JP5450905B1 - A method for predicting the remaining creep life of bainite structure. - Google Patents

Abstract

A method for predicting the remaining creep life of a bainite structure is provided.
An electromagnetic ultrasonic probe is used to excite ultrasonic waves in a bainite structure in a non-contact manner to generate ultrasonic resonance in the bainite structure, and to measure the resonance frequency of the ultrasonic resonance. A step of measuring an ultrasonic wave transition at a resonance frequency, a step of determining a sound velocity at the resonance frequency, a step of determining a first damage rate of the bainite structure from the ultrasonic wave shift, and a second of the bainite structure from the sound velocity. The creep remaining life prediction method includes a step of obtaining a damage rate and a step of obtaining a corrected damage rate of the bainite structure based on the first damage rate and the second damage rate.

Description

  The present invention relates to a method for predicting the creep remaining life of a bainite structure.

  Mechanical parts used in thermal power generation facilities, nuclear power generation facilities, and the like are subjected to high temperature and high pressure conditions for a long period of time, so that they gradually undergo plastic deformation and break when the creep life is reached. Therefore, in order to operate thermal power generation facilities and nuclear power generation facilities safely and economically, the machine parts must be replaced at the optimal time by accurately predicting the remaining creep life of the machine parts used. Is required.

As a method of predicting the remaining creep life of heat-resistant steel used in such machine parts, for example, detection of cracks occurring at the end of life such as visual inspection, magnetic particle inspection, ultrasonic inspection, and radiation inspection There are known methods for detecting creep voids and microcracks by the replica method, but these methods cannot predict the remaining life before cracks are generated. Moreover, as disclosed in Japanese Patent Laid-Open No. 63-235861, a specimen is cut out from a heat-resistant steel of a mechanical part of a thermal power generation facility or a nuclear power generation facility that is actually in operation, and a creep rupture test is performed. However, in this method, it is necessary to cut out a test piece from a facility that is actually in operation and perform a test for a long time, which is complicated.
For these methods, as disclosed in JP-A-2001-343368, it is possible to predict the remaining life before a crack occurs, and there is no need to cut out a test piece from an actually operating facility. In addition, a method has been reported in which ultrasonic resonance is generated by exciting ultrasonic waves in a magnetic heat-resistant steel in a non-contact manner and the remaining life is predicted from the attenuation of the ultrasonic resonance.

  An object of the present invention is to provide a method for predicting the remaining life of creep of a bainite structure.

  The creep remaining life prediction method according to the present invention includes a step of generating ultrasonic resonance in a bainite structure by exciting non-contact ultrasonic waves in the bainite structure using an electromagnetic ultrasonic probe, A step of measuring a resonance frequency of the acoustic resonance, a step of measuring a transition of the ultrasonic wave at the resonance frequency, a step of obtaining a sound velocity at the resonance frequency, a step of obtaining a first damage rate of the bainite structure from the transition of the ultrasonic wave, A step of obtaining a second damage rate of the bainite structure from the speed of sound, and a step of obtaining a corrected damage rate of the bainite structure based on the first damage rate and the second damage rate.

When there are a plurality of first damage rates, the method further includes selecting a first damage rate closest to the second damage rate from among the first damage rates, the first damage rate closest to the second damage rate, and It is preferable to obtain a corrected damage rate based on the second damage rate.
It is preferable to obtain the corrected damage rate by averaging the first damage rate and the second damage rate.

  It is preferable to calculate the attenuation coefficient from the change of the ultrasonic wave and obtain the first damage rate from the attenuation coefficient, or to calculate the non-linear ultrasonic amount from the change of the ultrasonic wave and obtain the first damage rate from the non-linear ultrasonic amount. It is preferable.

  According to the present invention, it is possible to provide a method for predicting the creep remaining life of a bainite structure.

It is the schematic of EMAT which transmits / receives the magnetostrictive axisymmetric SH wave in one Embodiment. 2 is a schematic diagram of a magnetic field and an axisymmetric SH wave in one embodiment. FIG. 4 is a graph showing a plurality of resonance peaks in one embodiment. In one _embodiment, it is a graph showing a resonance peak of ^{f 1 (99).} 4 is a graph illustrating an attenuation curve according to an embodiment. It is a graph which shows the relationship between an attenuation coefficient and a damage rate in one Embodiment, and the relationship between a sound speed and a damage rate. It is a graph which shows the resonant frequency at the time of using an undamaged sample in one Embodiment. It is a graph which shows the resonant frequency at the time of using the damaged sample in one Embodiment. It is a graph which shows the relationship between the amount of non-linear ultrasonic waves and a damage rate, and the relationship between a sound speed and a damage rate in one Embodiment. In one embodiment, it is a graph showing the measurement results of the attenuation coefficient of the f 1 ^_(99). In one embodiment, it is a graph showing the relative amount of movement of the resonant frequency at f 1 ^_(99). It is a graph which shows the amount of nonlinear ultrasonic waves in one embodiment.

  Hereinafter, an embodiment of the present invention completed based on the above knowledge will be described in detail. The objects, features, advantages, and ideas of the present invention will be apparent to those skilled in the art from the description of the present specification, and those skilled in the art can easily reproduce the present invention from the description of the present specification. it can. The embodiments and specific examples of the invention described below show preferred embodiments of the present invention and are shown for illustration or explanation, and the present invention is not limited to them. It is not limited. It will be apparent to those skilled in the art that various modifications and variations can be made based on the description of the present specification within the spirit and scope of the present invention disclosed herein.

  The method for predicting the creep remaining life of a bainite structure according to the present invention is a step of generating ultrasonic resonance in a bainite structure by exciting non-contact ultrasonic waves in the bainite structure using an electromagnetic ultrasonic probe. Measuring a resonance frequency of ultrasonic resonance, obtaining a change in ultrasonic wave at the resonance frequency, obtaining a sound velocity at the resonance frequency, and obtaining a first damage rate of the beina iso tissue from the change in the ultrasonic wave. A process, a step of obtaining a second damage rate of the bainite structure from the speed of sound, and a step of obtaining a corrected damage rate of the bainite structure based on the first damage rate and the second damage rate.

The present inventors, when the bainite structure is the measurement object, obtain resonance frequencies such as attenuation coefficient and nonlinear ultrasonic quantity, which are obtained when non-contact ultrasonic waves are excited using an electromagnetic ultrasonic probe. It was found that the relationship between the transition of the ultrasonic wave and the time such as the damage rate does not have a one-to-one correspondence. That is, it has been found that there are a plurality of damage rates corresponding to a certain attenuation coefficient or nonlinear ultrasonic quantity. In such a case, there arises a problem that the corresponding damage rate cannot be obtained only from the attenuation coefficient or the nonlinear ultrasonic quantity.
In order to solve such a problem, the method for predicting the remaining life of creep of a bainite structure according to the present invention, the electromagnetic ultrasonic resonance method (electromagnetic acoustic resonance, hereinafter also referred to as “EMAR method”) at the resonance frequency. If the first damage rate is obtained from the transition of the ultrasonic wave, the second damage rate is obtained from the speed of sound measured by the EMAR method, and the first damage rate is corrected by the second damage rate, a corrected damage rate with higher accuracy can be obtained. It becomes possible to ask. Here, it is preferable to obtain the attenuation coefficient at the resonance frequency or the amount of nonlinear ultrasonic waves at the resonance frequency from the transition of the ultrasonic wave at the resonance frequency, and the first damage rate may be obtained from either of them.

  The EMAR method is a non-destructive method for measuring material properties by combining an electromagnetic ultrasonic probe (hereinafter also referred to as “EMAT”) and an ultrasonic resonance method. Since EMAT can transmit and receive ultrasonic waves in a non-contact manner by an electromagnetic action (Lorentz force or magnetostriction), it does not require an acoustic coupling agent or a retarder. For this reason, the EMAR method using EMAT can accurately measure only energy loss in the material to be measured. Furthermore, the EMAT method is known to be low because EMAT can be combined with the ultrasonic resonance method to receive multiple echoes in the same phase in the resonance state and improve the S / N ratio of the EMAT. Conversion efficiency can be greatly improved.

As the EMAT, a Lorentz force type EMAT may be used, or a magnetostrictive type EMAT may be used. However, since a bainite structure having ferromagnetism is targeted for prediction, it is preferable to use a magnetostrictive type EMAT. As the magnetostrictive EMAT, for example, an EMAT that transmits and receives a magnetostrictive axisymmetric SH wave may be used.
Hereinafter, the method for predicting the remaining life of creep of a bainite structure according to the present invention will be described by taking as an example the case of using EMAT that transmits and receives magnetostrictive axisymmetric SH waves.

  As shown in FIG. 1, an EMAT 1 that transmits and receives magnetostrictive axisymmetric SH waves includes a solenoid coil 3 that provides a static magnetic field along a major axis direction of a test piece 2 that is a measurement target, and a dynamic magnetic field in a circumferential direction. A meandering coil 4 is provided. The principle that EMAT1 generates an axisymmetric SH wave is as follows. First, by applying a direct current to the solenoid coil 3, a static magnetic field Hο is generated in the major axis direction of the test piece 2. Next, a high-frequency current is passed through the meandering coil 4 to excite the variable magnetic field Hω in the direction perpendicular to the static magnetic field immediately below the meandering coil 4. For this reason, as shown in FIG. 2, the surface of the test piece 2 is magnetized by the combined magnetic field Ht (Hο + Hω) of these two magnetic fields. Note that the direction of the arrow of the meandering coil 4 in FIG. 2 indicates the direction of current flow. When the synthetic magnetic field is periodically changed, the surface of the test piece 2 is periodically sheared due to magnetostriction, and this becomes an ultrasonic source, and the axially symmetric SH wave 5 can be generated.

（式中、ρは密度であり、μは剛性率である。）The axially symmetric SH wave is a surface SH wave that is deflected in the major axis direction of the test piece 2 and propagates in the circumferential direction. If the displacement in the major axis direction of an axisymmetric SH wave is represented by u _z (r, θ, z) in a cylindrical coordinate system represented by r, θ and z, the equation of motion for a homogeneous isotropic medium is It is represented by (1).

(Where ρ is the density and μ is the stiffness)

（式中、Ｒ（ｒ）は半径ｒに依存する変位振幅であり、ωはＳＨ波の角速度であり、ｎは整数である。）Further, when the periodic boundary condition u _z (θ) = u _z (θ + 2π) is applied, the displacement u _z is expressed by Expression (2).

(Where R (r) is the displacement amplitude depending on the radius r, ω is the angular velocity of the SH wave, and n is an integer.)

（式中、Ｖｓは横波の音速であり、√（μ／ρ）である。）Substituting equation (2) into equation (1) and rearranging results in equation (3).

(In the formula, Vs is the speed of sound of the transverse wave and is √ (μ / ρ).)

（式中、Ｊ_ｎ及びＹ_ｎは、それぞれ、ｎ次の第一種及び第二種ベッセル関数であり、ｒ’は、ｒω／Ｖ_ｓとした。）Since Equation (3) is a Bessel differential equation, its general solution can be expressed as Equation (4) using c ₁ and c ₂ .

(In the formula, J _n and Y _n are nth-order first-type and second-type Bessel functions, respectively, and r ′ is rω / V _s .)

（式中、Ｒ_ａ及びＲ_ｂは、それぞれ、中空の棒の外半径及び内半径である。）Here, when a hollow rod is used as the test piece 2, the frequency equation represented by the equation (5) is obtained from the boundary condition that the stress is 0 on the inner and outer peripheral surfaces.

(Wherein R _a and R _b are the outer radius and the inner radius of the hollow rod, respectively)

（式中、Ｋ_ｓは波数であり、ω／Ｖ_ｓである。また、Ｒ_ａは、中実の棒の半径である。）On the other hand, when a solid bar is used as the test piece 2, c ₂ = 0 so that R (r ′) becomes a finite value at the center of the bar, and the stress is 0 on the surface of the bar. From the boundary condition that is, the frequency equation represented by the equation (6) is obtained.

(Where K _s is the wave number and is ω / V _s , and R _a is the radius of the solid bar.)

（式中、δは、蛇行コイル４の平行部分の間隔であり、Ｒ_ａは、中空の棒の外半径または中実の棒の半径である。）
例えば、δ＝０．９ｍｍの蛇行コイル４を用いた場合には、中空の棒（外径φ５６．５ｍｍ）を用いるとｎは９９となり、中実の棒（直径φ６ｍｍ）では１０となる。
式（５）または式（６）を解くことによって、共鳴周波数ｆ_ｍ ^（ｎ）（但し、ｍは、１以上の整数である）が得られる。In Expressions (5) and (6), n is the number of turns of the meandering coil 4 and is an integer of 1 or more determined by Expression (7).

(Where δ is the spacing between the parallel portions of the serpentine coil 4 and R _a is the outer radius of the hollow rod or the radius of the solid rod.)
For example, when the meandering coil 4 of δ = 0.9 mm is used, n is 99 when a hollow rod (outer diameter φ56.5 mm) is used, and 10 when a solid rod (diameter φ6 mm) is used.
By solving Equation (5) or Equation (6), the resonance frequency f _m ⁽ⁿ⁾ (where m is an integer of 1 or more) is obtained.

The attenuation coefficient at the resonance frequency can be obtained by the following method. First, the ultrasonic wave is excited in the test piece 2 by inputting a high-output burst wave signal to EMAT. A high-power burst wave signal can be appropriately set by those skilled in the art. For example, the high-power burst wave signal may be 50 μs or less, and may circulate a few times in the burst wave time at the speed of sound. May be set. The SH wave propagates and is received by the same meandering coil 4 every time it passes directly under the meandering coil 4. When the amplitude of the received signal is measured by sweeping the frequency, for example, a plurality of resonance peaks as shown in FIG. 3 can be observed. The resonance frequency f _m ⁽ⁿ⁾ can be obtained from the equation (5) or the equation (6). In addition, FIG. 3 shows a hollow rod (outside diameter) made of a chromium molybdenum steel material having a bainite structure as a test piece 2 using a meandering coil 4 having a δ of 0.9 mm as shown in the examples. It is a result at the time of using (phi) 56.5mm, internal diameter 47.5mm).
As shown in FIG. 4, the attenuation coefficient representing the attenuation of the ultrasonic wave per unit time is shown in FIG. 5 by measuring the reverberation of the ultrasonic wave after exciting the ultrasonic wave at each resonance frequency to create a resonance state. It is possible to obtain an attenuation curve as shown and further approximate the exponential function to this attenuation curve.

  The speed of sound at the resonance frequency can be obtained from Equation (5) and Equation (6).

FIG. 6 shows the relationship between the attenuation coefficient and the damage rate and the relationship between the sound speed and the damage rate in the bainite structure thus obtained. As shown in FIG. 6, there are a plurality of corresponding damage rates for a certain attenuation coefficient. For this reason, the damage rate of a bainite structure cannot be calculated | required only from an attenuation coefficient. Accordingly, the first damage rate is obtained from the attenuation coefficient, the second damage rate is obtained from the sound velocity, and a corrected damage rate with excellent accuracy is obtained based on both the first damage rate and the second damage rate. be able to.
The method for obtaining the corrected damage rate is not particularly limited. For example, the correction damage rate may be obtained by averaging any one of the plurality of first damage rates and the second damage rate. It is preferable to obtain by selecting the one closest to the second damage rate from the rates and averaging the first damage rate and the second damage rate closest to the second damage rate.
From the corrected damage rate thus obtained, the creep life of the bainite structure can be accurately predicted.

In the above method, the first damage rate is obtained from the attenuation coefficient. However, the first damage rate may be obtained from the amount of nonlinear ultrasonic waves.
The amount of nonlinear ultrasonic waves is determined by measuring the shift of the resonance frequency using the EMRA method (Nonlinear Resonant Ultraspectometry, hereinafter also referred to as “NRUS method”). Specifically, the test piece 2 is vibrated with a relatively low amplitude, for example, a strain amplitude of the order of 10 ⁻⁶ , and the movement of the resonance frequency of the test piece 2 accompanying a change in the excitation force is measured. When an undamaged sample is used as the test piece 2, no resonance frequency shift is observed as shown in FIG. 7, but when a damaged sample is used as the test piece 2, FIG. As shown, resonance frequency shift is observed. The amount of nonlinear ultrasonic waves can be obtained by dividing the amount of movement Δf of the resonance frequency by the resonance frequency f ₀ having no amplitude dependency as shown in FIG.

The relationship between the nonlinear ultrasonic quantity and the damage rate in the bainite structure thus obtained is shown in FIG. 9 along with the relationship between the sound speed and the damage rate. As in the case of the attenuation coefficient, there are a plurality of corresponding damage rates in a certain nonlinear ultrasonic quantity. For this reason, the damage rate of a bainite structure cannot be calculated | required only from the amount of nonlinear ultrasonic waves. Accordingly, the first damage rate is obtained from the nonlinear ultrasonic quantity, and the second damage rate is obtained from the sound velocity. Based on both the first damage rate and the second damage rate, the corrected damage rate with excellent accuracy is obtained. Can be requested.
The method for obtaining the corrected damage rate is the same as that for obtaining the first damage rate from the attenuation coefficient. From the corrected damage rate thus obtained, the creep life of the bainite structure can be accurately predicted.

Using a hollow rod (outer diameter 56.5 mm, inner diameter 47.5 mm, length 35.0 mm) made of chromium molybdenum steel having a bainite structure as a sample, the temperature was 550 ° C. and the stress was 145 MPa. The resonance frequency, the attenuation coefficient, and the amount of nonlinear ultrasonic waves were measured at a 10.0 mm length of the sample. In addition, the outer diameter and the wall thickness at the 10.0 mm length of the sample were measured.
The attenuation coefficient was measured using EMAT (spacing of parallel portion of meander coil δ 0.9 mm) that transmits and receives magnetostrictive axisymmetric SH waves and RAM10000 manufactured by RITEC. The amount of nonlinear ultrasonic waves was measured by changing the excitation force from 10 to 100 in 10 units using EMAT that transmits and receives magnetostrictive axisymmetric SH waves and RAM5000 manufactured by RITEC. The outer diameter of the sample was measured using a vernier caliper with the oxide film still attached to the sample. The thickness of the sample was measured using a Model 26MG-XT manufactured by Panametric after removing the oxide film of the sample.

Table 1 shows the measurement results of the outer diameter and thickness of the sample, and the measurement results of the resonance frequency and attenuation coefficient at f ₁ ⁽⁹⁹⁾ and f ₂ ⁽⁹⁹⁾ . Moreover, the measurement result of the attenuation coefficient in f ₁ ⁽⁹⁹⁾ is shown as a graph in FIG.

As is apparent from FIG. 10, when the bainite structure is a measurement object, for example, a certain attenuation coefficient such as 0.005 μs ⁻¹ has a plurality of corresponding damage rates. It was shown that the damage rate cannot be obtained.

In addition, FIG. 11 shows the relative shift amount of the resonance frequency obtained by normalizing the resonance frequency for each amplitude force in f ₁ ⁽⁹⁹⁾ . Further, Δf = f ₀ −f _max is obtained by setting the resonance frequency when the excitation force is 10 as f ₀ which is a resonance frequency having no amplitude dependence, and setting the resonance frequency when the excitation force is 100 as f _max. FIG. 12 shows the result of converting FIG. 11 into a nonlinear ultrasonic quantity (Δf / f ₀ ) × 100 by the above.
As is apparent from FIG. 12, when the bainite structure is the measurement object, for example, a certain attenuation coefficient such as 0.10 has a plurality of corresponding damage rates. It was shown that the damage rate cannot be obtained.

1 EMAT
2 Specimen 3 Solade coil 4 Meander coil 5 Axisymmetric SH wave

Claims (3)

Using an electromagnetic ultrasonic probe to generate ultrasonic resonance in the bainite structure by exciting non-contact ultrasonic waves in the bainite structure; and
Measuring the resonance frequency of the ultrasonic resonance;
Measuring the transition of the ultrasound at the resonance frequency;
Obtaining a sound velocity at the resonance frequency;
Obtaining a first damage rate of the bainite structure from the transition of the ultrasonic wave;
Obtaining a second damage rate of the bainite structure from the sound velocity;
A step of based on the first damage rate and the second damage rate obtaining the correction damage rate of the bainite seen including,
A method for predicting a remaining creep life , wherein a nonlinear ultrasonic amount is calculated from the change of the ultrasonic wave, and a first damage rate is obtained from the nonlinear ultrasonic amount . Selecting a first damage rate closest to the second damage rate from the first damage rates when there are a plurality of first damage rates;
The method according to claim 1, wherein the corrected damage rate is obtained based on the first damage rate and the second damage rate that are closest to the second damage rate.   The method according to claim 1, wherein the corrected damage rate is obtained by averaging the first damage rate and the second damage rate.

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