GB2338786A

GB2338786A - Inspection device and method

Info

Publication number: GB2338786A
Application number: GB9813790A
Authority: GB
Inventors: Anthony David Hall
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-06-26
Filing date: 1998-06-26
Publication date: 1999-12-29
Anticipated expiration: 2018-06-26
Also published as: GB9813790D0; GB2338786B

Abstract

A device for examining an elongate object, such as chains or pipes, said device comprising two clamps 1 each adapted to hold a camera in parallel spaced relation to each other, and locating means 6 arranged to locate said device on said object such that at least a portion of its length falls within the field of view of cameras held by the clamps. The device is used for example to measure chain length and stretch in sub sea environments; a scale bar is held within the field of view of the camera to aid this. Methods of examining objects such as chains or pipes using the device, which involve comparing images obtained from cameras located within the clamps, are also described and claimed.

Description

1) 1 2338786 Inspection Device and Method The present invention relates to

a device used in the inspection or examination of elongate objects such as chains or pipes, as well as to a method of carrying out such inspections. In particularly, the device can be used as a sub-sea chain measuring tool.

Multiple arrays of large diameter mooring chains are commonly used to tether to the sea floor a wide variety of floating offshore structures. These chains are subject to continuous wear due to the action of wind and sea conditions on the floating structures.

All mooring chains have strictly designed and dimensional tolerances for wear, which can be defined as the maximum allowable change in specific dimensions before the mooring is considered to have become operationally unreliable.

Failure of an offshore mooring chain can have severe operational consequences, and is considered to be totally unacceptable.

FEstorically, there has been no means to reliably make accurate in situ dimensional measurements of mooring chains. Consequently, to ensure dimensional tolerances are not exceeded, chains are periodically replaced on a calendar basis with new chains.

The costs of removing and replacing offshore chains are substantial, and in many cases may be conducted prematurely for the actual level of wear.

A capability to perform accurate and reliable in situ dimensional measurements of mooring chains offers substantial cost savings through a reduction in numbers of unnecessary chain replacements.

2 Other subsea structures such as pipelines are also subject to similar forces and therefore similar wear and tear. Again, failure of these pipes can have significant adverse effects operationally.

According to the present invention there is provided a device for examining an elongate object, said device comprising two clamps each adapted to hold a camera in parallel spaced relation to each other, and locating means arranged to locate said device on said object such that at least a portion of its length falls within the field of view of cameras held by the clamps.

Images obtained from two parallel cameras which are spaced at a precise and predetermined distance apart can be used to examine various properties of the elongate object. For example, where the elongate object is a chain, the images will allow a precise measurement of the distance between links of the chain, to be calculated and therefore the degree of any stretching to be determined.

Where the elongate objects are pipes, particularly sub sea pipes, the angles at which the pipes are inclined would indicate the level of movement or stress to which the pipes have been subjected. Images obtained from cameras held in the device as described above could be used to determine such angles.

The space between the clamps is suitably of a predetermined length. This may be variable to allow the device to be used in the inspection of various elongate objects, such as chains of differing link size. In general the space between the clamps will be in the range of from 50Omm to 2m for chain measurement, for example about 80Omm. In order to achieve this, the clamps of the device are suitably spaced from each other by means of a spacer shaft which is arranged perpendicular to the direction of cameras held in the clamps. The length of the spacer shaft may be varied, for example by providing a series of fixing means along its length and moving one or both clamps to appropriate fixing means within the series. Alternatively, the device is of a modular form and the spacer shaft is -m 3 replaceable by others of differing lengths to suit the requirements of the particular inspection being undertaken, The clamps are suitably attached to base units provided at each end of the spacer bar by means of support posts. The length of these posts may also be variable depending upon the the size of the camera being used as well as the size of the elongate object being inspected and the distance the cameras are to be spaced. Although these may be of variable length, for example by slideably mounting the clamps on the support posts, with braking or fixing means at predetermined distances along the posts. Alternatively, in a modular device, the support posts may be replaceable by others of different lengths.

The locating means of the device is suitably arranged such that it can removeably hold the device in a fixed relationship to the elongate object.

For example, the locating means may comprise a U-shaped hook, with opposing sides which are arranged to abut around a single link of a chain, between the perpendicular links on either side.

The locating means are suitably arranged on the spacer shaft, intermediate the support posts. Again, these may be replaceable in a modular device with hooks or other forms of attachment of various sizes to allow the device to be used in the inspection of more than one type of elongate object.

In a preferred embodiment, the device further comprises one or more scale bars, arranged to project into the field of view of a camera when in place in the clamps. The presence of the scale bars in the image obtained from the camera can assist in the measurement of a length or distance in a particular direction. Suitably a scale bar is provided for each camera. Preferably, for chain measurement in particular, a pair of scale bars are provided and arranged such that they project into the camera image in parallel relationship to one another on either side of a chain link.

When an image is produced, these parallel scale bars can be used to assist in 4 determining whether there has been any twisting of the chain. Again, these scale bars may be removable from a modular device so that they may be replaced by bars of differing sizes depending upon the elongate object being measured.

The scale bars are suitably arranged on the base units which allow for the interconnection of the support posts of the camera clamps and the spacer bar.

The device is suitably made of a rigid material, preferably one which can withstand the strong buffeting which is associated with the use of the device in sea and sub sea conditions. Suitable materials include rigid polymers such as acetyl copolymers for example, those sold under the trade name "Delrin", as well as metals such as steel.

Suitably the device comprises two camera clamps although it may clearly comprise more than two clamps, support posts etc., for example up to six such arrangments, provided the spacer shaft is long enough and strong enough to accommodate them.

Where the device is modular, it may be provided as a complete device. or as a kit of parts, for example comprising a pair of base units, one or more pairs of clamps, one or more sets of support posts, one or more spacer shafts and one or more guide brackets. Additionally the kit may comprise one or more sets of scale bars adapted for insertion into the base units.

Thus in a preferred embodiment, the device of the invention is a modular sub-sea chain measuring tool comprising two replaceable adjustable camera clamps, two replaceable support posts for said clamps, and two base units, separated by a replaceable horizontal shaft on which is located a replaceable guide bracket.

As discussed above, the device of the invention is used in the examination or inspection of elongate objects such as pipes and chains, where access to these is difficult, in particular in sub-sea locations. In use a camera, such as a video camera or a subsea image camera is held in each of the clamps of the device of the 1\ invention. This is then manipulated for example by means of a remotely operate vehicle (ROV) such as the remote arm of a submarine, or a diver, so that the locating means fixes the device onto the elongate object, such as the chain.

An image is then obtained from each camera preferably simultaneously, for example by synchronising the camera exposures, or, when the camera is a video camera, using for example, computer synchronisation technology to select images at precisely the same point in time.

A comparison of the images obtained in this way, from parallel cameras, a predetermined distance apart, will allow an analysis of features such as stress or stretch of the object to be undertaken.

Thus in a further aspect, the invention provides a method for examining an elongate object along at least a portion of its length, said method comprising forming an image of said object at at least two intervals along its length using parallel imaging devices arranged at a predetermined distance from each other, and comparing images obtained thereby.

The comparison may allow the measurement of lengths such as the distance between chain links, angles or circumferences, depending upon the requirements of the inspection.

As mentioned above, the images used in the comparison are suitably those obtained simultaneously, and computer technology, such as the digital time codes, may be used in order to assist in ensuring that this is the case.

Furthermore, the comparison may be carried out either manually, or using computerised digital image analysis. For this purpose, the images will be in digital form or are converted to digital form using conventional methods.

6 A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 shows in perspective, a tool which is a device according to the invention; Figure 2 shows a side view of the tool correctly deployed on a mooring chain; and Figure 3 shows a top view of the tool correctly deployed on a mooring chain.

Figure 1 shows a tool which comprises two replaceable adjustable camera clamps 1 mounted parallel to each other on fixed vertical posts 2. Each post 2 is inserted into a support base 3. At the distal end of each support base 3 are inserted two parallel projecting scale bars 4. Into the proximal end of each support base 3 is inserted a replaceable shaft 5 of predetermined length, which has in the centre of the span a replaceable guide bracket 6.

Securing bolts 7 are provided in order to allow the clamps to be tightened around a camera to hold it in position. The device is modular in structure and therefore release of the securing bolts 7 allows the camera clamps 1 to be removed if desired and replaced by different size camera clamps 1.

Each vertical post 2 is attached to the base unit 3 by securing bolts 8. Removal of these bolts 8 allows the post 2 to be pulled vertically from the support base 3 and replaced by differently sized posts.

Each scale bar 4 is fixed into position using securing bolts 9 which are removeable to allow replacement of the scale bars.

The shaft 5 is fixed to the base units 3 by way of securing bolts 10. Removal of these will allow the base units 3 to be slid off the shaft 5. To insert a replacement shaft 5 the steps described above are carried out in the reverse sequence.

1 7 The guide bracket 6 is held in place by securing bolts 11, which can be loosened to allow removal of the guide bracket 6 by sliding off either end of the shaft 5. To insert a replacement guide bracket 6 the steps described above are carried out in the reverse sequence In use, the tool is placed on a chain by a remotely operated vehicle (ROV) or a diver in the orientation illustrated in Figures 2 and 3. The central guide bracket 6 is arranged to ensure that the tool is orientated into the correct position on the chain. The tool is placed in such a manner that the central guide bracket 6 both hooks over the top of the central chain link 12 and is positioned between the adjacent ends of the two perpendicular links 13.

Images taken from cameras (not shown) held within the clamps will allow accurate positioning of the ends of the link adjacent the links 13. The scale bars 4 will assist in this. Since the length of the spacer shaft 5 is also known, the distance between these two can be accurately measured. The measurement can be compared to that expected for the chain to determine the degree of stretching which has taken place.

8

Claims

A device for examining an elongate object, said device comprising two clamps each adapted to hold a camera in parallel spaced relation to each other, and locating means arranged to locate said device on said object such that at least a portion of its length falls within the field of view of cameras held by the clamps.
2. A device according to claim 1 wherein the space between the clamps is of a predetermined length.
3. A device according to claim 2 wherein the said predetermined length is variable.
4. A device according to any one of the preceding claims wherein the clamps of the device are spaced from each other by means of a spacer shaft which is arranged perpendicular to the direction of cameras held in the clamps.
5. A device according to claim 4 wherein the clamps may be positioned at variable distances from the spacer shaft.
6. A device according to claim 5 wherein the clamps are mounted on support posts which are replaceable.
7. A device according to any one of the preceding claims wherein the locating means comprises a guide bracket in the form of a U-shaped hook, with opposing sides which are arranged to abut around a single link of a chain, between the perpendicular links on either side.
8. A device according to any one of the preceding claims which further comprises one or more scale bars, arranged to project into the field of view of a camera when in place in the clamps.
9 9. A device according to claim 8 wherein pairs of parallel scale bars are provided in the field of view of each camera.
10. A device according to claim 1 which is a modular sub-sea chain measuring tool comprising two replaceable adjustable camera clamps, two replaceable support posts for said clamps, and two base units, separated by a replaceable horizontal shaft on which is located a replaceable guide bracket.
11. A method for examining an elongate object along at least a portion of its length, said method comprising (i) forming an image of said object at at least two intervals along its length using parallel imaging devices arranged at a predetermined distance from each other, and (ii) comparing images obtained thereby.
12. A method according to claim 11 wherein in step (ii), the distance between points in the images are measured.
13. A method according to claim 11 or claim 12 wherein the images used in the comparison are taken at simultaneous points in time.
14. A method according to any one of claims 11 to 14 wherein step (ii) is effected using computerised digital image analysis.
15. A kit of parts which forms a device according to any one of claims 1 to 10.
16. A kit according to claim 15 which comprises a pair of base units, one or more pairs of clamps, one or more sets of support posts, one or more spacer shafts and one or more guide brackets.
17. A kit according to claim 16 which further comprises one or more sets of scale bars adapted for insertion into the base units.
18. A device for examining an elongate object substantially as hereinbefore descibed with reference to the accompanying drawings.
19. A method according to claim 11 substantially as hereinbefore described.