GB2376077A

GB2376077A - Pipeline inspection apparatus

Info

Publication number: GB2376077A
Application number: GB0130916A
Authority: GB
Inventors: Mikhail Nikolaevich Tevrjukov; Alexandr Sergeevich Uryadov; Boris Alexeevich Karagin; Alexandr Fedorovich Gavrjushin; Mikhail Semenovich Tsatsuev; Grigory Petrovich Ferchev
Original assignee: NGKS International Corp
Current assignee: NGKS International Corp
Priority date: 2000-12-26
Filing date: 2001-12-24
Publication date: 2002-12-04
Anticipated expiration: 2021-12-24
Also published as: DE10163430B4; GB2376077B; FR2819313A1; GB0130916D0; DE10163430A1; FR2819313B1; RU2176082C1

Abstract

A magnetic flaw detector for in-tube diagnostics of pipelines measures magnetic flux leakage in the pipe wall. It comprises a housing, two belts of brushes (4, 5) on magnets of a ferromagnetic material for magnetising the wall, and sets of multiple-unit magnetic field converters (6, 7) based on Hall effect elements, and means for processing and recording data. Collars (9, 10) enable the detector to move with the flow in the pipeline and odometers and temperature sensors are also included. The outputs of the field converters are fed into a multiplexer connected to an amplifier and measured data is analysed to identify defects in the pipeline.

Description

1 2376077

Pipeline Inspection Apparatus The invention relates to devices for intube nondestructive tests of pipelines mainly buried 5 trunk gas pipelines by skipping inside the tested pipeline of a device consisting of one or several transport modules, moved inside the pipeline by the pressure of the flow of gas being conveyed through the pipeline, said 10 module having sensors installed thereon and sensing any parameters reflecting the technical state of the trunk pipeline. The device can also be used for in-tube control of oil pipelines and oil products.

15 Known in the art is an in-tube magnetic flaw detector ("On Present-day State of Monitoring the Reliability of Trunk Pipelines", "Defectoscopy" No. 1, 2000, page 3-17, [1]), including a housing, means for magnetization of 20 the pipeline wall installed on the housing, and magnetic field converters made in the form of

impedance ferromagnetic probes.

The indications of the ferromagnetic sensors depend in a complex manner on the mutual 25 orientation of the sensor and flaw field of the

material, and this makes it difficult to identify the material defects on the uneven spots of the pipeline internal surface.

Also known in the art is an in-tube magnetic 30 flaw detector of the British Gas Corporation (GB2044459, IPC: GOlN27/82, 15.10.1980, [2], patent-analog: US (4330748), as well as an in tube magnetic flaw detector of the Vetco Pipeline Services Inc. (US5532587, IPC:

I r GOlN27/72, 02.07.1996, [3], the patent document-analog: CA2085048), comprising a housing, means for magnetization of the pipeline wall affixed to the housing, elastic 5 collars, induction magnetic flux density sensors installed as two belts in such a manner that sensors of the second belt overlap the areas on the pipeline walls corresponding to the gaps between the sensors of the first belt 10 of sensors.

The induction sensors measure the magnetic flux density only at the moment of moving in the pipeline and this complicates the measurement on the spots of the pipelines, where a 15 significant deceleration of the flaw detector is observed (in particular, at places of contraction of the pipeline and at low-radius bends). Well known in the art is an in-tube magnetic 20 flaw detector (SU1157443, IPC: GOlN27/82, 23.05.85, [4]), including a housing, a system of magnetization of the pipeline wall, magnet sensitive means placed inside an inner cavity of an elastic (rubber) gasket.

25 The disposition of sensitive means in a cavity of a single gasket does not allow one to scan the inner surface of the pipe at a place of strong distortion of the cross-section geometry resulting in partial contortion of the collars.

30 Also known in the art is an in-tube magnetic introscope (Abakumov A.A. "Magnetic Introscopy", Moscow, 1996, [5], pp. 258-262), including a housing, means for magnetization of the pipeline wall affixed to the housing, and

l semiconductor magnetic flux density sensors in the form of magnetic diodes or magnetic resistors. As stated in [5], page 260, 17th line from 5 below, the application of semiconductors is complicated in the case of a temperature drop of the working medium of the object being tested in a range from -40 C to +50 C.

In non-isothermal pipelines (cf. Novoselov 10 V.F., Golianov A.I., Muftakhov E.M. in "Standard Calculations in Design and Maintenance of Gas Pipelines", Moscow, 1982, [6], page 52) the average gas temperature can vary within 5-10 C/km and more and this at a 15 speed of the flaw detector in the gas pipeline of 3-10 m/s corresponds to a change of the temperature of the medium passing through the flaw detector of 60 C per minute. In so doing at each instant of time the temperature of the 20 pipeline wall differs from the average temperature of the gas in the given section of the pipeline, which, in turn, differs from the average temperature of the flaw detector units.

A change of the flow rate of the medium through 25 the flaw detector results in a change of the temperature distribution between the units of the in-tube flaw detector. The use of semiconductor sensors and electronic devices under such conditions requires heat sink from 30 these units.

Known in the art is an in-tube magnetic flaw detector of the Vetco Corporation ("Vetcolog Pig Technical Information", USA, 1977, presented for discussion at the Ministry of Gas

Industry on July 27, 1977 [7], and US patent US3 399734, lPC: GOlR33/12, 12.08.75, [a], r levs; patents: CA1007299, DE2423113, FR2229970, GB1471595, JP50017694). This device 5 comprises a housing' means for magnetization or the pipeline wall affixed to the housing, elastic collars and semiconductor magnetic flux density sensors in the form of magnetic diodes.

A special scheme of paired connection of the 10 magnetic diodes allows one to substantially neutralize the thermal dependence of the readings of the magnetic diodes. However, this scheme does not allow one to avoid the metering error associated with thermoelectric and 15 thermomagnetic effects appearing due to the temperature gradients on the elements of the circuit connecting the groups of sensors to the measuring instruments and data processing devices. These errors are significant when 20 monitoring pipelines conveying gases and gas liquid mixtures.

Known in the art is an in-tube magnetic flaw detector ("Rules of Technical Diagnostics of Trunk Oil Pipelines by in-tube Test Pigs", 25 Moscow, 1999, a guide RD 153-39.4-035-99, [9], pages 137-139) including a housing, elastic collars affixed to the housing, means of magnetization of the pipeline wall, a magnetic field converter and temperature sensors,

30 measuring instruments installed in the flaw detector housing, means for data processing and recording. The use of temperatures sensors allows one to check the temperature conditions of the

r electronics during the diagnostic pass of the flaw detector, however, the turbulence and random processes in the medium being conveyed result in temperature gradients between the 5 temperature sensors, magnetic field converters

and data processing devices, as well as between the interface circuits of the sensors and converters with the processing means that results in errors in the measuring data 10 appearance of thermoelectric and thermomagnetic phenomena. Known in the art is an in-tube magnetic flaw detector of the private company "VNIIST-POISK" (RU2133032, IPC: GOlN27/83, 10.07.1999 [10]) 15 including a housing, a system of magnetization of the pipeline wall, a plurality of elements sensitive to a magnetic field, each element

being connected to one of the inputs of the corresponding differential amplifier arranged 20 in the flaw detector housing.

The fact that the sensitive elements located within the inner surface of the pipeline are far from the corresponding differential amplifiers arranged in the flaw detector 25 housing, increases the external stray signals and thermomagnetic effects associated with the temperature gradient between the place of location of the converters and the area of location of the amplifiers.

30 Known in the art is an in-tube magnetic flaw detector Pipetronix Ltd. (EP0825435, IPC: GOlN27/90, 25.02.1998, [11], relevant patents: US5864232, CA2184327, JP10090230, N0971959),

including a housing, means for magnetization of

the pipeline wall affixed to the housing, elastic collars, multiple-unit magnetic field

converters, each converter comprising several sensitive elements sealed with polyurethane and 5 forming a parallelogram with ceramic inserts on the surface of the multiple-unit converter sliding along the pipeline inner surface.

The polyurethane compound allows one to neutralize the temperature effects within the 10 multiple-unit converter, however, the remote location of the sensitive elements arranged near the inner surface of the pipeline relative to the corresponding measurement data processing devices of placed in the flaw 15 detector housing increases the external stray signals, as well as the thermoelectric and thermomagnetic effects associated with the temperature gradient between place of location of the multiple-unit converters and the place 20 of location of the electronic modules when testing the non-isothermal pipelines.

The prior art includes a tube defect control

device of the British Gas Corporation (USSR patent SU745386, IPC: GOlN27/82, 30.06.1980, 25 [12]) including a housing, multiple-unit magnetic field converters affixed to the

housing, each converter comprising a group of four elements in the form of Hall-effect devices installed in the perforated panel of 30 the housing.

In the modular construction of the converters of the said flaw detector with plug-type connections the Hall-effect elements have a different thermal contact with the panel, case

and other components, therefore, a change in the temperature of the medium being conveyed through the pipeline has a different effect on the different Hall-effect elements, and this 5 results in a different response of the Hall effect elements depending on the medium temperature and, besides, the remote location of the sensitive elements disposed within the inner surface of the pipeline, on the 10 corresponding measurement data processing devices arranged in the flaw detector housing, increases the external stray signals and thermomagnetic effects associated with the temperature gradient between the location of 15 the multiple-unit converters and the of location of electronic modules (particularly, when testing non-isothermal gas pipelines).

The claimed in-tube the magnetic flaw detector passing inside the tested pipeline also 20 includes a housing, means of magnetization of the pipeline wall and multiple-unit magnetic field converters, as well as means for

measuring, processing and recording the measuring data, each multipleunit magnetic 25 field converter comprising a group of elements

sensitive to magnetic field.

In contrast to the prior art, each claimed flaw

detector of said multiple-unit magnetic field

converters includes a multiplexer and an 30 amplifier. The outputs of the sensitive elements are connected to the inputs of the multiplexer, the outputs of the multiplexer are connected to the inputs of the amplifier, the output of the amplifier is connected to the

means for measuring, processing and data recording. The main technical result attained due to the application of the claimed invention is high 5 operational stability of the flaw detector and reliability of checking the pipeline due to exclusion of external stray signals, thermoelectric and thermomagnetic effects in the interfaces of the elements sensitive to 10 magnetic field and low noise in the devices for

scanning the elements and amplifying the signals in the integrated multiple-unit converter (what is especially important when checking nonisothermal trunk pipelines). The 15 organization of scanning the elements in the integrated converter allows one to exclude extra amplifying elements from the converter and to significantly reduce the power consumption of the electronic components of the 20 converter, therefore, to reduce the heat generation in the converter.

In the claimed invention the sensitive elements are made as semiconductors, the means for magnetization of the pipeline wall include two 25 belts of brushes secured on magnets and made of a ferromagnetic material, the brushes being in contact with the inner surface of the pipeline; the semiconductor magnetic field converters are

installed between the belts of brushes as a set 30 of multiple-unit semiconductor magnetic field

converters adjacent to the inner surface of the pipeline along its crosssectional perimeter behind the belts of brushes) in the direction from the front part of the flaw detector

( housing a second set of multiple-unit semiconductor magnetic field converters is

installed. Mounted on the flaw detector housing is a 5 temperature sensor, said sensor being installed behind the means for magnetization of the pipeline wall in the direction from the front part of the flaw detector housing.

The detector housing carries a temperature 10 sensor which is installed in the area behind the above-said first and/or second set of multiple- unit semiconductor magnetic field

converters. The use of semiconductor magnetic field

15 converters allows one to accurately determine the magnetic field shape for determining

critical defects irrespective of the speed of the flaw detector in the pipeline. The use of temperature sensors makes it possible to 20 correct the readings of the semiconductor magnetic field converters during the data

processing after completing the diagnostic pass of the flaw detector. The second set of magnetic field converters allows one to

25 determine the location of the defects relative to the pipeline inner wall. The above arrangement of the temperature sensor allows one to avoid sticking of garbage to the temperature sensor due to mechanical contact of 30 the magnetization means and magnetic field

converters with the inner surface of the pipeline at turbulent movement of the flow between the collars and, accordingly, to avoid

changes in the thermal inertia of the temperature sensor.

These sensitive elements are Hall-effect elements, the amplifier is made as a 5 differential amplifier whose diferentiai inputs are connected to the multiplexer outputs corresponding to the pairs of outputs of the Halleffect elements.

The temperature coefficient of the magnetic 10 sensitivity of the Halleffect elements makes (0.01-0.1)%/0 C.

The large values of the coefficient in the claimed construction result in instability of the readings exceeding permissible limits 15 because of a change of the mean temperature during the diagnostic pass; at the values of the coefficient lower than those mentioned above, the Hall-effect elements feature low resolution of the measured magnetic field.

20 The flaw detector includes a D.C. power supply connected to the inputs of the sensitive elements, the measuring means including power metering means connected to the outputs of said sensitive elements. The magnetic field

25 converter includes a current stabilizer, the sensitive elements being connected in series to the power supply circuit of the current stabilizer. The location of the stabilizer in the integrated magnetic field converter allows

30 one to avoid passage of stray signals through the power supply cable connected to the power source and to eliminate the power supply instability due to heating of the cable.

The inner space of the magnetic field converter

is filled with a sealing compound, each sensitive element has an area sensitive to the magnetic field surrounded by insensitive area,

5 the thickness of the thinnest layer of the compound between the housing of any converter and the conveyed medium makes 1-10 mm.

The inner space of the magnetic field converter

is filled with a compound, the thickness of its 10 thinnest layer between the housing of any of the elements of the magnetic field converter

and conveyed medium is not less than 1 mm.

The insensitive layers and the compound layers within the above-mentioned limits provide 15 thermal inertia of the sensitive areas of the elements sufficient for excluding the thermal effects stipulated by short-term local temperature fluctuation characteristic for checking the nonisothermal pipelines and makes 20 it possible to correct the measuring data after the diagnostic pass with an account of the temperatures sensor readings.

The flaw detector housing has at least one odometer whose output is connected to the input 25 of the sensitive element address scanning generator, the control inputs of the multiplexer being digital inputs connected to the outputs of the sensitive element address scanning generator.

30 In a preferred embodiment the claimed in-tube magnetic flaw detector includes a housing, elastic collars installed on the housing and forming bonding contact pads with the inner surface of the pipeline, means for

magnetization of the pipeline wall and the above-mentioned multiple-unit magnetic field

converters, and means for measuring, processing and measuring data recording. The front portion 5 of the flaw detector housing has a Call cai collar; in front of said conical collar there is installed at least one said elastic collar forming a contact pad with the pipeline inner surfacer the external surface of the conical 10 collar forming a side surface of a cylinder whose diameter does not exceed 0.98 external diameter of the pipeline; a side conical surface adjacent thereto, a cone generating line forming an angle with the main axis of the 15 pipeline of not more than 50 . The part of said conical collar in the diameter of said cone of 0.75 maximum diameter is capable of deforming, the area of the medium being conveyed through the pipeline in front of said conical collar 20 communicating with the area of the conveyed medium behind said conical collar through the openings in the conical collar and/or in the flaw detector housing. These multiple-unit magnetic field converters are semiconductor

25 devices, a temperature sensor is installed on and/or in the flaw detector housing, said temperature sensor being installed in the area behind said conical collar. The means for magnetization of the pipeline wall include two 30 belts of brushes secured on magnets and made of a ferromagnetic material in contact with the pipeline inner surface, said semiconductor multiple-unit magnetic field converters are

installed between the belts of brushes as a set

of converters and adjoin the pipeline inner surface along the perimeter in the cross section of the pipeline; installed behind the belts of brushes is a second set of 5 semiconductor multiple-unit magnetic field

converters; in the area behind the second set of semiconductor magnetic field converters

there is installed at least one temperature sensor. Each of said semiconductor multiple 10 unit magnetic field converters includes some

Hall-effect elements connected to said means for measuring, processing and data recording, the inner space of the sensor being filled with compound. The means for measuring, processing 15 and data recording include means for digital conversion of analog data, the flaw detector housing includes, at least, one hermetic shell with axial symmetry containing said digital conversion means, the temperature sensor being 20 installed at the external side of the shell.

Said conical collar is made of polyurethane and is installed in front of said means for magnetization of the pipeline wall and said magnetic field converters. Installed on the

25 flaw detector housing are at least 4 and at most 10 said elastic collars, forming a contact pad with the pipeline inner surface; in front of said conical collar there are installed at most three elastic collars; behind said conical 30 collars there are installed at least two elastic collars. The generating line of said conical side surface forms an angle with the main axis of the pipeline of 20 to 50 , while the extension of the side surface of the

cylinder in the direction of the main axis of the pipeline is not less than 0.2 diameter of the cylinder. The cylinder diameter is equal to 0.940.97 external diameter of the tested 5 pipeline, and the thickness of the freely deformable portion of said collar is 0.03-0.08 external diameter of the pipeline. The area of the medium being conveyed through the pipeline in front of the conical collar communicates 10 with area of the conveyed medium behind the conical collars in the direction from the front part of the flaw detector housing through the holes in the collar and/or in the flaw detector housing, the total through passage section of 15 the holes making 0.4% to 4% of the cross section of the pipeline. In the conical part of said conical collar in the area of the external diameter of the collars from 0.8 maximum value to the maximum through holes are made, the 20 total through cross section of the holes is 0.4% to 4% of the cross section of the pipeline. The temperature sensor is made as an integral component. 25 The coefficient of the heat transfer of the temperature sensor with the conveyed medium exceeds the coefficient of heat transfer of the sensitive area of the semiconductor magnetic field converter with the conveyed medium for

30 not more than by 5 times.

The elastic collars including the conical collar, are made of polyurethane having Shore hardness of 70-100 A.

Such a flaw detector is preferably used for checking pipelines whose external diameter does not exceed 600 mm.

In order that the invention may be well 5 understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the drawings, in which: Fig. 1 illustrates an in-tube a magnetic flaw 10 detector; Fig. 2 is a block diagram illustrating the operation of the in-tube magnetic flaw detector; Fig. 3 a block diagram illustrating the 15 operation of the multiple-unit magnetic field

converter; Fig. 4 illustrates a part of the flaw detector housing with conical collar affixed thereto; 20 Fig. 5 is a graphical representation of the data measured by the second set of multiple unit magnetic field converters depending on the

measured distance passed by the flaw detector inside the pipeline; 25 Fig. 6 is a graphical representation of the data measured by the first set of multiple-unit magnetic field converters depending on the

measured distance passed by the flaw detector inside the pipeline; 30 Fig. 7 is a graphical representation of the data obtained from the flaw detector in the area of corrosion loss of metal on the pipeline wall; and

Fig. 8 is a graphical representation of the data detector given in the field of corrosion

loss of metal of the pipeline walls.

Fig. 1 illustrates a magnetic flaw detector for 5 in-tube checking pipelines wraith an external (passage) diameter of 20" (529 mm), whose principle of operation is based on the method of measurement of the magnetic flux leakage.

The developed in-tube magnetic flaw detector 10 for nondestructive checking of pipelines has been successfully tested and is presently operated. The flaw detector is divided into three main sections: a battery section 1, a magnetic section 2 and a hardware section 3.

IS The device includes two belts of magnets 4 and 5 on the magnetic section 2 capable of magnetizing the pipeline walls, a set of magnetic field converter 6, installed on the

magnetic section 2 between the belts of 20 magnets, and a set of magnetic field converters

7, affixed to the hardware section 3. The device also includes sensors responding to the length of the path passed inside the pipeline (odometers) 28, 29 (Figs. 1-3) installed on the 25 hardware section 3.

The blast-proof electronic devices for digital processing of the measuring data are installed in the shells of the flaw detector housing, the length of the gap in the connections is not 30 less than 12.5 mm, the length of the gap to the hole is not less than 8 mm, the gap width is not more than 0.15 mm.

Installed in the shell of the battery section 1 (Fig. 2) are a battery power supply 21, a unit

22 for conversion of the battery voltage into a voltage necessary for power supply of the electronic modules, and a spark protection unit 23. 5 The output of the battery power supply 21 is connected to the input of the voltage conversion unit 22 whose outputs are connected through the spark protection unit 23 to the power supply distribution unit 25 of the 10 hardware section 3. The outputs of the power supply distribution unit 25 are connected to all electronic modules and elements in the hardware section.

Installed on the magnetic section housing 15 (Figs.1-2) is a set 6 of semiconductor multiple-unit magnetic field converters in

contact with the pipeline inner surface, and blocks of 24 analog-todigital data converters.

The magnetic field converters are connected to

20 the analog-to-digital converters whose outputs are connected to the elements of digital conversion of the data 32 in the hardware section 3.

In the hardware section 3 there are installed a 25 power supply distribution unit 25, an on-board computer 26 with a solid-state memory device 27, an external pressure sensor 30, a sensor 31 of an angle of turn of the flaw detector about the main axis of the pipeline, modules 32 for 30 digital conversion of the data (Fig. 2).

On the housing of the hardware section 3 there is installed (Figs.1-3) a set of semiconductor multiple-unit magnetic field converters 7,

pressed by a retention means to the pipeline

inner surface, odometers 28, 29 and analog-to digital converters 33, a temperature sensor 34 being installed in the housing of each of these units. The analog-to-digital converters 33 are 5 connected to the magnetic field converters and

to the odometers.

The units 33 are also connected to the external pressure sensor 30, angleof-turn sensor 31 and to the temperature sensors installed in the 10 housing of said units. The outputs of the analog-to-digital converters 33 are connected to the digital conversion modules 32 whose outputs are connected to the on-board computer 26. 15 The flaw detector sections are coupled through a hinged linkage and electric cables in contact with the medium conveyed inside the tested pipeline, the circuits of the cables being provided with spark protection elements 20 23.

The integrated temperature sensors "Analog Devices" and Hall-effect elements with magnetic sensitivity of at least 350 MV/MT1 and a magnetic sensitivity temperature coefficient of 25 not higher than 0.05%/ C are used. The Hall effect elements in the magnetic field converter

are filled with epoxy compound.

Each of the multiple-unit converters (Fig. 3) includes Hall-effect elements 71, 72, 73, 74, a 30 current stabilizer 75, a multiplexer 76, a differential amplifier 77. The data digital conversion module 32 includes an address scanning generator 35 to scan the Hall-effect elements. The Hall-effect elements 71-74 are

connected in series to a power supply circuit at the outputs of the current stabilizer 75.

The first outputs of the Hall-effect elements are connected to the first inputs of the 5 multiplexer 76, the second outputs of the Hall effect elements are connected to the second inputs of the multiplexer 76. The first output of the multiplexer (transmitting the data from the first inputs of the multiplexer) is 10 connected to the first input of the differential amplifier 77. The second output of the multiplexer (transmitting the data from the second inputs of the multiplexer) is connected to the second input of the differential 15 amplifier 77. The output of the differential amplifier 77 is connected to one of the inputs of the analog-to-digital data converters 33.

The outputs of the odometers 28, 29 are connected to the corresponding inputs of the 20 analog-to-digital converters 33. The output of the analog-to-digital converter 33 corresponding to the digitized data from one of the odometers 28 or 29 is connected to the input of the address scanning generator 35 25 whose digital output is connected to the digital control input of the multiplexer 76.

The level of the output signals of the generator 35 meets the appropriate international standards.

30 Each section (Fig. 1, Fig. 4) carries polymer collars lo, each collar forming a bonding contact pad with the pipeline inner surface and a conical polyurethane collar 9 being installed at the front part of the flaw detector housing.

The external surface of the collar 9 has a cylindrical side surface 41 (Fig. 4) and an adjacent conical side surface 42. A part 43 of the conical collar 9 is rigidly fixed to the 5 flaw detector housing and cannot be freely deformed, while the other part of the collar is freely deformablewhen passing with the flaw detector inside the pipeline. The cylinder diameter makes 505 mm and the side surface 10 forms a cone with an angle to the main axis of the pipeline of 40 . The extension of the side surface of the cylinder in the pipeline main axis direction makes 0. 23 diameter of the cylinder, in the conical part of the conical 15 collars in the area of the external diameter collars equal to 0.85 maximum diameter through holes are made, the total open flow area of these holes being 0.5% of the cross-sectional area of the pipeline. The elastic collars are 20 made of polyurethane with Shore hardness of 85 A. The diameter of the guide collars 10 in the maximum diameter makes 527 mm.

The device operates as follows.

The magnetic flaw detector is placed into the 25 pipeline and the gas (or petroleum) is pumped through the pipeline. During the movement of the magnetic flaw detector along the pipeline the generated magnetic flux is measured near the pipeline inner surface, the measuring data 30 being recorded in the memory device 27 of the on-board computer 26.

Magnetization of the pipeline wall occurs within the zone located between wire brushes 4 and 5 magnetic sections 2. The multiple-unit

converters 6 are located in same zone and used for measurement of the magnetic induction.

The method of magnetic flaw detection consists in magnetization of the pipeline wall to a 5 saturation state and measurement of the magnetic induction near the magnetized area.

The magnetization is carried out with the help of permanent magnets in a direction coinciding with the longitudinal axis of the pipeline. The 10 magnetic induction measured above zero-defect area carries information on the width of the pipeline walls. The presence of cracks or defects associated with the loss of metal (corrosion, scratches) results in a change of 15 the value and character of distribution of the magnetic induction.

After the diagnostic pass on a given area of the pipeline has been performed, the magnetic flaw detector is extracted from the pipeline 20 and the data accumulated during the diagnostic test are transferred to an external computer.

Subsequent analysis of the recorded data allows one to draw a conclusion on the presence of

defects and to determine their size.

25 During movement of the flaw detector inside the pipeline, the wheels of the odometers 28 and 29 are pressed by springs to the pipeline wall, and trains of analog pulses are formed at the outputs of the odometers These pulses are 30 digitized in the analog-to-digital converters 33. The digitized data of the odometers is recorded in the memory device 27 of the on board computer 26. Besides, in the digital conversion module 32 the digitized signals of

one of the odometers are applied to the element address scanning generator 35. When a pulse from the odometer arrives to the generator 35, the two-bit output of the generator 35 produces 5 a cycle of four addresses, each of the four addresses applied to the control input of the multiplexer 76 allows the data to pass from one of the four Hall-effect elements 71-74. The signals from the Hall-effect elements are by a LO differential amplifier directly in the integrated multiple-unit magnetic field

converter and is applied to the analog-to digital converter 33 installed at the external side of the shells of the flaw detector 15 housing.

When using the flaw detector in a preferred embodiment, an increase in the pressure drop across the conical collar results in stretching of the collar, closing the open flow area 20 between the outer surface of the conical collar and the inner surface of the pipeline, compensation of the low speed and closing the flow of expanding gas from the areas behind the conical collars.

25 Figs. 5-8 illustrate the results of processing the data obtained from a diagnostic pass of the in-tube magnetic flaw detector. The path passed inside the pipeline is plotted on the abscissa axis L and the angle about main axis of the 30 pipeline is plotted on the ordinate axis Fi.

The curves represent the measured deviation of the magnetic field strength dH near the

pipeline inner surface. The displayed areas (Figs. 5-6) identify the transversal weld

joints 51, 52, branch 53 and a metal buildup 54 due to welding the tested pipe and branch 53.

The areas displayed in Figs. 7-8, identify a crack-like defect 55 in the pipe wall, 5 corrosion loss of metal 56 and a transverse weld. The correlation analysis of the data from the first and second sets of magnetic field

converters based on mathematical models of the defects allows one to unambiguously identify 10 the location of the defects in the pipe depth, to determine their parameters and to calculate the strength of the maintained pipelines.

The magnetic flaw detector of the embodiment is intended for in-tube diagnostics of pipelines 15 conveying natural and industrial gases, petroleum and petroleum products by measuring the magnetic flux leakage. The flaw detector comprises a housing, two belts of brushes secured on magnets of a ferromagnetic material, 20 magnetizing the pipeline wall, and two sets of multiple-unit magnetic field converters based

on Hall-effect elements, as well as means for measuring, processing and recording the measuring data. On the flaw detector housing 25 there are installed polyurethane collars enabling the flaw detector to move by the flow of conveyed medium, temperatures sensors, and odometers measuring the path passed by the flaw detector inside the pipeline. Each of the 30 multiple-unit converters includes a multiplexer and a differential amplifier. The outputs of the Hall-effect elements are connected to the multiplexer inputs, the multiplexer outputs are connected to the differential amplifier. The

l signals from the amplifier outputs are digitized and recorded in a memory device of an on-board computer while binding these signals with the signals from other sensors. After the 5 diagnostic pass over a given area of the pipeline, the magnetic flaw detector is extracted from the pipeline and the data acquired during the diagnostics are transferred to the computer located outside the flaw 10 detector. The subsequent analysis of the recorded data allows one to draw a conclusion

on the presence of defects and to determine their size. The analysis of the data from the first and second sets of magnetic field

15 converters with application of mathematical models of the defects allows one to unambiguously identify the location of the defects in the pipe depth, to determine their parameters and to calculate the durability of 20 the maintained pipeline.

Claims

L; CLADdS 1. An in-tube magnetic flaw detector to be passed inside a

tested pipeline, comprising a 5 housing, means for magnetization of the pipeline wall, and multiple-unit magnetic field

converters, as well as means for measuring, processing and recording the measuring data, each of said multiple-unit magnetic field

10 converters including a group of elements sensitive to magnetic field, said multiple-unit

magnetic field converter also including a

multiplexer and an amplifier, the outputs of said sensitive elements being connected to the 15 multiplexer inputs, the multiplexer outputs being connected to the amplifier inputs, and the amplifier output being connected to said means for measuring, processing and recording the measuring data.

20
2. A detector as claimed in claim 1, wherein said sensitive elements are semiconductor elements, said means for magnetization of the pipeline wall include two belts of brushes of a ferromagnetic material installed on magnets in 25 contact with the pipeline inner surface; said semiconductor magnetic field converters are

installed between said belts of brushes as a set of multiple-unit semiconductor magnetic field converters adjoining the pipeline inner

30 surface along the perimeter of the cross section of the pipeline, a second set of multiple-unit semiconductor magnetic field

converters being installed in the area behind the belts of brushes in the direction from the

front part of the flaw detector housing.
3. A detector as claimed in claim 2, wherein the flaw detector housing carries a temperature sensor, said temperature sensor being installed S in the area behind said first and/or second set of multiple-unit semiconductor magnetic field

converters.
4. A detector as claimed in claim 1, wherein the sensitive elements are Hall-effect 10 elements, the amplifier is a differential amplifier whose differential inputs are connected to the outputs of the multiplexer corresponding to the pairs of outputs of the Hall-effect elements.

15
5. A detector as claimed in claim 4, wherein the temperature coefficient of magnetic sensitivity of the Hall-effect elements of claim is (0.01-0.1)%/ C.
6. A detector as claimed in any one of the 20 preceding claims, further comprising a D.C.

power supply source connected to the inputs of the sensitive elements, and wherein said measurement means includes voltage metering means connected to the outputs of said 25 sensitive elements.
7. A detector as claimed in any one of the preceding claims, wherein said magnetic field

converter includes a current stabilizer and the sensitive elements are connected in series to 30 the power supply circuit formed by said current stabilizer.
8. A detector as claimed in any one of the preceding claims, wherein cavities of the magnetic field converter are filled with a

compound, each sensitive element has an area sensitive to magnetic field surrounded by an

insensitive area, the thickness of the least layer of the insensitive area of the elements 5 and the compound between the sensitive area and each sensitive element and the conveyed medium is equal to 1-10 mm.
9. A detector as claimed in any one of claims 1 to 7, wherein cavities of the magnetic field
10 converter are filled with a compound, the thickness of the least compound layer between the housing of any of the sensitive elements of the magnetic field converter and the conveyed

medium is not less than 1 mm.

15 10. A detector as claimed in any one of the preceding claims, wherein at least one odometer is installed on the flaw detector housing, the odometer output is connected to the input of a sensitive element address scanning generator, 20 and control inputs of the multiplexer are digital inputs connected to the outputs of said sensitive element address scanning generator.
11. Apparatus for inspecting internal surfaces of a pipeline, said apparatus comprising mean 25 for magnetizing such an internal surface, at least one means for providing a signal responsive to a detected magnetic field and

means for receiving said signals, said signal providing means comprising at least one array 30 of magnetic field sensors and an amplifier

connected with said sensors via a common input/output means.
12. Apparatus for inspecting internal surfaces of a pipeline substantially as herein described

with reference to Figures 1 to 4.