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

Abstract

The invention discloses a method for estimating the service life of a heat transfer tube of a nuclear power steam generator. The method comprises the following steps: S1, acquiring the wall thickness reduction and distribution of the heat transfer tube in a selected time period; s2, the wall thickness reduction rate of the heat transfer tube is obtained through calculation according to the wall thickness reduction amount; s3, a relation curve of the internal pressure load of the heat transfer pipe and the defect depth is obtained through finite element calculation, and the limit load of the heat transfer pipe is obtained through calculation according to the internal pressure load of the heat transfer pipe; s4, acquiring a corresponding wall thickness defect depth limit value under the target internal pressure load according to the relation curve of the internal pressure load and the defect depth of the heat transfer pipe, and calculating and acquiring a wall thickness limit size according to the wall thickness defect depth limit value; and S5, calculating to obtain the estimated service life of the heat transfer tube. According to the method, the wall thickness reduction rate of the heat transfer pipe is combined with finite element calculation, and the service life of the heat transfer pipe is estimated, so that the residual strength of the heat transfer pipe can be quickly evaluated, and whether the heat transfer pipe can be continuously used or not is judged.

Description

Technical Field

[0001] The invention relates to the technical field of safety assessment of nuclear power steam generators, and in particular to a method for estimating the service life of heat transfer tubes of nuclear power steam generators. Background Art

[0002] The steam generator is an indispensable key equipment in the nuclear power system. Its heat transfer tube, as an important component of the primary circuit main system, plays the role of a bridge for thermal energy conversion. It can efficiently transfer the heat generated by the reactor in the primary circuit to the water in the secondary circuit, thereby generating steam and promoting 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, it will cause the heat transfer tube to vibrate. This vibration will cause the heat transfer tube to collide and wear with its supporting components (anti-vibration strips, support plates), which will cause local thinning or even rupture of the heat transfer tube over time, greatly endangering the safe operation of the nuclear power plant. In addition, local corrosion of the heat transfer tube will also cause its pressure bearing capacity to decrease and then rupture. According to statistics, the rupture of the steam generator heat transfer tube is one of the most frequent accidents in nuclear power plants. In the relevant nuclear power plant environmental radiation protection regulations, the rupture of a single heat transfer pipe and the rupture of multiple pipes of the steam generator are listed as rare accidents and extreme accidents respectively.

[0004] In-depth research on how defects erode the ultimate load-bearing capacity of heat transfer tubes and accurately define the extent to which the defect size develops, it should be judged as unrepairable and take pipe blocking measures, which has become an urgent need to ensure the safe operation of the system. Based on this, it is particularly critical and necessary to build a scientific and accurate rapid prediction method for the judgment threshold. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for estimating the service life of heat transfer tubes of a nuclear power steam generator.

[0006] The technical solution adopted by the present invention to solve the technical problem is: to provide a method for estimating the service life of a heat transfer tube of a nuclear power steam generator, comprising the following steps:

[0007] S1. Obtain the wall thickness reduction and distribution of the heat transfer tube in a selected time period;

[0008] S2. Calculating the wall thickness reduction rate of the heat transfer tube according to the obtained wall thickness reduction amount of the heat transfer tube;

[0009] S3. According to the defects on the heat transfer tube, a relationship curve between the internal pressure load of the heat transfer tube and the defect depth is obtained through finite element calculation, and the limit load of the heat transfer tube is obtained according to the internal pressure load calculation of the heat transfer tube;

[0010] 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 according to the wall thickness defect depth limit value;

[0011] S5. The estimated life of the heat transfer tube is calculated 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 positions of the defect on the heat transfer tube is obtained through 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: the wall thickness thinning rate of the heat transfer tube is combined with finite element calculation to estimate the service life of the heat transfer tube, thereby being able to quickly evaluate the remaining strength of the heat transfer tube and determine whether the heat transfer tube pipeline can continue to be used; the present invention 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 the internal pressure load and the 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 in a selected time period.

[0023] 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. The selected time is selected according to 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 thinning of the tube wall per unit time, and the thinning includes the thinning caused by erosion, wear, etc.

[0026] The wall thickness reduction rate of the heat transfer tube can be obtained 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 reduction rate of the heat transfer tube = (minimum thickness measured last time - minimum thickness measured this time) / 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 last time, and the current measured minimum thickness is the minimum wall thickness of the heat transfer tube measured last time. The predetermined time interval can be selected as monthly or annual according to actual conditions.

[0029] S3. Calculate and analyze the bearing capacity of the heat transfer tube: According to 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, and obtain the ultimate load of the heat transfer tube based on the internal pressure load calculation of the heat transfer tube.

[0030] Specifically, the relationship curve between the internal pressure load and the defect depth at different lengths and widths at different positions of the defect on the heat transfer tube is obtained through finite element calculation. 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.

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

[0032] Furthermore, the defects on the heat transfer tube include circumferential defects and axial defects on the outer wall of the heat transfer tube. The relationship curve between the internal pressure load and the defect depth under different lengths and widths of the circumferential defects and axial defects is obtained through finite element calculation, and the limit load is calculated in combination with the safety factor under the predetermined working conditions. The load-bearing capacity of the heat transfer tube can be obtained according to the limit load.

[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 according to 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. The estimated life of the heat transfer tube is calculated 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 measured at that time - wall thickness limit size) / 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 is 0.98 mm, the minimum thickness measured this time is 0.87 mm, and 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 last minimum thickness measured 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] Firstly, 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 limit 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 the internal pressure load = limit load / 1.4, and a relationship curve between the internal pressure load and the 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 size

[0049]

[0050] Step (5): Service life estimation

[0051] The estimated service life of the pipeline can be obtained according to the estimated service life = (minimum thickness measured this time - 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 the circumferential defect and the axial defect are different and the circumferential defect and the axial defect are independent of each other (not crossed), 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 specification 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 heat transfer tube of a nuclear power steam generator, characterized in that: The following steps are involved: S1. Obtain the wall thickness reduction and distribution of the heat transfer tube in a selected time period; S2. Calculating the wall thickness reduction rate of the heat transfer tube according to the obtained wall thickness reduction amount of the heat transfer tube; S3. According to the defects on the heat transfer tube, a relationship curve between the internal pressure load of the heat transfer tube and the defect depth is obtained through finite element calculation, and the limit load of the heat transfer tube is obtained according to the internal pressure load calculation of the heat transfer tube; 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 according to the wall thickness defect depth limit value; S5. The estimated life of the heat transfer tube is calculated 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 = (the minimum thickness measured at that time - the wall thickness limit size) / the 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 reduction rate of the heat transfer tube = (minimum thickness measured last time - minimum thickness measured this time) / 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: In step S3, the relationship curve between the internal pressure load and the defect depth at different lengths and widths at different positions of the defect on the heat transfer tube is obtained through finite element calculation, and the limit load is calculated based on the safety factor under the predetermined working condition and the internal pressure load = limit load / safety factor under the predetermined working condition.

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

4.

7. The method for estimating the service life of a heat transfer tube of a nuclear power steam generator according to claim 5, 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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