JP2012037315A - Total carbon amount measuring instrument and carburized depth evaluation device for ferritic steel pipe containing chromium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an instrument which accurately measures a total amount of carbon including a carburized layer of a ferritic steel pipe containing Cr.SOLUTION: The total carbon amount measuring instrument calculates the total amount of carbon including the carburized layer of the ferritic steel pipe containing Cr from DC magnetic characteristics and includes: an electromagnet provided with an excitation coil and yokes for magnetizing a pipe wall portion of the steel pipe in an axial direction; a detection coil which is disposed between the yokes and is wound in a circumferential direction of the steel pipe to detect a magnetic flux change of the pipe wall portion of the steel pipe; a magnetic measurement part which measures the DC magnetic characteristics of the pipe wall portion of the steel pipe in accordance with a magnetic field intensity of the electromagnet and a magnetic flux density based on an integral of an output value of the detection coil; and an arithmetic part provided with prescribed data of relation between the DC magnetic characteristics of the pipe wall portion of the steel pipe and the total amount of carbon. The total amount of carbon including the carburized layer is calculated from the measured DC magnetic characteristics of the pipe wall portion of the steel pipe.

Description

The present invention relates to a measuring instrument for measuring the total amount of carbon inside a ferritic steel pipe containing Cr by a magnetic property by a non-destructive method, and is difficult to directly measure in a ferritic steel pipe containing Cr. The present invention relates to an apparatus for evaluating the carburization depth of an inner surface portion of a steel pipe.

It is known that a cracking tube using austenitic stainless steel used in an ethylene production process of a petrochemical plant generates a carburized layer on an inner surface portion when used for a long time. Since the occurrence of this carburized layer is a factor that greatly reduces the life of the cracking tube, it is necessary to periodically measure the depth of the carburized layer (carburized depth) and accurately grasp its progress. . In this case, non-magnetic chromium carbide (Cr—C) is generated by carburization, the Cr concentration in the vicinity of the generation is lowered, and a part thereof is changed to ferritic stainless steel which is a ferromagnetic material. By grasping the change in the magnetic characteristics due to the formation of the ferromagnetic material from the base material which is a non-magnetic material, it is possible to accurately estimate the carburizing amount and evaluate the degree of carburizing.

On the other hand, in the case of a ferritic steel pipe containing Cr used for a tube for a heating furnace of a petrochemical plant, both the outer surface portion and the inner surface portion of the steel pipe are affected by carburizing and are made of non-magnetic Cr—C. However, since the base material is a ferromagnetic material, it is not easy to estimate the Cr—C amount of the non-magnetic material generated by carburization.

JP 2009-139220 A

The method disclosed in Patent Document 1 is a method of measuring the carburization depth of the inner and outer surfaces of a steel material made of a magnetic material using an electromagnetic property by an alternating current magnetization method, and includes the shape of a sensor probe, the magnetic field direction, and the excitation current intensity. The excitation frequency is optimized. As the shape of the sensor probe, a C-shaped coil probe is used, the excitation frequency is 40 to 50 Hz, the horizontal magnetic field is used for the magnetic field direction, and the carburization depth of the inner and outer surfaces is obtained by the third harmonic intensity. .

In this method, the carbon concentration in the local region (longitudinal direction) of the steel pipe can be measured, but the carbon concentration in the circumferential direction cannot be measured. In the third harmonic intensity measurement of the AC magnetization method, the oxide scale on the outer surface of the steel pipe, etc. There is a problem that the measurement accuracy is lacking because the signal strength is not large.

As a result of diligent research to solve the above problems, it was found that the total amount of carbon in the circumferential direction of the steel pipe can be accurately measured by evaluating the magnetic properties of the steel pipe using a direct current magnetization method. Completed.

In order to solve the above-mentioned problem, the carbon total amount measuring device according to claim 1 of the present invention is a carbon total amount measuring device that calculates the total amount of carbon including the carburized layer of the ferritic steel pipe containing Cr from the direct current magnetic characteristics. And an electromagnet having an exciting coil and a yoke for magnetizing a tubular portion of the steel pipe in the axial direction, and disposed between the yokes, and the coil is wound around the circumferential direction of the steel pipe. A detection coil for detecting a change in magnetic flux of the part, a magnetic measurement part for measuring a DC magnetic characteristic of the tubular part of the steel pipe from a magnetic flux density based on an integration of the magnetic field strength of the electromagnet and an output value of the detection coil, and Cr Calculation to calculate the total amount of carbon, including the carburized layer, from the measured DC magnetic properties of the pipe wall of the steel pipe based on the predetermined data on the relationship between the DC magnetic properties of the ferritic steel pipe and the total amount of carbon. Special features It is a total carbon measuring instrument to be.

According to the carbon total amount measuring apparatus of the first aspect of the present invention, an electromagnet including an exciting coil and a yoke for magnetizing a tube portion of a ferritic steel pipe containing Cr in the axial direction is disposed between the yokes. The coil is wound in the circumferential direction of the steel pipe to detect the magnetic flux change in the pipe wall, and from the magnetic flux density based on the integration of the magnetic field strength of the electromagnet and the output value of the detection coil, Based on the measured DC magnetic characteristics of the tube section of the steel pipe based on the predetermined data of the relationship between the DC magnetic characteristics of the ferritic steel pipe containing Cr and the total amount of carbon in the magnetism measuring section that measures the DC magnetic characteristics And a calculation unit that calculates the total amount of carbon including the carburized layer, so that the total amount of carbon including the carburized layer can be calculated with higher accuracy than the conventional AC magnetization method.

When a ferritic steel pipe containing Cr is carburized, Cr—C, which is a non-magnetic material, is generated from the ferrite structure of the base material, which is a ferromagnetic material. The DC magnetic characteristics of the present invention are the conventional AC magnetic characteristics. For example, it is superior to the detection of the total amount of carbon than the method using the third harmonic intensity. In addition, since a method is adopted in which a coil is wound in the circumferential direction of the steel pipe to detect the magnetic flux change in the pipe wall, the measurement results reflect the amount of carburizing in the circumferential direction of the steel pipe, and the measurement accuracy is reliable. Will increase.

The total carbon measuring machine according to claim 2 is the total carbon measuring machine according to claim 1, wherein the DC magnetic characteristic is a saturation magnetic flux density or a coercive force.

According to the invention of the carbon total amount measuring machine according to claim 2, if the DC magnetic characteristic is the saturation magnetic flux density or the coercive force, the correlation coefficient with the total amount of carbon is high, and the tube wall portion of the steel pipe is accurately obtained. The total amount of carbon can be calculated.

In the carbon total amount measuring machine according to claim 3, the cross-sectional shape of the yoke end surface in contact with the steel pipe is a semicircular shape having a radius substantially equal to the radius of the outer diameter of the steel pipe so as to contact the steel pipe from the circumferential direction. It is a carbon total amount measuring machine of Claim 1 or 2 characterized by the above-mentioned.

According to the invention for measuring the total amount of carbon according to claim 3, the cross-sectional shape of the yoke end surface in contact with the steel pipe is a semicircular shape having a radius substantially equal to the radius of the outer diameter of the steel pipe so as to contact the steel pipe from the circumferential direction. Therefore, the magnetic flux generated by the exciting coil uniformly penetrates into the steel pipe in contact with the yoke through the yoke, and the measurement accuracy of the DC magnetic characteristics of the tube wall portion is improved.

5. The total carbon measuring machine according to claim 4, wherein the yoke includes first and second members each having a semicircular shape in which a cross-sectional shape of an end surface is substantially equal to a radius of an outer diameter of the steel pipe. The carbon total amount measuring machine according to claim 1 or 2, wherein the yoke is a yoke that surrounds and contacts the steel pipe from all circumferential directions by a combination of the first and second members.

According to the invention for measuring the total amount of carbon according to claim 4, the configuration of the yoke includes first and second members each having a semicircular shape in which the cross-sectional shape of the end surface is substantially the same as the radius of the outer diameter of the steel pipe. Since the steel pipe is surrounded and touched by the combination of the first and second members from the whole circumferential direction, the magnetic flux generated by the exciting coil is from the whole circumferential direction of the steel pipe that is in contact with the yoke through the yoke. It penetrates uniformly and the accuracy of measuring the DC magnetic characteristics of the tube wall is further improved.

The total carbon measuring machine according to claim 5, wherein the ferritic steel pipe containing Cr contains 1.9 wt% or more and 10 wt% or less of Cr. This is a total carbon measuring machine.

According to the invention of the carbon total amount measuring machine according to claim 5, the ferritic steel pipe containing the target Cr contains 1.9 wt% or more and 10 wt% or less of Cr, It is particularly effective for carburization evaluation of Cr—Mo steel pipes, such as 2.25Cr-1Mo steel pipes and 9Cr-1Mo steel pipes, which are often used in tubes for heating furnaces in chemical plants. In addition, in the standard of 2.25Cr-1Mo steel pipe, the lower limit of Cr is 1.9 wt% or more, and in the standard of 9Cr-1Mo steel pipe, the upper limit of Cr is 10 wt% or less.

The concentration distribution evaluation apparatus according to claim 6 is a carbon total amount measuring device that calculates a total amount of carbon in a ferritic steel pipe containing Cr from a direct current magnetic characteristic, and an external that measures the carbon concentration in the outer surface portion of the steel pipe. Based on the carbon concentration measured by the surface carbon concentration measuring device and the carbon concentration measured by the outer surface carbon concentration measuring device, the carburizing amount of the outer surface portion is calculated according to a predetermined formula, and the carburizing amount of the outer surface portion and the mother amount are calculated from the total amount of the carbon amount. Subtracting the amount of material carbon, obtaining the carburizing amount of the inner surface portion of the steel pipe, and the concentration of the carburizing amount of the inner surface portion of the steel pipe equipped with a concentration distribution evaluation machine for evaluating the concentration distribution of the carburizing amount of the inner surface portion according to a predetermined formula A distribution evaluation device, wherein the carbon total amount measuring machine is disposed between an electromagnet including an exciting coil and a yoke for magnetizing a tube wall portion of a steel pipe in an axial direction, and the circumference of the steel pipe. Coiled in the direction of the A detection coil for detecting a change, a magnetic measurement unit for measuring a DC magnetic characteristic of a tubular portion of the steel pipe from a magnetic flux density based on an integration of a magnetic field strength of the electromagnet and an output value of the detection coil, and a ferrite containing Cr An arithmetic unit that calculates the total amount of carbon including the carburized layer from the measured DC magnetic characteristics of the steel tube tube based on predetermined data on the relationship between the DC magnetic properties of the steel pipe and the total amount of carbon. It is the concentration distribution evaluation apparatus of the carburizing amount of the inner surface part of the ferritic steel pipe containing Cr characterized by having provided.

According to the invention of the concentration distribution evaluation apparatus according to claim 6, a carbon total amount measuring machine for calculating the total amount of carbon of the ferritic steel pipe containing Cr from the DC magnetic characteristics, and measuring the carbon concentration of the outer surface portion of the steel pipe Calculate the carburizing amount of the outer surface part according to a predetermined formula based on the carbon concentration measured by the outer surface carbon concentration measuring machine and the outer surface carbon concentration measuring machine, and calculate the carburizing amount of the outer surface part from the total amount of carbon and the mother Subtracting the amount of material carbon, obtaining the carburizing amount of the inner surface portion of the steel pipe, and the concentration of the carburizing amount of the inner surface portion of the steel pipe equipped with a concentration distribution evaluation machine for evaluating the concentration distribution of the carburizing amount of the inner surface portion according to a predetermined formula It is a distribution evaluation device, and a carbon total amount measuring machine is disposed between an electromagnet having an exciting coil and a yoke for magnetizing a tube portion of a steel pipe in an axial direction, and a coil in a circumferential direction of the steel pipe. Is used to detect magnetic flux changes in the pipe wall of the steel pipe A detection coil, a magnetic measurement unit for measuring a DC magnetic characteristic of a tube portion of the steel pipe from a magnetic flux density based on an integration of a magnetic field strength of the electromagnet and an output value of the detection coil, and a direct current of a ferritic steel pipe containing Cr An arithmetic unit for calculating the total amount of carbon including the carburized layer from the measured DC magnetic characteristics of the steel pipe portion based on predetermined data on the relationship between the magnetic properties and the total amount of carbon. The present invention proposes a concentration distribution evaluation apparatus for carburizing amount of an inner surface portion of a ferritic steel pipe containing Cr. Therefore, by subtracting the carburizing amount of the outer surface part and the base material carbon amount from the total amount of carbon in the steel pipe, the carburizing amount of the inner surface part is obtained, and the inner surface part of the steel pipe that is difficult to measure directly according to a predetermined formula. The concentration distribution of the amount of carburizing can be evaluated nondestructively.

The concentration distribution evaluation apparatus according to claim 7, wherein the DC magnetic characteristic is a saturation magnetic flux density or a coercive force, and the concentration distribution evaluation of the carburizing amount of the inner surface portion of the ferritic steel pipe according to claim 6. Device.

According to the invention of the concentration distribution evaluation apparatus according to claim 7, since the total amount of carbon in the steel pipe is calculated with a saturation magnetic flux density or coercive force having a high correlation coefficient with the total amount of carbon, the calculated amount of carbon The reliability of the total amount is high, and the accuracy of concentration distribution evaluation of the carburizing amount on the inner surface of the steel pipe is high.

According to the present invention, the total amount of carbon including the carburized layer of the ferritic steel pipe containing Cr can be accurately calculated from the DC magnetic characteristics which are a non-destructive technique, and the carburizing amount of the inner surface portion of the steel pipe Therefore, it is useful for maintenance management of ferritic steel pipes by carburizing.

FIG. 1 is a distribution diagram of carbon concentration of a steel pipe used as a tube for a heating furnace of a petrochemical plant. FIG. 2 is a conceptual diagram of the carbon concentration distribution in the thickness direction of the carburized material. FIG. 3 is a configuration example of a total carbon amount measuring machine for calculating the total amount of carbon according to the present invention. (A) Schematic diagram viewed from a direction parallel to the axial direction of the steel pipe (b) Schematic diagram illustrating the relationship with the yoke viewed from a direction perpendicular to the axial direction of the steel pipe FIG. 4 is a modification of the configuration of the total carbon measuring device for calculating the total amount of carbon according to the present invention. (A) Schematic diagram viewed from a direction parallel to the axial direction of the steel pipe (b) Schematic diagram illustrating the relationship with the yoke viewed from a direction perpendicular to the axial direction of the steel pipe FIG. 5 is a diagram showing magnetic characteristic loops of steel pipes having different total carbon contents. FIG. 6 is a diagram showing the relationship between the total amount of carbon and the normalized saturation magnetic flux density. FIG. 7 is a diagram showing the relationship between the total amount of carbon and the normalized coercivity. FIG. 8 is a diagram showing the relationship between the total amount of carbon and the normalized residual magnetic flux density. FIG. 9 is a configuration example of a concentration distribution evaluation apparatus for carburizing amount of the inner surface portion of a ferritic steel pipe containing Cr according to the present invention.

In Fig. 1, the inner and outer surfaces of a 5.2mm thick 9Cr-1Mo steel pipe used as a tube for a heating furnace in a petrochemical plant are descaled and cut out 0.3mm each from the inner and outer surfaces to obtain EPMA. Using this, the carbon concentration (C concentration) distribution is obtained. From these data, it was found that the C concentration distribution from the inner and outer surfaces decreased almost linearly from each surface even though the carburizing amount was different. When the inclination K _O from the outer surface of this C concentration is K _i and the inclination from the inner surface is K _i , the K _{O in} 9Cr-1Mo steel is about −0.4 (wt% / mm), and K _i is 0 It was found to be about 3 (wt% / mm).

Also, in the results of carburizing treatment of steel types containing other Cr, it was found that the C concentration distribution from the inner and outer surfaces decreased almost linearly from the respective surfaces even though there was a difference in the amount of carburizing. It was found that the inclination K _O from the outer surface of the C concentration and the inclination K _i from the inner surface are different.

From the above results, in the thickness direction of the steel pipe containing Cr to be carburized from the inner and outer surfaces, the total amount S _CA of carbon content of the steel pipe after carburization, is minus the base material carbon content S _CB before carburization, carburization The amount of carbon increased by the treatment. The carbon content is the sum of carburizing quantity S _CI from carburizing quantity S _CO and the inner surface portion of the outer surface, steels K _O, K _i is given, the C concentration C _O of the steel pipe outer surface If measured, the carburizing amount from the outer surface portion is calculated, and the carburizing amount _SCI of the inner surface portion is determined. Further, the inner surface carburization depth d _i can be evaluated from the carburizing amount of the inner surface portion and K _i .

As described above, if non-destructively measuring the amount S _CA of the steel pipe wall thickness direction of the carbon content of carburized, by measuring the C concentration C _O of the steel pipe outer surface, evaluating the state of carburization in the steel pipe inner surface It will be possible. In FIG. 2, the conceptual diagram of C concentration distribution of such a carburized material is shown. In Figure 2, the outer surface carburized depth d _O decreases at inclination K _O from C concentration C _O of the outer surface, the base material C concentration C _b a thickness, the inner surface carburization depth d _i is the inner surface C The thickness decreases from the concentration C _{i with a} slope K _i to the base material C concentration C _b , and the sum of the outer surface carburization depth d _O and the inner surface carburization depth d _i is smaller than the steel pipe wall thickness t. It is assumed that. Incidentally, the total amount S _CA of carbon content is represented by ∫C (t) dt obtained by integrating the steel pipe wall thickness direction C concentration C (t) to a thickness t.

Therefore, the total amount S _CA of the carbon amount in the thickness direction of the steel pipe, the base material carbon amount S _CB , the carburizing amount S _CO from the outer surface portion, and the carburizing amount S _CI from the inner surface portion can be obtained by the following calculation formulas.
S _CA = S _CO + S _CI + S _CB = ∫C (t) dt (A)
S _CB = C _b × t (B)
S _CO = (C _O −C _b ) × d _O / 2 (C)
S _CI = (C _i −C _b ) × d _i / 2 (D)
Further, the outer surface carburization depth d _O and the inner surface carburization depth d _i are:
d _O = (C _O -C _b ) / K _O (E)
d _i = (C _i −C _b ) / K _i (F)
The inner surface carburization depth d _i is further determined by d _i = 2 {S _CA − (C _O −C _b ) ² / (2 × K _O ) −C _b × t} / K _i. G)
Is required.

In the above formula (G), if the C concentration C _{O of the} outer surface of the steel pipe is measured in advance, C _O , C _b , K _O , K _i , t are known, and the total amount of carbon in the thickness direction of the steel pipe It is clear from the calculation that if the _SCA is measured, the inner surface carburization depth d _i can be obtained. Therefore nondestructive measurement technique capable of total S _CA carbon amount after carburization ferritic steel containing Cr is required.

The conceptual diagram of the carbon total amount measuring device 1 which calculates the total amount of the carbon content of this invention to Fig.3 (a), (b) is shown. The total carbon measuring machine 1 includes an electromagnet 11 for magnetizing a tube portion of the steel pipe P to be measured in the axial direction, a detection coil 12 for detecting a magnetic flux change in the magnetized tube portion, and a DC magnetic characteristic. The magnetic measurement unit 13 for measuring the magnetization curve, based on the predetermined data of the relationship between the DC magnetic characteristics and the total amount of carbon, from the measured DC magnetic characteristics of the tube portion of the steel pipe P, the carbon content including the carburized layer It is comprised from the calculating part 14 which calculates total amount.

The electromagnet 11 includes an exciting coil 111 and a yoke 112 made of a soft magnetic material such as soft iron. The exciting coil 111 is attached so as to wind the yoke 112, and both ends of the yoke 112 have a half-section with a radius substantially equal to the outer diameter of the steel pipe so as to contact the steel pipe P to be measured from the circumferential direction. It has a circular shape. Therefore, the magnetic field generated by the exciting coil 111 magnetizes the yoke 112, and the magnetic flux flows into the steel pipe P to be measured from one end of the yoke 112, and magnetizes the tubular portion of the steel pipe P in the axial direction. Then, the magnetic flux flows out from the end of the other yoke 112 and forms a magnetic path. As described above, in the present invention, the cross-sectional shape of the end face of the yoke 112 is a semicircular shape having a radius substantially equal to the outer diameter of the steel pipe P, so there is little loss of the magnetic path length, and the steel pipe P can be uniformly saturated. It becomes possible to magnetize.

A detection coil 12 for detecting a change in magnetic flux in the magnetized tubular portion is disposed between the yokes 112. The configuration of the detection coil 12 is such that the coil is wound in the circumferential direction of the steel pipe P, and the time change of the magnetic flux in the plane surrounded by the coil is detected as an electromagnetic induction voltage. The detected voltage is input to the amplifier / integrator 133 of the magnetic measurement unit 13. In the case of an actual machine pipe, it may be difficult to wind the detection coil 12 at the site. In such a case, the connector connection between the two terminals is a neighboring cable with a flat cable coil. Thus, a coil or the like in which the cable is spirally connected can be used.

In this embodiment, the magnetic measurement unit 13 amplifies and integrates the induced voltage from the detection coil 12, the oscillator 131 and the power amplifier 132 for exciting the excitation coil 111, and the amplification / integrator 133. Is converted into magnetic flux density, and the output from the power amplifier 132 is converted into magnetic field strength to generate a magnetization curve. In order to suppress the generation of eddy current, the frequency of the oscillator 131 is preferably a low frequency, for example, about 0.01 Hz, and a triangular wave or a SIN wave can be used. The power amplifier 132 amplifies the output of the oscillator 131 and outputs the amplified output to the exciting coil 111 and simultaneously outputs an output signal to the magnetic property evaluator 134. The magnetic property evaluator 134 converts this output signal into the magnetic field strength of the electromagnet 11, and converts the magnetic flux corresponding to the output from the amplifier / integrator 133 from the cross-sectional area of the tubular portion of the steel pipe P to the magnetic flux density to generate a direct current. Generate a magnetization curve of magnetic properties. It is also possible to adopt a method in which a Hall element is installed at the tip of the yoke portion, the magnetic field strength is measured, and the measured value is input to the magnetic property evaluator 134.

Data such as initial permeability μ, maximum magnetic flux density Bm, saturation magnetic flux density Bs, residual magnetic flux density Br, coercive force Hc, and the like are obtained from the magnetization curve of the DC magnetic characteristics. If the residual magnetization remains in the steel pipe P, it is not possible to start from the origin. Therefore, before the measurement, the frequency of the oscillator 131 is set to, for example, about 60 Hz, and demagnetization that gradually decreases the output of the power amplifier may be performed.

The calculation unit 14 that calculates the total amount of carbon including the carburized layer has predetermined data on the relationship between the DC magnetic characteristics of the ferritic steel pipe containing Cr and the total amount of carbon. That is, it has data indicating the correlation between each magnetic characteristic such as the initial permeability μ, the maximum magnetic flux density Bm, the saturation magnetic flux density Bs, the residual magnetic flux density Br, the coercive force Hc, and the total amount of carbon. The computing unit 14 calculates the total amount of carbon including the carburized layer by comparing the DC magnetic characteristics of the measured thickness of the steel pipe P with the data indicating the correlation between the DC magnetic characteristics and the total amount of carbon. . As will be described later, in the 9Cr-1Mo steel pipe, the maximum magnetic flux density Bm or saturation magnetic flux density Bs and the total amount of carbon show a negative correlation, and when the total amount of carbon increases, the maximum magnetic flux density Bm and the saturation magnetic flux density Bs are Although it decreases, the coercive force Hc and the total amount of carbon show a positive correlation, and the coercive force Hc increases as the total amount of carbon increases. No correlation was found between the residual magnetic flux density Br and the total amount of carbon. Further, the correlation coefficient between the maximum magnetic flux density Bm or the saturation magnetic flux density Bs and the total amount of carbon, and the correlation coefficient between the coercive force Hc and the total amount of carbon are relatively high. In particular, the maximum magnetic flux density Bm or the saturation magnetic flux density Bs If the data showing the correlation with the total amount of carbon is used, the total amount of carbon including the carburized layer can be calculated with extremely high accuracy.

4 (a) and 4 (b) show a modification of the total carbon amount measuring machine 1 for calculating the total amount of carbon according to the present invention. In this modification, the yoke 112 in contact with the steel pipe P is composed of a first member 112a and a second member 112b, each of which has a semicircular shape with a cross-sectional shape of the end face substantially equal to the outer diameter of the steel pipe. The member 112b is screwed or the like to the first member 112a, so that the yoke 112 surrounds and contacts the steel pipe P from the entire circumferential direction by a combination of the first member 112a and the second member 112b. It is characterized by. With such a yoke 112 configuration, the tube wall portion of the steel pipe P can be magnetized in the axial direction from the entire circumferential direction of the steel pipe P, so that the magnetic flux penetrating the tube wall portion of the steel pipe P becomes more uniform. The electromagnetic induction voltage detected from the detection coil 12 can be detected more accurately.

If the two electromagnets 11 shown in FIGS. 3 (a) and 3 (b) are used and the ends of the yoke 112 are brought into contact with each other, the tubular portion of the steel pipe P is removed from the entire circumferential direction of the steel pipe P. Since the magnet can be magnetized more uniformly in the axial direction, the magnetic flux penetrating the tubular portion of the steel pipe P becomes more uniform, and the electromagnetic induction voltage detected from the detection coil 12 can be detected more accurately.

The present invention was examined using seven samples of a new 9Cr-1Mo steel pipe (sample No. 1) and a 9Cr-1Mo actual steel pipe (samples No. 2 to 7) exposed to various carburizing atmospheres. The steel pipe has an outer diameter of 114 mm, an inner diameter of 102 mm, and a wall thickness of 6 mm. The C concentration of the new 9Cr-1Mo steel pipe is determined to be 0.12 (wt%) by chemical analysis, and since there is no carburized layer, the total amount of carbon is obtained by multiplying the C concentration by the thickness of 6 mm. The sample number is 0.72 (wt% · mm). Similar to 2-7, the steel pipe was cut out and cut out by 0.3 mm from the inner and outer surfaces, and it was confirmed that the C concentration in the thickness direction was 0.12 (wt%) using a portable emission analyzer. . Sample No. In the case of 9Cr-1Mo actual steel pipe exposed to 2 to 7 carburizing atmosphere, cut out the steel pipe, descal the inner and outer surfaces, and then cut out 0.3 mm each from the inner and outer surfaces using a portable emission analyzer. The C concentration distribution C (t) in the thickness direction was determined. Then, the total amount of carbon was calculated from ∫C (t) dt obtained by integrating C (t) with thickness t. Table 1 shows the total amount of carbon in each sample.

DC magnetism measurement is performed by the apparatus shown in FIGS. 4A and 4B. The yoke 112 uses soft iron equivalent to SS400, and the radius of each of the first member 112a and the second member 112b of the yoke 112 is a steel pipe. It was designed as 57.6 mm which is 1% larger than the radius of the outer diameter of P. The oscillator 131 outputs a triangular wave of 0.01 Hz, and the current amplifier 132 outputs a maximum value of 10 A and a minimum value of −10 A corresponding to the output of the triangular wave. The maximum value 10A corresponds to 4000 A / m as a magnetic field that acts on the steel pipe P from the yoke 112 by exciting the exciting coil 111.

FIG. 5 shows the sample No. with the smallest total amount of carbon with no carburized layer. No. 1 (indicated by the solid line) and sample No. with the largest total carbon content with carburized layers. 7 shows a magnetic characteristic loop 7 (indicated by a broken line). From the loop of this magnetic characteristic, it turns out that the maximum magnetic flux density Bm is so low that the total amount of carbon is large. In the case of the present embodiment, since the magnetic field acting on the steel pipe P from the yoke 112 is as large as 4000 A / m, the maximum magnetic flux density Bm can be regarded as the saturation magnetic flux density Bs. Strictly speaking, it is preferable to directly evaluate the saturation magnetic flux density Bs. New material sample No. Table 1 shows the relative values of the magnetic characteristics of each sample normalized by the saturation magnetic flux density Bs, the coercive force Hc, and the residual magnetic flux density Br, which are the magnetic characteristics of No. 1.

6 shows the relationship between the total amount of carbon and the relative value of the saturation magnetic flux density Bs, FIG. 7 shows the relationship between the total amount of carbon and the relative value of the coercive force Hc, and FIG. 8 shows the total amount of carbon and the residual amount. The relationship of the relative value of magnetic flux density Br is shown, respectively. As is clear from FIG. 6, the relative value of the total amount of carbon and the saturation magnetic flux density Bs is expressed by a linear function and shows an extremely high correlation (correlation coefficient R = 0.97). It can be determined from the saturation magnetic characteristics of the magnetic characteristics. Further, from FIG. 7, it was found that when the relationship between the total amount of carbon and the relative value of the coercive force Hc was evaluated by a linear function, a correlation coefficient R = 0.64 was obtained, and there was a certain degree of correlation. On the other hand, when the relationship between the total amount of carbon and the relative value of the residual magnetic flux density Br is evaluated by a linear function, it is clear from FIG. 8 that there is almost no correlation.

With the above configuration, data of a linear function showing a high correlation between the saturation magnetic flux density Bs, which is the DC magnetic characteristic of the 9Cr-1Mo ferritic steel pipe, and the total amount of carbon was obtained. Based on this data, The total amount of carbon including the carburized layer in the thickness direction of the steel pipe can be calculated in reverse from the measured DC magnetic characteristics of the pipe wall portion of the steel pipe, for example, the saturation magnetic flux density Bs.

FIG. 9 is a configuration example of the concentration distribution evaluation apparatus 100 for the carburizing amount of the inner surface portion of the ferritic steel pipe containing Cr of the present invention. The carburizing amount concentration distribution evaluation device 100 for the inner surface portion of the steel pipe measures the carbon concentration measuring device 1 for calculating the total carbon amount of the steel pipe P from the DC magnetic characteristics, and the carbon concentration of the outer surface portion of the steel pipe P. Based on the carbon concentration measured by the outer surface carbon concentration measuring device 15 and the carbon concentration measured by the outer surface carbon concentration measuring device 15, the carburizing amount of the outer surface portion is calculated according to a predetermined formula, and the carburizing amount of the outer surface portion is calculated from the total amount of carbon. A total carbon amount measuring machine is provided with a concentration distribution evaluator 20 that subtracts the base material carbon amount, determines the carburizing amount of the inner surface portion of the steel pipe P, and evaluates the concentration distribution of the carburizing amount of the inner surface portion according to a predetermined formula. 1 is disposed between the yoke 112 and the electromagnet 11 including the exciting coil 111 and the yoke 112 for magnetizing the tube portion of the steel pipe P in the axial direction, and the coil is wound in the circumferential direction of the steel pipe P. Detecting carp for detecting magnetic flux change in the pipe wall of steel pipe P 12, a magnetic measurement unit 13 that measures the DC magnetic characteristics of the tube wall portion of the steel pipe P from the magnetic flux density based on the integration of the magnetic field strength of the electromagnet 11 and the output value of the detection coil 12, and the ferritic steel pipe P containing Cr. A calculation unit 14 for calculating the total amount of carbon including the carburized layer from the measured DC magnetic characteristics of the tube portion of the steel pipe P based on predetermined data on the relationship between the DC magnetic characteristics and the total amount of carbon. It is characterized by that.

In the present embodiment, a portable emission analyzer is used as the outer surface carburizing amount measuring device 15 for measuring the carbon concentration of the outer surface portion. However, if the C concentration of the outer surface portion can be measured, the emission analyzer is used. Not limited to. The concentration distribution evaluation machine 20 includes the total amount of carbon of the steel pipe P calculated from the calculation unit 14 of the total carbon amount measuring machine 1 and the C concentration of the outer surface portion of the steel pipe P measured from the outer surface carbon concentration measuring machine 15. Entered. Based on the carbon concentration of the outer surface portion that is input, the concentration distribution evaluator 20 uses the data of the inclination K _O from the outer surface of the C concentration corresponding to the steel type, the inclination K _i from the inner surface, and the base material C concentration. The carburizing amount of the outer surface portion is calculated, and the carburizing amount of the outer surface portion and the base material carbon amount are subtracted from the total amount of carbon to obtain the carburizing amount of the inner surface portion of the steel pipe P. Furthermore, according to the data of the inclination K _i from the inner surface, the concentration distribution of the carburizing amount on the inner surface portion can be evaluated so as to be obtained by the aforementioned equations (F) and (G).

The present invention was examined using a 9Cr-1Mo real steel pipe exposed to a carburizing atmosphere. The steel pipe has an outer diameter of 114 mm, an inner diameter of 102 mm, and a wall thickness of 6 mm. 4A and 4B, the total amount of carbon calculated from the saturation magnetic flux density Bs of the DC magnetic characteristics was 2.7 (wt% · mm). The C concentration of the outer surface of the measured steel pipe emission spectrometer portable is 1.1 (wt%), a concentration distribution evaluator of the apparatus, K _O = -0.4 (wt% / Mm), K _i = 0.3 (wt% / mm), and the C concentration of the base material 0.12 (wt%), the carburizing amount of the outer surface portion is calculated as 1.2 (wt% · mm). Moreover, from the base material C amount of 0.72 (wt% · mm), the carburizing amount of the inner surface portion was calculated as 0.78 (wt% · mm). Furthermore, from K _i = 0.3 (wt% / mm), the inner surface carburization depth d _i = 2.28 mm was evaluated.

On the other hand, in order to evaluate the validity of the evaluation of the concentration distribution evaluation apparatus for the carburizing amount distribution on the inner surface of the steel pipe, a part of the 9Cr-1Mo actual steel pipe is cut out and cut out by 0.25 mm from the inner surface. The distribution of carburizing amount from the inner surface portion was obtained using an emission spectrometer. As a result, the carburizing distance from the inner surface portion was measured as 2.25 mm, and it was confirmed that the evaluation of the carburizing amount of the inner surface portion obtained from the concentration distribution evaluation apparatus was appropriate.

As described above, the carbon total amount measuring apparatus according to the present invention calculates the total amount of carbon including the carburized layer of the ferritic steel pipe containing Cr from the DC magnetic characteristics, and thus has been used for the measurement of ferritic steel pipe. Compared with the conventional alternating current magnetization method, the total amount of carbon including the carburized layer can be calculated with higher accuracy because it is less affected by the oxide scale on the outer surface of the steel pipe and the signal strength is large. In addition, a predetermined calculation is performed from the signals output from the above-mentioned total carbon measuring device, outer surface carbon concentration measuring device, carbon total measuring device and outer surface carbon concentration measuring device, and the concentration distribution of the carburizing amount on the inner surface portion is calculated. According to the concentration distribution evaluation device for the carburizing amount on the inner surface of the steel pipe equipped with a concentration distribution evaluation machine to evaluate, it is possible to accurately evaluate the carburizing depth of the inner surface of the steel pipe, which was difficult to measure directly. It became.

DESCRIPTION OF SYMBOLS 1 Carbon total amount measuring machine 11 Electromagnet 12 Detection coil 13 Magnetic measuring part 14 Calculation part 15 Outer surface carburizing amount measuring machine 20 Concentration distribution evaluation machine 100 Concentration distribution evaluation apparatus 111 Excitation coil 112 Yoke 112a 1st member 112b 2nd member 131 Oscillator 132 Power Amplifier 133 Amplifier / Integrator 134 Magnetic Characteristic Evaluator P Steel Pipe

Claims (7)

A total carbon measuring machine that calculates the total amount of carbon including carburized layers of ferritic steel pipes containing Cr from direct current magnetic characteristics,
An electromagnet including an exciting coil and a yoke for magnetizing a tubular portion of a steel pipe in an axial direction;
A detection coil that is disposed between the yokes and that detects a magnetic flux change in a tubular portion of the steel pipe by winding the coil in a circumferential direction of the steel pipe;
A magnetic measurement unit for measuring a DC magnetic characteristic of a tubular portion of the steel pipe from a magnetic flux density based on an integration of a magnetic field strength of the electromagnet and an output value of the detection coil;
Calculate the total amount of carbon, including the carburized layer, from the measured DC magnetic properties of the pipe wall of the steel pipe based on the prescribed data on the relationship between the DC magnetic properties of the ferritic steel pipe containing Cr and the total amount of carbon. A total carbon measuring machine, comprising: The total carbon amount measuring machine according to claim 1, wherein the DC magnetic characteristic is a saturation magnetic flux density or a coercive force. The cross-sectional shape of the yoke end surface in contact with the steel pipe is a semicircular shape having a radius substantially equal to the radius of the outer diameter of the steel pipe so as to contact the steel pipe from the circumferential direction. The total carbon measuring machine described in 1. The yoke has first and second members each having a semicircular shape with a cross-sectional shape of an end surface substantially equal to the radius of the outer diameter of the steel pipe, and the combination of the first and second members. The carbon total amount measuring machine according to claim 1 or 2, wherein the yoke is a yoke that surrounds and contacts the steel pipe from all circumferential directions. 5. The carbon total amount measuring machine according to claim 1, wherein the ferritic steel pipe containing Cr contains 1.9 wt% or more and 10 wt% or less of Cr. A carbon total amount measuring machine for calculating the total amount of carbon of ferritic steel pipes containing Cr from DC magnetic characteristics;
An outer surface carbon concentration measuring machine for measuring the carbon concentration of the outer surface portion of the steel pipe;
Calculate the carburizing amount of the outer surface portion according to a predetermined formula based on the carbon concentration measured by the outer surface carbon concentration measuring device, and subtract the carburizing amount of the outer surface portion and the base material carbon amount from the total amount of carbon, A concentration distribution evaluation device for the carburizing amount of the inner surface portion of a steel pipe, comprising a concentration distribution evaluator that calculates a carburizing amount of the inner surface portion of the steel pipe and evaluates a concentration distribution of the carburizing amount of the inner surface portion according to a predetermined formula,
The total carbon measuring machine is
An electromagnet including an exciting coil and a yoke for magnetizing a tubular portion of a steel pipe in an axial direction;
A detection coil that is disposed between the yokes and that detects a magnetic flux change in a tubular portion of the steel pipe by winding the coil in a circumferential direction of the steel pipe;
A magnetic measurement unit for measuring a DC magnetic characteristic of a tubular portion of the steel pipe from a magnetic flux density based on an integration of a magnetic field strength of the electromagnet and an output value of the detection coil;
Calculate the total amount of carbon, including the carburized layer, from the measured DC magnetic properties of the pipe wall of the steel pipe based on the prescribed data on the relationship between the DC magnetic properties of the ferritic steel pipe containing Cr and the total amount of carbon. And an arithmetic unit for performing
An apparatus for evaluating the concentration distribution of the amount of carburization of the inner surface of a ferritic steel pipe containing Cr. 7. The concentration distribution evaluation apparatus for carburizing amount of an inner surface portion of a ferritic steel pipe containing Cr according to claim 6, wherein the DC magnetic characteristic is a saturation magnetic flux density or a coercive force.

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