WO2018178649A1

WO2018178649A1 - Fluid-monitoring probe apparatus and system

Info

Publication number: WO2018178649A1
Application number: PCT/GB2018/050793
Authority: WO
Inventors: Jeremy Knight
Original assignee: Jdse Limited
Priority date: 2017-03-27
Filing date: 2018-03-27
Publication date: 2018-10-04
Also published as: GB201704856D0; GB2560917A

Abstract

A fluid monitoring system (10) for the monitoring of liquid natural gas in a portion of pipe section (12), via insertion of a fluid-monitoring probe apparatus (14) into an access port (16). The fluid-monitoring probe apparatus (14) comprises a proximal probe body part (20) engagable with the access port (16) via an inlet element (23) thereof. A cooling-fluid channel (26) at or adjacent to the proximal probe body part (20) enables liquid natural gas to pass therethrough to cool the proximal probe body part (20) and the associated portion of a liquid-natural-gas sampling passage (22).

Description

Fluid-Monitoring Probe Apparatus And System

The present invention relates to a system for monitoring a liquid-natural-gas pipeline by intermittent or continuous sampling, and to a fluid-monitoring probe for application in such a system. More specifically, the invention relates to improving cooling of a proximal sampling or measurement passage of or associated with a probe body and/or valve body to prevent or limit loss of one or more constituent fractions, and/or to improve a thermal equilibrium between a section of pipe and an attachment connected to the section of pipe.

Sampling of low temperature liquid from a liquid-natural-gas pipeline is necessary to accurately determine the composition of the fluid flow. Furthermore, it can be important to monitor the temperature of the fluid flow of a liquid-natural-gas pipeline to ensure safe liquid-natural-gas transit.

Presently, liquid natural gas is typically extracted from a liquid-natural-gas pipeline at a monitoring point using a sampling probe. The captured liquid natural gas is subsequently vaporised to give a gas at ambient temperature to be analysed, for example, by gas chromatography. It is essential in this process that there is no loss of any constituent fractions; this is difficult to ensure due to the ease of partial vaporisation of many fractions, some of which are very close to their boiling points at the operational temperature of the liquid natural gas flow. Hence it is desirable for the liquid natural gas to be sub-cooled or kept as sub-cooled on sampling. However, this is difficult to achieve as the liquefied gas sample is typically in relatively poor thermal communication with the bulk liquefied gas flow during the sampling process.

It is therefore advantageous to sample from a point on the central throughbore axis of the pipeline, rather than from near the interior surface where the liquefied gas is most likely to be unrepresentative of the average composition, due to interactions with the surface. Currently, it is typical for probes in industrial applications to extend between one third and two thirds of the diameter of the pipe cross-section. However, excessively long probes, as required for large pipelines, can be disadvantageous, principally as they can be fragile. Similar considerations apply in the case of temperature monitoring or other measurement taking of a liquid-natural-gas pipeline, where the sample probe is replaced with a thermowell or other probe having a body for accepting a measurement device. In all cases, accurate readings are essential, and having an improved thermal equilibrium between the pipe-section and any attached device is important.

The liquid natural gas can be extracted continuously or intermittently. Continuous sampling methods are most common, although intermittent sampling methods are still typically used for impurity analysis of liquid natural gas, and are often used as back-up systems in case of the failure of a continuous sampling system. ISO standard 8943 covers appropriate apparatus and procedures for the monitoring of liquid-natural-gas pipelines.

The object of this invention is to provide a method of monitoring a liquid-natural-gas pipeline which integrates a fluid channel in the proximal probe body part of a fluid-monitoring probe, creating a passage around the captured sample fluid, to ensure a subcooled sample, and hence to solve the problem with the prior art outlined above.

According to a first aspect of the invention, there is provided a liquid-natural-gas monitoring system comprising: a liquid-natural-gas pipe section including a main throughbore and an access port; and a fluid-monitoring probe having a proximal probe body part, a distal probe body part, a liquid-natural-gas monitoring passage which extends between the proximal and distal probe body parts, and a cooled-fluid channel at or adjacent to the proximal probe body part to in use enable liquid natural gas to pass therethrough to cool the proximal probe body part and the associated portion of the liquid-natural-gas sampling passage.

Advantageously, this allows for the sub-cooling of fluid captured by a fluid-sampling probe, or retention of thermal equilibrium with the bulk gas flow for a temperature probe such as a thermowell or other measurement device.

Preferably, the fluid channel is at least partially contained within the distal probe body part. This is advantageous as it allows the efficient cooling of the section of the liquid-natural-gas monitoring passage furthest from the main throughbore of the pipeline.

The fluid-monitoring probe may be a fluid-sampling probe. This allows the sampling of liquid natural gas from the bulk gas flow to allow for further analysis of composition by gas chromatography or other suitable means. Additionally or alternatively, the proximal probe body part may comprise one or more valves to allow isolation of an external portion of the sampling system, vapouriser, analytical instruments and associated items from the liquefied gas flow of the pipeline.

Furthermore, the fluid-monitoring probe may be a thermowell. This allows for the monitoring of the temperature of the bulk gas flow at a specific point in the pipeline. Although typically rectilinear, preferably, the fluid channel through the proximal probe body part may define a helical fluid flow path. This may enhance the cooling of the fluid-monitoring probe by maximizing the surface area contact between the fluid channel and the fluid-monitoring probe.

In this case, the fluid channel through the distal probe body part may extend out into the throughbore of the pipe section. The flow path within the fluid channel of the distal probe body part may preferably comprise three substantially cylindrical sections, confined by a plane bisecting each section, in order to discourage partial vaporisation of the liquid. This is advantageous in that it reduces the risk of cavitation events which may damage the fluid channel. Preferably, the liquid-natural-gas monitoring system may include a fluid pressure sensor and/or a fluid temperature sensor and/or a fluid flow velocity sensor. The or each sensor advantageously allows the monitoring of these parameters in addition to those measured by an insertable probe. One or more sensor or sensors may preferably be located within or partially within the distal probe body part. This results in a compact design of the liquid-natural-gas monitoring system and allows easy access to the sensors.

An indicator may be provided on the exterior of the distal probe body part to provide indicia from one or more of the sensors. Such an indicator allows quick routine monitoring of the parameters, and may assist in alerting the operator to unusual conditions which may be further monitored by sampling with an insertable probe.

According to a second aspect of the invention, there is provided a fluid-monitoring probe for use in a liquid-natural-gas monitoring system, preferably according to the first aspect of the invention, the fluid-monitoring probe comprising: a proximal probe body part engagable with an access port of a liquid-natural-gas pipeline; a distal probe body part extending from the proximal probe body part and insertable via the access port into a liquid natural gas flow path; a monitoring passage which extends between the proximal and distal probe body parts; and a cooling-fluid channel which at least in part extends into and/or through the proximal probe body part to enable in use cooling of the monitoring passage.

Beneficially, the fluid-monitoring probe may be a fluid- sampling probe.

Preferably, the proximal probe body part comprises one or more valves to allow isolation fluid contained by the fluid-sampling probe from the liquefied gas flow of the pipeline. The distal probe body part may advantageously be adapted to be engagable with a sample container. The fluid-monitoring probe may be a thermowell.

Optionally, the fluid channel through the proximal probe body part may define a helical fluid flow path.

The fluid channel through the proximal probe body part may extend out into the pipeline. Additionally or alternatively, the flow path within the fluid channel of the proximal probe body part comprises three substantially cylindrical sections, confined by a plane bisecting each section, in order to discourage partial vaporisation of the liquid.

Preferably, the fluid-monitoring probe comprises a fluid pressure sensor and/or a fluid temperature sensor and/or a fluid flow velocity sensor. In this case, one or more sensor or sensors may be located within or partially within the proximal probe body part.

At least one indicator may be provided on the distal probe body part to provide indicia from one or more sensors.

Preferably, the fluid-monitoring probe may be provided as a kit of parts. This may advantageously enable facile customization and maintenance and result in lower manufacturing costs. According to a third aspect of the invention there is provided a method of maintaining sub-cooled fluid at or within an in use fluid-monitoring probe, preferably in accordance with the second aspect of the invention and on a liquefied natural gas pipeline, the method comprising the steps of: a) providing a fluid-sampling probe including a cooling-fluid channel; and b) inserting said fluid- sampling probe into a suitable access port of the pipeline such that fluid from a main fluid-flow of the liquefied natural gas pipeline is redirected through the internal fluid channel around the external surface of the fluid-monitoring probe within the pipeline.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic cross-section of a first embodiment of a liquid-natural-gas pipeline monitoring system, in accordance with the first aspect of the present invention and having a fluid-monitoring probe;

Figure 2a is a plan view, in the direction of a distal probe body part to a proximal probe body part of the fluid-monitoring probe, showing an inlet and outlet of an internal passage through the proximal probe body part;

Figure 2b is a longitudinal cross-section of the proximal probe body part along the line A-A in Figure 2a;

Figure 3 shows a second embodiment of a liquid-natural-gas monitoring system, in accordance with the first aspect of the present invention; and Figure 4 shows a third embodiment of a liquid-natural-gas monitoring system, in accordance with the first aspect of the present invention.

Referring firstly to Figure 1 of the drawings, there is provided a fluid monitoring system, indicated globally by 10, preferably but not necessarily exclusively for the monitoring of liquid natural gas in a portion of pipe section 12, via attachment of a fluid-monitoring probe apparatus to an access port 16. The fluid-monitoring probe apparatus is typically in the form of or comprises an elongate monitoring element 14, and the access port 16 is typically an inlet port or alternatively an outlet port. The elongate monitoring element 14 is or includes in this case a fluid-monitoring probe 50 having a distal probe body part 18, a proximal probe body part 20, and a monitoring passage 22 which extends between the distal and proximal probe body parts 18, 20. The in use distal probe body part 18 extends into the pipe section 12, preferably to or substantially to a middle third region. The in use proximal probe body part 20 engages with the inlet port 16 via inlet element 23.

To enable sample extraction of a portion of process fluid in the in use pipe section, the monitoring passage 22 may have an opening at the end or end portion of the distal probe body part 18, and the monitoring passage 22 extends typically to a valve element 25 at or adjacent to the proximal probe body part 20.

Alternatively, the monitoring passage may have a closed or sealed end at the distal probe body part 18 to accommodate other monitoring devices, such as a temperature sensor.

The proximal probe body part 20, which may be or include a flange, block and/or valve body, comprises a fluid channel 26 which is in communication with the fluid flow in the main throughbore of the pipe section 12 via an inlet 27 and an outlet 28.

The portion of pipe section 12 is preferably cylindrical or substantially cylindrical, and the inlet port 16 may be located at any point on the cross-section of the pipeline. The inlet port 16 is shown orientated so that the throughbore or neck thereof is perpendicular to the main throughbore of the portion of pipe section 12. However, the neck may be at an acute or obtuse angle to the pipe section 12 and/or the fluid flow therethrough.

The inlet port 16 preferably comprises an inlet element 23, which is preferably provided as a neck portion external to the portion of pipe section 12. The inlet element 23 is engagable with the proximal probe body part 20 of the fluid-monitoring probe 50; this may be achieved by providing the inlet element 23 as a flange inlet element adapted to seat the proximal probe body part 20, in this case being a matable flange. Alternatively, the inlet element may be or include an at least partially screw-threaded interior or exterior surface to engage the probe by means of a screw-threaded connection. The inlet element 23 may be adapted in other ways in order to facilitate releasable or permanent engagement with the proximal probe body part 20. For instance, it may be desirable to provide an inlet element 23 with integral holes suitable for the insertion of bolts and/or rivets, and a proximal probe body part 20 with matching holes. Alternatively, the proximal probe body part 20 and the inlet element 23 may be welded together or otherwise sealed.

The fluid channel 26 inside the proximal probe body part 20 provides a fluid flow path for liquid natural gas around the proximal probe body part 20. This is advantageous in the case where the fluid-monitoring probe 50 is a fluid- sampling probe, as the captured fluid sample is retained at a sub-cooled temperature by convective cooling from the fluid passing through the fluid channel 26, preventing the vaporisation of fractions of the sample and hence allowing representative sampling of the fluid flow through the main throughbore 24 of the pipe section 12.

In the case where the fluid-monitoring probe 50 is a thermowell, the convective cooling from the fluid passing through the fluid channel 26 keeps the captured fluid sample in improved or complete thermal equilibrium with the fluid flow through the main throughbore 24 of the pipe section 12, resulting in more accurate temperature monitoring.

Preferably, the proximal probe body part 20 is formed of a material suitable for operating at cryogenic temperatures. Such materials include stainless steels, high carbon steels, and nickel-based performance alloys. Austenitic stainless steels, which do not have a ductile-brittle transition at low temperatures, may be particularly preferred.

The fluid channel 26 may be integrally formed with the proximal probe body part 20. This is advantageous over an alternative of forming the fluid channel 26 as a conduit element insertable into a void in the proximal probe body part 20 in that it reduces the likelihood of damage to or leakage from the fluid channel 26 in operation. However, it may be more advantageous to form the fluid channel 26 as an insertable conduit element for various reasons, including the possibility of removing the conduit element for inspection, maintenance or replacement, and the facilitation of the manufacture of a wide variety of conduit elements and hence fluid channels 22.

Furthermore, it may be preferable to provide an insertable conduit element manufactured from a material with greater tensile strength than the bulk material of the proximal probe body part 20, to avoid failure of the conduit element due to cavitation or other causes. For instance, an insertable conduit element may be formed from a nitriding austenitic steel/nickel/chromium alloy.

Various designs of fluid channel 26 may be chosen, and are discussed in detail below.

In this embodiment, the valve element 25 may be at least one ball valve 32, and most preferably a plurality of ball valves. It may be appropriate to include other valves, instead of or additional to the ball valve or valves, in the proximal probe body part 20; for instance, a butterfly valve, check valve, globe valve or needle valve. If the fluid-monitoring probe is a fluid- sampling probe, the valves may preferably be used to control fluid communication from the probe to a suitable sample container (not shown). Valves may also be included so that fluid captured by the fluid-sampling probe can be isolated from the bulk fluid flow in situ. Alternatively, the fluid-monitoring probe and/or one or more valve components could be integrally formed with the proximal probe body part 20.

The proximal probe body part 20 may beneficially be adapted to be engagable with a sample container, so that in the case where the fluid-monitoring probe 50 is a fluid- sampling probe, communication of fluid directly from the fluid-sampling probe to the sample container can be achieved via the proximal probe body part 20, controlled by the ball valve or valves 32 as discussed above. For example, the upper part of the proximal probe body part 20 may be screw-threaded to facilitate engagement with a corresponding screw-threaded member of a sample container. Other modes of engagement would also be evident to the person skilled in the art. Alternatively, the proximal probe body part 20 may preferably be adapted to facilitate the direct transfer of sampled fluid from the pipeline to an analytic apparatus or machine, such as a gas chromatograph, a high-performance liquid chromatograph, or a Raman spectrometer, or to a high-pressure accumulator. The presence of the distal probe body part 18 of the fluid-monitoring probe 50, in the fluid flow of the main throughbore of the pipe section 12, may preferably create a pressure differential across the fluid channel 26, which may advantageously increase the velocity of the fluid flow through the fluid channel 26, and hence improve the sub-cooling of the fluid-monitoring probe 50. When the fluid-monitoring probe 50 is provided as a fluid- sampling probe, the distal probe body part 20 of the fluid-sampling probe may be provided as a sampling tube.

The orientation of the fluid-monitoring passage 22 preferably may be designed so that it is complementary to that of the fluid channel 26. For instance, the fluid channel 26 may be provided as a helical passage around the fluid-monitoring passage 22 in the proximal probe body part 20 to maximise the proximity of the cooling fluid flow.

The liquid-natural-gas monitoring system 10 may include one or more sensors, which may be distinct from the fluid-monitoring probe 14. In particular, it may be desirable to provide one or more of each of a fluid pressure sensor, a fluid velocity sensor and a fluid temperature sensor at one or more points in the system 10. In particular, sensors may be provided to monitor fluid flow velocity, temperature, and/or pressure in the fluid channel 26. It may be particularly useful to monitor fluid temperature in the fluid channel 26, due to the fast nature of flow through the relatively constricted passage, the fluid contained therein may be expected to be in thermal equilibrium with the bulk fluid flow through the main throughbore 24 of the pipe section 12. Measurement of the pressure through the fluid channel 26 is desirable for maintenance and safety purposes.

Such sensors may be incorporated into the distal probe body part 18 of the system 10, but also may be incorporated into other elements of the system 10, if appropriate. For instance, a sensor provided to monitor fluid flow velocity, temperature and/or pressure in the main throughbore of the pipe section 12 may advantageously be incorporated into the elongate monitoring element.

If incorporated into the proximal probe body part 20 of the system, the sensors may preferably be located in a void integral to the proximal probe body part 20. In this case, the same void may house the fluid channel 26, preferably provided as an insertable conduit element. Alternatively, the fluid channel 26 may be preferably provided as a channel integral to the proximal probe body part 20 and the sensor located inside the channel 22, preferably with a suitably sealed outlet for electronic communication with a proximal or remote processing and/or display unit.

All sensor units may preferably be miniaturised and adapted for operation at cryogenic temperature. A pressure sensor may be provided as a piezoelectric pressure transducer, a velocity sensor as an ultrasound sensor, and a temperature sensor as a Raman effect optical fibre sensor. However, the use of other types and/or combinations of sensors may be evident to the person skilled in the art.

The proximal probe body part 20 may comprise one or more indicators which provide indicia from one or more sensors. The indicators may be dials and additionally or alternatively may include an electronic display for indicia display.

A fluid-monitoring-probe assembly, being the components of the liquid-natural-gas monitoring system 10 which are not integral to the section of pipe 12, may preferably be provided as a kit of parts. This may effectively allow for custom use, with a choice of sensors, proximal probe body part material and fluid-monitoring probe 14 allowing specific user-end modification for a pipeline infrastructure and/or fluid composition. The modular provision of the fluid-monitoring-probe assembly may also facilitate maintenance of the fluid-monitoring-probe assembly.

Referring to Figure 2, the fluid channel 26 may preferably comprise an inlet channel 34 and an outlet channel 36 parallel to the throughbore of the access port 16 and in communication via a third channel 38 perpendicular to the throughbore of the access port 16, such that the central axes of the three constituent channels 34, 36, 38 of the fluid channel 26 lies in the same plane.

Preferably, the fluid-monitoring passage 22 is located centrally in the proximal probe body part 20. The fluid-monitoring passage 22 preferably extends at least partially through the proximal probe body part 20 of the fluid-monitoring probe 50. It is preferably circular or substantively circular in cross-section.

The inlet channel 34 and outlet channel 36 of the fluid channel 26 are preferably offset from the fluid-monitoring passage 22. The degree of offset may be modified to optimize sub-cooling of the proximal probe body part 20.

The channels 34, 36, 38 are preferably coplanar and spaced to one side of the monitoring passage 22 to be parallel with a plane thereof. However, alternatively, the plane of the channels 34, 36, 38 could be inclined at an angle to the central axis of the fluid-monitoring passage 22 so that the channel 38 is disposed on the other side of the said passage 22 to the inlet and outlet channels 34 and 36. In this case, the inlet and outlet channels 34 and 36 are inclined away from the central axis of the throughbore of the access port.

In any case, these arrangements are particularly advantageous as it minimizes the propensity of the fluid to partially vaporise due to the Venturi effect, while it sub-cools the fluid-monitoring probe. Partial vaporisation of fluid may have deleterious effects: the collapse of vapour cavities may cause cavitation damage to the fluid channel 26 and/or proximal probe body part 20, and hence lower fluid flow velocities may be required to reduce the risk of failure of the system 10. The fluid channel 26 of the present embodiment may be advantageously economical to produce relative to more complex designs where the fluid channel is not confined to a single plane. There may be further economic advantage to using other fluid channel designs. For example, reducing the temperature of the bulk gas flow to avoid partial vaporisation and hence cavitation damage to the system 10. Nevertheless, other fluid channel designs may be contemplated. For instance, a helical fluid channel design may be advantageous due to the optimised surface area contact between the fluid channel and the secondary channel through which the elongate monitoring element is insertable, increasing the efficiency of convective heat transfer from the elongate monitoring element to the sub-cooled fluid flowing through the fluid channel. The fluid channel could also be preferably provided as a sheath around the secondary channel with similar effect. The fluid channel is preferably provided, in any case, as an uninterrupted conduit, to maximize fluid flow velocity and avoid excessive turbulence, although designs may be contemplated in which the fluid channel is interrupted by a grill or baffle element to modulate the turbulence of the flow.

It may be preferable to include multiple fluid channels in the proximal probe body part in order to improve the sub-cooling; the fluid channel of the present embodiment may preferably be provided at multiple different angles to the secondary channel to provide homogenous convective cooling. Otherwise it may be desirable to combine diverse designs of fluid channel in order to optimize convective cooling.

Referring now to Figure 3, there is shown a second embodiment of a liquid-natural-gas monitoring system. For the sake of clarity, elements which are similar to those shown in the first embodiment use the same or similar references plus one hundred, and further detailed description of such elements has been omitted for conciseness. There is provided a fluid monitoring system, indicated globally by 110, preferably but not necessarily exclusively for the monitoring of liquid natural gas in a pipe section 112, via insertion of an elongate monitoring element 114 into an access port 116. The elongate monitoring element 114 is again preferably a fluid-monitoring probe 150 having a distal probe body part 118, a proximal probe body part 120, and a monitoring passage 122 which extends between the distal and proximal probe body parts 118, 120.

As above, the proximal probe body part 120 is engagable with access port 116 via inlet element 123 thereof. The proximal probe body part 120 comprises a fluid channel 126 which is in communication with the fluid flow in the main throughbore 124 of the pipe section 112 via inlet 127 and outlet 128. The inlet channel 134 and outlet channel 136 may preferably communicate with the bulk fluid flow of the pipe section 112 via inlet 127 and outlet 128. The inlet 127 and outlet 128 may preferably be provided simply as apertures connecting the inlet channel 134 and outlet channel 136 respectively with the bulk fluid flow. The inlet channel 134 and/or outlet channel 136 may extend into the pipe section 112. In this case the inlet 127 and/or outlet 128 may preferably be provided as a nozzle 142 which may advantageously direct the fluid flow to and/or from the fluid channel 126.

The nozzle 142 may be formed simply as a, preferably curvate, extension of the inlet channel 134 and/or outlet channel 136. As shown, preferably the mouth of the inlet nozzle 142 opposes the direction of fluid flow. This arrangement maximizes the velocity and minimizes the turbulence of fluid flow through the fluid channel 126.

The nozzle 142 may also preferably be provided with a mouth substantially broader than the diameter of the inlet channel 134 and/or outlet channel 136. In any case, the nozzle 142 is preferably formed integrally with its respective extended inlet channel 134 and/ or outl et channel 136.

Referring to Figure 4 of the drawings, there is shown a third embodiment of a liquid-natural-gas monitoring system. As before, elements which are similar to those shown in the first and/or second embodiment use the same or similar references plus a prefix of '2', and further detailed description of such elements has been omitted for conciseness.

There is provided a fluid monitoring system, indicated globally by 210, preferably but not necessarily exclusively for the monitoring of liquid natural gas in a pipe section 212, via insertion of an elongate monitoring element 214 into an access port 216. The elongate monitoring element 214 is again preferably a fluid-monitoring probe 250 having a distal probe body part 218, a proximal probe body part 220, and a monitoring passage 222 which extends between the distal and proximal probe body parts 218, 220.

The proximal probe body part 220 is engagable with the access port 216 via inlet element 223 thereof. The proximal probe body part 220 comprises a cooling-fluid channel 226 which is in communication with the fluid flow in the main throughbore 224 of the pipe section 212 via inlet 227 and outlet 228.

As in the second embodiment, described above, the inlet 227 is defined by an elongate nozzle 242 which extends from the proximal probe body part 220, through the neck of the access port 216 and to or adjacent to the main flow through the pipe section 212. The inlet 227 of the nozzle 242 again faces the on-coming flow, causing a portion of the sub-cooled process fluid to enter the mouth of the nozzle 242 and be forced along the fluid channel, thus improving the cooling of the proximal probe body part 220 and the associated monitoring passage 222.

The outlet 228 of the fluid channel 226 is defined by a tubular element 252, preferably being rigid and which may beneficially be attached to the nozzle 242 for improved support and rigidity. The tubular element 252, leading from the proximal probe body part 220 and terminating at a discharge mouth 254 of the outlet 228, preferably has a lateral dimension along at least a majority of its longitudinal extent which is greater than that of a majority of the nozzle 242. This consequently creates a low-pressure region at or adjacent to the discharge mouth 254, encouraging fluid flow through the fluid channel 226. A length of the tubular element 252 is preferably such that the discharge mouth 254 is positioned in or adjacent to the main flow of process fluid in the pipe section 212.

It may be beneficial to include a deflector element or baffle at or adjacent to the nozzle 242, diverting an increased volume of process fluid in the pipe section 212 into the neck of the access port 216. This would advantageously form a higher-pressure region at or adjacent to the mouth of the nozzle 242, further promoting fluid flow into and through the fluid channel 226.

The nozzle, tubular element and/or deflector element may be mounted on the proximal probe body part, the distal probe body part, the access port, pipe section and/or a dedicated support element associated therewith, and/or to each other or a combination thereof. This would enhance robustness and longevity in a harsh working environment.

The deflector element may be a simple flat apertured or unapertured flat or curved plate, or any other suitably shaped device. It is therefore possible to provide a fluid monitoring system, in particular a liquid-natural-gas monitoring system, in which a fluid-monitoring probe is cooled by the presence of a fluid passage through the distal probe body part thereof, allowing the transfer of heat from the fluid-monitoring probe to the fluid passing through the distal probe body part, via said distal probe body part. The words 'comprises/comprising' and the words 'having/including' when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention herein described and defined.

Claims

1. A liquid-natural-gas monitoring system (10; 110; 210) comprising: a liquid-natural-gas pipe section (12; 112; 212) including a main throughbore and an access port (16; 116; 216); and a fluid-monitoring probe apparatus having a proximal probe body part (20; 120;

220), a distal probe body part (18; 118; 218), a liquid-natural-gas monitoring passage (22; 122; 222) which extends between the proximal and distal probe body parts (20, 18; 120, 118; 220, 218), and a cooled-fluid channel (26; 126; 226) at or adjacent to the proximal probe body part (20; 120; 220) to in use enable liquid natural gas to pass therethrough to cool the proximal probe body part (20; 120; 220) and the associated portion of the liquid-natural-gas monitoring passage (22; 122; 222).

2. A liquid-natural-gas monitoring system (10; 110; 210) as claimed in claim 1, wherein the cooled-fluid channel (26; 126; 226) is at least partially contained within the proximal probe body part (20; 120; 220).

3. A liquid-natural-gas monitoring system (10; 110; 210) as claimed in claim 2, wherein the fluid-monitoring probe apparatus is a fluid-sampling probe.

4. A liquid-natural-gas monitoring system (10; 110; 210) as claimed in claim 3, wherein the proximal probe body part (20; 120; 220) comprises one or more valves to allow isolation of fluid contained by the fluid-sampling probe from the liquefied gas flow of the pipeline.

5. A liquid-natural-gas monitoring system (10; 110; 210) as claimed in any one of the preceding claims, wherein the cooled-fluid channel (26; 126; 226) at or adjacent to the proximal probe body part (20; 120; 220) extends out into the throughbore of the pipe section (12; 112; 212).

6. A liquid-natural-gas monitoring system (10) as claimed in any one of the preceding claims, wherein the cooled-fluid channel (26) comprises three substantially cylindrical sections (34, 36, 38), confined by a plane bisecting each section, to prevent or inhibit partial vaporisation of the liquid.

7. A liquid-natural-gas monitoring system (10; 110; 210) as claimed in any one of the preceding claims, wherein one or more sensors is/are located within or partially within the proximal probe body part.

8. A fluid-monitoring probe apparatus for use in a liquid-natural-gas monitoring system (10; 110; 210) as claimed in any one of the preceding claims, the fluid-monitoring probe apparatus comprising: a proximal probe body part (20; 120; 220) engagable with an access port (16; 116; 216) of a liquid-natural-gas pipeline; a distal probe body part (18; 118; 218) extending from the proximal probe body part (20; 120; 220) and insertable via the access port (16; 116; 216) into a liquid natural gas flow path; a monitoring passage (22; 122; 222) which extends between the proximal and distal probe body parts (20, 18; 120, 118; 220, 218); and a cooling-fluid channel which at least in part extends into and/or through the proximal probe body part (20; 120; 220) to enable in use cooling of the monitoring passage.

9. A fluid-monitoring probe apparatus as claimed in claim 8, wherein the fluid-monitoring probe apparatus is or includes a fluid-sampling probe.

10. A fluid-monitoring probe apparatus as claimed in claim 9, wherein the proximal probe body part (20; 120; 220) comprises one or more valves to allow isolation of fluid contained by the fluid-sampling probe from the liquefied gas flow of the pipeline.

11. A fluid-monitoring probe apparatus as claimed in any one of claims 8 to 10, wherein the cooling-fluid channel (26; 126; 226) through the proximal probe body part (20; 120; 220) extends out into the pipeline.

12. A fluid-monitoring probe apparatus as claimed in any one of claims 8 to 11, wherein the cooling-fluid channel (26) comprises three substantially cylindrical sections (34, 36, 38), confined by a plane bisecting each section, in order to prevent or inhibit partial vaporisation of the liquid.

13. A fluid-monitoring probe apparatus as claimed in any one of claims 8 to 12, wherein one or more sensors is/are located within or partially within the proximal probe body part (20; 120; 220).

14. A fluid-monitoring probe apparatus as claimed in any one of claims 8 to 13, provided as a kit of parts.

15. A method of maintaining sub-cooled fluid at or within an in use fluid-monitoring probe apparatus as claimed in any one of claims 8 to 14 and on a liquefied natural gas pipeline, the method comprising the steps of: a) providing a fluid- sampling probe including a cooling-fluid channel (26; 126; 226); and b) inserting said fluid- sampling probe into a suitable access port (16; 116; 216) of the pipeline such that fluid from a main fluid-flow of the liquefied natural gas pipeline is redirected through the internal fluid channel around the external surface of the fluid-monitoring probe apparatus within the pipeline.