JP7294367B2 - Eddy current flaw detector, steel material manufacturing equipment, steel pipe manufacturing equipment, eddy current flaw detection method, steel material manufacturing method, and steel pipe manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an eddy current testing apparatus, steel manufacturing equipment, steel pipe manufacturing equipment, an eddy current testing method, a steel manufacturing method, and a steel pipe manufacturing method.

A butt-welded steel pipe is produced by forming a hot-rolled steel sheet heated to a predetermined temperature into a tubular shape by a forge welding machine, joining the joint (hereinafter referred to as the "seam") by diffusion bonding, and then reducing the diameter to a predetermined diameter by a stretch reducer.・Manufactured by rolling, then cutting into predetermined lengths, and cooling.

A butt-welded steel pipe is used for applications such as water piping, and is sometimes constructed by a method called flaring. Flaring is a processing method in which the ends of steel pipes (hereinafter referred to as "pipe ends") are flared by cold working and joined by flanges. This flare processing does not require welding and can be easily processed to any length at the construction site, so it has the advantage of being excellent in terms of workability and cost. On the other hand, flaring is a cold widening process, and since the amount of processing is large, it is also characterized in that defects such as cracks are likely to occur in the processed portion.

In particular, in butt-welded steel pipes, if oxides or scratches from handling are mixed in the coil end faces before forge welding, joint failures or defects will occur at the seams. Insufficient bonding and defects at the seam cause cracks during flaring. In flaring, it is known that scratches and inclusions on the inner surface, which undergo strong elongational deformation, cause cracks during flaring. .

In addition, while flaring has the great advantage of being able to be processed on-site, the processing is performed at any position on the butt-welded steel pipe. Furthermore, since there is a high possibility that flaring is normally performed from the pipe end, it is necessary to guarantee the entire length including the pipe end.

Generally, in order to assure the quality of butt-welded steel pipes, after cutting and cooling, penetrating EDDY CURRENT TESTING (Eddy Current Testing), hydraulic inspection, or visual inspection is performed. For example, in Patent Document 1, an eddy current flaw detector is installed in the latter stage of the forge welder in a butt welded steel pipe production line, and the eddy current flaw detector is used to perform hot flaw detection on the steel pipe for flaws and cracks. Techniques for quality assurance over time are disclosed. Further, Patent Document 2 discloses a technique for performing eddy current flaw detection on a material to be inspected by penetrating eddy current flaw detection.

JP-A-53-25260 JP-A-2006-162540 JP 2005-181134 A

Although Patent Document 1 does not disclose a specific configuration of the eddy current testing device, an eddy current testing method, conditions for eddy current testing, etc., it is aimed at inspecting flaws and cracks in steel pipes. Therefore, in Patent Document 1, as in Patent Document 2, it is presumed that penetrating eddy current testing is performed to detect flaws on the entire surface of the steel pipe in the circumferential direction. This penetrating eddy current flaw detection can detect flaws around the entire circumference of a steel pipe. There is a problem that

When detecting flaws in a cut steel pipe, a dead zone is generated at the pipe end due to flaw detection noise due to the pipe end edge effect. As described above, since flaring is often performed from the end of the pipe, there is a high possibility that the end of the pipe will be processed without quality assurance. For this reason, it is difficult to guarantee the full length of the seam portion of the steel pipe by penetrating eddy current testing performed after cutting the steel pipe.

Further, in Patent Document 3, probe-type eddy current testing is performed, but contact with the material by the wheel and maintenance of liftoff are performed, and it is premised on testing (cold testing) after the seam portion has cooled. In this cold flaw detection, flaw detection noise increases due to uneven magnetic properties and the like, so it is difficult to detect flaws in the seam portion with high sensitivity.

The present invention has been made in view of the above problems, and includes an eddy current testing apparatus capable of detecting a seam of a steel pipe with high sensitivity, a steel manufacturing facility, a steel pipe manufacturing facility, an eddy current testing method, and a steel manufacturing method. The object is to provide a method and a method of manufacturing steel pipes.

In order to solve the above-described problems and achieve the object, an eddy current testing apparatus according to the present invention uses a probe having an excitation coil and a detection coil to perform eddy current testing on an object to be inspected. The apparatus includes a probe protection member covering the side and bottom surfaces of the probe, the interior of the probe protection member is filled with a first cooling medium, and the probe is cooled by the first cooling medium. Cooled down.

Further, in the eddy current testing apparatus according to the present invention, in the above invention, the probe includes a coil protection member that covers the excitation coil and the detection coil, and a second cooling medium is provided inside the coil protection member. is satisfied, and the excitation coil and the detection coil are cooled by the second cooling medium.

In order to solve the above-described problems and achieve the object, the steel material manufacturing equipment according to the present invention includes: a probe; and an eddy current flaw detector that performs eddy current flaw detection of the steel material using the probe in a state where the temperature of the steel material is equal to or higher than the transformation point.

In order to solve the above-described problems and achieve the object, a steel pipe manufacturing facility according to the present invention is a butt welder that forms a steel strip heated to a predetermined temperature into a tubular steel pipe and joins seams by forge welding. a cutting machine that cuts the steel pipe to a predetermined length; a probe that is installed after the forge welding machine and before the cutting machine; and an eddy current testing apparatus for performing eddy current testing of the seam portion using the probe in a state in which the temperature of the steel pipe is equal to or higher than a transformation point.

In order to solve the above-described problems and achieve the object, an eddy current testing method according to the present invention performs eddy current testing on an object to be inspected using a probe having an excitation coil and a detection coil. The method includes a flaw detection step of performing eddy current flaw detection on the inspection object with the probe while cooling the probe with a first cooling medium.

Further, in the eddy current testing method according to the present invention, in the testing step, while cooling the excitation coil and the detection coil with a second cooling medium, the probe is applied to the inspection object. Conduct eddy current testing.

Further, in the eddy current flaw detection method according to the present invention, in the flaw detection step, the temperature of the inspection object is 300° C. or higher.

In order to solve the above-described problems and achieve the object, a method for manufacturing a steel material according to the present invention cools a probe with a first cooling medium in a state where the temperature of the steel material is equal to or higher than the transformation point, and cools the probe includes a flaw detection step of performing eddy current flaw detection on the steel material.

In order to solve the above-described problems and achieve the object, the method for manufacturing a steel pipe according to the present invention includes a joining step in which a steel strip heated to a predetermined temperature is formed into a tubular steel pipe, and the seam portion is joined by butt welding. and cooling the steel pipe with a first cooling medium in a state where the temperature of the steel pipe is equal to or higher than the transformation point between the cutting step of cutting the steel pipe to a predetermined length and the joining step and the cutting step and a flaw detection step of performing eddy current flaw detection of the seam portion using a probe.

According to the present invention, the inside of the probe protection member is filled with a cooling medium, and the eddy current inspection is performed while the entire probe is cooled, whereby the seam portion of the steel pipe can be inspected with high sensitivity. This makes it possible to guarantee the quality of the entire length of the seam portion of the steel pipe.

FIG. 1 is a diagram showing a schematic configuration of a steel pipe manufacturing facility to which an eddy current testing apparatus according to an embodiment of the present invention is applied. FIG. 2 is a cross-sectional view showing an example of a probe cooling structure in the eddy current testing apparatus according to the embodiment of the present invention. FIG. 3 is a perspective view showing an arrangement example when a plurality of probes are used for eddy current flaw detection in the eddy current flaw detection apparatus according to the embodiment of the present invention. FIG. 4 is a cross-sectional view showing a specific configuration of the probe of the eddy current flaw detector according to the embodiment of the present invention. FIG. 5 is a graph showing lift-off characteristics in the eddy current flaw detector according to the embodiment of the present invention. FIG. 6 is a graph showing the relationship between the thickness of the sensor cover made of stainless steel and lift-off. FIG. 7 is a diagram showing a configuration example of a sensor cover made of ceramics and a sensor cover made of stainless steel. FIG. 8 is a graph showing an example of measuring the signal intensity while changing the thickness of the sensor cover made of stainless steel.

An eddy current testing apparatus, a steel manufacturing facility, a steel pipe manufacturing facility, an eddy current testing method, a steel manufacturing method, and a steel pipe manufacturing method according to embodiments of the present invention will be described with reference to the drawings.

(eddy current flaw detector)
An eddy current testing apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. An eddy current flaw detector is applied to a production facility (steel pipe production line) for butt-welded steel pipes (hereinafter simply referred to as "steel pipes") as shown in FIG. This steel pipe manufacturing facility includes a heating furnace 1 , a forge welding machine 2 , an eddy current flaw detector 3 , a stretch reducer 4 , and a cutting machine 5 . In this embodiment, an example in which the eddy current flaw detector 3 is applied to a steel pipe manufacturing facility (a steel pipe manufacturing line) will be described. In this embodiment, an example in which the inspection object is a steel pipe will be described. A metal material or the like may be used.

A heating furnace 1 heats a steel strip (slit coil) W1 to a predetermined temperature (for example, 1200° C.). The forge welding machine 2 forms the steel strip W1 into a tubular shape and joins the seams by forge welding. The eddy current flaw detector 3 also inspects the seam portion of the steel pipe W2, which is the object to be inspected. Further, the stretch reducer 4 reduces and rolls the steel pipe W2 to a predetermined diameter. Then, the cutting machine 5 cuts the diameter-reduced and rolled steel pipe W2 to a predetermined length. Although not shown in FIG. 1, equipment for cooling and straightening the cut steel pipe W2, for example, is arranged after the cutting machine 5. As shown in FIG.

The eddy current flaw detector 3 is installed in a range after the forge welding machine 2 and before the cutting machine 5 in the manufacturing facility for the steel pipe W2. More specifically, the eddy current flaw detector 3 is installed between the forge welder 2 and the cutting machine 5 in the conveying direction of the steel pipe W2 (the axial direction of the steel pipe W2). The eddy current flaw detector 3 includes a probe 31 , a probe protection member 32 , a signal processing device 35 and a display device 36 .

The eddy current flaw detection by the eddy current flaw detector 3 brings the coil of the probe 31 close to the inspection object to excite the coil, induces eddy current in the inspection object, and detects the distribution and change of the eddy current with the coil. It is something to do. In eddy current flaw detection, if there are flaws or cracks (hereinafter referred to as "flaws") in the measurement range, the distribution of eddy currents will change compared to the part without flaws. Defects are detected based on changes in coil impedance.

The eddy current flaw detector 3 performs eddy current flaw detection of the seam portion of the steel pipe W2 using the probe 31 while hot, that is, in a state where the temperature of the steel pipe W2 is equal to or higher than the transformation point (Curie point). When the steel pipe W2 is at or above its transformation point, the steel material loses its magnetism, so it is possible to perform flaw detection with high sensitivity, including the inner surface side of the seam portion of the steel pipe W2.

In the vicinity of the transformation point, the magnetic properties fluctuate greatly and become noise, so it is preferable to perform flaw detection at a temperature sufficiently higher than the transformation point, for example, 1000° C. or higher. A butt-welded steel pipe is generally welded by heating it to 1200° C. to 1400° C. in the heating furnace 1. Therefore, by installing the eddy current flaw detector 3 on the output side of the forge welder 2, flaw detection can be performed stably. can.

In the case of cold testing (for example, below the transformation point), the steel pipe W2 is cut into lengths and cooled. Eddy current flaw detection cannot detect the vicinity of the pipe end in principle, that is, a pipe end dead zone occurs, so it is difficult to inspect the entire length of the steel pipe W2 after cutting. In addition, after cutting, the position of the seam becomes unknown due to transportation, so a mechanism for detecting and following the seam is required in order to apply probe-type eddy current testing. This complicates the equipment and makes online installation difficult in terms of efficiency and cost.

Further, in the manufacturing equipment for the steel pipe W2, following the joining by the forge welder 2, the diameter is reduced to the product diameter by the stretch reducer 4, and after cutting by the cutting machine 5, cooling is often carried out. Furthermore, at this time, materials having one or two types of plate widths are forge-welded to form mother pipes, and further the pipes are contracted to the product diameter by the stretch reducer 4 . Therefore, since there is little variation in the diameter of the mother pipe, eddy current testing is performed on the delivery side of the forge welding machine 2 before diameter reduction and on the entry side of the stretch reducer 4, as in the eddy current testing device 3 according to the present embodiment. , sensitivity change due to change in tube diameter can be reduced. In addition, the seam portion of the steel pipe W2 may rotate due to tube shrinkage, but since the seam portion rotates less immediately after forge welding, the seam portion is less likely to come off.

During operation, the position of the seam portion of the steel pipe W2 may fluctuate to some extent due to twisting of the steel pipe W2 or the like. In this case, it is conceivable to provide a head moving mechanism to follow the seam.

(Probe cooling structure 1)
The eddy current flaw detector 3 according to this embodiment includes a cooling structure for cooling the probe 31 from the outside. The cooling structure of this probe 31 will be described with reference to FIG.

The cooling structure of the probe 31 includes a probe protection member 32 that covers at least the side surface and the bottom surface of the probe 31, a cooling medium supply unit 33 that supplies a cooling medium (first cooling medium) C1 into the probe protection member 32, A cooling medium discharge part 34 for discharging the cooling medium C1 in the probe protection member 32 to the outside is provided. Although FIG. 1 shows an example in which three probes 31 are provided in the probe protection member 32, the number of probes 31 may be plural, or only one may be provided. Further, in the probe 31 shown in the figure, only the ferrite core 311 and the coil 312 are illustrated, and other configurations are omitted.

The probe protection member 32 covers at least the side surface and the bottom surface of the probe 31 and has a space formed between the probe 31 and the probe protection member 32 inside. Also, the cooling medium supply unit 33 and the cooling medium discharge unit 34 function as a supply system for supplying the cooling medium C1. The inside of the probe protection member 32 is filled with a cooling medium C1, and the probe 31 (specifically, the coil protection member 315) is cooled by the cooling medium C1. Since the probe protection member 32 covers at least the side surface and the bottom surface of the probe 31, it can hold the cooling medium C1. The cooling medium C1 is composed of water, for example. Inside the probe protection member 32, the cooling medium C1 is supplied up to a height at which the top of the probe 31 is buried (a height at which the top of the probe 31 is not exposed). The "upper portion of the probe 31" indicates a portion of the probe 31 facing the inspection object (for example, the steel pipe W2).

The cooling medium C1 forms a thin water film on the top of the probe 31 . It is preferable that the thickness of this water film is, for example, about 2 mm at the minimum. The cooling medium C1 is supplied to the inside of the probe protection member 32 so that the thickness of the water film is constant and the water film is replaced in a short period of time. As described above, inside the probe protection member 32, the cooling medium C1 is replaced in a short period of time so that the cooling medium C1 itself does not generate heat.

A cooling medium C1 is constantly supplied to the interior of the probe protection member 32, thereby cooling the coil protection member 315 and washing away scale deposited on the surface of the coil protection member 315. there is When the liquid level of the cooling medium C1 exceeds a certain height, the cooling medium C1 is discharged to the outside from the cooling medium discharge portion 34 on the side, and the liquid level is always kept constant.

The liquid surface level of the cooling medium C1 is such that the upper portion of the coil protection member 315 can be covered with the cooling medium C1, and the water film of the cooling medium C1 on the coil protection member 315 is as thin as possible for the lift-off proximity. It is preferable to set the level as FIG. 2 shows an example of a cooling structure for cooling the coil protection member 315 from both sides. A structure in which the cooling medium C1 is applied from the outside toward the .

FIG. 2 shows an example in which the liquid level of the cooling medium C1 is set at a position lower than the edge of the probe protection member 32. If the requirement that the water film is constant and the water film is replaced in a short period of time is met, then the liquid surface level of the cooling medium C1 is set at the same position as the edge of the probe protection member 32, or the cooling medium C1 is set at the probe The cooling medium C<b>1 may be supplied inside the probe protection member 32 so as to always overflow the edge of the protection member 32 .

In addition, instead of circulating the cooling medium C1 in the probe protection member 32 as a whole, for example, the cooling medium C1 is always replaced only at the upper position of the probe 31, and at the bottom of the probe protection member 32 The supply of the cooling medium C1 may be controlled so that the cooling medium C1 stays. By allowing the cooling medium C1 to stay at the bottom of the probe protection member 32 in this manner, the scale on the surface of the coil protection member 315 washed away by the cooling medium C1 can be retained at the bottom of the probe protection member 32. . As a result, high-temperature scale is prevented from depositing and adhering to the surface of the probe protection member 32, so that thermal effects and sensitivity reduction can be suppressed. A known cooling medium can be used as the cooling medium C1 inside the probe protection member 32 . Specifically, water, an antifreeze solution, and the like can be mentioned. Water is most preferred due to its high cooling efficiency and ready availability.

Here, when the butt welded steel pipe before cutting is inspected, the whole butt welded steel pipe is inspected at a high temperature (hot inspection). In general, an eddy current flaw detection probe used for hot flaw detection needs to take countermeasures against heat. A structure has been proposed in which the coil is covered with a sensor cover and a cooling medium is circulated within the sensor cover. However, the butt-welded steel pipe has a larger diameter than the wire rod, and the radiant heat received by the probe during hot flaw detection is extremely large. Therefore, the structure as proposed in the reference cannot completely reduce the wear and tear of both the sensor cover and the probe. In addition, it is assumed that scale may separate from the steel pipe, deposit and adhere to the surface of the sensor cover, and adversely affect sensitivity.

On the other hand, in the eddy current flaw detection apparatus 3 according to the present embodiment, the cooling medium C2 is circulated within the coil protection member 315 that accommodates the ferrite core 311 and the coil 312, and is cooled within the probe protection member 32 that accommodates the probe 31. A double cooling structure is adopted to circulate the medium C1. As a result, it is possible to suppress the wear of the probe 31 during hot testing, and the cooling medium C1 can wash away the scale peeled off from the steel pipe W2, thereby suppressing the decrease in sensitivity due to scale deposition and the like.

Here, in an electric resistance welded pipe or the like, the temperature of the base material is normal temperature, and only the seam portion becomes high temperature, so the seam portion can be easily detected by a thermal image. On the other hand, in a butt-welded steel pipe, the temperature of the base material is high in addition to the seam, so it is difficult to detect the seam by thermal imaging. Therefore, in order to cope with such misalignment of the seam portion (hereinafter referred to as "seam misalignment"), as shown in FIG. good too.

For example, as shown in FIG. 3, the plurality of probes 31 are arranged along the axial direction of the steel pipe W2, and each probe 31 is arranged with a constant angle. In the example shown in the figure, the center probe 31 is arranged perpendicular to the axial direction of the steel pipe W2, the right probe 31 is arranged with an angle θ of 5° to the back side, and the left probe 31 is arranged with an angle θ are shifted 5° to the front side. As shown in the figure, by arranging three to five probes 31 while changing the angle θ of each probe 31 by 5°, a seam deviation of ±5° in the case of three and ±10° in the case of five can correspond to Further, depending on the width of the probes 31 (the radial width of the steel pipe W2), for example, by arranging the probes 31 while changing the angle .theta.

As shown in FIG. 3, when a plurality of channels of probes 31 are provided, for example, when a signal is output from any of the plurality of probes 31 as signal processing, it is determined that there is a flaw or the like. As a result, even if the position of the defect changes due to seam misalignment, the defect can be detected by any of the probes 31 .

Next, an example of a specific configuration of the probe 31 will be described with reference to FIG. The probe 31 includes an E-shaped (E-shaped) ferrite core 311, a coil 312 wound around the ferrite core 311, a resin member 313, a base portion 314, and a coil protection member that covers the ferrite core 311 and the coil 312. 315, a cooling medium supply unit 316 that supplies the cooling medium C2 into the coil protection member 315, and a cooling medium discharge unit 317 that discharges the cooling medium C2 inside the coil protection member 315 to the outside. there is

Among the coils 312 wound around the ferrite core 311, the coil 312 wound around the center leg of the E shape is used as an excitation coil, and the coils 312 wound around both sides of the E shape are used as detection coils. preferably. Further, the detection coil is of a self-comparison type, and the difference between the two detection coils is used to stabilize against disturbance such as lift-off fluctuation.

The coil 312 having the E-shaped ferrite core 311 is an example of an advantageous structure for detecting flaws in the seam portion of the steel pipe W2 with high sensitivity in this embodiment. Any structure having a detection coil is applicable. Also, the size of the coil 312 can be designed according to the flaw or the like to be detected.

Further, in the present embodiment, an example of using the mutual induction probe 31 in which the excitation coil and the detection coil are respectively composed of separate coils 312 is shown, but instead of this mutual induction probe 31, A self-inductive probe 31 in which the same coil 312 is used as the excitation coil and the detection coil may be used.

The resin member 313 covers the ferrite core 311 and the coil 312, and is formed in a rectangular parallelepiped shape, for example. The thickness T1 of the resin member 313 located above the ferrite core 311 is preferably formed as thin as possible, for example, about 0.5 mm.

The base portion 314 is fixed to the coil protection member 315 with an adhesive. Further, the base portion 314 is formed with a recessed portion 314a. The bottom of the resin member 313 is fitted into the recess 314a.

Here, in addition to the probe-type eddy-current flaw detection as in this embodiment, a penetrating-type eddy-current flaw detection in which a coil is installed outside the inspection object and flaws are detected while the inspection object passes through the internal space of the coil is also possible. However, the probe type is more sensitive. This is because the penetrating type eddy current flaw detection has the advantage of being able to detect flaws all around the steel pipe at once, and it is possible to detect flaws on the entire circumference of the steel pipe in addition to defects in the seam. This is because the ratio of the flaw signal to the entire circumference and the total area included in the coil reduces the sensitivity to minute flaws and the like. In particular, the lack of sensitivity when detecting minute flaws on the inner surface of the seam portion during flaring is conspicuous.

The dimensions of the E-type ferrite core 311 may be designed according to the size of the flaw or the like to be detected. For example, when it is desired to detect a flaw having a length of about 2 mm to 5 mm, it is preferable that the ferrite core 311 has a leg interval S of 5 mm to 20 mm and a thickness T2 of 1 mm to 5 mm. Note that both the foot spacing S and the thickness T2 of the ferrite core 311 indicate the length of the steel pipe W2 along the conveying direction (see FIG. 4).

Further, it is preferable to increase the size of the ferrite core 311 when it is desired to detect a larger flaw or the like, and to decrease the size of the ferrite core 311 to bring it closer to the inspection object when a smaller flaw is to be detected. Also, the depth of the ferrite core 311 is preferably 5 mm to 50 mm, more preferably 15 mm to 25 mm. The depth of the ferrite core 311 indicates the length in the radial direction orthogonal to the axial direction (see FIG. 3) of the steel pipe W2. As the depth of the ferrite core 311 is increased, the signal can be detected more strongly, but noise is also received at the same time. Therefore, it is preferable to set the optimum depth in consideration of the balance between the signal and the noise.

The lift-off, which indicates the distance from the steel pipe W<b>2 to be inspected to the probe 31 , is preferably determined according to the foot interval S of the ferrite core 311 . Specifically, the lift-off is preferably 0.5 to 2 times the leg spacing S of the ferrite core 311, and is preferably 0.75 to 1.5 times the leg spacing S of the ferrite core 311. more preferred. For example, when the foot spacing S of the ferrite core 311 is about 10 mm, it is preferable to place the probe 31 at a position about 10 mm±5 mm from the steel pipe W2 (that is, set the liftoff to 5 mm to 15 mm).

Basically, the closer the probe 31 is to the steel pipe W2, the higher the sensitivity. There is a possibility that the probe 31 may burn out due to the radiant heat of a certain steel pipe W2. Therefore, it is necessary to secure an appropriate minimum value of lift-off in consideration of these factors.

Also, the pass line variation in the steady state is within ±1 mm (99% interval). In addition, the weld bead of the welded (connection welded) portion of each steel strip W1 is approximately 2 mm or less. Furthermore, at the start of pipemaking from the steel strip W1, the pass line variation in an unsteady portion such as the end is within 4 mm. In order to prevent the steel pipe W2 from coming into contact with the cooling medium C1 outside the coil protection member 315, a margin corresponding to the thickness of the cooling medium C1 (water film) above the coil protection member 315 (at least about 2 mm) is provided. is necessary. Therefore, the minimum lift-off value is preferably 5 mm in consideration of these factors.

Also, when the lift-off increases, the ratio of the component directly entering the ferrite core 311 from leg to leg increases. As a result, the component that contributes to the induction of eddy current in the steel strip W1 is reduced, the sensitivity is lowered, and it becomes difficult to detect the flaw signal. Therefore, it is preferable to determine the maximum lift-off value in consideration of these factors.

FIG. 5 is a graph showing the lift-off characteristics of the eddy current flaw detector 3 according to this embodiment, where the vertical axis is the S/N ratio (dB) and the horizontal axis is the lift-off value (mm). The figure also shows the results of detecting a slit flaw with a depth of 1 mm on the inner surface of the steel pipe W2 while changing the lift-off using a probe 31 having an E-shaped ferrite core 311 with a leg interval S of 10 mm. The S/N ratio is shown.

As shown in FIG. 5, it can be seen from the approximation straight line (dotted line in the graph) from the measurement results that a favorable S/N ratio of 7 dB is ensured when the lift-off is around 14 mm. On the other hand, when the lift-off is 16 mm, the S/N ratio becomes 1 dB and the observation becomes impossible. Therefore, when the foot spacing S of the ferrite core 311 is about 10 mm, it is preferable to set the lift-off to about 10 mm±5 mm. Further, it is preferable to set the lift-off that can ensure an S/N ratio of 9 dB or more regardless of the size of the foot distance S of the ferrite core 311 .

Note that FIG. 5 also shows the S/N ratio when a 2 mmφ penetrating flaw processed on the steel pipe W2 is detected. It is possible to detect flaws up to around 20 mm lift-off. Therefore, if it is desired to detect only large scratches, a larger lift-off may be ensured within the detectable range.

(Probe cooling structure 2)
Since the eddy current flaw detector 3 according to the present embodiment measures a high-temperature inspection object (for example, 300° C. or higher), it is necessary to take heat countermeasures for the coil 312 . Therefore, as shown in FIG. 4, the probe 31 is provided with a coil protective member 315 for heat countermeasures. The coil protection member 315 is made of a non-magnetic metal plate and covers the ferrite core 311 and the coil 312 . The space covered by the non-magnetic metal plate, that is, the inside of the coil protection member 315 is filled with a cooling medium C2 for cooling the coil 312 . At least the surface of the coil protection member 315 facing the object to be inspected (upper surface in the drawing) should be made of a non-magnetic metal plate. Although not shown in FIG. 2, the probe 31 is provided with a cooling medium C2 supply system for passing the cooling medium C2 inside the coil protection member 315 (water supply and drainage). With this supply system, the inside of the probe 31 is filled with the cooling medium C2, and the cooling medium C2 at an appropriate temperature can be supplied at an appropriate timing.

The thickness of the coil protection member 315 is preferably 0.2 mm to 1 mm. The thickness of the cooling medium C2 of the coil protection member 315 (thickness of the cooling medium C2 interposed between the coil 312 and the inspection object) is preferably 1 mm to 5 mm. The material of the coil protection member 315 may be appropriately selected from non-magnetic materials, but it is preferable to use a stainless steel material such as SUS304 or SUS303 in consideration of strength and availability.

The cooling medium C2 is composed of water, for example. However, if the temperature of the test object is not high (for example, less than 300° C.), the probe 31 is less likely to burn out, so the cooling medium C2 may be made of air.

Moreover, the cooling medium C2 is, as in the present embodiment,
(a) Although the objects are the same (both the cooling medium C1 and the cooling medium C2 are water in this embodiment), different systems are used as the systems for supplying the cooling mediums C1 and C2 to each other.
but also
(b) Separate bodies (for example, cooling medium C1 is water and cooling medium C2 is air), and a different supply system is used.
(c) The object is the same (for example, when both the cooling medium C1 and the cooling medium C2 are water), and the system supplying the cooling mediums C1 and C2 is also the same (that is, the inside of the probe protection member 32 and the coil The inside of the protective member 315 is in a state where water can pass),
is also possible. again,
(d) The interior of the probe protection member 32 and/or the interior of the coil protection member 315 may be sealed so as to seal the cooling medium C1 and/or C2.
Which of the above cases (a) to (d) should be selected may be appropriately selected according to the state (especially the temperature) of the inspection target and the state of the probe 31 at the time of inspection. Since the temperature inside the probe 31 can be finely adjusted, it is preferable to use separate supply systems for the cooling mediums C1 and C2, as in (a) or (b) above.

The signal processing device 35 is implemented by a general-purpose computer such as a workstation or a personal computer, and processes signals detected by the probe 31 using a memory storing processing programs and the like and a CPU executing the processing programs. A signal detected by the coil 312 is phase-detected in the probe 31 and output as a flaw detection signal. The output signal is appropriately recorded and subjected to threshold determination in the signal processing device 35 . At that time, a Lissajous display may be performed to distinguish between electrical noise and backlash noise associated with transportation, and a scratch signal. That is, by appropriately setting the phase of phase detection, it is possible to set the phase to minimize the signal associated with electrical noise and backlash/liftoff fluctuations, thereby reducing the influence of these noises.

The display device 36 is realized by, for example, an LCD display, a CRT display, or the like, and displays the signal processing result (flaw detection result of the steel pipe W2) by the signal processing device 35 .

According to the eddy current testing apparatus, the steel manufacturing equipment, the steel pipe manufacturing equipment, the eddy current testing method, the steel manufacturing method, and the steel pipe manufacturing method according to the present embodiment as described above, the ferrite core 311 and the coil 312 are made non-magnetic. A cooling medium C2 is circulated in the coil protection member 315, and a cooling medium C1 is circulated in the probe protection member 32 to cool the coil protection member 315. By cooling with the medium C1, the influence of radiant heat from the steel pipe W2 to the coil 312 (especially characteristic deterioration, damage, etc.) is suppressed, and deposition and adhesion of high-temperature scale on the surface of the coil protection member 315 is suppressed. be able to. Therefore, it is possible to appropriately cool the probe 31 during hot testing, and to suppress the decrease in the life of the probe 31 .

Further, according to the eddy current testing apparatus, the steel material manufacturing equipment, the steel pipe manufacturing equipment, the eddy current testing method, the steel manufacturing method, and the steel pipe manufacturing method according to the present embodiment, by performing the probe type eddy current testing, the penetrating The seam portion of the steel pipe W2 can be detected with high sensitivity compared to the eddy current flaw detection of the formula. In addition, it is possible to improve the sensitivity of detecting minute flaws in the seam portion, particularly during flaring. This makes it possible to guarantee the quality of the entire length of the seam portion of the steel pipe W2.

Further, according to the eddy current flaw detection apparatus, the steel material manufacturing equipment, the steel pipe manufacturing equipment, the eddy current flaw detection method, the steel material manufacturing method, and the steel pipe manufacturing method according to the present embodiment, by performing the hot eddy current flaw detection after forge welding, , the noise during flaw detection can be reduced compared to cold eddy current flaw detection, so the seam portion of the steel pipe W2 can be detected with higher sensitivity.

Further, according to the eddy current testing apparatus, the steel manufacturing equipment, the steel pipe manufacturing equipment, the eddy current testing method, the steel manufacturing method, and the steel pipe manufacturing method according to the present embodiment, the steel pipe can be It is possible to detect a flaw signal with high sensitivity while suppressing contact/damage of the probe 31 due to fluttering of W2 and burning of the probe 31 due to radiant heat of the steel pipe W2.

Further, according to the eddy current flaw detection apparatus, the steel material manufacturing equipment, the steel pipe manufacturing equipment, the eddy current flaw detection method, the steel material manufacturing method, and the steel pipe manufacturing method according to the present embodiment, the ferrite core 311 and the coil 312 are made of a non-magnetic metal plate. By circulating the cooling medium C2 in the coil protection member 315, the influence of the radiant heat from the steel pipe W2 on the coil 312 (in particular, characteristic deterioration, damage, etc.) can be suppressed. can be done.

(Modification 1)
A first modification of the eddy current flaw detection method according to this embodiment will be described. In this modified example, hot probe-type eddy current testing (modified example) and cold penetration-type eddy current testing (comparative example) were performed on the artificial defects added to the steel pipe, and the testing results were obtained. compared.

First, drill holes of 3 mmφ and 1.6 mmφ were artificially added to the coil edge of a pipe base material (outer diameter of 114.3 mm) having a product nominal diameter of 100A, and butt welded steel pipes were manufactured under normal manufacturing conditions.

In a modified example, a probe with an E-type ferrite core with a foot interval of 10 mm is covered with a sensor cover with a front plate (made of SUS304) with a thickness of 0.2 mm, and a cooling medium is circulated inside the sensor cover to cool the coil. did Also, the space between the inner surface of the sensor cover and the coil of the probe was set to 2 mm to secure a water channel for the cooling medium. Also, the lift-off, which indicates the distance from the steel pipe to the probe, was set to 10 mm. Then, probe-type eddy current flaw detection was performed on the steel pipe to be inspected at a position immediately after the forge welding machine to investigate whether or not artificial defects could be detected.

In a comparative example, a penetrating eddy current flaw detection was performed on the steel pipe subjected to inspection flaw detection at a position immediately after the cutting machine to investigate whether or not artificial flaws could be detected. In the comparative example, a general penetrating eddy current flaw detection as disclosed in Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2006-162540) was performed. Table 1 shows the detection results of the modified example and the comparative example.

As shown in Table 1, in the case of a drill hole of 3 mmφ, detection was possible by both methods of the modified example and the comparative example. That is, in the modified example, since the S/N ratio is 7, detection is possible. In the comparative example, the signal intensity on the paper chart is 36 mm, but in normal operation, it is judged that there is a flaw at 20 mm or more, so detection is possible.

On the other hand, a drill hole of 1.6 mmφ could be detected only by the modified method. That is, in the modified example, detection was possible because the S/N ratio was 2.1. On the other hand, in the comparative example, the signal intensity on the paper chart was 7 mm, which was less than 20 mm, and thus could not be detected. In addition, in the comparative example, since the flaw detection is performed after cutting the steel pipe, a dead zone is generated at the pipe end, and there is also a region in which measurement and assurance are impossible.

From the above results, it was found that probe-type eddy current testing in hot conditions can detect steel pipes with higher sensitivity than penetration-type eddy current testing in cold conditions.

(Modification 2)
A second modification of the eddy current flaw detection method according to the present embodiment will be described with reference to FIGS. 6 to 8. FIG. In this modified example, the material of the sensor cover of the probe was examined.

In some conventional eddy current flaw detectors, the sensor cover is made of a non-magnetic material such as ceramics, but it is inferior to stainless steel in the following points.
(1) There is a possibility of cracking due to thermal shock. If it cracks, it will not be able to hold the cooling medium, and there is a risk that the probe will burn out.
(2) Since the thickness is as thick as about 1 mm to 2 mm, the actual lift-off is large and the sensitivity is lowered (see the graph of lift-off characteristics in FIG. 5).

In addition, since ceramics is a non-magnetic and non-electric material, the sensor cover does not reduce electrical sensitivity. On the other hand, since the ceramic sensor cover actually has a thickness of about 2 mm, it is necessary to substantially increase the liftoff in order to secure the distance between the probe and the inspection object.

FIG. 6 shows the relationship between sensor cover thickness and signal sensitivity. In the figure, the vertical axis is the signal sensitivity, and the horizontal axis is the thickness (mm) of the sensor cover. In addition, in the same figure, in order to investigate only the effect of the thickness of the sensor cover, the lift-off was fixed at 12 mm, and the signal was generated while changing the thickness of the stainless steel sensor cover installed between the probe and the inspection object. Strength was measured. As shown in the figure, the signal intensity decreases to about 95% when the thickness of the sensor cover is 0.2 mm, and to about 75% when the thickness is 1 mm.

The relationship between the thickness of the ceramic sensor cover and lift-off is shown in FIG. 7(a), and the relationship between the thickness of the sensor cover made of stainless steel and lift-off is shown in FIG. 7(b). Here, it is assumed that a lift-off of 10 mm, which indicates the distance from the steel pipe to be inspected to the probe, is secured. In this case, in addition to the lift-off of 10 mm, it is necessary to consider the thickness of the sensor cover and the width of the coolant channel.

In the case of a ceramic sensor cover, as shown in FIG. 7A, the substantial liftoff is "liftoff 10 mm+sensor cover thickness 2 mm+channel width 2 mm=14 mm". On the other hand, in the case of a sensor cover made of stainless steel, as shown in FIG. 7B, the actual liftoff is "10 mm lift-off+0.2 mm thickness of sensor cover+2 mm width of channel=12.2 mm". As described above, the sensor cover made of ceramics has a large thickness, and the substantial lift-off increases. Therefore, it can be seen that the sensitivity of the sensor cover made of stainless steel is superior up to a certain thickness.

Next, FIG. 8 shows an example of measuring the signal intensity while changing the thickness of the sensor cover made of stainless steel under the conditions of a lift-off of 10 mm and a channel width of 2 mm. In the figure, the vertical axis is the signal sensitivity, and the horizontal axis is the thickness (mm) of the sensor cover. In the same figure, as a comparative example, the signal intensity measured by a probe equipped with a ceramic sensor cover with a thickness of 2 mm under the conditions of a lift-off of 10 mm and a channel width of 2 mm is plotted at the position of 0 mm on the horizontal axis. . As shown in the figure, the sensitivity of the sensor cover made of stainless steel with a thickness of 0.2 mm to 1 mm is superior to that of the sensor cover made of ceramics with a thickness of 2 mm. In addition, stainless steel is superior to ceramics in terms of mechanical properties such as thermal shock and toughness.

(Example)
An example of the eddy current flaw detection method according to this embodiment will be described with reference to FIG. In this embodiment, a probe protection member installed for cooling a probe coil protection member was examined.

In conventional hot eddy current testing probes, the coil protective member is made of a non-magnetic material, and the inside of the coil protective member is water-cooled to insulate heat. When the temperature is (for example, 300° C. or higher), it may not be possible to prevent the probe from being damaged only by cooling the inside of the coil protection member.

Therefore, in this embodiment, as shown in FIG. A hot eddy current testing was performed for a case where a sufficient amount of water was circulated inside the member and a case where no water was circulated inside the probe protection member.

First, the results of a comparative example in which a hot eddy current flaw detection test was performed on a butt-welded steel pipe without circulating water in the probe protective member will be described. This comparative example corresponds to a conventional system in which only the inside of the coil protection member is water-cooled. In the comparative example, the entire surface of the coil protective member turned black after several operations, and the coil inside was damaged. The direct cause of this was that the water-cooling structure inside the coil protection member was clogged and the cooling was delayed. can no longer be secured. In other words, it can be said that when the temperature of the test object is high, the wear of the probe cannot be suppressed only by internal water cooling of the coil protective member.

In addition, in this test, the thickness of the channel in the coil protection member (thickness of water interposed between the coil and the test object) was only 2 mm, and it can be said that the possibility of clogging was high in the first place. On the other hand, in eddy current testing, it is necessary to make the distance between the inspection target part and the probe as close as possible, and the expansion of the waterway leads to a decrease in sensitivity. In addition, since heat loss was observed in the coil protection member, it is considered that even if the water channel in the coil protection member is expanded, it will only serve as a temporary remedy, prolonging the time until the coil is damaged.

On the other hand, when a hot eddy current test was conducted on a butt welded steel pipe with a structure in which a sufficient amount of water was circulated inside the protective member for the probe, it was found that the protective member for the coil was not heated even after one year from the start of the test. There was no damage or deterioration, and the coil continued to operate without breaking. From the above test results, it is clear that, in addition to internal water cooling of the coil protection member, it is also necessary to water-cool the entire coil protection member from the outside in order to avoid long-term wear.

As described above, the eddy current flaw detection apparatus, the steel material manufacturing equipment, the steel pipe manufacturing equipment, the eddy current flaw detection method, the steel material manufacturing method, and the steel pipe manufacturing method according to the present invention are specifically described with the embodiments and examples for carrying out the invention. However, the gist of the present invention is not limited to these descriptions, and should be broadly interpreted based on the descriptions of the claims. Further, it goes without saying that various changes and alterations based on these descriptions are also included in the gist of the present invention.

Reference Signs List 1 heating furnace 2 forge welder 3 eddy current flaw detector 31 probe 311 ferrite core 312 coil 313 resin member 314 pedestal 314a recess 315 coil protection member 316 cooling medium supply unit 317 cooling medium discharge unit 32 probe protection member 33 cooling medium supply unit 34 cooling medium discharge unit 35 signal processing device 36 display device 4 stretch reducer 5 cutting machine C1, C2 cooling medium T1, T2 thickness W1 steel strip W2 steel pipe

Claims (9)

An eddy current testing apparatus that performs eddy current testing on an object to be inspected using a probe equipped with an excitation coil and a detection coil,
A probe protection member covering the side surface and the bottom surface of the probe,
The interior of the probe protection member is filled with a first cooling medium, and the probe is cooled by the first cooling medium,
A water film of the first cooling medium is formed between the probe and the inspection object, the water film being replaced at predetermined times ,
The top of the probe protection member is open,
The interior of the probe is filled with a second cooling medium for cooling the excitation coil and the detection coil,
Eddy current flaw detector. The probe includes a coil protection member that covers the excitation coil and the detection coil,
The inside of the coil protection member is filled with the second cooling medium, and the excitation coil and the detection coil are cooled by the second cooling medium.
The eddy current flaw detector according to claim 1. a probe; and a probe protection member covering the side and bottom surfaces of the probe and filled with a first cooling medium. Equipped with an eddy current flaw detector for eddy current flaw detection of steel materials,
Between the probe and the steel material, a water film of the first cooling medium is formed, which is replaced at a predetermined time ,
The top of the probe protection member is open,
The interior of the probe is filled with a second cooling medium for cooling the excitation coil and the detection coil,
Steel manufacturing equipment. a forge welding machine that forms a steel strip heated to a predetermined temperature into a tubular steel pipe and joins the seam portion by forge welding;
a cutting machine that cuts the steel pipe to a predetermined length;
a probe installed in a range subsequent to the forge welding machine and upstream of the cutting machine; and a protective member for the probe covering the side surface and the bottom surface of the probe and having an interior filled with a first cooling medium; an eddy current flaw detection apparatus that performs eddy current flaw detection of the seam portion using the probe in a state where the temperature of is equal to or higher than the transformation point;
with
A water film of the first cooling medium is formed between the probe and the steel pipe, the film being replaced at a predetermined time ,
The top of the probe protection member is open,
The interior of the probe is filled with a second cooling medium for cooling the excitation coil and the detection coil,
Manufacturing equipment for steel pipes. An eddy current testing method for performing eddy current testing on an object to be inspected using a probe equipped with an excitation coil and a detection coil,
A flaw detection step of performing eddy current flaw detection on the inspection object with the probe while cooling the probe with a first cooling medium,
A water film of the first cooling medium is formed between the probe and the inspection object, the water film being replaced at predetermined times ,
an upper portion of a probe protection member covering the side surface and the bottom surface of the probe and filled with the first cooling medium is open;
The interior of the probe is filled with a second cooling medium for cooling the excitation coil and the detection coil,
Eddy current flaw detection method. In the flaw detection step, while cooling the excitation coil and the detection coil with a second cooling medium, perform eddy current flaw detection on the inspection object with the probe.
The eddy current flaw detection method according to claim 5. In the flaw detection step, the temperature of the inspection object is 300° C. or higher.
The eddy current flaw detection method according to claim 6. A flaw detection step of performing eddy current flaw detection on the steel material with the probe while cooling the probe with a first cooling medium in a state where the temperature of the steel material is equal to or higher than the transformation point,
Between the probe and the steel material, a water film of the first cooling medium is formed, which is replaced at a predetermined time ,
an upper portion of a probe protection member covering the side surface and the bottom surface of the probe and filled with the first cooling medium is open;
The interior of the probe is filled with a second cooling medium for cooling the excitation coil and the detection coil,
A method of manufacturing steel. A joining step of forming a steel strip heated to a predetermined temperature into a tubular steel pipe and joining the seam portion by forge welding;
a cutting step of cutting the steel pipe into a predetermined length;
a flaw detection step of performing eddy current flaw detection of the seam portion using a probe cooled by a first cooling medium in a state where the temperature of the steel pipe is equal to or higher than the transformation point, between the joining step and the cutting step; ,
including
Between the probe and the steel pipe, a water film of the first cooling medium is formed, which is replaced at a predetermined time ,
an upper portion of a probe protection member covering the side surface and the bottom surface of the probe and filled with the first cooling medium is open;
The interior of the probe is filled with a second cooling medium for cooling the excitation coil and the detection coil,
A method of manufacturing steel pipes.

Images