Marine riser coupling assembly

A marine riser coupling assembly comprised of a pair of flanged couplings (14, 16). A pin insert (36) is retained (44, 54) within tubular portions (22, 24) of the couplings. The insert has multiple outside diameters (50, 50), and seals (66, 74) on each.

BACKGROUND OF THE INVENTION 
This invention relates to marine risers for deep subsea drilling and 
production and in particular to a coupling assembly therefor. 
Marine risers are run from floating vessels or platforms to subsea 
wellheads for drilling and production operations. The riser sections are 
tubular, in the order of 20 inch diameter and 50 feet long. They are 
assembled at the surface and are run from the vessel to the wellhead. In 
assembling these, a successive section is first stabbed into a preceding 
section and the connector then bolted up. Accordingly, easy stabbing is 
desired. 
The riser is usually highly tensioned at the upper end to avoid buckling 
and is also subject to cyclical bending caused by current and/or vessel 
drift. The riser must remain leak tight over its life to prevent ingress 
of sea water and/or leakage of mud during drilling, and potential oil 
during production. This despite the cyclical loading placed thereon. 
Handling of large risers sections can cause damage to the couplings. A 
design tolerant of such damage and/or one easily repaired is therefore 
desirable. 
SUMMARY OF THE INVENTION 
The coupling assembly is comprised of a pair of couplings, at the end of an 
adjacent marine riser pipe sections with a tubular pin insert fitting 
within the couplings. Each coupling is flanged with the flange being 
integral with a tubular portion of the connector which is in turn welded 
to the riser pipe section. 
The tubular portions of each coupling have a portion of the inside diameter 
greater than that of the riser pipe sections to which they are connected 
and the pin fits within this larger diameter portion, preferably having an 
inside diameter approximately equal to that of the adjacent riser pipe 
sections. The flanges have a plurality of alignable bolt holes and a 
plurality of bolts secure the flanges together in mutually contacting 
relationship. 
The pin is radially sealed to the coupling with the groove in the pin 
containing an O-ring. A contractable retaining ring operates in a groove 
within the pin and a groove within the coupling to secure the pin within 
one of the couplings. 
Stabbing is facilitated since the pin insert has a small diameter portion 
near its outboard end and a larger diameter portion towards its center. 
Furthermore, the stabbing overlap between the pin insert and coupling is 
greater than the stabbing overlap between attached choke and kill lines so 
that the initial stab is made over the insert and the riser may thereafter 
be rotated to easily stab the choke and kill lines. 
Both couplings are preferably identical so that the pin inserts may be 
located in either coupling, thereby providing the ability to run the riser 
either pin up or pin down as desired. Furthermore, should the pin be 
damaged it may be removed and replaced. Any repair work need be done only 
on the relatively easy handled pin insert rather than handling the entire 
riser section. 
Even a rigidly bolted flanged connector has some movement during bending as 
experienced by the riser. Even if the pin insert were forced in with an 
interference fit it would be loose compared to a pin which is machined at 
the end if a riser section. Accordingly, bending strain of the connector 
is absorbed at two ends of the pin thereby taking half of the differential 
movement at each end. This minimizes the differential movement which must 
be taken by the seals thereby improving the long term sealing of the 
connector. 
Even with the most precise machining of large couplings is known that some 
out of roundness develops after the machining has been completed. With a 
pin integrally formed with one of the flanges, out of roundness of the 
adjoining sections cannot be readily absorbed by deflection of the pin. 
With the relatively loose pin insert, which is not reinforced by a flange, 
it may deflect to absorb the out of roundness of the adjoining sections, 
thereby improving the sealing capabilities.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Marine riser pipe sections 10 and 12 have couplings 14 and 16 welded 
thereto at locations 18 and 20. Each connector includes a tubular portion 
22 and 24 and a flange portion 26 and 28 integral therewith. 
Each tubular portion has a portion of the inside diameter 30 greater than 
the inside diameter 32 of the riser section. The inside diameter 34 of pin 
insert 36 is substantially the same as the inside diameter of the riser 
pipe section. 
The pin insert is tubular and has the outside of each end substantially 
conforming to the inside shape of the corresponding tubular portion. The 
pin is also located entirely within the tubular portion. 
Each tubular portion has a box retaining groove 38 and 40 around the inner 
periphery. A pin retaining groove 42 is located on the outer periphery of 
the pin insert 36. A split retaining ring 44 is located partially within 
the box retaining groove and remains partially within the pin retaining 
groove so that the pin insert 36 is retained within connector 16. 
The flange portion of each coupling has a plurality of alignable bolt holes 
46 with a plurality of bolts 48 securing the flanges together in mutually 
contacting relationship. 
The pin insert 36 has a first larger outside diameter 50 toward its central 
portion and a second lesser diameter 52 toward its outboard end. As best 
seen in FIG. 4 this facilitates initial stabbing of the connector. 
Each of the connectors is identical. While box retaining groove 38 is not 
used as illustrated, the retaining ring could be located in the upper 
portion of the pin insert groove so that the pin insert is retained in the 
upper connector 14 rather than the lower connector 16. 
Retaining ring 44 is preferably inwardly biased so that it is normally in 
the position illustrated in FIG. 2. In any event the ring must be 
compressed to this position for installation of the pin insert 36 within 
coupling 16. Locking ring 54 is held at this time in the upward position 
shown in FIG. 2. 
When the pin insert has been placed within the coupling, if the retaining 
ring 44 snaps outwardly into groove 40, the locking ring 54 is simply 
moved down to backup the retaining ring. If the retaining ring does not 
snap outwardly, face 56 of the locking ring will force the retaining ring 
outwardly as retaining ring 54 is moved down. After the locking ring 54 
has been moved downwardly a blocking ring 58, which may be in the form of 
a O-ring, is inserted above the locking ring thereby guarding against 
undesired upward movement of the locking ring. 
A notch 60 on the locking ring permits it to be grasped for upward movement 
during disassembly of the connection. Furthermore, should the retaining 
ring not disengage, a 45.degree. face 62 urges the ring inwardly on upward 
movement of the pin insert. 
A radially sealing means in the form of an O-ring 66 in groove 68 is 
provided on the smaller diameter portion of the pin insert at one end. A 
similar O-ring 70 in groove 72 is located on the opposite end of the pin 
insert. On the larger diameter portion of the pin insert, O-rings 74 are 
located in grooves 76 providing a second sealing means on each end of the 
pin. These not only provide double sealing on each end of the pin but they 
contribute to the centering of the pin inserts within the tubular portion 
thereby improving the sealing ability of each of the O-rings. 
The pin is free to remove with respect to the couplings by slight amounts 
since it is not welded to either. Accordingly, strain occurring in the 
couplings under bending can be absorbed at both ends of the pin insert as 
contrasted the connectors where the pin is integrally formed with one of 
the couplings. Therefore, differential movement between the sealing 
surfaces is cut in half, thereby improving the ability of the connector to 
seal throughout the cyclical bending which occurs. 
Choke and kill lines 80 and 82 are loosely secured to corresponding flanges 
26 and 28, line 80 has a female stab connection 84 or line 82 has a male 
stab connection 86. 
The stab overlap is the depth of penetration of the stabbed connection. It 
follows that the stab member with the maximum stab overlap will be the 
first to engage during the stabbing operation. As best seen in FIG. 4 the 
initial stabbing engagement occurs between outside diameter 52 of the pin 
insert 36 and the outside diameter 30 of connector 14, this being the 
portion of the connector with the maximum stab overlap. This difference in 
diameters simplifies the initial stabbing of the connection. 
After guidance from the initial stab the larger outside diameter 50 of the 
pin insert 36 engages the inner surface 30 bringing the connection into 
accurate alignment. This stab overlap is greater than that of the choke 
and kill lines. 
After achieving the proper rotation for the choke and kill lines to engage 
the stab is fully made engaging connector 86 and 84 of the choke and kill 
lines. 
The flange is thereafter securely tightened with a plurality of bolts 48.