Patent Publication Number: US-2023138338-A1

Title: Fluid end with selectively coated surfaces

Description:
TECHNICAL FIELD 
     The present disclosure relates to a fluid end for a fluid system. Specifically, the present disclosure relates to a coating that is applied to selected portions of a fluid end of a hydraulic fracturing system (or other well-service system) to improve the durability of the fluid end, as well as reduce required maintenance during the usable life of the fluid end. 
     BACKGROUND 
     Various types of fluid conduit are in widespread use in a variety of industries. For example, fluid conduit may be used in a variety of applications in the petroleum industry. One such application includes hydraulic fracturing, which is a well stimulation technique that typically involves pumping hydraulic fracturing fluid into a wellbore at a rate and pressure sufficient to form factures in a rock formation surrounding the wellbore. This well stimulation technique often enhances the natural fracturing of a rock formation in order to increase the permeability of the rock formation, thereby improving recovery of water, oil, natural gas, and/or other fluids. In order to fracture such rock formations, the hydraulic fracturing fluid is injected into the wellbore at pressures and rates sufficient to exceed a fracture gradient of the target formation. In some conventional arrangements, a series of pumps is used to pressurize the hydraulic fracturing fluid within a fluid end which then distributes the pressurized hydraulic fracturing fluid to a fracturing manifold. The fracturing manifold receives the pressurized hydraulic fracturing fluid from the pumps and delivers the hydraulic fracturing fluid to an injection point (e.g., a frac tree) at the necessary pump rate. 
     In these types of applications, the hydraulic fracturing fluid (in the form of a slurry), having hard proppant particles therein, is pressurized to high pressures, such as 15,000 pounds per square inch (psi). As slurry is compressed in the fluid end, the fluid end is subject to high levels of abrasion due to the highly pressurized slurry and is subject to high pressure differentials as the hydraulic fracturing fluid is compressed in the fluid end. Excessive wear of the fluid can lead to reduced lifetimes of the conduit. Increased frequency of maintenance and/or reduced lifetime of the fluid end can result in reduced levels of uptime of processes reliant on the fluid end. 
     An example fluid end is described in U.S. Patent Publication Application No. 2020/0182240A1 (hereinafter referred to as the &#39;240 reference). In particular, the &#39;240 reference describes a flangeless fluid end. The &#39;240 reference describes various configurations that are designed to transfer wear from a body of a fluid end to removeable components of the fluid end. For examples, the &#39;240 reference describes a seal that is located within a groove in the body of the fluid end and contacts a discharge plug. The &#39;240 reference explains that erosion wear is transferred from the body of the fluid end to the discharge plug in such a configuration that the discharge plug can be replaced once erosion of the discharge plug occurs. The &#39;240 reference also notes that transferring erosion wear to replaceable components can reduce the cost associated with repairing or replacing the body of the fluid end. 
     However, while the &#39;240 reference describes transferring erosion wear to various components of the fluid end that can be easily replaced, the system described in the &#39;240 reference does not describe reducing, slowing, or otherwise inhibiting wear that is experienced by various components within the fluid end. As a result, the &#39;240 reference could be subject to increased maintenance due to the need to replace parts that experience wear that has been transferred by the configuration described in the &#39;240 reference. Such increased maintenance could result in increased down time of the fluid end and/or increased costs associated with maintenance and replacement parts. 
     Example embodiments of the present disclosure are directed toward overcoming the deficiencies described above. 
     SUMMARY 
     An example fluid end includes a block, a suction bore formed in the block and having a suction valve disposed within the suction bore, and a discharge bore formed in the block and having a discharge valve disposed within the discharge bore. The fluid end also includes a plunger bore formed in the block and having a plunger disposed therein, the plunger moveable within the plunger bore in a first direction and a second direction opposite the first direction such that the plunger directs fluid through the suction valve when the plunger moves in the first direction and directs fluid through the discharge valve when the plunger moves in the second direction. The fluid end further includes a seal pack disposed within the plunger bore and between the plunger and the block, thereby forming a fluid seal between the plunger and the block, the seal pack configured to maintain sealing contact with the plunger as the plunger moves in the first direction or the second direction and a coating disposed on a surface of the block within the plunger bore between the seal pack and the block. 
     An example fluid end includes a block, a suction bore formed in the block on a first axis, a discharge bore formed in the block on the first axis, and a plunger bore formed in the block on a second axis that is substantially perpendicular to the first axis. The fluid end also includes a pump chamber formed at least partially between the suction bore, the discharge bore, and the plunger bore, and a coating applied to the block and applied within at least a portion of the suction bore, at least a portion of the discharge bore, and at least a portion of the plunger bore. 
     In a further example, an example fluid system includes a fluid block, and a plunger bore formed in the fluid block and having a plunger disposed at least partially within the plunger bore, the plunger being moveable in a first direction and a second direction opposite the first direction. The fluid system further includes one or more seals disposed between the fluid block and the plunger, the one or more seals configured to maintain sealing contact with the plunger as the plunger moves in the first direction or the second direction, and a coating applied to the fluid block between the one or more seals and the fluid block. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a partial schematic view of an example fluid system having a fluid end in accordance with an example of the present disclosure. 
         FIG.  2    is a cross-sectional view of an example fluid end in accordance with an example of the present disclosure. 
         FIG.  3    is a cross-sectional view of an example fluid end block in accordance with an example of the present disclosure. 
         FIG.  4    is a flowchart illustrating a method of selectively coating portions of a fluid end in accordance with an example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    depicts an example fluid system  100 . The fluid system  100  shown in  FIG.  1    is part of a well service, workover, or well stimulation system for an oil and gas well. For example, the fluid system  100  is implemented in a hydraulic fracturing system, which is a well stimulation technique that involves pumping hydraulic fracturing fluid into a wellbore at a rate and pressure sufficient to form fractures in a rock formation surrounding the wellbore. In some examples, the fluid system  100  shown in  FIG.  1    forms a portion of a hydraulic fracturing system or other well service system and may include additional and/or alternative components than the components shown and described in  FIG.  1   . 
     In some examples, the fluid system  100  includes at least one motor  102  coupled to a pump  104 . The motor  102  is coupled to the pump  104  and is configured to drive operation of the pump  104 . In some examples, the motor  102  may be a diesel engine or other type of internal combustion engine. Alternatively, the motor  102  may be an electric motor. In either example, the motor  102  may be directly or indirectly coupled to the pump  104  and may be configured to drive the pump  104 . 
     In some examples, the pump  104  may be a hydraulic fracturing pump (or other type of well service or workover pump). The pump  104  may include various types of high-volume hydraulic fracturing pumps such as triplex pumps, quintuplex pumps, or other types of hydraulic fracturing pumps. Additionally, and/or alternatively, the pump  104  includes other types of reciprocating positive-displacement pumps or gear pumps. A number of pumps implemented in the fluid system  100  and designs of the pump  104  (or pumps) may vary depending on the fracture gradient of the rock formation that will be hydraulically fractured, the number of pumps  104  used in a fluid system  100 , the flow rate necessary to complete the hydraulic fracture, the pressure necessary to complete the hydraulic fracture, etc. The fluid system  100  includes any number of pumps  104  in order to pump hydraulic fracturing fluid at a predetermined rate and pressure. The exact configuration of the fluid system  100  varies from site to site. 
     The pump  104  includes at least one plunger  106  that is at least partially disposed within a fluid end  108 . In some examples, the pump  104  includes multiple plungers  106  disposed within the fluid end  108 . When the pump  104  is operating, the pump  104  drives the plunger  106  in reciprocating motion. For example, the pump  104  moves the plunger  106 , at least partially within the fluid end  108 , in a first direction  110  and a second direction  112 . In some examples, the pump  104  may be configured to move the plunger  106  in reciprocal directions in order to draw fluid into the fluid end  108 , compress the fluid within the fluid end  108 , and pump the fluid out of the fluid end  108 . For example, when the pump  104  moves the plunger  106  in the first direction  110 , the plunger  106  draws fluid through a valve (shown in  FIG.  2   ) into the fluid end  108  from a fluid source  114 . The fluid source  114  includes a fluid manifold configured to distribute hydraulic fracturing fluid to one or more fluid ends and corresponding pumps that are implemented in a hydraulic fracturing system. Additionally or alternatively, the fluid source  114  include one or more water tanks, hydration units, liquid additive systems, etc. 
     Furthermore, when the pump  104  moves the plunger  106  in the second direction  112 , the plunger  106  compresses the fluid in the fluid end  108  until the fluid reaches a predetermined pressure. Once the fluid is compressed to the predetermined pressure, a valve (shown in  FIG.  2   ) within the fluid end opens and allows the fluid to move from the fluid end  108  to a fluid manifold  116 . In some examples, the fluid manifold  116  receives pressurized fluid from one or more fluid ends and directs the fluid to a wellhead  118  where the fluid is injected into a wellbore. 
     In some examples, the fluid end  108  includes a block  120  having one or more bores (or fluid passages) formed in the block  120  of the fluid end  108 . The block  120  may be formed from stainless steel, carbon steel, or other material. In some examples, the fluid end  108  includes a suction bore  122  formed in the block  120 . The suction bore  122  provides a fluid passageway for fluid to enter the fluid end  108  when the plunger  106  moves in the first direction  110 . The suction bore  122  includes a suction valve (shown and described with respect to  FIG.  2   ) disposed within the suction bore  122 . The suction valve is configured to control flow of fluid into the fluid end  108 . For example, when the plunger  106  moves in the first direction  110 , the movement of the plunger  106  causes the suction valve to open, thereby drawing fluid into the fluid end  108 . Conversely, when the plunger  106  moves in the second direction  112 , the suction valve remains closed, allowing the plunger  106  to compress fluid within the fluid end  108 . 
     The fluid end  108  also includes a discharge bore  124  formed in the block  120 . The discharge bore  124  provides a fluid passageway for fluid to be discharged from the fluid end  108  to the fluid manifold  116  (or other component). The discharge bore  124  includes a discharge valve (shown and described with respect to  FIG.  2   ) disposed within the discharge bore  124 . The discharge valve is configured to control fluid flow from the fluid end  108 . For example, the discharge valve remains closed until the fluid has been compressed to a predetermined pressure as the plunger  106  compresses the fluid by moving in the second direction  112 . Once the fluid is compressed to the predetermined pressure, the pressurized fluid causes the discharge valve to open, allowing the fluid to be discharged from the fluid end  108 . 
     The fluid end  108  further includes a plunger bore  126  formed in the block  120  of the fluid end  108 . The plunger bore  126  is sized to receive the plunger  106  of the pump  104  at least partially therein. As mentioned previously, the plunger  106  is moveable in the first direction  110  and the second direction  112  within the plunger bore  126  to draw fluid into the fluid end  108  via the suction bore  122 , compress the fluid, and discharge the fluid from the fluid end  108  via the discharge bore  124 . The fluid end  108  further includes a suction cover bore  128  formed in the block  120  of the fluid end  108 . The suction cover bore  128  remains sealed during operation of the pump  104 . However, the suction cover bore  128  provides access to the plunger  106  or portions of the fluid end  108  for maintenance or other reasons, while the pump  104  is not operating. 
     The fluid end  108  also includes a pump chamber  130  disposed between the suction bore  122  and the discharge bore  124 . The pump chamber  130  is a chamber formed within the fluid end  108  that is formed at least in part by a convergence of the suction bore  122 , the discharge bore  124 , the plunger bore  126 , and the suction cover bore  128 . In some examples, the plunger  106  compresses the fluid in the pump chamber  130  to a predetermined pressure, which may cause the discharge valve to open, allowing the fluid to exit the pump chamber  130  via the discharge valve. 
     The fluid end  108  further includes one or more sealing surfaces  132  (e.g., surfaces  132 ( 1 )- 132 ( 5 ) shown in  FIG.  3   ). The sealing surfaces  132  are surfaces of the block  120  (e.g., internal surfaces thereof) where one or more seals (shown in  FIG.  2   ) are disposed in contact with the block  120 . In some examples, the one or more seals are disposed (e.g., radially and/or axially) between one or more components of the fluid end  108  and the block  120  (e.g., disposed between one or more internal components of the fluid end  108  and corresponding internal surfaces of the block  120 ) of the fluid end  108 . Sealing surfaces  132  of fluid ends  108  are often subject to high pressures and abrasive fluids. In some examples, fluids may flow (e.g., in an axial direction) between the seals and the block  120  due to the high-pressure environment of the fluid end  108 . As such, the sealing surfaces  132  of the block  120  experience abrasive forces during operation of the pump  104  because of fluid that flows between a seal and a corresponding sealing surface  132  of the block  120 . Such abrasion could result in washboard failure of the sealing surfaces  132 , or other types of failure. 
     In some examples, a coating  134  may be applied to one or more of the sealing surfaces  132 . In some examples, the coating  134  may be applied to each of the sealing surfaces  132  of the fluid end  108 . The coating  134  may include a hardness that is greater than the hardness of the material used for the block  120  of the fluid end  108  and may, therefore, resist abrasive forces and/or resist corrosion which may result in a longer usable life, when compared to fluid ends without coating applied to sealing surfaces. In some examples, other surfaces of the block  120  of the fluid end  108  are substantially free of the coating  134 . As used herein, a surface that is “substantially free” of coating is a surface to which a coating is not directly or intentionally directly applied, but may still be subjected to some hardening. For example, in a spray-coating hardening process, some overspray may occur on surfaces adjacent to or otherwise proximate surfaces intended to be hardened. However, in some examples, all interior surfaces (e.g., each bore and the pump chamber  130 ) of the fluid end  108  may be coated in addition to, or instead of, the surfaces described previously. 
     In some examples, the coating  134  may include a metallic alloy (e.g., formed from a powdered metal alloy). The powdered metal alloy may include at least one of tungsten carbide, cobalt, chromium, or combinations thereof and may include any combination (percentage) of such materials. In some examples, the coating  134  may be a thermal spray coating that is applied using a high velocity air fuel (HVAF) thermal spray process or a high velocity oxygen fuel (HVOF) thermal spray process. Furthermore, the coating  134  may instead be applied via a plating, diffusion, a spray and fuse process, or physical vapor deposition (PVD) process, among other processes. Other techniques, including, but not limited to, plasma twin wire arc, may also be used to apply the coating  134  to the desired surfaces. The process may vary based on the type of material used for the block  120  of the fluid end and/or the type of material used for the coating  134 . Any technique that allows for a robust mechanical bond of the coating  134  to the desired surfaces may be used. By including the coating  134  on the sealing surfaces  132 , the coating  134  may reduce wear on the block  120 , while increasing the resistance of the sealing surfaces  132  to erosive forces caused by pumping a fluid (e.g., hydraulic fracturing fluid or other abrasive slurry) through the fluid end  108 . 
     In some examples, the coating  134  may include any suitable thickness. By way of example, and not limitation, the coating  134  may include a thickness between approximately 0.00001 inches and approximately 0.1 inches. In some examples, the coating  134  may have a thickness between approximately 0.0001 inches and approximately 0.01 inches. Additionally, and/or alternatively, the coating  134  may have a thickness between approximately 0.001 inches and approximately 0.009 inches. In further examples, the coating  134  may include a thickness greater than or less than the example ranges described previously. Furthermore, the coating  134  may be substantially uniform in thickness. Moreover, the coating  134  may have a suitable surface finish. For instance, the coating  134  on the sealing surfaces  132  may have a desirable finish (e.g., a smooth and/or homogeneous surface finish to ensure that the coating  134  does not include cracks, rough patches, or other inconsistencies that may be particularly disposed to erosion). In examples, a thermal spray technique such as HVAF and/or HVOF may result in a desired surface finish without requiring subsequent finishing, polishing, or the like. Furthermore, the coating  134  may be applied to additional or fewer surfaces of the fluid end  108  than described herein. 
     In some examples, by selectively applying the coating  134  to one or more of sealing surfaces  132 , the useful life of the block  120  of the fluid end  108  may be significantly increased and/or down time due to maintenance may be decreased. Furthermore, by applying the coating  134  to the sealing surfaces  132  while excluding other surfaces, cost associated with the coating  134  may be minimized, while potentially increasing the useful life of the block  120 . Moreover, the coating  134  may be reapplied to the sealing surfaces  132 , thereby further increasing a usable life of the block  120  of the fluid end  108 . 
       FIG.  2    depicts a cross-sectional view of the fluid end  108  and components thereof. The fluid end  108  shown in  FIG.  2    may be substantially similar to and/or the same as the fluid end  108  shown and described in  FIG.  1   . In some examples, the fluid end  108  includes the block  120  having one or more bores formed in the block  120  of the fluid end  108 . For example, the fluid end  108  includes the suction bore  122  formed in the block  120  along a first axis  200 . In some examples, the suction bore  122  may provide a fluid passageway extending from an exterior surface of the block  120  to the pump chamber  130 . The suction bore  122  allows fluid to enter the fluid end  108  when the plunger  106  moves in a first direction  110 , drawing fluid into the pump chamber  130  of the fluid end  108 . The suction bore  122  includes a suction valve  202  disposed within the suction bore  122  that is configured to control fluid flow through the suction bore  122 . The suction bore  122  also includes a suction valve seat  204  disposed within the suction bore  122 . The suction valve seat  204  provides a surface against which the suction valve  202  rests when the suction valve  202  is closed. That is, when the plunger  106  moves in the first direction  110 , the plunger  106  creates sufficient suction within the pump chamber  130  to unseat (e.g., lift) the suction valve  202  to open the suction valve  202  thereby drawing fluid into the pump chamber  130 . 
     In some examples, the suction valve seat  204  may include an annular seal  206  (e.g., seal, O-ring, gasket, etc.) disposed in contact with the suction valve seat  204  and the suction bore  122  of the block  120 . The seal  206  is configured to form a fluid seal between the suction valve seat  204  and the block  120 . However, as described previously, fluid may flow between the seal  206  and the block  120  due, at least in part, to the cyclic high-pressure environment experienced within the fluid end  108  during operation of the pump  104 . As such, the coating  134  (shown and described in  FIG.  1    and further shown in  FIG.  3   ) may be applied to the suction bore  122  between the seal  206  and the block  120  to prevent, reduce, slow, and/or otherwise inhibit wear that may be caused by fluid that flows between the seal  206  and the suction bore  122  of the block  120 . 
     The fluid end  108  further includes a discharge bore  124  formed in the block  120  along the first axis  200 . The discharge bore  124  forms a fluid passageway extending between an exterior surface of the block  120  and the pump chamber  130 . The discharge bore  124  allows fluid to be discharged from the fluid end  108  to a fluid manifold  116  via an outlet  208  of the fluid end  108 . The discharge bore  124  includes a discharge valve  210  disposed within the discharge bore  124  that is configured to control fluid flow through the discharge bore  124 . The discharge bore  124  also includes a discharge valve seat  212  disposed within the discharge bore  124 . In some examples, the discharge valve seat  212  provides a surface against which the discharge valve  210  rests when the discharge valve  210  is closed. That is, when the plunger  106  moves in the second direction  112 , the plunger  106  compresses fluid within the pump chamber  130  until a pressure within the pump chamber  130  reaches and/or exceeds a threshold pressure, thereby forcing the discharge valve  210  to unseat (e.g., lift) opening the discharge valve  210 . The plunger  106  directs the fluid out of the outlet  208  of the fluid end  108  and into a fluid manifold or other component. 
     In some examples, the discharge valve seat  212  includes an annular seal  214  (e.g., seal, O-ring, gasket, etc.) disposed in contact with the discharge valve seat  212  and the discharge bore  124  of the block  120 . The seal  214  is configured to form a fluid seal between the discharge valve seat  212  and the block  120 . However, as described previously, fluid may, at times, flow between the seal  214  and the discharge bore  124  due, at least in part, to the cyclic high-pressure environment experienced within the fluid end  108  during operation of the pump  104 . As such, the coating  134  (shown and described in  FIG.  1    and further shown in  FIG.  3   ) may be applied to the discharge bore  124  between the seal  214  and the block  120  to prevent, reduce, slow, and/or otherwise inhibit wear that may be caused by fluid that flows between the seal  214  and the discharge bore  124  of the block  120 . 
     In some examples, the discharge bore  124  further includes a discharge cover  216  and discharge cover retainer  218  that are disposed at least partially within the discharge bore  124 . The discharge cover  216  causes fluid that flows through the discharge valve  210  to flow out of the fluid end  108  via the outlet  208 . Furthermore, a spring  219  (or other type of biasing member) is disposed between the discharge valve  210  and the discharge cover  216 . The spring  219  is configured to maintain the discharge valve  210  in a closed position (pictured in  FIG.  2   ) until fluid within the pump chamber  130  reaches and/or exceeds a threshold pressure. That is, the spring  219  exerts a force on the discharge valve  210  to maintain the discharge valve  210  in the closed position. Once the fluid is compressed to the threshold pressure, the fluid overcomes the force exerted on the discharge valve  210  by the spring  219 . The discharge cover retainer  218  is coupled to the block  120  of the fluid end  108  via threading or other coupling means and is configured to maintain a position of the discharge cover  216  within the discharge bore  124 . 
     In some examples, the discharge cover  216  includes an annular discharge cover seal  220  (e.g., seal, O-ring, gasket, etc.) disposed between the discharge cover  216  and the block  120  of the fluid end  108 . The discharge cover seal  220  is configured to form a fluid seal between the discharge cover  216  and the block  120 . However, as described previously, fluid may, at times, flow between the discharge cover seal  220  and the block  120  due, at least in part, to the cyclic high-pressure environment experienced within the fluid end  108  during operation of the pump  104 . As such, the coating  134  (shown and described in  FIG.  1    and further shown in  FIG.  3   ) may be applied to the discharge bore  124  between the discharge cover seal  220  and the block  120  to prevent, reduce, slow, and/or otherwise inhibit wear that may be caused by fluid that flows between the discharge cover seal  220  and the discharge bore  124  of the block  120 . 
     The fluid end  108  further includes the plunger bore  126  formed in the block  120  along a second axis  221  that is substantially perpendicular to the first axis  200 . The plunger bore  126  is sized to receive a plunger  106  of the pump  104  at least partially within the plunger bore  126 . Furthermore, the plunger bore  126  is sized to allow the plunger  106  to move in the first direction  110  and the second direction  112  at least partially within the plunger bore  126  to draw fluid into the fluid end  108  via the suction bore  122 , compress the fluid in the pump chamber  130 , and discharge the fluid from the fluid end  108  via the discharge bore  124 . 
     In some examples, the fluid end  108  includes a seal pack  222  that is comprised of one or more seals that maintain sealing contact with the plunger  106 , even as the plunger  106  moves in the first direction  110  and the second direction  112 . As such, the seal pack  222  creates a fluid seal between the plunger  106  and the plunger bore  126 . However, as described previously, fluid may, at times, flow between the seal pack  222  and the plunger bore  126  due, at least in part, to the cyclic high-pressure environment experienced within the fluid end  108  during operation of the pump  104 . As such, the coating  134  (shown and described in  FIG.  1    and further shown in  FIG.  3   ) may be applied to the plunger bore  126  between the seal pack  222  and the block  120  to prevent, reduce, slow, and/or otherwise inhibit wear that may be caused by fluid that flows between the seal pack  222  and the plunger bore  126  of the block  120 . 
     The fluid end  108  includes a suction cover bore  128  formed in the block  120  of the fluid end  108  along the second axis  221 . In some examples, the suction cover bore  128  includes a suction cover  224  and a suction cover retainer  226  that are disposed at least partially within the suction cover bore  128 . The fluid end  108  includes a spring  228  (or other biasing member) disposed between the suction valve  202  and a suction valve retainer  230 . The suction valve retainer  230  extends between the spring  228  and the suction cover  224  and is configured to maintain a position of the spring  228  such that the spring  228  exerts a force on the suction valve  202  to maintain the suction valve  202  in a closed position. In some examples, when the plunger  106  moves in the first direction  110 , the plunger  106  creates suction within the pump chamber  130  that overcomes the force exerted on the suction valve  202  by the spring  228 , thereby opening the suction valve  202 . 
     In some examples, the suction cover  224  includes an annular suction cover seal  232  (e.g., seal, O-ring, gasket, etc.) disposed between the suction cover  224  and the block  120  of the fluid end  108 . The suction cover seal  232  is configured to form a fluid seal between the suction cover  224  and the block  120 . However, as described previously, fluid may, at times, flow between the suction cover seal  232  and the block  120  due, at least in part, to the cyclic high-pressure environment experienced within the fluid end  108  during operation of the pump  104 . As such, the coating  134  (shown and described in  FIG.  1    and further shown in  FIG.  3   ) may be applied to the suction cover bore  128  between the suction cover seal  232  and the block  120  to prevent, reduce, slow, and/or otherwise inhibit wear that may be caused by fluid that flows between the suction cover seal  232  and the suction cover bore  128  of the block  120 . 
     In some examples, by selectively applying the coating  134  to one or more of sealing surfaces  132  between the respective seals and the block  120 , the useful life of the block  120  of the fluid end  108  may be significantly increased and/or down time due to maintenance may be decreased. Furthermore, the coating  134  may be reapplied to the sealing surfaces  132 , thereby further increasing a usable life of the block  120  of the fluid end  108 . 
       FIG.  3    depicts a cross-sectional view of the block  120  of the fluid end  108 . As shown in  FIG.  3   , many of the components shown and described in  FIG.  2    have been removed to depict the coating  134  (represented by the stipple shading in  FIG.  3   ) and the various surfaces and/or portions of the block  120  to which the coating  134  may be applied. As described previously, the coating  134  may be applied to various sealing surfaces  132  where one or more seals are disposed in contact with the block  120  of the fluid end  108 . In some examples, the coating  134  may be applied to each of the sealing surfaces  132  of the fluid end  108 . However, the coating  134  may be applied to fewer than all of the sealing surfaces  132  of the fluid end  108 , in some examples. Furthermore, other surfaces of the block  120  of the fluid end  108  may be substantially free of the coating  134 . However, in some examples, other surfaces of the block  120  may be coated with the coating  134 . In some examples, the coating  134  may be applied to the sealing surfaces  132  of the block  120  such that the coating  134  extends past either axial end of a seal or seal pack so as to cover an entirety of a sealing surface  132 . In some examples, the coating  134  may extend about 5% or more, such as about 5% to about 25%, such as about 10% to about 20% beyond one or both axial ends of the corresponding seal or seal pack, when measured in relation to an axial length of the corresponding seal or seal pack. In some examples, the coating  134  may extend about 1/32 inch or more, such as about 1/32 inch to about ⅛ inch such as about 1/16 inch to about ⅛ inch beyond one or both axial ends of the corresponding seal or seal pack. 
     As described previously, the coating  134  may include a hardness that is greater than the hardness of the material used for the block  120  of the fluid end  108  and may, therefore, resist abrasive forces and/or resist corrosion which may result in a longer usable life, when compared to fluid ends without coating applied to sealing surfaces. As such, the sealing surfaces  132  of the fluid end  108  may include a longer usable life than sealing surfaces of fluid ends that do not include a hard coating that is applied to sealing surfaces. Furthermore, in some examples, as the coating  134  may wear over time, the coating  134  may be reapplied (or otherwise remanufactured) to the sealing surfaces  132  of the fluid end  108 . As such, the coating  134  may be configured to wear before the sealing surfaces  132  of the block  120  of the fluid end  108 , which may increase a usable life of a fluid end  108  and/or decrease downtime due to servicing a fluid end  108 , among other potential benefits. 
     For example, the fluid end  108  may include a first sealing surface  132 ( 1 ) that is located within the suction bore  122 . The first sealing surface  132 ( 1 ) includes a portion of the suction bore  122  where the seal  206  of the suction valve seat  204  contacts the block  120  (shown in  FIG.  2   ). In  FIG.  3   , the suction bore  122  includes an enlarged-diameter portion  122   a  and a reduced-diameter portion  122   b  extending downward therefrom (as in the figure), which direction may also be considered the upstream direction. Downstream from the enlarged-diameter portion  122   a  is a neck portion  122   c , which is reduced in diameter relative to the enlarged-diameter portion  122   a . As shown in  FIG.  3   , the first sealing surface  132 ( 1 ) may comprise at least a portion of an inner cylindrical surface of the reduced-diameter portion  122   b . As described previously, fluid may, at times, flow between the seal  206  and the block  120 , which may cause wear on the block  120  and may cause failure of the fluid end  108  due to a washboard failure (or other abrasive wear) of the block  120 . As such, the coating  134  may be applied to the first sealing surface  132 ( 1 ) such that the coating  134  is applied to the block  120  between the block  120  and the seal  206 . As shown in the example of  FIG.  3   , the coating  134  may be applied to the inner cylindrical surface of the reduced-diameter portion  122   b . In some examples, the coating  134  may be continuous in a circumferential direction about the inner cylindrical surface of the reduced-diameter portion  122   b . The coating  134  may be disposed radially outside the corresponding seal (e.g., seal  206  of the suction valve seat  204  shown in  FIG.  2   ) and radially inside the inner cylindrical surface of the reduced-diameter portion  122   b . The coating  134  may prevent and/or inhibit wear on the block  120  at the first sealing surface  132 ( 1 ) and may, therefore, extend a usable life of the fluid end  108 . 
     Furthermore, the fluid end  108  may include a second sealing surface  132 ( 2 ) that is located within the discharge bore  124 . The second sealing surface  132 ( 2 ) includes a portion of the discharge bore  124  where the seal  214  of the discharge valve seat  212  contacts the block  120  (shown in  FIG.  2   ). In  FIG.  3   , the discharge bore  124  includes an enlarged-diameter portion  124   a  and a reduced-diameter portion  124   b  extending downward therefrom (as in the figure), which direction may also be considered the upstream direction. Downstream from the enlarged-diameter portion  124   a  is a neck portion  124   c , which is reduced in diameter relative to the enlarged-diameter portion  124   a . As shown in  FIG.  3   , the second sealing surface  132 ( 2 ) may comprise at least a portion of an inner cylindrical surface of the reduced-diameter portion  124   b . In some examples, the coating  134  may be applied to the second sealing surface  132 ( 2 ) such that the coating  134  is applied to the block  120  between the block  120  and the seal  214 . As shown in the example of  FIG.  3   , the coating  134  may be applied to the inner cylindrical surface of the reduced-diameter portion  124   b . In some examples, the coating  134  may be continuous in a circumferential direction about the inner cylindrical surface of the reduced-diameter portion  124   b . The coating  134  may be disposed radially outside the corresponding seal (e.g., seal  214  of the discharge valve seat  212  shown in  FIG.  2   ) and radially inside the inner cylindrical surface of the reduced-diameter portion  124   b . The fluid end  108  may also include a third sealing surface  132 ( 3 ) that is located within the discharge bore  124 . The third sealing surface  132 ( 3 ) includes a portion of the discharge bore  124  where the discharge cover seal  220  contacts the block  120  (shown in  FIG.  2   ). As shown in  FIG.  3   , the third sealing surface  132 ( 3 ) may comprise at least a portion of an inner cylindrical surface of the neck portion  124   c . In some examples, the coating  134  may be applied to the third sealing surface  132 ( 3 ) such that the coating  134  is applied to the block  120  between the block  120  and the discharge cover seal  220 . As shown in the example of  FIG.  3   , the coating  134  may be applied to the inner cylindrical surface of the neck portion  124   c . In some examples, the coating  134  may be continuous in a circumferential direction about the inner cylindrical surface of the neck portion  124   c . The coating  134  may be disposed radially outside the corresponding seal (e.g., discharge cover seal  220  shown in  FIG.  2   ) and radially inside the inner cylindrical surface of the neck portion  124   c.    
     The fluid end  108  may further include a fourth sealing surface  132 ( 4 ) that is located within the plunger bore  126 . The fourth sealing surface  132 ( 4 ) includes a portion of the plunger bore  126  where the seal pack  222  contacts the block  120  (shown in  FIG.  2   ). In  FIG.  3   , the plunger bore  126  includes a packing bore  126   a  and a reduced-diameter portion  126   b  extending to the left therefrom (as in the figure). The packing bore  126   a  may include an enlarged-diameter portion which may be sized to receive the packing seal  222 . Further to the left (as in the figure), the reduced-diameter portion  126   b  may be continuous with (e.g., having the same inner diameter as) an inner cylindrical surface of the pump chamber  130 . As shown in  FIG.  3   , the fourth sealing surface  132 ( 4 ) may comprise at least a portion of an inner cylindrical surface of the packing bore  126   a . In some examples, the coating  134  may be applied to the fourth sealing surface  132 ( 4 ) such that the coating  134  is applied to the block  120  between the block  120  and the seal pack  222 . As shown in the example of  FIG.  3   , the coating  134  may be applied to the inner cylindrical surface of the packing bore  126   a . In some examples, the coating  134  may be continuous in a circumferential direction about the inner cylindrical surface of the packing bore  126   a . The coating  134  may be disposed radially outside the corresponding seal (e.g., seal pack  222  shown in  FIG.  2   ) and radially inside the inner cylindrical surface of the packing bore  126   a.    
     The fluid end  108  may also include a fifth sealing surface  132 ( 5 ) that is located within the suction cover bore  128 . The fifth sealing surface  132 ( 5 ) includes a portion of the suction cover bore  128  where the suction cover seal  232  contacts the block  120  (shown in  FIG.  2   ). In  FIG.  3   , the suction cover bore  128  includes an enlarged-diameter portion  128   a  and a reduced-diameter portion  128   b  extending to the right therefrom (as in the figure). As shown in  FIG.  3   , the fifth sealing surface  132 ( 5 ) may comprise at least a portion of an inner cylindrical surface of the reduced-diameter portion  128   b . In some examples, the coating may be applied to the fifth sealing surface  132 ( 5 ) such that the coating  134  is applied to the block  120  between the block  120  and the suction cover seal  232 . As shown in the example of  FIG.  3   , the coating  134  may be applied to the inner cylindrical surface of the reduced-diameter portion  128   b . In some examples, the coating  134  may be continuous in a circumferential direction about the inner cylindrical surface of the reduced-diameter portion  128   b . The coating  134  may be disposed radially outside the corresponding seal (e.g., suction cover seal  232  shown in  FIG.  2   ) and radially inside the inner cylindrical surface of the reduced-diameter portion  128   b.    
     In some examples, by selectively applying the coating  134  to one or more of sealing surfaces  132 ( 1 )- 132 ( 5 ) between the respective seals and the block  120 , the coating  134  may reduce wear on the block  120  while increasing the resistance of the sealing surfaces  132 ( 1 )- 132 ( 5 ) to erosive forces caused by pumping the fluid through the fluid end. As such, the coating  134  may extend the useful life of the block  120  of the fluid end  108  and/or down time due to maintenance may be decreased. Furthermore, the coating  134  may be reapplied to the sealing surfaces  132 ( 1 )- 132 ( 5 ), thereby further increasing a usable life of the block  120  of the fluid end  108 . 
       FIG.  4    illustrates an example method  400  of coating portions of the fluid end  108 . The fluid end  108  described herein may be better suited to resist corrosion, erosion, and/or abrasion than conventional fluid ends and may be cost effective to produce and/or to remanufacture. The method  400  shows some example steps for achieving such benefits. It is to be understood, that certain steps of the method  400  described herein may be conducted contemporaneously or sequentially. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described steps may be performed in any order and/or the described steps may be combined in parallel to implement the process. 
     Specifically, at  402 , the method  400  includes providing a block of a fluid end. In examples described herein, the block  120  includes a bare block without some and/or all of the components other than the block  120  of the fluid end  108 . 
     At  404 , the method  400  includes inserting a tool within one or more bores of the fluid end  108 . The one or more bores include one or more of the suction bore  122 , discharge bore  124 , plunger bore  126 , and/or the suction cover bore  128 . In some coating processes, a tool may be stationary while a coated part is rotated around the tool. However, due to the size and weight of a block  120  of a fluid end  108 , the tool used to coat portions of the block  120  may be rotated relative to the block  120 , while the block  120  remains stationary during a coating process. 
     At  406 , the method  400  includes applying the coating  134  to the desired surfaces. For example, the coating  134  may be applied to the sealing surfaces  132  (described previously) of the block  120 . In the examples of  FIGS.  1 - 3   , the operation  406  includes applying the coating  134  to each of the sealing surfaces (e.g., sealing surfaces  132 ( 1 )- 132 ( 5 )). However, in some examples, the coating  134  may be applied to fewer than all of the sealing surfaces  132 . Additionally, and/or alternatively, the coating  134  may be applied to additional surfaces, such as the pump chamber, other portions of the bores, or other surfaces. In some instances, the coating  134  may be a metal alloy powder applied using a thermal spray technique, such as HVAF, HVOF, or other thermal spray technique. Alternatively, the coating  134  may instead be plated to the above described surfaces. In some examples, the coating  134  may be a metal alloy powder including tungsten carbide. 
     At  408 , the method  400  optionally includes finishing the surfaces to which the coating  134  was applied. In some examples, step  408  may be omitted as the natural surface finish (e.g., surface finish after step  406 ) of the coating process at  406  may be suitable. However, in some examples, the coated sealing surfaces  132  may be finished to ensure that the sealing surfaces  132  have a suitable surface finish. For instance, the coating  134  on the sealing surfaces  132  may be polished, buffed, washed, cleaned, or otherwise finished to ensure that the coating includes a desirable finish, (e.g., to ensure that the coating  134  does not include cracks, rough patches, or other inconsistencies that may be particularly disposed to erosion). 
     The method  400  allows for cost-effective and efficient manufacture of a fluid end, as detailed herein. For instance, because selected surfaces are coated, the fluid end  108  may be more resistant to corrosion, erosion, and/or abrasion. While the method  400  may include an additional step, e.g., the coating step, compared to conventional fabrication, the coating can meaningfully increase life expectancy of the fluid end  108  and/or the components thereof. 
     Furthermore, it is to be noted that the fluid end  108  may be remanufactured after the fluid end  108  has been operable for an amount of time. In such an example, the coating  134  may be reapplied to the sealing surfaces  132  according to the method  400  shown and described in  FIG.  4   . In some examples, following step  402 , the sealing surfaces  132  may be cleaned and/or the old coating may be stripped from the block  120 . However, in some examples, such a cleaning step may not be necessary and anew coating may be applied directly to the old coating. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure describes an improved fluid end (“fluid end”) and methods of making the fluid end. The fluid end may be used in a variety of applications. For example, the fluid end may be used in gas, oil, and hydraulic fracturing applications. The fluid end may be particularly useful in high pressure applications and/or with fluids containing abrasive particles. The disclosed fluid end may be in use for extended periods of time before failing and/or requiring replacement, which can result in a decrease in down time for fluid systems and/or reduce maintenance time and expense. Furthermore, the fluid end may be easily remanufactured to reapply a coating to the fluid end, further extending a usable life of the fluid end. 
     According to some embodiments, a fluid end  108  may include a coating  134  applied to sealing surfaces  132  of a block  120 . By selectively applying the coating  134  to one or more of sealing surfaces  132 , the useful life of the block  120  of the fluid end  108  may be significantly increased. Moreover, by purposefully excluding the coating  134  from other surfaces, deleterious effects can be avoided and/or cost associated with the coating  134  can be minimized while increasing wear resistance of the block  120   
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.