Method for monitoring and identifying micro-crack propagation of high-temperature pipeline

Abstract

The present application belongs to the technical field of sensing and monitoring, and provides a method for monitoring and identifying micro-crack expansion of high-temperature pipelines, which comprises the following steps: calculating accurate strain transmission efficiency m1 between bare optical fiber and plane metal base; calculating accurate strain transmission efficiency m2 between plane metal base without fiber and cylindrical pipeline; obtaining temperature sensitivity coefficient a of the optical fiber sensor; monitoring strain caused by interference of pipeline thermal expansion effect; and monitoring and identifying strain caused by crack expansion. The present application obtains accurate strain transmission efficiency of different interfaces by eliminating abnormal points caused by abnormal factors, and then removes the influence of temperature on strain sensor measurement and the influence of temperature on pipeline thermal expansion effect by using temperature sensitivity coefficient and a self-built pipeline model, so that the change of strain caused only by crack expansion is finally obtained, which is of great significance for evaluating crack development trend, life evaluation and safety warning of high-temperature pipelines.

Description

Technical Field

[0001] This invention belongs to the field of sensing and monitoring technology, specifically relating to a method for monitoring and identifying the propagation of microcracks in high-temperature pipelines. Background Technology

[0002] Pipelines are common structures in aerospace, industrial production, and other fields. Due to the influence of their working environment, such as the extreme temperatures of aerospace, the high stress of industrial production, and the high-temperature and high-pressure environments of transported materials, they are susceptible to cracking and crack propagation risks. Crack propagation poses a significant risk to the safe operation of the system. Monitoring the crack condition of pipelines, especially the crack propagation of high-temperature pipelines, is crucial for assessing their lifespan. Conventional methods for monitoring pipeline crack propagation include ultrasonic testing, X-ray testing, and eddy current testing. Ultrasonic testing offers high sensitivity, but its disadvantages include the need to apply a coupling agent to the surface of the structure under test, introducing unwanted material and making it less suitable for high-temperature environments. X-ray testing is fast and accurate, but it cannot provide 24-hour real-time monitoring and requires customization for complex structures with steep slopes. Eddy current testing offers convenient detection of cracks and fatigue damage in pipelines, but its limitations are significantly affected by the oxide layer on the high-temperature pipeline surface, further influencing the measurement results.

[0003] For cylindrical high-temperature pipes, cracks often occur in the following situations:

[0004] In the first case, cracks are arranged circumferentially. The fiber optic sensor is installed in the direction perpendicular to the crack. The fiber optic sensor is equivalent to the direction along the axial direction of the pipe.

[0005] In the second case, the cracks are arranged axially, and the fiber optic sensor is installed in the direction perpendicular to the crack. The fiber optic sensor is equivalent to the direction along the circumference of the pipe.

[0006] Comparing the two scenarios above, the second scenario is more complex. This is because in the first scenario, the fiber optic sensor is installed along the axial direction of the pipe, and the bonding area is approximately planar (straight line) for monitoring; in the second scenario, the fiber optic sensor is installed along the circumferential direction of the pipe, and the bonding area is curved (curve) for monitoring. If the second scenario is effectively resolved, the first scenario will be readily solved. Therefore, this invention addresses the second scenario, namely, the propagation monitoring of cracks arranged along the axial direction of the pipe. Summary of the Invention

[0007] To address the problems existing in the background art, the present invention provides a method for monitoring and identifying the propagation of microcracks in high-temperature pipelines. This method includes the following steps:

[0008] S1. The accurate strain transfer efficiency m1 between the bare optical fiber and the planar metal substrate is obtained by automatically eliminating data anomalies introduced by abnormal factors.

[0009] S2. By bonding the curved surface structure with the same curvature of the pipe to the non-fiber planar metal substrate, and combining the method of automatically eliminating data anomalies introduced by abnormal factors, the accurate strain transfer efficiency m2 between the non-fiber planar metal substrate and the cylindrical pipe is obtained.

[0010] S3. Obtain the temperature sensitivity coefficient α of the fiber optic sensor;

[0011] S4. Strain monitoring of interference caused by pipeline thermal expansion effect;

[0012] S5. Install fiber optic sensors at specific locations of pipe cracks to assess the strain caused by crack propagation.

[0013] The specific process of step S1 includes:

[0014] S11. Measure the wavelength shift Δλ of bare optical fiber under different strains Δε;

[0015] S12. By automatically eliminating data anomalies caused by abnormal factors, the accurate sensitivity coefficient η1 of the bare optical fiber without planar metal encapsulation is obtained:

[0016]

[0017] S13. The accurate sensitivity coefficient η2 of the fiber optic sensor with a planar metal substrate is obtained by automatically eliminating abnormal data anomalies.

[0018] S14. The accurate strain transfer efficiency between the bare fiber and the planar metal substrate is obtained by comparing the sensitivity coefficient η2 of the fiber sensor with the bare fiber's encapsulation with the sensitivity coefficient η1 of the bare fiber:

[0019]

[0020] The specific processes of steps S12 and S13 include:

[0021] S121. Measure the strain value Δε under different gradient tensions. k And the corresponding offset Δλ of the center wavelength of the fiber optic sensor k (k = 0, ..., b-1)

[0022] S122, Substitute into the fitting equation:

[0023]

[0024] Where s represents the distance from the origin to (Δλ)k ,Δε k The distance of the fitted straight line. To fit the angle between the straight line and the coordinate axis;

[0025] When k takes a constant value between 0 and b-1, that is, when the strain value Δε under a certain gradient stretching and the corresponding offset Δλ of the center wavelength of the fiber optic sensor are substituted into the fitting equation, s and There is one and only one curve that can be determined; when s and When the value is constant, there is one and only one straight line between the offset Δλ of the center wavelength of the fiber optic sensor and the strain value Δε.

[0026] Given the set of measurement points (Δλ) k ,Δε k A line can be uniquely determined by s, so s and There exists a fixed value that makes this true, i.e., the set of measurement points (Δλ) k ,Δε k ) drawn The curve passes through a fixed point; once that fixed point is determined, (Δλ) can be obtained. k ,Δε k Fit a straight line.

[0027] S123. The specific fitting process is as follows:

[0028] S1231. Record the measured value Δλ of the fiber optic sensor obtained from n tensile tests performed on a bare optical fiber without planar metal substrate encapsulation using a tensile machine. k (k=0,…,14) and their corresponding strain values ​​Δε k ;get curve;

[0029] S1232. Discretize the curve. Point set (Δλ) k ,Δε k There are n measured values, each measured value is processed according to the discretized... The values ​​are taken from N scattered points. The s values ​​corresponding to the total nN scattered points are statistically analyzed. The point with the most repeated s values ​​in the statistical results is used for curve fitting to obtain the accurate bare fiber sensitivity coefficient value.

[0030] S1233. The number of times the function value corresponding to the abnormal data point introduced by abnormal factors during the measurement process appears is much less than the number of times the function value corresponding to the normal data point appears. Since the curve fitting is performed on the point where the s value appears most frequently in the statistical results, the abnormal data point has no impact on the fitting result. The abnormal value is automatically discarded, and the accurate value η1 of the bare fiber sensitivity coefficient is obtained.

[0031] S131. After obtaining the accurate bare fiber sensitivity coefficient η1, refer to steps S121-S123 and perform the same stretching steps on the fiber optic sensor with planar metal substrate encapsulation to obtain the sensitivity coefficient η2 of the fiber optic sensor with planar metal substrate encapsulation.

[0032] The specific process of step S2 includes:

[0033] S21. Using an equal-strength beam as a calibration tool, the equal-strength beam is bent by adding weights until the curvature of the equal-strength beam approximates the curvature of the pipe.

[0034] S22. Attach a fiberless planar metal substrate to the bent equal strength beam, and attach unidirectional resistance strain gauge one and resistance strain gauge two to the equal strength beam and the planar metal substrate respectively.

[0035] S23. By slightly changing the weights and recording the strains measured by the resistance strain gauge as ε1 and ε2, the strain transfer efficiency is:

[0036] S24. Automatically eliminate data anomalies introduced by abnormal factors to obtain the accurate strain transfer efficiency m2 between the planar metal substrate and the pipe.

[0037] In step S23, adding or removing weights requires ensuring that the change in strain does not exceed 200 με.

[0038] The specific process of step S3 includes:

[0039] The fiber optic sensor was placed in a temperature chamber to ensure that it was not subjected to any stress. The wavelength change at different temperatures was obtained, and the temperature sensitivity coefficient α of the fiber optic was obtained through linear fitting.

[0040] The specific process of step S4 includes:

[0041] S41. Based on the material properties and dimensions of the pipe, create a local model of the pipe and attach resistance strain gauges along the circumferential direction of the pipe.

[0042] S42. Place the pipe model with the resistance strain gauge attached into the temperature chamber. The initial temperature of the temperature chamber is the initial temperature T0 before the pipe is heated. At this time, the reading of the resistance strain gauge is cleared to zero.

[0043] S43. Heat the chamber to the high-temperature pipeline operating temperature T1, and record the strain value ε of the resistance strain gauge at this time. T After repeated measurements, the average value ε′ was obtained. T .

[0044] The specific process of step S5 includes:

[0045] S51. Given a crack length l, in order to determine the propagation direction of a high-temperature pipe crack, one fiber optic sensor is installed at each end of the crack perpendicular to the crack direction; another fiber optic sensor is installed at l / 3 and 2l / 3 of the distance from the crack head perpendicular to the crack direction; the four sensors are labeled A, B, C, and D.

[0046] S52. After completing the above calibration and installation work, start the fiber optic sensor monitoring and record the initial wavelength λ of the four fiber optic sensors at the initial temperature T0 of the pipeline. A0 , λ B0 , λ C0 , λ D0 ;

[0047] S53. Heat the pipeline until it reaches the pipeline operating temperature T1. After the pipeline temperature stabilizes, record the wavelength values ​​λ of the four fiber optic sensors in real time. A ′、λ B ′、λ C ′、λ D ′;

[0048] S54. Calculate the strain caused only by crack propagation based on the strain expression to obtain the propagation identification result;

[0049] The strain expression is:

[0050] ε A =(λ A ′-λ A0 -α×(T1-T0))×η1 / (m1×m2)-ε T ′

[0051] ε B =(λ B ′-λ B0 -α×(T1-T0))×η1 / (m1×m2)-ε T ′

[0052] ε C =(λ C ′-λ C0 -α×(T1-T0))×η1 / (m1×m2)-ε T ′

[0053] ε D =(λ D ′-λ D0 -α×(T1-T0))×η1 / (m1×m2)-ε T ′

[0054] The extended recognition result judgment method is as follows:

[0055] (1) If εA ε B ε C ε D The lack of significant changes indicates that the cracks in the high-temperature pipeline are not showing a tendency to propagate and are in a stable state.

[0056] (2) If ε A Significantly increased, ε B ε C ε D The lack of significant changes indicates that the crack in the high-temperature pipeline tends to extend and lengthen towards end A, but does not show any tendency to extend in the width direction.

[0057] (3) If ε B Significantly increased, ε A ε C ε D The lack of significant changes indicates that the crack in the high-temperature pipeline tends to extend and lengthen towards end B, but does not show any trend of expansion in the width direction.

[0058] (4) If ε C Significantly increased, ε A ε B ε D The lack of significant changes indicates that the crack in the high-temperature pipeline tends to extend in the width direction around 1 / 3, but not in the length direction.

[0059] (5) If ε D Significantly increased, ε A ε B ε C The lack of significant changes indicates that the crack in the high-temperature pipeline near 2l / 3 has a tendency to expand in the width direction but not in the length direction.

[0060] (6) If ε A ε B Significantly increased, ε C ε D The lack of significant changes indicates that the crack in the high-temperature pipeline tends to extend and lengthen towards both end A and end B, but does not show any trend of expansion in the width direction.

[0061] (7) If ε C ε D Significantly increased, ε A ε B The lack of significant changes indicates that the cracks in the high-temperature pipeline tend to extend in the width direction but not in the length direction.

[0062] (8) If ε A ε B ε C ε DBoth values ​​increased significantly, indicating that the cracks in the high-temperature pipeline have a tendency to expand in both length and width directions.

[0063] The beneficial effects achieved by this invention are as follows:

[0064] First, this invention proposes a method for automatically eliminating abnormal points caused by abnormal factors and a method for calibrating the strain transfer efficiency of the same curvature / fiberless planar substrate. This method obtains the accurate strain transfer efficiency of different interfaces. Combined with the calibration of the same curvature of the equal strength beam, it removes the influence caused by the different shapes and amounts of adhesives between the optical fiber planar substrate and the cylindrical pipe, and finally obtains the accurate strain transfer efficiency between the bare optical fiber and the pipe.

[0065] Secondly, in order to obtain the strain change caused by the single factor of crack propagation, this invention firstly removes the influence of temperature on the measurement value of the fiber optic strain sensor when the pipeline is heated from room temperature to high temperature, and secondly removes the increase in strain of the structure itself caused by thermal expansion during the heating process, effectively solving the problem of accurate differentiation of multiple components.

[0066] Third, this invention uses a temperature sensitivity coefficient and a self-built pipeline model to remove the "influence of temperature on strain sensor measurement" and "influence of temperature on pipeline thermal expansion effect" in the total strain, and finally obtains the strain change caused only by crack propagation. Then, based on the criteria proposed by this invention, it can determine whether the crack propagates along the crack extension direction, perpendicular to the crack direction, or both directions simultaneously.

[0067] Fourth, by installing fiber optic strain sensors at the beginning, end, and middle sections of cracks in cylindrical pipes, and combining this invention with the method specific to this patent, accurate values ​​of strain at different locations under high-temperature conditions can be obtained. This allows for accurate assessment of the longitudinal, transverse, and simultaneous longitudinal and transverse propagation of existing cracks in high-temperature pipes. This is of great significance for assessing the crack development trend, life assessment, and safety early warning of high-temperature pipes. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of sensor installation for monitoring the propagation of cracks in a cylindrical pipe.

[0069] Figure 2 This is a structural diagram of a fiber optic sensor with a planar metal substrate mounted on the surface of a cylindrical pipe.

[0070] Figure 3 This is a schematic diagram of an installation structure that uses a beam of equal strength to measure the strain transfer efficiency between a planar metal substrate and a cylindrical structure with the same curvature.

[0071] Figure 4 This is the overall flowchart of the present invention.

[0072] Numbering on the map:

[0073] 1. Pipe; 2. Adhesive; 3. Contact boss; 4. Planar metal substrate; 5. Fiber optic sensor; 6. Resistance strain gauge one; 7. Resistance strain gauge two; 8. Weight; 9. Equal strength beam. Detailed Implementation

[0074] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0075] like Figure 1 As shown, the fiber optic sensor 5 with a planar metal substrate 4 is directly attached to both ends and the middle section of the crack in the pipe 1. The pipe is connected to the planar metal substrate 4 through adhesive 2 and contact boss 3. The planar metal substrate 4 is connected to the fiber optic sensor 5. The crack propagation and direction are evaluated by accurately monitoring the strain under high temperature environment.

[0076] There are three key issues here:

[0077] First, there is the issue of accurately obtaining the strain transfer efficiency. On one hand, the optical fiber encapsulated on the planar metal substrate has its own strain transfer efficiency m1. On the other hand, and most importantly, the planar metal substrate is fixed to the cylindrical pipe with adhesive, resulting in a strain transfer efficiency m2 under bending conditions. These two transfer efficiencies, m1 and m2, need to be accurately measured to obtain the accurate strain value after crack propagation; otherwise, it will lead to false alarms regarding whether crack propagation has occurred.

[0078] Secondly, it automatically eliminates outliers caused by abnormal factors. In obtaining transmission efficiency, the conventional method is to use a standard resistance strain gauge as a reference and apply a gradient strain value to perform linear fitting between strain and wavelength. In this invention, through steps one and two, data anomalies introduced by abnormal factors can be automatically eliminated, resulting in a more accurate transmission efficiency.

[0079] Finally, there is the issue of accurately distinguishing the multiple components of strain. The strain value measured by the fiber optic strain sensor is not only due to the strain caused by crack propagation, but also includes two other parts: first, the influence of temperature on the fiber optic strain sensor measurement value when the pipeline rises from room temperature to high temperature, and this factor must be eliminated; second, the increase in strain of the structure itself due to thermal expansion when the pipeline rises from room temperature to high temperature, and this factor must also be eliminated.

[0080] By solving the above three key problems, this invention can accurately obtain the strain change caused solely by crack propagation, which is of great significance for accurately assessing whether cracks are propagating and the direction of propagation.

[0081] Reference Figures 1-4 The specific operation of this invention is divided into the following steps:

[0082] Step 1: Obtain the accurate strain transfer efficiency m1 between the bare optical fiber and the planar metal substrate by automatically eliminating data anomalies introduced by abnormal factors.

[0083] First, a bare optical fiber without planar metal substrate encapsulation is stretched b times with different gradient values ​​using a stretching machine. Simultaneously, the offset Δλ of the fiber optic sensor's center wavelength under each stretching gradient (which can be recorded as the strain value Δε) is recorded. Through transformation (detailed operation below), abnormal data points caused by non-normal factors can be automatically eliminated, yielding the accurate sensitivity coefficient η1 of the bare optical fiber without planar metal substrate encapsulation.

[0084] The specific transformation process of the method for automatically removing data outliers introduced by abnormal factors is as follows:

[0085] (1) Definition: The strain value Δε measured under different gradient tensions k And the corresponding offset Δλ of the center wavelength of the fiber optic sensor k (k = 0, ..., b-1);

[0086] (2) Substitute into the fitting equation

[0087]

[0088] Here, s represents the distance from the origin to (Δλ). k ,Δε k The distance of the fitted straight line. To fit the angle between the straight line and the coordinate axis;

[0089] From the above equation, it can be seen that when k takes a constant value between 0 and b-1, that is, when the strain value Δε under a certain gradient stretching and the corresponding offset Δλ of the center wavelength of the fiber optic sensor are substituted into the fitting equation, s and There is one and only one curve that can be determined; when s and When the value is constant, there is one and only one straight line between the offset Δλ of the center wavelength of the fiber optic sensor and the strain value Δε.

[0090] Given the set of measurement points (Δλ) k ,Δε k A line can be uniquely determined by s, so s and There exists a fixed value that makes this true, i.e., the set of measurement points (Δλ)k ,Δε k ) drawn The curve passes through a fixed point; once that fixed point is determined, (Δλ) can be obtained. k ,Δε k Fit a straight line.

[0091] (3) Specific fitting process

[0092] Taking b=15 as an example, first record the measured value Δλ of the fiber optic sensor obtained from the 15 tensile tests conducted on the bare fiber optic cable without planar metal substrate encapsulation using a tensile machine. k (k=0,…,14) and their corresponding strain values ​​Δε k .get The curve is discretized. The point set (Δλ) is then processed. k ,Δε k There are 15 measured values. Assume each measured value is discretized... A total of 100 scatter points were selected, and the s-values ​​corresponding to these 1500 scatter points were statistically analyzed. Curve fitting was then performed on the point with the most repeated s-values ​​in the statistical results to obtain the accurate bare fiber sensitivity coefficient. Using this fitting method, the function values ​​s corresponding to data anomalies introduced by abnormal factors during the measurement process occur very infrequently and are automatically discarded, thus yielding the accurate value η1 of the bare fiber sensitivity coefficient.

[0093] After obtaining the accurate bare fiber sensitivity coefficient η1, the same stretching steps are then performed on the fiber optic sensor with a planar metal substrate to obtain the sensitivity coefficient η2 of the fiber optic sensor with a planar metal substrate.

[0094] The accurate strain transfer efficiency between the bare fiber and the planar metal substrate is obtained by comparing the sensitivity coefficient η2 of the fiber sensor packaged with the sensitivity coefficient η1 of the bare fiber.

[0095] Step 2: By fitting the curved surface structure with the same curvature of the pipe to the non-fiber planar metal substrate, and combining this with a method to automatically eliminate data anomalies introduced by abnormal factors, the accurate strain transfer efficiency m2 between the non-fiber planar metal substrate and the cylindrical pipe is obtained.

[0096] Typically, it's relatively easy to obtain strain transfer efficiency by mounting fiber optic sensors with planar metal substrates onto structures with planar contact surfaces; for example, a tensile testing machine can be used to directly stretch the planar structure under test. However, for cylindrical pipes, the large size and structural complexity make tensile testing impossible. Furthermore, the circular cross-section of the pipe, with its varying curvature, is affected by the shape and amount of adhesive used between the planar fiber optic substrate and the cylindrical pipe, which in turn affects the accurate calibration of the transfer coefficient between the planar substrate and the cylindrical pipe.

[0097] This invention uses an equal-strength beam 9 as a calibration tool. To obtain an accurate m2 value, the equal-strength beam 9 is bent by adding weights 8 until its curvature approximates that of the pipe. At this point, the strain transfer efficiency m2 is measured. A planar metal substrate without fiber optic sensors is attached to the equal-strength beam. Then, unidirectional resistance strain gauges 6 and 7 are attached as references to the equal-strength beam and the metal substrate without fiber optic sensors, respectively. The measured strains are ε1 and ε2, respectively. The strain transfer efficiency is then calculated as follows:

[0098] This is fundamentally different from the conventional method of attaching metal substrates and resistance strain gauges to beams of equal strength before bending deformation occurs. If the substrates are attached in the initial state, the optical fiber planar metal substrate will undergo significant deformation when the beam of equal strength bends, resulting in a large difference from the state of the optical fiber planar metal substrate attached to a high-temperature pipeline, thus introducing a large error.

[0099] After completing the above operations, add and remove weights in a small range on the beam of equal strength so that the curvature of the beam remains basically unchanged. Record the strain values ​​of the two resistance strain gauges at this time. In order to keep the curvature basically unchanged, the addition and removal of weights should ensure that the change in strain does not exceed 200με.

[0100] Similarly, by using the transformation method in step one, abnormal data points introduced by abnormal factors are automatically eliminated, thereby obtaining the accurate strain transfer efficiency m2 value between the planar metal substrate and the cylindrical pipe under test.

[0101] Step 3: Obtain the temperature sensitivity coefficient α of the fiber optic sensor.

[0102] The fiber optic sensor was placed in a temperature chamber to ensure that it was not subjected to any stress. The wavelength change at different temperatures was obtained, and the temperature sensitivity coefficient α of the fiber optic was obtained through linear fitting.

[0103] Step 4: Monitoring the interference strain caused by the thermal expansion effect of the pipeline

[0104] Based on the material properties and dimensions of the pipeline, a partial model of the pipeline is created. Resistance strain gauges are attached to the pipeline along its circumference. The pipeline model with the strain gauges is then placed in a temperature chamber. The initial temperature of the chamber is T0, the initial temperature before the pipeline is heated, and the strain gauge readings are reset to zero. The temperature chamber is then raised to the high-temperature operating temperature T1 of the pipeline, and the strain value ε of the strain gauges is recorded at this point. T After repeated measurements, the average value ε′ was obtained. T .

[0105] Step 5: Mounting the fiber optic sensor on the pipe crack

[0106] Assuming a crack length of l, to determine the propagation direction of the high-temperature pipe crack, one fiber optic sensor is installed at each end of the crack, perpendicular to the crack direction. Another fiber optic sensor is installed at a distance of l / 3 and 2l / 3 from the crack head, perpendicular to the crack direction. The four sensors are labeled A, B, C, and D.

[0107] Step Six: Power-on Test

[0108] After completing the above calibration and installation work, start the fiber optic sensing monitoring system and record the initial wavelength λ of the four fiber optic sensors at the initial temperature T0 of the pipeline. A0 , λ B0 , λ C0 , λ D0 .

[0109] The pipeline is heated until it reaches its operating temperature T1. After the pipeline temperature stabilizes, the wavelength values ​​λ of the four fiber optic sensors are recorded in real time. A ′、λ B ′、λ C ′、λ D ′.

[0110] Furthermore, the expression for strain caused solely by crack propagation is obtained as follows:

[0111] ε A =(λ A ′-λ A0 -α×(T1-T0))×η1 / (m1×m2)-ε T ′

[0112] ε B =(λ B ′-λ B0 -α×(T1-T0))×η1 / (m1×m2)-ε T ′

[0113] ε C =(λ C ′-λ C0-α×(T1-T0))×η1 / (m1×m2)-ε T ′

[0114] ε D =(λ D ′-λ D0 -α×(T1-T0))×η1 / (m1×m2)-ε T ′

[0115] Criterion:

[0116] (9) If ε A ε B ε C ε D The lack of significant changes indicates that the cracks in the high-temperature pipeline are not showing a tendency to propagate and are in a stable state.

[0117] (10) If ε A Significantly increased, ε B ε C ε D The lack of significant changes indicates that the crack in the high-temperature pipeline tends to extend and lengthen towards end A, but does not show any trend of expansion in the width direction.

[0118] (11) If ε B Significantly increased, ε A ε C ε D The lack of significant changes indicates that the crack in the high-temperature pipeline tends to extend and lengthen towards end B, but does not show any trend of expansion in the width direction.

[0119] (12) If ε C Significantly increased, ε A ε B ε D The lack of significant changes indicates that the crack in the high-temperature pipeline tends to extend in the width direction around 1 / 3, but not in the length direction.

[0120] (13) If ε D Significantly increased, ε A ε B ε C The lack of significant changes indicates that the crack in the high-temperature pipeline near 2l / 3 has a tendency to expand in the width direction, but not in the length direction.

[0121] (14) If ε A ε B Significantly increased, ε C ε D The lack of significant changes indicates that the crack in the high-temperature pipeline tends to extend and lengthen towards end A and end B, but does not show any trend of expansion in the width direction.

[0122] (15) If ε C ε D Significantly increased, ε A ε B The lack of significant changes indicates that the cracks in the high-temperature pipeline tend to extend in the width direction but not in the length direction.

[0123] (16) If ε A ε B ε C ε D Both values ​​increased significantly, indicating that the cracks in the high-temperature pipeline have a tendency to expand in both length and width directions.

[0124] In summary, this invention first obtains accurate strain transfer efficiency at different interfaces by using the method proposed in steps one and two to automatically eliminate abnormal points caused by abnormal factors and the method of calibrating transfer efficiency without substrate and with the same curvature. Then, by using the temperature sensitivity coefficient and a self-built pipeline model, the "influence of temperature on strain sensor measurement" and "influence of temperature on pipeline thermal expansion effect" in the total strain are removed, ultimately obtaining the strain change caused only by crack propagation. Furthermore, based on the criteria proposed by this invention, it is possible to accurately assess whether the crack is propagating along the crack extension direction, perpendicular to the crack direction, or both directions simultaneously. This is of great significance for assessing the crack development trend, life assessment, and safety early warning of high-temperature pipelines.

[0125] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for monitoring and identifying microcrack propagation in high-temperature pipelines, characterized in that, It includes the following steps: S1. The accurate strain transfer efficiency m1 between the bare optical fiber and the planar metal substrate is obtained by automatically eliminating data anomalies introduced by abnormal factors. S11. Measuring bare optical fiber at different strain values wavelength offset ; S12. By automatically eliminating data anomalies caused by abnormal factors, the accurate sensitivity coefficient of bare optical fiber without planar metal substrate encapsulation is obtained. : ； S13. The sensitivity coefficient of the fiber optic sensor with a planar metal substrate is obtained by automatically eliminating data outliers introduced by abnormal factors. ; S14. Sensitivity coefficient of the fiber optic sensor with a planar metal substrate. With bare fiber sensitivity coefficient The accurate strain transfer efficiency between the bare optical fiber and the planar metal substrate is obtained by comparison: ； S2. By fitting the curved surface structure of the pipe with the planar metal substrate under the same curvature, and combining this with a method to automatically eliminate data outliers introduced by abnormal factors, the accurate strain transfer efficiency between the planar metal substrate and the cylindrical pipe is obtained. ; The specific process of step S2 includes: S21. Using an equal-strength beam as a calibration tool, the equal-strength beam is bent by adding weights until the curvature of the equal-strength beam approximates the curvature of the pipe. S22. Attach a planar metal substrate to the bent equal strength beam, and attach unidirectional resistance strain gauge one and resistance strain gauge two to the equal strength beam and the planar metal substrate respectively. S23. Change the weights slightly and record the strain measured by the resistance strain gauge. and Then the strain transfer efficiency is ; S24. Automatically eliminate data anomalies introduced by abnormal factors to obtain the accurate strain transfer efficiency m2 between the planar metal substrate and the pipe. S3. Obtain the temperature sensitivity coefficient α of the fiber optic sensor; S4. Strain monitoring of interference caused by pipeline thermal expansion effect; S5. Install fiber optic sensors at specific locations of pipe cracks to assess the strain caused by crack propagation.

2. The method for monitoring and identifying microcrack propagation in high-temperature pipelines according to claim 1, characterized in that: The specific processes of steps S12 and S13 include: S121. Measure the strain values ​​under different gradient tensions. and the corresponding offset of the center wavelength of the fiber optic sensor ; S122, Substitute into the fitting equation: ； in, Indicates the distance from the origin of the coordinate system to the origin of the coordinate system. The distance of the fitted straight line, To fit the angle between the straight line and the coordinate axis; when Take a constant value between 0 and b-1, that is, the strain value under a certain gradient stretching. Offset from the center wavelength of the corresponding fiber optic sensor Substitute into the fitting equation, and There is one and only one curve that can be determined; when and When the value is constant, the offset of the center wavelength of the fiber optic sensor and strain value There is one and only one straight line that can determine the relationship between them; Known measurement point set It can uniquely determine a straight line, so and There exists a fixed value that makes this true, i.e., a set of measurement points. Drawing The curve passes through a fixed point; once that fixed point is determined, the result is obtained. Fit a straight line; S123. The specific fitting process is as follows: S1231. Record the offset of the center wavelength of the fiber optic sensor obtained from n tensile tests performed on a bare optical fiber without planar metal substrate encapsulation using a tensile machine. and their corresponding strain values ; get - curve; S1232. Discretize the curve; point set There are n measured values, each measured value is processed according to the discretized... The values ​​are taken from N scattered points, and the values ​​corresponding to the total nN scattered points are... The values ​​were statistically analyzed, and the results were used to analyze the data. Curve fitting is performed on the point with the highest number of repetitions to obtain the accurate bare fiber sensitivity coefficient value. S1233. The number of times the function value corresponding to the abnormal data point introduced by abnormal factors during the measurement process appears is much less than the number of times the function value corresponding to the normal data point appears. Since the curve fitting is performed on the point where the s value appears most frequently in the statistical results, the abnormal data point has no effect on the fitting result. The abnormal value is automatically discarded, and the bare fiber sensitivity coefficient η1 is obtained. S131, Obtain the bare fiber sensitivity coefficient Then, referring to steps S121-S123, the same stretching steps are performed on the fiber optic sensor with a planar metal substrate to obtain the sensitivity coefficient of the fiber optic sensor with a planar metal substrate. .

3. The method for monitoring and identifying microcrack propagation in high-temperature pipelines according to claim 2, characterized in that: In step S23, adding or removing weights must ensure that the change in strain does not exceed 200. .

4. The method for monitoring and identifying microcrack propagation in high-temperature pipelines according to claim 3, characterized in that: The specific process of step S3 includes: The fiber optic sensor was placed in a temperature chamber to ensure it was free from any stress, and the wavelength changes at different temperatures were obtained. Furthermore, the temperature sensitivity coefficient of the fiber optic sensor was obtained through linear fitting. .

5. The method for monitoring and identifying microcrack propagation in high-temperature pipelines according to claim 4, characterized in that: The specific process of step S4 includes: S41. Based on the material properties and dimensions of the pipe, create a local model of the pipe and attach resistance strain gauges along the circumferential direction of the pipe. S42. Place the local model of the pipe with the resistance strain gauge attached into a temperature chamber. The initial temperature of the temperature chamber is the initial temperature of the pipe before heating. At this point, the resistance strain gauge reading is reset to zero; S43. Heat the chamber to the pipeline operating temperature. Record the strain value of the resistance strain gauge at this time. After repeated measurements, the average value of the hardware was obtained. .

6. The method for monitoring and identifying microcrack propagation in high-temperature pipelines according to claim 5, characterized in that: The specific process of step S5 includes: S51. Given a crack length l, in order to determine the direction of crack propagation in the pipe, one fiber optic sensor is installed at each end of the crack perpendicular to the crack direction; another fiber optic sensor is installed at l / 3 and 2l / 3 of the distance from the crack head perpendicular to the crack direction; the four fiber optic sensors are labeled A, B, C, and D. S52. After completing the calibration and installation, start the fiber optic sensor monitoring and record the initial temperature of the pipeline using the four fiber optic sensors. The initial wavelength below , , , ; S53. Heat the pipeline until it reaches the pipeline's operating temperature. After the pipe temperature stabilizes, the wavelength values ​​of the four fiber optic sensors are recorded in real time. , , , ; S54. Calculate the strain caused only by crack propagation based on the strain expression to obtain the propagation identification result; The strain expression is: The extended recognition result judgment method is as follows: (1) If ε A ε B ε C ε D The absence of significant changes indicates that the pipe cracks are not showing a tendency to propagate and are in a stable condition. (2) If ε A Significantly increased, ε B ε C ε D The lack of significant changes indicates that the pipe crack tends to extend and lengthen towards end A, but does not show any tendency to extend in the width direction. (3) If ε B Significantly increased, ε A ε C ε D The lack of significant changes indicates that the pipe crack tends to extend and lengthen towards end B, but does not show any tendency to extend in the width direction. (4) If ε C Significantly increased, ε A ε B ε D The lack of significant change indicates that the pipe crack tends to extend in the width direction near l / 3, but not in the length direction. (5) If ε D Significantly increased, ε A ε B ε C The lack of significant change indicates that the crack near 2l / 3 of the pipe has a tendency to expand in the width direction but not in the length direction. (6) If ε A ε B Significantly increased, ε C ε D The lack of significant changes indicates that the pipe crack tends to extend and lengthen towards both end A and end B, but does not show any trend of expansion in the width direction. (7) If ε C ε D Significantly increased, ε A ε B The lack of significant changes indicates that the pipe crack has a tendency to extend in the width direction but not in the length direction. (8) If ε A ε B ε C ε D Both values ​​increased significantly, indicating that the pipe cracks tend to expand in both length and width directions.

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