GB2415256A - Determining the looseness of a joint by imparting and measuring vibrations - Google Patents

Abstract

An apparatus for assessing the join between two mechanically cooperating subsea components (eg a stud 14 and line of a stud link mooring chain 9) comprises an exciting means (eg motorised hammer 25, acoustic source, magnetic source, projectile) for effecting propagation of a signal in one of the components and a receiving means (eg accelerometer (16), hydrophone 15, laser interferometer, strain gauge) for receiving a signal induced in at least one of the components. The received signal is processed to determine whether the components are joined in a loose or not loose condition. Alternatively the system may comprise a magnetic flux loss system, an eddy current system, a nuclear magnetic resonance system or an x-ray system.

Description

24 1 5256 1 UNDERWATER INSPECTION APPARATUS AND METHOD 3 The invention

relates to an apparatus and method for 4 underwater inspection, and in particular to a remote in situ underwater non-destructive inspection apparatus and 6 method for assessing the looseness of an interference fit 7 or welded piece, such as a stud in a stud link chain or a 8 spindle. More particularly, it relates to non 9 destructive inspection of looseness of a piece by analysis of vibration generated in the piece by an 11 exciting unit.

13 A significant proportion of the world's offshore 14 hydrocarbon reserves is produced by turret moored floating, production, storage and offloading facilities 16 (FPSOs). These large vessels are expected to remain 17 permanently on location for periods of between 5 and 25

18 years. In oil fields that are becoming marginal

19 producers such as the North Sea, FPSOs reduce the number of platforms by enabling multiple wells to be tied back 21 to a single production point.

A: . :.

. .. ce. e:e . e.:: . . . . . 1 For an FPSO to remain in position it is moored by wires, 2 synthetic fibre ropes, stud link and open link chains, or 3 a combination. Pertaining to mooring chains, the 4 offshore industry dictates periodic inspection to check for wear, damage and position. The inspection process 6 leads to re-certification of the systems for another 7 subsequent period of use. The frequency of inspection 8 has, until recently, been based upon the estimated 9 operation lifetime of the mooring line. These operation lifetimes are now recognized as overestimates since 11 occurrences of catastrophic mooring line failure well 12 within the operation lifetime. Inspection for chain wear 13 and re-certification is currently carried out on deck or 14 onshore after recovery of the chain and is a costly and time consuming necessity. Mooring chain weighs in the 16 region of 95 to 700 kg per metre and can measure up to 17 4,500 metres in length, depending on the mooring 18 requirement. Its recovery and inspection involves large 19 winching and inspection equipment, requires a lot of space and furthermore causes damage to the chain.

22 A large percentage of mooring chains are stud linked 23 where a section of steel is inserted midway into each 24 link, its function is to prevent entanglement. The stud is either interference fit or welded into the link but 26 over time it can become loose or even absent out of the 27 link during the operation lifetime of the chain. Stud 28 looseness is an integral part of chain re-certification 29 and a hand looseness test is carried out during a certification inspection to assess the status of the 31 stud. Stud looseness is defined in the hand test as 5 mm 32 movement longitudinally in two directions and a 3 mm 33 movement axially for interference fit studs, and no e.: ë:.

. . . ::: e. .: 3 .. .:. 1 movement for welded studs. However the industry is now 2 moving towards a no looseness" policy for both stud 3 types. To enable chain re-certification on site any 4 loose studs are re-pressed or re-welded back into the link during the inspection process.

7 One problem of particular concern is a significant 8 percentage of FPSO mooring chain cannot be recovered for 9 maintenance and inspection. Instead, its condition has to be assessed while it is in service. In-service 11 condition monitoring is undertaken by permanent or 12 ROY/A W deployed underwater video camera systems.

13 However, due to the absence of an in-situ stud looseness 14 assessment method chains cannot be re-certified in service. This is also valid for Tension Leg Platforms, 16 Floating Production Systems, Semi-submersibles, Moored 17 buoys, Guyed Towers, Offshore Mariculture Platforms and 18 any other type of offshore structure that requires chain 19 link moorings.

21 The Tap Test is a well-known method for assessing the 22 structural integrity of a wide range of structures. In 23 its simplest form a bar or hammer is used as an impactor 24 to produce a vibration in the structure. In a loose structure the vibration generated by being struck with a 26 bar or hammer is different compared to that of a 27 correctly fitted piece.

29 Although the Tap Test can be employed with confidence manually, its automation offers several advantages, not 31 least the ability to deploy in hostile or inaccessible 32 environments. Furthermore electronic recording, 33 processing and analysis of the vibration signal removes see ë . . . . . . ::: : .: 4 .. .:. 1 subjectivity about the condition of the structure and 2 allows data to be stored and compared. Processing of the 3 data includes filtering of interfering signals and signal 4 comparison between different structures, or against standards. The final result is a clear "loose" or "not

6 loosen statement presented to the end user. The

7 invention described will make it possible to determine 8 the looseness of a piece under inspection, for example 9 the looseness of a stud in a stud link chain and so enable the assessment of mooring chain integrity during 11 an in-situ re-certification inspection.

13 It is an object of the invention to provide an assessment 14 method and apparatus for underwater inspection alternative to the manual Tap Test.

17 It is a further object of the invention to provide an 18 assessment method and apparatus for underwater inspection 19 that obviates or mitigates drawbacks and deficiencies of

prior art assessment methods and apparatus.

22 It is a further object of the invention to provide an 23 apparatus and method for underwater remote inspection.

Additional aims and objects of the invention will become 26 apparent from reading the following description.

28 According to a first aspect of the invention there is 29 provided apparatus for assessing a join between two mechanically cooperating subsea components, the apparatus 31 comprising an exciting means for effecting a vibration in 32 at least one of the mechanically cooperating components, 33 a receiving means for receiving a vibration signal I: ë:.

a... '.. Id.. . '... : 1 induced in at least one of the mechanically cooperating 2 components, processing means for processing the received 3 signal and determining whether the mechanically 4 cooperating components are joined in a loose or not loose condition.

7 Preferably, the apparatus is adapted to assess the join 8 between a stud and a link of a stud link mooring chain.

According to a second aspect of the invention there is 11 provided apparatus for assessing a join between a stud 12 and a link of a subsea stud link mooring chain, the 13 apparatus comprising: 14 - a frame for locating the apparatus with respect to the stud link mooring chain, the frame supporting an 16 exciting means and a receiving means, wherein the 17 exciting means functions to effect a vibration in at 18 least one of stud or link and the receiving means 19 functions to receive a vibration signal induced in at least one of the stud or link; 21 - processing means for processing the received signal 22 and determining whether the stud and link are joined 23 in a loose or not loose condition.

Preferably, the apparatus comprises means for generating 26 an output signal indicative of a loose or not loose 27 condition of the join.

29 The apparatus may comprise a frame, and an exciter unit and a receiver unit mounted thereon. Preferably, the 31 frame is adapted to locate the exciter unit and receiver 32 unit with respect to the mechanically cooperating 33 components.

Be: ë:- . . . ::: .: 6 .. .:. 2 The apparatus may further comprise a control unit adapted 3 to control actuation of the exciting means.

The frame may comprise a U-shaped bracket adapted to be 6 locate the apparatus with respect to a link of a stud 7 link mooring chain.

9 The frame may be adjustable in size, thereby allowing location of the apparatus with respect to mechanical 11 components of different dimensions.

13 The exciting means may comprise an impacting mass for 14 striking a part of one of said mechanically cooperating components.

17 Preferably, the exciter unit comprises a hammer coupled 18 to a motor. Preferably, a displacement encoder is 19 provided to determine the position of the hammer.

21 Preferably, the speed of the hammer can be adjusted 22 automatically or from the topside control unit.

Preferably, the receiver unit comprises an accelerometer.

26 More preferably, the receiver unit further comprises a 27 hydrophore.

29 The apparatus may be provided with means for attaching the accelerometer to one of the mechanically cooperating 31 components.

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. e. e: .e.: 7 .' .:. 1 Preferably, the apparatus comprises a first subsystem 2 located beneath the surface of the water, and a second 3 subsystem located at or above the surface of the water, 4 the first and second subsystems being connected by a communication link.

7 Preferably, the first subsystem comprises an underwater 8 receiving means for receiving a vibration signal, and an 9 underwater processing means for analysing the received signal.

12 Preferably, the second subsystem comprises a processing 13 unit, a control unit, and a user interface.

According to a third aspect of the invention, there is 16 provided a method of non-destructive testing of two 17 mechanically coupled subsea components, the method 18 comprising the steps of: 19 - Inducing a vibration in at least one of the mechanically cooperating components; 21 Detecting a vibration signal induced in at least one 22 of the mechanically cooperating components and 23 generating a detection signal; 24 - Processing the detection signal, and; - Determining whether the mechanically cooperating 26 components are joined in a loose or not loose 27 condition.

29 The method may comprise the additional steps of: - Digitising the detection signal using an underwater 31 processing module, and; 32 Storing the digitised signal in a memory of the 33 underwater processing module.

2 The method may comprise the additional steps of: 3 - Analysing the digitised signal to obtain a signal 4 dataset; - Comparing the signal dataset to reference datasets 6 in a database.

8 The method may comprise the step of transmitting signal 9 data to a subsystem located at or on the surface of the water.

12 According to a fourth aspect of the invention, there is 13 provided apparatus for assessing a join between two 14 mechanically cooperating subsea components, the apparatus comprising transmission means for effecting propagation 16 of a signal in at least one of the mechanically 17 cooperating components, a receiving means for receiving a 18 signal induced in at least one of the mechanically 19 cooperating components, processing means for processing the received signal and determining whether the 21 mechanically cooperating components are joined in a loose 22 or not loose condition.

24 The invention described is an apparatus and method for assessing the looseness of a piece under inspection such 26 as studs in stud link mooring chain while the mooring is 27 in-service; looseness being defined as the existence of 28 movement or space for movement between two mechanically 29 cooperating components, for example the stud and the link. The apparatus is designed to be deployed by any 31 standard underwater means such as ROV, A W. robot or 32 diver.

, , 9 9 *, 'me 2 ::e 1 The apparatus may include means for the induction and 2 recording of vibration in the interference fit or welded 3 piece such as the stud, and/or the chain link itself, and 4 the processing and analysis of the recorded vibration signal, the characteristics of which differ if the piece 6 is loose or not loose. Signal processing interprets and 7 converts the recorded data into a 'loose/not loose' 8 statement that appears on a display unit. The deployment 9 of the apparatus and the looseness test are conducted underwater.

12 In the preferred embodiment, the apparatus is made up of 13 two separate parts joined by a communication link. One 14 part is deployed underwater, the other topside such as onboard a floating vessel, offshore platform or other 16 surface facility. The topside part of the apparatus 17 comprises a user interface, a control unit and a 18 processing unit. The underwater part comprises a control 19 unit, an exciting unit, receiving unit/e and a processing unit.

22 An optional feature of the topside part is an interface 23 allowing the operator to control and monitor the activity 24 of the underwater unit.

26 Another optional feature of the topside part is a 27 controlling unit that manages the data exchanged between 28 the topside and underwater units.

Another optional feature of the topside part is a 31 processing unit that analyses the data sent by the 32 underwater unit.

'I' ' ' ' ''..22 1 An optional feature of the topside processing unit is a 2 means to make the final result of the signal processing, 3 such as a "loose" "not looses, signal, available to the 4 end user via an output unit.

6 Another optional feature of the topside part is the 7 ability to connect to a remote server in order to send 8 and receive signal and control data.

An optional feature of the underwater part is that it is 11 ruggedised to a standard adequate to prevent damage to 12 any of its units during underwater deployment.

14 Another optional feature of the underwater part is that it can be fixed onto a rigid framework designed to bring 16 the exciting unit and the receiving unit/e in the correct 17 position to excite vibration in the piece under 18 inspection, and to receive the resulting vibration 19 signal.

21 An optional feature of the rigid framework structure onto 22 which the underwater part of the apparatus is mounted is 23 it is adjustable to accommodate the various sizes of 24 mooring chains. The framework may also be suitable for deployment by a platform such as an ROV or A W so that 26 exciting unit and receiving unit/e are brought into 27 correct proximity to the piece under inspection, such as 28 the stud of a stud link mooring chain, during in-service 29 inspection.

31 An optional feature of the rigid framework structure onto 32 which the underwater part of the apparatus is mounted is 33 that it is capable of deploying two underwater parts e . ë . . . . 11 . .:. ee. e..

1 positioned at right angles from each other in such a way 2 that two consecutive chain links can be tested 3 simultaneously.

Another optional feature of the underwater part is a 6 means of conveying the processed data real time to the 7 topside part so that the looseness status of the piece 8 under inspection can be known real time during the course 9 of the inspection.

11 An optional feature of the exciting unit of the 12 underwater part is a means to produce single and multiple 13 energy impulses into the piece under inspection.

Another optional feature of the exciting unit is it is 16 capable of operating underwater down to the operating 17 depth of submersible vehicles.

19 Another optional feature of the exciting unit is that is is controllable by a control unit so that the required 21 energy impulse is delivered at the appropriate location 22 and time on the piece under inspection.

24 An optional feature of the control unit of the underwater part is the automatic determination of the position of 26 the piece under inspection such as the stud in relation 27 to the exciting unit. This ensures that the exciting 28 unit is always in the correct position for delivering 29 energy impulses into the piece under inspection.

31 An optional feature of the receiving unit/e of the 32 underwater part is a means to detect the vibration 33 induced in the piece under inspection such as a * * * c ^ 12. . . . . . * 1 hydrophore and/or accelerometer with a sensitivity and 2 frequency range appropriate for detection of the 3 vibration. Preferably, the frequency range of the 4 vibration is several tens of kHz or less.

6 Another optional feature of the receiving unit/e is a 7 means to send the recorded signal to a processing unit 8 where the signal will be analysed and the looseness of 9 the piece determined.

11 An optional feature of the processing unit of the 12 underwater part is a means to digitise and store in 13 memory the recorded signal from the receiving unit/e.

Another optional feature of the processing unit is a 16 means to analyse the data by the use of mathematical 17 algorithms and techniques well known in signal processing 18 such as Fast Fourier Transformation (FFT).

Another optional feature of the processing unit is a 21 means to compare the processed data to set of references 22 used to determine if the analysed data matches that of a 23 loose piece or a not loose piece.

There will now be described, by way of example only, an 26 embodiment of the invention with reference to the 27 following drawings, of which: 29 FIG. 1 is a block diagram illustrating the preferred embodiment of the present invention; . . . e*e e .

* 1 . . ....

J 1 FIG. 2 is a perspective schematic of the preferred 2 embodiment of the apparatus being deployed on a stud 3 link mooring chain; FIG. 3 is a cross section schematic of the 6 pressurized housing showing detail of the motor and 7 hammer part of the exciting unit and its position on 8 the chain; FIG. 4 is a cross section schematic of the receiving 11 units and their position in relation to the mooring 12 chain.

14 Fig. 1 is a block diagram illustrating the preferred embodiment of the present invention.

17 In Fig. 1 a non-destructive inspection apparatus 18 according to the present invention includes an underwater 19 exciting unit 1 for generating an energy impulse into the piece under inspection 2 to produce a vibration in the 21 piece under inspection 2. The vibration induced in the 22 piece 2 is detected by the underwater receiving unit or 23 units 3 where the vibration signal is converted into an 24 electrical signal that can be transferred to the underwater processing unit 4 via the underwater control 26 unit 5.

28 The underwater signal processing unit 4 conditions the 29 electrical signal using well-known techniques such as amplification and filtering. Using well known techniques 31 in the art of signal conversion, unit 4 then performs an 32 analogue to digital conversion of the conditioned signal 33 and stores the digitised data in its electronic memory.

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ëe e e e e ee ee e e ee e ee seee e e e 1 A e ee e e e eese e e e 1 This digitised data can be either further processed in 2 the underwater processing unit 4 and/or be transferred 3 via the underwater control unit 5 to the topside control 4 unit 6 using well known data transmission protocol. The digital information is then analysed using or underwater 6 processing unit 4 and/or the topside processing unit 7, 7 and algorithms such as FFT. The resulting dataset is 8 then analysed by either unit 4 or 7 and compared to known 9 reference datasets obtained from loose and not loose pieces in order to determine the looseness of the piece 11 under inspection 2. The final "loose" or "not loose" 12 information is stored and/or sent to the topside user 13 interface 8.

Fig. 2 is a view illustrating a schematic construction of 16 a stud looseness diagnosis apparatus according to the 17 preferred embodiment of the present invention correctly 18 deployed on a link 9 of a mooring chain by an underwater 19 vehicle (not illustrated).

21 The apparatus is placed over the link 9 by means of a 'U' 22 shaped bracket 10. The bracket 10 is designed so that it 23 fits over link 9, which can vary in size. Fitting is 24 achieved through the use of brackets of different size or by being made adjustable by means of screws and sliding 26 parts.

28 The pressurized housing 11 is fixed to the bracket 10 29 with clamps 12 and screws 13. The pressurized housing 11 contains the underwater processing unit 4, the underwater 31 control unit 5 and the underwater exciting unit 1 32 comprised of a motor (not shown) and a hammer 25. In an 33 alternative implementation, units 4, 5 and 1 are placed . ce . . 1 C 1 J 1 in separate pressurised housings linked by communication 2 means.

4 FIG. 3 is a schematic of the pressurized housing showing detail of the hammer of the exciting unit and its 6 position on the chain. The exciting unit 1 is composed 7 of a hammer 25, linked to the axle 23 of a motor 24 via 8 couplings 26. The hammer 25 is composed of a base 25a 9 which is fixed to the coupling 23 of the motor 24, which is situated inside the pressure housing 11, a shaft 25b 11 connecting an impacting mass 25c to the base 25a. The 12 impacting mass 25c can be of varying shapes such as a 13 sphere or a conic form.

The position of the hammer 25 is determined using a shaft 16 rotation encoder (not illustrated) linked to the axle 23 17 of the motor 24 present in the pressurised housing 11 and 18 linked to the underwater control unit 5.

Under control of the underwater control unit 5 the hammer 21 25 is rotated by the motor 24 to first detect the 22 presence and location of the stud 14 of link 9 through a 23 controlled rotation preferably through 300 . If the 24 hammer 25 intercepts the stud 14 during this rotation the movement is halted and the position of the hammer 25 is 26 recorded by the shaft rotation encoder. The control unit 27 5 returns the hammer 25 back to its preset start 28 position. The information from the shaft rotation 29 encoder is used by the control unit 5 to drive the motor 24 actuating the hammer 25 through the angle recorded by 31 the shaft rotation encoder. This ensures that the hammer 32 25 will strike the stud 14 correctly.

. . . e a.

. . 1 f TO . - 1 Under the control of the underwater control unit 5 the 2 hammer 25 is rotated to strike the stud 14 at a speed 3 controlled by the underwater control unit 5.

Under the control of the underwater control unit 5 and 6 topside control unit 6 the angle of rotation of the 7 hammer 25 during a strike can be changed by a variable 8 amount to ensure a good hit on the stud 14.

The preset start position is set by the design of the 11 apparatus so that in this reset position the hammer 25 is 12 retracted into a protective housing (not illustrated) 13 that can be attached to part of the bracket 10. The 14 start position is set such that the apparatus can be deployed over the link 9 without endangering the 16 integrity of the hammer 25 when the hammer 25 is in its 17 reset position.

19 Once the hammer 25 has struck the stud all subsequent movement is immediately ceased to allow for the vibration 21 signal induced in the stud 14 to be detected by the 22 underwater receiving unit or units 3. When the vibration 23 signal has been detected the hammer 25 is allowed to 24 return to the reset position under the control of the underwater control unit 5.

27 Fig.4 is a view illustrating a schematic construction of 28 the underwater receiving units 3 composed of a hydrophore 29 15 and an accelerometer 16. A good contact between the accelerometer 16 and the link 9 is achieved via the use 31 of a magnetic mount 17 fixed securely to the 32 accelerometer 16 and the force exerted by a spring 18.

me- .: me: ë:e c. . . 17 . . . . . . 1 By bringing the accelerometer 16 into direct contact with 2 the link 9 via the magnet 17 makes this receiving unit 3 less sensitive to extraneous acoustic and vibration noise 4 signals than the hydrophore 15.

6 The hydrophore 15 is not placed in direct contact with 7 the link 9 or the stud 14 but fixed next to the 8 pressurized housing 11. Alternatively the hydrophore 15 9 can be replaced by a microphone inside the pressurised housing 11.

12 The hydrophore 15 detects the acoustic energy emitted by 13 the either the link 9 or the stud 14 after it has been 14 struck by the hammer 25. The resulting signal is used in the processing of the signal in the underwater processing 16 unit 4 and top side processing unit 7.

18 The hydrophore 15 also provides a background noise signal 19 reference that is used in the processing of the signal in the underwater processing unit 4 and topside processing 21 unit 7.

23 A stopper 19 on the accelerometer cable 20 ensures the 24 correct disengagement of the magnet mount 17 from the link 9 when the apparatus is pulled away from the link 9 26 under the power of the method used to deploy the system 27 (e.g. an underwater vehicle).

29 The signal recorded by the hydrophore 15 is sent to the underwater control unit 5 present in the pressurised 31 housing 11 via an underwater cable 21.

. . . .. . . . e.

ë e e e 1tS ace e 1 The signal recorded by the accelerometer 16 is sent to 2 the underwater control unit 5 present in the pressurised 3 housing 11 via an underwater cable 20.

The signals from the accelerometer 16 and hydrophore 15 6 are amplified and filtered within the underwater 7 processing unit 4 in order to eliminate signals of 8 unwanted frequencies. Preferably, the frequency range 9 retained is from 200Hz to several tens of kHz. The signal is then digitised using analogue to digital 11 techniques and the resulting data is stored in the 12 underwater control unit 5 memory.

14 The digitised data present in the underwater control unit 5 memory is transferred to the topside processing unit 7 16 via a communication link such as a subsea cable 22 and/or 17 via an underwater communication link (not illustrated) 18 such as the optical fibre umbilical of an ROV or an 19 acoustic modem. These types of communication links are known to those skilled in the art.

22 The topside processing unit 7 applies known processing 23 techniques such as algorithms, FFT, filters, neural 24 networks and pattern recognition to the data to generate a frequency, amplitude and phase spectrum. The spectrum 26 is compared to reference spectra that correspond to 27 "loose" and not loose,' studs. These data processing 28 techniques are well known to those skilled in the art of 29 signal processing. The result of this comparison gives the status of the stud, which is then displayed to the 31 end user via the topside user interface 8.

. c. . ee C . . . . 19. . . . . 1 The stud status information can then be sent to server 2 networks located anywhere in the world via standard 3 telecommunication means such as radio, telephone and 4 satellite links.

6 Various modifications may be made within the scope of the 7 invention herein intended.

9 In one alternative embodiment the accelerometer is placed in contact with the stud instead of the link. In another 11 alternative embodiment the underwater exciting unit 1 is 12 positioned so that it induces energy impulses into the 13 link instead of the stud.

In another alternative embodiment vibration is induced in 16 the piece under inspection 2 by an underwater exciting 17 unit 1 comprised of a laser that fires pulses of light 18 energy at the piece under inspection 2 from a few cm 19 distance.

21 In another alternative embodiment the underwater exciting 22 unit 1 includes an acoustic source that fires pulses of 23 acoustic energy at the piece under inspection 2 in order 24 to induce vibration in the piece.

26 In another alternative embodiment the underwater exciting 27 unit 1 includes a means to deliver pressure waves created 28 by compressed gas or fluids targeted at the piece under 29 inspection 2 in order to induce vibration in the piece.

31 In another alternative embodiment the underwater exciting 32 unit 1 includes a magnetic source that fires pulses of eve c .. e 20..

1 magnetic energy at the piece under inspection 2 in order 2 to induce vibration in the piece.

4 In another alternative embodiment the underwater exciting unit 1includes a device that fires projectiles at the 6 piece under inspection 2 in order to induce vibration in 7 the piece.

9 In another alternative embodiment the underwater exciting unit 1 is comprised of a hydraulic or electric actuator 11 that moves or strikes the piece under inspection 2 with 12 an impacting mass in order to induce vibration in the 13 piece.

In another alternative embodiment the underwater exciting 16 unit 1 includes a vessel that can be inflated and 17 deflated against the piece under inspection 2 to induce 18 vibration or motion in the piece.

In another alternative embodiment the underwater exciting 21 unit 1 includes a vibrating device that is placed in 22 contact with the piece under inspection 2 to induce 23 vibration or motion in the piece.

In another alternative embodiment the underwater 26 receiving unit 3 includes a laser interferometer that 27 measures small displacements at the surface of the piece 28 under inspection 2 from a distance.

In another alternative embodiment the underwater 31 receiving unit 3 comprises of a video measurement system 32 that measures small displacements at the surface of the 33 piece under inspection 2 from a distance.

. c : : : :e . : : ce.

21 aim. . .. 2 In another alternative embodiment the underwater 3 receiving unit 3 includes an ultrasound transducer that 4 measures small displacements at the surface of the piece under inspection 2.

7 In another alternative embodiment the underwater 8 receiving unit 3 includes a strain gauge that measures 9 strain variations induced by small displacements of the piece under inspection 2.

12 In another alternative embodiment the underwater 13 receiving unit 3 includes an acoustic interferometer 14 system that measures small displacements at the surface of the piece under inspection 2 at a distance.

17 In another alternative embodiment the underwater exciting 18 unit 1 and the underwater receiving unit 3 comprise a 19 magnetic flux loss system that measures discontinuities between two closely abutted parts such as the joint 21 between the stud 14 and the link 9.

23 In another alternative embodiment the underwater exciting 24 unit 1 and the underwater receiving unit 3 comprise of a pulsed eddy current system that measures discontinuities 26 between two closely abutted parts such as the joint 27 between the stud 14 and the link 9.

29 In another alternative embodiment the underwater exciting unit 1 and the underwater receiving unit 3 comprise a 31 Nuclear Magnetic Resonance system that measures density 32 of various materials between two closely abutted parts 33 such as the joint between the stud 14 and the link 9.

e ë ea C om C . 2 In another alternative embodiment the underwater exciting 3 unit 1 and the underwater receiving unit 3 comprise of an 4 X-ray system that detects discontinuities between two closely abutted parts such as the joint between the stud 6 14 and the link 9.

Claims (1)

1. .ë ce . . . e he .. o-2 - _} 1 Claims 3 1.

   Apparatus for assessing a join between two 4 mechanically cooperating subsea components, the apparatus comprising transmission means for 6 effecting propagation of a signal in at least one 7 of the mechanically cooperating components, a 8 receiving means for receiving a signal induced in 9 at least one of the mechanically cooperating components, processing means for processing the 11 received signal and determining whether the 12 mechanically cooperating components are joined in 13 a loose or not loose condition.

   2. Apparatus as claimed in claim 1 adapted such that 16 the transmission means effects propagation of the 17 signal in a first component, and the receiving 18 means receives a signal induced in a second 19 component, mechanically cooperating with the first component.

   22 3. Apparatus for assessing a join between two 23 mechanically cooperating subsea components, the 24 apparatus comprising an exciting means for effecting a vibration in at least one of the 26 mechanically cooperating components, a receiving 27 means for receiving a vibration signal induced in 28 at least one of the mechanically cooperating 29 components, processing means for processing the received signal and determining whether the 31 mechanically cooperating components are joined in 32 a loose or not loose condition.

   < # ..

   HA e = , 1 1 4. Apparatus as claimed in claim 3 adapted such that 2 the exciting means effects vibration in a first 3 component, and the receiving means receives a 4 vibration signal induced in a second component, mechanically cooperating with the first component.

   7 5. Apparatus as claimed in any preceding claim, 8 adapted to assess the join between a stud and a 9 link of a stud link mooring chain.

   11 6. Apparatus as claimed in claim 5 comprising means 12 for generating an output signal indicative of a 13 loose or not loose condition of the join.

   7. Apparatus as claimed in any preceding claim, 16 further comprising a frame having an exciter unit 17 and a receiver unit mounted thereon.

   19 8. Apparatus as claimed in claim 7 wherein the frame is adapted to locate the exciter unit and receiver 21 unit with respect to the mechanically cooperating 22 components.

   24 9. Apparatus as claimed in claim 7 or claim 8 wherein the frame comprises a U-shaped bracket adapted to 26 be locate the apparatus with respect to a link of 27 a stud link mooring chain.

   29 10. Apparatus as claimed in any of claims 7 to 9 wherein the frame is adjustable in size, thereby 31 allowing location of the apparatus with respect to 32 mechanical components of different dimensions.

   . . V V 8 8. 8 8 ' C 8 8 8 In, , ,, 1 11. Apparatus as claimed in any of claims 3 to 10 2 further comprising a control unit adapted to 3 control actuation of the exciting means.

   12. Apparatus as claimed in any of claims 3 to 11 6 wherein the exciting means comprises an impacting 7 mass for striking a part of one of said 8 mechanically cooperating components.

   13. Apparatus as claimed in claim 12 wherein the 11 exciting means comprises a hammer coupled to a 12 motor.

   14 14. Apparatus as claimed in claim 13 wherein a displacement encoder is provided to determine the 16 position of the hammer.

   18 15. Apparatus as claimed in any of claims 12 to 14 the 19 speed of the impacting mass is adjustable.

   21 16. Apparatus as claimed in claim 15 wherein the speed 22 of the impacting mass is adjustable automatically.

   24 17. Apparatus as claimed in claim 15 or claim 16 wherein the speed of the impacting mass is 26 adjustable from a topside control unit.

   28 18. Apparatus as claimed in any preceding claim 29 wherein the receiving means comprises an accelerometer.

   e em see .e e e e 8 e e ee e eve I e e 26 e e e e e C 1 19. Apparatus as claimed in any preceding claim 2 wherein the receiving means comprises a 3 hydrophore.

   20. Apparatus as claimed in claim 18 or claim 19 6 provided with means for attaching the 7 accelerometer to one of the mechanically 8 cooperating components.

   21. Apparatus as claimed in any preceding claim 11 comprising a first subsystem located beneath the 12 surface of the water, and a second subsystem 13 located at or above the surface of the water, the 14 first and second subsystems being connected by a communication link.

   17 22. Apparatus as claimed in claim 21 wherein the first 18 subsystem comprises an underwater receiving means 19 for receiving a vibration signal and an underwater processing means for analysing the received 21 signal.

   23 23. Apparatus as claimed in claim 21 or claim 22 24 wherein the second subsystem comprises a processing unit, a control unit, and a user 26 interface.

   28 24. A method of non-destructive testing of two 29 mechanically coupled subsea components, the method comprising the steps of: 31 - Inducing a vibration in at least one of the 32 mechanically cooperating components; ece ee.

   27 ee. 1 - Detecting a vibration signal induced in at 2 least one of the mechanically cooperating 3 components and generating a detection signal; 4 - Processing the detection signal, and; - Determining whether the mechanically 6 cooperating components are joined in a loose 7 or not loose condition.

   9 25. The method as claimed in claim 24 comprising the additional steps of: 11 - Digitising the detection signal using an 12 underwater processing module, and; 13 - Storing the digitised signal in a memory of 14 the underwater processing module.

   16 26. The method as claimed in claim 25 comprising the 17 additional steps of: 18 - Analysing the digitised signal to obtain a 19 signal dataset; - Comparing the signal dataset to reference 21 datasets in a database.

   23 27. The method as claimed in any of claims 24 to 26 24 comprising the step of transmitting signal data to a subsystem located at or on the surface of the 26 water.