GB1576624A - Leak detection - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO LEAK DETECTION (71) We, THE PLESSEY COMPANY LIMITED, a British Company of 2/60 Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus for locating leaks in pipes.

The invention has in view more especially although not exclusively apparatus for locating leaks in oil pipe lines which are under the sea and which are several miles in length. It will be appreciated that the location of leaks in such pipes can be a problem.

According to the present invention apparatus for locating leaks in a pipe comprises a pig for introduction into the pipe, the pig comprising means for measuring flow direction and for measuring flow rate, means for sealing the pig against the inside wall of a pipe when located therein whereby flow between the wall and the pig is prevented and transmitter means for transmitting data appertaining to flow rate and flow direction.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which, Figure 1a is a generally schematic sectional view of a pipe having one leak, Figure 1b is a graph showing flow rate along the pipe of Figure 1 a under conditions in which the pipe is pressurised so that fluid in the pipe is constrained by reason of the pressure within the pipe to flow along the pipe towards the leak, Figure 2 is a generally schematic sectional view of a pig located within a pipe, and Figure 3 is a generally schematic sectional view of a pig located within a pipe and showing means for sealing the pig against the inside wall of the pipe.

Referring now to the drawings, Figure la shows a pipe 1 having a leak 2 in its wall. If the pipe 1 is pressurised and sealed apart from the leak, then due to the elasticity of the fluid within the pipe and the elasticity of the wall of the pipe, fluid will flow along the pipe towards the leak at a rate which varies along the pipe as shown in Figure lb. It is assumed that the elasticity of the fluid and the pipe wall is constant over the length of the pipe and therefore it will be seen that the slope of the flow rate/distance graph line 3 is constant until the position of the leak is reached whereat a flow reversal occurs as shown by the discontinuity 4 in Figure lb. If one leak only is present in the pipe in order to find the location of the leak, it is merely necessary to locate the position of the discontinuity 4 as shown in Figure 1b which corresponds with the location of the leak. If more than one leak is present however, a flow reversal may not take place, but at the location of the leak there will be a step change in flow rate and the position of the leak may be located by detecting the step change.

In order to detect the location of the discontinuity as indicated in Figure lb, a pig is introduced into the pipe carrying means for detecting flow direction and for communicating information relating thereto to a receiver located externally of the pipe. The construction of such a pig will later herein be described. Having introduced the pig into the pipe it is moved to an approximately central location 5 the pipe is then sealed and pressurised and a measurement of flow direction is carried out. Data relating to this measurement is transmitted from the pig to a receiver located externally of the pipe. The seal on the pipe is then removed and the pig is then moved in the flow direction indicated to a position 6 which is halfway between one end of the pipe and the original location 5 at which the first measurement was made.The pipe is resealed and pressurised and a further measurement is then made to determine flow direction at the new position 6, data then being transmitted to the receiver relating to flow direction at position 6. The seal on the pipe is then removed and the pig is then moved off in the direction of flow to the fresh location 7 which is midway between the locations 5 and 6. The pipe is resealed and pressurised and a further measurement is made in the same manner and after release of the seal the pig is moved once more in the direction of flow to the location 8 which is midway between the location 6 and 7. It will be appreciated that by means of this binary progression towards the leak, the location of the leak may be determined to a required degree of accuracy by making an appropriate number of measurements.

The pig is moved within the pipe by controlling the flow of fluid in the pipe after removal of the seal so that the fluid flow from end to end of the pipe drives the pig to the desired location. If the pressure is increased on one side of the pig, the pig will then be pushed from that side and will stop when the pressure differential is reduced or removed.

If more than one leak is present in the pipe, then it is necessary not only to measure the direction of flow but also to determine the flow rate and in order to do this the pig is provided with means whereby it is sealed against the inside wall of the pipe so that flow within the pipe as described with reference to Figure la and 1b passes through a flowmeter contained within the pig.

Means for sealing the pipe and measuring apparatus for flow rate and direction determination may take any suitable form but one particular form will later be described. The precise position of the pig within the pipe may be determined by means of acoustic signals transmitted along the pipe from one end to be reflected from the pig, the distance being indicated in accordance with the time an echo signal is received after transmission, or alternatively the position may be determined by signals transmitted from the pig which are detected externally of the pipe.

Such signals may conveniently be acoustic signals or alternatively they may be magnetic signals.

Referring now to Figure 2, a pipe line 9 is shown within which is situated a pig comprising annular rubber driving bands 10 and 11 which normally have a clearance fit within the pipe 9 so that the pig may move freely along the pipe 9 driven by the flow of liquid moving along the pipe. A seal which will prevent flow past these bands will hereinafter be described, together with measuring apparatus contained within a body shell 12.

The body shell 12 is a hollow cylindrical tube vented via vents 13 to a pressure P1 which obtains on one side of the bands 10 and 11.

The pressure on the other side of the bands 10, 11 being P2 as indicated in the drawing.

A pressure measuring transducer 14 is provided within the body shell 12 which comprises a pressure sensing device and tubes 15 and 16 which are vented to fluid within the pipe at the pressures P1 and P2 respectively.

The tube 15 is vented to the pressure P1 which obtains within the body cavity, and the tube 16 is vented to fluid at pressure P2 via a sealing plate 17 provided on one end of the body shell 12. There is provided also a bypass tube 18 via which fluid flows through the pig when a good seal against the pipe wall is effected. The fluid flow rate through the bypass tube is to a first order proportional to the pressure differential measured by the transducer 14. The signal generated by the transducer 14 is converted into data by means of electronic circuitry enclosed within a container 19, data signals produced being applied to an acoustic transducer 19a for transmission to a receiver situated externally of the pipe. Signals relating to the flow direction as well as flow rate are easily derived in accordance with the sense of the pressure differential across the tubes 15 and 16.The circuits contained in the container 19 may take any conventional form and data may be transmitted utilising amplitude, pulse, or frequency modulation. In addition to data signals further signals may be transmitted to indicate the status of the sensor system, i.e.

condition of the power supply, and a high energy acoustic signal may also be transmitted to assist in location of the pig, the signal being picked up by a ship or helicopter using a hydrophone placed in the sea in the vicinity of the pipe.

Referring now to Figure 3, in order to seal the pig against the pipe wall a ram 20 is provided, one side of which is exposed to pressure from a compressed air cylinder 21 and the other side of which is exposed to the pressure P1 via an oil filled bag 22. Thus it may be seen that when the pressure P1 exceeds the pressure provided by the compressed air in cylinder 21, the oil filled bag will be compressed and fluid from the bag will be constrained to operate the ram 20 so that a plate 23 connected to the ram 20 acts against a flexible rubber sealing tyre 24 which is deformed under the action of the plate so as to seal against the inside wall of the pipe. In order to hold the rubber sealing tyre 24 in position, it is fixed by means of bolts 25 to an annular support member 26 which is secured to the body shell 12 of the pig and carries the band 10 shown also in Figure 2.

Various modifications may be made to the arrangement described without departing from the scope of the invention. For example the pig may include means for radiating data carried by an a.c. magnetic field. The field may be generated by means driven by fluid pressure to which the pig is exposed and for example the field may be produced by one or more magnets which are constrained to rotate by a turbine which is driven by fluid pressure to which the pig is exposed.

WHAT WE CLAIM IS: 1. Apparatus for locating leaks in a pipe comprising a pig for introduction into the pipe, the pig comprising means for measuring flow direction and for measuring flow rate, means for sealing the pig against the inside wall of the pipe when located therein whereby a flow between the wall of the pipe and the pig is prevented and transmitter means for transmitting data appertaining to flow rate and flow direction.

2. Apparatus as claimed in claim 1, wherein the transmitter means includes an acoustic transducer for transmitting acoustic signals appertaining to flow direction and flow rate.

3. Apparatus as claimed in claim 1 or claim 2, wherein the means for measuring flow rate comprises a pressure transducer responsive to pressures obtaining at each end of the pig when introduced into a pipe and a bypass tube arranged to permit of flow from one end of the pig to the other when the pig is sealed against the wall of the pipe.

4. Apparatus as claimed in any preceding claim, wherein the means for sealing the pig against the pipe wall comprises a ram responsive on one side thereof to pressure obtaining within a pipe in which the pig is situated, and on the other side thereof to the pressure in a pressurised gas cylinder, the ram being attached to means for compressing an annular flexible seal when the pressure in the pipe exceeds the pressure in the gas cylinder whereby the ram is constrained to operate to compress the seal against the inside wall of the pipe in which the pig is situated.

5. Apparatus for locating leaks in a pipe substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. Figure 2. Various modifications may be made to the arrangement described without departing from the scope of the invention. For example the pig may include means for radiating data carried by an a.c. magnetic field. The field may be generated by means driven by fluid pressure to which the pig is exposed and for example the field may be produced by one or more magnets which are constrained to rotate by a turbine which is driven by fluid pressure to which the pig is exposed. WHAT WE CLAIM IS:

1. Apparatus for locating leaks in a pipe comprising a pig for introduction into the pipe, the pig comprising means for measuring flow direction and for measuring flow rate, means for sealing the pig against the inside wall of the pipe when located therein whereby a flow between the wall of the pipe and the pig is prevented and transmitter means for transmitting data appertaining to flow rate and flow direction.

2. Apparatus as claimed in claim 1, wherein the transmitter means includes an acoustic transducer for transmitting acoustic signals appertaining to flow direction and flow rate.

3. Apparatus as claimed in claim 1 or claim 2, wherein the means for measuring flow rate comprises a pressure transducer responsive to pressures obtaining at each end of the pig when introduced into a pipe and a bypass tube arranged to permit of flow from one end of the pig to the other when the pig is sealed against the wall of the pipe.

4. Apparatus as claimed in any preceding claim, wherein the means for sealing the pig against the pipe wall comprises a ram responsive on one side thereof to pressure obtaining within a pipe in which the pig is situated, and on the other side thereof to the pressure in a pressurised gas cylinder, the ram being attached to means for compressing an annular flexible seal when the pressure in the pipe exceeds the pressure in the gas cylinder whereby the ram is constrained to operate to compress the seal against the inside wall of the pipe in which the pig is situated.

5. Apparatus for locating leaks in a pipe substantially as hereinbefore described with reference to the accompanying drawing.