Patent Description:
In order to contact hot or cold fluids, a pipe is often implemented as a double-walled pipe, i.e. a pipe having an inner lumen radially surrounded by an outer lumen, wherein the outer lumen is used for insulating the inner lumen. For instance, liquid hydrogen is kept at very low temperatures (approximately -<NUM>). This requires a good insulation of the inner lumen holding the low-temperature hydrogen.

However, such double-walled pipes require couplings or other connecting ports, which usually provide an interruption of the insulation in a radial direction. For instance, if the coupling includes a flange reaching the inner pipe, the flange creates a heat ingress path. Since this may affect the liquid state of the hydrogen, such ingress should be avoided.

For instance, <CIT> relates to a double pipe joint for cryogenic fluid, wherein a heat insulation cylinder in form of a bellows is arranged between an inner pipe and an outer pipe of the double pipe. <CIT> and <CIT> disclose background technology for pipe couplings.

It is therefore an object of the present disclosure to provide a coupling for a double-walled pipe having a low heat ingress.

This object is solved by the present invention as defined in the independent claim.

According to a first aspect to better understand the present disclosure and only reflecting some of the features of the independent claim, a coupling for a double-walled pipe comprises an inner section and an outer section. The double-walled pipe has an inner wall and an outer wall, the inner wall having an inner lumen, and the inner wall and the outer wall delimiting an outer lumen. A lumen is a space or cavity of a tubular body. The lumen is delimited by one or more hulls or walls, i.e., the hull or wall encloses a volume. The inner lumen may be employed to hold and/or conduct a fluid, such as a gas or liquid. The outer lumen is provided for insulation purposes.

For example, a vacuum may be applied to the outer lumen, as the vacuum has very good insulation capabilities. Alternatively, an inert gas or an insulating material, such as a foam, may be filled into the outer lumen.

The inner section of the coupling forms a passage in fluid communication with the inner lumen. In other words, the inner section is arranged at a longitudinal end of the inner wall, for example, an end where the double-walled pipe is to be connected to another double-walled pipe or the like. The passage of the inner section may have a cross-section of substantially the same (open) area as a cross-section of the inner wall. Thus, the fluid can flow from the inner lumen through the passage without (much) constriction.

The outer section of the coupling is arranged radially adjacent to the inner section. Moreover, a material of the outer section is interrupted in a radial direction multiple times in an area corresponding to a radial range between the inner wall and the outer wall.

A longitudinal direction of the coupling corresponds to a longitudinal direction of the pipe, i.e., an axial direction of the pipe and coupling, which usually coincides with the direction of flow of the fluid through the inner lumen. A radial direction is perpendicular to the longitudinal direction. Usually, a cross-section of the double-walled pipe is in a plane defined by the radial direction. A circumferential direction lies within such plane and is around the longitudinal axis of the pipe.

The material of the outer section being interrupted multiple times in the radial direction means that through the material of the outer section a direct path in the radial direction is not possible. Thus, a heat ingress path is extended compared to a coupling having a continuous material in the radial direction, i.e. being a full block coupling. In order to have a complete interruption of the heat ingress path, the interrupted material forms a through hole in the longitudinal direction, i.e. the material of the outer section is completely interrupted in a cross-section taken along the longitudinal direction.

The outer section comprises one or more pockets forming the interruption of the material of the outer section. A pocket is to be understood as a three-dimensional opening, notch or chamber. Such pocket may have any dimensions in the radial direction, circumferential direction and longitudinal direction. As indicated above, the pocket is open on both sides along the longitudinal direction, in order to avoid a radial heat ingress through material of the outer section. A heat ingress path, hence, can only follow along the sides of the pocket, particularly along a circumferential direction, and in a radial direction only where the pocket has a circumferential end.

The one or more pockets include an inner pocket and a radially outwardly arranged outer pocket. Thus, the inner and outer pocket form two of the multiple interruptions in the radial direction. A heat ingress path can only lie along the circumferential sides of each of the inner and outer pockets, which significantly increases the heat ingress path.

In an implementation variant, the one or more pockets can include a spiral pocket spiralling around a longitudinal direction of the coupling. Thus, when viewing along the longitudinal direction or axial direction and pipe, the pocket spirals in a circumferential direction with increasing diameter.

As a mere example, the spiral pocket has a radial length of less than <NUM>°. The coupling is provided with one or more inner and/or outer pockets and one spiral pocket lying radially inward or outward to the other pockets.

A further exemplary coupling may include only a spiral pocket having a radial length of more than <NUM>°, such as <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>° or more. In other words, the spiral pocket forms a spiral (when viewing in the longitudinal direction) having an overlapping section, there the spiral overlaps itself once, twice, three times, four times or more.

In any case, a spiral pocket allows the heat ingress path only along the corresponding spirally arranged material of the outer section. This leads to a huge increase of the heat ingress path compared to a full block coupling.

In another implementation variant, two or more inner pockets can be arranged adjacent to one another in a circumferential direction. In other words, a circumferential end of one inner pocket is close to a circumferential end of another pocket.

In this case, the coupling can further comprise at least one inner spoke connecting the inner section with the outer section in a radial direction and separating a pair of the two or more inner pockets. In such spoke provides rigidity and stiffness of the coupling, particularly in a radial direction. In addition, when compared to a spiral pocket, the coupling with a spoke is more resistant with respect to warpage or bulging in the longitudinal direction. The heat ingress path may lie along the spoke, but has to circumscribe one of the two or more inner pockets.

In yet another implementation variant, two or more outer pockets can be arranged adjacent to one another in a circumferential direction. In other words, a circumferential end of one outer pocket is close to a circumferential end of another pocket.

As with the two inner pockets and spoke, the coupling can further comprise an outer flange, and at least one outer spoke connecting the outer section with the outer flange in a radial direction and separating a pair of the two or more outer pockets.

In a further implementation variant, the at least one outer spoke can be arranged at a circumferential position deviating from a circumferential position of the at least one inner spoke. In other words, the inner spoke and outer spoke not arranged on a radial line, but are offset on different radial lines, i.e. are offset in circumferential direction. This allows heat ingress path only on a line circumscribing one of the outer pockets, through the outer spoke, circumscribing one of the inner pockets, and through the inner spoke. Thus, the heat ingress path is significantly increased compared to a full block coupling.

In an implementation variant, the coupling can further comprise an insulating barrier arranged in each of the one or more pockets in a fluid tight manner. Irrespective of a pocket along a circumferential line having a continuous radius or a spiral pocket, an insulating barrier can be placed in the pocket and can be fixed therein in a fluid tight manner. The barrier has the same form as the associated pocket. This avoids a fluid connection between both sides of the coupling in a longitudinal direction through the pocket, for example, from the outer lumen of the double-walled pipe to an opposite side of the coupling. Due to the insulating material of the barrier, the heat ingress path will most likely circumscribe the pocket and barrier, as the material of the coupling will have a higher heat propagation than the insulating material.

In another implementation variant, any of the above couplings can have an outer flange configured to be fastened to another flange of a corresponding coupling. For instance, the outer flange may have one or more through holes, through which a fastener, such as a screw or bolt, can fit. The other flange of a corresponding coupling has corresponding through holes receiving such fastener, so that both couplings can be fixed to one another.

In yet another implementation variant, any of the disclosed couplings can have a circumferentially arranged groove configured to receive a seal. Such seal is squeezed between two corresponding couplings, in order to provide a fluid tight inner space in the coupling, and particularly a fluid tight space for the passage in the inner section. For instance, the coupling can comprise one inner groove at the inner section and one outer groove at the outer section or outer flange, each groove configured to receive a respective seal.

According to a second aspect to better understand the present disclosure, but not reflecting the claimed subject-matter, a coupling for a double-walled pipe comprises a pair of inner couplings and a sleeve. The double-walled pipe has an inner wall and an outer wall, the inner wall having an inner lumen, and the inner wall and the outer wall delimiting an outer lumen. The inner lumen may be employed to hold and/or conduct a fluid, such as a gas or liquid. The outer lumen is provided for insulation purposes. For example, a vacuum may be applied to the outer lumen, as the vacuum has very good insulation capabilities. Alternatively, an inert gas or an insulating material, such as a foam, may be filled into the outer lumen.

Each of the pair of inner couplings is mounted to a respective inner wall, wherein the pair of inner couplings is configured to be coupled one another. Thus, the pair of inner couplings is configured to connect two inner pipes of the double-walled pipe. Each of the inner couplings can be configured to provide a fluid tight coupling between the inner pipes.

The sleeve is configured to cover the inner coupling, a portion of the inner wall and a portion of the outer wall. Such sleeve can provide insulation for the inner pipe and the pair of couplings. The sleeve can further provide a continuation of the insulating capabilities of the outer lumen.

This allows a simple coupling of the inner pipes, since the pair of inner couplings can be kept simple. Similar to the insulating capabilities of the outer wall the sleeve provides insulation for the pair of inner couplings.

Furthermore, the outer wall forms a plurality of circumferentially extending pockets, wherein each pair of the plurality of pockets is arranged adjacent to one another in an axially direction of the coupling. Since heat ingress will follow the outer wall even inside of the sleeve, the plurality of pockets increases the length of the outer wall in a longitudinal direction. For instance, when viewing a cross-section along a longitudinal direction, the outer wall has a meandering shape which provides for an increased length of the heat ingress path.

In an implementation variant not covered by the claims, the sleeve can comprise an axial extension fitting on the outer wall in a fluid tight manner, and is configured to hold a vacuum and/or an insulation in a space between the sleeve and the portion of the inner wall and the portion of the outer wall including the pockets. The sleeve may be made of a thin rigid material, so that it forms an empty space between the outer wall and the pair of couplings, on the one hand, and the sleeve, on the other hand. Such rigid material should withstand the vacuum or outer pressure acting on the sleeve.

The axial extension fitting can have the form of a tube or hose snugly fit on the outer wall. Optionally, the axial extension fitting may be pressed onto the outer wall by an associated compression ring, belt, collar, clip or bracket, in order to facilitate fluid tightness.

In a further implementation variant not covered by the claims, the sleeve can comprise a plurality of circumferentially extending protrusions, wherein each protrusion fills a pocket of the outer wall. For instance, the sleeve and/or the protrusions can be made of an insulating material, such as a multilayer insulation MLI, metalized foils, aerogels, microspheres, a foam or the like. This insulating material can have a form corresponding to the pockets in the outer wall, so that each pocket is filled by the insulating material. Preferably, the insulating material also covers the outer wall between the pockets (when viewing along a longitudinal direction).

In yet a further implementation variant not covered by the claims, a cross-section of at least some of the plurality of pockets has a rectangular shape, an omega-shape, a star-shape, a triangular shape, and elliptical shape, and/or a polygonal shape. This cross-section is meant to be along the longitudinal direction. In addition, it is to be understood that each pocket may have its individual shape, all pockets have the same shape, or groups of pockets have respective same shapes. Any of the rectangular shape, omega-shape, star-shape, triangular shape, elliptical shape or polygonal shape increases the length of a line on a surface of the outer wall along the longitudinal direction and, hence, increases a length of the heat ingress path.

The present disclosure is not restricted to the aspects and variants in the described form and order. Specifically, the description of aspects and variants is not to be understood as a specific limiting grouping of features.

In the following, the present disclosure will further be described with reference to exemplary implementations illustrated in the figures, in which:.

It will be apparent to one skilled in the art that the present disclosure may be practiced in other implementations that depart from these specific details.

<FIG> schematically illustrates different views of a first exemplary coupling <NUM> for a double-walled pipe. The double-walled pipe has an inner wall <NUM> defining an inner lumen <NUM>, and an outer wall <NUM>, which together with the inner wall <NUM> delimits an outer lumen <NUM>. Thus, the outer lumen <NUM> encircles the inner wall <NUM>. The inner lumen <NUM> can be used to hold and conduct a fluid, such as a gas or liquid. The outer lumen <NUM> is used to provide insulation to the inner wall <NUM> and inner lumen <NUM>. As a mere example, the inner lumen <NUM> can be used to transport a very cold fluid, such as liquid hydrogen, which is insulated by a vacuum applied to the outer lumen <NUM>.

In order to connect two double-walled pipes to one another in a longitudinal direction, two couplings <NUM> can be mounted to one another face-by-face, as can be derived from the exploded view of the two couplings <NUM> in <FIG>. The following description is directed to one of these couplings <NUM>, while both couplings <NUM> have the same shape and structure and correspond to one another.

The exemplary coupling <NUM> has an inner section <NUM> forming a passage in fluid communication with the inner lumen <NUM>, and has an outer section <NUM> arranged radially adjacent to the inner section <NUM>. The inner section <NUM> may have a rather simple form, such as a ring, which can be connected to the inner wall <NUM>. The inner section <NUM> can be welded, adhered or otherwise connected to the inner wall <NUM>, so that a fluid tight connection between inner wall <NUM> and coupling <NUM> is provided.

The material of the outer section <NUM> is interrupted in a radial direction multiple times in an area corresponding to a radial range between the inner wall <NUM> and the outer wall <NUM>. In other words, the outer section <NUM> comprises one or more pockets <NUM>, <NUM> forming the interruption of the material of the outer section. <FIG> shows four pockets arranged along two virtual concentric rings. Specifically, the one or more pockets <NUM>, <NUM> include an inner pocket <NUM> and an outer pocket <NUM> arranged radially outwardly from the inner pocket <NUM>.

The coupling <NUM> comprises at least one inner spoke <NUM> connecting the inner section <NUM> with the outer section <NUM> in a radial direction. In case of a single pocket, the inner spoke <NUM> separates the circumferential ends of the inner pocket <NUM> from one another. In the example illustrated in <FIG>, two inner pockets <NUM> and two outer pockets <NUM> are provided. The two inner pockets <NUM> are arranged adjacent to one another in a circumferential direction. The inner spoke <NUM> separates a pair of the two or more inner pockets <NUM>. Thus, in the example having two inner pockets <NUM>, two inner spokes <NUM> are formed at the respective circumferential ends of the two inner pockets <NUM>.

Likewise, the exemplary coupling <NUM> comprises at least one outer spoke <NUM> separating circumferential ends of one pocket or separating a pair of two or more outer pockets <NUM> in a circumferential direction. Each outer spoke <NUM> connects the outer section <NUM> with a portion of the coupling being radially outward from the outer section <NUM>. For example, the outer spokes <NUM> connect the outer section <NUM> with an outer flange <NUM> or a tubular portion <NUM>. Such outer flange <NUM> may have the largest extent in the radial direction. The outer flange <NUM> and the tubular portion <NUM> may extend in the radial direction further outward than the outer wall <NUM>.

Furthermore, the at least one outer spoke <NUM> is arranged at a circumferential position deviating from a circumferential position of the at least one inner spoke <NUM>. In other words, when viewing at the front face of the coupling, a circumferential position of the inner spokes <NUM> is offset with respect to a circumferential position of the outer spokes <NUM>. Thus, a heat ingress path starting at the outer flange <NUM> can only go along an outer spoke <NUM> (in radial direction), along the outer section <NUM> between inner and outer pockets <NUM>, <NUM> in the circumferential direction, and along an inner spoke <NUM> (in radial direction again) before reaching the inner section <NUM>. This increased length of the heat ingress path facilitates the insulating capabilities of the coupling <NUM>.

Thus, the outer flange <NUM> can be employed to be connected to another outer flange <NUM> of a corresponding or mating coupling <NUM>. As a mere example, the two outer flanges <NUM> of both couplings can be fixed to one another with a clamp <NUM> (illustrated in the cross-sectional view), such as a V-clamp.

Alternatively, the outer flanges <NUM> can each be a bolted flange (not illustrated in <FIG>), so that the couplings <NUM> can be fastens to one another using a plurality of bolts.

For increased stability of the coupling <NUM>, the coupling <NUM> can comprise the tubular portion <NUM> fitting over the outer wall <NUM>. Such tubular portion <NUM> can be considered as a part of the outer flange <NUM> and/or part of the outer section <NUM>. It provides a certain overlap in longitudinal direction with the outer wall <NUM>, so that an optimal position of the coupling <NUM> at the longitudinal end of the double-walled pipe can be achieved.

When connecting to couplings <NUM> to one another, one or more seals <NUM>, <NUM> can be arranged therebetween. For instance, each coupling <NUM> can include one or more circumferentially arranged grooves <NUM>, <NUM> configured to receive a respective seal <NUM>, <NUM>. Such seal <NUM>, <NUM> is squeezed between two corresponding couplings <NUM>, in order to provide a fluid tight inner space in the coupling <NUM>, and particularly a fluid tight space for the passage in the inner section <NUM>. For instance, the coupling <NUM> can comprise one inner groove <NUM> at the inner section <NUM> and one outer groove <NUM> at the outer section <NUM> or outer flange <NUM>, each groove <NUM>, <NUM> being configured to receive a respective seal <NUM>, <NUM>.

<FIG> schematically illustrates different views of a second exemplary coupling <NUM> for a double-walled pipe. The double-walled pipe and a majority of the features of the coupling <NUM> are identical or at least quite similar to those of the first exemplary coupling <NUM>. Such features common to both couplings <NUM> are indicated by the same reference numerals, and their description is omitted to avoid redundant disclosure.

The second exemplary coupling <NUM> has a plurality of through holes <NUM> in the outer flange <NUM>. Each through hole <NUM> can be used to put a bolt <NUM> therethrough, in order to fasten the coupling <NUM> to a corresponding coupling <NUM> using the bolt <NUM> and a corresponding through hole <NUM>.

Furthermore, the material of the outer section <NUM> is interrupted in the radial direction multiple times. This is achieved by providing one or more pockets including a spiral pocket <NUM> spiralling around a longitudinal direction of the coupling <NUM>. <FIG> illustrates only one spiral pocket <NUM>. It is to be understood that an inner pocket <NUM> and/or an outer pocket <NUM> (see <FIG>) can be arranged radially inside and outside of the spiral pocket <NUM>, respectively. The illustrated spiral pocket <NUM> makes more than three turns, i.e. the spiral pocket <NUM> has a radial length of about <NUM>°, which is to be understood as a mere example. The heat ingress path is, hence, along the likewise spiral outer section <NUM> between the outer flange <NUM> and the inner section <NUM>. This spiral achieves a large increase of the heat ingress path.

<FIG> schematically illustrates a perspective view of a cut-out of a third exemplary coupling <NUM> for a double-walled pipe. The double-walled pipe is not illustrated in <FIG> for clarity reasons. Again, a majority of the features of the third exemplary coupling <NUM> are identical or at least quite similar to those of the first exemplary coupling <NUM>. Such features common to both couplings <NUM> are indicated by the same reference numerals, and their description is omitted to avoid redundant disclosure.

The coupling <NUM> of <FIG> includes one or more pockets <NUM>, <NUM> as well as inner and outer spokes <NUM>, <NUM>. Such pockets <NUM>, <NUM> provide a fluid connection between opposite sides of the coupling <NUM> in a longitudinal direction. Thus, as the pockets <NUM>, <NUM> are arranged in an area corresponding to a radial range between the inner wall <NUM> and the outer wall <NUM>, the pockets <NUM>, <NUM> would allow a fluid to pass from the outer lumen <NUM> to a corresponding outer lumen <NUM> of a coupled double-walled pipe. In case both outer lumens <NUM> are applied with a vacuum, the maintaining of the vacuum may be more difficult as the connected (and hence combined) outer lumen <NUM> is larger.

In case such fluid connection should be avoided, an insulating barrier <NUM>, <NUM> can be arranged in each of the one or more pockets <NUM>, <NUM>. The insulating barrier <NUM>, <NUM> can be arranged in the respective pocket <NUM>, <NUM> in a fluid tight manner, so that any fluid is hindered from passing through the coupling.

As illustrated in <FIG>, such insulating barrier <NUM>, <NUM> can be made longer in the longitudinal direction than the pockets <NUM>, <NUM>. Thus, a heat ingress path can be extended in the longitudinal direction. As a mere example, the insulating barrier <NUM>, <NUM> can have a hollow tubular body which is closed at its longitudinal ends. Thus, the heat ingress path has to follow an inner and outer side of the body around the longitudinal end.

It is further to be understood that <FIG> shows only half of a coupling <NUM> and, hence only portions of the insulating barriers <NUM>, <NUM>. The insulating barriers <NUM>, <NUM> are continuing in a circumferential direction until a further spoke <NUM>, <NUM> is reached, in order to completely close the pocket <NUM>, <NUM>.

<FIG> schematically illustrates a cross-sectional view of a coupling <NUM> for a double-walled pipe in two states not forming part of the claimed invention. Actually, a corresponding pair of couplings <NUM> is illustrated. On the left side, <FIG> illustrates the coupling <NUM> in a connected state, while the right side of <FIG> illustrates the coupling <NUM> in a dissembled state.

The left coupling 300a comprises interruptions in the material of an outer section <NUM> in a radial direction, i.e. comprises pockets <NUM>, <NUM>. Likewise, the right coupling 300b comprises interruptions in the material of an outer section <NUM>, <NUM> in a radial direction, i.e. comprises a pocket <NUM>. When arranged next to each other with a common longitudinal centre axis, the left and right couplings 300a,b have the pockets <NUM>-<NUM> arranged in radially adjacent positions. Thus, each pocket <NUM>, <NUM> and <NUM> is configured to receive a corresponding outer section <NUM>, <NUM> and <NUM>, respectively. In case of the left coupling 300a, an inner section <NUM> is present, and the right coupling 300b has a corresponding pocket <NUM>.

When put together, i.e. when each inner and outer section <NUM>-<NUM> is received in a corresponding pocket <NUM>-<NUM>, the left and right couplings 300a,b can be fastened to one another. As a mere example, corresponding flanges 115a and 115b may be provided, which can be connected by a clamp (not illustrated) or bolts (not illustrated) as in the exemplary couplings <NUM> of <FIG> and <FIG>, respectively. In the connected state (left side of <FIG>) a heat ingress path is achieved that meanders from an outer flange 115a,b along the outer and inner sections <NUM>-<NUM> (i.e. along the pockets <NUM>-<NUM>).

In order to facilitate a fluid tight connection, one or more seals <NUM>, <NUM>, <NUM> can be provided. For example, the longitudinal length of a pocket <NUM>-<NUM> can be (slightly) larger than a longitudinal length of the corresponding inner and outer section <NUM>-<NUM>. In the remaining space, a corresponding seal <NUM>, <NUM>, <NUM> can be introduced.

Such seal <NUM>, <NUM>, <NUM> can form a ring, such as seals <NUM>, <NUM> illustrated in <FIG> and <FIG>.

<FIG> schematically illustrates a cross-sectional view of a coupling <NUM> for a double-walled pipe not forming part of the claimed invention. The double-walled pipe has an inner wall <NUM> defining an inner lumen <NUM>, and an outer wall <NUM>, which delimits together with the inner wall <NUM> an outer lumen <NUM>. Thus, the outer lumen <NUM> encircles the inner wall <NUM>. The inner lumen <NUM> can be used to hold and conduct a fluid, such as a gas or liquid. The outer lumen <NUM> is used to provide insulation to the inner wall <NUM> and inner lumen <NUM>. As a mere example, the inner lumen <NUM> can be used to transport a very cold fluid, such as liquid hydrogen, which is insulated by a vacuum applied to the outer lumen <NUM>.

In order to connect two double-walled pipes to one another in a longitudinal direction, the coupling <NUM> comprises a pair of inner couplings <NUM>, each mounted to a respective inner wall <NUM>. Each of the inner couplings <NUM> can correspond to the inner section of the first to third exemplary couplings <NUM>. The pair of inner couplings <NUM> is configured to be coupled to one another. As a mere example, the pair of inner couplings <NUM> can be fixed to one another by a clamp <NUM> or bolts (not illustrated in <FIG>, but as in <FIG>).

The coupling <NUM> further comprises a sleeve <NUM> configured to cover the inner coupling <NUM>, a portion of the inner wall <NUM> and a portion of the outer wall <NUM>. In other words, the sleeve <NUM> surrounds circumferentially the pair of inner couplings <NUM>, the inner wall <NUM> and the outer wall <NUM>, and covers these components also in the longitudinal direction.

In order to have a fluid tight connection between the respective outer lumens <NUM>, the sleeve <NUM> can comprise an axial extension <NUM> fitting on the outer wall <NUM> in a fluid tight manner. This axial extension <NUM> can be additionally fixed to the outer wall <NUM> by a clamp <NUM>, ring, collar, bracket or the like. Such axial extension <NUM> is provided on both the longitudinal ends of the sleeve <NUM>, one for each outer wall <NUM> of the to-be-connected double-walled pipes.

Furthermore, the outer wall <NUM> forms a plurality of circumferentially extending pockets <NUM> wherein each pair of the plurality of pockets <NUM> is arranged adjacent to one another in an axial direction of the coupling <NUM>. These pockets <NUM> provide for an increased longitudinal length of the outer wall <NUM> from the "normal" (cylindrical) section of the pipe towards the inner couplings <NUM>.

<FIG> schematically illustrates perspective views and corresponding cross sections of an outer wall <NUM> at these pockets <NUM> showing two possible examples of the shape of the outer wall <NUM>. When viewing along a longitudinal direction, a cross-section of at least some of the plurality of pockets <NUM> can have a rectangular shape <NUM>, an omega-shape 65a, a star shape 65b, a triangular shape, and elliptical shape and/or a polygonal shape. <FIG> exemplarily illustrates an omega-shape 65a and a star shape 65b, wherein the star shape 65b has rounded corners.

Any of such cross-sectional shapes of the outer wall <NUM> increase the heat ingress path along the outer wall.

Referring back to <FIG>, the sleeve <NUM> can be configured to hold a vacuum in a space between the sleeve <NUM> and the portion of the inner wall <NUM> and the portion of the outer wall <NUM> including the pockets <NUM>. For instance, the sleeve <NUM> can be formed of a material rigid enough to withstand the vacuum (i.e., the outer pressure).

Alternatively or additionally, the sleeve <NUM> can comprise a plurality of circumferentially extending protrusions <NUM>, each of which fills a pocket <NUM> of the outer wall <NUM>. In other words, the interior space of the sleeve <NUM> can be filled with an insulating material, which has radially inwardly extending protrusions <NUM> filling each pocket <NUM>. Such insulating sleeve <NUM> may be applied, if a vacuum source cannot be provided or a vacuum cannot be maintained.

Claim 1:
A coupling (<NUM>, <NUM>) for a double-walled pipe having an inner wall (<NUM>) and an outer wall (<NUM>), the inner wall (<NUM>) having an inner lumen (<NUM>), and the inner wall (<NUM>) and the outer wall (<NUM>) delimiting an outer lumen (<NUM>), the coupling comprising:
an inner section (<NUM>) forming a passage in fluid communication with the inner lumen (<NUM>); and
an outer section (<NUM>) arranged radially adjacent to the inner section (<NUM>), wherein
a material of the outer section (<NUM>) is interrupted in a radial direction multiple times in an area corresponding to a radial range between the inner wall (<NUM>) and the outer wall (<NUM>),
wherein the outer section (<NUM>) comprises one or more pockets (<NUM>, <NUM>, <NUM>) including an inner pocket (<NUM>) and a radially outwardly arranged outer pocket (<NUM>) forming the interruptions of the material of the outer section (<NUM>),
characterised by each of the one or more pockets (<NUM>, <NUM>, <NUM>) forming a through hole open on both sides along a longitudinal direction of the coupling and having respective ends in a circumferential direction.