METHOD AND APPARATUS FOR MEASURING A PIPE WELD JOINT

Abstract

An internal line-up clamp (20), for aligning two pipes to be welded together, includes a hi-lo measurement system, for example includes a laser source (24) and camera system (22), mounted on the internal line-up clamp (20) and arranged to make a hi-lo measurement (d), indicative of the degree of alignment of the pipes (10a, 10b). The measurement may be made when two pipes are clamped together by means the internal line-up clamp (20). The pipes may then be welded together, whilst the pipes remain clamped together in the same position, and whilst the hi-lo measurement system remains inside the pipes.

Claims

1. An internal line-up clamp for aligning two pipes to be welded together, wherein the internal line-up clamp includes a hi-lo measurement system mounted on the internal line-up clamp and arranged to make a hi-lo measurement when two pipes are clamped together by means the internal line-up clamp.

Description

DESCRIPTION OF THE DRAWINGS

[0029] An embodiment of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0030] FIG. 1 is a partial cross-sectional view of two pipes arranged end-to-end showing the hi-lo distance to be measured;

[0031] FIG. 2 is a perspective view of an internal line-up clamp according to a first embodiment of the invention;

[0032] FIG. 3 is a perspective view of a conventional internal line-up clamp for aligning two pipes in end-to-end configuration;

[0033] FIG. 4 is a perspective view of a hi-lo measurement system of the internal line-up clamp of FIG. 3; and

[0034] FIG. 5 is a plan view of the hi-lo measurement system of FIG. 4.

DETAILED DESCRIPTION

[0035] An embodiment of the present invention is shown in FIG. 2 and includes an internal line-up clamp (ILUC) device 20 on which there is mounted a hi-lo measurement system. The hi-lo measurement system includes a camera 22 and a laser light source 24, both of which being illustrated schematically in FIG. 2. A conventional internal line-up clamp device is shown in FIG. 3. The ILUC device is attached to an umbilical (not shown). The ILUC device 20 has two sets of expandable clamp members 26 spaced around the circumference of the device 20, one set being associated with one pipe end and the other set being associated with the other pipe end. The ILUC device 20 holds two pipes (not shown in FIG. 3) in end-to-end configuration by means of expanding the clamp devices 26 so that they all move outwardly in the radial direction and engage the inner surfaces of the pipes. A welding apparatus mounted on the exterior of the pipes may then weld the joint between the two pipe ends. A copper backing plate (or shoe) is typically provided to assist in this welding process, and during welding the copper plate 18 is urged against the interior walls of the pipes to support the weld joint.

[0036] It will be seen that the internal line-up clamp device of FIG. 2 (in accordance with the embodiment of the invention) is very similar to the device shown in FIG. 3, apart from the fact that the internal line-up clamp device of FIG. 2 includes a hi-lo measurement system in place of the copper backing plate. In use, it will be appreciated that the hi-lo measurement system is thus arranged directly adjacent to the joint.

[0037] FIGS. 4 and 5 show in greater detail the hi-lo measurement system separate from the internal line-up clamp device 20. The hi-lo measurement system is generally arcuate in shape when viewed from the side (see FIG. 5) and extends around about half of the circumference of the pipes. The hi-lo measurement system when installed on the internal line-up clamp device is mounted for movement along the joint (i.e. it rotates about the longitudinal axis 40 of the pipe). For this purpose the hi-lo measurement system includes a motor (not shown in FIGS. 4 and 5) powered by a local power supply 28 disposed on the hi-lo measurement system.

[0038] As mentioned above, the hi-lo measurement system includes a camera system and a laser light source 24. The camera system 22 comprises a camera-image converter board 30, a camera lens 32, and a CMOS (active-pixel sensor) 4 mega-pixel camera chip 34. The light from the laser light source 24 is in use reflected by a mirror 36 so that the light is emitted in a radial direction. The components 30, 34 forming the camera system and the laser light source 24 are powered by the local power supply 28. By providing a local power supply, for example in the form of a rechargeable battery, there is no need to draw power via the umbilical connected to the ILUC device 20.

[0039] The hi-lo measurement system is based on an optical triangulation method between the camera's field of view and a laser line projected orthogonally to the joint to be welded. Thus, in use, laser light 38 is produced by the light source 24 in the form of a beam of light divergent in only one plane thus producing a flat sheet of light 38, which is reflected by the mirror 36 so that the interior surface of the pipe in the region of the joint to be welded is illuminated by a line of laser light 38. The line of light incident on the interior surfaces of the pipes is orientated parallel to the longitudinal axis 40 of the pipes. As a result of the planar nature of the emitted light, any steps from one pipe end to the other will be revealed by means of a corresponding step in the line of light on the surface of the pipes. The camera system views the incident light via the lens 32, and thus receives a visual indication of the profile of the joint to be welded. The camera's field of view is illustrated schematically in FIG. 4 by the broken lines 42. In use, the hi-lo measurement system moves along the joint to be welded, and effects a hi-lo measurement every degree (equivalent to over 1,000 measurements around the circumference). The joint is thus effectively scanned by the laser-light and camera system. The images are received by the converter board 30 and then transmitted via the umbilical to a local welding control system including a computer processor. The hi-lo measurements can then be processed and analysed to provide an indication of the degree of alignment.

[0040] The arrangement of the camera and laser light source is such that an absolute accuracy of measurement of the order of 0.1 mm or better (absolute accuracy, accounting for all variation in parameters and drift due to for example temperature) is achievable.

[0041] A method of welding two pipes together including measuring the alignment of the pipes with the internal line-up clamp device 20 of the first embodiment will now be described.

[0042] A first pipe end is defined by a pipeline (having an internal diameter of about 600 mm), which in this embodiment is being laid at sea and thus leads to the sea-bed. A second pipe end is defined by a free pipe section to be welded to the end of the pipeline thereby extending the length of the pipeline. In this case, the pipes are INOX (steel) pipes. The pipe ends are brought together and into alignment. An operator rotates the free pipe section about its axis and translates the pipe-section so that the pipe ends are brought into a position of best alignment as judged by manual inspection by the operator. The ILUC device 20 is operated, the clamp members 26 moving radially outwardly, to clamp the two pipe ends together, with the ends touching, in this position. The welding apparatus is mounted on the exterior of the pipes and all other fit-up actions are completed so that the welding apparatus and pipes are all ready for performance of the welding step.

[0043] After fit-up has been completed and the pipes are ready to be welded, the hi-lo measurement system is then operated to measure the degree of alignment. Thus, the hi-lo measurement system rotates about the axis of the pipes, such that the hi-lo measurement system completes a whole rotation about the circumference of the interior of the pipes and performs a continuous scan of the profile of the joint. The data is sent from the hi-lo measurement system to the computer of the local welding control system.

[0044] The computer processes the received data and produces output data representative of the degree of (mis-)alignment between the pipes. The data processing step includes analysing the data representative of the profile of the joint in consideration of alignment criteria derived from previous tests and calibration. The alignment criteria are a form of reference data, which may be set having regard to a desired specification. The computer thus outputs an indication of the degree of alignment including an indication as to whether the joint should be welded or whether the pipes need to be better aligned before welding can be commenced. The operator of the local welding control system may also be displayed, via a visual display unit, a representation of the profile of the joint to be welded (showing how the hi-lo measurement varies along the length of the joint).

[0045] If the degree of alignment between the pipes is deemed to be unacceptable, then the manual operator is warned and the pipes are manipulated in an attempt to improve the alignment between them.

[0046] If the measured data is such that the control unit deems the alignment to be acceptable, then the welding is immediately performed, with the ILUC device, and therefore also the hi-lo measurement system, still inside the pipes and in the region of the joint. The position in which the pipes are clamped together also remains substantially unchanged.

[0047] The welding step is therefore performed without delay after the hi-lo measuring step, so that the measurement is made in conditions that very closely match the post-welding conditions, thus reducing the chance of error.

[0048] The welding process is accurate and completed entirely from the exterior of the pipes. The root weld is performed sufficiently slowly and accurately that a copper backing plate, copper shoes or the like are not required.

[0049] The above embodiment may be considered as a method of welding two pipes together, wherein the method includes the steps of (a) clamping two pipes in a position in which a joint to be welded is defined between the ends of the two pipes, (b) obtaining, by means of a measurement system positioned inside the pipes, an indication of the degree of alignment of the pipes in the region of the joint, whilst the pipes are clamped together in said position, and (c) welding together the two pipes, whilst the pipes remain clamped together in the same said position.

[0050] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0051] The hi-lo measurement system could be used to recommend how the pipes should be manipulated in order to improve their alignment, if the pipes are found not to be sufficiently well-aligned. The computer could for example output the movements required to attain the best alignment between the pipes.

[0052] The hi-lo measurement system could be used to measure additionally the alignment of the pipes after welding, to verify that the pipes have not become misaligned during the welding process.

[0053] The internal line-up clamp and hi-lo measurement system could be used in welding pipes together both onshore and offshore.

[0054] In the illustrated embodiments, the hi-lo measurement system is effectively mounted on the exterior of the ILUC. It will of course be appreciated that the hi-lo measurement system could alternatively be mounted on the ILUC in such a way as parts of the hi-lo measurement system are not clearly visible from the exterior of the ILUC. Parts of the hi-lo measurement system may for example be integrated inside the ILUC.

[0055] The local power supply powering the hi-lo measurement system need not be in the form of a battery, but may instead be a local power unit that is powered by electric power from the umbilical attached to the ILUC. In such a case, the local power unit may regulate and/or transform the power received from the umbilical into electrical power suitable for use by the hi-lo measurement system.

[0056] Whilst the illustrated hi-lo measurement system is generally arcuate in shape when viewed from the side, it will be appreciated that other shapes of hi-lo measurement system are possible, especially if components of the hi-lo measurement system are smaller than those illustrated.

[0057] There may be a dedicated computer for receiving and processing the data from the hi-lo measurement system.

[0058] The illustrated embodiment can of course be used to weld pipes of different materials such as for example cladded or corrosion resistant alloy (CRA) pipes.

[0059] The alignment criteria may utilise reference data yielded from numerous previously conducted experiments. Those experiments may for example include measuring the alignment of pipe joints with the hi-lo measurement system and then fatigue testing the welded joint to test the reliability of the weld so performed. From the experiments, correlation between the hi-lo measurements and the reliability/acceptability of the weld joint may be derived and then used in the field in order to assess the reliability/acceptability of the alignment of the pipes in view of the hi-lo measurement data.

[0060] The laser light and camera system of the hi-lo measurement system may be in a form similar to that utilised in WO2006/112689. The hi-lo measurement system may utilise means other than a laser light and camera system to perform the measurement. The light source may for example be a non-coherent, but sharply focussed, light source. The camera system may be able to map the geometry of the weld joint without the need for any reference light source. As another alternative, a mechanical, contact-based, measurement system may for example be employed.

[0061] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.