JP2008249739A - Magnetizing equipment for detecting magnetic flaw in steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide magnetizing equipment for detecting a magnetic flaw in a steel pipe which can be magnetized so as to accurately detect a flaw extending in the steel pipe in the axial, circumferential or any direction. <P>SOLUTION: The magnetizing equipment 1 is provided with a first coil 11 spirally wound in the axial direction of the steel pipe P, a pair of second coils 12a and 12b disposed in the first direction orthogonal to the axial direction of the steel pipe and facing each other through the steel pipe, a pair of third coils 13a and 13b disposed in the second direction orthogonal to the axial direction of the steel pipe and the first direction and facing each other through the steel pipe, a three-phase AC power supply 14 for supplying an AC current to coils, and a current adjusting circuit for adjusting the AC current outputted from the three-phase AC power supply and making an amplitude of the AC current carried to one of the second and third coils 0-0.4 times as large as an amplitude of the AC current carried to the other coil. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetizing device for magnetic flaw detection (magnetic particle flaw detection, etc.) of a steel pipe, and in particular, it is possible to magnetize so that any defect extending in each direction such as the axial direction or the circumferential direction of a steel pipe can be detected with high accuracy. The present invention relates to a magnetizing apparatus.

  2. Description of the Related Art Conventionally, there is known a magnetic particle flaw detection method for detecting defects generated on the inner and outer surfaces of a steel pipe by magnetizing a steel pipe (particularly, a pipe end) that is a magnetic body. More specifically, in the magnetic particle flaw detection method, if the magnetic powder liquid is sprayed on the magnetized steel pipe, the magnetic powder is magnetized and agglomerated and adsorbed by the leakage magnetic flux generated at the defect occurrence site. This is a flaw detection method for detecting defects by visual observation.

  Here, the leakage magnetic flux is remarkably generated when the defect extends in a direction perpendicular to the direction of the magnetic flux generated by the magnetization of the steel pipe. On the other hand, as defects generated on the inner and outer surfaces of the steel pipe, there are various defects extending in each direction such as an axial direction and a circumferential direction of the steel pipe depending on the generation factor. Therefore, in order to accurately detect any defect in various directions that can occur in the steel pipe, a magnetization method (magnetization apparatus) is adopted in which the magnetic flux is generated substantially uniformly in all directions along the inner and outer surfaces of the steel pipe. Ideally.

  Therefore, for the purpose of generating magnetic flux substantially uniformly in all directions, conventionally, the first coil wound in a spiral shape along the axial direction of the steel pipe, and extending along the axial direction of the steel pipe, and A pair of second coils disposed opposite to each other across the steel pipe along a horizontal axis direction perpendicular to the axial direction of the steel pipe, and electrically connected to each other; and extending along the axial direction of the steel pipe; and A pair of third coils arranged opposite to each other across the steel pipe along the axial direction perpendicular to the axial direction of the steel pipe and the horizontal axis direction, and electrically connected to each other, the first coil, and the second coil And a magnetizing device provided with a three-phase AC power source for supplying AC currents having a phase difference of 120 degrees to each of the third coils has been proposed (see, for example, Patent Document 1).

However, when the inventors of the present invention actually tested a steel pipe with artificial defects in various parts and directions using the magnetizing apparatus described in Patent Document 1, a defect extending in a predetermined direction of a predetermined part of the steel pipe. It was found difficult to detect.
Japanese Patent Laid-Open No. 7-103942

  The present invention has been made to solve such problems of the prior art, and can be magnetized so that any defect extending in each direction such as the axial direction or circumferential direction of a steel pipe can be detected with high accuracy. An object of the present invention is to provide a magnetizing device for magnetic flaw detection of a simple steel pipe.

  In order to solve the above-mentioned problems, the inventors of the present invention have made extensive studies and as a result, it is supplied to the first coil, the second coil, and the third coil that a defect extending in a predetermined direction of a predetermined portion of the steel pipe cannot be detected. This is because the magnetic flux due to magnetization does not occur in all directions along the inner and outer surfaces of the steel pipe due to the phase difference between the alternating currents being 120 degrees (for example, paragraph 4 of page 4 of Patent Document 1). I found out.

  More specifically, as shown in FIG. 6, the first coil 11 wound in a spiral shape along the axial direction of the steel pipe P (the depth direction in FIG. 6), and the axial direction of the steel pipe P A pair of second coils 12a and 12b arranged opposite to each other across the steel pipe P along a horizontal axis direction orthogonal to each other, and the steel pipe P along a vertical axis direction orthogonal to the axial direction of the steel pipe P. A phase difference of 120 degrees between the pair of third coils 13a and 13b that are arranged opposite to each other and electrically connected to each other (the phase difference between the first coil 11 and the second coils 12a and 12b is 120 degrees). When an alternating current (amplitude and frequency are the same) having a phase difference of 240 degrees between the first coil 11 and the third coils 13a and 13b is supplied, the magnetic field distribution (the locus of the magnetic field vector) as shown in FIG. Was found to form. Here, FIG. 7 is a view showing a magnetic field (magnetic permeability of the steel pipe P is not considered) distribution formed by the coil arrangement shown in FIG. 6, and (a) shows the second coil 12a and the third coil 13a. A magnetic field distribution formed in a region between the second coil 12b and the third coil 13b (hereinafter referred to as A region as appropriate), (b) is between the second coil 12b and the third coil 13a. The results of calculating the magnetic field distribution formed in the region (hereinafter referred to as B region as appropriate) between the second coil 12a and the third coil 13b (hereinafter referred to as B region as appropriate) are shown. In FIG. 7, the horizontal axis indicates the magnetic field strength along the axial direction (L direction) of the steel pipe P, and the vertical axis indicates the magnetic field strength along the circumferential direction (T direction) of the steel pipe P. Moreover, the point (●) in the graph shown in FIG. 7 indicates the magnetic field strength plotted every time the phase of the alternating current supplied to each coil advances by 20 degrees.

  As shown in FIG. 7, when an alternating current having a phase difference of 120 degrees is supplied to the first coil 11, the second coils 12a and 12b, and the third coils 13a and 13b, the region B is increased as the phase of the alternating current advances. In FIG. 7, an elliptical magnetic field distribution is formed (FIG. 7B), but in the area A, a linear magnetic field distribution is obtained (FIG. 7A). In other words, as the phase of the supplied alternating current advances, the magnetic field vector in the B region follows all directions along the inner and outer surfaces of the steel pipe P, whereas the magnetic field vector in the A region only changes in magnitude. Therefore, it follows only one predetermined direction along the inner and outer surfaces of the steel pipe P. Therefore, in the area A, it is possible to detect a defect extending in a direction perpendicular to the one direction, but the detection ability of the defect extending in the other direction is lowered, and in particular, a defect extending in parallel to the one direction. Will be very difficult to detect. As described above, the result of this numerical calculation substantially coincided with the result of actually testing a steel pipe with an artificial defect, thereby confirming the validity of the analysis by this numerical calculation.

  As a result of intensive studies, the inventors of the present invention have determined that the amplitude of the alternating current supplied to one of the second coil and the third coil is set to 0 to 0. 0 of the amplitude of the alternating current supplied to the other coil. It was found that the magnetic field vector traces in all directions along the inner and outer surfaces of the steel pipe in both the A region and the B region by making the ratio four times, and the present invention was completed based on such knowledge. That is, the present invention includes a first coil wound in a spiral shape along the axial direction of the steel pipe, and a first direction extending along the axial direction of the steel pipe and orthogonal to the axial direction of the steel pipe. A pair of second coils disposed opposite to each other across the steel pipe and electrically connected to each other, and extending in the axial direction of the steel pipe and orthogonal to the axial direction of the steel pipe and the first direction. To supply an alternating current to each of the pair of third coils that are disposed opposite to each other across the steel pipe along two directions and are electrically connected to each other, and the first coil, the second coil, and the third coil. And a three-phase AC power source, wherein the amplitude of the AC current applied to one of the second coil and the third coil is 0 of the amplitude of the AC current supplied to the other coil. ~ 0.4 times so that The AC current output from the phase AC power source is adjusted, the adjusted AC current is supplied to the second coil and the third coil, and the magnetic field vector formed by the magnetizing device is applied to the inner and outer surfaces of the steel pipe. The present invention provides a magnetizing device for magnetic flaw detection of a steel pipe, characterized by comprising a current adjusting circuit for following all directions along.

  The second coil according to the present invention is configured by arranging a plurality of metal elongated members extending along the axial direction of the steel pipe in a direction perpendicular to the axial direction, as described in Patent Document 1. It is possible. More specifically, the second coils having the above-described configuration are arranged opposite to each other with the steel pipe interposed therebetween, and the start end portion of the elongated member constituting one second coil and the elongated member constituting the other second coil are arranged. It is possible to employ a configuration in which the terminal portions are sequentially electrically connected. Further, as the second coil, a so-called yoke coil is formed by winding a winding around a yoke extending in the axial direction of the steel pipe, and the windings of the yoke coils arranged opposite to each other with the steel pipe interposed therebetween are electrically connected. A configuration for connection may be employed. Similarly, for the third coil according to the present invention, the configuration described in Patent Document 1 and the configuration using a yoke coil can be employed.

  According to such invention, since the magnetic field vector follows all directions along the inner and outer surfaces of the steel pipe in both the A region and the B region, any defect extending in each direction such as the axial direction or the circumferential direction of the steel pipe is accurately detected. It can be magnetized so that it can be detected. The specific configurations that can be employed as the second coil and the third coil according to the present invention are as described above. In addition, as the current adjustment circuit according to the present invention, various known current adjustment circuits can be used.

  Moreover, in order to solve the above-mentioned problems, the inventors of the present invention have intensively studied. As a result, the phase differences of the alternating currents supplied to the first coil, the second coil, and the third coil, respectively, should not be 120 degrees. Thus, the magnetic field vector was found to follow all directions along the inner and outer surfaces of the steel pipe in both the A region and the B region, and the present invention was completed based on such knowledge. That is, the present invention provides a first coil wound in a spiral shape along the axial direction of the steel pipe, and extends along the axial direction of the steel pipe, and further along a first direction orthogonal to the axial direction of the steel pipe. A pair of second coils that are arranged opposite to each other with the steel pipe interposed therebetween and are electrically connected to each other, and extend along the axial direction of the steel pipe, and are further orthogonal to the axial direction of the steel pipe and the first direction. To supply an alternating current to each of the pair of third coils that are disposed opposite to each other across the steel pipe along two directions and are electrically connected to each other, and the first coil, the second coil, and the third coil. A three-phase alternating current power source, wherein the three currents supplied to the first coil, the second coil, and the third coil do not have a phase difference of 120 degrees with respect to each other. Output from phase AC power supply The phase of the alternating current is shifted, the alternating current after the phase shift is supplied to the first coil, the second coil, and the third coil, and the magnetic field vector formed by the magnetizing device is There is provided a magnetizing device for magnetic flaw detection of a steel pipe, comprising a phase shifter for tracing all directions along the inner and outer surfaces.

  According to such invention, since the magnetic field vector follows all directions along the inner and outer surfaces of the steel pipe in both the A region and the B region, any defect extending in each direction such as the axial direction or the circumferential direction of the steel pipe is accurately detected. It can be magnetized so that it can be detected. The specific configurations that can be employed as the second coil and the third coil according to the present invention are as described above. In addition, as the phase shifter according to the present invention, various known phase shifters can be used.

  Furthermore, as a result of intensive investigations by the inventors of the present invention in order to solve the above-mentioned problems, at least one of the alternating current frequencies supplied to the first coil, the second coil, and the third coil remains. It was found that the magnetic field vector traces all directions along the inner and outer surfaces of the steel pipe in both the A region and the B region by making the frequency different from the frequency of the alternating current, and the present invention was completed based on such knowledge. That is, the present invention includes a first coil wound in a spiral shape along the axial direction of the steel pipe, and a first direction extending along the axial direction of the steel pipe and orthogonal to the axial direction of the steel pipe. A pair of second coils disposed opposite to each other across the steel pipe and electrically connected to each other, and extending in the axial direction of the steel pipe and orthogonal to the axial direction of the steel pipe and the first direction. To supply an alternating current to each of the pair of third coils that are disposed opposite to each other across the steel pipe along two directions and are electrically connected to each other, and the first coil, the second coil, and the third coil. A three-phase AC power source, wherein the frequency of at least one AC current among the AC currents supplied to the first coil, the second coil, and the third coil is the remaining AC. Different from current frequency The frequency of the alternating current output from the three-phase alternating current power source is converted, and the alternating current after the frequency conversion is supplied to the first coil, the second coil, and the third coil. The present invention provides a magnetizing device for magnetic flaw detection of a steel pipe, comprising a frequency conversion circuit for causing a magnetic field vector to be formed to follow all directions along the inner and outer surfaces of the steel pipe.

  According to such invention, since the magnetic field vector follows all directions along the inner and outer surfaces of the steel pipe in both the A region and the B region, any defect extending in each direction such as the axial direction or the circumferential direction of the steel pipe is accurately detected. It can be magnetized so that it can be detected. The specific configurations that can be employed as the second coil and the third coil according to the present invention are as described above. Further, as the frequency conversion circuit according to the present invention, various known frequency conversion circuits can be used.

  As described above, according to the magnetizing apparatus for magnetic testing according to the present invention, the magnetic field vector generated by the magnetization follows all directions along the inner and outer surfaces of the steel pipe. It is possible to magnetize so that any extending defect can be detected with high accuracy.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a perspective view schematically showing a configuration of a magnetic testing magnetizing apparatus according to an embodiment of the present invention. As shown in FIG. 1, a magnetizing device for magnetic flaw detection (hereinafter, appropriately referred to as a magnetizing device) 1 includes a first coil 11 wound in a spiral shape along the axial direction of a steel pipe P, and an axial direction of the steel pipe P. A pair of second coils 12 a that extend along the first direction (horizontal direction in the present embodiment) perpendicular to the axial direction of the steel pipe P and are opposed to each other with the steel pipe P interposed therebetween and are electrically connected to each other. 12b and extending along the axial direction of the steel pipe P, and opposed to each other across the steel pipe P along the axial direction of the steel pipe P and a second direction (vertical direction in the present embodiment) orthogonal to the first direction. And a pair of third coils 13 electrically connected to each other, and three for supplying alternating currents having a phase difference of 120 degrees to the first coil 11, the second coils 12a and 12b, and the third coils 13a and 13b, respectively. And a phase AC power source 14. Furthermore, the magnetizing apparatus 1 according to the present embodiment adjusts the alternating current output from the three-phase alternating current power supply 14, and supplies the adjusted alternating current to the second coils 12a and 12b and the third coils 13a and 13b. Current adjustment circuit 15 is provided.

  The second coils 12a and 12b according to the present embodiment are configured by arranging a plurality of metal elongated members extending along the axial direction of the steel pipe P in the vertical direction, and each of the elongated coils constituting the second coil 12a. The terminal end portion (end portion on the downstream side in the energization direction) of the member and the start end portion (end portion on the upstream side in the energization direction) of each elongated member constituting the second coil 12b are sequentially electrically connected (connection lines are not shown) ), An elongate member positioned at the end of the second coil 12a (the elongate member positioned lowest in FIG. 1) and an elongate member positioned at the end of the second coil 12b (elongated member positioned uppermost in FIG. 1) ) Is electrically connected to the current adjusting circuit 15 and thus to the three-phase AC power source 14. In the above configuration, when AC power is supplied from the three-phase AC power supply 14, currents in opposite directions are supplied to the second coils 12a and 12b along the axial direction of the steel pipe P. A magnetic field along the direction will be formed.

  The third coils 13a and 13b according to the present embodiment are configured by arranging a plurality of metal elongated members extending along the axial direction of the steel pipe P in the horizontal direction, and each of the elongated coils constituting the third coil 13a. The terminal end portion (end portion on the downstream side in the energization direction) of the member and the start end portion (end portion on the upstream side in the energization direction) of each elongated member constituting the third coil 13b are sequentially electrically connected (connection lines are not shown) ), An elongated member positioned at the end of the third coil 13a (the elongated member positioned closest to the front in FIG. 1), and an elongated member positioned at the end of the third coil 13b (the elongated member positioned deepest in FIG. 1) ) Is electrically connected to the current adjusting circuit 15 and thus to the three-phase AC power source 14. In the above configuration, when AC power is supplied from the three-phase AC power supply 14, currents that are opposite to each other in the axial direction of the steel pipe P are supplied to the third coils 13a and 13b. A magnetic field along the direction will be formed.

  The current adjustment circuit 15 is configured such that the amplitude of the alternating current supplied to one of the second coils 12a and 12b and the third coils 13a and 13b is 0 to 0.4 times the amplitude of the alternating current supplied to the other coil. The AC current output from the three-phase AC power source 14 is adjusted so that the adjusted AC current is supplied to the second coils 12a and 12b and the third coils 13a and 13b. As the current adjustment circuit 15, various known current adjustment circuits can be used.

  FIG. 2 is a diagram showing an example of a magnetic field (the magnetic permeability of the steel pipe P is not considered) distribution (trajectory of the magnetic field vector) formed by the magnetizing apparatus 1 described above, and (a) shows the second coil 12a and The magnetic field distribution formed in the region between the third coil 13a (or between the second coil 12b and the third coil 13b) (hereinafter referred to as A region as appropriate), (b) shows the second coil 12b and the second coil 12b. The results of calculating the magnetic field distribution formed in the region between the three coils 13a (or between the second coil 12a and the third coil 13b) (hereinafter referred to as B region as appropriate) by numerical calculation are shown. Here, the horizontal axis in FIG. 2 indicates the magnetic field strength along the axial direction (L direction) of the steel pipe P, and the vertical axis indicates the magnetic field strength along the circumferential direction (T direction) of the steel pipe P. Further, a point (●) in the graph shown in FIG. 2 indicates the magnetic field strength plotted every time the phase of the supplied alternating current advances by 20 degrees.

  In addition, as a numerical calculation method for obtaining the result shown in FIG. 2, each coil 11, 12 a (12 b) and 13 a (13 b) is formed by each coil alone in consideration of the amplitude and phase of the alternating current flowing through each coil The magnetic field strength at a predetermined location (for example, in the case of the A region, the intermediate point between the second coil 12a and the third coil 13a) is calculated using Bio-Savart's law, and each calculated magnetic field is calculated. A simple method of obtaining the magnetic field intensity at the predetermined location by superimposing the intensity was used.

  The results shown in FIG. 2 are obtained when the current Ix applied to the second coils 12a and 12b is set to 0, and the current Iz supplied to the first coil 11 and the current Iy supplied to the third coils 13a and 12b are the same. The obtained results show that the magnetic field vector follows all directions along the inner and outer surfaces of the steel pipe P in both the A region and the B region. Similarly, the amplitude of the alternating current supplied to one of the second coils 12a, 12b and the third coils 13a, 13b should be 0 to 0.4 times the amplitude of the alternating current supplied to the other coil. For example, the magnetic field vector follows all directions along the inner and outer surfaces of the steel pipe P in both the A region and the B region, and thereby any defects extending in each direction such as the axial direction and the circumferential direction of the steel pipe P are accurate. Magnetization is possible so that it can be detected well.

  In addition, although this embodiment demonstrated the structure which supplies the alternating current after adjustment to each coil 11, 12a (12b) and 13a (13b) via the current adjustment circuit 15 from the three-phase alternating current power supply 14, this book The invention is not limited to this, and a configuration using a phase shifter instead of the current adjustment circuit 15 may be employed.

  More specifically, the three-phase AC power supply 14 is set so that the phase differences of the AC currents supplied to the first coil 11, the second coils 12a and 12b, and the third coils 13a and 13b are not 120 degrees from each other. A configuration comprising a phase shifter for shifting the phase of the alternating current output from, and supplying the alternating current after the phase shift to the first coil 11, the second coils 12a and 12b, and the third coils 13a and 13b. It may be adopted. As such a phase shifter, various known phase shifters can be used.

  FIG. 3 is a diagram showing an example of a magnetic field (the magnetic permeability of the steel pipe P is not considered) distribution (trajectory of the magnetic field vector) formed by the magnetizing device having such a configuration, and (a) is similar to FIG. The magnetic field distribution formed in the A region and (b) show the results of calculating the magnetic field distribution formed in the B region by numerical calculation. The meanings of the horizontal axis, the vertical axis, the point (●), and the numerical calculation method in FIG. 3 are the same as those in FIG.

  The result shown in FIG. 3 is that the phase difference between the current Ix flowing through the second coils 12a and 12b and the current Iy flowing through the third coils 13a and 13b is 90 degrees, and the current Ix flowing through the second coils 12a and 12b. And the phase difference between the current Iz applied to the first coil 11 and the current Iz are 90 degrees, and the magnetic field vector is in all directions along the inner and outer surfaces of the steel pipe P in both the A region and the B region. I knew I would follow. Similarly, if the phase shift is performed by the phase shifter so that the phase differences of the alternating currents supplied to the first coil 11, the second coils 12a and 12b, and the third coils 13a and 13b are not 120 degrees, the A region In both the B and B regions, the magnetic field vector follows all directions along the inner and outer surfaces of the steel pipe P, whereby any defect extending in each direction such as the axial direction or the circumferential direction of the steel pipe P can be detected with high accuracy. Can be magnetized.

  It is also possible to adopt a configuration using a frequency conversion circuit instead of the current adjustment circuit 15. More specifically, at least one of the alternating currents supplied to the first coil 11, the second coils 12a and 12b, and the third coils 13a and 13b has a frequency of the remaining alternating current. The frequency of the alternating current output from the three-phase alternating current power supply 14 is converted, and the alternating current after the frequency conversion is supplied to the first coil 11, the second coils 12a and 12b, and the third coils 13a and 13b. A configuration including a frequency conversion circuit for the purpose may be employed. As such a frequency conversion circuit, various known frequency conversion circuits can be used.

  FIG. 4 is a diagram showing an example of a magnetic field (the magnetic permeability of the steel pipe P is not considered) distribution (trajectory of the magnetic field vector) formed by the magnetizing device having such a configuration, and (a) is similar to FIG. The magnetic field distribution formed in the A region and (b) show the results of calculating the magnetic field distribution formed in the B region by numerical calculation. The meanings of the horizontal axis, the vertical axis, the point (●), and the numerical calculation method in FIG. 4 are the same as those in FIG.

  The result shown in FIG. 4 is that the frequency of the alternating current supplied to the first coil 11 is 0.95 times the frequency of the alternating current supplied to the second coils 12a and 12b and the third coils 13a and 13b, respectively. It was found that the magnetic field vector followed all directions along the inner and outer surfaces of the steel pipe P in both the A region and the B region. Similarly, the frequency of at least one alternating current out of the alternating currents supplied to the first coil 11, the second coils 12a and 12b, and the third coils 13a and 13b is different from the frequency of the remaining alternating current. If the frequency conversion is performed by the frequency conversion circuit, the magnetic field vector follows all directions along the inner and outer surfaces of the steel pipe P in both the A region and the B region, and thereby, in each direction such as the axial direction and the circumferential direction of the steel pipe P. It is possible to magnetize so that any extending defect can be detected with high accuracy.

  Further, the second coils 12a and 12b and the third coils 13a and 13b according to the present embodiment are provided by arranging a plurality of metal elongated members extending along the axial direction of the steel pipe P in a direction perpendicular to the axial direction. However, the present invention is not limited to this. As shown in FIG. 5, the second coil 12a, 12b and the third coil 13a, 13b are used as the axial direction of the steel pipe P (perpendicular to the plane of FIG. 5). A so-called yoke coil is formed by winding a winding C around a yoke Y extending along a certain direction), and the windings of the yoke coils arranged opposite to each other with the steel pipe P interposed therebetween are electrically connected (yoke coil). It is also possible to adopt a configuration in which 12a and 12b are connected and yoke coils 13a and 13b are connected.

FIG. 1 is a perspective view schematically showing a configuration of a magnetic testing magnetizing apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a magnetic field distribution formed by the magnetic flaw detector for magnetic testing according to one embodiment of the present invention. FIG. 3 is a diagram showing an example of a magnetic field distribution formed by a magnetic flaw detection magnetizing apparatus according to another embodiment of the present invention. FIG. 4 is a diagram showing an example of a magnetic field distribution formed by a magnetic flaw detection magnetizing apparatus according to another embodiment of the present invention. FIG. 5 is a longitudinal sectional view schematically showing the configuration of a coil used in a magnetic flaw detection magnetizing apparatus according to another embodiment of the present invention. FIG. 6 is a longitudinal sectional view schematically showing an arrangement configuration of coils used in a conventional magnetic flaw detector. FIG. 7 is a diagram showing a magnetic field distribution formed by a conventional magnetizing device for magnetic flaw detection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Magnetizing apparatus for magnetic flaw detection 11 ... 1st coil 12a, 12b ... 2nd coil 13a, 13b ... 3rd coil 14 ... Three-phase alternating current power supply 15 ... Current adjustment circuit P ... Steel pipes

Claims (3)

A first coil wound spirally along the axial direction of the steel pipe;
A pair of second coils that extend along the axial direction of the steel pipe and are opposed to each other across the steel pipe along a first direction orthogonal to the axial direction of the steel pipe, and are electrically connected to each other;
A pair of first electrodes that extend along the axial direction of the steel pipe and that are opposed to each other across the steel pipe along a second direction orthogonal to the axial direction of the steel pipe and the first direction, and are electrically connected to each other. 3 coils,
A magnetizing device comprising a three-phase AC power source for supplying an AC current to each of the first coil, the second coil, and the third coil;
The three-phase AC power supply so that the amplitude of the AC current supplied to one of the second coil and the third coil is 0 to 0.4 times the amplitude of the AC current supplied to the other coil. The AC current output from the magnet is adjusted, the adjusted AC current is supplied to the second coil and the third coil, and the magnetic field vector formed by the magnetizing device is all along the inner and outer surfaces of the steel pipe. A magnetizing device for magnetic flaw detection of a steel pipe, characterized by comprising a current adjusting circuit for following the direction. A first coil wound spirally along the axial direction of the steel pipe;
A pair of second coils that extend along the axial direction of the steel pipe and are opposed to each other across the steel pipe along a first direction orthogonal to the axial direction of the steel pipe, and are electrically connected to each other;
A pair of first electrodes that extend along the axial direction of the steel pipe and that are opposed to each other across the steel pipe along a second direction orthogonal to the axial direction of the steel pipe and the first direction, and are electrically connected to each other. 3 coils,
A magnetizing device comprising a three-phase AC power source for supplying an AC current to each of the first coil, the second coil, and the third coil;
The phase of the alternating current output from the three-phase alternating current power supply is shifted so that the phase difference between the alternating currents supplied to the first coil, the second coil, and the third coil does not become 120 degrees each other, The alternating current after the phase shift is supplied to the first coil, the second coil, and the third coil so that the magnetic field vector formed by the magnetizing device follows all directions along the inner and outer surfaces of the steel pipe. A magnetizing device for magnetic flaw detection of a steel pipe, characterized by comprising a phase shifter for making the steel pipe. A first coil wound spirally along the axial direction of the steel pipe;
A pair of second coils that extend along the axial direction of the steel pipe and are opposed to each other across the steel pipe along a first direction orthogonal to the axial direction of the steel pipe, and are electrically connected to each other;
A pair of first electrodes that extend along the axial direction of the steel pipe and that are opposed to each other across the steel pipe along a second direction orthogonal to the axial direction of the steel pipe and the first direction, and are electrically connected to each other. 3 coils,
A magnetizing device comprising a three-phase AC power source for supplying an AC current to each of the first coil, the second coil, and the third coil;
Output from the three-phase AC power supply so that at least one of the AC currents supplied to the first coil, the second coil, and the third coil has a frequency different from that of the remaining AC current. The frequency of the alternating current is converted, the alternating current after the frequency conversion is supplied to the first coil, the second coil, and the third coil, and a magnetic field vector formed by the magnetizing device is A magnetizing apparatus for magnetic flaw detection of a steel pipe, comprising a frequency conversion circuit for following all directions along the inner and outer surfaces.

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