GB2405467A - Leak detection method and apparatus - Google Patents

Abstract

The invention relates to detection apparatus 10 for detecting leaks from structures 40 such as sub-sea pipelines or risers. The detection apparatus 10 comprises a generation means 14, such as a laser, which is capable of generating radiation, a direction means 18, 20, 22 which is capable of directing the radiation toward the structure 40 and a detection means 62, 52, 50 to detect radiation received such as fluorescence from oil or fluorescent dye leaking from the structure 40. There is also provided a method of detecting a leak in a structure 40.

Description

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. ...DTD: 1 Detection Method and Apparatus 3 This invention relates to a detection method and 4 apparatus for detecting leaks, particularly but not exclusively hydrocarbon or fluorescein leaks, from 6 submerged structures, such as pipelines and risers.

8 Subsea pipeline networks and riser networks which 9 transport oil to shore, or tankers for example, are essential and major parts in the overall oil 11 production process. The current Norwegian oil 12 pipeline network, for example, is longer than 1000 13 kilometres. In the United States there are over 14 275,000 Km of oil and oil product pipelines.

16 In addition to the pipelines there are associated 17 risers, several hundred of which are in the North 18 Sea. The increase in environmental legislation 19 means that there is ever more demand on oil and operating companies to minimise leaks of oil from 21 these pipelines and risers.

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1 Damage to the external sheathing of e.g. flexible 2 risers can result in seawater penetrating the riser 3 body. This can lead to a dramatic reduction in the 4 fatigue life of the dynamic (i.e. moving) portions of the riser, from around 20 years to nearer 3 to 5 6 years. Furthermore, the effect of chemicals / oil 7 seeping into the marine environment has led to an 8 increase in environmental legislative demands on oil 9 companies in recent years requiring them to minimise leaks from risers.

12 The challenge of minimising leaks in such an 13 extensive system is a large task.

Traditionally, oil and/or fluorescein seeping from a 16 leak in risers/pipelines has been observed visually 17 by a diver swimming alongside the riser, often aided 18 by a back light system. However, divers can only 19 inspect relatively shallow risers/pipelines and even then such a method may not detect medium or small 21 leaks.

23 Visual cameras may be held by divers or mounted on 24 Remotely Operated Vehicles (ROVs) but these also fail to efficiently detect small and medium sized 26 leaks and their accuracy is largely dependent on the 27 clarity and current of the water in which the ROV is 28 operating.

W back lights (for example those supplied by 31 Kongsberg-Simrad Limited, Aberdeen, Scotland) and 32 acoustic instruments have also been used but are .: . .e 1 also insensitive to smaller leaks and, in the case 2 of W back light, can be dangerous to divers as it 3 can cause blindness whereas when mounted on a ROV, 4 the ROV light must be switched off which creates the risk of the ROV crashing into the pipeline.

7 It is also known to use a fluoromometer (e.g. 8 Aquatracker supplied by Chelsea Instruments) mounted 9 on an ROV which provides better sensitivity, but measures a single point over a limited sensitivity 11 range and is therefore inefficient and time 12 consuming at detecting leaks and so is normally used 13 to pinpoint known leaks. Moreover, the sample has 14 to pass into the instrument for it to be detected.

16 To minimise the impact caused by damaged external 17 sheathing of flexible risers, an inhibitor mix laced 18 with a clearly visible fluorescein dye (which can be 19 fed into the annulus of the riser from fill-pots within e.g. an FPSO turret) is typically provided in 21 order to positively expel seawater and provide a 22 visual indication of the leak. This is performed by 23 surrounding the hydrocarbon pipeline with an annular 24 void in the form of an outer sheath filled with fluorescein or any other liquid which is easier to 26 detect than hydrocarbons. In the event of a 27 fracture of the pipeline, the fluorescein escapes 28 and is more readily detected by the various 29 detection devices than hydrocarbons; the detection of fluorescein being indicative of a hydrocarbon 31 leak. A riser with an outer sheath filled with :- .:' ::e : : : ce 1 fluorescein or any other liquid which is easier to 2 detect, is shown schematically in Fig. 1.

4 According to a first aspect of the present invention there is provided a detection apparatus for 6 detecting leaks from sub-sea structures, 7 comprising: 8 a generation means adapted to generate 9 radiation; a direction means adapted to direct radiation 11 toward a structure; and 12 a detection means adapted to detect radiation 13 received from the structure.

Preferably, the direction means is adapted to direct 16 radiation from inside of the apparatus to outside 17 the apparatus.

19 Preferably, the radiation is light, more preferably laser light.

22 Preferably, the direction means comprises a 23 conversion means to convert the generated light 24 which may have a variety of cross-sections into light which has a generally planar cross-section.

26 Preferably, the conversion means also converts the 27 planar cross-section light such that its cross 28 section increases as it travels towards the 29 structure. To provide for this, the conversion means may comprise a concave lens.

32 The structure may be a riser or pipeline.

: I. e:e ce Hi: el : : 2 Preferably, the generation means generates light at 3 a wavelength suitable for excitation of a material, 4 the presence of which is indicative of the presence of hydrocarbons. The material may be fluorescein, a 6 hydrocarbon or mixture of hydrocarbons, or any other 7 material.

9 The direction means may further comprise a varying means to vary the dimensions of the light beam 11 emitted by the apparatus and more preferably, 12 emitted by the generation means. Such varying means 13 may comprise a beam expander and may be controlled 14 by a motor mechanism. More preferably, the varying means is adapted to selectively vary the width of 16 the beam and also optionally vary the length and 17 angle of the light beam.

19 Preferably the apparatus further comprises a ranging means. The ranging means is preferably adapted to 21 emit light from the apparatus toward the structure 22 and detect its reflection and thereafter calculate 23 the distance between the apparatus and the 24 structure. Preferably this data is used to control the motor mechanism of the varying means.

27 Preferably, the detection means comprises a means to 28 focus the light received from the structure, such as 29 a convex lens. Preferably, the detection means detects light generated by the excitation of the 31 material whose presence is indicative of the 32 presence of e.g. hydrocarbons or fluorescein.

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2 The detection means may comprise an optical filter 3 which is adapted to permit the passage of said light 4 and prevent the passage of light of other wavelengths which are not generated by the 6 excitation of said material.

8 Preferably, the detection means comprises a means to 9 photo-multiply and, more preferably, detect the signal of the light detected. Such means may 11 comprise a photo-multiplier tube.

13 Preferably, the detection means comprises a means to 14 further filter, preferably electronically filter, the signal of light detected. Such means may 16 comprise a lockin-amp.

18 Preferably, the apparatus comprises an internal 19 calibration system. Preferably the internal calibration system directs a portion of the light 21 from the light generation means to a known sample of 22 material. Preferably the internal calibration 23 system comprises a detector to detect the presence 24 and characteristics of light emitted from said sample material. The internal calibration system 26 may also comprise a rotatable wheel controlled by a 27 stepping motor, the wheel having a plurality of 28 material samples thereon which can each interact 29 with the light directed from the light generation means.

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1 The apparatus may also comprise sensors such as 2 temperature, vacuum, pressure and humidity sensors, 3 and a power supply voltage monitor. Signal 4 processing electronics may connect the lockin-amp, the detector of the internal calibration unit, the 6 various sensors to a data transmission unit and 7 onward to a remote control station such as an 8 offshore platform, ship or onshore base.

The apparatus may also comprise control and output 11 display software to provide for remote control of 12 the apparatus.

14 According to a second aspect of the invention there is provided a method of detecting a leak in a 16 submerged structure, the method comprising: 17 generating radiation; 18 directing the radiation towards a submerged 19 structure; and detecting at least a portion of the radiation 21 received from said structure.

23 Preferably, the method of detecting a leak further 24 comprises step of determining the characteristics of the detected radiation.

27 Preferably, the method according to the second 28 aspect of the invention is performed with the 29 apparatus according to the first aspect of the invention.

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: :: ece 1 Preferably, the radiation is light, more preferably 2 laser light.

4 Preferably, the light directed towards the structure has a fan shape.

7 Preferably, the light directed towards the structure 8 has a planar shape when it comes into contact with 9 the structure.

11 More preferably, the light directed towards the 12 structure has a planar fan shape.

14 Embodiments of the invention will now be described, by way of example only, with reference to the 16 following drawings in which: 18 Fig. 1 is a sectional schematic view of a riser 19 or pipeline for conveying hydrocarbons; Fig. 2 is a sectional schematic view of the 21 pipeline of Fig. 1 and a detection apparatus 22 according to the present invention; 23 Fig. 3 is a perspective view of the detection 24 apparatus and pipeline of Fig. 2; Fig. 4a and Fig. 4b are further perspective 26 views of the detection apparatus of Fig. 2; 27 Fig. 5a is a schematic view of a beam expander 28 and associated components which form part of 29 the detection apparatus of Fig. 2; Fig. 5b is a diagrammatic view of the optical 31 path of light which travels from the beam 32 expander of Fig. 5a to the pipeline of Fig. 2; : '. t:' ::.

ece .: :: ec: 1 Fig. 6 is a schematic view of an internal 2 calibration unit which forms part of the 3 apparatus of Fig. 2; 4 Fig. 7a is a top view of a Remotely Operated Vehicle (ROY) with the detection apparatus of 6 Fig. 2 attached; 7 Fig. 7b is an end view of the ROV and apparatus 8 of Fig. 7a; 9 Fig. 7c is a side view of the ROV and apparatus of Fig. 7a; 11 Fig. 8a is a second, more detailed, top view of 12 the ROV and attached detection apparatus of 13 Fig. 7a; 14 Fig. 8b is an end view of the ROV and apparatus of Fig. 8a; 16 Fig. 8c is a side view of the ROV and apparatus 17 of Fig. 8a; 18 Fig. 9 is a schematic view of a second 19 embodiment of a detection apparatus in accordance with the present invention and the 21 riser or pipeline of Fig. 1; 22 Fig. 10 is a perspective view of the detection 23 apparatus of Fig. 9 attached to an ROV, in use; 24 Fig. lla is a front view of a third embodiment in accordance with the present invention; 26 Fig. llb is an end view of the embodiment of 27 Fig. 1 la; 28 Fig. Tic is an opposite end view of the 29 embodiment of Fig. lla; and Fig. 12 is a perspective view of the detection 31 apparatus mounted on a pan and tilt unit.

1 As shown in Fig. 1, a hydrocarbon pipeline or riser 2 40 is surrounded by an outer sheath 43 thus 3 providing an annular void therebetween which is 4 filled with fluorescein or any other liquid which is easier to detect than hydrocarbons. Thus, in the 6 event of a fracture of the pipeline 40, the 7 fluorescein escapes.

9 A schematic representation of a detection apparatus 10 is shown in Fig. 2. The detection apparatus 10 11 comprises a housing 12 which is a watertight sub-sea 12 bottle or cylinder that has a transparent end plate 13 11 fitted. The housing 12 houses an excitation 14 source 14, an output filter 16, a beam expander 18, line generation optics 20, an internal calibration 16 unit 70 (not shown in Fig. 2), a laser ranging 17 device 30, mirrors 32 & 34, an input filter 56, a 18 Photo-Multiplier Tube (PMT) 52 and a lockin 19 amplifier 50. A camera (not shown) may also be provided within the housing 12 for visual camera 21 tracking. An output concave lens 22 and input 22 convex lens 62 are provided in a wall 13 of the 23 housing 12.

The components within the housing 12 are mounted on 26 a shock resistant chassis (not shown) which 'floats' 27 within the housing 12 on plastic leaf springs (not 28 shown) and allows for approximately lmm of movement.

The excitation source 14 is typically a W laser 14 31 (which may be generated using Nd-YLF third harmonic 32 generation or a violet laser diode) which is :e c:. .:e'.

: : : 1 suitable for excitation of the intrinsic oil or 2 using a blue laser suitable for excitation of the 3 intrinsic fluorescein provided within the sheath 43 4 of the pipeline 40 to produce fluorescence. A suitable laser may be a Coherent Sapphire 488-200 6 blue laser obtained from Coherent of Cambridge UK.

8 Alternatively the W laser 14 will be able to 9 generate light at a wavelength of 349nm which is suitable for the excitation of hydrocarbons. A 11 suitable laser for the generation of light at 349nm 12 can be obtained from Crystal laser of Reno, NV 13 89502, USA.

The filter 16 filters light emanating from the W 16 laser 14 and travelling to the beam expander 18 to 17 ensure that the specific wavelength of light, for 18 example 488nm, enters the beam expander 18.

The line projected by the apparatus 10 onto the 21 pipeline 40 would normally vary in width L as the 22 distance between the apparatus 10 and the pipeline 23 40 varies. The beam expander 18, shown in more 24 detail in Fig. 5a, counteracts the variance in width L in order to maintain the projected line L at a 26 constant width, for example lm, regardless of the 27 distance between the detection apparatus 10 and the 28 pipeline 40.

To achieve this, the beam expander 18 includes a 31 zoom lens which can magnify the width of the light 32 by up to 10 times.

: t:..- ;: . . 2 A stepping motor 19 receives information from the 3 laser ranging device 30 regarding the distance 4 between the detection apparatus 10 and the pipeline 40. The stepping motor 19 controls the beam 6 expander 18 accordingly so that the width of the 7 light exiting therefrom varies to counter the effect 8 on the width L of the projected line by the 9 apparatus moving towards and away from the pipeline 40. This provides a consistent line width L, for 11 example lm, on the pipeline 40.

13 The optics 20 for line generation may be formed as 14 one with the output lens 22 in the housing, although they are shown as separate components in Fig. 2.

16 The optic 20 converts the beam of light exiting the 17 beam expander 18 which has a generally circular 18 cross section to a planar beam of light generally 19 referred to as a 'line scan' whereas the concave lens 22 directs the light outwardly so that the 21 length of its cross section increases as it travels 22 from the detection apparatus 10. Such optics and 23 lenses are commercially available, one manufacturer 24 being Optosigma and a distributor being Laser 2000, Northants UK. The line scan will be approximately lm 26 wide at a range of 1.5m putting aside any effects of 27 the beam expander (that is the distance from the 28 detection apparatus 10 to the pipeline 40), thus 29 covering the typical width of the pipeline 40 and the water immediately adjacent thereto.

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: : : 1 A Gaussian line may be generated, that is a line 2 which is relatively bright at its centre, but 3 reduces in intensity along its length.

Alternatively, a non-Gaussian line may be generated, 6 that is a line which is generally of a homogeneous 7 intensity throughout its length. Generally non 8 Gaussian lines are preferred although Gaussian lines 9 may be employed when concentrating the scan on the pipeline 40.

12 Providing a projected laser line as described allows 13 the entire riser/pipeline 40 to be visually 14 inspected for any leaks allocated within the laser plane. In addition, the greater the width of the 16 laser line, the further the intensity of the laser 17 will be reduced since the same amount of laser power 18 is effectively spread over a greater area along the 19 line. The reduction in laser power projected onto any given point reduces the hazard to both the 21 marine environment and the structure of the 22 riser/pipeline 40.

24 In the embodiment shown in Figs. 2 and 9, projecting a laser line of 1 m at the riser 40 will reduce the 26 laser intensity by a factor of around 100 when 27 compared with a laser projected onto a single point.

28 Even with the reduction in the laser power at any 29 single point, the leak can still be easily observed with a moderate laser power of e.g. 100 mW.

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1 In contrast, if the laser is not projected along a 2 line, but is instead projected on a single point, 3 visualizing and locating the leak would be very 4 difficult. On the other hand prior systems which employ sensors based on LED devices that produce a 6 cone of light will not be sensitive enough to detect 7 any leaks since the laser power is spread over too 8 great an area. For example a cone of light 9 projected in a 1 m diameter circle will lose around 7850 times its original power (assuming that the 11 source size is 1 cm2) therefore dramatically 12 reducing the detection sensitivity available to the 13 apparatus 10.

The optic 20 and lens 22 may be rotatably mounted 16 within the housing 12 so that the projected line 17 scan can be aligned with the pipeline 40 regardless 18 of the pipeline's orientation. This is preferable 19 to orientating the ROV which is more difficult.

Moreover the optic 20 and lens 22 can be spun which 21 results in the line scan spinning and illuminating a 22 circular shape with light.

24 As an alternative, the line scan may be generated by providing a scanning mirror (not shown) rather than 26 using lenses.

28 To ensure data quality, the detection apparatus 10 29 comprises an internal calibration unit 70, shown in Fig. 6, for optical power monitoring for continual 31 on-line calibration/performance correction. A beam 32 splitter 72 is provided between the filter 16 and : ;'s t:c.. :: :.

: : : 1 the beam expander 18 (not shown in Fig. 2) to 2 reflect around 8% of the laser beam emanating from 3 the W laser 14 towards the internal calibration 4 unit 70. The internal calibration unit 70 comprises a motorised optical wheel 74 which has six different 6 concentrations of fluorescence dye 77 moulded in 7 polymer thereon. The fluorescent dye 77 is chosen 8 to emit light at a similar wavelength to the 9 fluorescein or the oil in the sheath 43 of the pipeline 40. A stepping motor 79 can be used to 11 turn the optical wheel 74 so that a variety of 12 readings at different concentrations of fluorescent 13 dye may be taken.

When using the internal calibration unit 70, the 16 light is directed onto one of the fluorescent dyes 17 77 which causes excitation thereof and emits light 18 accordingly. A filter 76 removes light having a 19 wavelength of that omitted by the W or blue laser 14 and the photodiode detector 78 detects the light 21 emitted by the fluorescent dye 77 on the optical 22 wheel 74.

24 On the occasion where the detection apparatus detects no light in the photo-multiplier tube 52, a 26 reading on the photodiode detector 78 of the 27 internal calibration unit 70 is indicative of the 28 detection apparatus 10 operating. Some previous 29 systems without internal calibration units, required the ROV to be flown back to its station to check if 31 the components were operating and so embodiments of 32 the present invention with an internal calibration : ':' ce:: :. e

1 unit 70 can save time in operating a ROV with 2 detection equipment.

4 The data from the photodiode detector 78 is also useful as a reference to ensure the quality of the 6 data received from the photo-multiplier tube 52 and 7 lockin-amp 50.

9 The laser ranging device 30 emits a laser at a wavelength of, for example 532nm, which is directed 11 by the mirrors 32, 34 out of the housing 12 towards 12 the pipeline 40. The data from the laser ranging 13 device 30 is forwarded to the stepping motor 19 of 14 the beam expander 18 so that the beam expander 18 is adjusted to maintain a constant width of the 16 projected line L on the pipeline 40. The 17 combination of the projected laser line and the 18 laser spot provided by the laser ranging device can 19 contribute significantly in fully automating the device so that the cent re of the projected laser 21 line is always centred on the riser/pipeline 40.

23 A suitable laser ranging device may be obtained from M) 24 Hiltiof Manchester UK. It should be noted that the laser wavelength of the ranging device should be in 26 the range of blue-green in order to avoid light 27 attenuation by sea water.

29 The input components of the detection apparatus 10 comprise the convex lens 62 in the wall 13 of the 31 housing 12 which receives light reflected from the : 4e.:. ct. :: :.

: : : 1 pipeline 40 and its immediate vicinity, the filter 2 56, photo-multiplier tube 52 and lock-in amp 50.

4 The convex lens 62 focuses the light from a cone shaped area outside of the housing 12 into the 6 housing 12. This is preferable to a window which 7 would allow more light from outside the housing 12 8 to enter the housing 12. Thus the use of the lens 9 62 stops some 'optical noise' from entering the housing 12.

12 The filter 56 removes the light which has a 13 wavelength corresponding to that of the W or blue 14 laser 14, for example 488nm. Other wavelengths of light may also be removed by the filter 56, leaving 16 only the wavelength of light which corresponds with 17 the wavelength produced by the excitation of the oil 18 or fluorescein escaping from the sheath 43, that is 19 520nm for the fluorescein and 450nm for the oil.

21 The photo-multiplier tube 52 multiplies and detects 22 the input signal. A suitable photo-multiplier tube 23 52 is available from Hamamatsu Photonics UK Limiter) 24 Welwyn Garden City, Hertfordshire, UK.

26 The lock-in amp 50 electronically filters the signal 27 so that only the precise frequency corresponding to 28 that emitted by excited fluorescein (520nm) remains.

29 This is further amplified and sent to a data transmission unit (not shown). A suitable lockin 31 amp may be purchased commercially from Scitec 32 Instruments Ltd. Cornwall, UK.

lit t:l tth::: ct. .: :: it: 2 The housing 12 is provided with a number of sensors 3 such as temperature, vacuum, water ingress, magnetic 4 safety switches, pressure and humidity sensors. A 12 or 24 volt, 3-6 amp power supply is also provided 6 within the housing 12 and connected to the various 7 components.

9 Signal processing electronics (not shown) connect the lockin-amp 50, the photodiode detector 78 of the 11 internal calibration unit 70, and the various 12 sensors within the housing 12 to the data 13 transmission unit and onward to a remote control 14 station such as an offshore platform, ship or onshore base (not shown).

17 Control and output display software will also 18 typically be provided within the housing 12 to allow 19 the detection apparatus 10 to be controlled from the remote control station. This can be done using a 21 Picture In Picture (PIP) display which superimposes 22 the relevant data on top of a real time video 2 3 recording. This allows the precise nature of the 24 leak to be monitored in real time.

26 A second, simplified, embodiment of detection 27 apparatus 110 in accordance with the present 28 invention is shown in Fig. 9. The detection 29 apparatus 110 comprises a laser source 114, mirrors 121, 123, optics 122, an input lens 162, filter 156, 31 detector 150, computer controller 180, 32 laser ranger 130 and mirrors 132, 134.

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: : : 2 Many features of the detection apparatus 110 are 3 common with the detection apparatus 10 and will not 4 be described further. The second embodiment differs in that mirrors 121, 123 are used to direct the 6 laser emitted by the blue laser 114 towards the 7 pipeline 40. Also, the line generation optics 122 8 of the detection apparatus 110 comprises a single 9 unit 122. Moreover, although an internal calibration unit 70 is preferred, this is not 11 utilised in the second embodiment 110; instead a 12 single calibration sample (not shown) is placed 13 adjacent the photo-multiplier tube 52 to provide an 14 indication that the device is operating correctly.

16 A third embodiment 210 of a detection apparatus is 17 shown in Figs. lla-llc. The detection apparatus 210 18 comprises a housing 212 which houses similar 19 components as the housing 12 of the first embodiment 10, like components not being described further. The 21 housing 212 is made up from a main cylindrical body 22 281 and sealed by lids 282, 283. The lids 282, 283 23 and windows 96, 97 are sealed by way of various o 24 ring seals 284. A vacuum release valve 285 and power and communication socket 286 are provided 26 within the lid 282 of the housing 212.

28 An output window 96 and an input window 97 are 29 provided in the lid 283 of the housing 212, through which the light from a laser (not shown) exits and 31 light reflected enters the housing 212 respectively, 32 to allow for detection of fluorescein or I. : : r 1 hydrocarbons. Laser light from a laser ranging 2 device (not shown) also exits and enters the housing 3 212 via the windows 96, 97.

Lenses (not shown) are provided within the housing 6 212 to generate the line scan as described in 7 relation to the first embodiment 10 except that they 8 are not provided within the wall 213 of the housing 9 212 but rather enclosed or housed by the housing 212.

12 The detection apparatus 10 is shown in perspective 13 view in Fig. 4a and 4b and in slightly more detail 14 in Fig. 3. The detection apparatus 10 will be connected to a remotely operated vehicle (ROY) 90 as 16 shown in Fig. 7a and 7c, 8a -8c. A Hercules type 17 ROV with manipulators 92 and camera (not shown) is 18 suitable for mounting the detection apparatus 10.

To ensure that the detection apparatus 10 is 21 monitoring the pipeline 40, the projected beam 24 is 22 synchronized with the view from the camera of the 23 ROV, and/or, if provided, the camera provided in the 24 housing 12.

26 In this way an operator can be confident that the 27 entire pipeline 40 has been effectively monitored.

28 The synchronization can be achieved either by 29 fitting a standard sensor unit (not shown) onto a pan-and-tilt camera unit such as the camera of the 31 ROV or by attaching the standard sensor unit to a 32 separate, but linked pan-and-tilt unit (As shown in :le c:. ::.

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1 Fig. 12). This allows full articulation of the 2 apparatus 10, enabling it to survey the entire 3 structure 40 regardless of the angle / orientation 4 of the location being surveyed.

6 Before use, the air within the housing 12 is 7 evacuated. Upon immersion in water, any water 8 leaking into the apparatus 10 will be detected by a 9 loss of the vacuum within the apparatus 10 and will also be detected by the water ingress sensor (not 11 shown) which is adapted to automatically send 12 signals to the apparatus control system (not shown) 13 in order to immediately shut down the power supply 14 thereby avoiding further damage of the apparatus 10.

16 As described subsequently, for safety reasons the 17 apparatus 10 is configured to only allow the laser 18 30 to power up at a water depth greater than 15m.

19 This is achieved using two pressure sensors (not shown) wired in series in order to detect the depth 21 of the apparatus 10. The redundant pressure sensor 22 is employed in the event that the other malfunctions 23 in order to create a failsafe system. However, in 24 order to check the operation of the device before deploying it, two magnetic switches are provided on 26 a cover plate. The purpose of these magnetic 27 switches is to override the pressure sensors only 28 when the cover plate is on,thereby allowing the 29 operation of the laser 30 to be checked in an environment where no laser exposure could escape 31 outside the apparatus 10.

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1 In use, the ROV 90 with attached detection apparatus 2 10 is flown to a pipeline for inspection and 3 positioned around 3-5 metres therefrom. The W or 4 blue laser 14 emits a beam of light 5a and directs it towards the filter 16. The filter 16 removes all 6 light other than the wavelength of the light which 7 is known to excite fluorescein or oil, that is light 8 with a wavelength of 488nm (fluorescein) or 405nm 9 (oil). The filtered beam of light 5b is split by a beam splitter 72 (not shown in Fig. 2) and around 8% 11 of the light is directed into the internal 12 calibration unit 70 and onto fluorescein samples on 13 the optical wheel 74. The characteristics, for 14 example wavelength & intensity, of the light emitted from the fluorescein samples are detected by the 16 photodiode detector 78.

18 The rest of the beam of light 5b, around 92%, enters 19 the beam expander 18 which varies the width of the beam of light 5b so that the eventual width of the 21 light on the pipeline 40 is of a consistent size.

22 The beam of light 5c continues from the beam 23 expander 18 into the line generation optics 20 where 24 it is changed from a beam of light having a circular cross section to a beam of light having a planar 26 cross section. The beam of light Ed exits the 27 housing 12 of the detection apparatus 10 through a 28 concave lens 22 and is directed towards the pipeline 29 40. The concave lens 22 causes the beam of light Be to gradually dissipate outwardly so that the width 31 of the beam of light Be is greater the further away : .:' . i If:: : : c.

1 the beam of light is from the detection apparatus 2 10.

4 Concurrently, the laser ranging device 30 emits a laser which is reflected by the mirrors 32, 34 and 6 also directed out of the housing 12 towards the 7 pipeline 40. The information gained from the laser 8 ranging device 30 is used to automatically control 9 the stepping motor 19 of the beam expander 18 to ensure a consistent width L of light being projected 11 upon the pipeline 40 by the W or blue laser 14.

13 Thus the beam of light 24 forms an excitation line L 14 upon the pipeline 40, where the pipeline may typically be in the region of 40cm in width, and the 16 immediate vicinity of the pipeline 40.

18 Fluorescein or oil which has escaped from the 19 pipeline 40 and is present in this beam of light Be will absorb the light and re-emit fluorescence light 21 at a longer wavelength (typically green, with a 22 wavelength of 520nm for the fluorescein or 450nm for 23 the oil).

Any light reflected or emitted in the direction of 26 the input convex lens 62 will be absorbed by it 62.

27 The input filter 56 removes the frequency of the 28 light which was emitted by the W or blue laser 14 29 (in this example, 488nm or 450nm) so that reflected but unabsorbed light will not travel any further 31 into the detection apparatus 10.

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1 The filtered light continues into the photo 2 multiplier tube 52 which multiplies the signal and 3 detects its presence. The light then proceeds to 4 the lockin-amp 50 which amplifies the signal, and electronically filters the light so that only the 6 specific frequency corresponding to the excitation 7 of fluorescein (520nm) and oil (450nm) remains.

9 Frequency sensitive electronics quantify the fluorescence intensity and relate it to the amount 11 of fluorescein or oil in the beam Be. This data is 12 transmitted to the base via standard ROV data 13 connections and displayed on a PC using customised 14 software. In this way regions of high fluorescein or oil concentration may be detected in real time, 16 giving an indication of likely riser or pipeline 17 leak locations. In addition to providing a graphic 18 intensity, and thus fluorescein or oil concentration 19 map of the riser or pipeline, the software can be set to generate an alarm when specified fluorescein 21 or oil concentration thresholds are reached.

23 The second 110 and third 210 embodiments of the 24 invention function in a similar manner to the function of the first embodiment 10 described above.

27 An alternative embodiment directly detects the 28 presence of hydrocarbons by emitting light of the 29 frequency 349nm which will excite hydrocarbons. The lockin-amp 50 will be similarly calibrated to detect 31 the presence of light excited by hydrocarbons rather 32 than fluorescein.

: the t. : :e e: a: .: 2 As certain lasers, such as the laser 14, may be 3 dangerous to use because they can blind people, 4 certain embodiments of the apparatus include a safety device to prevent the laser from being 6 activated above a depth of 15m.

8 An advantage of embodiments of the present invention 9 is that they may be utilised around 3-5m away from the pipeline whereas some conventional systems 11 require a far closer inspection of a few 12 centimetres.

14 The detection apparatus 10, 110 may be mounted on a pan and tilt mechanism (as shown in Fig. 12) on the 16 ROV in order to direct it towards the pipeline 40.

18 An advantage of embodiments of the present invention 19 is that they are straightforward to use and, due to their ability to monitor even minor leaks quickly in 21 real time, can be used to activate an audible alarm 22 sensor when a critical level of fluorescein or oil 23 is detected. The high speed inspection provided by 24 the apparatus 10 also reduces the time and cost involved in conducting the survey.

27 Embodiments of the present invention such as the 28 detection apparatus 10, 110, 210, have the advantage 29 that these are the first effective remote or stand off type sensor for such applications designed 31 specifically for use with ROVs. As discussed above, 32 this allows the survey to be conducted from a safe '' e: 1 distance e.g. around 3 metres from the structure 40 2 being surveyed.

4 Furthermore, an advantage of embodiments of the present invention is the speed at which data may be 6 obtained given the use of a line scan opposed to a 7 point scan. Thus leaks may be detected at an 8 earlier stage which may reduce the repair costs.

A further advantage of certain embodiments is that 11 the precise source of the leak can be determined 12 whereas for previous single point detection lasers, 13 the actual source of the leak can be difficult to 14 pinpoint. This is possible even in murky water with the ROV light switched on since neither of these 16 factors will affect the signal detected by the 17 apparatus 10.

19 Furthermore, an advantage of certain embodiments of the invention is that the use of a line scan can 21 provide for visualization of the leaks to determine 22 the direction in which the fluorescein/hydrocarbon 23 is flowing and thus aid the location of the source 24 of the leak.

26 A further advantage of certain embodiments of the 27 invention is the ability of the apparatus to both 28 detect and provide a degree of quantification of the 29 leak will allow informed decisions to be made on the likely impact of the leak, both on pipeline 31 efficiency and on the environment.

: .:. t. : a: . e., , e Be,, 1 Improvements and modifications may be made without 2 departing from the scope of the invention.

Claims (1)

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   : : : 1 Claims 3 1. Detection apparatus adapted to detect leaks 4 from a structure, comprising: a generation means adapted to generate 6 radiation; 7 a direction means adapted to direct radiation 8 toward a structure; and 9 a detection means adapted to detect radiation received from the structure.

   12 2. Detection apparatus according to claim 1, 13 wherein the direction means is adapted to direct 14 radiation from inside of the apparatus to outside the apparatus.

   17 3. Detection apparatus according to either of 18 claims 1 or 2, wherein the radiation generated by 19 the generation means is light.

   21 4. Detection apparatus according to claim 3, 22 wherein the light is laser light.

   24 5. Detection apparatus according to any preceding claim, wherein the direction means comprises a 26 conversion means adapted to convert the radiation 27 generated by the generation means into radiation 28 which has a substantially planar cross-section.

   6. Detection apparatus according to claim 5, 31 wherein the conversion means is also adapted to 32 convert the planar cross-section radiation such that : es. l:e te' :: :.

   1 its cross section increases as the radiation travels 2 towards the structure.

   4 7. Detection apparatus according to either of claims 5 or 6, wherein the conversion means 6 comprises a concave lens.

   8 8. Detection apparatus according to any preceding 9 claim, wherein the structure is a sub sea riser or pipeline.

   12 9. Detection apparatus according to any preceding 13 claim, wherein the generation means generates 14 radiation at a wavelength suitable for excitation of a material, the presence of which is indicative of 16 the presence of hydrocarbons.

   18 10. Detection apparatus according to claim 9, 19 wherein the material comprises fluorescein or hydrocarbons.

   22 11. Detection apparatus according to any preceding 23 claim, wherein the direction means further comprises 24 a varying means adapted to vary the dimensions of the radiation beam emitted by the generation means.

   27 12. Detection apparatus according to claim 11, 28 wherein the varying means comprises a beam expander.

   13. Detection apparatus according to either of 31 claims 11 or 12, wherein the varying means is : t:d t' :: : : : 1 further adapted to selectively vary the width, 2 length and angle of the radiation beam.

   4 14. Detection apparatus according to any preceding claim, wherein the apparatus further comprises a 6 ranging means.

   8 15. Detection apparatus according to claim 14, 9 wherein the ranging means is adapted to emit light from the apparatus toward the structure in order to 11 detect reflection of the light and thereafter 12 calculate the distance between the apparatus and the 13 structure.

   16. Detection apparatus according to either of 16 claims 14 or 15, wherein the ranging means is 17 adapted to allow control of the varying means.

   19 17. Detection apparatus according to any preceding claim, wherein the detection means comprises a means 21 to focus the radiation received from the structure.

   23 18. Detection apparatus according to claim 17, 24 wherein the means to focus the radiation comprises a convex lens.

   27 19. Detection apparatus according to either of 28 claims 17 or 18, wherein the detection means is 29 adapted to detect radiation generated by the excitation of the material whose presence is 31 indicative of the presence of fluorescein or 32 hydrocarbons.

   : '. .:e' :::e : :: .e 2 20. Detection apparatus according to any preceding 3 claim, wherein the detection means comprises an 4 optical filter adapted to permit the passage of said radiation and prevent the passage of radiation of 6 other wavelengths which are not generated by the 7 excitation of said material.

   9 21. Detection apparatus according to any preceding claim, wherein amplification means is provided to 11 multiply the radiation detected by the detection 12 means.

   14 22. Detection apparatus according to claim 21, wherein the amplification means comprises a photo 16 multiplier tube.

   18 23. Detection apparatus according to any preceding 19 claim, wherein the detection means comprises a means to electronically filter the signal of radiation 21 detected.

   23 24. Detection apparatus according to any preceding 24 claim, wherein an internal calibration system is provided which directs a portion of the radiation 26 from the generation means to a known sample of 27 material.

   29 25. Detection apparatus according to claim 24, wherein the internal calibration system comprises a 31 detector to detect the presence and characteristics 32 of radiation emitted from said sample material.

   : I. c:. .:: : : : 2 26. Detection apparatus according to either of 3 claims 24 or 25, wherein the internal calibration 4 system comprises a rotatable wheel controlled by a stepping motor, the wheel having a plurality of 6 material samples thereon which can each interact 7 with the radiation directed from the radiation 8 generation means.

   27. Detection apparatus according to any of claims 11 24 to 26, wherein signal processing electronics 12 connect the amplification means and the detector of 13 the internal calibration unit to a data transmission 14 unit and onward to a remote control station such as an offshore platform, ship or onshore base.

   17 28. Detection apparatus according to any preceding 18 claim, wherein the apparatus is communicable with 19 control and output display software to allow remote control of the apparatus to be performed.

   22 29. A method of detecting a leak in a structure, 23 the method comprising: 24 generating radiation; directing the radiation towards a structure; 26 and 27 detecting at least a portion of the radiation 28 received from the structure.

   30. A method of detecting a leak in a structure 31 according to claim 29, wherein the method further :. c' :: : : : le 1 comprises the step of determining the 2 characteristics of the detected radiation.

   4 31. A method of detecting a leak in a structure according to either of claims 29 or 30, wherein the 6 structure is a submerged structure.

   8 32. Detection apparatus substantially as 9 hereinbefore described with reference to Figs. 1 to 12.

   12 33. A method of detecting a leak in a structure 13 substantially as hereinbefore described with 14 reference to Figs. 1 to 12.