WO2014147830A1

WO2014147830A1 - Method for predicting remaining creep life expectancy of product with bainite structure and method for producing standard curve used in this prediction method

Info

Publication number: WO2014147830A1
Application number: PCT/JP2013/058372
Authority: WO
Inventors: 西田　秀高
Original assignee: 中国電力株式会社
Priority date: 2013-03-22
Filing date: 2013-03-22
Publication date: 2014-09-25
Also published as: JP5355832B1; JPWO2014147830A1

Abstract

The present invention provides a method for predicting the remaining creep life expectancy of a product with a bainite structure. More specifically, the method for predicting remaining creep life expectancy includes a step for determining a first relationship between the hardness and Larson-Miller parameter of a first product that has a bainite structure and has deteriorated as a result of heating, a step for determining a second relationship between the hardness and Larson-Miller parameter of a second product that has a bainite structure and has deteriorated as a result of heating and pressure, a step for using the first relationship and the second relationship to determine the difference between the hardness of the first product and the second product for a given Larson-Miller parameter and thereby determine a third relationship between the hardness of the second product and said difference, a step for determining a fourth relationship between the hardness and damage rate of the second product, a step for using the third relationship and the fourth relationship to determine a fifth relationship between said difference and the damage rate of the second product, a step for using the third relationship to obtain the difference corresponding to the hardness of a product for which remaining creep life expectancy is to be predicted, and a step for using the fifth relationship to determine the product damage rate corresponding to the obtained difference.

Description

Method for predicting the remaining creep life of a product having a bainite structure, and a method for creating a calibration curve used in this prediction method

The present invention relates to a method for predicting the remaining creep life of a product having a bainite structure and a method for creating a calibration curve used in this prediction method.

Mechanical parts used in thermal power generation facilities and nuclear power generation facilities are subjected to high temperature and high pressure conditions for a long period of time, so that they gradually undergo plastic deformation and break when the creep life is reached. Therefore, in order to operate thermal power generation facilities and nuclear power generation facilities safely and economically, the machine parts must be replaced at the optimal time by accurately predicting the remaining creep life of the machine parts used. Is required.

As a method of predicting the remaining creep life of heat-resistant steel used in such machine parts, for example, detection of cracks occurring at the end of life such as visual inspection, magnetic particle inspection, ultrasonic inspection, and radiation inspection There are known methods for detecting voids and microcracks by the replica method, but these methods cannot predict the remaining life before cracks occur.
As a method of predicting the remaining life before cracks are generated, as disclosed in Japanese Patent Laid-Open No. 63-235861, testing is performed from heat-resistant steel of mechanical components of a thermal power generation facility or a nuclear power generation facility that is actually operating. A method is known in which a piece is cut out, a creep rupture test is performed, and the remaining life is predicted from the rupture time. In this method, a piece of specimen is cut out from a facility that is actually in operation for a long time. It is necessary to test and is complicated.

An object of the present invention is to provide a method for predicting the creep remaining life of a product having a bainite structure and a method for creating a calibration curve used in this prediction method.

The method for producing a calibration curve used in the method for predicting the creep remaining life of a product having a bainite structure according to the present invention is the first relationship between hardness and Larson mirror parameters of a first product having a bainite structure and deteriorated by heating. Determining the second relationship between the hardness and the Larson mirror parameter of the second product having a bainite structure and deteriorated by heating and pressing, the first relationship and the second relationship A calibration curve representing the third relationship between the hardness of the second product and the difference is created by calculating the difference between the hardness of the first product and the hardness of the second product at a predetermined Larson mirror parameter using And the step of obtaining the fourth relationship between the hardness and the damage rate of the second product, the third relationship and the fourth relationship, and the difference and the damage rate of the second product. Calibration representing the fifth relationship with And a step to create a.

The method for predicting the creep remaining life of a product having a bainite structure according to the present invention may use a calibration curve created in this way.

The method for predicting the remaining creep life of a product having a bainite structure according to the present invention includes a step of obtaining a first relationship between hardness and Larson mirror parameter of a first product having a bainite structure and deteriorated by heating, and a bainite structure. A predetermined Larson using a step of obtaining a second relationship between the hardness and the Larson mirror parameter of the second product deteriorated by heating and pressurization, and the first relationship and the second relationship. Determining the third relationship between the hardness of the second product and the difference by determining the difference between the hardness of the first product and the hardness of the second product in the mirror parameters; and the hardness and damage of the second product. Determining a fourth relationship between the rate, a third relationship and a fourth relationship, and determining a fifth relationship between the difference and the damage rate of the second product; Creep afterlife using the relationship of 3 From the hardness of the product for predicting comprises the step of obtaining the difference corresponding, using a fifth relationship, from the resulting difference, and a step of determining the damage rate of the corresponding the product.

In order to obtain the difference corresponding to the hardness of the product that predicts the remaining creep life, it is preferable to use a hardness range that is substantially proportional among the third relationships. Further, in order to obtain the damage rate of a product that predicts the creep remaining life, it is preferable to use a range of difference that is substantially proportional among the fifth relation.

The products that predict the creep remaining life, the first product, and the second product are preferably hollow tubes, and may be, for example, boiler piping having a bent portion. In these cases, the pressurization is preferably performed by applying an internal pressure.

Moreover, it is preferable that the hardness is Vickers hardness.

It is preferable that the temperature applied to the first product and the temperature applied to the second product are the same.

According to the present invention, it is possible to provide a method for predicting the remaining creep life of a product having a bainite structure and a method for creating a calibration curve used in this prediction method.

It is a graph which shows the relationship between Vickers hardness and a Larson mirror parameter in one Embodiment. It is a graph which shows the relationship between (DELTA) H and the hardness at the time of deterioration by internal pressure creep in one Embodiment. It is a graph which shows the relationship between (DELTA) H and the damage rate at the time of deterioration by internal pressure creep in one Embodiment. It is a figure which shows the result of the structure | tissue examination by a transmission electron microscope when the damage rate is 0 in one Embodiment. It is a case where it is a case where it deteriorates by the thermal aging in one Embodiment, and when the damage rate is about 0.5, it is a figure which shows the result of the structure | tissue examination by a transmission electron microscope. It is a case where it is a case where it deteriorates by the thermal aging in one Embodiment, and when the damage rate is about 0.9, it is a figure which shows the result of the structure | tissue examination by a transmission electron microscope. It is a case where it is a case where it deteriorates by internal pressure creep in one Embodiment, Comprising: It is a figure which shows the result of the structure | tissue examination by a transmission electron microscope when a damage rate is about 0.5.

Hereinafter, an embodiment of the present invention completed based on the above knowledge will be described in detail. The objects, features, advantages, and ideas of the present invention will be apparent to those skilled in the art from the description of the present specification, and those skilled in the art can easily reproduce the present invention from the description of the present specification. it can. The embodiments and specific examples of the invention described below show preferred embodiments of the present invention and are shown for illustration or explanation, and the present invention is not limited to them. It is not limited. It will be apparent to those skilled in the art that various modifications and variations can be made based on the description of the present specification within the spirit and scope of the present invention disclosed herein.

Conventionally, when predicting the remaining creep life of a product having a ferrite structure or pearlite structure, the creep remaining amount is determined from the relationship between the amount of plastic deformation when the product is subjected to high temperature and high pressure conditions and the damage rate of the product. A method for obtaining the lifetime has been generally used.
However, as with products having a bainite structure, as in the case of products having a ferrite structure or pearlite structure, an attempt was made to predict the remaining creep life from the relationship between the amount of plastic deformation and the damage rate of the product. occured.
(1) Products with a bainite structure are firmer than products with a ferrite or pearlite structure, so the amount of deformation is very small when the damage rate is low, and the remaining life at the stage where the damage rate is low is accurate. It is difficult to predict.
(2) A product having a bainite structure undergoes a large deformation only when the damage rate is high, but once the deformation occurs, it suddenly breaks, so the life expectancy at the stage where the damage rate is high is predicted. Is complicated because it requires frequent measurement.
(3) Since the product having a bainite structure has a smaller amount of plastic deformation than a product having a ferrite structure or a pearlite structure, the remaining life of the product whose structure is unknown is given as a ferrite structure or a pearlite. When the relationship between the amount of deformation of a product having a structure and the damage rate is used, the damage rate may be lower than the actual rate, resulting in the risk of unexpected breakage.

The present inventor has completed the method for predicting the remaining creep life of a product having a bainite structure according to the present invention by paying attention to the hardness of the product having a bainite structure.
The method for predicting the remaining creep life according to the present invention can predict the remaining creep life of a product having a bainite structure even when the damage rate of the product is small. Further, the creep remaining life prediction method according to the present invention can predict the remaining creep life of a product having a bainite structure even at a stage where the damage rate of the product is large. In addition, the creep remaining life prediction method according to the present invention can appropriately predict the creep remaining life of a product having a bainite structure.
Specifically, it is as follows.

The method for predicting the remaining creep life of a product having a bainite structure according to the present invention includes a step of obtaining a first relationship between hardness and Larson mirror parameter of a first product having a bainite structure and deteriorated by heating, and a bainite structure. A predetermined Larson using a step of obtaining a second relationship between the hardness and the Larson mirror parameter of the second product deteriorated by heating and pressurization, and the first relationship and the second relationship. Determining the third relationship between the hardness of the second product and the difference by determining the difference between the hardness of the first product and the hardness of the second product in the mirror parameters; and the hardness and damage of the second product. Determining a fourth relationship between the rate, a third relationship and a fourth relationship, and determining a fifth relationship between the difference and the damage rate of the second product; Creep afterlife using the relationship of 3 From the hardness of the product for predicting comprises the step of determining the difference corresponding, using a fifth relationship, from the resulting difference, and a step of determining the damage rate of the corresponding the product.

The first product deteriorated by heating refers to a product having a bainite structure deteriorated by being placed under normal pressure and a constant high temperature. The temperature range is not particularly limited as long as the first product has a bainite structure. For example, the temperature range may be 210 ° C to 550 ° C, and preferably 350 ° C to 550 ° C.

Moreover, the 2nd product deteriorated by heating and pressurization means the product which has a bainite structure | tissue which deteriorated by putting on the conditions of constant high temperature and constant pressure higher than normal pressure.
The temperature range is not particularly limited as long as the second product has a bainite structure. For example, the temperature range may be 210 ° C to 550 ° C, and preferably 350 ° C to 550 ° C. The temperature applied to the first product and the temperature applied to the second product may be the same or different, but are preferably the same.
The pressure range is not particularly limited as long as it is higher than normal pressure (0.1 MPa), but may be, for example, 0.2 MPa to 1000 MPa, preferably 0.3 MPa to 500 MPa, and preferably 0.5 MPa to 300 MPa. It is more preferable that
The method of applying pressure is not particularly limited. For example, it may be performed by a uniaxial creep test or an internal pressure creep test. However, when the structure of the second product is a hollow tube, it is performed by an internal pressure creep test. It is preferable. The internal pressure creep test is a method for predicting or measuring the remaining life or life of a hollow tube by applying an internal pressure to the hollow tube in a high-temperature furnace and creep-breaking the hollow tube as necessary. Since the internal pressure creep test can be performed on hollow tubes, the effects of altered layers such as oxides on the outer surface and inner surface of the hollow tube that occur when the hollow tube is actually used as boiler piping, for example. It is excellent in that it can be tested. Furthermore, since the stress due to the internal pressure is applied to the hollow tube as in the case where it is actually used in a boiler, it is possible to accurately predict or measure the remaining life or life.

The structure of the first product and the second product, and the structure of the product having a bainite structure that is the target of the creep remaining life are not particularly limited, and can be, for example, a hollow tube, a plate, or a rod. Is preferably a hollow tube. The cross section of the hollow tube may have any shape, for example, it may be circular, elliptical, or polygonal, but it does not have corners considering the strength of the hollow tube. It is preferably a circle or an ellipse, and more preferably a circle.
As such a hollow tube, for example, a boiler pipe having a bent portion can be cited. Conventionally, boiler piping has been considered to have a ferrite structure or a pearlite structure, and thus the creep remaining life has been predicted according to a method for predicting the creep remaining life of a product having a ferrite structure or pearlite structure. However, the present inventor has found that the bent portion changes into a bainite structure with the slow heating when the bent portion of the boiler piping is created. Therefore, if the creep remaining life of a boiler pipe having a bent portion is predicted using the creep remaining life prediction method according to the present invention, it is possible to accurately predict the creep remaining life of the boiler pipe. .
It should be noted that the structure of the first product, the structure of the second product, and the structure of the product having a bainite structure that is the target of prediction of the remaining creep life are the same as long as they are made of the same material having the bainite structure. It may be different or different, but the same is preferable.

The method for measuring the hardness of each product is not particularly limited, and a known method can be used. However, it is preferable to measure Vickers hardness or micro Vickers hardness, and measure Vickers hardness. Is more preferable. When measuring the Vickers hardness, a load of 1 kg or more is used, and when measuring the micro Vickers hardness, a load of less than 1 kg is used.
Hardness measurement may be performed at only one location of the product, but considering the improvement of accuracy, it is performed at multiple locations and the average value of the measured values obtained is adopted as the hardness of the product. It is preferable.
The hardness of the product is preferably measured at a plurality of different damage rates of the product.

The product damage rate is a ratio representing how much time has elapsed with respect to the life of the product. The life of a product is the time required for the product to break due to heating and / or pressurization. For example, when the lifetime of a certain product is 10,000 hours and the elapsed time is 8000 hours, the damage rate can be calculated as 8000 ÷ 10000 = 0.80. Conversely, when the lifetime of a product is 10,000 and the damage rate is 0.80, the remaining lifetime of the product can be calculated as 10000 × 0.80 = 2000 hours.
The lifetime of a product can be determined by known methods, for example, by measuring a product of the same structure made from the same material as the product by heating and / or pressurizing until it actually breaks.

The Larson mirror parameter LMP is calculated from the heating temperature, heating time and hardness of the first product and the second product. Larson-Miller parameter LMP is, LMP = T (C + logt r), [ wherein, T is heating temperature expressed in absolute temperature (K), _{t r} is the heating time (h), C is a constant] , Can be obtained using. In a product having a bainite structure, 20 is preferably used as C.

The first relationship between the hardness of the first product and the Larson mirror parameter obtained in this way is obtained. If this relationship is made into a graph, for example, it becomes a curve.
In determining the relationship between the hardness of the first product and the Larson mirror parameter, only the product A heated at a certain temperature is used as the product deteriorated by heating, and the relationship between the hardness of the product A and the Larson mirror parameter is obtained. Also good. Or using two types of products A heated at a certain temperature and a product B heated at a different temperature, or three or more types of products heated at different temperatures, the hardness and Larson mirror in each of these products A relationship with parameters may be obtained, and a relationship common to these products may be obtained. For example, in Example 1 of the present application, two types of products, a product heated at 525 ° C. and a product heated at 550 ° C., were used, and the approximate curve shown in FIG. 1 was obtained as a relationship common to these products.

Similarly, the hardness of the second product is measured, and further, the Larson mirror parameter LMP is calculated from the heating temperature, heating time, and hardness of the second product.
A second relationship between the hardness of the second product thus obtained and the Larson mirror parameter is determined. If this relationship is made into a graph, for example, it becomes a curve.
In determining the relationship between the hardness of the second product and the Larson mirror parameter, only the product a heated at a certain temperature and pressurized at a certain pressure is used as a product deteriorated by heating and pressurization. You may obtain | require the relationship between hardness and a Larson mirror parameter. Or two types of products b heated at a certain temperature and pressurized at a certain pressure and products b heated at a temperature different from a certain temperature and pressurized at a pressure different from a certain pressure, or respectively Using three or more types of products heated at different temperatures and pressurized at different pressures, the relationship between hardness and Larson mirror parameters in each product may be obtained, and a relationship common to these may be obtained. For example, in Example 1 of the present application, two types of products, a product heated at 525 ° C. and pressurized at 240 MPa and a product heated at 550 ° C. and pressurized at 145 MPa, are common to these products. As a relationship, an approximate curve shown in FIG. 1 was obtained.
In addition, when the relationship common to these is calculated | required using 2 or more types of products as a 2nd product, it is preferable that the lifetime of these 2 or more types of products is comparable. The same degree means that the lifetimes of two or more types of products are preferably within 20% of each other, and more preferably within 10% of each other. A person skilled in the art can appropriately set the temperature and pressure applied to each product so that two or more types of products have the same life.

Using the first relationship between the hardness of the first product and the Larson mirror parameter and the second relationship between the hardness of the second product and the Larson mirror parameter obtained in this way, The difference between the hardness of the first product deteriorated by heating and the hardness of the second product deteriorated by heating and pressurization in the Larson mirror parameter is obtained. For example, when the hardness of the first product is 191 HV and the hardness of the second product is 190 HV when the Larson mirror parameter is 19.0, the hardness of the first product and the first The difference between the hardness of the two products is 1.

Next, by performing this operation with a plurality of Larson mirror parameters, the third relationship between the hardness difference between the two products and the hardness of the second product is obtained. It is preferable that the obtained relationship is substantially proportional at least in part, and desirably in whole. That is, when a calibration curve representing this relationship is created, it becomes a substantially straight line at least partially, preferably as a whole.

The accuracy of the creep remaining life prediction method according to the present invention can be evaluated based on whether or not the third relationship between the hardness difference between the two products and the hardness of the second product is proportional. . For example, if there is a proportional relationship between the hardness difference between the two products and the hardness of the second product in the entire measured region, the creep remaining life prediction method according to the present invention is applied to the entire region. By using it, the creep remaining life of a product having a bainite structure can be accurately measured.
On the other hand, for example, in the region where the hardness of the second product is 150 or more, the relationship between the hardness difference between the two products and the hardness of the second product is proportional, but the hardness of the second product is In the region of less than 150, if this relationship is an exponential function or the like and is not proportional, by using the method for predicting the remaining creep life according to the present invention when the hardness of the product to be predicted is 150 or more, It can be seen that the creep remaining life of the product can be accurately predicted. In this case, although the accuracy decreases in the region where the hardness of the product to be predicted is less than 150, the creep remaining life of the product can be predicted using the creep remaining life prediction method according to the present invention. Alternatively, the remaining creep life of the product may be predicted using known alternative methods.

Thus, in the method for predicting the remaining creep life according to the present invention, the third relationship between the hardness difference between the first product and the second product and the hardness of the second product is proportional. However, it is possible to evaluate to what extent the remaining creep life can be predicted in a product having a target bainite structure. For this reason, it is possible to prevent an accident such as the target product being damaged early against the prediction.

Furthermore, the fourth relationship between the hardness of the second product and the damage rate is obtained by converting the hardness of the second product into the damage rate of the second product when the hardness is given.

Then, using the third relationship and the fourth relationship, the fifth relationship between the difference in hardness between the two products and the damage rate of the second product is obtained. It is preferable that the obtained relationship is substantially proportional at least in part, and desirably in whole. That is, when a calibration curve representing this relationship is created, it becomes a substantially straight line at least partially, preferably as a whole.

Similar to the third relationship between the hardness difference between the two products and the hardness of the second product, the fifth relationship between the hardness difference between the two products and the damage rate of the second product is proportional. The accuracy of the creep remaining life prediction method according to the present invention can be evaluated depending on whether or not it is present. For example, if the relationship between the hardness difference between the two products and the damage rate of the second product is proportional to the total damage rate, the prediction is made by using the creep remaining life prediction method according to the present invention. Regardless of the value of the damage rate of the target product, the creep remaining life of the product having a bainite structure can be accurately measured.
On the other hand, for example, in the region where the damage rate of the second product is 0.8 or less, the relationship between the hardness difference between the two products and the damage rate of the second product is proportional. In a region where the damage rate is greater than 0.8, when this relationship is not an exponential function or the like and is not proportional, if the damage rate of the product to be predicted is 0.8 or less, the remaining creep life according to the present invention It can be seen that the creep remaining life of the product can be accurately predicted by using this prediction method. In this case, when the damage rate of the product to be predicted is greater than 0.8, the accuracy decreases, but the creep remaining life of the product is predicted using the method for predicting the remaining creep life according to the present invention. Alternatively, the remaining creep life of the product may be predicted using a known alternative method.

Thus, the method for predicting the remaining creep life according to the present invention is based on whether the difference in hardness between the first product and the second product and the damage rate of the second product are in a proportional relationship. In a product having a bainite structure, it is possible to evaluate to what extent the remaining creep life can be predicted. For this reason, it is possible to prevent an accident such as the target product being damaged early against the prediction.

The creep remaining life prediction method according to the present invention includes the third relationship between the difference in hardness between the first product and the second product and the hardness of the second product, and the two products. By using the fifth relationship between the difference in hardness and the damage rate of the second product, the remaining creep life of the product having a bainite structure can be predicted. That is, the third relationship is used to determine the difference in hardness between products from the hardness of the product that predicts the creep remaining life, and the fifth relationship is used to determine the difference in hardness obtained. By obtaining the damage rate of the product to be obtained, the damage rate of the product that predicts the remaining creep life can be obtained.

In addition, the method for creating a calibration curve used in the creep remaining life prediction method according to the present invention is the difference between the hardness difference between the first product and the second product and the hardness of the second product obtained in this way. A calibration curve representing the third relationship and a calibration curve representing the fifth relationship are obtained using the relationship of 3 and the fifth relationship between the difference in hardness between the two products and the damage rate of the second product. Can be created.

Hereinafter, using the method for predicting the remaining life of creep according to the present invention as an example of the case where a product having a bainite structure, which is heated and pressurized by being used as a boiler pipe, is used as a prediction target, A method for predicting the lifetime will be described.
First, the hardness of the boiler piping is measured. Next, the value of the measured hardness is substituted for the hardness of the second product in the “third relationship between the hardness difference of the first product and the second product and the hardness of the second product”. To obtain the difference in hardness corresponding to the measured value. By substituting the value of the difference in hardness corresponding to the measured value into the difference in hardness between the two products in the “fifth relationship between the difference in hardness between the two products and the damage rate of the second product”, The damage rate corresponding to the measured value can be obtained. From the obtained damage rate, it is possible to predict the remaining life of the pipe of the hoiler that is the prediction target.

The creep remaining life prediction method according to the present invention includes “a third relationship between the hardness difference between the first product and the second product and the hardness of the second product”, and “the difference in hardness between the two products. And the fifth relationship between the damage rate of the second product and the remaining life of the product having a bainite structure is predicted. As is apparent from the fact that neither temperature nor pressure parameters are used in both of the relations based on the above, the method for predicting the remaining creep life according to the present invention is based on the temperature applied to the first product and the second product. Even if the product is used under conditions of temperature and pressure different from the pressure, the remaining creep life can be accurately predicted using these relationships.

[Example 1]
A deterioration test due to thermal aging and an internal pressure creep test were performed using a cylindrical tube (outer diameter φ56.5 mm, inner diameter 47.5 mm, length 35.0 mm) made of chromium molybdenum steel material and having a bainite structure as a sample. The deterioration test by thermal aging is performed under the condition of a temperature of 525 ° C. (Test 1) or 550 ° C. (Test 2), and the internal pressure creep test is performed by applying an internal pressure of 240 MPa when the temperature is 525 ° C. (Test 3). When the temperature was 550 ° C., an internal pressure of 145 MPa was applied (Test 4). Note that the life of the sample in Test 3 and the life of the sample in Test 4 are within 10% of each other and are almost the same.

For each test, when the damage rate was 0.19, 0.26, 0.50, 0.70, 0.80 and 0.90, Vickers hardness was measured at 10 points of the sample, and the average was obtained. . The relationship between the obtained average hardness and the Larson mirror parameter is shown in FIG. Incidentally, Larson-Miller parameter LMP is, LMP = T (C + logt r), in the Expression, T is heating temperature expressed in absolute temperature (K), _{t r} is the heating time (h), C is a constant 20 ].
As shown in FIG. 1, between the approximate curve obtained from the measurement result of degradation due to thermal aging (Tests 1 and 2) and the approximate curve obtained from the measurement result of degradation due to internal pressure creep (Tests 3 and 4), There was a difference in hardness for the same LMP. The difference in hardness was calculated as ΔH, and the relationship between the calculated ΔH and the hardness at the time of deterioration due to internal pressure creep when the ΔH was given was obtained. The results are shown in FIG. As is clear from FIG. 2, it is shown that ΔH and the hardness at the time of deterioration due to internal pressure creep are in a proportional relationship.
Furthermore, the result of converting the hardness at the time of deterioration due to internal pressure creep in FIG. 2 into the damage rate when the hardness is given is shown in FIG. FIG. 3 shows the relationship between ΔH and the damage rate. As is clear from FIG. 3, the relationship between ΔH and the damage rate is also proportional.

[Example 2]
In Example 2, the remaining creep life of a hollow tube having a bainite structure was predicted using FIGS. 2 and 3 created in Example 1. FIG.
Piping (STPA 22, JIS standard G 3457 “arc-welded carbon steel pipe for piping”) made of chromium molybdenum steel was slowly bent while heating so that it could be used in a boiler of a thermal power plant. When the structure of the bent part of the processed piping was examined with a transmission electron microscope (TEM), a bainite structure was generated. An internal pressure of 145 MPa was applied to the pipe thus processed at a temperature of 550 ° C.
When a certain time had elapsed, the Vickers hardness of the bent part of the pipe was measured and found to be 190 HV. From FIG. 2, ΔH at 190 HV is determined to be 1.0, and from FIG. 3, the damage rate when ΔH is 1.0 is determined to be 0.10. Could be predicted to be 0.10. In other words, it was possible to predict that the remaining life of the bent portion of this pipe was about 9 times the service time up to now.

In the present embodiment, the same temperature and pressure were applied when creating FIGS. 1 to 3 and when actually estimating the remaining life, but the parameters of temperature and pressure in FIGS. As is clear from the fact that it is not used, even if the pipes are used under different temperature and pressure conditions, as long as they are made of the same material, the remainder will be described with reference to FIGS. Life expectancy can be predicted.

[Example 3]
In Example 1, when the damage rate is 0, when the damage rate is about 0.5 and about 0.9 in Test 2, and when the damage rate is about 0.5 in Test 4, the structure of the sample by TEM Inspected. Specifically, the structure was examined at two magnifications of each sample at a magnification of 10,000 times and 40 million times centering on the inside of the crystal grains.
FIG. 4 shows the results when the damage rate is 0, FIG. 5 shows the results when the damage rate in test 2 is 0.5, FIG. 6 shows the results when the damage rate in test 2 is 0.9, and The results when the damage rate in Test 4 is 0.5 are shown in FIG.

As shown in FIG. 4, when the damage rate is 0, it can be seen that there are many dislocations appearing as black lines in the crystal grains, and the entire sample is solid. On the other hand, as shown in FIGS. 5 and 6, it can be seen that in the sample deteriorated by thermal aging, the dislocation decreased as the heating time increased, and the sample became softer. Further, as shown in FIG. 5 and FIG. 7, the damage rate is approximately the same at about 0.5. However, comparing the sample deteriorated by thermal aging with the sample deteriorated by internal pressure creep, the sample deteriorated by internal pressure creep It can be seen that there were fewer dislocations and the tissue became softer.
In this way, between samples degraded by thermal aging and samples degraded by internal pressure creep, even if samples made of the same material are compared at the same damage rate, Differences were also shown by histology.

Claims

A method for preparing a calibration curve used in a method for predicting the remaining creep life of a product having a bainite structure,
Obtaining a first relationship between hardness and Larson mirror parameters of a first product having a bainite structure and deteriorated by heating;
Determining a second relationship between hardness and Larson mirror parameters of a second product having a bainite structure and degraded by heating and pressing;
By using the first relationship and the second relationship to obtain the difference between the hardness of the first product and the hardness of the second product at a predetermined Larson mirror parameter, the difference between the hardness of the second product and the difference is obtained. Creating a calibration curve representing the relationship of 3;
Determining a fourth relationship between hardness and damage rate of the second product;
Creating a calibration curve representing the fifth relationship between the difference and the damage rate of the second product using the third relationship and the fourth relationship.
A method for predicting a remaining creep life of a product having a bainite structure, wherein a calibration curve created by the creating method according to claim 1 is used.
A method for predicting the remaining creep life of a product having a bainite structure,
Obtaining a first relationship between hardness and Larson mirror parameters of a first product having a bainite structure and deteriorated by heating;
Determining a second relationship between hardness and Larson mirror parameters of a second product having a bainite structure and degraded by heating and pressing;
Using the first relationship and the second relationship, the difference between the hardness of the second product and the difference between the hardness of the first product and the hardness of the second product in a predetermined Larson mirror parameter is obtained. Obtaining a third relationship;
Determining a fourth relationship between hardness and damage rate of the second product;
Using a third relationship and a fourth relationship to determine a fifth relationship between the difference and the damage rate of the second product;
Using the third relationship to obtain the corresponding difference from the hardness of the product that predicts the remaining creep life,
A method for predicting a remaining creep life, comprising: calculating a damage rate of the corresponding product from the obtained difference using a fifth relationship.
The range of hardness that is substantially proportional among the third relationships is used to obtain the difference corresponding to the hardness of the product that predicts the creep remaining life. The prediction method of the creep remaining life as described.
5. The creep according to claim 3, wherein a range of a difference that is substantially proportional among the fifth relationships is used to obtain a damage rate of a product that predicts the creep remaining life. How to predict the remaining life.
The creep remaining life prediction method according to any one of claims 3 to 5, wherein the products for predicting the remaining creep life, the first product, and the second product are hollow tubes.
6. The creep remaining life prediction method according to claim 5, wherein the product for which the creep remaining life is predicted is a pipe for a boiler having a bent portion.
The method for predicting a remaining creep life according to claim 6 or 7, wherein the pressurization is performed by applying an internal pressure.
The creep remaining life prediction method according to any one of claims 3 to 8, wherein the hardness is Vickers hardness.
The creep remaining life prediction method according to any one of claims 3 to 9, wherein the temperature applied to the first product and the temperature applied to the second product are the same.