GB2285510A - Detection apparatus for use with a cylindrical member - Google Patents

Abstract

Strain in a cylindrical pipe (1) is detected by an apparatus having spaced attachment members (4, 5) each fixed to the pipe (1) by magnets (12) or other connecting means. The attachment members (4, 5) are connected by an intermediate member (6) e.g in the form of a diaphragm plate and a strain sensing element (7) such as a strain gauge. A sound or vibration sensor may he mounted on diaphragm plate (6). In a pipe which includes concrete cladding, a stop member of elastomeric material may be located on the underside of the diaphragm plate to help locate contact pads diametrically opposite each other on the outer surface of the cladding. <IMAGE>

Description

"Detection Apparatus" The invention relates to detection apparatus and in particular detection apparatus for detecting a change in the circumferential separation of two points on a cylindrical member.

Conventionally, changes in the dimensions of members, such as pipelines, in a direction parallel to the central longitudinal axis of the pipeline are detected by using apparatus which is fixed onto the surface of the pipeline and which comprises two magnets located at each end of the apparatus and a strain sensing device located between the magnets so that changes in the separation of the magnets is represented by changes in the output from the strain sensing device. This type of apparatus is known as an axial strain gauge because it detects strains in an axial direction. The apparatus is attached to the surface of the pipeline by means of the magnets and also an adhesive which prevents slippage of the magnets across the surface of the pipeline during changes in dimension of the pipeline.

Although this conventional apparatus is satisfactory for detecting longitudinal (or axial) dimensional changes in pipelines, to date it has not been possible to develop apparatus which can reliably and accurately detect changes in the radial and circumferential dimensions of pipelines, or other tubular members other than by, for example, bonding the strain sensing device directly onto the pipe.

In accordance with the present invention, detection apparatus for detecting a change in the circumferential separation of two points on a cylindrical member comprises a first attachment member; a second attachment member; an intermediate member connecting the first and second attachment members; a movement sensing device coupled to the intermediate member; and first and second coupling means adapted to contact the cylindrical member, at circumferentially spaced apart locations, to couple the first and second attachment members respectively to the outside surface of the cylindrical member, each coupling means having an axis defined by a point of contact of the coupling means with the cylindrical member and a point of contact of the coupling means with the respective attachment member, whereby the coupling forces between each coupling means and the cylindrical member are in a direction substantially parallel to said axis of the respective coupling means.

An advantage of the invention is that a change in circumferential separation of two points on a cylindrical member is a measure of the hoop strain in the material between the two points.

Typically, said axes of the first and second coupling means are substantially co-axial with radii of the cylindrical member.

Preferably, where the cylindrical member comprises a magnetic material, the first and second coupling means each comprise a magnetised member which is typically fixed to the respective attachment member, and each magnetised member typically, contacts the outside surface of the cylindrical member, in use, to couple the apparatus to the cylindrical member by the magnetic force between the magnetised members and the cylindrical member. Typically, the cylindrical member comprises a ferromagnetic or ferritic material.

Preferably, the surface of each magnetised member which contacts the surface of the cylindrical member comprises a plane which is substantially at right angles to a radius of the cylindrical member adjacent the point of contact of the magnetised member with the cylindrical member.

The magnetised members may comprise high energy (rare earth) magnets and/or electro-magnets.

Alternatively, or in addition, when the cylindrical member is non-magnetic, the first and second coupling means may comprise contact pads which are biased into engagement with the cylindrical member, typically by a biasing force which may be provided by flexing of the intermediate member. Preferably, in this instance the first and second coupling means contact the cylindrical member substantially diametrically opposite each other.

Typically, a biasing force may be used when magnets are inappropriate.

Typically, the intermediate member is located between the movement sensing device and the surface of the cylindrical member.

Typically, the direction of movement of the movement sensing device is substantially parallel to the intermediate member connecting the first and second attachment members.

Preferably, the intermediate member has a flexibility which is greater than the flexibility of the first and second attachment members. This has the advantage that relative movement of the first and second attachment members as a result of a change in the circumferential separation of the points at which the coupling means contacts the cylindrical member produces flexing of the intermediate member with little or no flexing of the first and second attachment members.

Typically, the flexing of the intermediate member produces a change in an output signal from the movement sensing device.

In one example of the invention, the movement sensing device may be attached directly on to the intermediate member, and the movement sensing device may comprise a conventional axial strain sensing device.

In another example of the invention, the movement sensing device may be coupled to the intermediate member by being attached between the attachment members, and flexing of the intermediate member causes a corresponding relative movement between the attachment members.

Preferably, the movement sensing device may be a strain gauge, such as a load cell utilising one or more electrical resistance foil strain gauges or a vibrating wire type strain gauge.

Preferably, the apparatus may also comprise manipulation means to permit the apparatus to be installed and removed from the surface of the cylindrical member. Typically, the manipulation means permits removal of the device without causing damage to the movement sensing device. Preferably, this is achieved by rotating the detection apparatus about an axis parallel to the movement sensing device.

Preferably, the manipulation means is designed to permit installation and removal of the apparatus from the cylindrical member by a remotely operated vehicle (ROV).

The apparatus may also include a sound or vibration transducer mounted on the intermediate member which contacts the surface of the cylindrical member.

Preferably, the sound or vibration transducer is mounted on the intermediate member so as not to interfere with the flexing of the intermediate member.

Preferably, the cylindrical member is a tubular member, such as a pipe which may form part of a pipeline. The cylindrical member may be located underwater.

Examples of detection apparatus in accordance with the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 shows a cross-sectional view through a tubular member with a first example of detection apparatus mounted on a steel pipe; Fig. 2 is a side view showing the detection apparatus mounted on the steel pipe of Fig. 1; Fig. 3 is a cross-sectional view through a steel pipe with the detection apparatus of Fig. 1, in use; Fig. 4 shows a second example of the detection apparatus mounted on a steel pipe; Fig. 5 shows a third example of detection apparatus mounted on a steel pipe; and, Fig. 6 shows a fourth example of detection apparatus mounted on a concrete clad pipe.

Figs. 1 and 2 show a tubular member in the form of a steel pipe 1. The pipe 1 has a cylindrical outer surface 2. The pipe 1 may form part of a pipeline located on the seabed. Mounted on the outside surface 2 of the pipe 1 is apparatus 3 for detecting changes in the radial dimensions of the pipe 1. The apparatus 3 comprises two attachment members 4, 5 interconnected by an intermediate member, or diaphragm plate 6 and a strain sensing element 7. The thickness "u" of the attachment members 4, 5 is greater than the thickness "s" of the diaphragm plate 6.

Attachment members 4, 5 each have a top portion 8, 9 respectively and a bottom portion 10, 11 respectively.

The strain sensing element 7 is connected between the top portions 8, 9 of the members 4, 5. The bottom portions 10, 11 of the members 4, 5 each have two magnets 12 attached by means of bolts 13 and attached to the portion 11 also by means of one of the bolts 13 is a manipulation handle 14. The magnets 12 are high energy (rare earth) magnets and the longitudinal axis of the magnets 12 are arranged such that they are co axial with imaginary radial lines extending from the centre of the pipe 1. Hence, end surfaces 15 of the magnets 12 define a circle with a circumference substantially equal to the circumference of the outside surface 2 of the pipe 1.

Hence, changes in the radial dimensions of the pipe 1 are essentially co-axial with the magnetic attractive force between the magnets 12 and the pipe 1. This reduces or obviates shear forces on the magnets 12 and reduces the likelihood of slippage or movement of the magnets 12 with respect to the outer surface during changes in the radial dimensions of the pipe 1.

Typically, the apparatus 3 is installed on the pipe 1 by means of a remote operated vehicle (ROV) which engages the handle 14 and manipulates the apparatus 3 such that the magnets 12 on one of the members 4, 5 come into contact first with the surface of the pipe 2 followed by the other set of magnets 12, while ensuring that the plane of the device defined by the magnets 12, diaphragm plate 6 and strain sensing device 7 is perpendicular to the central longitudinal axis of the pipe 1. That is, the magnets 12 lie on the same circumference. Typically, signals from the sensing device 7 will be transmitted via cable to a display device and/or a recording device, such as a chart plotter in order to monitor changes in the signals emitted by the strain sensing device 7.

Fig. 3 shows the apparatus 3 in use and for purposes of clarity, the handle 14 is not shown in Fig. 3.

If the pressure within the pipe 1 increases, there will be an expansion of the pipe in the direction of the arrows P1. This expansion causes the portions 10, 11 to move outwards also, substantially in the direction of the arrows P1. The movement of the portions 10, 11 outwards causes the portions 8, 9 to move inwards in the direction of the arrows P2 and cause a flexing of the diaphragm plate 6, as shown in phantom in Fig. 3.

Hence, the members 4, 5 tend to pivot about the flexing point of the diaphragm plate 6. The movement of the portions 8, 9 in the direction of the arrows P2 causes a change in the reading from the strain sensing element 7. This change is indicative of a change in the radial dimensions of the pipe 1.

As can be seen from Fig. 3, the further away from the diaphragm plate 6 the strain sensing element 7 is located, the greater the movement of the points at which the sensing device 7 is connected to the portions 8, 9 and the greater the difference there will be in the reading obtained from the sensing device 7.

Fig. 4 shows a second example of a apparatus 15 for detecting a radial dimensional change in a cylindrical member. The apparatus 15 is similar to the apparatus 3 and the same components as in the apparatus 3 have the same reference numerals. As in Fig. 3, the manipulating handle 14 is not shown in the drawing for reasons of clarity.

The difference between the apparatus 15 and the apparatus 3 is that the apparatus 15 has a sound or vibration sensor 16 mounted on the diaphragm plate 6, without interfering with the flexibility of the diaphragm plate 6, and this can be used to perform acoustic measurements on the pipe 1.

Similarly, the sensor 16 will be coupled to a display and/or recording device by means of a cable (not shown).

Fig. 5 shows a third example of detection apparatus 22 mounted on the outside surface 2 of the pipe 1. The apparatus 22 is very similar to the apparatus 3 of Fig.

1. However, in the apparatus 22 the top portions 8, 9 of the attachment members 4, 5 are not present. In place of the top portions 8, 9, there is a diaphragm plate 20 which extends across the top of the attachment members 4, 5. Mounted on the diaphragm plate 20 is a conventional axial strain gauge which comprises two mounting posts 21 and a strain sensing element 7 mounted between the mounting posts 21.

Typically, the mounting posts 21 are magnetised or include magnets to couple the mounting posts 21 to the top of the diaphragm plate 20, as shown in Fig. 5. In addition, if desired or if necessary, adhesive can be used in addition to or as an alternative to magnetisation of the members 21 to secure the mounting posts 21 to diaphragm plate 20.

In the apparatus 22, the mounting posts 21 perform the same function as the top portions 8, 9 so that flexing of the diaphragm plate 20 causes a change in the separation of the mounting posts 21. Hence, a change in the reading from the strain sensing element 7 is obtained.

Fig. 6 shows a fourth example of apparatus 35 which can be used to detect a change in the circumferential separation of two points on a pipe 1 which has a concrete cladding 30. In this example, it is not possible to use magnetic attraction to fix the apparatus 34 on to the outside surface 31 of the concrete cladding 30 as, due to the separation imposed by the concrete cladding 30, there is not sufficient attraction between the magnets on the outside surface 31 and the steel pipe 1 to secure the device to the outside surface 31. In addition, the apparatus 35 has the advantage of permitting it to be used with any form of pipe, irrespective of the material of construction.

The apparatus 35 comprises two contact pads 33 which are located diametrically opposite each other on the outside surface 31 of the concrete cladding 30. The contact pads 33 are coupled to the diaphragm plate 20 by arm portions 32 and the diaphragm plate 20 is flexible relative to the arm portions 32. A stop member 34 is located on the underside of the diaphragm plate 20 and engages with the top section of the outside surface 31 of the concrete cladding 30. The stop member 34 helps locate the contact pads 33 in the correct position on the outside surface 31. Typically, the stop member 34 may be made of a soft rubber or elastomeric material and the shape and material are chosen so that the flexing characteristics of the diaphragm plate 20 are not unduly affected by the presence of the stop member 34 when the apparatus 35 is located on the outside surface 31 of the concrete cladding 30.

Mounted on top of the diaphragm plate 20 is a conventional axial strain sensing device which comprises mounting posts 21 and a strain sensing element 7. However, the mounting posts 21 and strain sensing element 7 are only mounted on top of the diaphragm plate 20 after the other sections of the apparatus 35 have been mounted on the outside surface 31 of the concrete cladding 30. The reason for this is that in order to ensure a good fit on the outside surface 31 it is necessary to use the diaphragm plate 20 as a leaf spring so that the contact pads 33 are moved away from each other to provide sufficient separation to permit engagement with the outside surface 31 across a diameter.After the apparatus 35 has been placed in position on the outside surface 31, the conventional axial strain sensing element, comprising the mounting posts 21 and strain sensing element 7, can be mounted on top of the diaphragm plate 20. The mounting can be performed using an adhesive to fix the mounting posts 21 to the plate 20 and/or can include magnetisation of the mounting posts 21 to couple the mounting posts 21 to the diaphragm plate 20.

In use the apparatus 35 with the mounting posts 21 and strain sensing element 7 mounted on the diaphragm 20, operates in the same manner to the apparatus shown in Fig. 5. That is, relative movement of the contact pads 33 in response to expansion or contraction of pipe 1 results in flexing movement of the diaphragm plate 20 which translates into movement of the mounting posts 21 relative to each other. This causes a change in the reading from the strain sensing element 7.

The advantages of the apparatus 3, 15, 22, 35 described above in Figs. 1 to 6 are that they have high sensitivity to hoop strain. For example they will typically detect a pressure change of 10 psi in a one inch wall steel pipe. They also permit rapid attachment, recovery and redeployment underwater with or without using divers and there is no need to clean or to bond the device to the pipe.

In addition, the use of magnetised members, where appropriate, permits the device to operate on tubular or cylindrical members of magnetic material through a plastic (epoxy) coating of normal thickness used for corrosion protection. Furthermore, the apparatus 35 of Fig. 6 can be used on tubular or cylindrical member of any material.

Applications of the device include location of blockages and severe restrictions in pipes or pipelines due for example to waxing and trapped inspection pigs, by moving the device along the pipe or pipeline and noting how the response of the device to changes in pressure within the pipe or pipeline changes along the length of the pipe or pipeline. The device can also be used to detect leakage across a valve when such leakage produces a change in pressure differential across the valve or ice plug and, in conjunction with an orifice plate by monitoring of the pressure drop across the orifice plate, flow rate within a pipeline can be determined.

In addition, the apparatus can be used to determine whether wellhead process pipework or valves are functioning correctly, provide warning of pressure pulses associated with for example slugs within pipelines and can be used to identify specific pipework in areas where there is a lot of pipework and internal inspection to determine which pipes are carrying what material would be difficult or impossible.

In operation, for the apparatus shown in Figs. 1 to 5, it is only necessary to obtain access to a reasonably clean sector of pipes, for example, of quarter circumference, or for the apparatus 35 of Fig. 6 to a near half circumference. The apparatus 3, 15, 22, are then secured to the pipe 1 by pairs of high energy magnets and the apparatus 3, 15, 22 can be removed by simply rotating the device approximately 30 degrees about an axis substantially parallel to the axis of the strain sensing element 7.

Typically, after attachment to the pipe 1 the apparatus is left for ten to fifteen minutes to stabilise before making measurements.

After a time period of ten to fifteen minutes, the pressure at one end of the pipe 1 is raised and the strain sensed by the strain sensing element 7 is recorded. Pressurisation of up to twenty bar within an underwater pipeline is normal and can be either steady or rapid. Measurements from the strain sensing element 7 are recorded as well when the pipe 1 is depressurised. When a pipe is clean of obstruction, a pressure ramp of just 1 to 2 bar can be detected unambiguously.

Using this procedure, one end of a blockage can be located by a series of strain measurements from, for example, downstream and the other end of the blockage can be located by repeating the measurement process from the upstream end of the pipe 1.

The invention is particularly advantageous for locating obstructions within a pipeline as radial or circumferential changes in the dimensions of a pipe on which the device is located can be correlated to the pressure within the pipe. Hence, by taking readings with the apparatus along the length of a pipeline or tubular member while increasing and decreasing the pressure within the pipeline, the location of a blockage can be located as the pressure characteristics in the vicinity of the blockage will be different from the pressure changes in non-obstructed sections of the pipeline.

A further advantage of the apparatus 3, 15, 22 is that it is not necessary to use adhesive or another form of fixing other than the use of the magnets 12. In the case of the apparatus 35, a spring force is used to maintain the apparatus 35 in contact with the outside surface.

In addition, the apparatus can be adapted for use on different diameters of tubular members by altering the angle of the bends in the members 4, 5 and/or using angled shims to change the relative angles of the longitudinal axis of the magnets 12.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims (17)

1. Detection apparatus for detecting a change in the circumferential separation of two points on a cylindrical member, comprising a first attachment member; a second attachment member; an intermediate member connecting the first and second attachment members; a movement sensing device coupled to the intermediate member; and first and second coupling means adapted to contact the cylindrical member, at circumferentially spaced apart locations, to couple the first and second attachment members respectively to the outside surface of the cylindrical member, each coupling means having an axis defined by a point of contact of the coupling means with the respective attachment member, whereby the coupling forces between each coupling means and the cylindrical member are in a direction substantially parallel to said axis of the respective coupling means.

2. Detection apparatus according to Claim 1, in which said axes of the first and second coupling means are substantially co-axial, in use, with radii of the cylindrical member.

3. Detection apparatus according to Claim 1 or Claim 2, in which the first and second coupling means each comprise a magnetised member.

4. Detection apparatus according to Claim 3, in which the surface of each magnetised member which, in use, contacts the surface of the cylindrical member comprises a plane which is substantially at right angles to a radius of the cylindrical member adjacent the point of contact of the magnetised member with the cylindrical member.

5. Detection apparatus according to any preceding Claim, in which the first and second coupling means comprise contact pads which are biased into engagement with the cylindrical member.

6. Detection apparatus according to Claim 5, in which said biasing force is provided by flexing of the intermediate member.

7. Detection apparatus according to Claim 6, in which the first and second coupling means are arranged such that, in use, they contact the cylindrical member substantially diametrically opposite each other.

8. Detection apparatus according to any preceding Claim, in which the intermediate member is located between the movement sensing device and the position which, in use, is occupied by the surface of the cylindrical member.

9. Detection apparatus according to any preceding Claim, in which the direction of movement of the movement sensing device is substantially parallel to the intermediate member connecting the first and second attachment members.

10. Detection apparatus according to any preceding Claim, in which the intermediate member has a flexibility which is greater than the flexibility of the first and second attachment members.

11. Detection apparatus according to any preceding Claim, in which the movement detection device is attached directly to the intermediate member.

12. Detection apparatus according to Claim 11, in which the movement sensing device comprises an axial strain sensing device.

13. Detection apparatus according to any of Claims 1 to 10, in which the movement sensing device is coupled to the intermediate member by being attached between the attachment members; and flexing of the intermediate member causes a corresponding relative movement between the attachment members.

14. Detection apparatus according to Claim 13, in which the movement sensing device is a strain gauge comprising a load cell utilising one or more electrical resistance foil strain gauges or a vibrating wire type strain gauge.

15. Detection apparatus according to any preceding Claim, further comprising manipulation means to permit the apparatus to be installed and removed from the surface of a cylindrical member.

16. Detection apparatus according to Claim 15, in which the manipulation means is operable to rotate the detection apparatus about an axis parallel to the movement sensing device.

17. Detection apparatus according to any preceding Claim, including a sound or vibration transducer mounted on the intermediate member so as, in use, to contact the surface of the cylindrical member.