GB2099153A - Pipeline fault detecting and recording device - Google Patents

Abstract

An "intelligent" pig for surveying the inside surface of a pipeline comprises a pressure-resistant body (12) housing a solid state memory device, and one or more sensor arms in continuous contact with the surface of the pipeline. Movement of the sensor arm or arms is recorded in the memory device and the information stored therein is decoded at the end of a run, the information suitably being presented on a VDU. The pig can also be provided with odometer wheels and be activated when it has travelled a set distance along the pipeline. An attitude sensor can also be provided. <IMAGE>

Description

SPECIFICATION Pipeline fault detecting and recording device This invention relates to pipeline travellers, or as they are more colloquially called, "pigs".

Pipeiine pigs are generally cylindrical or torpedo-shaped devices which move along pipelines, for example gas or oil pipelines. Broadly speaking there are two kinds of pigs. The first kind, which has been in use for many years, may be referred to as the "non-intelligent" type, and is used for such operations as swabbing, cleaning and scouring the internal walls of the pipes. For this purpose pigs of this type are normally provided with an abrasive surface, which may take the form of a series of scouring pads or brushes arranged around the periphery of the pig. The second type of pig is known as the "intelligent" type, and is used for collecting information by internally surveying the pipeline. For example, it locates, measures and records variations in the inner diameter of the pipes.Thus, this second kind of pig can detect corrosion in the line, obstructions in the pipe, and variations in wall thickness. It is with this second kind of pig that the present invention is concerned.

A number of different types of survey or "intelligent" pig are known. They all are provided with sensing devices which contact and respond to changes in the internal wall of the pipeline, and provide a permanent record of these. Thus, one known form of survey pig comprises fore and aft rubber cups, the latter having a finger mechanism located inside it which is sensitive to changes in pipe diameter and records these changes on a charting device. Another known form of survey pig utilises sensors in the form of spring-loaded needles, the movement of which can be recorded.

In some pigs a multi-track highly sophisticated tape recorder, powered by batteries, produces a permanent record of the pipe inside wall based upon signals received from electro-magnetic sensors fitted on the pig and in contact with the internal surface of the pipe.

All of these known pigs are highly sophisticated in their design, and extremely sensitive. Indeed, they are too sensitive. When used on pipelines previously un-pigged, and in which therefore the amount of corrosion is unknown, they may well be damaged. It is the object of the present invention to provide a pig, used for surveying the inside of pipelines, but which is more robust than survey pigs used hitherto.

According to the present invention a pipeline traveller or pig (hereinafter called "pig" for convenience) comprises at least one sensor arm provided with means for continuously contacting the pipeline surface, said sensor arm being movable in response to changes in the pipeline internal dimensions, movement of the sensor arm being recorded in a solid state memory device contained within a pressure-resistant housing forming part of the pig.

Suitably the sensor arm is of robust construction, and terminates in a wheel, preferably rubber or rubber-tyred, which is held in contact with the surface of the wall of the pipeline by spring means. As the pig travels along the pipeline the wheels will be deflected in accordance with irregularities in the pipeline surface, and this movement of the wheels, and hence sensor arms, will be recorded. In general, a number of sensor arms and terminal wheels will be associated with each pig, the precise number depending upon the size of the pipeline. Thus, for small pipelines four sensors may be adequate. For large diameter pipelines as many as sixteen sensors, and possibly more, may be used. The object will be to survey as much of the pipe internal surface as possible.

The pig is suitably also provided with a travelling wheel or other device which enables recordal of the distance travelled in the pipeline by the pig. Preferably also means are provided for generating a signal at a fixed point outside the pipeline, which signal can be recorded by the pig recording equipment and thus serve as a check on the actual distance travelled by the pig.

The recording device in the pig is a solid state memory device which preferably uses EPROM storage of data.

In one form of the invention the pig comprises two or more rubber-like cups which are a tight fit inside the pipeline. The cups surround a pressureresistant body in which is housed the recording device and batteries for powering it. By "pressureresistant" in this context, we mean able to withstand without damage the pressures normally to be expected in a pipeline. The reason for this is that the device of the invention will be required to be used whilst the pipeline is fully operational. The housing for the memory device is suitably a metal housing.

Fitted to the pig body are a series of sensor arms which are spring loaded to ensure that they press tightly against the inner wall of the pipeline.

As mentioned previously, the precise number of sensor arms depends upon the size of the pig, itself dependent upon the size of the pipeline. The sensor arms may terminate in wheels having elastomeric tyres, or they may terminate in elastomeric pads. In the larger sizes of pig the main body of the pig will incorporate the recording device and carry the sensor arms around its periphery. In smaller sizes of pig, it may be necessary to have the sensor arms mounted on a separate pig section from that carrying the pressure-resistant housing for the recording device. In such a case the pig will be formed in two or more sections each connected to the other by a universal joint. The sensor arms are suitably in intimate contact with a sensor which will signal outward or inward movement of the sensor arms to the recording device.

As the pig passes through the pipeline the sensor arms will move with any variation in the position of the pipeline wall, i.e. signifying a weld, a dent or a region of different pipeline thickness, or with any internal debris. Such movement of the sensor arms will be transmitted therefrom through the electrical sensors which will in turn pass a signal to the memory device.

An additional signal device is also preferably arranged so that the position of the sensors relative to the bottom of the pipe is always known.

This means that the orientation of a fault relative to the axis of the pipe bore may be recorded.

In addition, each wheel or sensor arm of the pig is suitably arranged so that the wheels on the sensor arms rotate over a known distance per revolution. This distance is converted into a pipeline distance and recorded in the memory device so that the position of any fault can be identified by reference to the distance reading obtained from the beginning of the travel of the pig. It is common for one or two wheels to be used forthis purpose but it is known that wheel slip can occur.

In the present device it is preferred that every sensor arm be equipped with a distance reading feature and the memory system will be programmed to accept only the highest reading which is received, the lower readings being rejected. A further check on the distance travelled by the pig is obtained by an external signalling source which can be located at some known position. The signal is passed from the outside of the pipeline to the pig inside the pipeline where provision is made for recording the position on the memory device.

In very long cross country or undersea pipelines, the capacity of the memory or the life of the electrical batteries may be insufficient to cover the entire length of the pipeline. In such cases, the pig electronic system may be arranged so that should a first pass of the pig take place which does not record the entire distance inside the pipeline, on second or subsequent pig runs the memory device will only be switched on when the pig approaches the last recorded position on the previous run.

Once the pigging run has been completed, the pig can be removed from the pipeline and the solid state memory device recovered.

This memory device can then be placed immediately into a local, preferably portable, test apparatus and the stored memory date reproduced onto an initial video display unit. This replay has the double function not only of checking that the memory has worked correctly but also of giving an immediate on site recording of the data. This compares most favourably with other known devices where it is common for the final graphical presentation to be available only after some passage of time whilst the tape recording is transposed into a printed graphical paper type.

As the memory is being checked and played back, the stored memory may be converted from the solid state memory device onto a tape recording. Once the play back is completed the memory can be erased, enabling the memory device to be re-used.

The tape may then be placed into a peripheral of a micro computer where the data is transposed onto a floppy disc.

The floppy disc is a permanent recording and may be played back through a micro computer giving a fully pictorial or graphical presentation on a video display unit.

All these operations may be accomplished immediately upon completion of the pig run, thus ensuring that faults in the pipeline may be identified without loss of time.

The permanentfloppydisc can be retained indefinitely. Thus, if the work is repeated after the lapse of some time, the new record can be compared with the old in order to establish whether or not changes have taken place.

In the drawings, which are of a diagrammatic nature.

Figure 1 is a side view of a sensor and sensor arm attached to a pig body, within the bore of a pipeline; Figure 2 is a plan view of the device of Figure 1; Figure 3 is a block diagram of the electronic equipment mounted on the pig body; and Figure 4 is a block diagram of the electronic equipment contained in the analysis unit.

Referring to the drawings, reference 1 indicates the internal surface of a pipeline, along which travels a pig, generally designated 2. This comprises a chassis 3 on which is mounted a bracket 4 provided with a pivot 5. Pivotted about pivot axis 5 is a sensor arm 6 carrying at its outer end a wheel 7 having an elastomeric, e.g. rubber, tyre 8. Bracket 4 also carries a coil spring 9, which biases the wheel 7 into contact with the wall 1.

Mounted between bracket 4 and sensor arm 6 is a sensor device 10. This may be any device for converting the mechanical deflections of the sensor arm into electrical signals, and as shown it comprises a wound bobbin with a reciprocating ferrite core thereinside. Either the bobbin or the core is fitted to the bracket 4, the other component of the sensor being attached to sensor arm 6. Movement of the core within the bobbin, in dependence upon the movement of the sensor arm, creates electrical signals which are stored in the memory store device. Alternatives to this linear displacement transducer include changes in electrical resistance produced by a movable contact, as in a potentiometer, and changes in capacitance between two metal plates due to the variation in distance between the plates.

Also mounted on the pig body is one or more distance sensors 11 (see Figure 2). In a typical arrangement a pig 2 is provided with twelve sensor arms 6 and six distance sensors 1 The latter suitably take the form of odometer wheels.

Mounted on the chassis 3, or on a separate unit universally coupled thereto, is a pressure-resistant metal housing 12 (see Figure 3). This contains all the components of the solid state memory device.

This records the displacement of the various pipeline wall sensors; it identifies the lowermost sensor; it records the distance travelled by the pig; and it records the distance at which an external marker signal is received.

When the pig has completed its run along the pipeline, the memory is removed from its pressure-resistant housing and is plugged into an analysis unit 13 (see Figure 4). This may reproduce stored information, by means of an external microprocessor or micro computer, on a chart recorder, printer or visual display unit. The information reproduced gives a full picture of the shape of the pipeline bore, the condition of the pipe bore surface, and the position of the external markers.

The output information can be displayed on a linear distance scale, by using the mircocomputer to interpret the information stored by the microprocessor in the pig.

The external marker or markers can be used to give accurate position marks on the final display.

This helps to minimise the inaccuracies caused by the odometer wheels slipping. The external markers can be magnetic or possibly ultrasonic.

The incremental displacement could be stored to signify that the distance refers to a marker. The external marker receiver could be used to drive an interrupt to the microprocessor.

Each input to the memory store will be multiplexed before analogue to digital conversion, assuming the output of the transducers is an analogue voltage.

The attitude sensor may consist of a hollow ring with mercury and a damping fluid in it and eight probe wires. The wires can then be connected to an input port and scanned by the microprocessor to detect the orientation of the pig.

Since the wheel of an odometer may slip it is logical to have two (or more) wheels, and to take the highest reading. However, since they both may slip at some time in the pipe then the highest reading over a short distance, added to an accumulated distance would allow for both wheels slipping but not in the same "short distance". The odometer could consist of a wheel with a magnet on it with a fixed reed switch which causes an interrupt to the microprocessor to increment a counter in the microprocessor RAM.

An optical counting system with a radially striped wheel could also be used.

The present invention also includes, as well as the pipeline pig described above, a memory programmed to accept the readings from the sensors and the distance wheel revolutions as described; a memory which can be switched on automatically after a time lapse or distance of pig travel lapse; a memory capable of accepting a signal transmitted from outside the pipeline; a memory capable of reproducing its results onto a tape recording once it has been removed from the pig; a local test apparatus capable of checking that the memory device has worked satisfactorily immediately after this is removed from the pig and of giving an immediate indication of any faults in the pipeline bore; a computer capable of accepting the above-mentioned tape recording and storing this on floppy disc; a computer programme suitable for reproducing information from the above-mentioned tape orfloppydisc and illustrating this either pictorially or graphically on a video display unit; and a computer programme which will output the deflection of the sensor arms and transverse of sensor wheels in numerical form.

Claims (1)

1. A pipeline traveller comprising at least one sensor arm provided with means for continuously contacting the pipeline surface, said sensor arm being movable in response to changes in the pipeline internal dimensions, movement of the sensor arm being recorded in a solid state memory device contained within a pressure-resistant housing forming part of the pipeline traveller.

2. A pipeline traveller as claimed in claim 1 wherein the or each sensor arm terminates in a wheel which is held in contact with the pipeline surface by spring means.

3. A pipeline traveller as claimed in claim 2 wherein the or each wheel is of rubber or is rubber-tyred.

4. A pipeline traveller as claimed in any of claims 1 to 3 additionally comprising distance recording means.

5. A pipeline traveller as claimed in claim 4 wherein each sensor arm is provided with distance recording means and said solid state memory device is programmed to accept the highest recorded distance received.

6. A pipeline traveller as claimed in any of claims 1 to 5, formed in two sections connected together by a universal joint, one section carrying the sensor arm or arms and the other section comprising or carrying said pressure-resistant housing and said solid state memory device.

7. A pipeline traveller as claimed in any of claims 1 to 6 comprising means for indicating the position of the or each sensor arm relative to the bottom of the pipeline.

8. A pipeline traveller comprising a pressureresistant body housing a solid state memory device and a battery or batteries for powering it, two or more rubber or rubber-like cups surrounding said body and being a tight fit inside the pipeline, a series of spring-loaded sensor arms attached to said body and continuously contacting the surface of said pipeline, and means for transmitting information about the movement of said sensor arms to said memory device.

9. A pipeline traveller as claimed in claim 1, substantially as described with reference to the drawings.

1 0. Apparatus for surveying the internal surface of a pipeline comprising a pipeline traveller as claimed in any of claims 1 to 9, and means for reading the information recorded in said solid state memory device.

1 Apparatus as claimed in claim 10 wherein said reading means is a microprocessor or microcomputer and said information is displayed by means of a chart recorder, printer or visual display unit.

1 2. A solid state memory device programmed for use in a pipeline traveller as claimed in any of claims 1 to 9.

13. A solid state memory device as claimed in claim 12, programmed to accept information from said sensor arm or arms only after a determined period or distance of travel in said pipeline.

14. A solid state memory device as claimed in claim 12 or 13 programmed to accept a signal transmitted externally of the pipeline during travel of the pig traveller along the pipeline.

15. A computer programmed to decode information stored in the solid state memory device of any of claims 12 to 14.