Abstract:
A system for monitoring wear of pump casing liners is disclosed. The system may include a wear sensor disposed in proximity to the pump casing liner so that the sensor wears at substantially the same rate as the lining. The wear sensor may include a plurality of circuit loops having different lengths. As the pump casing liner and the sensor wear during use, the plurality of circuit loops are sequentially breached. A control system monitors the signals from the plurality of circuit loops to develop liner wear information. This information is employed to signal a user when one or more predetermined wear thresholds are exceeded. Other embodiments are described and claimed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a non-provisional of pending U.S. Provisional Patent Application Ser. No. 61/472,984, filed Apr. 7, 2011, the entirety of which application is incorporated by reference herein. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The disclosure is generally related to the field of fluid handling systems, and more particularly to an improved system for monitoring wear of pump linings. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    Screw pumps are rotary, positive displacement pumps that use two or more screws to transfer high or low viscosity fluids or fluid mixtures along an axis. Generally, a three-screw pump is a positive rotary pump in which a central one of three screws is motor-driven, and the two further screws are idlers meshing with diametrically opposed portions of the driven central screw, the idlers acting as sealing elements that are rotated hydraulically by the fluid being pumped. The volumes or cavities between the intermeshing screws and a liner or casing transport a specific volume of fluid in an axial direction around threads of the screws. As the screws rotate the fluid volumes are transported from an inlet to an outlet of the pump. In some applications, these pumps are used to aid in the extraction of oil from on-shore and sub-sea wells. 
         [0004]    Often the liquids pumped through these pumps include entrained solids, such as sand. The presence of sand and other solids can cause damage to the pump internals, most notably to the pump casing, where the solids can pass between the screws and the casing. Substantial wear of the pump casing can undesirably result in reduced discharge flow rates. Repair of pump casings can be expensive, and thus, many manufacturers line the pump casing with a self-repairing liner material. Such liners are typically made from material that is much softer than the casing and screws. Thus, damage due to entrained solids is borne by the liner and not the more expensive casing. Such liners may be “self-repairing,” in that over time, scratches and gouges caused by contact with entrained solids may be smoothed over, mitigating their impact on performance of the pump. 
         [0005]    While such liners can improve pump lifecycle, periodic liner refurbishment is still required. A difficulty remains, however, in determining when liner replacement should occur. As noted, liner degradation may manifest itself in reduced output flow from the pump. Where multiple pumps serve a single outlet, however, it can be difficult to identify which pump may be the cause of reduced overall flow. Thus, it would be desirable to provide a system and method for continuously monitoring wear of pump casing liners so that repair can be performed in a timely manner. 
         [0006]    Wear monitoring systems, in general, are known. For example, U.S. Pat. No. 6,945,098 to Olson discloses a wear detection system for use in determining wall thinning in hydrocyclone applications, U.S. Pat. No. 6,290,027 to Matsuzaki, U.S. Pat. No. 5,833,033 to Takanashi, and U.S. Pat. No. 4,274,511 to Moriya disclose systems for detecting wear of brake pads, and U.S. Pat. No. 3,102,759 to Stewart discloses a system for detecting wear of journal bearings. The problem with these systems is that they may not be as accurate as desired. This is because the systems employ wear sensors made of materials that have compositions and properties different from the compositions and properties of the components being monitored. Owing to such differences, the sensors may wear at a faster or slower rate than the monitored components. As will be appreciated, where sensor wear is not consistent with component wear, the accuracy of the monitoring system is adversely affected. 
         [0007]    Thus, there remains a need for an improved wear monitoring system that can continuously monitor wear of pump casing liners so that repair can be effected in a timely manner. Such a system should overcome the deficiencies inherent in current systems, and should be highly accurate. It would also be desirable to provide a system and method for storing liner wear information so that wear trending can be accomplished. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    This disclosed wear detector is designed to detect erosion wear in a screw pump. This device detects wear in the idler bores. The idler bores are designed to provide an oil film build up with the idler rotors according to journal bearing theory. As such, under normal operating conditions the idler rotors do not come in contact with the idler bores, but rather they ride on an oil film. The disclosed wear detector is design to erode away at the same rate as the Babbitt lined pump bores when heavy debris is present. Therefore it is important that the sensor be made from a material that erodes at the same rate as the Babbitt material of the pump lining. The disclosed design can also detect film type failure modes. Film failure is where the pump&#39;s conditions change and the idlers come into contact with the idler bores. 
         [0009]    A system for monitoring wear of pump casing liners is disclosed. The system may include a wear sensor disposed in proximity to the pump casing liner so that the sensor wears at substantially the same rate as the lining. A signal representative of the sensor wear is provided to a control system which logs the wear information and uses that information to signal a user when one or more predetermined wear thresholds are exceeded. 
         [0010]    A system is disclosed for monitoring pump lining wear. The system may comprise a wear detector having a housing portion and a circuit portion. The wear detector may be disposed in a casing of a pump, where the pump has a casing liner. The housing portion may include a nose portion that is made from substantially the same material as the casing liner. The nose portion can be positioned flush with an inner surface of the casing liner adjacent a screw of the pump. The circuit portion can be disposed in or on the nose portion. The circuit portion may have at least one circuit loop electrically coupled to a conductor, and the conductor may be coupled to a controller for providing one or more signals to the controller representative of a thickness of the casing liner. 
         [0011]    A system is disclosed for monitoring pump lining wear. The system may comprise a wear detector comprising a housing portion and a circuit portion, the wear detector disposed in a casing of a pump, the pump having a casing liner. The housing portion may have a nose portion that is made from substantially the same material as the casing liner. The nose portion may be positioned flush with an inner surface of the casing liner adjacent a screw of the pump. The circuit portion may be disposed in or on the nose portion. The circuit portion may have at least one circuit loop electrically coupled to a conductor. The conductor may be coupled to a controller to enable the controller to determine a thickness of the casing liner. 
         [0012]    The circuit portion may comprise a flexible circuit including a plurality of conductive traces that form first and second circuit loops. The first circuit loop may be coupled to first and second contact openings, the second circuit loop may be coupled to the second contact opening and a third contact opening, and the first and second circuit loops may share a common ground. The first circuit loop may be longer than the second circuit loop such that the first circuit loop extends closer to the nose portion of the housing portion than the second circuit loop. When the nose portion is worn away by a first predetermined amount the first circuit loop may be broken, resulting in an open circuit configured to be sensed the controller. When the nose portion is worn away by a second predetermined amount the second circuit loop may be broken, resulting in an open circuit configured to be sensed by the controller. 
         [0013]    The controller may be configured to recognize the opening of the first and second circuit loops as corresponding to respective first and second predetermined thickness reductions in the casing liner. The controller may include a processor and a memory, and may be configured to execute instructions for recognizing signals received from the wear detector as representative of one or more wear conditions of the casing liner. The memory may store data representative of the one or more wear conditions of the pump liner associated with time stamp data. 
         [0014]    A wear detector is disclosed for monitoring pump lining wear. The wear detector may comprise a housing portion and a circuit portion. The housing portion may have a nose portion positionable flush with an inner surface of a pump casing liner adjacent a screw of a pump. The circuit portion may be disposed in or on the nose portion and may have at least one circuit loop electrically coupled to a conductor. The conductor may be coupled to a controller for providing one or more signals to the controller representative of a thickness of the casing liner. The circuit portion may comprise a flexible circuit including a plurality of conductive traces that form first and second circuit loops. The first circuit loop may be coupled to first and second contact openings, the second circuit loop is coupled to the second contact opening and a third contact opening, and wherein the first and second circuit loops share a common ground. The first circuit loop may be longer than the second circuit loop such that the first circuit loop extends closer to the nose portion of the housing portion than the second circuit loop. When the nose portion is worn away by a first predetermined amount the first circuit loop may be broken, resulting in an open circuit configured to be sensed the controller, and when the nose portion is worn away by a second predetermined amount the second circuit loop may be broken, resulting in an open circuit configured to be sensed by the controller. 
         [0015]    A method is disclosed for monitoring pump lining wear. The method comprises: at a controller, determining a thickness of a pump casing liner based on signals received from a conductor associated with a wear detector; wherein the wear detector having a nose portion positioned flush with an inner surface of the pump casing liner, the nose portion made from substantially the same material as the pump casing liner, the wear detector having a circuit portion with at least one circuit loop disposed adjacent the nose portion, the at least one circuit loop electrically coupled to the conductor. The at least one circuit loop may comprise first and second circuit loops, the first circuit loop being longer than the second circuit loop such that the first circuit loop extends closer to the nose portion than the second circuit loop. The method may further comprise, at the controller, sensing a first open circuit condition when the nose portion is worn away by a first predetermined amount that breaks the first circuit loop and results in a first open circuit. The method may also comprise at the controller, sensing a second open circuit condition when the nose portion is worn away by a second predetermined amount that breaks the second circuit loop and results in a second open circuit. The controller may correlate the opening of the first and second circuit loops as corresponding to respective first and second predetermined thickness reductions in the pump casing liner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    By way of example, a specific embodiment of the disclosed device will now be described, with reference to the accompanying drawings: 
           [0017]      FIG. 1  is cross-section view of an exemplary three-screw pump; 
           [0018]      FIG. 2A  is a cross-section view of a pump casing portion of the pump of  FIG. 1  taken along line  2 - 2 ;  FIG. 2B  is a detail view of a liner portion of the pump casing of  FIG. 2A ; 
           [0019]      FIG. 3  is an exploded isometric view of an exemplary wear sensor; 
           [0020]      FIG. 4A  is a transparent plan view of the wear sensor of  FIG. 3 ;  FIG. 4B  is a cross-section view taken alone line  4 B- 4 B of  FIG. 4A ; 
           [0021]      FIG. 5  is a plan view of an exemplary circuit portion of the wear sensor of  FIG. 3 ; 
           [0022]      FIG. 6A  is a cutaway view of the circuit portion of  FIG. 5 ;  FIG. 6B  is a detail cutaway view of a portion of the cutaway view of  FIG. 6A ; 
           [0023]      FIGS. 7-9  show the disclosed wear sensor installed in an exemplary pump casing; 
           [0024]      FIG. 10  is a block diagram of a system for monitoring pump casing liner wear using the disclosed wear sensor; 
           [0025]      FIG. 11  is a diagram of an exemplary display for use in the system of  FIG. 10 ; and 
           [0026]      FIGS. 12 and 13  show a local readout for displaying pump lining condition. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Referring now to the drawings,  FIG. 1  is a schematic cross-section of a screw pump  10 . The pump  10  includes an inlet-suction end  12 , an outlet-discharge end  14 , and a casing  16  defining a screw channel  18  there-between. As illustrated in  FIG. 2A , the screw channel  18  comprises a larger center bore  20  and a pair of smaller bores  22  juxtaposed on opposed sides of the center bore  20 , for respectively receiving a drive screw  24  and a pair of idler screws  26 . Operating power for the drive screw  24  is transmitted by means of a drive screw spindle  28  ( FIG. 1 ), which is rotated by a motor or other drive unit (not shown). In the schematic pump  10  shown in  FIG. 1 , fluid is conveyed from left to right. 
         [0028]    One or more inner surfaces of the pump casing  16  may be lined with a material that is different from the casing material to protect the pump casing  16  from damage during operation.  FIG. 2B  shows such a lining  30  disposed on the inner surfaces of the casing  16  adjacent one of the idler screws  26 . In practical application, this lining  30  may be disposed on the inner surfaces of the casing  16  adjacent the idler screws  26  and the drive screw  24 . In one embodiment, the lining  30  comprises Babbit metal. Babbitt metal is soft and has a structure is made up of small hard crystals dispersed in a softer metal, which makes it a metal matrix composite. As the Babbit metal wears, the softer metal erodes, which creates paths for lubricant between the hard high spots that provide the actual bearing surface. The lining  30  may be provided in any of a variety of desired thicknesses. In one embodiment, the thickness “T” of the lining  30  is about 3/16-inch. 
         [0029]    During operation, when entrained solids pass between the screws  24 ,  26  and the liner  30 , the screws and liner may become worn or damaged. To maintain desired performance, the screws and liner may be periodically replaced. Traditionally, the liner is replaced at the same time the screws are replaced, since direct inspection of the liner throughout the casing is difficult. Changing the liner, however, requires that the pump be taken out of service and shipped to a maintenance facility. The problem with such a procedure is that liner replacement is not always necessary. With the disclosed system, the user is provided with a constant indication of liner thickness, and thus, if the system indicates that the liner remains above a certain critical thickness when it is time for the screws to be replaced, then only screw replacement can be carried out. The benefit is that screw replacement can be performed in the field, whereas liner replacement must be performed in the shop. As will be appreciated, this can result in lower cost and impact on operations, resulting in lower overall life cycle cost for the pump. 
         [0030]    Referring now to  FIGS. 3-5 , the wear sensor  32  may include a housing  34  and a wear circuit  36  disposed within the housing. In the illustrated embodiment, the housing  34  comprises first and second housing halves  34 A, B and the wear circuit  36  comprises a flexible circuit containing a plurality of conductive traces  37 . The housing halves  34 A, B and the wear circuit  36  may be held together using a suitable adhesive, such as epoxy. First and second recesses  38 A, B may be provided in the housing halves  34 A, B to enable the wear sensor  32  to accept fasteners  40  for fastening the wear sensor to the pump casing  16  at an appropriate location, as will be described in greater detail later. Although the housing is shown as being two pieces, it will be appreciated that a single-piece housing could also be used. 
         [0031]    As can be seen, the wear circuit  36  may have a first end  42  with a plurality of contact openings  44  for coupling to a plurality of conductors  46  ( FIG. 4B ) and a second end  48  that extends adjacent to a nose portion  50  of the first housing half  34 A. A plurality of holes  52  are disposed in the wear circuit  36  between the conductive traces, to facilitate bonding of the circuit to the housing  34  ( FIG. 5 ). 
         [0032]    As can be seen in  FIG. 5 , the wear circuit  36  may include a plurality of conductive traces  37  which, in the illustrated embodiment, make up first and second circuit loops  37 A, B. The first circuit loop  37 A is coupled to contact openings  44 A and  44 B, while the second circuit loop  37 B is coupled to contact openings  44 B and  44 C. The loops  37 A, B share a common ground  44 B. Although the illustrated embodiment shows two separate circuit loops, the wear circuit  36  could include greater or fewer circuit loops, as desired. 
         [0033]      FIGS. 6A and 6B  show additional detail of the wear circuit  36 . Specifically, the wear circuit is shown as a laminate structure in which the conductive traces  37  and the contact openings  44  are sandwiched between first and second layers  54 A,  54 B of flexible material. In one embodiment, this flexible material is a polyimide. Other flexible laminates can also be used. The laminate structure is held together using a suitable adhesive, such as epoxy. The individual conductors  46  ( FIG. 4B ) can be connected to the contact openings  44  via soldering. 
         [0034]      FIGS. 7-9  show the wear sensor  32  installed in an exemplary pump casing  16 . The wear sensor  32  is shown disposed within a recess  56  formed in the casing  16  and is fixed to the casing via the fasteners  40 . As can be seen, the sensor  32  is positioned so that the nose portion  50  of the sensor is substantially flush with the inner surface of the casing liner  30 . 
         [0035]    In one embodiment, the first and second housing halves  34 A, B of the wear sensor  32  are made from the same material as the casing liner  30 . Thus, in an exemplary embodiment the first and second halves  34 A, B are made from Babbit metal of a similar composition as that of the casing liner  30 . Because the housing is made from the same material as the casing liner  30 , the nose portion  50  of the sensor will experience wear at substantially the same rate as the liner. As the nose portion  50  wears, so does the circuit  36  which is disposed in or on the nose portion  50 . As a result, wear of the wear circuit is directly proportional to wear of the liner  30 . 
         [0036]    Referring back to  FIG. 5 , it can be seen that the first circuit loop  37 A is longer than the second circuit loop  37 B (i.e., the first circuit loop  37 A extends closer to the second end  48  of the wear circuit  36  than does the second circuit loop  37 B). Since the second end  48  of the wear circuit  36  is disposed adjacent to the nose portion  50  of the first housing half  34 A, the second end  48  of the wear circuit will wear away at or about the same rate as the nose portion  50  (liner  30 ). As the second end  48  of the wear circuit is worn away by a first amount (identified as “T 1 ” in  FIG. 5 ), the first circuit loop  37 A is broken, resulting in an “open circuit,” which can be sensed by a monitoring controller. As wear progresses, the wear circuit  36  eventually wears away by a second amount “T 2 ,” and the second circuit loop  37 B is broken, thus resulting in an “open circuit” which can be sensed for the second circuit loop. 
         [0037]    The system may be configured to recognize the “opening” of each circuit  37 A, B as corresponding to particular predetermined thickness reductions in the casing liner  30 . In this way, the in situ thickness of the casing liner  30  can be continuously monitored, and the pump  10  can be taken off line and refurbished when the liner thickness reaches a critical value. 
         [0038]      FIG. 10  shows a system  100  for monitoring pump liner wear. Wear sensor  32  is installed in pump  10 , and conductors  46  are routed through the casing using an appropriate gland seal, such as a high pressure gland seal offered by Conax Technologies, 2300 Walden Avenue, Buffalo, N.Y. 14225. Signals from the conductors  46  may be communicated to a control box  58  via a hard-wired or wireless communication link  60 . The control box  58  may include a processor  60  and associated memory  62 . The processor may be configured to execute instructions for receiving input signals from the wear sensor  32  and for recognizing the signals as representative of one or more wear conditions of the pump liner  30 . The memory  62  may be used to store data representative of the one or more wear conditions of the pump liner. Such data may also include time stamp data which can be used to develop wear trend information for the pump  10 . In one embodiment, this wear trend information can be used to predict an end-of-life for the pump liner  30 . The system  100  may also include a display  64  in communication with the control box  58 . The display  64  may be used to display one or more pump liner conditions or warnings to a user. Visible and/or audible indications of pump liner condition may be included. 
         [0039]      FIG. 11  shows an exemplary display  64  for a system that includes a pair of wear sensors  32 . More than one wear sensor may be used where the pump  10  has multiple idler screws  26 . It will be appreciated that a multiplicity of wear sensors  32  can be disposed throughout the pump casing as desired, to provide information on the casing liner  30  at various locations throughout the pump. 
         [0040]    The display  64  of  FIG. 11  includes a visual indication of the wear state of first and second wear sensors  32 . In the illustrated embodiment, a visual indication is provided indicating that a first predetermined thickness reduction in the liner  30  has been observed (termed “Stage  1 ”). This would, for example, correlate with the breaking of the first circuit loop  37 A in each wear sensor. “Stage  2 ” does not display a warning condition, and thus the second circuit loop  37 B in each wear sensor has not been breached. 
         [0041]    As will be appreciated, in addition to this local display  64 , a further remote display of data can also be provided. Further, an e-mail, fax or SMS text message can be sent to a predetermined address when one or more circuit loop breaks are sensed. 
         [0042]      FIG. 12  shows an implementation of the disclosed wear sensor in which a local readout of lining condition is provided in lieu of a separate control box. In this embodiment, a local display  66  is provided, with LED&#39;s (light emitting diodes)  68  ( FIG. 13 ) illuminating in sequence as each wear interval is reached (i.e., as each circuit loop is breached). A reset button  70  can be provided to reset the display  68  when a new wear sensor  32  is installed. The display  66  of this embodiment can be locally powered by an internal battery or small solar cell. In some embodiments, additional digital outputs can be provided to connect to external data acquisition components. 
         [0043]    Based on the foregoing information, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those specifically described herein, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing descriptions thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purpose of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended to be construed to limit the present invention or otherwise exclude any such other embodiments, adaptations, variations, modifications or equivalent arrangements; the present invention being limited only by the claims appended hereto and the equivalents thereof. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for the purpose of limitation.