Method for estimating service life of nuclear power steam generator heat transfer tube

Abstract

The application discloses a kind of nuclear power steam generator heat pipe service life estimation method, comprising the following steps: S1, obtains the wall thickness thinning amount and its distribution of heat pipe in selected time period;S2, wall thickness thinning amount is calculated to obtain the wall thickness thinning rate of heat pipe;S3, the relationship curve of internal pressure load and defect depth of heat pipe is obtained by finite element calculation, and the limit load of heat pipe is calculated according to the internal pressure load of heat pipe;S4, according to the relationship curve of internal pressure load and defect depth of heat pipe, the corresponding wall thickness defect depth limit value under target internal pressure load is obtained, and the wall thickness limit size is calculated according to wall thickness defect depth limit value;S5, the estimated life of heat pipe is obtained.This application combines the wall thickness thinning rate of heat pipe with finite element calculation, estimates the service life of heat pipe, so as to quickly evaluate the residual strength of heat pipe, and judge whether heat pipe line can continue to be used.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear power steam generator safety evaluation, and particularly relates to a nuclear power steam generator heat transfer pipe service life prediction method. BACKGROUND

[0002] The steam generator is an indispensable key equipment in the nuclear power system, and the heat transfer pipe thereof plays a bridge role in heat energy conversion as an important component of the primary system, can efficiently transfer the heat generated by the reactor in the primary system to the water in the secondary system, so as to generate steam and then drive the subsequent power generation process.

[0003] During the operation of the nuclear power system, when the coolant flows through the steam generator at a certain flow rate, vibration of the heat transfer pipe is caused, which can cause the heat transfer pipe and the support component (anti-vibration strip, support plate) to collide and wear, and the local thinning of the heat transfer pipe and even the rupture of the heat transfer pipe can be caused after a long time, thereby greatly endangering the safe operation of the nuclear power plant. In addition, the local corrosion of the heat transfer pipe can also cause the pressure bearing capacity of the heat transfer pipe to decrease and then the heat transfer pipe to rupture. According to statistics, the rupture of the heat transfer pipe of the steam generator is one of the accidents with a higher frequency in the nuclear power plant, and the rupture of a single heat transfer pipe and the rupture of multiple heat transfer pipes of the steam generator are respectively listed as rare accidents and extreme accidents in the relevant nuclear power plant environmental radiation protection regulations.

[0004] It is an urgent requirement to ensure the safe operation of the system to deeply study how the defects erode the ultimate bearing capacity of the heat transfer pipe and accurately define the extent to which the defect size develops so as to determine that the heat transfer pipe is unrepaired and take the pipe plugging measure. Therefore, it is particularly crucial and necessary to construct a fast prediction method for judging the threshold value scientifically and accurately. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a nuclear power steam generator heat transfer pipe service life prediction method.

[0006] The technical scheme adopted by the present application to solve the technical problem is as follows: a nuclear power steam generator heat transfer pipe service life prediction method is provided, comprising the following steps:

[0007] S1, obtaining the wall thickness thinning amount and distribution of the heat transfer pipe in a selected time period;

[0008] S2, calculating the wall thickness thinning rate of the heat transfer pipe according to the obtained wall thickness thinning amount of the heat transfer pipe;

[0009] S3, obtaining the relationship curve between the internal pressure load of the heat transfer pipe and the defect depth according to the defects on the heat transfer pipe through finite element calculation, and calculating the ultimate load of the heat transfer pipe according to the internal pressure load of the heat transfer pipe;

[0010] S4. Obtain the wall thickness defect depth limit value corresponding to the target internal pressure load based on the relationship curve between the internal pressure load and the defect depth of the heat transfer tube, and calculate the wall thickness limit size based on the wall thickness defect depth limit value;

[0011] S5. Calculate the estimated life of the heat transfer tube based on the minimum thickness of the heat transfer tube measured at that time, the obtained wall thickness thinning rate, and the wall thickness limit size of the heat transfer tube.

[0012] Preferably, in step S5, the estimated life of the heat transfer tube = (minimum thickness measured at that time - wall thickness limit size) / wall thickness thinning rate.

[0013] Preferably, in step S2, the wall thickness thinning rate of the heat transfer tube = (minimum thickness measured last time - minimum thickness measured this time) / time interval between two measurements.

[0014] Preferably, in step S1, the wall thickness reduction and its distribution of the heat transfer tube in a selected time period are obtained by a non-destructive testing method.

[0015] Preferably, in step S3, a relationship curve between the internal pressure load and the defect depth at different lengths and widths at different locations of the defect on the heat transfer tube is obtained by finite element calculation, and combined with the safety factor under the predetermined working condition, the limit load is calculated according to internal pressure load = limit load / safety factor under the predetermined working condition.

[0016] Preferably, the predetermined operating condition includes an accident operating condition, and the safety factor under the accident operating condition is 1.4.

[0017] Preferably, in step S3, the defects include circumferential defects and axial defects on the outer wall of the heat transfer tube.

[0018] The beneficial effects of the present invention are as follows: by combining the wall thickness thinning rate of the heat transfer tube with finite element calculation, the service life of the heat transfer tube can be estimated, thereby quickly evaluating the remaining strength of the heat transfer tube and judging whether the heat transfer tube pipeline can continue to be used; it has the advantages of being scientific, accurate and fast. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0020] Figure 1 1 is a graph showing the relationship between internal pressure load and defect depth in one embodiment of the present invention. DETAILED DESCRIPTION

[0021] A method for estimating the service life of a heat transfer tube of a nuclear power steam generator according to an embodiment of the present invention may include the following steps:

[0022] S1. Obtain the wall thickness reduction and distribution of the heat transfer tube within a selected time period.

[0023] The amount of wall thickness reduction and its distribution of the heat transfer tube within a selected time period are obtained through non-destructive testing methods. The selected time period is selected based on actual conditions.

[0024] S2. Calculate the wall thickness reduction rate of the heat transfer tube according to the obtained wall thickness reduction amount of the heat transfer tube.

[0025] The wall thickness reduction rate of the heat transfer tube refers to the amount of wall thickness reduction per unit time, and the reduction includes the reduction caused by erosion, wear, etc.

[0026] The wall thickness reduction rate of the heat transfer tube can be calculated by dividing the difference between the minimum wall thickness of the heat transfer tube obtained in two measurements at a predetermined time interval by the predetermined time interval. Specifically, it can be calculated according to the following relationship:

[0027] The wall thickness thinning rate of the heat transfer tube = (minimum thickness of the last measurement - minimum thickness of the current measurement) / time interval between two measurements.

[0028] It can be understood that the last measured minimum thickness is the minimum wall thickness of the heat transfer tube measured previously, and the current measured minimum thickness is the minimum wall thickness of the heat transfer tube measured next. The predetermined time interval can be selected as monthly or annually according to actual conditions.

[0029] S3. Calculate and analyze the load-bearing capacity of the heat transfer tube: Based on the defects on the heat transfer tube, obtain the relationship curve between the internal pressure load of the heat transfer tube and the defect depth through finite element calculation. Then, calculate the ultimate load of the heat transfer tube based on the internal pressure load of the heat transfer tube.

[0030] Specifically, finite element calculation is used to obtain the relationship curve between the internal pressure load and the defect depth at different lengths and widths at different locations on the heat transfer tube. Combined with the safety factor under the predetermined working conditions, the ultimate load is calculated according to the formula: internal pressure load = ultimate load / safety factor under the predetermined working conditions.

[0031] Among them, the predetermined operating conditions include accident conditions, and the safety factor under accident conditions is 1.4.

[0032] Furthermore, defects on heat transfer tubes include circumferential and axial defects on the outer wall of the heat transfer tube. Finite element calculations are used to obtain curves showing the relationship between internal pressure load and defect depth for circumferential and axial defects of varying lengths and widths. Combined with the safety factor under predetermined operating conditions, the ultimate load is calculated. This ultimate load provides the load-bearing capacity of the heat transfer tube.

[0033] S4. According to the relationship curve between the internal pressure load and the defect depth of the heat transfer tube, the corresponding wall thickness defect depth limit value under the target internal pressure load is obtained, and the wall thickness limit size is calculated based on the wall thickness defect depth limit value.

[0034] The wall thickness defect depth limit refers to the maximum wall thickness defect depth that can withstand the internal medium pressure. When the defect depth exceeds this value, the heat exchange tube will fail.

[0035] S5. Calculate the estimated life of the heat transfer tube based on the minimum thickness of the heat transfer tube measured at that time, the obtained wall thickness thinning rate, and the wall thickness limit size of the heat transfer tube.

[0036] Estimated life of heat transfer tube = (minimum thickness at the time of measurement - wall thickness limit) / wall thickness thinning rate.

[0037] The present invention will be further described below by means of specific examples.

[0038] Taking a heat transfer tube of a steam generator as an example, it is known that the outer diameter of the heat transfer tube is 19.05 mm, the wall thickness is 1.09 mm, the minimum thickness measured last time was 0.98 mm, and the minimum thickness measured this time is 0.87 mm. The time interval between the two measurements is 2 years.

[0039] The specific implementation steps of the steam generator heat exchange tube service life estimation method are as follows:

[0040] Step (1): Pipeline (i.e. heat transfer tube) thinning data collection

[0041] Using relevant non-destructive testing instruments, the minimum thickness measured last time was 0.980mm, and the minimum thickness measured this time was 0.870mm. The time interval between the two measurements was 2 years.

[0042] Step (2): Determination of pipeline thinning rate

[0043] According to the thinning rate = (minimum thickness of the last measurement - minimum thickness of this measurement) / time interval between two measurements, it can be concluded that: pipeline thinning rate = (0.980mm-0.870mm) / 2 years = 0.055mm / year.

[0044] Step (3): Carrying capacity analysis

[0045] First, the finite element calculation software is used to study the circumferential and axial defects on the outer wall of the pipeline (i.e., the heat transfer tube) and the ultimate loads that different defect depths can withstand when the defect length is 2mm, 10mm, 30mm, and the defect width is 0.2mm. Then, the internal pressure load values ​​that different defect depths can withstand are obtained according to internal pressure load = ultimate load / 1.4, and a relationship curve between internal pressure load and defect depth is drawn, as shown in the figure. Figure 1 shown.

[0046] Step (4): Calculation of limit dimensions

[0047] It is known that the internal pressure load of the pipeline is 15.5 MPa. By interpolating the relationship curve between the internal pressure load and the defect depth in step (3), the maximum defect depth and the wall thickness limit size can be obtained as shown in Table 1.

[0048] Table 1. Maximum defect depth and wall thickness limit

[0049]

[0050] Step (5): Service life estimation

[0051] The estimated service life of the pipeline can be obtained according to the formula: estimated service life = (minimum thickness of this measurement - wall thickness limit size) / pipeline thinning rate, as shown in Table 2.

[0052] Table 2. Estimated service life under different defects

[0053]

[0054]

[0055] When the estimated service life of circumferential defects and axial defects is different and the circumferential defects and axial defects are independent of each other (do not cross each other), the minimum estimated service life is taken as the final consideration.

[0056] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for estimating the service life of a nuclear power steam generator heat transfer tube, characterized in that: The following steps are involved: S1. Obtain the wall thickness reduction and distribution of the heat transfer tube within a selected time period; S2. Calculating a wall thickness reduction rate of the heat transfer tube according to the obtained wall thickness reduction amount of the heat transfer tube; S3. Based on the defects on the heat transfer tube, finite element calculation is performed to determine the ultimate load that defects at different locations on the heat transfer tube can withstand at different lengths, widths, and depths. Then, a curve is drawn showing the relationship between internal pressure load and defect depth, using the formula: internal pressure load = ultimate load / safety factor under predetermined operating conditions. S4. Obtain the wall thickness defect depth limit value corresponding to the target internal pressure load based on the relationship curve between the internal pressure load and the defect depth of the heat transfer tube, and calculate the wall thickness limit size based on the wall thickness defect depth limit value; S5. Calculate the estimated life of the heat transfer tube based on the minimum thickness of the heat transfer tube measured at that time, the obtained wall thickness thinning rate, and the wall thickness limit size of the heat transfer tube.

2. The method for estimating the service life of a heat transfer tube of a nuclear power steam generator according to claim 1, characterized in that: In step S5, the estimated life of the heat transfer tube = (minimum thickness measured at that time - wall thickness limit size) / wall thickness thinning rate.

3. The method for estimating the service life of a heat transfer tube of a nuclear power steam generator according to claim 1, characterized in that: In step S2, the wall thickness thinning rate of the heat transfer tube = (minimum thickness of the last measurement - minimum thickness of the current measurement) / time interval between two measurements.

4. The method for estimating the service life of a heat transfer tube of a nuclear power steam generator according to claim 1, characterized in that: In step S1, the wall thickness reduction and its distribution of the heat transfer tube in a selected time period are obtained by a non-destructive testing method.

5. The method for estimating the service life of a heat transfer tube of a nuclear power steam generator according to claim 1, characterized in that: The predetermined operating condition includes an accident operating condition, and the safety factor under the accident operating condition is 1.

4.

6. The method for estimating the service life of a heat transfer tube of a nuclear power steam generator according to claim 1, characterized in that: In step S3, the defects include circumferential defects and axial defects on the outer wall of the heat transfer tube.

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