JP3848902B2 - Heat-resistant material selection method and heat-resistant material selection program - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat-resistant material selection method and a heat-resistant material selection program used for heat-resistant steel of a power plant or the like.
[0002]
[Prior art]
Usually, since a superheater, a reheater, a water wall, a economizer, etc. of a power plant are exposed to high temperatures, a predetermined heat resistant material is used in consideration of corrosion resistance and the like. Devices used at these high temperatures (such as small-diameter pipes) are designed based on the allowable tensile stress determined in consideration of the tensile properties and creep strength at the assumed temperature.
[0003]
[Problems to be solved by the invention]
However, equipment (such as small-diameter pipes) used at these high temperatures often becomes higher than the set temperature depending on the combustion gas flow of the thermal power plant, the properties of the fuel, the combustion conditions, etc. In that case, the tensile strength In addition, the creep strength may be reduced, causing destruction earlier than expected. In particular, in the case of high strength ferritic steels developed recently as materials with excellent heat resistance, high allowable tensile strength has been obtained even at high temperatures. May cause destruction.
[0004]
The present invention has been made to solve the above-described problems, and provides a heat-resistant material selection method and a heat-resistant material selection program that can select a material that does not cause a significant decrease in strength or early destruction even when the temperature is higher than a set temperature. Objective.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the heat-resistant material selection method of the present invention, when selecting a heat-resistant material having a predetermined set strength at a certain set temperature, the target destruction when the predetermined temperature rises from the set temperature to the high temperature side Based on the strength regression curve of each heat-resistant material, the time reduction rate or the target destruction time reduction amount is determined, and the failure time reduction rate or the destruction time reduction amount when the predetermined temperature rises from the set temperature is the target destruction time reduction A material having a rate or a target destruction time reduction amount or less is selected.
In this case, even if the temperature is higher than the set temperature, only the material having a target destruction time reduction rate (amount) or less is selected, so that there is no problem of causing unexpected failure due to temperature rise.
[0007]
In the heat resistant material selection method of the present invention, the target strength reduction rate, the target strength reduction amount, the target destruction time reduction rate, or the target destruction time reduction amount may be calculated based on a standard sample.
In this way, there is a sufficient track record as a heat-resistant material from the past, and a standard sample with less trouble due to stress reduction at the time of temperature rise can be used as a target standard. A material that does not break easily can be selected more appropriately.
[0008]
The boiler according to the present invention is characterized in that the heat-resistant material selected by the heat-resistant material selection method is used.
[0010]
The heat-resistant material selection program of the present invention determines a target destruction time reduction rate or a target destruction time reduction amount when a heat-resistant material having a predetermined strength at a certain temperature is selected and the temperature rises from that temperature to a high temperature side. And, based on the strength regression curve of each heat-resistant material, select a material whose failure time reduction rate or destruction time reduction amount is lower than the target destruction time reduction rate or target destruction time reduction amount when the predetermined temperature is increased from the selected temperature. It is characterized by causing a computer to execute the processing to be performed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a computer for realizing a heat-resistant material selection program according to the present invention.
In this figure, a computer 10 includes a CPU (control unit) 2, a stress-temperature curve DB 4, a stress-LMP curve DB 6, an input means 8, an output means 9, and a memory (not shown) for storing a heat-resistant material selection program. Yes. Note that “LMP” is an abbreviation for Larson-Miller Parameter, which will be described in detail later. In addition, the stress-LMP curve is an example of a “strength regression curve” for the creep rupture (rupture) strength of each heat-resistant material. The intensity regression curve may be appropriately selected and used.
[0012]
The CPU 2 controls the computer 10 as a whole, and the input means 8 receives input from the operator. The output means 9 outputs the processing result. The stress-temperature curve DB4 and the stress-LMP curve DB6 each store characteristic data for each heat-resistant material, details of which will be described later. The CPU 2 executes a heat-resistant material selection program based on the input items to the input means and the DBs 4 and 6 and outputs the result.
[0013]
FIG. 2 shows a stress-temperature curve of a certain heat-resistant material (2.25Cr-1Mo steel, JIS STBA24, hereinafter referred to as “standard sample”). In this figure, the “permissible tensile stress” on the vertical axis is a value set in consideration of a predetermined safety factor in the tensile strength and creep strength of the material at a certain temperature. In general, the allowable tensile stress of a material decreases as the operating temperature increases, but the rate of decrease becomes a problem. That is, for example, in the figure, when a material having an allowable tensile stress of σ0 at the use temperature T0 is selected, when the temperature rises to T0 + ΔT in the actual use environment, the stress decreases by Δσ. Accordingly, when the stress drop becomes significant compared to the load stress in the usage environment of the material, creep fracture or the like occurs at an early stage. Therefore, the present invention intends to select a material with little stress reduction (or breakage) even when the temperature rises.
[0014]
Next, a processing flow for selecting a heat-resistant material performed on the computer 10 will be described with reference to FIG. In this figure, first, the operator inputs a set temperature T1 and a set stress σ1 of a material used in a certain use environment, and the CPU 2 receives the input (step S10). For example, when the material in the heat transfer tube of the boiler is used, the case where the temperature of the heat transfer tube material is T1 and the load stress of the tube is σ1 is applicable. The stress here may be, for example, the above-described allowable tensile stress. The CPU 2 extracts material data whose stress at T1 is σ1 or more from the stress-temperature curve DB4 (step S12).
[0015]
Next, the CPU 2 accepts input of the use temperature T0 of the standard sample and the temperature rise degree ΔT (step S14). Then, the CPU 2 calculates the stress reduction rate at the time of temperature increase (T0 + ΔT) from the stress-temperature curve of the standard sample (step S16). Here, a specific example of the processing in steps S14 and S16 will be described with reference to FIG. 2. The amount of change Δσ of the allowable tensile stress when the operating temperature of the standard sample is changed from T0 to T0 + ΔT is obtained, and the stress is reduced from this. The rate (Δσ / σ0) will be calculated. Thus, if the stress reduction rate in the standard sample is obtained, the stress reduction rate of a material that has been used as a heat-resistant material and has few troubles due to stress reduction at the time of temperature rise can be used as a reference. If the stress reduction rate is known in advance, the target stress reduction rate may be directly input instead of steps S14 and S16. In addition, since the standard sample is often inferior in heat resistance per se to the actually used material, the relationship is usually T0 <T1. However, in the present invention, the stress reduction rate in the vicinity of the operating temperature of the standard sample is used as an index, and an object is to select a material that does not lower the stress. Therefore, it is not essential that T0 and T1 match.
[0016]
Next, the CPU 2 calculates a stress reduction rate when the temperature rises (T1 + ΔT) from the material data extracted in step S12 (step S18). And CPU2 extracts the material whose stress reduction rate calculated by step S18 is below a standard sample, and outputs an extraction result (step S20).
[0017]
FIG. 4 shows a specific example of the processing of steps S18 and S20. First, it is assumed that the stress-temperature curve data of the materials 1 and 2 are extracted in step S12. Each of these materials 1 and 2 has an allowable tensile stress at T1 of σ1 or more. Next, the change amounts Δσ1 and Δσ2 of the allowable tensile stress when the use temperature of each heat-resistant material 1 and 2 is changed from T1 to T1 + ΔT are obtained, and the stress reduction rate of each material is calculated therefrom. Here, the value of ΔT is the same as ΔT of the standard sample in step S14. That is, the stress reduction rate of each heat-resistant material when the same degree of temperature rise as that in the standard sample is anticipated. In this example, although material 1 has a higher stress at T1 than material 2, it is not adopted because the stress reduction rate when the temperature rises is larger than that of the standard sample (Δσ), while the stress reduction when the temperature rises Material 2 is selected whose rate is less than that of the standard sample (Δσ).
[0018]
Next, a second embodiment of the present invention will be described. This embodiment is characterized in that selection is performed using the failure time reduction rate as an index instead of the stress reduction rate. Therefore, in this embodiment, the stress regression curve is used as material characteristic data. First, the stress regression curve will be described with reference to FIGS.
FIG. 5 shows a stress-creep rupture time curve of the standard sample (STBA24) with reference to a creep data sheet issued by the Institute for Metallic Materials Technology. The creep rupture time curve varies depending on the temperature. FIG. 6 shows a curve obtained by arranging the data of FIG. 5 by LMP. Here, LMP is expressed by Equation 1.
LMP = (T + 273) × (C + logtr) / 1000 (1)
(T: temperature (° C.), C: fitting coefficient, tr: creep rupture time (hr)).
[0019]
For example, the creep rupture time when this material (standard sample) is used at a stress of 70 MPa and an operating temperature of 550 ° C. is obtained from the curve of FIG. 6 by calculating the LMP when the stress is 70 MPa (LMP = 20.7 × 10 ³ ). It can be calculated by substituting T into Equation 1 above. In this example, tr = 142000 hr at 550 ° C., tr = 18500 hr at 580 ° C., and the breakdown time reduction rate associated with the temperature rise can be obtained from this.
[0020]
Next, a processing flow on the computer 10 will be described with reference to FIG. In this figure, first, the operator inputs a set temperature T1 and a set stress σ1 of a material to be used in a certain use environment, and the CPU 2 receives the input (step S30). The CPU 2 extracts material data whose stress at T1 is σ1 or more from the stress-temperature curve DB4 (step S32). Steps S30 and 32 are the same as steps S10 and S12.
[0021]
Next, the CPU 2 accepts input of the use stress σ0, the use temperature T0, and the temperature rise ΔT of the standard sample (step S34). Then, the CPU 2 calculates the creep rupture time reduction rate at the time of temperature rise (T0 + ΔT) from the stress-LMP curve of the standard sample (step S36). Here, a specific example of the processing in steps S34 and 36 will be described with reference to FIG. 6. First, the LMP at σ0 of the standard sample is obtained from the curve, and then T0 and T0 + ΔT are respectively substituted into Equation 1. , T0 and T0 + ΔT are calculated as fracture life tr0 and trΔ, respectively. Then, a rupture time reduction rate (trΔ / tr0) is calculated from each rupture time. Thus, if the rate of decrease in fracture time in a standard sample is obtained, there is a track record as a heat-resistant material from the past, and the rate of decrease in fracture time of a material with less trouble due to stress reduction at the time of temperature rise can be used as a reference. . If the rupture time reduction rate is known in advance, the target rupture time reduction rate may be directly input instead of steps S34 and S36.
[0022]
Next, CPU2 extracts the stress regression curve data corresponding to the material from DB6 regarding the material data extracted by step S32. Then, by the same method as in the case of the standard sample, the fracture time reduction rate when the extracted material rises by ΔT from the set temperature T1 is calculated (step S38). Here, the value of ΔT is the same as ΔT of the standard sample in step S14. That is, the stress reduction rate of each heat-resistant material when the same degree of temperature rise as that in the standard sample is anticipated. Then, the CPU 2 extracts a material whose fracture time reduction rate calculated in step S38 is equal to or less than the standard sample, and outputs the extraction result (step S40).
In each of the above-described embodiments, attention is paid to the strength reduction rate and the destruction time reduction rate of the heat-resistant material, but the strength reduction amount and the destruction time reduction amount may be noted. The case where attention is paid to the amount corresponds to, for example, a case where determination is made based on whether or not the destruction time exceeds 10,000 hours.
[0023]
【The invention's effect】
As described above, according to the present invention, only a material having a target strength reduction rate or a target failure time reduction rate or less is selected even when the temperature is higher than the set temperature. There is no problem of causing early destruction at high temperatures. Therefore, a safer material can be selected at a high temperature.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a computer for realizing a heat-resistant material selection program according to the present invention.
FIG. 2 is a diagram showing a stress-temperature curve of a standard sample.
FIG. 3 is a diagram showing a processing flow for selecting a heat-resistant material.
FIG. 4 is a schematic diagram showing a specific example of processing in steps S18 and S20.
FIG. 5 is a diagram showing a stress-creep rupture time curve of a standard sample.
6 is a diagram showing curves obtained by classifying the data of FIG. 5 by stress-LMP. FIG.
FIG. 7 is another diagram showing a processing flow for selecting a heat-resistant material.
[Explanation of symbols]
Step S10: Step S16 for selecting a heat-resistant material having a predetermined set strength σ1 at a set temperature T1. Step S18, 20 for determining a target strength reduction rate when the predetermined temperature ΔT is increased from the set temperature to the high temperature side. Procedure for selecting a material whose strength decrease rate is less than or equal to the target strength decrease rate when the temperature rises from the set temperature to the specified temperature based on the strength regression curve

Claims (4)

When selecting a heat-resistant material having a predetermined set strength at a set temperature,
The target destruction time reduction rate or the target destruction time reduction amount when the predetermined temperature rises from the set temperature to the high temperature side is determined,
Based on the strength regression curve of each heat-resistant material, select a material whose fracture time reduction rate or fracture time reduction amount is less than the target fracture time reduction rate or target fracture time reduction amount when the predetermined temperature rises from the set temperature. The heat-resistant material selection method characterized by this.   The heat resistant material selection method according to claim 1, wherein the target strength reduction rate, the target strength reduction amount, the target destruction time reduction rate, or the target destruction time reduction amount is calculated based on a standard sample. . Boiler characterized by using a heat-resistant material selected by the heat-resistant material selection method according to claim 1 or 2. When selecting a heat-resistant material having a predetermined strength at a certain temperature,
When the target destruction time reduction rate or the target destruction time reduction amount when the predetermined temperature rises from that temperature to the high temperature side is determined,
A process of selecting a material whose fracture time reduction rate or fracture time reduction amount is less than the target fracture time reduction rate or target fracture time reduction amount when the predetermined temperature rises from the selected temperature based on the strength regression curve of each heat-resistant material A computer program for selecting a heat-resistant material.

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