GB2190168A - Supporting and protecting submersible pipe lines and cables - Google Patents

Abstract

Means 2 for supporting and protecting submersible pipe line and cable systems during transport and after submersion comprises longitudinally extending tubular supports 4, 6 which form buoyancy chambers and have means for adjusting their buoyancy. The supports 4, 6, 53, 54 are connected by spaced-apart transverse structures 7 which carry pipes 8, 10 and cables 58 of the system. The supports may be bent (Fig. 14a) or provided with passages (Fig. 15), Fig. 19 to allow for pipe branching. Extra floats 246, Fig. 19 may be situated at the branch points. The pipes 8, 10 may be releasably held on the support structure by flexible clamps (Fig. 11 a-c) and have covers (e.g. Fig. 10). The pipe/cable systems and support structure may be assembled on shore and pulled into the water (Figs. 22-24). <IMAGE>

Description

SPECIFICATION Means for supporting and protecting submersible pipe line systems and methods of making such systems and the supporting means The present invention relates generally to support systems for submerged pipe lines, more particularly means for supporting, protection and transport of one or more pipe lines designed for installation on the sea bottom to be used in connection with production and transport of petroleum products or other. Furthermore, the invention includes a method for making an installation of such pipe systems.

The invention is developed for installations comprising one or several pipe lines which shall be installed on the sea bottom as a "bundle", but it shall be understood that the invention can with similar advantages be used with installations comprising only one single pipe line.

Pipe lines installed on the sea bottom can be made and installed individually in accordance with several known methods. When several pipe lines, however, shall be installed between two or more locations on the sea bed, it is advantageous to gather these lines together in socalled "flowline bundles", hereinafter named "pipe bundles". The making and assembly of such pipe bundles are known technology, in that the separate lines are placed inside a protectional pipe ("carrier pipe") which has several functions beyond the function of serving as section. Such other functions may consist in providing necessary strength and buoyancy for transport and installation of the unit.

Such constructions are relatively complicated and require a production site which either can take up the entire pipe bundle, i.e. having an extent up to 3,5 to 4 km, or at least can serve as part of the total length for instance for 600 to 800 meters of the pipe bundle and which simultaneously has good possibilities for storage of the produced part of the construction in floating condition in a shielded, not traffic burdened ocean area, for instance in a fjord arm or along the fjord bottom.

The pipe lines in a such carrier pipe are subsequent to installation practically speaking not accessible for inspection, repairs and replacements. Neither is it possible to increase the number of pipe lines in a ready made bundle.

The conventional method for making pipe bundles is further complicated inasmuch as the carrier pipe in short length (about 12 to 22 meters) are pulled along on the outside of on beforehand welded pipe sections, cables or the like. A such operation requires that a great part of or the entire length of the pipe bundle (usually about 1/2, 1/3 or sometimes 1/4, i.e. up to 800 meters) is positioned on the production site on shore. The production plant support consists of a long series of rollers or slides positioned on a production site ashore. A such operation represents several hazardious elements during the making, since the pipes must in this stage be carefully handled such that the vulnerable pipe lines are not being injured in any way.

Production of gas and/or oil from sea bottom wells require further connection with a plant or production handling, and a plant for controlling the production. A submerged pipe system will in addition to pipe lines from the separate production wells, include other lines for liquids and cables for electric powers and controls for the separate wells. These line systems represent a substantial part of the total costs for submerged offshore production plants for petroleum products. In connection with the technique usually utilized today, pipe lines from each separate well are leading to a receiving station, manifold or the like. From such location main lines are leading to plants for handling and/or production.

The laying and installation of submerged pipe lines and pipe line systems are with conventional technique both time consuming and expensive. Especially in connection with the laying of pipe lines along uneven terrain problems frequently turn up, such as critical stresses in the pipe tubings due to bending of the piping. In connection with larger crevices in the sea bottom the limited strength and rigidity of the piping prevent that the same can follow the contour of the sea bed, a fact which frequently results in that free spans are formed. Such free hanging spans may give rise to vibrations and other movements which results in a strength reduction of the pipe lines which may result in fatigue failures. Further, a free hanging pipe span will if not protected obviously easily be damaged by fishing gear and the like.

Known ways to avoid such problems are to select alternative layng routes, levelling off the terrain, i.e. digging, mass transportation of stone, gravel and the like, utilization of flexible pipe lines which more or less can follow the bottom contour.

It is furthermore proposed to utilize different forms for protection and support of the pipe lines such as for instance shown in Norwegian patent No. 149 289 describing the use of concrete culverts surrounding the pipe lines.

The main object of the present invention has been to provide new solutions for protection, support and installation of submerged pipe lines, particularly bundles of such pipe lines, and which can constitute elimination or reduction of a substantial part of the various problems and shortcomings which appear in connection with known solutions, particularly in regard the aim to obtain greater safety, and a reduction of the work in connection with the making and the laying of such submerged pipe lines.

A further important object of the present invention is to provide a simplified method and simplified equipment for establishing a communication between a submerged pipe line system with a plant for production handling, such as for instance a process plant on a platform.

A special object of the invention has been to provide a solution which facilitates the possibility to instal branch lines from the separate pipe lines in a pipe bundle.

A further object of the invention has been to provide the support system for pipe lines which makes it possible to instal the pipe lines in areas whereinn the pipes would be subjected to unacceptable large environmental loads and along relatively uneven sea bed without carrying out any levelling work or the like and without establishing risk for creation of critical stress concentrations in the piping as a result of bending. Typical examples are landing and transport along terrain with depressions and ice bergs.

A further object of the invention is to provide a support- and protection means for the piping which facilitates replacement of or repairs on the separete pipe lines in the installation.

A further object of the invention has been to provide a support- and protection means for one or more pipe lines which makes it possible to make the same in very long units either on shore or in floating position for subsequent transport, submerging and installation of the pipe lines including the support means as a unit along the pre-selected route along the sea bottom. The support system can also be used for removal of the pipe lines.

The support means in accordance with the invention is generally of the type wherein the pipe line or -lines in installed position on the sea bed are connected with more or less rigid protection and support means, and the present invention is generally characterized in that the support means consists of either a substantially upwards open, two-part divided construction which straddles or confines the pipe lines or pipe bundle on both sides and follows the pipes, or a means wherein the pipe lines are positioned below for fittings or pipes. A further important feature of the invention consists in that the pipes are releasably attached in a suitable fashion on transverse elements between the two longitudinally extending support means, or below a support means, depending upon which particular arrangement shall be used.A further important feature of the invention consists in that the support means or elements are more or less pipeshaped and are provided with preferably adjustable buoyancy.

In a preferred embodiment of the invention the support means consists of two parallelly extended mutually spaced pipe-shaped buoyant elements which are interconnected with transverse spacers which form support for the pipe lines.

A pipe line unit in accordance with the invention may with this solution for instance possess a limited flexibility in the vertical plane, but will present large rigidity in the horizontal plane. Thereby a pipe line system in accordance with the invention, i.e. a support means together with one or more pipe lines, may to a certain extent follow the contour of the bottom contour, possibly with a span across smaller depressions in the sea bed, without causing a risk for formation of critical bending stresses in the piping, simultaneously as the unit will present large rigidity in the horizontal plane, whereby is reduced risk for vibrations and the like, and the support means will present a protectionagainst environmental burdens and possible accidents.

By the present invention may furthermore be reduced the required length on the pipe lines in connection with specific installations, simultaneously as the need for conventional manifold stations is reduced or eliminated in that the invention makes it possible to establish branch lines from a main bundle of lines. Furthermore is established possibilites to integrate manifold- and transport functions through use of one separate pipe line.

The solution in accordance with the present invention is particularly suitable for i) support and protection for pipe lines in general, typically one pipe line, and then preferably in areas where problems such as ashore zones, shallow waters and uneven bottom. Pipe lines for installation in other areas may be made as one unitary construction, which usually can be transported and installed independent of the protection means.

ii) protection, transport, fabrication and protection of pipe lines and pipe bundles in that the structure extends above the pipe line, pipe bundle over their entire length. The pipes/pipe bundle may have branch lines. The branch lines can either be transported separated from the unit, or preferably together with the unit, the support means then functioning as buoyancy members.

A special advantage of the invention is that one has provided a system which makes it easy to add new pipe lines side by side with already existing lines or a bundle of lines.

The invention also includes further features and advantages which will appear from the following description in connection with attached drawings which are showing some embodiments for support means and pipe systems in accordance with the invention and wherein: Figure 1 is showing a cross-sectional view through a support means in accordance with the invention, wherein two important pipes are being used.

Figure 2 is showing a similar view through another embodiment, Figure 3 is showing a perspective view of a third embodiment of the invention, Figures 4a and 4b are showing a plan view and an elevational view of a support means as generally shown in figures 1-3, respectively, said means being in installed position crossing a depression in the sea bed, Figure 5 is showing a longitudinal section through an embodiment for a pipe-shaped support element in accordance with the invention, Figures 6a-c are cross-sectional schematic views illustrating a further embodiment for a support means in accordance with the invention and shown in three different stages of ballasting the element, Figure 7 is showing a cross-section through a support means in accordance with the invention adapted for a pipe bundle, the pipes being supported in special holders attached to the spacer elements between the two pipeshaped support elements, Figure 8 is showing a cross-section similar to Figure 7 through a different embodiment for attachment of a pipe bundle wherein the separate pipe lines are positioned in several horizontal levels, Figure 9 is showing a similar cross-section of a further embodiment wherein some of the pipe lines are positioned on the outside of the support elements, Figure 10 is a schematic cross-sectional view through a further embodiment of the invention wherein the support means for the separate pipe lines are being attached by means of a super-imposed yoke member, Figures 1 la-c are showing schematic details in section illustrating the design and use of special members in the shape of clips or clamps for releasable attachment of the pipe lines, Figures 12a and 12b illustrate methods for submersion of the support means including the pipe lines and the unit from sea level to position on the sea bed, Figures 13a and 13b are two plan views schematically showing two pipe installations in accordance with the invention and which illustrate, respectively, lateral branching of one separate pipe line from a bundle and branching of one lateral pipe line from a continuous pipe line in a bundle, Figures 14a and 14b are showing a lateral view and a side view of a solution for providing an end off branching of one separate pipe line forming part of a pipe line system as shown in Figure 13a, in the position wherein the pipe lines are deviated sideways below one of the pipe-shaped support elements, Figure 15 is showing a solution wherein a pipe line is passed through a recess or cut out in the pipe-shaped support element, Figures 16a and 16b are showing a lateral view and a plan view, respectively, on an alternative solution for end point branching of a pipe positioned in a support means in accordance with the invention, and whereby the branching pipe is directed laterally above the pipe-shaped support element, Figure 17 is a plan view similar to Figure 14b illustrating lateral branching of one of the pipe lines in a bundle, and showing a lateral restriction of the support means including the remainder of the pipe bundle after the off branching, Figure 18 is a similar plan view illustrating a solution for lateral branching of several pipe lines from continuing pipe lines in a bundle, Figure 19 is a lateral view along the plane A-A shown in Figure 18 and illustrating a means in the shape of a buoyancy member or float construction utilized in connection with a disrupted pipe-shaped support element, Figure 20 is a plan view of the solution shown in Figure 19, Figure 21 illustrates a method for providing a lateral branching of a pipe from a bundle positioned in a support means in accordance with the invention, Figure 22 illustrates a method for making and transporting pipe line systems in accordance with the invention, Figure 23 illustrates schematically a plant for supporting pipe line systems in accordance with the invention during production on a shore site and prior to transporting the same to floating position, Figure 24 is a schematic cross-sectional view through a pipe system in accordance with the invention in floating position and including means for adjustment of the free board and buoyancy.

Figures 1 and 2 are showing cross-sections through two simple embodiments for support means in accordance with the invention.

The support means 2 shown in Figure 1 comprises two side by side positioned pipeshaped support elements 4 and 6 which are assembled together by means of spacers or the transverse element 7 which are positioned at suitable longitudinally spaced intervals along the support means. If the pipe-shaped support means consists of steel piping, the spacers suitably consist of steel elements which are welded to the steel piping. Between the two support elements 4 and 6 are positioned pipe lines 8 and 10, for instance pipe lines for conveying oil.

Figure 2 is showing a similar cross-section through a second embodiment of the invention wherein the spacers consist of concrete elements 12 which are moulded around the two pipe-shaped support buoyant elements 14 and 16. The number 18 designates one single larger pipe line. The pipe lines may be attached to the spacers by means of not shown clamps or the like to the extent permanent attachement is assumed necessary.

Figure 3 is a perspective view of a support means similar to Figure 1 wherein on the under side of the pipe elements 22,24 are mounted elongated ribs 26 adapted to protrude down into the sea bed and thereby prevent lateral displacements of the unit when installed on the sea bottom. Spacers are here on the top side given a V-shaped configuration 28 which can serve as a seat for a pipe line.

The support means as shown in figures 1-3 will in general possess much larger rigidity in the horizontal plane than in the vertical plane, whereby the system better can sustain hydrodynamic forces simultaneously as one obtains a further defined flexiblity in the vertical plane.

The rigidity in the vertical plane can be conformed to the actual pipe lines which shall be positioned in the support means, the characteristics on the sea bed, etc.

Figures 4a and 4b illustrate the support means in accordance with the invention when installed on a sea bottom. On the plan view shown in figure 4 the pipe line 30 extends without support means along the path 32 shown to the right, whereafter the pipe line runs into the support means for instance as shown in Figures 1-3. Figure 4b is a lateral view of the installation shown in Figure 4a and illustrates how the support means including the pipe line can extend as a downwardly curved free span 34 ascross a depression 36 in the sea bottom 37. The support means supports the pipe or pipes, prevents substantial lateral movements and reduces thereby risk for vibrations and too much downward deflection of the pipe lines.

A very important characteristics of the support means in accordance with the invention is that the buoyancy or the submerged weight can be adjusted in accordance with the need.

It is usually two types of adjustments which are usually tangible, namely: 1) Adjustments along the pipe line, and 2): Adjustments in time stages. In regard type 1) it may for instance be desirable to obtain larger weight on a section a) than a section b) as shown in Figure 4b. Section a) is in contact with the bottom 37 and transfers loads (horizontally and vertically) from the construction down into the bottom 37. Stability is only obtained when the contact pressure has a certain magnitude.

When making and installing support means with pipe lines in accordance with the invention the operations will usually take place subject to type 2), namely the following time stages: 1) Fabrication or launching (not always necessary, for instance not with very short length.

2) Transport of the support means with or without pipe lines to the installation site, 3) Assembly prior to installation.

4) Installation (submersion, positioning).

5) Operation (operation, environment forces and accident risks).

It can also be of interest to carry out inspections, repairs, and removal of the entire unit.

The support means absorbs a part of the gravity forces on the pipe lines and it will be subjected to hydrodynamic forces. Together with increased bending rigidity in the system the resistance force of the unit against hydroelastic vibrations will be improved, in comparison with a not protected pipe line or bundle of pipe lines. Such vibrations are created by turbulence in the water streams around the separate elements constituting the unit and which spans above the sea bed. This resistance can be increased further by means of conventional "vibration depressors" such as for instance shown with stithced lines 39 in Figure 1.

The necessary adjustment of the weight of the support means, buoyancy and buoyancy variations can be obtained by regulation and circulation of the content in the pipe-shaped support elements 4, 6 and 22,24 as shown in Figures 1 and 3.

In Figure 5 is shown a pipe-shaped element divided into chambers or bulk heads 40,42 and 44, by means of transverse walls 45. The contents therein may be air, gas, buoyancy material such as foam, or water. For transporting purposes or operations on sea level the elements will normally be filled with gas.

Between the chambers are suitably positioned communicating pipes 46.

In areas with large wave forces (shore zones) it may be necessary to fill the chambers in the installed construction with concrete in order to reinforce same and for obtaining increased weight in submerged position. If the sea bed simultaneously is uneven, it may be necessary to supply the concrete in two or more steps in order to avoid overloading of the support means during the time period prior to that the concrete attains sufficient strength.

Alternatively one may utilize spacers of concrete as shown in Figure 2.

A second method for obtaining a suitable reinforcement of the support means is to divide the pipe elements in internal rooms with vertical walls 50 as shown in Figures 6a-c.

Filling (injection) of concrete 52 can then take place in two steps with a time interval between the fillings sufficiently long in order that the support means attains sufficient strength in connection with the hardening of the concrete, such that the strength is sufficient in order to receive the weight of floating concrete during step 2. The end opening of the pipe element can be sealed off by means of a closure or bulkhead 54, as shown in Figure 5.

The geometrical configuration of the crosssection can influence on the hydrodynamic forces, particularly in direction of lifting forces (upwards or downwards). This possibility can be utilized for a total optimum utilization of the support means.

A further reinforcement of the support means can be obtained in different fashions, for instance by means of further support elements or in that the pipe elements for instance are provided with longitudinal internal or external ribs 56 as shown in Figures 6a-c.

If it is considered necessary to protect the pipe lines against falling objects, wear, etc., the pipe lines may be covered with covers 58 which may be loosely positioned or attached to the support elements.

Subject to difficult conditions, for instance relatively long free spans and large hydrodynamic forces due to water streams or the like, it may be necessary to anchor the support means to the sea bottom. Conventional stay means can be used, for instance chains with anchors, palls etc. Horizontal soil resistance against sliding and displacements may be improved by providing the underside of the support means with ribs, both longitudinal ribs 26 as shown in Figure 3, and/or transverse ribs (not shown), which also will contribute to transmittance of forces along the pipe line in result of thermical expansions and internal pressures in the pipe lines.

If support means are used having large rigidity in the vertical plane, and the rigidity is much larger than the pipe lines which shall be positioned in the support means, it may be correct to subject the support means or actual sections of the same, and initial bending during the production of same in order to reduce the length of free spans. It will be understood that support means in accordance with the invention may be used along the entire length of the pipe line to be laid or a bundle of such, or possibly only along certain parts of the total extension of same, for instance along areas having especially uneven bottom, large hydrodynamic forces etc., in connection with oiland gas production pipe lines in areas where it would be natural that the support means also supports and protects the lines along their entire length.

Figures 7 to 10 are vertical sections through additional embodiments of the invention and wherein equal numbers designate equal parts, in that the numbers 53, 54 designate two pipe-shaped support elements which are built together mutually spaced by means of cross peaces 56 forming support for one or more production pipe lines, cables or the like 58 (only some are furnished with numbers). The pipe-shaped support elements 53,54 are such dimensioned that they circumscribe and thereby protect the pipe lines on both sides. If desired/required, one may as already described, position closures or protectional elements 60 bridging between the support elements 52,54 as shown in Figure 8, whereby the pipe lines are protected for instance against fishing gear.

In Figure 7 the pipe lines are shown positioned in holders or "stalls" 64, such that each separate pipe line is laterally supported, but free upwards such that each separate pipe line can be replaced or the like, if necessary, for instance to prevent relative movement between the pipe lines and the support means due to thermical movements.

In Figure 8 the pipe bundle is positioned in one separate holder 63, possibly such that the bundle can be replaced as a unit for replacement, and for mounting, such that the support means will be left on the sea bottom.

In Figure 9 the cross pieces 60 are designed as a construction on the underside of the support elements 53,54, proper, such that these normally come into position above the sea bed 66 as shown. In this embodiment a pipe line 68,69 is positioned on the outside of the cross pieces 60. The cross pieces or spacers 60 are positioned with certain longitudinal intervalls along the support construction, for instance in intervalls of 6 to 12 meters. If the pipe lines have sufficient negative buoyancy in all operational phases, including installation and operation in the field, it may not as shown be necessary to fasten the pipe lines in the support means. In other cases the pipe lines must be fastened to the support means, for instance as shown in the Figures or by means of clamps.

This embodiment, which has support pipes 53,54 positioned at a higher level relative to the bottom surface of the support means and renders thereby possibilities for i) improved floating stability of the support means in that the distance between the buoyancy-and gravity center is increased and ii) the stiffness in the vertical plane is increased, if the pipe lines are rigidly attached to the support means. This stiffness adjustment is important for long support means which demands that the cross-section is symmetrical in regard the stiffness in all directions, especially in the vertical plane. In this fashion is also obtained tilting stability during installation, also when the unit is subjected to transverse water streams.

Possible asymmetrical conditions should be compensated with axial tension in the structure.

In Figure 10 is shown a further embodiment for the invention wherein the pipes are positioned in special two-part holders with an under imposed 72 and super imposed "yoke" 74, formed with complementary recesses for grasping around the pipe lines or pipe bundle.

Some of the pipe lines may as shown be positioned under such yokes, while other pipe lines 79 may rest freely on the supports. The "yokes" may in some cases consist of longitudinal continuous roughs completely circumscribing the pipes in the bundle in order to insulate the same.

Figures 11a-c illustrate the design and use of special clamps or clips 80 for holding the pipe lines. In Figure 11a is shown a pipe 82 which has been clamped down in place between two flexible upstanding arms 84 holding the pipe lines in a locked position. Figure 11 b illustrates release of the pipe by pulling the same upwards, while 11 c illustrates mounting by pushing the pipe line down between the clamps. A such solution will greatly facilitate mounting and removal of each separate pipe line. It is simple to configurate the elements such that a less force is required for mounting by downward pushing than release by upwards pulling.

It may be desirable to further improve the floating stability of the support means and also the lateral stability in submerged position prior to that the support means and pipe line system are being sunk down to the sea bottom if the support means including the pipe lines are subjected to horizontal hydrodynamic forces induced by stream and/or waves. This can be obtained by increasing the distance between the center of buoyancy and center of gravity of the unit by means of ballast trimmings.

Ballasting may for instance be realized as shown in Figures 12a, 12b, wherein Figure 12a shows an arrangement for stabilizing the support means in horizontal position, while Figure 12b shows an arrangement for stabilizing the support means when the same is in tilted position. In the embodiment shown in Figure 12a the support means 90 is provided with a briddle 92, a wire strap 94, and weights/ballast bodies 96. The briddles 92 are attached to the support means 90 by means of hinges 98. The hinges 98 make it possible to pivot the briddles 92 and the weight 96 in below the support means to a withdrawn position when the support means has been installed on the sea bottom. The hinges or briddles may be provided with stopping means (not shown) which limit the apex angle of the briddles during the transport and installation operations.In this fashion the stoppers contribute to that the briddles may be positioned below the support means in a defined direction subsequent to that the means with or without pipe lines has been positioned on the sea bottom.

If the support means are transported and submerged in a tilted position such as shown in Figure 12b, the briddles 92 ought to be asymmetrical. The length of the briddles 92,100 and the gravity of the weight 96 are calculated on basis of the requirements to the floating- and protectional stability.

In order to increase the distance between the center of gravity and the center of buoyancy further, it may be possible to utilize special buoyant bodies. These may by means of hinged briddles (not shown) be attached to the upper side of the support means. The buoyant bodies must, however, either be removed subsequent to installation, or laid down such that fishing gear may pass unobstructed over the support means including the pipe lines in areas where such measures are required.

If installation and the coupling procedures require that the support means is being kept hovering in position above the sea bottom and/or with a very low contact pressure against the bottom, in order to move the support means along the sea bottom in controlled fashion, it is natural to utilize chains 100 hanging vertically down in a similar fashion as the weight 96. Use of chains in this fashion is known technology in connection with installation of conventional pipe bundles.

If required, the pipe lines may be insulated in order to reduce heat losses in the pipe medium being conveyed. This may be carried out in conventional fashion, for instance such that some of the pipe lines are furnished with separate insulation. A such solution makes it possible to inspect, replace individual pipe lines. If inspection/replacement is not of interest and/or large demands are required from the installation, the pipe lines may be encased in special insulating elements, for instance in the shape of continuous two-part insulating elements which in section can be compared with the attachment means shown in Figure 10. Such insulating elements can thus partly serve as attachment means, partly as protectional means and partly as insulation.If the elements shall serve as insulation, they should of course extend continuously along the pipe line and be attached to the spacers between the support elements by means of not shown fastening elements.

Temperature variations in the production pipe lines will frequently be different from the temperatures prevailing in the support means and will thereby induce forces or relative movements, or a combination of such, between the pipe lines and the support means.

From a constructional point of view it is advantageous to reduce or elimiate relative movements between the pipe lines and the support means at each end. This will otherwise lead to actual forces in the pipe lines.

The pipe lines can either be very rigid, for instance by positioning the support means with very little mutual spacing, such that they can withstand the thermal forces, and one can see to that the spacers on the support elements make it possible to open for a pipe buckling at a certain maximum load with reference to a particular design pattern, such that one avoids damage on the pipe lines. Alternatively the pipe lines may be equipped with expansion elements in order to compensate for variations in dimensions in longitudinal direction. With regard to buckling, it may be advantageous to provide the pipe lines with a small, but sufficient longitudinal bend in order to monitor the buckling direction.Thermal elongations in the goods may be assumed to be 0,001 of the length, which elongation may result in a buckling from the type axis on about 0,005 to 0,001, of the pipe length which buckles. A typical pipe length in the construction as described and which may buckle, will be about 10 meters, which gives a buckling of 50-100 mm in the centre between two support points.

The effect of pressures- and temperature variations may be reduced in that the pipe lines and the support means are positioned on the sea bottom with a permanent tension (in unloaded condition relative to pressure and temperature). A such more or less permanent or residual tensional stress will frequently be a natural result when installing the entire unit.

A further important aspect of the invention rests in the possibilities of the design to offer various solutions for establishing pipe branches from a pipe bundle installed in a support means in accordance with the invention.

A common feature of the branching solutions which shall be described in the following is that the support means including installed pipe lines etc. serve as supporting basis for the branch piping such that these receive sufficient support in the joints or nodes between the support means including the pipe bundle and the branching pipe line. Thereby one may avoid that critical stress concentrations arise in the pipe goods in the pipe joints or nodes.

It is neither necessary to penetrate the walls in the support pipes in connection with the branch lines. These problems have prior to the present invention resulted in that one has found it difficult to establish direct branch lines from continuous pipes for instance positioned inside a support pipe and which shall be installed on the sea bottom.

Such pipe branching systems shall be described in connection with the enclosed Figures.

Figures 13a and 13b are plan views schematically illustrating two different branch line aspects in accordance with the invention, namely end- or terminal branching of one separate pipe line in a bundle as shown in Figure 13a, and branch lines from continuous single pipe lines in a bundle as shown in Figures 13b.

In Figure 13a a production plant 110 is connected to sea bottom wells 112,113,114,115, which may be productionor injection wells, by means of pipe lines 116,117,118,119 which transport media, signals or energy in accordance with the need.

Individual wells under this concept are directly connected to the process plant 110. Pipe lines between the plant and branching points 120,121, and 122 run together by means of a support means 124 (described earlier). From the branching points branch lines 126,128 and 130 lead to the wells 112,113,114, respectively. In the shown example the monitoring of the wells is carried out from plant 1. Choke valves are preferably positioned also on plant 1.

The branch solution or "manifold principle" in accordance with the invention is generally illustrated in Figure 13b. This solution is designated as alternative 2. The Figure shows the connection of the plant 131 to wells 132,134,136 and 138 by means of collecting lines represented in Figure 2 with line 140.

The collecting lines have in this arrangement the function of a manifold. Lines 140 have branches in lines 142,144 and 145 which go to the separate wells. Collecting lines 140 are installed in a support- and protection means 146. The pressure in the collecting lines for well production may be controlled and monitored on plant 131. The pressure in branch lines 142,144 and 145 is controlled from the plant 131 and directly controlled on wells 132,134 and 136.

If one or more of the wells shown in Figures 13a and 13b are injection wells, the injection fluidum is conveyed in separate pipes or in the pipes forming the main elements in the support means. This is not shown in the Figures.

The location of the support means 124 and 146 is such selected that the costs are kept at a minimum. From safety measures the construction should be positioned at a sufficient distance from the wells (in order to reduce the risk for damage due to falling objects from drilling rigs and vessels) and at sufficient distance from an anchor zone. This arrangement is also advantagous from a point of safety.

The branch lines 126,128,130,142,144 and 145 may in the principle be: a) "Rigid" and be installed subsequent to that the support means 146 including the collecting lines 140 is installed on the sea bottom.

b) Rigid or flexible and being transported and sunk together with the support means 146.

Production- and service lines 116,117,118,119 and 140 can with advantage be rigid (for instance of steel). In any case a connection must exist for the production- and service lines at the branching points 120,121 and 122. Other lines (for signal and power transmission) do not need couplings (divisions) in or at the branching points.

The branching in both alternatives require that the support pipe elements in the support means 124 and 146 must be traversed with pipe lines 126,128,130,142,144 and 145 in the points 120,121,122,150,154 and 155.

The principle under alternative 2 requires further that valves must be arranged in the vicinity of the branching in order to be able to operate the branch lines separately and thereby particular wells independent of other pipe lines and wells.

The bypass or crossing may be arranged without need for interruption of the support means 124 in order to provide space for the pipe lines. The arrangement shown in Figure 9 wherein the support pipes are lifted above the pipe lines renders a simple passing of branching pipe lines below the support pipes. Otherwise a satisfactory passing can be realized realized in the following fashions: a) As shown in Figures 14a and 14b the branch lines 160 pass below the support pipe 162 and is along a longitudinal section L lifted over a connecting frame 163. The support pipe has been bent in beforehand in known fashion and is being attached to the frame in correct distance by means of spacers 165,166,168 and 170 in order to minimize elastic deformations and stress concentrations in various phases when the support means must sustain tension.The support means supporting the pipe lines can be such arranged that point 162 is positioned higher than the uppermost point of the pipe line which is branching off along a certain length, or along the entire construction length as described above. The latter case is realistic if the support means is not provided with a throughgoing frame 163, and it is then not necessary to bend the support pipe.

b) In the embodiment shown in Figure 15 the branch line 170 passes directly through the support pipe 172 through a suitable passage 174. The spacers or transverse elements 175 between the pipe-shaped support elements 172 may in the branching zone be connected by means of longitudinally extending support means 176.

c) In Figure 15a (seen along plane B-B in Figure 16b) and 16b the branch pipe line 180 is such configurated that it passes above the support pipe 182. It may be necessary to arrange a protection of the pipe line 180 shown with double stitched lines 183. A such protection is known for a man skilled in this art and should not be necessary to describe in details.

In Figures 14a,14b,15,16a and 16b equal numbers designate equal parts.

For a pipe installation as schematically shown in Figure 13a the support means may be reduced gradually as the separate pipe lines are laterally branched off and leaving the pipe installation. An example of a such lateral restriction is illustrated in Figure 17. A pipe line 190 leaves the support means and from this point on the lateral dimension of the support means is reduced. It is important that the support pipes 192 and 194 are such arranged that the distance between the longitudinal axis of the support means and the support pipes 192 is equal to the distance between the axis and the other support pipe 194 in order to maintain axis symmetrical balance and also due to the transfer of axial forces arising in connection with towing and pre-tensioning of the support means, possibly with compression of the support pipes.Pipe lines 196 and 198 are being bent in order to maintain a symmetrical position in the support means. Restriction of the support means is possibly not necessary if the pipe lines are positioned in the support means in horizontal layers opposing each other, or if it is acceptable that the support means is made wider than necessary only with regard to the question of space.

Branching from continuous pipe lines as shown in alternative 2 in Figure 13b can either be carried out as in alternative 1 wherein the valves are positioned on the outside of the support means. It may be advantageous from a view point of safety to confine the valve equipment inside the outer boundary of the pipe system. Further, with a view to the floating stability, it is desirable to position the equipment as close as possible to the longitudinal axis of the construction. A possible design of a such passing and positioning of the valve equipment is shown schematically in Figure 18.Pipelines 200,202,204 and a cable 206 are branched off for connection to a sea bottom well to "manifold lines" 210,212,214 positioned on the support means, consisting of support pipes 216,218 and a frame 220 as support basis for the lines (not shown) in addition to the earlier described, at suitable intervals positioned spacers or transverse elements 222. The pipe line may in the branching point be such arranged that bending of the line 212 having the larger diameter is avoided, in that pipes having smaller diameter are passed in the vertical plane such that the branching pipe stubs 225 and 227 are not necessary to be bent. On pipes 224,226 and 228 are mounted valves including actuators 230,232 and 234 and other necessary equipment. On inlets of the valves are mounted couplings for connecting branch lines 200,202, and 204.

In the passing or passage point the support pipe 216 as shown at 240, 242, respectively, is disrupted in order to provide space for valves, fittings and other equipment. The frame 220 which constitutes a special part of the support means is covering the entire base and is as a safety measure made rather rigid and strong in the vicinity of the pipe line passage. Due to the need for internal pressure in the support pipe 216 and for water filling a connecting pipe 248 is positioned in the uppermost part of the pipe 216 between the two disrupted ends as shown in Figure 19. In order to compensate for the reduced buoyancy of the support pipe 216 and also due to the increased weight caused by the valve equipment etc.,a special buoyant body or float 246 is mounted on the top side of the support pipe 216 as shown in Figure 19 which is showing a lateral view along the plane A-A shown in Figure 18. The positioning and size of this float are decided on basis of the need to floating stability and buoyancy of the construction unit. The float may be made of steel piping and such shaped that it does not create an obstruction for passing of fishing gear. For controlling the pressure and water ballasting are arranged pipe fittings 250,252, It can also be necessary to provide the float with vents 253 in order to obtain complete water filling subsequent to installation.In order to carry out repairs, inspections and possibly replacement of valve equipment and the like in connection with branch lines, it is necessary to have sufficient access to the equipments. Horizontal axis, for instance to carry out operations utilizing remotely controlled submarine vessels, it is easy to obtain such possibilities by adjusting the width of the disruption or opening in the support pipe 216. Possible buoyant bodies or floats 246 can be relasably mounted on to the frame 210. A such arrangement is not shown in the Figures. Vertical access, for instance for replacement of equipment, can be obtained in that the float 246 is provided with one or more vertical openings 254 as shown in Figure 20 which shows a plan view of the "manifold unit".

Branch pipe lines which extend from pipe stubs on the valves 230,232,234 may be made of steel, or may be composed of other materials (for instance COFLEXIP).

The branch lines in alternatives 1 and 2 may be transported and installed either in a conventional fashions which are based upon transport of the branches separate from the support means and being joined to the unit in the installation area, or in the following fashions.

The branch lines 68,69 shown in Figure 9 are joined to the support means ashore and transported together with the support means in supported position thereon to a suitable storage place. When the pulling to the terminal point shall be carried out, the branch pipe line is released and is thereafter pulled away from the support means until the end reaches the pre-selected production well and it is thereafter coupled to same. This pulling operation can be done in a known fashion suitably adapted to the present system. Special operations consist in precautions in order to prevent acceptable bendings along the connection pipe line, for instance such as axial tension loads or the lifting of the connecting pipe line.

(Other steps are further described in connection with the second pulling method). This method is based on horizontal pulling. Its utilization is limited and can therefore be carried out within a certain range in regard relationship between the weight and the length of the pipe line, and the characteristics of the sea bottom.

A second method for carrying out the pulling of the branch line is illustrated in Figure 21, and this consists in pulling the line from a position along the support means to a further defined location, for instance to a production well, by means of an obliquely directed axial force which alters direction during the pulling and in this fashion lifts and maneuvres the pipe line. Thereby one can obtain a tension in the pipe line as well as an elimination or reduction of the contact pressure against the sea bottom. In order to obtain the desired bending of the pipe line one can control the same by means of wires, chains or the like 260 as shown in Figure 21, and which are given a suitable length. These are attached to the support means 262 and to the pipe line 264 which shall be bent to the side.The pipe line 264 is shown in transport position with stitched lines 263 either in sea surface position or in a position at the sea bottom. In this position the wires or chains 260 are finally mounted on to the support means and to the pipe line.

The invention also comprises different methods for making, transport and installation of pipe line systems in accordance with the invention.

A fabrication of relatively short support means can be made in conventional manner and shall not be described here. The following description applies to the most complicated embodiment of the various methods to make support means and pipe line systems in accordance with the invention, namely very long pipe bundles produced in special production plants and having a limited length.

With this solution it is possible to make pipe bundles on production sites with limited extent (down to about 100-200 meters) if these sides are located along a shielded ocean area (for instance a fjord arm). The production can also be carried out on a floating production plant if the demands to environment conditions are fulfilled.

The production can be carried out continuously by welding together both the pipe lines and the support means (hereafter called PSI), for instance into lengths of about 12 meters, and intermittently after being assembled pulling the ready made section of the unit 1, including PSI down into the water wherein the pipe bundle 1 will float supported by PSI, while other sections are successively produced ashore.

An example of a such continuous method for production and arrangement is schmatically illustrated in Figure 22. The process is split up into eight working stations 320-327. A steel frame 328 for mounting the support means in the shape of pipe-shaped support elements (BB-piping) having transverse spacers are put together in station 320. The pipes are attached to the spacers and the joints are tested/inspected in station 321. Pipe lines (production- service lines) are welded together sectionaily and tested/inspected in station 322. In accordance with the need the pipe joints are furnished with corrosion protection and insulation in station 323. In station 324 the steel frame 328 is positioned below the BB-piping 329 and are welded together to form the support unit.At this stage one can, if necessary, furnish the unit with corrosion protection and possibly with sacrificial anodes.

In station 325 ready made pipe lines 330 are positioned in the support means and are attached in accordance with the need as previ ously described. In station 326 cables 331 are positioned in the produced unit including the pipe lines. Cables (electric, hydraulic) are delivered in full or maximum lengths on a drum 332.

The stations 320, 321 and 322 are parallelly arranged. It is preferred to position station 320 below station 321, such that the support means 329 forms a straight line and the flexible 328 is bent into contact with the support means for welding. The station 322 may on the other side be positioned on the same level as station 321, and the station 323 can be subjected to slight bending caused by its own weight when these are lifted into place in the support means 321 in the working station 325. Stations 323, 324, 325 and 326 are arranged in series with parallel stations 300,321 and 322. If necessary, 5ballasting frames with ballast 341 and 342 are mounted on station 327.The steel frame 321, the support means 329, the pipe lines 320 and also the part of the finished construction 333 which is not floating in the water can be journalled on rollers which both support and permit horizontal transport of the elements 328,329,330 and 333. The floating part of the finished support means 334 is subjected to a certain tension in order to increase the stiffness and thereby the resistance against environment wear (streams, wind- and wave forces). The tension is obtained by means of winches 335,336 and cables 337 and 338. The tension is maintained between two fixed points, one point ashore at the production site 333 and a second in the water, provided with an anchoring system 340. This anchoring point can be established also ashore on the opposite side of the production site, if necessary.The anchoring point 339 can for instance be devised as one or several pairs of wheels (having rubber tyres and brakes) which clamp against the BB-pipe, or in the principle by one or more movable gripper arms which intersects a transverse element on the steel frame 321 and thereby prevents movement of the entire support means 334.

A second method is to a larger degree based upon prefabrication. Sections of ready made support means (for instance in sections of 24-26 meters) are transported to the production site and welded together. The remainder of the process is in the principle equal to the method described above.

A second arrangement of the support means, for instance without continuous connected frame, or a means based upon one support pipe would naturally demand a modification of the process which has been described.

An arrangement for supporting the various parts 328 and 329 of the support means, the pipe lines 330 and the finished construction 333 is schematically shown in Figure 23. Rollers 343 on a support structure 344 are such arranged that they form a rectilinear base for the structure in section A. In section B the parts 343 and 344 are such arranged that they form a transition ramp which guides the construction down into floating position without inducing unacceptable stresses. A second support- and conveyor method based upon use of slides or wheel-going supports which are removed piecemeal as the structure is transferred to floating position. Such method does not demand that control surface between the structure and the support is "smooth" without protruding parts, for instance transverse elements or spacers joining the support pipes together.

When the entire support means is ready, its tail part is maintained ashore for testing of pipe lines, BB-piping and cables. Possible errors are repaired. Water used for possible testing of pipe lines etc. is compensated by the buoyancy of the support means. If required, the BB-piping can be filled with nitrogene and subjected to pressure. The safety for all handling in water is increased if the pressure in the BB-piping is measured, and in case of pressure drop, loss of gas, will automatically be compensated for.

When all testing is completed and the support means is ready for launching, the tail end still attached to shore is connected to a wire and a winch providing the required tension in the support means subsequent to that the entire length of same has passed the anchoring point 339 on Figure 22. In floating condition the support means may be handled by means of two towing vessels. The support means can now be moved to a storage or a trimming place.

Regardless the towing- and sinking method, the buoyancy- and weight characteristics of the completed support means is being checked and if necessary, adjusted. This operation can be done in known fashion if the support means shall have negative buoyancy in order to be transported below the sea surface in accordance with the so-called "controlled depth tow" principle. If the means shall have positive bouyancy (for transport on the sea surface), the same can be adjusted for adding or removing suitable ballast, for instance chains, until a desirable buoyancy has been obtained. Figure 24 is showing a means for defining the buoyancy by means of measuring the draft of thhe structure 345. A frame 346 is fixed to the structure 345. The frame supports two equal, transparent pipes 346, 347 furnished with a scale for reading the water stand in the pipes. In order to dampen the water stand movement inside the piping the same are provided with hoses 348,349, extending down to a depth wherein the water pressure is not being influenced by short surface waves. Thereby the water level in the pipes are kept quiet.

Different reasons can cause that the support means must be made in sections and thereafter be joined together.

If only production factors cause that the support means must be made in several sections, the same can be joined together prior to the towing out into a shielded sea area.

If maximum construction length is defined by shielded towing, the joining can take place prior to that the ocean towing begins. The joining can then take place in a shielded area.

If maximum construction length is defined by ocean towing, the joining must be carried out at the installation site.

The joining of the support pipes is firstly carried out in accordance with known methods, for instance by means of screwthreaded elements and flanges or by means of welding. The end walls of the support pipes are water-tight in order to obtain the desired buoyancy. When the sections are joined together, it is not necessary to open the entire internal space of the support piping. The necessary communication between the various sections for conveyance of air and water during the sinking can be established by means of smaller pipes which preferably are furnished with check valves.

The joining of the separate pipe lines in the support means can be carried out in accordance with known methods, for instance using couplings or fittings or welding. In order to simplify the joining or coupling operation, it is possible to lift the separate pipe lines out of the support means, position the same preliminary on a support carried by the support pipes and then carry out the joining and the testing in the air. Thereafter the pipe lines are again positioned in the support means and the lines may be attached.

The transport of the support means can be made in the same fashion as in connection with the transport of conventional pipe bundles, for instannce bottom pulling (bottom tow) or "controlled depth tow" (CDT). These methods are known and not described here.

It is also possible to transport the support means in surface floating position. Its strength, flexibility, buoyancy and size will together with the prevailing wave- and stream conditions determine whether this is possible.

The rigidity of the support means vertically can be increased and the wave forces reduced substantially if the transport is carried out in tilted position as shown in Figure 12b. This position is specially attractive if the transport takes place parallel with the wave direction.

If two or more support means shall be used one after the other with end to end contact, adjacent ends ought to be joined such that mutual lateral displacement is prevented. This requirement can be obtained by means of known means, for instance by furnishing adjacent ends with special transition sockets trough-shaped transition pieces or other auxiliary means for accomplishing the necessary locking.

Claims (25)

1. A support means for supporting, and protecting a submersible pipe line system during transport and after submersion, including means for confining one or more pipe lines after installation on the sea bed, said support means comprising a longitudinally extending divided structure which has means for adjusting its buoyancy and which defines one or more centrally extending upwardly substantially open channels or passages provided with supporting elements for receiving and supporting the pipe line system.

2. A support means in accordance with claim 1, wherein the structure comprises two laterally spaced pipe-shaped buoyant bodies which are mutually connected with transverse elements constituting the support members for the pipe lines.

3. A support means in accordance with Claim 1 and/or 2, wherein the transverse members consist of longitudinally spaced transverse spacers permanently attached to the pipe-shaped buoyant bodies, which spacers may be interconnected with longitudinally extending stayers in order to increase the strength and stiffness of the support means, especially in the horizontal plane.

4. A support means in accordance with any of preceding Claims, wherein the pipe-shaped support elements are divided into separate chambers by means of bulkheads, and in that said chambers are interconnected with a pipe system in order to make it possible to adjust the buoyancy in the pipe-shaped support elements along their longitudinal extension.

5. A support means in accordance with any of preceding Claims, wherein the support means on the underside is provided with longitudinal and possible transverse downwardly pointing ribs or the like adapted to be pressed down into the sea bed and thereby prevent lateral or longitudinal displacements.

6. A support means in accordance with any of preceding Claims, wherein the spacers are provided with holder means for each separate pipe line, and possibly holders for the pipe bundle.

7. A support means in accordance with Claim 6, wherein the holder means consists of upwardly open holders shaped as mutually spaced upright plate elements or the like, able to receive the pipe lines and prevent lateral displacements of same.

8. A support means in accordance with claim 6, wherein the holder means consists of two-legged flexible clamps or clips into which the pipe lines can be pressed downwards to a locked position with a snap effect.

9. A support means in accordance with any of preceding claims, wherein one or more of the pipe lines in the pipe system are releasably locked in the support means by means of transverse yokes or the like.

10. A support means in accordance with any of preceding claims, wherein one or more of the pipe lines in the systems are insulated, for instance by means of split insulating elements provided with cup-shaped recesses, the undermost of which suitably is attached to the spacers.

11. A support means in accordance with any of preceding claims, wherein the pipe line system is covered with protecting elements resting on to and if desired, attached to the pipe-shaped support elements on either side of the structure.

12. A support means for submersible pipe line systems of the kind wherein one or more of the pipe lines in installed position in the support means on the sea bottom are designed to be connected to one or more different terminal points, for instance a number of sea bottom oil wells, wherein a junction for joint including a pipe stub for connecting a branch line is arranged, which pipe joint fitting is firmly fixed to the spacers or a spacer frame connecting the pipe-shaped support elements such that the branch pipe line leading from the pipe stub is given the desired lateral diverted angle prior to that the branch line is leaving the support on the support means.

13. A support means in accordance with claim 12, having one or more pipe lines, wherein a pipe line which shall be branched off is loosely or releasably positioned in the support means until the support means including the pipe line system is installed on the sea bottom whereafter the pipe line to be branched off is lifted out from position in the support means in order to be pulled laterally in order to be connected to a designed terminal point, for instance a production well.

14. A support means for submersible pipe line system in accordance with any of claims 1 to 13, wherein the pipe lines are porovided with valves, pipe joint fittings adapted for branch pipe lines, prior to positioning the pipe line system in the support means and before the same is installed on the sea bottom, the branch pipe lines to be connected to the pipe lines positioned in the support means subsequent to that the same has been installed on the sea bottom.

15. A support means for submersible pipe line system in accordance with any of preceding claims, wherein said pipe-shaped support elements are provided with one or more disrupted sections in order to provide space and access for valve equipment, pipe joints and the like in order to establish branch pipe lines such that the same unobstructed of the pipeshaped support elements can be diverted out laterally.

16. A support means in accordance with claim 15, wherein between two opposing disrupted ends of one of the pipe-shaped support elements is mounted a pipe line connection for maintainance of communication for fluidum through the pipe-shaped support elements.

17. A support means in accordance with claims 14 to 16, wherein a buoyant body is releasably attached to the support means above a disrupted section of one of the pipeshaped elements in order to compensate for lost buoyancy due to removal of a part of said pipe-shaped elements.

18. A support means for submersible pipe line system in accordance with any of preceding claims 1 to 17, wherein said branched pipe line diverted laterally extends in an arch above the adjacent support element.

19. A support means for pipe line system in accordance with any of preceding claims 1 to 18, wherein a branched pipe line is laterally diverted through an opening or recess in the adjacent pipe-shaped support elements or below or above the support elements

20. A support means for submersible pipe line system, wherein the width of the support means structure is reduced gradually in accordance with the number of pipe lines axially positioned in the support means relative to the number of branched off pipelines.

21. A method of making and transporting a submersible pipe line system intended for installation on the sea bottom using support means in accordance with any one of the preceding Claims, pipe lines of the system and the support means being assembled as a continuous unit on a suitable site ashore, wherein the pipe lines are conveyed through various working stations arranged one after the other or one above the other in order to carry out simultaneous production of the support means and of the pipe line system by joining sections of pipe lines together, whereafter the produced unit is pushed or pulled out into the water and is floated by means of the buoyancy in the support structure, whereafter the pipe line system is towed in sections formed by the units or as a continuous length formed by units joined together to the installation area where the units are sunk to desired position on the sea bed by reducing the buoyancy in the support structure.

22. A method in accordance with Claim 22, wherein the pipe system is submerged subject to gradual and controlled reduction of the buoyancy such that the pipe line system can be submerged in controlled gradual fashion avoiding any section of the pipe line system being subjected to undue bending and critical stresses.

23. A method in accordance with any of Claims 21 or 22, wherein the support means in connection with the submersion operation is provided with downwardly suspended stabilisation elements in the shape of weights or the like, simultaneously as the support means preferably also are provided with longitudinally spaced holding means which during any stage of the submersion extends from the support means up to flat members at the sea surface.

24. A support means according to Claim 1, substantially as described with reference to the accompanying drawings.

25. A method according to Claim 21, substantially as described with reference to the accompanying drawings.