CN112665961B - A test device and method for monitoring SCC crack initiation signal based on DCPD method - Google Patents

Abstract

The invention provides a test device and a test method for monitoring an SCC crack initiation signal based on a DCPD method, wherein the test device comprises a sample, a direct current power supply and a nanovoltmeter, wherein two ends of the sample are shaft shoulder sections, and the middle section is a gauge length section; the sample is connected with the servo machine through the shaft shoulder section; the ends of the two shaft shoulder sections of the sample are connected with a direct current power supply; both ends of the gauge length section and one of the shaft shoulder sections are connected with a receiving voltmeter; according to the invention, through designing a sample and introducing a reference potential, signal fluctuation caused by temperature fluctuation or material conductivity drift is obviously reduced, and high-precision monitoring of crack initiation is completed.

Description

A test device and method for monitoring SCC crack initiation signal based on DCPD method

technical field

The invention belongs to the technical field of safety analysis of nuclear power structural materials, and in particular relates to a test device and method for monitoring SCC crack initiation signals based on a DCPD method.

Background technique

In the field of nuclear power, the main key structural materials are in high temperature and high pressure water environment. Nuclear structural materials under stress corrosion environment are prone to crack initiation. With the increase of service time, there is a risk of further expansion of cracks, which will lead to the failure of nuclear structural materials, which will seriously threaten the safe operation of nuclear power plants. Bring catastrophic consequences to people's life safety and environmental protection. The crack initiation time of a material can directly reflect its susceptibility to stress corrosion cracking. Therefore, accurate monitoring of stress corrosion cracking (SCC) crack initiation is a key technical means to study the environmental damage of nuclear power structural materials, and it is of great significance for material service life prediction and nuclear power plant safety management.

The monitoring of SCC crack initiation and growth rate is very important to the research of SCC. The electrical signal test technology is used as an important means of in-situ monitoring in SCC research due to its characteristics of no damage to the sample and high accuracy of test results. Electrical signal testing techniques include two methods: alternating current potential drop (ACPD) and direct current potential drop (DCPD). The ACPD method is not suitable for the monitoring of small-sized samples due to the skin effect of alternating current. In addition, the signal noise increases with the The increase of AC frequency further limits the application of ACPD method in the field of SCC crack initiation and growth rate monitoring. At present, the measurement of SCC crack growth rate by DCPD method has been developed relatively maturely, but due to the weak SCC crack initiation signal, it is still facing great difficulties to monitor SCC crack initiation signal by DCPD method. The measurement accuracy of DCPD can be significantly improved by reducing the sample size, but it is difficult to perform wire welding on a small sample and realize DCPD measurement.

Up to now, there are few reports on the monitoring of SCC crack initiation signals in small samples by DCPD method.

Contents of the invention

The purpose of the present invention is to provide a test device and method for monitoring SCC crack initiation signals based on the DCPD method, so as to solve the defects of high difficulty in monitoring and low precision in the existing monitoring method of SCC crack initiation signals.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A test device for monitoring SCC crack initiation signals based on the DCPD method provided by the present invention includes a sample, a DC power supply and a nanovoltmeter, wherein the two ends of the sample are shoulder sections, and the middle section is a gauge section; The sample is connected to the servo machine through the shoulder section; the ends of the two shoulder sections of the sample are connected to a DC power supply; both ends of the gauge section and one of the shoulder sections are connected to a nanovolt meter.

Preferably, sample clamps are provided at both ends of the sample, and are connected to the servo through the sample clamps.

Preferably, the sample fixture includes a fixture body, and a second-step stepped hole is opened on the fixture body, and a sample is installed in a small end hole of the second-step stepped hole; a large end hole of the second-step stepped hole cooperates with Connect the servo machine; a zirconia ceramic gasket is arranged between the fixture body and the sample.

Preferably, the ends of the two shaft shoulder sections are connected to the DC power supply through current wires; the current wires are welded at the ends of the shaft shoulder sections.

Preferably, a potential wire is welded to both ends of the gauge length section and one of the shoulder sections, and each potential wire is connected to a nanovoltmeter.

Preferably, the two ends of the gauge length section of the sample are respectively provided with platform structures, and the potential wires at the two ends of the gauge length section are respectively welded to the two platform structures.

Preferably, both the DC power supply and the nanovoltmeter are connected to a computer control system, and the computer control system is used to control the DC power supply to alternately output different current polarities; simultaneously read the voltage collected by the nanovoltmeter, and then generate a strain A plot of values over time.

A kind of test method based on DCPD method monitoring SCC crack initiation signal, based on described a kind of test device based on DCPD method monitoring SCC crack initiation signal, may further comprise the steps:

Step 1, output current to the sample through a DC power supply; and collect the initial working voltage of the gauge length section and the initial reference voltage of the shaft shoulder section through a nanovoltmeter;

Step 2, after applying a constant load to the sample for t seconds through the servo machine, collect the working voltage and the reference voltage of the shaft shoulder segment at different time intervals during the loading process through a nanovoltmeter,

Step 3, calculate the strain value according to the working voltage of the gauge length section and the reference voltage of the shoulder section obtained in step 2, and the initial working voltage of the gauge section and the initial reference voltage of the shoulder section obtained in step 1;

Step 4, according to the multiple strain values corresponding to different times obtained in step 3, obtain the relationship diagram of the strain value versus time, and obtain the time when the sample starts to crack initiation according to the relationship diagram of the strain value versus time combined with the tangent method.

Preferably, the DC power supply alternately outputs different current polarities.

Compared with prior art, the beneficial effect of the present invention is:

A kind of test device based on DCPD method monitoring SCC crack initiation signal that the present invention provides, the two ends of the sample that adopts are shaft shoulder section, as the auxiliary section that connects with servo machine; The size of the sample obtained by this design is smaller, which solves the defect that the existing small sample is difficult to measure DCPD; at the same time, when monitoring the crack initiation signal through DCPD technology, it has a higher sensitivity;

At the same time, the present invention sets collection points at both ends of the gauge length section and one of the shaft shoulder sections, and introduces reference potential measurement, which can significantly reduce signal fluctuations caused by temperature fluctuations or material conductivity drift, and the reference potential The potentials of the gauge section and the gauge section all come from different positions of the same sample, and there is no need to set up additional reference samples, which improves the test accuracy and simplifies the test process; the invention has a wide range of applications and can realize crack initiation in corrosive environments under normal temperature and high temperature conditions high-precision monitoring.

Further, the sample fixture designed in the present invention can be insulated from the sample and realize the welding of the current lead and the potential lead on the sample.

The present invention provides a test method for monitoring SCC crack initiation signals based on the DCPD method. The two ends of the sample are used as the shoulder section, the middle section is the gauge section, and the two ends of the gauge section and one of the shoulder sections are The acquisition point is set on the upper surface, and the reference potential measurement is introduced, which can significantly reduce the signal fluctuation caused by temperature fluctuation or material conductivity drift, and the reference potential and the potential of the gauge section come from different positions of the same sample, no need to set additional parameters. Compared with the sample, the test accuracy is improved and the test process is simplified; at the same time, it solves the defect that it is difficult to realize the DCPD measurement of the existing small sample.

Further, the DC power supply is controlled to alternately output the polarity of the current passing through the sample, and the control system averages the absolute values of the measured potentials under different current polarities.

Description of drawings

Fig. 1 is the schematic diagram of sample and sample fixture;

Figure 2 is a schematic diagram of the in-situ monitoring device for DCPD crack initiation signals

Figure 3 is a process diagram of acquisition voltage-signal ratio and loading time.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

As shown in Figure 1, a test device based on the DCPD method for monitoring SCC crack initiation signals provided by the present invention specifically includes a sample 1, a sample fixture 2, a DC power supply 3, a computer control system 4, a nanovolt meter 5, an oxidation Zirconium ceramic gasket 6, nut 7, hole 8, current wire 9 and potential wire 10, wherein, the two ends of the sample 1 are respectively connected with a sample fixture 2, and the servo machine is connected externally through the sample fixture 2; The power supply 3 and the current wire 9 apply a constant current to the sample 1, measure the potential change on the sample 1 in real time through the nanovolt meter 5 and the potential wire 10, and apply a constant load to the sample 1 through the servo machine, in a common stress and corrosion environment Under the action, crack initiation occurs in sample 1, so the resistance increases, and the measured potential also increases accordingly.

The sample fixture 2 includes a fixture body, and the fixture body is provided with a second-order step hole, and the small end hole of the second-order step hole is equipped with the sample 1; the large end hole of the second-order step hole is mated and connected Servo machine; a zirconia ceramic gasket 6 is provided between the fixture body and the sample 1 for insulation.

The end of the sample 1 is connected with the nut 7; the nut 7 is installed in the big end hole.

The sample holder 2 is provided with a hole 8 through which the current lead is connected to the end of the sample 1; the axis of the hole 8 is perpendicular to the axis of the second-step hole.

The two ends of the sample 1 are thicker shoulder sections, and the section of the shoulder section is a circular structure with a diameter of about 3-4 mm; it is used to cooperate and connect with the sample fixture.

The middle section of the sample 1 is a thinner gauge section, and the section of the gauge section is a square or a circle with a side length of 1 to 2 mm; the gauge section is made according to the test requirements, and can reach the .

The cross-sectional area of the shaft shoulder section is larger than the cross-sectional area of the gauge length section.

The joint between the gauge length section and the shaft shoulder section is chamfered, the total length of the sample is 44 mm, and the length of the gauge length section is 8.5 mm.

A platform structure with a width of 0.6 mm and a height of 0.2 mm is provided on the side of the shoulder section close to the gauge section; the platform structure is used to weld potential wires 10 to both sides of the gauge section to complete the gauge section. Acquisition of working potential signals.

A potential wire 10 is welded on the two platform structures and one side shoulder section of the sample 1, and the other end of the potential wire 10 is connected to a nanovolt meter 5; the nanovolt meter 5 is used for the gauge length section Acquisition of working potential and reference potential of shaft shoulder.

The two ends of the sample 1 are respectively welded with a current wire 9 , and the free end of the current wire 9 passes through the hole 8 to connect to a DC power supply 3 , and the DC power supply 3 is used to provide a stable DC current to the sample 1 .

The computer control system 4 is used to control the DC power supply 3 to alternately output different electrodes; at the same time, it reads the voltage collected by the nanovoltmeter 5, and then generates a graph of the strain value changing with time.

A kind of test method based on DCPD method monitoring SCC crack initiation signal provided by the invention comprises the following steps:

Step 1, install the thicker sections at both ends of the sample 1 on the sample holder 2 through the nut 7 and the zirconia ceramic gasket 6;

Step 2, pass the current wire 9 through the hole 8 on the sample fixture 2 and spot weld it on the two ends of the sample 1, spot-weld the potential wire 10 at the potential collection point of the gauge section and the reference potential collection point respectively, and then Install the sample 1 with the sample holder 2 into the servo machine;

Step 3, setting the water environment temperature, Li ion concentration, B ion concentration and hydrogen concentration of sample 1 to stabilize the corrosion environment required for the test;

Step 4, lead the current wire 9 out of the hole 8, connect the positive and negative poles of the high stability DC power supply 3, and connect the high stability DC power supply 3 and the computer control system 4;

Step 5, the working potential collection point of the gauge length section of the sample 1 and the potential wire 10 of the reference potential collection point of the shaft shoulder section are connected to the nanovoltmeter 5, and the nanovoltmeter 5 is connected to the computer control system 4;

Step 6, use the computer control system 4 to control the DC power supply 3 so that the output current passes through the sample 1, and measure the initial working voltage of the gauge length section V _a0 and the initial reference voltage of the shaft shoulder section through the nanovoltmeter 5 is V _r0 ;

Step 7, apply a constant load to the sample 1 through the servo machine, and control the DC power supply to alternately output the polarity of the current passing through the sample 1 through the computer control system 4, and control the absolute value of the potential measured by the control system 4 under different current polarities take the average. After the preset time, the working voltage V _a of the gauge length section at any time during the loading process and the reference voltage V _r of the shaft shoulder section are collected through the nanovolt meter 5 ;

Step eight, according to the obtained V _a0 , V _r0 , V _a and V _r , calculate the strain value ε _r at any moment to obtain multiple strain values;

The calculation formula of the current strain value is as follows:

Step 9: Obtain a relationship graph of strain values versus time based on the plurality of strain values obtained in step 8, and obtain the time at which crack initiation occurs in the sample according to the graph of strain values versus time combined with the tangent method.

Example

In this embodiment, a method for monitoring SCC crack initiation signals based on the DCPD method is applied to the monitoring of crack initiation signals of 600 alloy samples, and the specific implementation steps are as follows:

Step 1: Install the thicker sections at both ends of the 600 alloy sample 1 on the sample holder 2 through the nut 7 and the zirconia ceramic gasket 6 .

Step 2: Spot-weld the current wire 9 on both ends of the 600 alloy sample 1, spot-weld the potential wire 10 at the potential collection point of the gauge section and the reference potential collection point respectively, and then place the sample 1 with the sample holder 2 installed into the test system;

Step 3: Set the temperature of the test water environment where sample 1 is located to 350°C, the concentration of Li ions to 2ppm, the concentration of B ions to 1000ppm, the concentration of dissolved hydrogen to DH=19.7cc H ₂ /kg H ₂ O, and the corrosion required for the stability test environment.

Step 4: Lead the metal current wire 9 out of the hole 8, connect it to the positive and negative poles of the DC power supply 3, and connect the high-stable DC power supply 3 to the computer control system 4.

Step 5, the potential wire 10 of the 600 alloy sample 1 gauge section working potential collection point and the shaft shoulder section reference potential collection point is connected to the nanovolt meter 5, and the nanovolt meter 5 is connected to the computer control system 4;

Step 6, use the computer control system 4 to control the DC power supply 3 so that the output current passes through the sample 1, and measure the initial working voltage of the gauge length section V _a0 and the initial reference voltage of the shaft shoulder section through the nanovoltmeter 5 is V _r0 ; Step 7: Slowly load the 600 alloy sample 1, stop loading after the stress reaches 350Mpa and keep it constant, and alternately change the polarity of the current passing through the sample 1 through the control system 4, and the control system 4 pairs different currents The absolute values of the measured potentials under polarity were averaged. After 92 hours, the working voltage V _a of the gauge length section at any time during the loading process and the reference voltage V _r of the shaft shoulder section are collected by nanovoltmeter 5, where the value of V _a /V _r is 6 , the value of V _a0 /V _r0 is 5.9, to calculate the current strain value, the strain calculation formula is as follows:

Step 8, calculate the strain value after 92 hours under the constant load of 350Mpa by the above formula to be 0.84%. As shown in Figure 3, the total load holding time is 116h, and the strain gradually increases with the prolongation of the loading time. It can be seen from the tangent method that the 600 alloy sample begins to initiate cracks when the constant load is loaded to 81h.

Claims (5)

1. The test device for monitoring the SCC crack initiation signal based on the DCPD method is characterized by comprising a sample (1), a direct current power supply (3) and a nanovoltmeter (5), wherein the two ends of the sample (1) are shaft shoulder sections, and the middle section is a gauge length section; the sample (1) is connected with a server through a shaft shoulder section; the ends of the two shaft shoulder sections of the sample (1) are connected with a direct current power supply (3); both ends of the gauge length section and one of the shaft shoulder sections are connected with a receiving voltmeter (5);

sample clamps (2) are arranged at two ends of the sample (1), and the sample clamps (2) are connected with a servo machine;

the sample clamp (2) comprises a clamp body, a second-order step hole is formed in the clamp body, and a sample (1) is mounted in a small end hole of the second-order step hole; the big end hole of the second-order step hole is connected with a servo machine in a matched mode; a zirconia ceramic gasket (6) is arranged between the clamp body and the sample (1);

two ends of the gauge length section and one of the shaft shoulder sections are welded with a potential wire (10), and each potential wire (10) is connected with a receiving voltmeter (5);

the two ends of the gauge length section of the sample (1) are respectively provided with a platform structure, and potential wires at the two ends of the gauge length section are respectively welded on the two platform structures; the width of the platform structure is 0.6mm, and the height of the platform structure is 0.2mm on one side of the shaft shoulder section, which is close to the gauge length section;

the section of the shaft shoulder section is of a circular structure with the diameter of 3-4 mm;

the section of the gauge length section is square or round with the side length of 1-2 mm;

the total length of the sample is 44mm, and the length of the gauge length section is 8.5mm;

the end part of the sample (1) is connected with a screw cap (7) in a matching way; the nut (7) is arranged in the big end hole;

a hole (8) is formed in the sample clamp (2), and a current wire penetrates through the hole (8) to be connected with the end part of the sample (1); the axis of the hole (8) is perpendicular to the axis of the second-order stepped hole.

2. The test device for monitoring an SCC crack initiation signal based on a DCPD method according to claim 1, wherein the ends of the two shaft shoulder sections are connected with a direct current power supply (3) through current wires; the current lead is welded at the end part of the shaft shoulder section.

3. The test device for monitoring the SCC crack initiation signal based on the DCPD method according to claim 1, wherein the direct current power supply (3) and the nanovoltmeter (5) are connected with a computer control system (4), and the computer control system (4) is used for controlling the direct current power supply (3) to alternately output different current polarities; and simultaneously reading the voltage acquired by the nano-volt meter (5), and then generating a time-varying relation graph of the strain value.

4. A test method for monitoring an SCC crack initiation signal based on a DCPD method, which is characterized in that the test device for monitoring an SCC crack initiation signal based on a DCPD method according to any one of claims 1 to 3 comprises the following steps:

step 1, outputting current to a sample (1) through a direct current power supply (3); collecting initial working voltage of the gauge length section and initial reference voltage of the shaft shoulder section through a nano-volt meter (5);

step 2, applying a constant load to the sample (1) through a servo

After seconds, working voltages of different time scale distance sections and shaft shoulder section reference voltages in the loading process are acquired through a nanovoltmeter (5),

step 3, calculating a strain value according to the working voltage of the gauge length section and the reference voltage of the shaft shoulder section obtained in the step 2 and the initial working voltage of the gauge length section and the initial reference voltage of the shaft shoulder section obtained in the step 1;

and 4, obtaining a time-varying relation chart of the strain values according to the strain values corresponding to the different times obtained in the step 3, and obtaining the initiation of cracks of the sample according to the time-varying relation chart of the strain values and the tangent method.

5. The test method for monitoring an SCC crack initiation signal based on a DCPD method according to claim 4, wherein the dc power supply (3) alternately outputs different current polarities.

Images