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CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a 35 U.S.C. §371 National Phase conversion of PCT/FR2009/050983, filed May 27, 2009, which claims benefit of French Application No. 08 53587, filed May 30, 2008, the disclosure of which is incorporated herein by reference. The PCT International Application was published in the French language. 
     BACKGROUND OF THE INVENTION 
     This invention relates to a device for mounting a flexible line on a structure, of the kind comprising:
         a hollow rigid member, intended to be integral with the structure, the hollow rigid member defining a traveling way of the flexible line;   a curvature limiter defining an insertion lumen of the flexible line, with the insertion lumen having a travel axis of the flexible line, the curvature limiter being movable relative to the hollow rigid member between a position away from the hollow rigid member and a position mounted on the hollow rigid member;   releasable means for axial immobilization of the curvature limiter on the flexible line in at least one first direction along a travel axis, for moving the flexible line together with the curvature limiter relative to the hollow rigid member between the position away from the hollow rigid member and the mounted position.       

     Such mounting devices are used in hydrocarbon exploitation installation on a body of water, including for instance a fixed rigid structure on the seabed, an oscillating structure secured to the seabed, or a floating structure, such as a surface naval base, a semisubmersible platform, a floating vertical column, or a vessel. 
     The flexible line to be mounted on the structure is for instance a flexible rising fluid carrying pipe, a so-called riser. Herein “flexible pipes” are understood to mean those described in the standards published by the American Petroleum Institute (API), API 17J and API RP 17 B, and well known to the person skilled in the art. More generally, the flexible line can be a bundle-like composite harness, a set of umbilicals or electrical cables. 
     A mounting device of the aforementioned type is used when installing and connecting the flexible line to the surface structure. 
     For this purpose, in order to reduce the risks of damaging the structure and the flexible line, it is known to immerse the flexible line into the body of water below the surface structure and to lift it up to the connecting area located on the surface structure by means of a hoist. Such a connection is referred to by the term pull-in. 
     The flexible line is guided over the structure by introducing the same through a hollow rigid tube integral with the structure and oriented vertically, which is a protective sleeve. The hollow tube is for instance of the “I tube” or “J tube” type. 
     At the upper outlet of the tube, the flexible line is connected to the surface installation. 
     In order to avoid any deterioration of the flexible line, namely under the effect of water agitation likely to bring it into contact with the structure, it is known to engagedly mount around the flexible line a curvature limiter adapted to locally impose a radius of curvature greater than the minimum radius of curvature which may be adopted by the flexible line. 
     Hereafter, curvature limiters are understood to both curvature limiters, composed e.g. of articulated rigid elements called “vertebrae”, and stiffeners, composed e.g. of plastic molded blocks, as well as combinations thereof. 
     A stiffener is for instance arranged around the flexible line close to the upper end thereof, so as to cooperate with the hollow tube when the flexible line is inserted into the tube. 
     For this purpose, first of all, the stiffener and the flexible line are moved together to the lower end of the hollow tube until the stiffener has been partially inserted into the hollow tube. Next, in a second stage, the flexible line is moved upward in relation to the stiffener for lifting the same up through the hollow tube in view of connecting it to the surface structure. 
     During this second phase, the stiffener is maintained to be translationally immobile within the hollow tube through embedding and/or fastening by means of hose clamps. 
     For these two steps to be performed successively, pulling systems are known using at least two different hoists. The cable of a first hoist is connected to the stiffener so as to be lifted up toward the lower end of the hollow tube, and the cable of a second hoist is connected to the upper end of the flexible line so as to move the same in relation to the stiffener. Such a system requires precise control of the lifting of the cables, and therefore is not easy to use, in particular if the hollow tube is bent. 
     In order to compensate for this problem, it is known from WO 98/23845 to use a single hoist for pulling the flexible line and the stiffener by temporarily integrating the stiffener with the flexible line by means of a frangible pin. 
     When the stiffener is lifted toward the lower end of the hollow tube, the stiffener and the flexible line will move together. Next, the stiffener is fastened to the lower end of the tube. Sufficient traction is then applied upward on the flexible line so as to break the frangible pin in order to allow for the flexible line to move upward in relation to the stiffener. 
     Such a device is not entirely satisfactory. In fact, such a device according to prior art is complex and requires mechanical parts to be highly reliable. Furthermore, once the frangible pin has broken, it is no longer possible to disconnect the line from the structure, then to reconnect it to the same structure or to another structure, without reinstalling a pin, which requires for the flexible line and the stiffener to be lifted up to the surface. 
     SUMMARY OF THE INVENTION 
     One objective of the invention is to obtain a device for mounting a flexible line on a structure, which is simple to use, and which reduces the risks of deteriorating the flexible line. 
     For this purpose, the object of the invention is a device of the above-mentioned type, characterized in that the axial immobilization means comprise:
         a locking member, axially integral with the first one of the flexible line and the curvature limiter, and   a member for engaging the locking member, axially integral with the second one of the flexible line and the curvature limiter,       

     the locking member and the engaging member being mounted to be rotatably movable in relation to each other around the travel axis between a configuration for axial immobilization in the first direction of the flexible line on the curvature limiter, and at least one first angularly shifted configuration for axial travel in the first direction of the flexible line through the curvature limiter. 
     The device according to the invention can have any or several of the following characteristics, taking individually or in any technically possible combination:
         the locking member and the engaging member are movable in relation to each other along the travel axis between:   at least one disengaged axial position, in which the locking member and the engaging member are remote from each other and adopt a first configuration for axial travel in the first direction of the flexible line inside the curvature limiter;   an axial position for engaging the locking member inside the engaging member, in which the locking member and the engaging member are moved closer to each other;   an engaged axial position, in which the locking member and the engaging member adopt the configuration for axial immobilization in the first direction of the flexible line inside the curvature limiter;       

     the engaged axial position being located axially between the disengaged axial position and the engaging axial position;
         the locking member and the engaging member have complementary surfaces suitable for cooperating so as relatively rotate the locking member in relation to the engaging member around the travel axis from the travel configuration to the configuration for axial immobilization, during the relative axial movement of the locking member in relation to the engaging member, successively between the disengaged axial position, the engaging position, and the engaged position;   the locking member comprises at least one transverse retaining projection, with the engaging member comprising at least one axial retaining stop of the or each projection, the axial retaining stop defining a main groove for engaging the projection axially opening in a second direction opposite the first direction,       

     the or each projection being received inside the main groove in the configuration for axial immobilization;
         the engaging member comprises a guiding stop axially shifted in relation to the or each axial retaining stop, with the guiding stop defining at least one secondary groove for guiding the retaining projection opening opposite the main groove in the first direction;   the complementary surfaces are respectively defined by the or each retaining projection on the one hand, and by the or each guiding stop and/or the or each axial retaining stop on the other hand;   one of the locking member and the engaging member is mounted to be freely rotatable around the travel axis, respectively on the first or the second one of the flexible line and the curvature limiter;   one of the locking member and the engaging member defines a receiving housing suitable for receiving the other one of the locking member and the engaging member in the configuration for axial immobilization; and   the locking member and the engaging member are movable in relation to each other around the travel axis between the configuration for axial immobilization and at least one second configuration for axial travel, angularly shifted in relation to the first configuration for axial travel, with the configuration for axial immobilization being angularly located between the first and second configuration for axial travel.       

     Also an object of the invention is a fluid exploitation installation, of the type comprising:
         a flexible line to be connected to the structure; and   a device as defined above, the hollow rigid member being integral with the structure.       

     The invention may include the following characteristic: the structure, the hollow rigid member, and the flexible line are at least partially immersed into a body of water. 
     Also an object of the invention is a method for mounting a flexible line on a structure by means of a device as defined above, characterized in that it comprises the following steps:
         axially immobilizing in the first direction the curvature limiter on the flexible line by engaging the locking member with the engaging member, so that the locking member and the engaging member adopt their configuration for axial immobilization in the first direction of the flexible line on the curvature limiter;   moving the curvature limiter and the flexible line together from the position away from the hollow rigid member to the position mounted on the hollow rigid member;   relatively rotating the locking member in relation to the engaging member around the travel axis, so as to transfer the locking member and the engaging member from the configuration for axial immobilization to a configuration for axial travel;   axial travelling of the flexible line through the curvature limiter and through the hollow rigid member, the curvature limiter remaining substantially axially immobile in relation to the hollow rigid member.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood by the following review, provided only by way of example, and given with reference being made to the enclosed drawings, where: 
         FIG. 1  is a schematic sectional view along a medial vertical plane, of a fluid exploitation installation, comprising a first mounting device according to the invention; 
         FIG. 2  is a partial sectional view, taken along a transverse plane, of the relevant parts of the means for axial immobilization of the flexible line inside the curvature limiter of the mounting device represented in  FIG. 1 , during engagement of the immobilization means; 
         FIG. 3  is a view similar to  FIG. 2 , during axial immobilization of the flexible line inside the curvature limiter; 
         FIG. 4(   a ),- 4 ( i ) are a partial views from a side perspective of the immobilizing projections and the corresponding stops of the immobilization means represented in  FIGS. 2 and 3 , during the successive steps of engaging, locking, and unlocking of the flexible line inside the curvature limiter; 
         FIG. 5  is a detail view of the lower end of a rigid protecting tube of the mounting device according to the invention, when the curvature limiter is fastened to this tube; 
         FIG. 6  is a view similar to  FIG. 1 , during axial travel of the flexible line inside the curvature limiter. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 to 6  illustrate an installation  10  for exploitating fluids according to the invention. This installation is for instance intended to collect a fluid, namely a hydrocarbon tapped at the bottom  12  of a body of water  14 , or transfer said hydrocarbon to a transport vessel. 
     The installation  10  comprises a structure  16  floating on the body of water  14 , a flexible line  18  to be connected to the floating structure  16 , and a first device  20  for mounting the flexible line  18  to the structure  16 . 
     The body of water  14  is for instance a lake, a sea, or an ocean. The depth of the body of water perpendicular to the floating structure  16  is e.g. between 15 m and 3000 m. 
     The floating structure  16  is e.g. a surface naval base, a semisubmersible platform, a floating vertical column, or a vessel. 
     Alternatively, structure  16  is a jacket-like fixed rigid structure or an oscillating structure secured downward of the sea. 
     Floating structure  16  has an upper surface  22 , on which is mounted a hoist  24  for handling the flexible line  18  and a manifold  26  adapted for connecting one end of the flexible line  18 . 
     The hoist  24  comprises a single cable  28 , which can be deployed for pulling the flexible line  18 . 
     In the example represented in  FIG. 1 , the flexible line  18  is a fluid-carrying flexible tubular pipe  30  internally defining a fluid flow path. This pipe is also referred to as a rising pipe, or riser, and is to connect a wellhead located at the bottom  12  of the body of water to the manifold  26  located at the surface  22  of the floating structure  16 . 
     Alternatively, flexible line  18  is e.g. an umbilical-like composite harness or “integrated service umbilical” (ISU) or IPB, well known by the person skilled in the art and described in the standards published by the American Petroleum Institute (API) API RP 17 B paragraph 4.3.4. Alternatively, the flexible line may be a harness of electrical cables. 
     Pipe  30  has at the upper end  32  thereof a head  33  for connecting the working line to the cable  28 . 
     As illustrated in  FIG. 2 , head  33  comprises a connecting sleeve  34  fastened to the upper end of the pipe  30 , and an eyelet  35  for inserting the lower end of the working line to the cable  28 , rotatably mounted on an upper part of the sleeve  34  around a travel axis X-X′ of line  18 . 
     Sleeve  34  defines in the lower part thereof an annular channel  36  circumferentially extending around axis X-X′ and opening radially away from axis X-X′. 
     Pipe  30  is e.g. unwound and immersed into the body of water  14  from a surface laying vessel and is stored at the bottom  12  of the body of water  14 , next the end of pipe  30  (section not laid on the seabed) is abandoned at the bottom  14  via a drop cable. 
     Mounting device  20  comprises a hollow rigid tube  40  for guiding and protecting the tubular line  18 , which is integral with equipment  16 , a local curvature limiter  42  of line  18 , engaged around line  18  remote from the upper end  32 , and means  44  for fastening the curvature limiter  42  to the lower end of the hollow rigid tube  40 . 
     According to the invention, mounting device  20  further comprises releasable means  46  for axially immobilizing the flexible line  18  in the curvature limiter  42 . 
     In the example represented in  FIG. 1 , the hollow rigid tube  40  is a J tube having a vertical straight upper part and a bent lower end. Alternatively, the hollow rigid tube  40  is a straight tube of the I tube type. 
     Tube  40  comprises a hollow vertical sleeve  50 , integral with the floating structure  16 , and a lower end collar  52  located at the lower end  54  of sleeve  50 . 
     Sleeve  50  defines a lower passageway opening into the body of water  14  at lower end  54  and opening at the upper end  56  thereof close to the upper surface  22  of the structure, above the body of water  14 . 
     The end collar  52  is immersed into the body of water  14 . It has a truncated shape converging upward. It is attached to a fastening flange located at the lower end  54  of sleeve  50 . Collar  52  flares out downward up to a lower flange  58  supporting fastening means  44 , apparent in  FIG. 5 . 
     The curvature limiter  42  comprises, from bottom to top in  FIGS. 2 and 3 , a rigid lower assembly  62  and an articulated upper assembly  64  attached to the flexible lower assembly  62 . 
     The flexible lower assembly  62  comprises a stiffening block  66  and an intermediate fastening flange  68  on the hollow rigid tube  40 . 
     The lower block  66  is for instance molded from plastic material, such as polyurethane. It has a truncated shape converging downward. 
     Flange  68  is attached above block  66 . It has a peripheral edge protruding radially remote from axis X-X′ in relation to the stiffening block  66 . 
     The articulated upper assembly  64  comprises a plurality of tubular vertebrae  70 A,  70 B axially assembled end to end via annular collars  72 . 
     The lower vertebra  70 A is fastened to an angle bracket  74  carried by the flange  68  via an annular collar  72 . 
     Vertebrae  70 A,  70 B are slightly movable in relation to each other between a linear configuration along the axis X-X′ and a configuration which is slightly curved in relation to the linear configuration. 
     Block  66 , flange  68 , and vertebrae  70 A,  70 B internally define a center lumen  76  for travel of the flexible line  18  specifying the travel axis X-X′ of line  18  inside the curvature limiter  42 , coinciding with the longitudinal axis of line  18 . 
     In Block  66  and in vertebrae  70 A,  70 B, the lumen  76  has a cross-section which is substantially conjugate with the external cross-section of line  18 . 
     Blocks  66  and vertebrae  70 A,  70 B thus locally enforce upon the flexible line  18  a radius of curvature which is greater than the minimum radius of curvature which could be adopted by the flexible line  18 . 
     As will be apparent below, the curvature limiter  42  is movable between a dismantled position represented in  FIG. 1 , in which it is placed remote from the hollow rigid tube  40 , and a position mounted on the hollow rigid tube  40 , represented in  FIGS. 5  et  6 , in which the intermediate flange  68  of the limiter  42  is fastened to the lower supporting flange  58 , at the lower end of collar  52 . 
     The fastening means  44  comprise an annular collar  78  for retaining the intermediate flange  68  against the lower flange  58 . 
     According to the invention, the axial immobilization means  46  in a first direction of the curvature limiter  42  on flexible line  18  are formed by a reversible rotatable latch, a so-called “rotolatch”. 
     Such axial immobilization means  46  thereby comprise a rotatable latching member  90 , mounted to be axially integral with line  18 , and an engaging member  92  of the locking member  90 , mounted to be axially integral with curvature limiter  42 . 
     The locking member  90  comprises a rotatable bell  94  and a plurality of transverse projections  96  radially extending toward axis X-X′ inside the rotatable bell  94 . 
     The bell  94  has an upper annular wall  96  mounted to be freely rotatable in relation to line  18  around axis X-X′ in groove  36 , and a substantially cylindrical side wall  98  opening downward. 
     The locking member  90  is thus mounted to be axially fixed in relation to line  18 , while being mounted to be freely rotatable around axis X-X′. 
     The upper annular wall  96  and the side wall  98  internally define a housing  100  for receiving the engaging member  92 . Housing  100  extends along axis X-X′ and opens downward. 
     In the example represented, the locking member  90  comprises a plurality of retaining projections  96 , angularly distributed around axis X-X′. 
     Each projection  96  radially extends toward axis X-X′ within the receiving housing  100 , from the side wall  98  to the proximity of the lower rim of bell  94 . 
     Each projection  96  comprises a stud  102  fastened in the side wall  98  and a runner  104  rotatably mounted around a radial axis at the free end of the stud  102 . Each runner  104  defines an external running surface  105  on the engaging member  92 . 
     The engaging member  92  comprises a ring  106  mounted to be axially fixed and mounted to be freely rotatable around axis X-X′ at the upper end of vertebrae  70 . The ring  106  defines a plurality of upper axial retaining stops  108  of the projections  96 , and a lower annular stop  110  for guiding the projections  96 . 
     The ring  106  comprises a substantially cylindrical sleeve  112  having an axis X-X′ and a lower fastening collar  114  on the upper vertebra  70 B extending sleeve  112  downward. 
     The collar  114  is fastened to the upper vertebra  70 B via an annular clamping collar  116 . 
     The upper retaining stops  108  radially project away from axis X-X′ toward the rotatable bell  94 , from an external surface of sleeve  112 . They are angularly distributed around axis X-X′ on a circumference of sleeve  112 , while being angularly spaced from each other. 
     As illustrated in  FIG. 4 , each upper stop  108  has a polygonal outline. Each stop  108  thereby defines an upper rim  120  convex upward and having a pointed shape, a lower rim  122  concave upward and defining a main groove  124  for engaging a projection  96 , and two side rims  126 A,  126 B extending substantially in parallel to axis X-X′. 
     The side rims  126 A,  126 B opposite each pair of adjacent upper stops  108  define therebetween axial passageways  128  for inserting and removing a projection  96  into/from the groove  124 . 
     Each passageway  128  axially opens upward in a first direction, between the upper rims  120  of two adjacent upper stops  108  and axially downward in a second direction opposite the first direction, close to the groove  124 . 
     Groove  124  is axially sealed upward in the first direction and axially opens downward in a second direction. It has a cross-sectional shape like an inverted V. 
     The lower retaining stop  110  radially projects away from axis X-X′ from the external surface of sleeve  112 . It extends under the retaining stops  108 . It defines a plurality of teeth  130  projecting upward in the first direction from a solid annular base  132 . 
     The teeth  130  together define, opposite each main groove  124 , two secondary guiding grooves  134 A,  134 B. 
     Grooves  134 A,  134 B are sealed in the second direction downward and open in the first direction upward opposite the main groove  124 . 
     Each groove  134 A,  134 B is defined to the left by the inclined lateral surface  136  of a first tooth  130 , and is defined to the right by a straight surface  138  of a tooth  130  adjacent to the first tooth  130 . 
     The left-hand groove  134 A partially opens along the inclined surface  136  opposite an insertion and removal way  128  located to the left of stop  108 . The right-hand groove  134 B partially opens opposite an insertion and removal way  128  located to the right of stop  108 . 
     Each upper stop  108  and the lower stop  122  thereby together define a traveling way of a projection  96 , which is substantially W-shaped. 
     As will be apparent below, the locking member  90  is movable along the travel axis X-X′ in relation to the engaging member  92  in the second direction, between a first disengaged axial position, represented in  FIG. 4(   a ), in which the locking member  90  and the engaging member  92  are axially remote from each other, and an axial position engaging the locking member  90  with the engaging member  92 , represented in  FIG. 4(   c ), in which the locking member  90  is moved closer to the engaging member  92 , and the projections  96  come into abutment at the bottom of the secondary guiding grooves  134 A. 
     Starting from the engaging position of  FIG. 4(   c ), the locking member  90  is further movable in the first direction upward along axis X-X′ toward an engaged axial position, represented in  FIG. 4(   e ), located axially between the first disengaged axial position, in which each projection  96  is placed at the bottom of a main groove  124 . 
     During such movements, the locking member  90  is further rotatably movable around the axis X-X′ in relation to the engaging member  92  and in relation to the line  18  between a first travel configuration of the flexible line  18  through the curvature limiter  42  ( FIG. 4(   a )) and an configuration for axial immobilization in the first direction of the flexible line  18  on the curvature limiter  42  ( FIG. 4(   e )). 
     Advantageously, the immobilization means  46  can comprise a releasable member (not shown) for blocking the locking member  90  in relation to the engaging member  92  translatably in the engaged axial position and rotatably in the configuration for axial immobilization. This blocking member is for instance a screw or a pin, which can be fitted and released without mechanical breakage of the blocking member by a remotely operated vehicle (referred to by the abbreviation ROV). 
     Starting from the engaged axial position, the locking member  90  is movable downward along axis X-X′ in relation to the engaging member  92 , between the engaged position and a disengaging position, represented in  FIG. 4(   g ), in which the projections  96  are located in abutment in secondary grooves  134 B adjacent to grooves  134 A, then upward up to a second disengaged axial position represented in  FIG. 4(   i ). 
     During such movements, the locking member  90  is rotatably movable around the engaging member  92  between the configuration for axial immobilization in a first direction and a second configuration for axial travel of the flexible line  18  through the curvature limiter  42 , angularly shifted in relation to the first configuration for axial travel, without mechanical breakage of a linking member between the engaging member  92  and the locking member  90 . 
     A method for mounting the flexible line  18  to the floating structure  16  will now be described with reference to  FIGS. 1 to 6 . 
     Initially, when the flexible line  18  is stored in a vessel or ashore, a curvature limiter  42  is engaged around the line  18 , remote from the upper end  32 . 
     For this purpose, the line  18  is inserted into the lumen  76  successively through lower block  66 , intermediate flange  68  and vertebrae  70 A,  70 B. Next, the connecting head  33 , on which the locking member  90  is mounted rotatably, is axially and angularly fastened to line  18 , at the upper end  32  of pipe  30 . 
     The curvature limiter  42  is maintained to be axially fixed, line  18  is moved in the second direction downward in relation to the limiter  42  so as to move the locking member  90  closer to the engaging member  92  and bring them into the first disengaged axial position, represented in  FIGS. 2 and 4(   a ). 
     When the engaging member  92  enters into the receiving housing  100 , each runner  104  comes into abutment at the upper rim  120  of a stop  108  and is guided toward an inserting passageway  128 . 
     The locking member  90  and the engaging member  92  then adopt the first configuration for axial travel in the first direction of the flexible line  18  through the curvature limiter  42 . 
     Next, the axial movement downward in the second direction of the line  18  in relation to the limiter  42  continues. The runner  104  of each projection  96  moves down the passageway  128 , next into the secondary groove  134 A located opposite this passageway, running downward along an inclined surface  136 . 
     As represented in  FIG. 4(   b ), the cooperation between the external surface  105  of the runner  104  and the inclined side surface  136  of the tooth  130  causes partial rotation of the locking member  90  in relation to the engaging member  92  through a cam effect from the first travel configuration to the configuration for axial immobilization. 
     With reference to  FIG. 4(   c ), when the projection  96  comes into abutment at the bottom of the left-hand groove  134 A, line  18  is then moved axially upward in the first direction in relation to the limiter  42 . Projection  96  then moves upward along the right-hand surface  138  of the secondary groove  134 A and enters into the main groove  124  ( FIG. 4(   d )). 
     The runner  104  then runs on the convex lower rim  122  of the upper stop  108 . Running of the runner  104  causes the locking member  90  to be rotatably driven around axis X-X′ in relation to the engaging member  92  up to the configuration for axial immobilization represented in  FIG. 4(   e ). 
     In this configuration, each projection  96  is placed inside a main groove  124  in abutment against an upper retaining stop  108 . This will axially immobilize the flexible line  18  in the first direction inside the curvature limiter  42 , namely when a upward pulling force is applied to line  18 . Thereby, axial immobilization means  46  are activated. 
     Line  18  is then immersed into the body of water  14 . When line  18  is to be connected to the manifold  26  of the structure  16 , the hoist  24  is activated for lowering the cable  28  through the hollow rigid tube  40 , next connecting the lower end of the cable  28  to the connecting head  33  located at the upper end  32  of line  18 . Line  18  and the curvature limiter  42  are placed under the end collar  52  of the hollow rigid tube  40  away from tube  40 . 
     The hoist  24  is then activated for lifting the cable  28  up to the upper end  56  of the hollow rigid tube  40 . Lifting the cable  28  causes the line  18  to be moved together with the curvature limiter  42  toward the collar  52  up to the intermediate position represented in  FIG. 1 . 
     Next, the curvature limiter  42  is partially introduced into the rigid tube  40 . 
     For this purpose, the flexible upper assembly  64  is introduced into the end collar  52 , until the intermediate flange  68  rests on the lower flange  58  of the collar. 
     With reference to  FIG. 5 , the collar  78  is then placed around the flanges  58 ,  68  for immobilizing the curvature limiter  42  axially in relation to the hollow tube  40 . 
     As vertebrae  70 A,  70 B are linked together by flexible links, they adopt a slight curvature corresponding to the slightly curved shape of the lower end of tube  40 . 
     Immobilization means  46  are then released to allow for line  18  to be lifted up through curvature limiter  42  and tube  40 . 
     For this purpose, the hoist  24  is activated to move the connecting head  33  in the second downward direction. 
     As illustrated in  FIGS. 4(   f ) to  4 ( g ), each projection  96  then moves down into the straight groove  134 B adjacent to the left-hand groove  134 A, guided by the runner  104  on the inclined surface  136  defining groove  134 B. 
     Cooperation between the external surface  105  of the runner  104  and the inclined surface  136  inside the groove  134 B will rotatably drive the locking member  90  around axis X-X′ from the configuration for axial immobilization thereof to a second travel configuration of line  18 , represented in  FIG. 4(   i ), axially spaced apart from the first travel configuration represented in  FIG. 4(   a ). 
     The locking member  90  turns around axis X-X′ always in the same direction between the first travel configuration, the configuration for axial immobilization, and the second travel configuration. 
     With reference to  FIG. 4(   g ), when each projection  96  comes into abutment at the bottom of the secondary groove  134 B, the hoist  24  is then activated to move head  33  upward in the first direction. 
     The locking member  90  then moves away from the engaging member  92 , causing each projection  96  to be moved outside straight groove  134 B, next along the straight rim  126 B of the upper stop  108  inside the removal passageway  128  ( FIGS. 4(   h ) and  4 ( i )). 
     The locking member  90  then adopts a disengaged axial position located above the engaging member  92 , in which the engaging member  92  has been removed from the housing  100 . 
     With reference to  FIG. 6 , line  18  is then lifted up through the center lumen  76  of the limiter  42  and through the traveling way of the tube  40 , up to the manifold  26 , the curvature limiter  42  remaining immobile in relation to tube  40 . Line  18  is then connected to the manifold  26 . 
     The releasable immobilization means  46  formed by a rotatable lock are thus easily activated, so as to allow, by means of a single hoist, a common movement of the curvature limiter  42  and line  18  up to the hollow rigid tube  40 . Next, once the limiter  42  has been fastened to the hollow rigid tube  40 , the immobilization means are reversibly released, simply by moving line  18 , so as to allow for line  18  to move up through the curvature limiter  42  and through tube  40 . 
     It is not necessary to apply considerable pulling force to the immobilization means  46 , or break a linking member between the locking member  90  and the engaging member  92  for axially releasing line  18  in relation to curvature limiter  42 . The risk of deteriorating line  18  is thus very limited. 
     When line  18  is to be removed from the structure  16 , it is moved down into the hollow tube  40 , until the locking member  90  engages around the engaging member  92  in the configuration for axial immobilization thereof, as described before. 
     The collar  78  of the fastening means  44  is then removed, so as to remove the curvature  42  from the collar  52  and move line  18  together with curvature limiter  42  down, away from the hollow tube  40 .

Summary:
A device includes a hollow rigid member ( 40 ) and a curvature limiter ( 42 ) movable relative to the hollow rigid member ( 40 ). A releasable device ( 46 ) for axial immobilization of the curvature limiter ( 42 ) on the flexible line ( 18 ) in at least one first direction along a travel axis (X-X′). The axial immobilization device ( 46 ) includes a locking member ( 90 ) axially secured to the flexible line ( 18 ), and a member ( 92 ) for fitting the locking member ( 90 ), axially secured to the curvature limiter ( 42 ). Those members ( 90, 92 ) are movable relative to each other around the travel axis (X-X′) between a configuration for axial immobilization of the flexible line ( 18 ) on the curvature limiter ( 42 ), and a configuration for axial travel of the flexible line ( 18 ) across the curvature limiter ( 42 ).