JPH0651090A - Flaw detecting method for heat conducting pipe - Google Patents

Abstract

PURPOSE:To judge whether any flaw exists in heat conduction pipes from change in the intensity of radioactivity sensed, by filling the space outside of each heat conduction pipe with uniform radiation source, and moving a flaw detection probe upon inserting into an applicable pipe. CONSTITUTION:To make flaw detection of heat conduction pipes 6 of a heat exchanger, the inner space of the trunk 5 is filled with a flaw detection inspecting liquid 9 having radioactiveness, and the space outside of each pipe 6 is filled with uniform radiation source. The lid 8 to the head part 1 is removed, and a flaw detecting probe 10 is inserted through any applicable heat conduction pipe 6 from chambers 3, 4, and a cable 13 is pulled to cause moving in the pipe 6. If a crack A is initiated at the peripheral surface of the pipe 6, it shortens the distance to the inner surface of the pipe 6 from radioactive particles in the inspecting liquid having permeated the crack, so that the intensity of the radioactivity permeating to the inside increases. When the probe 10 passes the place where crack A is generated, therefore, the intensity, of the radioactivity transmitted to the outside by the cable 13 as the dosage data upon sensing 11 and converting 12 increases. The obtained is compared with the past dosage data, and judgement as with flaw is passed accordingly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting flaws in heat transfer tubes such as heat exchangers and steam generators.

[0002]

2. Description of the Related Art In a heat exchanger or the like used in a nuclear facility, a liquid containing radioactivity flows in the heat transfer tube, so that the heat transfer tube has "cracks", "pitting corrosion", "dents", etc. May cause serious accidents. Therefore, this type of heat transfer tube is obliged to carry out flaw detection during service, and a higher flaw detection capability is desired for this inspection.

As a conventional flaw detection method for such a heat transfer tube, a so-called eddy current flaw detection method is known, which detects the presence or absence of a flaw or the like from a change in eddy current. In the eddy current flaw detection method, a flaw detection probe a as shown in FIG. 3 is inserted into the heat transfer tube and moved, and an alternating voltage is applied to the two coils b, b built in this probe a to cause vortexes to move to different positions of the heat transfer tube. Generate an electric current. Now
When the eddy current generated by one coil b passes through the flaw, the path of the eddy current changes. Therefore, if the change in this eddy current is detected from the impedance difference between the coils b and b, the heat transfer tube It is possible to determine whether there are scratches in the tube wall.

[0004]

However, the above-mentioned eddy current flaw detection method has the following drawbacks.

(1) When a voltage is applied to the coil b of the flaw detection probe a, the magnetic field lines generated from the coil b pass through the tube wall of the heat transfer tube along its axial direction, and an eddy current is generated in a direction orthogonal to this. Therefore, the eddy current hardly changes with respect to the circumferential “crack” of the heat transfer tube, which is difficult to detect.

(2) Normally, the heat transfer tube is supported on the fixed side by a support plate or a stopper plate, but in this case, the magnetic force lines leak from the tube wall of the heat transfer tube to the support plate or the stopper plate, and The detection accuracy at the support part is degraded.

(3) If the heat transfer tube is U-shaped, the U
In the character portion, the eddy currents generated by both coils b, b are different, and the detection accuracy deteriorates.

An object of the present invention is to provide a novel flaw detection method for a heat transfer tube, which can overcome the above-mentioned conventional drawbacks all at once and greatly improve the flaw detection ability.

[0009]

In order to achieve the above object, the flaw detection method of the present invention detects the radiation dose inside the heat transfer tube after the outside of the heat transfer tube is filled with a uniform radiation source. The flaw detection probe is inserted and moved, and the presence or absence of a defect in the heat transfer tube is determined by the change in the radiation dose detected by the flaw detection probe.

[0010]

According to the above method, by filling the outside of the heat transfer tube with a uniform radiation source, the defective portion such as cracks and pitting corrosion can be prevented.
The amount of radiation transmitted to the inner surface side of the heat transfer tube is higher than that of other portions. Therefore, if a flaw detection probe capable of detecting the radiation dose is inserted into the heat transfer tube and moved, the presence or absence of a defect in the heat transfer tube can be determined from the change in the radiation dose detected by the probe.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example of a heat transfer tube type heat exchanger to which the method of the present invention is applied. In the figure, 1 is a hollow head body, and the inner space of the head body 1 is divided by a partition plate 2 into two chambers 3 and 4. A substantially bottomed tubular body 5 is attached to one end of the head body 1 in a liquid-tight state, and a large number of substantially U-shaped heat transfer tubes 6, 6 ... Are disposed in the inner space of the body 5. There is. The heat transfer tube 6 heat-exchanges the fluid introduced into the one chamber 3 of the head 1 with another fluid introduced into the body 5, and discharges the heat through another chamber 4 of the head 1. Both ends of the heat pipe 6 are communicated with the chambers 3 and 4 of the head body 1, respectively. Further, the middle portion of the heat transfer tube 6 is supported by a plurality of support plates 7, 7 ... Attached to the inner peripheral surface of the body 5 at predetermined intervals.

When conducting a flaw detection inspection of the heat transfer tubes 6 in the heat exchanger having the above-mentioned structure, first, the space inside the body 5 is filled with a radioactive flaw detection inspection liquid 9, and the outside of each heat transfer tube 6 is uniformly irradiated with a radiation source. And fill up with. As the flaw detection test liquid 9, here, radioactive fine particles (eg, cesium isotope powder) are used.
A liquid containing is used. Next, the lid 8 of the head 1 is removed to open the chambers 3 and 4, and the flaw detection probe 10 is inserted into the predetermined heat transfer tube 6 from one of the chambers 3 and 4 as shown in FIG. The flaw detection probe 10 mainly includes a detection unit 11 that detects a radiation dose such as a γ-ray monitor, a conversion unit 12 that converts the radiation dose detected by the detection unit 11 into an electric signal, and a conversion unit 12.
It is composed of a cable 13 for transmitting the dose signal converted by the data to an external microcomputer (not shown). Therefore, when the flaw detection probe 10 is inserted into the heat transfer tube 6 from its one end using air pressure and the cable 13 is pulled and moved in the heat transfer tube 6, the flaw is transmitted from the outer peripheral side to the inner surface side of the heat transfer tube 6 at any time. The coming radiation amount is detected by the detection unit 11, converted into an electric signal by the conversion unit 12, and then transmitted as dose data to the outside by the cable 13.

As shown in FIG. 2, when a crack A is formed on the outer peripheral surface of the heat transfer tube 6, radioactive fine particles in the flaw detection test liquid 9 penetrate into the crack A, and from the radioactive fine particle to the inner surface of the heat transfer tube 6. Is shortened, and the amount of radiation transmitted to the inner surface of the tube 6 is increased. Then, the flaw detection probe 10 is cracked A
The radiation amount detected by the probe 10 increases when passing through the occurrence point of the, and an external microcomputer or the like determines that "there is a defect" based on comparison with past dose data. In addition, even when there is a dent B due to corrosion or the like on the inner surface of the heat transfer tube 6, the dose transmitted to the inner surface side of the heat transfer tube 6 increases due to the thin tube wall at that location, and it is determined that there is "a defect". It

As described above, according to the flaw detection method of this embodiment, the outside of the heat transfer tube 6 is filled with the radioactive flaw detection inspection liquid 9 (radiation source), and the radiation amount from the inspection liquid 9 is transferred to the heat transfer pipe 6.
By detecting with the flaw detection probe 10 in the heat transfer tube 6,
It is possible to directly detect the presence or absence of a defect in the heat transfer tube 6 regardless of the shape or the like. That is, “cracking” occurs in the circumferential direction of the heat transfer tube 6.
Even if such a problem occurs, the radiation dose increases on the inner surface side of the heat transfer tube 6, so that such a defect can be detected quickly and reliably. The same applies to the U-shaped portion of the heat transfer tube 6. Further, when the flaw detection probe 10 passes through the inside of the support plate 7, the radioactive fine particles enter the gap between the support plate 7 and the heat transfer tube 6, so that the heat transfer tube 6 support portion is also treated in the same manner as other portions. Inspection can be performed, and extreme deterioration of accuracy can be prevented.

The flaw detection probe 10 of the above embodiment is
Although the dose data is transmitted to the outside via the cable 13, it goes without saying that a wireless probe may be used. In this case, the flaw detection probe 10 may be provided with an antenna, and the antenna may wirelessly transmit the dose data to the outside. Further, in the above-mentioned embodiment, the flaw detection inspection of the heat transfer tube type heat exchanger in the nuclear facility has been described, but the present invention is not limited to this, and can be applied to a heat transfer tube such as a steam generator.

[0017]

In summary, according to the present invention, after the outside of the heat transfer tube is filled with a uniform radiation source, the flaw detection probe is moved within the heat transfer tube, and the radiation dose detected by the probe is transferred. Since it is determined whether or not there is a defect in the heat pipe, it is possible to improve the inspection accuracy and the inspection time as compared with the conventional eddy current flaw detection method, and it is possible to significantly improve the flaw detection capability.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a heat transfer tube heat exchanger to which a flaw detection method for a heat transfer tube according to the present invention is applied.

FIG. 2 is a diagram showing a state in which a flaw detection probe is inserted into a heat transfer tube of a heat exchanger.

FIG. 3 is a sectional view showing a flaw detection probe used in a conventional eddy current flaw detection method.

[Explanation of symbols]

 1 head body 5 body 6 heat transfer tube 9 flaw detection test liquid (radiation source) 10 flaw detection probe 11 detection section 12 conversion section 13 cable

Claims (1)

[Claims] 1. After filling the outside of the heat transfer tube with a uniform radiation source, a flaw detection probe for detecting the radiation dose is inserted into the inside of the heat transfer tube and moved, and the radiation dose detected by the flaw detection probe is changed. A flaw detection method for a heat transfer tube, characterized in that the presence or absence of a defect in the heat transfer tube is determined by a change.