TW202338341A - Piping life prediction method - Google Patents

Abstract

This piping life prediction method includes: a step of polishing the surface of a piping which is formed from stainless steel and through which a high-temperature fluid flows; a step of taking a replica sample from the surface of the polished piping; a step of acquiring the quantity of microvoids formed in the replica sample by observing the replica sample with a scanning electron microscope or a laser microscope; and a step of predicting the service life of the piping on the basis of the quantity of the microvoids formed.

Description

Pipe life prediction method

This disclosure is about the life prediction method of piping. This application claims priority based on Japanese Patent Application No. 2022-055622 filed in Japan on March 30, 2022, and the content is incorporated herein by reference.

The piping through which high-temperature fluid flows in boilers, etc. is affected by the pressure and heat of the high-temperature fluid. Therefore, in order to maintain the piping at an appropriate time, it is necessary to predict the piping life until creep damage or the like occurs in the piping and the piping becomes unusable. Regarding the prediction of piping life, various non-destructive inspection methods can be used.

As one of such non-destructive inspection methods, for example, Patent Document 1 discloses a flaw detection inspection based on ultrasonic flaw detection or the like on a target portion of a piping.

As another non-destructive inspection method, there is a method of measuring the outer diameter of piping. This method focuses on the fact that piping will be deformed by bulging due to the influence of pressure and heat after long-term use. By measuring the outer diameter of the piping, the bulging on the surface of the piping is understood, and the life of the piping can be estimated. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2021-6801

[Problem to be solved by the invention]

However, for piping made of materials with high strength at high temperatures, the measurable change in outer diameter occurs late to the end of the life of the piping. Therefore, it is difficult to grasp the life of the pipe earlier by measuring the outer diameter of the pipe.

The purpose of this disclosure is to provide a pipe life prediction method that can predict the pipe life earlier. [Technical means to solve problems]

The disclosed method of predicting the life of pipes is a method of predicting the life of pipes made of stainless steel through which high-temperature fluids flow. The method includes: a process of grinding the surface of the pipe, and sampling from the surface of the pipe after grinding. The process of copying a sample, the process of observing the copied sample using a scanning electron microscope or a laser microscope and obtaining the amount of microvoids produced in the copied sample, and predicting the piping based on the amount of microvoids produced. The process of service life. [Effects of the invention]

According to the piping life prediction method disclosed in the present disclosure, the piping life can be predicted earlier.

Hereinafter, a mode for implementing the pipe life prediction method of the present disclosure will be described with reference to the attached drawings. However, the present disclosure is not limited to this embodiment.

(Piping) The piping life prediction method of this embodiment predicts the life of piping through which high-temperature fluid flows. As shown in FIG. 1 , the pipe 1 as the target of life prediction has an annular cross section and extends continuously in a cylindrical shape in the extending direction. The piping 1 is used in a machine through which high-temperature steam, such as a boiler or the like, flows as a high-temperature fluid. The piping 1 is used in a power plant, for example. The piping 1 is made of stainless steel that is not easily corroded even if it is exposed to high-temperature steam. The pipe 1 is, for example, a pipe made of high-strength stainless steel with an outer diameter of approximately 30 mm to 40 mm and a wall thickness of approximately 3 mm to 4 mm. The pipe 1 is affected by the heat and pressure of the high-temperature fluid flowing in the pipe 1 .

The inventors of the present invention discovered that in the pipe 1 made of stainless steel through which a high-temperature fluid flows, micropores 101 are present at an earlier time than when creep damage or the like occurs and the life of the pipe 1 is reached. Occurs on the surface of pipe 1. Here, microvoids refer to extremely small defects of 1 nm to 1 μm that are generated after the middle period of life. Hereinafter, defects of this size will be referred to as "microvoids" in this specification.

Specifically, as shown in FIG. 2 , the inventors of the present invention found that when the period from the start of use of the pipe 1 to the occurrence of creep damage and the end of the life of the pipe 1 is set to 100%, the life span ratio is 50%. , there will be no holes in pipe 1. Then, as time passes and the lifetime ratio reaches about 60%, micropores 101 begin to be generated in the pipe 1 near the surface 1f of the outer side Dro facing the radial direction Dr. As time passes, at a stage where the lifetime ratio is about 80%, holes 102 larger than the microholes 101 will be generated, and the range of the holes 102 will also expand from the surface 1f toward the inner side Dri in the radial direction Dr. As time passes, at a stage where the lifetime ratio is about 90%, a plurality of holes 102 are connected to cause microcracks 103 to be generated. In this way, when many holes 102 and microcracks 103 are generated (for example, the life ratio is 80% or 90%), the outer diameter of the pipe 1 begins to change to a measurable extent. On the other hand, at the stage where only the micropores 101 are generated (for example, the lifetime ratio is 60%), the outer diameter of the pipe 1 cannot change to a measurable extent.

Here, in the past, the hole size that could be detected using optical microscopes and ultrasonic flaw detection was, for example, 0.2 μm or more. As shown in FIG. 3 , the size of the holes 102 at the stage where the lifetime ratio is about 80% is about 1 μm to 20 μm, and the occurrence of the holes 102 can be detected based on observation with an optical microscope. On the other hand, the size of the micropores 101 generated at the stage where the lifetime ratio is about 60% is 1 nm to 1.0 μm, and it is difficult to detect the micropores 101 based on observation with an optical microscope. Therefore, it has been conventionally considered that no detectable damage occurs inside the pipe 1 until the outer diameter of the pipe 1 begins to change to a measurable extent. However, the inventors of the present case discovered that the microvoids 101 were generated at an earlier stage than the time when the pores 102 of a size detectable by observation based on optical microscopy or flaw detection based on ultrasonic flaw detection were generated.

(Piping life prediction method) In the pipe life prediction method S10 of this embodiment shown below, the life of the pipe 1 is predicted by detecting the occurrence of micropores 101 that are difficult to detect using an optical microscope. As shown in FIG. 4 , the pipe life prediction method S10 includes: a process of grinding the pipe S11 , a process of taking a replica sample S12 , a process of obtaining the amount of micropores produced S13 , a process of predicting the service life of the pipe S14 , and creating Master data process S21.

In the pipe polishing step S11, the surface 1f of the pipe 1 is polished. The surface 1f of the pipe 1 is preferably polished by a method that can suppress the falling of precipitates precipitated on the surface 1f and enable the detection of the micropores 101. To polish the surface 1f of the pipe 1 in this way, for example, CMP (Chemical Mechanical Polishing) using colloidal silica or electrolytic polishing using oxalic acid can be used.

In the process of collecting the replica sample S12, the replica sample is collected from the surface 1f of the polished pipe 1. The duplicate sample is collected in a manner that does not damage the polished pipe 1. Replicate samples are collected using the well-known replica method. For example, a liquid resin is applied to the surface 1 f of the pipe 1 and the resin is hardened, thereby obtaining a replica sample in which the surface 1 f of the pipe 1 is transferred. Furthermore, the solid polymer is heated and pressurized to be molded on the surface 1f of the pipe 1, thereby obtaining a replica sample with the surface 1f of the pipe 1 transferred. If a replica sample is taken from the surface of the polished pipe 1, if micropores 101 are generated on the surface 1f of the pipe 1, the micropores 101 will be transferred to the replica sample.

In step S13 of obtaining the amount of microvoids, the replicated sample taken in step S12 is observed using a scanning electron microscope (SEM) or a laser microscope, thereby obtaining the amount of microvoids in the replicated sample. . Micropores 101 of the above-mentioned size can be fully observed using a scanning electron microscope or a laser microscope. Figure 5 is an example of an observation image obtained by observing a replicated sample using a scanning microscope. For comparison, FIG. 6 is an example of an observation image obtained by observing the surface 1f of the actual pipe 1 using a scanning microscope. As shown in FIGS. 5 and 6 , by observing the replica sample obtained as described above using a scanning electron microscope or a laser microscope, the occurrence of micropores 101 similar to those in the actual pipe 1 can be observed. In step S13, as the amount of microvoids 101 produced in the replica sample, for example, the number of microvoids 101 per unit area, that is, the hole number density, is obtained.

In the step S14 of predicting the service life of the pipe, the service life of the pipe 1 is predicted based on the generation amount of micropores obtained in the step S13. In step S14 of this embodiment, the amount of microvoids produced in step S13 is compared with the data showing the correlation between the amount of microvoids produced and the service life of pipe 1, thereby predicting the pipe 1. service life. In step S14, the actual service life of the pipe 1 is predicted by comparing the occurrence state (amount of occurrence) of the micropores 101 in the actual pipe 1 with the master data described below. Specifically, among the plurality of data included in the master data, it is determined that the production amount of microvoids 101 obtained in step S13 is closest to the actual production state (production amount) of microvoids 101 in the pipe 1 information. Then, the service life associated with the determined data is obtained as the service life of the pipe 1 .

When the master data is used in step S14, the step S21 is first executed to create the master data before the step S14 of predicting the service life of the pipe 1 is executed. In the step S21 of creating master data, master data used in the step S14 of predicting the service life of the pipe 1 is created. The master data is created using a test body that simulates the piping 1 instead of the actual piping 1. In this case, a plurality of test bodies simulating a plurality of pipes 1 in different usage states are used. The test body has the same material, diameter, and wall thickness as the pipe 1. Conduct creep tests and observations on multiple test specimens to obtain the data necessary to create master data.

The test performed on the test body is a creep test that simulates the flow of a high-temperature fluid at a predetermined temperature and applies stress. At this time, for example, the elapsed time from the start of the test is divided into a plurality of different stages, and the occurrence state of the micropores 101 on the surface of the test object in each stage is observed. Furthermore, the temperature and applied stress during the test were changed, and the occurrence state of the micropores 101 on the surface of the test object at each stage was observed. The test is continued until the test body finally breaks due to creep damage. Thereby, the test is carried out using a plurality of test bodies simulating a plurality of pipes 1 in different usage states.

Furthermore, the test performed on the test body is preferably conducted under conditions of temperature and stress that are more severe than those of the high-temperature fluid flowing through the actual pipe 1 . In this way, master data can be created in a shorter time.

When observing the test object, first, the surface of the test object is polished using the same polishing method as in step S11 of polishing the pipe. Then, similarly to the step S12 of obtaining the replica sample, a replica sample of the surface of the test object is obtained. Next, similar to the step S13 of obtaining the amount of microvoids 101, the obtained replica sample of the test body is observed using a scanning electron microscope or a laser microscope, and the amount of microvoids 101 in the replica sample is obtained. . In this way, the data of the plurality of replicate samples are obtained from the surfaces of the plurality of test bodies simulating the plurality of pipes 1 in different usage states. For another example, the life ratio (T/Tb) of each test body is calculated based on the elapsed time T from the time of observation of each test body and the elapsed time Tb from the start of the test to fracture. The elapsed time T during observation is the timing to obtain the replica sample and the amount of microvoids 101 generated. Then, a replica sample is obtained from the surface of the test object according to the lifetime ratio (T/Tb). In this way, data on the temporal change in the amount of microvoids 101 produced in the test body are obtained. That is, the correlation between the temporal change in the amount of microvoids 101 generated and the elapsed time (lifetime) until fracture is obtained as the main data.

FIG. 7 shows an example of the specific conditions of the test object when the master data is created in the above-mentioned step S21. As shown in FIG. 7 , for example, a creep test is performed at 750° C. and 61 MPa is applied to the test body. The test is interrupted every 1000 hours from the start of the test, a replica sample is taken from the surface of the test object, and the state of the replica sample (surface condition of the test object) is observed using a laser microscope. The test body broke due to creep damage 11911 hours after the start of the test. Therefore, the master data is created by correlating the generation amount of microvoids 101 at 7000 hours, 8000 hours, and 9000 hours from the start of the test before fracture and the lifetime ratio.

In addition, Figure 7 is only an example of the specific conditions of the test body when creating the master data. In fact, it is a test in which the test body when creating the master data is appropriately selected according to the type of piping 1 to extend the life and the environment in which it is used. condition.

In this way, the obtained production amount of micropores 101 is compared with the master data to predict the service life of the pipe 1 .

(Effect) In the method S10 for predicting the life of the pipe having the above structure, the surface 1 f of the pipe 1 is polished, and a replica sample is taken from the polished surface of the pipe 1 . When micropores 101 are generated on the surface 1f of the pipe 1, the micropores 101 are transferred to the replica sample. By observing the replicated sample with the transferred microholes 101 using a scanning electron microscope or a laser microscope, the amount of micropores produced in the replicated sample can be obtained with high precision. According to the above new findings, that is, micropores 101 are generated at an earlier stage than when the size of the pores grows to be detectable by observation based on optical microscopy or flaw detection based on ultrasonic flaw detection, and by observing micropores hole 101 to obtain the amount of microholes 101 produced. In this way, the service life of the piping 1 can be predicted at an earlier time than measurement of the outer diameter of the piping 1, observation using an optical microscope, or flaw detection using ultrasonic flaw detection. Therefore, the life of the pipe 1 can be predicted earlier. In this way, it becomes possible to predict the life span of the pipe 1 in the medium term, which was difficult to evaluate in the past. Furthermore, by enabling mid-term life prediction, various constructions such as replacement construction of the piping 1 during inspection can be efficiently planned.

In step S14 of predicting the service life of the piping, the service life of the piping 1 is predicted based on the master data indicating the correlation between the amount of microvoids generated and the service life of the piping 1 and the actual amount of microvoids generated. By creating master data in advance, the correlation between the amount of micropores 101 generated and the service life of the pipe 1 can be grasped in advance with high accuracy. As a result, the service life of the pipe 1 can be predicted more easily and accurately.

Replicate samples are also obtained from the surfaces of a plurality of test bodies simulating a plurality of pipes 1 in different usage conditions. Furthermore, the amount of microvoids produced in replicate samples of a plurality of test bodies is obtained to create master data. By creating the master data in this way, it is possible to obtain data close to the occurrence state of the micropores 101 of the actual pipe 1 in different usage conditions. By predicting the service life of the piping 1 based on the master data obtained in this way, the service life of the piping 1 can be predicted with higher accuracy.

(Other embodiments) As mentioned above, the embodiment of the present disclosure has been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiment and includes design changes within the scope that does not deviate from the gist of the present disclosure.

Furthermore, in the above-mentioned embodiment, the procedure of the life prediction method S10 of the pipe 1 is explained, but the work content and the details of the procedure in each step can be changed as appropriate.

For example, the prediction of the life of the pipe 1 is not limited to using master data indicating the correlation between the amount of micropores generated and the service life of the pipe. In this case, the process S14 of predicting the service life of the piping may be implemented instead of the process S21 of creating the master data. At this time, in the step S14 of predicting the service life of the piping, the data on the actual amount of micropores 101 generated at the time of measuring the piping in the past is accumulated in a storage (storage) in advance, and the accumulated data is used as the representation of the micropores. Data on the correlation between the production volume and the service life of piping 1. Therefore, the generation amount of microvoids 101 can be compared with the accumulated data to predict the service life.

In addition, when the process S21 of creating master data is implemented, when the piping 1 is regularly inspected a plurality of times, the process S21 of creating master data may be implemented only once, or may be implemented every time. That is, the same master data created in advance can be used for each periodic inspection of the piping 1, or the master data can be newly created every time the piping 1 is regularly inspected.

In addition, the step S21 of creating the master data is not limited to executing tests on a plurality of test bodies simulating a plurality of pipes 1 in different usage states to create the master data. In the step S21 of creating the master data, for example, the master data may be created through simulation instead of actual testing.

The high-temperature fluid flowing through the inside of the pipe 1 is not limited to steam. It may also be a high-temperature gas or liquid that causes damage such as corrosion to the pipe 1 made of stainless steel.

Furthermore, the polishing method in step S11 of polishing the pipe is not limited to CMP using colloidal silica or electrolytic polishing using oxalic acid. As for the polishing method, it is preferable to try different types of abrasives and polishing methods on the pipe 1 and the test body in advance, and then use the most appropriate polishing method for the pipe 1 to be predicted.

＜Note＞ The life prediction method S10 of the pipe 1 described in the embodiment can be grasped as follows, for example.

(1) The life prediction method S10 of the pipe 1 of the first aspect is a method S10 for predicting the life of the pipe 1 made of stainless steel through which a high-temperature fluid flows, and includes the step S11 of grinding the surface 1 f of the pipe 1 Step S12 of taking a replicated sample from the surface 1f of the polished pipe 1, and observing the replicated sample using a scanning electron microscope or a laser microscope to obtain the amount of micropores produced in the replicated sample S13 , and a step S14 of predicting the service life of the pipe 1 based on the amount of micropores produced.

The inventors of the present case discovered that the pipe 1 made of stainless steel through which a high-temperature fluid flows is affected by the temperature and pressure of the high-temperature fluid over time, causing generation near the surface 1f in the radial direction Dr of the pipe 1 Microvoids 101. The micropores 101 start to be generated earlier than the time when the outer diameter of the pipe 1 changes to a measurable degree. Compared with the size of holes that can be detected by optical microscope observation and ultrasonic flaw detection, the micropores 101 are very small. That is, microvoids 101 are generated at an earlier stage than when the size of the pores grows to be detectable by observation based on optical microscopy or flaw detection based on ultrasonic flaw detection.

The life prediction method S10 of the pipe 1 is based on the above-mentioned new discovery to obtain the amount of micropores in the replica sample. This makes it possible to predict the service life of the pipe 1 at an earlier time than measurement of the outer diameter of the pipe 1, observation with an optical microscope, or flaw detection with ultrasonic flaw detection. Therefore, the life of the pipe 1 can be predicted earlier.

(2) The life prediction method S10 of the piping 1 in the second aspect is the life prediction method S10 of the piping 1 in (1), and further includes a step S21 of creating master data. In the step S21 of creating the master data, Master data indicating the correlation between the occurrence amount of the micropores and the service life of the piping 1 is prepared. In the step S14 of predicting the service life of the piping 1, the prediction is made based on the master data and the occurrence amount of the microvoids. The service life of the aforementioned pipe 1.

By creating master data in advance, the correlation between the amount of micropores 101 generated and the service life of the pipe 1 can be grasped in advance with high accuracy. As a result, the service life of the pipe 1 can be predicted more easily and accurately.

(3) The life prediction method S10 of the piping 1 in the third aspect is based on the life prediction method S10 of the piping 1 in (2). In the step S21 of creating the aforementioned master data, a plurality of the aforementioned pipings are simulated in different usage states. Obtain replica samples from the surfaces of a plurality of test objects in 1, and obtain the production amount of micropores in the replica samples of a plurality of the test objects, thereby creating the aforesaid master data.

By creating the master data in this way, it is possible to obtain data close to the occurrence state of the micropores 101 in the actual piping 1 in different usage conditions. By predicting the service life of the pipe 1 based on the master data obtained in this way, the service life of the pipe 1 can be predicted with higher accuracy. [Industrial Applicability]

According to the piping life prediction method disclosed in the present disclosure, the piping life can be predicted earlier.

1:Piping 1f: surface 101:Micropores 102:hole 103:Micro cracks Dr:radial direction Dri: inside Dro: outside S10: Life prediction method of piping S11: Process of grinding pipes S12: The process of taking duplicate samples S13: The process of obtaining the amount of microvoids produced S14: The process of predicting the service life of piping S21: The process of creating master data T: elapsed time during observation Tb: The elapsed time from the start of the test to the break

[Fig. 1] is a cross-sectional view showing an example of a piping that is a life prediction target of the piping life prediction method according to the embodiment of the present disclosure. [Figure 2] shows the occurrence state of microvoids, holes, and microcracks in the above-mentioned piping. [Figure 3] shows the correlation between the size of holes and the number density of holes produced in steam piping with different life ratios. [Fig. 4] is a flowchart showing the procedure of the pipe life prediction method according to the embodiment of the present disclosure. [Figure 5] is an example of an observation image obtained by observing a replicated sample using a scanning microscope. [Fig. 6] is an example of an observation image obtained by observing the actual piping surface with a scanning microscope. [Figure 7] shows an example of the specific conditions of the test body when master data is created according to the above-mentioned piping life prediction method.

Claims (3)

A method of predicting the life of piping, which is a method of predicting the life of piping made of stainless steel through which high-temperature fluids flow, and includes: The process of grinding the surface of the aforementioned pipes, The process of taking a replica sample from the aforementioned surface of the aforementioned piping after grinding, The process of observing the aforementioned replicated sample using a scanning electron microscope or a laser microscope and obtaining the amount of micropores produced in the aforementioned replicated sample, and A process of predicting the service life of the piping based on the amount of micropores produced. The method for predicting the life of piping as described in claim 1 further includes the process of creating the aforementioned master data, In the process of creating the aforementioned master data, master data showing the correlation between the amount of the aforementioned micropores and the service life of the aforementioned piping is created in advance. In the process of predicting the service life of the aforementioned pipes, the service life of the aforementioned pipes is predicted based on the aforementioned master data and the aforementioned amount of micropores produced. The life prediction method of piping as described in claim 2, wherein, In the process of creating the aforementioned master data, replicated samples are obtained from the surfaces of a plurality of test bodies simulating different usage conditions of the aforementioned pipes, and the amount of micropores produced in the replicated samples of the plurality of aforementioned test bodies is obtained. This creates the aforementioned master data.

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