JPH0713637B2 - Method for evaluating remaining life of heat-resistant steel - Google Patents

Description

The present invention relates to a method for evaluating the remaining life of heat-resistant steel used at high temperatures.

[Conventional technology]

For example, since the boiler superheater tube for thermal power generation is used in a high temperature and high pressure environment, the material deteriorates with use for a long time,
Consuming 100% of its service life will cause accidents such as blowout. Conventionally, as a residual life evaluation method aimed at preventing accidents due to consumption of the life of heat-resistant steel parts, attention has been paid to the method of evaluating the remaining life by creep rupture test of the members used and changes in mechanical properties such as hardness. The method of doing is known.

[Problems to be solved by the invention]

However, the method based on the creep rupture test cannot cut the remaining life in a short time non-destructively because it requires cutting of the member in use and a long-term test. Moreover, in the method that focuses on changes in mechanical properties such as hardness, especially when the cause of deterioration is mainly creep damage, the changes vary widely, and the remaining life cannot be accurately evaluated.

In addition, it is known that minute pores are formed in the grain boundaries of heat-resistant steel during long-term use, and there is a method to evaluate the remaining life of heat-resistant steel from its rough morphology. There was no method to quantify and evaluate the remaining life.

The present invention has been made in view of the gap between the above-mentioned conventional technology and actual needs, and non-destructively determines the remaining life of the heat-resistant steel from the distribution of microscopic holes in the heat-resistant steel used for a long time. Moreover, the purpose is to provide an evaluation method that enables accurate evaluation in a short time.

[Means for solving problems]

That is, the present invention is a method for evaluating the remaining life of a heat-resistant steel used at high temperature, in which the diameters and surface densities of micropores generated at the grain boundaries of the heat-resistant steel are measured, and various conditions determined in advance are measured. Based on the residual life evaluation reference line showing the relationship between the life consumption rate based on the fracture test of the material used below or the stress analysis and the linear density which is the product of the diameter of the micropores and the surface density A gist of a method for evaluating a remaining life of a heat-resistant steel is characterized in that a predicted value of a remaining life of the heat-resistant steel is obtained from the linear density of the minute holes.

[Action]

By the way, the inventors of the present invention have studied the ferritic heat-resistant steel and the austenitic heat-resistant steel that have been used at high temperature for a long time. It was found that the product of the micropores per unit area, that is, the length of the micropores per unit area, has a good correlation with the creep rupture life consumption rate or the life consumption rate by stress analysis. It was found that the remaining life can be evaluated easily and accurately.

The present invention is based on the above findings, the diameter of the micropores formed in the grain boundary of the heat-resistant steel used for a long time under high temperature and high pressure environment, the measurement of the areal density and the linear density which is the product of both, Destruction of the remaining life of the heat-resistant steel by using the remaining life evaluation reference diagram showing the relationship between the life consumption rate by the fracture test of the prepared material used or the life consumption rate by the stress analysis and the linear density of the micropores. This makes it possible to evaluate easily and accurately in a short period of time without using it for tests.

That is, the number of creep voids generated in heat-resistant steel exposed to high temperature and stress for a long time may increase depending on the type of heat-resistant steel, or the length of each creep void may increase. Therefore, in the present invention, regardless of the type of heat-resistant steel, as a method of quantifying the generation state of creep voids, by using the physical property value of linear density obtained by multiplying the number of generations of creep voids by the average diameter, any type It is possible to objectively and accurately evaluate the life evaluation from the creep voids that are generated even with respect to the heat resistant steel of.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

First, it was used for a long time as a superheater tube for a commercial boiler. 2
Microscopic holes in 1 / 4Cr-1Mo steel were observed by a scanning electron microscope, and their diameter and areal density were measured. The diameter of the micropores is the diagonal length in the grain boundary direction, and the average value of the measurement of 20 micropores is the measured value of the diameter. Next, FIG. 1 to FIG. 3 showing the relationship between the above-mentioned physical property values of the micropores of 2 1 / 4Cr-1Mo steel used under various conditions as a high temperature pressure resistant member and the creep rupture life consumption rate of the resistant member. The remaining life evaluation standard diagram such as

It was then used for a long time as a boiler superheater tube for business2
The surface of 1 / 4Cr-1Mo steel was polished, and the micropores of the steel were transferred to the replica film by the replica method. The micropores were mounted on a scanning electron microscope and the diameter and surface density of the micropores were measured. The linear density, which is the product of the above, was calculated, and the creep rupture life consumption rate of the superheater tube was estimated.
77%, the estimated value based on the areal density of micropores was 82%, and the estimated value based on the linear density of micropores was 79%. When the creep rupture test of the superheater pipe was carried out to determine the creep rupture life consumption rate, the value was 75%, which was in good agreement with the life consumption rate obtained by the method of the present invention.

〔The invention's effect〕

As described above in detail, according to the method of the present invention, it is possible to evaluate (quantify) the remaining life of the heat-resistant steel used in a high temperature environment for a long time nondestructively and in a short time without using a destructive test. Therefore, it is possible to provide a residual life evaluation method with sufficiently high estimation accuracy.

[Brief description of drawings]

Fig. 1 is a residual life evaluation standard diagram showing the relationship between the diameter of micropores and creep rupture life consumption rate, and Fig. 2 is a graph showing the relationship between the surface density of micropores and creep rupture life consumption rate. A life evaluation reference diagram, FIG. 3 is a remaining life evaluation reference diagram showing the relationship between the linear density of micropores and the creep rupture life consumption rate.

Claims (1)

[Claims] 1. A method for evaluating the remaining life of a heat-resistant steel used at high temperature, wherein the diameter and areal density of micropores generated at a grain boundary of the heat-resistant steel are measured, and various conditions determined in advance are measured. Based on the residual life evaluation reference line showing the relationship between the life consumption rate based on the fracture test of the material used below or the stress analysis and the linear density which is the product of the diameter of the micropores and the surface density A method for evaluating the remaining life of a heat-resistant steel, characterized by obtaining a residual life prediction value of the heat-resistant steel from the linear density of microscopic holes.