JP2011058980A - Method and device for measuring carburized layer of tubular body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for measuring a carburized layer of a tubular body capable of measuring the carburized layer accurately and precisely, while guaranteeing high measurement accuracy. <P>SOLUTION: The carburized layer formed on a prescribed portion of the tubular body 101 is measured by using an ultrasonic wave. One or a pair of probes 11 are moved along the outer circumference of the tubular body 101, and a change of an ultrasonic characteristic caused by passing through the tubular body is detected, and the carburized layer depth is measured based on the detection result. The ultrasonic wave is transmitted from the transmission side to the reception side of the pair of probes 11 so that an ultrasonic route propagating inside the tubular body 101 passes an approximately plate thickness center part of the tubular body 101. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and apparatus for measuring a carburized layer formed on the inner surface of a tubular body such as a steel pipe or a pressure vessel.

  For example, when carburization occurs on the inner surface of a cracking furnace tube in an ethylene production apparatus, cracks are generated due to a difference in thermal expansion from the outer surface side of the tube. In order to measure the depth of the carburized layer, it has been conventionally measured using an electromagnetic carburization meter. In a heat-resistant centrifugal cast tube used as this kind of cracking furnace tube, nitride is precipitated on the outer surface side of the tube in addition to carburizing as a change with time of the material.

  The nitride on the outer surface side of the tube affects the measured value of the electromagnetic carburization meter. In addition, the measurement accuracy in measuring the depth of the carburized layer from the measured value of the electromagnetic carburizer is not necessarily high, and for these reasons, a method for measuring the carburized layer using ultrasonic waves has been recently studied. For example, in the carburized layer detection method described in Patent Document 1, the transmitting probe emits a pulse that easily causes a transverse wave / longitudinal wave mode conversion to the specimen, and the receiving probe detects the mode from the bottom surface of the specimen. The converted mode conversion pulse is incident. Patent Document 2 also discloses this type of detection method and apparatus.

JP 2006-29939 A JP 2005-345138 A

  However, the prior art including the above-described Patent Document 1 is a transmission method in which an ultrasonic probe is arranged in the tube axis direction and ultrasonic waves reflected by the inner surface of the tube are received, or alternatively, on the outer surface side of the tube. This is a method of receiving ultrasonic waves reflected at the boundary between the uncarburized portion and the pipe inner surface side carburized portion. Furthermore, there is a method for analyzing backscattered echo, and any of these conventional techniques is affected by corrosion or thinning of the inner surface of the tube, and it is impossible to ensure good measurement accuracy.

  In view of such circumstances, an object of the present invention is to provide a method and an apparatus for measuring a carburized layer of a tubular body that guarantees high measurement accuracy and can accurately measure a carburized layer with high accuracy.

The tubular body carburized layer measuring method of the present invention is a tubular body carburized layer measuring method for measuring a carburized layer formed in a predetermined portion of the tubular body using ultrasonic waves,
One or a pair of probes are moved along the outer periphery of the tubular body, a change in ultrasonic characteristics due to the passage of the carburized layer is detected, and the carburized layer depth is measured based on the detection result. Features.

  In the method for measuring a carburized layer of a tubular body according to the present invention, the ultrasonic path propagating through the tubular body is received from the transmitting side of the pair of probes so that it passes through a substantially central portion of the tubular body. It is characterized by transmitting ultrasonic waves to the side.

  In the method for measuring a carburized layer of a tubular body according to the present invention, the probe travels and scans over the entire circumference of the tubular body.

The tubular body carburized layer measuring device of the present invention is a tubular body carburized layer measuring device for measuring a carburized layer formed in a predetermined portion of the tubular body using ultrasonic waves,
A probe holder for holding the probe so that one or a pair of probes can transmit and receive ultrasonic waves at a predetermined position and angle;
And a traveling guide for guiding the probe to move around the tubular body via the probe holder.

  Further, in the tubular body carburized layer measuring apparatus according to the present invention, the holder has an ultrasonic path propagating through the tubular body transmitted from the transmitting side to the receiving side of the pair of probes. The pair of probes is held so as to pass through a substantially central portion of the plate thickness.

  According to the present invention, the transmission method is applied in the typical embodiment, and thereby the ultrasonic main beam passes near the center of the tube thickness, so that the shape on the tube inner surface side is not uniform, The carburized layer can be accurately and accurately measured. Moreover, the carburized layer depth can be accurately evaluated by comparing the ultrasonic velocity values or attenuation constants of the uncarburized part and the carburized part.

It is a figure which shows schematic structure around the decomposition furnace in the ethylene manufacturing apparatus which concerns on this invention. It is a figure which shows the arrangement | positioning relationship between the cracking furnace tube and the burner in the cracking furnace of the ethylene manufacturing apparatus which concerns on this invention. It is a perspective view which shows the carburized layer measuring apparatus by the permeation | transmission method by this invention. It is a perspective view which shows the carburized layer measuring apparatus by the vertical method by this invention. It is a figure which shows the test piece used for the carburized layer measurement in the carburized layer measuring apparatus of this invention. It is a figure which shows the relationship between the path | route of the ultrasonic beam which passed the carburized part, and ultrasonic sound velocity in the carburized layer measurement by the vertical method by this invention. It is a figure which shows the relationship between the test plate thickness and attenuation constant in the carburized layer measurement by the vertical method by this invention. It is a figure which shows the relationship between the path | route of the ultrasonic beam which passed the carburized part, and ultrasonic sound velocity in the carburized layer measurement by the transmission method by this invention. It is a figure which shows the structural example of the probe and probe holder of the carburized layer measuring apparatus by the transmission method of this invention. It is a figure which shows the structural example of the probe and probe holder of the carburized layer measuring apparatus by the vertical method of this invention. It is a figure which shows the structural example of the traveling guide of the carburized layer measuring apparatus of this invention.

Hereinafter, preferred embodiments of a tubular body carburized layer measuring method and apparatus according to the present invention will be described with reference to the drawings.
First, the outline of the cracking furnace in the ethylene production apparatus according to the present invention will be described. FIG. 1 shows a main part of the cracking furnace 100. A plurality of cracking furnace tubes 101 are arranged in the cracking furnace 100, and each cracking furnace tube 101 is arranged vertically between the hearth 100a and the ceiling portion 100b. Is done. Further, as shown in FIG. 2, a plurality of burners 102 are arranged on both the left and right sides with respect to the direction in which the cracking furnace tubes 101 are arranged, and each cracking furnace tube 101 is heated from the left and right. Raw materials such as naphtha are charged into the cracking furnace tube 101, and ethylene is decomposed and generated as it flows through the cracking furnace tube 101 as indicated by the arrows in FIG. 1, and the generated ethylene is sent to the quench boiler 103.

  Next, FIG.3 and FIG.4 has shown the carburized layer measuring apparatus 10 by this invention. FIG. 3 shows an example in which the transmission method is applied, and FIG. 4 shows an example in which the vertical method is applied. The apparatus of the present invention measures a carburized layer formed on a predetermined portion of a tubular body typified by the cracking furnace tube 101, that is, an inner surface of the tube, using ultrasonic waves. The carburized layer measuring device 10 by the transmission method has a pair of probes 11 (transmitting side and receiving side) as shown in FIG. 3, and the carburized layer measuring device 10 by the vertical method is a single unit as shown in FIG. It has a probe 11.

  These probes 11 are held by a probe holder 12 so as to have a predetermined position and angle with respect to the decomposition furnace tube 101. In addition, a traveling guide 13 is provided for guiding the probe 11 to move around the cracking furnace tube 101 via the probe holder 12 (see arrows in FIGS. 3 and 4). These details will be described later. As shown in FIGS. 3 and 4, an ultrasonic flaw detector 14 is connected to the probe 11, and a pen recorder 15 is further connected to the ultrasonic flaw detector 14.

  Here, the basic configuration of the present invention will be described in principle. When carburization occurs on the inner surface side of the cracking furnace tube of the ethylene production equipment, cracks due to the difference in thermal expansion from the outer surface side of the tube occur, and this carburized layer depth is measured by the ultrasonic method. A locally forced carburized test piece 1 of a heat-resistant centrifugal cast tube as shown in the drawing was manufactured, and the ultrasonic characteristic values (sonic velocity value and attenuation constant) of the carburized portion and the uncarburized portion were measured. From the measurement results, the ultrasonic characteristics effective for evaluating the carburized layer depth were examined.

  In the test piece 1 shown in FIG. 5, the depth of the carburized layer 2 (2A to 2C) was measured from the macro structure of the etched pipe cross section. Next, the ultrasonic probe used 5 MHz in the vertical method and 2.25 MHz in the transmission method. Further, in order to change the local carburized layer depth in FIG. 5 sequentially and measure the ultrasonic characteristics by the vertical method, grinding machining was performed to reduce the thickness of the inner surface 1a side of the pipe in stages (flattened inner surface). 1a ′).

As a result of measuring the longitudinal wave sound velocity value of the new ultrasonic characteristic material by the vertical method, it was 5751 m / S (average value) (FIG. 6, mark ♦). FIG. 6 shows the results of measuring the longitudinal wave sound velocity value of the test piece 1. As the carburized layer depth increased, the sound velocity tended to increase. The tendency was more remarkable in the columnar crystal structure having no granular crystal structure on the tube inner surface side. FIG. 7 shows the result of measuring the attenuation constant of the carburized part. In the columnar crystal structure having no granular crystals on the inner surface side of the tube, the damping constant tended to decrease as the carburized layer depth increased.

Ultrasonic characteristics by transmission method The vertical method described above is affected by the inner surface of the tube (such as corrosion thinning), so if the ultrasonic main beam passes through the center of the tube thickness, Unaffected. Therefore, the probe mounting position of the probe holder was calculated from Snell's equation so that the main beam passed through the central part of the plate thickness. FIG. 8 shows the result of measuring the longitudinal wave sound velocity of the test piece 1. It was recognized that the longer the distance that the ultrasonic wave passes through the local carburized portion, the higher the sound speed value. 8A shows the relationship between the path of the ultrasonic beam that has passed through the carburized portion and the speed of sound, and FIG. 8B shows the path of the ultrasonic beam corresponding to FIG. 8A.

The carburized layer measuring apparatus 10 according to the present invention is configured based on the principle that both the transmission method and the vertical method increase the speed of sound as the distance that the ultrasonic wave passes through the local carburized portion increases.
In the present invention, the ultrasonic characteristic value (longitudinal wave sonic value or attenuation constant, etc.) on the tube row side (uncarburized part) of the cracking furnace in the ethylene production apparatus is compared with the ultrasonic characteristic value on the burner side (carburized part). Then, the carburized layer depth is measured from the amount of change. Since the cracking furnace of the ethylene production apparatus has coiled tubes arranged in the vertical direction, the burner side (flame side) tends to be hotter than the tube row side. Therefore, carburization from the inner surface side of the pipe tends to occur on the burner side (local carburization).

  The device of the present invention will be described more specifically. First, in the carburized layer measuring apparatus 10 by the transmission method, as shown in FIG. 9, a pair of probes 11 are arranged on the circumference of the decomposition furnace tube 101 by the probe holder 12. In the present invention, in particular, after the main beam of the ultrasonic wave S transmitted from one probe 11 (11A) passes near the central portion of the tube thickness of the cracking furnace tube 101, the other probe 11 (11B). To be received. The probe holder 12 is preferably made of acrylic.

  In the above case, the carburized layer depth of the cracking furnace tube 101 (heat-resistant centrifugal cast tube (JIS SCH24 equivalent), 25% Cr-35% Ni steel, etc.) of the ethylene production equipment reached the tube thickness center. In many cases, it is time to replace the cracking furnace tube. Therefore, whether the carburized layer depth has reached the vicinity of the center of the tube thickness was evaluated. For this reason, the probe holder 12 allows the ultrasonic main beam to pass through the central portion of the tube thickness. The mounting position of the probe 11 was calculated from Snell's formula (ultrasonic reflection / refraction formula). Since the main beam of ultrasonic waves is not reflected on the inner surface side of the tube, there is an advantage that it is difficult to be affected by the shape on the inner surface side of the tube (such as corrosion / thinning or spiral fins).

  In the carburized layer measuring apparatus 10 by the vertical method, a single probe 11 is arranged on the circumference of the cracking furnace tube 101 by a probe holder 12 as shown in FIG. As the probe holder 12 in the vertical method, a probe holder 12 in which the sound pressure of an ultrasonic wave is a far-field sound field region is used. When the ultrasonic probe 11 is brought into direct contact with the decomposition furnace tube 101 that is the subject, the amount of change in ultrasonic characteristics is evaluated within the near field limit distance where the sound pressure of the ultrasonic wave is complex. Therefore, it is set as the probe holder 12 which becomes a long-distance sound field region.

  In the case of the vertical method, it is necessary that the tube inner surface shapes of the tube row side (uncarburized portion) and the burner side (carburized portion) are the same. Further, if the thickness of the cracking furnace tube 101 is locally different, it greatly affects the measurement of the ultrasonic longitudinal wave sound velocity value and the attenuation constant.

Further, the carburized layer measuring apparatus 10 of the present invention includes a traveling guide 13 for guiding the probe 11 to travel around the cracking furnace tube 101 via the probe holder 12 in both the transmission method and the vertical method. .
FIG. 11 shows a specific configuration example of the travel guide 13. The traveling guide 13 is formed of an acrylic annular body that can be divided into two parts, and includes a connector or a binder 16 for integrally joining the half parts. The binder 16 may be a clamp type. Further, along the inner peripheral surface of the travel guide 13, a rubber contact material 17 is attached. As shown in FIG. 3 and the like, the traveling guide 13 has a probe holder 12 mounted thereon, and the probe holder 12 (and hence the probe 11) is manually placed on the same circumference of the decomposition furnace tube 101. Functions as a fixing jig for rotation.

  It should be noted that a rotation jig for automatically rotating the probe holder 12 around the decomposition furnace tube 101 (consisting of a fixed part that can be attached to and detached from the subject and a motor driving part that rotates the probe holder 12). It is also possible to apply an automatic rotating jig). According to such an automatic rotating jig, the local carburizing range can be estimated more accurately than when the probe holder 12 is manually rotated.

According to the carburized layer measuring apparatus 10 of the present invention, first, in the case of the transmission method, as shown in FIG. 3, the waveform of the pen recorder 15 (in this case, the horizontal axis is the center position of the probe holder 12 on the pipe circumference, The vertical axis can accurately estimate the range of the local carburized portion from the echo height of the focused transmitted echo waveform (the output value of the echo height at the gate position of the ultrasonic flaw detector).
Also in the case of the vertical method shown in FIG. 4, the range of the local carburized portion can be estimated from the waveform of the pen recorder 15 as in the case of the transmission method.

  Now, the effect of the present invention will be described in relation to the prior art (using the ultrasonic method). First, in the transmission method of the prior art, two ultrasonic probes are arranged in the tube axis direction. In this method, the ultrasonic main beam is reflected on the inner surface of the tube. Therefore, it cannot be applied to the inner spiral finned tube and the inner fin-extruded tube. In addition, in order to measure the carburized layer depth, a reflection echo from the carburized layer boundary surface is used. In this case, when carburization occurs, a carbon concentration profile based on a diffusion model of carbon atoms is formed, so that a carburized layer boundary surface that can be identified by an ultrasonic method cannot be defined.

According to the present invention, by using the permeation method in particular, the present invention can be applied to the inner surface spiral finned tube and the inner surface finned extruded tube. That is, since the ultrasonic main beam passes near the central portion of the tube thickness, the present invention can be applied even if the shape on the tube inner surface side is not uniform.
Further, the depth of the carburized layer can be evaluated by comparing the ultrasonic sound velocity values or attenuation constants on the tube row side (uncarburized portion) and the burner side (carburized portion). When evaluating the carburized layer depth, it is necessary to create in advance a master curve indicating the correlation between the ultrasonic sound velocity value or attenuation constant and the carburized layer depth for each material of the reaction tube.
Further, among the factors affecting the ultrasonic sound velocity value or the attenuation constant, the influence of the nitride and oxide scale deposited on the outer surface side of the tube is substantially the same on the tube row side (uncarburized portion) and the burner side. It is assumed that the amount of change in the ultrasonic sound velocity value or attenuation constant is influenced only by the carburized layer depth.

As mentioned above, although this invention was demonstrated with various embodiment, this invention is not limited only to these embodiment, A change etc. are possible within the scope of the present invention.
In principle, even when carburization occurs from the inside surface of a heating furnace tube (5% Cr-0.5% Mo steel, 9% Cr-1% Mo steel, SUS310, etc.) such as an oil refinery. Is possible. That is, the present technology can be applied to a heating furnace tube other than the centrifugal cast tube. In principle, the present invention can also be applied to detection of a decarburized layer (reaction with in-pipe fluid steam) generated on the inner surface side of the boiler tube.

DESCRIPTION OF SYMBOLS 10 Carburized layer measuring apparatus 11 Probe 12 Probe holder 13 Running guide 14 Ultrasonic flaw detector 15 Pen recorder 16 Binder 17

Claims (5)

A method for measuring a carburized layer of a tubular body for measuring a carburized layer formed in a predetermined portion of the tubular body using ultrasonic waves,
A tubular body in which one or a pair of probes are moved along the outer periphery of the tubular body, a change in ultrasonic characteristics due to the passage of the carburized layer is detected, and the depth of the carburized layer is measured based on the detection result. Carburized layer measurement method.   The ultrasonic wave is transmitted from the transmitting side of the pair of probes to the receiving side so that an ultrasonic path propagating through the tubular body passes through a substantially central thickness portion of the tubular body. Item 2. A method for measuring a carburized layer of a tubular body according to Item 1.   The method of measuring a carburized layer of a tubular body according to claim 1 or 2, wherein the probe travels and scans the entire circumference of the tubular body. A carburized layer measuring device for a tubular body for measuring a carburized layer formed at a predetermined portion of the tubular body using ultrasonic waves,
A probe holder for holding the probe so that one or a pair of probes can transmit and receive ultrasonic waves at a predetermined position and angle;
An apparatus for measuring a carburized layer of a tubular body, comprising: a traveling guide for guiding the probe to move around the tubular body through the probe holder.   The holder is configured so that an ultrasonic path propagating through the tubular body transmitted from the transmitting side to the receiving side of the pair of probes passes through a substantially central portion of the tubular body. 5. The tubular carburized layer measuring device according to claim 4, wherein the tentacle is held.

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