Patent Publication Number: US-RE38458-E

Title: Vertical stab tendon bottom connector and method for securing and releasing the same

Description:
This application claims benefit of provisional application 60/027,490, filed Sep. 27, 1996. 
    
    
     TECHNICAL FIELD 
     This invention relates in general to remotely operable connectors and in particular to an improved vertical entry bottom connector for the tendon of a tension leg platform. 
     BACKGROUND ART 
     The bottom connector of a tension leg platform (TLP) tendon connects the lower end of the tendon to an anchor template or pile on the sea floor in order to transfer tendon loads into the anchor structure. 
     There are two primary types of bottom connectors. Side entry bottom connectors are installed into a tendon bottom receptacle by inserting the connector through a slot in the side of the receptacle. Vertical entry bottom connectors are inserted downward through the top of the receptacle. 
     Typically, vertical entry bottom connectors are large and expensive to manufacture. Some prior art versions require rotation to engage and disengage the receptacle. Other versions require landing on a shoulder within the receptacle to release the connector. These latter devices have the additional, potential disadvantage of subjecting the tendons of the TLP to compressive forces. 
     DISCLOSURE OF INVENTION 
     In this invention, the receptacle on the sea floor has a bore with an inner profile and a recess located below the inner profile. A connector body is secured to the lower end of a tendon and lowered into the receptacle. An outwardly-biased latch is carried by the body and has an outer profile which engages the inner profile of the receptacle in an engaged position to limit upward movement of the body. The latch also has a retracted position wherein the latch is retracted out of engagement with the inner profile. 
     A retainer is mounted to the body and has a released position relative to the latch which allows the latch to move to the engaged position. The retainer has a locked position which holds the latch in the retracted position. Lowering the body until the retainer engages the recess causes the retainer to assume the locked position, thereby allowing the body to be withdrawn from the receptacle with the latch being held in the retracted position. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a sectional side view of a first embodiment of a bottom connector shown engaged to a receptacle for the tendon of a tension leg platform and is constructed in accordance with the invention. 
     FIGS. 2-8 are half-sectional views of the bottom connector and receptacle of FIG. 1 at various stages of engagement. 
     FIG. 9 is a sectional side view of the bottom connector, tendon and receptacle of FIG. 1 undergoing deflection. 
     FIG. 10A is a half-sectional views of a second embodiment of the bottom connector and receptacle of FIG. 1 prior to engagement. 
     FIG. 10B is an enlarged portion of the half-sectional view of FIG.  10 A. 
     FIGS. 11-21 are half-sectional views of the embodiment of FIG. 10A at various stages of engagement. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring to FIG. 1, a bottom connector  11  for a tension leg platform tendon  13  is shown. Connector  11  has an inner tubular body  14  which is secured to a lower end of tendon  13 . Connector  11  is provided for anchoring tendon  13  to a cylindrical receptacle  15  located on the sea floor (not shown). Once connector  11  is installed, tendon  13  and body  14  are in tension; no downward-directed force is applied to the assembly. Inner body  14  has a central axis  16  and a hub or flange  17  on a lower end with an upward-facing shoulder  19  on an outer side, and a coaxial bore  21 . 
     Connector  11  has three substructures: a lower portion which is used to facilitate entry into a bore  18  in receptacle  15 , an intermediate portion which accommodates for extraneous movement of tendon  13 , and an upper portion which interfaces with bore  18  of receptacle  15 . 
     The lower portion of connector  11  comprises an end plate  23  which is welded to the lower end of inner body  14  over bore  21  perpendicular to axis  16 . End plate  23  has a coaxial, concave recess  24  on a lower side which receives a convex upper end  26  of a pivot member  25 . Pivot member  25  extends upward into engagement with end plate  23  from a bottom plate or brace  27 . End plate  23  is pivotal relative to pivot member  25  as shown in FIG. 9. A tow eye  29  extends downward from a lower side of bottom plate  27 . The lower end of connector  11  also comprises a rigid guide funnel  31 . Guide funnel  31  has a lower frustoconical portion  33  and an upper cylindrical portion  35 . A lower end of frustoconical portion  33  is welded to bottom plate  27 . Cylindrical portion  35  is concentric with axis  16  and has an outer diameter that is slightly less than the inner diameter of receptacle  15 . The upper end of cylindrical portion  35  is welded to an annular retainer plate  37  which is perpendicular to axis  16 . 
     The intermediate portion of connector  11  comprises a flexible element  41  which is landed on shoulder  19  of flange  17 . Flexible element  41  extends upward from shoulder  19  and is fastened to tendon  13  with an annular clip  43 . A spacer ring  45  is fastened to an upper end of flexible element  41  with bolts  47 . 
     Referring to FIG. 2, the upper portion of connector  11  has an outer body  51  which is fastened to spacer ring  45  and retainer plate  37  with bolts  53 . The lower inside and the upper outside portion of body  51  are generally concave recesses  55 ,  57 , with the lower inside portion  55  receiving spacer ring  45 . A retainer cap  59  is fastened to the upper end of body  51  with bolts  61 . Cap  59  has a generally V-shaped groove  63  and a lip  65  along an outer edge. 
     A latch  71  is located within recess  57  and groove  63 . In the embodiment shown in FIG. 2, latch  71  comprises a plurality of segmented latches. Each segment of latch  71  is outwardly pivotal about a pivot point on a lower end. Latch  71  has a pair of external teeth or grooves  73  which are designed to mate with an inner profile  75  at the upper end of receptacle  15 . Grooves  73  have outer flanks which are inclined upward. Latch  71  also has a small step or shoulder  77  on an upper end which engages lip  65  in cap  59 . An outwardly-biased split ring spring  79  locates within a recess  81  between cap  59  and body  51 . Spring  79  engages an inner side of latch  71 . A rib  83  extends outward from latch  71  just below grooves  73 . 
     Latch  71  is retained within bottom connector  11  by an annular blocking sleeve or retainer  85 . Retainer  85  is a solid ring and is axially movable relative to body  51 . Retainer  85  has an inner profile which generally mates with the outer surface of latch  71 , including a lip  87  which lies between lower groove  73  and rib  83 , and an internal groove  89  which engages rib  83 . Retainer  85  also has an upward facing shoulder  91  which mates with a downward facing shoulder  93  on body  51  located just below recess  57 . Retainer  85  is sliclably movable along body  51  from the upper released position shown in FIGS. 1-6, to the lower locked position shown in FIGS. 7-8. A lock member  95  is located below and is part of retainer  85  for restricting its movement relative to body  51  and latch  71 . Lock member  95  is an outwardly-biased split ring. An entrapment pin  97  lies between lock member  95  and retainer  85  for maintaining the position of retainer  85 . Pin  97  is spring-biased and releasable from a detent in a lower portion of retainer  85 . Lock member  95  has an outer profile which is designed to mate with an intermediate groove  98  located below inner profile  75  in receptacle  15 . In its expanded position of FIG. 1, lock member  95  has an outer diameter which is greater than the outer diameter of retainer  85 . Referring back to FIG. 1, receptacle  15  also has a recess  99  on a lower end. 
     In operation, connector  11  is secured to tension leg platform tendon  13  and receptacle  15  is anchored to the sea floor. As shown in FIG. 2, the lower end of connector  11  is lowered into receptacle  15 . If the axes of connector  11  and receptacle  15  are slightly misaligned, frustoconical portion  33  will assist in their proper alignment. Once the axes are aligned, cylindrical portion  35  drops into receptacle  15 . As the upper portion of connector  11  enters receptacle  15 , lock member  95  is collapsed radially inward, with its outer diameter flush with the inner diameter of receptacle  15  (FIG.  3 ). Latch  71  is pivoted radially inward, thereby collapsing spring  79  inward. Latch  71  is now in a retracted position. 
     During its descent, the upward inclined flanks of grooves  73  prevent latch  71  from engaging inner profile  75 . Retainer  85  slides over inner profile  75  and does not engage it since retainer  85  has an axial dimension which is longer than the axial dimension of inner profile  75 . As shown in FIG. 4, connector  11  continues its descent into receptacle  15 , generally unimpeded. Once grooves  73  are below inner profile  75 , connector  11  is raised upward until latch  71  springs outward under the influence of spring  79  and grooves  73  engage inner profile  75  (FIG.  5 ). Once this step occurs, latch  71  is in an engaged position and prevents the upward movement of body  51 . Lock member  95  snaps into intermediate recess  98 , releasably preventing downward movement of connector  11  in receptacle  15 . In this figure, retainer  85  is in a released position relative to latch  71  which allows latch  71  to move to the engaged position. 
     Referring to FIG. 9, once connector  11  is anchored into receptacle  15 , it is capable of accommodating a significant amount of pivotal movement by tendon  13 . By pivoting between end plate  23  and spacer plug  25 , and flexing about flexible elements  41 , connector  11  allows tendon  13  to pivot up to ten degrees relative to axis  16 . 
     To disengage connector  11 , it is once again lowered (FIG.  6 ). As described above, the inclined flanks of grooves  73  do not impede the downward motion of connector  11 . The resistance to downward movement by retainer  85  and lock member  95  is overcome with a selected weight applied in a downward direction. The downward motion of connector  11  is stopped when retainer  85  is located in or below recess  99  of receptacle  15  (FIG.  6 ). Connector  11  is then lifted upward. When lock member  95  engages recess  99  (FIG. 7) it engages a downward-facing shoulder  99 a, which causes pin  97  to release from the detent on retainer  85 . Continued upward movement causes body  51  to move upward relative to retainer  85  and lock member  95 . With this motion, lip  87  of retainer  85  is moved onto a radially outer surface of rib  83 , thereby shifting retainer  85  from the released position to a locked position which holds latch  71  in the retracted position. Latch  71  is axially movable relative to retainer  85  while retainer  85  engages recess  99 . Rib  83  engages internal groove  89  when retainer  85  is in the released position (FIGS.  5 - 6 ), and disengages from groove  89  when retainer  85  is in the locked position (FIGS.  7 - 8 ). As shown in FIG. 8, continued upward movement of body  51  moves latches  71  past inner profile  75 , thereby allowing connector  11  and tendon  13  to be withdrawn from receptacle  15  with latch  71  being held in the retracted position. 
     A second embodiment of the invention is shown in FIGS. 10A and 10B. A bottom connector  111  for a tension leg platform tendon (not shown) is provided for anchoring the tendon to a cylindrical receptacle  115  located on the sea floor (not shown). The tendon is substantially similar to tendon  13  of FIG.  1 . Like connector  11 , connector  111  has lower, intermediate and upper portions. 
     The lower and intermediate portions of connector  111  are very similar to those of connector  11 . A rigid guide funnel  131  has an outer diameter which is slightly less than the inner diameter of receptacle  115 . The upper end of funnel  131  is fastened to an annular outer body  145  with bolts  147 . Connector  111  also has an inner body (not shown) which attaches to a tendon and preferably mounts to outer body  145  with flex elements. 
     The upper outside portion of outer body  145  is a generally concave recess  149  with a downward sloping lower surface. An uppermost portion  145 a of outer body  145  extends vertically and is threaded on an outer surface. A generally L-shaped housing  151  is threadingly fastened along its lower, inner surface to uppermost portion  145 a. A retainer cap  159  is fastened to the upper end of housing  151  with bolts  161 . Cap  159  has a generally downward facing U-shape with a lower outer edge  159 a. 
     A latch  171  is located in recess  149  below an inclined, lower side  151 a of housing  151 . Side  151 a is generally parallel to the lower surface of recess  149 . In the embodiment shown in FIG. 10B, latch  171  comprises a split ring which is biased in a radially outward direction. Latch  171  is radially movable within recess  149  between an outer position shown in FIG. 10B and a contracted position shown in FIG.  18 . Latch  171  has an upward-facing shoulder  173  which is designed to mate with an inner profile  175  at the upper end of receptacle  115 . Latch  171  also has neck  177  on an upper end which engages side  151 a. 
     Latch  171  may be retained within recess  149  in a retracted position by a split ring retainer  185 . Retainer  185  is axially and radially movable relative to housing  151  and latch  171 . Retainer  185  has an outer profile which generally mates with an upper profile  115 a located above inner profile  175  in receptacle  115 . Retainer  185  also has a lip  187  which extends downward toward latch  171 , and an internal rib  189  which extends diagonally downward and inward and engages a slot  186  in housing  151 . Retainer  185  also has an upper vertical portion  191  which engages edge  159 a on cap  159 . 
     A release spring or lock member  195  is located along an outer edge of outer body  145  below latch  171  for accommodating its movement relative to outer body  145 , housing  151  and retainer  185 . A spring  194  extends between a lower portion of lock member  195  and outer body  145  for biasing lock member  195  in an upward direction. A positioner pin  197  extends between lock member  195  and outer body  145  for maintaining the position of lock member  195 . The head of pin  197  locates in an elongated slot in lock member  195  to allow limited axial movement of lock member  195  relative to outer body  145 . Lock member  195  has an upper surface  195 a which is designed to engage the lower surface  171 a of latch  171  and is flush with the lower surface  149 a of recess  149  while in the upper position of FIGS. 10-14. Surface  195 a and surface  171 a have the same radial thickness and are inclined at the same angle as surface  149 a. Lock member  195  has an upper, outer lip  196  for limiting the outward movement of latch  171 . Like receptacle  15 , receptacle  115  also has a recess  199  on a lower end (FIGS.  16 - 18 ). 
     Connector  111  operates very similarly to connector  11 . As shown in FIG. 11, connector  111  is lowered into receptacle  115 . As the upper portion of connector  111  enters receptacle  115 , latch  171  and retainer  185  are collapsed radially inward until they have an outer diameter that is flush with the inner diameter of receptacle  115  (FIG.  12 ). Latch  171  is shown in a retracted position. 
     During its descent, the outer profile of latch  171  prevents it from locking into inner profile  175 . Retainer  185  slides over inner profile  175  (FIG. 13) and does not engage it since retainer  185  has an axial dimension which is longer than the axial dimension of inner profile  175 . Retainer  185  is compressed axially upward and radially inward during the descent. As shown in FIG. 13, connector  111  continues its descent into receptacle  115 , generally unimpeded. Once latch  171  is below inner profile  175 , the tendon and connector  111  are raised upward until latch  171  springs outward and engages inner profile  175  (FIG.  14 ). Once this step occurs, latch  171  is in an engaged position and prevents the upward movement of housing  151 . Referring to FIG. 15, additional upward pull is then applied to the tendon which moves body  145  upward slightly relative to lock member  195 . An outer edge  149 b of recess  149  abuts an inner lower edge of latch  171  to prevent it from moving inward. Housing  151  moves upward slightly relative to lock member  195 , compressing spring  194 . Lock member  195  releasably prevents radially inward movement of latch  171  and, thus, downward movement of connector  111 . In this figure, retainer  185  is in a released position relative to latch  171  which allows latch  171  to move to the engaged position. 
     To disengage connector  111 , it is once again lowered (FIG.  16 ). Latch  171  and retainer  185  do not impede the downward motion of connector  111 . The resistance to downward movement by these components is overcome with a selected downward weight on the tendon. After being compressed upward and radially inward during the descent, retainer  185  springs downward and outward into recess  199  at the bottom of receptacle  115 . The diagonal portion of retainer  185  located below vertical portion  191  slides along edge  159 a to assist in this propagation. The downward motion of connector  111  is stopped when retainer  185  is located in or below recess  199  of receptacle  115  (FIG.  17 ). Latch  171  is axially and radially slidable relative to retainer  185  while retainer  185  engages recess  199 . Connector  111  is then lifted upward. When retainer  185  engages recess  199  (FIG.  17 ), it springs outward relative to housing  151  and latch  171 . Recess  199  has a downward-facing shoulder  199 a which contacts retainer  185  as housing  151  is lifted. With this motion, lip  187  of retainer  185  is moved onto a radially outer surface of shoulder  173  on latch  171 , thereby shifting retainer  185  from the released position to a locked position which holds latch  171  in the retracted position (FIG.  18 ). Rib  189  is simultaneously placed within slot  186  to prevent further axial movement of retainer  185 . Lip  187  does not engage shoulder  173  when retainer  185  is in the released position (FIGS.  10 - 17 ), and engages shoulder  173  when retainer  185  is in the locked position (FIGS.  18 - 20 ). Lowering housing  151  until retainer  185  engages recess  199  causes retainer  185  to assume the locked position, thereby allowing connector  111  and the tendon to be withdrawn from receptacle  115  with latch  171  being held in the retracted position (FIGS.  19 - 21 ). Like connector  11 , connector  111  is similarly capable of accommodating up to ten degrees of deflection by the tendon relative to its vertical axis. 
     The invention has several advantages. This vertical entry bottom connector does not require rotation or bottoming-out on a shoulder within the receptacle to disengage it. The invention employs a compact design, has very few moving parts and has a pivotal lower end which allows limited deflection of the connector inner body relative to the receptacle. 
     While the invention has been shown or described in only two of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.