JP2007298482A - Magnetic particle inspection device for steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic particle inspection device for a steel pipe capable of certainly detecting a flaw in all directions on the outer peripheral surface and inner peripheral surface in a predetermined range of the steel pipe. <P>SOLUTION: The magnetic particle inspection device for the steel pipe magnetizes the steel pipe with a composite magnetic field by a magnetization coil for generating magnetic fluxes in three axes orthogonal to each other around the steel pipe. The magnetic particle inspection device comprises one pair of first magnetization coils Lx that are arranged in facing positions along the pipe radial direction outside the steel pipe and generate a magnetic flux in the pipe radial direction, one pair of second magnetization coils Ly that are arranged in facing positions outside the steel pipe orthogonal to the facing direction of the coils Lx and generate a magnetic flux in the pipe radial direction, and one pair of third magnetization coils Lz that are wound around the steel pipe, are arranged in facing positions gripping the first and second magnetization coils in the pipe axis direction, and generate a magnetic flux in the pipe radial direction. These magnetization coils Lx, Ly and Lz include respective excitation circuits for supplying magnetizing currents of frequencies that are lower than 50 Hz and have a relation of mutually non-integral multiple. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention provides a magnetic particle flaw detector for a steel pipe that includes a triaxial magnetizing coil that surrounds a steel pipe and generates magnetic fluxes in three axial directions orthogonal to each other, and the generated magnetic fluxes are combined to permeate the steel pipe. It is about.

  As is well known, the principle of a magnetic particle flaw detector is to magnetize the surface of a magnetic material and then spray the magnetic powder before or after it, and if there are scratches such as cracks, magnetic poles are generated according to the shape and the distribution of magnetic particles When the pattern is formed by changing the density, flaw detection is performed by observing the fluorescent magnetic powder pattern by ultraviolet irradiation. At that time, if the direction of the magnetic flux is aligned with the direction of the crack, it is not effectively magnetized. Therefore, it is preferable to generate the magnetic flux in the cross direction or particularly in the orthogonal direction. Therefore, Patent Document 1 discloses a steel tube by combining two single-pole yokes in a cross shape to form a composite yoke, and applying a current having a phase difference to the magnetic poles of each single-pole yoke to generate a circular magnetic field. There is disclosed a magnetic particle flaw detector for a steel pipe that enables the flaw detection of the outer peripheral surface and the inner peripheral surface of the end portion of the steel pipe and the end face in order by rotating the steel pipe across the end of the body portion of the steel pipe. According to Patent Document 2, instead of excitation having a phase difference, a plurality of magnetizing coils are supplied with alternating currents having different frequencies, and the direction of detection sensitivity is eliminated by vector composition of magnetic field lines. A magnetic device for flaw detection is also disclosed.

On the other hand, according to Patent Document 3, in order to detect flaws in a steel pipe, a first magnetization means for generating a direct current or an alternating magnetic field in the pipe axis direction of the steel pipe in which magnetic powder is dispersed on the surface, and a direction orthogonal to the pipe axis direction Discloses a magnetic particle flaw detector provided with a second magnetization means for transversely magnetizing a steel pipe by generating a rotating magnetic field.
JP-A-6-249835 JP-A-11-160283 Japanese Patent Laid-Open No. 7-253412

  The method according to Patent Document 3 is a method in which the magnetic flux in the tube axis direction is periodically deflected laterally by the magnetic flux in the tube radial direction by combining the magnetic field in the tube axis direction and the rotating magnetic field in the direction orthogonal thereto. The scratches on the end face are detected regardless of the direction, but if the magnetic flux in the tube axis direction is simply deflected by the rotating magnetic field in the orthogonal direction, a circular magnetic field along the tube peripheral surface as in Patent Document 1, that is, It is not possible to generate a magnetic field that changes direction over a range of 360 °. Further, Patent Document 2 does not mention the point of generating a magnetic field in any direction along the pipe peripheral surface. In addition, Patent Document 3 does not mention the flaw detection on the inner peripheral surface of the steel pipe, and Patent Document 1 can only flaw the inner peripheral surface of the pipe end. Furthermore, when the inner diameter is reduced, the yoke needs to be correspondingly reduced in size, and its cooling is also required due to a reduction in efficiency. Conventionally, a method of inserting a magnetizing coil separately has been employed for flaw detection in a region that has penetrated into the inner peripheral surface of a steel pipe.

  In view of such a point, the present invention provides a magnetic particle flaw detector for a steel pipe that can reliably detect scratches in all directions on an outer peripheral surface and an inner peripheral surface of a predetermined range of a steel pipe having a normal thickness. With the goal.

  In order to achieve this object, the present invention provides a magnetic powder for a steel pipe according to claim 1, wherein the steel pipe is magnetized by a synthetic magnetic field generated by a magnetizing coil that surrounds the steel pipe and generates magnetic flux in three axial directions perpendicular to each other. In the flaw detection apparatus, a first pair of magnetized coils that are arranged at opposing positions along the pipe radial direction outside the steel pipe and generate magnetic flux in the pipe radial direction, and are opposed to the outside of the steel pipe perpendicular to the opposing direction. A second pair of magnetized coils that are arranged at positions and generate magnetic flux in the radial direction of the tube, and are positioned so as to surround the steel pipe, and at opposite positions sandwiching the first and second magnetized coils in the tube axis direction And a third pair of magnetizing coils that generate magnetic flux in the tube axis direction by being arranged, and the first, second, and third magnetizing coils have a relationship lower than 50 Hz and a non-integer multiple of each other. Circuit for supplying a magnetizing current of a frequency having Steel pipe for magnetic particle flaw detection apparatus characterized in that it comes respectively.

  As a result, by the excitation of the frequency having a non-integer multiple relationship, three of the uniaxial magnetic flux in any forward / reverse direction and the remaining two axial forward / reverse magnetic fluxes are generated inside the orthogonal triaxial magnetizing coil. The combined magnetic flux of one axis, the biaxial synthetic magnetic flux of one uniaxial magnetic flux in the forward / reverse direction and the remaining one axial forward / reverse magnetic flux, and the uniaxial magnetic flux in either forward / reverse direction for a predetermined time. Magnetic fields are generated in all directions that change with time along the circumferential surface and the end surface of the steel pipe. Corresponding to a frequency lower than that of a general commercial power source, the inner peripheral surface can also be flawed by magnetization from the outside of the steel pipe.

  In particular, in order to enable flaw detection on the inner peripheral surface of a thick steel pipe, the frequencies having a non-integer multiple relationship with each other are made lower than 10 Hz.

  According to the first aspect of the present invention, the magnetic flux changes in all directions along the circumferential surface of the steel pipe or the end face of the steel pipe surrounded by the magnetizing coil by synthesizing the magnetic fluxes in the orthogonal three-axis directions with different frequencies of non-integer multiples. A magnetic field is formed, enabling highly reliable flaw detection regardless of the direction of the flaw. Moreover, the flaw detection of the inner peripheral surface of a steel pipe having a thickness of about 5 mm is also possible by a synthetic magnetic field having a frequency lower than 50 Hz. According to the invention of claim 2, flaw detection can be performed on the inner peripheral surface of a steel pipe having a wall thickness of about 18 mm.

  A magnetic particle flaw detector for steel pipes according to an embodiment of the present invention will be described with reference to FIGS. The flaw detection coil is a pair of magnetizing coils Lx arranged at opposite positions in the vertical X-axis direction passing through the center of the steel pipe to be inspected, opposite in the horizontal Y-axis direction passing through the steel pipe center and orthogonal to the X-axis. A pair of magnetizing coils Ly arranged at a position, and a pair of magnetizing coils arranged between the magnetizing coils Lx and Ly at opposite positions in the Z-axis direction passing through the center of the steel pipe and orthogonal to the X-axis and Y-axis Lz.

  The magnetizing coils Lx and Ly are attached by fitting their air core portions to the protruding portions 1a of the square yoke 1 surrounding the outer peripheral surface of the steel pipe 1, and around the X axis and the Y axis, respectively. It is wound nine times and generates magnetic flux in the tube diameter direction perpendicular to each other. The magnetizing coil Lz is wound nine times so as to surround the steel pipe to be inspected, and is attached to the tip of a U-shaped bracket 2 attached to the yoke 1 in the transverse direction. The pair of magnetizing coils Lx, Ly, and Lz are connected in series so as to generate magnetic fluxes in the same direction along the X axis, the Y axis, and the Z axis, respectively. The separation distance between each pair of magnetizing coils Lx and Ly located outside the steel pipe is set to be, for example, about 35 cm larger than the outer diameter of the steel pipe to be inspected, and the inner diameter of the magnetizing coil Lz is set to about 35 cm. The separation distance in the tube axis direction is set to about 40 cm corresponding to the width of the magnetizing coils Lx and Ly.

  As shown in FIG. 3, the magnetizing coils Lx, Ly, and Lz include rectifier circuits 1x, 1y, and 1z that receive a three-phase commercial AC voltage of 50 or 60 Hz, and attached switching control means 3x, 3y, and 3z. Each of the inverters 2x, 2y, 2z composed of controlled thyristors is provided, and an excitation circuit for supplying an alternating magnetizing current of about 600 A, for example, to the associated magnetizing coils Lx, Ly, Lz is attached. The switching control means 3x performs switching control so that the inverter 2x performs DC / AC conversion, and outputs a 9 Hz magnetizing current. The switching control means 3y causes the inverter 2y to output a magnetizing current of 7 Hz, and the switching control means 3z causes the inverter 2z to output a magnetizing current of 5 Hz.

  Since these excitation frequencies have a non-integer multiple relationship, a synthetic magnetic field whose direction changes based on magnetic fluxes φx, φy, and φz in which the relationship between each other's strength and polarity changes over time over a plurality of periods, It occurs in the magnetizing coils Lx, Ly, Lz. Further, although it is generally known that the permeability depth to the iron material becomes deeper as the frequency is lowered according to the following formula, the steel pipe body is set by lowering the commercial power supply frequency of 50 Hz by a test. It has been confirmed that even when the thickness of the portion is about 5 mm, the inner peripheral surface can be sufficiently reached, and when the thickness is 10 Hz or less, even the thickness of about 18 mm can be sufficiently permeable to the inner peripheral surface of the steel pipe.

δ = √ {ρ / (πμf)}
δ: penetration depth [m], μ: permeability, ρ: resistivity [Ωm], f: frequency [Hz]

  The operation of the magnetic particle flaw detector for steel pipes configured as described above is as follows. For example, a steel pipe 9 having an outer diameter of 30 cm and a wall thickness of 18 mm is sprayed with magnetic powder liquid on the outer peripheral surface, the inner peripheral surface, and the end surfaces of both end portions, and between the air core portion of the magnetizing coil Lz and the magnetizing coils Lx and Ly When the associated magnetization current is supplied in the state of being inserted at the center position, as shown in FIG. 5A, a magnetic flux of 5 Hz in which the strength in the tube axis direction is changed by the pair of magnetization coils Lz inside the flaw detection coil. φz is generated in the forward direction and the reverse direction, and the magnetizing coil Lx changes the forward and reverse vertical strength as seen in FIG. A magnetic flux φy of 7 Hz is generated.

  As a result, a combined magnetic field is generated by the orthogonal three-axis magnetic fluxes φx, φy, and φz in the entire region of the steel pipe 9 having a high permeability. FIG. 4 shows the respective magnetization currents from the time when the phase positions 0 ° are aligned with each other. Actually, as shown in Table 1 below for 1 second, various values are obtained with respect to φz due to the + amplitude excitation current. In the illustrated timings a to i, a combined magnetic field is formed by the magnetic fluxes φx and φy in the ± X or ± Y axis directions in the remaining two-axis tube cross sections. That is, + φz in the tube axis direction along the tube peripheral surface is deflected in the lateral direction, and the magnetic field whose direction and strength change from the tube axis direction to the orthogonal direction on the tube peripheral surface according to the amplitude relationship of each excitation current. Will occur. At φz = 0, a completely transverse magnetic field perpendicular to the Y-axis direction in the X-axis or Y-axis direction is also generated, and a similar magnetic field is formed for −φz in the reverse tube axis direction.

  After the next 1 second, the phase positions are shifted from each other by a non-integer multiple from the state in which the phases are aligned at 0 °, so that the phase position is shifted from each other by the magnetic fluxes φx, φy, and φz over the next 1 second. Forms a composite magnetic field under different polarity and strength relationships. In fact, in about 10 seconds, a magnetic field whose direction changes in the range of 360 ° with sufficient strength is generated along the peripheral surface of the tube, and scratches in all directions on the outer peripheral surface and the inner peripheral surface are detected. It has been confirmed. That is, even if a weak magnetic field is changed, as shown in FIG. 5B, the polarity is reversed in the tube axis direction, and a sufficiently strong magnetic field φ changes along the tube peripheral surface while changing the direction. It is generated in the range of 360 °. Even along the end face of the steel tube, when φz = 0, a combined magnetic field of φx and φy generates a sufficiently strong magnetic field whose direction changes in the range of 360 °. The least common multiple of each frequency 9, 7, and 5 corresponds to 315, that is, 315 cycles of 35 seconds of 9 Hz, which is the shortest cycle, and 245 cycles of 7 Hz and 175 cycles of 5 Hz are combined into one cycle. The synthetic magnetic field is periodically generated with a pattern period of 35 seconds. As described above, a sufficient rotating magnetic field can be obtained within the range.

  Thus, a steel tube having a high magnetic permeability is obtained by a combined magnetic field of a magnetic flux φx of 9 Hz along the pipe radial direction and a magnetic flux φy of 7 Hz along the orthogonal pipe radial direction and a magnetic flux φz of 5 Hz along the pipe axis direction. A magnetic field whose direction changes in a range of 360 ° along the entire area of the inner peripheral surface by deeply penetrating not only the outer peripheral surface but also the inner peripheral surface is formed in the body portion 9. Therefore, flaws in all directions are reliably detected by the disturbance of the fluorescent magnetic powder pattern caused by ultraviolet irradiation. Thereby, the steel pipe 9 is slid for every flaw detection in a predetermined range by excitation for 10 seconds, and the whole area is flaw detected. At both ends in the tube axis direction of the steel pipe 9, a combined magnetic field whose direction changes in the range of 360 ° along the end surface is generated by the magnetic flux φx and the magnetic flux φy, and the flaw is similarly detected. In particular, when the inner diameter becomes small and it is difficult to visually check the inner peripheral surface, it can be observed with a scope.

  Incidentally, regardless of the non-integer multiple relationship, if at least two axes have an integral multiple relationship, such as 5, 7, 10 Hz, or 4, 8, 10 Hz, for example, 5 Hz or Two-axis composite magnetic flux having the same pattern is repeatedly generated at 4 Hz, and the direction change of the composite magnetic field is restricted. When the thickness of the steel tube body is reduced, it can be configured as an excitation switching type to a higher frequency having a non-integer multiple relationship when the thickness is about 11, 13, 15 Hz or even thinner.

It is a front view of the magnetic particle flaw detector for steel pipes by embodiment of this invention. It is a perspective view explaining the arrangement | positioning relationship of the orthogonal three-axis magnetizing coil of the same magnetic particle flaw detector. It is a figure which shows the excitation circuit of the same magnetic particle flaw detector. It is a figure explaining the phase relationship of the magnetizing current which the same excitation circuit outputs. It is a figure explaining operation | movement of the same magnetic particle flaw detector.

Explanation of symbols

9 Steel tube Lx Magnetization coil in X-axis direction Ly Magnetization coil in Y-axis direction Lz Magnetization coil in Z-axis direction

Claims (2)

In a magnetic particle flaw detector for a steel pipe that is adapted to magnetize the steel pipe by a synthetic magnetic field generated by a magnetization coil that generates magnetic flux in three axial directions that are orthogonal to each other surrounding the steel pipe,
A first pair of magnetizing coils that are arranged at opposing positions along the pipe radial direction outside the steel pipe and generate magnetic flux in the pipe radial direction, and are arranged at opposing positions outside the steel pipe perpendicular to the opposing direction. And a second pair of magnetized coils that generate magnetic flux in the tube radial direction and a position that is wound around the steel tube and sandwiches the first and second magnetized coils in the tube axis direction. A third pair of magnetizing coils that generate magnetic flux in the tube axis direction by being disposed;
The first, second and third magnetizing coils are each provided with an excitation circuit for supplying a magnetizing current having a frequency lower than 50 Hz and having a non-integer multiple relationship with each other. Magnetic particle inspection equipment.   2. A magnetic particle flaw detector for steel pipes according to claim 1, wherein the frequencies having a non-integer multiple relationship are all lower than 10 Hz.

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