JPH0875107A - Method for estimating life time of high temperature pressure resistant part - Google Patents

Abstract

PURPOSE: To estimate the life time of a site highly accurately by analyzing the site in a time series along an operation history with respect to the stress thereof for estimation of the life time using predetermined material properties corresponding to use history based upon the operation history of the site until the life time is appraised. CONSTITUTION: There is provided a method for estimating the life time of a high temperature pressure resistant part including a site selection step 1 for selecting the site used at high temperature, and a thermal stress analysis step 2 for each start mode for stress-analyzing the site for each operationw history of one or more. There are further provided a rearrangement step 3 of each operation history in time series, a calculation step 4 of Larson-Mirror parameter for estimating use history based upon each operation history of the site until the life time is estimated, and a selection step 6 of creep breakage data for selecting material physical properties from a data base 5 predetermined for each used history. There are further provided a life time calculation step 7 for i-th start mode for stress-analyzing the site in a time series along each operation history for calculation of the life time, and a total sum step 8 for the life time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a life evaluation of a material used at a high temperature for a long period of time, and more particularly to a life evaluation method of a high temperature pressure resistant part suitable for evaluating a life of a part of a boiler for thermal power generation. .

[0002]

2. Description of the Related Art It is well known that materials used in thermal power plants, chemical plants, etc., which are used for a long time under high temperature and high pressure, suffer from damage such as creep and fatigue during operation and consume their lives. ing. At the time of designing such a plant, life evaluation is performed to determine the structure, dimensions and material of each member (part). Also, not only at design time,
When operating for a long time, it may be necessary to evaluate the service life of parts that were unpredictable at the time of design. Furthermore, the stress state of the evaluation site may change due to changes in usage conditions, and in such a case as well, it is necessary to evaluate the remaining life from that point.

In the conventional method for evaluating the life of a high temperature withstand voltage portion, as shown in FIG. 6, first, an evaluation portion selecting step 1 for selecting a portion to be used under high temperature and under severe operating conditions is carried out.
And the thermal stress analysis step 2 for each start mode to analyze the stress state of the part by the finite element method, etc., and the life of the part by comparing the creep rupture data and low cycle fatigue data of the new material used. It has a life calculation step 7a in each starting mode by comparison with new material data to be calculated, and a total life step 8a. In this case, in addition to the stress generated in the steady operation state, a considerably large thermal stress is generated when the engine is stopped or when the load is changed, and then relaxed.
In the boiler for thermal power generation, the start mode (operation history) includes cold start (start from a completely cold state such as during periodic inspection), warm start (start from a slightly high temperature state at weekend stop), and hot start (start. It can be categorized into 3 to 4 types, such as starting and stopping every day when the temperature is quite high).

Regarding creep rupture, life evaluation considering stress relaxation at startup such as cold start, warm start and hot start is performed by comparing with the creep rupture data of the new material (unused material), and each start mode is determined. The total creep life is calculated by counting the total number of occurrences and summing. In this case, life evaluation considering stress relaxation is performed by the following method.

As shown in FIG. 7, a considerably large thermal stress is generated at the time of starting. However, this thermal stress sharply decreases with time due to a phenomenon called stress relaxation, and becomes a constant value. Therefore, the time step is cut as shown in the figure, and the life per unit time is summed up. It is considered that the stress is constant during the time Δt, the average stress σi during that time is calculated, the rupture time tri at the average stress is obtained from the creep rupture data of the new material, and the creep damage rate is calculated and summed. The creep damage rate φc is calculated by the equation (1).

Φc = Σ (Δt / tri) (Equation 1) With respect to low cycle fatigue, since the stress amplitude differs depending on each start mode and load change, the number of times of the same start mode is counted to calculate the stress amplitude. Fatigue damage for each is calculated based on the fatigue data of the new material, and the sum total is taken as fatigue damage.

[0007]

In the conventional method for evaluating the life of a high temperature withstand voltage portion, when the remaining life is evaluated by stress analysis, material data for comparison (material physical property values), that is, creep rupture data and high temperature low temperature are used. Cycle fatigue data is needed. Such material data is tested by public authorities,
We often use publicly available material data. For example,
Creep data sheets and fatigue data sheets issued by National Institute for Metals Technology are widely used due to their high reliability and rich data. Such a data sheet is a so-called new material data sheet obtained by obtaining a material from a material manufacturer and testing it as a test material. But,
In reality, the material deteriorates and its strength changes due to use at high temperatures. That is, the material data for comparison needs to be changed depending on the time of evaluation, but currently, the material data of the new material is used for convenience. In this case, regarding low cycle fatigue, the change in material data due to use at high temperature is small, but regarding creep rupture, there is a high possibility that the material data changes due to use at high temperature. Further, the material data of the base metal is used on the assumption that the weld metal is equivalent to the base metal, but the strength of the weld metal may be lower than that of the base metal due to long-term use at high temperature.

There is a method of selecting creep rupture data based on hardness measurement values for turbine materials in consideration of material deterioration due to high temperature use (Thermal Nuclear Power Generation Vol.
40, No. See 10). However, this method is for turbine materials in which the relative relationship between hardness and creep damage is relatively clear, and boiler materials are used at high temperatures because the carbon content is kept low in consideration of workability and weldability. Hardness change due to is small and this method cannot be applied. In addition, although it is necessary to measure hardness with this method, the location where life is evaluated by stress analysis is basically a place where hardness measurement is difficult, such as the inner surface of a pipe, and where hardness measurement is possible. There is another non-destructive diagnostic method using a replica. Even if the hardness can be measured, the hardness changes continuously in the weld, especially in the heat affected zone, and it is unclear at which position in the weld affected zone the hardness should be adopted. is there. Furthermore, although the creep rupture strength at the time of measuring the hardness can be specified, originally, the creep rupture strength changes continuously due to high temperature use, and in order to evaluate the life or remaining life, the creep rupture strength used for the evaluation It is necessary to continuously change the fracture data.

In addition to creep rupture data and high temperature low cycle fatigue data, stress relaxation characteristics, longitudinal elastic modulus and stress-strain diagram are required for stress analysis, but these data also change due to use at high temperature. To do. Among these, the change in longitudinal elastic modulus due to high temperature use is small, but the stress-strain diagram and stress relaxation characteristics change considerably. As described above, in evaluating the life of the selected part, there is a problem that the material physical property value according to the usage history of high temperature is not determined and the evaluation accuracy is low.

It is an object of the present invention to provide a method for evaluating the life of a high temperature pressure resistant portion, which can accurately evaluate the life of a portion used at high temperature.

[0011]

In order to achieve the above-mentioned object, the method for evaluating the life of a high temperature withstand voltage part according to the present invention selects a part to be used at high temperature, and selects the part according to at least one operation history. In the life evaluation method of high temperature withstand voltage part which analyzes stress and evaluates life, use history is calculated based on the operation history of each part up to the time of evaluating life, and it is determined in advance corresponding to each use history. Using the physical properties of the material, stress analysis is performed on the parts in chronological order along each operation history and the life is calculated to sum the life of each operation history.

The physical property value of the material may be a creep rupture property.

The physical property values of the material may be creep rupture characteristics, stress relaxation characteristics, longitudinal elastic modulus and stress-strain diagram of the base material and the welded portion.

First, similarly to the normal remaining life evaluation, stress analysis of the target portion is carried out for each starting mode. Next, the start-up modes are time-sequentially arranged according to an actual driving pattern or an expected driving pattern. Then, the life is calculated in order, but at this time, the usage history (Larson-Miller parameters) until reaching the start mode targeted for the life calculation is calculated, and the creep rupture data corresponding to the material deterioration is calculated. Use to calculate the life. The usage history related to material deterioration is a function of usage temperature and usage time, and the material data corresponding to that degree, that is, creep rupture data, is prepared beforehand by analyzing the creep rupture data of aged materials and preparing for each usage history. Keep it. Also, since the base material and the welded part differ in the degree of decrease in creep rupture strength due to the use of high temperature, the material data is prepared separately from the base material and the welded part,
Use properly depending on the target part.

In this way, the life is sequentially calculated using the creep rupture data for each usage history in consideration of material deterioration, and the life is finally summed.

In order to perform a more rigorous evaluation, material data used for stress analysis, that is, longitudinal elastic modulus, stress relaxation characteristics and stress-strain diagram corresponding to the usage history are used. The procedure in this case is to calculate the usage history sequentially according to the start mode, select the material data corresponding to the usage history,
Repeat stress analysis and life evaluation and sum them.

[0017]

According to the present invention, the following is clarified because it is based on the result of collecting and analyzing a lot of data on various aged materials of CrMo steel for boilers.

Regarding low cycle fatigue, there was almost no difference between the new material and the aged material, and there was also no difference between the base material and the welded portion. Therefore, for low cycle fatigue strength, the data of new materials can be used even for aged materials.

Regarding creep rupture, a clear difference between the new material and the aged material was recognized. That is, the creep rupture strength changes depending on the usage history up to the time when the life is evaluated,
The accuracy of life evaluation can be improved by evaluating the life using the creep rupture data corresponding to the usage history. Further, in the base material and the welded portion, the degree of decrease in creep rupture strength due to high temperature use is larger in the welded portion, and it is necessary to distinguish the base material and the welded portion.

Further, the material data required for stress analysis, that is, the stress relaxation characteristics, the longitudinal elastic modulus and the stress-strain diagram also change with high temperature use. The impact of these materials on life assessment is not as significant as the creep rupture data,
Strict evaluation is possible by considering this change. Among these, the change in longitudinal elastic modulus due to high temperature use is small, but the stress relaxation characteristics and the stress-strain diagram are relatively large.

As described above, by using the material data for each base material and welded portion corresponding to the usage history up to that time,
Accurate life evaluation is possible.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a flowchart of this embodiment. As shown in FIG. 1, an evaluation site selection step 1 for selecting a site to be used at high temperature, and a thermal stress analysis step 2 for each startup mode for performing stress analysis on the site for each one or more operation histories (startup modes). A method for evaluating the life of a high-temperature withstand voltage part, which has a life history, including a step 3 of time-sequential rearrangement of each operation history and each operation history of parts up to the time when the life is evaluated. The Larson-Miller parameter calculation step 4 for calculating the mirror parameter (LMP) and the material property value is selected from a database (creep rupture database for aged materials etc.) 5 which is predetermined corresponding to each usage history. Step 6 of selecting creep rupture data, and Step 7 of life calculation in the i-th start mode in which stress analysis and life calculation of parts are performed in chronological order along each operation history. A configuration including a summation step 8 of each life.

That is, first, the site to be evaluated is selected. The part to be evaluated in this example is the main steam pipe Y-piece part (material: 2.25Cr-1Mo) of the boiler shown in FIG.
Steel), which has been used in an actual machine for about 120,000 hours. In order to evaluate the lifetime consumption of this part up to the present and to evaluate the soundness of this part, a stress analysis is next performed. In this example, the three-dimensional finite element method was used. Thermal conduction analysis was performed based on the temperature data of the thermocouple attached to the actual machine. Figure 3 shows the finite element division of the target part. With such element division, the transient temperature distribution of each starting mode such as cold start, warm start, and hot start was calculated, and the thermal stress was calculated from the result. . The part with the highest stress is inside the corner, and the creep life and fatigue life are evaluated by the equivalent stress of the part A.

Also in this embodiment, the evaluation regarding low cycle fatigue is the same as the conventional method. This is based on the research results that the high temperature low cycle fatigue data hardly changed between the new material and the aged material.

Regarding the creep rupture, unlike the conventional method, deterioration of the material due to long-term use at high temperature is taken into consideration.
Therefore, as shown in FIG. 1, the start-up modes are arranged in a time series based on a record (evaluation up to the present time) or a plan (evaluation in the future), and each use history is calculated. This usage history is represented by a Larson-Miller parameter P (LMP) calculated by the equation (2) as a function of the usage temperature and usage time of the evaluation site.

[0026]

[Equation 2]

The creep rupture data used for damage calculation is selected according to the Larson-Miller parameter P value. The creep rupture data changes from moment to moment depending on the operating time and the operating temperature.However, when arranging many creep rupture data, it is difficult to classify them in detail because of the large variation in creep rupture data. I understood. That is, originally, the creep rupture data should be changed depending on the P value, but in the present embodiment, the P value of 20, 21, 22 is found from the result of examining the creep rupture data of aged materials of 1000 points or more. 4 as the boundary
The creep rupture data shown in FIG. 4 was used according to each P value. Among these, the data with a P value of 20 or less is the data of the new material, and it can be seen that the strength decreases with use at high temperature for a long time. Especially on the high stress side, the degree of decrease in the P value is remarkable. This creep rupture data shows the lower limit of the 90% confidence interval, so that the safety side can be evaluated.

The consumption life due to creep rupture is calculated by sequentially calculating the usage history for the start modes arranged in time series, selecting an appropriate creep rupture strength corresponding to the usage history from the database, and observing each creep life. Calculate the consumption rate and finally sum.

Table 1 shows the results of the evaluation of the life in this manner in comparison with the conventional method.

[0030]

[Table 1]

The evaluation according to the present embodiment has a longer consumption life than the evaluation according to the conventional method, because the deterioration of the material due to high temperature and long time is taken into consideration. Although the base metal is evaluated in this example, the creep rupture strength is different from that of the base metal in the case of a welded portion. This is the result of investigating the creep rupture data of many aged materials, and in the present example, when selecting the creep rupture strength according to the usage history, the base metal or the welded part was selected, and the creep rupture strength corresponding to it was selected. It is designed to be selected.

FIG. 5 shows a flowchart of another embodiment of the present invention. In this embodiment, the data used for the stress analysis is also adapted to the usage history. That is, the stress relaxation characteristics, the longitudinal elastic modulus, and changes in the stress-strain diagram due to high temperature use are prepared as a database 5a, and the usage history is calculated in chronological order according to the operation pattern (step 4), and the usage history is recorded. The physical properties of the material (stress relaxation characteristics,
Longitudinal elastic modulus, stress-strain diagram and creep rupture characteristics of base material and weld zone) are selected (step 6a), stress analysis (step 2a) and life evaluation (step 7) are repeated, and finally the life is summed. (Step 8). In this embodiment, since stress analysis is carried out for each physical property value of the material, it takes a lot of time for evaluation, but more strict evaluation is possible.

According to the present invention, it is possible to evaluate the service life in consideration of the deterioration of the material due to the high temperature heating for a long time. Since the conventional method does not consider material deterioration, it is evaluated on the unsafe side, and there is a possibility that damage may progress unexpectedly and may lead to unexpected damage. It is an evaluation of accuracy, and since the time of damage can be accurately grasped, planned maintenance management is possible, and its industrial value is extremely large.

[0034]

According to the present invention, the use history is calculated based on the operation history of the part used at high temperature, and the life is calculated based on the material physical property value determined in advance corresponding to the use history. Considering the safety side, it is possible to evaluate the service life with high accuracy, and it is possible to accurately understand the time of damage, which has the effect of enabling planned maintenance management.

[Brief description of drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 is a diagram showing a main steam pipe Y-piece portion of a boiler, which is an evaluation part of FIG.

FIG. 3 is a diagram showing finite element division of an evaluation site used in the stress analysis of FIG.

FIG. 4 is a graph showing creep rupture data according to usage history of 2.25Cr-1Mo steel.

FIG. 5 is a flowchart showing another embodiment of the present invention.

FIG. 6 is a flowchart showing a conventional technique.

FIG. 7 is a diagram illustrating a stress relaxation state.

[Explanation of symbols]

 1 Selection step of evaluation site 2 Thermal stress analysis step by start mode 3 Time series rearrangement step of start mode 4 Larson-Miller parameter calculation step 5 Creep rupture database of aged material 6 Creep rupture data selection step 7 Life calculation step in i-th start mode 8 Sum of life

Claims (3)

[Claims] 1. A method for evaluating the life of a high temperature pressure resistant part, wherein a part to be used at high temperature is selected, stress analysis is performed on the part according to at least one operation history, and the life is evaluated. A usage history is calculated based on the operation history of each of the parts, and a material property value determined in advance corresponding to each usage history is used, and stress analysis is performed on the parts in chronological order along each operation history and A life evaluation method for high temperature pressure resistant parts, characterized by calculating the life and summing the lifespan of each operation history. 2. The method for evaluating the life of a high temperature withstand voltage part according to claim 1, wherein the material physical property value is a creep rupture property. 3. In the method for evaluating the life of a high temperature pressure resistant part according to claim 1, the physical properties of the material are creep rupture characteristics, stress relaxation characteristics, longitudinal elastic modulus and stress-strain diagram of the base material and the welded part. A method for evaluating the life of a high temperature pressure resistant part, which is characterized by: