Wash Pipe System and Method

Abstract

To solve the problem in which damaged washpipe seals can cause leakage of drilling fluids, which is common in many drilling rigs, and can cause contamination and destruction of surrounding components and the environment.SOLUTION: In a wash pipe seal and method, a first sliding mechanical face seal is provided between two sealing elements to seal a mud pipe. A second mechanical face seal is provided between two additional sealing elements to define a cavity within a housing of the washpipe between first and second mechanical face seals, independent of the mud pipe. During operation, a buffer fluid may be provided therein.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims the benefit of U.S. Provisional Patent Application No. 62 / 898,223, filed September 10, 2019, which is incorporated by reference.

[0002] Technical Field of the Disclosure TECHNICAL FIELD The present disclosure relates to top drive systems for well drilling, and more particularly to a washpipe system and method for sealing a rotatable interface along a drilling fluid conduit. [Background technology]

[0003] 2. Background of the Invention Well drilling applications typically use a downhole drilling rig or drilling swivel that is located at the end of a drill string that extends above ground. At surface, the tip of the drill string is engaged with a top drive and rotated. The drill string is typically hollow to allow drilling fluids, such as mud and concrete for stabilizing the borehole, to be delivered from above ground to the drilling rig or the side of the hole. Drilling fluid is delivered to the drilling swivel through a high-pressure swivel device, commonly called a "washpipe," that has a seal called a "washpipe packing" assembly. This packing assembly typically includes a tubular component that is held stationary, through which the high-pressure drilling fluid flows. A rotating seal assembly, a contact lip seal, is mechanically secured to the top drive or swivel shaft and rotates with it, forming a dynamic seal against the exterior surface of the tubular washpipe as the shaft rotates during drilling.

[0004] A variety of factors can affect the quality of the seal and head provided by conventional washpipe packing assemblies. For example, drilling fluids are typically provided at high pressure (e.g., 6 to 7 kpsi). Furthermore, drilling fluids often contain small gravel particles that can corrode and / or physically wear away the seal interface. Friction and heat generated by high speed drilling also accelerate seal degradation. Washpipe seal failure can result in drilling fluid leakage, which is common on many drilling rigs, causing contamination and damage to surrounding components and the environment.

[0005] In top drive and rotary drilling, the wash pipe sealingly engages a series of circumferential seals that are typically contained within a seal housing. In many cases, the wash pipe remains stationary as the seals and seal housing rotate. Such seal assemblies traditionally include a series of chevron-type elastomeric reinforced seals incorporating a series of reinforcing backup rings. In some prior art systems, one side of a seal is exposed to full hydraulic pressure and the other side is exposed to atmospheric pressure. The full drilling mud pressure differential acts on one seal until it breaks and the next seal in the assembly then serves as the primary seal. Some prior art swivel designs attempt to address potential wear and offset issues by allowing the wash pipe and seal housing to be articulated. Summary of the Invention

[0006] Summary of the Invention In one aspect, the present disclosure provides a fluid conduit disposed between a rotating mechanical component and a non-rotating mechanical component along with a fluid conduit extending through the rotating mechanical component. A wash pipe seal structure is described. The wash pipe seal structure includes a non-rotating frame connected to a non-rotating machine part. The non-rotating frame includes a non-rotating seal carrier having a generally hollow cylindrical shape forming an internal cavity. A first non-rotating seal is connected to the non-rotating seal carrier, and a second non-rotating seal is connected to the non-rotating seal carrier. The first and second non-rotating seals are disposed in the internal cavity in spaced relation to each other. A rotatable seal carrier is rotatably disposed at least partially within the internal cavity. The first rotating seal is connected to the rotatable seal carrier and disposed adjacent to the first non-rotating seal, and a second rotating seal is connected to the rotatable seal carrier and disposed adjacent to the second non-rotating seal. In operation, the first rotating seal abuts the first non-rotating seal to define a first sliding mechanical seal configured to seal the fluid conduit, and the second rotating seal abuts the second non-rotating seal to define a second sliding mechanical face seal configured to seal a first portion of the internal cavity separated from the fluid conduit and extending toward the first sliding mechanical seal.

[0007] In another aspect, the disclosure describes a wash pipe seal structure for use with a mud pipe in a drilling operation. The mud pipe may extend between a top drive and a drill string. The wash pipe seal structure includes a non-rotating frame connected to a non-rotating mechanical component of the top drive, the non-rotating frame including a generally hollow cylindrically shaped non-rotating seal carrier forming an internal cavity. A first non-rotating seal is connected to the non-rotating seal carrier, and a second non-rotating seal is connected to the non-rotating seal carrier. The first and second non-rotating seals are spaced apart from one another within the internal cavity. The rotatable seal carrier is rotatably disposed at least partially within the internal cavity. The first rotating seal is connected to the rotatable seal carrier and positioned adjacent to the first non-rotating seal, and the second rotating seal is connected to the rotatable seal carrier and positioned adjacent to the second non-rotating seal.

[0008] In operation, the first rotating seal abuts the first non-rotating seal to define a first sliding mechanical seal configured to seal the mud pipe, and the second rotating seal abuts the second non-rotating seal to define a second sliding mechanical face seal configured to seal a first portion of the internal cavity separated from the mud pipe and extending toward the first sliding mechanical seal. A buffer fluid is provided at a pressure at least equal to or greater than the pressure of the mud in the mud pipe. The buffer fluid is provided to the first portion of the internal cavity.

[0009] In yet another aspect, the disclosure describes a method for operating a wash pipe seal arrangement. The method includes providing at least one non-rotating seal carrier disposed at least partially surrounding a mud pipe, where the mud pipe extends across a rotating mechanical component and a non-rotating mechanical component, and where the wash pipe seal arrangement defines at least a section of the mud pipe. The method further includes creating a first sliding mechanical face seal between two seal elements included in the wash pipe seal arrangement, the first sliding mechanical face seal disposed at an interface between the rotating mechanical component and the non-rotating mechanical component. The method also includes creating a second mechanical face seal between two additional seal elements included in the wash pipe seal arrangement, and defining a cavity independent of the mud pipe within a housing of the wash pipe seal arrangement between the first and second mechanical face seals. In accordance with the method, a buffer fluid is provided within the cavity during operation. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of an exemplary drilling system according to the present disclosure. [Diagram 2] FIG. 2 is a partially exploded view of a washpipe assembly embodied as a rotating union as installed in a drilling system according to the present disclosure. [Diagram 3] FIG. 3 is a cross-sectional view of a wash pipe assembly according to the present disclosure. [Figure 4] FIG. 4 is an enlarged detail view of a portion of FIG. [Diagram 5] FIG. 5 is a schematic diagram of a fluid pathway according to the present disclosure. [Figure 6] FIG. 6 is a cross-sectional view of an intensifier device for use with a washpipe assembly according to the present disclosure. [Figure 7] FIG. 7 is a flow chart of a method of operating a washpipe assembly according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Detailed Description of the Invention The present disclosure relates to a wash pipe seal arrangement for drilling operations, and more particularly to a wash pipe seal arrangement including a dual sealing interface buffered by lubricant to improve sealing and extend seal life over known designs. To illustrate the disclosure, a drilling system 100 is shown in FIG. 1 as an example application of the disclosed systems and methods.

[0012] The drilling system 100 shown in Figure 1 includes a support tower or derrick 102 that supports various drilling equipment that operates a drill to drill a borehole 104 in the ground 106 using a drill bit 108 located at one end of a drill string 110. In the embodiment shown, the drill bit 108 is driven by a turbine 112 located at the end of the drill string 110 adjacent the drill bit 108. In a typical embodiment, mud or other liquid or agglomerate fluid is provided under pressure through the hollow drill string 110 to power the turbine 112. Fluid discharged by the operating turbine 112 is returned to the surface through the borehole 104 carrying cuttings with it.

[0013] The drill string 110 is pushed downwardly, which may be rotated by engagement with a splined section or kelly 114 that is rotatably engaged to a top drive 116. The top drive is a rotary drive that moves up and down the height of the derrick 102 to add and remove drill pipe to and from the drill string, to rotate the kelly 114, and to provide mud through the drill string to operate the turbine 112. The top drive 116 may be raised and lowered using a system of pulleys, such as a traveling block 118 and a crown block 120 connected by a cable 122 that is wound by a winch or drawworks 124, as shown. Releasing and retracting the cable 122 raises and lowers the top drive 116 while advancing the drill string through the borehole 104. The top drive 116 includes a drive mechanism 126 that drives the drill string 110, and also includes a fluid line 128 that provides mud through the drill string 110. A wash pipe seal arrangement 130 is used to provide a seal to prevent leakage of mud between the rotating portion of one end of the drill string and the stationary portion of the drive mechanism of the drill string on the top drive. As shown, mud may be provided from a tank 132 from which a pump 134 draws mud and provides it to the top drive 116 through a hose 136 connected between the top drive 116 and the pump 134 and which follows the vertical movement of the top drive during operation.

[0014] A close-up partial view of a portion of the top drive 116, removed for illustrative purposes from the drilling system 100, is shown in Figure 2. In this view, a mud inlet or gooseneck opening 202 is shown through which mud is provided under pressure to the top drive via the drill string. 110 (FIG. 1). The opening 202 is formed in the end of a fluid conduit 204 that is integral with the intensifier housing 206. Fluid is supplied through a washpipe seal 130 that engages and rotates the drillstring 110, which is disposed between a stationary component, such as a top drive frame 208, and a rotatable drive 210. The intensifier housing 206 (described in more detail below with reference to FIG. 6, which shows a cross section) includes a piston housing 212 that is attached to the intensifier housing 206 by a threaded nut 214. Coupled to the piston housing 212 is a fluid shutoff valve 216, which is described in more detail below with reference to FIG. 6.

[0015] Figure 3 shows a cross section of the wash pipe seal structure 130, and Figure 4 shows an enlarged detailed view. With reference to these figures, it can be seen that the wash pipe seal structure 130 is an assembly of parts disposed between a stationary fluid conduit 204 that is part of the top drive 116 and a rotatable drive 210 that rotatably engages the rotating drill string 110. Thus, the wash pipe seal structure 130 includes portions that are configured to rotate relative to one another while providing a seal along a mud pipe 302 that extends through the top drive, the washpipe, and the drill string.

[0016] More specifically, the wash pipe seal arrangement 130 includes a non-rotating frame 304 connected to the fluid conduit 204. The non-rotating frame 304 includes a mounting plate 306 connected to one end of the fluid conduit 204 along a sealed interface with a fastener 308. An extension plate 310 is connected to the mounting plate 306 along a sealed interface. The extension plate 310 includes a flared opening forming a conical surface 312 that increases the flow area for mud passing through the mud tube 302 in the direction indicated by arrow F. The extension plate 310 further includes a buffer fluid inlet 314 that extends radially through at least a portion of the extension plate 310 and is fluidly connected to a buffer fluid pathway 316 that fluidly connects the buffer fluid inlet 314 to a transfer pathway 318 formed in the first non-rotating seal carrier 320.

[0017] The first non-rotating seal carrier 320 has a generally hollow cylindrical shape and is disposed against the extension plate 310 facing the mounting plate 306, such that an internal cavity or bore 322 of the first non-rotating seal carrier 320 is fluidly connected to an internal end or opening of the transfer path 318 and the buffer fluid inlet 314. The first non-rotating seal carrier 320 slidably and non-rotatably supports a first non-rotating seal 324. The first non-rotating seal 324 is biased in a direction away from the extension plate 310 (downward in the plane of FIG. 3 ) by a spring 326. The spring 326 is disposed between a portion of the first non-rotating seal carrier 320 and the first non-rotating seal 324. A pin 327 extending through aligned components of first non-rotating seal carrier 320 and first non-rotating seal 324 axially and slidably engages the two parts while preventing rotation of the two parts relative to one another.

[0018] The second non-rotating seal carrier 328, which may be a separate component or, as shown in the illustrated embodiment, a single component integral with the first non-rotating seal carrier 320, is sealably connected or integral with the first non-rotating seal carrier 320 facing the extension plate 310 by one or more elongated fasteners 330. The second non-rotating seal carrier 328 includes a second non-rotating seal 332 connected thereon and rotatably engaged therewith by a pin 334. The second non-rotating seal carrier 328 is also a hollow cylindrical shape forming a bore 336 generally aligned to be fluidly mated or connectable with the bore 322 of the first non-rotating seal carrier 320. The bore 336 formed in the second non-rotating seal carrier 328 includes the second non-rotating seal 332. In this manner, first and second non-rotating seals 324 and 332 are disposed in opposed, mated bores 322 and 336, but in the direction of the spring biasing the seals. It should be noted that either the seal or the seal itself can be reversed. The second non-rotating seal carrier 328 further includes an additional buffer fluid inlet 315 that is fluidly connected to a buffer fluid path 317 that extends radially through at least a portion of the second non-rotating seal carrier 328 and fluidly connects the additional buffer fluid inlet 315 to the inside of the bore 336.

[0019] A hollow tubular shaped rotating seal carrier 338 includes a central tubular passage that defines a section of the mud pipe 302 surrounded by a generally cylindrical wall. The rotating seal carrier 338 is rotatably disposed within the coupled bores 322 and 336. The wall includes a flange 340 (shown in an enlarged view in FIG. 4) that extends in a radially outward direction relative to the axis of rotation R, which extends through the mud pipe 302. The flange 340 is disposed completely within the coupled bores 322 / 326 both radially and axially relative to the axis R. A first rotating seal 342 is connected to the rotating seal carrier 338 on one side of the flange 340 in the axial direction along the axis R. In the illustrated embodiment, the first rotating seal 342 is sized to fit into one end of the cylindrical wall 344 and is disposed radially inward relative to the flange 340. The wall 344 adjacent the first rotating seal 342 includes a convergent opening forming a conical surface 313 which reduces the flow area for mud passing through the mud pipe 302 in the direction indicated by arrow F.

[0020] A second rotating seal 346 is slidably connected to the rotating seal carrier 338 and is axially disposed on the opposite side of the flange 340 from the first rotating seal 342 along the axis R. One or more springs 348 bias the second rotating seal 346 away from the flange and also bias the first rotating seal 342 (e.g., downward in the plane of the paper in FIG. 3), although the springs could be reversed or applied to both rotating seals. On one end opposite the flange 340, the rotating seal carrier is connected to and sealingly engaged with the rotatable drive 210 through a mounting collar 349, which in turn is fastened to the rotatable drive 210 using fasteners 350. Secondary seal 352, which in the illustrated embodiment is embodied as a pressure seal including a U-shaped cross-section open in a direction towards first non-rotating seal carrier 320, is sealably disposed or engaged between an outer surface of rotating seal carrier 338 and an inner surface of bore 336 formed in second non-rotating seal carrier 328. An exhaust port 353 extends through second non-rotating seal carrier 328 and is fluidly connected to bore 336 between secondary seal 325 and second non-rotating seal 332 in a region adjacent secondary seal 325.

[0021] In operation, the wash pipe seal structure 130 is configured and operates to provide a sliding seal around the mud pipe 302 to prevent mud (or generally any fluid or liquid containing gravel) from leaking into the sliding interfaces disposed along the mud pipe 302 between the rotating and non-rotating structures comprising different sections of the mud pipe 302.

[0022] In the illustrated embodiment, the wash pipe seal arrangement 130 includes a first sliding or mechanical face seal 354 formed by a circular, sliding contact area or interface between the first non-rotating seal 324 and the first rotating seal 342. The first mechanical face seal 354 is disposed along the mud pipe 302 to provide a sealing function to prevent fluid passing through the mud pipe 302 from leaking or escaping from the mud pipe into a cavity 356 (FIG. 4) defined within the bores 322 and 336. A second sliding mechanical face seal 355 is formed by a circular, sliding contact area or interface between the second non-rotating seal 332 and the second rotating seal 346. Thus, the cavity 356 defined within the bores 322 and 336 is generally sealed to prevent the first mechanical face seal 354 from leaking or escaping from the mud pipe into a cavity 356 (FIG. 4) defined within the bores 322 and 336. 3. A cavity 356 is at least partially defined within bores 322 and 336 between second mechanical face seal 354 and second mechanical face seal 355. Cavity 356 is externally fluidly accessible via both buffer fluid inlet 314 and additional buffer fluid inlet 315. A second cavity 358 is also defined at least partially within bores 322 and / or 336 and extends between second mechanical face seal 355 and secondary seal 352. Second cavity 358 is externally accessible via exhaust port 353.

[0023] In operation, a constant flow of mud or other fluid is provided through the mud pipe 302 at pressure P1 while the rotating seal carrier 338 rotates relative to the first and second (or combined) non-rotating seal carriers 320 and 328. Mud flowing through the mud pipe 302 accelerates as it passes through the convergent conical surface 313, thus reducing its dynamic pressure as it passes through the first mechanical face seal 354. A buffer fluid, such as hydraulic oil, is provided through the buffer fluid inlet 314 or 315 and fills the first chamber 356. The buffer fluid is provided at a pressure P2, which is at least equal to, and preferably higher than, the mud pressure P1, such that P1≦P2. In this manner, the first mechanical face seal 354 is exposed to no pressure differential or, preferably, a pressure differential that will move buffer fluid toward and into the mud pipe 302. Given the abrasive nature of muddy water, when the buffer fluid enters the mechanical face seal interface it serves both to lubricate and cool the sliding contact portions of the first non-rotating and rotating seals 324 and 342.

[0024] The buffer fluid is maintained at a pressure P2 in the first cavity by the first mechanical face seal 354 and also by the second mechanical face seal 355. The second mechanical face seal 355 is exposed on one side to the pressure P2 and also to a lower pressure P3 < P2 or to the atmospheric pressure P3. The pressure P3 exists on the side of the seal exposed to the second cavity 358. The buffer fluid or hydraulic oil may be sealed or, alternatively, leakage may be permitted at a controlled rate through the second mechanical face seal 355 into the second cavity 358. The buffer fluid present in the second cavity 358 may be recovered by the secondary seal 352 and removed through the discharge opening 353. The rate at which leakage of the buffer fluid through the second mechanical face seal 355 is permitted or designed may be selected based on the amount of heat absorbed by the buffer fluid from the first mechanical face seal 354, whereby the resulting or steady-state desired temperature of the buffer fluid in the first chamber 356 can be achieved. The buffer fluid permitted to move into the second chamber 358 is replenished in the first chamber 356 by fluid supply, thus ensuring that the first chamber 356 is filled with fluid for the operating time (e.g., 8 hours). Also, by increasing the buffer fluid tank providing the buffer fluid to the first chamber 356, it can be used for a longer period.

[0025] A schematic diagram of the various fluid components associated with the wash pipe seal 130 is shown in FIG. 5. For ease of explanation, the same reference numbers as previously used are used for previously mentioned elements. In this figure, a fluid supply system 400 includes a mud supply 402, which provides a flow of mud to a mud pipe 302, for example, through a hose 136 (FIG. 1). The system 400 also includes a buffer fluid supply 404, which may include a tank containing buffer fluid (e.g., hydraulic oil). The buffer fluid supply 404 provides buffer fluid at a low pressure (e.g., pressure P3) through a supply conduit 408 to a pressure regulator or intensifier 406. Similarly, the mud supply 402 provides mud, or at least fluid, to the intensifier 406 through a generally static pressure conduit 410 at a mud supply pressure P1. During operation, the augmentation device 406 operates to automatically control or augment the buffer fluid pressure P3 to the buffer fluid pressure P2 using the mud pressure P1 such that variations in the mud pressure P1 are taken into account by corresponding variations in the buffer fluid pressure P2, thereby always maintaining the relationship P1≦P2 for the reasons discussed above.

[0026] A possible exemplary embodiment of the intensifier 406 is shown in cross section in Figure 6. The intensifier 406 includes a mud piston chamber 502 having a first diameter D1. The mud piston chamber 502 is fluidly connected to a mud inlet port 504 that is open to and in fluid communication with the mud flow F provided to the mud line 302 (Figure 3), such that the fluid within the mud piston chamber 502 is at a pressure P1 of the mud fluid supply passing through the mud line 302. The mud piston chamber 502 is formed in a bottom member 506, which is shown connected to the intensifier housing 206 in Figure 2.

[0027] The piston housing 212 forms a buffer fluid piston chamber 508 having a diameter D2 which is smaller than D1, i.e., D2 < D1. Chambers 502 and 508 are aligned along their center lines and open to each other, thus forming a stepped chamber having a center line L. The stem 510 is slidably and sealably disposed in the bushing 512 and extends into chambers 502 and 508 along the center line L. Depending on whether pressure enhancement (P2 > P1) is desired or simple follow-up (P1 = P2) is desired, the stem 510 may include one plunger 514 or two plungers (i.e., plunger 514 and an additional plunger 516 shown by the dotted line). When one plunger 514 is used, the pressure P1 from chamber 502 acts on one side of the plunger 514, whereby the fluid pressure P1 causes an equal pressure P2 to exist in the buffer fluid present in chamber 508 (P2 = P1). When enhancement is desired, the pressure P1 acts on one side of the additional plunger 516 with a larger diameter D2, whereby when the first plunger 514 acts on the buffer fluid present in chamber 508, enhancement occurs by a coefficient depending on the ratio of the areas derived from D2 and D1. The enhanced buffer fluid is provided by the port 518. A valve system 520 replenishes the buffer fluid in chamber 508.

[0028] A flow chart of a method of operating a wash pipe seal assembly is shown in FIG. 7. According to the method, at least one non-rotating seal carrier is disposed at least partially surrounding a mud pipe, which may be provided as part of a drilling rig. The mud pipe extends across the rotating and non-rotating mechanical components. The wash pipe seal assembly may form at least a section of the mud pipe at 602 and includes a first sliding mechanical face seal defined between two seal elements at 604 and disposed at an interface between the rotating and non-rotating mechanical components. The wash pipe seal assembly may further include a second mechanical face seal formed between two additional seal elements at 606 and defines a cavity in the housing between the first and second mechanical face seals at 608. Pressurized buffer fluid may be provided to the cavity at 610 to stop leakage of fluid from the mud pipe past the first mechanical face seal. Optionally, a buffer fluid may be provided at a pressure at least equal to the pressure of the fluid in the mud pipe as a type of fluid that lubricates and convectively cools the sealing elements participating in forming the first and / or second mechanical face seals. A controlled leakage of buffer fluid past the second mechanical face seal may also be provided to contribute to the cooling function of the buffer fluid, in which case a replenishment of buffer fluid may be provided. A hydraulic intensifier or pressure regulator may automatically adjust the pressure of the buffer fluid provided to the cavity at 612. The secondary seal may further collect any buffer fluid that flows past the second mechanical face seal in an additional cavity for drainage.

[0029] All publications cited in this specification, including publications, patent applications, and patents, are herein incorporated by reference to the same extent as if each publication was individually and specifically indicated to be so indicated and set forth in its entirety herein.

[0030] In the context of describing the present invention (and particularly in the context of the claims below), the terms "a," "an," and "the" referring to one and "at least one" referring to one or more of the following elements are used interchangeably. The use of "at least one" and similar language should be construed to include both the singular and the plural, unless otherwise indicated herein or the context clearly contradicts. The use of the term "at least one" with a list of one or more items (e.g., "at least one of A and B") should be construed as meaning one item selected from the list (A or B) or any combination of two or more of the list (A and B), unless otherwise indicated herein or the context clearly contradicts. The terms "comprising," "having," "including," and "containing" should be construed as meaning an exemplary enumeration (i.e., meaning "including, but not limited to"), unless otherwise indicated herein. Recitation of numerical ranges herein is merely intended to serve as a shorthand method of referring to each individual numerical value contained in the range, and each individual numerical value is incorporated herein as if each was individually referred to herein. All methods described herein may be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The use of any example or illustrative language (e.g., "etc.") herein is intended merely to better illustrate the invention and does not limit the scope of the invention unless otherwise stated in the claims. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0031] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of the preferred embodiments will become apparent to those skilled in the art upon reading the above description. The inventors expect those skilled in the art to adopt those variations as appropriate, and the inventors intend the invention to be practiced other than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in any possible variation is encompassed by the invention unless otherwise expressly stated herein or clearly contradicted by context.

Claims

1. 1. A wash pipe seal arrangement for placement between a non-rotating mechanical component and a rotating mechanical component and along a fluid conduit extending throughout said rotating mechanical component and said non-rotating mechanical component, said wash pipe seal arrangement comprising: a non-rotating frame connected to the non-rotating machine components, the non-rotating frame including a non-rotating seal carrier, the non-rotating seal carrier being of generally hollow cylindrical shape defining an interior cavity; a first non-rotating seal connected to the non-rotating seal carrier; a second non-rotating seal connected to the non-rotating seal carrier, the first and second non-rotating seals being spaced apart from one another within the internal cavity; a rotatable seal carrier rotatably disposed at least partially within the internal cavity; a first rotating seal connected to the rotatable seal carrier and disposed adjacent to the first non-rotating seal; In the above wash pipe seal arrangement, the wash pipe seal arrangement further comprises a second rotating seal connected to the rotatable seal carrier and disposed adjacent to the second non-rotating seal, in operation, the first rotating seal abuts the first non-rotating seal to define a first sliding mechanical seal configured to seal the fluid conduit; and In operation, the second rotating seal abuts the second non-rotating seal to define a second sliding mechanical face seal between the non-rotating seal carrier and the rotatable seal carrier and separated from the fluid conduit and configured to seal a first chamber of the internal cavity aligned with the fluid conduit, the first chamber of the internal cavity extending from the second sliding mechanical face seal toward the first sliding mechanical seal, and the wash pipe seal arrangement comprises: a buffer fluid inlet in fluid communication with the first chamber of the internal cavity, wherein in operation, fluid in the fluid conduit is provided at a first pressure P1 and buffer fluid is provided to the first chamber of the internal cavity at a second pressure P2, where P1≦P2. Wash pipe seal structure.

2. a first biasing member between the non-rotating seal carrier and the first non-rotating seal; the first non-rotating seal is slidably disposed on the non-rotating seal carrier, and the first biasing member biases the first non-rotating seal in a direction toward the first rotating seal; a second biasing member disposed between the rotatable seal carrier and the second rotating seal; the second rotating seal is slidably disposed on the rotatable seal carrier, and the second biasing member is adapted to bias the second rotating seal in a direction toward the second non-rotating seal. The wash pipe seal structure according to claim 1 .

3. 3. The wash pipe seal arrangement of claim 2, wherein said first biasing member comprises at least one spring and said second biasing member comprises at least one spring.

4. 2. The wash pipe seal structure of claim 1, further comprising a secondary seal configured to seal a second chamber of the internal cavity separated from the fluid conduit and the first chamber of the internal cavity, the second chamber of the internal cavity extending between the second sliding mechanical face seal and the secondary seal.

5. 5. The wash pipe seal structure of claim 4, further comprising an exhaust port in fluid communication with the second chamber of the internal cavity, the exhaust port configured to allow exhaust of the buffer fluid entering the second chamber of the internal cavity.

6. 5. The wash pipe seal arrangement of claim 4, wherein the second sliding mechanical face seal is configured to allow controlled leakage of buffer fluid from the first chamber to the second chamber of the internal cavity.

7. 2. The wash pipe seal arrangement of claim 1, further comprising a flow reduction section in said fluid conduit located at an upstream location relative to said first sliding mechanical seal relative to a direction of fluid flow in said fluid conduit.

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