SPECIFICATIONApparatus, system and method for detecting a discontinuity in a pipe or conduitThe invention relates to an apparatus, system and a method for detecting a discontinuity in a pipe or conduit, such as a gas main.
Various methods such as the use of close circuit television have been used to detect surface discontinuities such as joints, cracks, fissures and the like in the walls of pipes and conduits, but such methods, particularly the use of close circuit television are time-consuming and expensive.
It is an object of the invention to seek to mitigate these disadvantages.
According to one aspect of the invention there is provided apparatus for locating a discontinuity such as a joint or crack in a metal pipe or conduit from the interior of the pipe or conduit, comprising a means for inducing a magnetic field in the pipe or conduit and a sensor exhibiting the Hall effect, whereby any change in electrical output from the sensor owing to a discontinuity in the pipe or conduit can be monitored.
The means for inducing a magnetic field may comprise a permanent magnet.
There may be electrical/electronic circuitry for driving the Hall effect sensor, which circuitry may be connectible in use with equipment externally of the pipe of conduit for monitoring any change in output from the sensor.
The sensor may comprise two Hall effect devices with matched outputs.
The electrical/electronic circuitry may comprise two operational amplifiers which are connected in a differential configuration, whereby to cancel the effect of variations on temperature in the respective outputs of the two Hall effect devices.
The circuitry may be connectible by a cable to the external equipment.
The external equipment may comprise an operational amplifier for receiving the output from the sensor.
One of the operational amplifier inputs from theHall effect devices may be controllably offset, whereby to set up the apparatus for use in different types of pipe, for example mild steel, cast iron etc.
This output from the operational amplifier may be fed to a voltage analog indicator and to a logic device.
The logic device may include means to provide an audible warning when the sensor detects a discontinuity.
There may be spaced rotatable means for engaging the inner surface of the pipe or conduit, whereby the apparatus can be drawn therethrough.
The rotatable means may be spaced apart wheels.
The apparatus may be mounted on a non-electrically or magnetically conductive carrier.
The carrier may be plastic.
There may be resilient mounts whereby the apparatus is mounted on the carrier.
According to a second aspect of the invention there is provided a system for detecting a discontinuity such as a joint or crack in a metal pipe or conduit from the interior of the pipe or conduit, comprising a carrier for being drawn through the pipe or conduit, apparatus as hereinbefore defined carried by the carrier, external equipment for monitoring the output of the sensor and means connecting the sensor and the external equipment.
Preferably the means connecting the sensor and the external equipment is an elongated electrical connector.
The electrical connector may be a cable.
There may be a plurality of apparatuses as hereinbefore defined carried by the carrier.
There may be four apparatuses spaced equidistantly round the outer surface of the carrier.
According to a third aspect of the invention there is provided a method for locating a discontinuity such as a joint or crack in a metal pipe or conduit, comprising inserting apparatus as hereinbefore defined into the pipe or conduit, moving the apparatus through the pipe or conduit and monitoring the output from the sensor whereby to detect any change in the output resulting from the presence of a discontinuity.
The method may comprise the step of feeding the output to external monitoring equipment.
The method may comprise the step of providing an audible signal resulting from a change in the output.
A plurality of outputs may be obtained and those outputs may be selectively monitored whereby to confirm the presence of a joint or crack.
Apparatus embodying the invention is hereinafter described, by way of example, with reference to the accompanying drawings.
Brief description of drawingsFigure 1 is a side view of apparatus according to the invention with parts broken away for clarity;Figure 2 is a sectional view of a carrier with four apparatuses according to Figure 1 spaced equidistantly therearound;Figure 3 is a plan view, partly broken away, of the carrier according to Figure 2;Figure 4 is a block diagram of circuitry which can be used with the apparatus of Figure 1; andFigure 5 shows schematically the apparatus ofFigure 1 in use in a pipe with a graphical representation of output voltage as a joint is located.
Referring to the drawings, Figure 1 shows apparatus 1 for locating a discontinuity such as a joint or crack in a metal pipe or conduit from the interior of the pipe of conduit, comprising a means in the form of a magnet 2 for inducing a magnetic field in the pipe or conduit, and a sensor 3 exhibiting the Hall effect, whereby any change in electrical output from the sensor owing to a discontinuity in the pipe or conduit can be monitored.
The apparatus 1 comprises a skid or elongate member 4 which has rotatable means in the form of spaced wheels 5 for mounting the apparatus 1 on the interior surface of a pipe or conduit for passage thereover as the apparatus 1 is drawn through the pipe or conduit.
The magnet 2 is a permanent magnet which comprises in the embodiment described a plurality of ceramic discs.
The sensor 3 comprises two matched Hall effect devices, the devices being matched so that both voltage outputs are of the same magnitude, one being inverted to cancel the effect of one magnetically induced pole of the pipe.
The apparatus 1 also includes electrical/electronic circuitry in the form of two operational amplifiers or pre op-amps 6, which are electrically wired in a differential configuration (a half bridge arrangement) to cancel the effects of variations in temperature on the outputs of the two Hall effect devices.
In the embodiment described, a system for detecting discontinuities comprises four apparatuses spaced circumferentially round a carrier in the form of two spaced circular mountings 7 and 8 the whole arrangement effectively comprising a pig which can be drawn through the pipe or conduit.
Each apparatus 1 is resiliently mounted on the carrier 7, 8 by a spring loaded bolt 9, whereby smooth passage along the pipe is obtained even when the wheels 5 pass over surface irregularities or disconformities such as bumps (Figure 3).
The pre op-amps 6 of each apparatus 1 are connected by a cable 10 to external monitoring equipment 11 which also drives the Hall effect devices 3.
The length of the cable 10 depends on the length of pipe or conduit to be traversed, for example 100 metres.
The outputs from the two Hall effect devices of each sensor are fed to an operational amplifier 12 of the external equipment 11. One of the outputs (or looking at it another way, one of the op-amp 12 inputs) is given a controllable offset by say a potentiometer 13, for setting up the sysem incorporating the apparatuses for use in pipes or conduits of different construction, for example mild steel, cast iron or other metal. The output of the op-amp is connected to a + 10 volt analog indicator 14 and through a logic system 15 which can be connected to a circuit to provide an audible indication of when the sensors detect a discontinuity.The circuit comprises a buzzer 16 selection circuit and provides not only the audible indication of the detection of a discontinuity, but also allows the operator externally of the pipe or conduit to check as to whether a visual indication on the indicator fromone sensor 3 is in fact indication of a joint or crackrather than a branch line of the pipe. The operator can check by selecting one or more of the readings from the four sensors to confirm the presence of the discontinuity.
Passage of the apparatus 1 along the interior ofa pipe 17 is shown in Figure 5 with the change in voltage on the graph being indicated with reference letters which correspond with the referenceletters used to indicate the position of the apparatus. Thus 'A' indicates the position and the voltageat the position to the left of the joint 18, as viewedin Figure 5, the apparatus moving from left to rightas viewed in that figure.
In a system for sealing a joint or crack, the pig can tow a sealing pig which when located over the joint or discontinuity 18 (after passage of the pig thereover and hence detection by an operator) can be actuated to seal the joint or crack.
It will be understood that in every case as the apparatus 1 passes over the discontinuity a disturbance in the magnetic field is produced by the discontinuity and thus affects the output of the Hall effect devices, which can then be monitored as described to indicate the presence of the discontinuity.
However, the apparatus 1 also functions when stationary.