinforcement layer 4 is reduced, so that it is pressed firmly against the outer surfaces of the two pipe elements. It has been found that this contact force is sufficient to create a gas-tight connection between the metallic first pipe element 1 and the ceramic second pipe element 2. Optionally, the sleeve 3 can be integrally bonded to the pipe element 2. Fig. 8 shows a detailed view of the joint with an integral connection between the pipe element 2 and the sleeve 3.The adhesive, filler, or solder fills the gap 14 between the outer surface of the tubular element 2 and the inner surface of the sleeve 3, thus sealing the joint. The advantage of this design is that it tolerates a rougher fit between the tubular element 2 and the sleeve 3, thereby facilitating assembly and reducing manufacturing costs.

[0194] In addition to the force-locking connection due to the shrinkage process of the reinforcement layer 4, the covering of the bulge 6 with its changed outer contour causes a form fit between the first pipe element 1 and the reinforcement layer 4, which has a beneficial effect on the durability of the pipe connection and reliably prevents the components from slipping apart in the axial direction.

[0195] Fig. 5 shows a schematic detailed view of a longitudinal section through a portion of a first tubular element 1 having a region with an enlarged outer diameter in the form of a bulge 6. The bulge 6 shown in Fig. 5 differs from that shown in Fig. 4, among other things, in that it is asymmetrical in the longitudinal direction and its shape in the longitudinal direction resembles a non-equilateral triangle.

[0196] The difference between the non-enlarged outer diameter of the first tubular element 1 and the largest diameter of the bulge 6 is designated "dh" in Fig. 5. It can, for example, range from 3 mm to 20 mm.

[0197] Since the shape of the bulge 6 is asymmetrical in the longitudinal direction, it has a shorter flank (in Fig. 5, to the right of the largest diameter of the bulge) and a longer flank (in Fig. 5, to the left of the largest diameter of the bulge). The transitions from the non-enlarged outer surface to the bulge 6 are rounded, with the radii of the rounding ranging from 1 mm to 3 mm.

[0198] The pitch angle of the shorter flank of the transition from the non-enlarged outer diameter of the first pipe element 1 to the largest outer diameter of the bulge 6 is designated by (p) in Fig. 5. It can be calculated, for example, from the diameter difference dh and the axial length of the shorter flank, designated as “dl” in Fig. 3, as (p) = arctan(dh / dl). The pitch angle (p) is, for example, 18°. Fig. 6 shows a schematic longitudinal section through a pipe connection according to a fifth embodiment of the invention. The pipe connection is rotationally symmetrical; the dashed line in Fig. 6 designates the axis of symmetry. A first pipe element 1 and a second pipe element 2 are connected to one another at their end faces via a sleeve made of a metallic material s.

[0199] The first tube element 1 is made of a metallic material, for example, Centralloy® G 4852 Micro. Its inner diameter is 42 mm, and its outer diameter is 50 mm.

[0200] The first tubular element 1 has a widened portion 5, where the inner diameter of the first tubular element 1 increases toward the front end. The transition from the smallest inner diameter of the first tubular element 1 before the widened portion 5 to the largest inner diameter at the end of the widened portion 5 is linear in this example. The resulting cone of the widened portion 5 has, for example, an axial length of 30 mm, and the half-opening angle of the cone is 7.5°.

[0201] The sleeve 3 covers approximately half of the area of ​​the expansion 5 in the longitudinal direction. The material of the sleeve 3 is, for example, Alloy 800 H (material number 1.4876 according to DIN EN 10027-2).

[0202] The wall thickness of the sleeve 3 can be, for example, 0.25 mm to 0.3 mm. The sleeve 3 can be prefabricated, for example, by suitably turning a thick-walled tube or a cylindrical rod. The length of the sleeve 3 can be, for example, 30 mm to 50 mm. The inner diameter of the sleeve can be, for example, 49 mm. The inner diameter of the sleeve can, for example, be designed with an H7 fit or an H8 fit. In the area of ​​the fit, the inner wall of the sleeve 3 can have a mean roughness Ra according to DIN EN ISO 4287 of less than 1.6 pm.

[0203] The sleeve 3 is completely connected to the first tubular element 1 in the circumferential direction. In the example shown, the sleeve 3 is integrally connected to the outer surface of the first tubular element 1 by a circumferential weld seam 8.

[0204] The second tubular element 2 is made of a ceramic material, for example Aising 99.7. Its inner diameter is, for example, 42 mm, and its outer diameter 50 mm. In this example, the outer surface of the second tubular element 2 has a reduced outer diameter in the area covered by the sleeve 3. The end of the second tubular element 2 can be designed over a length of, for example, 20 mm to 50 mm with a diameter of 49 mm and a fit f7, h7 or h8. In the area of ​​the fit, the outer wall of the second tubular element can have a mean roughness Ra according to DIN EN ISO 4287 of less than 1.6 pm.

[0205] To fasten the sleeve 3 to the outer surface of the second tubular element 2, the inner diameter of the sleeve 3 can be matched to the outer diameter of the outer surface of the second tubular element 2 without any play, so that the sleeve 3 can be pushed precisely onto the end face of the second tubular element 2. In an alternative variant of the fastening, the sleeve 3 is heated so that it expands and is then pushed onto the end face of the second tubular element 2 in the heated state. After the sleeve 3 has cooled, its inner diameter decreases so that it is shrunk onto the outer surface of the second tubular element 2. The sleeve 3 thus spans the second tubular element 2 completely in the circumferential direction and partially in the longitudinal direction.

[0206] Optionally, before mounting the sleeve 3, the outer surface of the second tubular element 2, which is to be covered by the sleeve 3, can be coated with a glass solder paste, for example G018-346 (trade name of Schott AG, Germany). Furthermore, optionally, a wire made of solder can be inserted in a ring shape into a groove in the outer surface of the second tubular element 2. The material of the solder ring 7 formed in this way can be, for example, Palniro®-4. Optionally, the sleeve 3 can be glued to the tubular element 2. The assembly paste from the manufacturer INTERFLON with the trade name HT 1200 can be used as the adhesive, for example. Fig. 8 shows a detailed view of the joint with a material-to-material connection between the tubular element 2 and the sleeve 3. The adhesive, the filler compound, or the solder fills the gap 14 between the outer surface of the tubular element 2 and the inner surface of the sleeve 3 and thus seals the joint.The advantage of this embodiment is that it tolerates a coarser fit between the tubular element 2 and the sleeve 3, which facilitates assembly and reduces manufacturing costs.

[0207] Arranged on the outer surface of the sleeve 3 is a reinforcement layer 4 made of a ceramic fiber composite material. In this example, the ceramic fiber composite material comprises a hybrid fiber fabric made of ceramic fibers and metallic fibers. The weave pattern is, for example, 4 / 4 twill. For the warp threads of the fabric, a yarn of the type NEXTEL 610-1500 denier can be used, for example. As weft threads, ceramic yarns of the type NEXTEL 610-1500 denier and metallic strands made of an FeCrAl alloy with, for example, five cores each with a diameter of 100 μm can be used. The fabric can, for example, comprise predominantly ceramic fibers. In an edge section of the fabric web that is, for example, 100 mm long, ceramic yarns and metallic strands are used alternately as weft threads.

[0208] The proportion of metallic fibers 10 at the end of the reinforcement layer 4 adjacent to the first tubular element 1 is greater than the proportion of ceramic fibers. In the part of the reinforcement layer 4 adjacent to the second tubular element 2, the proportion of ceramic fibers is greater than the proportion of metallic fibers. The sequence of the weft threads in the edge region of the fabric web and in the direction of the end adjacent to the first tubular element 1 can be, for example, as follows: 10K-1M-6K-1M-4K-1M-3(3K-1M)-4(2K-1M)-8(1K-1M)-4(1K-2M)-3(1K-3M)-1K-4M-1K-6M-1K-10M-1K-10M. Where iK denotes the number i of consecutive ceramic weft threads, jM denotes the number j of consecutive metallic weft threads and n in the specification n(iK-jM) denotes the number of repetitions of the pattern (iK-jM).

[0209] The ceramic matrix of the ceramic fiber composite material can, for example, be a mixture of 85% aluminum oxide and 15% zirconium dioxide, such as that commercially offered under the name WPS FW12 by Walter EC Pritzkow Spezialkeramik (70794 Filderstadt-Sielmingen, Germany). The thickness of the reinforcement layer 4 in the radial direction is, for example, 2.5 mm.

[0210] The reinforcement layer 4 covers both the sleeve 3 and sections of the outer surface of the first pipe element 1 and the second pipe element 2 completely in the circumferential direction and partially in the axial direction.

[0211] To complete the pipe connection, the reinforcement is first dried in a drying oven, for example at a temperature of 80°C for a period of 12 hours. After the ceramic fiber composite material has been applied and dried as a reinforcement layer 4, the component is then fired in a furnace, for example at a temperature of 1200°C. During the firing process, the diameter of the reinforcement layer 4 is reduced, so that the sleeve 3 is pressed firmly against the outer surface of the second pipe element 2. It has been found that this contact force is sufficient to create a gas-tight connection between the metallic first pipe element 1 and the ceramic second pipe element 2. To increase mechanical stability, the metal fibers 10 at the end of the reinforcement layer 4 are integrally connected to the outer surface of the first pipe element 1 via a weld seam 9.

[0212] List of reference symbols

[0213] 1 ... first pipe element

[0214] 2 ... second pipe element

[0215] 3 ... sleeve made of a metallic material

[0216] 4 ... Reinforcement layer

[0217] 5 ... widening

[0218] 6 ... bulge

[0219] 7 ... solder ring

[0220] 8 ... weld or solder joint

[0221] 9 ... weld seam

[0222] 10 ... metal fibers

[0223] 13 ... Gap in shrink-fitted sleeve-pipe connection

[0224] 14 ... Gap in a material-fit sleeve-pipe connection

Claims

Patent claims 1. Pipe connection for the end-face connection of pipe elements comprising a first pipe element (1) made of a metallic material, a second pipe element (2) made of a ceramic material and a reinforcement layer (4) which surrounds the first pipe element (1) and the second pipe element (2) are each completely encompassed in the circumferential direction and at least partially encompassed in the longitudinal direction and are connected both to the outer surface of the first pipe element (1) and to the outer surface of the second pipe element (2), characterized in that the reinforcing layer (4) is made of a ceramic fiber composite material which has a fiber framework which comprises metallic fibers and ceramic fibers, wherein the proportion of metallic fibers at the end of the reinforcing layer (4) adjacent to the first pipe element (1) is greater than the proportion of ceramic fibers, the proportion of ceramic fibers at the end of the reinforcing layer (4) adjacent to the second pipe element (2) is greater than the proportion of metallic fibers, and the fiber framework is embedded in an oxide-ceramic matrix.

2. Pipe connection according to claim 1, characterized in that the first pipe element (1) has a widening (5) in which the inner diameter of the first pipe element (1) increases in the direction of the front end, wherein the outer circumferential surface of the first pipe element (1) is at least partially covered by the reinforcing layer (4) in the region of the widening (5).

3. Pipe connection according to claim 1 or 2, characterized in that the first pipe element (1) has a section with a reduced and / or enlarged outer diameter in an area covered by the reinforcing layer (4).

4. Pipe connection according to claim 3, characterized in that the section has a notch and / or a bulge (6), wherein the difference between the non-reduced outer diameter of the first pipe element (1) and the smallest diameter of the notch is from 0.25 mm to 10 mm, and / or the difference between the largest diameter of the bulge (6) and the non-enlarged outer diameter of the first pipe element (1) is from 0.25 mm to 50 mm.

5. Pipe connection according to claim 3 or 4, characterized in that the pitch angle of the shorter flank in the longitudinal direction of the first pipe element (1) of the transition from the non-reduced and / or enlarged outer diameter of the first pipe element (1) to the smallest outer diameter or to the largest outer diameter in the section from 5° to 60°.

6. Pipe connection according to one of the preceding claims, characterized in that a sleeve made of a metallic material (3) is completely connected to the first pipe element (1) and to the second pipe element (2) in the circumferential direction.

7. Pipe connection according to claim 6, characterized in that the sleeve (3) is connected to the front side of the first pipe element (1), preferably forming the front end section of the first pipe element (1).

8. Pipe connection according to claim 6 or 7, characterized in that the sleeve (3) rests completely in the circumferential direction and at least partially in the longitudinal direction on the inner circumferential surface or on the outer circumferential surface of the second pipe element (2), or is connected to the end face of the second pipe element (2), preferably is connected in a materially bonded manner to the end face of the second pipe element (2) or is embedded in the end face of the second pipe element (2).

9. Pipe connection according to one of claims 6 to 8, characterized in that a circumferential seal is arranged between the outer surface of the second pipe element (2) and the inner surface of the sleeve (3).

10. Pipe connection according to one of the preceding claims, characterized in that the metallic fibers of the ceramic fiber composite material of the reinforcement layer (4) are at least partially accessible on the surface of the reinforcement layer (4) and are integrally connected, preferably welded, to the outer surface of the first pipe element (1).

11. A method for producing a frontal connection of pipe elements comprising the steps: (a) providing a first tube element (1) made of a metallic material and a second tube element (2) made of a ceramic material, (b) applying a reinforcement layer (4) made of a ceramic fiber composite material to the outer surface of the first pipe element (1) and the outer surface of the second pipe element (2), wherein the ceramic fiber composite material has a fiber framework comprising metallic fibers and ceramic fibers, wherein the proportion of the metallic fibers in the the end of the reinforcement layer (4) adjacent to the first pipe element (1) is greater than the proportion of ceramic fibers, the proportion of ceramic fibers at the end of the reinforcement layer (4) adjacent to the second pipe element (2) is greater than the proportion of metallic fibers, and the fiber framework is embedded in an oxide-ceramic matrix, and (c) connecting the reinforcement layer (4) to the outer surface of the first pipe element (1) and to the outer surface of the second pipe element

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