Abstract:
A connector for the connection of pressure vessels utilizing toroidal surfaces to achieve a maximum of contact area sliding parallel to motion of locking segment when achieving high preload to minimize high stress contact points and the resultant wear when subjected to multiple operations and orientation means to cause any wear to be repeatedly in the same area such that selected critical areas will not be subjected to high contact stress wear.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The field of this invention is that of remotely actuated connectors for connecting pressure vessels together. Most typically, the connection is made between the wellhead housings of oil or gas wells on the ocean floor and a blowout preventer stack. The connection is also frequently used between portions of the blowout preventer stack.  
           [0002]    The connectors typically have shoulders on each of the pressure vessels and interconnecting sections or dogs which engage the shoulders. The sections or dogs are driven into engagement by tapered surfaces approaching them. These connectors can be seen in patents such as Haeber U.S. Pat. No. 3,222,088, Ahistone U.S. Pat. No. 3,096,999, Herring U.S. Pat. Nos. 3,492,027, and 3,554,579. These connectors have the characteristic of a tendency to release due to the 4 degree angle of engagement. Literally these connectors frequently have an additional connector means to keep them connected. In some cases they lock the hydraulic fluid in the operating cylinders to keep them locked.  
           [0003]    An additional problem with the connectors is that a high make-up preload is desired, but the coefficient of friction can vary between 0.1 and 0.2. The angle of 0.1 coefficient of friction is 5.7 degrees and the angle of 0.2 coefficient of friction is 11.3 degrees. The preload of the connector is a function of the pressure times the sum of the connector angle plus the coefficient of friction angle. This sum is 4°+5.7°=9.7° in one case and 4°+11.30 =15.3° in the other case. This is a 15.3°/9.70 =57% variation in preload. Contemporary connectors are seeking a 7,000,000 lb. preload, so a 57% change in preload is considerable.  
           [0004]    U.S. Pat. No. 4,516,795 Baugh addressed these problems by utilizing a torus ring to actuate the segments, such that the torus ring balanced the forces or even went slightly over center to prevent the tendency to release. A torus is basically a donut shape, with a portion of a torus being any section around the donut. While solving a first problem, the inter-relationship of the torus ring and the conical surfaces of the pressure vessels causes some high contact stress locations which were not desirable. Additionally, when the opposing surfaces of the torus were slipped in relationship to one another, the fit of the parts caused other high contact stress areas.  
           [0005]    The Baugh U.S. Pat. No. 4,516,795 connector attempted to control the variation of preload by having a fixed torus diameter, which was not affected by friction angles. A problem associated with this was that the high stress areas would tend to cause wear and require readjustment on the diameter to maintain the predicted preload.  
           [0006]    The inter-relationship of the torus profile and the locking of the connector was functionally to “roll” the locking segment into position over conical clamp hubs. The “rolling” onto conical clamp hubs inherently caused high stress areas and wear.  
         SUMMARY OF THE INVENTION  
         [0007]    The object of this invention is to provide a connector which provides the predictable preload and lack of release tendency associated with the Baugh 4,516,795 connector, but minimizes the tendency for high stress contact areas associated with the mating torus surfaces between the actuating torus and the locking segments.  
           [0008]    A second object of the present invention is to provide a second torus profile for facilitating movement and stress reduction between the locking segment and the locking shoulders on one of the two pressure vessels.  
           [0009]    A third object of the present invention is to provide a known orientation between the locking segments during the locking movement such that any wear which occurs will be in the same area and the remaining areas will not be subjected to dimension altering wear movements.  
           [0010]    Another object of the present invention is 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a quarter section of the connector in the unlocked position.  
         [0012]    [0012]FIG. 2 is a quarter section of the connector in a partially locked position.  
         [0013]    [0013]FIG. 3 is a quarter section of the connector in the locked position.  
         [0014]    [0014]FIG. 4 is a cross section of the connector.  
         [0015]    [0015]FIG. 5 is an overlay of a portion of the locking segment being closed showing various positions as defined by being engaged with the actuating torus and contacting the lower, outer corner of the housing hub. A locus of points is shown illustrating the position of the surface to mate with first connector hub.  
         [0016]    [0016]FIG. 6 is an expanded view of the locus of points from FIG. 5 showing that the departure angle of the locking segment with relationship with the first connector hub is approximately 17.1° in this embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.  
         [0018]    Referring now to FIG. 1, a connector  1  is shown having a body  2  with an upper hub profile  3 , and a seal area  4  for interconnection to a subsea blowout preventer stack. At the lower end the connector body  2  has a first connector hub  10 , a second connector hub  11 , an orientation pin  12 , a seal surface  13  and a seal ring  14 .  
         [0019]    Bolts  20  connect cylinder  21  to the upper flange portion  22  of body  2  and bolts  23  connect lower plate  24  to the lower end of cylinder  21 .  
         [0020]    Inner piston  30  and outer piston  31  are moved in response to flow in ports  32  and  33  to lock or unlock the connector  1  respectively. Actuating torus  40  engages the inner profile of the inner piston  30  via a thread  41  and tapered sections  42  and  43 . The actuating torus  40  is split and when the tab  44  is removed the actuating torus  40  can be rotated along thread  41  and tapered sections  42  and  43  to change the torus internal diameter and thereby to adjust the preload of the connector.  
         [0021]    The wellhead housing  50  has a housing hub  51 , a seal area  52  as are well understood in the industry. The surface  53  which is to be engaged by surface  60  of locking segment  61  is an industry standard conical surface.  
         [0022]    Locking segment  61  has an outer toroidal surface  62  for engaging the actuating torus  40 . The locking segment  61  also has toroidal surfaces at  63  and  64 , which will be discussed later.  
         [0023]    Referring now to FIG. 2, the inner piston  30  and outer piston  31  are moved down with the actuating torus  40  rocking the locking segment  61  onto the hubs  51 ,  10 , and  11 .  
         [0024]    Referring now to FIG. 3, the inner piston  30  and outer piston  31  have moved fully down such that the actuating torus  40  contacts the lower plate  24  at  70 , such that the connector is fully locked. Torus center  71  is shown which is the geometric center of the torus profile  62 . As the actuating torus moved down to the present position, the portion of the locking segment below the torus center  71  was moving toward the housing centerline  72  and the portion of the locking segment above the torus center  71  was moving away from the housing centerline  72 .  
         [0025]    Line  75  extends from the surface  76  at approximately  17 . 1  degrees with respect to the housing centerline  72 . The rationale for the  17 . 1  degrees will be discussed later. The intersection of line  75  and the line  77  from the center  71  intersect at  78 . As will be discussed later, the locking segment approximately rotates about the point at  78 . As the locking segment  61  is approximately rotating about point  78  when at the highest loaded condition as seen in FIG. 3, it is appropriate that the surfaces at  76  and  80  be concentric torus surfaces about the circular centerline which is implied by the point  78  in this figure. By making these surfaces torus surfaces about the centerline of movement, the wear causing mismatch is minimized to the greatest extent possible.  
         [0026]    To some degree, as the surfaces are rotated, some mismatch cannot be avoided and some question will always arise as to how much wear this will actually cause. In some cases the wear will be at the edges of the segment, and in some cases the wear will be at the centerline of the segments. The propose of the orientation pin  12  and the matching slot  81  are to keep the locking segments  61  in the same orientation at all times. This will cause the wear to be restricted always to the same area (i.e. at the edges of the locking segment) and will allow the other areas to remain unworn. When the connector is fully locked, unworn contact areas will be engaged giving a known fit and preload characteristic.  
         [0027]    Referring now to FIG. 4, the locking segments  61  are shown with the contact with the actuating torus  40  only existing near the centerline of the locking segment  61 . The purpose of this is that the wider the locking segment, the more mismatch will occur when the locking segment is rolled out of the position of original orientation. As one might imagine, if the locking segment  61  were infinitely thin, it would be able to move always around a mating torus and stay in full contact all the time. The wider the torus, the more the surfaces will mismatch as the locking segment moves around the torus. Due to the relatively complex torus profile on the back of the locking segments, a preferred way to machine these clearances  90  on the sides of the locking segments  61  is to first machine the torus section on a lathe, and then put the cut locking segments in a fixture at a smaller diameter than the original diameter and the partially remachining the back profiles. This will provide a clearance profile which has a similar contour to the original profile. This reduction in the contact area on the back side of the locking segments will not cause high stress conditions as the remaining surface areas are still much larger than the projected areas of the hubs the locking segment is engaging.  
         [0028]    Referring now to FIG. 5, the profile of the housing hub  51  is shown, with point  100  indicating the outer corner of engagement with the locking segment. Line  101  indicates the position of locking segment  61  when it is fully engaged and line  102  indicates the position of locking segment  61  when it is rotated 5 degrees out of position. Lines indicated at  103  give a variety of positions in between. Line  104  indicates the inner tangent to the torus section, such that the locking segment is kept tangent to this line in all positions. At  105  is a locus of points on the torus surface  76  of the locking segment, assuming the contact is maintained with the clamp hub  51  and the line  104 .  
         [0029]    Referring now to FIG. 6, an enlarged view of the locus of points at  105  is shown. Point  110  is the position of a point when the connector is fully locked. Point  111  is the position of the same point when the connector is unlocked 5 degrees. Points  112  indicate various points in between. The line  113  indicates that the curve  114  connecting the various points has a starting tangent at approximately 17.1 degrees. This means that the surface at  76  is sliding at the angle of approximately 17.1 degrees when the maximum preload is being exerted. This was the reason that the angle of 17.1 degrees was used in the layout of FIG. 3 to determine the centerline point of the optimal torus profile for the connector.  
         [0030]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.