The present invention relates to a spacer for a double walled marine conduit. In particular, the invention relates to a spacer for double walled marine conduits with an inner conduit surrounded by a protective outer conduit, such as a Pipe-in-Pipe (PiP) arrangement.

With ever increasing demand for fossil fuels, petroleum companies tab new oil resources continuously. Naturally, since nearly three-quarters of the earth's surface is covered with oceans, a majority of the fossil fuel reserves are located underwater, and hence challenging to reach. Consequently, more and more off-shore oil fields are built with ever increasing technological standards for off-shore drilling, which is a mechanical process to drill a well bore below the seabed. One major challenge of offshore plants is pumping the fossil fuels from the seabed to an oil platform. For many sub-sea developments, this includes issues with maintaining the appropriate fuel temperature within a pipeline infrastructure to avoid the formation of hydrates or wax resulting in a detrimental impact on the pumping process. In recent years, this issue became even more prominent in view of an increasing utilisation of subsea tiebacks, which is a link between a satellite oil field and an existing production facility. Connecting a satellite field to a facility in-place improves the economics of a marginal field as it requires significantly lower initial investment. Tiebacks, therefore, do not require the installation of a new oil platform to the marginal oilfield. Instead new wells are tied back (connect) to the existing oil platforms using long distance conduits, which in some cases may travel for more than a kilometre.

In order to maintain appropriate pipe temperatures over a long distance, it is known in the art to use Pipe-in-Pipe (PiP) solutions, which exhibit superior thermal insulation performance while withstanding high effective axial force exposure. The PiP arrangement consists of an inner conduit for transporting fossil fuels from the seabed to the oil platform, which is sleeved into an outer protective conduit. The outer protective conduit, also known as a "carrier pipe", is designed for mechanical protection of the inner conduit and in particular to withstand both the hydrostatic pressure resulting from the projects' water depth and sea currents present at the sub-sea wellbore. The inner conduit is arranged inside the outer protective conduit and spaced from the inner surface of the outer conduit by means of spacers, which are clamped at discrete intervals along the outer surface of the inner conduit. The spacers, which are also known as "centralisers", are commonly arranged to keep the inner conduit centred within the outer protective conduit in an insulating manner.

Spacers known in the art include so-called "bow-spring centralisers", which are metal strips shaped like a hunting bow and attached to the outer surface of the inner conduit, wherein the spring tension is used to distance the outer surface of the inner conduit from the inner surface of the outer protective conduit. A known problem with these common centralisers is that the metallic structure has limited insulation properties and adds unnecessary weight to the PiP assembly. Other prior art centralisers include plastic rings which can fail to withstand the high temperature conditions of off-shore oil pumps and often involve high manufacturing costs.

In view of the above, it is an object of the present invention to provide a centraliser for a double walled marine conduit, which is easy and cost efficient to produce and able to withstand the high pressure and high temperature demands of modern off-shore oil platforms.

In a first embodiment, the invention relates to a spacer for a double walled marine conduit with an inner conduit surrounded by a protective outer conduit. The spacer comprises a main body adapted to surround at least a part of the inner conduit of the marine conduit, wherein the body comprises an inner surface and an opposite outer surface. The spacer further comprises a heat barrier having an inner surface adapted to engage the inner conduit of the marine conduit and an opposite outer surface shaped to align with the inner surface of the body part, wherein the main body is made of a first material different to a second material of the heat barrier, and wherein the second material is more heat resistant than the first material.

The spacer of the present invention is constructed from at least two different materials, the first of which is suited for mechanical stability and forms the main body. The main body preferably makes up more than 50%, preferably more than 80%, of the volume, i.e. the major part, of the spacer. The mechanically robust first material of the main body is preferably a relatively low cost material, whereas the heat barrier is made from a, normally, more expensive second material, which can withstand the high temperature stresses of modern offshore oil production sites and exhibits excellent heat insulation properties. The spacer is constructed such that the main body is only in contact with the outer protective tube of the conduit and adapted to align the conduits with respect to each other. The heat barrier is a heat resistant lining, which - in use - is arranged between the outer surface of the inner conduit and the main body, and shields the main body from the high temperatures of the inner conduit. Since the material of the heat barrier is usually more expensive than the material of the main body, the heat barrier is constructed with as little material as possible, i.e. just enough material to provide for sufficient heat insulation. The mechanical stresses, on the other hand, are almost entirely absorbed by the main body.

In this disclosure, the terminology, "more heat resistant", refers to the fact that the second material is able to withstand the temperatures of the inner conduit, that is the ability of the second material to resist and remain unaffected by the heat present along the outer surface of inner conduit during use. In some embodiments, the second material may additionally have a lower thermal conductivity than the first material and/or a lower coefficiency of expansion than the first material.

According to another aspect of the present invention, the heat barrier may be releasably mounted to the main body. It is thus possible to adapt the spacer to the specific heat insulation requirements of the particular sub-sea oil pump, while the shape and the material of the main body may not need to be changed for a variety of different pipes. Of course, it is also feasible to permanently mount the heat barrier to the main body, for example by virtue of an adhesive or welding. In another alternative, the heat barrier could be separate from the main body and only attached to the main body and an outer surface of the inner conduit by means of a clamping force exerted by the main body.

In another embodiment, the first material of the heat barrier comprises any one or more of a polyimide, a polyamide imide, PEK, PEEK, PEKK, PPSU, or PSU. The invention is not limited to the particular material of the heat barrier and the skilled person would understand that a material, which is suitable to withstand the high temperatures of the inner conduit, is generally suitable. It is generally preferred to use plastic materials, which are easy to form into the shape of the heat barrier and can be attached to the material of the main body by means of an adhesive or welding. However, as detailed above, it should be noted that the heat barrier is preferably releasably mounted to the main body and may only optionally be fixed permanently (adhesive, welding, etc.) to the main body. The first material of the heat barrier may comprise glass filled PEEK, which will deliver enhanced mechanical performance, while providing the necessary temperature resistance. While glass filled PEEK is a particular example of a suitable first material, it is also feasible to use other reinforced plastics for constructing the heat barrier.

According to another embodiment, the second material of the main body comprises polypropylene and/or polyethylene. In particular, the second material of the main body may comprise nylon, which exhibits excellent mechanical stability at low cost.

According to another aspect of the present spacer, the inner surface of the main body comprises a recess adapted to receive at least part of the heat barrier such that the inner surface of the heat barrier protrudes beyond the inner surface of the main body. Consequently, the heat barrier will be received within the recess of the main body in a form fitting manner which will avoid slippage of the main body and the heat barrier with respect to each other. Alternatively, or in addition to the recess, the heat barrier may be affixed to the main body by virtue of an adhesive or welding to avoid slippage.

The main body and the heat barrier may comprise a cylindrical shape. However, it should be understood that the shape of the main body and the heat barrier is always adapted to fit the shape of the inner and outer conduits of the respective double walled marine conduit, which is generally tubular for conventional Pipe-in-Pipe solutions.

In accordance with another embodiment of the present invention, the main body is designed as a clamping member, which comprises first and second separate body parts. In particular, the first and second body parts comprise identical shapes and can be attached to each other by means of fastening members, such as screws, to attach the main body and the heat barrier to the outer surface of the inner conduit via the clamping force of the first and second body parts.

The first and second body parts may comprise at least one through hole adapted to receive a fastening member for releasably attaching the first and second body parts to each other at a first end. At another end, the first and second body parts may be attached to each other by means of a hinge or another fastening member, which can be received within a second through hole that is designed substantially identical to the first through hole.

In another aspect, the first and second body parts comprise at least one counterbore adjacent to the at least one through hole. The counterbore can be used to fully receive the fastening member, such that no part of the fastening member protrudes beyond the outer surface of the main body, and thus will not affect alignment of the main body with the inner surface of the outer protective conduit.

In yet another embodiment of the present invention, the heat barrier may comprise first and second separate parts, which is particularly useful if the main body is constructed as a two piece assembly. The first and second parts of the heat barrier may comprise identical shapes, which are preferably in alignment with the shape of the main body parts.

The present invention further relates to a double marine conduit comprising an inner conduit adapted to transport fluid from a sub-sea well to a floating platform and a protective outer conduit surrounding the inner conduit and adapted to protect the inner conduit from mechanical stresses. The double walled marine conduit of the present invention comprises a plurality of the aforementioned spacers located between the inner and outer conduit such that the outer surface of each main body contacts an internal surface of the outer conduit and the inner surface of each heat barrier contacts an outside surface of the inner conduit.

According to another aspect, the double walled marine conduit may comprise a thermal insulation arranged adjacent to the plurality of spacers, between the interior surface of the protective outer conduit and the outside surface of the inner conduit.

For a further understanding of the nature and objects of the present invention, reference is made to the following detailed description, in which like elements may be given the same or analogous reference numbers, and wherein:

FIGURE 1 is a schematic perspective view of a first embodiment of a spacer 1 according to the present invention; FIGURE 1 shows a first embodiment of the spacer of the present invention. The spacer 1 has a substantially ring-shaped construction with a main body 2, surrounding a heat barrier 3. As shown, the main body 2 and the heat barrier 3 comprise a cylindrical shape, wherein the main body is depicted with a slightly wider construction than the heat barrier 3. It should be understood, however, that the heat barrier 3 could also have the same width or a greater width than the main body 2. The outer surface (not shown) of the heat barrier 3 is aligned with the inner surface 21 of the main body 2, such that the inner surface 31 of the heat barrier 3 protrudes beyond the inner surface 21 of the main body 2. In other words, the inner surface 31 of the heat barrier 3 represents the inner surface of the spacer 1.

The main body 2, which is generally made of a cheaper first material, constitutes more than 50%, preferably more than 80%, of the volume of the main body 2, while the more expensive heat barrier is constructed as a liner using as little of the second, more costly material as possible.

In the embodiment shown in Figure 1, the heat barrier 3 is attached to an even inner surface 21 of the main body 2. However, as mentioned before, it is equivalently feasible to introduce a recess into the inner surface of the main body, which will receive parts of the heat barrier.

The heat barrier 3 and the main body 2 are shown in a two-piece construction with identical halves 2a, 2b and 3 a, 3b. The identical halves 2a and 2b of the main body 2 can be attached to each other by means of fastening members 27 and nut 28, which are received within counterbores 26a, 26b so as not to protrude beyond the outer surface 22 of the main body 2. By tightening nut 28 of the fastening member 27, flange faces 25 of the halves 2a, 2b are drawn into engagement with each other, thereby pressing the inner surface 31 of the heat barrier 3 onto an outside surface of the inner conduit (not shown).

The disclosure and description of the invention is illustrative and explanatory of a preferred embodiment of the invention and variations thereof. It will be appreciated by those skilled in the art that various changes in the design may be made without departing from the spirit of the invention. In particular, the spacer may be made of a one-piece main body and/or heat barrier, which is elastically deformable so as to adapt to the shape of the inner conduit.