JP5233978B2 - Eddy current flaw detection method and gap forming member used therefor - Google Patents

Description

  The present invention relates to an eddy current flaw detection method and a gap forming member used therefor, and more particularly to an eddy current flaw detection method for a metal tube and a gap forming member used therefor.

  JP-A-2-66447 (Patent Document 1), JP-B-6-87051 (Patent Document 2), JP-A-2-208552 (Patent Document 3) and JP-A-2-173561 (Patent Document 4). ) Discloses an eddy current flaw detection apparatus and a eddy current flaw detection method for flaw detection of a steel pipe. The eddy current flaw detector disclosed in these documents includes a penetration coil. When the steel pipe to be inspected passes through the through coil, it receives a magnetic flux from the through coil. An eddy current is generated in the steel pipe by the magnetic flux. If there is a flaw in the steel pipe, the eddy current is disturbed. The eddy current flaw detector detects eddy current disturbance and detects flaws formed in the steel pipe.

  In the eddy current flaw detection method, the sensitivity of the eddy current flaw detection apparatus is set using an artificial flaw typified by an artificial through hole before flaw detection is started. Specifically, a steel pipe having the same nominal outer diameter as the steel pipe to be inspected (hereinafter referred to as a contrast test piece) is prepared. An artificial flaw is produced on the prepared contrast specimen. Industrial standards such as JIS (Japanese Industrial Standards), EN (European Norm: European Standard), and ASTM (American Society for Testing and Materials: American Material Testing Boundary) Standards are used to specify the dimensions and shape of artificial flaws and the nominal size of steel pipes. Defined according to the outer diameter. That is, these industrial standards define a plurality of artificial flaw dimensions corresponding to a plurality of nominal outer diameters of steel pipes.

  Sensitivity setting of the eddy current flaw detector is performed as follows. First, an artificial flaw having a size and shape corresponding to the nominal outer diameter of a steel pipe is specified based on a predetermined industrial standard. The identified artificial flaw is made into a contrast test piece. The contrast test piece on which the artificial flaw is produced is passed through the through coil. At this time, the eddy current flaw detector detects an artificial flaw and generates a flaw detection signal. The sensitivity of the eddy current flaw detector is set based on the generated flaw detection signal.

JP-A-2-66447 Japanese Patent Publication No. 6-87051 JP-A-2-208552 JP-A-2-173561

  A normal manufacturing process of a steel pipe includes a pipe manufacturing process, a heat treatment process, a correction process, and an eddy current flaw detection process. In the pipe making process, billets and slabs are made into steel pipes. In the heat treatment step, the sized steel pipe is heat treated. In the straightening process, the bending of the heat-treated steel pipe is straightened. The eddy current flaw detection process is performed on the straightened steel pipe. In the eddy current flaw detection process, a flaw detection signal of an artificial flaw is used as a reference signal, and a flaw in the steel pipe is detected based on the reference signal.

  The manufacturing process described above includes one eddy current flaw detection process. However, the steel pipe manufacturing process may include a plurality of eddy current flaw detection processes. For example, the first eddy current flaw detection process is performed between the pipe making process and the heat treatment process, and the second eddy current flaw detection process is performed after the correction process. In this case, the steel pipe in which the first eddy current flaw detection process cannot be detected is excluded from the product target and is not subjected to the heat treatment process or the correction process. Therefore, compared with the case where the eddy current flaw detection process is performed only once, it is possible to reduce an extra man-hour for a steel pipe that is not a product target.

  However, if a comparison test piece having an artificial flaw according to the above-mentioned predetermined industrial standard is prepared for each eddy current flaw detection process, the working efficiency is lowered. In the first place, the sensitivity setting using the artificial flaw according to the industrial standard is sufficient if it is performed in the final eddy current flaw detection process in the manufacturing process. Therefore, in the eddy current flaw detection process other than the last eddy current flaw detection process, it is not necessary to set the sensitivity using the artificial flaw according to the industry standard. However, even in the eddy current flaw detection process that is executed before the last eddy current flaw detection process, the flaw detection accuracy decreases unless the sensitivity is set to be equal to or close to the sensitivity based on the artificial flaw.

  An object of the present invention is to provide an eddy current flaw detection method capable of detecting a flaw in a steel pipe without using an artificial flaw according to a predetermined industrial standard such as JIS, EN, or ASTM standard.

Means for Solving the Problems and Effects of the Invention

  In the eddy current flaw detection method according to the present invention, a plurality of metal tubes are flawed using an eddy current flaw detection apparatus having a through coil. The eddy current flaw detection method according to the present invention includes a step of selecting two metal tubes from among a plurality of metal tubes having the same nominal outer diameter, a step of arranging the two metal tubes in a row, and two rows arranged in a row. A step of forming a rigid gap forming member between the metal tubes, forming a gap having a size corresponding to the nominal outer diameter between the two metal tubes, and two metal tubes sandwiching the gap forming member through the coil And a step of flaw detection of the gap and a step of setting the sensitivity of the eddy current flaw detection device based on the flaw signal generated by flaw detection of the gap. The term “rigid body” as used herein means that it has such a rigidity that deformation due to a force received from the metal tube can be ignored when it is conveyed while being sandwiched between the metal tubes.

  In the eddy current flaw detection method according to the present invention, a gap formed between two metal tubes substitutes for artificial flaws. Therefore, sensitivity can be set without using artificial flaws according to industrial standards, and flaws in steel pipes can be detected.

  Preferably, the eddy current flaw detection method according to the present invention further includes a step of preparing a plurality of gap forming members corresponding to a plurality of nominal outer diameters. The gap forming member has a first surface and a second surface. The first surface is in contact with the end face of one of the two metal tubes. A 2nd surface is arrange | positioned on the opposite side to a 1st surface, and contacts the end surface of the other metal tube of two metal tubes. Each gap forming member further has a thickness. The thickness is the distance between the first surface and the second surface and corresponds to a predetermined nominal outer diameter. The eddy current flaw detection method further includes a step of selecting a gap forming member having a thickness corresponding to the nominal outer diameter of the metal tube from the plurality of gap forming members. In the step of forming a gap, the gap is formed by sandwiching the selected gap forming member between two metal tubes.

  In this case, the size of the gap can be changed according to the nominal outer diameter. Therefore, the sensitivity can be set according to the nominal outer diameter.

  Preferably, the size of the gap is the volume of the artificial through-hole corresponding to the nominal outer diameter of the metal tube among the plurality of artificial through-holes defined by a predetermined standard for eddy current testing and corresponding to the plurality of nominal outer diameters. To be determined.

  In this case, the gap to be formed can more accurately replace the artificial through hole defined by a predetermined industrial standard.

  The gap forming member according to the present invention is used in the above-described eddy current flaw detection method.

It is a schematic diagram which shows the structure of the eddy current flaw detector by embodiment of this invention. It is a functional block diagram which shows the structure of the flaw detector in FIG. It is a figure which shows the vector display of the flaw detection signal produced | generated with the eddy current flaw detector shown in FIG. It is a perspective view of the steel pipe and gap formation member in FIG. It is a perspective view of the clearance gap formation member pinched | interposed into two steel pipes and two steel pipes in FIG. It is a schematic diagram for demonstrating the role of the clearance gap formation member in FIG. It is a flowchart of the eddy current flaw detection method by embodiment of this invention. It is a schematic diagram for demonstrating the relationship between the volume of the clearance gap formed between two steel pipes, and the volume of an artificial through-hole. FIG. 5 is a perspective view of another gap forming member different from FIG. 4. FIG. 10 is a perspective view of another gap forming member different from FIGS. 4 and 9. FIG. 11 is a perspective view of another gap forming member different from FIGS. 4, 9, and 10. It is a schematic diagram which shows the usage example of the clearance gap formation member shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Overall configuration of eddy current flaw detector]
The eddy current flaw detection method according to the present embodiment uses the eddy current flaw detection apparatus shown in FIG. With reference to FIG. 1, the eddy current flaw detector 1 includes a penetration coil 2, a flaw detector 3, and a feed device 4.

  The through coil 2 is a self-inductive self-comparison test coil. The through coil 2 includes coils 21 and 22. The coil 21 is arranged coaxially with the coil 22. Since the through coil 2 is a self-induction type, it serves both as excitation and detection. A coil mount (not shown) is disposed below the through coil 2. A coil mount raises / lowers the penetration coil 2, and matches the central axis of the coils 21 and 22 with the central axis of the steel pipes 100F and 100R which are inspection objects. The penetration coil 2 and the flaw detector 3 generate a flaw detection signal.

  The feeding device 4 conveys the steel pipes 100F and 100R and passes them through the penetration coil 2. The feeding device 4 includes a plurality of transport rolls 5 and 6, a pair of guide rolls 7 </ b> A and 7 </ b> B, and a plurality of pinch rolls 8.

  The plurality of transport rolls 5 are disposed in front of the through coil 2, and the plurality of transport rolls 6 are disposed behind the through coil 2. The plurality of transport rolls 5 and 6 are arranged in a row. The plurality of transport rolls 5 and 6 are connected to a drive source (not shown) and are rotated by the drive source. And the conveyance rolls 5 and 6 convey the steel pipes 100F and 100R from the front of the penetration coil 2 to back. Each of the transport rolls 5 and 6 is a so-called V-roller whose central portion is recessed in a V shape.

  The pair of guide rolls 7 </ b> A are disposed on the left and right in front of the through coil 2. Similarly, the pair of guide rolls 7 </ b> B are disposed on the left and right sides of the through coil 2. The steel pipes 100F and 100R conveyed by the conveyance roll 5 pass between the pair of guide rolls 7A and the pair of guide rolls 7B. The guide rolls 7A and 7B suppress the steel pipes 100F and 100R being conveyed from vibrating left and right.

  The plurality of pinch rolls 8 are respectively disposed in front and rear of the through coil 2. The plurality of pinch rolls 8 of the penetration coil 2 are arranged above the transport roll 5. A plurality of pinch rolls 8 behind the penetrating coil 2 are arranged above the transport roll 6. Each pinch roll 8 is supported so as to be movable up and down by a lifting device (not shown). When the steel pipes 100F and 100R are conveyed, each pinch roll 8 descends and comes into contact with the steel pipes 100F and 100R. The pinch roll 8 suppresses the steel pipes 100F and 100R being conveyed from vibrating up and down.

[Configuration of the flaw detector 3]
FIG. 2 is a functional block diagram showing the configuration of the flaw detector 3 in FIG. Referring to FIG. 2, flaw detector 3 includes transmitter 301, power amplifier 302, bridge circuit 303, amplifier 304, phase shifter 305, synchronous detectors 306 and 307, filters 308 and 309. And a display 310.

  The transmitter 301 outputs a sine wave alternating current. The power amplifier 302 amplifies the output of the transmitter 301 and supplies it to the through coil 2 via the bridge circuit 303. If there is a flaw in the steel pipe passing through the penetration coil 2, the impedance of the penetration coil 2 changes. The bridge circuit 303 outputs a flaw detection signal according to the change in impedance.

  The amplifier 304 amplifies the flaw detection signal. The amplification degree of the amplifier 304 is normally adjusted using an artificial flaw defined by the above-mentioned industry standard before starting the eddy current flaw detection. The adjustment of the amplification degree of the amplifier 304 is called sensitivity setting. In this example, the description will be made assuming that an artificial through hole (so-called drill hole) is used as an artificial flaw.

  The amplified flaw detection signal is input to the two synchronous detectors 306 and 307. The synchronous detectors 306 and 307 receive the control signal output from the phase shifter 305, and from the flaw detection signal, a component corresponding to the X axis on the impedance plane (hereinafter referred to as X signal) and a component corresponding to the Y axis (hereinafter referred to as the X axis). (Hereinafter referred to as Y signal). The phase shifter 305 appropriately shifts the phase of the AC signal output from the transmitter 301 and outputs a first control signal and a second control signal that is 90 degrees out of phase with the first control signal. The synchronous detector 306 synchronously detects the flaw detection signal with the first control signal and outputs an X signal. The synchronous detector 307 synchronously detects the flaw detection signal with the second control signal and outputs a Y signal.

  The X signal and the Y signal include electric noise and noise based on vibrations during conveyance of the steel pipes 100F and 100R, respectively. Each of the filters 308 and 309 removes noise from the corresponding signal (X signal, Y signal) and outputs the result to the display 310.

  The display 310 displays the flaw detection signal as a vector. Specifically, the display 310 displays the X signal and the Y signal on the impedance plane. Thereby, the flaw detection signal is displayed two-dimensionally. FIG. 3 shows the flaw detection signal displayed in vector. Such a signal waveform is called a Lissajous waveform. Referring to FIG. 3, the amplitude A1 of the flaw detection signal ET is proportional to the volume of the flaw. If the amplitude A1 is small, the flaw volume is also small. If the amplitude A1 is large, the volume of the flaw is also large.

[Outline of Eddy Current Testing Method According to this Embodiment]
As described above, the size (volume) of the flaw detected by the eddy current flaw detection is evaluated by the amplitude A1 of the flaw detection signal displayed as a vector. In order to determine the size of the flaw based on the amplitude A1, it is necessary to know in advance the amplitude A1 for the reference flaw. Therefore, normally, before performing eddy current flaw detection on a plurality of steel pipes to be inspected, the sensitivity of the eddy current flaw detector 1, more specifically, the amplification degree of the amplifier 304 is set using an artificial through hole.

  The sensitivity setting is generally performed as follows. First, an arbitrary steel pipe is selected from a plurality of steel pipes to be inspected. The selected steel pipe is used as a comparison specimen. Next, an artificial through hole is formed in the comparison test piece. The size and shape of the artificial through hole in the eddy current flaw detection of a steel pipe is defined by industrial standards such as JIS, EN, and ASTM standards. For example, in JIS, it is defined in JIS G0583. In these industrial standards, artificial through holes having a plurality of dimensions corresponding to a plurality of nominal outer diameters are defined. Based on a predetermined industrial standard, an artificial through hole having a shape corresponding to the nominal outer diameter of a steel pipe to be inspected is specified. And the specified artificial through-hole is produced in a contrast test piece. After the fabrication, the contrast test piece in which the artificial through hole is formed is flawed and the sensitivity is set.

  As described above, in the case where a plurality of eddy current flaw detection processes are included in the manufacturing process, it is troublesome to prepare a contrast test piece in which an artificial through hole is formed for each eddy current flaw detection process, and the workability is poor. In addition, when a plurality of eddy current flaw detection processes are included in the manufacturing process, the location of each eddy current flaw detection process may be remote, and it may be difficult to share the same contrast test piece with a plurality of eddy current flaw detection processes. is there.

  Therefore, in the present embodiment, the sensitivity is set using the gap forming member 10 shown in FIG. 4 instead of the artificial through hole. In short, the gap forming member 10 replaces the artificial through hole.

  Referring to FIG. 4, the gap forming member 10 includes a disk-shaped main body 11 and annular insertion members 12 and 13. The main body 11 has a surface 11F and a surface 11R disposed on the opposite side of the surface 11F. The annular insertion member 12 is attached to the surface 11 </ b> F and is disposed coaxially with the main body 11. The annular insertion member 13 is attached to the surface 11 </ b> R and is arranged coaxially with the main body 11. The outer diameters of the insertion members 12 and 13 are slightly smaller than the inner diameters of the steel pipes 100F and 100R. The insertion members 12 and 13 are inserted into the steel pipes 100F and 100R.

  As shown in FIG. 5, the gap forming member 10 is sandwiched between the steel pipes 100F and 100R arranged in a line. That is, the gap forming member 10 forms a gap S10 between the steel pipe 100F and the steel pipe 100R. The gap forming member 10 is a rigid body and has a rigidity that does not cause deformation due to the force received from the steel pipes 100F and 100R. The gap forming member 10 is further made of an insulator. The insulator is, for example, resin, ceramics, wood, or the like. No eddy current is generated in the gap forming member 10 made of an insulator. Therefore, when the gap forming member 10 passes through the penetration coil 2, the eddy current flaw detector 1 recognizes the gap forming member 10 as a flaw. That is, as shown in FIG. 6, the gap S10 formed by the gap forming member 10 is a virtual space formed over the entire circumference of the steel pipe 120 when the steel pipe 100F and the steel pipe 100R are assumed to be one steel pipe 120. It corresponds to an annular through hole T10. Hereinafter, the virtual annular through hole T10 formed by the gap forming member 10 is referred to as a “virtual through hole”.

  Thus, if the clearance gap S10 is formed between the steel pipes 100F and 100R using the clearance gap formation member 10, the virtual through-hole T10 will be formed. If the virtual through hole T10 is used, the sensitivity of the flaw detector 3 can be set without producing an artificial through hole in the comparison test piece. Details of the eddy current flaw detection method according to this embodiment will be described below.

[Details of eddy current flaw detection method]
FIG. 7 shows a flowchart of the eddy current flaw detection method according to this embodiment. With reference to FIG. 7, first, the nominal outer diameter of the steel pipe to be inspected is specified (S1). Next, the gap forming member 10 corresponding to the specified nominal outer diameter is selected (S2).

  As described above, industrial standards such as JIS define artificial through holes having a plurality of shapes and dimensions corresponding to a plurality of nominal outer diameters. Similarly, in the present embodiment, a plurality of gap forming members 10 corresponding to the nominal outer diameter are prepared. In the following description, the industrial standard is assumed to be JIS, but the same applies to the EN and ASTM standards.

The volume of the virtual through hole T10 formed by each gap forming member 10 is the same as the volume of the corresponding artificial through hole for a nominal outer diameter. Referring to FIG. 8, the steel tube 100 having a nominal outer diameter _{D 100,} the volume _{V 200} of the artificial through-hole 200 on the JIS standard corresponding to the nominal outer diameter _{D 100} is defined by the following equation (1) .

V ₂₀₀ = π × (D _200/2 ) ² × W ₁₀₀ (1)
Here, D ₂₀₀ is the diameter of the artificial through hole, and W ₁₀₀ is the wall thickness of the steel pipe 100.

As described above, the amplitude A1 of the flaw detection signal ET displayed in vector is proportional to the volume of the flaw. Therefore, if the volume V ₁₀₀ of the virtual through hole T10 formed by the gap forming member 10 is the same as the volume V ₂₀₀ described above, the amplitude of the flaw detection signal by the gap S10 is the same as the amplitude of the flaw detection signal of the artificial through hole 200. Be the same.

The volume _{V 100} of the virtual through hole T10 multiplies the size of the gap S10 of the area in the cross section of the steel pipe 100F and 100R (i.e., an area of the annular portion of the outer diameter _{D 100,} inner diameter _{D 100 -2W} 100) Is required. Specifically, the volume V100 is represented by the following formula (2).

The volume ^{_{V 100 = π × {(D}} 100/2) 2 - (D 100/2-W 100) 2} × L (2)
Here, L is the size of the gap S10, corresponds to the distance between the steel pipe 100F and the steel pipe 100R, and corresponds to the thickness of the main body 11 of the gap forming member 10.

In each gap forming member 10 having a nominal outer diameter, the thickness L of the main body 11 is determined so that the volume V ₁₀₀ of the virtual through hole T 10 is the same as the volume V ₂₀₀ of the artificial through hole 200. Specifically, from the formulas (1) and (2), the thickness L of the main body 11 is represented by the following formula (3).

L = D ₂₀₀ ² / {4 × (D ₁₀₀ × W ₁₀₀ −W ₁₀₀ ² )} (3)
As described above, the thickness L of the main body 11 of the gap forming member 10 corresponds to the size of the gap S10. Therefore, the main body 11 of the gap forming member 10 corresponding to each nominal outer diameter has a thickness L that satisfies Equation (3).

  After the gap forming member 10 corresponding to the nominal outer diameter of the steel pipe to be inspected is selected, two steel pipes 100F and 100R are selected from the plurality of steel pipes to be inspected. Then, the selected steel pipes 100F and 100R are arranged in a line (S3). Specifically, the two steel pipes 100F and 100R are arranged in a row on the plurality of transport rolls 5.

  Subsequently, as shown in FIG. 5, the gap forming member 10 selected in step S2 is sandwiched between the two steel pipes 100F and 100R (S4). The insertion members 12 and 13 of the gap forming member 10 are inserted into the steel pipes 100F and 100R, and the gap forming member 10 is sandwiched between the two steel pipes 100F and 100R. Preferably, an adhesive is applied to the outer peripheral surfaces of the insertion members 12 and 13. In this case, the gap forming member 10 is fixed between the two steel pipes 100F and 100R. When the gap forming member 10 is sandwiched between the steel pipes 100F and 100R, a gap S10 having a size corresponding to the nominal outer diameter of the steel pipes 100F and 100R is formed.

  Subsequently, the steel pipes 100F and 100R are transported with the gap forming member 10 interposed therebetween and passed through the penetration coil 2 (S5). For example, if the rotational speed of the transport roll 5 is made faster than the rotational speed of the transport roll 6, the steel pipes 100F and 100R are transported in a row with the gap forming member 10 interposed therebetween. In this case, even if the above-described adhesive is not applied, the gap forming member 10 is conveyed while being sandwiched between the two steel pipes 100F and 100R. At the time of conveyance, the gap forming member 10 which is a rigid body does not deform even if it receives a force from the steel pipes 100F and 100R. Therefore, the size of the gap S10 is kept constant.

The two steel pipes 100F and 100R sandwiching the gap forming member 10 are subjected to eddy current testing. At this time, the eddy current flaw detector 1 detects the gap S10 formed by the gap forming member 10, that is, the virtual through hole T10, and generates a flaw detection signal. Based on the generated flaw detection signal, the sensitivity of the eddy current flaw detection apparatus 1 is set (S5). Specifically, the eddy current flaw detection apparatus 1 displays a flaw detection signal as a vector on the display 310 as shown in FIG. The operator sets the sensitivity by adjusting the amplitude A1 of the flaw detection signal displayed in vector. Here, the volume V ₁₀₀ of the virtual through hole T10 is the same as the volume V ₂₀₀ of the corresponding artificial through hole 200. Therefore, the amplitude A1 of the flaw detection signal generated in step S5 is the same as the amplitude of the flaw detection signal generated when the corresponding artificial through hole 200 is flawed. Therefore, sensitivity setting equivalent to the case where the artificial through-hole 200 is used can be performed. After the sensitivity is set, eddy current flaw detection is performed on a plurality of steel pipes to be inspected (S6).

In the eddy current flaw detection method according to the present embodiment, instead of using the artificial through hole 200, the sensitivity is set by using the gap S10 (virtual through hole T10). Therefore, the trouble of producing the artificial through hole 200 can be saved. The volume V ₁₀₀ of the virtual through hole T10 is the same as the volume V ₂₀₀ of the artificial through hole 200. Therefore, if the gap S10 is flawed, a flaw detection signal having the same amplitude as that of the corresponding artificial through hole 200 is generated. Therefore, eddy current flaw detection can be performed using the flaw detection signal corresponding to the artificial through-hole 200 as a reference without using the artificial through-hole 200 defined by the standard.

[Configuration example of gap forming member]
The shape of the gap forming member 10 is not limited to the shape of FIG. Any shape that can form the gap S10 between the steel pipe 100F and the steel pipe 100R may be used. For example, the gap forming member 10 may be a disk as shown in FIG. 9 or a ring as shown in FIG. The gap forming member 10 having these shapes also has a surface in contact with the end face of the steel pipe 100F and a surface in contact with the steel pipe 100R, and has a thickness L corresponding to the distance between these two surfaces. These gap forming members 10 are bonded to the front end face of the steel pipe 100F or the rear end face of the steel pipe 100R using an adhesive, for example.

  Moreover, as shown in FIG. 11, it may be plate-shaped. In this case, as shown in FIG. 12, both ends of the gap forming member 10 are sandwiched between the steel pipes 100F and 100R to form a gap S10.

  Preferably, when the gap forming member 10 is sandwiched between the two steel pipes 100F and 100R, the end of the gap forming member 10 does not protrude outside the outer peripheral surfaces of the steel pipes 100F and 100R. This is because if the end portion of the gap forming member 10 protrudes, it may come into contact with the through coil 2.

[Setting example of gap volume]
In the above embodiment, as the volume _{V 200} of the artificial through-hole 200 and the volume _{V 100} virtual through hole T10 are the same, it sets the size of the gap S10 L (thick L). However, to satisfy the following equation (4) the volume _{V 100} is the volume _{V 200,} may set the size L of the gap S10 for each nominal outer diameter.

V ₁₀₀ = n × V ₂₀₀ (4)
Here, n is a natural number. As described above, the amplitude A1 of the flaw detection signal generated by the eddy current flaw detection apparatus 1 is proportional to the volume of the artificial through hole 200. If the volume V ₁₀₀ of the virtual through hole T10 formed by the gap S10 is n times the volume V ₂₀₀ of the artificial through hole 200, the amplitude of the flaw detection signal generated by the gap S10 is the flaw detection of the corresponding artificial through hole 200. N times the amplitude of the signal. Therefore, if the amplitude of the flaw detection signal generated by the gap S10 is multiplied by 1 / n, it can be set to the same amplitude as the flaw detection signal of the corresponding artificial through hole 200, and the sensitivity can be set based on the artificial through hole 200. .

Furthermore, n may not be a natural number. In short, if you know the ratio of the volume _{V 200} due to volume _{V 100} and the artificial through-hole 200 by a gap S10, by utilizing the gap S10, it sets the sensitivity that the corresponding reference the artificial through-hole 200. In other words, the size L of the gap S10 may be determined based on the volume of the artificial through hole 200 corresponding to a predetermined nominal outer diameter defined by a predetermined standard.

  In the above-described embodiment, the through coil 2 is a self-induction self-comparison system. However, other types of through coils may be applied. For example, the through coil 2 may be a mutual induction type, a single method, or a standard comparison method.

  Further, the gap forming member 10 shown in FIGS. 10 and 11 may include insertion members 12 and 13 as shown in FIG. In this case, the gap forming member 10 is unlikely to come off from the steel pipes 100F and 100R.

  In the above-described embodiment, the steel pipe is flawed. However, the inspection target is not limited to the steel pipe, and a metal pipe made of a metal other than steel may be used.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

  The eddy current flaw detection method according to the present invention can be widely used in the eddy current flaw detection process of a steel pipe. In particular, when a plurality of eddy current flaw detection processes are included in the manufacturing process, the present invention can be used for the eddy current flaw detection process performed before the final eddy current flaw detection process.

DESCRIPTION OF SYMBOLS 1 Eddy current flaw detector 2 Penetration coil 3 Flaw detector 11 Main body 11F Front end surface 11R Rear end surface 100F, 100R Steel pipe 200 Artificial through hole

Claims (4)

An eddy current flaw detection method for flaw detection of a plurality of metal tubes using an eddy current flaw detection apparatus having a penetrating coil,
Selecting two of the metal tubes from the plurality of metal tubes having the same nominal outer diameter;
Arranging the two metal tubes in a line;
Sandwiching a rigid gap forming member between the two metal tubes arranged in a row, and forming a gap having a size corresponding to the nominal outer diameter between the two metal tubes;
Passing the two metal tubes sandwiching the gap forming member through the penetration coil, and flaw detection of the gap;
And a step of setting sensitivity of the eddy current flaw detector based on a flaw detection signal generated by flaw detection in the gap. The eddy current flaw detection method according to claim 1, further comprising:
Providing a plurality of gap forming members corresponding to the plurality of nominal outer diameters,
The gap forming member is
A first surface in contact with an end face of one of the two metal tubes;
A second surface disposed opposite to the first surface and in contact with an end surface of the other of the two metal tubes;
A distance between the first surface and the second surface, the thickness corresponding to a predetermined nominal outer diameter;
The eddy current flaw detection method further includes:
A step of selecting a gap forming member having a thickness corresponding to a nominal outer diameter of the metal tube from the plurality of gap forming members;
In the step of forming the gap, an eddy current flaw detection method in which the selected gap forming member is sandwiched between the two metal tubes. The eddy current flaw detection method according to claim 1 or 2,
The size of the gap is the volume of the artificial through-hole corresponding to the nominal outer diameter of the metal tube among the plurality of artificial through-holes defined by a predetermined standard for eddy current testing and corresponding to the plurality of nominal outer diameters. Eddy current flaw detection method determined based on this.   A gap forming member used in the eddy current flaw detection method according to claim 2.

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