GB2336674A

GB2336674A - Sub-sea detector for checking alignment

Info

Publication number: GB2336674A
Application number: GB9903713A
Authority: GB
Inventors: Rowan Patterson
Original assignee: UWG Ltd
Current assignee: UWG Ltd
Priority date: 1998-02-24
Filing date: 1999-02-19
Publication date: 1999-10-27
Anticipated expiration: 2019-02-19
Also published as: GB2336674B; GB9903713D0; GB9803669D0

Abstract

A detector for use in setting up a sub-sea structure which has a sealed water-tight housing 10 with a transparent window 18, a pitch and roll sensor (29, 30 fig.3a) and also a fluxgate compass assembly (31) being mounted within the housing 10. The sensors and compass assembly provide electrical outputs to a processor (26) which drives a display device 27 visible through the window 18. Also mounted within the housing is a solar cell array 35, positioned to receive light entering the housing through the window 18, the solar call array powering the other components within the housing. The detector includes a memory device to store information even when no light falls on the array 35.

Description

Ref.1l^p 2336674 Sub-sea Detectors This invention relates to a detector

for use in setting up or adjusting a sub-sea structure, such as a guide base, template or manifold. In particular, the invention concerns such a detector suitable for use in setting or checking the alignment of a sub-sea structure with certain predefined planes, such as the horizontal and vertical planes.

When a sub-sea structure such as a guidebase, template or manifold is set up on a seabed, it is most important that the principal axis of the structure is set substantially vertical. Moreover, for many designs of structure, it is important that the structure is set with a component of the structure aligned with a predefined horizontal heading, for example if the structure is to couple with a fixed pipeline. Various techniques are employed to achieve these end results, depending upon the accuracy with which a structure must be set.

In a case where a structure must be set with its principal axis generally vertical but not critically so, it is known to use a so-called bulls eye, where a ball is freely moveable within a curved dish marked with concentric rings to indicate each degree out of true. The bulls eye is clamped to a suitable part of the structure, and visual observation allows the structure to be set with an accuracy of, at best, 1/20.

Unfortunately, greater accuracy is frequently required than can be obtained with a bulls eye and a very expensive transponder systei- is Ref. 1 1686sp usually employed for this purpose. In view of the cost of such a system, it cannot be left in place on the strucuture once it has been used; it is always necessary to retrieve it from the structure so that it may subsequently be re-used next time another structure is to be set accurately.

So far as orienting a structure in a particular direction is concerned, the normal procedure is to employ a gyrocompass assembly. Such equipment is relatively sensitive to shock and mis-handling, and so is difficult to install in a sub-sea location. Again, a gyrocompass is expensive and cannot be left in situ, once it has been used to align a structure in a particular direction; economically it always is necessary to retrieve a gyrocompass assembly for subsequent re-use. The set-up procedure for a gyrocompass is relatively slow and technically involved, and normally a specialist surveyor is required, to ensure its proper operation.

It is a principal aim of the present invention to provide a detector suitable for use in setting up or checking a sub-sea structure such as a guidebase, template or manifold which detector reduces or overcomes the disadvantages of the known procedures, as discussed above.

According to the present invention, there is provided a detector for use in setting up a sub-sea structure, comprising a sealed water-tight housing having a transparent window, a pitch and roll sensor mounted within the housing and arranged to provide an output dependent upon the relative angular position of the housing about two axes mutually at right angles with respect to a predefined datum, a display device mounted within Ref 11 p the housing and visible through the window, a control circuit connected to the sensor and adapted to operate on the output thereof and to drive the display device, and power supply means arranged to provide power to the control circuit and the display device.

It will be appreciated that the detector of the present invention is especially adapted for use in sub-sea operations, for example in the setting of a structure with its principal axis precisely vertical, or for checking the alignment of a structure. The detector may be completely self-contained and is easy to review by a diver, a ROV or a sub-sea camera, during a setting-up operation. Moreover, by having a display device immediately visible through the window of the housing, a diver or other viewing device may readily see the progress of the setting up procedure, and know when it has been performed to a sufficient degree of accuracy.

In order to allow the setting of a sub-sea structure with a principal axis substantially vertical, the two axes about which the pitch and roll sensor detects deviation from a datum should be essentially horizontal, when the principal axis is vertical. However, the sensor may provide a further output dependant upon the relative angular position of the housing about a third axis mutually at right angles to both of said two axes, which further output is supplied to the control circuit for display on the display device. This third axis thus would be parallel to or coincident with the principal axis of the structure, so as to give an indication of the heading of the structure, relative to a datum. Thus, this further output may act as a Ref. 1 1686sp compass, giving an indication of the heading of the structure relative to magnetic North. A fluxgate compass module may be provided for this purpose.

Most preferably, the power supply means for the detector comprises a solar cell array (panel) mounted within the housing and arranged for illumination by light from a source external of the housing but passing through the window. In this way, a light operated by a diver, on a ROV or associated with a sub-sea camera may be used to activate the detector whenever an output from the detector is required. The array will be energised simply by shinning a sufficiently bright light source through the window of the housing. In the alternative, for short-term use, a battery pack may be provided within the housing. Yet another possibility is to have an external power supply unit, for example on a surface vessel, which power supply unit is coupled to the housing of the detector by means of an umbilical cable. Preferably, such an umbilical cable is releasably connected to the housing, for example to allow the housing to be left attached to a sub-sea structure following installation of that structure, ready for use in the event that the alignment of the structure needs checking or adjusting. Conveniently, the detector is primarily operated by the solar cell array though incorporates at least one other powering option.

In one embodiment of this invention, the pitch and roll sensor comprises a part of capacitive liquid based inclinometers arranged with their axes mutually at right angles and having integrated sensor and Ref. 1 1686sp excitation electronics. Such inclinometers may have a resolution of 0. 0020 over a measuring range of 100, with a linear output or a digital pulse width modulated signal, suitable for driving the display device. In the alternative, and where a lesser accuracy is required, a gravitational position cell may be employed, having a chamber within which is provided a weight member such as a ball, the weight member moving under gravity to a stable position. Such a cell should be provided with means to detect the position of the weight member within the chamber in the cell. So as not to interfere with the movement of the weight member, such detection may be performed optically or, in the case of a ferromagnetic weight member, magnetically.

By having a self-contained unit of a simple sealed construction, it is possible to manufacture the unit relatively cheaply, so that it is no longer an economic necessity to move the unit from the structure following its use.

Instead, the unit may be left in position on the structure, ready for a subsequentuse.

By way of example only, one specific embodiment of sub-sea detector this invention will now be described in detail, reference being made to the accompanying drawings, in which:- Figure 1 is a plan view of the embodiment of detector of this invention; Figure 2 is a diagrammatic cross-section through the housing and lid of the detector of Figure 1, but with the internal components removed; Ref. 116 -6 Figures 3A, 313 and 3C are respectively plan, end and side views of a component board mounted within the housing; Figure 4 is an asymmetric view of the component board of Figures 3A, 313 and 3C; and Figure 5 is a block diagram of the components within the housing.

Referring initially to Figures 1 and 2, there is shown a housing 10 having a cylindrical body 11 and a lid 12. The body 11 has a side wall 13 and an integral ly-formed base wall 14, which [after may be provided with suitable arrangements for mounting the housing on to a sub-sea structure.

For example, the base wall 14 may have a flange (not shown) by means of which the housing may be clamped to a mounting surface of the structure, or to a well-head. In the alternative, threaded blind holes may be provided into the base wall 14 from the outer surface thereof, to receive mounting screws, or a cylindrical receptacle may be provided on the subsea structure, into which the housing may be secured.

The lid 12 has a portion 15 which is received within the cylindrical side wall 13 of the body 11, the periphery of the portion 15 being provided with two annular groves 16 in each of which may be located a respective 0ring (not shown) to effect a water-tight seal between the lid 12 and body 11. A ring of holes 17 is provided around the lid, through which screws may pass into the side wall 13, for clamping the lid 12 to the body 11 in a water-tight manner.

Ref.11686sp A window 18 is located in a recess in the lid, the window being sealed to the lid by means of a sealing strip 19. A clamping ring 20 extends around the window 18 and is held in place by means of screws received in threaded holes 21.

A waterproof four-pin electrical connector 22 is also mounted on the lid 12, which connector allows electrical connections to be made to components mounted within the housing 10, without disturbing the lid 12.

An electronic component board 25 (Figures 3 and 4 but not shown in Figures 1 and 2) is mounted within the housing 10 and includes a pre- programmed microprocessor 26 which receives input signals as will be described below, and drives a seven segment display device 27 (Figure 1) connected to the board 25 through multi-way connector 28. The circuit board carries two capacitive liquid based inclinometers 29 and 30, arranged with their respective axes at 900. Such inclinometers may measure angles extremely accurately (typically 100 with a resolution of 0. 0020, or 300 with a resolution of 0.0050). The inclinometers require excitation and detector electronics, provided on the board 25, and yield a positional signal in the form of a linear DC output proportional to the angle or a digital pulse-width modulated output. The inclinometers thus are able to sense and provide a respective output for positional variations respectively about the X and Y axes shown on Figure 3A. The board 25 additionally carries a flux gate compass module 31, providing an output of Ref. 116 the angular position of the board about the Z axis, with respect to magnetic North. The outputs from the inclinometers and compass module are received by the microprocessor, and are appropriately decoded to drive a display device 27 separately mounted within the housing 10, so as to lie immediately beneath the window 18. The display device is connected to the board 25 through a multi-way cable and connector 28. Also exposed through that window 18 is a solar cell array 35, arranged so that light shone into the housing through the window will fall on that array, so generating electrical power. As shown in Figure 5, the solar panel is connected to the board 25, for powering the components located thereon. Also as shown in Figure 5, the connector 22 on lid 12 is wired back to the board 25, so that power may instead be supplied to the board through the connector 22. The other two terminals of the connector 22 are employed for the transmission of data and for a calibrate signal.

In use, the housing 10 should be firmly secured to the sub-sea weli head, guidebase or to some other structure, with the housing as level as possible and arranged along a known axis of the structure, so that the heading information can correctly be interpreted. An umbilical cable may then be connected to connector 22 of the housing, and at the surface the other end of the umbilical cable is connected to a control unit or, for example, to a PC or laptop computer. Then, the detector may be calibrated for local magnetic fields, caused by metal work in the proximity of the detector, and to establish true horizontal datum lines. Once mounted

Ref.11 on a structure and appropriately powered, the detector is calibrated by rotating the housing 10 and the structure to which that housing is fixed through one or two complete turns over a period of about two minutes. During this, the calibration signal must be present on the appropriate pin of the connector 22. On removing the calibration signal, the display 27 will indicate the quality of the calibration. Immediately after removal of the calibration signal, the system is ready for use and will provide data, both on the display device 27 and up the umbilical cable, if still connected to connector 22. Even if the cable is removed, the calibration data for that particular installation will be retained and the detector can be re- energised by illumination from under water lights such as diver's lamps, a ROV or drill string mounted camera and lighting equipment. So long as the solar panel receives sufficient light to power the system, the display device will scroll through data as determined by the sensors.

It will be appreciated that the detector as described above is simple to use and can be left sub-sea or retrieved after use, as required. The detector is relatively inexpensive to manufacture and easy to use, and depending upon the type of sensors employed, pitch and roll may be detected over the range of 300 with a resolution of better than 0.10. A typical fluxgate compass will allow detection over 3600 range, with a resolution of 10.

Ref. 1 1686sp

Claims

1 A detector for use in setting up a sub-sea structure, comprising a sealed water-tight housing having a transparent window, a pitch and roll sensor mounted within the housing and arranged to provide an output dependent upon the relative angular position of the housing about two axes mutually at right angles with respect to a predefined datum, a display device mounted within the housing and visible through the window, a control circuit connected to the sensor and adapted to operate on the output thereof and to drive the display device, and power supply means arranged to provide power to the control circuit and the display device.

2. A detector as claimed in claim 1, wherein the sensor provides a further output dependent upon the relative angular position of the housing about a third axis mutually at right angles to both of said two axes and with respect to the predefined datum, the further output also being supplied to the control circuit.

3. A detector as claimed in claim 2, wherein there is a compass module mounted within the housing which compass module provides an output to the control circuit to permit the display of the heading of the housing with respect to magnetic North.

4. A detector as claimed in any of the preceding claims, wherein the power supply means comprises a solar cell array also mounted within the Ref. 11 p housing and arranged for illumination by light from a source external of the housing and passing through the window.

5. A detector as claimed in any of claims 1 to 3, wherein the power supply means comprises a power supply unit disposed externally of the 5 housing and coupled thereto by means of an umbilical cable.

6 A detector as claimed in claim 5, wherein the umbilical cable is releasably connected to the housing.

7. A detector as claimed in claim 5 or claim 6, wherein the umbilical cable carries data signals generated by the control circuit, to feed information back to the surface when the detector is in use, sub-sea.

8. A detector as claimed in any of claims 5 to 7, wherein the detector also includes a solar cell array mounted within the. housing and arranged for illumination by light from a source external of the housing and passing through the window, whereby the detector may be powered by either the solar cell array or by power fed along the umbilical cable from the external power supply unit.

9. A detector as claimed in any of the preceding claims, wherein the pitch and roll sensor comprises a pair of inclinometers arranged mutually at right angles.

10. A detector as claimed in claim 9, wherein each inclinometer comprises a capacitive liquid based device together with excitation and detector electronics.

Ref11686sp

11. A detector as claimed in any of claims 1 to 8, wherein are two three similar gravitational position cells each having an elongate linear chamber, and the axes of the chambers of the cells being arranged mutually at right angles.

12. A detector as claimed in claim 1 and substantially as herein before described, with reference to and as illustrated in the accompanying drawings.