Scanning method and apparatus

Abstract

A method of assessing the condition of a tubular member comprises driving an ultrasonic probe to fire a short pulse ultrasonic beam at the outer surface of the tubular member and analyzing the reflected signals from the tubular member to assess the condition of the tubular member. The apparatus comprises an ultrasonic probe (22), means for driving the probe to fire a short pulse ultrasonic beam at the outer surface of the tubular member and means for converting the reflected ultrasonic beam into image signals which can be analyzed to assess the condition of the tubular member.

Claims

1. An apparatus for assessing a condition of an annulus of a flexible pipe, the apparatus comprising: an ultrasonic probe; an ultrasonic transducer element that drives the ultrasonic probe to fire a short pulse ultrasonic beam at an external sheath of the flexible pipe; a control pack that converts reflected ultrasonic beam into image signals, the image signals including front and back walls of the flexible pipe; and which can be analysed to assess the condition of the flexible pipe; and wherein at least one of natural frequencies and mechanical behaviors of materials of the ultrasonic probe and the external sheath of the flexible pipe are matched.

2. The apparatus according to claim 1 comprising a display that displays the image signals.

3. The apparatus according to claim 2 wherein an umbilical is provided between the probe or probes and the display device.

4. The apparatus according to claim 1, wherein the ultrasonic probe is adapted to be driven at a voltage of around 700V to 1 Kv.

5. The apparatus according to claim 1, wherein the probe fires pulses of between 4 and 6 Mhz with a focal length of between 5 and 100 mm.

6. The apparatus according to claim 1, comprising a frame adapted to be mounted adjacent to or around an outer surface of the flexible pipe.

7. The apparatus according to claim 6 wherein the ultrasonic probe is mounted upon the frame in an orientation perpendicular to a longitudinal axis of the frame.

8. The apparatus according to claim 6 comprising a rack and pinion for moving the frame relative to the flexible pipe.

9. The apparatus according to claim 6 comprising a rack and pinion for moving the frame along or across the outer surface of the flexible pipe.

10. The apparatus according to claim 6 wherein the frame comprises a hinged collar which can open to allow the frame to be mounted around a flexible pipe.

11. The apparatus according to claim 6 wherein means are provided on the frame for moving the probe or probes vertically and/or horizontally over a surface of the flexible pipe.

12. The apparatus according to claim 1 wherein the apparatus further comprises a plurality of probes.

13. The apparatus according to claim 12 wherein the apparatus comprises a pair of probes mounted in a frame in opposing diametric alignment.

14. The apparatus according to claim 13 wherein a second pair of probes is provided perpendicularly to the first pair such that a longitudinal axes of the two pairs of probes cross within the flexible pipe when the frame is mounted on a flexible pipe and the ultrasonic beams fired by the probes converge on a centre of the flexible pipe.

15. The apparatus according to claim 14 comprising a collar of the frame.

16. The apparatus according to claim 1 wherein the probe has a front face diameter of between 9 and 12 mm.

17. The apparatus according to claim 1 wherein the probe comprises polyvinylidenefluoride (PVDF).

Description

(1) An embodiment of the present invention will now be described with reference to the enclosed Figures in which:

(2) FIG. 1 is a schematic part sectional view of a first form of flexible riser;

(3) FIG. 2 is a further schematic part sectional view of a second form of flexible riser, and

(4) FIGS. 3 and 4 are schematic perspective views of an apparatus for assessing the condition of a tubular member such as a flexible riser shown in FIG. 1 or 2, according to one aspect of the present invention.

(5) Turning now to the figures, FIG. 3 shows an inspection apparatus 10 comprising a frame 11 which is adapted to be mounted around the outer surface of a tubular member such as a flexible riser as shown. The frame comprises a substantially rectangular U-shaped channel member 12 which is open along the upper surface 13. A collar 14 is mounted on either end of the channel member, the collar comprising a rear portion 15 mounted to the upper and lower ends of the channel member and a pair of arms 16 which extend from either end of the rear portion and can be pivotally moved between a first position in which the arms are in an open position and a second closed position in which the arms are moved towards each other to grip onto a flexible riser when the frame is placed adjacent to the riser.

(6) Gripping means 17 are provided at the free end of each arm for gripping a riser. The gripping means comprise upper and lower plates 18 which are generally L-shaped with a curved front face 19. The plates are mounted to the ends of the arms through a pivot pin 20 at the junction of the legs of the plates. Rollers 21 are provided between the upper and lower plates serving to grip the outer surface of the riser.

(7) The collars are shown as being at the upper and lower ends of the channel member in this embodiment although they could of course be provided at any position and in any number(s) along the frame.

(8) An ultrasonic probe 22 is mounted on the frame. The probe is fixed to a curved mounting plate 23. Means are provided for adjusting the position of the plate within the frame, and thereby the position of the probe within the frame. In this embodiment a hydraulic cylinder 24 is mounted within the open channel member of the frame and the plate is mounted to an arm 25 extending laterally from the hydraulic cylinder towards the open ends of the arms of the collars. Thus as the hydraulic cylinder extends and retracts within the channel member, the arm moves with respect to the channel member between the upper and lower ends and carries the mounting plate and the probe vertically within the frame between the two collars.

(9) The probe has a front face diameter of between 9 and 12 mm and comprises or is constructed with a piezoelectric material, preferably a copolymer such as for example polyvinylidenefluoride (PVDF) which is a versatile engineering plastic. It is intended that probes for use in the present invention are marinised using known techniques to facilitate their use subsea in depths of up to 3000 m.

(10) The probe comprises an ultrasonic transducer element (not shown) for emitting an ultrasonic beam to a flexible riser and for receiving echoes of the ultrasonic beam reflected from the riser which echo signals can then be converted into an image signal as described below. It is envisaged that the single transducer element may be replaced with a phased array of elements which are fired consecutively to produce a signal over a wider area.

(11) Driving means (not shown) are provided on the frame and coupled to the ultrasonic transducer elements for driving the transducer elements for generating the ultrasonic beam. The driving means are adapted to drive the probe at a voltage of around 700V to 1 Kv such that the probe produces short pulses of between 4 and 6 MHz frequency and a focal length of between 5 and 100 mm.

(12) A control pack 26 is mounted on the frame and includes known means for converting the reflected signals into image signals which can then be viewed at a display means as will be described further below.

(13) Means 27 are provided on the mounting plate and the arm of the frame for moving the mounting plate laterally with respect to the arm. The mounting plate can be moved with respect to the arm to allow the probe to be moved both horizontally and vertically with respect to the frame. The means may for example be a rack and pinion arrangement.

(14) A sensor 28 is mounted within each collar on a rod 29 which extends outwardly from the channel member between the pivotal arms of the collar as will be described further below.

(15) In the illustrated embodiment a single probe is mounted on the frame although multiple probes may be provided as is described further below.

(16) The frame is adapted to be deployed by a remotely operated vehicle (ROV) from a platform or vessel into seawater surrounding the riser and mounting means (not shown) are provided on the frame to facilitate connection and operation by the ROV.

(17) An umbilical 30 is connected between the control means on the frame and a display device (not shown) on the vessel or platform from which the frame is deployed and the umbilical carries the converted image signals to the display means where they can be viewed by an operator of the apparatus.

(18) The method of scanning the flexible riser will now be described.

(19) The frame 11 is prepared on board a vessel or on a platform in the vicinity of the riser to be assessed. The probe 22 is mounted into the frame on the mounting plate 23 and the frame is mounted onto the ROV. The umbilical 30 is connected between the control package 26 and the display means. The arms 16 of the collars are set in the open condition. The ROV is then deployed from the vessel or platform into the water surrounding the riser and the ROV is flown to the appropriate location adjacent the section of the riser to be scanned paying out the umbilical as it goes.

(20) When the ROV reaches the desired position, the frame, with the arms of the collars in the open position, is presented to the riser and the ROV moves the frame into position. As the outer surface of the riser comes into contact with the sensors 28 extending into the frame, the arms 16 of the collars are pivoted into the closed position and the gripping means 17 contact the outer surface of the riser. At this point a signal may be generated by further sensors on the arms to automatically halt the movement of the arms or the operation may be halted by the operator from a remote location. For example a camera may be mounted on the frame to facilitate close control of the arms. The frame can be used to service risers of different diameters as the arms are closed around the outer surface of the riser and can be set at different positions to accommodate different diameters of risers.

(21) The operator then passes a control signal to the frame 11 and the hydraulic cylinder 24 is moved vertically within the channel member 12 to move the probe and therefore the ultrasonic beam emitted from the probe vertically along the outer surface of the riser. As the probe is driven to such a high voltage, the ultrasonic beam generated can assimilate the characteristics of the outer sheath polymer of the riser and penetrate the armour wires thus improving the strength of the resulting reflected signals and providing improved accuracy in the converted image signals that are generated. These signals representing a visual image of the front and back surface of the armour wires and the level or extent of any flooding in the riser determined by locating interfaces between fluid filled sections of the annulus and those sections without fluid are passed along the umbilical 30 and back to the display device on the vessel or platform where they can be viewed and analysed by the operator.

(22) The operator also controls the horizontal movement of the probe relative to the frame by driving the mounting plate 23 over the arm 25 of the frame. As the mounting plate is curved, any movement of the mounting plate horizontally with respect to the channel member keeps the probe at a fixed distance from the outer surface of the riser.

(23) Once the scan is complete in the section covered by the frame, a signal can be passed from the operator to the frame to pivot the arms into the open position thereby releasing the frame 11 from the riser. The frame can then be recovered by the ROV back to the surface or alternatively the ROV can be operated to move the frame to another section of the riser where a further scanning operation can be carried out.

(24) It will be appreciated that the method and apparatus of the present invention provides for real time assessment of the condition of the annulus of a riser and particularly a flexible riser and real time inspection of the armour wire thickness which allows the operator to take remedial action where necessary to address any issues which are identified.

(25) It is to be appreciated that modifications to the invention may be made such as for example in a non illustrated embodiment multiple probes may be mounted within the frame and multiple ultrasonic beams moved over the surface of the riser. For example two pairs of probes may be provided, each mounted at 90 degrees to the next around the frame such that each opposing pair of probes fire ultrasonic beams along the same longitudinal axis. By providing two off set pairs of probes as described, two perpendicular ultrasonic beams can be fired at the riser to provide for a self centering operation of the frame and or the probes.

(26) It will be appreciated that whilst the apparatus described above is intended to be mounted on a riser and the probe or probes moved to scan the ultrasonic beam(s) over the surface of the riser, means may be provided on the frame to facilitate movement of the frame along the riser when the frame is in the closed position. It will be further appreciated that the driving means for moving the frame along the riser may be controlled remotely by the operator by incorporating known control equipment either on the frame or on the ROV. This would enable the frame to complete a scan of a riser without having to be removed and repositioned along the length of the riser.

(27) The embodiments if the apparatus have been described above as used in monitoring the condition of a flexible pipeline, however the apparatus as described may equally be used in relation to other tubular members including rigid pipes and pipelines or risers.

(28) Such rigid pipes may for example be formed of or comprise steel and may have a polymer sheath or coating applied to the surface of the pipe. This polymer sheath or coating provides corrosion protection and or insulation for the pipe.