JP2670182B2 - High-temperature damage evaluation method for heat-resistant steel - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nondestructive inspection method applied to maintenance and management of high temperature equipment members used as high temperature equipment for a long time.

[Conventional technology]

Conventionally, as a nondestructive inspection method for heat-resistant steel used in high-temperature equipment, the generation number density of creep voids generated in the creep process in the heat-resistant steel or the grain boundaries where creep voids are formed There is an A-parameter method by ratio.

[Problems to be solved by the invention]

However, with the above-mentioned method, the quantitative value of the measured creep void, that is, the creep void surface density or the A parameter can obtain only average information of damage. However, since the destruction in the actual machine occurs at the maximum damage position, in the latter half of the service life, the average value of the life consumption rate evaluated from a part of the investigation target part is a dangerous side to predict the destruction of the investigation target part. The results could be shown.

In view of the above circumstances, the present invention seeks to provide a means for evaluating the life of a device based on the maximum value of creep damage.

[Means for solving the problem]

Therefore, when the present inventors measured a large number of creep void quantitative values of heat-resistant steel used as mechanical parts by using a replica or the like, the frequency distribution curve of the creep void quantitative values shows a normal distribution, It was found that the maximum value distribution fits the Gumbel distribution.

That is, a replica or real sample taken from the investigation site is divided into a number of regions of the same area, and the maximum creep void length in each region or the maximum creep void quantitative value consisting of the maximum creep void density in each region Based on the measurement result of the value, obtain the maximum value of the creep void quantitative value of the entire surveyed site by the double exponential (Gumbel) probability distribution, and obtain the remaining life of the entire relevant site based on the maximum value. It is characterized by.

Here, the "creep void length" is the length in the grain boundary direction of each creep void, and the sampled replica is divided into several places (for example, each field of view of the scanning electron microscope), and the creep void Length can be determined.

The "maximum creep void length in each area" is the longest creep void length in each area (field of view).

The "maximum creep void density in each region" is a value obtained by taking the number of creep voids per unit area in each region (field of view) as a parameter.

"Maximum quantitative value of creep voids in each region" is a general term for "maximum creep void length in each region" or "maximum creep void density in each region".

[Action]

According to the above-mentioned method of the present invention, the creep void length of the maximum damaged portion that determines the life of the mechanical component can be detected based on the measurement result of the creep void of a part of the mechanical component. The evaluation accuracy can be increased and the reliability of the machine can be increased.

〔Example〕

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

Used for high temperature steam piping for thermal power generation for over 100,000 hours
1 1m of 2 1 / 4Cr-1Mo steel welded steel pipe was removed. Since the high temperature steam pipe was used for a long time, a creep void was generated in the weld heat affected zone of its longitudinal weld, but since the total length is 88 m, the maximum damage that determines the life of the high temperature steam pipe. In order to understand the degree of damage to the part, it was necessary to investigate the full length, which was impractical in terms of cost and construction period. Therefore, replicas 1 as shown in Fig. 1 were sampled from a total of 11 locations in 100 mm intervals of the longitudinal welded part of the extruded 1 m steam pipe. First, both ends and the central part of each replica were collected. The average length of creep voids and the surface density of creep voids in the weld heat affected zone 2 at 33 places were measured. Both the creep void average length and the creep void surface density were obtained from 10 fields of the photograph taken 500 times by a scanning electron microscope centering on the heat affected zone. The average creep void length is obtained as the average value of the length of the creep voids at each position in the grain boundary direction, and the creep void areal density is the value obtained by dividing the number of creep voids generated in 10 fields of view at each position by the observation area. did. The frequency distribution of the average creep void length and the frequency distribution of the creep void areal density at all 33 locations are shown in FIGS. 2 and 3, respectively. All the distributions showed a log-normal distribution, and the maximum value distribution was expected to show a double exponential distribution (Gumbel Gumbel distribution). Therefore, the replicas collected from the 11 locations described above for the creep void length are left end, center, and
The result is plotted on the Gumbel probability statistical paper by dividing into three places on the right end, obtaining the maximum creep void length at each position, obtaining the cumulative probability using the average rank method, and plotting the result on the Gumbel probability statistical paper.
As shown in the figure, the data show a good linear relationship and it was found that the maximum creep void length fits the Gumbel distribution.

Therefore, the maximum creep void length existing in the welded portion of the test steel pipe (1 m) was estimated by the method of the present invention. First, the maximum creep void length distribution shown in Fig. 4 is 0.16 mm of the test steel pipe (the length of the welded part included in one replica).
Since × 10 field of view = 1.6 mm, the maximum creep void length of the test steel pipe (1 m) is calculated from the maximum creep void length distribution shown in Fig. 4 by the maximum creep void length in the recursion period shown in the following formula. It can be obtained by asking.

T = (length of section to be estimated = 1000 mm) / (measurement section 1.6 mm) = 625 Fig. 4 shows the result of estimating the maximum creep void length of the test steel pipe 1 m in this way. The creep void length was estimated to be 140 μm.

Therefore, the sample material was polished, and the creep voids were directly observed with a stereoscopic microscope, and the maximum creep void length was calculated to be 125 μm, which was almost the same as the maximum creep void length 140 μm estimated by the method of the present invention. I was

〔The invention's effect〕

As described in detail above, according to the method of the present invention, it is possible to provide a method of accurately evaluating the maximum damage of a mechanical component made of heat-resistant steel used under high temperature stress from a partial measurement result. The damage evaluation can be performed in an extremely short time as compared with the whole area inspection, and the accuracy of the damage evaluation performed in the stripping inspection can be improved and the reliability of the mechanical component can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a replica taken from a high temperature steam pipe weld of a long-term use thermal power plant as one embodiment of the present invention, and FIG. 2 is a creep of the steam pipe weld measured as one embodiment of the present invention. Frequency distribution chart of void length, FIG. 3 is a frequency distribution chart of creep void areal density of the steam pipe weld measured as one embodiment of the present invention, and FIG. 4 is a maximum creep void length distribution chart (Gumbel probability). FIG. 1 ... Replica, 2 ... Welding heat affected zone, 3 ... Weld metal, 4 ... Base metal, 5 ... Replica base plate for sticking replica.

Claims (1)

(57) [Claims] 1. A replica or a real sample taken from a survey site is divided into a large number of regions having the same area, and the maximum creep void length in each region or the maximum creep void density in each region is defined in each region. Based on the measurement result of the maximum value of the creep void quantitative value, the maximum value of the creep void quantitative value of the entire surveyed site is obtained by the double exponential probability distribution, and the remaining life of the entire relevant site is calculated based on the maximum value. A method for evaluating high-temperature damage to heat-resistant steel, characterized in that