JP2743109B2 - Non-destructive inspection method of heating tube - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for performing non-destructive inspection of a heating tube (referred to as a heating radiation tube and a heat exchanger tube) using eddy current.

[Conventional technology]

The 8-10mm heating radiant tube (also called a radiant tube) used in the annealing process at steel works is broken by the inside because high-temperature gas flows inside, and the inspection is currently performed by visual inspection from the outside. I just did it.

On the other hand, the eddy current flaw detection method has been used in heat exchangers and the like for a long time.The method will be briefly described. An electric current is induced, but if there are defects such as wall thinning and cracks in the tube, the eddy current will be disturbed, and this will change the impedance of the probe coil. We are performing flaw detection.

In this case, a tube is inserted into the probe coil to detect a flaw in the tube.

[Problems to be solved by the invention]

As described above, the visual inspection of the heating radiation tube can only find a penetration defect in which a crack from the inner surface is exposed to the outside. It was done and, therefore, replaced the tube without having to overlook the defect and replace it.

Therefore, it is most preferable to non-destructively inspect flaws and the like generated inside from the outside. As the method, the inventor of the present invention considered that it is appropriate to use the eddy current flaw detection method as described above, and made intensive studies.

However, as described above, when the inspection is performed by inserting the probe coil inside the heating radiation tube, since the heating radiation tube is meandering, it is necessary to partially disassemble the heating radiation tube. There is a problem that it takes time.

Therefore, it is theoretically possible to form a probe coil so that the heating radiation tube is located inside the probe coil and perform flaw detection. However, the heating radiation tube is likely to be deformed by heat, and is smoothly circular. There is a problem that the probe coil cannot be brought into contact with the surroundings.

In addition, there is a method to perform inspection from the surface of the heating radiation tube using a probe coil using a magnetic core, but if a magnetic core is used, it becomes a pencil type probe, and it will perform flaw detection of a point close to a point, When inspecting a heating radiation tube having a relatively large diameter, there is a problem that the efficiency is extremely low.

Furthermore, it is also possible to use a probe coil with a circular cross section to detect flaws in the heating radiant tube while keeping it parallel to the axis of the heating radiant tube.However, the magnetic field generated by the coil is effective for heating. Since it does not penetrate the radiation tube, there is a problem that the measurement accuracy is poor.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a non-destructive inspection method for a heating tube that has relatively high measurement accuracy and can be performed without requiring labor such as disassembling the heating tube. Aim.

[Means for solving the problem]

A non-destructive inspection method for a heating tube according to claim 1, which meets the above object, is a method for eddy current detection in which a probe coil is disposed outside a heating tube and a crack generated from an inner surface of the heating tube is detected from the outside. The probe coil is formed by a pair of coils, and the winding shape of the coil is a closed shape having a linear portion, and the linear portion of the pair of coils is brought into contact with or close to the heating tube from outside to detect flaws. It is configured to perform.

Here, the closed shape having a linear portion refers to a shape obtained by dividing a closed shape such as a circle, an ellipse, a polygon, or an oval by a straight line.

According to a second aspect of the present invention, there is provided a non-destructive inspection method for a heating tube, wherein the alternating current flowing through the probe coil comprises a dual frequency alternating current obtained by mixing two different alternating currents. ing.

[Action]

In the nondestructive inspection method for a heating tube according to claim 1, the probe coil is constituted by a pair of coils, and the winding shape of the coil is constituted by a closed shape having a straight portion. When abutting or approaching the heating tube, the magnetic flux generated from the probe coil can pass through more inside the heating tube, thereby generating an eddy current generated orthogonal to the magnetic flux, and If there is an intersecting crack or the like, the balance of the paired coils is lost, and thus the crack or the like can be detected.

In the nondestructive inspection method for a heating tube according to claim 2, alternating currents of different frequencies are mixed and applied to the probe coil, so that magnetic flux generated by the high frequency alternating current flows near the surface of the heating tube, and the Since the lower alternating current flows from the surface of the heating tube to the middle layer, it is possible to increase the flaw detection depth, remove the noise component by calculating each signal value to be detected, and output only the signal component. it can.

〔Example〕

Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.

FIG. 1 is a sectional view showing a state in which a nondestructive inspection method for a heating tube according to one embodiment of the method of the present invention is applied, FIG. 2 is a perspective view of a probe used in the above embodiment, FIG. FIG. 3 is a schematic configuration diagram of the flaw detector used in the above embodiment.

As shown in FIG. 2, first, a probe 10 used for a nondestructive inspection method of a heating tube according to one embodiment of the present invention is shown.
As shown in the figure, a groove having a depth of 1 to 3 mm (preferably 2 mm) is provided around a bakelite core 11 having a semicircular cross section, and probe coils 12 and 13 are wound around this groove.

The probe coils 12 and 13 each have about 200 turns in this embodiment, and the interval is a = 5 mm, b = 4 mm
The dimensions of the core 11 were c = 50 mm and d = 50 mm.

As shown in FIG. 3, the probe 10 is connected to an eddy current flaw detector 14 having a well-known structure.
Two frequencies of 10 kHz and 40 kHz are transmitted by transmitting devices 15 and 16, mixed by a mixer 17 and added to a bridge circuit 18. The bridge coil 18 has the probe coil
12 and 13 are connected, and the voltage source is the upper dual frequency mixed voltage,
After detecting the output of the bridge circuit 18 and appropriately amplifying it with an amplifier, comparing with a reference frequency to detect its phase and absolute value, and applying necessary phase rotation, vector outputs corresponding to 10 kHz and 40 kHz (X ₁ , y ₂ ) and (x ₁ , y ₂ ) are output.

This is added to the display device 19 with the next CRT,
The above vector output to CRT20 and x obtained by adding / subtracting it appropriately
Lissajous figures of y output are drawn.

Therefore, when inspecting the heating radiation tube 21 (SCH22) as shown in FIG. 1 using these devices 14 and 19, the heating radiation tube 21 is made of the same material and shape as before without any defect. A test pipe is prepared, and the probe 10 is brought into contact with the probe so that the centers of the straight portions 22 and 23 of the probe coils 12 and 13 exactly coincide with the side lines of the test pipe, and the devices 14 and 19 detect noise. Adjust the whole so as not to. This adjustment is 10kH
This is carried out while displaying on the CRT 20 two-frequency signals of z and 40 kHz, and signals obtained by phase-rotating and adjusting the respective signals.

Next, the probe 10 is brought into contact with the heating radiation tube 21 to be measured in the direction shown in FIG. 1, and is gradually moved in the length direction (in some cases, in the circumferential direction). .

In this case, the magnetic flux generated by the probe coils 12 and 13 passes through the inside of the heating radiation tube 21 around the straight portions 22 and 23, respectively, and generates an eddy current in the heating radiation tube 21 which is a conductor. The impedance is changed as the resistance.

If the heating radiation tube 21 is damaged, a change occurs in the eddy current. Therefore, the balance of the bridge circuit 18 of the eddy current flaw detector 14 is lost depending on the position of the probe coils 12 and 13, and an output is generated.

When eddy current testing was performed by the above method, the experimental results shown in Table 1 were obtained.

Therefore, from this table, by using the above method, it is possible to reliably detect scratches, cracks, and the like at a position 3 mm from the outer surface.

In the above embodiment, a coil having a semicircular winding shape is used.However, if the coil has a straight portion, it is also possible to use a coil having a triangular or square winding shape.
Further, the number of turns of the coil can be changed according to the frequency or the detection depth.

In the above embodiment, the dual-frequency alternating current is applied to the probe coils 12 and 13 to remove noise and increase the measurement depth. However, depending on conditions, a single-frequency alternating current corresponding to the detection depth may be used. It is also possible.

〔The invention's effect〕

As is apparent from the above description, the nondestructive inspection method for a heating tube according to claim 1 heats a large amount of magnetic flux by abutting or bringing a probe coil having a straight portion outside the heating tube into close proximity. The change in the eddy current that is caused to pass through the tube makes it possible to detect cracks generated from the inside of the heating tube from the outside, which were difficult to measure using a conventional cylindrical coil.

In this case, the probe coil has a straight section, and the inspection can be performed while simultaneously abutting or extremely close to the surface of the heating tube over a long distance, so that the probe coil can be compared with a conventional pencil-type probe. As a result, eddy current flaw detection can be performed efficiently.

In the non-destructive inspection method for a heating tube according to claim 2, since alternating currents having different frequencies are mixed and applied to the probe coil, flaw detection from a shallow range to a deep range can be performed. Since the noise can be removed by calculating the signal value, the defect can be detected more accurately.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a state in which a nondestructive inspection method for a heating tube according to an embodiment of the present invention is applied, FIG. 2 is a perspective view of a probe used in the above embodiment, and FIG. It is a schematic structure figure of the flaw detector used in the above-mentioned example. [Description of Signs] 10: Probe, 11: Core, 12, 13: Probe coil, 14: Eddy current flaw detector, 15, 16: Oscillator, 17:
Mixer, 18 Bridge circuit, 19 CRT display device, 20 CRT, 21 Heating tube, 22, 23
Straight section

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Yoshiyuki Uemura, Inventor 4- 10-13 Ibori, Kokurakita-ku, Kitakyushu-shi, Fukuoka Prefecture Inside the New Japan Non-Destructive Inspection Co., Ltd. (56) References JP-A-56-110048 (JP, A) JP-A-56-65456 (JP, U) JP-B-58-11571 (JP, B2) JP-B-60-2619 (JP, B2) JP-B Hei6- 72873 (JP, B2) Jiko 4-16934 (JP, Y2)

Claims (2)

(57) [Claims] 1. A probe coil is arranged outside a heating tube,
In the eddy current flaw detection method for detecting cracks generated from the inside of the heating tube from the outside, the probe coil is formed by a pair of coils, and the winding shape of the coil is a closed shape having a linear portion, and the coil is formed as a pair. A non-destructive inspection method for a heating tube, wherein flaw detection is performed by bringing a straight portion of a coil into contact with or approaching the heating tube from outside. 2. The nondestructive inspection method for a heating tube according to claim 1, wherein the alternating current flowing through the probe coil is a dual frequency alternating current obtained by mixing alternating currents of two different frequencies.