GB2167829A

GB2167829A - Pipe crawlers

Info

Publication number: GB2167829A
Application number: GB08527180A
Authority: GB
Inventors: Edward Leonard Jones; Robin John Luxmoore
Original assignee: British Nuclear Fuels PLC
Current assignee: Sellafield Ltd
Priority date: 1984-11-29
Filing date: 1985-11-05
Publication date: 1986-06-04
Also published as: GB8527180D0; GB2167829B; GB8430131D0

Abstract

A pipe crawler 1 has a piston and cylinder assembly in which a piston rod 4 and the cylinder 3 are respectively associated with members 6, 5 biassed into engagement with a pipe wall 2. Fluid pressure in connection 7 can move the piston rod in or out of the cylinder. The move the crawler along the piston is extended (Fig. 1b, not shown), the member 5 resisting movement of the cylinder, the supply to the cylinder is reversed and the cylinder moved forward, the member 6 resisting movement of the piston rod. The cylinder may trail a bladder which can be inflated to hold the cylinder whilst the sequence is operated, the members 5, 6 being reversible, to reverse the members 5, 6 and allow the crawler to be withdrawn by reverse step-by-step movement as above. Added force can be obtained using a second piston/cylinder assembly (Fig. 4, not shown). <IMAGE>

Description

SPECIFICATION Improvements in pipe crawlers The present invention concerns pipe crawlers, that is, apparatus capable of moving along the bores of pipes and tubes. Pipe crawlers are employed for conveying inspection equipment along the bores of pipes and tubes.

According to the present invention a pipe crawler comprises a double-acting piston and cylinder assembly having members on axially displaceable component parts of the assembly to support the assembly substantially centrally within the bore of a pipe or tube, the members being normally of an effective lateral dimension greater than the diameter of the bore and having a rigidity such that when the pipe crawler is inserted into the bore the members are inclined to the axis of the pipe and their outer edges are continuously biassed into engagement with the wall of the pipe, and means for introducing pressure fluid to the assembly in such manner as to effect step-bystep travel of the crawler along the bore, the members on the axially displaceable component parts of the assembly acting to alternately anchor and release the respective component parts.

The invention will be described further, by way of example, with reference to the accompanying drawings; in which: Figure 1 shows diagrammatically a first embodiment of a pipe-crawler and a sequence of operating stages; Figure 2 shows diagrammatically a second embodiment having means for effecting reversal of movement of the pipe crawler; Figure 3 shows diagrammatically a detail of Fig. 2; Figure 4 shows diagrammatically yet another embodiment of a pipe crawler and a sequence of operating stages; and Figure 5 shows an arrangement of pipe crawlers for negotiating bends in a pipe.

Fig. 1 shows a pipe crawler 1 located within a pipe 2 for step-by-step movement in the direction indicated by the arrow. The operating stages in completing a single step comprises three stages as indicated at (a), (b) and (c). The pipe crawler 1 comprises a double-acting piston and cylinder assembly having a cylinder 3 containing a piston with a piston rod 4 extending through an end wall of the cylinder 3. The piston and cylinder assembly is positioned and supported within the bore of the pipe 2 by means of members 5 and 6, respectively mounted on the cylinder 3 and the free end of the piston rod 4, which are inclined radially outwardly in a direction away from the direction of movement of the pipe crawler 1 as indicated by the arrow.The members 5 and 6 are such as to be continuously urged or biassed into engagement with the wall of the pipe whilst having sufficient stiffness or rigidity to support the piston and cylinder assembly within the bore. For example, the members 5 and 6 can be annular plates or diaphragms secured to the cylinder and the free end of the piston rod and which initially, prior to insertion of the pipe crawler into the bore of the pipe, have an outside diameter or effective lateral dimension greater than the bore of the pipe. On insertion of the pipe crawler into the bore of the pipe the members assume the inclination as shown in Fig. 1 and their outer edges are continuously biassed into engagement with the wall of the pipe. Alternatively, instead of being annular plates or diaphragms the members 5 and 6 can be spiders engaging the wall of the pipe at angularly spaced apart regions.A pressure fluid can be supplied to opposite ends of the cylinder 3 by means of a supply link 7.

In operation and starting at position (a) in Fig. 1 pressure fluid is introduced into the trailing end of the cylinder to result in a forward force on the piston and hence the piston rod 4 and an equal opposite reaction on the end wall of the cylinder 3. Due to the inclination of the members 5 and 6 the trailing member 5 tends to bite into the wall of the pipe while the leading member 6 tends to collapse away from the wall of the pipe. The result is to extend the piston rod 4 by the stroke of the piston with the cylinder 3 remaining stationary to arrive at position (h) in Fig. 1. Thereafter, the pressure fluid is introduced into the leading end of the cylinder 3.

The effect now is to cause the member 6 to bite into the wall of the pipe while the member 5 tends to incline more towards the axis of the pipe with the result that the cylinder 3 moves along the pipe towards the member 5 to arrive at the position (c) in Fig. 1. Continued repeat operations cause the pipe crawler to advance step-by-step along the bore of the pipe.

The direction of travel of the pipe crawler can be reversed by pulling on the pipe crawler, for example by means of a pull cord, wherehy to cause the members 5 and 6 to snap or flip over to assume an opposite inclination with respect to the axis of the pipe.

In the embodiment of Fig. 2 the pipe crawler is provided with means for remote reversal of travel without resorting to a mechanical link such as a pull cord. In Fig. 2, member 16 at the end of the piston rod 4 is stronger, that is stiffer, than member 15 secured to the cylinder 3. Fig. 2(a) shows the rod in its extended position, the direction of movement being as indicated by the arrow. An inflatable bladder 18 is towed by the cylinder along the pipe. To reverse the direction of travel the bladder 18 is inflated in the Fig. 2(a) position of the pipe crawler. Inflation of the bladder 18 to bear against the wall of the pipe serves to anchor the cylinder in position 2(a) and the application of pressure fluid to the opposite end of the cylinder now acts to retract the piston rod within the cylinder at the same time causing the member 16 to flip over and as shown in Fig. 2(b).In this position the members 15 and 16 are facing in opposite directions. Thereafter the bladder is deflated.

Pressure fluid is then introduced into the end of the cylinder at the member 15. This causes the member 15, which is weaker than the member 16, to flip over and the cylinder can advance in a reverse direction and as shown in Fig. 2(c). Thereafter, and with the bladder remaining deflated, the pipe crawler can be withdrawn from the pipe step-by-step by alternate application of pressure fluid to the opposite ends of the cylinder.

Fig. 3 shows a valving arrangement whereby inflation and deflation of the bladder can be achieved from a pressure fluid line to the cylinder and without resorting to an additional pressure line. The bladder 18 is positioned on pressure line 20 to enclose a pressure relief valve 21 and a non-return valve 22.

The valve 21 can be a rubber sleeve 23 supported by spring fingers 24 and operable to provide communication between the line 20 and the interior of the bladder 18 when the pressure in the line reaches a certain value, for example, 90% of maximum line pressure.

For normal operation it is now required that the pipe crawler can be moved at a line pressure below 90% maximum, for example at 80% maximum line pressure. To inflate the bladder the line pressure is increased to exceed 90% maximum to thereby open the valve 21. Following reversal of the member 15 to assume the Fig. 2(c) position the line pressure is reduced below the 90% maximum value, eg. the line is exhausted, to thereby cause the bladder to deflate through the valve 22. In Fig. 3, the upper portion of the bladder is shown in its inflated condition against the wall 2 and the lower portion shows the bladder when deflated. Fig. 3 also depicts the equivalent circuit diagram. In a modification the non-return value 22 is replaced by a restrictor that discharges into the pipe 2.This makes the bladder easier to operate in that the air line pressure would only have to be reduced to 90% maximum.

The tractive force available for advancing the pipe crawler is reduced by the need to pull any trailing items including the fluid pressure line or push any leading items such as a camera.

Fig. 4 shows an arrangement for enhancing the tractive force by coupling a second piston and cylinder assembly 30 to the pipe crawler 1. The assembly 30 can be supported on rollers or the like within the bore of the pipe and the pressure line 7 to the pipe crawler can be coiled about the second assembly. Initialiy, the crawler 1 and assembly 30 are arranged within the pipe as shown in position (a) in Fig.

4. The piston rod of the crawler is then advanced to position (b) and as described with reference to Fig. 1. Thereafter the cylinder is advanced and, at the same time the cylinder of the assembly 30 is advanced to achieve the position (c) in Fig. 4. Finally, pressure fluid is applied through a separate line to the cylinder of the assembly 30 to thereby advance the piston, and hence the piston rod 32, of the assembly to the position (d) in Fig. 4. The piston rod advances the pressure line for the crawler 1 and any other trailing load connected thereto. In this arrangement both the members 5 and 6 on the pipe crawler act to resist the load applied to the cylinder of the assembly 30 for advancing the piston rod 32 thereby enhancing the capacity of the arrangement.Similarly, another cylinder assembly can be fitted to the front of the pipe crawler to push items, such as a camera, whilst the crawler is stationary. Such an arrangement is advantageous in negotiating vertical or upward travel.

A practical limitation to the use of pipe crawlers lies in the number of bends in the pipe. After a relatively few sharp bends in a pipe the crawler can be incapable of further advance due to the self-locking effect of the trailing pressure lines at the bends. Fig. 5 illustrates an arrangement comprising a plurality of pipe crawlers of the kind described with reference to Fig. 1 passing along a convoluted pipe 40. The crawlers 41, 42 and 43 are actuated from common feed/return fluid pressure lines 44 with the leading crawler pushing equipment 45 for inspection of the pipe bore.

The crawlers are operated in series, the function of the trailing crawlers 42 and 43 being to provide slack in the fluid pressure lines. To advance the inspection equipment the crawlers are actuated in the sequence 43, 42 and 41.

The same operating sequence is employed during retraction of the equipment.

Advantageously, as a means for reducing drag a thin wire, open spring can be provided about the pressure fluid supply line within the pipe.

Claims

1. A pipe crawler comprising a double-acting piston and cylinder assembly having members on axially displaceable component parts of the assembly to support the assembly substantially centrally within the bore of a pipe or tube, the members being normally of an effective lateral dimension greater than the diameter of the bore and having a rigidity such that when the pipe crawler is inserted into the bore the members are inclined to the axis of the pipe and their outer edges are continuously biassed into engagement with the wall of the pipe, and means for introducing pressure fluid to the assembly in such manner as to effect step-by-step travel of the crawler along the bore, the members on the axially displaceable component parts of the assembly acting to alternately anchor and release the respective component parts.

2. A pipe crawler as claimed in Claim 1, in which the elements are annular plates.

3. A pipe crawler as claimed in Claim 1, in which the elements are spiders.

4. A pipe crawler as claimed in any preceding claim, in which the elements are movable between a first position in which the members are inclined to the axis in a first sense and a second position in which the members are inclined to the axis in an opposite sense.

5. A pipe crawler as claimed in any preceding claim, including an inflatable and deflatable bladder engageable with the pipe when inflated and movable with one of said component parts.

6. A pipe crawler as claimed in Claim 5, including a pressure supply connection to the cylinder, said bladder being associated with said connection for inflation and deflation.

7. A pipe crawler as claimed in any of Claims 1 to 4, comprising a further piston and cylinder assembly the cylinder of which is movable with the cylinder of the first-mentioned assembly, and means for introducing pressure fluid to the further assembly.

8. A pipe crawler as claimed in Claim 7, in which the piston of the further assembly is associated with a pressure fluid supply connection for the first-mentioned assembly.

9. A pipe crawler substantially as hereinbefore described with reference to and as shown in Figure 1, or Figure 2, or Figure 3, or Figure 4 of the accompanying drawings.