Method for evaluating and grading oxygen absorption corrosion degree of nuclear power plant fire extinguishing system pipeline

Abstract

The present invention relates to the field of fire protection, and in particular to a method for assessing and grading the degree of oxygen absorption corrosion of pipelines in a nuclear power plant fire protection system. The method comprises: determining the environmental conditions of the pipelines of the fire water system; calculating the oxygen content of the fire water in a stagnant flow state inside the fire water pipeline based on the inner diameter of the pipeline and the dissolved oxygen concentration under normal temperature and pressure; obtaining data on the change of dissolved oxygen concentration under the effect of oxygen absorption corrosion based on simulation experiments, and fitting a function to obtain a functional relationship DO(t) of the change of dissolved oxygen concentration of the fire water with time under the effect of oxygen absorption corrosion of the fire water still water pipeline; and obtaining a functional relationship f(t) of the change of the corrosion rate of the fire water still water pipeline with time based on the relationship between the corrosion rate of the inner wall of the fire water still water pipeline and the dissolved oxygen concentration. O (t); Based on the corrosion data and dissolved oxygen concentration data of the fire water still water pipes in the nuclear power plant fire protection system, the oxygen absorption corrosion degree of the fire water still water pipes in the nuclear power plant fire protection system is assessed. This invention improves the theoretical basis and methods for fire water pipe corrosion degree assessment, and the data obtained is precise and the results are accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fire fighting, in particular to a method for evaluating and grading the oxygen absorption corrosion degree of a nuclear power plant fire fighting system pipeline. BACKGROUND

[0002] Fire fighting systems can quickly and effectively extinguish fires and control fire spread, preventing accidents from expanding and spreading, and minimizing the losses caused by accidents. The construction and use of fire fighting systems are an important part of the safety assurance system of nuclear power plants, which can provide necessary safety barriers and protection for nuclear power plants, ensuring safe and reliable operation of nuclear power plants. In nuclear power plants, fire fighting system pipelines carry important fire fighting tasks and play a crucial role in the safe and stable operation of the entire nuclear power plant. In nuclear power plants, pipelines may come into contact with corrosive substances, which can cause damage to the pipelines. Therefore, the materials of these pipelines must have corresponding corrosion resistance to ensure that they do not break or leak during long-term use.

[0003] The material of the fire water pipeline in the nuclear power plant is mainly carbon steel or galvanized carbon steel. Fire water and drinking water come from the same water source, but in most cases, the fire water pipe network system is in a relatively static and closed state. The internal corrosion of the fire water pipe under this condition has unique characteristics. After inspecting the internal corrosion condition of the fire water pipeline of a certain domestic nuclear power plant, it was found that the main problem of internal corrosion of the fire water pipeline was oxygen absorption corrosion.

[0004] The oxygen absorption corrosion inside the fire water pipeline is mainly due to the long-term static state of the fire water in the pipeline, which gradually reduces the dissolved oxygen concentration in the water, thereby promoting the oxidation reaction of iron elements. This corrosion forms a rust layer inside the fire water pipeline, which gradually thickens over time, affecting the flowability and pressure of the fire water.

[0005] Currently, there is only theoretical analysis of the influence of oxygen content in the static water pipeline in the nuclear power plant fire fighting system on the oxygen absorption corrosion rate of the pipeline, and there is no complete and reliable mathematical model that can simulate and analyze the oxygen absorption corrosion rate in the static water pipeline and evaluate the corrosion degree of the static water pipeline, which is insufficient to explain the corrosion degree of the fire water pipeline in the nuclear power plant fire fighting system under the stagnant flow state. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a method for evaluating and grading the oxygen absorption corrosion degree of a nuclear power plant fire fighting system pipeline, which obtains an effective and reliable mathematical model to evaluate the corrosion rate of the fire water static water pipeline and the corrosion evaluation of the fire water pipeline through specific tests and data analysis.

[0007] The present application provides a method for evaluating and grading the oxygen absorption corrosion degree of a nuclear power plant fire fighting system pipeline, comprising the following steps:

[0008] Step S1: determining the environmental condition of the fire water system pipeline;

[0009] Step S2: calculating the oxygen content M of the fire water in the fire water pipeline under the internal stagnant flow state according to the inner diameter of the pipeline and the dissolved oxygen concentration DO under the normal temperature and pressure environment O ;

[0010] According to the simulation test, the change data of the dissolved oxygen concentration under the oxygen absorption corrosion effect are obtained, and the function relationship formula DO(t) of the change of the dissolved oxygen concentration of the fire water with time t under the oxygen absorption corrosion effect of the fire water static water pipeline is obtained by fitting the function;

[0011] Step S3: according to the relationship between the corrosion rate of the inner wall of the fire water static water pipeline and the dissolved oxygen concentration under the condition that the oxygen content in the fire water static water pipeline is continuously reduced under the oxygen absorption corrosion effect, the function relationship formula f O (t) of the change of the corrosion rate f of the fire water pipeline with time t is obtained; O

[0012] Step S4: according to the corrosion data and the dissolved oxygen concentration data of the fire water static water pipeline of the nuclear power plant fire protection system, the oxygen absorption corrosion degree of the fire water static water pipeline of the nuclear power plant fire protection system is evaluated.

[0013] In a specific embodiment of the present application, the environmental condition of the fire water system pipeline is a temperature of 20℃, a pressure of one standard atmosphere, and the influence of other chemical elements is not considered.

[0014] In a specific embodiment of the present application, in the step S2, the calculation method of the oxygen content M O of the fire water in the fire water pipeline under the internal stagnant flow state is as follows:

[0015] M O =DO·V

[0016] V is the volume of the stagnant fire water in the fire water static water pipeline;

[0017] V=π·(d / 2) 2 ·L

[0018] Wherein, d is the inner diameter of the pipeline, and the unit is m;

[0019] L is the length of the pipeline, and the unit is m.

[0020] In a specific embodiment of the present application, the empirical formula for calculating the dissolved oxygen concentration DO is as follows:

[0021] DO=1.117·10 -6 e 1746.5 / T ·P​

[0022] T is temperature, unit is ℃;

[0023] P is pressure, unit is Pa.

[0024] In a specific embodiment of the present application, in the step S2, the simulation test is an oxygen absorption corrosion experiment in the fire-fighting system pipeline, specifically:

[0025] Blind plates are installed on both sides of the fire-fighting system pipeline, and fire-fighting water is injected into the pipeline to remove the pressure in the pipeline, so that it is in the normal pressure environment under the actual working condition, and is placed in the room temperature condition, the dissolved oxygen concentration is monitored in real time by the dissolved oxygen concentration sensor, and the data table is recorded.

[0026] In a specific embodiment of the present application, the data of the dissolved oxygen concentration changing with time in the data table is fitted according to the oxygen absorption corrosion formula, and a function relationship formula DO(t) of the dissolved oxygen concentration changing with time t under the action of oxygen absorption corrosion in the fire-fighting system static water pipeline is obtained:

[0027] DO(t)=α-m·exp(-t / n)

[0028] α is a correction coefficient of the dissolved oxygen concentration, m represents a carbon steel anti-oxygen corrosion parameter, and n is an oxygen absorption corrosion coefficient.

[0029] In a specific embodiment of the present application, the step S3 comprises:

[0030] A function relationship formula of the corrosion rate and the dissolved oxygen concentration is obtained:

[0031] f O (t)=K·DO(t)+β

[0032] In the formula, K is an oxygen absorption corrosion coefficient, and β is an oxygen absorption corrosion correction coefficient;

[0033] According to the relationship between the dissolved oxygen concentration and the pipeline inner wall corrosion under the action of oxygen absorption corrosion in the fire-fighting water static water pipeline, the function relationship formula of the dissolved oxygen concentration is fitted to obtain a function relationship formula f O (t) of the fire-fighting system static water pipeline changing with time t under the stagnant water state. O (t);

[0034] Combined with the function relationship formula of f O (t), a data table of the corrosion rate changing with time in the fire-fighting system static water pipeline under the stagnant water state is calculated.

[0035] In a specific embodiment of the present application, the step S4 specifically comprises:

[0036] Corrosion rate f in a fire water pipeline O Function relationship f changing with time t O The corrosion rate, corrosion time and internal corrosion thinning amount of the fire water pipeline are calculated by the function relationship (t);

[0037] According to the data of the change of the dissolved oxygen concentration with time, the days of complete oxygen consumption are obtained;

[0038] The corrosion data and the dissolved oxygen concentration data are compared, and the oxygen absorption corrosion degree of the fire static water pipeline of the nuclear power plant fire fighting system is evaluated.

[0039] Compared with the prior art, the nuclear power plant fire fighting system pipeline oxygen absorption corrosion degree evaluation grading method of the present application establishes a method for evaluating the oxygen absorption corrosion degree of the inner wall of the fire water pipeline based on a mathematical model, improves the theoretical basis and means for evaluating the corrosion degree of the fire water pipeline, and the data obtained is accurate and the result is accurate. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The corrosion degree evaluation method flow chart of the oxygen absorption corrosion of the static water pipeline of the nuclear power plant fire fighting system is shown;

[0041] Figure 2 The dissolved oxygen concentration change graph with time under the static water state of the static water pipeline of the nuclear power plant fire fighting system is shown;

[0042] Figure 3 The corrosion rate change graph with time of the oxygen absorption corrosion under the static water state of the static water pipeline of the nuclear power plant fire fighting system is shown. DETAILED DESCRIPTION

[0043] In order to further understand the present application, the embodiments of the present application are described below in conjunction with the examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not limitations of the present application.

[0044] The basic principle of oxygen absorption corrosion is:

[0045] In the fire fighting system pipeline, the inner surface of the pipeline in the static water state occurs oxygen absorption corrosion. When the metal occurs oxygen absorption corrosion, the anode is still Fe losing electrons and being oxidized to Fe 2+ ion, and the cathode impurity becomes oxygen electrode. In the cathode, the oxygen dissolved in the water film gets electrons, and the reaction formula is as follows:

[0046] Anode (Fe) Fe-4e = Fe 2+

[0047] Cathode (impurity) O2+H2O+4e = OH - .

[0048] In the present invention, the corrosion rate of a metal material refers to the weight lost by the metal material per unit area per unit time, or the average amount of thinning lost by the metal material per unit time.

[0049] The corrosion rate of the inner wall of the static water pipe of the nuclear power plant fire protection system is the amount of thinning of the inner wall of the pipe per unit time. The present invention uses mpy as the unit of thinning.

[0050] An embodiment of the present invention discloses a method for evaluating and grading the degree of oxygen absorption corrosion of pipelines in a nuclear power plant fire protection system, comprising the following steps:

[0051] Step S1: Determine the environmental conditions of the fire water system pipeline;

[0052] Only the corrosion effect of oxygen absorption corrosion on the fire water still water pipe is considered, without considering the influence of other chemical elements, and the environmental conditions of the fire water system pipe are ideal.

[0053] The temperature is 20°C and the pressure is one standard atmosphere, 100KPa.

[0054] Step S2: Calculate the oxygen content M of the fire water in the stagnant state inside the fire water pipe based on the inner diameter of the pipe and the dissolved oxygen concentration DO under normal temperature and pressure environment. O ;

[0055] The dissolved oxygen concentration DO calculation formula is as follows:

[0056] DO = 1.117·10 -6 e 1746.5 / T ·P

[0057] T is temperature, in °C;

[0058] P is pressure, unit is Pa.

[0059] Oxygen content M of fire water in stagnant state inside fire water pipe O The calculation method is:

[0060] M O =DO·V

[0061] V is the volume of stagnant fire water inside the fire water still water pipe;

[0062] V=π·(d / 2) 2 ·L

[0063] Where d is the inner diameter of the pipe, in meters;

[0064] L is the length of the pipeline in meters.

[0065] According to the simulation test, the change data of the dissolved oxygen concentration under the action of oxygen absorption corrosion are obtained, the simulation test is the oxygen absorption corrosion experiment in the fire fighting system pipeline, specifically:

[0066] Blind plates are installed on both sides of the fire fighting system pipeline, fire fighting water is injected into the pipeline, the pressure in the pipeline is removed, it is placed in the normal pressure environment under the actual working condition, the data of the change of the dissolved oxygen concentration with time are monitored in real time by the dissolved oxygen concentration sensor, and a data table is formed.

[0067] The data change rule in the data table conforms to the Euler equation, and the formula of the simplified Euler equation is:

[0068] y=y0-m·exp(-t / n)

[0069] In the formula, y is the dissolved oxygen concentration after oxygen absorption corrosion for t time, y0 is a correction coefficient of the dissolved oxygen concentration, m represents a carbon steel oxygen absorption corrosion parameter, and n is an oxygen absorption corrosion erosion coefficient;

[0070] The data of the change of the dissolved oxygen concentration with time in the data table are fitted according to the simplified formula of the Euler equation, and a function relationship formula DO(t) of the change of the dissolved oxygen concentration with time t under the action of oxygen absorption corrosion in the fire fighting system static water pipeline is obtained.

[0071] DO(t)=α-m·exp(-t / n)

[0072] DO(t) is the dissolved oxygen concentration after oxygen absorption corrosion for t time, α is a correction coefficient of the dissolved oxygen concentration, m represents a carbon steel oxygen absorption corrosion parameter, and n is an oxygen absorption corrosion erosion coefficient.

[0073] Step S3: According to the relationship between the corrosion rate of the inner wall of the fire fighting water static water pipeline and the dissolved oxygen concentration under the condition that the oxygen content in the fire fighting water static water pipeline is continuously reduced under the action of oxygen absorption corrosion, the function relationship formula f O (t) of the change of the corrosion rate with time t is obtained. O

[0074] Specifically, it includes:

[0075] According to the corrosion mechanism of oxygen absorption corrosion, when the oxygen content in the water is high, that is, in the initial stage of oxygen absorption corrosion, the corrosion rate of oxygen absorption corrosion is fast, and with the continuous oxygen absorption corrosion, the oxygen content in the water is continuously reduced, and the corrosion rate is also continuously reduced, based on this, the function relationship formula of the corrosion rate and the dissolved oxygen concentration is obtained:

[0076] f O (t)=K·DO(t)+β

[0077] ​In the formula, K is an oxygen absorption corrosion coefficient, and β is an oxygen absorption corrosion correction coefficient.

[0078] The corrosion rate of the oxygen absorption corrosion is exponentially slowed down, and the oxygen absorption corrosion coefficient K is an exponential function:

[0079]

[0080] The oxygen absorption corrosion correction coefficient β is related to the diameter of the pipeline and the dissolved oxygen concentration in water.

[0081] The function relationship formula f O (t) is combined to calculate a data table of the corrosion rate of the fire-fighting system static water pipeline under the stagnant water state and the change over time.

[0082] Step S4: According to the corrosion data and the dissolved oxygen concentration data of the fire-fighting water static pipeline of the nuclear power plant fire-fighting system, the oxygen absorption corrosion degree of the fire-fighting static pipeline of the nuclear power plant fire-fighting system is evaluated.

[0083] The step S4 specifically includes:

[0084] The function relationship formula f O (t) is combined to calculate the corrosion rate, corrosion time, and internal corrosion thinning amount of the fire-fighting water pipeline. O

[0085] According to the data of the change over time of the real-time monitoring dissolved oxygen concentration, the number of days for complete oxygen consumption is obtained.

[0086] The corrosion data and the dissolved oxygen concentration data are compared, and the oxygen absorption corrosion degree of the fire-fighting static pipeline of the nuclear power plant fire-fighting system is evaluated.

[0087] In order to further understand the present application, the nuclear power plant fire-fighting system pipeline oxygen absorption corrosion degree evaluation grading method provided by the present application is described in detail below in combination with examples, and the protection scope of the present application is not limited by the following examples.

[0088] Example 1

[0089] Step S1: Determine the environmental conditions of the fire-fighting water system pipeline.

[0090] Only the corrosion influence of the oxygen absorption corrosion on the fire-fighting water static pipeline is considered, the influence of other chemical elements is not considered, and the environmental conditions of the fire-fighting water system pipeline are ideal,

[0091] According to the temperature of 20℃, the pressure of one standard atmosphere, and the pressure of 100KPa.

[0092] Step S2:

[0093] ​The fire water pipe size is DN150, and the pipe inner diameter is 159mm; according to the pipe volume formula, the volume of the fire water in the pipe is calculated as:

[0094] V = π·(d / 2) 2 ·L≈0.02m 3 =20L

[0095] The dissolved oxygen concentration DO in the fire water under normal temperature and pressure environment is calculated, and the empirical formula for calculating the dissolved oxygen concentration DO is as follows:

[0096] DO = 1.117·10 -6 e 1746.5 / T ·P

[0097] T is the temperature, in ℃;

[0098] P is the pressure, in Pa.

[0099] Under the fire fighting system 20℃, 100kPa, the dissolved oxygen concentration is 9mg / L.

[0100] According to the diameter size D of the pipe and the dissolved oxygen concentration DO under normal temperature and pressure environment, the oxygen content M of the fire water in the pipe under the stagnant flow state is calculated O :

[0101] M O = DO·V = 9×20 = 180mg

[0102] The oxygen absorption corrosion experiment in the fire fighting system pipe is carried out, the DN150 fire fighting system pipe with a unit length of 1m is installed on both sides of the blind plate, and the fire water is injected into the pipe, the pressure in the pipe is removed, and it is placed in the normal pressure environment under the actual working condition and the room temperature condition, the dissolved oxygen concentration sensor is used to monitor the data of the change of the dissolved oxygen concentration with time in real time, and the data is recorded. The data is shown in Table 1 and Figure 2

[0103] Table 1 Change of dissolved oxygen concentration with time in stagnant water state of static water pipe of fire fighting system of nuclear power plant

[0104]

[0105] According to the change data of the dissolved oxygen concentration with time in the stagnant water state of the static water pipe of the fire fighting system of the nuclear power plant, the change rule conforms to the Euler equation, and the simplified formula is:

[0106] y = y0-m·exp(-t / n)

[0107] In the formula, y is the dissolved oxygen concentration after oxygen absorption corrosion t, y0 is the correction coefficient of the dissolved oxygen concentration, m represents the carbon steel oxygen absorption corrosion parameter, and n is the oxygen absorption corrosion coefficient.​

[0108] According to the data of the change of the dissolved oxygen concentration with time, the data fitting is carried out according to the simplified formula of the oxygen absorption corrosion, the function relationship formula DO(t) of the change of the dissolved oxygen concentration with time t of the fire-fighting system static water pipeline under the action of the oxygen absorption corrosion is obtained, and the coefficient R is determined 2 =0.988:

[0109]

[0110] The coefficient R 2 is the closeness between the fitting function formula and the function data curve, which is used for expressing the reliability of the fitting function, and the fitting function is directly mechanically calculated by the numerical simulation software.

[0111] Step S3: According to the corrosion mechanism of the oxygen absorption corrosion, it can be obtained that when the oxygen content in the water is high, that is, in the initial stage of the oxygen absorption corrosion, the corrosion rate of the oxygen absorption corrosion is fast, and with the continuous progress of the oxygen absorption corrosion, the oxygen content in the water is continuously reduced, and the corrosion rate is also continuously reduced, based on which the function relationship formula of the corrosion rate and the dissolved oxygen concentration is obtained:

[0112] f O (t)=K·DO(t)+β

[0113] In the formula, K is an oxygen absorption corrosion coefficient,

[0114] β is an oxygen absorption corrosion correction coefficient.

[0115] The oxygen absorption corrosion coefficient is an exponential function formula: The oxygen absorption corrosion correction coefficient β is related to the diameter of the pipeline and the dissolved oxygen concentration in the water, and the β correction value of the DN150 fire-fighting water pipeline with an initial concentration of 9 mg / L is-0.055.

[0116] According to the relationship between the dissolved oxygen concentration and the corrosion of the inner wall of the pipeline of the fire-fighting water static pipeline under the action of the oxygen absorption corrosion, the function relationship formula f O (t) of the change of the corrosion rate of the fire-fighting system static water pipeline in the stagnant water state with time t is obtained according to the function relationship formula of the dissolved oxygen concentration and the fitting function. O

[0117]

[0118] Combined with the function relationship formula of f O (t), the data of the change of the corrosion rate of the fire-fighting system static water pipeline in the stagnant water state with time is calculated, and the data is shown in Tables 2 and Figure 3

[0119] Table 2 Change data of the corrosion rate of the fire-fighting system static water pipeline in the stagnant water state with time in a nuclear power plant ​​

[0120]

[0121] Step S4:

[0122] According to Table 1, under stagnant water conditions in a nuclear power plant fire protection system still water pipe with a diameter of DN150, and at normal temperature and pressure (as defined in the industry), an ambient temperature of 20°C and an ambient pressure of 100 kPa, the initial dissolved oxygen concentration in a 1-meter-long still water pipe with stagnant water is 9 mg / L. After 8.42 days, the dissolved oxygen in the water is nearly depleted.

[0123] As shown in Table 2, based on the functional expression of the corrosion rate, the trend data of the corrosion rate over time was calculated. It can be seen that when the dissolved oxygen concentration is high, the corrosion rate is faster. As the dissolved oxygen concentration continues to decrease, the corrosion rate also slows down. When the oxygen absorption corrosion continues to the 6.5th day, the corrosion rate is 0.003 mpy. At this time, the thinning amount Δd of the pipe inner wall is only 0.00007 mm, which is almost negligible. At this time, the dissolved oxygen concentration is less than 0.1 mg / L. It can also be seen that when the dissolved oxygen concentration in the water of the nuclear power plant fire protection system static water pipe is less than 0.1 mg / L in the stagnant state, the corrosion almost stops.

[0124] By comparing the data in Table 1 and Table 2, the degree of oxygen absorption corrosion of the fire-fighting still water pipes in the nuclear power plant fire-fighting system is evaluated.

[0125] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0126] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for evaluating and grading the degree of oxygen absorption corrosion of pipelines in a nuclear power plant fire protection system, characterized in that: The following steps are involved: Step S1: Determine the environmental conditions of the fire water system pipeline; Step S2: Calculate the oxygen content M of the fire water in the stagnant state inside the fire water pipe based on the inner diameter of the pipe and the dissolved oxygen concentration DO under normal temperature and pressure environment. O ; Based on the data on the change of dissolved oxygen concentration under the action of oxygen absorption corrosion obtained from the simulation test, the fitting function is used to obtain the functional relationship DO(t) of the change of dissolved oxygen concentration in fire water under the action of oxygen absorption corrosion in the fire water still water pipe. The simulation test is an oxygen absorption corrosion experiment in the fire protection system pipe, specifically: Install blind plates on both sides of the fire protection system pipes, inject fire water into the pipes, remove the pressure in the pipes, and place them in a normal pressure environment under actual working conditions. Leave them at room temperature and use a dissolved oxygen concentration sensor to monitor the dissolved oxygen concentration over time in real time, and record the data in a data table. The data of dissolved oxygen concentration changing with time in the data table are fitted according to the simplified formula of Euler equation to obtain the functional relationship DO(t) of dissolved oxygen concentration changing with time t under the action of oxygen absorption corrosion in the static water pipe of the fire protection system: DO(t)=α-m·exp(-t / n) α is the correction coefficient of dissolved oxygen concentration, m expresses the anti-oxygen corrosion parameter of carbon steel, and n is the oxygen corrosion erosion coefficient; Step S3: The fire water pipe internal corrosion rate f is obtained based on the relationship between the fire water pipe inner wall corrosion rate and the dissolved oxygen concentration under the condition that the fire water pipe is subjected to oxygen absorption corrosion and the oxygen content in the fire water pipe is continuously reduced. O The functional relationship f that changes with time t O (t); The functional relationship between corrosion rate and dissolved oxygen concentration is obtained: f O (t)=K·DO(t)+β Where: K is the oxygen absorption corrosion coefficient, β is the oxygen absorption corrosion correction coefficient; According to the relationship between dissolved oxygen concentration and inner wall corrosion of fire water static pipe under oxygen absorption corrosion, the function relationship of dissolved oxygen concentration is used to fit the function to obtain that the static pipe of fire protection system is in stagnant water state, f O The functional relationship f that changes with time t O (t); Combined with f O (t), and calculate the data table of the corrosion rate of the static water pipe of the fire protection system under stagnant water state over time; Step S4: evaluating the degree of oxygen absorption corrosion of the fire water still water pipe of the nuclear power plant fire protection system based on the corrosion data and dissolved oxygen concentration data of the fire water still water pipe of the nuclear power plant fire protection system; Specifically include: using the corrosion rate f in the fire water pipeline O The functional relationship f that changes with time t O (t) Calculate the corrosion rate, corrosion time and internal corrosion thinning of fire water pipelines; According to the real-time monitoring data of dissolved oxygen concentration changes over time, the number of days for complete oxygen consumption is obtained; The corrosion data were compared with the dissolved oxygen concentration data to evaluate the degree of oxygen absorption corrosion of the fire still water pipes in the nuclear power plant fire protection system.

2. The method for evaluating and grading the degree of oxygen absorption corrosion of pipelines in a nuclear power plant fire protection system according to claim 1 is characterized in that: The environmental conditions of the fire water system pipeline are a temperature of 20° C. and a pressure of one standard atmospheric pressure, without considering the influence of other chemical elements.

3. The method for evaluating and grading the oxygen absorption corrosion degree of pipelines in a nuclear power plant fire protection system according to claim 1 is characterized in that: In step S2, the oxygen content M of the fire water in the stagnant state inside the fire water pipe is O The calculation method is: M O =DO·V V is the volume of stagnant fire water inside the fire water still water pipe; V=π·(d / 2) 2 ·L Where d is the inner diameter of the pipe, in meters; L is the length of the pipeline in meters.

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