NO346277B1

NO346277B1 - Weigthed pipe

Info

Publication number: NO346277B1
Application number: NO20200603A
Authority: NO
Inventors: Steinar Tragethon; Sverre Tragethon
Original assignee: Hallingplast As
Priority date: 2020-05-20
Filing date: 2020-05-20
Publication date: 2022-05-23
Also published as: NO20200603A1

Description

Weigthed pipe

The present invention relates to a pipe having an outer casing according to the preamble of patent claim 1, and a method for adjusting the weight according to patent claim 8.

Pipelines, for instance for drinking water from a water cleaning plant to households, may be several kilometers long, and may have to cross rivers, lakes and fjords. The pipeline should be lowered into the water, and installed on the seabed in order to avoid any risks or troubles with boats, vessels, and/or persons. Further, when the pipeline is resting on the seabed, stress and tension on the pipeline is reduced to a minimum. Submerged pipelines are also used offshore to transport hydrocarbons for instance from a platform or drill site to vessels or to the shore, and even fiber cables and optical cables are sometimes submerged or installed at the seabed when crossing lakes, rivers and the like.

Pipelines of plastic, such as PP (polypropylene) or PE (polyethylene) have a density of less than 1, and thus they float in water even if they are filled 100% with water. This is a well known problem especially related to pipes transporting fluids, and weights are often attached to the outside of the pipelines, such as described in US3267969. However, there is a problem during installation, as it is a time consuming and accurate work to attach the weights at the correct site, and precautions must be taken to prevent that the weights are moving along the pipe during installation. The weights also represent a problem later as water current may displace the weights and thus create stress and tension to the pipeline. Yet another problem is that the weighs give the pipeline an uneven surface, and other equipment, such as anchors or fishing tools, may get entangled in the weights and cause damage to the pipe, weight and/or fishing tools. If more pipelines are running in the same area, care must be taken to avoid that the weights of one pipeline breaks or interferes with another pipeline.

Another well known solution to the buoyancy problem, is to coat the pipelines with a coating enriched with metals or minerals, such as described in for instance US 4606378 or US4198450. Such coatings are often stiff and hard, and the flexibility of the pipeline is reduced. If the seabed is not sufficiently straight, a pipeline being too stiff will not follow the seabed but will be partly raised above. Further, if the pipeline is too stiff it can not be lowered by the same method as non-coated pipes, and requires special attention. SU1448157 and GB2269877 describes two other pipes, also being too stiff. Another problem with coatings, such as coating described in NO335676, is related to the maximum weight which may be added. A pipe having a larger diameter needs more weight than a pipe having a smaller diameter, and thus the needed thickness of the coating increases as the diameter of the pipe increases. However, these coatings are normally extruded onto the pipe, and the manufacture will be problematic as the thickness increases.

Yet another problem related to the known pipes is that the lifetime of weights and/or coating are shorter than the lifetime of a pipe. The most used weight is concrete having reinforcements of iron, but during time the concrete may crack and the reinforcement corrode which will reduce the lifetime of the weight. The weights are fastened to the pipe by fastening means, and these may have yet another lifetime. If a coating is used rather than a weight, the coating may dissolve over time, it may be broken or damaged by the surroundings and thus the lifetime may be reduced. The location of the pipe, surroundings such a sea water, fresh water, current and depth will also influence the lifetime of the weight, fastening means and/or coating while the lifetime of the pipe remains substantially the same. The weight, fastening means and/or coating may thus need to be replaced before the pipe. This is time a consuming and labour intensive work.

Thus there is need for a flexible pipeline having weight higher than water, but without the problems mentioned above. Further, there is a need for a pipeline having adjustable weight, in such a way that the same type of pipeline may be used in relation to several cases having buoyancy problems. Even further, there is a need for a pipeline which may be used at all sites, both above and below the water, and even during the lowering into the water.

Summary of the invention

The objects above are met by a pipe and a method according to the characterizing part of the independent claims 1 and 8. Further features are stated in the corresponding dependent claims 2-7 and 9-10.

The invention is related to a pipe comprising an outer casing, wherein the casing is arranged at a distance around the pipe, leaving an annulus between the pipe and the casing. The annulus comprises granular material having a specific gravity larger than water.

The pipe may be any pipe suitable for the intended purpose, such as water pipes, both for drinking water and drainage or sewage water, hydrocarbon pipes, gas pipes and pipes for cables. A skilled person would know which pipe and pipe characteristics would be needed for the intended use and environment. The size, thickness and flexibility of the pipe will also depend on the intended use, and be adapted for every project. In the following we will refer to water pipes, but the scope of the claims are not limited to this.

Water pipes are preferably made of PE (polyethylene) having a density larger than 0,9, such as 0,96, which will make them float in water. The size and thickness of the pipe will of course influence the flexibility of the pipe, however, water pipes are normally sufficiently flexible to bend from the surface of the water to the seabed. In the context of this application, "flexibility of a pipe" is related to how much the pipe can bend in a curve, without reducing the inner diameter, and without breaking.

The casing of the pipe should be made of any suitable material, being sufficiently strong to keep the granular material in the annulus and protect the pipe from any forces acting on it from the environment. In a preferred embodiment, the casing is a second pipe having the same characteristics as the pipe, and a preferred material of the casing is PE, preferably having a density larger than 0,9, such as 0,96.

The casing is arranged at a distance around the pipe, meaning that the inner radius of the casing is larger than the outer radius of the pipe, and that the pipe is running axially through the casing. The length of the casing may be equal to the length of the pipe, or the pipe may be longer than the casing, wherein the casing only surrounds an axial part of the pipe.

The difference between the inner radius of the casing and the outer radius of the pipe is the size of the annulus when the casing is arranged around the pipe. The size of the annulus is determinant for the amount of granular material which may be added to the annulus, and affects thus the maximum weight which may be added to the pipe.

In an alternative embodiment, a cross section of the casing is not circular, and thus the size of the annulus between the casing and the pipe is not equal around the periphery of the pipe.. The term "annulus" should be interpreted to mean the volume between the outside of the pipe and the inside of the casing, once the casing is arranged around the pipe. In any of these embodiments, the amount of granular material may not be equally distributed around the pipe.

When the pipe is submerged in water, and water current and/or tide is acting on it, it must be sufficiently heavy to keep its position and not be displaced. Further, if air/gas is partly or fully flowing in the pipe, the pipe will increase its buoyancy, and start to rise. The granular material may be any material having a specific gravity larger than water, and is added to the annulus to increase the weight of the pipe, to avoid such displacement and/or rising. The amount of material needed to be added is both related to specific gravity of the material, the expected buoyancy of the pipe when gas/air is flowing through it, and the water current conditions at the site of submerging. Such calculations are well known to a skilled person, and often expressed as percentage of the pipe filled with air, or a percentage of the displaced water.

The annulus may be partly or fully filled with granular material, but it should not be packed, as the material should be allowed to move in relation to each other.

Therefore, the material should not change the flexibility of the pipe substantially. The flexibility of PE pipes is calculated on the basis of the outer diameter, and in this case the flexibility should thus be calculated on the basis of the outer diameter of the casing, regardless of the amount and type of granular material. Any remaining space of the annulus may be filled with water when the pipe is submerged.

The granular material should preferably have a size less than 1/2, preferably less than 1/3 of the distance between the casing and the pipe, that is the difference between the inner radius of the casing and the outer radius of the pipe should be at least 2 preferably 3 times the average size of the granular material. In a preferred embodiment, the distance between the casing and the pipe is about 25 mm, and the size of the granular material is 2-6 mm. The inner radius of the casing and the size of the granular material must thus be chosen in relation to each other, in order to achieve the desired weight of the pipe.

A preferred material is minerals such as Olivine and/or barite, but rocks such as granite, marble and/or shale may also be used. Even granular plastics and rubber having a specific gravity larger than water may be used. Metals may also be used, but if the annulus is filled with water, the metals may corrode. In an alternative embodiment, the granular material is replaced by a liquid having a specific gravity larger than water.

In a preferred embodiment, end pieces are fastened at the ends of the casing, preferably between the casing and the pipe. The end pieces are configured to fasten the casing to the pipe and keep the granular material inside the annulus. In a preferred embodiment, the end pieces are circular having an inner radius corresponding the outer radius of the pipe, and an outer radius larger or equal to the inner radius of the casing.

Centering elements to center the pipe in the casing are arranged between the pipe and the casing. The centering elements are resting on the pipe on one side, and supporting the casing on the other side, and should have a height corresponding to the distance between the pipe and the casing. The elements may protrude axially and/or radially to the pipe, and in an alternative embodiment they are arranged on the outside of the pipe or inside of the casing, before the casing is arranged around the pipe

The centering elements are arranged at the ends of the casing. In a more preferred embodiment, the centering elements are shaped as a wedge, wherein a narrow end of the wedge is inserted into the annulus until the casing is sufficiently fastened. The centric element may be circular, and enclosing the whole circumference of the pipe.

In a preferred embodiment, the end piece and the centering element are combined to one circular, wedge shaped part configured to enclose the circumference of the pipe, wherein the narrow end of the wedge may be inserted into the annulus until the casing is fastened, and the opening to the annulus is sufficiently closed to keep the granular material in the annulus.

The end piece and/or the centering elements may preferably have holes to allow water to flow into the annulus when the pipe is submerged, and to allow air or gas to flow into the annulus when the pipe is above the water.

In one embodiment, the length of the pipe and the length of the casing is equal, and thus the end pieces are arranged at the end of the pipe, possibly together with any pipe flange or similar means to attach two pipes to each other. In another embodiment, the pipe is substantially longer than the casing, and in such an embodiment the end pieces will be separate from any means or flanges for attaching two pipes.

When the granular material is to be added to the annulus, any end piece must be removed, but centering elements should be retained, or inserted in case they are combined with the end piece. In an alternative embodiment, the casing is provided with a separate inlet for the material, wherein the inlet is used to add or remove material from the annulus without removing the end piece.

The invention also relates to a method for adjusting weight of a pipe according to the description above. The method comprises the steps of

i) opening an entrance to the annulus,

ii) removing and/or adding granular material to the annulus, and

iii) closing the entrance to the annulus.

The entrance may be the end piece at the end of the casing as describe above, or an inlet for the material. When the entrance is the end piece at the end of the casing, and the centering elements are combined with the end piece, the method further comprises the steps of

- inserting centering elements between the pipe and the casing before step ii), and - removing the centering elements after step ii).

Removal of granular material may be performed upon discard of the pipe, and recycling or reuse of the materials. The materials are preferably removed by suction or by arranging the pipe in such a way that the material falls out due to gravity. Then they may be cleaned, dried, and possibly sorted before they are used in a new pipe.

In another embodiment, the granular material is removed to be replaced with another granular material, for instance if more weight is needed, then material having less average size may be used, or a material having higher specific gravity may be used.

The granular material may be added the annulus by blowing. When the end pieces and/or centering elements have holes, any air or gas used for blowing will pass axially through the annulus, while the material will remain in the annulus.

During manufacturing, the pipe and the casing are preferably manufactured separately, and then the pipe is led into the casing. When the casing is at the desired place around the pipe, an end piece and centering element(s) is installed at a first end of the casing, and only centering elements are installed at the second end. Then the granular material is added to the annulus from the second end, and when sufficient material is added, the end piece is installed. This may be performed at a factory, or at the site of use. In another embodiment, the casing, end piece and possibly centering elements are installed at a factory, but the granulate material and/or water is added at the site of use.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

The invention will now be described with the help of the enclosed Figures, wherein Figure 1 shows an axial cross section of a pipe according to the invention, Figure 2 shows an enlarged detail of circle B of Fig.1, and

Figure 3 shows a radial cross section of a pipe taken along line C-C of Figure 1.

The different parts of the figure are not necessarily to scale in relation to each other, as the diagram is merely for illustrating the invention.

Figure 1 shows an axial cross section of a part of a pipe 1 according to the invention, the pipe is a water pipe, arranged to accommodate drinking water in the interior 2 of the pipe. A casing 3 is arranged around the pipe 1, and the axial cross section of Figure 1 is taken at an end of the casing. Figure 2 shows details of the end of the casing, and Figure 3 shows a cross section taken along line C-C of Figure 1, and shows a cross section of the pipe and casing.

The casing 3 is arranged at a distance from the pipe 1, creating an annulus 4 between, and granular material 5 is added to the annulus. The granular material 5 is shown in Fig.1, but not in Fig.3 due to clarity. The inner radius and the thickness of the pipe is related to the purpose of the pipe, and a skilled person would know which radius and thickness the pipe should have at all times. The distance between the pipe 1 and the casing 3, and thereby the size of the annulus 4 may therefore be determined by choosing the inner radius of the casing.

At the end of the casing 3, as shown in Figure 1 and in detail in Figure 2, a circular end piece combined with a centering element is installed. The shown end piece comprises one end piece 6 and the centering element which is shaped as a wedge 7. An inner side 7a of the wedge is resting against the outer side of the pipe 1, and a narrower end 7b of the wedge inserted into the annulus 4 until the inner side of the casing 3 is resting against the outer side 7c of the wedge. Further, in the shown embodiment, the end piece 6 has an outer radius 6a equal to the outer radius of the casing, and the maximum radius of the wedge 7 is equal to the inner radius of the casing, in such a way that once the end piece is completely installed, the end of the casing is abutting the end piece part 6, while the outer side 7c of the wedge is abutting the inner side of the casing. In the shown embodiment, a stopper 8 is arranged on the pipe, to keep the end piece in correct position. Both the end piece 6 and the centering element 7 have holes (not shown) allowing water and air/gas to flow in and out of the annulus.

When the weight of a pipe shown in the Figures should be added or removed, the stopper 8, end piece 6 and wedge 7 is removed at one end of the casing, whereby an entrance to the annulus 4 is opened. Any granular material 5 may then be removed and recycled. If any granular material should be added, separate (not shown) centering elements must be installed to keep the pipe 1 centred in the casing 3 before the material is added. Such elements must be removed once the addition of material is completed. Once the adjustment is completed, the end piece with the wedge is inserted again.

When a water pipe is being used, it may become partly filled with air, and thus when the pipe is submerged in water, it will be given a buoyancy. Further, forces from water current and tides will act on the pipe, and move it along the seabed. These forces should be counteracted by increasing the weight of the pipe by adding granular material 5 to the annulus 4. Once the inner radius and the thickness of the pipe 1 and how much forces the pipe should be able to withstand is known, the weight needed to be added can be calculated. Based on this, and the choice of granular material, the amount of material necessary can be calculated. Once the volume of the material is known, the minimal volume of the annulus is given, and thereby the inner radius of the casing can be determined.

Table 1 gives an example of a water pipe having a casing, wherein the annulus is filled with Olivine. The water pipe and casing are made of polyethylene having a density of 960 kg/m3.

* This means that 688 kg (submerged weight) must be added to each pipe in order to keep the pipe submerged when the forces acting on the pipe corresponds to the buoyancy when 15% of the pipe is filled with air. ;;* 1550 kg olivine above water corresponds to 688 kg under fresh water, and thus the amount of olivine needed is 1550 kg pr pipe.

In a preferred embodiment, the length of a pipe is 20 m, and the length of the casing is 18 m.1 m of the pipe is protruding on each side of the casing, to ease connection to another pipe.

The embodiment described in detail above, and the example of an calculation refers to the drawing of an embodiment is not meant or intended to limit the invention. Instead, the scope of the invention is defined by the appended claims.

Claims

1. A pipe (1) comprising an outer casing (3),

characterized in that the outer casing (3) is arranged at a distance around the pipe (1), leaving an annulus (4) between the pipe and the casing, and in that the annulus (4) comprises granular material (5) having a specific gravity larger than water, wherein the annulus is continuous in such a way the granular material may be equally distributed around the pipe,

and in that centring elements (7) are arranged between the pipe and the casing, at each end of the casing (3).

2. A pipe according to claim 1, characterized in that the casing is another pipe.

3. A pipe according to claim 1 or 2, characterized in that the pipes are made of polyethylene, preferably having density above 0.9.

4. A pipe according to claim 1, characterized in that the distance between the casing and the pipe, should be at least 2 times the average size of the granular material, preferably at least 3 times the average size.

5. A pipe according to any one of the preceding claims, characterized in that the average size of the granular material is 2-6 mm.

6. A pipe according to any one of the preceding claims, characterized in that the granular material is a mineral, preferably Olivine and/or Barite.

7. A pipe according to any one of the preceding claims, characterized in that an end piece (6) is combined with the centring elements (7), and arranged at each end of the casing (3).

8. Method for adjusting the weight of a pipe according to claim 1-7, wherein the method comprises the following steps

i) opening an entrance to the annulus (4),

ii) removing or adding granular material (5) to the annulus (4), and

iii) closing the entrance to the annulus.

9. Method according to claim 8, wherein the pipe has an end piece (6) combined with centring elements (7), the method is further comprising steps for

- inserting centring elements between the pipe and the casing before step ii), and - removing centring elements step ii).

10. Method according to claim 8, wherein the step for adding granular material to the annulus comprising blowing.