Abstract:
An apparatus for and a method of supporting a tubular member in a vertical orientation are provided. A first and length of pipe ( 1, 4 ) are supported at their upper ends by detachable collars ( 2   a,    2   b ). The detachable collars ( 2   a,    2   b ) are engageable with collar flanges ( 3   a,    3   b ) which are attached to the pipes ( 1, 4 ). A pipe string elevator ( 5 ) is used to support the pipe ( 4 ) while an operator ( 70 ) attaches the lower end of pipe ( 4 ) to the upper end of the flange collar ( 3   a ).

Description:
FIELD OF THE INVENTION 
     The invention relates to apparatus for and a method of supporting a tubular member, such as a length of pipe, in a vertical orientation. 
     DESCRIPTION OF RELATED ART 
     It is known to install an underwater pipeline from a drill rig by what is known as a “J-lay” method. In this method of installation lengths of pipe are supported vertically while the individual lengths are welded together. The welded pipe is subsequently lowered towards the seabed through the rotary table on the drill rig. Thus, the pipe is lowered vertically from the drill rig and curves towards a generally horizontal orientation on the seabed. 
     SUMMARY OF THE INVENTION 
     The most convenient method of installing pipeline by a drilling rig is to attach a flange (or J-lay) collar to the pipe, and use the J-lay installation method. However, there are problems in using this method to install Steel Catenary Risers (SCR) which are attached to a floating production system such as a semi-submersible or a Floating Production Storage and Offloading vessel (FPSO). This problem is caused by the motion of the vessel and environmental loading during the operational lifetime of the SCR. Both of these may cause undesirable stressing at the stress concentrated locations adjacent to the collar flange attachments. This effect becomes more severe in harsher environmental conditions and stress levels become unacceptable due to the fatigue life limitation. 
     Installation of a SCR using the J-lay collar was performed in the Gulf of Mexico with a Tensioned Leg Platform (TLP). In a TLP, although the platform is semi-submersible, the platform is secured to the sea bed by tethers which are in tension between the sea bed and the platform. Hence, the tension in the tethers helps to minimise the lateral movement of the TLP and substantially eliminates the vertical movement. In addition, the sea state in the Gulf of Mexico is generally calm which also helps to minimise the movement of the TLP. 
     However, this arrangement for installation of SCRs is not suitable for a floating production system which incorporates anchor lines. In this type of platform, the movement of the platform can result in high flexing of the pipes which produces high cyclic stress loading in the area of the flanges which can potentially result in failure of the pipe. In addition, the arrangement is also unlikely to be suitable for a TLP in sea conditions more adverse than the Gulf of Mexico, such as the North Sea, where the movement of a TLP would be greater and could result in fatigue and failure of the pipe due to the high stress zones around the flanges attached to the pipe. 
     In accordance with a first aspect of the present invention, there is provided apparatus for supporting a tubular member comprising a first member comprising a first formation, the first member being adapted to be attached to the tubular member, and a detachable member adapted to engage the first formation; the detachable member having an internal formation which engages with the first formation, and an external formation for engagement by a lifting device to support the tubular member when the detachable member is placed against the tubular member and the internal formation is engaged with the first formation. 
     Preferably, the detachable member is also adapted to engage the tubular member adjacent the first formation. 
     In accordance with a second aspect of the present invention, there is provided a method of supporting a tubular member comprising attaching to the tubular member a first member comprising a first formation, placing a detachable member against the first formation so that the first formation engages an internal formation on the detachable member; and engaging an external formation on the detachable member with a lifting device to support the tubular member. 
     Optionally, the detachable member is also placed around a portion of the tubular member adjacent the first formation. 
     The first member typically comprises a collar and is typically coupled to the tubular member by any conventional means, such as by welding. The first formation can be in the form of a protrusion on the collar. 
     The detachable member is typically engageable with the collar. 
     An advantage of the invention is that by using a detachable member to engage with a first formation attached to the tubular member, it is possible to reduce the size of the first formation and therefore, decrease the stress concentration in the pipe adjacent to the first formation. 
     Preferably, the method further comprises the step of fixing the tubular member or the first member to another tubular member and subsequently detaching the detachable member from the first tubular member. 
     Preferably, the tubular member is supported with the central longitudinal axis of the tubular member in a substantially vertical orientation. 
     In accordance with a third aspect of the present invention, there is provided a method of laying underwater pipeline comprising a method of supporting a first tubular member in accordance with the second aspect of the present invention, attaching another tubular member also supported by a method according to the second aspect of the present invention to the first tubular member or the first member, such that the tubular members are in end to end relationship and the central longitudinal axis of the tubular members are substantially coincident, releasing the detachable member against the first formation on the first tubular member, and lowering the tubular members by means of the lifting device attached to the second detachable member to lower the tubular members towards the seabed. 
     Preferably, the first member may be attached to an end of the tubular member. However, in an alternative example of the invention, it is possible that the first member may be attached to an external surface of the first tubular member. Typically, the first member is attached to the tubular member by a welding operation, and a welding operation may also be used to attach the other tubular member to the first tubular member or the first member. 
     Preferably, the method of laying an underwater pipeline in accordance with a third aspect of the invention comprises laying the underwater pipeline from a semi-submersible vessel or floating vessel, such as a semi-submersible drilling rig, a floating production platform or a tensioned leg platform. 
     In one example of the invention, the first formation may be removed from the first member, for example by a reaming or machining operation, after detachment of the detachable member. This may be useful for applications where strictly no stress concentration condition along the SCR is permitted. 
     In one example of the invention the detachable member may be adapted to rest on a support pedestal located on the drill floor of the platform or vessel. Alternatively, the detachable member may be adapted to engage with and be supported by slips located in a rotary table on the platform or vessel. 
     Typically, the detachable member is hinged along an axis substantially parallel to the central longitudinal axis of the detachable member and the tubular member. Preferably, when placed around the formation and the portion of the tubular member adjacent to the formation, the detachable member is clamped to the first formation and the portion of the tubular member adjacent the first formation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Examples of apparatus for and a method of supporting a tubular member will now be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic diagram of a general arrangement for supporting a length of pipe using a first example of a detachable collar; 
     FIG. 2 is an exploded cross-sectional view of the detachable collar of FIG. 1 supported by a travelling block; 
     FIG. 3 is an exploded cross-sectional view of the detachable collar of FIG. 1 supported by a support pedestal; 
     FIG. 4 is a schematic view of a general arrangement for supporting a length of pipe showing a second example of a detachable collar; 
     FIG. 5 is an exploded cross-sectional view of the detachable collar of FIG. 4 supported by a travelling block; 
     FIG. 6 is an exploded cross-sectional view of the detachable collar of FIG. 4 supported by slips at a rotary table; 
     FIG. 7 is an end view of a collar flange for use with the detachable collars shown in FIGS. 1 to  6 ; 
     FIG. 8 is a side view showing the collar flange welded to an end of a length of pipe; 
     FIG. 9 is a first side view of the detachable collar shown in FIGS. 1 to  3 ; 
     FIG. 10 is a cross-sectional view along the line A—A of FIG. 9; 
     FIG. 11 is an end view of the detachable collar shown in FIG. 9; 
     FIG. 12 is a diametrically opposed side view of the detachable collar shown in FIG. 9; 
     FIG. 13 is a end view of the second example of the detachable collar shown in FIGS. 4 to  6 ; 
     FIG. 14 is a side view of the detachable collar shown in FIG. 13; 
     FIG. 15 is a cross-sectional view along the line A—A of the detachable collar shown in FIG. 14; 
     FIG. 16 is a perspective view showing a general arrangement of a support pedestal for the first example of the detachable collar; 
     FIG. 17 is a side view of the support pedestal shown in FIG. 16; 
     FIG. 18 is a side view of the support pedestal in the direction of the arrow B in FIG. 17; 
     FIG. 19 is a part cross-sectional view of the support pedestal in the direction of the arrow A in FIG. 17; and, 
     FIG. 20 is a plan view of the support pedestal. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a general schematic view showing a pipeline being assembled and laid from a drilling rig using a J-lay technique in which a first length of pipe  1  is supported at its upper end by a detachable collar  2   a  which encircles the upper end of the pipe  1  and engages with a collar flange  3   a  (FIG. 3) welded to the upper end of the pipe  1 . A second length of pipe  4  is supported at its upper end by another detachable collar  2   b  which engages round another collar flange  3   b  welded to the upper end of the pipe  4 . A pipe string elevator  5  (in this embodiment a hard shoulder bearing type) engages an external flange  6  on the detachable collar  2   b  to support and lift the pipe  4 . Exploded views of the upper end of the pipe  4  and the upper end of the pipe  1  are shown in FIGS. 2 and 3 respectively. The pipe string elevator  5  supports the upper pipe  4  by means of the detachable collar  2   b  while an operator  70  welds the lower end of the upper pipe  4  to the upper end of the lower flange collar  3   a.    
     After the upper pipe  4  has been welded to the lower flange collar  3   a,  the lower detachable collar  2   a  is detached from the lower flange collar  3   a  and the lower pipe  1 . The pipe string elevator  5  then lowers the upper pipe  4  (and the lower pipe  1 ) through the support pedestal  7  and the rotary table  8  until the lower edge of the upper detachable collar  2   b  rests on the upper edge of the support pedestal (ie when the upper pipe  4  is in the position shown in FIG. 3) A further length of pipe may then be manoeuvred into position above the upper pipe  4  (which now becomes the lower pipe) to permit the further pipe to be welded to the upper flange collar  3   b  on the upper end of the pipe  4 . 
     The flange collar  3  is shown in detail in FIGS. 7 and 8. Collar  3  has an internal diameter similar to the internal diameter of the length of pipe to which it is welded (shown in phantom in FIG.  8 ). It has external sections  10  of similar outer diameter to the outer diameter of the pipe  1 ,  4 . A formation  9  is located on the external surface of the flange collar  3  and is in the form of a flange which extends circumferentially around the collar  3 . The difference in diameter between the formation  9  and the external section  10  is such that the difference in diameter is insufficient to be engaged by the pipe string elevator  5  and support the weight of the hanging pipe from the vessel to the sea bed. 
     However, by engaging the detachable collar  2  around the upper end of the pipe  1 ,  4  and the flange collar  3 , it is possible for the pipe string elevator  5  to engage flange  6  on the detachable collar  2  as a bearing support. This provides sufficient engagement for the elevator  5  to support the weight of the hanging pipe  1 ,  4  from the vessel to the sea bed without the flange collar  3  and the pipe string slipping out of the detachable collar  2 . 
     With regard to the shape of the flange collar  3 , it can be seen from FIG. 8 that the transition from the diameter of external section  10  to the increased diameter of formation  9  is a gradual one. Specifically, the diameter of the flange collar  3  increases continuously from said external section  10  to the diameter of formation  9 , and with a continuous change in gradient, rather than an abrupt angle at the start of said transition. 
     The detachable collar  2  is shown in more detail in FIGS. 9 to  12 . Detachable collar  2  includes two sections  11 ,  12  secured by a hinge pin  13  at one side. Each section  11 ,  12  has two flanges  14 ,  15  diametrically opposite the hinge pin  13 . The flanges  14  have two bolt holes  16  and the flanges  15  have one bolt hole  17 . The holes  16 ,  17  permit the flanges  14 ,  15  to be bolted together to secure the detachable collar  2  around the flange collar  3  and pipe  1 ,  4 . The internal surface of the sections  11 ,  12  includes a machined recess  18  which engages with the machined formation  9  on the flange collar  3  to secure the detachable collar  2  to the flange collar  3  and the pipe  1 ,  4 . Hence, when the pipe string elevator  5  engages and lifts flange  6  in use, the detachable collar  2  lifts the flange collar  3  and the pipe string attached to the flange collar  3 . 
     Note that an end  50  of the flange collar  3  protrudes from the end of the detachable collar  2 . This protruding end  50  allows the flange collar  3  to be welded to a second length of pipe  4 . 
     FIGS. 16 to  20  show the support pedestal  7  in more detail. The support pedestal  7  includes two half sections  19 ,  20  which are connected together at one side by a hinge pin  21  which permits the two half sections  19 ,  20  of the support pedestal  7  to be opened using a hydraulic device or manual operation. 
     The support pedestal  7  has three support surfaces  22 . Advantages of the invention are that by using the detachable collars  2 ,  30  (or any other detachable device such as a split flange) it is possible to reduce the size of the formation  9  on the flange collar  3 . This minimises the stress concentrations in the steel catenary risers associated with a floating production platform such as a semi-submersible, a FPSO, a spar or a TLP, during the operation. In addition, the size of the formation  9  is such that after the detachable collar  2 ,  30  has been removed at the rig floor, the formation  9  may be removed from the lower flange collar  3  prior to lowering the pipe  1 ,  4  and the lower flange collar  3  below the drill floor towards the seabed. This can ameliorate the stress concentration problem. 
     This invention allows J-lay installation from a drilling vessel for the SCRs associated with floating platforms which move significantly and are subject to a harsh environment such as the North Sea. The J-lay method is not normally possible due to the stress concentration effect on the fatigue life limitation. Furthermore, the drilling vessel requires a major modification in order to use other methods of installation. 
     Modifications and improvements may be incorporated without departing from the scope of the invention. 
     For example, although the embodiments of the invention are described with reference to a drill rig, further embodiments can be used from a specially constructed lay system that does not have a drill floor because it does not do drilling operations and does not have a rotary table for the same reason. There are substantial advantages to laying from a specially designed system i.e. it can be made to fit so that pipe located on its upper end. Two of the support surfaces  22  are located on the upper end of the section  20  and one support surface  22  is located on the upper end of the section  19 . The support surfaces  22  engage with and support the lower end of the detachable collar  2  (and the lower flange collar  3  and lower pipe  1  to which the lower flange collar  3  is welded) as shown in FIG.  3 . 
     FIGS. 4 to  6  show a second example of a detachable collar  30  which is used and operated in a similar manner to the detachable collar  2  to engage and support the flange collar  3  and pipe  1 ,  4 . However, in this example the detachable collar  30  is adapted to be engaged by a slip type elevator  31  which engages the detachable collar  30  in order to support the weight of the hanging pipe from the vessel to the sea bed. The detachable collar  31  is also supported by slips  32 ,  33  in the rotary table  8  (as opposed to being supported by the support pedestal  7 ). 
     As shown in FIGS. 13 to  15 , the detachable collar  30  comprises two half sections  34 ,  35  which are coupled at one side by a hinge pin  36  and secured at the other side by a lock pin  37 . The detachable collar  30  includes a recess  38  on its internal surface which engages with the formation  9  on the flange collar  3 . The other features and the operation of the detachable collar  30  are similar to the other features and operation of the detachable collar  2 . 
     Note that an end  52  of the flange collar  3  protrudes from the end of the detachable collar  2 . This protruding end  52  allows the flange collar  3  to be welded to a second length of pipe  4 , similar to the protruding end  50  in FIG.  9 . can be laid in relatively shallow water.