GB2599700A

GB2599700A - A subsea pump and method for determining motion of the rotor

Info

Publication number: GB2599700A
Application number: GB2016035.4A
Authority: GB
Inventors: Hofstad Åge; Mohite Randhir; Walsh Goldvag Sergio
Original assignee: Aker Solutions AS
Current assignee: Aker Solutions AS
Priority date: 2020-10-09
Filing date: 2020-10-09
Publication date: 2022-04-13
Also published as: GB202016035D0

Abstract

A subsea pump comprises an outer housing 12 of two parts connected at a flange interface 32 and containing an inner housing 14 which supports a rotor comprising a drive shaft 20 and motor 26 and an impeller 22 which may be divided into two opposed sets to counterbalance thrust loads. A bearing arrangement 24a,b,c,d is located between the rotor and the housing to facilitate rotation of the rotor. The rotor comprises a motion indicator which may be a disc, a drive shaft surface or a feature thereon e.g. a depression or protrusion; there may be radial and axial indicators. One or more motion sensing arrangements comprise a pressure sealed housing and at least one sensor is located inside the housing and in communication with the motion indicator to detect movement of the motion indicator. The motion sensor may have axial and radial sensors which may be eddy current, optical or capacitive sensors, or proximity or capacity probes. Radial sensors may detect radial movement e.g. vibration. The sensing arrangement may be part annular. Improves information available about the pump.

Description

A Subsea Pump and Method for Determining Motion of the Rotor

Technical field

Some described examples relate to a subsea pump and a method for determining motion of a rotor in a subsea pump.

Background art

In the oil and gas industry, the process of recovering hydrocarbon reserves can be complex. In particular, as easily accessible hydrocarbon reserves are depleted, more complicated methods of extraction are required to access harder-to-reach reserves. Often, the method of extraction, and the equipment used, has to be selected based on the individual requirements of the hydrocarbon reserves. For example, access to one reserve of hydrocarbons may require chemical treatment of recoverable hydrocarbons, while access to another hydrocarbon reserve may not.

To complicate matters further, the pressure inside the hydrocarbon well may change over time, as may the gas/liquid fractions of the recovered hydrocarbons. In order to maintain consistent production of hydrocarbons, the use of subsea pumps may be necessary when additional fluid pressure is required to bring the hydrocarbons to the surface of the well. Additional pressure may be achieved by the use of a subsea fluid pump to increase the pressure of a production fluid, thereby allowing it to reach the surface of the well more easily.

While having a pump located subsea allows for hydrocarbons to be recovered to a surface location more easily, the physical location of the subsea pump may give rise to problems. In particular, as the location of the pump is remote from the operator, understanding the operation of the pump may be difficult. While initially a subsea pump may function as expected, over time the operation of the pump may degrade such that it becomes ineffective, or highly inefficient, at increasing the pressure and/or flowrate of a working fluid.

Therefore, remote monitoring of a subsea pump is necessary in order to ensure that it is functioning as expected. Should the subsea pump begin to operate in a way that is not as expected, then it may be necessary to repair or replace the pump.

Current methods of monitoring a subsea pump may permit information about the local operating conditions to be relayed to a user. However, due to the harsh environment in which a subsea pump is often located, the availability of comprehensive information regarding the real-time functioning of a subsea pump can be limited.

Summary

It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above mentioned problem. According to a first aspect there is provided a subsea pump, comprising: a housing; a rotor located inside the housing, a bearing arrangement being located between the rotor and the housing to facilitate rotation of the rotor therein, and the rotor comprising a motion indicator; a motion sensing arrangement comprising a pressure sealed housing and at least one sensor, the motion sensing arrangement being located inside the housing and in communication with the motion indicator, and the motion sensing arrangement being configured to detect movement of the motion indicator.

According to a second example, the motion indicator is in the form of a radially extending protrusion from the rotor.

According to a third example, the motion indicator is or comprises the drive shaft of the rotor.

According to a fourth example, the motion sensing arrangement is configured to detect at least one of rotational, axial and radial movement of the rotor.

According to a fifth example, the motion sensing arrangement is configured to detect vibration of the rotor.

According to a sixth example, the at least one sensor is an optical sensor, a capacitive sensor or an eddy-current sensor.

According to a seventh example, the motion sensing arrangement comprises at least one axially oriented motion sensor, and at least two radially oriented motion sensors.

According to an eighth example, the at least two radially oriented motion sensors are offset by 90 degrees.

According to a ninth example, the motion indicator is in the form of a disc extending from the rotor and axially aligned with the rotor.

According to a tenth example, the disc is a coded target disc and comprises at least two surface features on an axial surface thereof, and wherein the motion sensing arrangement is configured to detect rotational movement of the at least two surface features as a result of rotation of the rotor.

According to an eleventh example, a first of the at least two surface features has a different geometry to a second of the at least two surface features, and the motion sensing arrangement is configured to detect the circumferential direction of rotation of the at least two surface features.

According to a twelfth example, the motion sensing arrangement is configured to detect axial movement of the rotor.

According to a thirteenth example, the pressure sealed housing of the motion sensing arrangement is has a partial annulus shape.

According to a fourteenth example, the partial annulus shape is a quarter-annulus.

According to a fifteenth example, the motion sensing arrangement comprises at least three sensors, and wherein two sensors are located on a radially inner surface of the quarter-annulus pressure sealed housing, and one sensor is located on an axial surface of the quarter-annulus pressure sealed housing.

According to a sixteenth example, the pressure-sealed housing of the motion sensing arrangement is coupled to the housing at a predetermined distance from the motion indicator.

According to a seventeenth example, the subsea pump comprises a motor for turning the rotor, the motor additionally comprising a motion indicator, and the motion of the rotor being detectable by the motion sensing arrangement.

According to a second aspect, there is method for determining motion of a rotor in a subsea pump, comprising: providing a subsea pump in a subsea location, the subsea pump comprising a pressure-sealed motion sensing arrangement, and a motor comprising a motion indicator; operating the subsea pump to effect rotation of the rotor therein; using the motion sensing arrangement to detect movement of the rotor.

According to a second example of the second aspect, the method comprises determining the direction of rotation of the rotor by detecting the motion of a first surface feature and a second surface feature located on the motion indicator, the first surface feature having a different geometry to the second surface feature.

According to a third example of the second aspect, the method comprises locating the pressure-sealed motion sensing arrangement in an annulus surrounding the rotor, the pressure-sealed motion sensing arrangement having a partial annulus shape.

According to a fourth example of the third aspect, the method comprises detecting at least one of rotational movement and axial movement of the rotor via an optical sensor, a capacitive sensor or an eddy-current sensor located on an axial surface of the pressure-sealed motion sensing arrangement.

According to a fifth aspect of the second example, the method comprises detecting at radial movement of the rotor via at least two motion sensors located on an inner radial surface of the pressure-sealed motion sensing arrangement.

The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the device described or steps of the methods described since such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

Brief descriptions of the drawings

The above objects, as well as additional objects, features and advantages of the present disclosure, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of example embodiments of the present disclosure, when taken in conjunction with the accompanying drawings.

Figure 1 shows a sectional view of an example of a subsea pump.

Figure 2A is an isometric view of an example of a motion sensing arrangement. Figure 2B shows an example configuration of two motion sensing arrangements.

Figures 3A-C illustrate various readings that may be provided by a motion sensing arrangement.

Detailed description

The present description provides an improved subsea pump. According to an example embodiment there is provided a subsea pump, comprising: a housing; a rotor located inside the housing, a bearing arrangement being located between the rotor and the housing to facilitate rotation of the rotor therein, and the rotor comprising a motion indicator; a motion sensing arrangement comprising a pressure sealed housing and at least one sensor, the motion sensing arrangement being located inside the housing and in communication with the motion indicator, and the motion sensing arrangement being configured to detect movement of the motion indicator.

The subsea pump may be used in a subsea location, which may be a downhole location, while the motion sensing arrangement and motion indicator may be able to provide the user with information regarding the operation of the pump. As will be described, the motion sensing arrangement may be configured to measure rotational, axial and radial movement of the rotor and may provide this information to a user to allow assessment of the performance of the subsea pump. In some examples, the motion sensing arrangement enable a user to measure the axial and/or rotational vibration of the rotor of the subsea pump, which may also be an indicator of the performance of the subsea pump.

Figure 1 illustrates a cross-sectional view of an exemplary subsea pump 10. In this example, the subsea pump 10 is a multiphase pump such as a helico-mixed flow pump, or possibly a helico-axial pump. However, with regard to the description herein, the skilled person will appreciate that many of the described features and examples may be applicable to other types of subsea pumps, which may not be multiphase pumps, for example axial and/or centrifugal pumps and axial and/or centrifugal compressors.

In this example, the subsea pump 10 comprises an outer housing 12, and an inner housing 14. The outer housing 12 of this example is comprised of two parts, which are connected together at a connection interface 32 by a bolted flange arrangement, although the skilled reader will understand that other forms of connection arrangement may be possible such as a threaded connection, or a chemically bonded connection. While the outer housing contains a pump inlet 16 and outlet 18 and defines a flow path extending outside of the inner housing 14, the inner housing 14 supports and contains moving components of the subsea pump 10. For example, as shown in Figure 1, the inner housing 14 may support a drive shaft 20, having an impeller arrangement 22 coupled thereto, and a drive arrangement 26 which may be in the form of a motor such as an electrical motor. The configuration of the inner housing 14 may be such that the drive shaft 20 extends the entire length of the inner housing 14, or substantially the entire length of the inner housing 14, while the impeller arrangement 22 may be confined to one axial side of the drive shaft 20, and the drive arrangement 26 may be confined to an opposite side of the drive shaft 20, as is the case in this example. As such, the inner housing 14 may be able to be divided into a drive section 28 and a pumping section 30. Here, the inner housing 14 contains a plurality of bearing arrangements 24-in this case four bearing arrangements 24a-d -which are located between the inner housing 14 and the drive shaft 20. The bearing arrangements 24a-d enable engagement between the inner housing 14 and the drive shaft 20, and facilitate rotation of the drive shaft 20 in the inner housing 14.

Of the four bearing arrangements 24a-d, two are located in the drive section 28 of the inner housing 14, while another two are located in the pumping section 30 of the inner housing 14. Together, the bearing arrangements 24a-d support the entire drive shaft along its length and facilitate rotation thereof relative to the inner housing 14. The bearing arrangement may be or comprise any suitable type of bearing, for example a rotary bearing such as a thrust bearing.

In this example, the inner housing 14 is secured to the outer housing 12 at a plurality of locations, such that the inner housing 14 remains static relative to the outer housing 12 during operation of the subsea pump 10.

It can additionally be seen, in this example, that the impeller arrangement is divided into two sets 22a, 22b. The orientation of the impellers in the first set 22a is opposite to the orientation of the impellers in the second set 22b, such that the impellers are arranged in a back-to-back configuration. In doing so, some or all of the axial thrust caused by the first set 22a is cancelled or offset by an oppositely directed thrust from the second set 22b of impellers, thereby reducing the magnitude of any unbalanced axial force acting on the drive shaft 20 as a result of the impellers 22.

Figure 2A illustrates an example of a motion sensing arrangement 40 that may be used to detect motion in the subsea pump 10, such as motion of the drive shaft 20 relative to the inner housing 14. The motion sensing arrangement 40 as illustrated may be attached (e.g. fastened, bonded or coupled) to the inner housing 14, and located in proximity to the drive shaft 20 such that the motion sensing arrangement 40 is able to detect motion of the drive shaft 20. The motion sensing arrangement 40 may be used to detect one, or more than one, aspect of motion of the drive shaft 20. For example, the motion sensing arrangement 40 may be used to detect at least one, or all, of rotational, radial and axial movement of the drive shaft 20. The motion sensing arrangement 40 may be used to detect vibration of the drive shaft 20, for example radial and/or axial vibration. The motion sensing arrangement may additionally be configured to detect an indicator used for vibration analysis, for example a once-per-revolution indicator for vibration analysis.

The housing 12 may contain a motor located therein, or may comprise a motor coupled thereto. The motor may comprise a drive arrangement for turning the drive shaft 20, and in some examples a motion sensing arrangement 40 may be positioned so as to detect motion of the drive arrangement of the motor. In this way, the motion sensing arrangement 40 may additionally or alternatively be used to detect motion of a motor.

As illustrated in Figures 2A-B, the motion sensing arrangement 40 has the shape of a partial annulus -here a quarter-annulus shape. In this example, the motion sensing arrangement 40 may be shaped so as to fit around the drive shaft 20, and as such may comprise a radially inner and radially outer surface 44a, 44b, two axial surfaces 46a, 466 and two circumferential surfaces 48a, 48b. This shape of motion sensing arrangement 40 may be particularly beneficial as it may fit easily into a cylindrical or annular recess within the inner housing 14. In particular, having an annular or partial annular shape of motion sensing arrangement 40 may permit the motion sensing arrangement 40 to fit easily in an annulus defined between the drive shaft 20 and the inner housing 14, while also permitting a large surface area of the drive shaft 20 to be monitored. The skilled person will appreciate that other shapes of motion sensing arrangement 40 may be possible, such as a cubic or cuboid shape, or a cylindrical shape.

The shape of the motion sensing arrangement 40 may be defined by a sensor housing 47. The sensor housing 47 may be coupled (e.g. attached, affixed, bonded, or the like) to the inner housing 14 (see Figure 1) using bolts, chemical bonding, snapfits, or any other appropriate means. The sensor housing 47 may be precisely fitted on the inner housing 14 so as to permit the motion sensing arrangement 40 to be installed in the subsea pump 10 in a precise location relative to the drive shaft 20. As such, the distance between the motion sensing arrangement 40 may be known, and therefore reconfiguration of sensors in the motion sensing arrangement 40 after having been fitted to the inner housing 14 may not be necessary. The sensor housing may contain electronic components of the motion sensing arrangement as well as at least partially, or fully, housing sensors of the motion sensing arrangement. The housing may be sealed to both pressure and water. The housing may contain sensors such as temperature sensors, and the temperature sensors may be considered to be part of the motion sensing arrangement. The housing may additionally be sufficiently strong to withstand high pressures associated with subsea and/or downhole locations. For example, the housing 47 may have a minimum thickness so as to be able to withstand the high pressure of subsea/downhole environments. In some examples, the subsea pump 10 may be exposed to pressures in the range of 300 to 1000 bar. In cases where the pump 10 is shut-in, then the pressure may be particularly high (e.g. 1000 bar or higher) and as such the thickness of the housing 47 may be selected based on this requirement. Additionally, any sealing involved in the housing may be selected based on this requirement.

The motion sensing arrangement 40 may comprise one, or a number, of sensors for detecting motion (e.g. a motion sensor or motion sensors such as an eddy-current sensor, capacitive sensor and/or an optical sensor). In figure 2, the motion sensing arrangement comprises three sensors 42a, 42b, 42c. One sensor, hereinafter referred to as an axial sensor 42a, is located on one of the axial surfaces 46a of the motion sensing arrangement 40, while two sensors 42b, 42cc (hereinafter referred to as radial sensors) are located on the inner radial surface 44a of the motion sensing arrangement 40. Each of the sensors 42a-c may be of the same type, or at least one or all of the sensors 42a-c may be of differing types. In some examples, the sensors may also transmit a signal, the transmitted signal being used to detect motion. For example, in this example, the sensors 42a-c may transmit an electromagnetic field or a beam of electromagnetic radiation, and may then sense an electromagnetic return signal, with changes in the electromagnetic return signal indicating motion of an object. In one example, at least one or all of the sensors 42a-c may be motion sensors such as optical sensors, eddy-current sensors and/or capacitive sensors. In one example, at least one or all of the sensors may be in the form of proximity probes. In another example, some sensors may be proximity probes, while other sensors may be capacity probes.

The sensor 42a located on the axial surface 46a of the motion sensing arrangement 40 may be considered to be an axial sensor 42a. When the motion sensing arrangement 40 is positioned in proximity to the drive shaft 20, the axial sensor 42 may be able to be used to sense at least one of axial and rotational movement of the drive shaft 20. The sensors 42b, 42c that are located on the radially inner surface 44a of the motion sensing arrangement 40 may be considered to be radial sensors 42b, 42c. The radial sensors may be able to be used to sense rotational movement of the drive shaft 20. In this example, the radial sensors 42b, 42c may be offset by an angle, and positioned on the inner axial surface 44a. In this example, the angle of offset is approximately 90 degrees, which may be a preferable configuration for sensing radial movement of the drive shaft 20, as it may provide information of radial movement of the drive shaft 20 in two directions (e.g. in the direction of an x-axis and in the direction of a y-axis). However, the skilled person will understand that other angles of offset may be possible if desired.

In this example, each of the sensors 42a-c are used to sense or detect movement of a motion indicator. The motion indicator may simply be a surface of the drive shaft 20. In some examples, the motion indicator may comprise a surface feature such as a depression and/or a protrusion, or may comprise a plurality of surface features such as a plurality of depressions and/or protrusions. The surface feature or features may be located on the drive shaft, in some examples.

Although not shown in the Figures, the rotor may comprise a radially extending protrusion therefrom, for example a radially extending protrusion from the drive shaft 20. The radially extending protrusion may be in the form of a disc, or a partial disc, extending from the drive shaft 20, and the disc may be axially aligned with the drive shaft 20. The radially extending protrusion may be or form part of the motion indicator. For example, the motion indicator may be formed by the combination of the drive shaft (or a portion thereof) as well as the radially extending protrusion.

The motion sensing arrangement 40 may be positioned in the inner housing 14 radially outwardly of the drive shaft 20. Where the motion sensing arrangement 40 has an annular or partially annular shape, then the axis of the motion sensing arrangement 40 may be aligned with the axis of the drive shaft 20, such that the radial surfaces 44a, 44b run generally parallel to the outer surface of the drive shaft 20. Each of the sensors may be positioned adjacent and/or in close proximity to a surface of the motion indictor. For instance, a sensing surface of each of the sensors 42a-c may be positioned parallel to a surface of the motion indicator. Each of the radial sensors 42b,c may be positioned parallel to a surface of motion indicator on the drive shaft, while the axial sensor 42a may be positioned parallel to a surface of the motion indicated on the radially extending protrusion. In some examples, the axial sensor 42a may be able to measure the axial movement of the rotor (e.g. relating to the axial position of the rotor, or to axial vibration of the rotor) by sensing a change in the distance between the sensor 42a, which may be coupled to the inner housing 14 via the motion sensing arrangement 40. The axial sensor 42a may also be able to sense rotational movement of the rotor by sensing rotational movement of the radially extending protrusion, which may be in the form of a disc. The radially extending protrusion may comprise a surface feature, or a plurality of surface features thereon. The surface features may be in the form of one or more protrusions such as ribs, nipples and/or grooves, and/or may be in the form of one or more recesses, which may be of varying depth, height and/or width. In such an example, the radially extending protrusion may be considered to be a coded target disc, the rotation of which may be detected by the axial sensor 42a. As the rotor rotates, so too will the radially extending protrusion, and the axial sensor 42a is able to sense movement of the radially extending protrusion. Where there are surface features comprised on or defined by the radially extending protrusion, the axial sensor 42a may be able to detect differences in the geometry of each of these surfaces as they move, which may provide additional detail to a user regarding the nature of the rotational and/or axial movement of the rotor.

The radial sensors 42b, 42c may be configured to detect rotational movement of the rotor by detecting rotational movement of the drive shaft 20. The drive shaft may comprise on or a plurality of surface features (e.g. one or a plurality of protrusions thereof and/or one or a plurality of recesses) thereon, and the radial sensors 42b, 42c may be able to detect movement of the surface features on the drive shaft 20. The surface features may comprise protrusions and or recesses of different sizes (e.g. width, height or depth). As the drive shaft 20 rotates, the radial sensors may be able to detect movement, as well as differences in the sizes of each of the surface features, which may provide additional detail to a user regarding the nature of the rotation of the drive shaft 20, and therefore the rotor.

In addition, the radial sensors 42b, 42c may be able to detect radial movement (e.g. radial vibration) of the rotor by detecting radial movement of the drive shaft 20. Similar to as previously described, the surface features may assist the radial sensors 42b, 42c to provide information relating to the radial movement of the drive shaft relative to the interior housing 14 as a result of differing geometry of the surface features.

In use, there may be several motion sensing arrangements 40 located inside the interior housing 40 and providing information regarding the movement of the rotor in at least one, more than one, or all of rotational, axial and radial movement. In one example, there may be a sensing arrangement 40 located at or adjacent each of the bearing arrangements 24a-d (see Figure 1). The sensors may then be used to provide a user with information regarding the motion of the rotor in the subsea pump 10, and therefore provide an indication on the functioning of the subsea pump without the need for a physical inspection of the pump 10.

Although not explicitly shown in Figure 2A, the motion sensing arrangement 40 may comprise at least one pressure and/or temperature sensor, each of which may be located on an external surface thereof. The pressure and temperature sensor or sensors may provide a user with information regarding the pressure and temperature surrounding the motion sensing arrangement 40, which may be indicative of the pressure inside the subsea pump 10, thereby providing information on the operating condition of the subsea pump.

In addition to the sensors 42a-c, the motion sensing arrangement 40 may comprise a connection point 45 for the connection of cabling for power and/or communications purposes. For example, the connection point 45 may be used to provide electrical, and optionally fibre optic, cabling for the purposes of providing power to the motion sensing arrangement, as well as for communicating with the motion sensing arrangement 40 and may be used to relay signals from the sensors 42a-c to a location external to the motion sensing arrangement 40, e.g. to be sent to a user via cabling, or via wireless communication.

It may be necessary for the sensor housing 47 to comprise an aperture, or a number of apertures therein. For example, the connection point 45 may require the housing to have an aperture therein, as may each of the sensors 42a-c. The sensor housing 47 may comprise a sealing arrangement configured to prevent ingress of fluid (e.g. water or hydrocarbons) therein. In each the case of each aperture in the sensor housing 47, there may be a seal, or a plurality of seals, for this purpose, or in some examples the housing may be hermetically welded. For example, each aperture may comprise at least one 0-ring style static seal extending around the periphery thereof to prevent ingress of fluid therethrough.

Illustrated in Figure 2B is a side view of two motion sensing arrangements 40. As can be seen, each of the two motion sensing arrangements 40 are arranged to form a central void 50. The rotor (e.g. the drive shaft of the rotor) may extend through the central void 50, such that each of the motion sensing arrangement 40 are situated adjacent to the drive shaft of the rotor. In this arrangement, the inner radial surface 44a is located closer to the drive shaft than the outer radial surface 44b, and the surface of the inner radial surface 44a may extend substantially parallel to an outer surface of the drive shaft of the rotor. In addition, a cable is connected to each of the connection points 45 each motion sensing arrangement 40. In this example, both of the motion sensing arrangements 40 is located in a plane extending perpendicularly to the central axis of a drive shaft extending through the void 50, such that both of the motion sensing arrangements 40 have the same axial location relative to the axis of the drive shaft of the rotor. However, the skilled person will realise that other arrangement may be possible. For example each of the two motion sensing arrangements 40 may be located at different axial locations along the length of the drive shaft of the rotor.

The arrangement of Figure 2B may be used to provide a degree of redundancy of instrumentation in the subsea pump 10. For example, two motion sensing arrangements 40 may be placed adjacent each bearing arrangement 24a-d, with the intention of using one of each pairs of motion sensing arrangements 40. In the situation that one of the motion sensing arrangements is damaged or inoperable, then the other of the motion sensing arrangements may be used. In such a scenario, then having a motion sensing arrangement 40 that has a partial annulus shape may be beneficial, as it may allow multiple motion sensing arrangements 40 to be placed at a single axial location relative to the drive shaft of the rotor, as is shown in Figure 2B. As can be seen the motion sensing arrangements 40 extend at an angle of between 90 and 180 degrees in an annulus external to a drive shaft.

Figures 3A-C illustrate various readings that may be obtained from the motion sensing arrangements 40. Figure 3A illustrates a graph 60 showing the proximity of a motion indicator to a motion sensing arrangement 40 (e.g. to a sensor of a motion sensing arrangement). The X-axis 61 indicates time in seconds, while the Y-axis 63 indicates the proximity of the motion indicator to the motion sensing arrangement. As previously described, the motion indicator may comprise a surface feature, or a number of surface features thereon. In this example, the surface features cause the proximity of the motion indicator relative to the motion sensing arrangement 40 to vary as the rotor is rotated, resulting in a predictable oscillation of the proximity of the motion indicator to the motion sensing arrangement 40 and a number of peaks 62 and troughs 64 appearing on the graph 60. This feature may be useful, as it may indicated to a reader of the graph 60 that the rotor is turning. In addition, when the proximity of the motion sensing arrangement is measured relative to time, then the rotational velocity of the rotor may be ascertained by measuring the frequency of the oscillations on the graph 60, and comparing this to an expected number of oscillations for one revolution of the rotor, based on the number of surface features that are present on the motion indicator.

In this example, the motion indicator comprises two surface features that are greater in magnitude compared to the other surface features. In addition, of these two surface features, a first 64a is larger than a second 64b, resulting in there being two larger oscillations on the graph 60 for every rotation of the drive shaft. The surface features on the motion indicator may be in the form of either depressions or protrusions, resulting in a greater increase or reduction in the distance between the motion indicator and the motion sensing arrangement 40. A user, knowing the configuration of the surface features on the motion indicator, will then be able to identify whether the rotor is turning in the correct direction based on the position of the first larger oscillation 64a and the second smaller oscillation 64b.

For example, if it is expected that the first larger oscillation 64a should appear first, followed by the second smaller oscillation 64b when the rotor is turning in the correct direction, then the user will be able to easily identify this on the graph 60, and identify that the rotor is turning in the correct direction. Should the user see a result that is unexpected, then this allows action to be taken before any damage is caused to the pump, or to any other components. The action may be in the form of action by a user-e.g. a manual reduction in the operating speed of the rotor -or automatic action taken by a control system that is configured to trigger a reduction or arrest of rotational speed of the rotor in the event of an unexpected result. In the case of this example, such rotational movement may be measured by the axial and/or radial sensors of the motion sensing arrangement 40.

Figure 3B illustrates a further graph 70 that may be obtained based on the readings of the motion sensing arrangement 60. In this example, radial movement of the rotor is measured, and the change in radial position as the shaft rotates may be plotted as a line 72, 74 on the upper and lower graphs. The different graphs may relate to the radial movement of at different axial locations along the drive shaft. As such, a large difference between the readings on each graph may indicate to a user that the drive shaft is bending during use, which may be detrimental to its function. In addition, the graph 70 may be used to measure the radial vibration of the drive shaft. In cases where there is a large degree of radial movement of the drive shaft, then the user may be able to identify a large degree of radial vibration of the drive shaft, which may be detrimental to the functioning of the drive shaft, or may indicate that a repair of the drive shaft is necessary -for example it may indicate that a bearing has broken, seized or worn, or that a rotor or drive shaft has become bent or fractured. Worn, broken or seized bearings, and bend or fractured drive shafts, may occur as a result of rotordynamic vibration issues, which may be identified by taking measurements of radial movement/vibration of the drive shaft. Such measurements may be produced by the radial sensors 24b-c of the motion sensing arrangement 40.

The graph 80 of Figure 3C illustrates axial movement of the drive shaft in the interior housing 14 against force on a thrust bearing in the internal housing 14. Axial movement of the drive shaft of the rotor may be caused by an unbalanced axial force acting on the rotor as a result of rotation thereof, for example as a result of rotation of an impeller attached thereto.

In the graph illustrated, a broken line 82 is illustrated that shows a general thrust bearing force -displacement curve. This curve illustrates the force produced on a thrust bearing caused by an axial displacement and axial force acting on the rotor, for example the drive shaft of the rotor. Also illustrated are measurements which may be taken from a subsea pump of axial displacement plotted against a thrust bearing force on a thrust bearing. A motion sensing arrangement 40 as previously described may be used to detect at least the axial displacement of the rotor for the plotting of graph 80. In this graph the Y-axis 84 describes the axial displacement of the thrust bearing inn micrometres, while the X-axis describes the thrust bearing force in kilo-Newtons. An upper bearing limit 88 and lower bearing limit 90 are also illustrated in broken outline. These limits indicate the maximum displacement of the rotor before damage would likely be caused to the thrust bearing due to excessive force acting thereon. A user may then be able to use the value of axial displacement of the rotor provided by the motion sensing arrangement 40 to check whether the subsea pump is operating in an acceptable condition, or whether operation of the subsea pump is likely to be causing damage to components thereof. Additionally or alternatively, the value of axial displacement provided in the graph of Figure 3C may be used to evaluate dynamic axial motion of the rotor (e.g. motion of the rotor over time). In some cases, dynamic axial movement of the rotor may be in the form of resonant axial movements or vibrations, which may be detrimental to the operation of the pump, and therefore may be useful to identify for a user. Such motion may be identified on the graph of Figure 3C.

Claims

CLAIMS1. A subsea pump, comprising: a housing; a rotor located inside the housing, a bearing arrangement being located between the rotor and the housing to facilitate rotation of the rotor therein, and the rotor comprising a motion indicator; a motion sensing arrangement comprising a pressure sealed housing and at least one sensor, the motion sensing arrangement being located inside the housing and in communication with the motion indicator, and the motion sensing arrangement being configured to detect movement of the motion indicator.
2. The subsea pump of claim 1, wherein the motion indicator is in the form of a radially extending protrusion from the rotor.
3. The subsea pump of claim 1 or 2, wherein the motion indicator is or comprises the drive shaft of the rotor.
4. The subsea pump of any preceding claim, wherein the motion sensing arrangement is configured to detect at least one of rotational, axial and radial movement of the rotor.
5. The subsea pump of any preceding claim, wherein the motion sensing arrangement is configured to detect vibration of the rotor.
6. The subsea pump of any preceding claim, wherein the at least one sensor is an optical sensor, a capacitive sensor or an eddy-current sensor.
7. The subsea pump of any preceding claim, wherein the motion sensing arrangement comprises at least one axially oriented motion sensor, and at least two radially oriented motion sensors.
8. The subsea pump of claim 7, wherein the at least two radially oriented motion sensors are offset by 90 degrees.
9. The subsea pump of any preceding claim, wherein the motion indicator is in the form of a disc extending from the rotor and axially aligned with the rotor.
10. The subsea pump of claim 9, wherein the disc is a coded target disc and comprises at least two surface features on an axial surface thereof, and wherein the motion sensing arrangement is configured to detect rotational movement of the at least two surface features as a result of rotation of the rotor.
11. The subsea pump of claim 10, wherein a first of the at least two surface features has a different geometry to a second of the at least two surface features, and the motion sensing arrangement is configured to detect the circumferential direction of rotation of the at least two surface features.
12. The subsea pump of any preceding claim, wherein the motion sensing arrangement is configured to detect at least one of axial movement of the rotor, rotational velocity of the rotor, and a once-per-revolution indicator of vibration analysis.
13. The subsea pump of any preceding claim, wherein the pressure-sealed housing of the motion sensing arrangement is has a partial annulus shape.
14. The subsea pump of claim 13, wherein the partial annulus shape is a quarter-annulus.
15. The subsea pump of claim 14, wherein the motion sensing arrangement comprises at least three sensors, and wherein two sensors are located on a radially inner surface of the quarter-annulus pressure sealed housing, and one sensor is located on an axial surface of the quarter-annulus pressure sealed housing.
16. The subsea pump of any preceding claim, wherein the pressure sealed housing of the motion sensing arrangement is coupled to the housing at a predetermined distance from the motion indicator.
17. The subsea pump of any preceding claim, comprising a motor for turning the rotor, the motor additionally comprising a motion indicator, and the motion of the rotor being detectable by the motion sensing arrangement.
18. A method for determining motion of a rotor in a subsea pump, comprising: providing a subsea pump in a subsea location, the subsea pump comprising a pressure-sealed motion sensing arrangement, and a motor comprising a motion indicator; operating the subsea pump to effect rotation of the rotor therein; using the motion sensing arrangement to detect movement of the rotor.
19. The method of claim 18, comprising determining the direction of rotation of the rotor by detecting the motion of a first surface feature and a second surface feature located on the motion indicator, the first surface feature having a different geometry to the second surface feature.
20. The method according to claim 18 or 19, comprising locating the pressure-sealed motion sensing arrangement in an annulus surrounding the rotor, the pressure-sealed motion sensing arrangement having a partial annulus shape.
21. The method according to claim 20, comprising detecting at least one of rotational movement and axial movement of the rotor via a motion sensor located on an axial surface of the pressure-sealed motion sensing arrangement.
22. The method according to claim 20 or 21, comprising detecting at radial movement of the rotor via at least two motion sensors located on an inner radial surface of the pressure-sealed motion sensing arrangement.
23. The method according to any of claims 18 to 22, comprising installing the pressure sealed motion sensing arrangement at a predetermined distance from the motion indicator, without the requirement for readjusting said predetermined distance before operation of the pump.