Patent Description:
Fasteners and bolts are used to securely join structures or wheels, for example beams and joists, disks, bearings, valves, flanges and plates, used in industry, for example to assemble and retain the superstructure or crane on a ship, or a drilling derrick on an oil or gas rig. Likewise, bolts may be critical to the integrity of a valve, flanges, seal, pipe fitting or blowout preventer. An array of fasteners is provided throughout a structure to securely join rigid members such as beams, cranks, wheels or plates. Bolts, rivets or fasteners are used to secure joints between the sections of rail, beams or joists. The bolts are provided with nuts or fasteners as part of assemblies mounted to the structures. An assembly typically comprises: a bolt head, a thread, washers and a nut rotatably supported on the thread of the bolt. Nuts close to retain bolts joining structures.

Bolts and fasteners are routinely inspected to ensure the rigidity and mechanical integrity of structures. Bolts and fasteners deteriorate in a variety of ways. For example, vibration may cause bolts to loosen and environmental exposure causes corrosion and disintegration of fasteners. Stress may cause bolts to fatigue and shear, and strain may cause bolts to elongate, crack and fail. If a fastener is erroneously opened and a rigid member, such as a beam, is present then it may fail with catastrophic consequences and even fatalities. In a derrick, for example, excessive vibration due to drilling, jarring or stuck pipe can cause failure of structural elements such as elevator rails. Occasionally a bolt is loosened due to excessive and prolonged vibration with disruptive and serious consequences such as failure of a mechanical member, and a falling object.

In the context of the oil industry, risers are assembled from large sections of tubular and used to connect well-heads with platforms. Platforms can include production platforms, floating production and storage offshore (FPSO) vessels, mobile offshore drilling units (MODU) such as drill-ships, semi-submersibles or jack-ups. The riser sections are tubulars, for example pipes manufactured from steel, alloy or composite, that conduct formation fluids to the surface, or, during drilling, conduct drilling fluids to or from the well-bore. In injection wells risers may be deployed to inject fluids into the formation. Risers may connect networks of flow-lines and manifolds from multiple wells. Risers come in various dimensions and specifications and can include large sections for submarine deployment at high pressure. When assembled, riser sections are stacked and sealed flanges couple sections of riser into continuous conduits that covey fluids at pressure and preserve the integrity of the well and of the platform. Therefore, the condition of each section riser is critical and sections of riser are routinely inspected for defects, corrosion and leaks. The thickness, and condition of the fasteners such as bolts, are of particular importance. Non-destructive inspection (NDT) techniques, visual inspection and record-keeping are among the methods used for recording and validating the integrity of connections. Various measurements, such as bolt cross section thickness, surface condition and manual records may be used in calculations and models to analysis the condition and integrity of riser bolts. These methods may form part of special periodic service (SPS) or regulatory regimes to verify riser integrity and the safety of operations. For example, a record may be kept for each section of riser including logs for deployment underwater, tallies including depth and duration of deployment.

Riser sections, when not in use, are stacked on the deck of the vessel or platform. These sections of riser are labelled, often manually. The location, type and history of each section of riser is noted and generally recorded manually. These logs are inspected and produced whenever riser is deployed or validated by third parties as part of SPS or a certification process. The riser sections may be deployed permanently on a particular MODU or platform, or moved to other locations for operations. These sections of riser may be employed globally or in a particular region. Riser sections have a significant value and may be periodically reconditioned or repaired by manufacturers or contractors. an oil or gas rig. Accordingly, there is a requirement to monitor each section of riser throughout its lifetime both while deployed and in storage.

To validate the integrity of structures, routine inspection of fasteners may be obligatory and is frequently conducted in accordance with standards from industry bodies such as API, NAS, ASME, ASTI, BSEE. Similarly, inspection and testing may be required as part of obtaining or maintaining vessel class or type approval with organisations such as DNV-GL, ABS (American Bureau of Shipping) or Lloyds Register. Bolts and fasteners are used subsea temporarily and permanently. For example, bolts securing sections of lower marine riser packages, and BOPs (blowout preventers), may be inspected routinely as part of maintenance and verification during and between operations. This need to confirm the integrity of fasteners on joints in the structure is crucial.

Manual inspection by teams of specialists may include performing various tests of torsional rigidity and torque. These inspections are continuous during the lifetime of an offshore structure, be it a platform or mobile offshore drilling unit (MODU). These inspections can be labour intensive, hazardous and time-consuming requiring extensive training and safety precautions. Teams of technicians will manually inspect a structure and perform tests on fasteners for torque and rigidity by means of rope-access, or ladders or using a cherry-picker or otherwise, in often dangerous conditions. The technicians are exposed to weather, dropped objects, and other hazards from working at height. Interruptions to operations can be costly causing delays to the critical path of a drilling programme or production schedule. These serious incidents have created a requirement for a solution that can remotely, and without manual inspection by means of rope access or interruption of service and downtime for example, detect and confirm the status of a fastener in the derrick or on equipment.

Accordingly, there is a need for a device which will reduce the necessity for manual inspection of fasteners and fastener assemblies, thereby improving worker and operational safety, and reducing delays due to inspections. There is further a need for a device which may be easily retrofitted or installed either on, or in proximity to, a fastener and capable of permanently monitoring the integrity of the fastener while periodically transmitting, wirelessly or by other means, the status of the fastener to a controller for analysis and display of status, changes and trends.

<CIT>, on which the two-part form of claim <NUM> is based, discloses a sensor unit for a screw fastener, the sensor unit comprising a mounting in the form of a cap that rigidly attaches the sensor unit to an element of the screw fastener; an inductive sensor configured to sense movement of the screw fastener; and an evaluation device arranged to process the output of the sensor to detect relative movement of the elements of the screw fastener and enabling display of such relative movement.

<CIT> discloses a sensor unit that is incorporated into a core of a bolt, the sensor unit comprising a stress sensor configured to detect force, load, tension or compression forces on the bolt.

<CIT> discloses a sensor for a rotating element fastener, the sensor unit comprising a mounting in the form of a cap that rigidly attaches the sensor unit adjacent to the fastener; and a sensor configured to sense the presence or position of the screw fastener; and an evaluation unit arranged to process the output of the sensor to detect loosening of the fastener and outputting a warning signal in response to detecting such loosening.

<CIT> discloses a system for monitoring elements of drilling or well control equipment, the system comprising cameras that is arranged on a mobile drilling unit to image the elements of drilling or well control equipment; and a computer system that is arranged to process data received from the cameras to identify and monitor the elements of drilling or well control equipment. The computer system may analyse images sequentially in the time domain to track the direction of equipment, by locating specific elements of the drilling and well control equipment in the imagery data and comparing that location with locations from previous imagery data.

According to an aspect of the invention, there is provided a sensor unit for a fastener assembly, the sensor unit comprising a mounting arranged to rigidly attach the sensor unit to, or adjacent to, a fastener assembly; an optical flow sensor configured to sense movement of the fastener assembly; and a processor arranged to process the output of the optical flow sensor to detect loosening of the fastener assembly and to output a signal representing the status of the fastener assembly.

In this way the monitoring device has the advantage of reducing the frequency of manual inspection, and directing technicians to maintain certain fasteners based on analysis of data and trends, predictive maintenance and critical changes in status. Benefits would include reduced labour costs, defrayed expenses, minimised HSE risk and fewer interruptions of operations for scheduled maintenance. By providing an integrated processor in the sensor unit, a simple monitoring signal can be generated and transmitted by the sensor unit. This will be more robust and less prone to data loss than transmitting the output of a sensor directly.

The fastener assembly may be of any type, including those discussed above.

In an embodiment, the sensor unit further comprises a wireless communication unit arranged to communicate the signal. Communicating wirelessly is particularly advantageous when the sensor unit is mounted in an inaccessible or remote location.

In an embodiment, the sensor is configured to sense angular rotation or axial movement of the fastener assembly. Angular rotation and axial movement are indicative of loosening or potential failure of the fastener assembly, and so detecting this type of movement is particularly important.

In an embodiment, the sensor is configured to sense angular rotation or axial movement of the fastener assembly with respect to an object which the fastener assembly fastens. This type of movement may be indicative of stretching or fatigue of the fastener assembly, and detecting it promptly can prevent failure of the fastener assembly.

In an embodiment, the sensor is configured to sense angular rotation or axial movement of parts of the fastener assembly with respect to each other. This type of movement may indicate loosening of the fastener assembly, for example a nut losing on its respective bolt.

In an embodiment, the mounting is arranged to rigidly attach the sensor unit to the fastener assembly. This can be advantageous in connecting the sensor unit to the fastener assembly so that it remains in the correct position for robust sensing with respect to the fastener assembly.

In an embodiment, the fastener assembly includes an engagement portion which engages an object which the fastener assembly fastens, and the mounting is arranged to rigidly attach the sensor unit to the engagement portion of the fastener assembly. An engagement portion, such as a nut or the head of a bolt, will typically have a standardised shape and dimension, and therefore be particularly convenient as an attachment point.

In an embodiment, the optical flow sensor is configured to sense angular rotation of the engagement portion with respect to the object. Optical flow sensors are well-developed and provide a reliable method for detecting movement, particularly movement perpendicular to an axis of the sensor.

In an embodiment, the mounting is arranged to rigidly attach the sensor unit adjacent to the fastener assembly. In an embodiment, the sensor unit is mounted adjacent to the fastener assembly. Depending on the environment or design of the fastener assembly, it may be more convenient to locate the sensor unit adjacent to, rather than directly on, the fastener assembly. For example, the sensor unit may attached to a surface adjacent to the fastener assembly.

In an embodiment, the sensor unit further comprises an eddy current sensor configured to monitor the condition of the fastener assembly. In an embodiment, the sensor unit further comprises a processor arranged to process the output of the eddy current sensor. An eddy current sensor can be used to detect changes in the condition of the fastener assembly that may not cause movement of the fastener assembly, such as metal fatigue.

According to an aspect of the invention, there is provided a sensor unit according to the invention in combination with a fastener assembly. This may improve the convenience of installing the sensor unit, for example if the sensor unit is integrated into the fastener assembly.

Embodiments of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which:.

The present disclosure concerns a sensor unit <NUM> for a fastener assembly <NUM>. The sensor unit <NUM> may also be known as a monitoring unit, or a sensor assembly. The sensor unit <NUM> may be a wireless sensor unit <NUM> that may be retrofit to a fastener assembly <NUM> for detecting the orientation, and confirming the status, of a fastener, bolt, cap, bolt head, stud, screw, cap screw, washer or rivet for a rigid structure or mounting a rotating member. Applications of the sensor unit <NUM> may be for fasteners that are particularly critical, such as in hydrocarbon processing or high-pressure vessels or flammable atmospheres, or in locations that are difficult to reach, such as subsea risers or wind turbine blades. Equally, the sensor unit <NUM> may be applied to fastener assemblies <NUM> that are frequently made and broken, such as on connections for subsea drilling risers. The sensor unit <NUM> may be applied to monitoring of structures within the derrick that experience high shock, vibration or strain such as bolts securing guide rails for top-drives. Similarly, the sensor unit <NUM> may be mounted on fastener assemblies <NUM> on linkage mechanisms of a top drive, or on wheels or rotating machines, or on flanges, to confirm the status, integrity and condition of the equipment, rotating machinery and pipework, and to avoid dropped objects or failures of equipment in service inside the derrick or around an installation. Likewise, the sensor unit <NUM> could be used to monitor joints, fasteners, rivets, bolts and welds and to demonstrate compliance with API recommended practice <NUM> for operation, inspection, maintenance and repair of drilling and well servicing structures, and 4F for drilling structures. The sensor unit <NUM> could be deployed wherever fasteners are critical to integrity of connections and joints. For example, in difficult to inspect joints such as wind turbine blades, pylons, monopiles, railway joints, subsea bolts, subsea risers, subsea Christmas trees (x-trees), surface x-trees, choke lines, on fasteners or connections and flanges used in flammable atmospheres such as hydrocarbon processing, throughout hydraulic fracturing fleets, lower marine riser packages or jackets. In particular, failure of H4 bolts used on subsea drilling risers and lower marine riser packages can lead to leaks of drilling fluids and hydrocarbons or catastrophic loss of well control and a blow-out. The sensor unit <NUM> may be exploited as a monitoring system for a section of drilling or production riser. The sensor unit <NUM> may be utilised wherever fasteners are critical and frequently made and broken such as on bolts connection sections of drilling riser.

In operational use the sensor unit <NUM> may eliminate the need for a spotter in the derrick checking for loose joints, bolts and fasteners that are considered a DROPS risk. The sensor unit <NUM> could be used to track the status of a fastener in service on a critical structure, flange, plate, joint, valve, pipework or machine and its output used in feedback to plan and direct maintenance and prevent failure in a timely fashion.

The fastener assembly <NUM> depicted in <FIG> comprises two plates or surfaces <NUM> and <NUM> to form a joint, a threaded bolt <NUM> or screw, a head <NUM>, washers <NUM> and a nut <NUM>. Similarly, this could form a rivet or screw. Optionally, the fastener assembly <NUM> may be a riser fastener.

<FIG> shows examples of riser sections <NUM> commonly used in the oil and gas industry, which may be joined together using fastener assemblies <NUM> such as that shown in <FIG>. <FIG> shows further examples of riser sections <NUM> including buoyancy modules. <FIG> shows a riser <NUM>, composed of plural riser sections <NUM>, in use and connected to an oil derrick.

<FIG> shows the construction of a standard riser <NUM>, each with plural riser sections <NUM>. The riser sections <NUM> are provided each as part of respective riser assemblies <NUM> mounted in arrays along the riser <NUM>. Each riser assembly <NUM> may comprise two or more riser sections <NUM>.

Two types of riser assembly <NUM> will be described, the first type being for drilling and the second type being for production. The two types of riser assembly <NUM> have a construction that is generally the same, except that the specifications of the riser sections <NUM> are different, as appropriate to retain different types of fluids, with a corresponding change in width and materials of the pipe wall from which the riser sections <NUM> are fabricated. Therefore, a common description using common reference numerals is given. The following description applies equally to both the first and second types of riser assembly <NUM>, and indeed any riser assembly <NUM>, except where specific reference is made to one of the first and second types.

The riser assembly <NUM> comprises a riser section <NUM> that comprises a riser flange 3a and an elongated body 3b extending between the flanges 3a. The riser assembly <NUM> is coupled using studs (also referred to as bolts) <NUM> and nuts 4a attached through stud apertures in the riser flange 3a. The riser assembly <NUM> also comprises buoyancy jackets 5a and moorings 6a, both secured to the riser section <NUM>.

The sensor unit <NUM> may be retrofitted, or integrated with, riser stud <NUM> or nut 4a. The sensor unit <NUM> comprises a housing <NUM>, a power source <NUM>, one or more sensors and one or more light sources, acoustic or wireless communications means.

The sensor unit <NUM> may optionally be mountable on the riser section <NUM>, stud <NUM>, nuts 4a or flange 3a of a riser assembly <NUM>, which may be for example of the types described above with reference to <FIG>. For example, the sensor unit <NUM> may be provided integrally with the riser section <NUM> or stud <NUM> or nut 4a during manufacture. Alternatively, the sensor unit <NUM> may be configured to be attached to a pre-existing riser section <NUM>.

The sensor unit <NUM> comprises a mounting arranged to rigidly attach the sensor unit <NUM> to, or adjacent to, a fastener assembly <NUM>. The sensor unit <NUM> may optionally comprise a securing member, which acts as the mounting. The mounting may be configured to secure the sensor unit <NUM> to the riser section <NUM>, fastener assembly <NUM>, stud <NUM> or nut 4a.

<FIG> and <FIG> illustrate an embodiment in which the housing <NUM> of the sensor unit <NUM> may be inserted through a hole in the riser section <NUM>, such as a bolt hole or stud aperture, and a mounting provided on the opposite end of the hole to the housing <NUM> and configured to secure the housing <NUM> to the riser section <NUM>. For example, the securing member may be configured to screw into a thread inside the housing <NUM>. However, any securing system may be used to secure the mounting to the housing <NUM>. Alternatively, the housing <NUM> may be provided with a screw portion, and the sensor unit <NUM> configured to be screwed into a thread inside the riser section <NUM>. Alternatively, the sensor unit <NUM> may be provided with holes through which bolts may be threaded to retain the sensor unit <NUM>. Finally, the housing <NUM> may include holes, formed integrally, or plate that may be welded for permanent attachment to the riser fastener assembly <NUM> to provide a continuous record of riser fastener deployment, location and condition. Thus, a compact and easy to install sensor unit <NUM> may be provided. The sensor unit <NUM> may optionally further comprise a backup retention device that is configured to attach the sensor unit <NUM> to a component of the riser fastener assembly <NUM>. For example, the backup retention device may comprise a strand of wire or rope attached to both the riser section <NUM> and the sensor unit <NUM>. Thus, if the mounting fails, the backup retention device ensues that the sensor unit <NUM> does not fall and damage other equipment or personnel. A safer sensor unit <NUM> may thus be provided.

Optionally the sensor unit <NUM> may be integrated into the riser section <NUM>, or bolts <NUM>, or nuts 4a, or the flanges 3a of the riser section <NUM>. In this embodiment, the sensor unit <NUM> is provided as a package that may be mounted into the fastener of the riser section <NUM> inside a suitable cavity provided inside the fastener assembly <NUM>. The cavity may be in any part of the fastener assembly, e.g. the head of the bolt <NUM>, or the nut 4a. The head and nut 4a may also be referred to as an engagement portion. The cavity may also be provided adjacent to the fastener assembly <NUM>, e.g. within the flange 3a.

The sensor unit <NUM> may be an OEM device that incorporates all of the features disclosed herein, but which can be inserted into this cavity inside the body of the fastener or flange 3a or bolt <NUM>. The cavity may have access via a threaded hole such that sensor unit <NUM> can be replaced, for example when the battery is depleted or maintenance is required. The cavity may be preferably cylindrical and the sensor unit <NUM> may be a package with a threaded exterior. The sensor unit <NUM> may be inserted into the cavity and rotated into position until secure. The hole may be sealed with a lid <NUM> or a glue or epoxy. The sensor unit <NUM> may be encapsulated and secured inside the buoyancy jacket 5a using a resilient member, threaded parts, screws or a suitable potting compound, glue or epoxy.

<FIG> depict embodiments of the sensor unit <NUM> in which the mounting of the sensor unit <NUM> is arranged to rigidly attach the sensor unit <NUM> to the fastener assembly <NUM>. For example, the sensor unit <NUM> may be mounted to the fastener assembly <NUM>. Advantageously, the sensor unit <NUM> is mountable on a component of the fastener assembly <NUM> such as a bolt head <NUM>, screw, cap, washer or nut <NUM>. In some embodiments, the fastener assembly <NUM> may include an engagement portion, for example a bolt head <NUM>, washer, or nut <NUM>, which engages an object which the fastener assembly <NUM> fastens, and the mounting may be arranged to rigidly attach the sensor unit <NUM> to the engagement portion of the fastener assembly <NUM>. For example, in <FIG> and <FIG>, the sensor unit <NUM> is mounted to the head <NUM> of the bolt <NUM> of the fastener assembly <NUM>. In <FIG>, the sensor unit <NUM> is mounted to a nut <NUM> of the fastener assembly <NUM>. In other embodiments, the sensor unit <NUM> may be mounted to the bolt <NUM>.

In the embodiments of <FIG>, the sensor unit <NUM> comprises a casing <NUM> (equivalent to the housing <NUM> of <FIG> and <FIG>), a battery <NUM>, and a circuit board <NUM>. An O-ring <NUM> is present at the bottom of the sensor unit <NUM> to provide a seal against the surface of the plate <NUM> around the fastener assembly <NUM>. The O-ring can protect internal components of the sensor unit <NUM>, particularly when the sensor unit <NUM> is used on fastener assemblies <NUM> in hazardous environments, underwater, or similar.

In a preferred embodiment, the sensor unit <NUM> is packaged such that it may be retrofitted rapidly to a fastener assembly <NUM>, for example by mounting as a cap over the head <NUM> and/or nut <NUM> of a fastener. Advantageously, the sensor unit <NUM> is mountable on the riser fastener assembly <NUM>, for example retrofitted onto the head <NUM> or nut <NUM> of a H4 riser bolt <NUM>. Mounting the sensor unit <NUM> on the riser section <NUM> means that the sensor unit <NUM> detects the location and orientation from the motion or position of the riser <NUM> allowing the use of a sensor that is simpler and of lower-power than a manual inspection and record keeping. As such, the riser <NUM> is capable of being run for extended periods of time without offline inspection or NDT.

Mounting the sensor unit <NUM> on the fastener assembly <NUM> means that the sensor of the sensor unit <NUM> detects and confirms the position and axial orientation of the bolt head <NUM> and nut <NUM>, on either side of a structure or plate <NUM>, allowing the comparison of sensor data to detect changes in relative axial orientation or angular rotation. Similarly, sensors may measure tilt or alignment to detect distortion, buckling or fractures. The sensor unit <NUM> is attached to a fastener, bolt <NUM>, or rivet and wirelessly monitors the axial orientation of the bolt <NUM>, rivet or fastener in the same manner as a visual indictor. The sensor unit <NUM> may be mounted with the bolt <NUM> during assembly of a structure, or retrofitted subsequently, to measure, process, analyse, locally determine and transmit the status of a fastener. Alternatively, the sensor unit <NUM> may be integrated with the fastener assembly <NUM> during manufacture. The sensor unit <NUM> may be formed integrally into a component, or components, of a fastener assembly <NUM> and inserted into a recess of a bolt <NUM>, head <NUM>, stud, clip, nut <NUM>, or washer. The component of the fastener assembly <NUM> integrating the sensor unit <NUM> may be manufactured from composite, non-metallic, laminate or partially non-metallic materials in order to permit the transmission and reception of electro-magnetic radiation. In this manner, the sensor unit <NUM> incorporating sensors for detecting changes in absolute or relative movement between a component and a fixed surface, or between a component and another component, may be integrated into for example a composite nut <NUM> or bolt-head <NUM> to alert remotely to changes in the integrity or status or behaviour or functionality of a fastener assembly <NUM> or rigid structure.

<FIG> depicts various views of another embodiment of the sensor unit <NUM>. The sensor unit <NUM> incorporates a mounting arrangement that may be retrofitted to a fastener assembly <NUM> by clamping around a head <NUM> or nut <NUM>. The sensor unit <NUM> has a recess <NUM> that can be clamped over an existing bolt head <NUM> (but not a nut <NUM> as there is no hole for the bolt <NUM> to pass through). Various methods can be used to retain the sensor unit <NUM> such as a grub screw <NUM> coming in from the sides <NUM> and being tightened to the hex form of the bolt head <NUM> (see <FIG>). Alternatively, a cam <NUM> could be used to couple the head <NUM> into recess <NUM> (see <FIG>). By indexing the cam <NUM> firstly bite into, and clamp, the external hex form of the head <NUM> but also to rotate a physical constraint <NUM> under the hex form and into the chamfer / undercut (see <FIG>). A disadvantage to this design is that you need a dedicated recess <NUM> for each hex size, thereby requiring a range of sensor units <NUM> for every diameter of bolt head <NUM>.

<FIG> depicts the sensor unit <NUM> in <FIG> mounted over a bolt-head <NUM> and monitoring a fastener assembly <NUM> including a nut <NUM>, washer <NUM> and bolt <NUM>. The device <NUM> incorporates sensor technologies (such as optical flow sensors) for measuring the angular rotation or axial orientation of head <NUM> and determines and wirelessly communicates the status of fastener assembly <NUM> based on detecting tiny changes in the absolute inclination, vibration, offset, tilt, angular rotation or axial orientation of head <NUM>. Similarly, sensor unit <NUM> may incorporate sensor technologies to measure changes or trends in axial magnetic flux, eddy current and/or conductivity to detect the propagation of cracks, corrosion or other changes to the integrity of the fastener assembly <NUM>.

<FIG> depicts views of another embodiment of the sensor unit <NUM>. Sensor unit <NUM> is fully retrofittable to a variety of fastener assembly <NUM> components across a range of hex-head diameters. A recess <NUM> is provided with faces <NUM>. These faces <NUM> are part of leaves from an iris-style arrangement. By indexing knurled feature <NUM> the faces <NUM> clamp around the hex head and reduce the diameter of recess <NUM>. Multiple faces <NUM> or iris leaves are provided that interact with a ratcheting, self-locking mechanism that is actuated by knurled feature <NUM>. Twisting knurled feature <NUM> ratchets faces <NUM> until they lock around the head <NUM> or nut <NUM>. Sensor unit <NUM> incorporates a hole <NUM> to permit a bolt <NUM>, stud or screw to pass through sensor unit <NUM> as features <NUM> clamp around the hex head. The faces <NUM> may include the external features that couple and lock the hex form of head <NUM> but also to rotate a physical constraint <NUM> under the hex form and into the chamfer / undercut of the hex head <NUM>. <FIG> depicts the sensor unit <NUM> mounted over the head <NUM> and nut <NUM> with bolt <NUM> passing through recess <NUM> and hole <NUM>. The sensor unit <NUM> may be retrofitted to a range of fastener assemblies. Sensor unit <NUM> incorporates sensor technologies for measuring the angular rotation or axial orientation of head <NUM> or nut <NUM> and determines and wirelessly communicates the status of fastener assembly <NUM> based on detecting tiny changes in the optical flow of head <NUM> or nut <NUM>. Sensor units <NUM> may compare orientation of head <NUM> and nut <NUM> for optical flow that is indicative of loosening or loss of torque. Similarly, sensor unit <NUM> may incorporate sensor technologies to measure changes or trends in optical flow, axial magnetic flux, eddy current and/or conductivity to detect the propagation of cracks, corrosion or other changes to the integrity of the fastener assembly <NUM>, as will be discussed further below.

In the embodiment of <FIG>, the sensor unit <NUM> comprises a standard sensor package including the sensor of the sensor unit <NUM> for measuring rotation of one component of the fastener assembly <NUM> with respect to another component, for example the face of the bolt-end with respect to the a face of the nut <NUM>, and/or absolute movement of the fastener assembly <NUM> with respect to the joint, hole or fixed structure. The standard sensor package may be mounted on an interchangeable mounting module which acts as the mounting of the sensor unit <NUM> incorporating resilient gripping features (or 'teeth') for securing the mounting to the fastener assembly <NUM>. The mounting module may be selected for the fastener type, e.g. mountings for M10 through M40 etc. Additional retention may be provided by means of a lanyard.

As an alternative to rigidly attaching the sensor unit <NUM> to the fastener assembly <NUM>, the mounting may be arranged to rigidly attach the sensor unit <NUM> adjacent to the fastener assembly <NUM>. In other words, the sensor unit <NUM> may be mounted adjacent to the fastener assembly <NUM>.

<FIG> depict embodiments of the sensor unit <NUM> in which the mounting is arranged to mount the sensor unit adjacent to the fastener assembly <NUM>. In such an alternative embodiment, the sensor unit is mounted adjacent a fastener assembly <NUM> to detect rotation of a component, or of all, of the assembly. The device of the invention may be attached adjacent to the fastener assembly <NUM> of interest. The device may be mounted to an adjacent rigid structure, or joint, magnetically, through welding or using an adhesive. For example, the sensor unit <NUM> may be attached to the object which the fastener assembly <NUM> fastens. Secondary or additional retention may be provided by means of a retaining wire or composite material such as a Dyneema® lanyard or net.

Furthermore, the sensor unit <NUM> may be mounted in a manner that it is adjacent to, but not in contact with, the fastener assembly <NUM> and therefore would permit access to the fastener assembly <NUM> for visual inspection (for example for corrosion or discolouration) and for maintenance (for example attaching a wrench to check and apply torque and/or retighten the fastener).

<FIG> comprises several views of an embodiment of the sensor unit <NUM>. A sensor unit <NUM> may be mounted by means of a retrofittable mounting arrangement <NUM>, which acts as the mounting of the sensor unit <NUM>, including standard stainless steel (or polymer, mylar or Kevlar) banding <NUM> for securing to a range of fastener assemblies as shown in <FIG>. The banding <NUM> may be attached to a component of the fastener assembly <NUM> such as the hex form of a nut <NUM> or head <NUM> and retrofitted to wide variety of diameters. The sensor unit <NUM> uses a tooth <NUM> on the mounting arrangement <NUM> to bite and lock onto the chamfer or undercut of the nut <NUM> or head <NUM>. The banding <NUM> may be tightened to fit securely around the component of the fastener assembly <NUM> by means of a tightening screw <NUM>. A grub screw <NUM> may be turned to ratchet banding <NUM> until tooth <NUM> locks under the chamfer of nut <NUM> or head <NUM>. The locking mechanism of screw <NUM> provides secondary retention to prevent the sensor unit <NUM> from falling.

<FIG> depicts the sensor unit <NUM> of <FIG> mounted to a fastener assembly <NUM> and operably monitoring its tightness. The sensor unit <NUM> is securely attached to bolt <NUM> on its nut <NUM> and/or head <NUM> and used to detect small changes in the absolute or relative angular rotation or axial orientation of head <NUM> and/or nut105. If two sensor units <NUM> are mounted on both the nut <NUM> and the head <NUM>, comparison of their orientation or angular rotation can determine tiny changes in their relative angular rotation or axial orientation and may be indicative of nascent failure. The sensor unit <NUM> measurements axial orientation, angular rotation and processes measurements locally, determining the status of the fastener assembly <NUM> and communicating the status to a remote controller by means of radio frequency and/or optical communications interfaces integral to sensor unit <NUM>, as will be discussed below. The sensor unit <NUM> may comprise an optical flow sensor <NUM> mounted on nut <NUM> that periodically images the thread on bolt <NUM> for movement.

<FIG> depicts a further embodiment of the sensor unit <NUM>. In this embodiment, the sensor unit <NUM> fits under an existing bolt head <NUM> or nut <NUM>. The sensor unit <NUM> can be the standard device of any of <FIG> with a simple metallic plate <NUM> to suit the hex size of the head <NUM> and or the nut <NUM>. The sensor unit <NUM> is retained on the plate <NUM> with screws <NUM>. The nut <NUM> and/or bolt <NUM> need to be removed in order to fit plate <NUM>, which is disadvantageous for retrofitting but may be advantageous for new installations and may not be ideal when painting is considered. <FIG> depicts the sensor unit <NUM> mounted on a fastener assembly <NUM> including under head <NUM> and another sensor unit <NUM> under nut <NUM>. Sensor unit <NUM> incorporates sensor technologies for measuring the angular rotation or axial orientation of head <NUM> or nut <NUM> and determines and wirelessly communicates the status of fastener assembly <NUM> based on detecting tiny changes in optical flow of head <NUM> or nut <NUM>. Sensor units <NUM> mounted on the nut <NUM> and head <NUM> of the same fastener assembly <NUM> may compare the orientations of head <NUM> and nut <NUM> for relative changes in angular orientation that are indicative of loosening or loss of torque.

In an alternative embodiment shown in <FIG>, the sensor unit <NUM> is mounted adjacent a fastener assembly <NUM> to detect rotation of a component, or of all, of the fastener assembly <NUM>. A proximity sensor incorporated into the sensor unit <NUM> of the invention may be utilised to detect movement of the fastener assembly <NUM>. Changes in the clearance between the proximity sensor, which is an optical flow sensor, are used to determine if the fastener assembly <NUM> has moved and a threshold may be set above which a message is relayed to a central display, computer or controller.

The sensor unit <NUM> further comprises a sensor, that is an optical flow sensor <NUM> configured to sense movement of the fastener assembly <NUM>. For example, in an embodiment the sensor is configured to sense angular rotation or axial movement of the fastener assembly <NUM>. The sensor unit <NUM> incorporates sensors to measure and determine angular rotation, axial orientation, of a fastener assembly <NUM>. The sensor unit <NUM> measures rotation of the main body of the fastener with respect to the nut <NUM>, and of the fastener assembly <NUM> with respect to the fixed joint that it secures.

In particular, the sensors of the sensor units <NUM> shown in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG> are configured to sense angular rotation or axial movement of the fastener assembly <NUM> with respect to an object which the fastener assembly <NUM> fastens. Rotation of the fastener assembly <NUM> with respect to the structure that it is mounted through may be an indication of a loss of tension, for example if the nut <NUM> is seized due to corrosion or degradation, due to movement of the structure, thermal expansion, stretching of a bolt <NUM> or gradually thinning of a structure.

The sensor of the sensor unit <NUM> comprises an optical flow sensor <NUM>. In some embodiments, the fastener assembly <NUM> may include an engagement portion, for example a bolt head <NUM>, washer, or nut <NUM>, which engages an object which the fastener assembly <NUM> fastens. The mounting of the sensor unit <NUM> may be arranged to rigidly attach the sensor unit <NUM> to the engagement portion, and the optical flow sensor <NUM> may be configured to sense angular rotation of the engagement portion with respect to the object.

In general, optical flow sensors <NUM> are more reliable in detecting angular rotation of the fastener assembly <NUM>, or a part thereof. Rotation causes a more substantial change in the surface features in the field of view of the optical flow sensor <NUM>. Axial movement is still detectable using an optical flow sensor <NUM>, and may be more reliably detected when the sensor unit <NUM> is mounted adjacent to the fastener assembly so that the axial movement of the fastener assembly <NUM> occurs in the plane of view of the optical flow sensor <NUM> (for example where the mounting of the sensor unit <NUM> is of the type shown in <FIG>). When the mounting is of the type shown in <FIG> (i.e. arranged to mount the sensor unit <NUM> to the engagement portion), axial movement of the fastener assembly <NUM> will be perpendicular to the plane of view of the optical flow sensor <NUM>, and therefore only visible as a slight magnification or demagnification of the image.

<FIG>, and <FIG> show embodiments of the sensor unit <NUM> comprising an optical flow sensor <NUM>. The sensor unit <NUM> may utilise optical flow technology to detect angular rotation of a bolt <NUM>, fastener assembly <NUM> or nut <NUM> with respect to a fixed surface such as between a nut <NUM> and a bolt <NUM> or threaded screw, or bolt head <NUM> with respect to the surface it is fastened onto. An optical flow sensor <NUM> is a vision sensor capable of measuring optical flow or visual motion and outputting a measurement based on optical flow. An optical flow sensor <NUM> may be utilised to detect and measure changes in angular position or rotation of a shaft, thread. The optical flow sensor <NUM> could measure movement of discontinuities or roughness on the shaft, or movement in the surroundings of the optical flow sensor <NUM> such as prominent features such as nearby lights, or changes in contrast or brightness due to a change in orientation. Images would be taken periodically by a CCD or some other imaging device to determine by how much the screw thread or surface had moved relative to the fastener nut <NUM> or head <NUM>. The optical flow sensor <NUM> could either be mounted on a stationary surface with a view of a moving surface or the other way around. When the surface moved under the optical flow sensor <NUM> the amount of movement could be measured by matching the images obtained from the optical flow sensor <NUM>. Optical flow technology is widely used in optical mice with personal computers and is beginning to be used in drones and other autonomous flight machines because of widespread availability of generic, cheap, low-power consumption optical flow technology components and devices.

In the embodiments shown in <FIG>, <FIG>, and <FIG>, the optical flow sensor <NUM> or device detects relative motion between the part of the fastener assembly <NUM> onto which it is attached (e.g. the head <NUM> in <FIG> and the nut <NUM> in <FIG>) and some fixed surface such as a screw thread or fixed surface of a rigid structure around the fastener assembly <NUM>. Sequences of images are captured by a CCD imaging device or some optical detection device and compared to measure relative movement.

In the embodiments of <FIG>, the sensor unit <NUM> includes a lens <NUM> that focusses the image of the surface that the optical flow sensor <NUM> is observing. The O-ring <NUM> at the bottom of the sensor unit <NUM> can protect the lens <NUM> and other internal components of the sensor unit <NUM>. Alternatively, the sensor unit <NUM> may be sealed and provided with one or more transparent windows to allow the optical flow sensor <NUM> to image the surface.

The optical flow sensor <NUM> is connected to the circuit board <NUM> for receiving power and transferring data from the images. The circuit board <NUM> may comprise a processor for processing the images from the optical flow sensor <NUM> to detect loosening of the fastener assembly <NUM> and output a signal representing the status of the fastener assembly <NUM>. Alternatively, the optical flow sensor <NUM> may be an integrated package which includes the processor. In the case of <FIG>, <FIG>, and <FIG>, the sensor unit <NUM> comprises two optical flow sensors <NUM> and corresponding lenses <NUM>. Using multiple optical flow sensors <NUM> and combining their output can improve the reliability and accuracy of the output signal from the processor. For example, more than two optical flow sensors <NUM> may be used, such as three, four, or more. However, this is not essential, and a single optical flow sensor <NUM> may be used.

The optical flow sensor <NUM> may be mounted on the nut <NUM>, head <NUM> or some fixed or moving component of the fastener assembly <NUM> and used to measure changes in angular rotation and/or axial orientation of a component of a fastener assembly <NUM>.

The optical flow sensor <NUM> may be an application specific device that incorporates MEMS accelerometers, gyroscopes, Hall effect sensors and processing on the same die. The optical flow sensor <NUM> may incorporate a light source, such as a LED or solid-state laser, to periodically capture sequential images of a proximate surface. The imaged surface in close proximity may be a thread, or washer, or fixed surface, or pin, or a rigid structure, and these multiple sequential images may be processed to determine movement of optical flow sensor <NUM> with respect to the proximate surface. The sensor unit <NUM>, incorporating an optical flow sensor <NUM>, may determine and measure relative movement of a component of a fastener assembly <NUM> in this manner. The period of image capture may be infrequent, up to weeks or even months apart, since changes in the tension of the fastener assembly <NUM> are likely to be very gradual. Alternatively, the image capture frequency may be adjusted or intermittently triggered dynamically based on shock, vibration, motion, changes in magnetic flux, conductivity, pH, or changes in orientation detected by accelerometers, gyroscopes or inertial measurement units (IMUs).

The optical flow sensor <NUM> of the sensor unit <NUM> may be used to detect changes in fastener tension and confirm tension meets a specified threshold. Likewise, the optical flow sensor <NUM> may be utilised to detect changes in stress, strain or distortion. The optical sensor may be utilised to monitor the fastener assembly <NUM> for discolouration and surface quality as an indication of corrosion and degradation.

In some embodiments, the sensor of the sensor unit <NUM> is configured to sense angular rotation or axial movement of parts of the fastener assembly <NUM> with respect to each other. For example, the sensor may detect movement of the nut <NUM> relative to the bolt <NUM>. This may be achieved using optical flow sensors <NUM>.

<FIG> shows an embodiment using an optical flow sensor <NUM> to detect movement of parts of the fastener assembly <NUM> with respect to each other, in this case the nut <NUM> relative to the bolt <NUM>. The sensor unit <NUM> is mounted on the nut <NUM>, and the optical flow sensor <NUM> is placed to detect rotation of the bolt end. Alternatively, the sensor unit <NUM> may be mounted to the bolt <NUM> and the optical flow sensor <NUM> placed to detect movement of the nut <NUM>.

On a rotating machine or wheel, two sensor unit <NUM> mounted on the head <NUM> and nut <NUM> of the fastener assembly <NUM> may be installed to detect changes in their relative, rather than absolute, orientation or angular rotation thereby detecting nascent failure or loss of torque. Arrangements of this type are shown in <FIG>, and <FIG>. The sensor unit <NUM> may compare the relative orientation of the head <NUM> and its corresponding nut <NUM> for changes in the relative orientation of the head <NUM> and nut <NUM> in order to detect nascent movement and loosening of a fastener assembly <NUM>.

A schematic of the sensor unit <NUM> is shown in <FIG>. The sensor unit <NUM> includes the sensor <NUM>. A processor and memory are provided to record measurements and provide an electronic log for validation and inspection of riser condition. The device incorporates processor and memory to execute software and analysis measurements and determine status. In some embodiments, the sensor unit <NUM> further comprises a processor <NUM> arranged to process the output of the sensor <NUM> to detect loosening of the fastener assembly <NUM> and to output a signal representing the status of the fastener assembly <NUM>. The processor <NUM> may be included in the circuit board <NUM>, or provided separately.

Tiny changes in the angular rotation of a fastener assembly <NUM> or a component of a fastener assembly <NUM> may be detected and using to trigger warnings of nascent changes in integrity of a fastener assembly <NUM>. A small change or rotation of the fastener assembly <NUM>, of even one tenth degree of angular rotation, may be an indicator of nascent failure, reduced torque, cracking, corrosion or loss of rigidity. A threshold may be implemented to determine status, for example if the axial rotation exceeds a certain number of degrees or radians. Likewise, the sensor unit <NUM> may incorporate additional sensors to measure tension, torque, hardness, conductivity, corrosion, magnetic flux, shear, strain, load cells, compression, tilt, angular orientation, distortion and vibration.

The riser <NUM> may additionally include one or more position sensors for detecting the position of the riser <NUM>. Such a position sensor may be of any suitable type and may preferably be a low power sensor such as a MEMS sensor, which may be for example configured as an inclinometer or accelerometer. Examples of alternative types of position sensor that could be used include: tilt ball sensor; infrared; laser; acoustic; capacitive; magnetic or Hall Effect sensors. These may be integrated into the sensor unit <NUM>, and the processing of these signals combined with the processing of signals from the optical flow sensor. Position sensors for the sensor unit <NUM> may include location sensors such as GPS modules, inertial sensors such as accelerometers and gyroscopes.

The sensor units <NUM> may be located at bolts on both ends of the riser section <NUM>. In this instance these sensor units may monitor corresponding ends used to secure the same length of riser section <NUM>. In this case the sensor units <NUM> may be paired, or their outputs combined, such that the sensor unit <NUM> detects an anomaly if these corresponding ends (or flanges 3a) do not operate simultaneously. For example, if a riser section <NUM> has been placed in the riser stack, both of the corresponding sensor units <NUM> on the upper and lower ends of the riser section <NUM> should be in proximate location, and their orientation can be used to give the position of the riser section <NUM> in the riser <NUM>. The output of the 'paired' sensor units <NUM> on the upper and lower ends of the riser section <NUM> can be combined and compared to detect an anomaly and flag a warning to an operator via a display.

In some embodiments, the sensor unit <NUM> further comprises a processor <NUM> arranged to process the output of the sensor <NUM>, and an eddy current sensor configured to monitor the condition of the fastener assembly <NUM>, the processor <NUM> further being arranged to process the output of the eddy current sensor. The sensor unit <NUM> may comprise an eddy current sensor configured to measure electro-magnetic properties of a fastener assembly <NUM>. An example of such an embodiment is shown in <FIG>. The sensor unit <NUM> incorporates a coil <NUM>, or coils, that inductively senses the metallic fastener assembly <NUM> and measures its conductivity, magnetic flux and the presence or absence of corrosion in the fastener assembly <NUM>. The sensor unit <NUM> may further comprise a magnet <NUM>. Coils may be exploited to couple magnetic flux through the fastener assembly <NUM> to measure a trend and detect nascent corrosion, cracking or deformation. Eddy current sensing may be exploited to detect local cracking. This coil <NUM>, or coils, may be designed such that it has a second function and may be used for near field communications or RF communications with an adjacent device.

The sensor unit <NUM> may incorporate other condition sensors to measure shock, vibration and compression on the fastener assembly <NUM>. The condition sensors may rely on piezoelectric material mounted between a bolt head <NUM> and a surface or between the nut <NUM> and a surface to measure compression. Changes in the compression of the material will indicate a change in the tension of the fastener assembly <NUM> and predict nascent failure. Similarly, measurements of shock and vibration may be recorded and correlated or compared with other measurements such as axial orientation and angular rotation to predict nascent failure or operation of the fastener assembly <NUM> out of specification. Optionally, the sensor unit <NUM> may further comprise a condition sensor configured to sense the compression on a component of a fastener assembly100. The sensor unit <NUM> may incorporate an ultrasonic or acoustic transducer to measure the speed of sound, and any reflections, along the primary axis of the fastener assembly <NUM>. In this manner the ultrasonic or acoustic sensor technology could be exploited to detect reflection and time of flight of a pulse from a transducer to the opposing face or end of the bolt <NUM> or fastener assembly <NUM>, and measure any small changes in the length, or cross-sectional area, of the bolt <NUM> that correlate with changes in tension, compression and/or corrosion or cracking. The ultrasonic transducer may be incorporated into the sensor unit <NUM> and mounted on a component of the fastener assembly <NUM> by means of a cap, on the bolt head <NUM> or the hex-head, on the stud or inside a nut <NUM> or washer.

To measure riser assembly <NUM> condition, measurements of bolt condition may be made. Eddy current or inductive sensors may be used to measure cracking, corrosion, surface quality, pitting, degradation and condition based on magnetic susceptibility and conductivity across multiple frequencies. Measurements of frequency shift, and amplitude as well as 'Q' factor can be used to track changes in materials condition. At low frequencies skin depth is such that it may penetrate from one surface through the wall to another surface. Measurements of surface condition and scale can be taken in a similar fashion.

The sensor unit <NUM> may be retrofitted to a bolt head <NUM> or nut <NUM>, or both, and programmed to monitor the axial orientation of the head <NUM> or bolt <NUM>, or both, and detect changes and alert a user wirelessly via a controller and/or user interface or display, to changes in the absolute or relative axial orientation or angular orientation of a fastener assembly <NUM>, a bolt head <NUM>, a nut <NUM>, or component of a fastener assembly <NUM>. The sensor unit <NUM> may form part of a network that is interfaced with a OEM control system. For example, as shown in <FIG>, the sensor unit <NUM> may communicate with a monitoring system <NUM>. Accordingly, changes in the status, functionality, behaviour, condition or safety of critical fasteners may be monitored from a controller in the monitoring system <NUM> and used as feedback to control, slow-down or interlock equipment used during operations to prevent dropped objects or other incidents arising from failure of a fastener assembly <NUM> such as a loose bolt or nut in a critical location. Likewise, the sensor unit <NUM> could be used to monitor the status of critical bolts or screws, and to interface with an OEM control system, such as the monitoring system <NUM>, and communicate the status of fastener assemblies <NUM>. Changes in the status of fastener assemblies <NUM>, for example beyond a threshold, may be used to interlock machinery to ensure that equipment is not operated until the fastener assembly <NUM> is securely tightened or replaced. Modulating a signal in accordance with the orientation of a fastener assembly <NUM> allows for a wireless sensor unit <NUM> to be provided that is suitable for use in remote locations without the need to make an electrical connection, as the output of the sensor unit <NUM> may be monitored.

Multiple sensor units <NUM> installed on fastener assemblies <NUM> together may form a sensor array. The measurements from this array of sensor units <NUM> may be combined to predict failure, condition and behaviour of a structure. Data from this array of sensor units <NUM> together may be analysed and displayed as a three-dimensional model of a structure. The display may include torsion, vibration and orientation of fastener assemblies <NUM>. Over time, measurements may be logged and used to plot fatigue, and to predict failure, mechanical damage or concentrations of stress. These logs may be correlated or compared with other activities of a rig or structure, to log behaviour of critical structures, joints, gantries, cranes, welds, bolts and fastener assemblies <NUM> during drilling, jarring, completion, vibration, high winds, rough seas, storms, swell, heave, mooring, 'stick slip', stuck drill bits, the use of explosives during mining or drilling, hydraulic fracturing or `rocking' of a well. The log may be analysed, combining various measurements and parameters, to predict or anticipate failure, condition or service life of a structure or fastener assembly <NUM>. These logs from arrays of sensor units <NUM> mounted on fastener assemblies <NUM> could be used to predict and/or detect damage, buckling, distortion, cracking, degradation or fatigue on derricks, draw works, cranes, doors, davits, bulkheads or other critical pieces of equipment around a rig or vessel. The sensor units <NUM> may be deployed permanently or temporarily (e.g. during rig-up, lifting or decommissioning). When correlated with other sources of data such as weather, navigation, riser tension, mooring line tension, drilling depth, pressure, 'kicks', temperature, wind speed etc. the output of the model could include time to failure or the location of fatigued components, fastener assemblies <NUM> and structures. An array of sensor units <NUM> could together form a model for comparison with Finite Element Analysis models of a structure, and form nodes for modal analysis of a structure under certain operational and environmental conditions. Likewise, the data from arrays of sensor units <NUM> may be logged and analysed to generate a dynamic model for a structure, machine, flange or critical joint. These arrays, and analysis and stress testing of the resulting models, could be used for the purposes of securing class approval with notified bodies such as American Bureau of Shipping (ABS), DNV-GL and Lloyds Register.

The sensor unit <NUM> may incorporate GPS devices or other electronic positioning technology to confirm and track condition of fastener assemblies <NUM> and connections of the riser in the derrick and on the deck, or in storage on land. The sensor unit <NUM> may be mounted on critical components of the riser package such as choke, lower marine riser package and kill lines.

Data or meta-data generated by the sensor units <NUM> monitoring risers throughout the deployment will include riser bolt characteristics such as sensor ID, riser ID, date, time, number of pressure cycles, count of riser movements, count of riser immersion, sensor signal level, sensor battery power, self-diagnostic information, shock, vibration, position, angle, speed, acceleration, temperature, pressure, conductivity, salinity, magnetism, corrosion, scale, surface defects, surface hardness and surface quality etc. These data may be logged and analysed to identify risers that are not performing to specification or may be in need of maintenance or replacement. The data recorded may be used to compare riser package condition with requirements of industry standards, e.g. in accordance with API standards <NUM>, <NUM>, spec 15F, RP160, spec 16R, RP17G and DNV-RP-F206 and other standards for maintenance, monitoring and inspection of marine riser packages. The history logged by the sensor unit <NUM> may be analysed for its history and condition over a five-year interval in accordance with SPS and ABS requirements for periodic inspection. These data may be analysed for condition-based monitoring the risers to minimise downtime and, by planning maintenance based on likelihood of riser failure of inspection, maximise availability and operational efficiency. In addition, the data logs and meta-data may be presented to manufacturers, suppliers, customers, third-party auditors or regulators to validate equipment warranty, indicate safety performance and to demonstrate compliance with best practice and compliance with regulations. Finally, the sensor unit <NUM> may provide data for analysis in models or simulations of riser condition as part of its maintenance cycle or special periodic service. Indeed, this longitudinal collection of measurements of pipe condition may be used as an alternative to periodic NDT and inspection, saving on manual processes and auditing costs.

The sensor unit <NUM> may be used to monitor equipment in addition to the riser <NUM>, including drill pipe, casing, production tubing, cutting tools, bottom-hole assemblies, production risers, flexible riser and flowlines. The data from the sensor unit <NUM> may be used to provide integrity along the riser, and to monitor their position, location, orientation and condition to demonstrate the riser is secure.

The sensor unit <NUM> may be encapsulated in a suitable material that is resistant to drilling fluids, brine, cement, sunlight, UV radiation, grease, pipe dope, iron filings and other debris. Advantageously, the material may be PEEK plastic, which is chemically inert. In particular, grades of PEEK that include carbon such as TECAPEEK black, and TECAPEEK CF30 black (manufactured by Ensinger, UK) and that use Victrex PEEK <NUM> as the base component. These grades of PEEK may be welded to seal the sensor unit <NUM> and provide IP67 or IP68 water-proofing as well as certification to IECEx and ATEX standards for use in flammable atmospheres.

The sensor unit <NUM> and its mounting (securing member) may be fabricated from a tough, durable material to withstand shock, vibration, temperature extremes, ice, direct sunlight, UV degradation and washing with a high-pressure jet of water at over <NUM> Psi. Suitable materials used for manufacturing of the enclosure for sensor unit <NUM> and mounting include PEEK, carbon fibre, fibreglass, PEAK, PEEK reinforced with carbon fibre and other engineering thermoplastics and composites or elastomers. The material to manufacture sensor unit <NUM> and mounting may be a suitable composite, such as carbon fibre or fibre glass, or a plastic, for example Polyether ether ketone (PEEK), or an elastomer, for example a rubber. The sensor unit <NUM> and mounting may also incorporate non-metallic lining materials to provide additional friction, integrity and sealing to keep out oils and debris. These may be incorporate `o' rings that provide compression to accommodate riser tolerances for the dimensions of the riser arm which can be broad. The non-metallic materials used in the sensor unit <NUM> may be of a type known to be suitable for use as a lining of a in oil and gas applications. Suitable materials for the non-metallic lining in the sensor unit <NUM> can include, without limitation: polyisoprene, styrene butadiene rubber, ethylene propylene diene monomer rubber, polychloroprene rubber, chlorosulphonated polyethylene rubber, 'Viton' or nitrile butadiene rubber. The material may also be a mixture of these and/or other materials.

The sensing unit <NUM> may further comprise a power source, such as a battery <NUM>. The power source may be any type of standalone power source known in the art that is capable of providing power to the sensor unit <NUM> including the sensor and other components such as the processor <NUM> and wireless communication unit <NUM> (discussed further below). For example, the power source may comprise a battery <NUM>, solar cell or capacitor. The power source may optionally comprise an energy harvesting device that is configured to harvest energy from environment of the riser assembly <NUM>. For example, the power source may be configured to harvest energy from the motion, shock or vibration of the riser section <NUM>. The power source may be provided integral with the sensor unit <NUM>, or removably attached to the sensor unit <NUM>. A sensor unit <NUM> that is easily maintained for long periods of deployment may thus be provided. Integrated processing circuits may be implemented with the optical flow sensor <NUM> to minimise power consumption.

The power source such as a battery <NUM> with long life characteristics may be used to power the sensor unit10. The battery <NUM> is ideally compact in format and can fit within the sensor unit <NUM> mounted to the riser arm by the mounting. To avoid frequent replacement of the sensor unit10, the battery <NUM> ideally will have sufficient capacity to power the sensor unit <NUM> for tens of thousands of riser cycles over several years (e.g. five years between SPS). Optionally the battery <NUM> utilised may be a Lithium Thionyl Chloride battery that has been selected and configured to last the lifetime of the equipment. The battery <NUM> may be supplemented with a supercapacitor for storing and releasing charge, e.g. for broadcast of information wirelessly by radio or by means of modulated light signal.

The sensor unit <NUM> is capable of being run for extended periods of time from a remote power source such as a battery <NUM>. Energy scavenging may be exploited to generate power and to supplement power from a battery <NUM> or supercapacitor. Energy may be harvested from mechanical noise, vibration, shock, solar energy, pneumatic lines and pressurised air, hydraulic lines or thermal sources and thermal gradients (e.g. using a Peltier and heat sink).

As the sensor unit <NUM> is mounted on the riser, the sensor may be of a type that is relatively simple and of low power compared to a sensor mounted on the riser that indirectly senses the riser fastener assembly <NUM>. Thus, an inexpensive sensor unit <NUM> that is capable of being run from a standalone power source may be provided.

In an embodiment where the sensor unit <NUM> comprises a processor <NUM>, the sensor unit <NUM> may further comprise a wireless communication unit <NUM> arranged to communicate the signal from the processor <NUM>. The wireless communication unit <NUM> may be a radio communication interface arranged to communicate using radio frequency electromagnetic (EM) waves. The wireless communication unit <NUM> may be used to wirelessly communicate the signal to a monitoring system <NUM> under the control of the processor <NUM>.

In some applications, there may be no wireless communication unit <NUM>, in which case the signal from the processor <NUM> may be logged and communicated at a later time, for example over a wired connection. For example, the riser section <NUM> may comprise wiring used to transmit the signals from the processor <NUM>.

The wireless communication unit <NUM> may communicate to a monitoring system <NUM> which may have a similar configuration to the monitoring system for latches of a fingerboard latch system as disclosed in <CIT>. The monitoring system <NUM> provides an indication of the status of the fastener assemblies <NUM> to a user, for example on a display or audibly. The monitoring system <NUM> may provide a warning when the status of any fastener assembly <NUM> is loosened or otherwise in a dangerous state.

Ideally, the sensor unit <NUM> communicates wirelessly using a wireless communication unit <NUM> with a receiver, such as the monitoring system <NUM>, to control, collect, analyse, trend and display data from multiple sensor unit <NUM> mounted, attached or clamped onto critical fastener assemblies <NUM> around a structure or rigid member. The sensor unit <NUM> may communicate wirelessly using the network protocol described in <CIT>. The sensor unit <NUM> may communicate wirelessly by optical, radio-frequency or other electro-magnetic means. The sensor unit <NUM> may incorporate a LED as a visual indictor, or by optically by means of LiFi, or an RF communications interface relying on proprietary or commercially-available protocols such as Bluetooth, Bluetooth low energy (BLE), LORA, <NUM>, <NUM>, ZigBee or WIFI. Optical communication may be detected by a camera or photodiode to detect modulated light. LIDAR, time of flight cameras, time of flight radio may be used to locate the sensor units <NUM> and detect coarse changes in their orientation or behaviour. Alternatively, a wireless communication unit <NUM> is provided relying on radio communications.

To communicate wirelessly, the sensor unit <NUM> may utilise radio-frequencies. Optionally, a frequency may be selected that has a wavelength that does not suffer from attenuation or reflections from pipes and tubulars stacked or stored on the deck or in the yard. To minimise reflections and loss of signal, a radio frequency may be selected that has a wavelength that is less than the minimum spacing between tubulars when stacked in storage. This minimum spacing will be determined by the minimum pitch between the riser sections <NUM>. An embodiment for a sensor unit <NUM> with a mounting advantageously utilises a wireless communications frequency that has a wavelength that is less than the minimum spacing between risers. The frequency selected should not interfere with marine communications equipment, Optionally, the frequency selected may be between <NUM> and <NUM>. The communications frequency may be long-wave, or at a frequency suitable for transmission over long distances when location of a section of riser, and remotely determining its condition, is desirable. Optionally, underwater communications may be by means of ultrasonic transducers. The signal may be relayed from a sensor unit <NUM> to the surface, or via adjacent units.

A network of wireless sensor units <NUM> may be provided to communicate among the sensor units <NUM>, and with each other, to relay signals for processing and display of riser condition and location to an operator, e.g. via the monitoring system <NUM>. These sensor units <NUM> communicate with gateways to maximise reception and signal coverage. Optionally, these gateways may be located at four locations, forward, aft, port and starboard on the platform or rig. A further transceiver is mounted at, or near, the drillers' cabin and/or the Local Equipment Room (LER). The transceiver wireless gateway at the drillers' cabin and/or LER is the central transceiver which receives signals from the sensor units <NUM> and the network gateway transceivers around the rig.

Additionally, the sensor unit <NUM> use for near field communications (NFC). The NFC functionality may be used to switch on, or off, a completely sealed sensor unit <NUM> without any external contact or switch. NFC may be used via the sensor <NUM> to put the sensor unit <NUM> in a dormant or low power state prior to shipping, and to `wake' up the sensor unit <NUM> via NFC on arrival or when installed and put into operation. The one or more sensor coil <NUM> or coils may incorporate coils for sensing tubular and NFC devices, or both. The coils <NUM> may be mounted concentrically or adjacent to each other on a printed circuit board or flexible printed circuit board. Similarly, the NFC coil may be used to update the sensor unit <NUM> firmware and software, or to interrogate the sensor unit <NUM> during debugging. In these ways power may be saved during manufacture, assembly, transportation and storage, ready for reactivating on installation. Similarly, communications can be by means of RFID, modulation of light, barcode, QR code, retroreflection, wireless, radio, Bluetooth, power over ethernet, etc..

The mounting may comprise one or more light sources. Thus, the light sources are directed upwards. As riser assemblies are typically mounted vertically, this means they are visible from above. It also keeps them cleaner, reducing the risk of obscuring the output light. The light sources may emit light in any suitable wavelength band, for example infrared, visible or ultraviolet. Similarly, the light sources may be substituted or complemented with a radio-frequency wireless communications unit <NUM>.

The output of the one or more light sources is modulated in accordance with the position of the riser sensed by the sensor unit <NUM>. The modulation may be implemented in any number of ways. In the simplest case, the light sources may be in an on or off state corresponding to two different conditions, positions and locations of the riser, e.g. angular orientation, tension, pressure, temperature, tally etc. Alternatively, the modulation may convey more information. For example, the number of lit light sources may identify the position of the riser section <NUM>, or bolt thickness, or water salinity, conductivity or load. Alternatively, the modulation may be a change in the colour or flashing rate of lit light sources to identify the position of the riser section <NUM>. In another embodiment, a lit light source may identify that the riser section <NUM> is in a fault condition, and an unlit light source may indicate that the riser section <NUM> is functioning normally. Thus, a more reliable riser light source may be provided that clearly indicates when the riser is safely secured or in normal condition.

Modulating a light source in accordance with the output of the sensor unit <NUM> allows for a wireless sensor unit <NUM> to be provided that is suitable for use in remote locations without the need to make an electrical connection, as the output of the light source may be monitored and/or relayed sub-sea or on the surface.

Modulating a light source in accordance with the position of the riser allows for a wireless sensor unit <NUM> to be provided that is suitable for use in remote (submarine) locations without the need to make an electrical connection. The light sources provide instant indication of tubular integrity, as well as broadband data, which may be monitored by a person or remotely monitored via a detector system such as photodetectors or cameras mounted on each sensor unit <NUM> to relay messages to the surface, or to cameras at the surface while riser is stored on deck, for example. Image processing may be used to provide automated monitoring.

In some situations, the sensor unit <NUM> according to any embodiment described herein may be provided or manufactured in combination with a fastener assembly <NUM>. This may be particularly advantageous in situations such as where the sensor unit <NUM> is integrated into the fastener assembly <NUM>, e.g. into a cavity in the bolt <NUM>, head <NUM>, or nut <NUM>.

Claim 1:
A sensor unit (<NUM>) for a fastener assembly (<NUM>), the sensor unit (<NUM>) comprising:
a mounting arranged to rigidly attach the sensor unit (<NUM>) to, or adjacent to, a fastener assembly (<NUM>);
a sensor (<NUM>) configured to sense movement of the fastener assembly (<NUM>); and
a processor (<NUM>) arranged to process the output of the sensor (<NUM>) to detect loosening of the fastener assembly (<NUM>) and to output a signal representing the status of the fastener assembly (<NUM>),
characterised in that the sensor is an optical flow sensor.