A method for manufacturing an axial crack non-destructive testing calibration tube

Abstract

This invention discloses a method for manufacturing a calibration tube for nondestructive testing (NDT) with an axial crack. First, an initial defect of a certain depth is pre-fabricated on the pipe to which the crack needs to be created, serving as a crack initiation source. Then, a constant-amplitude cyclic internal pressure is applied to the pipe, inducing crack propagation through a certain number of fatigue load cycles, while simultaneously measuring the changes in the pipe's outer surface dimensions. Subsequently, the pipe with the fatigue crack is dissected, and the depth of the fatigue crack is determined by observing the fracture surface. This process is repeated multiple times to obtain the functional relationship between the change in the pipe's outer surface dimensions and the crack depth. Finally, based on the determined curve of the relationship between the change in the pipe's outer surface dimensions and the crack depth, a calibration tube sample containing a longitudinal crack of a specified depth is manufactured by applying a fatigue load and monitoring the change in the pipe's outer surface dimensions in real time. This invention effectively solves the problem of quantitative control of crack size in NDT calibration tubes and can be used to manufacture various types of NDT calibration tubes.

Description

Technical Field

[0001] This invention relates to the field of energy and power engineering, to a pressure pipeline manufacturing technology, and particularly to a method for manufacturing a pipe with axial cracks suitable for calibrating eddy current testing instruments. Background Technology

[0002] In nuclear power plants, the steam generator is the core equipment that converts primary loop thermal energy into secondary loop mechanical energy. The heat transfer tubes of the steam generator serve as both the pressure boundary between the primary and secondary loops and the boundary against radiation leakage. The heat transfer tubes of the steam generator are susceptible to cracks due to flow-induced vibration and stress corrosion cracking, which reduces their pressure-bearing capacity. Effective detection of cracks in the heat transfer tubes of the steam generator is a crucial task for ensuring the structural integrity of the steam generator and is essential for the safe operation of the nuclear power plant.

[0003] Cracks in the heat transfer tubes of steam generators require eddy current testing. To accurately identify the crack size, the eddy current testing instrument must be calibrated before eddy current testing. The pipe containing a crack of known depth used in the calibration process is called a calibration tube. Currently, calibration tubes are manufactured by creating very narrow grooves on the tube surface using machining or electrical discharge machining to approximate cracks in the heat transfer tube. This method causes a certain amount of metal loss, resulting in a volumetric defect that differs significantly from a crack (surface defect) in its eddy current signal characteristics. Using such calibration tubes leads to inaccurate calibration of the eddy current testing instrument, affecting the accuracy of non-destructive testing results for the steam generator heat transfer tubes. This could result in missed or false detections of cracks in the heat transfer tubes, threatening the operational safety of nuclear power plants. However, there is currently no technology to manufacture calibration tubes containing cracks of a specified depth. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention proposes a method for manufacturing a calibration tube with axial cracks for non-destructive testing. This method can manufacture pipes with axial cracks of a specified depth. The aim is to achieve quantitative control of the crack depth on the calibration tube by applying fatigue loading, thereby manufacturing an eddy current testing calibration tube with cracks of known depth. This invention has the advantages of strong operability, simple principle, high repeatability, and good stability of the manufactured crack size.

[0005] The technical solution of this invention is:

[0006] A method for manufacturing a non-destructive testing calibration tube containing axial cracks includes the following steps:

[0007] Step 1: Create an initial defect of acceptable size on the pipe to which the crack needs to be created, using machining or electrical discharge, as a crack source;

[0008] Step 2: Calculate the initial defect root crack propagation driving force σ(p) (for pipes with longitudinal cracks, this is the circumferential stress) using numerical or analytical methods. The crack propagation driving load p should satisfy...

[0009] σ(p)≤σ s (1)

[0010] Where, σ s Indicates the yield strength of the pipe material;

[0011] Step 3: Using the crack propagation driving load p calculated in Step 2 as the internal pressure of the pipe, perform internal pressure fatigue loading on the pipe containing the initial defect on a hydraulic or pneumatic fatigue testing machine, repeat a certain number of times, and record the dimensional changes near the initial defect on the outer surface of the pipe.

[0012] Step 4: Dissect the tube that underwent fatigue loading in Step 3 in the crack initiation area, and use microscopic characterization or visual measurement to obtain a set of data on [crack depth and outer surface dimension change].

[0013] Step 5: For multiple pipes with initial defects, repeat steps 3 to 4 to establish a crack depth-outer surface dimension change curve;

[0014] Step 6: For the pipe with initial defects, fatigue loading is performed using the crack propagation driving load p determined in Step 2, and the change value of its outer surface dimensions is measured in real time. Based on the crack depth-outer surface dimension change curve determined in Step 5, the depth of fatigue crack in the pipe can be determined while keeping the pipe intact.

[0015] Furthermore, the initial defect mentioned in step 1 is no greater than 30% of the pipe wall thickness.

[0016] Furthermore, the initial defect mentioned in step 1 may be a long groove or a circular pit formed by machining / electrical discharge machining, or a stress corrosion crack caused by chemical corrosion.

[0017] Furthermore, the initial defect size described in step 1 may not be kept constant.

[0018] Furthermore, the dimensional changes measured in step 3 can be diameter changes, circumference changes, defect opening angles, etc.

[0019] The present invention provides a method for manufacturing a non-destructive testing calibration tube containing axial cracks, which more specifically includes the following steps:

[0020] Step 1: Denote a batch as S1, S2, S3, ... S nFor pipes of the same size and material, an initial defect of no more than 30% of the pipe wall thickness is created on all pipes by machining or electrical discharge machining as a crack source. The initial defect can be a long groove or a circular pit created by machining / electrical discharge machining, or a stress corrosion crack caused by chemical corrosion. The size of the initial defect on each pipe may not be exactly the same.

[0021] Step 2: For pipe S1 containing initial defects, a numerical model of S1 is established using the finite element method. An internal pressure load p is applied, and the crack propagation driving force σ(p) at the root of the initial defect is calculated using the elastic finite element method (for pipes containing longitudinal cracks, this is the circumferential stress). The crack propagation driving load p should satisfy...

[0022] σ(p)≤σ s (1)

[0023] Where, σ s This indicates the yield strength of the pipe material.

[0024] Step 3: Using the crack propagation driving load p calculated in Step 2 as the internal pressure of the pipe, the pipe S1 containing the initial defect is subjected to internal pressure fatigue loading on a hydraulic or pneumatic fatigue testing machine. This is repeated a certain number of times, while recording the dimensional changes δ1 near the initial defect on the outer surface of the pipe. Changes in diameter, circumference, and defect opening angle can be recorded.

[0025] Step 4: In the crack initiation area, dissect the tube S1 that underwent fatigue loading in Step 3, and use microscopic characterization or visual measurement to obtain a set of data [crack depth a1, outer surface dimension change value δ1].

[0026] Step 5: For i-1 tubes S2, S3, S4, ... S with initial defects i Repeat steps 3 to 4 (changing the pipe codes in steps 3 and 4 to the corresponding pipes), using a1 to a1. i The x-axis is δ1~δ i Plot a curve showing the crack depth versus the change in outer surface dimensions, with i data points as the ordinate. 1～i ,δ 1～i ].

[0027] Step 6: For a pipe S that needs to be defective... i+1 The target crack depth is specified as a. i+1 Based on the curve [a] obtained in step 5 1～i ,δ 1～i ], determine a i+1 The corresponding ordinate δ on the curve i+1 .

[0028] Step 7: For pipe S i+1 Fatigue loading is performed under the crack propagation driving load p determined in step 2, and the change in its outer surface dimensions is measured in real time until the change in its outer surface dimensions equals δ. i+1 (The difference between the two is less than 0.01%, which can be considered equal), that is, the crack with a depth of a is completed. i+1 Manufacturing of calibration tubes for eddy current testing instruments.

[0029] This invention effectively solves the problem of quantitative control of crack size in calibration tubes for non-destructive testing, and can be used to manufacture various calibration tubes for non-destructive testing.

[0030] The present invention has the following advantages:

[0031] (1) The depth of longitudinal cracks on the pipe can be quantitatively controlled without damaging the pipe;

[0032] (2) For the same material, the fatigue test pressure and crack depth-outer surface size change curve are uniquely corresponding, so the present invention has strong repeatability;

[0033] (3) This invention only requires a hydraulic fatigue testing device and a dimensional measuring tool, without the need for expensive special equipment, and is highly operable. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating the implementation of the present invention;

[0035] Figure 2 This is a photograph of a defective heat transfer tube used in a specific embodiment of the present invention.

[0036] Figure 3 This invention is aimed at Figure 2 The example shown is a photograph of the fatigue test process.

[0037] Figure 4 This invention is aimed at Figure 2 The image shown is a photograph of fatigue crack depth measurement in an example.

[0038] Figure 5 This invention is aimed at Figure 2 The example shown establishes a crack depth versus heat transfer tube diameter rate curve;

[0039] Figure 6 To adopt Figure 5 The curve shown is a schematic diagram of the anatomical dimension re-verification of the calibration tube containing cracks manufactured according to the method of the present invention, i.e., for products S7 to S... 12 Dissection and measured crack photographs Figure 6 (a)- Figure 6 (f). Detailed Implementation

[0040] To better understand the present invention, the specific embodiments of the present invention will be further described in detail below through examples, so as to facilitate the understanding of those skilled in the art.

[0041] This invention is incorporated into the Inconel 690 heat transfer tube (size: [missing information]) of the steam generator in a pressurized water reactor nuclear power plant. The invention is further illustrated by an engineering case study of creating longitudinal cracks on a surface.

[0042] The implementation process of the method of the present invention is as follows:

[0043] Step 1: Denote a batch as S1, S2, S3, ... S 12 The dimensions and material are Inconel 690. The tubes, all heat transfer tubes, are machined with longitudinal grooves as initial defects. The finished heat transfer tubes with initial defects are as follows: Figure 2 As shown, the initial defect dimensions of all pipes are listed in Table 1 below.

[0044] Table 1 Initial Defect Dimensions of All Pipes

[0045]

[0046]

[0047] Step 2: Using the finite element method, establish a numerical model of S1, apply an internal pressure load p, and use elastic finite element method to calculate the initial defect root crack propagation driving force σ(p) (for pipes with longitudinal cracks, this is the circumferential stress). The crack propagation driving load p should satisfy...

[0048] σ(p)≤σ s (1)

[0049] Where, σ s This represents the yield strength of the pipe material. The yield strength of Inconel 690 alloy is approximately 290 MPa, and the calculated value is p = 27 MPa.

[0050] Step 3: Using the crack propagation driving load p = 27 MPa calculated in Step 2 as the internal pressure of the pipe, perform internal pressure fatigue loading on the pipe S1 containing the initial defect on a hydraulic or pneumatic fatigue testing machine, repeating the process a certain number of times (25,000 times in this example, fatigue loading from 0 to 27 MPa; the number of fatigue loading cycles should be changed for different pipes to obtain different δ values). Simultaneously record the pipe diameter change rate δ1 = 0.235% near the initial defect on the outer surface of the pipe. The test process is as follows: Figure 3 As shown.

[0051] Step 4: In the crack initiation area, dissect the tube S1 that underwent fatigue loading in Step 3, and use microscopic characterization or visual measurement to obtain a set of data [crack depth a1, outer surface dimension change value δ1].

[0052] Step 5: For the five pipes S2, S3, S4, S5, and S6 containing initial defects, repeat steps 3 and 4 (changing the pipe codes in steps 3 and 4 to the corresponding pipes). Plot a crack depth-outer surface dimension change curve with a1 to a6 as the x-axis and δ1 to δ6 as the y-axis, containing six data points, as shown below. Figure 5 As shown, the data used to draw this graph is listed in Table 2;

[0053] Table 2 Crack depth-diameter variation rate of pipes S1 to S6

[0054]

[0055]

[0056] Step 6: For pipe products S7 to S that require manufacturing defects. 12 The target crack depth is specified as a. i+1 Based on the curve obtained in step 5 Figure 5 Determine a i+1 The corresponding ordinate δ on the curve i+1 .

[0057] Step 7: For pipe products S7~S 12 Fatigue loading was performed under the crack propagation driving load p = 27 MPa determined in step 2, and the change in its outer surface dimensions was measured in real time until the change in its outer surface dimensions equaled δ. i+1 That is, it completes the process containing a crack depth of a. i+1 The calibration tube for the eddy current testing instrument was manufactured. After manufacturing, in order to verify the accuracy of the present invention, products S7 to S... 12 An autopsy was performed, and the actual crack images are as follows: Figure 6 As shown in Table 3, the data indicates that the method of the present invention has small error and good repeatability.

[0058] Table 3. S7 to S7 manufactured according to the method of the present invention 12 Calibration of crack size data from dissection and re-inspection of tube products

[0059] Sample number Sample type (diameter × wall thickness) Product specified crack depth / mm Anatomical re-examination depth / mm error / % <![CDATA[S7]]> Φ17.48×1.01 0.32 0.318 -0.63 <![CDATA[S8]]> Φ17.48×1.01 0.38 0.380 0.00 <![CDATA[S9]]> Φ17.48×1.01 0.45 0.451 0.22 <![CDATA[S 10 ]]> Φ17.48×1.01 0.58 0.578 -0.34 <![CDATA[S 11 ]]> Φ17.48×1.01 0.62 0.623 0.48 <![CDATA[S 12 ]]> Φ17.48×1.01 0.64 0.641 0.16

[0060] Table 3 shows that the crack size of the calibration tube with cracks manufactured by the method of the present invention is stable and the error is small.

[0061] Actual crack photos Figure 6The results showed that the crack sizes of the manufactured calibration tubes with cracks were consistent with the requirements. (a) The total depth of the initial defect crack in tube S7 was 0.318 mm; (b) The total depth of the initial defect crack in tube S8 was 0.380 mm; (c) The total depth of the initial defect crack in tube S9 was 0.451 mm; (d) S 10 The total depth of the initial defect crack in the pipe is 0.578 mm; (e)S 11 The total depth of the initial defect crack in the pipe is 0.623 mm; (f)S 12 The total depth of the initial defect crack in the pipe is 0.641 mm.

Claims

1. A method for manufacturing a calibration tube for non-destructive testing containing axial cracks, characterized in that, A method for manufacturing a calibration tube for non-destructive testing of heat transfer tubes in a nuclear power plant steam generator with axial cracks, comprising the following steps: Step 1: Create an initial defect of acceptable size on the pipe to which the crack needs to be created, using machining or electrical discharge, as a crack source; Step 2: Calculate the initial defect root crack propagation driving force σ(p) using numerical or analytical methods, where the crack propagation driving load p should satisfy... (1) where σ s represents the yield strength of the pipe material; Step 3: Using the crack propagation driving load p calculated in Step 2 as the internal pressure of the pipe, apply internal pressure fatigue loading to the pipe containing the initial defect on a hydraulic or pneumatic fatigue testing machine, repeat a certain number of times, and record the dimensional changes near the initial defect on the outer surface of the pipe; the measured dimensional changes are the diameter change, the circumference change, and the defect opening angle. Step 4: Dissect the tube that underwent fatigue loading in Step 3 in the crack initiation area, and use microscopic characterization or visual measurement to obtain a set of data on [crack depth and outer surface dimension change]. Step 5: For multiple pipes with initial defects, repeat steps 3 to 4 to establish a crack depth-outer surface dimension change curve; Step 6: For the pipe with initial defects, fatigue loading is performed using the crack propagation driving load p determined in Step 2, and the change value of its outer surface dimensions is measured in real time. Based on the crack depth-outer surface dimension change curve determined in Step 5, the depth of fatigue crack in the pipe can be determined while keeping the pipe intact.

2. A method of manufacturing an NDE calibration tube containing an axial crack according to claim 1, wherein The initial defect mentioned in step 1 is no greater than 30% of the pipe wall thickness.

3. A method of manufacturing an NDE calibration tube containing an axial crack according to claim 1, wherein The initial defects mentioned in step 1 are elongated grooves or circular pits caused by machining / electrical discharge machining, or stress corrosion cracks caused by chemical corrosion.

4. The method of claim 1, wherein the method further comprises: In step 1, the initial defect size is not kept constant.

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