JPS626160A - Carburization measuring probe - Google Patents

Abstract

PURPOSE:To decide with a high accuracy a carburized part having an expanse by providing a Hall element in the direction crossing a line of magnetic force in the center part between a pair of magnetic poles of a magnet, and also providing a Hall element in the vicinity of each magnetic pole, as well. CONSTITUTION:In case a carburized part 19 does not exist in a tube 16, an electromotive voltage of the first Hall element 13 shows a high level, and an output which has offset an electromotive voltage of the second Hall element 14 and the third Hall element 15 shows zero or its near value. In case when the carburized part 19 exists, a line of magnetic force which has been emitted from the N pole is attracted strongly to the side of the carburized part 19, and the electromotive voltage of the first Hall element 13 drops. On the other hand,in each magnetic pole side of the magnet 12, while it is opposed to the carburized part 19, a magnetic flux density between each magnetic pole and the tube 16 increases, and a signal which rises in both end parts of the carburized part 19 is obtained from a terminal 17, therefore, a range of the carburized part can be decided from between two signals.

Description

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

(Prior technology) As a cod 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% C
-25%Cr -20%Ni), HP45 (0,4
5%C-25%Cr-35%Ni), or HP improving material (Mo added to HP 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 if rapid heating and cooling are performed, the generation of tensile and compressive stress and the decrease in ductility in the low temperature range will overlap, causing the tube to Destruction 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. .

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. ing. 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 magnetic flux density of the carburized part is too small (about 2 to 3 gauss for IIP material) and is slightly larger than the earth's magnetism, making it impossible to accurately measure the carburized depth.

(Problems to be solved by the invention) On the other hand, the carburization depth measurement results obtained by the electromagnetic induction method,
Comparing the actual measurement results from destructive testing, although a relatively good response was obtained for the 11 and 40 material tubes,
For tubes made of bamboo or IIP-improved materials, the measurement values varied widely and were less reliable.

This is because tube 4 of HP material or IIP improved material has a decarburized layer formed on its outer surface (the depth of which depends on the temperature and time of use of the tube; 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 for a long time at high temperatures, even if the inner surface of the tube 4 is not carburized, the decarburized layer (approximately 50 to 500 μm deep) 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, when measuring the presence or absence and depth of the carburized portion 5 of the tube 4, it is necessary to remove the decarburized layer 6 on the outer surface of the tube 4 with a grinder or the like beforehand, 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.

(Means for Solving the Problems) The present invention aims to solve such conventional problems, and as specific means for that purpose,
For carburization measurement, which includes a magnet and a Hall element placed in the magnetic field of the magnet, and measures a carburized part inside a test material having a decarburized layer on the outer surface by changes in magnetic lines of force passing through the Hall element. In the probe, a first Hall element is provided at the center between a pair of magnetic poles of the magnet in a direction intersecting the lines of magnetic force, a second Hall element and a third Hall element are provided near each magnetic pole of the magnet, and these second Hall elements are provided in the vicinity of each magnetic pole of the magnet. The electromotive voltages of the Hall element and the third Hall element are canceled out.

(Function) If the carburized portion 19 exists, the magnetic flux density passing through the first Hall element 13 decreases, and the electromotive voltage decreases. On the other hand, the second Hall element 1
If there is a carburized part 19 on the 4th and 3rd Hall element 15 sides,
The magnetic flux density increases and the electromotive voltage increases. Therefore, when the two outputs are canceled out, signals appear at both ends of the carburized portion 19, and if the output of the first Hall element 13 is below a certain level between these signals, the carburized portion 19 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 measuring probe 10 is constructed by incorporating a permanent magnet 12 and first to third Hall elements 13, 14, and 15 into a protective container 11. magnet 12
has a U-shape, and is arranged so that its pair of magnetic poles N and S are located close to the cracking tube 16, which is the material to be tested, in the longitudinal direction.

The first Hall element 13 is located in the center between the pair of magnetic poles N-5 of the magnet 12, and is provided so as to intersect at right angles with the line of magnetic force from the N pole to the S pole. The second Hall element 14 is the magnet 1
The third Hall element 15 is arranged near one of the magnetic poles of 2 and between the respective magnetic poles and the tube 6, and parallel to the tube 16. Note that the first to third Hall elements 13, 14, and 15 are all within the magnetic field of the magnet 12, and when a current is passed in a direction perpendicular to the line of magnetic force that crosses the plate thickness direction, the current is perpendicular to the line of magnetic force and the current. The structure is such that an electromotive voltage is generated in the direction. The second Hall element 14 and the third Hall element 15 are connected in opposite directions, so that the terminal 17 outputs an output that cancels out their electromotive voltages. The tube 16 has a decarburized layer 18 over the entire outer surface and a carburized portion 19 on the inside.

When measuring the presence or absence of the carburized portion 19 inside the tube 16 using the probe 10 configured as described above, apply the probe IO to the outer surface of the tube 16 and
) is sequentially scanned in the longitudinal direction of the tube 16.

If the tube 16 does not have a carburized part 19, the magnetic lines of force coming out of the N pole of the magnet 12 enter the S pole as shown by the dotted line in FIG. 1, and the magnetic flux density of the lines of magnetic force crossing the first Hall element 13 is large, and the electromotive force of the first Hall element 13 is
Figure (A) shows a high level.

Furthermore, since the magnetic flux densities of the lines of magnetic force passing through the second Hall element I4 and the third Hall element 15, which are provided opposite to each magnetic pole, are both large, the electromotive force is as shown in Fig. 3 (B) and (C). The level is approximately the same. Therefore, the output of the terminal 17 obtained by canceling out both electromotive voltages shows a value of zero or a value close to it as shown in FIG. 3(D), and together with the output of the first Hall element 13 (high level), It can be seen that there is no carburized portion 19 in the tube 16.

When the carburized part 19 exists, its magnetic permeability is high and the cross-sectional area is large. Therefore, the lines of magnetic force coming from the N pole are strongly (attracted) to the carburized part 19, and the carburized part 19 is Since the magnetic flux passes through the first Hall element 13 and enters the south pole side, the magnetic flux density of the magnetic lines of force passing through the first Hall element 13 decreases significantly, and the electromotive voltage decreases as shown in FIG. 3 (8).

On the other hand, on each magnetic pole side of the magnet 12, the carburized portion 1
9, the lines of magnetic force are strongly attracted to the carburized part 19, so the magnetic flux density between each magnetic pole and the tube 16 increases, and the magnetic flux density passes through the second Hall element 14 and the third Hall element 15. Each electromotive voltage increases as the magnetic flux density increases. For example, when the probe 10 is in the position shown in FIG. 2(B), the electromotive voltage of the second Hall element 14 increases, and when the probe 10 is in the position shown in FIG. 2(C), the electromotive force of the second and third Hall elements 1
Both the electromotive voltages of 4.15 and 15 rise, and when the position shown in FIG. 2(D) is reached, the electromotive voltage of the third Hall element 15 rises.

In other words, the electromotive force of the second and third Hall elements 14.15 varies depending on the longitudinal position of the tube 16 as shown in FIG. 3(B).
Changes occur as shown in (C). When these electromotive voltages are canceled out, a signal is obtained from the terminal 17 that increases at both ends of the carburized portion 19 as shown in FIG. 3(D).

Therefore, between these two signals, the first Hall element 13
If the electromotive voltage has decreased below a certain level, it can be determined that the carburized portion 19 exists at that position, and it can be seen that the range corresponds to the area between the two signals.

In addition to connecting the second Hall element 14 and the third Hall element 15 in opposite directions as in the embodiment, the outputs of their respective electromotive voltages may be input into a subtracter or the like to electrically cancel each other out.

The permanent magnet 12 is replaced with an iron core 19 as shown in FIG.
An electromagnet 21 having a coil 20 wound around it may also be used.

Further, the shape, structure, etc. of the magnet 12 are not particularly limited, and can be arbitrarily changed in design depending on the material to be inspected.

(Effects of the Invention) According to the present invention, both ends of the carburized portion can be determined by canceling the outputs of the second Hall element and the third Hall element.
By using it together with the first Hall element □Therefore,
It is possible to accurately judge carburized areas that spread out, and in particular, there is no misidentification of carburized areas due to decarburized layers existing on the surface.
The effect is extremely large.

Furthermore, if there is a carburized portion, the first Hall element detects a decrease in the magnetic flux density, so the change is larger than that of a device that detects an increase, so reliability is improved.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing one embodiment of the present invention, Figure 2 (8)
3(A) to 3(D) are waveform diagrams, FIG. 4 is a block diagram showing another embodiment, and FIG. 5 is a diagram showing a conventional example. 10...Probe, 12...Permanent magnet, 13...
First Hall element, 14...Second Hall element, 15...
- Third Hall element, 16... cracking tube. Patent applicant Kubota Iron Works Co., Ltd. Figure 1 Figure 3 (A) L Ji--

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 first Hall element is provided at the center between a pair of magnetic poles of the magnet in a direction that intersects the lines of magnetic force, and a second Hall element and a third Hall element are provided near each magnetic pole of the magnet. A probe for carburization measurement, characterized in that the electromotive voltages of the second Hall element and the third Hall element are canceled out.