JPS6358253A - Method and device for eddy current flaw detection - Google Patents

Abstract

PURPOSE:To inspect even a thick tube with sufficiently good accuracy by moving a probe for flaw detection which is arranged in a magnetic body tube while the magnetic body tube is magnetized forcibly from outside. CONSTITUTION:The tube bundle 10 of a heat exchanger is installed as the member to be inspected on an installation jig 1. The bundle 10 is equipped with many U-shaped magnetic body tubes 11, whose opening end parts are fixed to an end plate 12. A magnetizing coil 20 is wound around the bundle 10 to the overall length of the U-shaped outward shape and fed with electricity to magnetic the bundle 10 intensely. The probe 30 for flaw detection is inserted into a specific magnetic tube 11 of the bundle 10 to a specific position by utilizing compressed air, etc., and defects of the tube 11 such as a flaw and thickness reduction are recorded on a pen recorder 33 through a signal cable 31 and a signal processor 32. Similar flaw detection is carried out for other tubes 11 and results are recorded. Thus, the flaw detection is carried out even for the thick tube.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an eddy current flaw detection method for detecting flaws, thinning, and other defects in a magnetic tube by moving a flaw detection probe placed inside the magnetic tube. This device can be used to inspect for defects in magnetic tubes such as tube heat exchangers and various types of piping.

[Background technology and its problems]

Conventionally, eddy current flaw detection has been widely used as a non-destructive method to inspect defects in tube heat exchangers using magnetic tubes.
Permanent magnets or magnetizing coils are attached to the flaw detection probe itself, which is placed inside the tube, and the internal magnetization method uses these magnetizing means to magnetize the tube only from within. However, with this internal magnetization method, the magnetization ability tends to be insufficient due to restrictions on the shape of the flaw detection probe, so it is necessary to control the inside of the tube 11 so as not to lack the magnetization ability. However, there was a problem in that it lacked versatility and, on the other hand, if such regulations were not followed, inspection accuracy would be compromised.

By the way, the i3 if ratio of a tube made of a ferromagnetic material such as steel, etc. changes sensitively depending on the tube's cold working, heat treatment, strain stress, etc. This non-uniform magnetic permeability becomes a large noise source during eddy current flaw detection.

For this reason, it is necessary to apply strong direct current magnetization to the test part of the magnetic tube to magnetically saturate the tube, lower the magnetic permeability, and eliminate the influence of magnetic permeability. If only a magnet was used, the magnetizing ability would be limited as described above.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an eddy current flaw detection method and apparatus that can sufficiently magnetize a magnetic tube without affecting tube wall thickness regulation or inspection accuracy.

[Means and effects for solving the problem] The above object is achieved by moving the wound probe so that a magnetic field that is not affected by the thickness of the magnetic tube, etc. It is something to do.

The apparatus of the present invention also includes a flaw detection probe movable within a magnetic tube, a magnetization means such as a magnetization coil for forcibly magnetizing the magnetic tube from the outside, and an output signal from the flaw detection probe. A signal processor performs mixed detection of the output frequency of the lever and the reference oscillation frequency, counts the output frequency, and performs other predetermined signal processing, and the flaw detection results are displayed as a waveform on a CRT, etc. using the signal from this signal processor. Alternatively, the pen recorder is equipped with a display for recording and displaying data, etc., and the magnetizing means is used to sufficiently magnetize the magnetic tube to achieve the above object.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. Here, the same reference numerals are used for the same or equivalent components in each embodiment of the present invention, and the explanation is omitted or simplified.

FIG. 1 shows a first embodiment of the apparatus of the present invention, in which a tube bundle 10 of a heat exchanger as a member to be inspected is installed on an installation jig l.

This tube bundle 10 includes several tens to several hundreds of tubes.
It includes U-shaped magnetic tubes 11, and the U-shaped open ends of these tubes 11 are fixed to end plates 12. Note that the tube bundle 10 is generally connected and fixed at appropriate intervals by baffle plates in the middle, but these are not shown because the drawings would be complicated. On the other hand, although the magnetic tube 11 is actually much thinner than the dimensions shown in the drawing with respect to the tube bundle 10, it is drawn extremely thick for convenience of illustration.

A magnetizing coil 20 is wound around the outer circumference of the tube bundle 10 along the entire length of the U-shaped outer shape.
Both terminals 21 of are connected to a DC power source (not shown).

Therefore, when the coil 20 is energized, the tube bundle lO is strongly magnetized and its iif east density is, for example, lo
KGs or more.

A flaw detection probe 30 having a detection coil is movably arranged inside the magnetic tube 11 . The probe 30 can be moved within the tube 11 by, for example, using compressed air to send it to a predetermined position in the tube 11, and then sequentially pulling out the probe 30 using a signal cable 31 connected to the probe 30 at one end. The probe 30 can be connected to an operating rod (not shown).

The other end of the signal cable 31 is connected to a signal processor 32, which receives the output from the flaw detection probe 30 (no. Signal processing that mixes and detects the given oscillation frequency and reference frequency and detects defects from the beats of both oscillation frequencies, or detects defects by counting the oscillation frequencies given from the detection coil (
No. 3 processing and further signal processing based on other detection methods are performed. A pen recorder 33 serving as a display for displaying flaw detection results is connected to the signal processor 32. At this time, the display may be a CRT or other display.

In this embodiment configured as described above, the eddy current flaw detection method for detecting defects such as flaws and thinning of each magnetic tube 11 constituting the tube bundle 10 is performed as follows.

A flaw detection probe 30 is inserted into a predetermined position in a predetermined magnetic tube ll of the tube bundle IO using compressed air or the like.Next, a predetermined direct current is applied between both terminals 21 of the magnetizing coil 20. A voltage is applied so that the tube bundle 10 has a predetermined magnetic flux density, for example 10, G3 or higher.

In this state, if the probe 30 is sequentially towed by the No. 3 cable 31 or a special towing cable (not shown), the signal from the probe 30 is given to the signal processor 32 via the cable 31, and the test result is displayed on the pen recorder 32. is recorded and displayed, and defects such as scratches and remaining flesh on the tube 11 are detected.

In this way, when the flaw detection of one magnetic tube 11 is completed, the probe 30 is inserted into the other magnetic tube 11 and flaw detection is performed in the same manner as described above. Perform flaw detection.

In addition, during flaw detection, as mentioned above, both terminals 21 of the magnetizing coil 20 are connected to il! ! If the probe 30 is not inserted, the part where the probe 30 is not inserted will also be magnetized, resulting in wasted power.
As shown by chain lines in FIG. 1, intermediate taps 22 are provided at predetermined intervals in the middle of the coil 20, and by using the intermediate taps 22 provided on the coil 20 in the portion where the probe 30 is inserted, the probe 30 is inserted only in that portion. It is also possible to save power by setting F+J+%n. At this time, which intermediate Knop 2
2 may be energized depending on the amount of pullout of the No. 3 cable 31, etc.

According to this embodiment as described above, since the magnetic tube 11 is forcibly magnetized from the outside, the magnetic tube 11
can be sufficiently magnetized and its magnetic permeability can be sufficiently lowered, thus making it possible to perform eddy current flaw detection on the tube 11 with a thick wall J7 and improving its accuracy. In addition, with the conventional magnetization only from inside the tubes, it was almost impossible to detect defects near the baffle plates that connect the tubes 11 due to the magnetic flux flowing through the buffle plates, but according to this embodiment, Since the buffful plate can also be sufficiently magnetized, defects in the temporary vicinity of the buffful can also be detected with high accuracy.

FIGS. 2 and 3 are diagrams showing that the magnetic flux density of the magnetizing coil 20 is required to be 10 KG or more when exciting the magnetic tube 11 using the embodiment shown in FIG. 1.

FIG. 2 shows the results of performing eddy current flaw detection using the apparatus shown in FIG. 1 and evaluating the noise in the output signal using the X-axis amplitude at each magnetic flux density. According to this result, in order to eliminate magnetic noise and evaluate defects, the magnetic flux density of the CR rod tube 11 is required to be 10 KGs or more, and 13
KG, preferably above, the magnetic flux density is 10 to G
If it is less than 1, the probe 30 is
It vibrates in the axial direction and causes noise. Also, the second
In the figure, the relationship between the magnetic flux density and the i3 magnetic permeability of the magnetic tube 11 is shown by a broken line, and this magnetic permeability also increases when the magnetic flux density is 1.
If it is 0KG3 or more, it is small enough and tube 11
It can be seen that the effects of cold working, heat treatment, etc. can be sufficiently minimized. From this i3 if rate point of view, the magnetic flux density is 15
KG or more is preferable.

Figure 3 shows 30% and 50% as representative defect signals.
The relationship between each magnetic flux density and the S/N ratio is shown when the % outer surface slit thinning defect is measured. According to this figure, the magnetic flux density is 10XG or more, preferably 12KGs
If the above values are met, it can be seen that both the 30% and 50% thinning defective tubes have a sufficiently large S/N ratio and are not affected by noise.

FIG. 4 shows a second embodiment of the device of the present invention, and in this embodiment, a tube bundle IO consisting of a plurality of magnetic tubes 11 is magnetized by a moving magnetizing coil 40. This moving magnetizing coil 40 is connected to the tube bundle 1
0, and is provided on a truck 41, and the wheels 42 of this truck 41 are movable on a pair of rails 43 provided on the installation jig l.

Therefore, during flaw detection, if the movable magnetizing coil 40 is energized and moved in synchronization with the movement of the probe 30, the test portion of the tube 11 can be sufficiently magnetized for flaw detection. The coil 40 may be moved by moving the cart 41 manually or by using a drive source such as a motor.

According to this embodiment, in addition to the effects of the first embodiment, there is an additional effect that the efficiency of flaw detection work can be improved because there is no need to wind the coil directly around the tube bundle 10. In addition, since the number of excitation parts is small, the power consumption can be reduced.

FIG. 5 shows a third embodiment of the device of the present invention. In this embodiment, a moving magnetizing coil 40 similar to that shown in FIG. 4 is used. This is an example in which the problem of difficulty in magnetizing the curved portion 13 has been solved. For this reason, in this embodiment, a fixed magnetizing coil 25 is provided at the U-shaped bent portion 13 of the tube handle 10 to specifically magnetize the bent portion 13, and both terminals 26 of this coil 25 are connected to each other. The bent portion 13 is inspected for flaws using a probe 30 while applying a DC voltage. At this time, depending on the size of the bent portion 13, the coil 2
5, an intermediate tap is provided as in the embodiment shown in FIG.
It may also be partially magnetized.

According to this embodiment, in addition to the effects of the second embodiment, there can be added the effect that flaw detection of the bent portion 13 of the tube bundle 10 can be performed with high accuracy.

Note that the present invention is not limited to the above-mentioned embodiments, and modifications within the range that can achieve the purpose of the present invention are included in the present invention. For example, the magnetic tube 11 may be a heat exchanger. The present invention is applicable not only to those constituting the tube bundle IO but also to general piping, piping in chemical plants, and the like.

However, if applied to the tube handle 10 of a heat exchanger, the external magnetization is performed on the entire bundle 10, so by increasing the number of probes 30, multiple tubes 11 can be tested simultaneously, increasing the flaw detection efficiency. The advantage is that it can be improved.

〔Effect of the invention〕

As described above, according to the present invention, the magnetic tube can be sufficiently magnetized, and even thick tubes can be inspected with sufficient accuracy.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing the first embodiment of the device of the present invention, FIGS. 2 and 3 are diagrams confirming the magnitude of magnetic flux density required for magnetizing the Eil magnetic tube, respectively, and FIG.
Figures 5 and 5 show the second and third views of the device of the present invention, respectively.
FIG. 1 is a schematic configuration diagram showing an example. XO...Tube bundle, 11...Magnetic tube, 13...Bending portion, 20...Magnetizing coil, 25...
. . . Fixed magnetization coil at bent portion, 30 . . . Flaw detection probe, 32 . . . Signal processor, 33 .

Claims (7)

[Claims] (1) In an eddy current flaw detection method in which a flaw detection probe placed inside a magnetic tube is moved to detect defects such as flaws and thinning of the magnetic tube, the magnetic tube is forcibly magnetized from the outside. An eddy current flaw detection method characterized in that the flaw detection probe is moved in a state in which the flaw detection probe is moved. (2) The eddy current flaw detection method according to claim 1, wherein the magnetization of the magnetic tube is performed by a magnetization coil arranged to surround the magnetic tube. (3) The eddy current flaw detection method according to claim 2, wherein the magnetizing coil is movable along a magnetic tube. (4) In claim 1, the magnetic tube is composed of a tube bent into a U-shape, and the magnetization of the magnetic tube is such that the magnetic tube is provided so as to surround the magnetic tube. An eddy current flaw detection method characterized in that it is carried out using a moving magnetized coil that is movable along a magnetic tube and a fixed magnetized coil that is wound around a U-shaped bent portion of a magnetic tube. (5) In any one of claims 1 to 4, the magnetized portion of the magnetic tube is moved, and the flaw detection probe is moved in synchronization with the movement of the magnetized portion. An eddy current flaw detection method characterized by: (6) In any one of claims 1 to 5, the magnetic tubes are formed into a plurality of bundles, and the bundle of magnetic tubes is forcibly forced from the outside surrounding the entire bundle. An eddy current flaw detection method characterized by magnetization. (7) A flaw detection probe that is movably arranged inside the magnetic tube and detects defects such as scratches and thinning of the magnetic tube; a magnetization means that forcibly magnetizes the magnetic tube from the outside; What is claimed is: 1. An eddy current flaw detection device comprising: a signal processor that receives an output signal from a probe and performs predetermined signal processing; and a display that displays flaw detection results based on the signal from the signal processor.