Strain monitor

Abstract

A strain monitor (1) for attachment to part of a submerged structure (100), the strain monitor comprises: a main body (5), the main body comprising an attachment assembly which is arranged to secure the strain monitor to the submerged structure, a plurality of strain gauge assemblies (3), carried by the main body, arranged in a spaced apart relationship, each strain gauge assembly comprising a strain gauge and a carrier (6), and the strain gauge attached to the carrier, and the strain gauge assembly arranged to selectively adopt a stowed condition and a deployed condition.

Claims

1. A strain monitor for attachment to part of a submerged structure to measure strain in said structure, the strain monitor comprising: a main body, the main body comprising an attachment assembly which is arranged to secure the strain monitor to the submerged structure, the main body comprising an inner side which is arranged to be positioned opposite to a part of the submerged structure, and an outer side which is oppositely directed to the inner side and is arranged to face away from the submerged structure, a plurality of strain gauge assemblies, carried by the main body, arranged in a spaced apart relationship, and provided at the inner side, each strain gauge assembly comprising a strain gauge and a carrier, and the strain gauge attached to the carrier, with the strain monitor secured to the submerged structure and the strain gauge assembly arranged to selectively adopt a stowed condition and a deployed condition, wherein in the deployed condition, the carrier contacts the submerged structure, and in the stowed condition, the carrier is positioned away from contact with the submerged structure.

2. The strain monitor of claim 1, further comprising a handle used by a remotely operated vehicle (ROV) for installation and/or detachment of the strain monitor to and/or from the submerged structure, and/or operation of the strain monitor.

3. The strain monitor of claim 1, further comprising a deployment assembly to cause the strain gauge carrier to move from the stowed condition to the deployed condition.

4. The strain monitor of claim 1, wherein the main body is of concave shape.

5. The strain monitor of claim 1, further comprising a data collection module which is detachably connectable to the main body.

6. The strain monitor of claim 5, wherein the data collection module is arranged to effect at least one of the following functions: data processing, signal processing, data storage, data communication external of the strain monitor, and power management.

7. The strain monitor of claim 1, wherein the carrier is provided with three contact portions or formations, which when the carrier is in the deployed condition are arranged to bear against the part of the submerged structure.

8. The strain monitor of claim 3, wherein the deployment assembly comprises a spring, which when actuated is arranged to urge the strain gauge carrier into the deployed condition.

9. The strain monitor of claim 8, wherein the deployment assembly comprises a hydraulic chamber and fluid therein is arranged to maintain the carrier in the stowed condition.

10. The strain monitor of claim 1, further comprising one or more magnets to attach the strain monitor to the submerged structure.

11. The strain monitor of claim 1, wherein the strain monitor is configured to extend partially around the part of the submerged structure when attached to said part.

12. The strain structure of claim 1, wherein the strain monitor measures strain in the submerged structure via the strain gauge assemblies.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments of the invention will now be described by way of example, in which:

(2) FIG. 1 is a perspective view of strain gauge monitor

(3) FIG. 2 is a perspective view of an opposite side of the strain gauge monitor of FIG. 1,

(4) FIG. 3 is a perspective view of strain gauge mounted on a strain gauge carrier,

(5) FIG. 4 is a circuit diagram of two strain gauges in a circuit,

(6) FIGS. 5, 6 and 7, are cross-sectional side views of a strain gauge housing with a strain gauge carrier transitioning from a stowed condition to a deployed condition.

(7) FIGS. 8 and 9 are perspective views a data collection module,

(8) FIG. 10 is a perspective view of a receptacle which is arranged to receive the data collection module,

(9) FIG. 11 is a schematic view of the data collection module's data transmission functionalities,

(10) FIGS. 12 to 14 show the procedure of attaching the strain monitor to a submerged structure, and

(11) FIG. 15 shows the process of detaching the strain monitor from the submerged structure.

DETAILED DESCRIPTION

(12) There is now described a strain monitor, for use in structural integrity management of a submerged structure, such as the support structure of an offshore platform. What is now described is a novel apparatus and system which allows strain measurement in a structural member of such a structure to be easily and safely installed, and ensure accurate monitoring data is obtained.

(13) In overview, the strain monitor 1 is arranged to attach magnetically to a brace member of an offshore platform, and comprises a half-circle shaped device which is installed by an ROV. The monitor 1 includes three strain gauges to allow monitoring of brace longitudinal strain at three locations, aligned at 90° to one another other. The strain monitor 1 further includes an ROV-removable data collection module which integrates the required electronics for enabling signal processing, data storage, communications, and power management electronics as well as a battery. The strain monitor 1 is advantageously configured so that it allows the installation from the outside of the platform jacket without the need to go inside of the jacket, minimising the risk for ROV operations

(14) Reference is made initially to FIG. 1 which shows the strain monitor 1 which includes three strain gauge assemblies 3. The assemblies 3 are mounted at equally angularly spaced positions on a rigid main body 5. The main body 5 is of substantially half-circle shape and has a concave inner side region 5a, which is arranged to be brought against an outward-facing surface of a brace member. The main body 5 also has an outer side region 5b.

(15) Each strain gauge assembly 3 comprises a strain gauge carrier 6. The carrier 6 of a strain gauge 3 as shown in FIG. 3, comprises a central web 6a, which is provided at each end thereof with a respective distal end portion 6b. Two strain gauges 3a are installed to the carrier and in particular are installed at the dimensionally central point of the web on opposite sides of the web 6a. Fitting two gauges isolates the longitudinal axis strain and helps exclude any bending effects from the output measurement.

(16) One of the distal end portions 6b comprises a single contact portion 6c, which may be described as a pointed stud, of conical shape. The other distal end portion 6b of the carrier comprises two spaced-apart contact portions 6c. The three contact portions 6c are arranged in a triangular configuration.

(17) Each pair of strain gauges 3a is connected in a half Wheatstone bridge circuit configuration, as shown in FIG. 4.

(18) Each strain gauge 3a is mounted within a gauge housing 7, and incorporates a deployment mechanism. The housing 7 and, the deployment of an individual gauge is now described, followed by a description of the overall mechanism which deploys all the gauges. The methodology of the strain monitoring disclosed here creates a requirement for a reaction force (contact force) between the brace member and the strain carrier in order to transfer strain load from the brace member onto the strain carrier and so to the strain gauge. In order to realise this, a spring-loaded deployment mechanism is used. The housing 7 contains compression springs 7e and 7f which create contact force between the strain gauge carrier 6 and the brace pipe once the strain gauge has been deployed. This is achieved by applying a force to a load transfer block 7h. This block in turn presses the strain carrier out from the housing until the three contact portions 6c, or studs, contact the brace pipe with the required force. These may be made of a suitable (hard) material.

(19) The housing 7 comprises, in broad terms, a hydraulic chamber which is arranged to releasably retain a quantity of fluid, such that the strain gauge carrier is maintained in a stowed condition. A valved port is provided which when opened is arranged to allow the liquid to flow out from the chamber, and thereby permit the springs 7e and 7f to urge the strain gauge carrier 6 into a deployed condition. The rate of the liquid from the chamber may be modulated or controlled, so as to ensure a gradual and smooth transition from a stowed condition to a deployed condition of the carrier is achieved.

(20) FIG. 5 shows the strain gauge assembly 3 in its housing 7 in the retracted, or stowed, condition, in which the strain gauge (subassembly) is fully withdrawn into the housing. The hydraulic system is sealed at a valved port (not shown), which communicates with ports 7b for the cylinders 7c in which hydraulic pistons 7d are located. In this condition, the springs 7e and 7f are compressed.

(21) Referring now to FIG. 6, the assembly is in a partially deployed condition in which the strain gauge carrier has moved towards the brace member. The valved port has been opened and so hydraulic pressure will begin to drop inside the chambers 7c as water is purged by the force of the transfer plate springs 7e, and due to the reduction in pressure. The strain gauge carrier 6 begins to move slowly, with the rate of movement being controlled by pre-configured flow restrictor valves, not shown, downstream of the chamber ports to ensure that the rate of deployment motion is controlled.

(22) FIG. 7, shows the strain gauge assembly in a fully deployed condition, in which it has reached its final, fully extended position. The chambers 7c are fully purged and the pistons 7d are lowered and held in position by the fully extended transfer plate springs 7e. In this condition, the contacts 6c partially embed into the outer surface of the brace pipe, or more generally to impact frictional contact.

(23) The strain gauge assemblies are provided in a stowed condition so as to protect from damage during shipping, lowering into the water and installation to the brace.

(24) Once the clamp is fully positioned and magnetically locked onto the brace pipe, all three strain gauges are deployed simultaneously. The deployment is brought about by a rotatable switch 10. Once the switch 10 is turned by ¼ rotation, this controls a valve hydraulic pressure is released, allowing the transfer plate springs to extend and cause the transfer plate to move the strain gauge subassemblies slowly into their final deployed positions against the wall of the brace pipe, as described above. The quarter turn action switch includes an ROV or diver operable handle which will be coupled to a suitable valve.

(25) The strain monitor 1 comprises a number of permanent magnets 12, with sufficient force such that the strain monitor 1 cannot become loose and slide along the tubular brace member once installed.

(26) As best seen in FIG. 2, there is also provided an ROV fishtail handle 25, and an installation stand-off mechanism 26.

(27) Also mounted are mounted on the main body of the strain monitor are buoyant entities 20.

(28) The main body 5 of the strain monitor 1 comprises a coupling 14 arranged to locate a data collection module 15. This allows the data collection module 15 to be detachably connectable to the main body 5. The coupling 14 comprises an electrical socket which allows signals from the strain gauges to be received by the module, when in a connected condition.

(29) Reference is now made to FIGS. 8 and 9. The data collection module 15 comprises pressure vessel housing 15a, which is provided: with a male locating feature 15b, and internally of the module there is provided data acquisition and signal processing electronics. The module 15 also comprises an ROV handle 15c. and the module comprises an electrical coupling 15f. The ROV handle 15c is provided at the end of the module to be used to insert and remove the module from the coupling 14. 15d and 15e are comms ports for data transfer in the acoustic and optical domains, respectively.

(30) Reference is made to FIG. 10 which shows the mounting coupling 14, arranged to receive the module 15. The coupling comprises a recess forming a socket 14c. A defining wall of the recess comprises a cut-out 14b, which serves to locate the locating feature 15b of the module 15. The coupling also comprises an electrical connector which is connected to a cable 14a.

(31) Data recovery, from the module may be achieved by one of several ways provided, such as module retrievable to surface and captured data being downloaded via a cable connection. Alternatively or in addition there may be provided an ROV carried optical modem, or an acoustic modem. Reference is made to FIG. 11 which schematically illustrates the latter two methods.

(32) There is now described the procedure of installing the strain monitor to a brace member. Reference is made to use of an ROV, which is not shown for reasons of clarity.

(33) Reference is made to FIG. 11. The strain monitor 1 is manoeuvred by the propulsion of the ROV towards the brace member 100. The ROV grips the strain monitor 1 using the fishtail handle 25 to achieve this.

(34) Referring to FIG. 12, the ROV brings the strain monitor into engagement with the brace 100. More specifically a moveable engagement portion 26a of the installation stand-off mechanism 26 engages with the outer surface of the brace member 100. This serves to prevent the magnets from causing the strain monitor to attach to the brace, by maintaining them in a spaced-apart relationship, as shown in FIG. 13. This advantageously serves to ensure that the attachment process is a controlled procedure. At this point the strain monitor 1 is located against the brace pipe. Very little magnet force should be experienced (by the ROV). The installation stand-off mechanism 26 comprises a closed D-handle, which is gripped by the ROV. The ROV positionally adjusts the strain monitor which may be moved until its position is correct relative to the brace member. Inclinometers provided on the strain monitor, and viewable by the ROV, can be used to help with alignment.

(35) Once correctly aligned and positioned, the ROV releases the D-handles. This results in the component 26a, translating rearwardly. This allows the magnets to attach to the brace member 100. FIG. 14 shows the strain monitor in the attached condition.

(36) The studs 6c provide positional stability and resistance to rotation in operational use. This is imperative, as once installed the gauge orientation must not alter in order for valid strain data analysis to be possible.

(37) Advantageously, the strain monitor when installed does not affect flexural or vibration characteristics of the brace member during operation.

(38) Reference is now made to FIG. 15, which shows the strain monitor removal or extraction procedure. The ROV may first remove the module 15 prior to executing this procedure, even though the module 15 is shown attached.

(39) The ROV first holds the strain monitor 1 by the fishtail 25 and grips the handle 27a of the extraction mechanism 27 with the other manipulator. The ROV pulls the extraction handle, and in so doing rotates the mechanism. This applies a leverage to the brace member. The strain monitor 1 is thereby pushed away from the brace by a lever action. At this point strain monitor 1 may be pulled fully free of the brace using the fishtail handle 25.

(40) In a variant embodiment a strain monitor is arranged to be attached to a flat, or substantially flat, surface of a submerged structure. The strain monitor comprises multiple strain gauge assemblies which are arranged in spaced apart fashion, arranged linearly or essentially in a two dimensional plane. Such a variant strain monitor may share some or all of the features and functionalities disclosed above in relation to the strain monitor 1. It will be readily understood however that because the variant strain gauge assembly is intended to attach to a flat surface of a submerged structure that its main body/support assembly will not be of curved shape of the strain monitor 1. For example, the variant strain monitor may comprise a main body which has a form factor with a principal dimension being a linear dimension.