GJERULL, Finn, Peter (Båtstøjordet 51, Høvik, N-1363, NO)
P a t e n t c l a i m s 1.
A power umbilical comprising a number of power cables (4) to transfer large amounts of electric power/energy, filler material (2, 3) in the form of rigid elongated plastic elements that are located at least partially around and between the power cables (4) and which are collectively gathered into a twisted bundle by means of a laying operation, and a protective sheath (1) that encompasses the power cables (4) and the filler material (2, 3), characterized in that the power cables (4) are made of aluminium, that the power cables (4) and the filler material (2, 3) are S-Z laid, i.e. laid alternating by continuously shifting laying direction, in the entire or part of the longitudinal extension of the power umbilical, combined with that the S-Z laid bundle is kept substantially torsional rigid by the protective sheath (1).
2. The power umbilical as defined in claim 1, characterized in that the power umbilical includes electric wires and/or optical conductors (5) which are also laid in an S-Z configuration and are located inside the sheath (1).
3. The power umbilical as defined in claim 1 or 2, characterized in that at least one load carrying element (6) is predetermined located in the transversal cross section of the power umbilical, which element (6) is also laid in S-Z configuration.
4. The power umbilical as defined in any of the claims 1-3, characterized in that the power umbilical includes an anti rotation band or strength band, or a tape, which is helically winded around the bundle just internal of the protective sheath (1).
5. The power umbilical as defined in claim 4, characterized in that the strength band, or the tape, is helically winded around the bundle in two or more layers, and laid in opposite directions.
6.
The power umbilical as defined in claim 4 or 5, characterized in that the strength band, or the tape, is helically winded around the bundle by relatively short laying length, like O 5 I to 0,5 meter.
7.
The power umbilical as defined in claim 4, 5 or 6, characterized in that the strength band (10) is of metallic material, like steel, lead or aluminium.
8.
The power umbilical as defined in any of the claims 4-7, characterized in that the strength band (9, 12, 9') includes fiber armoured ribbon, fiber armoured ribbon with friction liner and textile ribbon, where the fibre armoured ribbon can be reinforced with aramid fiber, carbon fiber, glass fiber and other synthetic materials.
9.
The power umbilical as defined in any of the claims 1-8, characterized in that the laying of the electric cables (4), the possible wires/conductors (5), filler material (2,3) and possibly other load carrying elements (6), shifts direction at irregular intervals, alternatively at regular intervals.
10.
The power umbilical as defined in any of the claims 1-8, characterized in that the laying of the electric cables (4), the possible wires/conductors (5), filler material (2,3) and the possibly load carrying elements (6) takes place over approximately one half to three revolutions before it shifts direction.
11. The power umbilical as defined in any of the claims 1-10, characterized in that the load carrying elements are lightweight rods of composite material and/or steel string or steel wire and/or fiber rope and/or polyester rope.
12.
The power umbilical as defined in any of the claims 1-11, characterized in that the power umbilical includes at least one fluid pipe (not shown) in the transversal cross section, made of metal and/or plastic material, and laid in the same S-Z configuration.
13.
The power umbilical as defined in any of the claims 1-12, characterized in that the filler material (2, 3) is designed such that longitudinally extending grooves (11) or splines are present into which the sheath material penetrates when extruded thereon, for the creation of friction forming means to increase the torsional rigidity of the power umbilical.
14. The power umbilical as defined in any of the claims 4-13, characterized in that the strength band (12) is winded with a certain gap between each winding so that interstices are present between each winding for the penetration of sheath material into the filler material. |
SZ-laid aluminium subsea umbilical
The present invention relates to a power cable, or power umbilical, comprising a number of electric cables for transfer of vast amounts of electric power/energy, possibly with the addition of electric wires and/or optical conductors, filler material in the form of stiff elongate plastic elements located at least partially around and between the electric cables and the possible wires/conductors and which are collectively gathered in a twisted bundle by means of a laying operation, a protective sheath that encompasses the electric cables, the possible wires/conductors and the filler material, and possibly with the addition of one or more load carrying element and/or fluid pipes predetermined located in the cross section of the power cable/umbilical.
A power cable/umbilical of this nature is described in NO 2006 5943 (PCT/NO2007/00444) with priority date 20th December 2006, and with the same applicant and inventor as the present invention.
The present invention has substantial similarity with the power cable/umbilical mentioned above, in the following termed power umbilical only, and distinguishes from this basically by two conditions. One is a simpler transversal cross section, i.e. very simple transversal cross section in the plainest embodiment. This simple transversal cross section is made possible by actively make use of the characteristics or properties of the elements in such a section. To recognize and make use of these properties have not been straight forward for the person skilled in the art. One such property is the polar moment of inertia of the outer sheath. This will be described in further detail later.
The other one is the choice of material of the electric power cables. The choice of material may appear obvious in this case, but this is not true. This because the S-Z laying as suggested in NO 2006 5943, opens up for new possibilities of manufacturing such cables having heavy transversal cross section in substantial lengths without the need to make frequent splices or joints. In addition, such larger dimensions and high weight will not complicate the production machinery in significant degree. Besides, in
this industry, it has been almost a tradition for the person skilled in the art to make conductors of copper, without looking neither to the right or the left for alternatives.
Nevertheless, it is known from the cable industries to use other metals in electric conductors. For example, it is known to make high- voltage cables of aluminium, i.e. high- voltage cables of the type that extend in long span over land and fiords. Normally these cables have a steel wire in centre as the load carrying element and aluminium conductors winded in a helix around the core element. The reason for using aluminium has been to reduce the weight, in order to enable the cable to pass over large spans between power pylons, in addition to reduce the material cost in some extent. Such conductor, however, is a different product than the one suggested by the present invention.
Such a power umbilical as the present application relates to, will be able to transfer vast amounts of electric power. In order to be able to do this, the transversal cross section area of the conductor will typically be 300mm2 and the electric voltages can be in the range of 36-145kV.
In the following description we will repeat many of the points from the above mentioned application about the particular excellence of the S-Z laying which again has importance for being able to realize the product in accordance with the present invention. Thus this is repeated and emphasized in the following text till page 4.
The traditional way to manufacture an umbilical is shown in NO 174 940 (WO 93/17176). When looking into the figures in the first document, in particular figure 1, the machinery normally required to manufacture such umbilical is shown. The shown method and machinery will also be guiding for the new power umbilical. As shown, the machinery is complicated, space demanding, voluminous, and accordingly very cost intensive. In addition, due to the size, the machinery necessarily needs to be stationary, i.e. be located in a large on shore facility, preferably close to a harbour.
The machinery necessarily needs to have these dimensions in order to fulfil its functions, namely be able to wind the elongate elements together into a bundle that extends helically in the longitudinal direction thereof having a predetermined laying length, typically 1,5 to 15 meters per revolution, depending on the intended application.
It is a distinct desire from the industries to be able to manufacture the new power umbilical by use of considerably simpler machinery. In addition, there is a desire to have a mobile facility that can produce at site, or close to the site, such as on board a lay vessel. How to enable this, in consideration of the premises above? Some regards have been necessary to take, such as the ability of the umbilical to take up tensional loads. This is discussed below.
The power umbilical is designed to be able to transfer vast amounts of electric power, for example from the sea surface to production equipment for oil and gas located on the sea bottom. The power umbilical includes heavy gauge cables for transportation of electric power to electric powered equipment on the sea bed, such as large pump stations that provides displacement of recovered oil and/or gas.
Another usage that is actualized is power cables from wind mills that are placed offshore in the sea. In order to be able to transfer the produced energy from the generators in the wind mills, heavy gauge power cables from the wind mills and to a land based terminal are deployed on the sea bed.
When such a power umbilical that includes a bundle of twisted, elongate elements are subjected to tensional loads, for example during deployment on deeper waters, the twisted, or winded, elements will tend to "straighten out" or "twist open". It is the load carrying elements of the cross section that are dedicated to take up the tensional loads. The load carrying elements can be steel wires or be made of composite material, either in the form of individual composite carbon rods distributed on the cross section or rods gathered in bundles.
Thus it is to be understood that the present power umbilical primarily is intended to be used for stationary purposes and needs its tension capacity first of all during the deployment thereof, for subsequently to remain more or less stationary on the sea bed without substantial axial loads.
These heavy gauge electric cables, normally produced of copper wire, are now integrated into the more traditional umbilical. These umbilicals are in turn in steady development and changes construction/design and functions in view of actual needs. These heavy gauge electric cables add substantial weight to the umbilical due to the specific gravity of the copper material. When we know that the copper material has a very poor load carrying capacity, it will be of great importance that the copper wires do not substantially participate in the load carrying function, which in practise involves the load carrying of its own weight.
With the now proposed solution for the laying operation of the power umbilical, which simplifies the manufacturing process substantially, the load carrying elements will not necessarily be able to fulfil their function, namely be able to transfer substantial loads, or tensional loadings. They will only tend to straighten out (unwind). However, such a new solution will require only a very simple machinery of manufacture compared with the traditional one. So all the desires set forth above will be fulfilled. But as one will understand, a new problem is created - how to enable the load carrying function?
This is an acknowledged problem and in this respect we refer to US patent 6,472,614 in the name Coflexip. In column 1, from the middle of the page and down, it is indeed described that the elements of the umbilical normally (traditionally) are winded together in the well known S-Z configuration, which means that it is winded alternating with shifting direction. Further it is described that since the S-Z configuration cannot withstand substantial tensile stress without unwinding (as described above), additional layers of armouring (steel or Kevlar, for example) must be winded counter helically around this bundle to take up the tensile stress. The armouring consists of a plurality of steel rods placed side by side with small pitch relative to the longitudinal axis of the umbilical.
In order to teach how this umbilical typically looks like, the US patent tells that this is disclosed in API (American Petroleum Institute) specification 17E, "Specification for Subsea Production Control Umbilicals", in particular pages 42, 43 and 44. Extracts from this are shown in figures 5-6 and are marked with "prior art".
Such is also included to illustrate the traditional way of thinking when it comes to S-Z laying (winding) combined with load carrying. This requires armouring rods that are helically winded (not S-Z) in at least two layers and each layer is winded in opposite directions to each other in order that they shall be able to act as the load carrying elements in the cross section.
Another problem with this type of subsea power cables, or power umbilicals, has been that they need to be spliced relatively frequently, perhaps every 500 meters. This results in a substantial number of joints if lengths of several tenths of kilometres are to be supplied. Every single splicing operation is time consuming. In complicated cross sections of the power umbilical, it may take a couple of days to perform such a splicing operation.
Thus a challenge has been prevailing in the task to be able to manufacture substantial lengths of power cables, or power umbilicals, having complicated cross sections and with fewer splices than before; in brief, achieve a more continuous and effective production. Similarly, as before, it is a demand that the power cable, or power umbilical can be coiled up on carousels or reels for shipping and transportation purposes.
One object of the present invention has been to reduce the cost per produced consecutive metre. By using new knowledge and experience with the elements included in the transversal cross section, it has been possible to simplify said section. I.e. omit the separate load carrying elements (armouring) integrated in the transversal cross section in the traditional way. The load carrying elements, if required, will in the present invention be integrated into the section in the same manner as the S-Z laid elements. By laying the load carrying elements in the same S-Z configuration, all the elements will
contribute to generate torsion with alternating direction tending to unwind the umbilical. If sufficient binding between the outer sheath and the S-Z elements is achieved, such torsional rotation will be kept in check (maintained stationary) by the outer sheath, which results in that the S-Z laid elements nearly provide a rigidity effect as if they were laid in a helical course.
This is possible because use is made of the polar moment of inertia of the outer sheath. The polar moment of inertia tells something about the rotational rigidity of an element, i.e. the ability to prevent that any angular deflection or rotation takes place in the outer sheath and thus the elements that the outer sheath encompasses. If one considers the outer sheath as an isolated element, the element behave as a rotationally rigid tubular that has great rotational rigidity due to the relatively large diameter thereof.
It is to be mentioned that the relatively long laying length (like one revolution per 15 meters) also contributes to keep the torque or torsion relatively low.
Another object with the present invention has been to reduce the material costs per consecutive meter. This has further been actualized in recent time with steadily increasing copper costs. When the weight per consecutive meter copper cable with 300mm cross sectional area is 7.15kg, it is easily understood that the cable costs will be high.
Another object with the present invention has been to reduce the weight per consecutive meter of the cable. If able to reduce the weight, it will be possible to deploy the cable in still deeper waters than previously expected.
A reduction in weight also provides the advantage that the threshold for when the load carrying elements need to be introduced into the section is considerably elevated. Said in other words, the power umbilical can be deployed into deeper waters without the addition of load carrying elements compared with a power cable where the power cables are made of copper. This results in that a substantially more reasonable power cable can
be used in depths where it was planned to use copper conductors with the addition of load carrying elements.
According to the present invention a power umbilical of the introductory said kind is provided, which is distinguished in that the power cables are made of aluminium, that the power cables and the filler material are S-Z laid, i.e. alternating laid with continuously shifting laying direction, in the entire or part of the longitudinal extension of the power umbilical, combined with that the S-Z laid bundle is retained substantially torsional rigid by the protective sheath.
By such a power umbilical a reduction in weight per running meter from 7.15kg to 5.85kg will be obtained, which will amount to approximately 20%. As mentioned, the use of load carrying elements could be avoided on power umbilicals designed for deeper waters, i.e. expand the critical limit for when it is needed to use load carrying elements in the form of steel wires or carbon rods. In addition to the pure economic savings, this will also positively contribute to all types of handlings, such as in the manufacturing machinery, during reeling onto carousels and transport to the deployment site.
Nevertheless, it has to be admitted that aluminium has poorer conductivity than copper. In order to transfer equal amounts of electric power/energy as in a copper cable having sectional area of 300mm 2 , the transversal cross section of an aluminium cable needs to be increased to approximately 500mm 2 . The weight per running meter for this aluminium cable will be 5.85kg, which is corresponding to that referred to above. It is also to be understood that by aluminium is also meant alloys of aluminium which are suited as electric conductors for this type of applications.
In spite of the above mentioned cross sectional area increase, the cost savings will be substantial. Included all involved factors that are influenced by the material of the conductor, a stipulated cost saving in the order of magnitude 40% will be achieved.
In a more complicated transversal cross section the power umbilical may include electric wires and/or optical conductors which is also laid in a S-Z configuration and is located inside the sheath.
The power umbilical can further include at leas tone load carrying element which is predetermined located in the transversal cross section of the power umbilical, in which said element(s) also is laid in S-Z configuration. The load carrying elements may possibly be included in combination with the wires and optical conductors as mentioned above, all designed in dependence of the actual application.
Further, the power umbilical may include a strength band, or a tape, which is helically winded about the bundle just internal of the protective sheath. The strength band, or the tape, functions like an anti rotation band or tape. The function of the band/tape is to increase the rotational rigidity.
The strength band, or the tape, is preferably helical winded around the bundle in two or more layers, and laid in opposite directions.
Moreover, the strength band can be of different nature and be varied according to which depths the power umbilical is to be deployed. As one will understand, in some applications the band can be omitted completely. At small depths the strength band can be one simple ribbon, strip or tape just to keep the bundle together until the outer sheath is extruded thereon. When the depth become deeper it may be necessary with a steel band that is winded around the bundle. A detailed explanation appears from the text below.
According to the idea of the present power umbilical, this umbilical is designed in such a way that the winded elements are prevented from straightening out (unwinding), in spite that they are S-Z winded. This is achieved in that: a) the winded elements are in engagement with the filler profiles which fully or partly encloses the winded elements
b) the umbilical is sufficiently torsional stiff to counteract the torque that the load carrying elements generates under axial tension c) the inner friction counteracts that the elements unwind.
By this new way to lay power umbilicals, i.e. S-Z laying, combined with an outer sheath and/or strength band, the above described is achieved. Said in a different way, engagement of filler profiles in combination with the torsional rigidity of the power umbilical and internal friction, counteracts that the S-Z laid bundle unwinds when the elements are put into tension. The described power umbilical immobilizes the load carrying elements and the remainder elongate elements of the transversal cross section, both with regard to radial motion, axial elongation and torsion, and at the same time the load carrying elements are able to fulfil their duty as load transferring elements in spite of their sinus configuration.
In addition, simpler and less comprehensive production machinery that requires less space and has lower cost, is achieved. It is also considered to be possible to make a mobile facility for direct use in the proximity of actual fields that are developed. It is further to be understood that to wind for example common electric conductors, or wires, by means of S-Z winding is commonly known. But to design and manufacture an S-Z laid power umbilical, where components are able to take load, has never been done before as far as we know, until this was proposed in NO 2006 5943.
In a suitable embodiment the strength band, or the tape, is helically winded about the bundle in two or more layers, laid in opposite directions. Further the strength band, or the tape, can be helically winded about the bundle by relatively short laying length, like 0,1 to 0,5 meter.
The strength band can be of metallic material, like steel, lead or aluminium. Alternatively the strength band can include fiber armoured ribbon, fiber armoured ribbon with friction liner and textile ribbon, where the fibre armoured ribbon can be reinforced with aramid fiber, carbon fiber, glass fiber and other synthetic materials.
It is to be understood that the laying of the electric cables, the possible wires/conductors, filler material and possibly other load carrying elements can alter direction at irregular intervals, while in another alternative embodiment it may alter direction at regular intervals. In a typical embodiment, as one can recognize today, the laying will take place over approximately one half to three revolutions before it shifts direction and is laid a corresponding number of revolutions in opposite laying direction before it once more alters direction.
As mentioned, it is to be understood that with this form for laying one looses, when viewed isolated, the ability of the individual components to receive and transfer tensional loads. If they are subjected to tension, they only tend to straighten out (unwind).
In one embodiment the load carrying elements can be light weight rods of composite material and/or steel string or steel wire and/or fiber rope and/or polyester rope.
It is also a possible variant that the power umbilical includes at least one fluid pipe in the transversal cross section, of metal and/or plastic material, laid in the same S-Z configuration.
In addition, the filler material can in one variant be designed such that longitudinally extending groves or splines, that the material of the outer sheath penetrates into when extruded thereon, are present for creation of friction forming means to increase the torsional rigidity of the power umbilical.
Moreover, the strength band can be winded with a certain gap between each winding so that interstices are present between each winding for the penetration of sheath material into the filler material, and possibly into the above mentioned grooves.
Other and further objects, features and advantages will appear from the following description of preferred embodiments of the invention, which is given for the purpose of description, and given in context with the appended drawings where:
Fig. IA shows a transversal cross sectional view through a first embodiment of a power umbilical according to the invention in its simplest form,
Fig. IB shows a transversal cross sectional view through a variant of the first embodiment of a power umbilical according to the invention,
Fig. 2 A shows a transversal cross sectional view through a second embodiment of the power umbilical according to the invention, where fibre tape is winded around the bundle of elongate elements,
Fig. 2B shows a transversal cross sectional view through a variant of the second embodiment of the power umbilical shown in figure 2 A, where steel band is winded around the bundle of elongate elements,
Fig. 3 shows a transversal cross sectional view through another variant of the second embodiment of the power umbilical shown in figure 2 A, where longitudinally extending grooves in the filler material are filled with sheath material, Fig. 4 shows a transversal cross sectional view through a third embodiment of the power umbilical according to the invention, where carbon rods are included in the cross section,
Fig. 5 (prior art) shows extracts from API (American Petroleum Institute) specification
17E, figure D-2 that shows schematically a S-Z laid cable and laying machine, Fig. 6 (prior art) also shows extracts from API (American Petroleum Institute) specification 17E, figures E-I and E-2 that show typical umbilicals having thermoplastic pipes laid in this way.
Three embodiments of the power umbilical cross sections shown in the figures 1 A-4, the first one in two, the second one in three and the third one in one variant only, will now be described. It is to be understood, however, that many embodiments and variants exist in further combinations of these and are within the scope of the appended claims.
For the detailed construction of a traditional umbilical and how it is manufactured, reference is given to the previously mentioned WO 93/17176.
The simplest embodiment is illustrated in figure IA and can nearly be called a pure power cable even if it is untraditional in its structure by the use of channel elements and
S-Z laying. The power umbilical is basically constructed of the following elements: a number of elongate elements in the form of channel elements 20, 25, 30, for example of polyvinylchloride (PVC), and heavy gauge power cables 40 of aluminium for transfer of huge amounts of electric power/energy.
The central channel element 20 has a transversal cross section like a three armed spider and is adapted to the shape and diameter of the heavy power cables 40. A set of intermediate channel elements 25 is inwardly defined against the central channel element 20, and outwardly defined against a set of outer channel elements 30. Between these they are defined against the heavy power cables 40. All of these elements are laid into an S-Z laid bundle. The channel elements 20, 25, 30 form cavities for receipt of the heavy gauge power cables 40. The bundle is kept together by an outer sheath 10, for example of polyethylene (PE), which is extruded onto the bundle. After the extruding operation, the polyethylene has some tendency to shrink during solidification. This provides a positive contribution to the function of the power cable under tensional loads.
In turn, each heavy gauge power cable 40 includes an aluminium core 14, a semiconductor layer 15, insulator material 16, outer semiconducting layer 17, an earth fault conductor 18 in the form of a screen and an outer sheath 19. A smaller gap C exists between the outer sheath 19 and the internal surface of said cavity within the assembled channel elements 20, 25, 30. This structure of the power cables 40 will be typical for all cable embodiments and variants.
Further, longitudinally extending grooves 110 are recessed into or between the outer channel elements 30. This is done to be able to extrude the sheath material 100 into the grooves 110 for thereby to interlock or increase the friction between the outer sheath 100 and the outer channel elements 30 in order to secure proper friction between the channel elements 30 and the outer sheath 100 and thus achieve required torsional rigidity.
In one or more variants the bundle may in addition be kept in place by a strength band, also called an anti rotation band. The strength band may in different variants be fibre bands or metal ribbons which are winded circurnferentially around the bundle before the outer sheath is extruded thereon.
In figure IB a variant is shown of the first embodiment shown in figure IA. AU the elements shown in figure IA are also found in figure IB, and will not be described again. However, more elements are now integrated into the transversal cross section. In addition to the power cables 40 of aluminium for the transfer of large amounts of electric power/energy, optical conductors 50 and load carrying elements in the form of steel wire 60, alternatively carbon rods, are now integrated and laid into said bundle. The bundle can in one variant be kept together and in place by a strength band, as described above. It is further to be understood that the transversal cross section also may include fluid pipes (not shown) for use in some applications if required. The way in which the umbilical is bundled and laid together, corresponds with the other variants.
In the second embodiment, the power umbilical according to figure 2A is basically constructed of the following elements: a bundle of elongate elements consisting of inner and outer channel elements 2, 3, for example of polyvinyl chloride (PVC), electric power cables 4 to transfer vast amounts of electric power/energy, optical conductors 5 and load carrying elements in the form of steel wires 6, that are laid together into said bundle. The bundle is kept together and in place by a strength band. In this variant, according to figure 2A 5 fiber ribbon 9 that is winded circurnferentially around the bundle before an outer sheath 1, for example made of polyethylene (PE), is extruded onto the bundle. As mentioned the cross section may also include fluid pipes (not shown) in some embodiments or variants.
As an illustrating example of the dimensions we talk about here, without thereby being considered as limiting, the electric power transferring part of the cable 4 can be twisted aluminium threads that together make a power conducting square section of 500mm 2 . The entire diameter of the power umbilical can, as an example, be 200-300mm. It is further to be understood that, in addition, regular electric wires (not shown) can be
included for control purposes in all of the embodiments and variants, all after actual needs.
The inner and outer channel elements 2, 3 are laying at least partly around and between the electric cables 4 and are typically made as rigid, elongate, continuous elements of plastic material. The electric cables 4, the possible wires/conductors 5, the filler material 2, 3 and the at least one load carrying element 6, sue as before alternating laid, i.e. having steadily shifting direction, in the entire or part of the longitudinal extension of the power umbilical. In addition, the laid bundle is kept substantially torsional stiff by the protective sheath 1 by the addition of a strength band in the form of a fiber ribbon 9 that is helically winded around the bundle immediate inside the protective sheath 1.
The power umbilical according to figure 2B is a variant of that shown in figure 2 A and most of the elements are the same and are denoted with the same reference numbers. However, it is to be noted that the strength band now is a metal band which is given the reference number 10 replacing the fiber ribbon shown in figure 2 A. This variant will normally be used when the deployment shall take place in deeper waters. The way in which it is bundled and winded together corresponds to the variant described above. As an example, without thereby being limiting, the metal band 10 in a typical embodiment can have a thickness of 0,8mm and be winded in two layers.
The power umbilical according to figure 3 is another variant of that shown in figure 2 A and most of the elements are the same and are denoted with the same reference number. However, it is to be noted that the strength band now is a tape only, which is given the reference number 12 and has, actually, only a temporary function. This is to keep the bundle of elongate elements together until the outer sheath 1 of polyethylene is extruded onto the bundle. Further, longitudinally extending grooves 11 are also made in or between the outer channel elements 3. As before this is done to be able to extrude the sheath material 1 into the grooves 11 thereby to lock the outer sheath 1 to the outer channel elements 3 or increase the friction therebetween in order to ensure sufficient torsional stiffness. In addition, the sheath material is extruded into the recess that the wire 6 is laying, and partly around the wire 6. To be able to extrude the sheath material
into the grooves 11 3 the tape 12 is winded circumferentially by a predetermined gap between each winding such that the sheath material can penetrate into the grooves 11. The way in which the umbilical is bundled and winded together corresponds with the variants described above.
Figure 4 shows a third main embodiment of the power umbilical. Most of the elements from the embodiment according to the figures 1-3 are the same and are denoted with the same reference number with the addition of a mark'. The power umbilical according to figure 4 is as before basically constructed of the following elements: a bundle of elongate elements consisting of inner and outer channel elements 2', 3', for example of polyvinyl chloride (PVC), electric power cables 4' of aluminium for transfer of vast amounts of electric power/energy, optical conductors 5' and load carrying elements, either in the form of steel wire 6', or in the form of carbon rods 7, or a combination thereof, that are laid together into said bundle. The carbon rods 7 can either be placed individually at several places in the transversal cross section, or gathered in bundles as illustrated by the reference number 8, or a combination thereof, just as shown in figure 4. The bundle is kept together and in place by a strength band, in this embodiment according to the variant of figure 1 where fiber ribbon 9' is winded circumferentially around the bundle before an outer sheath 1 ', for example made of polyethylene (PE), is extruded onto the bundle.
It is further to be understood that the power umbilical according to figure 4 can have several variants, for example similar to those shown in figure 2B having steel band and in figure 1 and 3 having grooves that the sheath material is extruded into. The steel band increases the torsional stiffness and this variant will normally be used when the deployment will take place in deeper waters. In addition they can include electric wires and/or fluid pipes in the transversal cross section.
Figure 5 and 6 show extracts from API (American Petroleum Institute) specification 17E, "Specification for Subsea Production Control Umbilicals", in particular pages 42 and 43. Figure 5 shows schematically in the lower view an S-Z laid, or oscillatory laid traditional umbilical. The upper figure shows fully schematic how the machinery for
this type of laying is contemplated. Figure 6 shows two variants of traditional umbilicals that can be laid in this way.
As one will understand a number of possible embodiments and variants are present by combining the described functional features in different ways. The simplest transversal cross section, primarily designed for shallow waters, or on shore, is shown in figure IA. The axial rigidity needs to be increased as required, in all determined from the axial load of the umbilical, like the deployment depth. Those elements that contribute to the increase of the axial rigidity are the outer sheath and the strength band, which may be of different materials from metals to fabrics, and the load carrying elements, which can be wire or carbon rods or corresponding elements.
What contributes to alter/increase the number of functions is to integrate one or more of the following alternatives: optical conductors for control and measurement functions, common electric wires to motors, aggregates, actuators and control purposes, and fluid pipes to hydraulic operation, activation or other fluid transport. These can be integrated in number and combinations which are determined from what is actual for each specific application.
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