JPS626155A - Carburization measuring probe - Google Patents

Abstract

PURPOSE:To measure not only depth of a carburized part but also the carburized part having an expanse 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 the direction in which a magnetic flux density decreases at the time when the carburized part has approached, respectively. CONSTITUTION:In case a carburized part 16 having an expanse in the inside of a tube 15, when a probe 10 approaches, a magnetic field of a magnet 12 is influenced by a high magnetic permeability of the carburized part 16 and attracted strongly, and an inclination is generated in a line of magnetic force passing through a Hall element 13. Therefore, an output waveform of the Hall element 13 goes to one which has raised an electromotive voltage in both end parts of the carburized part 16. On the other hand, when the line of magnetic force is attracted strongly by the carburized part 16, a magnetic flux density of the line of magnetic force passing through a Hall element 14 decreases, therefore, when the electromotive voltage of the Hall element 14 shows a value of a prescribed level or below, it is decided that the carburized part 16 having an expanse exists in its position, and also an area of its carburized part 16 can be decided.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is used for carburization measurement, which is used when non-destructively measuring carburized parts generated on the inner surface of cracking tubes for ethylene production in the petrochemical industry from the outer surface. It concerns probes.

(Prior art) As a cranking 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, 637M HK40 (0.4χC
-25χCr-20χNi), HP45 (0,45χ
C-25χCr-35χNl)% or IP improved material (IP
Materials in which MO% W, Nb, etc. are added singly or in combination) are used.

When a cranking tube is used for a long period of time, carbon generated as a result of a 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 in a low temperature range (approximately 800° C. or lower). Furthermore, since the coefficient of thermal expansion of the carburized portion of the tube is smaller than that of the non-carburized portion, rapid heating and cooling will result in the generation of tensile and compressive stress and a decrease in ductility in the low-temperature range. Tube breakage could occur.

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. 8, the measurement method using a Gaussmeter is to apply a probe 3 containing a Hall element 2 connected to a Gaussmeter main body l 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 it is not possible to accurately measure the carburized depth if it is slightly larger than the earth's magnetism.

On the other hand, the carburization depth measurement results obtained by electromagnetic induction method,
Comparing the results with actual measurement results from destructive testing, although relatively good results are obtained for the HK40 material tube,
Tubes made of P material and ■P improved material had large variations in measured values and poor reliability.

This is because tube 4 of HP material or HP improved material has a decarburized layer formed on its outer surface (the depth of which depends on the temperature at which the tube is used and the magnetism used; the higher the temperature and the longer the time, the deeper it becomes). ) 6, decarburization and Cr removal occur, and the magnetic permeability of that portion increases. In other words, when these tubes are used at high temperatures for long periods of time, even if the inner surface of the tube is not carburized, the depth of the decarburized layer (approximately 50 to 500 μm deep) formed on the outer surface increases. This is because when the value is large, a high indicated value is indicated, and this indicated value is 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. 9, this is a permanent magnet 7 and a Hall element arranged in a magnetic field at an intermediate portion between the N pole and the S pole of this magnet 7 so as to be in line with the magnet 7. 8 is used, 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. 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 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 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. 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, so
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.
Therefore, there is a case where there is a carburized part 5 that spreads, and a case where there is a carburized part 5 that is localized.
It was not possible to distinguish between the case where there was a carburized portion 5 at a location.

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 same time as a second Hall element is provided so that the magnetic flux density decreases when the carburized portion approaches.

(Function) When the first Hall element 13 approaches the carburized part 16 when measuring the carburized part 16 of the tube 15, 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 16 An electromotive force is generated that correlates to the depth of the

Further, when the carburized portion 16 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 16 is present, so the electromotive force thereof is also reduced. Therefore,
From the outputs of these Hall elements 13 and 14, not only the depth but also the area of the carburized portion 16 can be determined.

(Example) Hereinafter, the present invention will be described in detail with reference to the illustrated example.
As shown in the figure, this carburization measurement probe 10 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 is provided. The magnet 12 is rod-shaped, and the cracking tube (test material) 15 of this magnet 12
On the side, two Hall elements 13 and 14 are provided so as to be located approximately in the center between the magnetic poles N-3. 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 during normal operation. The second Hall element 14 is arranged substantially perpendicularly to the first Hall element 13, and the lines of magnetic force of the magnet 12 cross the second Hall element 14 at right angles under normal conditions, and the magnetic flux density decreases when the carburized part 16 approaches. It looks like this. The protective container 11 is made of non-magnetic material.

When measuring the carburized portion 16 of the cracking tube 15 using the probe 10 configured as described above, the probe 10 is
0 is applied to the outer surface of the tube 15, and the probe 10 is scanned in the axial direction and circumferential direction of the tube 15.

If the tube 15 does not have the carburized portion 16, 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-3. 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, since the magnetic lines of force cross the second Hall element 14 at right angles and the magnetic flux density is large,
The electromotive voltage of this second Hall element 14 is large. Therefore,
By the outputs of these Hall elements 13 and 14, the carburized part 1
It turns out that 6 does not exist.

When a carburized portion 16 with a wide spread exists inside the tube 15, when the probe 1O approaches, the magnetic field of the magnet 12 becomes strong (attracted) due to the influence of the high magnetic permeability of the carburized portion 16, so that the first Hall element An inclination occurs in the lines of magnetic force passing through the carburized portion 13. Therefore, the output waveform of the first Hall element 13 is such that the electromotive force rises at both ends of the carburized portion 16, as shown in FIG. 3B. When the lines of magnetic force are strongly attracted in the second Hall element 14, the magnetic flux density of the lines of magnetic force passing through the second Hall element 14 decreases. The lines of magnetic force coming out from the N pole of 12 are strongly attracted to the carburized part 16 side, and the carburized part 16 has high magnetic permeability.
Since the magnetic flux passes through the carburized portion 16 and enters the S pole side of the magnet 12, 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 voltage of the second Hall element 14 decreases in the central portion of the carburized portion 16, 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 16. However, the carburized part 16 is not necessarily clearly formed, and even if the depth is the same, the overall magnetic permeability of the tube 15 side becomes lower toward the end of the carburized part 16, so the second hole The output waveform of the element 14 changes smoothly as shown in FIG. 3A.

When the output waveforms shown in FIGS. 3A and 3B are obtained, there are two rises in the electromotive force of the first Hall element 13, and
When the electromotive force of the second Hall element 14 shows a value below a predetermined level during that time, it is known that a carburized portion 16 with a spread exists at that position, and the carburized portion 16
The area of can also be determined. Note that the carburization depth of the carburized portion 16 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 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 16, the magnetic lines of force of the magnet 12 are strongly drawn toward the tube 15, so the magnetic flux density of the magnetic lines of force passing through the second Hall element 14 becomes low, making it possible to measure the carburized part 16. It is.

Incidentally, the output waveforms of the second Hall element 13 and the first Hall element 13 in this case are as shown in FIGS. 5A and 5B.

Note that in the above embodiment, the first Hall element 13 is connected to the magnet 12.
Although the second Hall element 14 is arranged in parallel with the first Hall element 13 at substantially right angles to the first Hall element 13, it is not necessary to arrange them strictly like this, and the first ball element 13 is arranged in a direction along the lines of magnetic force. It is sufficient that the second Hall element 14 is arranged so that it can detect a decrease in magnetic flux density due to the proximity of the carburized portion 16.

The magnet 12 is not limited to a solid bar magnet, but may be square, cylindrical, etc., 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. For example, in the case of the electromagnet 18, it is appropriate to use a coil 2o wound around a U-shaped iron core 19 as shown in FIG.

A plurality of probes 10 may be provided in the circumferential direction of the tube 15.

(Effects of the Invention) According to the present invention, the first Hall element is provided on the specimen material 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 magnetic lines of force, and the Since the second Hall element is provided 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 wide carburized part, making it easy to judge the area of the carburized part. This makes it possible to significantly improve measurement accuracy compared to conventional methods. 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. Therefore, changes in the increase or decrease in magnetic flux density are
This makes it easy to distinguish between carburized and non-carburized parts.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing the first embodiment of the present invention, FIG. 2 is a diagram explaining the same operation, FIG. 3 is a waveform diagram of the same, and FIG. 4 is a diagram showing the second embodiment of the present invention.
A configuration diagram showing the embodiment, FIG. 5 is the same waveform diagram, FIGS. 6 and 7 are configuration diagrams showing another embodiment, FIG. 8 is a configuration diagram showing the conventional example, and FIG. 9 is different. FIG. 10 is a waveform diagram, and FIG. 11 is a sectional view of a tube. 10--probe, 12--permanent magnet, 13--first
Hall element, 14--Second Hall element, 15--Cracking tube, 16--Carburized portion, 17-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 was provided on the inspection material side and on the center side between a pair of magnetic poles so as to be substantially along the direction of the magnetic lines of force, and a second Hall element was provided so that the magnetic flux density decreased when the carburized part approached. A probe for carburization measurement that is characterized by: