Abstract:
A device for preventing rotation of a stuffing box cap to avoid leakage of contents, the device comprising an upwardly projecting stop member mounted on the stuffing box body which is configured to abut a protuberance on the cap and thereby prevent cap rotation. The stop member is preferably configured to pivot away from the stuffing box cap when cap removal is desired.

Description:
FIELD OF THE INVENTION 
     The invention relates to stuffing boxes and methods for maintaining seal integrity. 
     BACKGROUND OF THE INVENTION 
     Stuffing boxes are commonly used on oil and gas wellheads around a reciprocating or rotating shaft for sealing and preventing fluid/gas leakage into the environment. The shaft passes out of the well tubing and into the aboveground environment, and hence some form of sealing is required to prevent fluid loss and site contamination. Stuffing boxes are usually the final piece of equipment that is threaded onto the well tubing, with the shaft passing through the stuffing box and cap, creating a seal around the shaft as it moves in a vertical or rotational direction and thereby ensuring that the well fluids flow to the desired output rather than spill into the environment. The desired seal is created by the stuffing box, which contains packing material that is under pressure and in contact with the shaft and the inner stuffing box walls. The seal is only created where there is sufficient pressure on the packing, and this pressure is achieved by threading a cap onto the stuffing box housing, the cap being provided with an opening to allow for passage of the shaft. When sufficient pressure is applied to the packing by means of the cap, a tight seal is achieved and fluid leakage is avoided. 
     Stuffing boxes can leak despite proper tightening of the cap if there is packing material wear, which reduces the desired friction within the stuffing box that is required to counter the pressure of the downhole fluid. This is normal, expected wear, and it is usually addressed by retightening of the cap or replacement of the packing material. It has been found, however, that caps can also sometimes back off and loosen due to the significant pressures within a stuffing box, which can result in fluid leakage at the well site. Such leakage can contaminate the adjacent land, surface water and subsurface water, and the leaked fluid can have very high salt content that is harmful to plants in the area. Also, leaked gas can be poisonous and even fatal in high enough concentrations. There can be significant leakage depending on the pressure in the well bore, and substantial remediation costs can be incurred in subsequent attempts to address the spill. 
     Despite this substantial risk, there is presently no device on the market that can be used by the industry to prevent the stuffing box cap from backing off and causing leakage. The standard practice is simply manual observation, which may not be adequate where a large number of wells must be monitored. The only means currently employed in the oil and gas industry to ensure a proper seal at surface is to tighten and retighten the stuffing box cap and hope that the friction is sufficient to maintain the seal and prevent the cap from backing off. As stated above, however, the friction reduces with packing wear and the pressure on the cap decreases, thereby enhancing the risk of the cap backing off. 
     SUMMARY OF THE INVENTION 
     The present invention therefore seeks to provide a device that can be applied to a standard stuffing box to help avoid or prevent leakage caused by the cap backing off. The present invention also seeks to provide such a device that is of simple and inexpensive construction, and that is reliable and easy to install and maintain. 
     According to a first aspect of the present invention there is provided an anti-rotation device for a stuffing box, the stuffing box comprising a housing with a threaded opening and a correspondingly threaded cap configured to seal the opening, the cap rotatable in a first direction to seal the opening and in an opposite second direction to unseal the opening, the cap being provided with a protuberance on an outside edge thereof, the anti-rotation device comprising a stop member attached to the outside of the housing and extending at least adjacent the cap, such that upon rotation of the cap in the second direction the protuberance contacts the stop member and the cap is thereby prevented from further rotation in the second direction. 
     According to a second aspect of the present invention there is provided an anti-rotation device for use with a stuffing box, the stuffing box comprising a housing with a threaded opening and a correspondingly threaded cap configured to seal the opening, the cap rotatable in a first direction to seal the opening and in an opposite second direction to unseal the opening, the cap being provided with a protuberance on an outside edge thereof, the anti-rotation device comprising a stop member for attachment to the outside of the housing and for extending at least adjacent the cap, such that upon rotation of the cap in the second direction the protuberance contacts the stop member and the cap is thereby prevented from further rotation in the second direction. 
     According to a third aspect of the present invention there is provided an anti-rotation device for use with a stuffing box, the stuffing box comprising a housing with a threaded opening and a correspondingly threaded cap configured to seal the opening, the cap rotatable in a first direction to seal the opening and in an opposite second direction to unseal the opening, the anti-rotation device comprising: 
     a protuberance for mounting on an outside edge of the cap; and 
     a stop member for attachment to the outside of the housing and for extending at least adjacent the cap, such that upon rotation of the cap in the second direction the protuberance contacts the stop member and the cap is thereby prevented from further rotation in the second direction. 
     In exemplary embodiments of the present invention, the protuberance is of unitary construction with the cap, but it can also be a discrete device mounted on the cap to provide the necessary extension to contact the stop member. 
     The stop member may be either permanently mounted or removably attached to the housing. In a preferred embodiment, the stop member is attached to the housing by means of a bracket; in this case the bracket may be either permanently mounted or removably attached to the housing, and the stop member may be removably attached to the bracket. 
     In other preferred embodiments, the stop member is attached to the housing by pivotable mounting means, which pivotable mounting means can be part of the stop member or of the bracket where a bracket is used, such that the stop member may be pivoted away from the cap and out of contact with the protuberance, to enable removal of the cap when desired. Most preferably, the pivotable mounting means are provided with a disengageable locking mechanism to prevent pivoting of the stop member away from the cap when it is desired that the cap remain in place. 
     The present invention accordingly provides a simple device that is relatively easy to install on a standard stuffing box and retains the stuffing box cap in a tightened position, while being of inexpensive construction. 
     A detailed description of exemplary embodiments of the present invention is given in the following. It is to be understood, however, that the invention is not to be construed as being limited to these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, which illustrate exemplary embodiments of the present invention: 
         FIG. 1   a  is an elevation view of an embodiment of an anti-rotation device in accordance with the present invention; 
         FIG. 1   b  is a top plan view of the embodiment of  FIG. 1   a;    
         FIG. 2   a  is a side elevation view of the stop member of the embodiment of  FIG. 1   a;    
         FIG. 2   b  is a front elevation view of the stop member of the embodiment of  FIG. 1   a;    
         FIG. 3   a  is a top plan view of a stuffing box fitted with the embodiment of  FIG. 1   a;    
         FIG. 3   b  is an elevation view of the stuffing box of  FIG. 3   a;    
         FIG. 4   a  is an elevation view of a bolt-on protuberance in accordance with an embodiment of the present invention; and 
         FIG. 4   b  is a top plan view of a stuffing box cap provided with the bolt-on protuberance of  FIG. 4   a.    
     
    
    
     Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring now in detail to the accompanying drawings, two exemplary embodiments of the present invention are illustrated, one for use with a stuffing box cap having protuberances or lugs, and one for use with a stuffing box cap without protuberances or lugs. 
     Referring to  FIGS. 1   a  and  1   b , an anti-rotation device  10  according to the present invention is shown. The anti-rotation device  10  comprises a two-part bracket  32  that wraps around the housing of a stuffing box. The two parts of the bracket  32  are secured in a spaced apart manner at one end by a spacer  46  which is sized to correspond to the width of a stop member  28 , the stop member  28  being located at the opposite end of the bracket  32 . The spacer  46  is secured in place by means of a bolt and nuts, which bolt passes through holes  44  in the bracket  32 . The bracket  32  is shown in a hexagonal configuration, as many stuffing box housings have a hexagonal cross section, but even if the housing is not hexagonal it will have the same diameter and the illustrated embodiment can be used. 
     The stop member  28 , which is also shown in detail in  FIGS. 2   a  and  2   b , comprises an upper end  40  and a lower end  42 , the upper end  40  disposed at an angle to the lower end  42 . The stop member  28  is mounted on the bracket  32  by pivotable mounting means  34 , which in the illustrated embodiment comprises a bolt that passes through a pipe welded to the back of the lower end  42  of the stop member  28 . This pivotable mounting means  34  allows the upper end  40  of the stop member  28  to be pivoted away from its engaged position when desired. To prevent pivoting of the stop member  28 , the bracket  32  is provided with holes  38  through which a locking mechanism  36  can be inserted, which is explained in detail below. 
       FIGS. 3   a  and  3   b  illustrate an anti-rotation device  10  installed on a standard stuffing box  12 . The stuffing box  12  comprises a housing  14  and a cap  20 , which housing  14  and cap  20  are correspondingly threaded for mating of the parts in a manner well known in the art. As indicated above, the cap  20  is provided with an opening  24  through which a shaft may pass during use of the stuffing box  12 . In the standard stuffing box cap  20  illustrated in  FIGS. 3   a  and  3   b , the cap  20  comprises two opposed protuberances or lugs  26  which are of unitary construction with the cap  20  and extend outwardly from the outside edge of the cap  20 . The anti-rotation device  10  is installed by securing the bracket  32  around the circumference of the housing  14  of the stuffing box  12  by means of the bolts and nuts, as illustrated, with the bracket  32  spaced at opposite ends by the spacer  46  and the stop member  28  and pivotable mounting means  34 . The anti-rotation device  10  is provided with a locking mechanism  36 , which in the illustrated embodiment is a spring safety pin, although other means for locking the device would be clear to one skilled in the art. 
     The anti-rotation device  10  is of simple construction and can be fabricated using strap iron, small pipe, bolts, lock nuts, and a pin for a locking mechanism  36 . Preferably, the iron used in the manufacture of the anti-rotation device  10  is mild iron of ⅛ inch thickness and 1 inch width; while thicker iron could be used, the width is well-suited for a standard stuffing box housing. Mild steel is advantageous as it is readily available, inexpensive, and easy to weld; other metals such as aluminum or stainless steel could be used, but they would introduce greater expense and are more difficult to weld. 
     Although the embodiment illustrated in  FIGS. 1   a  to  3   b  shows a standard stuffing box  12  having protuberances or lugs  26 , not all stuffing box caps are provided with such protuberances  26 . In that case, the present invention can still be utilized, but some outward extension of the cap  20  needs to be incorporated into the anti-rotation device  10  to enable the prevention of cap  20  rotation. Referring now to  FIGS. 4   a  and  4   b , the stuffing box cap  20  has smooth edges, with no protuberances or lugs  26 . A two-part cap bracket  52  is accordingly attached to the outside edge of the cap  20  and secured in place by means of bolts and locking nuts. The result is that protuberances  30  now extend outwardly from the circumference of the cap  20  and can engage the stop member  28  during operation, as described below. 
     In operation, the anti-rotation device  10  is mounted on the housing  14  of the stuffing box  12  as described above and illustrated in  FIGS. 3   a  and  3   b . (If necessary, the cap bracket  52  is also mounted on the cap  20  if the cap  20  does not have protuberances  26 .) This is preferably undertaken after the cap  20  has been screwed onto the housing  14 , so that the bracket  32  can be adjusted to have the stop member  28  abut one of the protuberances  26 / 30 . As shown in  FIG. 3   a , the cap  20  is designed to rotate through the threaded connection to either tighten (direction D 1 ) or loosen (direction D 2 ), and the present invention is intended to block the cap  20  from rotating in direction D 2  once the cap  20  has been tightened. Accordingly, the bracket  32  should be secured in a position such that the stop member  28  abuts the protuberance  26 / 30  on the side where it would normally move when being loosened in direction D 2 . To maintain the upper end  40  of the stop member  28  in contact with the protuberance  26 / 30 , the locking mechanism  36  is engaged. If the cap  20  becomes disposed to loosen, the protuberance  26 / 30  will meet the resistance of the upper end  40  and loosening will be prevented. 
     As indicated above, it may also be desirable to loosen and even remove the cap, for example to replace worn packing. In that case, the locking mechanism  36  can be disengaged or removed; in the illustrated embodiment, the locking pin would be removed from the holes  38 . Once the locking mechanism  36  is no longer operative to restrict pivoting of the stop member  28 , the stop member  28  can pivot along the pivotable mounting means  34  such that the upper end  40  of the stop member  28  pivots away from the cap and free of the protuberance  26 / 30 . Once the upper end  40  of the stop member  28  is clear of the protuberance  26 / 30 , the cap  20  can be rotated in direction D 2  as desired. When it is desired to once more secure the stuffing box  12 , the cap  20  can be re-tightened in direction D 1  and the upper end  40  of the stop member  28  pivoted back into place abutting the protuberance  26 / 30 , with the locking mechanism  36  finally re-engaged. In the event that the protuberance  26 / 30  is no longer properly aligned with the stop member  28 , the bracket  32  can be loosened and re-adjusted to shift the upper end  40  of the stop member  28  into abutment with the protuberance  26 / 30 . 
     As can be readily seen, then, there are numerous advantages provided by the present invention. It can provide effective means for addressing a potentially significant problem in the oil and gas industry, with a device that is easy and inexpensive to construct and simple to use and maintain. It can be applied to new stuffing boxes, or can be employed with existing stuffing boxes already in use in the field. 
     The foregoing is considered as illustrative only of the principles of the invention. Thus, while certain aspects and embodiments of the disclosure have been described, these have been presented by way of example only and are not intended to limit the scope of the disclosure. For example, the illustrated embodiments show the stop member mounted on a bracket, but the stop member itself could be mounted on the stuffing box housing in a temporary or permanent arrangement. Indeed, the present invention may be embodied in a variety of other forms without departing from the spirit of the invention, which invention is defined solely by the claims below.