GB2566001A

GB2566001A - Condition monitoring device and safety system

Info

Publication number: GB2566001A
Application number: GB1708910.3A
Authority: GB
Inventors: Cowin Neil
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-06-05
Filing date: 2017-06-05
Publication date: 2019-03-06
Also published as: GB201708910D0

Abstract

The invention relates to a condition monitoring device for flexible risers or underwater structures, the device at least one strain gauge or sensor 61 configured to directly measure strain values at a surface 47 of the riser or structure 1,100 , an attachable housing for locating the strain gauge in contact with the surface of the riser or underwater structure, a signal converter to receive and convert electrical signals from the strain gauge into an acoustic signal, and an acoustic transmitter. A plurality of these devices can be used together in a system. The devices may have eddy current inspection or ECI array components 63, and a motion sensor. The housing may have a flexible jacket. The housing may be attachable by a clamp or collar.

Description

Condition Monitoring Device and Safety System

FIELD OF THE INVENTION

The present invention relates to a condition monitoring device and in particular, though not exclusively, to a condition monitoring device for measuring strain in flexible risers and underwater structures. The invention further relates to a condition monitoring system comprising a plurality of condition monitoring devices according to the invention.

BACKGROUND

The increased focus on health, safety and environment (HSE) in the offshore industry has increased the need for pre-emptive actions in order to increase safety and minimise unnecessary stress on the environment.

Risers are pipes used for the production, drilling and export of oil and gas from the seabed. A riser system is a key component for offshore drilling or floating production projects. The cost and technical challenges of the riser system increase significantly with water depth. The design of a riser system depends on factors such as the field layout, vessel interfaces, fluid properties and environmental conditions in the location.

There is a need for the protection of personnel from gross flexible riser failure and the resulting hydrocarbon fluid release subsea and into the facilities.

Various integrity management systems and techniques are utilised to ensure the safe continued working of risers. For example, close visual assessments and camera inspections may be carried out routinely. Remotely operated vehicles (ROVs) and automated riser inspection tools are also known examples of systems used to assess the integrity of risers in an array.

Techniques used to assess riser integrity include radiography, eddy current inspection (ECI), annular vacuum testing and the like.

Flexible risers consist of several layers of polymer. An exemplary flexible riser structure may include a carcass layer which prevents collapse under hydrostatic pressure, an internal pressure sheath acting as the boundary for the conveyed fluid, a pressure armour layer resists internal and external pressure in the hoop direction, tapes provide anti-wear and resistance to wire movement and are also present as a manufacturing aid. Further layers include tensile armour which provides axial strength with some additional hoop strength, an insulting layer to reduce heat loss and an outer sheath which protects against seawater ingress and external mechanical damage. Abrasion layers can be added for extra protection.

The costs of exchanging a flexible riser can make production unviable. Therefore, the monitoring of the structural integrity of the riser and its various layers is crucial to maintain operation.

Typically, external integrity and surveillance of the riser can be done visually by ROV.

Other condition monitoring processes include vent gas monitoring which monitors vent gas rates, annulus pressure and annulus free volume, in order to determine the integrity of the flexible riser. The system looks at the main components of the flexible riser such as the outer sheath, armour layer, the inner polymer sheath and the end-fitting. Sudden fluctuations in the monitored parameter(s) suggest a change of integrity of the riser.

Load monitoring can be used to observe motion within the flexible riser over time in order to estimate the level of fatigue. The level of fatigue is typically monitored in critical areas, such as the bend stiffener and the riser sag bend, which are the most fatigue prone areas of the flexible riser.

Magnetic Eddy Current Flexible Riser Inspection can be used to detect corrosion, cracking and misalignment in tensile armour wire layers. Eddy Current Inspection (ECI), utilises an alternating current applied to an inspection coil. A magnetic field is created and when placed next to a conductor it induces an eddy current field in the material. When the eddy current field is disrupted by a flaw in the material, it causes an imbalance which is magnified and can be reported. The technique is useful through non-conductive or conductive coatings to test the weld/material underneath the coating. As a result, Eddy Current Inspection (ECI) can be used for crack detection, material sorting and coating measurements.

Alternating Current Field Measurement (ACFM) is an electromagnetic technique for nondestructive testing detection and sizing of surface breaking cracks. ACFM is useful for all metals, ferrous or non-ferrous and, since it doesn't require direct electrical contact with the surface under testing, it can work through coatings such as paint or rust. The ACFM probe induces a uniform alternating current in the area under test and detects magnetic field of the resulting current near the surface. If no defects are present, the current is undisturbed. A crack redirects the current, therefore, the ACFM probe measures disturbances in the field and uses mathematical modelling to estimate crack size.

Various apparatus are available to deploy the testing devices at the required test site. ROVs are the most common, moving the device into the required location under the guidance of a remote pilot. ROVs are expensive to deploy on a regular basis and must be transported to the required location before deployment. Alternatively, a crawler apparatus is moveable along the riser to various locations. The crawler is connected to and operated from the topside by umbilical cables. It can be difficult to manoeuvre such crawlers around bends in the riser and monitoring of one location ends as the apparatus moves on down the riser to another location.

Regular and routine monitoring of flexible risers for would be advantageous. In particular, at the highest stress locations of the flexible riser.

BRIEF SUMMARY OF THE DISCLOSURE

Accordingly, it is an object of certain embodiments of the invention to provide a condition monitoring system for flexible risers and underwater structures which overcomes, at least partly, one or more of the problems associated with the prior art.

According to a first aspect of the invention there is provided a condition monitoring device for flexible risers or underwater structures comprising at least one strain gauge configured to directly measure strain values at a surface of the riser or structure, a housing for retaining the at least one strain gauge and configured to locate the strain gauge in contact with the surface of a riser or underwater structure, the housing being configured to be fixed onto the flexible riser or underwater structure with an attachment device, and a signal converter operable to receive and convert electrical signals from the strain gauge into an acoustic signal and an acoustic transmitter operable to transmit acoustic signals generated by the signal converter from the strain gauge measurement.

In certain embodiments, the housing comprises a jacket. More specifically, the jacket is a flexible jacket. Yet more specifically, the flexible jacket may be formed of a polymer matrix or the like. In this way, the jacket may be wrapped around the flexible riser and fixedly attached thereto.

It is much preferred that the jacket is adapted to encircle the circumference of a flexible riser. More specifically, the jacket may be sized to wrap around the full circumference of the flexible riser. In this way, the strain gauge may be configured to monitor strain in the flexible riser about its circumference.

In certain embodiments the housing may further comprise a former or a casing. The casing is preferably substantially rigid. In certain embodiments, the casing provides a support for the jacket. The casing may be a frame or the like. In this way, the jacket may be encased or enclosed by the casing.

In certain embodiments, the casing comprises a C-shaped hinged cage. More specifically, the hinged cage may be configured to wrap around the circumference of a flexible riser. In this way, the jacket may be encased or enclosed in the hinged cage and fixed about the flexible riser using attachment devices on the hinged cage.

In certain embodiments, the flexible jacket comprises a first layer. More specifically, the flexible jacket comprises a first layer configured to retain the at least one strain gauge. In this way, when the flexible jacket is fixed to the flexible riser or underwater structure, the strain gauge is located in direct and intimate contact with the surface of the flexible riser or underwater structure.

In certain embodiments, the condition monitoring device comprises a plurality of strain gauges in a strain gauge array. More specifically, each of the strain gauges in the array is configured to be located in direct contact with the surface of a flexible riser or underwater structure. Preferably the array of the strain gauges is retained in the housing which is arranged to locate each of the strain gauges in contact with the surface of a riser or underwater structure. In certain embodiments, the array of the strain gauges may be retained in the first layer of the flexible jacket.

In certain embodiments, the strain gauges in the strain gauge array are arranged to such that fibre stress in the riser is measured around substantially the entire circumference of the riser. More specifically, the strain gauge array is configured to measure strain in the flexible riser surface about its entire circumference. The strain gauge array preferably measured the inner and outer fibre stress in the surface of the flexible riser.

In certain embodiments, the strain gauge array comprises four strain gauges configured to measure strain about the entire circumference of the flexible riser.

In this way, the device is locatable such that the at least one strain gauge is positioned to directly measure strain values of tensile and compressive forces at a surface of a flexible riser or underwater structure. The strain gauge measures strain values on the surface of the flexible riser or underwater structure and the measured value used to predict the integrity and lifespan of the riser or structure. The strain gauge is configured and located to directly measure actual surface strain. More specifically, the at least one strain gauge is operable to gauge strain in the outer fibre of the flexible riser.

In certain embodiments, the condition monitoring device further comprises an Eddy Current inspection (ECI) array. In preferred embodiments, the Eddy Current inspection array is retained in the housing which is configured to locate the Eddy Current inspection array in proximity with the surface of a riser or underwater structure.

In certain embodiments, the flexible jacket comprises a second layer. More specifically, the flexible jacket comprises a second layer configured to retain the ECI array. In this way, when the flexible jacket is fixed to the flexible riser or underwater structure, the ECI array is located in proximate the surface of the flexible riser or underwater structure.

In certain embodiments, the second layer is outermost of the flexible jacket. In this way, when the flexible jacket is fixed to the flexible riser or underwater structure, the first layer is in contact with the surface of the riser or underwater structure and the second layer is in contact with the opposite side of the first layer.

In certain embodiments, the ECI array comprises a coil conductor or at least one transducer, an alternating current source and at least one detecting transducer. The ECI array is operable to monitor the integrity of in the armour wires of the flexible riser or underwater structure when in position about a flexible riser or underwater structure. Changes in the magnetic field flux strength detected from the ECI array are indicative of defects or breaks in the armour wires.

In certain embodiments the attachment device comprises a clamp. Preferably the clamp is operable to fixedly attach the housing to the flexible riser or underwater structure.

In certain embodiments the clamp is flexible.

In certain embodiments the clamp comprises a collar.

In certain embodiments the clamp comprises a collet.

In certain embodiments the clamp comprises a matrix polymer, Kevlar or the like. In this way, the clamp is flexible and may be wrapped around a flexible riser or the like.

In certain embodiments the clamp is affixed in position with fasteners, a resin or a gel former or a combination thereof.

In certain embodiments, the clamp is deployed by an ROV or a diver.

In certain embodiments, the housing comprises an attachment device at each end thereof. In such embodiments, the attachment devices may be a clamp, a collar or a combination thereof.

In certain embodiments the signal converter preferably comprises at least one transducer. The transducer is preferably operable to convert the electrical output signal from the at least one strain gauge into an acoustic transmission.

In certain embodiments, the, or a further signal converter is operable to receive and convert electrical signals from the ECI array into an acoustic signal. More specifically, the, or the further signal converter comprises at least one transducer. In preferred arrangements, the, or the further signal converter comprises a plurality of transducers.

In certain embodiments, the, or the further signal converter comprises a modem and a microprocessor. The microprocessor is operable to receive a low voltage signal from a modem which converts the signals received from the strain gauge and, if present the ECI array, to the low voltage signal. The microprocessor is operable to convert the low voltage signal to a noise output signal.

In certain embodiments, the acoustic transmitter is operable to transmit acoustic signals generated by the signal converter from the ECI array.

In certain embodiments, the acoustic transmitter operable to transmit acoustic signals generated by the signal converter from the strain gauge measurement.

In certain embodiments, the acoustic transmitter comprises an amplifier to enhance the noise output signal.

It is much by preference that each condition monitoring device comprises a power supply. More specifically, the power supply may be a battery. Yet more specifically, the power supply may be an extended life battery such as a lithium cell battery or the like.

In certain embodiment, the, or each, condition monitoring device further comprises a motion sensor. In this way, movement of the device may be assessed during storms or events.

According to a second aspect of the invention there is provided a condition monitoring system comprising a plurality of condition monitoring devices according to the first aspect of the invention.

In certain embodiments, each condition monitoring device is located on a flexible riser or underwater structure to monitor fatigue life, cracking and defects therein. More specifically, each condition monitoring device is located at a position on a flexible riser in a high stress location. Therefore each condition monitoring device is fixed to the flexible riser at a position on a flexible riser in a high stress location. Certain high stress locations include, but are not limited to: the hang off section below the bend stiffener, the pre-sag bend section adjacent the sag bend, the jumper section adjacent the sag bend, the drag section and adjacent the touchdown position on the seabed. It should be understand that the condition monitoring device of the invention may be fixed at any position on a flexible riser or underwater structure including known intrados and extrados and zones or high critical loadings. These zones include the highest propensity zones for defects and subsequent failure in the riser or structure due to events creating gross fatigue in the materials and/or the structure.

In certain embodiments, the system comprises five condition monitoring devices. More specifically, the five condition monitoring devices are fixed to the flexible riser at the hang off section below the bend stiffener, the pre-sag bend section adjacent the sag bend, the jumper section adjacent the sag bend, the drag section and adjacent the touchdown position on the seabed.

In certain embodiments, each condition monitoring device is fixed in location for a period of time ranging from 1 year to 10 years or more. Each device may be typically fixed in location for between 3 and 10 years or more, typically 5 to 10 years.

In certain embodiments, the system further comprises at least one acoustic signal receiver. More specifically, the acoustic signal receiver is a hydrophone. Preferably the hydrophone is located remote from the condition monitoring devices. The hydrophone is a microphone which detects sound waves underwater. In this way, acoustic signals transmitted from one or more of the condition monitoring devices is detectable by at least one hydrophone.

In certain embodiments, the system may comprise a plurality of hydrophones in an array.

The hydrophone(s) is typically located in the water adjacent a facility. The facility may be located at least partially above the water in order to provide a work station.

The acoustic data transmission underwater to the hydrophone(s) provides an acoustic telemetry communication system which is reliable and accurate. The acoustic communication system preferably comprises the signal converter operable to receive and convert electrical signals from the strain gauge and, if present, the ECI array into an acoustic signal, an acoustic transmitter operable to transmit acoustic signals generated by the signal converter from the strain gauge measurement and, if present, the ECI array measurement and at least one acoustic signal receiver.

Preferably, the, or each condition monitoring device comprises the signal converter operable to receive and convert electrical signals from the strain gauge and, if present, the ECI array into an acoustic signal, the acoustic transmitter operable to transmit acoustic signals generated by the signal converter from the strain gauge measurement and, if present, the ECI array measurement and the at least one acoustic signal receiver is remote from the, or each, location of the condition monitoring device.

In certain embodiments, the condition monitoring system comprises a data output interface. Preferably the data output interface comprises a computer processing unit (CPU) and/or a microprocessor. More specifically, the data output interface provides an operator output interface operable to provide data from the strain gauge(s) and, if present, from the Eddy current inspection (ECI) array to the operator. Yet more specifically, the data output interface provides an operator output interface operable to provide an output proportional to the acoustic data received by the hydrophone.

In certain embodiments, the operator output interface provides a graphical output. More specifically, the operator output interface comprises a graphical output for the data associated with work hardening of the armour wires of the flexible riser.

In this way, the system is operable to provide online monitoring of the data captured by the device.

In certain embodiments, the system provides a fixed system for deployment on flexible risers. More specifically, each condition monitoring device is fixedly attached to the flexible riser.

In certain embodiments, the system may be deployed and fixed to gas process flexibles and/or hydrocarbon production flexible risers.

In certain embodiments, the system comprises a power supply. Preferably the power supply is integral to the system. It is much by preference that each monitoring device comprises a power supply.

In certain embodiments, the system comprises analysis software. More specifically, the CPU and/or microprocessor of the system comprises analysis software.

The strain gauges are located on the flexible riser so as to measure directly the surface strain. In this way, it is possible to monitor the load the flexible riser is experiencing from surface data and through each layer.

The Eddy Current inspection (ECI) array is operable to define cracks and crack lengths within the armour wires in a flexible riser.

Thus, the data output interface receives strain and defect data from the condition monitoring devices and is programmed with the analysis software which is operable to analyse the actual loads in the flexible riser or underwater structure. In this way, it is possible to monitor and analyse, in real time, loads produced by, for example, storms and real subsea conditions.

Eddy current changes detected by the Eddy current inspection (ECI) array may also detect work hardened steels. In this way, by using magnetisation monitoring, it is possible to identify the ageing of a flexible riser under flexure and compare the data received to a baseline and a fatigue condition model on a time base.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described with reference to the accompanying drawings of which:

Fig. 1a is a schematic representation of the layers of a flexible riser;

Fig. 1b is a schematic representation of the layers of an alternative flexible riser;

Fig. 2 is a schematic representation of a facility above a field layout of flexible riser;

Fig. 3 is a schematic representation of a flexible riser subsea configuration;

Fig. 4 is a cross-sectional schematic representation of a condition monitoring device according to the invention fixed to the surface of a flexible riser;

Fig. 5 is a cross-sectional schematic representation of a condition monitoring device embodying the invention fixed to a flexible riser;

Fig. 6 is a schematic representation of a condition monitoring device embodying the invention in flattened configuration prior to fixing about a flexible riser;

Figs. 7a and 7b are schematic cross sections of an Eddy current inspection array suitable for use in a condition monitoring device embodying the present invention;

Figs. 8a and 8b show schematic representations of a signal converter and acoustic communication system for use in embodiments of the invention; and

Fig. 9 is a schematic representation of a condition monitoring system embodying the invention fixed to a flexible riser at the highest stress locations where the highest likelihood of detects and failure can occur.

Referring now to Fig. 1a this shows a cross sectional view of a typical configuration of a subsea hydrocarbon carrying flexible riser 1. The riser 1 is formed of multiple layers, each having a function within the riser. The cross section shown in Fig. 1a, beginning with the innermost layer and working radially outwards has a carcass 3, an internal pressure sheath 5, and interlocked pressure armour layer 7, a back-up pressure layer 9, an anti-wear layer 11, an inner layer of tensile armour 13, a further anti-wear layer 15, an outer layer of tensile armour 17 and an outer sheath 19. Fig. 1b shows an alternative riser 10, comprising a carcass layer 103, an inner liner layer 105, a pressure armour layer 107, a tensile armour layer 117 and an outer sheath 119.

The layers of the riser 1, 100 act to maintain the integrity of the flexible riser and is subject to large pressures and forces over the lifespan of the apparatus. Monitoring the condition of the layers of the flexible riser 1, 100 is critical in protecting against defects and failure.

In particular, it is crucial to monitor cracks and defects in the metallic armour wires forming layer 17, 117 below the outer sheath 19, 119. The armour layer 17, 117 is formed of metallic wires of typically 3mm depth in cross section. In the embodiment shown in Fig. 1b the layer 117 is formed of two rows of wires laid at 35 degrees to the longitudinal axis of the flexible riser 100.

Fig. 2 illustrates how the hydrocarbon carrying flexible risers 1, 100 are utilised in service subsea for a FPSO facility 21 or a semi-submersible facility (not shown) or fixed facility (not shown) and jacket (not shown). The riser 1, 100 hangs from the FPSO 21 and over a midwater arch supporting structure 23. The arch supporting structure 23 is attached to buoyancy 25 in order to maintain its position in the water. The riser 1, 100 hangs from the arch supporting structure 23 to the seabed 27. A FPSO 21 will have multiple risers 1, 100 hanging therefrom at any one time.

Fig. 3 shows a riser 1, 100 hanging from an FPSO 21. The five locations where the riser 1, 100 experiences the high levels of stress are shown as reference numerals 29, 31, 33, 35 and 37 respectively. Each of these locations has been modelled and is known to be a high stress zone in flexible risers used in hydrocarbon production. In the depicted arrangements, the five locations 29, 31, 33, 35 and 37 are the hang off section 29 below the bend stiffener, the pre-sag bend section 31 adjacent the sag bend 43, the jumper section 33 adjacent the sag bend 43, the drag section 35 after the arch section 45 and adjacent the touchdown position 37 on the seabed 27.

Fig. 3 also shows arch supporting structure 23 tethered to the seabed 27 by chain 39 attached to clump weight 41. The arch supporting structure 23 supports the arch section 45 of the flexible riser 1, 100.

Fig. 4 is a cross-sectional schematic representation of a condition monitoring device 50 according to the invention fixed to the surface 47 of a flexible riser 1, 100. The condition monitoring device 50 is formed of a flexible polymer jacket 51 and a first, inner layer 53 and a second outer layer 55. Collar 57 is formed of a matrix polymer and is located at a first end of the flexible jacket 51 and clamp 59 at an opposite end of the flexible jacket 51. The flexible jacket 51 wraps around the flexible riser 1, 100 and first, inner layer 53 is brought into intimate contact with the surface 47 of the riser 1, 100. Collar 57 and clamp 59 are tightened around the riser 1, 100 so as to fix the flexible jacket 51 to the riser 1, 100.

Inner, first layer 53 comprises one or more strain gauges (as best seen in Figures 5 and 6). When the jacket 51 is fixed to the riser 1, 100, the strain gauges are located in operable contact with the surface 47 of the riser 1, 100. The clamp 59 and collar 57 maintain the jacket 51 and, therefore the inner, first layer 53, in intimate contact with the surface 47 in order that the strain gauge(s) can measure directly the strain in the layers of the riser 1, 100. The clamp is preferably a C-shaped clamp fixture. In this way, the jacket is located about the circumference of a riser and fixed thereto to locate the inner circumference of strain gauges in the jacket against the external fibre surface of the riser to create a designed radial load to ensure the interface between the strain gauges and the fibres of the external surface of the riser. External pressure on the jacket created by the water depth will assist in the external fixing of the jacket to the riser.

Referring to Figure 5, the condition monitoring device 50 has a power supply (not shown) in the form of lithium cell batteries. The power supply is operably connected to a modem or transducer for the strain gauges 61 located in the first inner layer 53 and to an Eddy Current Inspection array 63 located in the second, outer layer 55.

The strain gauges 61 within first, inner layer 53 are fixed in contact with the surface 47 of riser 1, 100. In this way, the strain gauges are located and are operable to provide a strain measurement which is transferred to an electrical output proportional to the stress at the outer fibre surface 47 of the flexible riser 1, 100. The Eddy Current Inspection array 63 is maintained in position around the riser 1, 100 such that when the power supply (not shown) energises the coil conductor of the array 63, Eddy currents are established in the wires of the armour layers 13, 17, 117 of the riser 1, 100. Changes in the Eddy currents causes a change in the electrical output from the array 63. In this way, defects in the armour wires, such as cracks, can be measured and monitored.

Figure 6 shows an array of strain gauges 61 embedded in the first, inner layer 53 of the condition monitoring device 50. The device 50 is shown in a flat, pre-deployment configuration in which flexible polymer jacket 51 has a collar 57 and a clamp 59 at opposing ends of the first, inner layer 53. When the device 50 is deployed and fixed around the circumference of a riser, each of the strain gauges 61 is brought into operable contact with the surface of the riser in order to measure the strain in the outer sheath thereof.

When the device 50 is fixed about the flexible riser (not shown), a cylinder band of strain gauges 61 will be located against the elastomeric sheath of the riser so as to take the strain data of any fibre surface movement. The measured data will be converted into a voltage and communicated through the acoustic communication system. The system provides for online, real time monitoring of the strain data at the surface of the riser. That data may be used to conduct modelling exercises relating to the strain profile of the sheath of the riser in various environmental conditions and over various lifespans. It will then be possible to conduct fatigue assessment on current damage to the riser sheath and to simulate events from storms and correlate the loadings and the riser’s movements (via a motion sensor (not shown)) that the flexible riser is experiencing. This simulation can be done by the software utilised to conduct the modelling exercises of flexible riser to understand the worst case environmental loadings.

Although not shown, it should be understand that the second, outer layer of the condition monitoring device 50 can contain a similar array of Eddy Current Inspection sensors. Figures 7a and 7b depict an Eddy Current Inspection sensor 64 forming the, or at least a portion of the Eddy Current Inspection array 63 of the condition monitoring device 50.

The sensor 64 comprises a coil conductor 65 operably connected to a power supply (not shown). Energising conductor coil 65 establishes Eddy currents 67a, 67b in metallic armour wires 69 in the riser 1, 100. In Figure 7a, the Eddy Current 67a is undisturbed due to armour wires 69 being intact and defect free. In Figure 7b, the armour wires 69 have a crack 71 which causes a disturbance in the Eddy Current 67b. The change in the Eddy Current 67a, 67b caused by the crack 71 leads to a detectable change in the electrical output of the Eddy Current Inspection sensor 64 and the ECI array 63.

The SEC (saturation eddy current) 67a, 67b creates a magnetic field in the material 69 and is set to the correct intensity to limit the effects of the magnetic properties of the material 69. The Eddy Current Sensor 64 measures perturbations in the magnetic flux field in the material 69. The magnetic field can be induced through either an electromagnetic coil 65 or through magnetising transducers in an array. For flexible risers, a coil 65 is used to induce the ferro-magnetic field onto the armour wires 69 located 6mm beneath the sheath coating and it will be monitored by a detector coil or transducer receivers(not shown).

The monitored Eddy Current data is sent to a computer processing unit (CPU, not shown) in the FPSO via the acoustic communication system (not shown). The condition monitoring device is operable to detect cracks and pitting defects as small as 0.5 mm in the armour wires 69. The flexible riser coatings can be 6mm in thickness and more and the ECI technique can work through materials and flat surfaces up to 32 mm in thickness. This condition monitoring device allows a “stand -off” from the surface of up to 100 to 140 mm to allow the strain gauge array to be positioned on the surface of the elastomeric coating of the flexible riser. The “stand off’ is the optimal distance from the magnetic field source were field strength induced in the metal conductor (i.e. the item under inspection e.g. the armour wires)is at its highest flux density. At the “stand off” distance in the vicinity of a current carrying wire, the magnetic flux density is directly proportional to the current flow in amperes. In certain embodiments, the current carrying wire in the present invention may be a coil or can be transducers with small “D” coils included. Defects in the material 69 cause a change in the permeability of the material 69 and the position as the amount of eddy currents 67 at that point as depicted in Figure 7b.

The ECI (Eddy Current Inspection) technique provides good quality magnetic field strength below coatings and marine growth and into the ferro-magnetic materials below for inspection requirements. The ECI array comprises a coil conductor with transducers for monitoring the magnetic field. When the condition monitoring device is fixed in position around a flexible riser, the array of transducers will be tightly fixed around a cylinder former or jacket in a close spacing to ensure effective coverage of the armour wires underneath the elastomeric sheath of the flexible riser.

The ECI array will create a magnetic field in the armour wires in a 1.5 m zone. Any breaks in the wires will affect the magnetic field and this will be correlated to damage and surface area by the software of the condition monitoring system and specifically monitored in the computer system topside. It is also possible to monitor a percentage of corrosion in the zone.

The condition monitoring system further comprises an acoustic communication system. The acoustic communication system is depicted in Figures 8a and 8b.

Figures 8a and 8b together provide a schematic representation of how the condition monitoring system produces and conducts the acoustic communication, initially turning data from the strain gauge(s) and/or ECI array to an acoustic noise signal underwater and reconverting the acoustic noise signal back to a digital data output above the water level through the hydrophone and cable and onto the monitoring computer interface and providing a data link to a topside communication system to send it onshore.

The condition monitoring system comprising multiple condition monitoring devices has an acoustic telemetry communication system comprising an acoustic transmitter 87 and an acoustic receiver being hydrophone 88.

The, or each, condition monitoring device comprises a sensor attachment mechanism 75 in communication with a strain gauge electrical bridge 77. The ECI array may provide a further electrical bridge (not shown). The voltage output 79 from the electrical bridge 77 is electrically connected to a signal converter comprising a printed circuit board (PCB) 73 which comprises a modem 81 and a microprocessor 83. In this way, the data signal (voltage signal) is converted into an acoustic signal (sound wave) by microprocessor 83. The PCB further comprises an amplifier 85 which receives and amplifies the acoustic signal 86 before the amplified acoustic signal passes to the acoustic transmitter 87.

The signal converter comprises a modem 81 and a microprocessor 83. The microprocessor 83 is operable to receive a low voltage signal from the modem 81 which converts the signals 79 received from the strain gauge bridge 77 and, if present the ECI array, to the low voltage signal. The microprocessor 83 is operable to convert the low voltage signal to a noise output signal 86.

When the condition monitoring device is a device such as the one depicted in the embodiment shown in Figure 4, the ECI array and the strain gauge(s) of the subsea transponder both provide an output voltage to the signal converter at modem 81. The microprocessor 83 is then operable to receive a low voltage signal from the modem 81 which converts the signals received from the strain gauge bridge 77 and the ECI array to the low voltage signal. The microprocessor 83 is operable to convert the low voltage signal to a noise output signal 86.

The acoustic transmitter 87 comprises an amplifier 84 to enhance the noise output signal from amplifier 85.

As seen in Figure 8b, the system further comprises a hydrophone 88. The hydrophone 88 is a microphone which detects sound waves underwater from the acoustic transmitter 87 of a condition monitoring device 50. In this way, acoustic signals transmitted from one or more of the condition monitoring devices is detectable by the hydrophone 88. In operation, the hydrophone 88 may scan many channels and will receive data from varying frequencies. Thus, the subsea transponder is operable to transmit data from the ECI array and strain gauge array.

The acoustic communication system of the condition monitoring system comprises a topside computer having a data output interface 89. The data output interface 89 is operable to receive acoustic signals from the acoustic transmitter (not shown) and comprises a printer circuit board (PCB) 91 on which there is an amplifier 92 operably connected to receive the acoustic signal from the hydrophone 88 and a modem 93. The modem 93 is operably connected to a digital signal processor 95. The data output interface 89 further comprises a computer processing unit (CPU) 97 operably connected to a microprocessor in the form of the digital signal processor 95. The data output interface 89 provides an operator output interface in the form of a user interface 99 of CPU 97. The operator output interface 99 has a user display and control software such that it is operable to provide data from the strain gauge(s) and, if present, from the Eddy current inspection (ECI) array to the operator. The data output interface 89 provides an operator output interface 99 operable to provide an output proportional to the acoustic data received by the hydrophone 88.

The operator output interface 99 may provide a graphical output for the data associated with work hardening of the armour wires of the flexible riser. In this way, the condition monitoring system is operable to provide online monitoring of the data captured by the device.

The CPU 97 is preferably programmable. The CPU may be programmed with a number of software programmes such as, for example, an integrity decision software, a calibration software, an error correction and detection software and/or an extract unit identification and value software.

The data output interface 89 is preferably located on a facility or an FPSO (see 21, Figure 9). The data output interface 89 is preferably in data communication with at least one remote computer processing unit (CPU) or other programmable processing unit. In this way, the data output interface 89 is able to communicate to onshore or other remote offices or facilities by data acquisition, telemetry, wireless communication and/or telephone connection from the data output interface 89 to a remote data receiver. The remote data receiver may be a data server, computer processing unit (CPU) or other programmable processing unit, for example. In this way, it is possible to provide real time, online monitoring of the fixed ECI array output, the fixed strain gauge output and, if present, motion sensors on the condition monitoring device.

In use of the device, the transducers on the ECI array and the strain gauges emit data that is converted to a low voltage in a modem which then converts the signal into a noise output signal transferred through an amplifier in the acoustic transmitter and onto an underwater receiver attached underwater on a facility.

The “in water” transponder converts signals from the modem interface to noise which is then received by the hydrophone receiver. Data from the hydrophone is transmitted through the cable directly into the computer modem to be recorded into graphical output and data reports for strain movement. Thus, load, time base and changes in flux leakage which defines deformation and cracked armour wires can be monitored. The condition monitoring device is operable to monitor work hardening of the steel or the armour wires as resistance increases with that effect and thus so does current. Work hardening in the wires also affects the magnetic field therein which is monitored.

The acoustic underwater communication system is a very simple system and very reliable. This is a system using an amplifier and an acoustic receiver, powered by lithium cell batteries capable of 10 years or more power supply, without cabling. To date, the system is capable of communicating proficiently underwater in sea water or fresh water over an 8 km radius and at a depth capability of 6 km.

Figure 9 shows an exemplary embodiment of a condition monitoring system according to an embodiment of the invention. Five condition monitoring devices 50 are fixed to the flexible riser 1, 100 at locations 29, 31, 33, 35 and 37 (see Figure 3). Each condition monitoring device is powered by a separate, lithium cell battery and provides acoustic data as a result of measuring strain and eddy current changes in the flexible riser 1, 100. The acoustic data is transmitted from the condition monitoring devices 50 to a remote hydrophone 88 located in the water below FPSO 21. Data cables 101 transfer data from the hydrophone to the output interface (not shown) on FPSO 21. It should be understood that the system may comprise a plurality of hydrophones in an array to ensure data retrieval to the computer interface. In certain arrangements, the hydrophone(s) 88 will be positioned through a moon pool on FPSO 21 or affixed to the structure with cables 101 running topside to an area of the FPSO and a computer monitoring system interface unit (not shown).

The, or each condition monitoring device 50 will be fixed into the highest stress locations 29, 31, 33, 35 and 37 of a flexible riser 1,100. The deployment of the devices 50 can be done by a subsea former (e.g. C-clamp fixture) and attached by ROV, diver or during installation of the new flexible riser 1, 100 itself. In the latter embodiment, the, or each condition monitoring device 50 can be fixed in position on the flexible riser onshore or on the vessel before the flexible riser is deployed subsea.

Flexible risers are a high threat apparatus which, to date have largely relied upon ROVs to conduct a part inspection. The inspection is done mainly visually, by camera, which cannot monitor crack growth in sufficient detail to assess the fatigue life of the riser equipment.

It is, therefore, necessary to develop inspection equipment which can monitor fatigue in real time and enable receipt of constant inspection data and strain data for monitoring the defect growth.

The condition monitoring device of the present invention is operable to measure surface stress from an actual direct strain measurement. In this way, the device is operable to inspect cracks or present defects growth in the materials, such as the armour wires or zeta wires layer, which provide the structural strength of the flexible riser

Regular frequency monitoring of flexible risers can be achieved by the non-destructive examination (NDE) arrays in a condition monitoring device according to the invention. Eddy current inspection and strain gauges attached in a fixed array to the flexible riser provides the opportunity to conduct real time and online monitoring. Monitoring can be conducted on a high frequency due to the use of acoustic telemetry subsea equipment in the device of the invention. The data is sent by acoustic transmission through transceivers and transducers to a hydrophone attached to a facility. Online monitoring can be assessed via computer systems on a high frequency period.

The NDE fixed arrays based upon ECI (eddy current) or, alternatively alternating current field monitoring (ACFM) can ascertain defects and cracking defects within the flexibles armour wires specifically.

The strain gauge array is located in specific high stress positions across the subsea flexible. The strain gauge array is operable to assess fibre stress and subsurface stress /strain within the section of the flexible to which it is fixed across the highest risk zones in operation.

The condition monitoring system is operable to assist in the safe long term operation of risers beneath facilities and may be deployed to mitigate the risks from known defects in risers over a period of time and to allow a defined period of assessment to be put in place. The condition monitoring system may be used to provide a pre-warning of fatigue and cracking failures in risers which may evolve into hydrocarbon leaks below the facilities. The threat to loss of life is high in such a circumstance. This condition monitoring system provides a safety device which enhances early warning of impending flexible riser failures and reduces the threats of major incidents and ‘hydrocarbon leakage’.

In a condition monitoring device according to an embodiment of the invention, the EDI array and the strain gauge array will be placed in a formed structure, such as a flexible jacket or a casing, and clamped around the flexible riser in one or more, preferably five, of the highest stress and threat locations for the flexible riser suffering integral damage. This will thus enable constant monitoring of those locations on behalf of oil operators and the facility personnel, for example.

The condition monitoring device will communicate by its own power supplied by a battery system in an underwater environment and will be a fixed array supplying data to a topside computer for onwards assessment by experienced stress assessment engineers.

The condition monitoring system will be operable to send constant data back to an onshore facility. Events such as major storms will thus be critical items which can be analysed in real time.

Further condition monitoring devices may be fixed onto the riser in other zones on the flexible thought to require monitoring.

Condition monitoring devices according to embodiments of the invention can be built on to new flexible risers prior to their installation subsea.

The condition monitoring system provides a constant monitoring capability and online data management system. The data can be analysed by stress engineers and thus derive fatigue and longevity of the flexible riser by specific analysis. Onshore testing of supplied flexible items may be part of the engineering assessment prior to installation.

As an alternative to deployment on a flexible riser, a condition monitoring device according to embodiments of the invention can be affixed to underwater structures such as subsea pipelines, wellhead jumper lines and subsea structures, caissons and catenary steel and alloy risers to monitor across welded zones. A stress assessment of the underwater structure can then be monitored at a high frequency to demine the current and long term condition and integrity of the structure.

The condition monitoring device and system provide fixed position integrity monitoring for hydrocarbon production and/or gas production flexible risers subsea with online data transfer of the information for assessment. The device and system provides efficient subsea communication and a detailed stress assessment on a continual basis for the safety of personnel and facilities. The condition monitoring system is a high value-added integrity safety system and will reduce the threats of hydrocarbon leakage. The data from the system can be assessed by professional engineers to derive constant assessment of the condition monitoring of the flexible riser or underwater structure. This will advance the understanding of the condition of the riser or structure to assist in the threat and risk control to personnel and facilities.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A condition monitoring device for flexible risers or underwater structures comprising at least one strain gauge configured to directly measure strain values at a surface of the riser or structure, a housing for retaining the at least one strain gauge and configured to locate the strain gauge in contact with the surface of a riser or underwater structure, the housing being configured to be fixed onto the flexible riser or underwater structure with an attachment device, and a signal converter operable to receive and convert electrical signals from the strain gauge into an acoustic signal and an acoustic transmitter operable to transmit acoustic signals generated by the signal converter from the strain gauge measurement.

2. A device according to claim 1, wherein the housing comprises a jacket.

3. A device according to claim 2, wherein the jacket is a flexible jacket.

4. A device according to claim 2 or claim 3, wherein the jacket is adapted to encircle the circumference of a flexible riser.

5. A device according to any one of claims 1 to 4, wherein the housing comprises a former or a casing.

6. A device according to claim 5, wherein the casing comprises a C-shaped hinged cage.

7. A device according to any one of claims 3 to 6, wherein, the flexible jacket comprises a first layer configured to retain the at least one strain gauge.

8. A device according to any one of the preceding claims, comprising a plurality of strain gauges in a strain gauge array.

9. A device according to claim 8, wherein the array of the strain gauges is retained in the housing which is arranged to locate each of the strain gauges in contact with the surface of a riser or underwater structure.

10. A device according to claim 8 or 9, wherein the strain gauges in the strain gauge array are arranged such that fibre stress in the riser is measured around substantially the entire circumference of the riser.

11. A device according to any one of the preceding claims, wherein the, or each, strain gauge is configured and located to directly measure actual surface strain

12. A device according to any one of the preceding claims, further comprising an Eddy Current inspection (ECI) array.

13. A device according to claim 12, wherein the Eddy Current inspection array is retained in the housing which is configured to locate the Eddy Current inspection array in proximity with the surface of a riser or underwater structure.

14. A device according to any one of claims 7 to 13, wherein the flexible jacket comprises a second layer.

15. A device according to claim 14, wherein the flexible jacket comprises a second layer configured to retain the ECI array.

16. A device according to claim 14 or claim 15, wherein the second layer is outermost of the flexible jacket.

17. A device according to any one of claims 12 to 16, wherein the ECI array comprises a coil conductor or at least one transducer, an alternating current source and at least one detecting transducer.

18. A device according to any one of the preceding claims, wherein the attachment device comprises a clamp.

19. A device according to claim 18, wherein the clamp is operable to fixedly attach the housing to the flexible riser or underwater structure.

20. A device according to claim 18 or claim 19, wherein the clamp is flexible.

21. A device according to any one of claims 18 to 20, wherein the clamp comprises a collar.

22. A device according to any one of claims 18 to 21, wherein the clamp comprises a collet.

23. A device according to any one of the preceding claims, wherein the housing comprises an attachment device at each end thereof.

24. A device according to claim 23, wherein the attachment devices are a clamp, a collar or a combination thereof.

25. A device according to any one of the preceding claims, wherein the signal converter comprises at least one transducer.

26. A device according to claim 25, wherein the transducer is operable to convert the electrical output signal from the at least one strain gauge into an acoustic transmission.

27. A device according to any one of claims 12 to 26, wherein the, or a further signal converter is operable to receive and convert electrical signals from the ECI array into an acoustic signal.

28. A device according to any one of the preceding claims, wherein the, or the further signal converter comprises a modem and a microprocessor.

29. A device according to claim 28, wherein the microprocessor is operable to receive a low voltage signal from a modem which converts the signals received from the strain gauge and, if present the ECI array, to the low voltage signal.

30. A device according to claim 28 or claim 29, wherein the microprocessor is operable to convert the low voltage signal to a noise output signal.

31. A device according to any one of claims 12 to 30, wherein the acoustic transmitter is operable to transmit acoustic signals generated by the signal converter from the ECI array.

32. A device according to any one of the preceding claims, wherein the acoustic transmitter operable to transmit acoustic signals generated by the signal converter from the strain gauge measurement.

33. A device according to any one of the preceding claims, wherein the acoustic transmitter comprises an amplifier to enhance the noise output signal.

34. A device according to any one of the preceding claims, comprising a power supply.

35. A device according to claim 34, wherein the power supply is a battery.

36. A device according to any one of the preceding claims, comprising a motion sensor.

37. A condition monitoring system comprising a plurality of condition monitoring devices according to any one of claims 1 to 36.

38. A system according to claim 37, wherein each condition monitoring device is located on a flexible riser or underwater structure to monitor fatigue life, cracking and defects therein.

39. A system according to claim 37 or claim 38, wherein each condition monitoring device is located at a position on a flexible riser in a high stress location.

40. A system according to claim 39, wherein each condition monitoring device is fixed to the flexible riser at a position on a flexible riser in a high stress location.

41. A system according to any one of claims 37 to 40, comprising five condition monitoring devices.

42. A system according to claim 41, wherein the five condition monitoring devices are fixed to the flexible riser at the hang off section below the bend stiffener, the pre-sag bend section adjacent the sag bend, the jumper section adjacent the sag bend, the drag section and adjacent the touchdown position on the seabed.

43. A system according to any one of claims 37 to 42, comprising at least one acoustic signal receiver.

44. A system according to claim 43, wherein the acoustic signal receiver is a hydrophone.

45. A system according to claim 44, wherein the hydrophone is located remote from the condition monitoring devices.

46. A system according to any one of claims 44 to 45, wherein the system comprises a plurality of hydrophones in an array.

47. A system according to any one of claims 37 to 46, wherein the acoustic communication system comprises the signal converter operable to receive and convert electrical signals from the strain gauge and, if present, the ECI array into an acoustic signal, an acoustic transmitter operable to transmit acoustic signals generated by the signal converter from the strain gauge measurement and, if present, the ECI array measurement and at least one acoustic signal receiver.

48. A system according to any one of claims 37 to 47, wherein the, or each condition monitoring device comprises the signal converter operable to receive and convert electrical signals from the strain gauge and, if present, the ECI array into an acoustic signal, the acoustic transmitter operable to transmit acoustic signals generated by the signal converter from the strain gauge measurement and, if present, the ECI array measurement and the at least one acoustic signal receiver is remote from the, or each, location of the condition monitoring device.

49. A system according to any one of claims 37 to 48, comprising a data output interface.

50. A system according to claim 49, wherein the data output interface comprises a computer processing unit (CPU) and/or a microprocessor.

51. A system according to any one of claims 49 to 50, wherein the data output interface provides a graphical output.

52. A system according to any one of claims 37 to 51, wherein each condition monitoring device is fixedly attached to the flexible riser.

53. A system according to any one of claims 37 to 52, comprising analysis software.