JPH09281091A - Degradation method for heat resistant materials - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate the material deterioration degree of an article to be measured by using a specified formula by measuring the sonic velocity of a use material as the index reflecting the change of material deterioration, that is, the change of metal texture and a chemical compsn. SOLUTION: The surface of the desired part of an article to be measured is ground over a range of about 10×10mm, and a measuring element to be an ultrasonic oscillator/detector is brought into contact with the ground surface. The measuring element is connected to an ultrasonic oscillator and a waveform measuring instrument and has constitution capable of measuring and recording the oscillation of ultrasonic waves and the waveform of the reflected waves from a material. When the time exciting ultrasonic waves in the article to be measured is set to (to), the time detecting an echo is set to (te) and the thickness of a measuring region is set to W, sonic velocity Vs is calculated according to formula. It is necessary to form a master curve wherein the relation between the deterioration degree and sonic velocity of a heat- resistant material is investigated in relation to the heat-resistant material constituting the article to be measured. The deterioration degree of the characteristics of the heat-resistant material can be calculated on the basis of the observed sonic velocity and the master curve.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for nondestructively estimating the degree of characteristic deterioration during use of a heat resistant material applied to a power plant or the like.

[0002]

2. Description of the Related Art Most heat-resistant materials applied to commercial power generation plants and the like differ not only in the operating conditions and location environment between different plants but also in the same plant depending on the operating method depending on the operating environment. The fluctuations are large and it is not easy to estimate the material deterioration. For this reason, the degree of deterioration of high-temperature members during periodic inspections must rely on visual damage inspections such as the occurrence of cracks and corrosion, and the degree of deterioration of material properties cannot be directly detected. There wasn't.
Therefore, if there is no visible damage, despite the deterioration of the material, the part will continue to be used.
This was a serious problem in reliability management of the entire plant.

In response to this, nondestructive deterioration degree estimation methods for heat-resistant materials are being actively studied in various fields. JP 57
-29947, JP-A-58-92952, JP-A-62-5
Japanese Patent Laid-Open No. 9263 and Japanese Patent Laid-Open No. 3-45790 disclose a deterioration degree estimating method for a low alloy steel for a steam turbine. Further, in JP-A-2-227654, JP-A-3-20916, and JP-A-5-223809, a γ '(gamma prime) phase precipitation strengthening type alloy most frequently used as a heat-resistant material for gas turbines. There is disclosed a method of estimating deterioration degree for.

[0004]

The conventional non-destructive inspection methods are an electric resistance measuring method, a magnetic susceptibility measuring method, a replica method and the like. The electric resistance measuring method is a very simple measuring method and the measuring equipment is lightweight, so it is easy to measure at the plant site, but the measured value depends on the surface condition of the measured object, temperature, shape of the measured object, etc. However, it is difficult to secure the reliability of data. The magnetic susceptibility measurement method not only requires heating the object to be measured in order to measure the Curie temperature at the measurement site, but also makes it difficult to non-destructively measure the magnetic susceptibility of a specific part of the component. However, it is hard to say that this is a simple measurement method at the plant site. In addition, the replica method is often used in regular inspections of current plants, but it requires procedures such as mirror polishing, etching, replica film attachment, and microscope inspection of the surface of the object to be measured, and the data of the target surface structure is collected. It takes a lot of time and skill to do. Moreover, since only the information near the surface of the component can be obtained, there is a tendency to lack accuracy when determining the degree of deterioration of the entire component.

An object of the present invention is to provide a material deterioration degree estimating method capable of performing a regular inspection work at a plant site more quickly and accurately by a simple measurement procedure.

[0006]

The heat-resistant material generally used in power plants and the like undergoes some changes in its unique metal structure and chemical composition during use at high temperatures, and the material properties deteriorate accordingly. . Therefore, it is possible to estimate the degree of material deterioration by knowing this change directly or indirectly. All of the known examples described in the section of the problem of the invention are based on this method.

The present inventors have paid attention to the speed of sound waves propagating in a material as an index that reflects deterioration of the material, that is, changes in the metal structure and chemical composition.

Since the sound velocity depends on the density, crystal structure, state of different phase interface, etc. of the material, there is a clear distinction between the sound velocity of the material whose structure / composition changed at high temperature and that of the new material before use. Differences are likely to occur. Therefore, if the material whose sound speed monotonously increases or decreases as the material deterioration progresses, the material deterioration degree of the measured object can be estimated by measuring the sound speed of the material used.

The procedure required for measuring the sound velocity of a material will be described below.

The surface of a desired portion of the object to be measured is polished with abrasive paper or the like over a range of about 10 mm × 10 mm.
It is desirable that the surface of the polishing paper be smoothed by using the roughness of up to about # 1000. Next, a probe, which also serves as an ultrasonic oscillator and detector, is brought into contact with the polished surface. The tracing stylus is connected to an ultrasonic wave oscillator and a waveform measuring instrument, and has a device configuration capable of measuring and recording the waveform of an ultrasonic wave oscillation and a reflected wave (echo) from a material.

The time when ultrasonic waves are applied to the object to be measured is t ₀ ,
Assuming that the time at which the echo from the object to be measured is detected is t _e and the thickness of the measurement site is w, the sound velocity V _s is

[0012]

It is determined by the [number 1] _{V s = w / (t e} -t 0) ... ( number 1).

On the other hand, regarding the heat-resistant material constituting the object to be measured, the relationship between the degree of deterioration and the sound velocity must be investigated in advance. For this purpose, the material is experimentally heated and stressed for a long time to create simulated deterioration, and a master curve is created by investigating the relationship between the deterioration degree of the simulated deterioration and the sound velocity for a long time. There is a need. From the observed sound velocity and the above-mentioned master curve, it is possible to determine the degree of characteristic deterioration of the heat resistant material forming the object to be measured.

Although the sound velocity measuring method in the present invention requires surface polishing of the object to be measured, the subsequent measuring procedure is simple and data analysis can be performed in a short time using a general-purpose computer.

Further, since not only the surface of the object to be measured but also the thickness direction information can be obtained, the degree of deterioration of the object to be measured can be more accurately estimated, and the characteristics of the high temperature parts in the regular inspection on site such as a power plant. It is suitable as a deterioration degree evaluation method.

Further, the present invention can be applied to any material as long as it can obtain a master curve in which the characteristic deterioration degree and the sound velocity have a one-to-one relationship.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The method for estimating the degree of characteristic deterioration of a heat-resistant material according to the present invention will be described below with reference to Examples. Figure 1 shows γ '
14Cr-9.5Co-4W-4M which is a phase strengthening alloy
o-3Al-5Ti-Ni-based superalloy was heated in the laboratory for a long time and several kinds of test pieces and new superalloy materials were used to deteriorate the characteristics, and the sonic velocity and 0.2% proof stress were measured respectively. However, the graph shows the relationship between the two. The scale on the vertical axis is based on the 0.2% proof stress of the new material as 100, and the horizontal axis is the speed of sound. If the sound velocity of the measurement site of the high-temperature component whose deterioration degree is to be estimated is plotted on the horizontal axis, the characteristic deterioration degree of the measurement site can be obtained according to the master curve.

In addition to the 0.2% proof stress, the vertical axis is the most suitable index for measuring the degree of characteristic deterioration of the target high temperature parts such as tensile strength, creep rupture time, creep damage rate, fatigue damage rate. Can be used.

[0019]

EFFECTS OF THE INVENTION According to the present invention, for various heat-resistant materials used in power plants and the like, if the relationship between the characteristic deterioration and the sound velocity is obtained in advance, it is easy to evaluate the deterioration degree of high temperature parts at the plant site. In addition to being able to perform non-destructively and accurately, the accuracy of reliability management of the plant is improved, the time required for the periodic inspection can be shortened, and the efficiency of maintenance of the plant can be improved.

Furthermore, the present invention can be used in combination with other non-destructive inspection methods such as the existing electric resistance method, magnetic susceptibility measuring method, replica method, etc. to further improve the deterioration degree estimation accuracy.

[Brief description of drawings]

FIG. 1 14Cr-9.5Co-4W-4Mo-3Al
The sonic velocity and 0.2% proof stress were measured for each of the new -5Ti-Ni-based superalloy and the test material whose characteristics were deteriorated by heating this superalloy for a long time in the laboratory. .2
A characteristic diagram showing the relationship of% yield strength.

Claims (2)

[Claims] 1. A method for estimating a nondestructive deterioration degree of a high temperature component used under high temperature, wherein the sound velocity of a heat resistant material constituting the high temperature component is measured, and the characteristic deterioration of the heat resistant material created in advance is detected. A deterioration degree estimation method for a heat resistant material, comprising estimating the deterioration degree of the heat resistant material and a high temperature component composed of the heat resistant material based on a diagram showing a relationship of sonic speeds. 2. The deterioration degree estimating method according to claim 1, wherein the deterioration degree of a high temperature component made of a γ ′ phase precipitation strengthening alloy is estimated.