Abstract:
A J-lay system constructed to be positioned on board a pipeline-laying vessel, comprising a fixed pipeline support ( 12 ) and a movable pipeline support ( 12 ) configured for supporting a pipeline ( 10 ) which is suspended form the pipeline-laying vessel, —the movable pipeline support ( 12 ) comprising: —at least a first movable support member ( 20 A) configured for engaging a first collar ( 16 A) on the pipeline ( 10 ), —at least a second movable support member ( 20 B) configured for engaging a second collar ( 16 B) on the pipeline ( 10 ), —the fixed pipeline support ( 12 ) comprising: —at least a first fixed support member ( 20 A) configured for engaging a third collar on the pipeline ( 10 ), —at least a second fixed support member ( 20 B) configured for engaging a fourth collar on the pipeline ( 10 ), wherein the first ( 20 A) and second fixed support member ( 20 B) configured for engaging a fourth collar on the pipeline ( 10 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of International Application No. PCT/NL2009/000224, filed Nov. 18, 2009, which claims the benefit of Netherlands Application No. NL 2002291, filed Dec. 5, 2008, and U.S. Provisional Application No. 61/116,956, filed Nov. 21, 2008, the contents of which are incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention relates to a pipeline support, to a pipeline or pipe section, to a combination of a pipeline or pipe section and a pipeline support, and to a method for supporting a pipeline. The present invention also relates to a pipeline laying vessel having such a pipeline support. 
     BACKGROUND OF THE INVENTION 
     Methods and devices for laying pipelines are widely known. One method of laying a pipeline is the so-called J-lay method. Other methods are also known, such as S-lay. 
     Generally, the pipeline which is laid is suspended at a free end from a pipeline laying vessel during the laying thereof. New pipe sections are joined to the free end during the laying of the pipeline. 
     Generally, at a point at which the free end of the pipeline is suspended from the vessel, hereinafter referred to as the suspension point, large forces are transferred from the pipeline to the vessel. In the field of marine pipelaying, there is a gradual development that pipelines are laid in ever increasing water depths. This implies that longer and heavier pipelines are suspended from the vessel and thus, the force which is exerted on the pipeline support by the pipeline shows a gradual increase over time. 
     In one method of pipelaying, the forces are transferred from the pipeline to the vessel via a collar on the pipeline which engages a pipeline support on the vessel. 
     A problem which is encountered is that the forces may become too great for a collar of a known size. In some cases, it may be an option to increase the size of the bearing area of the collar. However, this is not always possible or preferable. A bigger diameter generally means an increase in cost. In the case collars are made from thick walled pipe, there may be fabrication limits to the outer diameter of the collar. 
     Also, for pipe-in-pipe systems of the sliding type, on certain locations collars may be required on the inner pipe. The outer diameter of a collar on an inner pipe may become too large to fit within the inner diameter of the outer pipe. In such a situation, an increase in the size of the collar would necessitate a larger outer diameter of the outer pipeline. This in turn substantially increases the cost of the total pipeline system. 
     Another problem encountered in the prior art is that the forces which are transferred from the pipeline to the pipeline support induce stress concentrations in the pipeline or in the pipeline support. Generally, the contact between the pipeline and the pipeline support occurs in a support surface. Depending on the situation, these local stress peaks may become too high and damage may occur in the pipeline or in the pipeline support. 
     U.S. Pat. No. 5,458,441 discloses an example of a traditional J-lay system. One of the embodiments shows each pipeline section containing two collars. A movable clamp  32  engages a bearing area on a first collar  12 , a fixed clamp  34  engages a bearing area on a second collar  18 . No load sharing between the two collars occurs during lowering of the pipeline or during adding a new pipe section. When loads in the pipeline increase, the bearing areas of the respective collars have to increase in order to carry the load. This will lead to an increased overall wall thickness and thus a larger protrusion of the collars from the pipeline wall. An increase of wall thickness generally leads to an increase of production cost and makes it more difficult to manufacture collars with the desired mechanical properties. 
     U.S. Pat. No. 6,273,643 discloses a similar system as U.S. Pat. No. 5,458,441 and has a similar disadvantages. 
     U.S. Pat. No. 6,729,803B1 discloses a system which is based on friction. Shoes  17  are provided having bearing surfaces  21 , A number of different shoes  17  are provided in different planes  11 , which are vertically spaced from one another, see  FIG. 3 . Some load sharing occurs between the planes  11 , see column 8, lines 51-67. However, a disadvantage of U.S. Pat. No. 6,729,803 is that it is difficult to ensure a proper distribution of the forces between the levels  11 . In practice, the actual distribution of the forces will be relatively unpredictable. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved J-lay system. 
     It is another object of the invention to provide a J-lay system which allows higher loads from the pipeline to be transferred to the pipeline laying vessel. 
     It is another object of the invention to provide a J-lay system which creates lower stress peaks in the pipeline and/or the pipeline support for a given load. 
     It is another object of the invention to provide a J-lay system which allows smaller collars to be used. 
     It is another object of the invention to provide a J-lay system which allows more cost-effective pipe-in-pipe systems. 
     It is another object of the invention to provide a J-lay system which allows a predictable way to transfer the forces from the pipeline to the J-lay system. 
     At least one object is achieved by a J-lay system constructed to be positioned on board a pipeline-laying vessel, the J-lay system comprising a fixed pipeline support and a movable pipeline support configured for supporting a pipeline which is suspended from the pipeline-laying vessel, 
     the movable pipeline support comprising:
         at least a first movable support member configured for engaging a first collar on the pipeline,   at least a second movable support member configured for engaging a second collar on the pipeline,
 
wherein the first and second movable support members are spaced apart at a movable support member distance along an intended firing line, wherein the first movable support member is resiliently mounted according to a substantially predetermined load-movement relationship relative to the second movable support member,
       

     the fixed pipeline support comprising:
         at least a first fixed support member configured for engaging a third collar on the pipeline,   at least a second fixed support member configured for engaging a fourth collar on the pipeline,       

     wherein the first and second fixed support member are spaced apart at a fixed support member distance along an intended firing line, wherein the first fixed support member is resiliently mounted according to a substantially predetermined load-movement relationship relative to the second fixed support member. 
     The J-lay system of the invention allows a distribution of the total axial load over at least two support members of the movable pipeline support or over at least two support members of a fixed pipeline support which are placed along the firing line of a J-lay system on board a pipeline laying vessel. Thus, each support member and each corresponding collar on the pipeline may carry a smaller load than the total axial load. In the invention, the distribution of the forces is no longer dependent on the amount of slip, as it is in U.S. Pat. No. 6,729,803. This is an advantage and increases the predictability of the distribution of the forces. Further the overall wall thickness of the collar can be reduced, allowing more cost effective fabrication as well as more control over the mechanical properties. 
     The movable pipeline support (sometimes indicated as a travelling block) is generally movably arranged on a tower-like construction and can make a stroke from an upper position to a lower position in order to lower a pipeline in a pipeline laying process. 
     The fixed pipeline support (sometimes indicated as a hang-off table) is generally provided in or below a welding station in which a new pipe section is joined to a free end of the pipeline which is suspended via the fixed pipeline support. 
     The total load may be distributed substantially evenly, but may also be distributed non-evenly in certain cases. 
     Multiple collars may be provided on the pipeline, spaced apart from one another such that in use, the combined collars transfer the total load of the pipeline to the vessel. 
     In a suitable embodiment,
         the movable pipeline support is configured such that when a load is exerted on the first movable support member, the first movable support member moves in the direction of the second movable support member over a substantially predetermined distance, thereby decreasing the movable support member distance,
 
and
   the fixed pipeline support is configured such that when a load is exerted on the first fixed support member, the first fixed support member moves in the direction of the second fixed support member over a substantially predetermined distance, thereby decreasing the fixed support member distance.       

     In this way, a relatively accurate load distribution is possible. A third and potentially even more support members can be provided, further reducing the load which each support member carries, and thereby giving the opportunity to further reduce the overall wall thickness of the collar. 
     In a suitable embodiment, the first and second movable support member are connected to one another via a movable frame, and the first and second fixed support member are connected to one another via a fixed frame, wherein at least part of the movable frame and at least a part of the fixed frame is configured to deform substantially elastically, such that the movable frame and the fixed frame act as a spring having the substantially predetermined load-movement relationship. A frame which deforms elastically is a simple and reliable way of creating a predetermined load-movement relationship. 
     In an embodiment, the at least first and second movable support members are integral with a movable frame connecting the at least first and second support members, and the at least first and second fixed support members are integral with a fixed frame connecting the at least first and second support members. An integral pipeline support, both for the movable and fixed pipeline support, is strong, easy to manufacture and reliable. 
     In another suitable embodiment, the substantially predetermined load-movement relationship is configured such that when in use the first collar of the pipeline exerts a typical load on the first movable support member, the first movable support member moves such a distance that the second collar of the pipeline engages the second movable support member, and that when in use the third collar of the pipeline exerts a typical load on the first fixed support member, the first fixed support member moves such a distance that the fourth collar of the pipeline engages the second fixed support member. 
     In a non-loaded state, the second collar does not engage the second movable support member and a gap exists between the second collar and the second movable support member. When the weight of the pipeline is added, the second collar approaches the second movable support member and at a substantially predetermined load engagement occurs. The same mechanism applies for the fourth collar and the second fixed support member when the pipeline is suspended from the fixed pipeline support. 
     In another embodiment, the support members are angled obliquely relative to the projected firing line. In other words, the support members taper with respect to the intended firing line. This provides a possibility of reducing the distance over which the collars protrude from the wall of the pipeline. The angled support members are constructed to engage tapering collars on the pipe section or pipeline. 
     In a suitable embodiment, the support member distance is adjustable. This allows the force distribution to be more accurately controlled. For this end an active system may be used, where the support member(s) which is (are) loaded above average is (are) lowered and the support member(s) which is (are) loaded below average is (are) raised. These options of variation can be achieved by this embodiment. 
     The invention also relates to a pipeline or pipe section constructed to be supported by a J-lay system comprising a fixed pipeline support and a movable pipeline support, the pipeline or pipe section comprising:
         a first set of collars comprising at least a first collar and a second collar constructed to engage the movable pipeline support of a J-lay system, wherein the second collar is positioned at a collar distance from the first collar in the longitudinal direction of the pipeline or pipe section,   a second set of collars comprising at least a third collar and a fourth collar constructed to engage the fixed pipeline support of a J-lay system, wherein the fourth collar is positioned at a collar distance from the third collar in the longitudinal direction of the pipeline or pipe section,   the first collar being configured to engage a first movable support member of the movable pipeline support,   the second collar being configured to engage a second movable support member of the movable pipeline support,   the third collar being configured to engage a first fixed support member of the fixed pipeline support,   the fourth collar being configured to engage a second fixed support member of the fixed pipeline support,       

     wherein the pipe section between the first and second collar and between the third and fourth collar is resilient according to a predetermined load-elongation relationship, such that when in use a certain axial load is applied on the first collar or on the third collar, the collar distance increases a substantially predetermined value such that the second collar engages the second movable support member or the fourth collar engages the second fixed support member. 
     This embodiment uses the pipeline itself as a spring with a known spring constant, thereby effectively distributing the total load over the collars. 
     Generally, the collars protrude from a wall of the pipeline. This is a simple way of applying the present invention. As explained before, it can be advantageous from cost and quality point of view to limit the protrusion. 
     In a suitable embodiment, the collars extend around the outer wall of the pipeline or pipe section. Collars are a simple and reliable way of creating support surfaces on the pipeline. 
     The invention further relates to a combination of a J-lay system and a pipeline or a pipe section, 
     the J-lay system comprising a fixed pipeline support and a movable pipeline support configured for supporting a pipeline which is suspended from the pipeline-laying vessel,
         the movable pipeline support comprising:
           at least a first movable support member configured for engaging a first collar on the pipeline,   at least a second movable support member configured for engaging a second collar on the pipeline,   
           wherein the first and second movable support members are spaced apart at a movable support member distance along an intended firing line,   the fixed pipeline support comprising:
           at least a first fixed support member configured for engaging a third collar on the pipeline,   at least a second fixed support member configured for engaging a fourth collar on the pipeline,
 
wherein the first and second fixed support member are spaced apart at a fixed support member distance along an intended firing line,
   
               

     the pipeline or pipe section comprising:
         a first set of collars comprising at least a first collar and a second collar constructed to engage a movable pipeline support of a J-lay system, wherein the second collar is positioned at a collar distance from the first collar,   a second set of collars comprising at least a third collar and a fourth collar constructed to engage a fixed pipeline support of a J-lay system, and wherein the fourth collar is positioned at a collar distance from the third collar,
 
wherein:
       

     the first collar is configured to engage the first movable support member, 
     the second collar is configured to engage the second movable support member, 
     the third collar is configured to engage the first fixed support member, 
     the fourth collar is configured to engage the second fixed support member, 
     wherein: 
     a) the first movable support member is resiliently mounted according to a substantially predetermined load-movement relationship relative to the second movable support member, and the first fixed support member is resiliently mounted according to a substantially predetermined load-movement relationship relative to the second fixed support member, such that the second collar engages the second movable support member or the fourth collar engages the second fixed support member
 
and/or
 
     wherein the pipe section between the first and second collar and between the third and fourth collar is resilient according to a predetermined load-elongation relationship, such that when in use a certain axial load is applied on the first collar or on the third collar, the collar distance increases a substantially predetermined value such that the second collar engages the second movable support member or the fourth collar engages the second fixed support member. 
     In a suitable embodiment, the collar distance is smaller than the support member distance. 
     In a suitable embodiment, the difference between the collar distance and the movable and fixed support member distance is tuned to the substantially predetermined load-movement relationship of the support members of the movable and fixed pipeline support and/or to the substantially predetermined load-elongation relationship of the pipeline or pipe section between the collars, such that:
         the second collar engages the second movable support member when the load on the first support member is a predetermined portion of the projected total load of the pipeline on the vessel and   the fourth collar engages the second fixed support member when the load on the first fixed support member is a predetermined portion of the projected total load of the pipeline on the vessel.       

     In a suitable embodiment, the predetermined portion is between 30% and 70% of the projected total load of the pipeline on the vessel, in particular between 40% and 60% of the total load. The present invention allows a more or less equal load distribution. 
     In a suitable embodiment, the pipeline comprises six or more collars spaced apart in the direction of a main longitudinal axis of the pipeline, three or more collars for the movable pipeline support and three or more collars for the fixed pipeline support and wherein the movable pipeline support comprises three or more movable support members which are spaced apart, and wherein the fixed pipeline support comprises three or more fixed support members which are spaced apart and wherein the distances between the collars are smaller than the distances between the movable support members and between the fixed support members and wherein the load-movement relationships and the load elongation relationships are chosen such that in use, the total load which the pipeline exerts on the pipeline laying vessel is spread over the respective collars which engage the movable pipeline support or over the collars which engage the fixed pipeline support. 
     When multiple collars are applied, each collar can be relatively small, which allows a reduction of the width of the collars when compared to a single collar. 
     In a preferred embodiment, the fixed and movable pipeline support compress in the same order in response to a certain load as the pipeline extends in response to the same load, such that the difference between the collar distance and the support member distance is closed by both an increase in the distance between the respective collars of the pipeline or pipe section as a decrease in the distance between the support members. In this embodiment, the deformation capability of all material is used effectively and the elastic properties of both pipeline and support structure are used. 
     In another embodiment, the movable and fixed pipeline support between the respective first and second support members compress much more in response to a certain load than the extension of the pipeline between the first and second collars and between the third and fourth collars in response to the same load, such that the greater part of the difference between the collar distance and the support member distance is closed by a decrease in the distance between the respective support members. 
     In this embodiment, the strain in the pipeline is small in comparison to the strain in the pipeline support. 
     The words “much more” indicate that the decrease in the support member distance is at least three times, preferably at least five times greater than the increase in the collar distance. 
     In another embodiment, the movable and fixed pipeline support between the respective first and second support members compress much less in response to a certain load than the extension of the pipeline between the first and second collars and between the third and fourth collars in response to the same load, such that the greater part of the difference between the collar distance and the support member distance is closed by an increase in the distance between the respective collars of the pipeline or pipe section. 
     In this embodiment, the deformation capability of the pipeline is used effectively and the pipeline support can be regarded as a more or less non-deformable object. 
     The words “much less” indicate that the decrease in the support member distance is at least three times, preferably at least five times smaller than the increase in the collar distance. 
     In another embodiment, deformable rings are positioned between the collars and the support members. The deformable rings further distribute the forces more evenly over the respective support members. 
     The present invention also relates to a method of laying a marine pipeline, comprising providing a pipeline laying vessel having a J-lay system and a pipeline or pipe section,
         the J-lay system comprising a fixed pipeline support and a movable pipeline support configured for supporting a pipeline which is suspended from the pipeline-laying vessel,
           the movable pipeline support comprising:
               at least a first movable support member configured for engaging a first collar on the pipeline,   at least a second movable support member configured for engaging a second collar on the pipeline,   
               wherein the first and second movable support members are spaced apart at a movable support member distance along an intended firing line,   the fixed pipeline support comprising:
               at least a first fixed support member configured for engaging a third collar on the pipeline,   at least a second fixed support member configured for engaging a fourth collar on the pipeline,   wherein the first and second fixed support member are spaced apart at a fixed support member distance along an intended firing line   
               
           the pipeline or pipe section comprising:
           a first set of collars comprising at least a first collar and a second collar constructed to engage a movable pipeline support of a J-lay system,   a second set of collars comprising at least a third collar and a fourth collar constructed to engage a fixed pipeline support of a J-lay system,
 
wherein the second collar is positioned at a collar distance from the first collar, and wherein the fourth collar is positioned at a collar distance from the third collar,
   
               

     the first collar being configured to engage the first movable support member, 
     the second collar being configured to engage the second movable support member, 
     the third collar being configured to engage the first fixed support member, 
     the fourth collar being configured to engage the second fixed support member, 
     wherein: 
     
         
         a) the first movable support member is resiliently mounted according to a substantially predetermined load-movement relationship relative to the second movable support member, and the first fixed support member is resiliently mounted according to a substantially predetermined load-movement relationship relative to the second fixed support member,
 
and/or
 
         b) wherein the pipe section between the first and second collar and between the third and fourth collar is resilient according to a predetermined load-elongation relationship, the method comprising exerting a force from the first or third collar of the pipeline or pipe section on the first movable support member or the first fixed support member, thereby increasing one of the collar distances and/or decreasing one of the support distances such that the second collar engages the second movable support member or the fourth collar engages the second fixed support member. 
       
    
     It is possible to distribute the total load of the pipeline substantially equally over the available collars. 
     The invention also relates to a vessel comprising a pipeline support according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a cross-sectional view of a step in the suspension of a pipeline from the pipeline support according to the invention, 
         FIG. 1B  shows a cross-sectional view of a subsequent step in the suspension of a pipeline from the pipeline support according to the invention, 
         FIG. 1C  shows a cross-sectional view of a next step in the suspension of a pipeline from the pipeline support according to the invention, 
         FIG. 2  shows an partial cross-sectional view of another embodiment of the invention, 
         FIG. 3A  shows a schematic cross-sectional view of the embodiment of  FIG. 2 , 
         FIG. 3B  shows a more detailed cross-sectional view of the embodiment of  FIGS. 2 and 3A , and 
         FIG. 4  shows a detailed cross-sectional view showing allowable margins in the combination of the pipeline support and the pipe section of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A ,  1 B and  1 C show a section  10  of a pipeline and a pipeline support  12  of a J-lay system. The pipeline support  12  can be a fixed pipeline support or a movable pipeline support. A fixed pipeline support is generally also referred to as a hang-off table (HOT). A movable pipeline support is often referred to as a movable clamp. The pipe section  10  may form the free end of a pipeline which is suspended from the vessel. The pipeline may extend all the way down to a seabed, which in practice may be a distance of several thousands of meters. 
     Because a substantial length of pipeline is suspended from the vessel, a substantial axial force  14  is present. This axial force  14  is to be transferred to the pipeline support  12 . To this end, the pipe section  10  is provided with at least a first collar  16 A and a second collar  16 B. It will be appreciated by the skilled person that such collars may have many different sizes and shapes. For instance, the collars may not extend completely around the pipeline but may protrude from the pipe wall over a limited circumferential length. The collars may have a rounded form when viewed in cross-section, such as a semi-circular form or a rectangular form having rounded corners. 
     The collars  16 A,  16 B are provided with a first support surface  18   a  and a second support surface  18   b  respectively. The first and second support surfaces  18 A,  18   b  are provided at a collar distance  19  from one another 
     In a suitable embodiment, the support surfaces are angled relative to the firing line (not shown in  FIGS. 1A-1C ). 
     The pipeline support  12  is provided with support members  20 A and  20 B. The support members protrude from a frame  22  of the pipeline support. The support members  20 A,  20 B have support surfaces  24 A,  24 B. The first and second support surface  24   a ,  24 B are provided at a support member distance  15  from one another. 
     The pipeline  10  has an outer wall  25  having a wall thickness  26  and the collars  16 A,  16 B protrude over a distance  28  from the outer wall  25 . 
     The collar distance  19  is smaller than the support member distance  15 . 
       FIG. 1B  shows how in use the pipeline  10  (or pipe section  10 ) contacts the pipeline support  12 . The first support surface  18 A of the pipeline  10  contacts the first support surface  24 A of the first support member  20 A. A gap  30  (also indicated with δ) occurs between the second support surface  18 B of the pipeline  10  and the second support surface  24 B of the pipeline support. Due to the force  14 , the section  11  of pipeline  10  between the first support surface  18 A and the second support surface  18 B will extend and the section  13  of the pipeline support  12  between the first support member  20 A and the second support member  20 B will be compressed, as is indicated with arrows  32  and  34 . The pipeline  10  and the pipeline support  12  deform elastically and act as springs. 
     It is preferred that the pipeline support  12  is much stiffer than the pipeline  10 , such that the pipeline  10  will extend much more than the pipeline support  12  will compress. 
     It is also possible that the pipeline  10  is much stiffer than the pipeline support  12 , so that the compression of the pipeline support  12  is much greater than the extension of the pipeline  10 . 
     Due to the extension of the pipeline section  11  and the compression of the pipeline support  12 , the gap  30  will close, so that the second support surface  18 B of the pipeline and the second support surface  24 B of the pipeline support  12  engage. This is shown in  FIG. 1C . 
     When the stiffness of the pipeline  10  and the pipeline support  12  are known, it is possible to determine a difference between distance  19  and distance  15 , i.e. a gap  30 , which is required for the second support surface  18 B to engage the second support surface  24 B of the pipeline support  12  for a certain force F. This force F occurs at the first support surface  18 A. 
     Thus, it is possible to determine a relationship between δ and F. For instance, the pipeline  10  and the pipeline support  12  may be designed such that the second support surface  18 B will meet the second support member  20 B when the load which is transferred via the first support surface is 1000 kN. 
     In such a way, it can be determined that the total load is distributed over the first and second support surfaces  18 A,  18 B according to a more or less predetermined distribution. A substantial equal distribution may be obtained. 
     The parameters which determine the value of the force at which the second support surface  18   b  meets the second support member  20 B include:
         1. The difference δ between the collar distance  19  and the support member distance  15 ,   2. The tensile stresses which occur in the section  13  of the pipe  10  and the compressive stresses which occur in the section  13  of the pipeline support  12 , which tensile stresses are determined by the size and shape of the pipeline  10  and which compressive stresses are determined by the size and shape of the pipeline support  12 ,   3. The elasticity of the respective materials from which both the pipeline and the pipeline support are made, i.e. the modulus of elasticity E.       

     When the Force F is known which acts on the first support surface  18 A, the tensile stresses in the pipeline  10  and the compressive stresses in the pipeline support  12  may be calculated based on the size and shape of these parts. Via Hooke&#39;s law, the known stresses and the known modulus of elasticity determine the strain in the pipeline  10  and the strain in the pipeline support  12 , i.e. the strain can be calculated based on the stresses and the elasticity modulus. 
     When the strain is known, the extension of the pipeline  10  and the compression of the pipeline support  12  can be calculated based on the collar distance  19  and the support member distance  15 . The combined extension and compression result in the gap  30  which is to be created in order to ensure that the second support surface  18 B and the second support member  20 B meet at the required Force F. Of course it is also possible to reverse this computation, i.e. to calculate the force F when the gap  30  is known. 
     Thus, it is possible to tune the gap  30  in such a way that the total load  14  on the pipeline is distributed substantially equally over the two collars  16 A,  16 B. This provides the possibility of replacing one large collar (not shown) of the prior art by two smaller collars  16 , such that the distance  28  by which the collars  16  protrude from the side wall of the pipeline  10  is decreased. Or, if the size of the collars is maintained substantially the same, it is possible to increase the total load which can be transferred from the pipeline  10  to the pipeline support  12 . 
       FIG. 2  shows another embodiment of the invention, in which the pipeline  10  comprises three collars  16 A,  16 B,  16 C and three support surfaces  18 A,  18 B,  18 C for a movable pipeline support. The pipeline comprises three similar collars comprising support surfaces for a fixed pipeline support which are not shown in  FIG. 2  and discussed further in relation to  FIGS. 3A and 3B . The support surfaces are oriented at an angle  21  relative to the main longitudinal axis of the pipeline  10 . In this example the angle  21  is &lt;90 degrees, which allows a further reduction in the distance  28  over which the collars protrude from the wall of the pipeline  10 . However, an angle of 90 degrees is possible as well. The first and second support surface  18 A,  18 B are located at a collar distance  191  from one another, and the second and third support surfaces  18   b ,  18   c  are located at a collar distance  192  from one another. 
     The pipeline support  12  is provided with three pipeline support members  20 A,  20 B and  20 C which are provided at support member distances  251 ,  252  from one another, respectively. The support member distance  251  is greater than the collar distance  191  and the support member distance  252  is greater than the collar distance  192 , creating gaps δ 1  and δ 2 . Since the gaps are small relative to the size of the pipe and the support, they are not distinctly visible in  FIG. 2 . The fixed pipeline support and the movable pipeline support each comprise three support members. 
     By deliberately introducing the gaps δ 1  and δ 2 , it is possible to make use of the elasticity of the materials of the pipeline and the pipeline support. 
     By manipulating δ 1 ,  191  and t 1  it is possible to control at what percentage of the total load the second support surfaces  18   b ,  24 B will engage one another. The formula that applies is: 
     
       
         
           
             
               δ 
               1 
             
             = 
             
               
                 ( 
                 
                   
                     σ 
                     A 
                   
                   - 
                   
                     σ 
                     B 
                   
                 
                 ) 
               
               ⁢ 
               
                 
                   L 
                   1 
                 
                 E 
               
             
           
         
       
     
     The same applies for the second gap δ 2 . 
     
       
         
           
             
               δ 
               2 
             
             = 
             
               
                 
                   ( 
                   
                     
                       σ 
                       A 
                     
                     - 
                     
                       σ 
                       B 
                     
                   
                   ) 
                 
                 ⁢ 
                 
                   
                     L 
                     2 
                   
                   E 
                 
               
               + 
               
                 δ 
                 1 
               
             
           
         
       
     
     In the equation, σ A  is the tensile stress (positive value for tension) in the pipeline  10 , σ B  is the compressive stress (positive value for compression) in the pipeline support  12 , L 1  is collar distance  191 , and L 2  is the collar distance  192 . 
     It is also possible to use four, five or six support surfaces for each of the fixed and movable pipeline supports which are spaced apart in the direction of the intended firing line. 
     A skilled person will understand that the axial force in the pipeline increases stepwise when travelling in a downstream direction  80 . Below each support surface, the axial force increases when compared to the axial force above the support surface. 
     Likewise, in the pipeline support  12 , the axial force increases when travelling in a downstream direction. It can be seen in  FIG. 2  that the thickness t 2  of the pipeline support  12  between the second and third pipeline support  20 B and  20 C is greater than the thickness t 1  of the pipeline support  12  between the first and second support member  20 A and  20 B. In this way, the increased force does not lead to an increased compressive stress and/or strain in the pipeline support  12  between the second support member  20 B and third support member  20 C. 
       FIGS. 3A and 3B  further show the embodiment of  FIG. 2 , wherein three support members are provided. It can be seen in  FIG. 3A  that three support surfaces  18 A 1 ,  18 A 2 ,  18 A 3  on the pipeline  10  are provided for a fixed pipeline support  12  and three support surfaces  18 A 4 ,  18 A 5 ,  18 A 6  are provided for a movable pipeline support  120 . The angle  21  of the support surfaces relative to the main longitudinal axis of the pipeline is about 60 degrees. The respective support surfaces distance  191 ,  192  are in the order of 50 mm. The gaps δ 1  and δ 2  are in the order of 0.10 to 0.50 mm. Generally the gaps are kept as small as possible in order to keep the total length of the upper pipe section as small as possible, which is preferred from an economical point of view. A typical total length  70  of the upper end of a pipe section will be approximately 800 to 1000 mm for the given gap values. 
     The form of the pipeline support members  20 A,  20 B,  20 C downstream of (or under) the actual support members is rounded, see radius  42 . Or in other words, the transition of the support members  20 A,  20 B,  20 C into the frame  22  is rounded in order to reduce peak stresses. 
     The transition of the collars to the pipe  10  is also rounded for the same reason which is indicated with radius  40 . Different radii of curvature may be used for both roundings. 
     The form of the collars  16 A,  16 B  16 C is thus defined by a curved section  40  which goes over in the actual support surface  18 A 1 , 2 , 3  resp.  18 A 4 , 5 , 6 . The support surfaces end at an outer end of the collar  16 A,  16 B,  16   c . The collars each have a part  46  which extends parallel to the pipe wall  25 . Next, an inclined section  44  tapers inward back to the pipe wall  25 . Other forms are also possible. 
     The form of the support members  20 A,  20 B, and  20 C is defined by a rounded section  42 , followed by a section  43  which extends parallel to the pipe wall  25 . This section ends at a corner  47  where the support surfaces  24 A,  24 B,  24 C of the support member  20 A,  20 B,  20 C starts. The support surfaces  24 A,  24 B,  24 C are oriented at an inclination and taper outwardly, back to a wall  50  of the frame  22 . 
     In the embodiment shown in  FIG. 3 , the thicknesses of the pipeline support  12  are calculated as 16 mm for t 1  and 21 mm for t 2 . 
     Generally, the initial gaps  30  are calculated analytically. For a known or chosen value of thickness of the pipeline support  12 , an optimal gap that would be required to obtain equal load distribution can be calculated. Also upper and lower gap limits can be calculated. 
     This is illustrated in  FIG. 4 . A detail of the gap between collar  16 B and support surface  24 B of  FIG. 1B  is schematically indicated. A nominal gap  400  is the gap where an optimal load distribution is obtained, for instance 50%-50% for a system with two support members. The distance between the minimum gap  401  and maximum gap  402  is the margin  410  which is available for fabrication tolerances. A deviation from the nominal gap  400  will result in a different load distribution between the support members. A smaller than nominal gap will lead to a lower than predicted load on an upper support member, and a larger than nominal gap will result in a higher than predicted load on an upper support member. Depending on the allowed deviation, for instance 60%-40% to 40%-60% between an upper and a lower support member, the allowable fabrication tolerances can be determined. The smaller the allowed deviation from a nominal gap  400  is, the tighter the fabrication tolerances will become. 
     It will be obvious to a person skilled in the art that numerous changes in the details and the arrangement of the parts may be varied over considerable range without departing from the spirit of the invention and the scope of the claims.