JP2004170162A - Method of screening crack image of ferritic steel material and method and system for evaluating fatigue damage lifetime of ferritic steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of accurately and nondestructively screening and evaluating fatigue damage cracks of a ferritic steel material in a short time even by a nonexpert. <P>SOLUTION: Magnetic particles are scattered on an surface of a region comprising the ferritic steel material. A magnetic field is applied to the magnetic particles. The magnetic particles are accumulated in the fatigue and magnetized. A binarized digital image is acquired from the surface of the region in such state. The cracks are screened from the digital image and a fatigue damage lifetime consumption rate of the region is estimated from a shape of the screened crack. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for selecting a crack image from a fatigue damage site of a ferritic steel material, a method and a system for evaluating fatigue damage life. More specifically, the present invention relates to a method for selecting a crack image from a fatigue damage site in a boiler pressure-resistant part made of a ferritic steel material, a method and a system for evaluating fatigue damage life.
[0002]
[Prior art]
Conventionally, a portion where fatigue damage is likely to occur, such as a boiler pressure-resistant portion of a thermal power plant, is conventionally inspected by a magnetic particle flaw detection method (for example, see Patent Document 1). Then, the transferred fatigue cracks are observed with a stereo microscope.
[0003]
Specifically, by observing with a stereoscopic microscope, the cracks are separated from the attached matter such as oxide scales and debris, and the dimensions of the selected cracks, such as the length, the distance between the crack and other cracks, etc. Measurements were performed to determine the maximum crack length from these data, and from the maximum crack length, a fatigue damage life evaluation diagram showing the relationship between the maximum crack length and the fatigue damage life consumption rate corresponding to the material of the relevant site was used. A technique for estimating the fatigue damage life consumption rate can be exemplified. In addition, the fatigue damage life consumption rate means a ratio of the fatigue damage life expected for the relevant portion, which has already been consumed. The fatigue damage life means the life until a predetermined macroscopic crack occurs. The macroscopic crack means a crack that has grown to the point where replacement or repair of the target site is required, that is, a crack on the pipe surface when the fatigue strength is reduced by 25%. The content of the predetermined macroscopic crack can be determined based on experience and experience.
[0004]
The fatigue damage life evaluation diagram can be determined by experiments or the like. The fatigue damage life evaluation diagram differs depending on the material of the target site. When the target portion is a boiler pressure-resistant part of a thermal power plant, a fatigue damage life evaluation diagram for carbon steel or low alloy steel can be used depending on the material.
[0005]
However, with the current technology, after transferring the fatigue crack to the transfer tape, take it back to the laboratory, measure the crack length etc. with a precision stereoscopic microscope capable of measuring dimensions, apply it to the evaluation diagram, and evaluate the fatigue damage life of the site. And it took a considerable number of days for inspection, analysis, and submission of the report.
[0006]
Furthermore, it is necessary to select the fatigue cracks in the transfer tape to determine the maximum crack length required for fatigue damage life evaluation. To determine the maximum crack length, measure the dimensions of each crack accurately. There are requirements such as the necessity, and a skilled technician with abundant experience was indispensable to perform these sorting and dimensional measurement. Therefore, an unskilled person could not respond to the fatigue damage life evaluation.
[0007]
[Patent Document 1]
JP-A-8-160008 (paragraphs 0002 to 0006)
[0008]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems and to provide a technique that enables non-experts to accurately and nondestructively sort and evaluate fatigue damage cracks in ferritic steel materials in a short period of time.
[0009]
Still other objects and advantages of the present invention will become apparent from the following description.
[0010]
[Means for Solving the Problems]
According to one aspect of the present invention, magnetic powder is sprayed on the surface of a portion made of a ferritic steel material, and a magnetic field is applied to accumulate and magnetize the magnetic powder in a crack, which is binarized from the surface of the portion in that state. And a method of selecting a crack image from the digital image. By this sorting method, even a non-expert can non-destructively sort a fatigue damage crack of a ferritic steel material in a short period of time.
[0011]
According to another aspect of the present invention, there is provided a ferrite-based steel material fatigue damage life evaluation method for estimating a fatigue damage life consumption rate of a site from a shape of a crack selected by the crack image selection method described above. You. The maximum crack length is calculated from the selected crack shape according to a predetermined standard, and the maximum crack length is calculated based on a predetermined relationship established between the maximum crack length and the fatigue damage life consumption rate based on the maximum crack length. It is preferable to estimate the fatigue damage life consumption rate of the steel.
[0012]
According to still another aspect of the present invention, an image acquisition device for obtaining a binarized digital image, and magnetic powder is sprayed on a surface of a portion made of a ferritic steel material, and a magnetic field is applied to the crack to apply a magnetic field. The magnets are collected and magnetized, and cracks are selected from digital images obtained by using the image acquisition device on the surface of the portion in that state, and the maximum crack length is determined from the shape of the selected cracks according to a predetermined standard. A fatigue damage life consumption rate evaluation device that calculates and estimates the fatigue damage life consumption rate of the relevant site based on a predetermined relationship established between the maximum crack length and the fatigue damage life consumption rate from the maximum crack length. A ferrite-based steel material fatigue damage life evaluation system is provided.
[0013]
According to the above-described evaluation method and system, even a non-skilled person can accurately and nondestructively select and evaluate fatigue damage cracks of ferritic steel materials in a short period of time.
[0014]
As the portion made of a ferritic steel material, a portion where low cycle fatigue damage occurs in a pressure resistant portion of a thermal power plant is preferable.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings, examples, and the like. It should be noted that these drawings, examples, etc., and the description are merely examples of the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments can also belong to the category of the present invention as long as they conform to the gist of the present invention. In these drawings, the same elements are denoted by the same reference numerals. In these figures, elements according to the invention are not necessarily to scale. For example, the size of the cracks is drawn large for easy understanding.
[0016]
According to the present invention, by obtaining a binarized digital image from the surface of a portion made of a ferritic steel material, even a non-skilled person can easily sort out minute cracks from oxide scale, dust, etc. It becomes possible to measure the size of the crack. In the binarized digital image, the cracks have sharp outlines, for example, according to simple conditions such as being linear, having the same directionality, and having a large blackness. Is clearly distinguishable from oxide scale, dust and the like.
[0017]
The dimensions of each crack selected in this way are measured, and the fatigue damage life consumption rate of the corresponding portion is estimated from the shape of the selected fatigue crack based on this.
[0018]
In order to obtain a binarized digital image from the surface of the ferrite-based steel material, for example, a magnetic powder of a ferromagnetic material is sprayed on the surface of the ferrite-based steel material, and a magnetic field is applied on the fatigue crack. Magnetic powder is accumulated and magnetized at the crack site, and a binary digital image is obtained from the surface, or the magnetic powder is transferred using a transfer tape, and a binary digital image is obtained from this transfer tape. do it. The magnetic powder is normally sprayed as a magnetic powder slurry. As a medium in this case, a volatile liquid such as ethanol is preferable. This is because it is dried in a short time and does not hinder the transfer of the magnetic powder with a transfer tape.
[0019]
Specifically, as shown in the cross-sectional view of FIG. 12, the ferritic steel material after use has an oxide layer 121 at the top, a decarburized layer 122 below it, and a ferrite-based steel The surface of the site is lightly polished until the decarburized layer is slightly exposed, and then magnetic powder is sprinkled. The polishing is performed to remove the oxide layer and facilitate the observation of the crack 6. However, since there are many cracks that remain in the decarburized layer and do not reach the base underneath, the polishing is slightly exposed to the decarburized layer. It is important to stay there.
[0020]
The method of estimating the fatigue damage life consumption rate of the relevant site from the shape of the selected fatigue crack can be arbitrarily determined.From the shape of the selected fatigue crack, the above-described maximum crack length is calculated according to a predetermined standard. However, a method of estimating the fatigue damage life consumption rate of the site based on the maximum crack length is preferable. This is because high evaluation accuracy can be realized.
[0021]
The process in which a minute crack is exposed as a macroscopic crack is not limited to the case where the minute crack simply grows, but may be a case where a plurality of minute cracks are combined and grow. Therefore, as for such a crack that may grow as a composite, it is useful to assume a crack in which the cracks are connected to each other (connectivity crack). In the present invention, the maximum crack length calculated according to a predetermined standard from the shape of the selected fatigue crack is the length of the connected crack thus assumed and the length of other independent cracks in one target region. Means the length of the longest crack in the set. A predetermined criterion for assuming a crack in which cracks are connected to each other based on the shape of the selected fatigue crack can be arbitrarily determined based on experience, experiments, and the like.
[0022]
As a method of estimating the fatigue damage life consumption rate of the part based on the maximum crack length, there is a method of estimating the fatigue damage life consumption of the target part based on a predetermined relation established between the maximum crack length and the fatigue damage life consumption rate. A method for estimating the rate is preferred. Since such a relationship differs depending on the material of the target portion, it is necessary to determine a predetermined relationship that is established between the maximum crack length and the fatigue damage life consumption rate for each material, but in most cases, a simple correlation is required. This is useful in performing reliable and quick evaluation.
[0023]
As a portion made of a ferritic steel material which is an object of the present invention, a portion where fatigue damage easily occurs, such as a welded portion of a boiler pressure-resistant portion, is suitable. In particular, it is useful to apply the present invention to a boiler pressure-resistant part of a thermal power plant. Such parts are highly demanded for reliability, but are susceptible to fatigue damage due to thermal stress at high temperatures and long periods of time. It is very important.
[0024]
In addition, the ferrite-based steel material fatigue damage life evaluation method, the image acquisition device for obtaining a binarized digital image, and sprinkling magnetic powder on the surface of the portion made of ferritic steel material, applying a magnetic field The magnetic powder is accumulated in the cracks and magnetized, and the surface of the relevant portion in that state is subjected to sorting of the cracks from the digital image obtained by using the image acquisition device. Calculating the length and estimating the fatigue damage life consumption rate of the part based on a predetermined relationship established between the maximum crack length and the fatigue damage life consumption rate from the maximum crack length, A ferrite-based steel material fatigue damage life evaluation system including an evaluation device, which can be easily and quickly performed even by an unskilled person.
[0025]
As an image acquisition device for obtaining a binarized digital image from the surface of a portion made of a ferritic steel material, any known device can be used.
[0026]
Fatigue damage that sorts cracks from digital images, calculates the maximum crack length according to a predetermined standard from the shape of the selected fatigue cracks, and estimates the fatigue damage life consumption rate of the site based on the maximum crack length As the life consumption rate evaluation device, for example, a personal computer can be used. If a personal computer is used, a procedure for calculating the maximum crack length according to a predetermined criterion from the shape of the selected fatigue crack and a procedure for estimating the fatigue damage life consumption rate of the relevant site based on the maximum crack length Can be programmed to automatically obtain the fatigue damage life consumption rate.
[0027]
【Example】
Next, embodiments of the present invention will be described in detail.
[0028]
[Example 1]
An example in which the fatigue damage life evaluation method according to the present invention is implemented with respect to a minute crack generated in a stress concentration portion of a toe portion of a furnace wall nozzle welded portion of a boiler pressure resistant portion will be described with reference to FIGS. I do. FIG. 1 is a flowchart of the fatigue damage life evaluation method according to the present invention, FIG. 2 is a diagram specifically showing the content of the fatigue damage life evaluation method, and FIG. 13 is a diagram showing a system for implementing the method. In FIG. 13, the ferrite-based steel material fatigue damage life evaluation system 133 includes, for example, an image acquisition device 131 for obtaining a binarized digital image from the transfer tape 5 and a fatigue damage life consumption rate evaluation device 132.
[0029]
First, according to step S1 of FIG. 1, a magnetic powder solution (ethanol slurry of magnetic powder) is sprayed on the toe 4 of the welded portion 3 of the furnace wall nozzle 2 of the boiler pressure-resistant part 1 of FIG. A magnetic field is applied on the fatigue crack 6 to accumulate and magnetize magnetic powder at the crack site. Then, according to step S2 of FIG. 1, the transfer tape 5 is attached to the toe 4 of the furnace wall nozzle as shown in FIG. 2, and the magnetic powder magnetized on the fatigue crack is transferred to the transfer tape. In addition to fatigue cracks, oxide scale, dust and the like are mixed and transferred to this transfer tape.
[0030]
Then, according to step S3 in FIG. 1, a digital image of the transfer tape is obtained by a digital stereo microscope, and stored in a personal computer. Instead of using a transfer tape, a digital image can be directly captured by a digital stereomicroscope from a welded nozzle of a real nozzle and stored in a personal computer.
[0031]
Next, according to step S4 in FIG. 1, the image stored on the personal computer is subjected to binarized image processing to be linear, have the same directionality, have a large blackness, etc. The fatigue cracks are distinguished from oxide scales, dusts, etc. based on the difference in the shape of the fatigue cracks, and only the fatigue cracks are selected. This sorting may be performed by a person, but since the shapes of the fatigue crack and the oxide scale, dust, etc. are clearly different, it is easy to automatically sort by a personal computer or the like.
[0032]
FIG. 3 is a diagram in which a digital image obtained in this way before sorting is modeled. The oxide scale 7 and dust 8 are represented by ellipses, and the cracks 6 are represented by lines. The use of the transfer tape turns the oxide scale 7 upside down. However, if there is a crack in the oxide scale 7 that is a residue of the oxide layer, the magnetic powder has penetrated into the inside of the crack. Cracks can be seen even in the open state. FIG. 4 is a diagram illustrating a model after the selection. The binarized image processing of the image may be performed by either a digital stereomicroscope as an image acquisition device or a personal computer as a fatigue damage life consumption rate evaluation device.
[0033]
Next, according to step S5 in FIG. 1, the maximum crack length is calculated from the selected shape of the fatigue crack according to a predetermined standard. Then, according to step S6 in FIG. 1, based on a predetermined relationship established between the maximum crack length and the fatigue damage life consumption rate, the nozzle weld toe portion, which is the relevant portion, is calculated from the calculated maximum crack length. The fatigue damage life consumption rate of steel.
[0034]
The predetermined criterion for calculating the maximum crack length can be arbitrarily determined, and can be automatically executed by a personal computer or the like.
[0035]
One example of the criterion is outlined with reference to FIGS. 5 to 7, the length direction of the crack is defined as an x-axis, and the direction orthogonal thereto is defined as a y-axis. x1 means the distance in the x-axis direction between two adjacent cracks A and B in the y-axis direction, and y1 means the distance in the y-axis direction between the two cracks A and B. For a distance in the x-axis direction between two cracks, a predetermined value is defined as a critical length, and for a distance in the y-axis direction between two cracks, a predetermined value is defined as a critical interval.
[0036]
Under these conditions, as shown in FIG.
y1> critical interval or
When x1> critical length, let the length b of the crack B be the maximum crack length for the two cracks A and B.
[0037]
Also, as shown in FIG.
y1 <critical interval or
When x1 <critical length, c, which is the overlap length of the cracks A and B, is defined as the maximum crack length for the two cracks A and B. That is, the length c of the connecting crack having the cracks A and B as constituent elements is defined as the maximum crack length.
[0038]
Note that x1 means the distance between the head of a crack and the tail of another crack when viewed in the x-axis direction, and is also used when two cracks A and B are separated as shown in FIG. Value and always has a positive sign.
[0039]
The procedure for actually determining the maximum crack length by this method is as follows, for example. First, several cracks are determined in the order of the largest crack length in the obtained images without considering the connectivity cracks. Next, the possibility of a connecting crack is examined for these cracks, and the length of the connecting crack is determined. Then, the largest one of these individual crack lengths and interconnecting crack lengths is determined as the maximum crack length.
[0040]
As for the predetermined relation established between the maximum crack length and the fatigue damage life consumption rate, a relation diagram as shown in FIG. 8 can be exemplified. Using this figure, the fatigue damage life consumption rate on the horizontal axis can be easily determined from the maximum crack length on the vertical axis.
[0041]
It has been found that the method according to the present invention enables non-experts to non-destructively and accurately select cracks and accurately estimate the fatigue damage life consumption rate in a short period of time.
[0042]
[Example 2]
In the welded portion 92 of the furnace wall fin end 91 which is a fatigue damage portion of the boiler pressure-resistant portion shown in FIG. 9, since steam flows through the tube 93, high temperature and high pressure applied to the tube cause fatigue, and thermal stress is concentrated. And cracks due to fatigue are likely to occur. After transferring the minute fatigue crack generated by the method according to the present invention to the transfer tape 5, the image is captured as an image by a digital stereo microscope, and the maximum crack length is measured by binarized image processing on a personal computer. As a result, it was found that even an unskilled person can non-destructively and accurately select cracks and estimate the fatigue damage life consumption rate accurately in a short period of time.
[0043]
[Example 3]
According to the method according to the present invention, a small fatigue crack generated in the welded portion 102 of the hardware (wall stopper) 101 attached to the furnace wall, which is a fatigue damage portion of the boiler pressure-resistant portion, shown in FIG. The images were captured as images with a stereomicroscope, binarized image processing was performed on a personal computer to measure the maximum crack length, and the results were applied to an evaluation diagram. It was found that the damage life consumption rate can be estimated accurately in a short period of time.
[0044]
[Example 4]
According to the method of the present invention, a small fatigue crack generated in the welded portion 112 of the manhole shield box 111, which is a fatigue damage portion of the boiler pressure resistant portion shown in FIG. 11, is transferred to the transfer tape 5 and captured as an image by a digital stereo microscope. The maximum crack length was measured by binarized image processing on a personal computer and applied to the evaluation diagram.As a result, even a non-skilled person could non-destructively select cracks accurately and reduce the fatigue damage life consumption rate in a short time. It was found that the estimation could be performed with high accuracy.
[0045]
【The invention's effect】
According to the present invention, even non-experts can accurately and non-destructively select and evaluate fatigue damage of ferritic steel materials in a short period of time.
[Brief description of the drawings]
FIG. 1 is a flowchart of a fatigue damage life evaluation method according to the present invention.
FIG. 2 is a diagram specifically showing the content of a fatigue damage life evaluation method according to the present invention.
FIG. 3 is a diagram modeling an image including a crack.
FIG. 4 is a diagram modeling a crack image after cracks are selected from the image of FIG. 3;
FIG. 5 is a diagram illustrating a criterion for calculating a maximum crack length from a selected crack shape.
FIG. 6 is another diagram illustrating a criterion for calculating a maximum crack length from a selected crack shape.
FIG. 7 is another diagram illustrating a criterion for calculating a maximum crack length from a selected crack shape.
FIG. 8 is an example of a fatigue damage life evaluation diagram showing the relationship between the maximum crack length and the fatigue damage life consumption rate.
FIG. 9 is a diagram showing a furnace wall fin end welded portion which is a fatigue damage portion of a boiler pressure-resistant portion.
FIG. 10 is a view showing a furnace wall adhered metal (wall stopper) welded portion which is a fatigue damage portion of a boiler pressure-resistant portion.
FIG. 11 is a view showing a welded part of a manhole shield box which is a fatigue damage part of a boiler pressure resistant part.
FIG.
It is a schematic diagram which shows the cross-section of a ferritic steel material after use.
FIG. 13
FIG. 2 is a schematic diagram showing a ferrite-based steel material fatigue damage life evaluation system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Boiler pressure-proof part 2 Furnace wall nozzle 3 Weld 4 Furnace wall nozzle weld toe 5 Transfer tape 6 Fatigue crack 7 Oxidation scale 8 Garbage 91 Furnace wall fin end 92 Furnace wall fin end weld 93 Tube 101 Furnace wall Attached hardware (wall stopper)
102 Welded part of the furnace wall adhesion (wall stopper) 111 Manhole shield box 112 Manhole shield box welded part 121 Oxidized layer 122 Decarburized layer 123 Structure of ferritic steel as a base 131 Image acquisition device 132 Fatigue damage life consumption rate evaluation device 133 Ferritic steel material fatigue damage life evaluation system

Claims (6)

Sprinkle magnetic powder on the surface of the part made of ferritic steel material, apply a magnetic field, accumulate magnetic powder in cracks and magnetize,
Obtain a binary digital image from the surface of the part in that state,
Selecting cracks from the digital image,
How to sort crack images. A method for evaluating the fatigue damage life of a ferritic steel material, wherein a fatigue damage life consumption rate of the site is estimated from a shape of the crack selected by the method for selecting a crack image according to claim 1. From the shape of the selected cracks, calculate the maximum crack length according to a predetermined criterion, and, based on the maximum crack length, the relevant portion based on a predetermined relationship established between the maximum crack length and the fatigue damage life consumption rate. The fatigue damage life evaluation method according to claim 2, wherein the fatigue damage life consumption rate of the ferrite-based steel material is estimated. The method for evaluating fatigue fatigue life of a ferritic steel material according to claim 2 or 3, wherein the portion made of the ferritic steel material is a pressure-resistant part of a boiler of a thermal power plant. An image acquisition device for obtaining a binarized digital image,
Spreading magnetic powder on the surface of the part made of ferritic steel material, applying a magnetic field, accumulating the magnetic powder in the cracks and magnetizing, from the digital image obtained using the image acquisition device on the surface of the part in that state The cracks are sorted, the maximum crack length is calculated from the selected crack shapes according to a predetermined standard, and the maximum crack length is used as a predetermined relationship between the maximum crack length and the fatigue damage life consumption rate from the maximum crack length. A fatigue damage life consumption rate evaluation device that estimates a fatigue damage life consumption rate of the site based on the
Ferritic steel material fatigue damage life evaluation system including The ferrite-based steel material fatigue damage life evaluation system according to claim 5, wherein the portion made of the ferrite-based steel material is a pressure-resistant part of a boiler of a thermal power plant.

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