The invention relates to a sensor assembly including a vibration sensor, and in particular to a thermowell sensor assembly for use in industrial process fluid monitoring systems for the monitoring of fluids flowing in conduits. The invention further relates to a conduit for a process fluid having one or more such sensor assemblies positioned for the monitoring of fluids flowing within. Industrial process sensor assemblies are widely used to sense various characteristics of industrial process fluids flowing through a conduit. Such sensor assemblies are typically provided in association with suitable data transmission systems to transmit information about the fluid characteristics to a control or monitoring system remotely located from the sensor.

Sensor assemblies for sensing fluid temperatures of a process fluid flowing in a conduit may typically include at least one temperature sensor in a housing known as a thermowell. Sensor assemblies for use in industrial process fluid monitoring systems may sense a variety of process parameters, usually including at least pressure, temperature, or flow rate. A typical thermowell comprises a hollow tubular body projecting through an aperture in a conduit wall into a conduit bore and into a fluid flow therein. This projecting body of the thermowell may be tapered or stepped to a narrower diameter at a distal end. The thermowell is typically metallic, and is for example machined from bar stock and gun drilled to define a well cavity in the thermowell projecting body.

One or more temperature sensors project into the well cavity so that the well cavity houses the temperature sensors so as to shield them from direct contact with the often harsh fluid environment and for example from the pressure, flow-induced forces, and chemical effects of the process fluid. The tubular wall of the thermowell projecting body facilitates heat transfer between the fluid and the temperature sensors to ensure effective temperature measurement. The assembly typically comprises also an external housing portion so configured that when the thermowell sensor assembly is in situ on a pipe the hollow tubular body projects into the conduit bore and the external housing portion is disposed externally of the conduit and defines a housing volume continuous with the well cavity. Suitable processing electronics to process the data from the one or more temperature sensors within the well cavity is for example contained in the external housing portion, which may also include means to transmit the processed data externally of the thermowell sensor assembly. The thermowell is typically mounted into the process stream by way of a threaded, welded, sanitary cap or flanged connection at an aperture in the conduit wall.

Thermowells find application in a range of industrial process fluid monitoring systems and in particular for monitoring of oil and gas pipelines. The present invention is discussed herein in that context by way of example, but is not limited to such applications.

The continued structural integrity of thermowells during operation is critical. A thermowell inlet represents an opening in a conduit wall, so damage to the thermowell may compromise this inlet and allow process fluid leakage. Moreover damaged portions that detach into the flow can cause problems downstream. A principal cause of damage to thermowells is vibration damage to the projecting body consequent upon the fluid flow. Accordingly the inclusion of vibration sensors in a thermowell sensor assembly in an attempt to monitor vibration behaviour over time is known. For example, US2014269828A1 describes a known thermowell in which a process transducer such as a temperature sensor is disposed within a thermowell and configured to produce a first sensor signal including at least a temperature signal, and an unpowered vibration sensor is provided on the external extension of the thermowell with the intention of producing a signal reflecting vibration of the thermowell. A problem with the sensor solution suggested by US2014269828A1 and similar prior art devices that provide vibration sensing on the flange or other connection or on an outward extension or external housing of the thermowell is that the vibration of the part being sensed is only indirectly coupled to the vibration of the thermowell body itself as it projects into the fluid flow. Various flow effects can adversely affect the thermowell projecting body mechanically. For example impingement of process flow on a thermowell projecting body may create turbulence in the process fluid via vortex shedding that can cause especially severe mechanical stresses in the thermowell projecting body itself. Vibration monitoring on the flange or other connection or of the external housing or other outward extension of the thermowell does not measure this directly, but instead requires complex signal processing of the indirectly measured vibration, such as is suggested in US2014269828A1 , to obtain a representative indication of the specific conditions at and experience by the thermowell projecting body. The invention seeks to obtain vibration data that is more closely coupled to the vibration of the thermowell projecting body itself, in particular to reflect vortex shedding effects at and about the thermowell projecting body, and thus to rely less on complex signal processing of a less directly coupled vibration signal. In accordance with the invention in a first aspect, there is provided a sensor assembly comprising:

a thermowell projecting portion having a wall defining a well cavity;

at least one temperature sensor positioned to measure the temperature of the inside of the well cavity;

at least one accelerometer sensor positioned inside the well cavity.

In accordance with the invention in a second more complete aspect, the sensor assembly of the first aspect is provided in-situ in a conduit for a process fluid. In accordance with this aspect, a conduit for a process fluid comprises:

an elongate conduit wall surroundingly defining a conduit flow channel;

a sensor assembly comprising:

a thermowell projecting portion having a wall defining a well cavity;

at least one temperature sensor positioned to measure the temperature of the inside of the well cavity;

at least one accelerometer sensor positioned inside the well cavity;

wherein the sensor assembly is fitted to an aperture in the conduit wall such that the thermowell projecting portion extends into the conduit flow channel.

In practice, multiple sensor assemblies will typically be provided arrayed along the length of an elongate conduit to monitor process fluid conditions along the length. In familiar manner, the sensor assembly will typically more completely comprise an external housing portion that defines a housing volume continuous with the well cavity. In use when the sensor assembly is in situ on a pipe the thermowell projecting portion projects into a conduit defined by the bore of the pipe and thus into a process fluid within the conduit and the external housing portion is disposed externally of the conduit and defines a housing volume continuous with the well cavity. The thermowell projecting portion defines a well cavity, in that it comprises a wall, the internal surface of which surrounds and defines the volume of the well cavity. For example it comprises a tubular wall with a closed tip at a distal end. The tubular wall may define a tube of reducing diameter towards the tip, for example being tapered or stepped. The thermowell projecting portion projects into the process fluid in such manner that the closed well cavity is protected environmentally from the process fluid but such that the process fluid transfers heat to the thermowell wall, which in turn transfer heats to the well cavity for detection by the temperature sensor. In particular the thermowell projecting portion projects into the process fluid in such manner that the external surface of the wall is in contact with the process flow and the wall is formed of a thermally conductive material so as to conduct heat from the process flow within the conduit to the well cavity.

The at least one temperature sensor is positioned to measure the temperature of the inside of the well cavity; most conveniently this is effected in that the at least one temperature sensor is positioned inside the well cavity. Additional temperature sensors or other condition sensors may be provided within or otherwise in sensory association with the well cavity.

The invention is characterised in that at least one accelerometer sensor is positioned inside the well cavity itself. The accelerometer sensor may for example be fixedly positioned in fixed mechanical association with and for example on the internal wall surface of the well cavity. The accelerometer sensor may for example be positioned at least a major part of the distance distally into the well cavity and for example essentially towards or at a distal end of the well cavity. The at least one accelerometer sensor is thus disposed to sense vibration of the thermowell projecting portion directly. Various flow effects can create adverse vibration effects in the thermowell projecting body. For example impingement of process flow on a thermowell projecting body may create turbulence in the process fluid via vortex shedding that can cause especially severe mechanical stresses in the thermowell projecting portion. The invention can measure these effects directly.

This can be contrasted with prior art systems that provide vibration sensing on the flange or other connection or on an outward extension or external housing of the thermowell where the vibration of the part being sensed is only indirectly coupled to the vibration of the thermowell projecting portion itself as it projects into the fluid flow. Vibration monitoring on the flange or other connection or of the external housing or other outward extension of the thermowell requires complex signal processing of the indirectly measured vibration, such as is suggested in US2014269828A1 , to obtain a representative indication of the specific conditions at and experience by the thermowell projecting body. The invention does not require such complex signal processing as the directly measured data is inherently more representative of the condition to be monitored. In a preferred case the sensor assembly includes at least one accelerometer sensor positioned so as to be aligned in use in-line to a fluid flow to be measured.

In consequence the sensor assembly of the first aspect of the invention is preferably configured so as to be orientated in an in-use direction when inserted into an aperture in an elongate conduit that is such that at least one accelerometer sensor within the well cavity is aligned in a conduit elongate direction corresponding to a direction in-line to a fluid flow to be measured in the conduit.

In consequence the conduit of the second aspect of the invention is fitted with a sensor assembly comprising:

a thermowell projecting portion having an internal wall defining a well cavity;

at least one temperature sensor positioned inside the well cavity;

at least one accelerometer sensor positioned inside the well cavity;

wherein the sensor assembly is fitted in such orientation that at least one accelerometer sensor within the well cavity is aligned in a conduit elongate direction. Preferably the thermowell includes at least two accelerometer sensors positioned so as to be aligned in use in-line to a fluid flow to be measured. The provision of two inline accelerometer sensors, for example spaced apart within the well cavity, for example spaced apart along the well cavity, for example spaced apart along the tubular wall of the thermowell projecting portion, gives a particularly effective direct measurement of strain experienced by the thermowell projecting portion during use.

Additional accelerometer sensors may be positioned so as to be aligned in use in other directions to an in-line flow direction.

In a possible arrangement the thermowell includes at least two accelerometer sensors having non-coincidental and for example orthogonal sensor directions. For example at least one and more preferably at least two accelerometer sensors may be provided having a sensor direction aligned in use in-line to a fluid flow to be measured and at least one further accelerometer sensor may be provided aligned in use transverse to a fluid flow to be measured.

The housing volume conveniently houses data collection, processing and control electronics, and for example at least a data collection module to collect data and for example also a processor to process the data from the one or more temperature sensors, and if applicable other condition sensors, and from the one or more accelerometer sensors. However the processing and diagnostic algorithms required to gain meaningful vibration data are simplified as the raw measured data is inherently more representative of the condition being monitored.

A data transmission connection and for example a wired data transmission connection is preferably provided between each sensor in the well cavity and the processor.

A process transmitter may be provided within the housing volume to transmit data collected by the processor externally of the sensor and for example to an external central processing unit or external data store or external data display. The process transmitter may be a wired or wireless transmitter. The sensor assembly conveniently comprises an engagement portion for engagement into an aperture in a conduit wall. An engagement portion is for example structured to effect a threaded, bolted, welded, flanged or sanitary cap connection to and into a conduit wall. An engagement portion is for example formed by a part of the thermowell projecting portion proximal to the aperture in the conduit wall in use and/ or by a part of the external housing portion proximal to the aperture in the conduit wall in use and/ or by a separate engagement module.

The sensor assembly may comprise a modular structure of a thermowell projecting module and an engagement module and an external housing module adapted to be assembled together in situ into an aperture in a conduit wall in a fluidly sealed manner to provide a sensor assembly in accordance with the invention. Alternatively a sensor assembly may comprise an integrally formed structure having a thermowell projecting part and an engagement part and an external housing module part adapted to be inserted into an aperture in a conduit wall in a fluidly sealed manner.

A temperature sensor for use in an assembly of the invention is for example a temperature transducer such as a thermocouple or a resistance temperature detector.

The temperature sensor projects into the well cavity, and is provided with a data connection and for example a wired data connection to a data collection module and for example to a data processor externally of the well cavity. The temperature sensor preferably projects into the well cavity for a major part of the length of the well cavity, and for example essentially towards or at a distal end of the well cavity.

The temperature sensor is for example in contact with an internal wall of the thermowell projecting portion, for example towards a distal end thereof and for example at a tip portion thereof.

The sensor assembly of the first aspect of the invention comprises in familiar manner a thermowell including a thermowell projecting portion that projects in use into a process fluid stream. In accordance with the second aspect of the invention, the thermowell is mounted into the process fluid stream by means of a suitable connection with, over and to close an aperture in the conduit wall.

The invention is distinctly characterised by the provision of one or more accelerometer sensors within the well cavity, to measure more effectively and directly the deflection of the thermowell projecting portion in-stream. Other features of the thermowell and of the thermowell projecting portion will be familiar and can be readily inferred from known thermowell principles. A thermowell for example comprises a tubular structure mountable to project through an aperture in the conduit wall into a process fluid stream, and closed at the distal end to define a well cavity containing the sensors. The tubular structure preferably has a circular cross-section. The tubular structure may have a reducing cross- section in a distal direction, for example having a tapering or stepped or stepped and tapered profile.

At least the thermowell projecting portion is typically fabricated from a good thermal conductor and for example metal, and for example from a solid bar stock into which a suitable bore is drilled, and for example gun-drilled, to define a well cavity. With the thermowell projecting portion in-situ in the process flow of a conduit, the process fluid transfers heat via the wall of the projecting portion to the temperature sensors contained within the well. Good conductivity is therefore required. A metallic material is preferred for its combination of thermal conductivity and mechanical strength.

The sensor assembly is adapted to be mounted onto and close an aperture in a conduit wall such that the projecting portion projects into the conduit flow channel. The sensor assembly preferably further comprises a connecting portion, for example as part of the thermowell, which may be a suitable known connection such as a threaded, welded, sanitary cap or flanged connection. In a particular preferred embodiment, the sensor assembly of the first aspect of the invention includes a flanged connecting portion.

Thus, in a preferred embodiment, the sensor assembly of the first aspect in the invention includes at least a connecting portion, a thermowell projecting portion containing at least a temperature sensor and one or more vibration sensors in the form of accelerometer sensors, and an external housing portion. Each of these portions may be formed integrally with one, other or both of the other named portions, or the three portions may be provided in modular form for assembly in-situ. Further components/modules/portions may be defined as required.

Each accelerometer sensor is for example unpowered, and is for example a direct effect transducer. Suitable transducers include piezoelectric transducers. The invention will now be described by way of example only with reference to the accompanying drawings, in which:

figure 1 shows in cross-section a portion of process fluid pipeline conduit with a sensor assembly in accordance with an embodiment of the invention in-situ;

figure 2 shows a plurality of sensor assemblies arrayed along a process fluid pipeline conduit.

As illustrated in the figures, a cylindrical pipeline conduit wall 1 defines a flow channel 3 for a process fluid. In use, the process fluid flows generally in a pipe elongate direction F, The representation in figure 1 shows a section transverse to this flow direction F.

The pipeline may be for example an elongate conduit to carry a process fluid such as a recovered or post-processed hydrocarbon in gas or liquid form. The wall 1 comprises an elongate conduit wall defining the conduit flow channel 3. The wall is of any suitable pipeline material, such as structural steel.

An apertured portion 5 in the pipeline wall 1 receives a sensor assembly in accordance with an embodiment of the first aspect of the invention, generally described as including a thermowell projecting portion 7, an external housing portion 9, and a connecting portion 8.

The thermowell projecting portion 7 includes a thermowell 12 with a thermowell wall that forms a protective body defining surroundingly a well cavity 13 and projecting into the process flow. In figure 1 , the representation is purely schematic and not to scale. In practice, the sensor assembly will be smaller relative to a typical pipeline conduit, and a projecting portion will project considerably less into the flow. Generally speaking, a projection of just a few percent of the diameter, for example 3 to 10 percent, is considered sufficient to get a realistic measurement. In the embodiment the thermowell 12 has a cylindrical form with a tapered end portion 14 and a closed tip 15. The external surface of the wall of the thermowell body is in contact in use with the process flow within the conduit 3. The internal surface of the wall is in thermal contact with the well cavity 13. The wall of the thermowell 12 is formed from metallic material with high thermal conductance, such as brass or stainless steel, so as to efficiently conduct heat from the process flow within the conduit 3 to the well cavity 13.

The well cavity 13 contains a temperature transducer 16 projecting downwardly into the well cavity and thus capable of producing a temperature signal reflecting a temperature or change in temperature in the process flow as thermal energy transfers through the wall of the thermowell 12. The temperature transducer may for instance be a thermocouple or resistive temperature detector. The thermowell 12 protects this temperature transducer environmentally in familiar manner. In the embodiment a temperature transducer is shown projecting directly into the well cavity, but alternative arrangements may be envisaged where the temperature within the well cavity is measure by a temperature sensor suitably positioned elsewhere in the assembly.

The invention is distinctly characterised by the provision of at least one accelerometer sensor positioned inside the well cavity. In the embodiment two piezoelectric vibration transducers 18 are shown spaced apart within the cavity defined by the inner wall of the thermowell body and orientated so as to be in-line in the process flow direction of a fluid flow to be measured, and thereby to measure deflection of the thermowell body in an in-line direction directly. It is this direct measurement that is the key to the solution offered by the invention. This can be contrasted with prior art systems where vibration is for example measured at the flange, requiring complex analysis for example of resonant frequencies and the like in order to get data on the deformation regime experienced by the projecting portion, and hence to get meaningful data by means of which failure may be predicted. The arrangement of the invention measures such data more directly. In practice, the two piezoelectric vibration transducers 18 will most conveniently be contained within a suitable carrier head housing, positioned towards the distal end of the thermowell cavity and for example as close to the tip as possible. The Figure 1 illustration omits this for clarity.

Other arrangements of accelerometer sensor may be envisaged in accordance with the principles of the invention. Further sensors may have different alignment directions to give further information. In a particularly preferred case at least one further sensor may have an orthogonal direction to at least one first sensor. Such a modification to the Figure 1 embodiment is shown in Inset A, in which the two piezoelectric vibration transducers 18 orientated so as to be in-line in use the process flow direction, and thereby to measure deflection of the thermowell body in an in-line direction are complemented by a further piezoelectric vibration transducer 18a orientated so as to be aligned in use transverse to a fluid flow to be measured. Again, a suitable carrier head housing, omitted for clarity, will typically contain the vibration transducers 18, 18a.

In the example embodiments each sensor is an unpowered direct effect piezoelectric transducer.

Solutions incorporating vibration transducers into the well cavity have not always been favoured, since it has been conventional to provide a well cavity bore that relatively closely surrounds the temperature probe, for example being only of marginally larger diameter. Accordingly, in accordance with the invention, accelerometer transducers which are of low profile, and for example the flat low profile piezoelectric transducers of the illustrated embodiment, are particularly preferred. The flange connection 20 effects a sealing engagement around the apertured portion 5 of the wall 1 to hold the projecting portion 7 sealingly in place such that the projecting portion projects into the process flow.

The third part of the sensor assembly is the external housing portion 9 comprising a housing 22 defining a housing volume 23 which is continuous with the well cavity 13 but which sits externally of the process pipeline 1. Wired data connections 25, 26 respectively connect the temperature probe 16 and the piezoelectric transducers 18 to a central processor 28 which includes data collection and processing electronics. Again, the general principles of such a component of a sensor assembly in accordance with the invention will be understood with reference to existing thermowell design.

A wireless transmitter 30 is provided to effect wireless connection with an external control system and/or to enable data to be downloaded to an external data store for further processing. Such further processing may include for example familiar diagnostic testing based on the sensed vibration, for example to warn a user when vibration levels have exceeded predetermined safety levels. It is an advantage of the invention that these vibrations levels are being measured more directly than is the case with prior art system, since they are being measured by the provision of accelerometer sensors such as the piezoelectric transducers 18 mounted directly on the wall of the thermowell projecting portion.

Figure 2 illustrates how a plurality of sensor assemblies in accordance with the invention, such as those illustrated in figure 1 , may be disposed along an elongate pipeline conduit to provide data along the flow direction.

An elongate pipeline conduit wall 1 is shown in which the bore of the pipe defines a conduit 3 for a process fluid flow in a flow direction F. An array of sensor assemblies 2 is provided along the conduit wall. Each sensor assembly 2 is fixed into an aperture 5 in the pipeline conduit wall by a connecting portion 8 such that a thermowell projecting portion 7 extends into the conduit flow channel and a housing portion 9 sits externally of the conduit.

In the preferred case sensor assemblies as illustrated in figure 1 are used and are fitted in such orientation that the accelerometer sensors 18 are aligned in a conduit elongate direction so as to be in-line in use the process flow direction, and thereby to measure deflection of the thermowell body in an in-line direction. Where these sensors are complemented by a further orthogonal piezoelectric vibration transducer 18a this is thereby aligned transverse to a conduit elongate direction. Suitable data transmission systems (not shown) may then be used to transmit information about the fluid characteristics from successive sensors progressively along the pipeline, and hence about conditions progressively along the pipeline, to a control or monitoring system remotely located from the sensor array. Thus a solution is offered that enables improved flow condition monitoring and control along the length of an elongate conduit to carry a process fluid such as a recovered or post- processed hydrocarbon in gas or liquid form.