JPS626156A - Carburization measuring probe - Google Patents

Abstract

PURPOSE:To measure not only depth of a carburized part but also the carburized part having an expense by providing a Hall element in the direction running roughly along a line of magnetic force of the side of a material to be inspected of a magnet, and a position where a magnetic flux density decreases at the time when the carburized part has approached, respectively. CONSTITUTION:In case a carburized part 18 having an expanse in the inside of a tube 17 exists, when a probe 10 approaches, a line of magnetic force of a magnet 12 is influenced by a high magnetic permeability of the carburized part 18 and a attracted strongly, and an inclination is generated in the line of magnetic force passing through a Hall element 13. Therefore, an output waveform of the Hall element 13 becomes that which has raised an electromotive voltage in both end parts of the carburized part 18. Also, when the line of magnetic force is attracted strongly by the carburized part 18, a magnetic flux density of the line of magnetic force passing through a Hall element 14 which is roughly equivalent to the side of a Hall element 15, due to existence of decarbonized layers 19, 20 of the high magnetic permeability of the tube 17 and a dummy piece 16, and when an output which has offset the electromotive voltage of the Hall elements 14, 15 shows a value of a prescribed level or above, it is decided that the carburized part 18 having an expanse exists.

Description

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

(Prior art) As a reaction tube for recovering ethylene, etc. by thermally decomposing raw material naphtha under high temperature and high pressure, a cod tube for ethylene production is manufactured using ASTM H) [40 (0,4χ
C-25χCr-20χNi), HP45 (0,45
χC-25XCr-35χNl), or IP improved material (1
1P material with Mo2N, Nb, etc. added singly or in combination), etc. are used.

Thalassoking tubes will be used for a long time
Immediately, carbon generated as a result of the 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 carburizing becomes Cr
When carbides are formed and carburization is accelerated, the Cr carbides become coarse, resulting in a significant decrease in ductility in a low temperature range (approximately 800° C. or lower). The coefficient of thermal expansion of the carburized part of the tube is
Since it is smaller than that of the non-carburized part, when it is heated and cooled rapidly, the generation of tensile and compressive stress and the decrease in ductility in the low temperature range are combined, and the tube may break.

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

As a non-destructive method for measuring the carburization depth, there are various magnetic measurement methods that utilize changes in the composition of the carburized part, that is, changes in magnetic properties due to Cr deficiency and relative increases in Fe and Ni. Are known. For example, there is a method of determining the carburization depth of the tube by electromagnetic induction, a method of using a Gauss meter that applies the Hall effect, etc.

As shown in FIG. 5, the measurement method using a Gaussmeter is to apply 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 to form a carburized portion 5 on the 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 is not able to accurately measure the carburized depth if it is slightly larger than the earth's magnetic field.

On the other hand, the carburization depth measurement results obtained by electromagnetic induction method,
Comparing with the actual measurement results from destructive testing, the HK40 material tube shows a relatively good response, but the I
For tubes made of IP material or good count material, the measurement values varied greatly and were unreliable.

This is due to the decarburized layer formed on the outer surface of the tube 4 of HP material and l (P improved material). This is due to the fact that Cr removal occurs along with decarburization, and the magnetic permeability of that part increases.In other words, when these tubes are used for a long time at high temperatures, the inner surface of the tube becomes Even if carburization has not occurred, if the depth of the decarburized layer (approximately 50 to 500 μm deep) that has formed on the outer surface is large, a high reading will be shown, so this reading may be mistaken for carburization. be.

Therefore, when measuring the presence or absence and depth of carburization on 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, the probe 9 is provided with a carburized part 5.
, the magnetic field of the magnet 7 is influenced by the carburized part 5, and the lines of magnetic force diagonally cross the Hall element 8 as shown by the dotted line. The carburized portion 5 is determined.

Therefore, if the decarburized layer 6 is partially present 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 is spread over the entire outer surface of the tube 4. Since it exists, the magnetic field of the magnet 7 changes, and the lines of magnetic force do not cross the Hall element 8 diagonally.

In other words, as long as there is no carburized part 5, the lines of magnetic force passing through the Hall element 8 remain parallel to the Hall element 8, and the lines of magnetic force passing through the Hall element 8 remain parallel to the Hall element 8.
Therefore, the decarburized layer 6 will not be mistaken for 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 , and the output electromotive voltage becomes zero, so there is a problem that it cannot be determined. In other words, at both ends of the carburized part 5, the lines of magnetic force cross diagonally with respect to the Hall element 8,
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 there is a 5.

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 carburized measurement probe that measures carburized parts by changes in magnetic lines of force caused by the carburized parts inside the material, a probe is placed on the side of the material to be inspected of the magnet and on the side of the center between a pair of magnetic poles so as to be approximately along the direction of the lines of magnetic force. A first Hall element is provided at the magnet, 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 a third Hall element is provided at the side opposite to the second Hall element with respect to the magnet. A dummy piece is provided near the third Hall element so that the magnetic field on the 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 portion.

(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 cross diagonally with respect to the first Hall element 13, and as its output, the carburized part 18 An electromotive force is generated that correlates to the depth of the

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. Also the third
In the Hall element 15, an electromotive force equivalent to the decarburized layer 19 is generated in the third Hall element 15, so by offsetting this from the output of the second Hall element 14, the influence of the decarburized layer 19 is reduced. Become.

(Example) Hereinafter, the present invention will be described in detail with reference to the illustrated example.
As shown in the figure, this probe 10 for carburization measurement includes a permanent magnet 12, a first Hall element 13, and a second Hall element 13 in a protective container 11.
A Hall element 14 and a third Hall element 15 are provided, and a dummy piece 16 is provided on the protective container 11. magnet 1
2 has a rod shape, and two Hall elements 13 and 14 are provided on the cranking tube (test material H7 side) of this magnet 12 so as to be located approximately in the center between the magnetic poles N and S. 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 provided parallel to the magnet 12 and substantially along the lines of magnetic force of the magnet 12 when there is no carburized portion 18.The second Hall element 14
is arranged substantially perpendicular to the first Hall element 13,
Normally, the lines of magnetic force of the magnet 12 cross the second Hall element 14 at right angles, and the magnetic flux density decreases when the carburized portion 18 approaches.

The dummy piece 16 is a portion of the tube 17 other than the carburized portion 18,
That is, it has approximately the same magnetic permeability as the decarburized layer 19 portion.For example, it is possible to cut a part of the cranking tube having the decarburized layer 20 and use it, or it is possible to use a completely different member. It's okay. This dummy piece 16 is the magnet 1
It is provided at an equal distance from the tube 17 so as to be substantially symmetrical with respect to the tube 17 with respect to the tube 17. The third Hall element 15 is the same as the second Hall element 14, and is arranged near the center between the magnetic poles of the pair of magnets 12A 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 without the carburized portion 18.

The third 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 is combined with a dummy piece 16.

When measuring the carburized portion 16 of the cranking tube 17 using the probe IO configured as described above, the probe l
A 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.

If 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-5. 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, the second Hall element 14 and the third Hall element 15
On the side, a decarburized layer 19120 of high magnetic permeability exists in the tube 17 and the dummy piece 16 in the vicinity thereof, and this attracts the magnetic lines of force of the magnet 12, but since the magnetic fields of both are approximately equivalent, each Hall element 14. The magnetic flux densities passing through the second Hall element 14 and the third Hall element 15 are both large, and their electromotive voltages are at 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 as follows. The value is almost zero, and it can be seen from this output and the output of the first Hall element 13 that there is no carburized portion 18 in the tube 17.

If there is a carburized part 18 that spreads inside the tube 17, when the probe lO approaches, the lines of magnetic force of the magnet 12 are strongly attracted by the high magnetic permeability of the carburized part 18, so that the first Hall element 13 There is a slope in the magnetic field lines that pass through. Therefore, the output waveform of the first Hall element 13 is such that the electromotive voltage rises at both ends of the carburized portion 18, as shown in the third diagram. 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. 18 and enters the S pole side of the magnet 12 from this carburized portion 18, so that the magnetic flux density of the magnetic lines of 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 clearly formed, and even if the depth is the same, the overall magnetic permeability of the tube 17 side becomes lower toward the end of the carburized part 18, so the second hole The output waveform of the 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. As a result, the electromotive voltages of the second Hall element 14 and the third Hall element 15 have waveforms as shown in FIGS. 3A and 3B.
The output of the terminal 21 obtained by canceling out both of these electromotive voltages is:
As shown in FIG. 3C, 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 higher than 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.

The second Hall element 14 and the third Hall element 15 are connected to the magnet 1
The carburized portion 18 is not limited to being disposed at the center between the two magnetic poles, but may be placed near the outer side of one of the magnetic poles in the longitudinal direction of the magnet, as shown in FIG. If they are close to each other, the lines of magnetic force of the magnet 12 will be strongly drawn toward the tube 17,
As a result, the magnetic flux density of the lines of magnetic force passing through the second Hall element 14 and the third Hall element 15 becomes lower, and the carburized part 1
It is possible to measure days.

Note that in the above embodiment, the first Hall element 13 is connected to the magnet 12.
In parallel, the second Hall element 14 and the third Hall element 15
are arranged approximately at right angles to the first Hall element 13,
It is not necessary to arrange them strictly as described above, and it is sufficient that the first Hall element 13 is arranged in a direction along the lines of magnetic force, and the second Hall element 14 is arranged so that a decrease in magnetic flux density due to the proximity of the carburized part 18 can be detected. be.

The magnet 12 is not limited to a solid bar magnet, but may be square or cylindrical, or 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 2-hole element is installed so that the magnetic flux density decreases when approaching the 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. It is also possible that the second 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 decreases. This makes it possible to increase or decrease the change in magnetic flux density, making it easy to distinguish between carburized and non-carburized parts. Moreover, the third Hall element is provided separately from the second Hall element, and the magnetic field on the second Hall element side is approximately equivalent to the magnetic field on the second Hall element side in the part of the test material that does not have a carburized part. Since a dummy piece is provided as shown in FIG. There are benefits to doing so.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIG. 2 is an explanatory diagram of the same operation, FIG. 3 is a waveform diagram of the same, FIG. The figure is a configuration diagram showing a conventional example.
The figures are a configuration diagram showing another conventional example, FIG. 7 is a waveform diagram, and FIG. 8 is a sectional view of the tube. 10--Ploop, 12-Permanent magnet, 13--First Hall element, 14--Second Hall element, 15--Third Hall element, 16-Dummy piece, 17--Cracking tube, 18--Carburized part , 19.-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 portion by changes in the lines of magnetic force caused by the carburized portion inside the material to be inspected. A first Hall element is provided on the inspection material side 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 portion. A probe for carburization measurement, characterized in that a dummy piece is provided near the third Hall element so that