WO2009045020A1

WO2009045020A1 - Apparatus for monitoring damage of pipe

Info

Publication number: WO2009045020A1
Application number: PCT/KR2008/005675
Authority: WO
Inventors: Jang Bom Chai; Young Sun Kim
Original assignee: M & D Co., Ltd.
Priority date: 2007-09-29
Filing date: 2008-09-24
Publication date: 2009-04-09
Also published as: KR20090033295A

Abstract

An apparatus for monitoring damage of pipe according to an exemplary embodiment of the present invention includes an electric power supply, a core which is formed long in a lengthy direction of a pipe and contacts the outer wall of the pipe, a coil which is wound around the outer circumferential surface of the core, an electric current detector which traces the electric current which flows in the coil and detects a magnetic saturation electric current when the second magnetic saturation state has been formed, and a comparator.

Description

[DESCRIPTION] [Invention Title]

APPARATUS FOR MONITORING DAMAGE OF PIPE [Technical Field]

<i> The present invention relates to an apparatus for monitoring damage of pipes, and more particularly to a pipe damage monitoring apparatus which easily detects wall thinning, that is, wear of the pipes whose thickness is thinned or damage of the pipes which may occurs on the inner wall of the pipes such as crack of the pipes, by high temperature and high pressure fluid or gas which flows in the pipes. [Background Art]

<2> In general, pipes or tubes play a very important role of transporting fluid or gas in almost all industrial facilities or daily lives.

<3> In the case of the pipes or tubes, wear of the pipes whose thickness is thinned or damage of pipes which may occurs on the inner wall of the pipes such as crack which deteriorates mechanical properties of the pipes, may happen by high temperature and high pressure fluid or gas which flows in the pipes. The wear of the pipes or the damage of pipes may ^'cause serious economical and manpower loss. Accordingly, it is necessary to have to monitor whether or not pipes are damaged.

<4> In the conventional cases, ultrasonic sensors have been used for monitoring whether or not wall thinning, that is, wear of the pipes or damage of pipes exists in the pipes. A pipe damage monitoring apparatus using an ultrasonic sensor generates an ultrasonic wave onto surface of a pipe, detects the ultrasonic wave reflected from the inner wall or crack of the pipe, and measures a propagation speed and a reflection time of the ultrasonic wave, to thereby monitor whether or not change of the thickness of the pipe or occurrence of the crack in the pipe happens.

<5> The pipe damage monitoring apparatus using the ultrasonic wave makes an ultrasonic generator contact the outer surface of the pipe using a liquid couplant such as gel in order to improve generation of ultrasonic waves on the outer surface of the pipe.

<6> The ultrasonic sensor is weak at a high temperature. In the case of a pipe which is applied at a high temperature, it is difficult to use the conventional pipe damage monitoring apparatus using the ultrasonic wave at a state of directly contacting the high temperature pipe. Even though a heat transfer prevention member is attached on the ultrasonic sensor, it is not so good to effectively generate ultrasonic waves due to the couplant which falls down along the outer surface of the pipe.

<7> In addition, even in the case that the conventional pipe damage monitoring apparatus using the ultrasonic wave is used for a pipe which is applied at a low temperature, the couplant between the outer surface of the pipe and the ultrasonic sensor is dried or disappears according to lapse of time. As a result, if a given time passes, the ultrasonic wave is not transferred into the inside of the pipe, to thereby cause the conventional pipe damage monitoring apparatus using the ultrasonic wave not to monitor whether or not the wear of the pipe or the damage of the pipe happens.

<8> In addition, the conventional pipe damage monitoring apparatus using the ultrasonic wave generates an ultrasonic wave onto surface of a pipe, detects the ultrasonic wave reflected from the inner wall or crack of the pipe, and measures a propagation speed and a reflection time of the ultrasonic wave, to thereby monitor whether or not change of the thickness of the pipe or occurrence of the crack in the pipe happens. As a result, it takes much time to detect whether or not the wear of the pipe or the damage of the pipe happens.

<9> Also, the conventional pipe damage monitoring apparatus using the ultrasonic wave monitors damage of a pipe only at a place where an ultrasonic sensor is placed, but cannot monitor damage of a pipe at a place where an ultrasonic sensor is not placed. Accordingly, a number of ultrasonic sensors should be contact the outer wall of the pipe in order to monitor damage of the pipe precisely. As a result, it takes long time to detect whether or not the wear of the pipe or the damage of the pipe happens. Further, it is not possible to monitor wear of the pipe or the damage of the pipe at a place where an ultrasonic sensor is not placed. [Disclosure] [Technical Problem]

<io> Therefore, to solve the above problems, it is an object of the present invention to provide an apparatus for monitoring damage of pipes which makes a core which is formed long in a lengthy direction of a pipe contact the outer wall of the pipe and then applies an electric current to a coil wound around the core, to thus generate a magnetic field into the inner wall of the pipe having contacted the core and thus form a first magnetic saturation region which is magnetically saturated, and then makes the electric current flowing in the coil increased to thus generate a magnetic field into the inner wall of the pipe except for the first magnetic saturation region and thus form a second magnetic saturation region which is magnetically saturated, to thereby keep track of change of the electric current flowing in the coil and monitor whether or not wear of the pipe or damage of the pipe happens on the inner wall in a wide area of the pipe. As a result, the pipe damage monitoring apparatus according to the present invention may shorten time which is taken to detect whether or not wear of the pipe or damage of the pipe happens, does not need a couplant such as gel but is made to be always mounted in the pipe and directly contact even a high temperature pipe, to thereby easily monitor and quickly detect whether or not wear of the pipe or damage of pipe happens, even in the case that the pipe is in use. [Technical Solution]

<π> To accomplish the above object of the present invention, according to an aspect of the present invention, there is provided an apparatus for monitoring wear such as wall thinning or damage such as crack on the inner walls of pipes, the pipe damage monitoring apparatus comprising: an electric power supply which supplies electric power; a core which is formed long in a lengthy direction of a pipe and contacts the outer wall of the pipe; a coil which is wound around the outer circumferential surface of the core to thus generate a magnetic field in the inside of the core by an electric current that flows by a supply voltage, wherein the magnetic field is introduced into the inner wall of the pipe having contacted the core, to thus form a closed loop magnetic field along the core and the inner wall of the pipe having contacted the core, wherein the voltage is increased to thus form a first magnetic saturation region which is magnetically saturated in a part of the inner wall of the pipe having contacted the core and wherein the voltage is then persistently increased after the first magnetic saturation region has been formed, to thus generate a magnetic field along the core and the other part of the inner wall of the pipe except for the first magnetic saturation region and to thereby form a second magnetic saturation region which is magnetically saturated; an electric current detector which traces the electric current which flows in the coil and detects a magnetic saturation electric current when the second magnetic saturation state has been formed; and a comparator which compares the magnetic saturation electric current detected from the electric current detector with a reference magnetic saturation electric current of a normal pipe and thus outputs a pipe damage signal if the magnetic saturation electric current is smaller than the reference magnetic saturation electric current.

<12> To accomplish the above object of the present invention, according to another aspect of the present invention, there is also provided an apparatus for monitoring wear such as wall thinning or damage such as crack on the inner walls of pipes, the pipe damage monitoring apparatus comprising: an electric power supply which supplies electric power; a core which is formed long in a lengthy direction of a pipe and contacts the outer wall of the pipe; a coil which is wound around the outer circumferential surface of the core to thus generate a magnetic field in the inside of the core by an electric current that flows by a supply voltage, wherein the magnetic field is introduced into the inner wall of the pipe having contacted the core, to thus form a closed loop magnetic field along the core and the inner wall of the pipe having contacted the core, wherein the voltage is increased to thus form a first magnetic saturation region which is magnetically saturated in a part of the inner wall of the pipe having contacted the core and wherein the voltage is then persistently increased after the first magnetic saturation region has been formed, to thus generate a magnetic field along the core and the other part of the inner wall of the pipe except for the first magnetic saturation region and to thereby form a second magnetic saturation region which is magnetically saturated! an electric current detector which traces the electric current which flows in the coil and detects a magnetic saturation electric current when the second magnetic saturation state has been formed! a look-up table which stores a number of preset magnetic saturation electric current values depending upon change of thickness of the inner wall of the pipe and size of crack generated on the inner wall of the pipe! and a pipe damage determiner which compares the magnetic saturation electric current detected from the electric current detector with the magnetic saturation electric current values stored in the look-up table to thus determine a degree of damage of the pipe.

<i3> Preferably but not necessarily, when the first and second magnetic saturation regions are magnetically saturated by an increase of the electric current flowing in the coil, the core has a magnetic flux density larger than that of the pipe so that the magnetic saturation state cannot be produced.

<14> Preferably but not necessarily, the pipe is made of cast iron and the core is made of a silicon steel plate.

<i5> Preferably but not necessarily, the voltage is a DC (direct-current) voltage. [Advantageous Effects]

<i6> As described above, an apparatus for monitoring damage of pipes makes a core which is formed long in a lengthy direction of a pipe contact the outer wall of the pipe and then applies an electric current to a coil wound around the core, to thus generate a magnetic field into the inner wall of the pipe having contacted the core and thus form a first magnetic saturation region which is magnetically saturated, and then makes the electric current flowing in the coil increased to thus generate a magnetic field into the inner wall of the pipe except for the first magnetic saturation region and thus form a second magnetic saturation region which is magnetically saturated, to thereby keep track of change of the electric current flowing in the coil and monitor whether or not wear of the pipe or damage of the pipe happens on the inner wall in a wide area of the pipe.

<π> As a result, the pipe damage monitoring apparatus according to the present invention may shorten time which is taken to detect whether or not wear of the pipe or damage of the pipe happens, does not need a couplant such as gel but is made to be always mounted in the pipe and directly contact even a high temperature pipe, to thereby easily monitor and quickly detect whether or not wear of the pipe or damage of pipe happens, even in the case that the pipe is in use. [Description of Drawings]

<i8> The above and/or other objects and/or advantages of the present invention will become more apparent by describing the preferred embodiments thereof in detail with reference to the accompanying drawings in which:

<i9> FIG. 1 is a schematic diagram of a pipe damage monitoring apparatus according to an embodiment of the present invention;

<20> FIG. 2 is a conf igurational diagram of the pipe damage monitoring apparatus of FIG. 1',

<2i> FIG. 3A is a schematic view showing a closed loop magnetic field formed along a core and a part of the inner wall of the pipe contacting the core;

<22> FIG. 3B is a schematic view showing a closed loop magnetic field formed at the core and the other part of the inner wall of the pipe!

<23> FIG. 4 is a waveform diagram showing a magnetic saturation property;

<24> FIG. 5 is a waveform diagram showing change of electric current flowing in a coil due to damage of a pipe;

<25> FIG. 6 is a waveform diagram showing respective magnetic saturation properties of a cast iron plate and a silicon steel plate; and

<26> FIG. 7 is a schematic diagram of a pipe damage monitoring apparatus according to another embodiment of the present invention. [Best Mode]

<27> Hereinbelow, an apparatus for monitoring damage of pipes according to preferred embodiments of the present invention will be described with reference to the accompanying drawings. Like reference numerals denote like elements through the following embodiments.

<28> FlG. 1 is a schematic diagram of a pipe damage monitoring apparatus according to an embodiment of the present invention, and FIG. 2 is a conf igurational diagram of the pipe damage monitoring apparatus of FIG. 1.

<29> As illustrated in FIGS 1 and 2, an apparatus for monitoring damage of pipes according to an exemplary embodiment of the present invention includes: an electric power supply 10 which supplies electric power; a core 20 which is formed long in a lengthy direction of a pipe 100 and contacts the outer wall of the pipe 100; a coil 30 which is wound around the outer circumferential surface of the core 20 to thus generate a magnetic field (CM) in the inside of the core by an electric current that flows by a supply voltage, wherein the magnetic field is introduced into the inner wall of the pipe having contacted the core, to thus form a closed loop magnetic field along the core 20 and the inner wall of the pipe 100 having contacted the core 20, wherein the voltage is increased to thus form a first magnetic saturation region (MSl) which is magnetically saturated in a part (Pa) of the inner wall of the pipe 100 having contacted the core 20 and wherein the voltage is then persistently increased after the first magnetic saturation region (MSl) has been formed, to thus generate a magnetic field along the core 20 and the other part (Pb) of the inner wall of the pipe 100 except for the first magnetic saturation region (MSl) and to thereby form a second magnetic saturation region (MS2) which is magnetically saturated; an electric current detector 40 which traces the electric current (I) which flows in the coil 30 and detects a magnetic saturation electric current (SI) when the second magnetic saturation region (MS2) has been formed; and a comparator 50 which compares the magnetic saturation electric current (SI) detected from the electric current detector 40 with a reference magnetic ^saturation electric current (RSI) of a normal pipe and thus outputs a pipe damage signal (PDS) if the magnetic saturation electric current (SI) is smaller than the reference magnetic saturation electric current (RSI).

<30> FIG. 7 is a schematic diagram of a pipe damage monitoring apparatus according to another embodiment of the present invention.

<3i> As illustrated in FIG. 7, an apparatus for monitoring damage of pipes, according to another embodiment of the present invention includes: an electric power supply 10 which supplies electric power; a core 20 which is formed long in a lengthy direction of a pipe 100 and contacts the outer wall of the pipe 100; a coil 30 which is wound around the outer circumferential surface of the core 20 to thus generate a magnetic field (CM) in the inside of the core by an electric current that flows by a supply voltage, wherein the magnetic field is introduced into the inner wall of the pipe having contacted the core, to thus form a closed loop magnetic field along the core 20 and the inner wall of the pipe 100 having contacted the core 20, wherein the voltage is increased to thus form a first magnetic saturation region (MSl) which is magnetically saturated in a part (Pa) of the inner wall of the pipe 100 having contacted the core 20 and wherein the voltage is then persistently increased after the first magnetic saturation region (MSl) has been formed, to thus generate a magnetic field along the core 20 and the other part (Pb) of the inner wall of the pipe 100 except for the first magnetic saturation region (MSl) and to thereby form a second magnetic saturation region (MS2) which is magnetically saturated; an electric current detector 40 which traces the electric current (I) which flows in the coil 30 and detects a magnetic saturation electric current (SI) when the second magnetic saturation region (MS2) has been formed; a look-up table 60 which stores a number of preset magnetic saturation electric current values depending upon change of thickness of the inner wall 110 of the pipe and size of crack generated on the inner wall 110 of the pipe; and a pipe damage determiner 70 which compares the magnetic saturation electric current (SI) detected from the electric current detector 40 with the magnetic saturation electric current values stored in the look-up table to thus determine a degree of damage of the pipe.

<32> In addition, when the first and second magnetic saturation regions (MSl and MS2) are magnetically saturated by an increase of the electric current (I) flowing in the coil, the core 20 has a magnetic flux density (T) larger than that of the pipe 100 so that the magnetic saturation state cannot be produced.

<33> In addition, the pipe 100 is made of cast iron and the core is made of a silicon steel plate.

<34> In addition, the voltage supplied from the electric power supply 10 is a DC (direct-current) voltage or an AC (alternating-current) voltage. Here, it is preferable that the voltage supplied from the electric power supply 10 is a DC (direct-current) voltage in order to make the electric current (I) flowing in the coil 30 stable and have a constant value.

<35> Operations of the pipe damage monitoring apparatuses according to the respective embodiments of the present invention having the above-described structures will follow with reference to the accompanying drawings.

<36> As illustrated in FIGS. 1 and 2, the apparatus for monitoring damage of pipes according to an exemplary embodiment of the present invention, includes: an electric power supply 10; a core 20; a coil 30; an electric current detector 40; and a comparator 50.

<37> Here, the core 20 is formed long in a lengthy direction of a pipe 100 and contacts the outer wall of the pipe 100. That is, one end 20a of the core 20 is made to contact one side of the outer wall of the pipe 100 lengthily along the lengthy direction of the pipe 100, and the other end 20b of the core 20 is made to contact the other side of the outer wall of the pipe 100 lengthily along the lengthy direction of the pipe 100. Then, the core 20 is fixed onto the pipe 100 using a string (not shown).

<38> The coil 30 is wound around the outer circumferential surface of the core 20 to thus generate a magnetic field (CM) in the inside of the core by an electric current (I) that flows by a supply voltage supplied from the electric power supply 10.

<39> The magnetic field (CM) generated in the core 20 is introduced into the inner wall (Pa and Pb) of the pipe 100 having contacted the core 20, to thus form a closed loop magnetic field along the core 20 and the inner wall (Pa and Pb) of the pipe 100 having contacted the core 20.

<40> As illustrated in FIG. 6, the pipe 100 may be chiefly made of a cast iron material. In the case that the pipe 100 is made of a cast iron tube, the core 120 may be made of a silicon steel plate whose magnetic flux density (T) is larger than that of the cast iron tube. In this case, if the voltage output from the electric power supply 10 is continuously made to increase, the electric current flowing in the coil 30 increases. Accordingly, as illustrated in FIGS. 2 and 3A, a first magnetic saturation region (MSl) which is magnetically saturated is formed in the inner wall (Pa) of the pipe 100 contacting the core 20 in which the magnetic flux density (T) of the pipe 100 is smaller than that of the core 20 at the time of the magnetic saturation.

<4i> As illustrated in FIG. 4, magnetic saturation means that the magnetic flux density (T) reaches a saturation point "A" on a magnetic saturation curve even if the electric current flowing in the coil 30 is continuously made to increase, and then the magnetic flux density (T) in a magnetic body is not linearly increased but is saturated. That is, if the electric current flowing in the coil 30 is made to increase before intensity of the magnetic field reaches a point "B," the magnetic flux density (T) is also linearly increased according to the electric current flowing in the coil 30. However, if intensity of the magnetic field reaches the point "B," the magnetic flux density (T) is not increased any more but saturated, even if the electric current flowing in the coil 30 is continuously made to increase.

<42> A first magnetic saturation region (MSl) which is magnetically saturated is formed in a part (Pa) of the inner wall of the pipe 100 having contacted the core 20. Thereafter, if the voltage is then persistently increased after the first magnetic saturation region (MSl) has been formed, the magnetic field is not introduced any more in the part (Pa) of the inner wall of the pipe 100 having contacted the core 20. Accordingly, as shown in FIGS. 1 and 3A, a magnetic field is generated along the core 20 and the other part (Pb) of the inner wall of the pipe 100 except for the first magnetic saturation region (MSl) to thereby form a second magnetic saturation region (MS2) which is magnetically saturated in the other part (Pb) of the inner wall of the pipe 100.

<43> A permeability is decreased if magnetic saturation occurs at the inner wall (Pb) of the pipe. Thus, reluctance of a magnetic circuit increases, and inductance which is flux linkage of the coil 30 decreases due to the increase of the reluctance of the magnetic circuit. Accordingly, impedance of the coil 30 decreases. As a result, the electric current (I) flowing in the coil 30 sharply increases at a point in time where the second magnetic saturation region (MS2) is formed at the inner wall (Pb) as illustrated in FIG. 5.

<44> In the case that thickness of a pipe is thinned due to a long use of the pipe, wear of the pipe, that is, the wall thinning of the pipe occurs on the inner wall of the pipe or crack occurs on the inner wall of the pipe, that is, damage of the pipe occurs in the pipe, magnetic saturation is accomplished at a damaged portion earlier in comparison with a normal pipe. That is, as illustrated in FIG. 5, a curve (3) represents an electric current waveform of a normal pipe having no wear of the pipe or the crack of the pipe along the inner wall of the pipe. It can be seen from the curve (3) of FIG. 5 that electric current sharply increases due to magnetic saturation on the inner wall of the pipe, at a point in time of t3. It can be also seen from a curve φ of FIG. 5 that wear of a pipe or crack of the pipe occurs along the inner wall of the pipe, to thus produce magnetic saturation on the inner wall of the pipe at a point in time of tl and to thus cause the electric current to be sharply increased. It can be seen that magnetic saturation of the curve (D has occurred earlier in comparison with the curve φ. It can be also seen from a curve φ of FIG. 5 that magnetic saturation has occurred earlier in comparison with the normal pipe and thus the inner wall of the pipe has been damaged. That is, it can be seen that damage of the inner wall of the pipe has been more serious in the case of the curve (T) in comparison with that of the curve (2).

<45> Therefore, in the case of the pipe damage monitoring apparatus according to the present invention, the voltage output from the electric power supply 10 is applied to the coil 30 and then the voltage is made to increase. Accordingly, a magnetic field (CM) occurs in the core 20 by electric current (I) flowing in the coil 30. The first magnetic saturation region (MSl) is formed in the inner wall (Pa) of the pipe 100 contacting the core 20 by the magnetic field due to the core 20. Thereafter, if the electric current (I) flowing in the coil 30 is made to further increase, the second magnetic saturation region (MS2) is formed in the inner wall (Pb) of the pipe 100. Since the electric current (I) flowing in the coil 30 sharply increases when the second magnetic saturation region (MS2) is formed, the electric current detector 40 traces the electric current (I) flowing in the coil 30, and detects a magnetic saturation electric current (SI) at the electric current value of the sharply increased electric current, that is, at the time when the inner wall (Pb) of the pipe 100 is magnetically saturated. The comparator 50 compares the magnetic saturation electric current (SI) detected from the electric current detector 40 with a reference magnetic saturation electric current (RSI) of a normal pipe and thus outputs an activated pipe damage signal (PDS) if the magnetic saturation electric current (SI) is smaller than the reference magnetic saturation electric current (RSI), and a deactivated pipe damage signal (PDS) if the magnetic saturation electric current (SI) equals the reference magnetic saturation electric current (RSI).

<46> Therefore, the comparator 50 cannot distinguish how much the inner wall of the pipe 100 is damaged, but it can only determine whether or not thickness of the inner wall 110 of the pipe decreases, wear (wall thinning) of the pipe occurs, and occurrence of crack along the inner wall of the pipe exists. Meanwhile, if the core 20 formed along the lengthy direction of the pipe 100 is lengthened, it can be determined whether or not a pipe is damaged at a wide area of the pipe at a one-time measurement.

<47> FIG. 7 is a schematic diagram of a pipe damage monitoring apparatus according to another embodiment of the present invention. The operation of the pipe damage monitoring apparatus shown in FIG. 7 equals that of FIG. 1. However, the pipe damage monitoring apparatus of FIG. 7 includes a look-up table 60 and a pipe damage determiner 70, instead of the comparator 50 of FIG. 1.

<48> As shown in FIG. 7, the look-up table 60 stores a number of preset magnetic saturation electric current values according to change of thickness of the pipe inner wall 110 and magnitude of crack having occurred in the pipe inner wall 110, and the pipe damage determiner 70 compares the magnetic saturation electric current (SI) detected from the electric current detector 40 with the magnetic saturation electric current values stored in the look-up table 60, to thereby determine a degree of damage on the inner wall of the pipe. That is, the pipe damage determiner 70 can determine how much thickness of the pipe inner wall 110 is thinned due to wear of the pipe, that is, wall thinning of the pipe, or how many degree a crack occurs on the pipe inner wall 110.

<49> In the case of the pipe damage monitoring apparatus according to the present invention, magnetic saturation should not occur in the core 20 earlier than the pipe inner wall 110 according to an increase of the voltage output from the electric power supply 10, but magnetic saturation should occur in the pipe inner wall 110 earlier than the core 20. Thus, the core 20 should use a material whose magnetic flux density is larger in comparison with the pipe 100, at the time of magnetic saturation. Since ordinary pipes 100 are made of cast iron, the core 20 is preferably made of a silicon steel plate whose magnetic flux density is larger than the cast iron, at the time of magnetic saturation. More preferably, the core 20 is formed of a lamination of the silicon steel plates. [Mode for Invention]

<50> As described above, the present invention has been described with respect to particularly preferred embodiments. However, the present invention is not limited to the above embodiments, and it is possible for one who has an ordinary skill in the art to make various modifications and variations, without departing off the spirit of the present invention. Thus, the protective scope of the present invention is not defined within the detailed description thereof but is defined by the claims to be described later and the technical spirit of the present invention. [Industrial Applicability]

<5i> As described above, an apparatus for monitoring damage of pipes according to the present invention can be applied to easily detect wear of the pipes whose thickness is thinned or damage of the pipes which may occurs on the inner wall of the pipes such as crack of the pipes, by high temperature and high pressure fluid or gas which flows in the pipes.

Claims

[CLAIMS] [Claim 1]

An apparatus for monitoring wear such as wall thinning or damage such as crack on the inner walls of pipes, the pipe damage monitoring apparatus comprising: an electric power supply which supplies electric power; a core which is formed long in a lengthy direction of a pipe and contacts the outer wall of the pipe; a coil which is wound around the outer circumferential surface of the core to thus generate a magnetic field in the inside of the core by an electric current that flows by a supply voltage, wherein the magnetic field is introduced into the inner wall of the pipe having contacted the core, to thus form a closed loop magnetic field along the core and the inner wall of the pipe having contacted the core, wherein the voltage is increased to thus form a first magnetic saturation region which is magnetically saturated in a part of the inner wall of the pipe having contacted the core and wherein the voltage is then persistently increased after the first magnetic saturation region has been formed, to thus generate a magnetic field along the core and the other part of the inner wall of the pipe except for the first magnetic saturation region and to thereby form a second magnetic saturation region which is magnetically saturated; an electric current detector which traces the electric current which flows in the coil and detects a magnetic saturation electric current when the second magnetic saturation state has been formed; and a comparator which compares the magnetic saturation electric current detected from the electric current detector with a reference magnetic saturation electric current of a normal pipe and thus outputs a pipe damage signal if the magnetic saturation electric current is smaller than the reference magnetic saturation electric current. [Claim 2]

The pipe damage monitoring apparatus according to claim 1, wherein when the first and second magnetic saturation regions are magnetically saturated by an increase of the electric current flowing in the coil, the core has a magnetic flux density larger than that of the pipe so that the magnetic saturation state cannot be produced. [Claim 3]

The pipe damage monitoring apparatus according to claim 1 or 2, wherein the pipe is made of cast iron and the core is made of a silicon steel plate. [Claim 4]

The pipe damage monitoring apparatus according to claim 1, wherein the voltage is a DC (direct-current) voltage. [Claim 5]

An apparatus for monitoring wear such as wall thinning or damage such as crack on the inner walls of pipes, the pipe damage monitoring apparatus comprising: an electric power supply which supplies electric power; a core which is formed long in a lengthy direction of a pipe and contacts the outer wall of the pipe; a coil which is wound around the outer circumferential surface of the core to thus generate a magnetic field in the inside of the core by an electric current that flows by a supply voltage, wherein the magnetic field is introduced into the inner wall of the pipe having contacted the core, to thus form a closed loop magnetic field along the core and the inner wall of the pipe having contacted the core, wherein the voltage is increased to thus form a first magnetic saturation region which is magnetically saturated in a part of the inner wall of the pipe having contacted the core and wherein the voltage is then persistently increased after the first magnetic saturation region has been formed, to thus generate a magnetic field along the core and the other part of the inner wall of the pipe except for the first magnetic saturation region and to thereby form a second magnetic saturation region which is magnetically saturated; an electric current detector which traces the electric current which flows in the coil and detects a magnetic saturation electric current when the second magnetic saturation state has been formed; a look-up table which stores a number of preset magnetic saturation electric current values depending upon change of thickness of the inner wall of the pipe and size of crack generated on the inner wall of the pipe; and a pipe damage determiner which compares the magnetic saturation electric current detected from the electric current detector with the magnetic saturation electric current values stored in the look-up table to thus determine a degree of damage of the pipe. [Claim 6]

The pipe damage monitoring apparatus according to claim 5, wherein when the first and second magnetic saturation regions are magnetically saturated by an increase of the electric current flowing in the coil, the core has a magnetic flux density larger than that of the pipe so that the magnetic saturation state cannot be produced. [Claim 7]

The pipe damage monitoring apparatus according to claim 5 or 6, wherein the pipe is made of cast iron and the core is made of a silicon steel plate. [Claim 8]

The pipe damage monitoring apparatus according to claim 5, wherein the voltage is a DC (direct-current) voltage.