Patent Publication Number: US-2023151912-A1

Title: Pipe connection

Description:
FIELD OF THE INVENTION 
     The present invention relates to a connection between pipes for use in the oil and gas drilling industry. The invention is particularly intended for use in respect of connections having a smaller outer radius than is typical for such joints. The invention also provides a pin section and a box section for use in such a connection. 
     BACKGROUND TO THE INVENTION 
     Atypical joint between oil and gas pipes in a pipe string, such as a riser joint, comprises two pipe sections: referred to herein as a pin section and a box section by virtue of the pin end of one section engaging the box end of the other section. The two sections are urged together under tension to form a fluid-tight seal preventing egress of the fluid flowing within the pipe string. The particular joint contemplated herein is formed by lowering a box end of one section onto the upwardly facing pin end of a vertically deployed pipe section. Simply securing the two sections together to prevent their moving relative to each other and relying on the mass of the string above the joint to force the pin and the box sections together is insufficient to maintain a seal therebetween which is fluid-tight or which would remain fluid tight under the conditions of a typical well. 
     Although many different methods are known in the art are known to urge and secure the pipe sections together in a fluid-tight manner, the one particularly contemplated herein employs dogs which act by exerting a radially directed force which is partially converted into an axial force to push the pin and box sections together. Because of the mode of action of the dogs as described in more detail below, there is produced in the outer section of the box end, an outward radial reaction force which tries to force the outer section outwards away from the pin end. In prior art joints, the radial thickness of the box section is sufficiently high to be able to withstand the outwardly directed force, with the material from which the box section being formed storing the energy applied. 
     However, in some applications, a much thinner overall pipe is required. This entails the radial thickness of the box end being thinner than in conventional pipes, and the ability of the pipe to resist the outward force is correspondingly reduced. This results in the box end bending outwards, away from the pin end resulting in a weakening of the seal between the two sections and the possibility arising of the seal therebetween being compromised. 
     It is an object of the present invention to provide an improved joint between a pin and a box section which addresses the above problems. It is a further object of the invention to provide a method of securing a pin and a box section together which addresses the above problems. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided a pipe joint formed between a pin section and a box section; 
     the pin and box sections each having a tubular pipe section, engaging at respective first ends in end-to-end arrangement and having a seal element partially therebetween, 
     the box section including a box stress collar extending from the first end, the box collar being generally cylindrical, axially aligned with the tubular box pipe section and having an inner diameter of the same size as the outer diameter of the pin section, enabling the box stress collar to be placed about the pin section, 
     the pin and the box sections being secured together by means of a one or more securing means housed in the box collar and actuable to exert radial pressure to urge the pin and box into sealing arrangement, 
     the pin section including a circumferential collar located to engage a profiled end surface of the box stress collar on make-up of the joint, the circumferential collar including a circumferential pin channel defined by a pin edge rim, the profiled end surface of the box section including a box channel defined by an inner rim and an outer rim, the circumferential pin channel housing the inner rim of the box and the box channel housing the pin edge rim. 
     The engagement of the circumferential collar of the pin with the profiled end surface of the box collar allows a thinner collar to be utilised and hence a thinner overall pipe string. 
     Preferably, the or each channel rim has an inner-facing channel wall parallel to the pipe joint axis to allow radial stress forces to be resisted and redistributed. 
     Preferably, the box channel has a rectangular cross-section to facilitate engagement of a rim with a channel. Further preferably, both the box and the pin channels have a rectangular cross-section. 
     Preferably, one or both of the box channel and the pin channel have internal corners, said internal corners being curved to reduce corrosion. 
     Preferably, the ratio of the depth of the channel to the width of the channel is from 0.15-0.25 and further preferably from 0.19-0.23. 
     Preferably, the securing means comprises a dog, movable radially, the dog having one or more oblique surfaces within the box section, the engagement of the dog and box surfaces acting to generate an axial force directing the box section towards the pin section. 
     Preferably, the joint includes a push screw, further preferably threadably mounted to the box section, actuation of the push screw engaging the dog and causing radial motion of the dog. Yet further preferably, the push screw includes a slot and key arrangement to ease actuation and resist accidental removal of the push screw. Still yet further preferably, the push screw includes an aperture to ease actuation and facilitate tightening of the push screw. Yet more preferably, the push screw has a frustoconical head, the head being housed within a channel in the dog, a key engaging the dog, across the end of the channel to prevent release of the head from the channel. 
     Preferably, the end of the box section is chamfered to better enable make up of the joint and the location of the box section within the channel of the pin section. 
     According to a second aspect of the invention there is provided a pin section the pin section having a tubular pipe section and comprising a circumferential collar, located to engage an end surface of a box stress collar on make up of the joint, the circumferential collar including a circumferential pin channel defined by a pin edge rim. 
     According to a third aspect of the invention there is provided a box section, the box section including a box stress collar extending from the first end, the box collar being generally cylindrical, axially aligned with the tubular box pipe section and including a profiled end surface, the profiled end surface of the box section including a box channel defined by an inner rim and an outer rim. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is now described with reference to the accompanying drawings which show by way of example only one embodiment of a joint between a pin section and a box section. In the drawings: 
         FIGS.  1   a  and  1   b    show views of a prior art joint; 
         FIG.  2    illustrates the internal elements of a joint; 
         FIG.  3    is a perspective view of a made-up joint; 
         FIG.  4    is a sectional view of a portion of the joint; 
         FIG.  5    is a further sectional view of the portion of the joint shown in  FIG.  4    and illustrating the stress forces within the joint; 
         FIG.  6    illustrates a pressure-testing port; and 
         FIGS.  7   a - 7   d    illustrate, respectively, a top, part view, sectional view and perspective view of a push screw mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The provision of a fluid-tight seal in a pipe string intended to convey oil and gas, for example, from a well to a storage facility, is a difficult undertaking. The seal must be able to withstand high internal pressures and/or pressure differentials. Moreover, any such joint needs to be capable of being made-up and separated on multiple occasions in order to allow for a pipe section to be re-used. Within the art, many different types of joint are available, such as utilising a screw-thread, or a clamp. The present invention utilises a clamping-type mechanism to releasably join together two pipe sections one of which is designated as a pin section and the other, the box section. 
     Referring initially to  FIG.  1   a  and  1   b   , these show a prior art joint formed between two vertically deployed pipe sections: a pin section  10  and a box section  20 . This arrangement has been described in an earlier application of the current Applicant, GB2005679.2 from which some of the following text is taken. 
     The general arrangement can be seen in  FIG.  1    in which a seal between two sections—a pin section and a box section—is shown. The pin, generally referenced  10 , is secured in position at its in use lower end to a rig floor. The box section  20  is lowered onto the free end of the pin  10 , with a metal-to-metal sealing gasket therebetween. Once the box  20  is in position, the two sections are sealed together to ensure they are fluid tight: typically to a pressure of around 17000 psi (1.17.10 5  kPa), but more generally to pressures of 3000 to 20000 psi (2.07.10 4 -1.38.10 5  kPa). As a visual guide, a marking is provided on one or both of the pin  10  or the box  20  to enable correct alignment of the box  20  and the pin  10  relative to each other. As an example of a suitable marking, a coloured band can be applied to the outer surface of the pin  10 , which enables both the axial position and also the mutual alignment of the pin&#39;s axis with the box&#39;s axis to be confirmed. 
     Generally, the box  20  has a tubular conduit  21  having an outer surface  21   a  and an inner surface  21   b , in contact in use with the pressurised fluid. The inner diameter of the tubular conduit  21  usually matches that of the inner surface  11   b  of the pin  10 , at least in their in-use immediate vicinities, to provide smooth flow along the pipe string formed. Extending from the end of the box  20  is a collar  22  having an outer radial face  23  generally parallel to that of the tubular conduit  21 . The diameter of the inner surface  24  of the collar  22  is such that the inner surface  24  is contiguous on make up of the joint with the outer surface  25  of the pin  10 , thus enabling a fluid tight seal to be easily made between these two surfaces  24 ,  25 . The collar  22  is connected to the tubular conduit  21  of the box  20  by a connecting section  26 . The connecting section  26  is generally frusto-conical. The outer face  27  of the connecting section  26  as shown is typically at an angle of around 45° with the tubular conduit  21 , although the angle is chosen to suit the task for which the box is designed. In an alternative embodiment, not illustrated, the collar is joined directly to the tubular conduit  21 , with no intermediate connecting section. 
     The collar  22  in the prior art box section is of a relatively high radius. This enables the collar  22  to withstand the radial forces which arise on make-up of the joint, as the energy generated can be withstood by the material from which the collar  22  is formed without the material beginning to flow. The origins of the radial force can be appreciated on inspection of  FIG.  4    relating to the current invention. This illustrates the mode of sealingly securing the pin and box sections  70 ,  80  together. 
     The box section  80  is lowered onto the pin section  70  until the surface  42  of the box section  80  rests on the surface  43  of the pin section  70 . A pre-load is then applied through a connector which causes a force in the direction of arrow A to drive the surfaces  42 ,  43  together. A plurality of dogs  40  housed within apertures  41  in the collar  82  of the box section  80 , are then caused to move generally radially inwards in the direction of arrow B, towards the main axis of the pin section  70 . This causes the obliquely orientated surfaces  44 ,  45  of a dog  40  to engage the corresponding obliquely orientated surfaces  46 ,  47  on the pin  70  and as a dog  40  continues to move inwardly, an axially directed force is generated in the direction of arrow C which causes a further increase in the force driving the surfaces  42 ,  43  together. Movement of a dog  40  is actuated by a push screw  48 , in screw-threaded engagement with the wall of the box section  80 . The push screw  48  is so housed within the box wall that it does not protrude beyond the outer diameter of the stress collar  51 , even when the dog  40  is retracted and so does not increase the effective diameter of the box section  80 . Release of a dog  40  is aided by the inclusion of an insert and key arrangement. Normally the push screw sits in a slot in the dog  40 . This however only provides a bearing area of around 50%. The use of an insert increases the bearing area to around 100%. The key is then slotted in to prevent the insert from pushing upwards as a result of the force exerted on the taper of the push screw/insert interface. 
     The above process causes stress forces to build up in the region of contact between the surfaces  42 ,  43  as might be expected. However, the stress forces are transferred, at least partially as a reaction to the movement of the dogs  40 , to the stress collar  51  as radially outward forces: shown as region W in  FIG.  4   . Where a thinner overall pipe string is required, the lower mass of material in the stress collar  51  can result in the stress collar  51  being insufficiently strong to withstand the force and eventually bending outwards. Indeed, it was believed in the industry to represent a limiting factor on how small the outer radius of a pipe joint of this kind in a pipe string could be made. To relieve the stresses which build up in other parts of the pipe, a groove  49 , in the form of an undercut is included. 
     The present invention addresses the problem through the provision of a shoulder on the pin section  70 , which shoulder includes a channel to engage a complementary structure on the end of the stress collar  51  of the box section  80 . 
     The shoulder  50  on the pin section  70  is in the form of an annular disc about the outer surface of the pin  70 . The shoulder  50  is preferably formed integral with the pin section  70  on manufacture. Running around the shoulder  50  of the pin section  70  is a channel  52 , of generally rectangular cross-section. The internal corners  53  of the channel  52  are preferably curved to reduce any corrosion which might occur. 
     The end surface  60  of the region W of the box section  80  also includes a channel  61 . The width of the channel  61  is sufficiently wide to allow the rim  54  of the channel  52  to be seated therein. Further, the inner rim  62  of the channel  61  is of width to allow the rim to be correspondingly seated within the channel  52 . 
     In use therefore, as the joint is made up, with the box section  80  being lowered onto the pin section  70 , the end surface  60  is lowered towards the shoulder  50 , preferably into touching engagement, with the shoulder bearing a portion of the wight of the box section  80 . The pin and box sections  70 ,  80  are aligned so that the rim of one section is housed within the channel of the other section. As the joint is energised, a force is generated which acts to force the region W radially outward. In the current invention this force is resisted by engagement between the rims  54 ,  62  and the respective channels  61 ,  52  in which the rims  54 ,  62  are housed. As a result, the region W is prevented from moving radially outwards and the integrity of the seal formed between the pin section  70  and the box section  80  maintained. 
     In the embodiment illustrated in  FIGS.  4  and  5   , the end region W includes an optional chamfered section  63  which aids in the make-up of the joint by allowing the box section  80  to slide more easily over the pin section  70  in the event the inner diameter of the box section  80  has been made too narrow. 
     It has been found advantageous to include a groove  64  in the pin section  70 , adjacent the shoulder  50 , which groove  64  acts indicate that the joint is correctly made up. Alternatively or additionally a coloured band can be included on one or both of the pin  70  and box  80  sections to provide an indication that the joint is correctly made up. 
     Typically two secondary Grayloc (RTM) seals  90  are installed between the pin and box sections and including a testing means to determine the pressure being held. This has been reduced to one, housed in the box as shown in  FIG.  5    thus reducing the seal to one. 
     In a further embodiment, the depth of the channel  61  in the box shoulder is 0.32 mm and the width of the channel  61  is 1.37 mm. The depth the channel  52  in the box shoulder is 0.29 mm and the width of the channel  52  is 1.477 mm. 
     The push screw mechanism is illustrated in more detail in  FIGS.  7   a - 7   d   . The mechanism comprises a dog  40  having the profiled surfaces  44  and  45  as shown in  FIG.  4   . On the obverse side  100  of the dog  40  is a seating arrangement for the push screw  48 . The push screw  48  has a threaded portion  101  to threadably engage a corresponding threaded portion within the box  80 . A hexagonal aperture  102  enables a tightening means to be utilised to exert torque on the push screw  48  to tighten the push screw into position. The push screw  48  includes a securing head  103  of frusto-conical cross-section. In use, the securing head  103  is slidably secured within a channel  104  in the obverse side  100 . The walls  105  of the channel  104  prevent the push screw  48  from exiting the channel  104  in a direction along the axis of the push screw  48  in that they are angled to correspond with the frusto-conical surface of the securing head  103 . An insert and key mechanism prevent the push screw  48  from sliding out of the channel  104 . The insert  110  slides into the channel  104  , with the curved surface  112  of the insert  110  contiguously engaging the frusto-conical surface of the securing head  103 . The walls  113  of the insert  110  engage the walls  105  of the channel  104 . The key  111  sits atop the key  110  and prevents the hey from sliding out of the channel  104 . A trapezoidal prismatic cut out  114  in the key engages the corresponding trapezoidal prismatic lock  115  on the insert  110 . The feet  116  on the key  111  are housed within apertures  116  in the dog  40 .