JPH07234207A - Evaluating method for cavity generation by hydrogen erosion - Google Patents

Abstract

PURPOSE:To provide detailed and quantitative information, which employs a frequency as a parameter, concerning hydrogen erosion by carrying out simultaneous measurement by using multiple frequencies. CONSTITUTION:A pulse introduced into a substance via a transducer undergoes contamination due to interaction with elements (crystalline grain, cavity, and the like) constituting the substance while transmitted in the substance, and the substance can be evaluated by analyzing the contamination. By an ultrasonic flaw detection method based on multiple frequency simultaneous measurement, cavity information employing a frequency as a parameter is obtained by using a broad probe, for example, output are flattened over a range of 5-40MHz so that sonic velocity and the quantity of attenuation in multiple frequencies can be measured at once. In this way, a value for an optional frequency can be obtained by a window function, and information found from a change in the sonic velocity and the quantity of attenuation based on a frequency, for example, the number of cavities and a diameter, can be obtained in a single measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the occurrence of cavities (microcracks) due to hydrogen attack.
In particular, the present invention relates to a new evaluation method that can evaluate the size and distribution density of cavities, the degree of erosion, etc. due to hydrogen erosion by the multi-frequency simultaneous measurement method, taking frequency as a parameter.

[0002]

2. Description of the Related Art In a petroleum / chemical plant or the like that handles high-temperature and high-pressure hydrogen, containers, pipes, equipment and other members are corroded by hydrogen, and cavities are formed inside these members. If the aging damage represented by such cavities is left unchecked, it will lead to a serious accident, and for that reason it is important to perform nondestructive inspection regularly. When hydrogen is attacked, the damage process that appears in the material does not suddenly change its mechanical properties but follows the following process: 1) Incubation period: submicron methane bubbles are ferrite Nucleate near or on carbides at grain boundaries,
grow up. In this state, the mechanical properties show almost no change. 2) Fischer growth period: Bubbles combine to form grain boundary fischer. 3) Saturated state: Fishers are connected and macro cracks occur.

Up to now, the following non-destructive inspections have been carried out using ultrasonic waves (Japanese Patent Publication No. 1-412).
(Quoted from the description of No. 19). (1) Ultrasonic attenuation method: There are fine cracks in the hydrogen attack region. Therefore, when the ultrasonic wave is propagated through the member that has been eroded by hydrogen, the ultrasonic wave is scattered by the action of the cracks, the sound pressure is attenuated, and the energy of the reflected wave is reduced accordingly.
This method is to estimate the presence or absence of hydrogen attack based on the degree of attenuation of the sound pressure. (2) Ultrasonic vertical flaw detection method: The phase thickness (dimension in the depth direction) of the hydrogen erosion region is measured based on the time difference between the reflection echo of ultrasonic waves and the bottom reflection echo caused by minute cracks existing in the hydrogen erosion region. To do.

However, the above method (1) has a drawback in that it is not possible to accurately evaluate the hydrogen erosion area because ultrasonic waves are attenuated even in sound steel materials and the attenuation degree varies from steel material to steel material. Hold. In the method of (2) above, the sensitivity of the flaw detector is set to be extremely large as compared with the usual ultrasonic flaw detection, so that flaw detection is performed, so that it is also reflected by other defects other than hydrogen erosion, such as inclusions in the material. Therefore, it may not be possible to distinguish whether the reflection of ultrasonic waves is based on hydrogen attack or the inclusions.

In view of such a point, the above Japanese Patent Publication No. 1-412.
The invention of No. 19 itself introduces the concept of longitudinal wave and transverse wave to propagate the ultrasonic wave in the thickness direction of the steel material as a method for accurately evaluating the degree of hydrogen erosion, and propagates the longitudinal wave of the ultrasonic wave. Time and shear wave propagation time are detected, their ratio is taken, and based on the value of this ratio, the ratio of the micro-cracking zone due to hydrogen attack to the thickness of the steel is estimated, and the hydrogen attack of steel is characterized. We have proposed a method for evaluating the micro-cracking area based on. That is, the ratio V _L / V _S of the propagation velocity V _L of the longitudinal wave and the propagation velocity V _S of the transverse wave when the longitudinal wave and the transverse wave of the ultrasonic wave are propagated in the thickness direction of the subject (for example, carbon steel material). The ratio T of the depth T _A of the hydrogen attack region to the thickness T of the subject
Focusing on the unique linear relationship with _A / T,
The longitudinal wave round trip propagation time t _L and the transverse wave round trip propagation time t _S from the time when the transmission pulse is applied to the probe from the transceiver to the time when the bottom echo of the longitudinal wave and the transverse wave is received by the transceiver are measured, and V _{Since L} / V _S = t _L / t _S , the propagation time of the longitudinal wave and the propagation time of the transverse wave are detected and their ratio is taken. Based on the value of this ratio, hydrogen erosion with respect to the thickness of the steel material is carried out. It is intended to estimate the ratio of the micro-cracking occurrence area due to.

Further, in connection with this technique, in order to eliminate the fixed time delay caused by the couplant and the like within the propagation time of the measured longitudinal wave and transverse wave, Japanese Patent Laid-Open No. 62-82347 discloses Waves and transverse waves 1st (B1) and 2nd (B
2) It is proposed that the bottom surface reflected wave (echo) is detected and the time from the detection time point of the first bottom surface reflected wave to the detection time point of the second bottom surface reflected wave is measured as the propagation time of the longitudinal wave and the transverse wave.

[0007]

However, such conventional methods, while providing rough information on the extent of the overall presence of the cavities that make up the hydrogen attack region, do not allow for maximum flaw detection. Even if sensitivity is used, deterioration of the material has progressed considerably, for example, the toughness of the material is about 5% of the initial value.
This is from the state of 0%. It does not provide information on the dimensions and distribution density of individual cavities.
With the recent increase in the size of equipment and the harsh operating environment, the demand for security of equipment materials is increasing more and more, and in order to more accurately and non-destructively evaluate aged damage due to hydrogen attack of various equipment in the future. Requires more quantitative and detailed information on erosion status from the earlier stage. It is an object of the present invention to establish a new ultrasonic nondestructive evaluation method that can provide more detailed and quantitative information regarding hydrogen attack.

[0008]

In the conventional ultrasonic flaw detection method, a probe having a narrow band width (narrow band) centering around a specific frequency is used. The narrow band probe has, for example, an output peak at 5 MHz and an output width within a range of ± 0.5 MHz. The present inventor believes that by introducing frequency as a parameter, more detailed hydrogen erosion information than before can be obtained at an early stage,
As a result of repeated studies to obtain hydrogen erosion information by using a large number of frequencies at the same time, it was confirmed that the multi-frequency simultaneous measurement method is extremely effective as a method for evaluating cavity generation due to hydrogen erosion. That is, by conducting simultaneous multi-frequency measurements using a broadband probe or using the resonance frequency of a single band probe, the power equation method is used to solve the wave equation for cavitation scattering. It is possible to obtain the number of cavities and the diameter of the cavities by analyzing the relational expressions relating to the number of cavities and the diameter of the cavities, and to obtain much information such as the relationship between the peak frequency and the Charpy test result. First confirmed in the field.

Based on these findings, the present invention provides
(1) In a method of evaluating a state of cavity generation due to hydrogen erosion using ultrasonic waves, a method of evaluating cavity generation due to hydrogen erosion, characterized in that cavity information having frequency as a parameter is obtained by simultaneous measurement using a large number of frequencies. , (2) Multi-frequency simultaneous measurement using a broadband probe or using the resonance frequency of a single band probe, (1) Method for evaluating cavity generation due to hydrogen attack, (3) The waveforms of the B ₁ reflected wave and the B ₂ reflected wave are simultaneously measured at multiple frequencies, continuously A / D converted and stored in a memory, and a fixed length of data is extracted from the beginning of this waveform and multiplied by a window function. Perform the FFT, then take out the data of the same length from the point shifted by Δt, multiply by the window function in the same way, and perform the FFT one after another. Into a ram, characterized by obtaining the two relationship between the frequency versus sound velocity and frequency versus attenuation from the peak value in the present time of the B ₁ reflected wave and B ₂ reflected wave of the specific frequency from the change over time of a particular frequency (1)
(4) The number of cavities and the diameter of the cavities based on the relational expression regarding the number of cavities and the diameter of the cavity induced by solving the wave equation for scattering of cavitation (3) The method for evaluating the generation of cavities due to hydrogen attack in (3), and (5) for the target material, the peak value of the B ₁ reflected wave is the highest among the measurement frequencies and the Charpy test. A method for evaluating the occurrence of cavities due to hydrogen erosion according to item (1) is provided, in which the relationship with the result is obtained and the peak frequency is measured to determine the hydrogen erosion state.

[0010]

[Function] The sound wave propagating through the substance can be captured as an information medium regarding the substance. The pulse introduced into a substance through a transducer is caused by interaction with the elementary factors (grains, impurity atoms, precipitates, cavitities, dislocations and other lattice defects) that compose the substance while propagating in the substance. Contamination (contaminatio
n) receive. The degree and mode of contamination are unique to each elementary factor, and a substance can be evaluated by analyzing this contamination. The ultrasonic flaw detection method by multi-frequency simultaneous measurement obtains cavity information with a frequency as a parameter using a broadband probe or using a resonance frequency of a single band probe. The narrow band probe used conventionally has an output peak at 5 MHz and the width of the output is set within a range of ± 0.5 MHz, while the broadband probe has a range of 5 MHz. 40M
The output is flat in the range of Hz. A broadband probe can measure sound velocity and attenuation at many frequencies with one measurement. Alternatively, the resonant frequency of a single band probe can be used. For example, using 5MHz, 10, 15,
It is possible to obtain a resonance frequency that is an integral multiple of 20, 25, or the like. However, it is preferable to use a broadband probe. With a broadband probe, it is possible to obtain a value at any frequency with a window function. Information (for example, the number and diameter of cavities) obtained from changes in sound velocity and attenuation depending on frequency can be obtained by one measurement, and it is not necessary to perform multiple measurements using narrow band probes with different center frequencies. An analysis item called a frequency domain (a peak frequency of B1 (first reflected wave) as an example) can be obtained by one measurement. This item has no relation to the thickness of the steel material, and is an effective analysis item for actual measurement. The intensity distribution of ultrasonic waves with respect to the frequency obtained from ultrasonic spectroscopy is
It can be regarded as a statistic representing the frequency distribution.

J. Phys. D: Appl. Phys. 14 (1981) 413-20
As described in the page and WAVE MOTION 7 (1985) 95-104C, according to CM Sayers, multiple scattering that can be applied to the evaluation of cavities caused by hydrogen attack, especially the evaluation of their diameter and number (distribution density). The theory is derived from the complex solution φ of the wave equation

[0012]

[Equation 1]

Rayleigh region of equation (1) (ka <1, a:
Sayers' solution for cavitation scattering at cavity diameter (m) is

[0014]

[Equation 2]

[0015] Here, approximated by the taking the speed of sound ratio _{K / k = V L / V} T , and the transverse wave, the constant A,
B and C are obtained. Incidentally, the value is as follows. _{V L = 5900 m / sec V} T = 3230 m / sec K / k = (5900/3230) = 1.8266 A = -1.2708 B = -1.8399 C = 3.4577

Since β = k + iα, (β /
k) ² = 1− (α / k) ² +2 (α / k) i, and from this, 2 (α /
^{k) = (4/3) πa 3} n o Ck 3 a 3 next, thus, alpha
Is represented as follows.

[0017]

[Equation 3]

When the cavity concentration is low, the following equation holds. (Sayers)

[0019]

[Equation 4]

A = -1.2708 and B =-calculated above
Substituting the numerical values of 1.8399 and C = 3.4577 into Equation 3 and Equation 4, respectively, the following relationship is obtained: That is, the absorption coefficient α, the wave number k of the longitudinal wave, the sound velocity _VL of the longitudinal wave without the cavity and the sound velocity _VL 'of the longitudinal wave with the cavity, the number n _{O of the} cavities and the diameter a of the cavity.
Relational expression (1) shown by the following equations 5 and 6 between
And (2) are induced.

[0021]

[Equation 5]

[0022]

[Equation 6]

Therefore, α, k (= ω / V _L ), (V _L '
/ V _L ), a measured value is obtained for each frequency, so α is plotted on the vertical axis and 7.2418 k ⁴ is plotted on the horizontal axis, and n _O a ⁶ is obtained from the slope, while 1-axis is plotted on the vertical axis. ( _VL '/
_VL ) and plotting k ² on the horizontal axis, and the intercept 2.
6616n _O a ³ n _O a ³ are obtained from, thus it is possible to obtain a diameter a few n _O and the cavity of the cavity.

Absorption coefficient α (dB / m) at each frequency
Can be obtained as follows, for example. The B1 and B2 reflected waves are simultaneously measured at multiple frequencies using a pulsar receiver and a wave memory, continuously A / D converted, and stored in the memory. A fixed length of data is taken out from the beginning of this waveform, multiplied by a window function, and FFT (Fast Fourier Transform) is performed. Next, the data of the same length is taken out from the point shifted by Δt, and similarly, the window function is multiplied to perform the FFT.
In this way, FFT is performed by shifting by Δt, and the obtained result is converted into a power spectrum. An example of creating such a power spectrum is shown in FIG. Paying attention to a certain frequency f ₁ of the power spectrum thus obtained, Δt
When each change is plotted, the change over time of the specific frequency f ₁ is obtained as shown in FIG. This graph is usually B1
Since there is a peak value at the time when the reflected wave and the B2 reflected wave exist, the sound velocities V _L and V _L 'of the longitudinal wave of the component of f ₁ can be found by finding the time difference between the two peak values, and If the amplitude ratio is obtained, the absorption coefficient α can be obtained.

Thus, the wave equation φ = exp [i (βx + ω) is used to evaluate the cavity generated by hydrogen attack.
t)] is an absorption coefficient α, derived based on the Sayers solution for scattering of cavitation in the Rayleigh region,
Wavenumber k of longitudinal wave, sound velocity V _L of longitudinal wave without cavity
, And the relational expression (1) α = 7.2418 n _O a ⁶ k ⁴ between the sound velocity V _L ′ of the longitudinal wave in the case where there is a cavity, the number n _{O of} cavities, and the diameter a of the cavity, and the relational expression (2) 1 − (V _L '/ V _L )
= 2.6616n _o a ³ + 3.8535n _O a ⁵ k ² , the absorption coefficient α measured at each frequency, the wavenumber k of the longitudinal wave, and the sound velocity V _L '/ cavity of the longitudinal wave in the presence of the cavity are The sound velocity V _L of the longitudinal wave in the absence of the wave is obtained, and α is plotted on the vertical axis and 7.241 on the horizontal axis.
8 k ⁴ is plotted, and n _O a ⁶ is plotted from the slope thereof, while 1- (V _L '/ V _L ) is plotted on the vertical axis and k ² is plotted on the horizontal axis, and the intercept 2.6616 n _O a ³ is plotted. n _O a ³ is obtained, whereby the number of cavities n _O and the diameter of the cavities a
And can be asked.

Further, for example, an analysis item called a frequency domain can be obtained by one measurement. This item has no relation to the thickness of the steel material, and is an effective analysis item for actual measurement. As an example, based on the relationship between the upper shelf energy of the Charpy V-notch test and the frequency at which the peak value of Joule (J) and B1 (first reflected wave) is the highest among the measured frequencies, such a graph By once preparing the steel material targeted for (1), the damage state of the reaction vessel or the like using the steel material can be measured by the nondestructive flaw detection method in which the peak frequency is measured.

[0027]

【Example】

(Example 1: Number and diameter of cavities) Sound velocity V _L and each of 0.5 Mo steel not subjected to hydrogen erosion, 100 hours of hydrogen erosion and 500 hours of hydrogen erosion. Frequency and absorption coefficient α
The frequency dependence of was investigated. 1 (a) and 1 (b) show the results thus obtained.

Based on FIGS. 1A and 1B, the relationship between the hydrogen attack time and the cavity diameter and number was determined. The results are shown in the graph of FIG.

(Example 2: Measurement of damage state by peak frequency) In the graph of FIG. 3, the abscissa represents the upper shelf energy of the Charpy V-notch test in Joule (J) and the ordinate represents B1 (first reflection). Wave) has the highest peak value among the measured frequencies. It is a plot of the average value of the peak frequency at 2500 points of each test piece and the result of the Charpy V-notch test of the test piece for five types of steel materials of interest up to 500 hours. By once preparing a steel material targeted for such a graph, a damage state of a reaction vessel or the like using the steel material can be measured by a nondestructive flaw detection method in which a peak frequency is measured.

[0030]

The present invention provides more detailed cavity information, which is different from the conventional rough information on the degree of the general existence of the cavities constituting the hydrogen attack region.
By performing multi-frequency simultaneous measurement, the number of cavities induced by solving the wave equation for the cavitation scattering using the power spectrum method and the relational expression with respect to the diameter of the cavity are analyzed. It is possible to obtain the diameter of the cavity and obtain a lot of information such as the relationship between the peak frequency and the Charpy test result.

[Brief description of drawings]

BRIEF DESCRIPTION OF THE FIGURES Figure 1: 0.5 Mo steel non-hydrogen eroded sample, 100 h hydrogen eroded sample and 50
(A) is a graph showing the frequency dependence of the sound velocity V _L for a sample subjected to 0 hour hydrogen attack and (b)
Is a graph showing the frequency dependence of the absorption coefficient α.

FIG. 2 is a graph showing the relationship between hydrogen erosion time and cavity diameter and number.

FIG. 3 shows the upper plate energy of the Charpy V-notch test on the horizontal axis in Joule (J) and the vertical axis on B1 (first
It is a graph which shows both relations when the peak value of the reflected wave is the highest peak frequency among the measurement frequencies.

FIG. 4 is an explanatory diagram showing an example of creating a power spectrum.

FIG. 5 is an explanatory diagram for obtaining a change with time by plotting a change in a frequency of a power spectrum for each Δt.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Nomura 2-10-1 Toranomon, Minato-ku, Tokyo, Japan Energy Co., Ltd. (72) Inventor Yuho Shimizu 3-2-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa No. NF Co., Ltd. In the circuit design block (72) Inventor Takuichi Imanaka 3-18-18-22 Kita, Tennoji-cho, Abeno-ku, Osaka-shi, Osaka

Claims (5)

[Claims] 1. A method of evaluating a cavity generation state due to hydrogen erosion using ultrasonic waves, wherein cavity information having a frequency as a parameter is obtained by simultaneous measurement using a large number of frequencies. Evaluation methods. 2. The method for evaluating the generation of cavities due to hydrogen attack according to claim 1, wherein multi-frequency simultaneous measurement is performed using a broadband probe or using a resonance frequency of a single band probe. 3. The waveforms of the B ₁ reflected wave and the B ₂ reflected wave are simultaneously measured at multiple frequencies, continuously A / D converted and stored in a memory, and a fixed length of data is extracted from the beginning of the waveform, Multiply the window function to perform FFT, then take out the data of the same length from the point shifted by Δt, and similarly multiply by the window function to perform FFT one after another to convert the result obtained into the power spectrum. The frequency-to-sound velocity and the frequency-attenuation relationship are determined from two peak values at the times when the B ₁ reflected wave and the B ₂ reflected wave of the specific frequency exist from the change with time of the specific frequency. Cavity generation evaluation method by hydrogen attack of 1. 4. The number of cavities and the diameter of the cavities are obtained based on a relational expression regarding the number of cavities and the diameter of the cavities induced by solving the wave equation for scattering of cavitation. Item 3. A method for evaluating cavity generation due to hydrogen attack according to item 3. 5. The relationship between the peak frequency at which the peak value of the B ₁ reflected wave becomes the highest among the measurement frequencies and the Charpy test result is obtained for the target material, and the peak frequency is measured to determine the hydrogen erosion state. The method for evaluating the generation of cavities due to hydrogen attack according to claim 1.