JP2005214928A - Deterioration diagnostic method for inner face of pipe screw-joined part by ultrasonic wave - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To diagnose deterioration in an inner face of pipe screw-joined part without inserting a probe into a pipe, to diagnose the deterioration without requiring operation stop and draining for a piping facility, and to diagnose the deterioration without executing work for a tapered part for ultrasonic measurement on an outer face of a pipe. <P>SOLUTION: An ultrasonic wave is made incident from an outside of the pipe, using the surface SH wave probe by an angle beam flaw detection method, echo data are sampled while moving the probe with an equal interval along a circumferential direction of the pipe, an echo in a pipe end part is extracted from the respective echo data, and corrosion is detected by detecting a position where an end face echo height gets minimum with respect to the circumferential direction of the pipe. An echo amplitude from a screw part is expressed by a numeral model to be compared with an envelope of the observed echo data, and a pipe axial-directional distance from the probe to the corrosion is estimated based on a time when an error gets maximum on a time axis. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for diagnosing local deterioration of an inner surface of a screw joint in an air conditioning pipe and various pipe structures using an ultrasonic flaw detection method.

The inspection of screw joints in piping is generally radiation inspection, but radiation inspection requires handling qualifications and is not practical because exposure measures at the time of measurement are required.
Residual wall thickness measurement by the ultrasonic flaw detection method is suitable, but even if ultrasonic waves are incident vertically on the threaded joint of the pipe (vertical flaw detection method), they are reflected and scattered by the screw surface and do not propagate to the inner surface of the pipe. It is difficult to detect corrosion on the inner surface of the screw joint.

  In the oblique angle flaw detection method using ultrasonic waves, when a pulse (longitudinal wave) is emitted from a quartz oscillator, it reciprocates in the plate when it is refracted at the boundary between the wedge and the metal. It is known that defects can be detected. In this case, an SV wave (vertically-polarized shear wave) in which molecules oscillate perpendicularly to the surface of the plate and an SH wave (horizontally-polarized shear wave) in which molecules oscillate parallel to the surface of the plate are generated. It is known.

Since screw joining is used for small-diameter pipes, the pipe thickness is thin. In a general SV wave probe as a bevel angle probe, the refraction angle is about 80 ° at the maximum, and when this is applied to a pipe thread portion, the ultrasonic wave reaches the pipe inner surface before reaching the pipe end. Since reflections are repeated between the screw surfaces, it is very difficult to analyze echo data.
In Japanese Patent Laid-Open No. 63-298054 “Screw joint ultrasonic inspection method for pipes”, ultrasonic data is measured by bringing a probe into contact with the inner surface of a pipe. However, it is necessary to insert a probe into the pipe, and it is necessary to stop the operation of the equipment and drain the water. It is necessary to machine an ultrasonic measurement taper part on the pipe outer surface, which is not practical. In JP-A-1-235848 “Ultrasonic flaw detection method and apparatus for screw of joint portion of pipe”, a defect of the screw portion can be detected by ultrasonic waves from the outer surface of the joint. However, defects on the female thread side (joint side) can be detected, but internal corrosion and defects on the male thread side (pipe side) cannot be detected. Japanese Patent Application Laid-Open No. 11-14608 “Electromagnetic ultrasonic probe” describes differences between an ultrasonic probe using an SH wave and an ultrasonic probe using an SV wave. The journal "Non-destructive inspection", Volume 45, No. 5, pages 343 and below contains a paper titled "Experimental study on the round-trip rate of SH waves". Published a paper entitled "Experimental study on directivity of echoes of surface SH waves and SH bevel probes".

A first object of the present invention is to provide a method for diagnosing deterioration of an inner surface of a pipe screw joint without inserting a probe into the pipe.
A second object of the present invention is to provide a method for diagnosing deterioration of the inner surface of a pipe screw joint without requiring operation stop of the piping facility or draining.
A third object of the present invention is to provide a method for diagnosing deterioration of the inner surface of a pipe screw joint without processing a taper for ultrasonic measurement on the outer surface of the pipe.

  In order to solve the above-described problem, in the present invention, as a first aspect, using a surface SH wave probe by an oblique flaw detection method, ultrasonic waves are obliquely incident from the front of the screw portion and are locally applied from the outside of the pipe. Provided is a method for detecting corrosion using the fact that echo information from a pipe end face changes when corrosion is present. At this time, the echo data is sampled while moving the probe at equal intervals in the pipe circumferential direction, the echo of the pipe end (end face echo) is extracted from each echo data, and the end face echo height with respect to the pipe circumferential direction. Corrosion is detected by detecting the position where becomes minimum. Thereby, the deterioration of the inner surface of the pipe screw joint is diagnosed.

  As a second aspect of the present invention, the echo amplitude from the screw portion is expressed by a numerical model, compared with the envelope of the actually measured echo data, and from the time when the error is maximum on the time axis, from the probe Estimate the axial distance of the pipe until corrosion. Thereby, the deterioration of the inner surface of the pipe screw joint is more specifically diagnosed.

  The surface SH wave probe used in the present invention transmits an SH wave having a transverse wave and a horizontal vibration direction, and the SH wave is mainly incident near the surface (refraction angle 85 to 90 °). A probe set at a corner.

The following equipment was used.
(1) Ultrasonic pulse transmitter / receiver: Pulse receiver, ultrasonic flaw detector, etc. (2) Ultrasonic probe: Surface SH wave probe (3) Echo data sampling equipment: PC, etc.

The procedure for detecting and detecting local corrosion is as follows.
(1) Finishing the pipe surface smoothly with a file or the like (2) Applying a contact medium (for example, trade name Sonicoat SHN-B25) and bringing the probe into contact with the pipe (3) Placing the probe in the pipe circumferential direction Echo data is sampled while moving at equal intervals. (4) Extracting pipe end echoes (end face echoes) from each echo data, and detecting the position where the end face echo height is minimized relative to the pipe circumferential direction. (5) The envelope of the echo data at the four measurement points is obtained and the position of the corrosion is estimated by comparing with the numerical model of the echo height.

(1) No handling qualification is required. (2) Inspection can be performed with the equipment in operation. It is not necessary to process the pipe for inspection. (3) Since the surface SH wave probe has a large refraction angle, it is possible to inspect the screw joint by ultrasonic waves. Defects can be detected.

  Hereinafter, the present invention will be described in more detail with reference to embodiments of the accompanying drawings.

  FIG. 1 shows a schematic diagram of propagation in the pipe thread portion 11 by the oblique flaw detection method using the ultrasonic probe 10, and FIG. 2 shows an example of echoes in the thread portion. This echo has a waveform in which an ultrasonic wave directly reflected by a screw portion and a reflection of the ultrasonic wave on the inner surface of the pipe and further reflected by the screw portion are superimposed.

  As shown in FIG. 3, when local corrosion 12 is present on the pipe inner surface of the screw joint portion, the echo (defect echo) reflected by the corrosion is superimposed on the echo from the screw portion as shown in FIG. It cannot be observed easily. Therefore, it is ideal to erase the echo of the screw part from the echo data, but the echo of the screw part varies greatly depending on the measurement position in the circumferential direction of the pipe, and the finished dimensions of the screw differ slightly depending on the adjustment of the machine during screw processing. Since the influence affects the echo, it is expected to be different for each pipe to be inspected, and it is not easy to eliminate the echo of the screw portion.

  When attention is paid to the echo (end-face echo) from the pipe end shown in FIG. 3, this echo is hardly observed in FIG. When local corrosion exists, as shown in FIG. 3, the propagation of ultrasonic waves is blocked by the corrosion and it is difficult to propagate to the end, so that the end echo height is reduced. Therefore, corrosion can be detected by extracting the end face echo height from echo data obtained by scanning the probe in the pipe circumferential direction and searching for a position where the end face echo height is minimized.

  The position of the corrosion can be determined from the time when the echo from the corrosion is observed. However, in the screw portion, it is observed superimposed on the echo of the screw portion, and it is very difficult to extract the echo from the corrosion. Here, the echo height of the screw part attenuates according to the distance from the probe if there is no corrosion, but when the echo from the corrosion is superimposed, the echo height changes greatly at the observed time. To do. Therefore, the echo height of the screw portion when there is no corrosion is expressed by a numerical model, and the corrosion position is estimated by extracting the time when the echo height changes greatly by comparing the model and the envelope of the echo data. Here, the envelope of the echo data is a line connecting peaks, and in the present invention, the envelope is obtained using only the positive peak.

  In this embodiment, as an artificial corrosion pipe, as shown in FIG. 5, a carbon steel pipe for piping (SGP black) 50A is threaded with JIS standard (B0203 taper screw for pipe), and artificial corrosion (flat bottom hole) 12 is formed on the inner surface thereof. The machined one is used.

6 patterns of artificial corrosion pipes shown in Table 1 are used as the artificial corrosion pipes. The depth of corrosion is all 1 mm.

  As shown in FIG. 6, assuming that the position of the local corrosion 12 in the axial direction is X and the position in the circumferential direction of the pipe is Y, the position where the corrosion exists (Y = 0) is the center, and the circumferential direction is 1 mm pitch plus or minus 7 mm. The echo data was sampled to measure the edge echo height. 7 and 8 show end face echo height curves, respectively. From this, it can be seen that the position of corrosion is a position where the height of the end face echo becomes a minimum value regardless of the magnitude and position of the corrosion. Therefore, corrosion can be detected by extracting the end face echo height from the entire circumference measurement data of the pipe thread portion and searching for the minimum value.

  Next, estimation of the position of local corrosion will be described. In the absence of corrosion, the observed echo data will decay in echo height over time. Therefore, a change in echo height due to attenuation of ultrasonic waves is represented by a numerical model.

ここで、Ｐ₀ ：振動子直前の音圧、ｘ：音波の伝搬距離、Ｐｘ：距離ｘだけ伝搬後の音圧である。このとき、αを減衰係数と称する。減衰係数αは、図９に示すようなφ１ｍｍの水平横穴を設けた試験片を用い、探触子との距離Ｌを変化させながら横穴からのエコー高さを実測することによって求める。ただし、図１０に示すように、超音波は指向性をもっているため、角度が変化するとエコーの振幅が変化するので、屈折角θに応じた指向性を考慮する必要がある。 The attenuation of ultrasonic waves is expressed by an exponential function as follows.

Here, P _{0 is} the sound pressure immediately before the transducer, x is the propagation distance of the sound wave, and Px is the sound pressure after propagation by the distance x. At this time, α is referred to as an attenuation coefficient. The attenuation coefficient α is obtained by measuring the echo height from the horizontal hole while changing the distance L to the probe using a test piece provided with a horizontal horizontal hole of φ1 mm as shown in FIG. However, as shown in FIG. 10, since the ultrasonic wave has directivity, the amplitude of the echo changes when the angle changes. Therefore, it is necessary to consider the directivity according to the refraction angle θ.

ここで ｋ＝２π／λ、ｋ’＝２π／λｗ、λ：鋼中の波長、λｗ：探触子アクリル内での波長、α：入射角、Ａ：振動子の入射面への投影面積である。 As shown in FIG. 11, (such as a crystal oscillator) vibrator Taken N equally divided vibrator in the longitudinal direction for 14 cross-section, the echo height H _D at point D is expressed by the following expression 2 It is confirmed that the measured values agree well.

Where k = 2π / λ, k ′ = 2π / λw, λ: wavelength in steel, λw: wavelength in the probe acrylic, α: incident angle, A: projected area on the incident surface of the transducer is there.

  In the case of the probe used in the present invention, when H = 10 mm and α = 24.9 °, and when the frequency is 5 MHz and the sound velocity is steel: 3230 m / s and acrylic: 1360 m / s, λ and λw are obtained respectively. The directivity as shown in FIG. 12 is required. Accordingly, the echo height obtained as shown in FIG. 9 is plotted after removing the influence of directivity by dividing the echo height obtained by the above equation at the angle φ at that time by the normalized value. Then, a graph as shown in FIG. 13 is obtained. When this is approximated by an exponential function by the least square method, the attenuation coefficient α can be obtained.

As described above, the attenuation and directivity of ultrasonic waves are quantified, and a simple echo height model is created. Since the propagation of ultrasonic waves in the threaded portion is very complicated, only the echo height reflected at the inner surface of the pipe and reflected at the top of the threaded valley is represented by the above attenuation and directivity as shown in FIG. . Attenuation and directivity are calculated from the ultrasonic propagation distance X (X ₀ + X _1n + X _2n ) and the angle φn to each screw root, and the echo height is obtained from the product of them. The echo height model thus obtained is shown in FIG. Piping was intended for SGP50A, and each screw dimension was in accordance with JIS standards.

  In the echo data measured by moving the probe in the circumferential direction, the measurement location where the end face echo is minimum is considered to be the central position of corrosion. Therefore, the envelope (envelope) of the echo data measured at this position is compared with the echo height model shown in FIG. 15, and the position where the difference in echo height is maximum (calculated from the value on the horizontal axis) is the presence of corrosion. It is determined that it is a position to perform. At this time, the horizontal axis (time axis) of the echo data is converted into the propagation distance by multiplying the sound velocity of the ultrasonic wave. Further, the level (horizontal direction) is adjusted by multiplying the model by an appropriate coefficient so that the error between the echo data envelope and the echo height model is minimized. Thereby, the influence on the echo height due to the difference in reflectance between the side hole of the test piece used for obtaining the attenuation and the reflection source of the actual screw can be taken into consideration.

As an experimental result, Table 2 shows an estimation experimental result of the corrosion position using artificial corrosion. The magnitude of corrosion was φ4 mm and φ6 mm, the depth was unified at 1 mm, and the horizontal distance from the probe was 43 mm for both. Here, the estimated value in Table 2 is a value obtained by converting the propagation distance of the ultrasonic wave obtained by the above method into a horizontal distance from the probe.

Here, the influence on the echo height by screw joining was confirmed. Since a tape-like or liquid sealant is applied to the male screw at the time of screw joining, the echo height is expected to decrease due to a decrease in the reflectance of the screw surface. Therefore, in some sample pipes (carbon steel pipe 50A), the echoes of the thread portions were measured before and after the sealing process and joint connection, and the absolute values of the respective echo heights were compared. In order to evaluate the difference in amplitude before and after processing, the absolute values of echo data were averaged to determine the difference before and after processing. This is shown in Table 3.

  As can be seen from Table 3, in the case of the seal tape, there is almost no decrease in the echo height, but in the case of using the liquid sealant, the echo height is decreased in all cases, and a maximum decrease of less than 20% is confirmed It was done. For the case where the echo height is increased, the influence of the contact state of the probe is considered to be large. Therefore, when a liquid sealant is used, it is necessary to reduce the influence by adjusting the amplification factor setting of a device such as a pulsar receiver or an ultrasonic flaw detector in consideration of a decrease in echo height. The above examples were performed using piping without sealing and joint connection.

  As described above in detail, according to the diagnostic method of the present invention, it is possible to diagnose the deterioration of the inner surface of the pipe screw joint without inserting a probe into the pipe, and at that time, the operation of the piping facility is stopped. No deterioration of the inner surface of the pipe screw joint can be diagnosed without processing the taper part for ultrasonic measurement on the outer surface of the pipe, and the technical effect is extremely remarkable. is there.

The schematic diagram showing the propagation of the ultrasonic wave by the bevel flaw detection method. The graph showing the echo data in a piping thread part. The schematic diagram showing propagation of an ultrasonic wave when corrosion exists. A graph representing echo data in the presence of corrosion. Sectional drawing of the state which gave artificial corrosion to the screw-joint part inner surface. Sectional drawing showing the measurement position of a screw junction part inner surface. The graph showing the change of end face echo height. The graph showing the change of end face echo height. The schematic diagram showing the measuring method of the attenuation factor in a bevel flaw detection method. The graph of the actual measurement value which measured the directivity of the probe. The schematic diagram showing the method of calculating the directivity of a probe. A graph showing the result of calculating the directivity of the probe. A graph showing a change in echo height due to attenuation. The schematic diagram showing the state which applies a bevel flaw detection method to a thread part. The graph showing the change of the ultrasonic propagation distance of an echo height model.

Explanation of symbols

10 Ultrasonic probe 11 Piping screw part 12 Artificial corrosion (flat bottom hole)
14 Crystal resonator

Claims (2)

It is a method for diagnosing local deterioration of the inner surface of a screw joint in air conditioning piping and various pipe structures using an ultrasonic flaw detection method,
Using a surface SH wave probe by the oblique angle flaw detection method, ultrasonic waves are incident obliquely from the front of the screw part from the outside of the pipe,
Sampling echo data while moving the probe at equal intervals in the pipe circumferential direction,
Extract echo at pipe end from each echo data,
Corrosion is detected by detecting the position where the end face echo height becomes minimum with respect to the pipe circumferential direction.
A method for diagnosing local deterioration of an inner surface of a screw joint using the ultrasonic flaw detection method, comprising the above steps. 2. The diagnostic method according to claim 1, further comprising: expressing the echo amplitude from the threaded portion by a numerical model, comparing it with an envelope of actually measured echo data, and determining the search from the time when the error is maximum on the time axis. A diagnostic method comprising a step of estimating a pipe axial direction distance from a contactor to corrosion.

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