A method for assessing the lifespan of nuclear-grade nitrile rubber seals.

Abstract

This invention relates to the field of life assessment of rubber sealing materials, and particularly to a method for assessing the life of nuclear-grade nitrile rubber sealing rings. The method includes: Step 1: Cutting samples that meet the compression set test requirements from finished secondary filter sealing rings; Step 2: Fixing the sample in a fixture, placing it under test conditions for 3 days, then opening the fixture, placing it again for one day, and measuring the height as the initial height; Step 3: Conducting aging experiments on the sample at several different aging temperatures; Step 4: Measuring the aging height of the sample at regular intervals and calculating the compression set until the compression set exceeds 50%; Step 5: Calculating the life based on the aging test data. This method uses two different standards and models to calculate the life using the aging test data, and the evaluation results using both models further demonstrate the validity and accuracy of the data.

Description

Technical Field

[0001] This invention relates to the field of life assessment of rubber sealing materials, and in particular to a method for assessing the life of nuclear-grade nitrile rubber sealing rings. Background Technology

[0002] Rubber seals are common components in nuclear power plants, primarily providing sealing for gaseous or liquid media, or buffering, shock absorption, and displacement compensation for rigid materials. Their performance directly impacts the intended functionality of the equipment. Failure of rubber seals generally leads to leakage of the sealed medium, causing anything from resource waste and environmental pollution to system failure. In the event of a failure in a nuclear power plant, irreparable losses can occur, severely impacting normal production. Rubber seals are susceptible to aging and degradation due to various environmental factors such as high and low temperatures, seawater, and ozone, ultimately leading to seal failure.

[0003] The nitrile rubber sealing ring used in the secondary filter core operates in contact with seawater. Seawater has an average pH of 8.2, is highly corrosive, and contains 3.5% salts, primarily composed of chlorine, sodium, sulfur, magnesium, calcium, potassium, and bromine. It is susceptible to humid heat, oxygen, and hydrolysis. Nitrile rubber is a random copolymer of butadiene and acrylonitrile monomers polymerized through emulsion polymerization. Due to the presence of unsaturated and double bonds in the butadiene, it is highly sensitive to oxidative degradation. Under the humid heat, oxygen, and hydrolysis of seawater, the macromolecules undergo structural changes such as cross-linking, polymerization, degradation, hydrolysis, cyclization, and isomerization. The complex composition of seawater and the presence of metal ions strongly catalyze the oxidation reaction of the nitrile rubber sealing ring, accelerating rubber oxidation and potentially causing the long chains of the nitrile rubber to break and small molecules to leak out, leaving voids. This leads to stress concentration at pressure points, ultimately causing the sealing ring to collapse and crack under external pressure. Therefore, it is necessary to conduct an accurate life assessment of the nitrile rubber seals for nuclear secondary filters based on the service environment, predict the service life of the seals, and ensure the reliability of equipment operation.

[0004] In the existing technology, the accelerated aging test for nitrile rubber focuses on media such as air, ethylene glycol, and hydraulic oil. There is a lack of systematic experimental methods for aging tests on the nitrile sealing ring used in the secondary filter core in the seawater medium environment. Summary of the Invention

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

[0006] This invention provides a method for evaluating the lifespan of nuclear-grade nitrile rubber seals, the method comprising:

[0007] Step 1: Cut a sample that meets the compression set test from the finished nitrile rubber sealing ring;

[0008] Step 2: Fix the sample on the fixture, leave the sample under the test conditions for A days, then open the fixture, leave it for B days, and then measure the sample height as the initial height.

[0009] Step 3: Set several groups of different aging temperatures for the samples and conduct aging experiments. The aging temperature should not exceed 110℃.

[0010] Step 4: Every D days, measure the aging height of the sample and calculate the compression set until the compression set of the sample is higher than 50%. The formula for calculating the compression set 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 lifespan of the sample based on the aging test data.

[0014] In some embodiments, the sample selected in step one that meets the requirements of the compression set test is specifically 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 initial height is determined after parking for B days in step two, and the average value is taken from six height measurements.

[0016] In some embodiments, step three involves setting several groups of different aging temperatures for aging experiments on the samples, specifically including:

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

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

[0019] Step 3.3: Place the sealed container into the aging chamber for aging experiment.

[0020] In some embodiments, in step three, several groups of different aging temperatures are set for the sample to conduct aging experiments. Specifically, a total of four aging test temperature points are set, with the aging temperatures set to 95℃, 85℃, 75℃, and 65℃.

[0021] In some embodiments, in step four, the aging height of the sample is measured every D days, where D days is 1 day. Specifically, this includes: measuring the aging height of the sample after it has been left to stand under test conditions for 1 day, and taking the average value after 3 measurements; wherein the number of samplings is not less than 10.

[0022] In some embodiments, step five involves calculating the lifetime 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 lifetime formula, wherein the fitting formula is referenced from formula (2):

[0023]

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

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

[0026] In some embodiments, step five involves calculating the lifespan based on the aging test data, specifically including: obtaining an evaluation lifespan formula by performing linear fitting on the aging test data collected at all sampling time points, with the fitting formula referring to formula (3):

[0027] y = a + bx (3)

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

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

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

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

[0032] This invention provides a life assessment method for nuclear-grade nitrile rubber sealing rings. The experimental conditions of this method are close to the actual service environment of nuclear-grade sealing rings, namely, under compression and immersed in seawater. At the same time, this method calculates the life using two different standards and models based on aging test data. The evaluation results from the two models can further illustrate the validity and accuracy of the data, and also corroborate the evaluation results. Attached Figure Description

[0033] Figure 1 The graph shows the compression set and aging time of a secondary filter sealing ring in a life assessment method for nuclear nitrile rubber sealing rings proposed in this embodiment of the invention.

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

[0035] Figure 3 The graph shows the logarithmic relationship between compression set and aging time in a life assessment method for nuclear nitrile rubber sealing rings proposed in this embodiment of the 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 Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention provides a method for assessing the lifespan of nuclear-grade nitrile rubber sealing rings, using compression set as the lifespan indicator. Compression set and elongation at break are two of the most commonly used performance parameters for predicting the lifespan of rubber materials. Since the sealing ring performs its sealing function by generating strong elastic stress through compression, thereby preventing gas or liquid leakage in the confined space, selecting compression set is closer to the actual service condition of the sealing ring.

[0039] like Figures 1 to 4 As shown, this invention provides a method for evaluating the lifespan of nuclear-grade nitrile rubber sealing rings, the method comprising:

[0040] Step 1: Cut a sample that meets the compression set test from the finished secondary filter sealing ring.

[0041] In step one, a sample conforming to the compression set test is 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: Under normal and high temperature conditions". As per the standard, the sample is a cylinder with a diameter of 12.5-13.5 mm and a height of 6.0 mm-6.6 mm. Three samples are prepared 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 two, after parking for another day, the height is measured as the initial height. The height is measured 6 times and the average value is taken as the initial height.

[0044] Step 3: Place the sample into the compression set measuring fixture, and then place the measuring fixture into a sealed container filled with seawater; place the sealed container into an aging chamber for aging, and set several different aging temperatures for aging experiments. Based on the characteristics of nitrile material and seawater medium, the aging temperature should not exceed 110℃.

[0045] In step three, the amount of seawater used should be such that the measuring fixture is submerged in seawater. A total of four aging test temperature points are set, with aging temperatures of 95℃, 85℃, 75℃, and 65℃.

[0046] Step 4: Every so often, remove the measuring fixture from the aging chamber, place the sample under standard test conditions for 1 day, and 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 four, the number of sampling times for calculating compressive permanent deformation shall not be less than 10, and the formula for calculating compressive permanent deformation 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: Lifetime prediction calculation using a high-precision recursive algorithm. The evaluation results are obtained by nonlinear fitting of data collected at all sampling time points. The fitting formula is referenced in formula (2):

[0052]

[0053] In the formula: t is the lifespan in years; y0 is the aging coefficient, which is the compression set 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, and b2 are undetermined coefficients to be fitted.

[0054] Method 2: Lifetime prediction calculations are performed using the material's performance aging time diagram and Arrhenius diagram. The Arrhenius equation is shown in formula (3):

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

[0056] In the formula: 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 equations (3) and (4), the logarithmic equation (5) is obtained by synthesizing the constant term:

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

[0060] Typically, the logarithm of time, lnt, exhibits an Arrhenius relationship with the reciprocal of thermodynamic temperature, 1 / T. Within the same temperature range for the main aging reactions, the activation energy E is constant. Rearranging equation (5), and setting x = 1 / (T + 273.15) and y = lnt, we obtain equation (6):

[0061] y = a + bx (6)

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

[0063] This invention provides a method for evaluating the lifespan of nuclear-grade nitrile rubber sealing rings. Using the method described above, the specific implementation results are as follows:

[0064] An aging test was conducted on a certain nuclear-grade nitrile rubber sealing ring. The compression deformation data of the secondary filter sealing ring under different temperatures and aging times are shown in Table 1 below.

[0065] Table 1. Results of compression set test on secondary filter sealing ring samples after aging (seawater)

[0066]

[0067] like Figure 1 As shown, a graph is plotted with compression set as the vertical axis and the corresponding aging time as the horizontal axis to show the trend of compression set of the secondary filter sealing ring with aging time.

[0068] Based on the high-precision recursive algorithm used in Method 1 for lifetime prediction calculation, and using the compression set data of the sealing ring, the relationship curves between the aging coefficient y and aging time t at different temperatures are plotted, as follows: Figure 2 As shown in Table 2, taking 50% as the critical compression set of the secondary filter sealing ring, the predicted lifespan of the secondary filter sealing ring from 10℃ to 40℃ is as follows.

[0069] Table 2. Lifespan predictions of secondary filter sealing rings at different operating temperatures.

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

[0071] The life prediction calculation is performed using the material's performance aging time diagram and Arrhenius plot as described in Method 2. A graph showing the relationship between compressive settling and the logarithm (lnt) of the aging time function is plotted, as shown below. Figure 3 As shown.

[0072] Select the linear region and use the least squares method to fit the linear data, specifically as follows: Figure 4 As shown, the critical compression set of the secondary filter sealing ring is taken as 50%. The predicted service life of the secondary filter sealing ring at 10℃-40℃ is calculated based on the Arrhenius equation and is shown in Table 3 below.

[0073] Table 3. Lifespan predictions of secondary filter sealing rings at different operating temperatures.

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

[0075] The calculations revealed that the evaluation results of the two models were very close, which further demonstrated the validity and accuracy of the data and also corroborated the evaluation results.

[0076] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for evaluating the lifespan of a nuclear-grade nitrile rubber sealing ring, characterized in that, The method includes: Step 1: Cut a sample that meets the compression set test from the finished nitrile rubber sealing ring; Step 2: Fix the sample on the fixture, leave the sample under the test conditions for A days, then open the fixture, leave it for B days, and then measure the height of the sample as the initial height. Step 3: Set several groups of different aging temperatures for the sample to carry out aging experiments. The aging temperature shall not exceed 110℃. Step 4: Every D days, take a sample to measure the aging height of the sample and calculate the compression set of the sample until the compression set of the sample is higher than 50%. The formula for calculating the compression set is as shown in Formula (1). Where C is the compression set, h0 is the initial height of the sample, and h1 is the aging height of the sample; Step 5: Calculate the lifetime of the sample based on the aging test data. The specific method includes: performing nonlinear fitting on the aging test data collected at all sampling time points to obtain the lifetime evaluation formula. The fitting formula is referenced in formula (2): In the formula: t is the lifespan in years; y0 is the aging coefficient, which is the compression set 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, and b2 are the undetermined coefficients to be fitted; and the aging test data collected at all sampling time points are used to obtain the lifespan evaluation formula by linear fitting. The fitted formula is referenced in formula (3): y = a + bx (3) Where y is the logarithm of lifetime lnt, x is 1 / (T+273.15), T is the aging test temperature, and a and b are undetermined constants.

2. The life assessment method for a nuclear-grade nitrile rubber sealing ring according to claim 1, characterized in that, The sample selected in step one that meets the requirements of the compression set test 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 for a nuclear-grade nitrile rubber sealing ring according to claim 1, characterized in that, In step two, the height is measured again after B days to obtain the initial height. The initial height is measured 6 times and the average value is taken.

4. The life assessment method for a nuclear-grade nitrile rubber sealing ring according to claim 1, characterized in that, Step three involves setting several groups of different aging temperatures for aging experiments on the sample, specifically including: Step 3.1: Place the sample into the compression set measuring fixture; Step 3.2: Place the measuring clamp into a sealed container filled with seawater, so that the measuring clamp is submerged in the seawater; Step 3.3: Place the sealed container into an aging chamber for an aging experiment.

5. The life assessment method for a nuclear-grade nitrile rubber sealing ring according to claim 1, characterized in that, In step three, several groups of different aging temperatures are set for the sample to conduct aging experiments. Specifically, a total of four aging test temperature points are set, with aging temperatures of 95℃, 85℃, 75℃, and 65℃.

6. The life assessment method for a nuclear-grade nitrile rubber sealing ring according to claim 1, characterized in that, In step four, the aging height of the sample is measured every D days, where D days is 1 day. Specifically, the aging height of the sample is measured after it has been left to stand under test conditions for 1 day. The average value is taken after 3 measurements. The number of samplings is no less than 10.

7. The life assessment method for a nuclear-grade nitrile rubber sealing ring according to claim 1, characterized in that, The method simultaneously performs control experiments on the three groups of samples.

8. The life assessment method for a nuclear-grade nitrile rubber sealing ring according to claim 1, characterized in that, In step two, day A specifically refers to 3 days, and day B specifically refers to 1 day.

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