Abstract:
A subsea pressure relief valve includes a water-filled nozzle fluidly connected to a hydrocarbon distribution manifold. A valve body is connected to the distribution manifold, with an outlet of the nozzle coincident with an interior water-filled chamber of the valve body. A first seal element is removably seated against the nozzle outlet and an arm is hinged to the body and configured to apply a force along a seal axis and bias the first seal element into sealing engagement with the nozzle outlet until hydrocarbon pressure exceeds a sealing pressure of the applied force and unseats the first seal element from the nozzle outlet such that excess hydrocarbons exit through an outlet of the valve body. A weight is disposed on the arm at a distance from the seal axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/479,671 filed Apr. 27, 2011, and incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND 
       [0003]    In producing oil and gas from offshore wells, a wellhead is employed at the seafloor and the hydrocarbons flow from the wellhead through tubular risers to the surface where the fluids are collected in a receiving facility located on a platform or other vessel. Normally, the flow of hydrocarbons is controlled via a series of valves installed on the wellhead, the risers, and in the receiving facility at the surface. At times, temporary flow lines from the wellhead to a receiving facility may be installed. In all such instances, it is important to prevent excessive pressure from building up in these lines. Such pressures could build up due to hydrate formation, sudden changes in pressure in the well bore, or back pressure from valve closings or from other processes. Pressures could cause equipment failures at the sea floor, which may be 5,000-7,000 feet or more below the surface. At those depths, the water pressure exceeds 2000 p.s.i. Because of the depth and pressures, effectuating repairs can require that equipment and tools be handled by deep diving, using, for example, remotely operated vehicles (ROV&#39;s) which are essentially robots controlled by an operator in a surface vessel. Controlling the vehicles from such distances and using the ROV&#39;s to repair and/or replace equipment and components is a difficult and time consuming task. 
       SUMMARY OF THE DISCLOSURE 
       [0004]    Accordingly, a device is required to limit pressures in the subsea flow lines and other hydrocarbon-containing equipment to non-destructive levels, and to relieve excess pressure when required. Any pressure relief device installed at the sea bed should be capable of reliable operation at the extreme pressures that are encountered, and withstand the highly-corrosive environment of the ocean. Further, it would be advantageous if the pressure setting at which the valve operates can be adjusted while the valve is installed and in position subsea, rather than having to disconnect the valve from a piping system and then make the lengthy trip to the surface for adjustment. 
         [0005]    These and other needs in the art are addressed in one embodiment of a pressure relief valve. In an embodiment, the pressure relief valve includes a body having a chamber. In addition, the pressure relief valve includes a first seal element in the chamber that engages a second seal element to thereby prevent fluid passage into the chamber up to a predetermined fluid pressure. Further, the pressure relief valve includes an arm hinged to the body and applying a force along a seal axis and biasing the first and second seal element into sealing engagement. Still further, the pressure relief valve includes a weight disposed on the arm at a distance from the seal axis. 
         [0006]    These and other needs in the art are addressed in another embodiment of a pressure relief valve for use submerged in a body of water. In an embodiment, the pressure relief valve includes a body. In addition, the pressure relief valve includes a first seal element disposed in the body in a chamber having an outlet into the body of water. Further, the pressure relief valve includes an arm coupled to the body and adapted to pivot. Still further, the pressure relief valve includes a weight positioned on the arm that supplies a moment that biases the first seal element into sealing engagement with a second seal element forming a seal effective against a predetermined pressure in the chamber. 
         [0007]    These and other needs in the art are addressed in another embodiment of a subsea system for recovering hydrocarbons. In an embodiment, the system includes a subsea container having hydrocarbons retained therein. In addition, the system includes a pressure relief valve coupled to the subsea container and adapted to relieve pressure in the container if the pressure rises to a predetermined value. The relief valve includes a chamber that is flooded with seawater. The relief valve also includes a metal to metal seal in the flooded chamber. Further, the relief valve includes a moment arm biasing a first seal member into sealing engagement with a second seal member when the hydrocarbon pressure in the container is less than the predetermined value. Moreover, the relief valve includes an outlet to port into the sea hydrocarbons that enter the chamber when the hydrocarbon pressure in the container rises to the predetermined value. 
         [0008]    These and other needs in the art are addressed in another embodiment of a pressure relief valve. In an embodiment, the pressure relief valve includes a nozzle in fluid communication with a container. In addition, the pressure relief valve includes a seal element disposed above the nozzle and adapted to move into and out of sealing engagement with the nozzle. Further, the pressure relief valve includes a weight positioned above the seal element and supported for reciprocal motion. The weight is adapted to force the seal element into sealing engagement with the nozzle until the pressure in the container equals or exceeds a predetermined pressure. 
         [0009]    Thus, embodiments described herein include a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    For a detailed description of the disclosed embodiments of the invention, reference will now be made to the accompanying drawings in which: 
           [0011]      FIG. 1  is a schematic view of an exemplary subsea hydrocarbon recovery system employing a subsea pressure relief valve made in accordance with principles described herein. 
           [0012]      FIG. 2  is an elevation view, partly in cross section, of the pressure relief valve of  FIG. 1 . 
           [0013]      FIG. 3  is a top view of the pressure relief valve of  FIG. 2 . 
           [0014]      FIG. 4  is an elevation view, partly in cross section, of another pressure relief valve made in accordance with principles described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    A pressure relief valve for underwater applications is disclosed herein. The valve can be employed in many underwater applications; however, it has particular application as a device to relieve overpressures that may develop in subsea flow lines, manifolds, tanks and vessels containing and/or transporting hydrocarbons from the sea floor. For convenience, the word “container” may be used herein to refer to at least all such hydrocarbon-containing lines, manifolds, tanks, and vessels. 
         [0016]    The following description is exemplary of embodiments of the invention, but these embodiments are not to be interpreted or otherwise used as limiting the scope of the disclosure, including the claims. One skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and is not intended to suggest in any way that the scope of the disclosure, including the claims, is limited to that embodiment. 
         [0017]    The drawing figures are not necessarily to scale. Certain features and components disclosed herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. 
         [0018]    The terms “including” and “comprising” are used herein, including in the claims, in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first component couples or is coupled to a second component, the connection between the components may be through a direct engagement of the two components, or through an indirect connection that is accomplished via other intermediate components, devices and/or connections. 
         [0019]    Referring to  FIG. 1 , an exemplary embodiment of an offshore system  200  for recovering hydrocarbons from a subsea wellbore  201  is shown. In this embodiment, system  200  includes a blowout preventer (BOP)  202  mounted to a wellhead  203  at the sea floor  204 , and a capping stack  205  mounted atop BOP  202 . In a typical system for producing from well  201 , hydrocarbons are allowed to flow through the BOP  202 , through a lower marine riser package (not shown), and through risers  213  to a hydrocarbon-receiving vessel at the surface, such as platform  211 . In this example, however, capping stack  205  has been substituted for a lower marine riser package in a situation, for example, where hydrocarbon flow is not controlled via the normal path and is instead diverted and collected via an alternate collection system. 
         [0020]    Capping stack  205  includes at least one fluid outlet  206  controlled by a valve  207  for controlling the flow of hydrocarbons from the well to various destinations, including into a distribution manifold  208 . In turn, one or more flowlines  209  are connected to valved outlets  210  in the manifold  208  and are employed to transport the hydrocarbons from the well to one or more hydrocarbon storage vessels at the surface, such as platform  211 . A pressure relief valve  10  is coupled to subsea manifold  208  and is in fluid communication with hydrocarbons contained in manifold  208 . When valved outlet  210  interconnecting flowline  209  and manifold  208  is open, pressure relief valve  10  is likewise in fluid communication with flow line  209 . 
         [0021]    Referring now to  FIGS. 2 and 3 , pressure relief valve  10  generally includes nozzle  12 , valve body  14 , closure member  16 , arm  18 , and weights  19   a ,  19   b . Valve  10  includes spindle  20 , guide member  24 , disk holder  26 , and disk  30 . 
         [0022]    Valve body  14  includes base flange  40  for attaching pressure relief valve  10  to the distribution manifold  208 , an outlet flange  42  suitable for connecting the valve body to another flow line or other vessel or container, and an interior chamber  44 . In this embodiment, flange  42  is left unconnected, such that chamber  44  is open to the ambient environment and thus is flooded with seawater that enters the chamber  44  at outlet  45 . The upper end of body  14  includes upwardly-extending studs  46  for attaching closure member  16 . 
         [0023]    Closure member  16  includes base plate  50 , hinge support  52  and circumferentially-spaced apertures  54  formed through plate  50 . Base plate  50  is circular in this embodiment; however base plates having other shapes may be employed. Hinge support  52  is an elongate member supporting hinge  60  at its upper end. Support  52  may be integrally formed with plate  50  or may be a separate member welded or otherwise coupled to the top of base plate  50 . 
         [0024]    Arm  18  is an elongated and substantially rigid member pivotally secured to hinge support  52  by hinge  60 . Arm  18 , which may be a bar, plate, channel or beam, such as an I-beam, extends from hinge  60  a predetermined distance and, in the embodiment shown in  FIG. 2 , includes an upwardly extending post  62  attached adjacent the unhinged end of the arm. 
         [0025]    In the embodiment shown in  FIG. 2 , weights  19  (e.g.  19   a  and  19   b ) are “donut” or toroidal-shaped, each including a through bore  64  having a diameter that is larger than the thickness or diameter of post  62  on arm  18 . Weights  19   a  and  19   b  are positioned on the arm  18  such that the post  62  is received within a through bore  64  of each weight. The engagement of post  62  through bores  64  retains the weights in position on arm  18 . Weights  19  include a plurality of handles  65  to allow the weights  19  to be lifted and manipulated by ROV&#39;s. Handles  65  may be T-shaped or looped or in another form that makes the weights convenient to be handled by ROV&#39;s, or to be connected by cables for transporting. To allow ample access by the ROV&#39;s, weights  19  are free of any type of enclosure or covering in the embodiment shown in  FIG. 2 . In this manner, the weights  19   a ,  19   b  may be said to be unencumbered. Also as shown in the embodiment of  FIG. 2 , weights  19   a  and  19   b  have different sizes and different weights. In particular, the weight of  19   a , in this example, is substantially greater than the weight of  19   b . To achieve the desired force, a single weight  19  or a number of weights  19   a ,  19   b , having differing weights, will be stacked on arm  18 . 
         [0026]    Although the disclosure to this point has described weights that are toroidal-shaped and that are retained on arm  18  via post  62 , it is to be understood that the weights  19   a ,  19   b  may take any of a variety of other shapes, and may be formed without post-receiving bores. Further, arm  18  may be formed without post  62  and may, for example, instead be fitted with a bin or platform for receiving weights that are placed and/or stacked within or on the bin or platform. 
         [0027]    Referring again to  FIG. 2 , hinge  60  interconnects hinge support  52  and arm  18  and is generally configured like a door hinge. More specifically, as best shown in  FIGS. 2 and 3 , in this embodiment, the ends of hinge support  52  and arm  18  include interlaced projections having aligned through-bores through which an elongate pin  61  is inserted. Hinge  60  serves to allow arm  18  to pivot about pin  61 . 
         [0028]    Referring again to  FIGS. 2 and 3 , nozzle  12  includes a lower base flange  80  and a tubular extension  81  extending along seal axis  87  and having interior  82  that is in fluid communication with the hydrocarbons in manifold  208 . The outside surface of extension  81  includes two externally threaded segments  83  and  84 , and seal groove  85 . Annular seal  86  is disposed in seal groove  85  and seals between the nozzle  12  and valve body  14 . Threaded segment  83  threadably engages a correspondingly threaded segment on the inner surface of valve body  14 . The upper end of nozzle  12  forms seal rim  90 , which engages sealing disk  30  when the pressure of the hydrocarbons within the manifold is below a predetermined value. 
         [0029]    Disk  30  is centered along seal axis  87  and includes extension  92  on its upper end which is received in a mating recess in disk holder  26  and is aligned with axis  87 . Retaining ring  98  retains disk  30  on disk holder  26 . The upwardly-extending portion  100  of disk holder  26  is slidably received in the sleeve  104  of guide  24 . Spindle  20  includes a flange portion  107  disposed between arm  18  and base plate  50 , and a projection extending along seal axis  87  having a connecting end  106  that is retained in the upper end of disk holder  26  via retaining ring  108 . Tube  110  extends between interior base chamber  44  through guide member  24  and opens into the annular chamber  105  that exists between the upper surface of guide  24  and closure member  16 , thereby placing annular chamber  105  in fluid communication with interior base chamber  44 . Given that outlet  45  of valve body  14  is open to receive sea water, and tube  110  extends between base chamber  44  and annular chamber  105 , both chambers  44 ,  105  will be flooded with seawater and will experience the same pressure. 
         [0030]    Studs  46  are connected to and extend upwardly from valve body  14  where they are received in aligned apertures  54  circumferentially spaced about base plate  50  of closure member  16 . Retaining nuts  47  are disposed about the studs  46  to attach the closure member  16  to the body  14 . Gaskets  120 ,  121  are optionally disposed between guide  24  and closure member  16 , and between guide  24  and valve body  14 , respectively. As sea water is intended to flood chambers  44 ,  105  in this application, a seal between closure  16  and valve body  14  is not required. 
         [0031]    Blow-down adjusting ring  124  is disposed about threaded segment  84  on nozzle  12 . Adjusting ring  124  is employed in order to adjust the size of the opening that is created after disk  30  lifts off nozzle rim  90  upon pressure in the manifold  208  reaching a predetermined maximum value, and thereby to adjust the pressure at which disk  30  will reseat on nozzle rim  90 . Once ring  124  is appropriately adjusted, pin  126  fixes the ring&#39;s position and prevents the adjusting ring  124  from moving axially along nozzle  12 . 
         [0032]    The moment created by weights  19   a ,  19   b  being positioned on arm  18  at a distance D from seal axis  87  creates a downward force F that is applied to spindle  20  and disk holder  26  and, in turn, to disk  30  so that disk  30  seals against seal rim  90  of nozzle  12 . The pressure brought to bear on those sealing surfaces of nozzle rim  90  and disk  30  is adjustable by means of adjusting the amount of weight applied to arm  18  and/or the distance it is applied from the seal axis  87 . Although two weights,  19   a  and  19   b , are shown in  FIG. 2 , the weight applied at distance D may be supplied by one, two, or more weights applied to arm  18 . Weights  19   a ,  19   b  will each be manufactured to have a predetermined weight and, for example, may be made of steel, suitably coated for the environment. In the embodiment shown in  FIGS. 2 and 3 , the combined weights of  19   a  and  19   b  may be, for example, 150 lbs. with that weight being applied at a distance D of 3 ft. through a fulcrum displaced by 6 in. from valve centre line, which would resist a 500 psi set pressure acting over a 2 sq inch port/orifice. In this example, arm  18  may be made of a carbon steel beam. 
         [0033]    Components of valve  10  may be made of corrosion-resistant materials such as Super Duplex stainless steel. Alternatively, components may be made of carbon steel. However, carbon steel is much more susceptible to corrosion. Due to the corrosive nature of seawater in this embodiment, cathodic protection is applied to slow corrosion, particularly if carbon steel is employed. Accordingly, as shown in the embodiment of  FIG. 2 , an anode  130  is disposed within chamber  44  and placed in direct engagement with body  14 . Anode  130 , which may be made of a material such as zinc or aluminum, for example, is fastened to body  14  in this embodiment by straps  132  and threaded fasteners  134 , although it may be attached to be in engagement with body  14  by other means. In this manner, a degree of cathodic protection is provided to all metal components that are coupled, directly or indirectly, to body  14 . Such cathodic protection can be accomplished by attaching anode  130  to other metallic portions of pressure relief valve  10 ; however, attaching anode  130  within chamber  44  is convenient, and also places the anode in a position less likely to be knocked loose and detached as the valve is transported and installed subsea. 
         [0034]    Certain metals and alloys are detrimentally affected by the hydrogen gas that is formed when cathodic protection is provided. In particular, hard materials employed in certain high-strength bolts, for example, are particularly susceptible to cracking when exposed to hydrogen gas. Accordingly, in the example described above, select components may optionally be made of a material that is less-susceptible to cracking in the presence of hydrogen gas. 
         [0035]    Base flange  80  of nozzle  12  is placed in engagement with the manifold  208  and positioned such that nozzle chamber  82  is in fluid communication with pressurized fluid within the manifold  208 . Base flange  40  of body  14  is then bolted to a corresponding flange  215  on the manifold  208 . Seal  88  seals between flange  80  and manifold  208 . In such position, the central chamber  82  of nozzle  12  will be filled with the hydrocarbons and pressurized to the same extent as the manifold  208 . Given that outlet  45  of valve body  14  is open to receive sea water, and that chamber  105  is in fluid communication with chamber  44  via tube  110 , the entire valve is flooded with sea water and will experience the same pressure, such that the lift pressure required to unseat disk  30  from nozzle rim  90  will be unaffected by the tremendous pressure of the seawater even at great depths. 
         [0036]    Should the pressure in manifold  208  and in chamber  82  of nozzle  12  create a force that exceeds the force provided by the predetermined and preapplied pressure supplied by arm  18  and weights  19   a ,  19   b  on disk  30 , disk  30  will be unseated from rim  90  of nozzle  12 , such that the pressurized hydrocarbons will exit nozzle  12  and enter chamber  44  and be expelled through outlet  45  into the surrounding seawater. When the excessive pressure is relieved and the pressure within manifold  208  drops to a pressure level less than that which causes the seal members to disengage, the force supplied by arm  18  and weights  19   a ,  19   b  will push the disk  30  back into sealing engagement with nozzle rim  90 . At this point, the flow of hydrocarbons from manifold  208  into chamber  44  and the surrounding sea water is stopped. 
         [0037]    The embodiment of  FIGS. 2 and 3  provides a reliable pressure relief valve having few moving parts and allowing for ease of manufacture and installation and allowing for subsea adjustment. Specifically, the valve need not be taken to the surface in order to be readjusted. Instead, a number of weights may be positioned on arm  18  adjacent the sea floor and, using an ROV, the weights may be selected in varying combinations in order to achieve the desired weight on arm  18  to apply the appropriate force to resist the pressure of hydrocarbons in manifold  208 . The pressure relief valve is free of springs, bellows and other components that may be susceptible to damage when used in the harsh subsea environment. Further, the valve, being completely flooded with seawater, is not susceptible to seal failure and is well-suited to operate at tremendous pressures that exist subsea. 
         [0038]    Referring to  FIG. 4 , an alternative subsea pressure relief valve  300  is shown and may be employed to control and relieve hydrocarbon pressure within manifold  208 . Pressure relief valve  300  generally includes a body portion  302 , seal disk  330 , and weight bin  340  supporting weight  19   a . In this embodiment, the weight  19   a  that is employed to resist the hydrocarbon pressure within manifold  208  and thereby control operation of seal disk  330  is disposed substantially aligned with seal axis  306 , rather than being disposed at a distance D from the seal axis as in the design of valve  10  described with reference to  FIG. 2 . 
         [0039]    Referring still to  FIG. 4 , valve body  302  includes central nozzle  303  having chamber  304  disposed about seal axis  306 . Body  302  further includes flange  308  coupled to flange  215  of manifold  208 . 
         [0040]    Seal disk  330  is disposed atop valve body  302 , the lower surface of disk  330  sealing against nozzle  303  when the appropriate force F is applied. Weight bin  340  is a weight-receiving cart or receptacle that is coupled to the upper surface of seal disk  330  and generally comprises bottom  342  and a pair of side panels  344 . In this embodiment of  FIG. 4 , weight bin  340  is open on its other sides and has no top. Extending along seal axis  306  is post  346  that is coupled to bottom  342  of the weight bin  340 . One or more toroidal-shaped weights, such as weight  19   a  previously described, is supported within weight bin  340  and disposed about post  346 . 
         [0041]    In the embodiment of  FIG. 4 , roller assemblies  345  extend between sides  344  of weight bin  340  and support members  350 . Support members  350 , shown schematically, are supported from the seabed or other rigid structure and located so as to position weight bin  340  in substantial alignment with seal axis  306 . 
         [0042]    Optionally, other means of retaining weights above valve body  302  and seal axis  306  may be employed. For example, bin  340  may be formed without post  346 , and weights may have shapes other than toroidal shapes and be retained on bottom  342  of bin  340  by gravity alone, or by other fastening configurations. Similarly, bin  340  may include portions that slide, without rollers, against support members  350 . 
         [0043]    In operation, the appropriate weight  19   a  is placed over post  346  in weight bin  340  to apply the predetermined force F against disk seal  330 . Weight  19   a  may be positioned in bin  340  after installation of valve  300  on manifold  208 . Similarly, weights can be added or exchanged in weight bin  340  in order to adjust the force F against seal disc  330 . When hydrocarbon pressure with the manifold  208  reaches a predetermined maximum and supplies a lifting force to seal disk  330  to cause it to unseat and lift, bin  340  raises when the disk becomes unseated. Bin  340  is allowed to move axially in a direction along seal axis  306  as rollers of roller assemblies  345  roll along supports  350 . 
         [0044]    As compared to pressure relief valve  10  previously described, valve  300  will require a substantially larger weight  19  for the same hydrocarbon pressure in manifold  208 . This is because the weight in valve  300  is supplied substantially along seal axis  306 , rather than at a distance D as in valve  10 . In other words, valve  10  shown in  FIG. 2  allows a substantially lower weight to achieve the same seal force as a result of the moment provided by arm  18 . Nevertheless, the design of valve  300 , like valve  10 , has few moving parts, is a generally simple and rugged design that can function subsea at great pressures, and that does not require that components be isolated from the surrounding seawater. Further, it allows for subsea weight adjustment when the valve is installed subsea, and eliminates the need to transport the valve to the surface in order to adjust the sealing force applied. 
         [0045]    While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only, and are not limiting. Many variations and modifications of the disclosed apparatus are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.