JPH0344665B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a carburizing method used for non-destructively measuring carburized parts generated on the inner surface of cracking tubes for ethylene production in the petrochemical industry from the outer surface. This relates to measurement probes.

(Prior technology) As a cracking tube for ethylene production, which is a reaction tube for recovering ethylene, etc. by thermally decomposing raw material naphtha under high temperature and high pressure, ASTM
HK40 (0.4%C-25%Cr-20%Ni), HP45 (0.45
%C-25%Cr-35%Ni), or HP improving material (HP material with Mo, W, Nb, etc. added singly or in combination).

When a cracking tube is used for a long period of time, carbon generated as a result of reaction adheres to the inner surface of the tube, and this adhered carbon diffuses into the metal at high temperatures, causing carburization. Carbon infiltrated by carburization forms Cr carbide, and when carburization is accelerated, the Cr carbide becomes coarse, resulting in a significant decrease in ductility at low temperatures (approximately 800°C or lower). Also, the coefficient of thermal expansion of the carburized part of the tube is smaller than that of the non-carburized part, so if rapid heating or cooling is performed,
The occurrence of tensile/compressive stress and the decrease in ductility in the low temperature range sometimes caused the tube to break.

Therefore, in order to prevent tube destruction and maintain safe and smooth operation, it is necessary to conduct carburization inspections periodically to accurately understand the presence or absence of carburization and its progress. be.

As a non-destructive method of measuring carburization depth,
Compositional changes in the carburized zone, i.e. Cr deficiency, Fe and Ni
Various magnetic measurement methods are known that utilize changes in magnetic properties due to a relative increase in the amount of . For example, a method of determining the carburization depth of a tube by electromagnetic induction,
There are methods such as using a Gaussmeter that applies the Hall effect.

The measurement method using a Gaussmeter is as shown in FIG. 5, by applying a probe 3 containing a Hall element 2 connected to a Gaussmeter body 1 to the outer surface of a tube 4, which is a material to be tested, and forming a carburized portion 5 on its inner surface. If there is, the depth of the carburized part 5 is measured by detecting the Hall electromotive force generated when the lines of magnetic force of the residual magnetism of the carburized part 5 cross the Hall element 2. However, the residual magnetic flux density of the carburized part is too small (about 2 to 3 gauss for HP material), and if it is slightly larger than the earth's magnetism, it is not possible to accurately measure the carburized depth.

On the other hand, when comparing the carburization depth measurement results obtained by the electromagnetic induction method with the actual measurement results by destructive inspection, a relatively good correspondence is obtained for the HK40 material tube, but the measurement results for the HP material and HP improved material tube are The values varied widely and were unreliable.

This is true for tube 4 of HP material and HP improved material.
Decarburization occurs in the decarburized layer (the depth of which depends on the operating temperature and magnetism of the tube; the higher the temperature and the longer the time, the deeper the depth increases) formed on the outer surface of the tube. This is due to the increase in magnetic permeability. That is, for these tubes,
When used for a long time at high temperatures, even if there is no carburization on the inner surface of the tube, a decarburized layer (approximately 50 to 500 μm deep) that forms on the outer surface will give a high reading if the depth is large. This is because this indicated value can be mistaken for carburization.

Therefore, when measuring the presence or absence and depth of the carburized portion 5 of the tube 4, it is necessary to first remove the decarburized layer 6 on the outer surface of the tube 4 with a grinder, etc., and then remeasure and evaluate. That is the reality. Therefore, even if the number of locations to be measured is small, if a large number of locations are to be measured, a large amount of time must be spent, which poses many problems in terms of practicality.

Therefore, the applicant has already proposed a technique that allows simple and quick measurement of the decarburized layer 6 without grinding it. That is, as shown in FIG. 6, this is a Hall element arranged approximately parallel to the permanent magnet 7 in the magnetic field between the N pole and the S pole of the magnet 7. 8, and when the probe 9 approaches the carburized part 5, the magnetic field of the magnet 7 is influenced by the carburized part 5, and the lines of magnetic force are influenced by the Hall element as shown by the dotted line. 8 is used to cross the tube diagonally, and the carburized portion 5 on the inner surface of the tube 4 is determined based on the electromotive force generated at that time.

Therefore, if the decarburized layer 6 partially exists on the outer surface of the tube 4, the magnetic flux distribution of the magnet 7 will change due to the influence of the decarburized layer 6, but the decarburized layer 6 covers the entire outer surface of the tube 4. Since the magnetic field exists across the Hall element 8, the magnetic field of the magnet 7 changes thereby, and the lines of magnetic force do not cross the Hall element 8 diagonally. In other words, unless there is a carburized part 5, the Hall element 8
The lines of magnetic force passing through remain parallel to the Hall element 8, and no electromotive force is generated in the Hall element 8.
Therefore, the decarburized layer 6 will not be mistaken as the carburized portion 5.

(Problem to be Solved by the Invention) However, when using the probe 9 having such a configuration, at the center of the part where the carburized part 5 has a wide spread, the lines of magnetic force passing through the Hall element 8 Since the voltage becomes parallel to the output voltage and the electromotive voltage of the output becomes zero, there is a problem that it becomes impossible to make a determination. That is, since the lines of magnetic force obliquely cross the Hall element 8 at both ends of the carburized part 5, the output waveform of the electromotive force of the Hall element 8 is as shown in FIG. However, this is the same as the output waveform when there are two locally carburized parts 5 as shown in FIG. It was not possible to distinguish between cases where part 5 was present.

In view of these problems, the present invention proposes a novel probe for measuring carburization that can determine the depth and range of a carburized portion.

(Means for Solving the Problems) As a specific means for solving the above-mentioned problems, the present invention includes a magnet and a Hall element disposed within the magnetic field of the magnet. In a probe for carburization measurement that measures a carburized part by changes in magnetic lines of force caused by the carburized part inside the material, on the side of the material to be inspected of the magnet and on the central part side between a pair of magnetic poles,
A first Hall element is provided so as to be substantially along the direction of the magnetic lines of force, a second Hall element is provided so that the magnetic flux density decreases when the carburized part approaches, and a third Hall element is provided on the opposite side of the second Hall element with respect to the magnet. Provide an element,
A dummy piece is provided near the third Hall element so that the magnetic field on the third Hall element side is approximately equivalent to the magnetic field on the second Hall element side in a portion of the material to be inspected that does not have a carburized part. .

(Function) When the first Hall element 13 approaches the carburized part 18 when measuring the carburized part 18 of the tube 17, the lines of magnetic force of the magnet 12 diagonally cross the first Hall element 13, and the output of the carburized part 18 is An electromotive force is generated that correlates with depth. Further, when the carburized portion 18 has a spread, the first Hall element 13 generates an output at both ends thereof. On the other hand, the magnetic flux density of the lines of magnetic force passing through the second Hall element 14 is reduced if the carburized portion 18 is present, so the electromotive voltage thereof is also reduced. Further, in the third Hall element 15, an electromotive force equivalent to the decarburized layer 19 is generated, so by canceling this from the output of the second Hall element 14, the decarburized layer 19 is generated. The impact will be less.

(Embodiment) Hereinafter, the present invention will be described in detail with reference to the illustrated embodiment. As shown in FIG.
A Hall element 13, a second Hall element 14, and a third Hall element 15 are provided, and a dummy piece 16 is provided on the protective container 11. The magnet 12 is rod-shaped, and two Hall elements 13 and 14 are installed on the cracking tube (test material) 17 side of the magnet 12 so as to be located approximately in the center between the magnetic poles N and S.
is provided. The Hall elements 13 and 14 have a flat plate shape, and when a current is passed in a direction perpendicular to a magnetic field in the thickness direction of the plate, an electromotive force is generated in a direction perpendicular to the magnetic field and current. .
The first Hall element 13 is parallel to the magnet 12, and
It is provided so as to substantially follow the lines of magnetic force of the magnet 12 during normal operation without the carburized portion 18 . Second Hall element 14
is arranged in a direction substantially perpendicular to the first Hall element 13, so that the lines of magnetic force of the magnet 12 normally cross the second Hall element 14 at right angles, and the magnetic flux density decreases when the carburized part 18 approaches. .

The dummy piece 16 has substantially the same magnetic permeability as the portion of the tube 17 other than the carburized portion 18, that is, the decarburized layer 19 portion, and is used by cutting, for example, a part of the cracking tube that has the decarburized layer 20. Alternatively, a completely different member may be used. This dummy piece 16 is attached to the tube 17 so that it is approximately symmetrical to the tube 17 with respect to the magnet 12.
are placed equidistant apart. The third Hall element 15 is the same as the second Hall element 14 and is arranged near the center between the pair of magnetic poles of the magnet 12 so as to be approximately symmetrical with the second Hall element 14 with respect to the magnet 12. Therefore, because of the presence of the dummy piece 16, the magnetic field on the third Hall element 15 side is approximately equivalent to the magnetic field on the second Hall element 14 side in the portion of the tube 17 where the carburized portion 18 is not present. This third
The Hall element 15 is connected in the opposite direction to the second Hall element 14 so that the electromotive force cancels out.
The protective container 11 is made of a non-magnetic material, and the dummy piece 1
It is combined with 6.

When measuring the carburized portion 16 of the cracking tube 17 using the probe 10 configured as described above, the probe 10 is applied to the outer surface of the tube 17, and the probe 10 is scanned in the axial direction and circumferential direction of the tube 17. do.

When the tube 17 does not have the carburized portion 18, the magnetic field of the magnet 12 is not disturbed, so that magnetic flux is distributed approximately parallel to the magnet 12 in the center between the magnetic poles N and S. Therefore, since the lines of magnetic force that cross the first Hall element 13 are substantially parallel, the output of the electromotive voltage exhibits a constant value of zero or a low level. on the other hand,
On the second Hall element 14 and third Hall element 15 sides, decarburized layers 19 and 20 of high magnetic permeability of the tube 17 and dummy piece 16 are present in the vicinity thereof, and the lines of magnetic force of the magnet 12 are attracted by this. Since the magnetic fields of both are approximately equivalent, each Hall element 14,
The magnetic flux densities passing through 15 are both large, and their electromotive voltages exhibit approximately the same level. Therefore, the output of the terminal 21 obtained by canceling out the electromotive voltages of the second Hall element 14 and the third Hall element 15 is almost a value close to zero, and this output and the output of the first Hall element 13 are It can be seen from the figure that no carburized portion 18 exists in the tube 17.

Carburized portion 18 that extends inside the tube 17
exists, when the probe 10 approaches, the magnetic lines of force of the magnet 12 are strongly attracted under the influence of the high magnetic permeability of the carburized part 18, so that the lines of magnetic force passing through the first Hall element 13 are tilted. Therefore, the output waveform of the first Hall element 13 is such that an electromotive voltage rises at both ends of the carburized portion 18, as shown in FIG. 3D. Furthermore, when the lines of magnetic force are strongly attracted by the carburized portion 18, the magnetic flux density of the lines of magnetic force passing through the second Hall element 14 decreases accordingly. For example, assuming that the probe 10 is located exactly in the center of the carburized part 18 as shown in FIG. Carburized part 1
8, and from this carburized part 18 the magnet 1
2, the magnetic flux density of the lines of magnetic force passing through the second Hall element 14 becomes sparse. Therefore, the level of the output waveform of the electromotive force of the second Hall element 14 decreases in the central portion of the carburized portion 18, as shown in FIG. 3A. In this case, the magnetic flux density of the second Hall element 14 mainly depends on the depth of the carburized portion 18.
However, the carburized part 18 is not necessarily formed clearly and conspicuously, and even if the carburized part 18 is at the same depth, the tube 1
Since the overall magnetic permeability of the 7-side becomes lower toward the end of the carburized portion 18, the output waveform of the second Hall element 14 changes smoothly as shown in FIG. 3A.

On the other hand, on the third Hall element 15 side, the lines of magnetic force of the magnet 12 are strongly attracted to the carburized part 18 side, which has high magnetic permeability and a large cross-sectional area, so although there is a dummy piece 16, the magnetic flux passing through this third Hall element 15 The density will decrease slightly. This results in the second
The electromotive voltages of the Hall element 14 and the third Hall element 15 have waveforms as shown in FIG.
As shown in FIG. C, the influence of the decarburized layer 19 of the tube 17 is removed, and the carburized portion 18 becomes conspicuous.

When the output waveform shown in FIG. 3 is obtained, there are two rises in the electromotive force of the first Hall element 13, and an output obtained by canceling out the electromotive voltages of the second Hall element 14 and the third Hall element 15 between them. When the value is above a predetermined level, it is known that a carburized portion 18 with a spread exists at that position, and the area of the carburized portion 18 can also be determined. Note that the carburization depth of the carburized portion 18 in this case is correlated with the peak value of the electromotive force of the first Hall element 13, and the carburization depth can be determined from this.

Second Hall element 14 and third Hall element 15
is not limited to being placed in the center between the magnetic poles of the magnet 12, but may be placed near the outside of one of the magnetic poles in the longitudinal direction of the magnet, as shown in FIG. 4, for example. In this case as well, if the magnet 12 is close to the carburized part 18,
Because the lines of magnetic force are strongly drawn toward the tube 17, the second Hall element 14 and the third Hall element 1
The magnetic flux density of the lines of magnetic force passing through 5 becomes lower, and the carburized part 1
8 measurements are possible.

In the above embodiment, the first Hall element 13 is placed parallel to the magnet 12, and the second Hall element 14 and the third Hall element 13 are placed parallel to each other.
Although the Hall elements 15 are arranged approximately at right angles to the first Hall element 13, it is not necessary to arrange them strictly in this way, and the first Hall element 13 is arranged in a direction along the lines of magnetic force, and the second Hall element 14 is arranged in a direction along the lines of magnetic force. Any arrangement that can detect a decrease in magnetic flux density due to the proximity of the carburized portion 18 is sufficient.

The magnet 12 is not limited to a solid bar magnet, but may also be a rectangular cylindrical magnet,
It may be cylindrical or the like, or it may be U-shaped as shown in FIG.

Further, as the magnet, it is also possible to use an electromagnet instead of the permanent magnet 12 as shown in the embodiment.

A plurality of probes 10 may be provided in the circumferential direction of the tube 17.

(Effects of the Invention) According to the present invention, the first Hall element is provided on the detected side of the magnet and on the center side between the pair of magnetic poles so as to be substantially along the direction of the lines of magnetic force, and the first Hall element Since the two-hole element is provided in such a way that the magnetic flux density decreases when approaching the carburized part, if there is no carburized part in the tube, the magnetic field of the magnet will not be disturbed, so the magnetic flux density will decrease when approaching the carburized part. The lines of magnetic force are approximately parallel, and the output of the electromotive voltage exhibits a constant value of zero or a low level. On the other hand, the second Hall element and the third
On the Hall element side, even if there is a decarburized layer in the tube, the dummy piece makes the two magnetic fields approximately equivalent, so the magnetic flux density passing through each Hall element is large, and the electromotive force is approximately the same. Indicates the level of Therefore, it can be seen from the outputs of the second Hall element, the third Hall element, and the output of the first Hall element that there is no carburized portion in the tube. In addition, if there is a carburized part inside the tube, when the probe approaches, the magnetic lines of force of the magnet are strongly attracted due to the influence of the high magnetic permeability of the carburized part, causing a slope in the lines of magnetic force passing through the first Hall element. . Therefore, the output waveform of the first Hall element is such that an electromotive voltage rises at both ends of the carburized portion. Furthermore, the magnetic flux density of the lines of magnetic force passing through the second Hall element decreases. Therefore, the level of the output waveform of the electromotive force of the second Hall element decreases in the central portion of the carburized portion. On the other hand, on the third Hall element side, the magnetic lines of force of the magnet are strongly attracted to the carburized part side, which has high magnetic permeability and a large cross-sectional area, so although there is a dummy piece, the magnetic flux density passing through this third Hall element decreases slightly. become. As a result, the electromotive force of the second Hall element and the third Hall element is influenced by the decarburized layer of the tube, and the carburized portion becomes more prominent. Therefore, for example, there are two places where the electromotive force of the first Hall element rises, and between them there are two places where the electromotive force of the first Hall element and the third Hall element rise.
When the output after canceling the electromotive force of the Hall element shows a value equal to or higher than a predetermined level, it is known that a carburized portion with a spread exists at that position, and the area of the carburized portion can also be determined.

In other words, by combining changes in the slope of the magnetic field lines and changes in magnetic flux density due to the presence of a carburized part, it is possible to measure not only the depth of the carburized part, but also the spread of the carburized part, making it possible to determine the area of the carburized part. Therefore, measurement accuracy is significantly improved compared to the conventional method. Also the second
It is conceivable that the Hall element is provided near the magnetic pole so that the magnetic flux density of the lines of magnetic force passing through the second Hall element increases when the carburized part approaches, but in the present invention, the magnetic flux density of the second Hall element is reduced. Therefore, it is possible to increase or decrease the change in magnetic flux density, and it becomes easy to distinguish between carburized parts and non-carburized parts. Moreover, since the dummy piece is provided, it is possible to eliminate the influence of parts other than the carburized part by the output of the second Hall element and the third Hall element, making reliable measurement easy and quick. There are benefits to doing so.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG.
3 is a waveform diagram, FIG. 4 is a sectional view showing another embodiment of the present invention, FIG. 5 is a configuration diagram showing a conventional example, and FIG. 6 is another conventional example. FIG. 7 is a waveform diagram, and FIG. 8 is a sectional view of the tube. 10...Probe, 12...Permanent magnet, 13...
...First Hall element, 14...Second Hall element, 1
5...Third Hall element, 16...Dummy piece, 17
... Cracking tube, 18 ... Carburizing section, 1
9...Decarburized layer.

Claims (1)

[Claims] 1. In a probe for carburization measurement, which is equipped with a magnet and a Hall element placed in the magnetic field of the magnet, and measures the carburized part by changes in the lines of magnetic force caused by the carburized part inside the material to be inspected. A first Hall element is provided on the side of the material to be inspected and on the center side between the pair of magnetic poles so as to be substantially along the direction of the lines of magnetic force, and a second Hall element is provided so that the magnetic flux density decreases when the carburized part approaches. , a third Hall element is provided on the opposite side of the second Hall element to the magnet, and the magnetic field on the third Hall element side is approximately equivalent to the magnetic field on the second Hall element side in a portion of the test material that does not have a carburized part. A probe for carburization measurement, characterized in that a dummy piece is provided near the third Hall element so that the following is achieved.