The invention concerns a coating/hood for pipelines for subsea transport of liquid and gas having a high temperature, and transport in other extreme environment, such as arctic and tropical environment The pipelines can transport oil, gas, water and other liquid material (media) having a temperature up to 180 °C to and from subsea wells or other sources The pipes are also suitable for water transport to water-poor areas A continuous pipe is situated on the sea bed, or can float freelv in a desired depth and cross larger faults without being dependent upon following the sea bed The pipes are also suited in arctic and tropical regions, above and below the surface The continuous pipeline is a steel pipe having a coating/ hood that gives the necessary negative buoyancy, while the coating/hood serves as corrosion protection, shock and other external strain, is thermal storing and thermal isolating, and is well suited in cold as well as in hot enwronment The pipes with coating/hood have such a quality that they can be coiled up on a large drum and subsequently be rolled out w ithout any damage

Today, no systems are known that can fulfill the requirements ior corrosion protection, thermal isolation thermal storing and thermal resistance at temperatures up to 180 °C Prior art neither ha\ e the properties mentioned above, at the same time as the coating/hood gives the necessary buoyancy If this new invention is used in connection with pipelines in maritime arctic or tropical environment, a product is achieved that is the only one having the properties that are mentioned above, and which may be coiled up on a drum and be rolled out without pipe or coating/hood is damaged The invention provides a pipeline having a coating/hood that has a very long lifetime, is corrosion protecting, thermal storing and thermal isolating, and has a thermal resistance that fulfill the requirements for tubes that should transport media having a temperature up to 180 °C

The invention has a coating/hood of polymeric concrete (2), which is an elastic material containing a filler material with high specific gravity and ability for thermal storing T he filler material ma> comprise up to 95 % of the polymeric concrete

The invention utilizes pol) mers that give a very good attachment to the steel pipe and to the filler material, and thus the filler material can comprise up to 95 % of the

polymer concrete, in contrast to the use of rubber or similar as attachment material. Iron ore (magnetite) is used, which is a lot cheaper than refined ore/material, and a coating/hood is achieved that is price competitive to known coating/hoods and provide properties as corrosion protection, elasticity and thermal isolation, resistance and storing, as no previously known coating/hoods have.

In the following the production method for the invention is described, with reference to the drawings, wherein

Fig. 1 shows a longitudinal section of the pipe,

Fig. 2 shows a section in larger scale, and Fig. 3 shows the invention with an external coating/hood of foamed thermal plastic (5).

Provision of coating/hood is performed by the steel pipe is located in vertical/sloping position and the plastic pipe is tread on the outside. Both pipes are held firmly so that a space is formed between the steel pipe and the plastic pipe, with the steel pipe in the centre of the plastic pipe. The space is filled with a material 2 comprising a polymer with added hardener with up to 95% filler material, preferably magnetite.

In Fig. 1 is shown the steel pipe 1 with an added protective coating/hood 2 according to the invention. The polymer concrete 2 has an external plastic pipe that during production is used as sheathing. After hardening, a layer of foamed thermal plastic 5 is added, having a thickness that is varying according to the requirements to the properties of the pipe and external environments.

The plastic pipe 3 is made of a material that has a great ability to withstand the stress it is subjected to, for example tension, shock, stroke and pressure. Thermal plastic seems to be a suited material. That is also very durable. The plastic pipe 3 can have a bead 4 on its inner wall, formed as a spiral. The bead 4 forms a foundation for the plastic pipe 3 in the polymer concrete 2 that sticks to the surface of the inner wall of the steel pipe, si that no displacement will occur between the plastic pipe 3, the polymer concrete and the steel pipe 1 , if extra security is required. As the attachment between the polymer concrete 2 and the plastic pipe 3 is sufficiently solid, a bead 4 is no absolute requirement.

The thickness of the polymer concrete 2 is dependent upon the diameter of the steel pipe 1 and the thickness of the wall, and the temperature in the medium that shall be transported. The thickness of the polymer concrete 2 varies from 20 to 100 mm, dependent upon the desired thermal storing and isolation of the coating/hood. The thickness of the plastic pipe is not of great importance, as it mainly act as sheathing during production.

After a sandblast to achieve an acceptable corrosion protection and attachment, prior pipes with coating/hood made of concrete are applied a very thin layer of epoxy powder in a high temperature, and a layer of glass-fibre armed epoxy tar. According to present invention, this step may be omitted if desired, and thus the production costs van be reduced.

The protective coating/hood according to the invention is applied by the plastic pipe 3 is tread on to the steel pipe 1 , after the steel pipe is sandblast and optionally coated with a layer of epoxy powder, hardened before the plastic pipe is applied. The space between the plastic pipe and the steel pipe is filled with filler material having a high specific gravity and a great ability to thermal storing, crushed after a certain sieve curve, making it possible to fill the space with up to 95 % of filler material. Subsequently, a thinly liquid polymer with a hardener is injected, filling the space to 100 % . After hardening, foamed thermal plastic 5 is added by means of an extruder. The production can also be performed by the filler is crushed in fine particles and mixed in a polymer with the weight percentage mentioned above, and then is filled or injected in the space between the plastic pipe and the steel pipe. This will lead to hardening to a polymer concrete having the same properties as with the production method described above. It seems that, practically and economically, the most favourable material to use as a filler material in the polymer concrete, is magnetite.

If desired, the invention sets no limit for using materials having a great specific gravity, for example olivine, titanium, lead or other material having a great ability to act as thermal storage. As mentioned previously, the invention can be used for pipes situated on the sea bed, but also in pipes in a free span in desired depth and above faults on the bottom. The coating/hood has superior properties in relation to prior coating/hoods in relation

to water penetration and mechanical strength. It can endure strokes, shock, pressure, tension and vibration in a way that so far is unknown for the conventional coating/hood, in addition to the properties corrosion protection, thermal storage, resistance and isolation. The water penetration is zero. The invention is especially well suited as riser from wellheads for production platforms.