WO2009001022A1

WO2009001022A1 - Profiling pig for detecting and quantifying internal corrosion in pipes

Info

Publication number: WO2009001022A1
Application number: PCT/GB2007/002396
Authority: WO
Inventors: Claudio Soligo Camerini; José Augusto Pereira DA SILVA; Miguel De Andrade Freitas
Original assignee: Petróleo Brasileiro S A - Petrobras; Benson, John, Everett
Priority date: 2007-06-27
Filing date: 2007-06-27
Publication date: 2008-12-31

Abstract

This invention relates to a piece of equipment intended for being sent through the inside of a pipe, with means to perceive and record irregularities caused by corrosion on the internal wall of the said pipe. It comprises elastomeric elements (1) which may be cups or discs and which are fastened axially at the ends of or along a body (2), which may be rigid or flexible. Also fastened along the body is a sensing unit (3) formed by a plurality of rings (31) which have a plurality of high precision angle sensors (311) fastened radially along the whole perimeter of each ring. Means (4) for recording the distance travelled in the pipe also form part of the pig in this invention. All the signals from all the sensors are transmitted to a microprocessed electronic system.

Description

PROFILING PIG FOR DETECTING AND QUANTIFYING INTERNAL CORROSION IN PIPES

FIELD OF THE INVENTION

This invention relates to equipment intended to be sent through the inside of a pipe, usually impelled by a fluid flowing in the said pipe. More particularly, the invention concerns such equipment which comprises means to perceive and record irregularities caused by corrosion on the internal wall of the pipe.

PRIOR ART

All the major industries use pipes. It is important for the operators in these industries to know, as much as they can, about the structural condition of pipes. One of the ways of checking the condition of a pipe is to cause a piece of equipment to pass through the inside of the pipe.

The purpose of this passing through can be both for maintenance in terms of cleaning the pipe internally and for inspection of the internal wall.

In the case of an inspection, the equipment is capable of transporting, within itself, instrumentation with a means of recording data relating to deviations in the internal configuration of the said pipe's walls.

This equipment is known generically by people skilled in the art, by the term "pig".

In an instrumented special application, they are known as "calibrating pigs" or "geometric pigs".

Geometric pigs normally comprise a body with at least two cups made of elastomeric material having a certain degree of flexibility, which touch the internal wall of the pipe through which they move. On passing through the inside of the pipe, the cup, if it finds some irregularity such as a bump for example, deforms, operates a transducer and, consequently, generates a record of an irregularity. An example of this type of pig is described in document US 3,755,908 to VerNooy and in document US 4,457,073 to Payne.

It cannot be said that these pigs do not work. They work very well in detecting physical dents and deformations, and they have been used frequently up to the present day.

These pigs, however, are not efficient in cases where the pipe internal walls are attacked by the phenomenon of corrosion. Due to the very nature of these pigs, only incrustations and mechanical deformations are capable of deforming the cups equipped with the pig's sensing elements and giving rise to recordings, as stated previously.

It must be noted that protuberances on a pipe's internal wall (i.e. a decrease in pipe diameter) can also be caused by corrosion. However, corrosion frequently causes depressions in the pipe wall (i.e. an increase in pipe diameter) and the above type of pig is not capable of perceiving these.

Other types of pig have however been developed to have the capability of perceiving and recording the irregularities caused by corrosion on the internal wall of the pipe through which they move.

In pipes for conveying petroleum and its derivatives, the occurrence of structural flaws due to internal corrosion is normally located in a horizontal pipe's lower part. This happens due to the presence of salt water, forming part of the fluid being conveyed. As it is heavier than hydrocarbons, the salt water migrates to the bottom region of the pipe and generates almost a line, localized and frequent in flaws caused by the phenomenon of corrosion. One type of pig for detecting the flaws referred to above is the Corrosion Magnetic Pig, also known internationally as the "Magnetic Flux Leakage Pig" or simply the "MFL Pig".

This type of pig acts in two almost instantaneous stages. A first stage acts to magnetize the pipe wall. A second stage, following immediately, acts to measure the magnetic field on the surface magnetized at the first stage. The detection of a flaw is interpreted by the occurrence of magnetic field leaks perceived by the detection sensors. A magnetic field leak means a loss of metal material, which indicates a flaw in the pipe thickness.

This type of pig has some limitations for accurately determining the type of flaw caused by the phenomenon of corrosion.

The first of them lies in the accuracy of quantifying this type of corrosion. As the flaws or defects can be very close to one another, the response is compromised in terms of grading the level of corrosion. The large number of defects generates a very complex disturbance in the magnetic field in the region of the lower part of the pipe and the end result is inaccurate. Furthermore, it is not possible to detect with this type of pig whether the defect is a protuberance or a depression.

The second limitation is related to the pipe wall thickness. For pipes with a wall thickness exceeding 12 mm, sensing equipment sensitivity is weakened drastically. As the pig is an independent piece of equipment and moves due to the fluid pressure at a certain flow velocity, it is not capable of carrying instrumentation with sufficient power to magnetize very thick walls.

A critical case is that of pipes with a very thick wall and a medium or small diameter. The internal space of this type of pipe is very small (diameter) and the volume to be magnetized is large (thickness). An example of this type of pipe is a submarine pipeline for petroleum production in deep water, in which the wall has to be thick to withstand the environment's high pressures.

As the trend, in terms of production, is towards installing pipes at even greater depths, greater pipe wall thickness can be expected. Under the present technological conditions and with the level of pipe wall thickness to be required, it can soon be expected that the MFL Pig will lose its level of efficiency altogether and, consequently, its usefulness in the inspection of submarine pipelines for deep water.

Another tool for inspecting the inside of pipes is known as the Ultrasonic Pig. The operating principle lies in emitting high frequency sound waves against the pipe wall and in picking up the echo corresponding to the wave emitted, with recording of the time between the wave's outward movement and the echo's return. The time between the emission of the wave and the return of the echo, when outside a homogeneous condition, is indicative of a flaw due to corrosion.

Although this system does not have as many problems with regard to the pipe thickness and can be made compact (so that it can be inserted in medium to small diameter pipes, both features which are advantageous over the MFL Pig described above) this type of equipment needs a high degree of pipe internal surface cleanness and needs the flow of liquid which is being conveyed to be homogeneous. This means that the pipe must be completely free from deposits of paraffin, scale and various other detritus.

The use of the Ultrasonic Pig thus becomes unviable in oil production pipes, where the presence of paraffin, sand and other detritus, in addition to the fluid, which is often mixed with gases, formation water and sand, is common.

In addition, the cost involved in the MFL and Ultrasonic Pig equipment is very high. Accordingly, a need is still felt for equipment which can accurately record the location, quantification and profile of an occurrence of corrosion inside a fluid conveying pipe.

SUMMARY OF THE INVENTION

The first aspect of the invention provides a high resolution profiling pig for monitoring the internal corrosion of pipes, said pig comprising a body, a first plurality of sensors disposed around the circumference of the body, and a second plurality of sensors disposed around the circumference of the body.

In order to achieve a high resolution, the second plurality of sensors are preferably longitudinally offset from the first plurality of sensors. In addition, the second plurality of sensors are preferably arranged in use to measure a different circumferential part of the pipe in which the pig is deployed than each of the first plurality of sensors.

In preferred embodiments, the first plurality of sensors are equally spaced around the circumference of the body and the second plurality of sensors has an identical configuration to the first plurality of sensors. The second plurality of sensors is preferably circumferentially offset with respect to the first plurality of sensors so as to maximise the number of circumferential positions inside the pipe that are sensed.

One or more further pluralities of sensors may be provided. For example, a third plurality of sensors having an identical configuration to the first and second plurality of sensors can be provided. This third plurality of sensors is preferably circumferentially offset with respect to both the first and second plurality of sensors.

The pig as a whole preferably contains a high number of sensors, for example 20 to 1 ,000 sensors. More preferably, the pig contains 35 to 500 sensors and more preferably still, 45 to 350 sensors. Each plurality of sensors preferably comprises a total of 20 sensors or more. 30, 40, 50, 60 or 70 sensors may be provided in each plurality, however. Furthermore, each plurality of sensors is preferably arranged in a ring and there are preferably several rings of sensors in the pig. For example, 2 to 20 rings, preferably 3 to 15 rings, more preferably 4 to 10 rings.

Particularly appropriate sensors are angle sensors that provide an electrical signal in accordance with the angle that the sensor probe moves through. All of the sensors in the pig are preferably of the same design although this is not essential.

The angle sensors preferably operate by measuring the angle through which a movement shaft rotates as a probe attached to the movement shaft moves in accordance with the change in the internal diameter of the pipe due to corrosion.

The pig preferably comprises a processing module arranged to receive the output of each sensor and the processing module is preferably arranged to receive and store each sensor output independently.

It is preferable that each sensor is arranged to directly contact the inside of the pipe during use as this can help to cut through deposits and also to enable a high resolution to be obtained.

As a consequence of the above design considerations, the pig of the present invention is capable of recording the length, width, depth or elevation of flaws caused by corrosion.

A second aspect of the invention provides a method of monitoring the internal corrosion of pipes, the method comprising: deploying a pig into a pipe, recording the output of a first and second plurality of sensors disposed around the circumference of the pig's body, and providing a high resolution profile of the inside of the pipe.

The first and second plurality of sensors are preferably longitudinally offset on the pig's body and there is preferably a processing module that records the output of each sensor independently.

This invention thus relates to a piece of equipment intended to be sent through the inside of a pipe, and a method of using such equipment, with means of perceiving and recording irregularities caused by corrosion on the internal wall of the said pipe, in such a way that the profile of the irregularity is determined exactly.

A further aspect of the invention provides a high resolution profiling pig for monitoring internal corrosion of pipes and intended to be sent through the inside of a fluid conveying pipe, characterized in that it has the capability of locating and quantifying, recording the length, width, depth or elevation of flaws caused by corrosion, supplying as a result the profile of each flaw detected on the internal wall of a pipe and, basically, comprising: - impelling elastomeric elements fastened to a body,

- a sensing unit, located on and fastened to the body in the region included between the elastomeric elements,

- at least one odometer, fastened to the body in a location which can be chosen from the following: after a sensing unit, before any of the elastomeric elements and immediately after one of the elastomeric elements and

- a processing electronic module, which is used for receiving, processing and storing all the data emitted both by the sensing unit and by the odometer.

The pig body of any aspect of the invention can be a substantially cylindrical, hollow and rigid element, or it may be a substantially tubular, flexible element. The elastomeric element of any aspect may be of the cup type, fitted to the ends of the body, or may be of the disc type fitted at intervals along the body.

The sensing unit of any aspect is preferably formed by a plurality of sensing rings fitted one after another, each sensing ring having, connected to the latter and in a radial position, a plurality of high precision angle sensors, each sensing ring being fitted with a rotational offset of a narrow angle in relation to the immediately preceding sensing ring, such that the high precision angle sensors of a given sensing ring have a small angular offset in relation to the high precision angle sensors of the immediately preceding or following sensing ring.

The sensing unit may be formed by a plurality of high precision angle sensors fitted radially and directly to the body with a small angular offset in relation to the immediately preceding or following high precision angle sensors.

Each high precision angle sensor preferably comprises an angle gauge, positioned in the movement shaft existing in the base of the high precision angle sensor, and is arranged to record a signal corresponding to the measurement of an angle and, fastened to the movement shaft, a probe extends, tensioned against the pipe wall.

The tension which each high precision angle sensor exerts on the pipe wall preferably performs the function of centralizing the pig in relation to the pipe's longitudinal centre-line.

The pig has great flexibility, capability of multi-diameter use, ease of passing through accentuated curved sections, of small diameter, as well as geometric obstacles and ease of movement in smaller diameter pipes, with profiling accuracy. The pig may comprise elastomeric elements which may be cups or discs and which are connected axially at the ends of a body, which may be rigid or flexible.

A sensing unit is connected axially along the rigid or flexible body. In the case whereby the body is rigid, the sensing unit is formed by a plurality of rings adapted and fastened to the body. Each ring has a plurality of sensors connected radially along its whole perimeter. In the case of a flexible body, the sensing unit is formed by a plurality of sensors fastened directly to the surface of the flexible body.

Each sensor for detecting and profiling corrosion is of the high precision angle type. In the present case, it comprises a probe, tensioned so that it is always deflected against the pipe wall. In the probe's main movement shaft, a gauge is fastened and this may be optical, resistive or magnetic. The depressions and/or protuberances caused by corrosion on the pipe's internal wall move the probes, causing the generation of signals from the measurements by the high precision angle sensors.

Means for recording the distance travelled in the pipe also form part of the pig in this invention.

All the signals from all the sensors are transmitted to a micro-processed electronic system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:-

FIGURE 1 is a perspective view of the equipment according to a first embodiment of this invention; FIGURE 2 shows schematically a longitudinal section AA¹ of the equipment in Figure 1 ;

FIGURE 3 is a perspective view of a ring of sensors according to the first embodiment of this invention;

FIGURE 4 shows schematically a front view of the longitudinal section of Figure 2, without the elastomeric cups;

FIGURE 5 is a perspective view of an embodiment of a sensor according to the invention;

FIGURE 6 is a side view of the sensor of Figure 5, with the dotted lines showing the sensor movement capability; and

FIGURE 7 is a perspective view of a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The pig of this invention is capable of perceiving, locating and recording the length, width and depth or elevation of an occurrence caused by corrosion on the internal wall of a fluid conveying pipe, in particular a petroleum conveying pipe.

The pig of this invention is represented in this specification by two possible embodiments: a first embodiment can be seen in Figures 1 and 2 and a second embodiment can be seen in Figure 7. Both embodiments comprise:

- a generally longitudinal body 2

- impelling elastomeric elements 1 fastened around the circumference of the body 2, - a sensing unit 3, located on and fastened to the body 2 in the region between elastomeric elements 1 , - at least one odometer 4, fastened to the body 2 in a convenient location which can be chosen from, for example, after the sensing unit 3, before any of the elastomeric elements 1 and after any of the elastomeric elements 1.

- a processing, and preferably electronic, module 5, which is used for receiving, processing and storing all the data emitted both by the sensing unit 3 and by the odometer 4.

The elastomeric elements 1 can be chosen from: elastomeric cups, which may be fitted to the ends of the body 2 which, in this case, can be rigid, cylindrical and hollow (illustrated in Figures 1 and 2) and a plurality of elastomeric discs which are fitted along a preferably flexible, tubular body 2, like a hose, (illustrated in Figure 7). The purpose of the elastomeric elements 1 is to form an at least partial seal with the pipe wall such that the pig can be propelled down the pipeline by the pressure of the fluid flowing in the pipeline. As shown in Figure 7, the elastomeric elements 1 do not need to form a complete seal and may contain gaps through which the fluid may flow. In the embodiment of Figures 1 and 2, the elastomeric cups 1 are intended to form a proper seal with the pipe wall.

In this specification, the embodiment of Figures 1 and 2 which contains elastomeric elements 1 of the cup type, fitted to the ends of a cylindrical, rigid and hollow body 2 will be taken as an example for more detailed explanation.

Referring to Figure 2, the pig body 2 is a generally rigid cylinder which may have an enlarged central portion. This enlarged central portion is useful for housing the processing module 5 that receives the outputs of the various sensors. Furthermore, this enlarged central portion is also suitable for having the sensors 31 mounted on it in a ring formation around the perimeter. The forward end of the pig (shown on the left in Figure 2) has two elastomeric cups 1 attached to the part of the cylindrical body that does not have the enlarged diameter. These cups help to form a seal with the pipeline such that the pig can be effectively propelled down the pipeline by the pressure of the fluid in use. Two elastomeric cups 1 of similar construction are also disposed at the rear of the pig, again on the part of the body 2 that does not have the increased diameter.

An odometer 4, used for measuring the distance travelled by the pig, and having a construction known in the art, for example as disclosed in US 3,755,908, is disposed at the rear of the pig and is attached via a linkage to the rearward part of the body 2. The linkage is resiliency tensioned such that the odometer bears against the pipe wall in use so that the distance travelled by the pig can be measured and recorded. The exact position of the odometer 4 is not critical and it may instead be located between the sensing unit and the elastomeric elements, between the two front elastomeric elements, between the two rear elastomeric elements, or at the front of the pig. It could even be located between adjacent rings of sensors if desired.

Turning to Figure 3, one of the sensing rings 31 which make up the sensing unit 3 can be seen. The sensing unit 3 is generally formed by a plurality of sensing rings 31 which are fitted and fastened to the body 2, one immediately after another. As shown in Figure 2, six sensing rings 31 are provided in the first embodiment. In general, a plurality of sensing rings are provided, the first sensing ring being designated as the frontmost sensing ring, the second sensing ring being next, the third sensing ring being next and so on. Each sensing ring comprises a plurality of high precision sensors 311. The sensors are preferably high precision angle sensors, as will be described later. The sensing ring shown in Figure 3 has 51 sensors uniformly spaced around the circumference of the ring, with each sensor being separated from its neighbour by an angle equal to 360°/N, where N is the number of sensors. The resolution achievable with the pig is partly determined by the number of sensors in each ring and it will be appreciated that fewer or more sensors may be provided in accordance with the size of the pig. In general, however, at least 20 sensors are provided on each sensing ring to achieve a reasonable resolution. Alternatively, as shown in Figure 7, fewer sensors can be provided on each ring, and more rings can be provided.

It will further be appreciated from Figure 2 that the sensors 311 bear directly upon the inside of the pipe. Accordingly, each sensor 311 is allowed to act totally independently and provide a signal that is directly related to the profile of the pipe at the position of the sensor. This contrasts with the systems of US 3,755,908 and US 4,457,073 in which the sensors measure the deflection of an intermediate elastomeric cup which comes into contact with the pipe wall. This means that the sensors do not act independently because a protrusion in the pipe wall will tend to deflect the cup and this deflection will be felt by sensors even at positions not directly adjacent to the protrusion. Accordingly, it is not possible to detect the shape and contour of protrusions in the prior art. This problem is overcome in the present invention by allowing the sensors to directly contact the pipe wall without any intermediate elastomeric member.

To further increase the resolution achievable with the pig, the plurality of sensor rings can be mounted such that the sensor 311 positions are offset with regards to the sensors in the other rings. This is illustrated in Figure 4. Here, two sensor rings are shown and it can be seen that the second sensor ring is rotated about the longitudinal axis relative to the first sensor ring by an angle α. This angle α is generally smaller than the angle between adjacent sensors on one ring. As a general rule, the angle α can be defined by 360°/NM, where N is the number of sensors on a ring and M is the number of rings. So, for example, if two rings were used having 20 sensors per ring, the angle between adjacent sensors on each ring would be 18° and the offset between sensors on the two rings would be 9°. This has the effect that, when viewed longitudinally as shown in Figure 4, sensors are disposed at circumferential locations every 9°. Accordingly, more of the internal circumference of the pipe can be monitored by offsetting the sensors in this way. 3, 4 or 5 rings of sensors can be used and the more rings that are used, the better the resolution. Furthermore, 25, 35, 45 or 55 sensors could be used per ring, and the more sensors per ring, the better the resolution. The example shown in Figure 2 has 51 sensors per ring and 6 rings and it will be appreciated from this that the resolution around the circumference of the pipe can be about 1.18° (i.e. 306 sensors each measuring at a different circumferential position).

In general, the more rings of sensors that are used, the less sensors are required on each ring. Figures 1 to 4 show a configuration in which a relatively large number of sensors are included in each ring and in which there are 6 rings of sensors. This configuration is suitable when the pipe diameter is large enough to accommodate the relatively large number of sensors around each ring. For smaller diameter pipes, a configuration such as is shown in Figure 7 whereby a relatively small number of sensors are included per ring but where there are many more rings of sensors, can be more suitable. For example, in Figure 7, there are four sensors per ring but 12 rings of sensors.

The invention is generally best practiced when each sensor in a ring is arranged in use to measure a different circumferential part of the pipe than each sensor of any other ring. Furthermore, it is preferable that the number of sensors on each ring is the same for each ring, although this can be varied if desired.

This offsetting of the sensors, so as to cover the 360° of circumference of the pipe enables a higher resolution to be achieved. In the processing unit 5, the output from each of the sensors, together with the output of the odometer, can be processed so as to provide a high resolution image of the defects in the pipe. In particular, the processing takes account of the fact that each sensor ring, at any one time, is measuring a different part of the pipe or, in other words, it takes account of the fact that for each longitudinal position of pipe, the sensors of each ring will measure it at different times and each ring will measure a slightly different set of points around the circumference.

In Figure 5, a high precision angle sensor 311 is seen in perspective. The angle gauge 3112 may be chosen from various types which can supply reliable, high precision measurements such as, for example, optical, resistive or magnetic types, positioned in the movement shaft 3113 existing in the base 3114 of the high precision angle sensor 311. The angle sensor is arranged to output a signal corresponding to the measurement of an angle. Each signal is independently routed to the processor 5 where it may simply be stored, for later processing, or where some local processing may be carried out to provide a high resolution profile of the pipe's internal surface.

The probe 3111 of the angle sensor is the contact point between the pig and the pipe's internal wall. The probe 3111 is tensioned at all times against the pipe wall. The source of this tension may be provided by a spring 3115, for example.

The flexibility of movement of the probe 3111 may be both in the direction from the pig to the pipe, in the case of a depression in the pipe wall and in the direction from the pipe to the pig, in the case of a protuberance in the pipe wall, both caused by corrosion on the pipe wail. This can be understood better by referring to the dotted lines showing the possible probe 3111 movements, illustrated in Figure 6.

EXAMPLE:

Let a situation be supposed in which a pig, according to this invention, passes along the inside of a pipe and is about to find a flaw, a depression for example. On beginning to pass through it, an angle gauge 3112 of a first high precision angle sensor 311 on one of the sensing rings 31 , indicates an angular change due to the entry of the probe 3111 of this high precision angle sensor 311 into the start of this flaw. While the probe 3111 of the first high precision angle sensor 311 goes more deeply into the flaw, the probes 3111 belonging to high precision angle sensors 311 which are positioned at an angular offset from the position of the first sensor 31 and which are on the second sensing ring 31 , begin to record an angular change corresponding to the edges of the flaw, and so on until the last recording generated by the last high precision angle sensor 311 on the last sensing ring 31 indicates the end of the flaw. While the flaw detection is carried out by the high precision angle sensors 311 , the odometer 4 continuously records the length of pipe through which the pig passes.

As can be followed in the above example, the sensing unit 3 is capable of recording the start of a flaw, its lateral progression, length, progression in terms of depth in the case of a depression or elevation in the case of a protuberance and, with the interpolation and processing of all the data, capable of drawing the exact profile of each flaw. The device may be programmed to count the flaws included in the section of the pipe which the sensing unit (3) covers for inspection.

The use of the probe 3111 having a generally rod-shaped configuration and which comes directly into contact with the pipe wall also offers a further advantage in petroleum applications. For example, the probe 3111 can be appropriately tensioned so as to cut through any deposits on the inside of the pipe wall like a knife. Thus, when the pig is to be used in a pipeline that can have deposits of paraffin or other adhering types of deposit, the tension of the spring 3115 for each angle sensor can be adjusted such that a greater pressure is applied by each probe 3111 to the pipe's internal wall. Then, as the probe 3111 reaches a paraffin or other type of deposit, it cuts through the deposit and thereby measures the internal profile of the pipeline, rather than the profile of the paraffin deposit. This type of action is simply not possible in the prior art pigs which utilise elastomeric members covering the sensor rods.

If the deposit fills a depression formed by the flaw, the cutting effect will make it possible for the probe 3111 to penetrate the inside of the flaw and to record the features of this depression type flaw.

Due to the operational flexibility of the sensing unit 3, which the sum of its components provides, the sensing unit has high tolerance with regard to changes of diameter which may occur in a conveying pipe. All the signals generated by each of the high precision angle sensors 311 of each sensing ring 31 of the sensing unit 3, as well as the signal coming from the odometer 4, are received, processed and stored by a processing electronic module 5. This processing electronic module 5 may or may not be housed in the pig body 2 itself. Wireless transmission means may be used to transmit the sensor signals in real time if desirable and operationally feasible.

In this embodiment and, merely by way of an example, the processing electronic module 5 is housed in the pig body 2. The data recorded is subsequently analysed in such a way that it supplies, as a result, the position, frequency and profile of each flaw caused by the phenomenon of corrosion on the pipe's internal wall. "Profile" can be taken to mean the quantification of the length, width and height or depth of the flaw.

A second embodiment of a pig, the body 2 of which is a flexible tube with elastomeric elements 1 in the form of a disc, can be seen in Figure 7.

In this case, the sensing unit 3 is formed by a plurality of high precision angle sensors 311 fastened directly to the body 2 so as to protrude radially and so as to be distributed about the circumference of the body 2. In this embodiment, there are fewer sensors in each sensing ring (in each case 4) but more sensing rings. Furthermore, elastomeric elements 1 may be disposed inbetween adjacent sensing rings so as to be distributed longitudinally along the body of the pig.

In this embodiment, due to the tension which each high precision angle sensor 311 exerts on the pipe wall, the sensing unit 3, which is formed by a plurality of high precision angle sensors 311 , as has been mentioned above, additionally acquires a function of centralizing the equipment in relation to the longitudinal centre-line of the pipe. If necessary, more elastomeric elements (e.g. in the form of a disc) can be added to improve the centralizing of the equipment as a whole.

The pig in this embodiment has the following as features: great flexibility, capability of multi-diameter use, ease of passing through accentuated curved sections, of small diameter, as well as other geometric obstacles and ease of movement in smaller diameter pipes, without losing the accuracy of profiling the inside of the said pipe. Due to considerations of clarity only, the representation and location of the odometers 4 have been omitted from Figure 7.

In addition to the profiling pigs described above, the present invention also comprises a method of monitoring the internal corrosion of pipes. The method is preferably carried out using one of the pigs disclosed above, but this is not essential. The method comprises deploying a pig into a pipe and recording the output of a first and second plurality of sensors disposed around the circumference of the pig body. Thereafter, either at the pig itself or in a remote location, a high resolution profile of the inside of the pipe may be provided utilising the output of the first and second plurality of sensors.

The use of a first and second plurality of sensors allows a higher resolution image which is capable of monitoring the internal corrosion of pipes to be attained.

The first and second plurality of sensors are longitudinally offset on the pig body, such as the rings of sensors disclosed above and this further allows the rings of sensors to be circumferentially offset so that a greater proportion of the circumference of the pipe can be probed. Furthermore, the method preferably comprises directly contacting each sensor with the inside of the pipe so as to provide an independent output.

In accordance with an embodiment of the method, the pig is propelled along the pipe utilising the pressure of the fluid already flowing in the pipe and comprises an odometer for measuring the distance along the pipe that the pig has travelled. This odometer data is preferably utilised when providing the high resolution profile of the inside of the pipe.

Claims

1. A high resolution profiling pig for monitoring the internal corrosion of pipes, said pig comprising: a body; a first plurality of sensors disposed around the circumference of said body; a second plurality of sensors disposed around the circumference of said body.

2. A pig according to claim 1 , wherein said second plurality of sensors are longitudinally offset from said first plurality of sensors.

3. A pig according to claim 1 or 2, wherein each of said second plurality of sensors is arranged in use to measure a different circumferential part of a pipe in which the pig is deployed than each of said first plurality of sensors.

4. A pig according to any of the preceding claims, wherein said first plurality of sensors are equally spaced around the circumference of said body and said second plurality of sensors has an identical configuration to said first plurality of sensors and wherein said second plurality of sensors is circumferentially offset with respect to said first plurality of sensors.

5. A pig according to claim 4, further comprising a third plurality of sensors having an identical configuration to said first and second plurality of sensors and being circumferentially offset with respect to both said first and second plurality of sensors.

6. A pig according to any one of the preceding claims, wherein said pig comprises a total of 30 sensors or more.

7. A pig according to any one of the preceding claims, wherein each said plurality of sensors comprises a total of 20 sensors or more.

8. A pig according to any one of the preceding claims, wherein each sensor is an angle sensor that provides an electrical signal in accordance with the angle the sensor probe moves through.

9. A pig according to claim 8, wherein each sensor comprises a movement shaft about which the sensor probe rotates and is arranged to measure the rotation about said shaft directly.

10. A pig according to any one of the preceding claims, further comprising a processing module arranged to receive the output of each sensor.

11. A pig according to claim 10, wherein said processing module is arranged to store each sensor output independently.

12. A pig according to any one of the preceding claims, wherein each sensor is arranged to directly contact the inside of the pipe during use.

13. A pig according to any one of the preceding claims, said pig being capable of recording the length, width, depth or elevation of flaws caused by corrosion.

14. A method of monitoring the internal corrosion of pipes, said method comprising: deploying a pig into a pipe; recording the output of a first and second plurality of sensors disposed around the circumference of the pig body; and providing a high resolution profile of the inside of said pipe.

15. A method according to claim 14, wherein said first and second plurality of sensors are longitudinally offset on the pig body.

16. A method according to claim 14 or 15, wherein a processing module records the output of each sensor independently.

17. A method according to any one of claims 14 to 16, wherein each sensor comprises a probe that directly contracts the inside of said pipe.