CONNECTOR SYSTEM FOR OFFSHORE RISERS BACKGROUND OF THE INVENTION

The present invention relates to a riser connector system for connecting individual riser joints together in offshore oil and gas installations. More particularly, the present invention relates to a riser connector system which is protected against both fire and corrosion near the splash zone.

Referring to Figure 1 , an exemplary prior art "dry-tree" offshore oil and gas installation includes one or more wellheads 10 positioned at the seafloor or mudline 12. Each wellhead is connected by a riser 14 to a corresponding Christmas tree 16 on a floating vessel or rig platform 18 above the water surface or water line 20. The riser 14 is a conduit made up of individual sections or joints 22. Each joint 22 includes a central pipe section 24, an upper pin connector 26 and a lower box connector 28, all of which are integrally machined or welded together. As shown in Figure 2, male tapered threads 40 on the upper pin connector 26 mate with female tapered threads 42 in lower box connector 28 to secure the two connectors together and thereby join successive riser joints 22 as the riser is being made up.

Referring to Figure 2a, the lower box connector 28 includes a relatively small diameter portion 50 which is welded to or integrally machined with the pipe section and a relatively large diameter portion 52 on which means, such as the threads 42, for connecting the lower box connector to the upper pin connector are formed. A shoulder 54 is formed between the small and large diameter portions. This shoulder is used by pipe handling elevators on the rig to lift and support the riser joints as the riser is being made up. Additionally, the cylindrical outer surface 56 of the large diameter portion 52 is gripped by tongs on the rig, which then rotate the riser joint to make up the threaded connection.

Referring again to Figure 1 , the area 30 immediately above and below the waterline is called the splash zone. In some cases riser joints, especially those in or near the splash zone, require corrosion protection. It is also desirable in some instances to protect the riser joints located above the waterline from fire. As shown in Figures 2 through 2b, for fire and corrosion protection in the splash zone and just above it, a high temperature resistant rubber coating 60 may be applied to the joints. FMCE-P177

However, one problem with rubber coatings is that threaded riser connectors, such as box and pin connectors, cannot be coated with rubber. This is due to the fact that metal-to-metal contact between the tongs and the outer diameter 56 of the connector is required in order to permit the tongs to torque the riser joint with the adjacent riser joint. In addition, the shoulder 54 on the box connector must be accessible to provide a lifting point for the elevators when the joint is handled on the rig. Therefore, the portions of the connectors not coated with rubber are commonly coated with a thin anti-corrosion coating 62, such as thermal spray aluminum (TSA). The thin coating is applied to the large diameter portion 52 of the connector and to enough of the small diameter portion 50 beyond the shoulder 54 (typically about 12 inches) to allow the pipe elevator to access the shoulder. The remainder of the small diameter portion 50 of the connector, as well as the pipe section of the joint, is coated with rubber 60.

Since the entire riser connector is not rubber coated, a fire protection shell 70 is usually installed over the connector sections once each connection is made up. The fire protection shell may include an inner shell 72 of stainless steel which is coated with the same rubber 60 used on the riser joints. The shell may be made of two semi-cylindrical halves which are joined at the seams with releasable latches.

While both the rubber coating 60 and TSA coating 62 help prevent corrosion, it has proven difficult in practice to get complete coverage of the connector in the interface region 80 between the two coatings. As a result, deep corrosion at the interface between the two coatings has been observed on existing risers connectors. This corrosion is especially problematic because the coating interface region is located on a relatively thin-walled section of the riser connector that is critical for strength and fatigue failure resistance.

The critical location of the coating interface region has prompted oil and gas operators to conduct routine inspections of the riser connectors in the splash zone. As can best be seen in Figure 2a, the fire protection shell 70 may be provided with a removable pipe plug 82 near the interface region 80 to allow for visual inspection of the connector surface. However, not only are such inspections costly and time consuming, but they are also inherently dangerous since they involve suspending an inspector from the rig over open water. FMCE-P177

Furthermore, weakening of the riser connectors could lead to catastrophic mechanical failure of the riser or require premature and costly replacement of the riser joints. Thus a need exists for a riser connector which comprises a fire and corrosion protection system that protects the riser connector sections against fire and eliminates corrosion in the thin-walled sections of the connectors.

SUMMARY OF THE INVENTION

The present invention addresses these and other limitations in the prior art by providing a novel riser connector system for connecting a first riser joint to a second riser joint. The riser connector system in accordance with one

embodiment of the invention includes a first connector section which is connected to or formed integrally with an end of the first riser joint and a second connector section which is connected to or formed integrally with an end of the second riser joint, the second connector section being releasably connectable to the first connector section to thereby connect the first riser joint to the second riser joint. The first connector section includes a generally cylindrical first lower portion which is connected to or formed integrally with a generally cylindrical first upper portion. The first lower portion comprises a first outer diameter and the first upper portion comprises a second outer diameter which is larger than the first outer diameter such that a downwardly facing first shoulder is formed between the first upper and first lower portions. In addition, a first coating is disposed around the first lower portion and over the first shoulder, he first coating comprising a third outer diameter which is approximately the same as the second outer diameter.

Thus, the first coating covers the substantially the first lower portion of the first connector up to an including the first shoulder. As a result, the relatively smaller diameter first lower portion is completely protected against corrosion while the relatively larger diameter first upper portion is fully engageable by the tongs.

In another embodiment of the invention, the first connector section comprises an outer circumferential groove which is formed in the first upper portion. In addition, a ring member is mounted in the groove and comprises a fourth outer diameter which is larger than the second outer diameter to thereby define a downwardly facing second shoulder on the first upper portion. The ring member may comprise, for example, a split ring. FMCE-P177

In an alternative embodiment of the invention, the first connector section comprises an annular projection which extends circumferentially around the first upper portion. The projection comprises a fourth outer diameter which is larger than the second outer diameter to thereby define a downwardly facing second shoulder on the first upper portion.

Thus, the second shoulder (of either the ring member or the annular projection) provides an easily accessible lifting point for the rig elevators.

In another embodiment of the invention, the riser connector system comprises a second coating which is disposed on the first upper portion. The second coating extends to the first shoulder and thereby defines an interface region between the first and second coatings which is located on the first upper portion. Thus, if corrosion should occur at the interface region, little damage will result since the interface region is located on the relatively large diameter first upper portion of the first connector section.

In a further embodiment of the invention, the second connector section includes a generally cylindrical second upper portion which is connected to or formed integrally with a generally cylindrical second lower portion. The second upper portion comprises a fourth outer diameter and the second lower portion comprises a fifth outer diameter which is larger than the fourth outer diameter such that an upwardly facing second shoulder is formed between the second upper and second lower portions. In addition, a second coating is disposed around the second upper portion and over the second shoulder, the second coating having a sixth outer diameter which is approximately the same as the fifth outer diameter. In this regard, the first and second coatings may be comprised of substantially the same material.

In yet another embodiment of the invention, the riser connector system includes a third coating which is disposed on the second lower portion of the second connector section. The third coating extends to the second shoulder to thereby define an interface region between the second and third coatings which is located on the second lower portion.

In accordance with still another embodiment of the invention, the riser connector system includes a generally cylindrical shell which is mounted over the first and second connector sections. The shell may comprise a lower end which surrounds at least a portion of the first coating on the first connector section and FMCE-P177 an upper end which surrounds at least a portion of the second coating on the second connector section. In addition, a first annular seal may be positioned between the lower end of the shell and the first coating on the first connector section and a second annular seal may be positioned between the upper end of the shell and the second coating on the second connector section.

Furthermore, the shell may comprise an inner diameter surface and a groove ring which is connected to or formed integrally with the inner diameter surface. In this embodiment, the groove ring is configured to be received in a circumferential groove which is formed in the first upper portion of the first connector section or the second lower portion of the second connector section to thereby connect the shell to the first or second connector section.

In accordance with one embodiment of the invention, the shell comprises a generally cylindrical inner shell and a coating which is disposed around the shell.

Thus, the present invention provides a connector system in which the interface region between the disparate protective coatings is located on the larger diameter portions of the first and second connector sections. While corrosion may still occur at the interface regions, the additional material in these portions of the connector sections ensures that the connector sections will be much less sensitive to the corrosion. Thus, the connector sections will be able to tolerate a much greater amount of corrosion with little concern for fatigue failure over the expected service life of the corresponding riser joints.

These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic representation of a prior art offshore riser installation;

Figure 2 is a longitudinal cross sectional view of a prior art box and pin riser connector;

Figure 2a is an enlarged view of the lower connector potion of the prior art connector shown in Figure 2;

Figure 2b is an enlarged view of the portion of the prior art connector designated "2b" in Figure 2a; F CE-P177

Figure 3 is a longitudinal cross sectional view of one embodiment of a riser connector system of the present invention;

Figure 3a is an enlarged view of the lower connector portion of the riser connector system shown in Figure 3;

Figure 3b is an enlarged view of the portion of the riser connector system designated "3b" in Figure 3a;

Figure 3c is an isometric view of the riser connector system of Figure 3 shown with the split ring component removed;

Figure 3d is an isometric view of the riser connector system of Figure 3 shown with the split ring component installed;

Figure 4 is a longitudinal cross sectional view of the riser connector system of Figure 3 showing a protective shell component installed around the upper and lower connectors;

Figure 4a is an enlarged view of the lower connector portion of the riser connector system shown in Figure 4;

Figure 4b is an enlarged view of the portion of the riser connector system designated "4b" in Figure 4a;

Figure 4c is an enlarged view of the upper connector portion of the riser connector system shown in Figure 4;

Figure 4d is a radial cross sectional view of the riser connector system shown in Figure 4;

Figure 4e is an enlarged view of the portion of the riser connector system designated "4e" in Figure 4d; and

Figure 5 is a partial cross sectional view of an alternative embodiment of the riser connector system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used in this disclosure and the appended claims, the terms "upper", "lower", "upwardly" and "downwardly" are used merely to describe the position or orientation of various features and components relative to each other. These terms are not intended to limit the position or orientation of any features or components relative to any external reference frame. Generally, the terms "lower" and "downwardly" refer to the direction toward the left hand side or bottom edge of the figure, and the terms "upper" and "upwardly" refer to the direction toward the right hand side or top edge of the figure . F CE-P177

Referring to Figures 3 through 3d and 4b, the riser connector system of one exemplary embodiment of the present invention includes a first or lower box- type connector section 128 and a second or upper pin-type connector section 126. The first connector section 128 comprises a lower portion 150 which is welded or otherwise rigidly and sealingly attached to the upper end of a first elongate pipe section (not shown). In other embodiments, the first connector section could also be integrally machined with the first pipe section. The first pipe section has substantially the same outer diameter as lower portion 150 and a central bore extending therethrough. The first connector section 128 also includes an upper portion 152 having a generally cylindrical outer surface 156 with a larger outer diameter than the lower portion 150. A first external, downwardly facing shoulder 154 is thus formed between the lower portion 150 and the upper portion 152. A through bore 130 extends through both the lower and upper portions and is in fluid communication with the central bore in the first pipe section. The through bore 130 preferably terminates in a set of tapered female threads 140 at the upper end of the upper portion 152.

A first coating 60 is disposed around the first pipe section and the lower portion 150 of the first connector section 128. The first coating 160 extends up to and substantially covers the first shoulder 154 and has substantially the same outer diameter as the upper portion 52. The first coating is preferably a high temperature resistant rubber compound, but in other embodiments any suitable coating could be used.

A second coating 162 is disposed around the outer surface 156 of the upper portion 152 and extends downwardly to the first shoulder 154. Thus, the interface region 180 between the first coating 160 and the second coating 162 is located on the outer surface 156 of the upper portion 152. The second coating is preferably a corrosion resistant coating such as thermal spray aluminum (TSA), but in other embodiments any suitable coating could be used.

An external groove 194 is formed circumferentially in the outer surface 56 of the upper portion 152. Prior to making up the riser, a split ring 200 is removably installed in the groove 194. The split ring 200 includes an inner portion 202 which is configured to be received in the groove 194 and an outer portion 204 having a larger outer diameter than the outer surface 156 of the upper portion 152. Thus, a second external, downwardly facing shoulder 206 is FMCE-P177 formed between the outer diameter of the split ring 200 and the outer surface 156 of the upper portion 152. When the riser is made up, the second shoulder 200 provides a lifting point for the riser elevators. Once the riser joint has been made up to the riser, the split ring 200 may be removed.

Referring again to Figure 3, the second connector section 126 comprises an upper portion 192 which is welded or otherwise rigidly and sealingly attached to the lower end of a second elongate pipe section (not shown). In other embodiments the second connector section could be integrally machined with the second pipe section. The second pipe section has substantially the same outer diameter as upper portion 192 and a central bore extending therethrough. The second connector section 126 also includes a lower portion 190 having a generally cylindrical outer surface 220 with a larger outer diameter than the upper portion 192. An external, upwardly facing shoulder 222 is thus formed between the upper portion 192 and the lower portion 190. A through bore 132 extends through both the upper and lower portions and is in fluid communication with the central bore in the second pipe section. The lower end of the lower portion 190 preferably terminates in a set of tapered male threads 142. The male threads 142 are adapted to engage the female threads 140 in the first connector section 128 to connect successive riser joints together when the riser is made up.

In other embodiments of the present invention, the relative positions of the male and female threads could be reversed. Also, other means may be used to connect the riser joints together, such as ratch-latch mechanisms, resilient biased load rings, and other means well known in the oil and gas industry.

A first coating 160 is disposed around the second pipe section and the upper portion 92 of the second connector section 126. The first coating 160 extends down to and substantially covers the upwardly facing shoulder 222 and has substantially the same outer diameter as lower portion 190. As discussed above, the first coating 160 is preferably a high temperature resistant rubber compound, but any suitable coating could be used.

A second coating 162 is disposed around the outer surface 220 of the lower portion 190 and extends upwardly to the upwardly facing shoulder 222. Thus, the interface region 224 between the first coating 160 and the second coating 162 is located on the outer surface 220 of the lower portion 190. As F CE-P177 discussed above, the second coating 162 is preferably a corrosion resistant coating such as TTSA, but any suitable coating could be used.

Referring now to Figures 4 through 4e, the riser connector system of the present invention further comprises a generally cylindrical fire protection shell 170. The shell 170 is releasably installed on and substantially surrounds the first connector section 128 and the second connector section 126 once the connection is made up. As shown in Figures 4d and 4e, in one embodiment of the invention the shell 170 comprises two generally semi-cylindrical halves 170a and 170b, which define two axially extending seams 240a and 240b

therebetween. When the shell 170 is installed on the connector sections, the two halves 170a and 170b are preferably joined by releasable latches (not shown) located generally proximate the seams 240a and 240b. In other embodiments, any suitable releasable connecting means may be used to join the two halves of the shell together, such as clamps, threaded fasteners, and other means well known in the industry. In a further embodiment, one or more hinges could be provided at one of the seams to allow the shell to be opened in a "clam-shell" manner.

The shell 170 preferably comprises an inner shell 172 made of stainless steel or any other suitable material. The inner shell 172 is preferably coated with the same first coating 160 used on the first and second connector sections 128, 126. As shown most clearly in Figure 4e, the first coating 160 may be sized to extend slightly beyond the edges of the two halves of the inner shell 172 into the axial seams 240a and 240b. In this configuration, when the two halves 170a and 170b are brought together, the edges of the coating 160 contact each other first, leaving a slight gap 242 between the inner shell halves. This allows the edges of the coating 160 to be compressed as the shell 170 is closed, effectively creating a seal along each seam 240a and 240b to exclude seawater from the interior of the shell 170.

Referring again to Figures 4 through 4b, the shell 170 includes a lower end 176 which extends downwardly at least beyond the first shoulder 154 of the first connector section 128, such that the lower end 176 surrounds at least a portion of the first coating 160 on the first connector section. A seal 230 is disposed between lower end 176 and the first coating 160 to exclude seawater from the interior of the shell 170. FMCE-P177

As shown in Figures 4 and 4c, the shell 170 also comprises an upper end 178 which extends upwardly at least beyond the upwardly facing shoulder 222 of the second connector section 126, such that the upper end 178 surrounds at least a portion of the first coating 160 on the second connector section. A seal 232 is disposed between the upper end 178 and the first coating 160 to exclude seawater from the interior of the shell 170. In other embodiments the seals 230 and/or 232 may be omitted.

As shown in Figures 4a and 4b, a groove ring 174 is welded or otherwise rigidly attached to the inside of shell 70. In one embodiment, the groove ring 174 comprises a split ring with two semi-circular halves, each of which is attached to a corresponding one of the two halves 170a, 170b of inner shell 172. When the shell 170 is installed on the connector sections 126 and 128, the groove ring 174 is received in the groove 194 in the first connector section 128. The groove ring 174 engages the groove 194 to prevent axial movement of the shell 170 relative to the first and second connector sections.

As shown in Figure 4c, one or more padeyes 234 may be provided at the upper end 178 of the shell 170 to allow handling of the shell on the rig. The padeyes 234 are welded, bolted or otherwise rigidly attached to the inner shell 172.

Referring now to Figure 5, in an alternative embodiment of the invention a first or lower box-type connector section 310 comprises a lower portion 250 and an upper portion 252. The upper portion 252 comprises a generally cylindrical outer surface 253 having an outer diameter that is larger than that of the lower portion 250. A first external, downwardly facing shoulder 254 is thus formed between the outer surface 253 and the lower portion 250. A first coating 160 is disposed on the lower portion 250 and extends up to and substantially covers the first shoulder 254. A second coating 162 is disposed around the outer surface 253 of the upper portion 252 and extends downwardly to the first shoulder 254. Thus, the interface region 320 between the first coating 160 and the second coating 162 is located on the outer surface 253 of the upper portion 252.

An annular projection 300 is formed circumferentially on the outer surface 253. The projection 300 has a larger outer diameter than the outer surface 253, such that a second external, downwardly facing shoulder 306 is formed between the outer diameter of the annular projection 300 and the outer surface 253. FMCE-P177

When the riser is made up, the second shoulder 306 provides a lifting point for the riser elevators. In various embodiments, the annular projection 300 may be integrally machined or forged with the first connector section 310, or a separate ring which is welded, bolted, or otherwise rigidly attached to the first connector section.

In the prior art riser connector system shown in Figures 2 through 2b, access to the shoulder 54 on the lower box connector 28 is necessary to allow for handling of the joint 22 by elevators on the rig floor. This requires that the rubber coating 60 be terminated before reaching the shoulder 54 to allow room for the riser elevator to support the connector. As discussed above, this places the interface region 80 between the rubber coating 60 and the TSA coating 62 in a relatively thin-walled section of the connector.

The present invention solves this problem by moving the interface region 180 to the much thicker-walled section 152 of the connector (Figure 3a). While corrosion may still occur at the relocated interface region 180, the additional connector material in this area makes it much less sensitive to any corrosion that may occur. In essence, a much greater amount of corrosion can be tolerated in the relocated interface region 180, with little concern for fatigue failure over the expected service life of the riser joint. Thus, there is no need to inspect the interface region, allowing for decreased operating costs and increased safety.

Furthermore, since interface regions 180, 224 on the lower and upper connector sections are moved closer to the threaded connection relative to the prior art, the fire protection shell 170 can be considerably shortened. This makes the shell less expensive and easier to handle on the rig.

It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.