JPH03105237A - Diagnosis of damage of structural member - Google Patents

Abstract

PURPOSE:To obtain a highly accurate isolation damage evaluation by applying data of physical and chemical changes in metal organization. CONSTITUTION:After a grinding of a structural member, a first replica for transferring a surface layer metal organization of an object to be inspected corroded and a second replica for transferring the surface layer metal organization ground and corroded again of the same object to be inspected are sampled. An equivalent value of the generation frequency of cumulative voids among voids produced with the first replica is determined from a ratio between the total area thereof and the minimum void surface area and the equivalent value of grain boundary unit length is determined from the grain size generated in the second replica. Then, a diagnosis of a degree of damage is accomplished from the equivalent value of generation frequency of cumulative voids per grain boundary unit length determined and a hardness of the object to be inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for diagnosing damage to structural members used, for example, in rotors of steam turbines, shells of pressure vessels in chemical plants, and the like.

(Conventional technology) Conventional techniques for diagnosing the degree of damage to structural members that have been used for a long time include analytical methods and non-destructive methods. The former method uses the finite element method to determine the degree of damage using actual data such as conditions such as temperature, pressure, and steam that act on structural members, operating time, number of starts and stops, and material property values.
M E Boi 1erand Pressure
The method is described in detail in the Vessel Code. The latter uses ultrasonic flaw detection equipment, hardness meters, etc. to recognize the decrease in strength of structural members, and estimates the degree of damage from this measurement data. By the way, the initial values of material properties of structural members that have been used for a long period of time decrease over time, and it is virtually impossible to know how those initial values have changed. Recently, for example, Japanese Patent Application Laid-Open No. 60-67873 has been published as a technique for determining changes in the initial value of a member using hardness measurements.

In addition, in order to know the degree of damage to structural members, it is important to know the physical and chemical changes in the metal structure, so this type of technology is disclosed in, for example, Japanese Patent Laid-Open No. 150901/1983. (Problem to be solved by the invention) In this type of technology, it is important to analyze and estimate the degree of damage using measurement data, but in order to accurately know the degree of damage, it is essential to understand the physical properties of structural members. It is even more important to know the changes in metal structure due to physical and chemical factors. This is because changes in metal structure are a direct factor in determining the degree of damage.

However, although a few techniques have been proposed that investigate this type of factor and determine the degree of damage from the formation of voids that appear on the metal structure, the solutions are not necessarily sufficient. This is because it is not enough to measure the degree of damage simply by measuring the formation of voids; it is also necessary to consider changes in crystal grain size and factors such as coarsening of carbides. I have yet to see any proposals that address these issues.

This invention takes a step further than conventional measurement techniques by focusing on the fact that changes in metal structure, that is, the formation of voids, changes in grain size, and coarsening of carbides, are important factors in determining the degree of damage. The purpose of this study is to publish a method for diagnosing damage to structural members.

[Structure of the invention]

(Means for Solving the Problems) A method for diagnosing damage to a structural member according to the present invention includes a first replica that transfers the surface metal structure of a corroded object after polishing, and a first replica that transfers the surface metal structure of a corroded object after polishing, and polishes and polishes the same object again. A second replica that transfers the corroded surface metal structure is collected, and a value equivalent to the cumulative number of voids generated is determined from the ratio of the total surface area and the minimum void surface area among the voids generated in the first replica. In addition, the value equivalent to the grain boundary unit length is determined from the grain size generated in the second replica, and the value equivalent to the cumulative number of void occurrences and the value equivalent to the grain boundary unit length determined above are determined. This is a method of diagnosing the degree of damage based on the value equivalent to the cumulative number of voids generated per hit and the hardness of the object. (Function) In the structure according to the present invention, a value equivalent to the cumulative number of void occurrences and a value equivalent to grain boundary unit length are determined from the first replica and the second replica that transfer the surface metal structure of the specimen, and these determined values are calculated. Since the method uses a method of diagnosing the degree of damage from the ratio and the hardness of the object, it is possible to obtain a higher level of accuracy than conventional methods.

(Example) An example of the method for diagnosing damage to a structural member according to the present invention will be described below.

The drawing is a schematic procedure diagram of the method for diagnosing damage to structural materials according to the present invention. First, the surface of the center hole of a test object, such as a steam turbine rotor, is polished. After polishing, measure the hardness of the specimen using a hardness meter. After measurement, the specimen is polished and etched again, washed with an organic solvent and dried, and the replica collection process begins.

Replica collection involves applying an organic agent to the specimen, pasting a film on the applied area, and transferring the surface metal structure of the specimen.It is very similar to pressing clay into a mold and copying the irregularities of the mold that appear in the clay. This is a well-known technique. In this way, the first replica is collected. Next, the same specimen is polished and etched again, further washed and dried, and a second replica is collected using the same method as above.

For both the collected first and second replicas, the transferred images were made clear using a vapor deposition device, and the I[l! It can be seen. *The detection results are input to the image processing device as data. The data input to the image processing device is used as the first and second metallographic parameters. Here, the first metallographic parameter is a value equivalent to the cumulative number of voids generated based on the size of the surface area of voids generated in the metallographic structure, and the second metallographic parameter is the value equivalent to the cumulative number of voids generated in the metallographic structure. It refers to the value equivalent to the grain boundary unit length determined based on the grain size. In determining the first metal parameter, the total void surface area Sv and the minimum void surface area Svllin are measured from the transferred image of the first replica. Then, the first metal parameter, that is, the value ny corresponding to the cumulative number of voids generated, is determined from the first equation.

nv=Sv/Svain
Q) Next, the grain boundary unit length equivalent value Ig, which is the second metal parameter, is obtained by measuring the grain size N from the transferred image of the second replica, and using the measurement result from the second equation.

I g=2 (N + 5) / 2
■Subsequently, the value n9 corresponding to the cumulative number of void occurrences obtained as described above. Using the grain boundary unit length equivalent value Ig, the third metallographic parameter (this means the value equivalent to the cumulative number of voids generated per grain boundary unit length) nV& is determined from the third equation. n vg= n v/I g (
') In this way, when the value nag corresponding to the cumulative number of voids generated per grain boundary unit length is obtained from the third equation, the damage accumulation degree φ of the structural member can be determined from that value and the hardness value of the test object. can be determined using the fourth equation.

φ. = f (n vg) + g (Hv)
■Here, f(nvg) is a value corresponding to the cumulative number of voids generated per unit length of grain boundary nVg, and g(Hv) is a function of the hardness value Hv of the specimen. As mentioned above, when diagnosing the degree of damage to structural members, the effects of voids and grain size, which are important factors but have not been sufficiently considered in the past, are The cumulative void occurrence number equivalent value nv and the grain boundary unit length equivalent value I.2 are metal structure parameters of No. 2. The equivalent value nV& of the cumulative number of void occurrences, which is the third metallographic parameter, is taken into consideration via the above equation, and the effect of carbide coarsening is reflected in the hardness measurement value Hv.

Therefore, if such a method is adopted, more accurate diagnostic results can be obtained than now.

In addition, when determining the first, second, and third metallographic parameters, it is very convenient to program the process so that it can be processed by an electronic computer, since the processing procedure can be speeded up.

〔Effect of the invention〕

As explained above, the method for diagnosing structural members according to the present invention is a new method that adds data on physical and chemical changes in the metal structure, so it is possible to evaluate unit damage much more accurately than before. Be expected.

[Brief explanation of drawings]

The drawing is a block diagram schematically illustrating the processing procedure of the structural member diagnostic method according to the present invention.

Claims (1)

[Claims] After polishing, a first replica that transfers the surface metal structure of the corroded object and a second replica that transfers the surface metal structure of the same object that has been polished and corroded again are collected.
Among the voids generated in the replica, the value equivalent to the cumulative number of voids generated is calculated from the ratio of the total surface area and the minimum void surface area, and the value equivalent to the grain boundary unit length is calculated from the grain size generated in the second replica. The value equivalent to the cumulative number of voids generated per grain boundary unit length is calculated from the ratio of the value equivalent to the cumulative number of voids generated above and the value equivalent to the grain boundary unit length, and the cumulative voids per grain boundary unit length are calculated. A method for diagnosing damage to structural members, characterized by diagnosing the degree of damage from a value equivalent to the number of occurrences and the hardness of the object.