JPS626158A - Probe for carburization measurement - Google Patents

Abstract

PURPOSE:To eliminate an influence caused by other part than a carburized part by providing the first Hall element in the vicinity of a magnetic pole of the side of a material to be inspected of a magnet, and providing a dummy piece in the vicinity of the second Hall element which has been provided in the vicinity of a magnetic pole of the opposite side. CONSTITUTION:In case a carburized part 18 does not exist in a tube 16, the tube 16 and a dummy piece 15 having a roughly equal magnetic permeability are provided symmetrically on both sides of a magnet 12, and an output which has offset an electromotive voltage of a Hall element 13 and 14 becomes zero or a low level. In case the carburized part 18 exists, its magnetic permeability is large, and its sectional area is large and the sectional area is large, therefore, since a line of magnetic force which has been emitted from the N pole of the magnet 12 is attracted strongly to the side of the carburized part 18, a magnetic flux density of the line of magnetic force passing through the Hall element 13 increases. Accordingly, the output which has offset the electromotive voltage of the Hall elements 13, 14 becomes high in the carburized part 18, therefore, existence of the carburized 18 and its range can be decided, and also, depth of the carburized part 18 can be decided from a peak value of its output.

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 thalassoking tubes for ethylene production in the petrochemical industry from the outer surface. This relates to probes for use.

(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, ^STM HK40 (0.4%℃
-25%Cr -20%Ni), HP45 (0,4
5%C-25%Cr-35%Ni), or IIP improved material (Mo added to IP material).

W, Nb, etc. are used singly or in combination.

When a cranking tube is used for a long period of time, carbon generated by 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). In addition, the coefficient of thermal expansion of the carburized part of the tube is smaller than that of the non-carburized part, so rapid heating and cooling will cause tension and
The generation of compressive stress and the decrease in ductility in the low temperature range may overlap, resulting in failure of the tube.

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. .

Various magnetic measurement methods are known as methods for non-destructively measuring the carburized depth, which 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. For example, there is a method of determining the carburization depth of a tube by electromagnetic induction, a method of using a Gauss meter that applies the Hall effect, etc.

As shown in FIG. 4, 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 the 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 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.

(Problem to be solved by the invention) However, when comparing the carburization depth measurement results obtained by such a magnetic measurement method with the actual measurement results by destructive inspection,
Although a relatively good response was obtained for the HK 40 material tube, the measurement values for tubes made of UP material and IP improved material varied widely and were poor in reliability.

This is due to the decarburized layer formed on the outer surface of the tube 4 made of IP material or IP improved material. ) 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 4 is not carburized, the decarburization layer (layer depth approximately 50 to 500 μs+) formed on the outer surface causes carburization. This is because when the depth is large, a high indicated value is shown, so this indicated value portion can be mistaken for carburization.

For this reason, conventionally, the tube 4 has a carburized portion 5.

When measuring the absence and depth, first remove the decarburized layer 6 on the outer surface of the tube 4 with a grinder, etc., and then measure again.
The reality is that it must be evaluated. 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.

(Means for Solving the Problems) The present invention is intended to solve such conventional problems, and as a specific means for that purpose, it includes a magnet and a magnet disposed within the magnetic field of the magnet. In a probe for carburization measurement, which is equipped with a Hall element and measures the carburized part inside the specimen material that has a decarburized layer on the outer surface by changes in the lines of magnetic force passing through the Hall element, a pair of magnetic poles are attached to the specimen material. A first Hall element for measurement is provided near the magnetic pole on the side of the material to be inspected, and a second Hall element for compensation is provided near the magnetic pole on the opposite side of the magnet. A dummy piece is provided near the second Hall element so that the magnetic field on the two-Hall element side is approximately equivalent to the magnetic field on the first Hall element side in a portion of the test material that does not have a carburized portion.

(Function) In the part where the carburized part 1B is not present, the output obtained by canceling the electromotive force of the first Hall element 13 and the second Hall element 14 shows a value of zero or a value close to zero. Because 12 lines of magnetic force are strongly attracted,
The magnetic flux density of the lines of magnetic force passing through the first Hall element 13 increases,
Although the electromotive voltage is large, it is approximately constant on the second Hall element 14 side. Therefore, by canceling out those electromotive voltages, the terminal 20
The output obtained from this becomes large, and the presence of the carburized portion 18 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 probe 10 for carburization measurement includes a permanent magnet 12 in a protective container 11 and a first Hall element 1 for measurement.
3. A second Hall element 14 for compensation is provided, and a dummy piece 15 is attached on the protective container 11. m stone 1
2 is a solid rod shape, and the pair of magnetic poles N-5 are in the far and near directions of the cranking tube 16, which is the test material.
It is arranged perpendicularly to the tube 16. The first Hall element 13 is disposed between the magnet 12 and the tube 16 near one of the magnetic poles, and parallel to the tube 16.
The Hall element 14 is arranged near the other magnetic pole of the magnet 12, and the first Hall element 13 and the second Hall element 14 are approximately symmetrical with respect to the magnet 12. 1st
The Hall element 13 and the second Hall element 14 are located within the magnetic field of the magnet 12, so that when a current is passed in a direction perpendicular to the lines of magnetic force that cross the plate thickness direction, an electromotive force is generated in the direction perpendicular to the lines of magnetic force and the current. It is configured.

Note that the tube 16 has a decarburized layer 17 over the entire outer surface, and a carburized portion 18 is generated on the inner side. Dummy piece 1
5 has substantially the same magnetic permeability as the portion of the tube 16 other than the carburized portion 18. For example, it is possible to cut a part of the cracking tube having the decarburized layer 19 and use it, or to use it completely. The dummy piece 15, which may be a separate member, is placed near the second Hall element 14 at a position that is approximately symmetrical to the tube 16 with respect to the magnet 12, and is attached to the protective container 11. Therefore, because of the presence of the dummy piece 15, the magnetic field on the second Hall element 14 side is applied to the first Hall element 13 in the portion of the tube 16 where the carburized portion 18 is not present.
The first Hall element 13 and the second Hall element 14 normally generate approximately the same high-level electromotive force. The first Hall element 13 and the second Hall element 14 are connected in opposite directions so that their electromotive voltages cancel each other out. The protective container 11 is made of non-magnetic material.

When measuring the presence or absence of the carburized portion 18 of the cracking tube 16 using the probe 10 configured as described above, the probe 10 is applied to the outer surface of the tube 16, and the
The proof lO is scanned in the axial direction and circumferential direction.

When the tube 16 does not have a carburized portion 18, the tube 16 and the dummy piece 15 having substantially the same magnetic permeability are symmetrically located on both sides of the magnet 12, and the first Hall element 13 and the second Hall element 14 are separated. The magnetic fields of are approximately equivalent.

Therefore, although some of the lines of magnetic force pass through the decarburized layer 17.19, the overall magnetic field is not disturbed, and the lines of magnetic force that exit the N pole of the magnet 12 cross the first Hall element 13 at right angles, and The lines of magnetic force entering the S pole cross the second Hall element 14 at right angles, and their magnetic flux densities are approximately the same for both. Therefore, the electromotive voltages of the first Hall element 13 and the second Hall element 14 are as shown in FIGS. 3(A) and 3(B).
As shown in FIG. 3(C), almost the same high level is shown, and by canceling this, the output obtained from the terminal 20 becomes zero or a low level as shown in FIG. can.

When the carburized part 18 exists, its magnetic permeability is high and its cross-sectional area is large, so the lines of magnetic force coming from the N pole of the magnet 12 are strongly directed toward the carburized part 18, as shown in FIG. Since the magnetic flux is attracted and enters the south pole side via the carburized portion 18, the magnetic flux density of the lines of magnetic force passing through the first Hall element 13 increases, and the electromotive voltage outputted thereby increases by the increase in magnetic flux density. On the other hand, on the second Hall element 14 side, the influence of the carburized portion 18 is small, and the magnetic flux density of the lines of magnetic force crossing it is approximately constant. Therefore, the output obtained by canceling out the electromotive voltages of both is the output of the carburized part 1
8, the degree becomes high as shown in FIG. 3(C), and from this the presence and range of the carburized portion 18 can be determined.

Also, in the output at this time, since the magnetic fields of both Hall elements 13 and 14 are equivalent in the part where there is no carburized part 18,
An electromotive force is obtained in which the influence of the decarburized layer 17 is almost eliminated. In other words, the output of the terminal 20 has a value that depends on the depth of the carburized portion 18, and the depth of the carburized portion 18 can also be determined from the peak value of this output.

The dummy piece 15 needs to be changed to a dummy with a magnetic permeability corresponding to the conditions of the material to be measured, for example, when the heating temperature is high and the decarburization depth becomes large. Therefore, if the dummy piece 15 is provided in a detachable manner with respect to the protective container 11, the versatility of the probe 10 can be obtained.

In addition to connecting the first Hall element 13 and the second Hall element 14 in opposite directions, the output of each electromotive voltage may be placed in a subtractor or the like to electrically cancel each other out.The magnet is a permanent magnet 12. An electromagnet may be used instead. Also magnet 12
The shape, structure, etc. are not particularly limited, and can be arbitrarily changed in design depending on the material to be examined.

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 second Hall element for compensation is provided separately from the first Hall element for measurement, and the magnetic field on the second Hall element side Since the dummy piece is provided so that the magnetic field is approximately equivalent to the magnetic field on the first Hall element side, it is possible to eliminate the influence of parts other than the carburized part when measuring the carburized part with the first Hall element. For example, in the case of a cranking tube, etc., there is no need to remove the decarburized layer on the outer surface, and there is an advantage that reliable measurements can be easily and quickly performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is a diagram explaining its operation, FIG. 3 is an output waveform diagram, and FIG. 4 is a block diagram showing a conventional example. 10... Proop, 12... Permanent magnet, 13...
First Hall element, 14...Second Hall element, 15...
・Dummy piece, 16...Cracking tube, 18・
...Carburized part. Patent applicant: Kubota Iron Works Co., Ltd. Vol. 1! J Figure 3 112 Figure 4

Claims (1)

[Claims] 1. A carburizing method that includes a magnet and a Hall element placed in the magnetic field of the magnet, and measures the carburized part inside the specimen having a decarburized layer on the outer surface by changes in magnetic lines of force passing through the Hall element. In the measurement probe, a magnet is installed so that a pair of magnetic poles are in the far and near direction with respect to the material to be measured, and a first Hall element for measurement is placed near the magnetic pole on the side of the material to be measured, and a first Hall element for measurement is placed near the magnetic pole on the opposite side. A second Hall element for compensation is provided in each of the
A dummy piece is provided near the second Hall element so that the magnetic field on the second Hall element side is approximately equivalent to the magnetic field on the first Hall element side in a portion of the material to be inspected that does not have a carburized portion. Carburization measurement probe.