Abstract:
A method of preventing wear in a blowout preventer includes the steps of forming an inner surface of a blowout preventer body to receive wear inserts at least one wear point in the blowout preventer body; and securing at least one wear insert on the formed inner surface of the blowout preventer body.

Description:
FIELD 
     This relates to the internal operating surfaces of a blowout preventer for oil field operations, namely, a blowout preventer having wear, seal and guide plate inserts. 
     BACKGROUND 
     A blowout preventer is basically a pressure vessel with moving parts, both inside and out. A key portion of the pressure vessel is the body. The body must have sufficient strength to contain pressured well fluids, (as a pressure vessel), and supply a guide and sealing means for the moving internal parts. 
     These two functions are contradictory in material requirements. To serve as a pressure vessel, the body and ram block material must meet certain specifications to resist stress cracking in the presence of such chemicals as hydrogen sulphide. This typically means that the material must be relatively soft. Unfortunately, this soft material must also provide a guide and seal means for the moving ram blocks in the extremely abrasive environment of the well fluid. Solving the deterioration of the contacting surfaces would normally require harder, more abrasive resistant materials. These materials however, are either expensive or do not meet the specifications of the soft materials to meet the requirements to resists stress cracking. 
     The normal practice is to manufacture the body, (pressure vessel), and the ram blocks from softer materials to meet stress cracking specifications, and repair all parts when necessary as they wear. The repair of the material of these components requires a specific weld procedure that is expensive. In addition, the weld material must also be soft and wears as readily as the original material. 
     Typically, the body is weld repaired several times over without regard to the consequences to the parent material when subjected to the numerous heat cycles involved. A weld repair is a fusion process that involves heat applied to the parent material in excess of it&#39;s′ “critical” temperature to fuse with the added weld material to the parent material. Repeated cycles of this nature can permanently change the structure of the parent material and lead to a host of other problems. 
     There are a number of solutions that have been attempted, but for various reasons, have been unable to solve the soft and hard material preferences for this application. One solution was to weld apply hard surfacing to the parent material where the moving ram blocks contacted the body. This process was unsuccessful due to the expense and inability to meet the material requirements to resist cracking. Because hard surfacing is a fusion process, the hard material becomes a part of the body and must meet the same property specifications to resist cracking. Unfortunately hard surfacing materials would not pass some specific requirements, usually associated with crack initiation. With fusion processes, cracks that initiate in the hard surfacing may propagate through to the parent material, the body, which is to be protected from cracks. Another process that has been attempted to improve the wear of the mating surfaces is an infusion process that relies on a heated gas process to harden a thin layer of the parent material of the body. As in welding hard surfacing material to the parent material, the infusion process also becomes part of the body, or pressure vessel, and must meet all of the required specifications. Testing suggests that not only does the hardened layer not meet specifications, but also suggests that cracks could be initiated at lower stresses than the parent material. Again, crack propagation into the parent material from the hardened surface is of major concern for a pressure vessel. 
     A more effective system has been used that provides a replaceable seal seat. It is locked into position with a sprung ring and setscrew arrangement that locks an “o-ring” sealed seat into position. The major problem with this arrangement is that it often corrodes and may be extremely difficult to remove. 
     SUMMARY 
     There is provided a method of preventing wear in a blowout preventer, comprising the steps of: forming an inner surface of a blowout preventer body to receive wear inserts at least one wear point in the blowout preventer body; and securing at least one wear insert on the formed inner surface of the blowout preventer body. 
     According to another aspect, the wear point may be a contact point between a moving component and the blowout preventer body. One or more wear inserts may be of a harder material than the blowout preventer body. The wear inserts may be secured using at least one of a pin connection and an adhesive. 
     According to another aspect, forming an inner surface may comprise forming a wear plate cavity around a tubular bore below a travel path of a ram block, and securing at least one wear insert may comprise securing a wear plate in the cavity, the wear plate engaging a bottom surface of the ram block in the closed position. At least one of the wear plate cavity and the wear plate may have flow channels to permit flow between the wear plate and the blowout preventer body. The wear plate may have a raised portion that raises the ram block in the closed position into a sealing engagement with a seal above the ram block. 
     According to another aspect, forming an inner surface may comprise forming a threaded cavity around a tubular bore above a travel path of a ram block, and securing at least one wear insert may comprise threading a seal insert into the threaded cavity, the seal insert engaging a top surface of the ram block in the closed position. The threaded cavity may comprise a rounded thread and the seal insert comprises a square thread. The seal insert may comprise at least one port for injecting a fill compound between the square thread and the rounded thread. An elastomeric seal may be positioned between the threaded cavity and the seal insert. 
     According to another aspect, forming an inner surface may comprise forming guide cavities along the sides of a ram block travel path, and securing at least one wear insert may comprise inserting ram block guides into the guide cavities, the ram block guides engaging the sides of the ram block as it moves along at least a portion of the ram block travel path. 
     According to another aspect, the method may further comprise the step of forming a ram shaft seal cavity in an outer surface of the blowout preventer body and inserting a ram shaft seal into the ram shaft seal cavity, the ram shaft seal engaging the ram shaft as it moves relative to the blowout preventer body. 
     According to another aspect, there is provided a blowout preventer formed by the method described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
         FIG. 1  is a top plan view of a blowout preventer. 
         FIG. 2  is a side elevation view of a blowout preventer. 
         FIG. 3  is an end elevation view of a blowout preventer. 
         FIG. 4  is a top plan view in section of the blowout preventer in an open position. 
         FIG. 5  is a side elevation view in partial section of the blowout preventer in an open position. 
         FIG. 6  is a top plan view in section of the blowout preventer in a partially closed position. 
         FIG. 7  is a side elevation view in partial section of the blowout preventer in a partially closed position. 
         FIG. 8  is a top plan view in section of the blowout preventer in a closed position. 
         FIG. 9  is a side elevation view in partial section of the blowout preventer in a closed position. 
         FIG. 10  is a top plan view in section of the blowout preventer with the pressure plate and ram shafts removed. 
         FIG. 11  is a detailed top plan view of a ram shaft seal. 
         FIG. 12  is a detailed end elevation view of a ram shaft seal. 
         FIG. 13  is a side elevation view in partial section of the blowout preventer with the pressure plate and ram shafts removed. 
         FIG. 14  is a detailed top plan view in section of an interior cavity of the blowout preventer. 
         FIG. 15  is a detailed side elevation view in section of an interior cavity of the blowout preventer. 
         FIG. 16  is a is a detailed top plan view in section of an interior cavity of the blowout preventer. 
         FIG. 17  is a detailed side elevation view in section of an interior cavity of the blowout preventer. 
         FIG. 18  is a side elevation view in section of an interior cavity of the blowout preventer with ram shaft seals installed. 
         FIG. 19  is a detailed side elevation view of a ram block seal insert. 
         FIG. 20  is a detailed top plan view in section of an interior cavity of the blowout preventer with ram block guides. 
     
    
    
     DETAILED DESCRIPTION 
     In the drawings, the blowout preventer is indicated by reference numeral  10 . Referring to  FIG. 1 through 3 , the blowout preventer  10  has a body  12 , ram shafts  14  (shown in  FIG. 4 ) controlled by actuators  15 , a tubular bore  16  for receiving a tubular member (not shown), and a removable pressure plate  18  that covers an access opening into the inner cavity of the body  12 . While there are four ram shafts  14  in the double-gate configuration depicted, single, triple, etc gate designs may also be used. Referring to  FIG. 4 , the ram shafts  14  control ram blocks  20 , which close about tubular members that pass through the tubular bore  16 . 
     The approach described below is to allow the material of the body  12  to perform its function as a pressure vessel with its relatively soft material, as specifications dictate, and provide other components specifically designed for abrasive resistance to provide the running surfaces for the internal moving parts. In other words, accommodate the moving parts without allowing them to contact the soft pressure-containing body material and eliminate abrasive wear damage to the body. 
     As depicted, the body  12  has been formed to accommodate removable and replaceable inserts. The inserts are specifically designed to protect the body  12  and resist abrasive wear during all of the necessary operating functions of a blowout preventer. As described below, inserts may be provided as the running surface for the ram blocks, the seal surface for the rubber parts, inserted into the ram blocks, a guide means for the ram block movement and finally, to contain the ram blocks when subjected to pressure, such as during closing. Each insert will now be discussed in detail as they relate to each gate. 
     Skid Plate  22   
     Referring to  FIGS. 4 and 5 , a skid plate  22  is provided to protect the body  12  from the bottom side  24  of the ram blocks  20 . It has an opening that matches the blowout preventer opening  16  through which pipe moves during well operations. The plate  22  may be configured many ways, such as smaller individual parts, but the preferred embodiment uses a single plate to accommodate both ram blocks closing from opposite sides of the opening  16 , as shown in  FIGS. 6 and 7 . This ensures that the ram blocks  20  exert equal and opposite forces on the skid plate  22  from either side as they close and open. 
     Referring to  FIG. 10 , the surface  26  of the body  12  that contacts the under side of the skid plate  22  is flat with flow channels  28  formed, such as by milling, into the surface  26  to allow fluid to pass under the skid plate  22  to the cavities behind the ram blocks  20  as they close and open. As shown, the skid plate  22  is preferably formed, such as by machining, to match these flow channels  28  to ensure there is no blockage. This configuration allows the plate  22  to be manufactured in a manner that allows easy removal and insertion of the ram blocks  20  through the access openings behind the pressure plate  18 . Referring to  FIG. 16  and  FIG. 17 , the top surface  30  of the plate is preferably recessed such as by milling toward either side to allow extra clearance for the ram blocks  20  to be removed and installed when the pressure plate  18  is removed, for example as shown in  FIG. 14  and  FIG. 15 . When the ram blocks are closed, they move up the ramp  31  formed by milling the top surface  30  to the engage surface  32  toward the middle of plate  22 . The area of the engage surface  32  is larger than conventional methods and is preferably continuous in nature. 
     Conventional methods generally rely on three integrally formed strips of body material, called skids, to provide the correct height for the blocks due to the flow channels in the body. These skids often wear, and wear into the blocks, due to the sliding operation of the ram blocks in the presence of abrasive well bore fluids. In addition, the ram block material is of a similar, if not the same, material as the skids. When two like steels rub against each other, they may pick-up or gaul causing damage and further wear. Many processes have been tried to provide a harder running surface for the skids, but because they are part of the pressure vessel, i.e. the body  12 , they must conform to the appropriate specifications to prevent cracking. 
     In this design, the skid plate  22  is not part of the pressure containing body. As it is a separate component, it may therefore be hardened to resist abrasive wear without affecting the pressure containing material requirements of the body  12  as any cracks in the skid plate will not propagate through to body  12 . 
     Seal Insert  34   
     Referring to  FIG. 18 through 20 , shows the seal insert  34  in detail. This insert  34  provides the surface that the rubber contained in the ram blocks  20  seals against to contain well bore pressure when they are in the closed position, as shown in  FIGS. 9 and 10 . While replaceable seats have been in use in the past, the attachment mechanism had flaws that produced many difficulties in use and replacement. Well fluids cause severe corrosion of the attachment parts and they are often difficult to remove. The present design provides a way to install and protect the attachment mechanism until it is desired to remove the seal insert  34 . 
     Referring to  FIG. 11 , the body  12  is machined to receive the seal insert  34  by using a specially designed thread. The female thread  38  in the body  12  has a large root radius in the female portion. The seal insert  34  has a square profile thread  40  on the male portion. When screwed together, there remains a space  44  between the major diameter of the female thread  38  in the body  12  and the major diameter of the male thread  42  on the seal insert  34 . In the depicted embodiment, intersecting the male thread  42  from the inside of the seal ring are four threaded plugholes  43  and plugs  46 . The seal insert  34  also has an “o”-ring seal  48  on the topside to seal against the body  12 . One advantage of using a thread as a means of attachment is that, when tightened, there is no extrusion gap for the “o”-ring  48 . The seal ring  34  is rotated until it meets the body  12 . 
     The threaded plugholes  43  serve two purposes. Firstly, they allow a way to attach an installation jig (not shown) for installation and removal of the seal ring  34 . Secondly, they intersect the seal ring thread  38  to communicate with the space between the mating threads  38  and  40 . The purpose of this feature is to inject a sealing/adhesive compound to fill the spaces between the seal ring  34  and the body  12 . While a preferred embodiment has four threaded plugholes  44  to aid these processes, any number may be used. Once the seal ring  34  is installed and filled with a compound, such as a chemically inert two-part epoxy, plugs  46  are installed and covered with the compound. The installation is becomes permanent until such time as it is required to be removed. This process will be discussed further. 
     The advantages of this feature and its design are several. The ram blocks  20  and sealing rubbers installed in the ram blocks never contact the soft body material to cause wear or deterioration. The seal insert  34  is not a part of the pressure containing body  12  and therefore crack propagation from the seal ring  34  to the body  12  is eliminated. The seal insert  34  may then be hardened to provide greater wear resistance to abrasive fluids. In addition, when in use and subjected to pressure, the seal ring  34  experiences compressive loading which further reduces the possibility of cracking. 
     Ram Block Guides  50   
     Referring to  FIG. 20 , there are four ram block wear pads  50  installed on the internal sides of each gate  17  to prevent the ram blocks  20 , shown in  FIG. 4 , from contacting the body  12 . Because they are not part of the pressure containing body  12 , they may be hardened to provide greater wear resistance to abrasive fluids. Ram block guides  50  are inserted into small cavities  51  in body  12 . 
     Ram Shaft Seal Inserts  52   
     Another common area of damage in a blowout preventer body  12  is in the area used to contain ram shaft seals  54 . In the present design, referring to  FIG. 18 through 20 , the seals  54  are contained in a removable, threaded insert  52 . The insert  52  may be made of a material that resists chemical attack, such as stainless steel. In this arrangement, the insert  52  is threaded into the body  12  and sealed on both sides of the thread  54  to ensure the area is kept clean and corrosion free. Additionally, sealing compounds may be used on the shouldering area  56  to further prevent exposure to corrosive chemical well fluids. The ram shaft seal insert  52  is installed and removed through the use of an internal hex  58 , as shown in  FIG. 12 . Referring to  FIGS. 18 and 20 , the insert  52  is designed to protrude from the body  12  and provide a close fit sealing guide means for accurate alignment of the operator. This feature ensures the ram shaft is positioned properly so that it does not contact the inside portion of the ram shaft seal insert  52  and cause wear from usage. 
     Sealing/Adhesive Compounds 
     All of the inserted wear parts of this design contact the body  12  when installed, and are all threaded or bolted in place for installation. This means, however that steel on steel contact provides surfaces that may be wetted by corrosive fluids, such as salt water, and cause pitting corrosion of the mating steel surfaces. To eliminate this type of damage and further ensure the inserts remain installed properly without moving, a sealing/adhesive compound is preferably used to secure contacted surfaces. The sealing/adhesive compound fills the spaces between the mating steels and denies corrosive gases and liquids access to these critical surfaces. With both abrasion and chemical deterioration eliminated, the body  12  can be repaired by replacing worn parts instead of using welding processes. 
     Although there are many adhesives, the compound is preferably a two part chemical adhesive that allows ample time to install and secure each piece and has excellent chemical resistance to typical well bore fluids, including gases such hydrogen sulphide and condensates from formation fracturing fluids. It has an operating range from −60 to 300 deg. F, with intermittent use up to 350 deg. F. This range is sufficient to accommodate most well conditions. 
     Another feature of the sealing/adhesive compound is its ability to be removed when desired. The process requires a thermal cycle up to 600 deg. F. This temperature changes the adhesive to a carbon powder that may be easily removed with compressed air. This heat cycle is also advantageous to remove undesirable gases and hydrocarbons from all well bore exposed steel surfaces without affecting the steel parts. 
     Corrosion Protection 
     The sealing/adhesive compound protects mating surfaces from corrosive chemicals by filling the gaps between the mating surfaces. These gaps may only be as large as 0.015″ thick to be 100% effective. To protect other exposed surfaces that do not have mating steel parts, a second compound is used as a sealant. It is also a two-part compound, however does not require a mating steel surface to be effective. Once the compound is mixed, it may be applied to clean bare steel. Once it has cured in place, it provides a protective barrier between the steel body and harsh well bore chemicals. It is also removed with the same thermal cycle as the sealing/adhesive compound. 
     The blowout preventer body described above is intended to provide more wear resistant contact points between moving parts in an abrasive environment, such as the ram blocks  20  and the blowout preventer body  12 , as they move from the open position shown in  FIG. 4  to the closed position shown in  FIG. 8 . These contact points are generally the point at which most wear occurs. By including all wear inserts described above, the blowout preventer body  12  can be completely isolated from contact with any moving components. By providing more wear resistant surfaces, the time between servicing is increased, and the servicing requirements are reduces, as it is a relatively simple matter to remove and replace the wear inserts compared to the amount of work required to service a pressure vessel. The wear inserts are generally replaced at a predetermined service event, which may be triggered by visual inspection, a detector, a failure, or a certain amount of time passing. 
     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
     The following claims are to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the described embodiments can be configured without departing from the scope of the claims. The illustrated embodiments have been set forth only as examples and should not be taken as limiting the invention. It is to be understood that, within the scope of the following claims, the invention may be practiced other than as specifically illustrated and described.