CN112630136A - Nuclear PEEK cable service life assessment method - Google Patents
Nuclear PEEK cable service life assessment method Download PDFInfo
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Abstract
The invention provides a method for evaluating the service life of a PEEK cable for a core, which is used for quickly evaluating the service life of a nuclear-grade cable. The service life of the cable cannot be accurately evaluated by the traditional thermal oxidation aging. The evaluation method combines thermal oxidation aging and irradiation aging, simulates the actual working condition of the nuclear cable to the maximum extent, and provides a method for rapidly evaluating the service life of the nuclear-grade cable. The assessment method provided by the invention is simple and efficient in process, and can be used for rapidly assessing the service life of other conventional nuclear-grade cable materials and composite materials by taking the PEEK cable as a template.
Description
Technical Field
The invention belongs to the field of nuclear materials, and particularly relates to a method for evaluating the service life of a PEEK cable for a nuclear cable.
Background
The cable in the containment vessel of the nuclear power plant is inevitably influenced by the accumulation of environmental factors such as temperature, irradiation, humidity, corrosive steam, ozone, stress and the like in the use process of being in different environments. The long-term influence of these complex factors causes chemical reactions such as thermal expansion, oxidation and decomposition of the material, and physical changes such as brittleness, hardening and cracking, which results in the destruction of insulation and mechanical properties, and serious damage to the safe operation of nuclear power plant systems, structures, equipment, etc.
Of the environmental factors that affect the aging of nuclear grade cables, the most important are temperature and radiation dose. Research has shown that thermo-oxidative aging is a major aging factor in the life cycle of nuclear-grade cables. The cable insulation material is degraded, the thermal decomposition of the insulation material and the internal additives can enhance the conductivity of the insulation material, and the risk of cable insulation failure is increased. Since the nuclear accident of the three miles island in the united states, researchers at home and abroad have conducted more research on the bearing capacity of the containment vessel under the extreme accident.
Polyetheretherketone (PEEK) is a polymer consisting of aromatic rings, ether bonds and ketone bonds, and is a typical representative of high performance engineering plastics. The polyetheretherketone has very good thermal stability, the glass transition temperature (Tg) of the polyetheretherketone is 143 ℃, the melting point is 334 ℃, the maximum crystallinity is 48 percent, and the crystallinity of a typical product is 20 to 30 percent.
Due to the high melting point of the PEEK material, the temperature required for processing is correspondingly high. The existing research on the thermal stability of PEEK mainly aims at the phenomena and reaction mechanisms of thermal crosslinking and thermal degradation reaction of PEEK under different heat treatment conditions. Hay et al studied the thermal stability of PEEK using pyrolysis mass spectrometry. Calculating the mass of the small molecules obtained by cracking, and indicating the specific position of the PEEK subjected to cracking and crosslinking reaction; m. day et al found that the thermal properties of the samples treated under air changed significantly more than those treated under nitrogen when heat treated at 400 c, and that the longer the treatment time, the greater the thermal property change. Cole et al studied the cracking and crosslinking reaction of PEEK by infrared spectroscopy, and qualitatively and quantitatively studied the samples by attenuated total reflection infrared; jonas et al investigated the thermal stability of PEEK by GPC, and found that the change in molecular weight of PEEK is not significant when treated at 440 ℃ in nitrogen at 385 ℃ and that the molecular weight is significantly increased when treated in air, indicating that PEEK is susceptible to cracking reactions in air when treated at high temperatures.
Due to the particularity of the reactor environment of the nuclear power station, the PEEK material is easily aged and cracked under the influence of high temperature, irradiation and the like, meanwhile, the great difficulty is caused in daily routine inspection, maintenance and use of the material due to the particularity of the laying and using environment of the PEEK material, the difficulty in replacement of the material after aging and cracking is great, and the use cost and the replacement cost are high. In order to ensure safe and stable operation of the nuclear power station, the PEEK insulating material for the nuclear power station needs to be subjected to physical and chemical performance tests, the aging state of the PEEK insulating material is evaluated, and the service life of the PEEK material is predicted.
The natural aging is the best method for evaluating the environmental life of the material, but the test period is long, the environmental condition cannot be controlled, and various influencing factors cannot be separately researched. The aging method for accelerating aging can shorten the test period, control the environmental conditions for research and obtain a result with comparability. The conventional accelerated thermal-oxidative aging method is to perform a hot air oxidative aging test for hundreds to thousands of hours at least three different temperatures until the physical property of a sample is reduced below a specified critical index or failure index to obtain at least three corresponding lives, obtain a linear life equation of a tested material through unary linear regression analysis, extrapolate the linear life equation to 20000 hours, and wait for the corresponding temperature to reach the heat-resistant grade of the material. The method is verified by a large number of tests for a long time, has high reliability, is a service life test method which is internationally acknowledged, but takes about 1 year once, and needs to consume a large amount of manpower and material resources.
Therefore, the invention adopts the method of oven accelerated thermal oxidation aging and thermal radiation accelerated aging to carry out thermal oxidation aging with different temperatures and different dosages on the PEEK cable insulation material, researches the performance change of the PEEK material in the aging process, and evaluates the thermal oxidation aging and thermal radiation aging states of the PEEK material. The PEEK material is subjected to quality control, and strict control is performed on the aspects of material performance improvement, aging state evaluation, service life, laying mode and the like, so that stable and safe operation of nuclear power station equipment is ensured, and economic benefits are improved.
Disclosure of Invention
The invention provides a method for evaluating the service life of a PEEK cable for a core, and aims to solve the problem that a method for evaluating the service life of a core-grade cable is not available quickly and accurately.
In order to achieve the purpose, the invention adopts the technical scheme that: a method for evaluating the service life of a PEEK cable for a core is characterized by comprising the following steps: the method comprises a thermal oxidation aging experiment, an irradiation aging experiment and life evaluation calculation;
the thermo-oxidative aging test comprises the following steps:
uniformly winding a PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, adjusting the temperature in the five thermal aging test boxes to be 310 ℃, 280 ℃, 240 ℃, 180 ℃ and 160 ℃, and adjusting the heating rate to be 50-60 ℃/min, taking out one metal rod wound with the PEEK cable from each of the five thermal aging test boxes after the temperature in the thermal aging test boxes is constant, taking the metal rod as a thermal oxidation aging initial sample, and then sampling from the five thermal aging test boxes every 24 hours to obtain the thermal oxidation aging sample;
secondly, storing each taken thermal-oxidative aging initial sample and each taken thermal-oxidative aging sample at 25 ℃ for at least 16 hours, testing the elongation at break of each thermal-oxidative aging initial sample and each thermal-oxidative aging sample, and calculating the retention value of the elongation at break of each thermal-oxidative aging sample, wherein the retention value of the elongation at break is the ratio of the elongation at break of each thermal-oxidative aging sample to that of the thermal-oxidative aging initial sample with the same aging temperature;
thirdly, drawing by taking the retention value of the elongation at break as an ordinate and the corresponding aging time as an abscissa, respectively drawing a coordinate graph of the retention value of the elongation at break and the aging time of the thermal-oxidative aging sample at different temperatures, and recording the aging time as tau according to the coordinate graph of the retention value of the elongation at break and the aging time, and dividing into tauRespectively fitting to obtain values of aging time when the retention value of elongation at break is 50% at the thermal oxidation aging temperature of 310 ℃, 280 ℃, 240 ℃, 180 ℃ and 160 ℃, and respectively recording the values as tau50 310、τ50 280、τ50 240、τ50 180、τ50 160The thermo-oxidative aging temperature is recorded as T, and tau50 310、τ50 280、τ50 240、τ50 180、τ50 160Corresponding aging temperature is ln τ -
Performing linear fitting on the coordinate graph to obtain a linear function of the service life and the thermal-oxidative aging temperature;
the irradiation aging test comprises the following steps:
uniformly winding a PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 25 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 25 ℃ irradiation aging sample;
secondly, uniformly winding the PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 55 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling the irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 55 ℃ irradiation aging sample;
uniformly winding a PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 90 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling the irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 90 ℃ irradiation aging sample;
fourthly, after the taken irradiation aging samples are stored for at least 16 hours at 25 ℃, testing the elongation at break of each irradiation aging sample, and calculating the retention value of the elongation at break of each irradiation aging sample, wherein the retention value of the elongation at break of each irradiation aging sample is the ratio of the elongation at break of each irradiation aging sample to the elongation at break of the irradiation aging sample with irradiation dose of 0 kGy at the same temperature;
fifthly, drawing by taking the retention value of the elongation at break as a vertical coordinate and the corresponding irradiation dose as a horizontal coordinate, respectively drawing a coordinate graph of the retention value of the elongation at break-the irradiation dose of the irradiation aging sample with different irradiation doses, respectively fitting the coordinate graph of the retention value of the elongation at break-the irradiation dose to obtain values of the irradiation dose when the retention value of the elongation at break is 50% at the temperature of 25 ℃, 55 ℃ and 90 ℃, respectively recording as y50 25、y50 55、y50 90The radiation ageing temperature is denoted as T, and y50 25、y50 55、y50 90Corresponding irradiation aging temperature y-
Performing linear fitting on the coordinate graph to obtain a linear function of the irradiation dose and the irradiation aging temperature;
the life assessment calculation includes the steps of:
firstly, calculating the service life tau of the PEEK cable at a specific temperature according to the service life obtained by the thermo-oxidative aging experiment and a linear function of the thermo-oxidative aging temperature1；
A second step according toThe linear function of the irradiation dose and the irradiation aging temperature obtained by the irradiation aging experiment is calculated by referring to the annual accumulated irradiation dose of the service environment where the PEEK cable is estimated to obtain the service life tau of the PEEK cable under the specific temperature and under the rated irradiation dose2；
Third, according to τ = 30%. tau1+ 70% * τ2The service life τ of the PEEK cable was calculated.
The temperatures involved in the calculation and drawing in the above scheme are converted to kelvin temperature calculations.
The relevant content in the above technical solution is explained as follows:
1. in the scheme, the air replacement times of the thermal aging test box are 3-60 times/hour, and each air exchange time is 4 minutes.
2. In the scheme, the diameter of the PEEK cable is 3-10 mm, and the diameter of the metal rod is three times of the measured PEEK cable.
3. In the above scheme, the metal rod is a high temperature resistant and radiation resistant metal rod.
4. In the scheme, during the thermo-oxidative aging experiment, each sample corresponding to the thermo-oxidative aging temperature aging time is not less than 6, and the average value of the elongation at break of each thermo-oxidative aging sample corresponding to the thermo-oxidative aging temperature aging time after the highest value and the lowest value are removed is taken as the elongation at break of each thermo-oxidative aging sample; and during the irradiation aging experiment, each sample corresponding to irradiation aging temperature irradiation dose is not less than 6, and the average value of the elongation at break of each corresponding irradiation aging temperature irradiation dose after the highest value and the lowest value are removed is taken.
5. In the scheme, the irradiation dose rate of the cobalt source is 1-5 kGy/h.
6. In the scheme, the heat aging oven is internally provided with an irradiation-resistant heat insulation layer, and the heat conductivity of the heat insulation layer is less than or equal to 0.03W/m.K.
7. In the scheme, the aging temperature range of the thermal aging test box is 35-350 ℃; uniformity: 2 ℃ C. Air exchange mode: automatic ventilation; the heating rate is as follows: 1-3 ℃/min; the setting range of the aging time is 0-9999 hours; each set of samples tested no less than 3 temperature points.
8. In the scheme, the absorption dose of a heat insulation layer of the thermal aging test box is not lower than 2500 kGy, and the thermal conductivity is not higher than 0.03W/m.K.
9 in the scheme, the thermal aging test box is internally provided with a sample rotating function, and the rotating speed of the placed sample is not lower than 30 r/min.
10. In the scheme, the irradiation source is a cobalt source, the irradiation dose rate is 1-5 kGy/h, and the absorption dose is within the range of 500-5000 kGy.
11. In the scheme, the test method of the breaking strength is a tensile test.
12. In the scheme, the metal rods for winding the PEEK cable are hung on the annular frame in the middle of the thermal aging test box, the distance between the metal rods is not less than 20mm, and the ratio of the total volume of the metal rods for winding the PEEK cable to the volume of the oven is not more than 2%.
The invention has the following design principles and effects:
1. the change of elongation at break of the PEEK cable at different aging temperatures along with time is obtained through a thermo-oxidative aging experiment;
according to the Arrhenius equation,
，
wherein, M-elongation at break change rate;
-rate of change of elongation at break at thermodynamic temperature T; k-Boltzmann constant; the activation energy of the Δ E-is;
performing fixed integration on two sides to obtain
；
Right side calculation can be made
；
Since it is common in the industry to use a retention of elongation at break of 50% (i.e., 50% of the initial elongation at break of the sample)For end of life indication of a material, let t be1As a starting time, M1Is t1Elongation at break, t2Time at 50% elongation at break, M2Is T2Elongation at break in the course of time of
= t2-t1I.e. by
The service life of the PEEK cable is prolonged;
can obtain the product
；
Taking the logarithm of e on two sides to obtain
；
Order to
，
；
Finally obtaining
So that ln can be fitted linearly
And
the relationship between them.
2. The irradiation aging experiment obtains the change of the elongation at break of the PEEK cable at different aging temperatures along with the irradiation dose; the equations and curves in the figures can be derived by fitting a linear formula through the plotting software. The higher the temperature, the lower the cumulative irradiation dose for the elongation at break to fall to 50% of the original data, and the lower the cumulative irradiation dose for the material to fail because the higher the temperature has a severe effect on the material.
The PEEK material has particularly good high temperature resistance, so that under a pure thermal oxidation condition (single factor), related experimental data are obtained through an accelerated aging experiment, formula extrapolation is carried out, and then the change parameters of the material performance at room temperature or use temperature can be obtained, so that generally, for the thermal oxidation experiment of the PEEK, higher experiment temperature is adopted to achieve the effect or the purpose. Under the common action (double factors) of thermal oxygen and radiation, the influence of external conditions on the material performance is more obvious, in the application, under the common condition of thermal oxygen and radiation, the key point is that under the appropriate temperature (the general PEEK material may be less than 100 ℃ under the actual use temperature condition of a nuclear power station), the influence of radiation dose on the material performance is focused, namely, through the aging of large dose, relevant experimental data is obtained, the formula extrapolation is carried out to obtain the service life, and then a relevant proportionality coefficient is introduced to obtain the theoretical actual service life.
4. The single thermal-oxidative aging and the irradiation aging are difficult to meet the actual requirements, so the two aging needs to be combined for calculation. In actual operation, the damage of PEEK is mainly caused by thermal oxidation aging, and the irradiation condition is an accelerating factor of the PEEK aging, so the theoretical service life of the material is calculated by weighted average. The calculation method considers comprehensive factors and is more reasonable.
5. The inventor finds out through a large amount of research and experiments that: the PEEK material has thermal crosslinking and thermal degradation reaction, and the reaction is intensified under the irradiation condition. The service life of the cable cannot be accurately evaluated by the traditional thermal oxidation aging. The evaluation method disclosed by the invention combines thermal oxidation aging and thermal radiation aging, simulates the actual working condition of the nuclear cable to the greatest extent, and provides a method for rapidly evaluating the service life of the nuclear-grade cable.
6. The assessment method provided by the invention is simple and efficient in process, and can be used for rapidly assessing the service life of other conventional nuclear-grade cable materials and composite materials by taking the PEEK cable as a template.
Drawings
FIG. 1 is a schematic view of a metal rod wrapped around a PEEK cable in accordance with the present invention;
FIG. 2 is a graph showing the relationship between the change in retention value of elongation at break and aging time of a material according to example 1 of the present invention;
FIG. 3 is a graph showing the relationship between the thermo-oxidative aging life and the reciprocal of the aging time of the material of example 1 in accordance with the present invention;
FIG. 4 is a graph of the retention of elongation at break of the material of example 1 of the present invention as a function of irradiation dose;
FIG. 5 is a graph showing the relationship between the irradiation dose of the material and the reciprocal of the aging time in example 1 of the present invention.
Detailed Description
The invention is further described with reference to the following figures and examples:
example (b): nuclear PEEK cable service life assessment method
A method for evaluating the service life of a PEEK cable for a core is characterized by comprising the following steps: the method comprises a thermal oxidation aging experiment, an irradiation aging experiment and life evaluation calculation;
the thermo-oxidative aging test comprises the following steps:
uniformly winding a PEEK cable to be detected on a metal rod for three weeks (see figure 1), vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, adjusting the temperature in the five thermal aging test boxes to be 310 ℃, 280 ℃, 240 ℃, 180 ℃ and 160 ℃, taking out one metal rod wound with the PEEK cable from each of the five thermal aging test boxes as a thermal-oxidative aging initial sample after the temperature in the thermal aging test boxes is constant, and then sampling from the five thermal aging test boxes respectively every 24 hours to obtain a thermal-oxidative aging sample;
secondly, storing the taken thermal-oxidative aging sample at 25 ℃ for at least 16 hours, testing the elongation at break of each thermal-oxidative aging initial sample and each thermal-oxidative aging sample, and calculating the retention value of the elongation at break, namely the ratio of the elongation at break of the thermal-oxidative aging sample to the elongation at break of the thermal-oxidative aging initial sample at the same aging temperature;
the test mode of the elongation at break is as follows: (1) cutting the sample into a certain length, measuring the sectional area, filling the cut sample into a sealed bag, marking according to the sampling time, and storing in a drying dish. (2) Before the sample is stretched, marking lines are drawn on the sample, and the distance between the marking lines is 20 mm. (3) And an upper clamp and a lower clamp of the tensile testing machine are installed to ensure that the sample is not twisted in the tensile process. (4) The tensile force and tensile speed of the tensile testing machine were set. (5) The sample is additionally arranged, the edge of the clamp coincides with the marking line, the lifting motion of the cross beam of the stretcher is controlled by the upper PC, the breaking elongation of each sample is recorded after the stretching of each sample is finished, and the sample is stored in a sealed plastic bag and a drying dish. (6) The number of samples per group was 6, the maximum and minimum values in the results were removed, and the average value of elongation at break, and the retention value of elongation at break were calculated.
The elongation at break and retention data obtained in the thermo-oxidative aging test of this example are shown in the following table:
thirdly, drawing by taking the retention value of the elongation at break as a vertical coordinate and the corresponding aging time as a horizontal coordinate, respectively drawing a coordinate graph of the retention value of the elongation at break and the aging time of the thermo-oxidative aging sample at different temperatures (see figure 2), respectively fitting the coordinate graph of the retention value of the elongation at break and the aging time to obtain values of the aging time when the elongation at break is 50% at 310 ℃, 280 ℃, 240 ℃, 180 ℃ and 160 ℃, respectively recording as tau50 310、τ50 280、τ50 240、τ50 180、τ50 160Will tau be50 310、τ50 280、τ50 240、τ50 180、τ50 160Corresponding aging temperature is ln τ -
(see fig. 3), linear fitting was performedSynthesizing to obtain a linear function of the service life and the thermal-oxidative aging temperature;
the irradiation aging test comprises the following steps:
uniformly winding a PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 25 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 25 ℃ irradiation aging sample;
secondly, uniformly winding the PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 55 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling the irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 55 ℃ irradiation aging sample;
uniformly winding a PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 90 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling the irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 90 ℃ irradiation aging sample;
and fourthly, storing the taken irradiation aging samples at 25 ℃ for at least 16 hours, testing the elongation at break of each irradiation aging sample, and calculating the retention rate of the elongation at break, namely the ratio of the elongation at break of the irradiation thermo-oxidative aging sample to the elongation at break of the irradiation thermo-oxidative aging sample with the irradiation dose of 0 kGy.
The data of elongation at break and elongation at break retention obtained in the irradiation and aging experiments of this example are shown in the following table:
fifthly, drawing by taking the retention value of the elongation at break as a vertical coordinate and the corresponding irradiation dose as a horizontal coordinate, respectively drawing a retention value-irradiation dose coordinate graph (shown in figure 4) of the elongation at break of the irradiation aging sample with different irradiation doses, respectively fitting the retention value-irradiation dose coordinate graph of the elongation at break to obtain values of the irradiation dose when the retention value of the elongation at break is 50% at 25 ℃, 55 ℃ and 90 ℃, respectively recording as y50 25、y50 55、y50 90Will y is50 25、y50 55、y50 90Corresponding irradiation aging temperature y-
Linear fitting is carried out to obtain a linear function of the irradiation dose and the irradiation aging temperature (see figure 5);
the life assessment calculation includes the steps of:
firstly, calculating the service life tau of the PEEK cable at a specific temperature according to the service life obtained by the thermo-oxidative aging experiment and a linear function of the thermo-oxidative aging temperature1；
Secondly, calculating the service life tau of the PEEK cable under the rated irradiation dose at a specific temperature according to the linear function of the irradiation dose and the irradiation aging temperature obtained by the irradiation aging experiment and by referring to the annual accumulated rated irradiation dose2；
In this embodiment, the accumulated failure irradiation dose (y) of the material at the actual use temperature can be obtained by substituting the actual use temperature into the formula shown in fig. 5, and the annual accumulated rated irradiation dose of the nuclear power plant area is about 100 kGy (assumed to be: a), and the theoretical use time can be calculated by the ratio (y/a) of the two. Examples are as follows: (1) the cumulative failure irradiation dose calculated from fig. 5 at 100 ℃ (373.15 k) is 1335 kGy, and the theoretical use time is: 1335/100=13.4 (years), i.e. the material can be used for about 13.4 years at 100 ℃; (2) under the condition of 200 ℃ (573.15 k), the cumulative irradiation dose is 771 kGy calculated by the calculation of figure 5, and the theoretical use time is as follows: 771/100=7.7 (years), i.e. at 200 ℃.
Third, according to τ = 30%. tau1+ 70% * τ2The service life τ of the PEEK cable was calculated.
The single thermal-oxidative aging and the irradiation aging are difficult to meet the actual requirements, so the two aging needs to be combined for calculation. In actual operation, the damage of PEEK is mainly caused by thermal oxidation aging, and the irradiation condition is an accelerating factor of the PEEK aging, so the theoretical service life of the material is calculated by weighted average. The service life calculated by the thermal oxidation aging test is 30 percent, and the service life calculated by the irradiation aging test is 70 percent). The theoretical life calculations are exemplified as follows: PEEK life under 100 ℃ service conditions, calculated from fig. 3 for PEEK under hot oxygen alone was 70 years. The theoretical life is calculated as follows by weighted average: 70 years × 30% +13.4 × 70% =30.38 years, i.e., the theoretical use time of PEEK at 100 ℃ is 30 years (rounded).
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (7)
1. A method for evaluating the service life of a PEEK cable for a core is characterized by comprising the following steps: the method comprises a thermal oxidation aging experiment, an irradiation aging experiment and life evaluation calculation;
the thermo-oxidative aging test comprises the following steps:
uniformly winding a PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, adjusting the temperature in the five thermal aging test boxes to be 310 ℃, 280 ℃, 240 ℃, 180 ℃ and 160 ℃, and adjusting the heating rate to be 50-60 ℃/min, taking out one metal rod wound with the PEEK cable from each of the five thermal aging test boxes after the temperature in the thermal aging test boxes is constant, taking the metal rod as a thermal oxidation aging initial sample, and then sampling from the five thermal aging test boxes every 24 hours to obtain the thermal oxidation aging sample;
secondly, storing each taken thermal-oxidative aging initial sample and each taken thermal-oxidative aging sample at 25 ℃ for at least 16 hours, testing the elongation at break of each thermal-oxidative aging initial sample and each thermal-oxidative aging sample, and calculating the retention value of the elongation at break of each thermal-oxidative aging sample, wherein the retention value of the elongation at break is the ratio of the elongation at break of each thermal-oxidative aging sample to that of the thermal-oxidative aging initial sample with the same aging temperature;
thirdly, drawing by taking the retention value of the elongation at break as a vertical coordinate and the corresponding aging time as a horizontal coordinate, respectively drawing a coordinate graph of the retention value of the elongation at break-the aging time of the thermo-oxidative aging sample at different temperatures, respectively recording the aging time as tau according to the coordinate graph of the retention value of the elongation at break-the aging time, respectively fitting to obtain values of the aging time when the retention value of the elongation at break is 50% at the thermo-oxidative aging temperature of 310 ℃, 280 ℃, 240 ℃, 180 ℃ and 160 ℃, respectively recording the values as tau50 310、τ50 280、τ50 240、τ50 180、τ50 160The thermo-oxidative aging temperature is recorded as T, and tau50 310、τ50 280、τ50 240、τ50 180、τ50 160Corresponding aging temperature is ln τ -
Performing linear fitting on the coordinate graph to obtain a linear function of the service life and the thermal-oxidative aging temperature;
the irradiation aging test comprises the following steps:
uniformly winding a PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 25 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 25 ℃ irradiation aging sample;
secondly, uniformly winding the PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 55 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling the irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 55 ℃ irradiation aging sample;
uniformly winding a PEEK cable to be detected on a metal rod for three weeks, vertically hanging a plurality of metal rods wound with the PEEK cable in five thermal aging test boxes respectively, uniformly placing the metal rods wound with the PEEK cable in each thermal aging test box at intervals, setting the temperature of the five thermal aging test boxes to be 90 ℃, then placing the five thermal aging test boxes into a cobalt source for irradiation, controlling the irradiation doses of the PEEK cable in the five thermal aging test boxes to be 0 kGy, 500 kGy, 1000 kGy, 1500 kGy and 2000 kGy respectively, and sampling to obtain a 90 ℃ irradiation aging sample;
fourthly, after the taken irradiation aging samples are stored for at least 16 hours at 25 ℃, testing the elongation at break of each irradiation aging sample, and calculating the retention value of the elongation at break of each irradiation aging sample, wherein the retention value of the elongation at break of each irradiation aging sample is the ratio of the elongation at break of each irradiation aging sample to the elongation at break of the irradiation aging sample with irradiation dose of 0 kGy at the same temperature;
fifthly, drawing by taking the retention value of the elongation at break as a vertical coordinate and the corresponding irradiation dose as a horizontal coordinate, respectively drawing a coordinate graph of the retention value of the elongation at break-the irradiation dose of the irradiation aging sample with different irradiation doses, respectively fitting the coordinate graph of the retention value of the elongation at break-the irradiation dose to obtain values of the irradiation dose when the retention value of the elongation at break is 50% at the temperature of 25 ℃, 55 ℃ and 90 ℃, respectively recording as y50 25、y50 55、y50 90The radiation ageing temperature is denoted as T, and y50 25、y50 55、y50 90Corresponding irradiation aging temperature y-
Performing linear fitting on the coordinate graph to obtain a linear function of the irradiation dose and the irradiation aging temperature;
the life assessment calculation includes the steps of:
firstly, calculating the service life tau of the PEEK cable at a specific temperature according to the service life obtained by the thermo-oxidative aging experiment and a linear function of the thermo-oxidative aging temperature1；
Secondly, calculating the service life tau of the PEEK cable under the rated irradiation dose at a specific temperature according to the linear function of the irradiation dose and the irradiation aging temperature obtained by the irradiation aging experiment and by referring to the annual accumulated irradiation dose of the service environment where the PEEK cable is evaluated2；
Third, according to τ = 30%. tau1+ 70% * τ2The service life τ of the PEEK cable was calculated.
2. The evaluation method according to claim 1, wherein: the air replacement times of the thermal aging test chamber are 3-60 times/hour.
3. The evaluation method according to claim 1, wherein: the PEEK cable diameter is 3-10 mm, and the metal pole diameter is three times of the PEEK cable diameter of survey.
4. The evaluation method according to claim 1, wherein: the metal rod is a high-temperature-resistant and radiation-resistant metal rod.
5. The evaluation method according to claim 1, wherein: when the thermal oxidation aging experiment is carried out, each sample corresponding to the thermal oxidation aging temperature aging time is not less than 6, and the average value of the elongation at break of each thermal oxidation aging sample corresponding to the thermal oxidation aging temperature aging time after the highest value and the lowest value are removed is taken; and during the irradiation aging experiment, each sample corresponding to irradiation aging temperature irradiation dose is not less than 6, and the average value of the elongation at break of each corresponding irradiation aging temperature irradiation dose after the highest value and the lowest value are removed is taken.
6. The evaluation method according to claim 1, wherein: the irradiation dose rate of the cobalt source is 1-5 kGy/h.
7. The evaluation method according to claim 1, wherein: an irradiation-resistant heat insulation layer is arranged in the thermal aging oven, and the heat conductivity of the heat insulation layer is less than or equal to 0.03W/m.K.
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