Abstract:
A particulate-accommodating fluid flow directing apparatus comprises a failure detection housing containing a flow directing insert, the housing serving as a pressure boundary; failure at any location along the insert being detectable by means associated with the housing. The insert can be manufactured of erosion resistant materials, including non-ductile materials such as ceramics. The insert is sealed to the housing at an inlet and a discharge forming a pressure chamber between the insert and housing. The pressure chamber can be maintained at a pad pressure complementary to the process pressure, the pad pressure being maintained and monitored for indication of insert failure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/720,554, filed on Dec. 19, 2012, and published as US 2014/0166149 on Jun. 19, 2014, the content of which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The disclosed embodiment relates to apparatus for fluid flow conduits for accommodating erosion prevalent in changes of direction of particulate-laden flow streams, and more particularly to an erosion resistant pipe bend insert supported within a pressure housing providing structure support of the insert and failure detection. 
     BACKGROUND 
     Gas and oil wells often produce fluids containing particulates which cause premature failures in piping. A wellhead conducts a fluid flow stream through equipment including chokes and metering apparatus. Particulates such as sand can be produced from the gas or oil formation itself or, in many cases, or introduced sand such as fracturing sand being recovered after stimulation operations. If desanding apparatus is not used, or not used long enough, upon initiating production, the sand concentration though downstream production piping causes accelerated degradation. The placement and orientation of various equipment can result in the occasional bend, including right angle or 90 degree elbows. The elbows result in a change in direction and marked increase in the erosive effect of contained particulates. When flow direction is changed in the bend, the particulates do not parallel the fluid flow, but resist a trajectory change and move against the outside of the turn, eroding the contact points. The erosions patterns in bends, tees, and blind tee connections can be complex, the ultimate point of failure from erosion being somewhat un-predictable. 
     Internal erosion of the piping is not readily detected until failure and failure can be catastrophic, the fluid flow such as gas being under pressure, flammable and often containing H 2 S which is fatal in even low concentrations. This establishes the need for an effective device. 
     One prior art early warning device is that disclosed in U.S. Pat. No. 7,246,825, which provides an elbow in a block having a main fluid passageway. The block further contains a matrix of passageways, separated from the main passageway by sufficient wall material that expected erosion to destruction will occur only over a reasonable operations period. The matrix of passageways is maintained at a low and differential pressure to that of the main flow stream. Erosion eventually breaks through the wall material, connecting the flow with the matrix of passageways. The matrix pressure is monitored and when the differential pressure climbs to the pressure in the process stream, breakthrough is detected and an orderly turnaround can be scheduled for replacement of the block. The matrix is rated for the process pressure. One shortcoming is that the matrix of holes have to intersect the area that was being eroded, being an uncertain science. The matrix cannot provide 100% coverage as the holes are inside the pressure boundary. 
     Another form of prior art apparatus includes ceramic lined pipes and machined ceramic elbows. 
     The ceramic material of the elbow forms part of the pressure boundary and is therefore required to have sufficient tensile strength to meet the pressure requirements. This requires special ceramics or overly thick material. As well, some regulatory codes would require special exemptions to use this material. 
     SUMMARY 
     Generally, a particulate-accommodating fluid conduit and failure detection apparatus is disclosed herein. In an embodiment, the conduit is a flow directing insert and failure detection is provided by locating the insert wholly within a failure detection housing serving as a pressure boundary; failure at any location therealong being detectable by means associated with the housing. The conduit or flow directing insert can be manufactured of erosion resistant materials, including non-ductile and ceramics not normally permitted by regulatory codes for pressure applications. The flow directing insert is wholly supported and contained within a pressure chamber of the failure detection housing. The pressure chamber and housing form a surrounding pressure boundary manufactured from conventional materials and authorized under appropriate regulatory codes for apparatus and operations under pressure. Within the pressure chamber, an intermediate fluid pad is formed about a substantial length of the flow directing insert, between the insert and the housing. The insert is sealed to the housing at an inlet and a discharge to separate the fluid flow from the fluid pad. 
     The fluid flow directing insert can be used in wellhead piping, typically conveying particulates and which is particularly susceptible to erosion. 
     In an embodiment, failure of an insert can be detected by monitoring changes in the pressure between the fluid stream and the fluid pad. Accordingly, should the flow directing insert fail at any location therealong, the fluid pad is exposed to the fluid flow and pressures equilibrate, signalling failure and need for replacement. 
     In other embodiments, similar inserts and housings can be provided for other challenging erosive flow arrangements including blinded tee&#39;s, reducers, and headers. Accordingly, the term flow directing insert includes a range of piping from straight runs through 90 degree elbows, a reducer also being contemplated and included herein, the fluid flow within the reducer being guided from one flow regime to another and resulting in enhanced risk of erosion. 
     In one aspect, flow directing apparatus is provided for conveying a fluid flow comprising a housing forming a pressure boundary, and a flow directing insert within the housing. The flow directing insert is fit sealably within the housing for forming a pressure chamber about the insert and between the insert and the housing, the insert having an inlet end for receiving the fluid flow and a discharge end for discharging the fluid flow. The insert can cause a trajectory change in the fluid flow such as a bend in the piping. The insert can be replaceable. 
     In another aspect, the fluid flow contains particulates and the insert is a wear resistant material, such as a non-ductile material like ceramic, resistive to erosion from the particulates. 
     In another aspect directed to insert failure detection, the flow directing apparatus further comprises a pressure monitor connected to the pressure chamber for detecting a pressure change in the pad pressure being indicative of failure of the insert. The process and pad pressure can be maintained at a pressure differential, the pressure differential being maintained by a make-up pressure source and may also include a regulator for introducing make-up pressure as necessary to maintain the differential pressure between the fluid flow and the pressure chamber. 
     In another aspect, the disclosed flow directing apparatus can be employed in wellhead piping as a flow bend, such as a 90 degree elbow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional view of one embodiment of a flow directing insert and pressure boundary housing fit into wellhead piping and having flanged connections to wellhead piping, the fasteners in this figure and others being omitted for simplicity of view; 
         FIG. 1B  is an enlarged view of an inside bend of an insert fit with a bleed port for equilibrating supportive pressures between the fluid flow and the fluid pad; 
         FIG. 2A  is a view of one embodiment of the flow directing insert fit to a pressure boundary housing and having a pressure sensing system; 
         FIG. 2B  is a view of one embodiment of the flow directing insert fit to a pressure boundary housing and having a pressure sensing and differential pressure maintenance system; 
         FIG. 3A  is a cross-sectional view of a liquid accumulator located in the pressure housing for pressure maintenance against a fluid pad for a liquid-filled pressure chamber for the pressure boundary housing; 
         FIG. 3B  is a cross-sectional view of an optional liquid accumulator as a device separate from the pressure housing; 
         FIG. 4  is a cross-sectional view of a pressure-differential reduction piston loop for automatic pressure maintenance of the fluid pad for a liquid-filled pressure chamber; 
         FIG. 5  is an exploded view of one methodology for installation of an insert for replacement or upon initial installation; 
         FIG. 5A through 5C  are various views of an embodiment of an insert retainer ring,  FIG. 5A  illustrating a plan view of a retainer ring of two half-circular and overlapping rings,  FIG. 5B  illustrating a side view of assembled rings of  FIG. 5A , and  FIG. 5C  illustrating yet another embodiment of a four-segmented retainer ring; and 
         FIG. 6  is a partial cross-section view of the connection of one end of the insert to the pressure boundary housing. 
     
    
    
     DESCRIPTION 
     As shown in  FIG. 1A , an erosion resistant conduit  10  and a pressure boundary housing  20  is disclosed herein. The housing  20  fit into wellhead piping and having flanged connections to wellhead piping  29 , the fasteners in this figure and others being omitted for simplicity of view. The housing  20  supports the conduit  10  and enables detection of failure thereof. The conduit directs the flow of fluid and is exposed to the action of erosion, such as by erosive particulates contained in a process stream or fluid flow F conducted therethrough. Conduits including bends are particularly subject to accelerated erosion including aggravating factors such as the particulates impacting the bend wall, undergoing a change in momentum and the boundary layer is breached. 
     An extensive analysis of erosive wear in piping systems can be found in “Recommended Practice RP O501 Erosive Wear in Piping Systems”, Rev. 4.2-2007 by Det Norske Veritas. 
     Herein, at least a flow directing or bend portion  12  of the conduit  10  is manufactured as a flow directing insert  14  formed of erosion resistant materials, including those not normally permitted by regulations for pressure applications. Such materials include non-ductile or brittle materials. 
     As shown in  FIGS. 1A, 2A through 5 , the arrangement of the housing  20  accommodates the form of insert  14 . The example flow directing insert  14  has a 90 degree bend and the housing  20  is provided with inlet and outlet ports at 90 degrees. A housing for a reducer insert would have aligned inlet and outlet ports, the housing for a 45 degree elbow having inlet and outlets oriented at 45 degrees and so on. 
     Such materials are firstly and generally unacceptable under regulatory codes for the instances as forming a pressure boundary to the environment, and secondly and related thereto, a failure of such materials can be catastrophic, the insert  14  is wholly supported and contained within a pressure chamber  22  of the failure detection housing  20  forming a surrounding pressure boundary that can be manufactured from conventional materials authorized under appropriate codes for pressure operations. In one aspect, pressure P 1  of fluid flow F in the insert and pressure P 2  of the pressure boundary can be controlled to an acceptable pressure differential dp (|P 1 −P 2 |) for controlling the magnitude of pressure-induced stresses in the insert  14 . Further, in another aspect, fluid release due to failure of the insert  14  is constrained by the housing  20 . As the housing  20  need not be designed for sustained fluid flow conditions, detection of a failure of the insert  14  can provided for an orderly shutdown and replacement thereof. 
     Responsive to both above-identified aspects, within the pressure chamber  22 , an intermediate fluid pad B can be formed about a substantial length of the flow directing insert, between the insert  14  and the housing  20 . The fluid pad B is maintained at a threshold pressure P 2  selected to be related to, and in one embodiment, different that the fluid flow pressure P 1 . The insert  14  is sealed to the housing  20  at an insert inlet end  24  and an insert discharge end  26  to separate the fluid flow F from the fluid pad B. Accordingly, should the flow directing insert  14  fail at any location therealong, the fluid pad B is exposed to the fluid flow F and pressures therebetween equilibrate, signalling failure and need for replacement of the insert  14 . 
     Pressure sensors and pressure differentials can be monitored for signalling failure and, in one embodiment, for initiating closure of an emergency shutdown (ESD) valve located in the piping upstream of the insert  14 , such as that in wellhead piping between the wellhead and the housing  20 . In other embodiments, an alarm can alert an operator of the need for remedial action. 
     In an embodiment, one suitable material for the flow directing insert  14  is a highly erosion resistant material such as that selected from the ceramics. Such materials are typically brittle and unsuitable for use as the pressure boundary in pressure applications according to applicable codes. One material that is usable includes silicon nitrile which is conventionally cost prohibitive when forming the entirely of a commercial structure. Other lower cost ceramics are quite brittle and are not listed in the various codes for pressure containment including NACE, ASME, CSA. As a consequence, use of such materials usually requires special applications and permission before use in a pressurized environment. 
     Herein, the pressure boundary is formed by manufacture of the housing of conventional fluid pressure containment materials. The housing  20 , such as one manufactured from steel, has an inlet interface  30 , shown as an inlet flange to the upstream fluid piping and a discharge interface  32 , shown as a discharge flange to the downstream fluid stream piping. The flow directing insert  14 , possibly formed from unlisted materials, are wholly within the housing  20 . The insert  14  is sealed to the housing  20  at a first insert interface or inlet seal  34  at the inlet  24  and at a second insert interface or discharge seal  36  at the discharge  26 , maintaining separation between the fluid flow F and the fluid pad B. The fluid flow F then enters the housing at the inlet interface flange  30  and flows through the flow directing insert  14 , sealed from the fluid pad B at the inlet seal  34 . Fluid flow exits the flow directing insert  14 , sealed from the fluid pad at insert discharge seal  36 . Finally, the fluid flow exits the housing  20 , sealed from the environment at the discharge interface flange  32 . 
     Brittle materials are typically unsuitable for pressure operations as they cannot withstand the tensile stresses resulting from pressure differentials imposed thereon. By maintaining pressure both within and without the insert, and a pressures not too dissimilar to one another, stresses are minimized or eliminated. 
     Accordingly, the flow directing insert  14 , such as that manufactured of brittle material, is immersed in the fluid pad B at pad pressure boundary pressures P 2  near those at the process flow conditions P 1 , limiting the pressure differential (P 1 −P 2 ) across the insert  14 . 
     In one embodiment, and with reference to  FIG. 1B , the pad pressure P 2  can be balanced to the fluid flow pressure P 1  by placing a bleed port  38  in the insert  14  on an erosion-protected area, such as on the inside bend  40 , the bleed port having a restricted flow therethrough. Fluid from the fluid flow F will bleed through the bleed port  38  into the fluid pad B, balancing the pressure (P 1 =P 2 ) across the insert, eliminating differential pressure stresses and minimizing stress overall. 
     With reference to  FIG. 2A , so as to enable detection of a failure along the insert, the pad pressure can be set to a threshold pressure P 2 , any change therein, particular that approaching process pressure P 1  signaling a failure. 
     Further, and with reference to  FIG. 2B , in another embodiment, so as to enable detection of failure along the insert, the pad pressure P 2  can be set to a threshold pressure that is different from that of the process pressure P 1 ; a differential pressure dp (dp&lt; &gt;0) of about 100 psi (700 kPa) is deemed sufficient to detect a breach. Upon failure anywhere therealong, the pad P 2  pressure will equilibrate with the gas process pressure P 1  and P 1 -P 2  with be about zero (|dp|=0). A pressure monitor or pressure monitoring devices, such as a pressure transducer or transducers, can have a set point for differential pressure between process and pad pressures or for a change in pad pressure. 
     Alternatively, the pad pressure P 2  can be controlled using a regulator  50  using the process pressure P 1  as a reference pressure, the regulator increasing the fluid pressure P 2  in the pressure chamber as the process pressure P 1  increases. The process pressure P 1  can be tapped into the fluid flow F. As shown, P 1  is monitored at about the inlet interface  30 . A differential pressure can be maintained, such as a lower pad pressure P 2  to a higher process pressure P 1 . Failure of the insert would cause the pad pressure P 2  to rise, signalling failure. A pressurized source  52  of pad fluid B, or pressure connected to the pad fluid, is provided to regulate a make-up pressure P 3  to the pad pressure. In another embodiment, the pad fluid is an incompressible fluid such as a liquid. 
     As shown in  FIG. 3A , so as isolate the source fluid of the make-up pressure from the pad fluid, the system can further include an intermediate isolation chamber  54 . The pad fluid can be a liquid which is to be separated from a gaseous pressure maintenance fluid or gas. The chamber  54  and make-up source act as a form of liquid accumulator. The chamber  54  forms a cylinder that can be incorporated into the housing  20 . Regulated make-up pressure P 3  can drive a piston  56 , movable within the chamber  54 , to displace pad fluid to and from fluid pad B and necessarily vary the fluid pad pressure P 2  as process pressure P 1  varies inside the flow directing insert  14 . The pressurized source of make-up pressure P 3  can be supplied by a pressure tank or bottle having pressurized fluid within such as gaseous nitrogen (N2). 
     As shown in  FIG. 3B , the isolation chamber  54  can alternatively be located external to the housing  20 . 
     Turning to the  FIG. 4 , one can eliminate need for a regulator using a pressure-differential reduction piston loop  60  comprising a stepped piston  62  and wherein the intermediate chamber is corresponding stepped cylinder  64 . Process pressure P 1  of the fluid flow F, through process connection  56  to the fluid flow F, is in fluid communication with and acts on a first smaller area A 1  of stepped piston  62  in stepped cylinder  64  to produce force F. Force F acts on a larger second area A 2  of the stepped piston  62 , which is in fluid communication with, and producing a fluid pressure P 2  on the fluid pad side, fluidly connected through pad connection  58  to the pressure chamber  22 . Accordingly, the fluid pressure P 2  is automatically maintained at a pressure lower than the process pressure P 1 . As the process pressure P 1  varies, so does the fluid pad pressure P 2 , only at a lower, and differential, pressure dp. 
     With reference to  FIG. 5 , the insert  14  is removably installable into the housing  20  and replaceable. The insert  14  is sealed to the housing  20  using end ring seals  70   a ,  70   b  between each of the insert&#39;s inlet and discharge ends  24 , 26 , and an inside of the housing. The insert  14  is secured within the housing  20  by first and second retainer rings  81   a ,  81   b . The seals  70   a ,  70   b  seal the insert  14  to the housing and separate the fluid flow F from the fluid pad B. 
     In an embodiment, the housing&#39;s pressure chamber  22  houses the insert  14  and forms a first annular base to which the inlet end  24  of the insert is fit, a first ring seal  70   a  being located therebetween. The first annular base is aligned with, and formed about, the inlet inner interface  34 . A second annular base is provided at the discharge interface for sealing with the other discharge end  26  of the insert  14 . A second ring seal  70   b  located therebetween. In this embodiment the inlet and discharge ends  24 , 26  of the insert  14  are formed with first and second flanges  71   a ,  71   b  for corresponding placement and sandwiching of their respective ring seals  70   a , 70   b  between the insert  14  and the housing  20 . 
     As shown in the exploded view of  FIG. 5 , for installation of an insert  14  into the housing  20 , the housing can be formed in four components, a main body  72 , an inlet body  74  for sealing a first opening  79 , a discharge body  76  for sealing a second opening  90 , and an access closure  78  for sealing a third opening  92 . The first, second and third openings  79 ,  90 ,  92  access the main body  72 . 
     The insert  14  can be initially fit to the discharge body  76  and installed through the second opening or outlet port  90  of the main body  72 . The discharge body  76  is sealed thereto using conventional flange ring seal  80 . The flanged discharge end of the insert  14  is secured to the discharge body  76  using the second insert seal  70   b  and the retainer ring  81   b . That portion of the discharge body  76  within the pressure chamber  22  forms the second insert or discharge interface  36 . The retainer ring  81   b  clamps the insert&#39;s flange  71   b  to the discharge interface  36  of the discharge body  76 . With reference to  FIGS. 5A, 5B and 5C , the retainer ring  81  can be configured in one of a variety of two or more sectional pieces  82 , as known in the art, so as to be arranged about the insert, yet form a substantially continuous clamp about each flange  71   a ,  71   b .  FIG. 5A  illustrates two sectional pieces while  FIG. 5C  shows four sectional pieces. The sectional pieces overlap and fasteners secure them together and to the underlying structure. 
     The inlet body  74  can be fit to the first opening or inlet port  79  of the main body  72  and sealed thereto using conventional flange ring seal  80  for forming a sealed housing  20 . That portion of the inlet body within the pressure chamber  22  forms the inlet first insert or inner interface  34 . The inlet end  24  of the insert  14  can be guided through an outlet port  90 , aligning the inlet end of the insert with the inlet inner interface  34 . 
     As shown in better detail in  FIG. 6 , an insert ring seal  70  is arranged between the inlet end  24  of the insert  14  and the inlet inner interface  34 . Retainer ring  81   a  can be guided through the third opening or access port  92  for clamping the insert&#39;s flange  71   a  to the inlet inner interface  34 . 
     Once the inlet end  24  of the insert  14  is secured, the access closure  78  can be secured to the main body  72  to seal the access port  92  and form the pressure chamber  22 . 
     The housing  20  is now closed to seal and form the fluid pad B. The housing closure is sealed and re-closable for permitting installation and replacement of the flow directing insert  14 . 
     The arrangement for the inlet and outlet is arbitrary and can be reversed.