A rapid detection and evaluation method for the service life of an inner coating

Abstract

The present invention discloses a rapid detection and evaluation method for the service life of an internal coating, which includes: accelerating the simulation of the change curves of the coating impedance values of different tubing internal coatings and different service times and the distribution diagrams of the coating impedance values within different time periods through experiments; accelerating the simulation of the change curves of the phase angles measured at a preset fixed frequency of different tubing internal coatings at different service times through experiments; constructing a coating service life database based on the change curves of the coating impedance values of different tubing internal coatings and different service times, the change curves of the phase angles of different tubing internal coatings at different service times, and the distribution diagrams of the coating resistance values of different tubing internal coatings at different service times; according to the specific coating on site, querying the database, selecting a reference coating system and a test part, using a portable impedance tester to test the phase angle data on site, and comparing the change curves of the phase angle and the service time and the coating impedance value distribution diagram, so as to rapidly evaluate the service performance of the coating.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline service performance evaluation, and particularly relates to a method for rapidly detecting and evaluating the service life of an internal coating. Background Art

[0002] During the oil and gas field exploitation process, associated gases such as hydrogen sulfide and carbon dioxide that seriously corrode oil and gas pipelines and equipment often accompany. To extend the service life of oil and gas pipelines and equipment and the safety of oil and gas field exploitation construction, anti-corrosion coatings are usually applied to the inner and outer surfaces of oil and gas pipelines and equipment. However, due to long-term service in a corrosive environment, the anti-corrosion coatings on their surfaces will be eroded and gradually fail, ultimately leading to the corrosion and damage of oil and gas pipelines and equipment. To ensure production safety, it is necessary to keep track of the coating service conditions of different parts of oil and gas pipelines at any time and conduct rapid and effective evaluation on them, which is conducive to timely maintenance, repair and other operations.

[0003] The literature (Zhang Xiuli et al., Evaluation method for the failure of anticorrosion coatings in cooling towers [J], Journal of University of Science and Technology Beijing, 2013, 35(8): 1058-1063) conducted hot water accelerated aging tests on phenolic epoxy coatings and coal tar epoxy asphalt coatings specimens in cooling towers in circulating water and demineralized water, measured the water absorption rate of the coating specimens during the aging process and observed their morphological changes. By analyzing the variation law of the water absorption rate of the coating specimens with the water absorption time and aging time, the evaluation method for the service life of the anticorrosion coatings in circulating water cooling towers was studied, and it was found that the service life of the coating at the test temperature could be deduced according to the inflection point of the water absorption rate-aging time curve of the cooling tower coating specimens during the aging process, and then the service life of the coating under the actual operating conditions could be deduced according to the Van't Hoff rule.

[0004] Patent CN101634623B reported a method and system for rapidly evaluating the corrosion resistance of an in-service coating. According to the change law of the phase angle of the coating / metal system at a specific frequency with the service time, which can reflect the change law of the impedance during the coating service process, an electrochemical method for rapidly evaluating the performance of an in-service coating was established. On this basis, a software system for rapidly evaluating and managing the performance of an in-service coating applicable to industrial sites was designed and developed, and it was equipped with a test probe, a portable impedance tester and a laptop computer. It is used for rapidly evaluating the corrosion resistance and life prediction of an in-service coating, focusing on application in industrial sites, with fast and convenient measurement, reliable data, simple instruments and no need to analyze impedance data.

[0005] Patent CN104076079A reports a rapid evaluation method for the critical corrosion damage of a multi-layer coating system. For specimens of an in-service multi-layer coating system or a multi-layer coating system undergoing natural environment tests, based on the characteristic that the corrosion damage degree of the first layer coating of the multi-layer coating system directly affects the protective performance of the coating system, a rapid evaluation method for the critical corrosion damage value of the coating based on macroscopic morphology characteristics and electrochemical characteristics is established. In the present invention, the macroscopic morphology characteristics of the multi-layer coating system are visually detected, the electrochemical impedance spectrum of the aging failure or severely damaged part is tested, and according to the preparation method of the multi-layer coating system and its characteristic of relatively large thickness, a physical model of the multi-layer coating system and an equivalent circuit model of the electrochemical impedance spectrum CM are established. The capacitance and resistance of each layer coating of the multi-layer coating system are obtained by analyzing with an electrochemical characteristic analysis system, and the critical corrosion damage value of the multi-layer coating system is rapidly evaluated according to the impedance value of the first layer coating. The method is simple, the data is reliable, and the evaluation result is accurate and practical.

[0006] To sum up, the rapid detection of the coating service life usually follows the principle of the phase angle change in the intermediate frequency range of the in-service coating, obtains the decay trend of the resistivity over time, and judges the remaining effective degree of the coating service. However, currently, the detection of the coating service life usually only collects the coating impedance values at different time periods, and rarely considers the mutual influence and correlation between the changes of the coating impedance values in different regions and at different time periods, resulting in a large difference between the detected coating service life and the actual service life, and the reference value of the evaluation result is reduced. Summary of the Invention

[0007] The object of the present invention is to provide a rapid detection and evaluation method for the service life of the inner coating in view of the deficiencies of the existing technology, including the following steps:

[0008] S1) Accelerate the simulation of the change curves of the coating impedance values of different inner coatings of oil pipes with different service times and the distribution maps of the coating impedance values within different time periods through laboratory tests. Different oil pipes are coated with different systems of inner coatings;

[0009] S2) Accelerate the simulation of the change curves of the phase angles measured at a preset fixed frequency of different inner coatings of oil pipes with different service times through laboratory tests;

[0010] S3) Construct a coating service life database according to the change curves of the coating impedance values of different inner coatings of oil pipes with different service times, the change curves of the phase angles of different inner coatings of oil pipes with different service times, and the distribution maps of the coating impedance values within different time periods of different inner coatings of oil pipes;

[0011] S4) According to the specific coating system on-site, query the coating service life database, select a reference coating system and a test part, use a portable impedance tester to on-site test the phase angle data of the coating system at the preset fixed frequency, and compare the change curve of the phase angle with the service time and the coating impedance value distribution map, so as to quickly evaluate the service performance of the coating;

[0012] Among them, it also includes introducing an adjacent influence factor and an adjacent influence number, and constructing an influence model of the coating impedance value distribution map and the coating impedance value curve. The method for constructing the influence model of the coating impedance value distribution map and the coating impedance value curve is as follows: Arbitrarily select X non-adjacent and differently corroded grids in the coating test sample as reference points, and record the coating impedance values of these X grids and several grids adjacent to them respectively at different service times; Evaluate according to the corrosion degree of several grid points adjacent to each grid in the X grids, and then obtain the adjacent influence number of several grid points adjacent to each grid. Among them, X is not less than 3; Draw the change curve of the coating impedance value of each grid in the X grids at different service times, and draw the change curve of the coating impedance value of the X grids and the adjacent influence number at the maximum service time of the test; Fit the change curve of the coating impedance value of each grid in the X grids at different service times and the change curve of the coating impedance value of the X grids and the adjacent influence number at the maximum service time of the test, and obtain the fitting curve: y = Ae x / t + B; This fitting curve is the fitting curve equation of the change curve of the coating impedance value of the coating in a unit grid at different service times and the change curve of the coating impedance value of the unit grid and the adjacent influence number at the maximum service time of the test. A and B are fitting parameters, t is the service time, y is the impedance value, and x is the adjacent influence number. Among them, the adjacent influence factor is the ratio of the adjacent influence number to A;

[0013] The adjacent influence number is the sum of the corrosion degree values of several unit grid coatings adjacent to a unit grid coating. The corrosion degree value is determined by the following method: Set the corrosion degree value of the completely corroded coating as the maximum value C, and set the corrosion degree value of the zero-corroded coating as the minimum value c; Divide the interval between the maximum value C and the minimum value c into n equal parts, and the corrosion degree value of the coating can be obtained according to the corrosion degree in the coating;

[0014] Multiply the adjacent influence factor by the coating impedance data in the coating service life database, correct to obtain the coating impedance correction data, and then the remaining service time of the coating can be obtained according to the coating impedance correction data.

[0015] Preferably, the preset fixed frequency is 10 kHz.

[0016] Preferably, the change curves of different service times and the distribution diagrams of the coating impedance values within different time periods are obtained by the following method:

[0017] Divide the laboratory test coating sample into several rectangular blocks by the grid method, mark each block, and measure the coating impedance value of each block at a certain service time of the coating sample. Recording the coating impedance value of each block can obtain the distribution diagram of the coating impedance value at this service time; divide the service time into several segments, and record the distribution diagrams of the coating impedance values at each service time node respectively, then the distribution diagrams of the coating impedance values at different service times can be obtained;

[0018] Record the distribution diagrams of the coating impedance values of different coating samples at different service times, and the distribution diagrams of the coating impedance values of different coatings at different service times can be obtained.

[0019] Preferably, the several grids are 8 grids.

[0020] Preferably, the corrosion rate at this point of the coating can be obtained according to the remaining service time of the coating.

[0021] A rapid detection and evaluation method for the service life of an internal coating provided by the present invention has the following technical effects.

[0022] The present invention aims at the problem that in order to ensure production safety, it is necessary to always master the coating service conditions of different parts of the oil and gas pipeline and conduct rapid and effective evaluation on it, which is beneficial to timely maintenance, repair and other operations. A rapid detection and evaluation method for the service life of an internal coating is provided. The service life of the coating is evaluated according to the linear relationship between the phase angle and the coating impedance value, and the adjacent influence factor is introduced to improve the influence factor that the coating corrosion rate is affected by the surrounding corroded equipment or coatings. The error between the predicted coating service life and the actual service life prediction is reduced, providing more accurate reference data for the selection of the repair time and scope of the coating. Specific embodiments

[0023] The following further illustrates the present invention with reference to embodiments.

[0024] A rapid detection and evaluation method for the service life of an internal coating specifically includes the following steps:

[0025] S1) Accelerate the simulation of the change curves of the coating impedance values and the distribution diagrams of the coating impedance values within different time periods of different tubing internal coatings through laboratory tests;

[0026] S2) Accelerate the simulation of the change curves of the phase angles measured at a frequency of 10 kHz of different tubing internal coatings at different service times through laboratory tests;

[0027] S3) Construct a coating service life database based on the change curves of the coating impedance values of different inner coatings of oil pipes with different service times, the change curves of the phase angles of different inner coatings of oil pipes at different service times, and the distribution maps of the coating resistance values of different inner coatings of oil pipes at different service times;

[0028] S4) According to the specific coating on site, query the standard database in the basic data module, select the reference coating system and the test part, use a portable impedance tester to measure the phase angle data of the coating system at a frequency of 10 kHz on site, and compare it with the change curve of the phase angle and the service time and the distribution map of the coating impedance value, so as to quickly evaluate the service performance of the coating.

[0029] The change curves at different service times and the distribution maps of the coating impedance values within different time periods are obtained through the following methods:

[0030] Divide the laboratory test coating sample into several rectangular blocks by the grid method, mark each block, and measure the coating impedance value of each block at a certain service time of the coating sample. Recording the coating impedance values of each block can obtain the distribution map of the coating impedance value at this service time; divide the service time into several segments, and record the distribution maps of the coating impedance values at each service time node respectively, then the distribution maps of the coating impedance values at different service times can be obtained;

[0031] Recording the distribution maps of the coating impedance values of different coating samples at different service times can obtain the distribution maps of the coating impedance values of different coatings within different service times.

[0032] Among them, an adjacent influence factor is also introduced to construct an influence model between the coating impedance value distribution map and the coating impedance value curve. The specific method is as follows:

[0033] Arbitrarily select X (X is not less than 3) non - adjacent and differently corroded grids in the coating test sample as reference points, and record the coating impedance values of these X grids and the eight grids adjacent to them respectively at different service times; evaluate the corrosion degree of the eight grid points adjacent to each of the X grids, and then obtain the adjacent influence number of the eight grid points adjacent to each grid;

[0034] Draw the change curves of the coating impedance values of each of the X grids at different service times, and draw the change curve of the coating impedance value of the X grids at the maximum service time of the test and the adjacent influence number; fit the change curves of the coating impedance values of each of the X grids at different service times and the change curve of the coating impedance value of the X grids at the maximum service time of the test and the adjacent influence number to obtain the fitting curve: y = Ae x / t+B; where A and B are fitting parameters, t is the service time, y is the impedance value, x is the adjacent influence number, and the adjacent influence factor is the ratio of the adjacent influence number to A.

[0035] In step S4), when evaluating the corrosion condition of the coating according to the phase angle change, by combining the coating impedance value distribution map and introducing the adjacent influence factor, the corrosion condition of the remaining service life of the coating can be inferred. That is, perform multi-point coating impedance value detection (at least 9 points) on the specific service coating, draw the coating impedance value distribution map according to the detection results, then select a central point as the reference point, then obtain the adjacent influence number based on the coating impedance values of the eight detection points around the reference point, then obtain the adjacent influence factor based on the adjacent influence number, and obtain the remaining service time and corrosion rate of this point of the coating according to the phase angle and the adjacent influence factor.

[0036] Among them, the corrosion degree value is determined by the following method: set the corrosion degree value of the completely corroded coating as the maximum value C, and set the corrosion degree value of the zero-corrosion coating as the minimum value c; evenly divide the interval between the maximum value C and the minimum value c into n parts, and the corrosion degree value of the coating can be obtained according to the corrosion degree in the coating.

[0037] Specific embodiments:

[0038] Taking the commercially available PC-400 coating as an example, apply this coating on a 45*45 cm steel plate, and after curing, divide it into 5*5 cm rectangular blocks with a marker pen and mark each block. Measure the coating impedance value of each rectangular block under the condition of no corrosion; then immerse the marked steel plate in a 5% sodium chloride aqueous solution and soak it at 90 °C, and regularly measure the coating impedance value of each rectangular block on the steel plate until at least one rectangular block is completely corroded, record its coating impedance value, which is the corrosion degree value of the completely corroded coating, and use the coating impedance value of the corresponding rectangular block under the condition of no corrosion as the corrosion degree value of the zero-corrosion coating, and obtain the coating impedance data of the PC-400 coating under different time conditions.

[0039] Regard the corrosion degree value of the completely corroded coating as 1; regard the corrosion degree value of the zero-corrosion coating as 0 and divide it into 100 equal parts, and the corrosion degree value of each rectangular block can be obtained.

[0040] Select 3 non-adjacent rectangular blocks on the steel plate as reference points, namely 1#, 2#, and 3#, and take the coating impedance values of each reference point at different times and the coating impedance values of the adjacent 8 grid points, and fit to obtain the relationship between the adjacent influence number M corresponding to each reference point and the coating impedance value N of the reference point:

[0041] M = 1.308N 2 +0.953N - 0.001(R2 = 0.999)(1) where R 2 = 0.999 represents a relatively high fitting accuracy.

[0042] Plot the change curves of the coating impedance values of each of the 3 grids at different service times, and plot the change curves of the coating impedance values of the 3 grids and the adjacent influence numbers at the maximum service time of the test; fit the change curves of the coating impedance values of each of the 3 grids at different service times and the change curves of the coating impedance values of the 3 grids and the adjacent influence numbers at the maximum service time of the test, and the fitting curves obtained by fitting are:

[0043] y = 0.847e x / t + 0.0205(R 2 = 0.902) (2)

[0044] That is, A = 0.847. Where R 2 = 0.902 represents a relatively high fitting accuracy.

[0045] Furthermore, the ratio of the adjacent influence number to A can be used to obtain the adjacent influence factor. Furthermore, multiply the adjacent influence factor by the coating impedance data of the coating PC-400 to correct and obtain the corrected coating impedance data of the coating PC-400.

[0046] Similarly, the corrected coating impedance data of other coatings can be constructed to obtain the coating impedance database of different coatings at different service time periods.

[0047] Take the oil pipe to be tested, obtain the coating type and coating service time of the oil pipe to be tested, measure the current coating impedance value of the oil pipe, and substitute it into the coating impedance database to obtain the remaining service time of the coating.

[0048] Taking the PC400 and PC300 coated oil pipes as examples, the remaining service time of the coating obtained by using the technical solution disclosed in this method, with the non-introduction of the adjacent influence factor as the comparative example, the following results are obtained:

[0049]

[0050] As can be seen from the above table, the remaining service time calculated in this application is closer to the actual remaining service time compared to the remaining service time without the introduction of the adjacent influence factor, and its error can be reduced to within 5%, providing a more accurate method for predicting the coating service time.

[0051] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the technical content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A rapid detection and evaluation method for the service life of an inner coating, characterized in that, It includes the following steps: S1) Accelerate and simulate, through laboratory tests, the change curves of the coating impedance values of different inner coatings of oil pipes with different service times and the distribution diagrams of the coating impedance values within different time periods. Different inner coatings are applied to different oil pipes; S2) Accelerate and simulate, through laboratory tests, the change curve of the phase angle measured at a preset fixed frequency of different inner coatings of oil pipes with different service times; S3) Construct a coating service life database based on the change curves of the coating impedance values of different inner coatings of oil pipes with different service times, the change curves of the phase angles of different inner coatings of oil pipes with different service times, and the distribution diagrams of the coating impedance values of different inner coatings of oil pipes within different time periods; S4) According to the specific coating system on site, query the coating service life database, select a reference coating system and a test site, use a portable impedance tester to measure the phase angle data of the coating system at the preset fixed frequency on site, and compare with the change curve of the phase angle and service time and the coating impedance value distribution diagram, so as to quickly evaluate the service performance of the coating; Among them, it also includes introducing adjacent influence factors and adjacent influence numbers to construct an influence model of the coating impedance value distribution map and the coating impedance value curve. The method for constructing the influence model of the coating impedance value distribution map and the coating impedance value curve is as follows: Arbitrarily select X non-adjacent grids with different corrosion degrees in the coating test sample as reference points, and record the coating impedance values of these X grids and several grids adjacent to them respectively at different service times; evaluate the corrosion degrees of several grid points adjacent to each of the X grids, and then obtain the adjacent influence numbers of several grid points adjacent to each grid, where X is not less than 3; draw the change curves of the coating impedance values of each of the X grids at different service times, and draw the change curve of the coating impedance value and the adjacent influence number of the X grids at the maximum service time of the test; fit the change curves of the coating impedance values of each of the X grids at different service times and the change curve of the coating impedance value and the adjacent influence number of the X grids at the maximum service time of the test to obtain a fitting curve: y = Ae x / t + B; this fitting curve is the fitting curve equation of the change curve of the coating impedance value of the coating within a unit grid at different service times and the change curve of the coating impedance value and the adjacent influence number of this unit grid at the maximum service time of the test. A and B are fitting parameters, t is the service time, y is the impedance value, and x is the adjacent influence number, where the adjacent influence factor is the ratio of the adjacent influence number to A; The adjacent influence number is the sum of the corrosion degree values of several unit grid coatings adjacent to a unit grid coating. The corrosion degree value is determined by the following method: Set the corrosion degree value of the completely corroded coating as the maximum value C, and set the corrosion degree value of the zero-corroded coating as the minimum value c; Divide the interval between the maximum value C and the minimum value c into n equal parts, and the corrosion degree value of the coating can be obtained according to the corrosion degree in the coating; Multiply the adjacent influence factor by the coating impedance data in the coating service life database, correct to obtain the coating impedance correction data, and further obtain the remaining service time of the coating according to the coating impedance correction data.

2. The rapid detection and evaluation method for the service life of the inner coating according to claim 1, wherein The preset fixed frequency is 10 kHz.

3. The rapid detection and evaluation method for the service life of the inner coating according to claim 1, wherein The change curves of different service times and the distribution diagrams of the coating impedance values within different time periods are obtained by the following method: Divide the laboratory test coating sample into several rectangular blocks by the grid method, mark each block, and measure the coating impedance value of each block at a certain service time of the coating sample. Recording the coating impedance values of each block can obtain the coating impedance value distribution diagram at this service time; Divide the service time into several segments, and record the coating impedance value distribution diagrams at each service time node respectively, and the coating impedance value distribution diagrams of different service times can be obtained; Recording the coating impedance value distribution diagrams of different coating samples at different service times can obtain the coating impedance value distribution diagrams of different coatings at different service times.

4. The rapid detection and evaluation method for the service life of the inner coating according to claim 1, characterized in that The several grids are 8 grids.

5. The rapid detection and evaluation method for the service life of the inner coating according to claim 4, characterized in that, The corrosion rate of this point of the coating can be obtained according to the remaining service time of the coating.

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