Method for evaluating service life of nuclear nitrile rubber sealing ring

Abstract

The invention relates to the field of service life evaluation of rubber sealing materials, in particular to a method for evaluating the service life of a nuclear nitrile rubber sealing ring, which comprises the following steps of: 1, intercepting a sample meeting a compression set test from a secondary filter screen sealing ring finished product; 2, fixing the sample on a clamp, standing the sample under the test condition for 3 days, opening the clamp, standing the sample again for one day, and measuring the height as the initial height; 3, setting a plurality of groups of different aging temperatures for the sample to carry out an aging experiment; 4, measuring the aging height of the sample at set intervals, and calculating the compression set of the sample until the compression set of the sample is higher than 50%; and 5, calculating the service life according to the test data of the aging experiment. According to the method, life calculation is carried out on aging experiment test data by utilizing two different standards and models, and the validity and accuracy of the data can be further explained through evaluation results of the two models.

Description

Technical Field

[0001] The invention relates to the field of life assessment of rubber sealing materials, in particular to a life assessment method for a nuclear nitrile rubber sealing ring. Background Art

[0002] Rubber seals are one of the common components in nuclear power plants. They mainly provide sealing functions for gaseous or liquid media, or provide buffering, shock absorption and displacement compensation functions for rigid materials. The quality of their performance directly affects the realization of the predetermined functions of the equipment. Failure of rubber products generally causes leakage of sealing media, which may cause resource waste and environmental pollution at the least, or even cause system failure at the worst. Once a failure accident occurs in a nuclear power plant, it will cause irreparable losses and seriously affect the normal production of the nuclear power plant. Rubber seals will age and degrade due to the influence of one or more environmental factors such as high temperature, low temperature, seawater, ozone, etc., which may lead to the occurrence of rubber seal failure events.

[0003] The service environment of the nitrile seal ring for the secondary filter core is contact with seawater medium. The average pH value of seawater is 8.2, which is highly corrosive. 3.5% of the seawater is salt, which is mainly composed of chlorine, sodium, sulfur, magnesium, calcium, potassium, bromine, etc., and has the effects of moisture, heat, oxygen and hydrolysis. Nitrile rubber is a random copolymer formed by emulsion polymerization of butadiene and acrylonitrile monomers. Due to the unsaturated bonds and double bonds in the butadiene in the copolymer, it is very sensitive to oxidative degradation. Under the effects of moisture, heat, oxygen and hydrolysis in the seawater medium, the macromolecules will undergo structural changes such as cross-linking, aggregation, degradation, hydrolysis, cyclization and isomerization. Due to the complex composition of seawater and the intervention of metal ions, the oxidation reaction of the nitrile seal ring has a strong catalytic effect, accelerating the oxidation and destruction of the rubber. At the same time, it may also cause the breakage of the long chain of nitrile rubber and the spillage of small molecular substances and leave holes, so that the stress of the rubber is concentrated at the pressure point. The seal ring is ultimately unable to withstand the external pressure and collapses and cracks. Therefore, it is necessary to conduct an accurate life assessment of the nitrile seal of the nuclear secondary filter according to the service environment, predict the service life of the seal, and ensure the reliability of equipment operation.

[0004] In the prior art, the accelerated aging experiments on nitrile rubber focus on media such as air, ethylene glycol, and hydraulic oil, and there is a lack of systematic experimental methods for aging experiments in the seawater medium environment where the nitrile seal ring used in the secondary filter core is located. Summary of the invention

[0005] The technical solution of the present invention is as follows:

[0006] The present invention provides a life assessment method for a nuclear nitrile rubber sealing ring, the method comprising:

[0007] Step 1: Take samples that meet the compression set test from the finished nitrile rubber sealing ring;

[0008] Step 2: Fix the sample on the fixture, place the sample under test conditions for A days, then open the fixture, and place the sample again for B days before measuring the sample height as the initial height;

[0009] Step 3: Set several groups of different aging temperatures for the samples to conduct aging experiments, and the highest aging temperature setting shall not exceed 110°C;

[0010] Step 4: Every D days, measure the aging height of the sample and calculate the compression permanent deformation of the sample until the compression permanent deformation of the sample is higher than 50%. The formula for calculating the compression permanent deformation is as shown in formula (1);

[0011]

[0012] Where C is the compression set, h0 is the initial height of the sample, and h1 is the aging height of the sample;

[0013] Step 5: Calculate the life of the sample based on the aging experiment test data.

[0014] In some embodiments, the sample obtained in step 1 that meets the compression set test is specifically: the sample is a cylinder with a diameter of 12.5-13.5 mm and a height of 6.0 mm-6.6 mm.

[0015] In some embodiments, the height measured after parking again for B days in step 2 is the initial height, and the initial height is measured 6 times and the average value is taken.

[0016] In some embodiments, step three sets several groups of different aging temperatures for the sample to perform an aging experiment, specifically including:

[0017] Step 3.1: Place the sample into the compression set measurement fixture;

[0018] Step 3.2: Place the measuring fixture into a sealed container filled with seawater, so that the measuring fixture is immersed in the seawater;

[0019] Step 3.3: Place the sealed container in an aging box for aging experiment.

[0020] In some embodiments, in step three, several groups of different aging temperatures are set for the sample to perform an aging experiment. Specifically, a total of 4 aging test temperature points are set, and the aging temperatures are set to 95°C, 85°C, 75°C, and 65°C.

[0021] In some embodiments, in step 4, samples are taken to determine the aging height of the samples every D days, where D days is 1 day, specifically including: the aging height of the samples is measured after being parked under test conditions for 1 day, and the average value is taken after 3 measurements; wherein the number of sampling times is not less than 10 times.

[0022] In some embodiments, in step 5, the life calculation is performed based on the aging experiment test data, specifically including: performing nonlinear fitting on the aging experiment test data collected at all sampling time points to obtain an evaluation life formula, and the fitting formula refers to formula (2):

[0023]

[0024] Where: t is the lifespan in years; y0 is the aging coefficient, which is the compression set rate C when the aging coefficient is 1 minus the aging time; B is a constant close to 1; T is the aging test temperature;

[0025] b0, b1, b2 are the unknown coefficients that need to be fitted.

[0026] In some embodiments, in step 5, the life calculation is performed based on the aging experiment test data, specifically including: the aging experiment test data collected at all sampling time points are linearly fitted to obtain an evaluation life formula, and the fitting formula refers to formula (3):

[0027] y=a+bx (3)

[0028] Where y is the logarithm of the life span lnt, x is 1 / (T+273.15), T is the aging test temperature, and a and b are unknown constants.

[0029] In some embodiments, the method performs control experiments on three groups of samples simultaneously.

[0030] In some embodiments, the A day in step 2 is specifically 3 days, and the B day in step 2 is specifically 1 day.

[0031] The implementation of the present invention has the following beneficial effects:

[0032] The present invention provides a life assessment method for a nuclear nitrile rubber sealing ring. The experimental conditions of the method are close to the actual service environment of the nuclear sealing ring, that is, in a compressed state and immersed in seawater. At the same time, the method uses two different standards and models to calculate the life of aging experimental test data respectively. The evaluation results of the two models can further illustrate the validity and accuracy of the data, and also provide mutual verification for the evaluation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A secondary filter seal ring compression permanent deformation and its variation trend with aging time in a life assessment method of a nuclear nitrile rubber seal ring proposed in an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of an aging coefficient and a life curve at different temperatures for a life assessment method for a nuclear nitrile rubber sealing ring proposed in an embodiment of the present invention;

[0035] Figure 3 A logarithmic function relationship diagram of compression permanent deformation and aging time of a life assessment method of a nuclear nitrile rubber sealing ring proposed in an embodiment of the present invention;

[0036] Figure 4 An Arrhenius diagram of a life assessment method for a nuclear nitrile rubber sealing ring proposed in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The present invention provides a life evaluation method for a nuclear nitrile rubber sealing ring, which uses compression permanent deformation as a life index. Compression permanent deformation and elongation at break are the two most commonly used performance parameters for life prediction of rubber materials. Since the sealing ring performs a sealing function by generating strong elastic stress through compression, thereby preventing gas or liquid in a confined space from leaking, the compression permanent deformation is selected to be closer to the actual service state of the sealing ring.

[0039] like Figures 1 to 4 As shown, the present invention provides a life assessment method for a nuclear nitrile rubber sealing ring, the method comprising:

[0040] Step 1: Take a sample from the finished secondary filter seal that meets the compression set test.

[0041] In step 1, samples that meet the compression set test are cut according to the standard test method of GB / T 7759.1.1-2015 "Determination of compression set of vulcanized rubber or thermoplastic rubber Part 1: At room temperature and elevated temperature". According to the standard, the sample is a cylinder with a diameter of 12.5-13.5mm and a height of 6.0mm-6.6mm. Three samples are made at the same time for the experiment to ensure the accuracy of the experiment.

[0042] Step 2: Fix the sample on the fixture, leave the sample under standard test conditions for 3 days, then open the fixture, leave it for another day and measure the height as the initial height.

[0043] In step 2, the height measured after parking for another day is taken as the initial height, and the average value of the height measurements taken 6 times is taken as the initial height;

[0044] Step 3: Place the sample into a compression set measuring fixture, and then place the measuring fixture into a sealed container filled with seawater; place the sealed container into an aging box for aging, and set several groups of different aging temperatures for aging experiments. According to the characteristics of nitrile material and seawater medium, the aging temperature is set to a maximum of no more than 110°C.

[0045] In step three, the amount of seawater used is such that the measuring fixture is immersed in the seawater. A total of four aging test temperature points are set, and the aging temperatures are set to 95°C, 85°C, 75°C, and 65°C.

[0046] Step 4: Take out the measuring fixture from the aging box at regular intervals, place the sample under standard test conditions for 1 day, and then measure its aging height. Take the average of 3 measurements and calculate the compression set until the compression set of the sample is higher than 50%.

[0047] In step 4, the sampling times for calculating the compression set are no less than 10 times, and the formula for calculating the compression set is as shown in formula (1):

[0048]

[0049] Where C is the compression set, h0 is the initial height of the sample, and h1 is the aging height of the sample.

[0050] Step 5: Calculate the lifespan using two different standards and models based on the aging test data;

[0051] Method 1: Use a high-precision recursive algorithm to perform life prediction calculations. Perform nonlinear fitting on the data collected at all sampling time points to obtain the evaluation results. The fitting formula refers to formula (2):

[0052]

[0053] Wherein: t is the lifespan in years; y0 is the aging coefficient, which is the compression set rate C when the aging coefficient is 1 minus the aging time; B is a constant close to 1; T is the aging test temperature in Kelvin (K); b0, b1, b2 are the unknown coefficients that need to be fitted.

[0054] Method 2: Use the material performance aging time diagram and Arrhenius diagram to predict the life span. The Arrhenius equation is as follows:

[0055] K(T)=Ae -E / RT (3)

[0056] Where: K(T) is the reaction rate; A is the proportionality constant; E is the activation energy (eV); R is the Boltzmann constant (equal to 8.617×10-5 eV / K); T is the thermodynamic temperature (K). At different reaction temperatures Ti, different reaction rates Ki reach the same critical value F at different reaction times ti. a , the chemical reaction relationship is expressed by formula (4):

[0057] Fa(t)=K i (T i )·t i (4)

[0058] Combining equation (3) and equation (4), the constant term is synthesized to obtain the logarithmic equation (5):

[0059] ln t i =E / RT i +B (5)

[0060] Generally, the logarithm of time lnt and the inverse of thermodynamic temperature 1 / T present an Arrhenius relationship curve. In the same temperature range of the main aging reactions, the activation energy E is a constant. Rearrange equation (5) and let x = 1 / (T + 273.15), y = lnt, and we get equation (6):

[0061] y=a+bx (6)

[0062] If the aging endpoint time ti and the aging test temperature T are determined, the coefficients a and b in formula (5) can be calculated using the least squares method. Based on the parameters a and b, the activation energy E and the proportional constant B can be calculated, thereby obtaining the life assessment model and estimating the remaining life of the sealing ring sample.

[0063] The present invention provides a life assessment method for a nuclear nitrile rubber sealing ring. Using the above method, the specific implementation results are as follows:

[0064] An aging experiment was carried out on a nuclear nitrile rubber sealing ring. The compression deformation data of the secondary filter sealing ring at different temperatures and different aging times are shown in Table 1 below:

[0065] Table 1 Compression permanent deformation test results of secondary filter seal ring samples after aging (seawater)

[0066]

[0067] like Figure 1 As shown, a graph is drawn with compression permanent deformation as the ordinate and the corresponding aging time as the abscissa, and a graph of compression permanent deformation of the secondary filter seal and its change trend with aging time is drawn.

[0068] According to the high-precision recursive algorithm used in method 1 to perform life prediction calculations, based on the compression permanent deformation data of the sealing ring, a relationship curve between the aging coefficient y and the aging time t used at different temperatures is drawn, such as Figure 2 As shown in Table 2, the critical compression permanent deformation of the secondary filter mesh seal ring is 50%, and the life prediction results of the secondary filter mesh seal ring from 10°C to 40°C are shown in Table 2.

[0069] Table 2 Life prediction results of secondary filter seal ring at different operating temperatures

[0070] Operating temperature / ℃ End of life (year) 10 11.04 20 5.73 25 4.20 30 3.11 35 2.32 40 1.75

[0071] According to the second method, the life prediction calculation is performed using the material performance aging time diagram and Arrhenius diagram. The relationship between the compression permanent deformation and the logarithm of the aging time function lnt is plotted, as shown in Figure 3 shown.

[0072] Select the linear regular area and use the least square method to fit the linear data, as follows: Figure 4 As shown, the compression permanent deformation = 50% is taken as the critical compression permanent deformation of the secondary filter mesh seal ring. The service life prediction results of the secondary filter mesh seal ring at 10°C-40°C are calculated according to the Arrhenius equation as shown in Table 3:

[0073] Table 3 Life prediction results of secondary filter seal ring at different operating temperatures

[0074] Operating temperature / ℃ End of life (year) 10 9.97 20 5.37 25 4.00 30 3.01 35 2.28 40 1.75

[0075] Through calculation, it was found that the evaluation results of the two models were very close, which further demonstrated the validity and accuracy of the data and also provided mutual verification for the evaluation results.

[0076] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A life assessment method for a nuclear nitrile rubber sealing ring, characterized in that: The method comprises: Step 1: Take samples that meet the compression set test from the finished nitrile rubber sealing ring; Step 2: Fix the sample on the fixture, place the sample under test conditions for A days, then open the fixture, and place the sample again for B days before measuring the height of the sample as the initial height; Step 3: setting several groups of different aging temperatures for the samples to perform aging experiments, wherein the highest aging temperature setting does not exceed 110° C.; Step 4: Every D days, take a sample to measure the aging height of the sample, and calculate the compression permanent deformation of the sample until the compression permanent deformation of the sample is higher than 50%. The formula for calculating the compression permanent deformation is as shown in formula (1); Wherein, C is the compression permanent deformation, h0 is the initial height of the sample, and h1 is the aging height of the sample; Step 5: Calculate the life of the sample based on the aging experiment test data.

2. The life assessment method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: The sample that meets the compression permanent deformation test in step 1 is specifically: the sample is a cylinder with a diameter of 12.5-13.5 mm and a height of 6.0 mm-6.6 mm.

3. The life assessment method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: In the step 2, the height measured after parking again for B days is the initial height, and the initial height is measured 6 times to take the average value.

4. The life evaluation method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: The step 3 sets several groups of different aging temperatures for the sample to perform aging experiments, specifically including: Step 3.1: placing the sample into a compression set measurement fixture; Step 3.2: placing the measuring fixture into a sealed container filled with seawater, so that the measuring fixture is immersed in the seawater; Step 3.3: Place the sealed container in an aging box to perform an aging experiment.

5. The life assessment method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: In the step three, several groups of different aging temperatures are set for the samples to carry out aging experiments. Specifically, a total of 4 aging test temperature points are set, and the aging temperatures are set to 95°C, 85°C, 75°C, and 65°C.

6. The life evaluation method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: In the step 4, samples are taken to measure the aging height of the samples every D days, where D days is 1 day, and specifically includes: the aging height of the samples is measured after being parked under test conditions for 1 day, and the average value is taken after 3 measurements; wherein the number of sampling times is not less than 10 times.

7. The life evaluation method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: In the step 5, the life calculation is performed based on the aging test data, specifically including: performing nonlinear fitting on the aging test data collected at all sampling time points to obtain an evaluation life formula, and the fitting formula refers to formula (2): In the formula: t is the life span in years; y0 is the aging coefficient, which is the compression permanent deformation rate C when the aging coefficient is 1 minus the aging time; B is a constant close to 1; T is the aging test temperature; b0, b1, b2 are the unknown coefficients that need to be fitted.

8. The life assessment method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: In the step 5, the life calculation is performed based on the aging test data, specifically including: the aging test data collected at all sampling time points are linearly fitted to obtain an evaluation life formula, and the fitting formula refers to formula (3): y=a+bx (3) Where y is the logarithm of the life span lnt, x is 1 / (T+273.15), T is the aging test temperature, and a and b are unknown constants.

9. The life evaluation method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: The method simultaneously performs control experiments on three groups of the samples.

10. The life evaluation method of a nuclear nitrile rubber sealing ring according to claim 1, characterized in that: In the step 2, the A day is specifically 3 days, and in the step 2, the B day is specifically 1 day.

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