Abstract:
An eddy-current flaw detection device comprises a magnetic element group of which a specified number of magnetic elements are evenly spaced in each of at least two rows around the surface of a column shaped casing that can be inserted into a conductive pipe, with one row being located at a different position from the other row by ½ the even spacing in the row direction, and switching circuits for switching the magnetic elements in the respective row at time-division. The elements of one row function as magnetic field excitation elements, the elements of the other row function as magnetic field detection elements, and the eddy-current flaw detection device performs eddy-current flaw detection of the conductive pipe by detecting magnetic field excited by magnetic field excitation element by two magnetic field detection elements located at different positions from the magnetic field excitation elements by 3/2 the even spacing.

Description:
[0001]    This application is the normal phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP2008/065504 which has an International filing data of Aug. 29, 2008 and designated the United States of America. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to improvements of an eddy-current flaw detection method, eddy-current flaw detection device and eddy-current flaw detection probe that are used in nondestructive inspection (eddy-current flaw detection testing) of a heat transfer pipe inside of a heat exchanger. 
         [0004]    2. Description of Related Art 
         [0005]      FIG. 1  is a perspective drawing schematically illustrating the external appearance of a conventional eddy-current flaw detection probe that is used in an eddy-current flaw detection device for a slim metal pipe, which is a heat transfer pipe (conductive pipe) inside of a heat exchanger. 
         [0006]    Eddy-current flaw detection testing is a nondestructive inspection that applies a magnetic field that changes over time (AC current or the like) to a conductor, and detects when an eddy current, which occurs in the conductor, changes due to flaws; and in eddy-current flaw detection testing of a slim metal pipe, detection is performed while moving an eddy-current flaw detection probe that has been gently inserted inside the slim metal pipe. 
         [0007]    This eddy-current flaw detection probe comprises a column-shaped casing (housing)  141  that is formed such that it can be gently inserted inside a slim metal pipe, and eight coils  111  to  118 ,  121  to  128 ,  131  to  138 , that are aligned around the outer surface of the casing  141 , are evenly spaced in each of three rows. The coils  111  to  118  of the first row of the three rows are arranged such that they are located at a position in the circumferential direction that differs from that of the coils  121  to  128  and  131  to  138  of the other two rows by ½ the equal spacing between coils. 
         [0008]      FIG. 2  is a block diagram illustrating the circuit construction inside the casing  141  and eddy-current flaw detection device. 
         [0009]    The coils  111  to  118  in the first row are coils that are jointly used as magnetic field excitation coils and magnetic field detection coils, and each of these is connected to a multiplexer (switching circuit)  151  for magnetic field excitation, and to a multiplexer (switching circuit)  152  for magnetic field detection. 
         [0010]    A lead wire  159  is connected to the multiplexer  151  for magnetic field excitation, and an AC current for exciting a magnetic field is applied to the lead wire  159  from the main unit  164  of the eddy-current flaw detection device. An amplifier  156 , which amplifies the output signal of the magnetic field that is detected by the coils  111  to  118 , is connected to the multiplexer  152  for magnetic field detection, and the signal that is amplified by the amplifier  156  is outputted to the main unit  164  of the eddy-current flaw detection device via a lead wire  160 . 
         [0011]    Moreover, the coils  121  to  128  in the second row are also coils that are jointly used as magnetic field excitation coils and magnetic field detection coils, and each of these coils is connected to a multiplexer (switching circuit)  153  for magnetic field excitation, and to a multiplexer (switching circuit)  154  for magnetic field detection. 
         [0012]    A lead wire  161  is connected to the multiplexer  153  for magnetic field excitation, and an AC current for exciting a magnetic field is applied to the lead wire  161  from the main unit  164  of the eddy-current flaw detection device. An amplifier  157 , which amplifies the output signal of the magnetic field that is detected by the coils  121  to  128 , is connected to the multiplexer  154  for magnetic field detection, and the signal that is amplified by the amplifier  157  is outputted to the main unit  164  of the eddy-current flaw detection device via a lead wire  162 . 
         [0013]    The coils  131  to  138  in the third row are magnetic field detection coils, and each of these is connected to a multiplexer (switching circuit)  155  for magnetic field detection. 
         [0014]    An amplifier  158 , which amplifies the output signal of the magnetic field that is detected by the coils  131  to  138 , is connected to the multiplexer  155  for magnetic field detection, and the signal that is amplified by the amplifier  158  is outputted to the main unit  164  of the eddy-current flaw detection device via a lead wire  163 . 
         [0015]    As shown in  FIG. 1 , the lead wires  159  to  163  are stored inside a cable  142  that connects the center section of the surface on one end of the casing  141  of the eddy-current flaw detection probe with the main unit  164  of the eddy-current flaw detection device. 
         [0016]    An oscillation circuit  165  that produces an AC current for exciting a magnetic field by coils  111  to  118  and  121  to  128 , a signal detection circuit  166  that obtains amplified detection signals of magnetic fields that are detected by coils  111  to  118 ,  121  to  128  and  131  to  138 , and a communication unit  167  for communicating with a personal computer (or workstation)  168  are stored inside of the main unit  164  of the eddy-current flaw detection device. The personal computer  168  receives the detection signal that was obtained by the signal detection circuit  166  via the communication unit  167  as detection data, and records and displays the received detection data. 
         [0017]      FIGS. 3A to 3D  are expanded views explaining the operation of an eddy-current flaw detection probe having this kind of construction, and illustrating a planar expansion of the coils  111  to  118 ,  121  to  128  and  131  to  138  shown in  FIG. 1 . 
         [0018]    According to such eddy-current flaw detection probe, in a first timeslot representing operation cycle ( FIG. 3A ), the multiplexer  151  selects coil  111  as the magnetic field excitation coil T, and multiplexer  152  selects coil  113 , which is located at a position that differs two coils amount ahead of coil  111  in the circumferential direction of selection, as the magnetic field detection coil R. In addition, multiplexer  155  selects coils  131  and  132  in the third row, which are separated from coil  111  by an amount of 0.5 coil in the circumferential direction, as magnetic field detection coils R. 
         [0019]    According to the eddy-current flaw detection probe, in a second timeslot ( FIG. 3B ), the multiplexer  153  selects coil  121  in the second row, which is located at a position that differs 0.5 coil amount behind coil  111  in the circumferential direction of selection, as the magnetic field excitation coil T, and the multiplexer  154  selects coil  123 , which is located at a position that differs two coils amount ahead of coil  121  in the circumferential direction of selection, as the magnetic field detection coil R. 
         [0020]    After that, in odd number timeslots, the multiplexer  151  sequentially selects coils  112 ,  113 ,  114 , . . . as the magnetic field excitation coil T, and the multiplexer  152  sequentially selects coils  114 ,  115 ,  116 , . . . as the magnetic field detection coil R. Moreover, the multiplexer  155  sequentially selects two coils  132 • 133 ,  133 • 134 ,  134 • 135 , . . . as magnetic field detection coils R. 
         [0021]    In even number timeslots, the multiplexer  153  sequentially selects coils  122 ,  123 ,  124 , . . . as the magnetic field excitation coil T, and the multiplexer  154  sequentially selects coils  124 ,  125 ,  126  as the magnetic field detection coil R. 
         [0022]    According to the eddy-current flaw detection probe, in a fifteenth timeslot ( FIG. 3C ), the multiplexer  151  selects coil  118  as the magnetic field excitation coil T, and the multiplexer  152  selects coil  112 , which is located at a position that differs two coils amount ahead of coil  118  in the circumferential direction of selection, as the magnetic field detection coil R. In addition, the multiplexer  155  selects coils  138 ,  131  in the third row, which are separated from coil  118  by an amount of 0.5 coil in the circumferential direction, as magnetic field detection coils R. 
         [0023]    According to the eddy-current flaw detection probe, in a sixteenth timeslot ( FIG. 3D ), the multiplexer  153  selects coil  128  in the second row, which is located at a position that differs 0.5 coil amount behind coil  118  in the circumferential direction of selection, as the magnetic field excitation coil T, and the multiplexer  154  selects coil  122 , which is located at a position that differs two coils amount ahead of coil  128  in the circumferential direction of selection, as the magnetic field detection coil R. 
         [0024]    From the above, this flaw detection probe can obtain, for each circumference around a slim metal pipe, eight channels of output from coils  111  to  118  for detecting flaws in the circumferential direction, eight channels of output from coils  121  to  128  for detecting flaws in the circumferential direction, and 16 channels of output from coils  131  to  138  for detecting flaws in the axial direction. The output signals from coils  111  to  118  and the output signals from coils  121  to  128  are in a positional relationship that interpolate between each other in the circumferential direction, so the output for detecting flaws in the circumferential direction becomes a total of 16 channels. 
         [0025]    Japanese Patent Application Laid-Open No. 2000-235018 discloses an eddy-current flaw detection probe that comprises a plurality of excitation coils, a plurality of detection coils, and a switching circuit for time-division driving of these coils, and that further comprises an insulation switching circuit between the coils and switching circuit. 
         [0026]    Japanese Patent Application Laid-Open No. 2000-235019 discloses an eddy-current flaw detection probe that comprises a plurality of magnet field excitation elements, a plurality of magnetic field detection elements, a switching circuit for time-division driving of these elements, and a detection signal amplification circuit that is provided further on the measurement instrument side than the switching circuit that time-division drives the plurality of magnetic field detection elements. 
         [0027]    Japanese Patent Application Laid-Open No. 2000-235020 discloses an eddy-current flaw detection device that comprises an eddy-current flaw detection probe having a plurality of magnetic field excitation elements and magnetic field detection element pairs, and means for time-division driving of the magnetic field excitation elements and magnetic field detection element pairs of that probe, and further comprises a control device that includes means for keeping output signals from each element pair over a number of time-division driving steps, and means for finding the difference between the output signals from adjacent element pairs. 
       SUMMARY 
       [0028]    In the conventional eddy-current flaw detection probe described above, there is a positional shift in the axial direction between the output of the 8 channels from coils  111  to  118  and the output of the 8 channels from coils  121  to  128  for detecting flaws in the circumferential direction, and when there is fluctuation in the scanning speed of the eddy-current flaw detection probe, it is difficult to compensate for that positional shift in the axial direction. When it is not possible to compensate for the positional shift in the axial direction, there are problems that the spatial resolution of the flaw detection signals drops, as well as the signal reproducibility during redetection of flaws drops. 
         [0029]    Moreover, in the eddy-current flaw detection probe described above, coils  111  to  118  and  121  to  128  are jointly used as magnetic field excitation coils and magnetic field detection coils, and are connected to both a switching circuit for magnetic field excitation and a switching circuit for magnetic field detection, so there are problems that circuit construction becomes complicated, and interference signals due to crosstalk occur. 
         [0030]    The present invention has been made with the aim of solving the above problems, and it is an object of first to third aspects of the invention to provide an eddy-current flaw detection method that improves the spatial resolution of flaw detection signals and the signal reproducibility during redetection of flaws, and reduces signal interference due to crosstalk with a simple circuit construction. 
         [0031]    The object of fourth to ninth aspects of the invention is to provide an eddy-current flaw detection device that improves the spatial resolution of flaw detection signals and the signal reproducibility during redetection of flaws, and reduces signal interference due to crosstalk with a simple circuit construction. 
         [0032]    The object of tenth to fifteenth aspects of the invention is to provide an eddy-current flaw detection probe that improves the spatial resolution of flaw detection signals and the signal reproducibility during redetection of flaws, and reduces signal interference due to crosstalk with a simple circuit construction. 
         [0033]    The eddy-current flaw detection method according to a first aspect of the invention is an eddy-current flaw detection method for performing eddy-current flaw detection of a conductive pipe by using a magnetic element group of which a specified number of elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into the conductive pipe, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction, and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division; and is characterized by comprising: a step of causing the switching circuit to switch magnetic elements in one row at time-division in order to excite a magnetic field; and a step of causing the switching circuit to switch, at time-division, two of the magnetic elements that are arranged in the other row and that are located at positions that differ from the magnetic element that excited the magnetic field by 3/2 the even spacing in the row direction in order to detect the excited magnetic field. 
         [0034]    The eddy-current flaw detection method according to a second aspect of the invention is an eddy-current flaw detection method for performing eddy-current flaw detection of a conductive pipe by using a magnetic element group of which a specified number of elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into the conductive pipe, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction, and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division; and is characterized by comprising: a step of preparing the magnetic elements in one row as magnetic field excitation elements that excite a magnetic field, and the magnetic elements in the other row as magnetic field detection elements that detect a magnetic field; a step of causing the switching circuit to switch magnetic field excitation elements at time-division in order to excite a magnetic field; and a step of causing the switching circuit to switch, at time-division, two of the magnetic field detection elements that are arranged in the other row and that are located at positions that differ from the magnetic field excitation element that excited the magnetic field by 3/2 the even spacing in the row direction in order to detect the excited magnetic field. 
         [0035]    The eddy-current flaw detection method according to a third aspect of the invention is characterized by comprising: a step of preparing a magnetic element group that is located in a row around the surface of the casing adjacent to the other row, and a switching circuit for switching the magnetic element group at time-division; and a step of causing the switching circuit to switch, at time-division, two magnetic elements that are located in the row in order to detect the excited magnetic field. 
         [0036]    The eddy-current flaw detection device according to a fourth aspect of the invention is an eddy-current flaw detection device for performing eddy-current flaw detection of a conductive pipe, and comprising: a magnetic element group of which a specified number of magnetic elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into the conductive pipe, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction; and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division, and is characterized by comprising: magnetic field excitation means for causing the magnetic elements in one row to function as magnetic field excitation elements that excite magnetic fields by being switched at time-division by the switching circuit; and magnetic field detection means for causing the magnetic elements in the other row to function as magnetic field detection elements that detect magnetic fields by being switched at time-division by the switching circuit, wherein the eddy-current flaw detection device performs eddy-current flaw detection of the conductive pipe by detecting each magnetic field that is excited by each magnetic field excitation element of the magnetic field excitation means by two magnetic field detection elements of the magnetic field detection means that are each located at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0037]    In the eddy-current flaw detection method according to the first aspect of the invention and the eddy-current flaw detection device according to the fourth aspect of the invention, a magnetic element group is provided of which a specified number of magnetic elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into the conductive pipe, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction, each switching circuit switches the magnetic elements in the respective row at time-division, and eddy-current flaw detection of the conductive pipe is performed. The magnetic elements in one row function as magnetic field excitation elements that excite magnetic fields by being switched at time-division, and magnetic elements in the other row function as magnetic field detection elements that detect magnetic fields by being switched at time-division. Eddy-current flaw detection of a conductive pipe is performed by detecting each magnetic field that is excited by each magnetic field excitation element by two of the magnetic field detection elements that are located at positions that differ from the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0038]    The eddy-current flaw detection device according to a fifth aspect of the invention is an eddy-current flaw detection device for performing eddy-current flaw detection of a conductive pipe, and comprising: a magnetic element group of which a specified number of magnetic elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into the conductive pipe, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction; and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division, and is characterized in that the magnetic elements in one row are magnetic field excitation elements that excite magnetic fields, the magnetic elements in the other row are magnetic field detection elements that detect magnetic fields, and eddy-current flaw detection of the conductive pipe is performed by detecting each magnetic field that is excited by each magnetic field excitation element being switched at time-division by the switching circuit by two magnetic field detection elements that are each located in the other row at positions that differ from the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0039]    In the eddy-current flaw detection method according to the second aspect of the invention and the eddy-current flaw detection device according to the fifth aspect of the invention, a magnetic element group is provided of which a specified number of magnetic elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into the conductive pipe, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction, each switching circuit switches the magnetic elements in the respective row at time-division, and eddy-current flaw detection of the conductive pipe is performed. The magnetic elements in one row are magnetic field excitation elements that excite a magnetic field, and the magnetic elements in the other row are magnetic detection elements that detect a magnetic field. Eddy-current flaw detection of the conductive pipe is performed by detecting each magnetic fields that are excited by each magnetic field excitation elements that are switched at time-division by two magnetic field detection elements that are each located in the other row at positions that differ from the magnetic field excitation element by 3/2 the even spacing in the row direction and that are switched at time-division. 
         [0040]    The eddy-current flaw detection device according to a sixth aspect of the invention is an eddy-current flaw detection device comprising a magnetic element group of which a specified number of magnetic elements are evenly spaced in each of at least two rows, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction, and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division; and is characterized by comprising: magnetic field excitation means for causing the magnetic elements in one row to function as magnetic field excitation elements that excite magnetic fields by being switched at time-division by the switching circuit, and magnetic field detection means for causing the magnetic elements in the other row to function as magnetic field detection elements that detect magnetic fields by being switched at time-division by the switching circuit, wherein the eddy-current flaw detection device performs eddy-current flaw detection by detecting each magnetic field that is excited by each magnetic field excitation element of the magnetic field excitation means by one or two magnetic field detection elements of the magnetic field detection means that are each located at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0041]    In the eddy-current flaw detection device according to the sixth aspect of the invention, a magnetic element group is provided of which a specified number of magnetic elements are evenly spaced in each of at least two rows, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction, and each switching circuit switches the magnetic elements of each row at time-division. The magnetic elements in one row function as magnetic field excitation elements that excite a magnetic field by being switched at time-division, and the magnetic elements in the other row function as magnetic detection elements that detect a magnetic field by being switched at time-division. Eddy-current flaw detection is performed by detecting each magnetic field that is excited by each magnetic field excitation element by one or two magnetic field detection elements that are each located at positions that differ from the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0042]    The eddy-current flaw detection device according to a seventh aspect of the invention is an eddy-current flaw detection device comprising: a magnetic element group of which a specified number of magnetic elements are evenly spaced in each of at least two rows, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction; and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division, and is characterized in that the magnetic elements in one row are magnetic field excitation elements that excite a magnetic field, the magnetic elements in the other row are magnetic field detection elements that detect a magnetic field, and eddy-current flaw detection is performed by detecting each magnetic field that is excited by each magnetic field excitation element that is switched at time-division by the switching circuit by one or two magnetic field detection elements that are each located in the other row at positions that differ from the magnetic field excitation element by 3/2 the even spacing in the row direction and that are switched at time-division by the switching circuit. 
         [0043]    In the eddy-current flaw detection device according to the seventh aspect of the invention, a magnetic element group is provided of which a specified number of magnetic elements are evenly spaced in each of at least two rows, with one of the two rows being located at a position that differs from the other row by ½ the even spacing in the row direction, and each switching circuit switches the magnetic elements in the respective row at time-division. The magnetic elements in one row are magnetic field excitation elements that excite a magnetic field, and the magnetic elements in the other row are magnetic field detection elements that detect a magnetic field. Eddy-current flaw detection is performed by detecting each magnetic field that is excited by each magnetic field excitation element that is switched at time-division by one or two magnetic field detection elements that are each located in the other row at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction and that are switched at time-division. 
         [0044]    The eddy-current flaw detection device according to an eighth aspect of the invention is characterized by further comprising a magnetic element group that is located in a row around the surface of the casing adjacent to the other row, and a switching circuit for switching the magnetic element group at time-division, and performing eddy-current flaw detection by detecting an excited magnetic field by two magnetic elements that are located in the row and that are switched by the switching circuit. 
         [0045]    In the eddy-current flaw detection method according to the third aspect of the invention and the eddy-current flaw detection device according to the eighth aspect of the invention, another magnetic element group is additionally located in a row around the surface of the casing adjacent to the other row, and that additionally provided magnetic element group is switched at time-division by an additionally provided switching circuit. Eddy-current flaw detection is performed by detecting an excited magnetic field by two magnetic elements that are located in the additional row and that are switched at time-division by the switching circuit. 
         [0046]    The eddy-current flaw detection device according to a ninth aspect of the invention is characterized by further comprising an amplifier circuit for amplifying a signal that each of the magnetic field detection elements outputted via the switching circuit. 
         [0047]    The eddy-current flaw detection probe according to a tenth aspect of the invention is an eddy-current flaw detection probe for performing eddy-current flaw detection of a conductive pipe, and comprising: a magnetic element group of which a specified number of elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into the conductive pipe, with one of the two rows being located at a position that differs from that of the other row by ½ the even spacing in the row direction; and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division, and is characterized in that the magnetic elements in one row are constructed as magnetic field excitation elements that excite a magnetic field by being switched at time-division by the switching circuit, the magnetic elements in the other row are constructed as magnetic field detection elements that detect a magnetic field by being switched at time-division by the switching circuit, and eddy-current flaw detection of the conductive pipe is performed by detecting each magnetic field that is excited by each magnetic element that functions as the magnetic field excitation element by two the magnetic elements that function as the magnetic field detection elements and that are located at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0048]    In the eddy-current flaw detection probe according to the tenth aspect of the invention, a magnetic element group is provided of which a specified number of elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into a conductive pipe, with one of the two rows being located at a position that differs from that of the other row by ½ the even spacing in the row direction. Eddy-current flaw detection is performed by causing the switching circuits to switch the magnetic elements in the respective row at time-division. The magnetic elements in one row function as magnetic field excitation elements that excite a magnetic field by being switched at time-division, and the magnetic elements in the other row function as magnetic field detection elements that detect a magnetic field by being switched at time-division. Eddy-current flaw detection of a conductive pipe is performed by detecting each magnetic field that is excited by each magnetic element that functions as the magnetic field excitation element by two of the magnetic elements that function as magnetic field detection elements and that are located at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0049]    The eddy-current flaw detection probe according to an eleventh aspect of the invention is an eddy-current flaw detection probe for performing eddy-current flaw detection of a conductive pipe, and comprising: a magnetic element group of which a specified number of elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into the conductive pipe, with one of the two rows being located at a position that differs from that of the other row by ½ the even spacing in the row direction; and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division, and is characterized in that the magnetic elements in one row are magnetic field excitation elements that excite a magnetic field, the magnetic elements in the other row are magnetic field detection elements that detect a magnetic field, and eddy-current flaw detection of the conductive pipe is performed by detecting each magnetic field that is excited by each magnetic field excitation element that is switched at time-division by the switching circuit by two magnetic field detection elements that are each located in the other row at positions that differ from the magnetic field excitation element by 3/2 the even spacing in the row direction and that are switched at time-division by the switching circuit. 
         [0050]    In the eddy-current flaw detection probe according to the eleventh aspect of the invention, a magnetic element group is provided of which a specified number of magnetic elements are evenly spaced in each of at least two rows that are formed around the surface of a column shaped casing that is formed such that it can be inserted into a conductive pipe, with one of the two rows being located at a position that differs from that of the other row by ½ the even spacing in the row direction. Eddy-current flaw detection is performed by causing the switching circuits to switch the magnetic elements in the respective row at time-division. The magnetic elements in one row are magnetic field excitation elements that excite a magnetic field, and the magnetic elements in the other row are magnetic field detection elements that detect a magnetic field. Eddy-current flaw detection of the conductive pipe is performed by detecting each magnetic field that is excited by each magnetic field excitation element that is switched at time-division by two magnetic field detection elements that are each located in the other row at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction and that are switched at time-division. 
         [0051]    The eddy-current flaw detection probe according to a twelfth aspect of the invention is an eddy-current flaw detection probe that comprises: a magnetic element group of which a specified number of elements are evenly spaced in each of at least two rows, with one of the two rows being located at a position that differs from that of the other row by ½ the even spacing in the row direction; and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division, and is characterized in that the magnetic elements in one row are constructed as magnetic field excitation elements that excite a magnetic field by being switched at time-division by the switching circuit, the magnetic elements in the other row are constructed as magnetic field detection elements that detect a magnetic field by being switched at time-division by the switching circuit, and eddy-current flaw detection is performed by detecting each magnetic field that is excited by each magnetic element that functions as a magnetic field excitation element by one or two of the magnetic elements that function as the magnetic field detection elements and that are located at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0052]    In the eddy-current flaw detection probe according to the twelfth aspect of the invention, a magnetic element group is provided of which a specified number of magnetic elements are evenly spaced in each of at least two rows, with one of the two rows being located at a position that differs from that of the other row by ½ the even spacing in the row direction, and each switching circuit switches the magnetic elements in the respective row at time-division. The magnetic elements in one row function as magnetic field excitation elements that excite a magnetic field by being switched at time-division, and the magnetic elements in the other row function as magnetic field detection elements that detect a magnetic field by being switched at time-division. Eddy-current flaw detection is performed by detecting each magnetic field that is excited by each magnetic element that functions as the magnetic field excitation element by one or two of the magnetic elements that function as the magnetic field detection elements and that are located at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction. 
         [0053]    The eddy-current flaw detection probe according to a thirteenth aspect of the invention is an eddy-current flaw detection probe that comprises: a magnetic element group of which a specified number of elements are evenly spaced in each of at least two rows, with one of the two rows being located at a position that differs from that of the other row by ½ the even spacing in the row direction; and switching circuits for switching the magnetic elements in the respective row of the magnetic element group at time-division, and is characterized in that the magnetic elements in one row are magnetic field excitation elements that excite a magnetic field, the magnetic elements in the other row are magnetic field detection elements that detect a magnetic field, and eddy-current flaw detection is performed by detecting each magnetic field that is excited by each magnetic field excitation element that is switched at time-division by the switching circuit by one or two magnetic field detection elements that are each located in the other row at positions that differ from the magnetic field excitation element by 3/2 the even spacing in the row direction and that are switched at time-division by the switching circuit. 
         [0054]    In the eddy-current flaw detection probe according to the thirteenth aspect of the invention, a magnetic element group is provided of which a specified number of magnetic elements are evenly spaced in each of at least two rows, with one of the two rows being located at a position that differs from that of the other row by ½ the even spacing in the row direction, each switching circuit switches the magnetic elements in the respective row at time-division. The magnetic elements in one row are magnetic field excitation elements that excite a magnetic field, and the magnetic elements in the other row are magnetic field detection elements that detect a magnetic field. Eddy-current flaw detection is performed by detecting each magnetic field that is excited by each magnetic field excitation element that is switched at time-division by one or two magnetic field detection elements that are each located in the other row at positions that differ from that of the magnetic field excitation element by 3/2 the even spacing in the row direction and that are switched at time-division. 
         [0055]    The eddy-current flaw detection probe according to a fourteenth aspect of the invention is characterized by further comprising: a magnetic element group that is located in a row around the surface of the casing adjacent to the other row; and a switching circuit for switching the magnetic element group at time-division, and performing eddy-current flaw detection by detecting the excited magnetic field by two magnetic elements that are located in the row and that are switched at time-division. 
         [0056]    In the eddy-current flaw detection probe according to the fourteenth aspect of the invention, a magnetic element group is additionally provided in a row around the surface of the casing adjacent to the other row, and an additionally provided switching circuit switches the additionally provided magnetic element group at time-division. Eddy-current flaw detection is performed by detecting the excited magnetic field by switching two magnetic elements of that magnetic element group at time-division. 
         [0057]    The eddy-current flaw detection probe according to a fifteenth aspect of the invention is characterized by further comprising an amplifier circuit for amplifying a signal that each of the magnetic field detection elements outputted via a switching circuit. 
         [0058]    With the eddy-current flaw detection method according to the first to third aspects of the invention, it is possible to provide an eddy-current flaw detection method that improves the spatial resolution of flaw detection signals as well as signal reproducibility during redetection of flaws, and reduces signal interference due to crosstalk with a simple circuit construction. 
         [0059]    With the eddy-current flaw detection device according to the fourth to ninth aspects of the invention, it is possible to provide an eddy-current flaw detection device that improves the spatial resolution of flaw detection signals as well as signal reproducibility during redetection of flaws, and reduces signal interference due to crosstalk with a simple circuit construction. 
         [0060]    With the eddy-current flaw detection probe according to the tenth to fifteenth aspects of the invention, it is possible to provide an eddy-current flaw detection probe that improves the spatial resolution of flaw detection signals as well as signal reproducibility during redetection of flaws, and reduces signal interference due to crosstalk with a simple circuit construction. 
         [0061]    The above and further objects and features will more fully be apparent from the following detailed description with accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0062]      FIG. 1  is a perspective drawing schematically illustrating the external appearance of a conventional eddy-current flaw detection probe; 
           [0063]      FIG. 2  is a block diagram illustrating the circuit construction inside the casing of a conventional eddy-current flaw detection probe and eddy-current flaw detection device; 
           [0064]      FIG. 3A  is an expanded view explaining the operation of a conventional eddy-current flaw detection probe during a first timeslot, and illustrating a planar expansion of the coils shown in  FIG. 1 ; 
           [0065]      FIG. 3B  is an expanded view explaining the operation of a conventional eddy-current flaw detection probe during a second timeslot, and illustrating a planar expansion of the coils shown in  FIG. 1 ; 
           [0066]      FIG. 3C  is an expanded view explaining the operation of a conventional eddy-current flaw detection probe during a fifteenth timeslot, and illustrating a planar expansion of the coils shown in  FIG. 1 ; 
           [0067]      FIG. 3D  is an expanded view explaining the operation of a conventional eddy-current flaw detection probe during a sixteenth timeslot, and illustrating a planar expansion of the coils shown in  FIG. 1 ; 
           [0068]      FIG. 4  is a perspective drawing schematically illustrating the external appearance of an eddy-current flaw detection probe that is used in an embodiment of a eddy-current flaw detection method, eddy-current flaw detection device and eddy-current flaw detection probe of the present invention; 
           [0069]      FIG. 5  is a block diagram illustrating circuit construction inside the casing of an eddy-current flaw detection probe and eddy-current flaw detection device of the present invention; 
           [0070]      FIG. 6A  is an expanded view explaining the operation of the eddy-current flaw detection method, eddy-current flaw detection device and eddy-current flaw detection probe of the present invention during a first timeslot, and illustrating a planar expansion of the coils shown in  FIG. 4 ; 
           [0071]      FIG. 6B  is an expanded view explaining the operation of the eddy-current flaw detection method, eddy-current flaw detection device and eddy-current flaw detection probe of the present invention during a second timeslot, and illustrating a planar expansion of the coils shown in  FIG. 4 ; 
           [0072]      FIG. 6C  is an expanded view explaining the operation of the eddy-current flaw detection method, eddy-current flaw detection device and eddy-current flaw detection probe of the present invention during a seventh timeslot, and illustrating a planar expansion of the coils shown in  FIG. 4 ; and 
           [0073]      FIG. 6D  is an expanded view explaining the operation of the eddy-current flaw detection method, eddy-current flaw detection device and eddy-current flaw detection probe of the present invention during an eighth timeslot, and illustrating a planar expansion of the coils shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0074]    The following description will explain the present invention in detail on the basis of the drawings illustrating some embodiments thereof. 
         [0075]      FIG. 4  is a perspective drawing schematically illustrating the external appearance of an eddy-current flaw detection probe that is used in an embodiment of the eddy-current flaw detection method, eddy-current flaw detection device and eddy-current flaw detection probe of the present invention. 
         [0076]    This eddy-current flaw detection probe comprises a column shaped casing (housing)  41  that is formed such that it can be gently inserted inside a slim metal pipe, and eight coils  11  to  18 ,  21  to  28 ,  31  to  38 , that are aligned around the outer surface of the casing  41 , are evenly spaced in each of three rows. The coils  11  to  18  of the first row of the three rows are arranged such that they are located at a position in the circumferential direction that differs from that of the coils  21  to  28  and  31  to  38  of the other two rows by ½ the equal spacing. 
         [0077]      FIG. 5  is a block diagram illustrating the circuit construction inside the casing  41  and eddy-current flaw detection device. 
         [0078]    The coils (magnetic elements, magnetic field excitation means)  11  to  18  in the first row are coils that are used as magnetic field excitation coils (magnetic field excitation elements) that generate an eddy current in the thickness section from the inner surface of a slim metal pipe, and each is connected to a multiplexer (switching circuit)  51  for magnetic field excitation. 
         [0079]    A lead wire  56  is connected to the multiplexer  51  for magnetic field excitation, and an AC current for exciting a magnetic field is applied to the lead wire  56  from the main unit  59  of the eddy-current flaw detection device. 
         [0080]    Moreover, the coils (magnetic elements, magnetic field detection means)  21  to  28  in the second row are coils that are used as magnetic field detection coils (magnetic field detection elements) that detect a magnetic field according to an eddy current that is generated in the thickness section of a slim metal pipe, and each is connected to a multiplexer (switching circuit)  52  for magnetic field detection. An amplifier (magnetic field detection means)  54 , which amplifies the output signals of the magnetic field that is detected by the coils  21  to  28 , is connected to the multiplexer  52  for magnetic field detection, and the amplified signal from the amplifier  54  is outputted to the main unit  59  of the eddy-current flaw detection device via a lead wire  57 . 
         [0081]    The coils (magnetic elements, magnetic field detection means)  31  to  38  in the third row are coils used for magnetic field detection, and each is connected to a multiplexer (switching circuit)  53  for magnetic field detection. An amplifier (magnetic field detection means)  55 , which amplifies the output signal of the magnetic field that is detected by the coils  31  to  38 , is connected to the multiplexer  53  for magnetic field detection, and the amplified signal from the amplifier  55  is outputted to the main unit  59  of the eddy-current flaw detection device via a lead wire  58 . 
         [0082]    As shown in  FIG. 4 , the lead wires  56  to  58  are stored inside a cable  42  that connects the center section of the surface on one end of the casing  41  of the eddy-current flaw detection probe with the main unit  59  of the eddy-current flaw detection device. 
         [0083]    An oscillation circuit (magnetic field excitation means)  60  that generates an AC current for exciting a magnetic field by the coils  11  to  18 , a signal detection circuit  61  that obtains amplified detection signals of magnetic fields they are detected by coils  21  to  28  and  31  to  38 , and a communication unit  62  for communicating with a personal computer (or workstation)  63  are located inside of the main unit  59  of the eddy-current flaw detection device. The personal computer  63  receives the detection signal that was obtained by the signal detection circuit  61  via the communication unit  62  as detection data, and records and displays the received detection data. 
         [0084]    The amplifiers  54  and  55  can also be located inside of the main unit  59  of the eddy-current flaw detection device, and when a small number of coils are in each row, the multiplexers  51  to  53  could also be located inside of the main unit  59  of the eddy-current flaw detection device. 
         [0085]      FIGS. 6A to 6D  are expanded views explaining the operation of an eddy-current flaw detection probe having this kind of construction, and illustrating a planar expansion of the coils  11  to  18 ,  21  to  28  and  31  to  38  shown in  FIG. 4 . 
         [0086]    This eddy-current flaw detection probe detects flaws for the amount of one circumference of the inner surface of a slim metal pipe in first through eighth timeslots indicating the cycle of the operation. 
         [0087]    According to the eddy-current flaw detection probe, in the first timeslot ( FIG. 6A ), the multiplexer  51  selects coil  11  as the magnetic field excitation coil T, and the multiplexer  52  selects coils  28  and  23  in the second row, which are separated from the coil  11  by the amount of 3/2 coils in the circumferential direction, as magnetic field detection coils R 1  and R 2 . In addition, the multiplexer  53  selects coils  31  and  32  in the third row, which are separated from coil  11  by the amount of 0.5 coil in the circumferential direction, as magnetic field detection coils R 3  and R 4 . 
         [0088]    The detection signals that are outputted by the magnetic field detection coils R 1 , R 2  are used for detecting flaws in the circumferential direction of the slim metal pipe (direction that orthogonally crosses the advancement direction of the eddy-current flaw detection probe), and the detection signals that are outputted by the magnetic field detection coils R 3 , R 4  are used for detecting flaws in the axial direction of the slim metal pipe (advancement direction of the eddy-current flaw detection probe). 
         [0089]    According to the eddy-current flaw detection probe, in the second timeslot ( FIG. 6B ), the multiplexer  51  selects coil  12  as the magnetic field excitation coil T, and the multiplexer  52  selects coils  21  and  24  in the second row, which are separated from the coil  12  by the amount of 3/2 coils in the circumferential direction, as magnetic field detection coils R 1  and R 2 . In addition, the multiplexer  53  selects coils  32  and  33  in the third row, which are separated from coil  12  by the amount of 0.5 coil in the circumferential direction, as magnetic field detection coils R 3  and R 4 . 
         [0090]    In each timeslot after that, the multiplexer  51  sequentially selects coils  13 ,  14 ,  15 , . . . as the magnetic field excitation coil T, and the multiplexer  52  sequentially selects pairs of coils  22 • 25 ,  23 • 26 ,  24 • 27 , . . . as the magnetic field detection coils R 1 •R 2 . In addition, the multiplexer  53  sequentially selects pairs of coils  33 • 34 ,  34 • 35 ,  35 • 36 , . . . as the magnetic field detection coils R 3 •R 4 . 
         [0091]    According to the eddy-current flaw detection probe, in the seventh timeslot ( FIG. 6C ), the multiplexer  51  selects coil  17  as the magnetic field excitation coil T, and the multiplexer  52  selects coils  26  and  21  in the second row, which are separated from the coil  17  by the amount of 3/2 coils in the circumferential direction, as magnetic field detection coils R 1  and R 2 . In addition, the multiplexer  53  selects coils  37  and  38  in the third row, which are separated from coil  17  by the amount of 0.5 coil in the circumferential direction, as magnetic field detection coils R 3  and R 4 . 
         [0092]    According to the eddy-current flaw detection probe, in the eighth timeslot ( FIG. 6D ), the multiplexer  51  selects coil  18  as the magnetic field excitation coil T, and the multiplexer  52  selects coils  27  and  22  in the second row, which are separated from the coil  18  by the amount of 3/2 coils in the circumferential direction, as magnetic field detection coils R 1  and R 2 . In addition, the multiplexer  53  selects coils  38  and  31  in the third row, which are separated from coil  18  by the amount of 0.5 coil in the circumferential direction, as magnetic field detection coils R 3  and R 4 . 
         [0093]    Depending on the first through eighth timeslots described above, the combinations of the magnetic field excitation coil T and magnetic field detection coil R 1 , and the magnetic field excitation coil T and magnetic field detection coil R 2  are suitably located for detecting flaws in the circumferential direction of the slim metal pipe (direction that orthogonally crosses the advancement direction of the eddy-current flaw detection probe). Also, the combinations of the magnetic field excitation coil T and the magnetic field detection coil R 3 , and the magnetic field excitation coil T and the magnetic field detection coil R 4  are suitably located for detecting flaws in the axial direction of the slim metal pipe (advancement direction of the eddy-current flaw detection probe). 
         [0094]    In the case of this embodiment, since output of the 16 channels by the coils  21  to  28  is obtained for the same circumference per one circumference of the slim metal pipe, there is no need for compensating for shifting in the axial direction, and thus the spatial resolution of flaw detection signals, and the reproducibility during redetection of flaws are improved. 
         [0095]    Moreover, as shown in  FIG. 5 , when compared with the conventional circuit shown in  FIG. 2 , there is no need for two multiplexers, as well as there is no need for wiring from coils  11  to  18  of the first row and coils  21  to  28  of the second row to each of the two multiplexers, so the circuit construction can be made more compact, and the entire circuit can be stored inside the casing  41  of the eddy-current flaw detection probe. In addition, by reducing the amount of wiring, interference signals due to crosstalk can be reduced. 
         [0096]    Depending on the performance and the like of the eddy-current flaw detection device, it is possible to combine two timeslots. For example, in the first timeslot, it is possible to simultaneously select coils  11  and  15  as magnetic field excitation coils, and to simultaneously select coils  31 ,  32 ,  28 ,  23 ,  35 ,  36 ,  24  and  27  as magnetic field detection coils. 
         [0097]    An amplifier circuit is normally necessary in order to amplify detection signals from the multiplexer, however, in cases where the deterioration of the detection signals is not especially a problem, it is also possible to omit the amplifier circuit. 
         [0098]    Moreover, this embodiment illustrates an example of an insert type probe that is inserted inside a slim metal pipe, however, the present invention can also be applied to a top placement type or penetrating type eddy-current flaw detection device and eddy-current flaw detection probe. 
         [0099]    Furthermore, in this embodiment, coils were used as both magnetic field excitation elements and magnetic field detection elements, however, the invention is not limited to this, and of course it is possible to use other elements. Also, a clear distinction is made between magnetic field excitation element groups and magnetic field detection element groups, so, for example, it is possible to combine different kinds of elements such using a coil as a magnetic field excitation element and using a magnetic detection element such as a hole element, magnetic resistance effect element and the like as a magnetic field detection element. 
         [0100]    Moreover, the direction of the coils is not limited to that shown in  FIG. 4 , and construction using other directions is possible. 
         [0101]    Furthermore, the number of coils is not necessarily limited to eight coils per row, and can be suitably increased or decreased as needed. In addition, similarly the number of channels of the multiplexer, which is a switching circuit, can be suitably increased or decreased as needed. Also, the most preferable location for the circuit to be located is inside the casing of the eddy-current flaw detection probe, however, in the case where that is physically impossible, the circuit can be provided inside of or around the pipe that stores the wiring. 
         [0102]    The present invention can be applied to an eddy-current flaw detection method, eddy-current flaw detection device and eddy-current flaw detection probe that are used in nondestructive inspection (eddy-current flaw detection testing) of a heat transfer pipe inside of a heat exchanger. 
         [0103]    As this description may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.