Wellhead connector locking device

A wellhead connector for connecting a riser to a wellhead in a subsea well remains connected even though hydraulic pressure is removed. The wellhead connector has a housing which slides over the wellhead, and dogs are carried by the housing for radial movement into engagement with grooves formed on the exterior of the wellhead. An axially moveable cam ring moves downward to push the dogs radially inward to a locked position. A wedge ring is carried on the inner side of the cam ring. The wedge ring locates between the dogs and the cam ring. The wedge ring has sides that are conical and converge in a downward direction. The wedge ring locks the cam ring in a lower position. A release ring carried by a piston shaft will move the wedge ring upward relative to the cam ring when the piston shaft is moving to the released position, to release the cam ring.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates in general to subsea wells, and in particular to a 
connector for connecting a riser to a subsea wellhead housing. 
2. Description of the Prior Art: 
In a subsea well of the type concerned herein, a wellhead is located on the 
sea floor. The wellhead is a tubular member. A riser extends from a vessel 
at the surface to the wellhead. A wellhead connector connects the lower 
end of the riser to the wellhead. 
The wellhead connector has a housing which slides over the wellhead. In one 
type, a plurality of dogs are carried by the connector. A cam ring moves 
the dogs radially inward into engagement with grooves formed on the 
exterior of the wellhead. A piston moves the cam ring axially between open 
and closed positions. 
Because of wave movement and currents, the riser will have some movement. 
This movement is transmitted to the wellhead connector and may tend to 
cause the wellhead connector to loosen its connection with the wellhead. 
SUMMARY OF THE INVENTION 
The wellhead connector of this invention has a wedge ring that locates 
between the cam ring and the dogs. The wedge ring is tapered on both its 
inner and outer sides. The tapered sides converge toward each other in a 
downward direction. These tapered sides mate with tapered sides on the cam 
ring and the wedge ring. The wedge ring prevents the cam ring from moving 
upward and loosening its engagement with the dogs, because the upward 
movement tends to further wedge the cam ring in place. 
A release ring is carried below the cam ring. The piston shaft which 
actuates the cam ring will move the release ring upward a slight distance 
relative to the cam ring when releasing the cam ring. This upward movement 
causes the release ring to contact the wedge ring and push it upward to 
release its wedging engagement.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, wellhead 11 is a tubular member located vertically on 
the sea floor. A plurality of circumferential grooves 13 are formed on the 
exterior of the wellhead 11 to provide a locking profile. A wellhead 
connector 15 is connected to the lower end of a string of risers (not 
shown) which extends from a vessel at the surface. 
The wellhead connector 15 includes a tubular housing 17. Housing 17 has an 
inner diameter that is slightly greater than the outer diameter of the 
wellhead 11. The housing 17 will slide over the wellhead 11 as the 
wellhead connector 15 is lowered into place. A plurality of dogs 19 are 
carried in apertures 20 in the wellhead connector 15. The dogs 19 will 
move between the retracted position shown in FIG. 1 to a locked position 
shown in FIG. 2. Springs 23 urge the dogs 19 outward to the retracted 
position. 
Each dog 19 has an outer side 25 that is inclined. That is, the outer side 
25 is a straight conical surface with a wider base at the bottom than at 
the upper end. It inclines radially outward in a downward direction. A 
beveled edge 27 is located at the upper end of the outer side 25 of each 
dog 19. The inclination of each outer side 25 is about four degrees 
relative to vertical. 
A cam ring 29 is reciprocally carried by the housing 17. The cam ring 29 is 
a solid annular member located on the exterior of the housing 17. Cam ring 
29 has an inner side 31 that is a frusto-conical surface. The inner side 
31 is inclined or tapered relative to the vertical axis of the wellhead 
connector 15. The inclination is radially inward in a downward direction, 
opposite to the inclination on the outer sides 25 of dogs 19. The upper 
end of the inner side 31 has a greater diameter than the lower end or base 
of the inner side 31. The degree of inclination is preferably about two 
degrees relative to vertical. 
A shoulder 33 is located at the upper end of the cam ring 29 above the 
inclined inner side 31. Shoulder 33 extends radially inward. The lower 
side of shoulder 33 is perpendicular to the axis of the wellhead connector 
15. 
A wedge ring 35 is carried on the inner side 31 of the cam ring 29. The 
wedge ring 35 is a split annular metal ring. It will contract and expand 
radially. Wedge ring 35 is tapered both on its inner and outer sides. The 
upper end of the wedge ring 35 is of greater radial thickness than the 
lower end. The degrees of taper of the inner and outer sides of the wedge 
ring 35 is the same as the degrees of taper of the dogs' outer sides 25 
and the cam ring inner side 31, respectively. The wedge ring 35 will thus 
mate with the dogs' outer sides 25 and the cam ring inner side 31, as 
shown in FIG. 2. The inclinations of the wedge ring 35 inner and outer 
sides are locking tapers. That is, a greater force is required to move the 
wedge ring 35 up relative to the dogs 19 than down after the wedge ring 35 
and dogs' outer sides 25 have been engaged for a period of time. 
The friction resultant or friction angle between the wedge ring 35 and the 
outer sides 25 of dogs 19 is selected to be greater than the friction 
resultant between the wedge ring 35 and the inner side 31 of the cam ring 
29. The friction resultant depends on the surface finishes and the 
inclination of the mating surfaces. Preferably, the surface finishes on 
the inner side of the wedge ring 35 and the dogs' outer sides 25 are 
roughened to provide selected static coefficients of friction. Preferably, 
the surface finishes on the outer side of the wedge ring 35 and the cam 
ring inner side 31 are polished or coated smooth to provide lesser 
coefficients of friction than the coefficients of friction of the inner 
side of the wedge ring 35 and the dogs' outer sides 25. 
If an upward force is applied to the cam ring 29, the cam ring 29 will 
slide upward relative to the wedge ring 35 rather than the wedge ring 35 
sliding upward on the outer sides 25 of the dogs 19. This result is due to 
the lesser degree of inclination on the cam ring inner side 31 and to the 
lesser coefficients of friction of the outer side of the wedge ring 35 and 
the cam ring inner side 31. The upward movement of the cam ring 29 
relative to the wedge ring 35 results in a horizontal force component 
which causes the wedge ring to further wedge the cam ring 29 and the dogs 
19 in place. 
A release ring 37 is located below the wedge ring 35. Release ring 37 is a 
solid metal ring with cylindrical inner and outer sides. The radial 
thickness of the release ring 37 is less than the radial thickness of the 
wedge ring 35 at the bottom of the wedge ring 35. The release ring 37 is 
supported by a collar 39. The collar 39 is rigidly mounted to a piston 
shaft 41. Collar 39 fits under the cam ring 29. Collar 39 has a bevelled 
inner side that mates with the bevelled edge 27 on the outer sides 25 of 
the dogs 19. 
A plurality of piston shafts 41 are spaced apart from each other 
circumferentially around the wellhead connector housing 17. Each piston 
shaft 41 has an upper portion 41a that extends slidingly through a passage 
43 in the cam ring 29 and a lower portion 41b. The upper and lower 
portions 41a, 41b are screwed together in the collar 39 so as to rigidly 
connect the collar 39 with the shaft 41. A washer 45 is rigidly attached 
to the upper end of each shaft 41. The washer 45 locates in a counterbore 
46 formed at the upper end of each passage 43. This allows the shaft 41 
and collar 39 to move up and down a slight amount relative to the cam ring 
29, as can be seen by comparing FIG. 1 and FIG. 2. 
The lower portion 41b of shaft 41 extends slidingly through a flange 47 
formed on the exterior of the wellhead connector housing 17. The lower 
portion 41b extends into a hydraulic cylinder 49. A piston 51 is carried 
reciprocally in the hydraulic cylinder 49. An upper port 53 provides 
access to hydraulic fluid on the upper side of the piston 51. A lower port 
55 provides access to hydraulic fluid on the lower side of the piston 51. 
In operation, the wellhead connector 15 will be lowered over the wellhead 
11 until reaching the position shown in FIG. 1. Initially, the dogs 19 
will be in the retracted position. The cam ring 29 and the piston 51 will 
be in an upper position. The collar 39 will support the cam ring 29 in the 
upper position. The release ring 37 will support the wedge ring 35 in the 
upper position. 
Then hydraulic fluid is supplied to the upper port 53. Piston 51 will move 
downward and will bring along with it the collar 39. The collar 39 will 
initially start the dogs 19 moving inward by the engagement with the 
beveled edge 27. The shaft 41 will continue downward movement with the 
piston 51 until the washer 45 bears against the top of the cam ring 29. 
The cam ring 29 will also move downward. This will cause the wedge ring 35 
to expand as it slides against the outer sides 25 of the dogs 19. The dogs 
19 will move radially inward to the locked position shown in FIG. 2. 
Once the wedge ring 35 reaches a locking position, the cam ring 29 will 
also stop downward movement due to contact of the cam ring shoulder 33 at 
the top of the wedge ring 35. The shoulder 33 thus serves as a stop means 
for preventing farther downward movement of the cam ring 29 once a 
sufficient amount of force has been reached. The hydraulic pressure will 
increase, and a control mechanism (not shown) will release the hydraulic 
fluid flow through the port 53. 
Even though the hydraulic fluid pressure acting on the piston 51 has been 
released, the locking tapers of the wedge ring 35 will prevent substantial 
upward movement of the cam ring 29. Some slight upward movement can occur 
if there is substantial movement of the riser string due to wave or 
current motion. If so, the shaft 41 and the cam ring 29 would move 
slightly upward relative to the wedge ring 35. However, this upward 
movement will be strongly resisted by the wedge ring 35, which will wedge 
more tightly. There will not be enough upward movement of the cam ring 29 
relative to the wedge ring 35 to cause the release ring 37 to contact the 
wedge ring 35. 
When it is desired to release the wellhead connector, hydraulic fluid 
pressure is supplied to the lower port 55. This causes the piston 51 to 
begin moving upward. The release ring 37 will move upward with the shaft 
41 and collar 39 a slight distance while the cam ring 29 remains 
stationary and locked in place. The release ring 37 will contact the lower 
side of the wedge ring 35 and begin to move it upward. The upward movement 
of the wedge ring 35 relative to the dogs 19 and cam ring 29 releases the 
locking wedging action. The cam ring 29 is then free to move back to the 
upper position as shown in FIG. 1. The springs 23 will cause the dogs 19 
to move to the outer retracted positions. 
The invention has significant advantages. The wedge ring with its tapered 
sides locks the cam ring in place to hold the dogs in the engaged 
position. 
While the invention has been shown in only one 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.