A method for ultrasonic detection of the corrosion condition of the pipe wall of a sedimentation pipe section

Abstract

This invention relates to the field of ultrasonic flaw detection technology, specifically to an ultrasonic detection method for the corrosion status of pipe walls in silted pipe sections. The method includes: using a variable-frequency ultrasonic probe to perform multi-frequency incremental A-scans at various detection locations on the outer side of the pipe wall, acquiring echo amplitude variation curves with thickness at different frequencies; calculating a first index of peak density difference and a second index of peak reduction rate with increasing frequency based on the curves at each frequency; selecting two thickness intervals with the highest overlap (the first index being largest at low frequencies and the second index being largest at high frequencies), and determining the thickness of the corrosion product layer as the detection result based on these two intervals. This invention effectively balances the penetration and resolution of ultrasonic detection, significantly improving the accuracy of detecting the corrosion status of pipe walls in silted pipe sections.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic flaw detection technology, specifically to an ultrasonic detection method for the corrosion condition of pipe walls in silted pipe sections. Background Technology

[0002] In fields such as oil and gas transportation and municipal water supply and drainage, pipelines in long-term service are susceptible to corrosion due to the transported media. When silt accumulates in the pipeline section, corrosion products coexist with the silt. Accurate detection of the degree of pipe wall corrosion is a core requirement for ensuring the safe operation of pipelines. Among existing pipe wall corrosion detection technologies using fixed-frequency ultrasound, low-frequency ultrasound has strong penetrating power but insufficient resolution, making it impossible to accurately locate the interface of the corrosion product layer; high-frequency ultrasound has high resolution but limited penetrating power, making it difficult to obtain a complete picture of the overall distribution of the corrosion product layer. This results in an inability to accurately quantify the degree of pipe wall corrosion and fails to meet the high-precision detection requirements for corrosion in silted pipeline sections. Summary of the Invention

[0003] To address the above problems, this invention provides an ultrasonic detection method for the corrosion status of pipe walls in silted pipe sections.

[0004] The ultrasonic detection method for the corrosion status of a silted pipe section according to the present invention adopts the following technical solution: One embodiment of the present invention provides an ultrasonic detection method for the corrosion condition of the pipe wall in a silted pipe section, the method comprising the following steps: A series of A-scans were performed at each detection location on the outside of the pipe wall using a variable frequency ultrasonic probe. After each A-scan, the ultrasonic frequency of the probe was increased by one. After each scan, the curve of echo amplitude versus thickness was obtained. In the variation curves obtained at each ultrasonic frequency, the first index of the thickness range is determined based on the difference between the peak distribution density within any thickness range and the peak distribution density outside the thickness range, and the reduction rate of the peak within any thickness range is recorded as the second index. Obtain a first interval and a second interval with the maximum overlap. At the same time, the first index obtained in the first interval at a first frequency and the second index obtained in the second interval at a second frequency each have a maximum value, wherein the second frequency is greater than the first frequency. The thickness of the corrosion product layer inside the pipe wall is determined based on the first and second intervals, and is used as the detection result of the pipe wall corrosion status.

[0005] Preferably, the specific steps for determining the first index of the thickness range based on the difference between the peak distribution density within any thickness range and the peak distribution density outside the thickness range are as follows: For any thickness interval on the change curve obtained at any ultrasonic frequency, calculate the peak distribution density within that thickness interval, denoted as the first density; where the first density is equal to the ratio of the number of effective peaks within that thickness interval to the length of the thickness interval. Calculate the peak distribution density outside the thickness range on the change curve, and denote it as the third density; at any ultrasonic frequency, the first index of the thickness range and the difference between the first density and the third density are positively correlated.

[0006] Preferably, the rate of reduction of the peak within any thickness range is denoted as the second index, and the specific steps include the following: For any thickness range on the change curve obtained at any ultrasonic frequency, the ultrasonic frequency is denoted as the center frequency, the ultrasonic frequency adjacent to the center frequency is denoted as the first frequency, and the ultrasonic frequency adjacent to the center frequency is denoted as the second frequency. The first frequency, center frequency, and second frequency are used as the abscissa, and the number of effective peaks in the thickness range on the change curve obtained at the first frequency, center frequency, and second frequency is used to determine the ordinate. For the straight line formed by all the coordinate points of the abscissa and ordinate, the second index is positively correlated with the absolute value of the slope of the straight line.

[0007] Preferably, the specific steps for obtaining the first interval and the second interval with the maximum overlap are as follows: For any pair of ultrasonic frequencies, the ultrasonic frequency with the smallest value is denoted as the first candidate frequency, and the ultrasonic frequency with the largest value is denoted as the second candidate frequency. For the two variation curves obtained under the first candidate frequency and the second candidate frequency, they are denoted as the first curve and the second curve, respectively. On the horizontal axis of the first curve, the closed interval between any two horizontal coordinate points is denoted as the first thickness interval. On the horizontal axis of the second curve, the closed interval between any two horizontal coordinate points is denoted as the second thickness interval. Based on the first index of any first thickness interval in the first curve, the second index of any second thickness interval in the second curve, and the overlap of the first and second thickness intervals, the integrity of the corrosion products of any pair of first and second thickness intervals at ultrasonic frequencies is determined; the integrity of the corrosion products is positively correlated with the first index, the second index, and the overlap, respectively. For all ultrasonic frequencies, the first and second thickness intervals at which the integrity of the corrosion products is maximized are denoted as the first interval and the second interval, respectively.

[0008] Preferably, the specific steps for determining the thickness of the corrosion product layer inside the pipe wall based on the first interval and the second interval are as follows: Calculate the average of the lower limits of the first interval and the second interval, and denote it as the first average. The upper limit of the first interval is denoteed as the first upper limit of thickness. On the curve obtained when the ultrasonic frequency is at its minimum, extract the curve segment with a thickness value greater than the first upper limit of thickness, and obtain the thickness value corresponding to the maximum value of the curve segment, which is denoteed as the second upper limit of thickness. The average of the first upper limit of thickness and the second upper limit of thickness is denoteed as the second average. The difference between the second average and the first average is taken as the thickness of the corrosion product layer.

[0009] Preferably, the difference between the nominal wall thickness of the pipe and the second average value is used as the thinning thickness, and the thinning thickness is also used as the detection result of the pipe wall corrosion status.

[0010] Preferably, when the thickness of the corrosion product layer at any detection location is greater than a first preset threshold or the thinning thickness is greater than a second preset threshold, the pipeline is repaired.

[0011] Preferably, the specific steps for calculating the peak distribution density outside the thickness range on the variation curve, denoted as the third density, are as follows: The variation curves outside the thickness range are spliced ​​together to obtain a spliced ​​curve. A sliding interval of length L is used to translate and slide on the spliced ​​curve. After each translation and sliding, the peak distribution density within the sliding interval is obtained and recorded as the second density. The maximum value of the second density obtained from all translations and sliding is recorded as the third density of the thickness range. L represents the length of this thickness range.

[0012] Preferably, the specific steps for obtaining the effective peak are as follows: For any sampling point on any curve, the horizontal axis of the sampling point is the thickness value and the vertical axis is the normalized echo amplitude. If the echo amplitude of the sampling point is greater than the preset threshold, and the echo amplitudes of several consecutive sampling points before and after the sampling point are all less than the echo amplitude of the sampling point, the sampling point is considered as a valid peak.

[0013] Preferably, the overlap between the first thickness interval and the second thickness interval is equal to the intersection-to-exchange ratio of the first thickness interval and the second thickness interval.

[0014] The beneficial effects of the technical solution of the present invention are: This invention comprehensively solves the problem that fixed-frequency ultrasonic testing cannot accurately obtain the corrosion status of pipe walls in silted pipe sections, achieving high-precision quantification of the thickness of corrosion product layers. First, a variable-frequency ultrasonic probe is used to perform multi-frequency incremental A-scans, acquiring echo response data at different ultrasonic frequencies, while simultaneously considering the penetration and resolution of ultrasonic testing, providing complete raw data support for the identification of corrosion product layers. Second, the acoustic response characteristics of the corrosion product layer are quantified from two dimensions: the difference in peak distribution inside and outside the thickness range and the rate of decrease in peak value with increasing frequency, using a first index and a second index respectively, thereby improving the accuracy of identifying the thickness range where the corrosion product layer is located. Finally, the thickness of the corrosion product layer was determined by selecting the two thickness intervals with the best corresponding indicators and the highest degree of overlap at different frequencies, namely the first interval and the second interval. The first interval was obtained under low-frequency ultrasound. Due to the strong penetration ability of ultrasound and the fact that the side of the corrosion product layer closer to the deposits is more porous, the echo is obvious. In this case, the first interval is located on the side of the corrosion product layer closer to the deposits. The second interval was obtained under high-frequency ultrasound. Due to the weak penetration ability of ultrasound, it is rapidly absorbed on the side of the corrosion product layer closer to the healthy metal, and the echo reduction rate is obvious. In this case, the second interval is located on the side of the corrosion product layer closer to the healthy metal. At this time, when the first interval and the second interval have the maximum degree of overlap, it means that the first interval and the second interval are more likely to completely describe the entire thickness region of the corrosion product layer. Therefore, obtaining the corrosion product layer based on the first interval and the second interval is more reliable. This process fully combines the response characteristics of the corrosion product layer at different frequencies, ultimately ensuring the reliability of the corrosion product layer thickness detection results. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart illustrating the steps of an ultrasonic testing method for detecting corrosion on the wall of a silted pipe section, as provided in one embodiment of the present invention. Detailed Implementation

[0017] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of an ultrasonic detection method for the corrosion status of pipe walls in silted pipe sections proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0019] The following describes in detail, with reference to the accompanying drawings, a specific scheme for ultrasonic detection of pipe wall corrosion in a silted pipe section provided by the present invention.

[0020] Please see Figure 1 The diagram illustrates a flowchart of an ultrasonic testing method for the corrosion status of a silted pipe section according to an embodiment of the present invention. The method includes the following steps: Step S101: Use a variable frequency ultrasonic probe to perform several A scans at each detection position on the outside of the pipe wall. After each A scan, increase the ultrasonic frequency of the ultrasonic probe by one. After each scan, obtain the curve of echo amplitude changing with thickness.

[0021] In this embodiment, the ultrasonic probe is brought into contact with the outer wall of the pipe. After entering the pipe, the ultrasonic waves pass sequentially through the healthy metal layer, the corrosion product layer composed of oxides, the sediment layer, and the fluid inside the pipe. For pipes without any corrosion, there is no corrosion product layer.

[0022] In this embodiment, to describe the pipe wall corrosion condition, it is necessary to extract the corrosion product layer. The corrosion product layer is coarser and more porous than the healthy metal layer. It is also denser than the sediment layer. The acoustic impedance difference between the healthy metal layer and the corrosion product layer is significantly smaller than the acoustic impedance difference between the corrosion product layer and the sediment layer (or the fluid).

[0023] This embodiment considers that if a fixed-frequency ultrasonic probe is used for ultrasonic flaw detection, at lower ultrasonic frequencies, the ultrasonic echo at the healthy metal layer / corrosion product layer interface is not obvious or non-existent, while the echo at the corrosion product layer / deposit layer (or fluid) interface is obvious. However, due to the low resolution at lower ultrasonic frequencies, the merging of multiple echo peaks can only roughly indicate the location of the corrosion product layer / deposit layer (or fluid) interface, but it is not precise. At higher ultrasonic frequencies, the echo at the healthy metal layer / corrosion product layer interface is obvious and the resolution is high, but the ultrasonic penetration ability is limited and cannot penetrate deep into the corrosion product layer, thus making it impossible to accurately determine the distribution of the corrosion product layer inside the pipeline.

[0024] In summary, using a fixed-frequency ultrasonic probe cannot accurately extract the corrosion product layer.

[0025] Based on this, this embodiment uses a variable frequency ultrasonic probe as the detection probe to obtain ultrasonic echo data at different frequencies. By utilizing the difference in response of ultrasound at different frequencies to media with different densities, the corrosion product layer can be distinguished from healthy metals and deposits, and the interface echo of the corrosion product layer can be accurately identified.

[0026] Furthermore, a variable frequency ultrasonic probe is used to perform several A-scans at each detection location on the outside of the pipe wall, and the ultrasonic frequency of the ultrasonic probe is increased once after each A-scan.

[0027] A-scan, or amplitude-time scan, is the most basic and original method of displaying ultrasonic signals. The probe emits an ultrasonic pulse into the pipe, and the horizontal axis (X-axis) of the collected data represents time, while the vertical axis (Y-axis) represents the received echo amplitude. It should be noted that when the ultrasonic wave encounters an interface (such as the interface of a corrosion product layer) while propagating in the pipe, some energy is reflected back and received by the probe, appearing as a peak in the collected data.

[0028] This embodiment calculates the time difference between the initial wave time and any time on the horizontal axis, and uses the sound velocity in the pipe to convert the time represented by the horizontal axis into the sound path distance, i.e., the thickness value. Specifically, this time difference t is converted into the thickness value h using the formula h = v × t / 2 (the ultrasonic wave travels back and forth, so it is divided by 2), where v represents the longitudinal wave velocity of the ultrasonic wave in carbon steel (in this embodiment, v = 5900 m / s). The initial wave time refers to the starting time of the probe emitting the ultrasonic wave, corresponding to the detection position on the outer surface of the pipe wall, with a thickness of 0.

[0029] In summary, the data collected after each scan in this embodiment is a variation curve, with the horizontal axis representing the thickness value (the distance inward along the axial direction from each detection position on the outer side of the pipe wall) and the vertical axis representing the echo amplitude. It should be noted that this embodiment only focuses on the relative magnitude of the echo amplitude, not its absolute magnitude. Therefore, all echo amplitudes on each variation curve are linearly normalized to remove dimensions and orders of magnitude. The echo amplitudes mentioned in this embodiment thereafter are all normalized results.

[0030] It should be noted that the nominal wall thickness h0 of the pipe in this embodiment is a fixed value, and the corrosion product layer must be within the range of [0, h0]. Therefore, only the variation curve within the range of [0, h0] is retained on the variation curve.

[0031] In summary, this step involves using a variable frequency ultrasonic probe to perform multiple A-scans at each detection location on the outside of the pipe wall with increasing frequencies. This yields curves showing the change in echo amplitude with thickness at different frequencies, providing complete raw data support for subsequent identification of corrosion product layer regions and calculation of indicators. This lays a data foundation for accurately obtaining the thickness of the corrosion product layer.

[0032] Step S102: In the change curves obtained at each ultrasonic frequency, the first index of the thickness interval is determined based on the difference between the peak distribution density within any thickness interval and the peak distribution density outside the thickness interval, and the reduction rate of the peak within any thickness interval is recorded as the second index.

[0033] The above process yielded multiple variation curves at various ultrasonic frequencies, which helps to distinguish or extract corrosion product layers based on ultrasonic response characteristics, thus avoiding the situation where a single-frequency curve cannot fully represent the frequency response pattern of the corrosion product layer.

[0034] This embodiment determines a first index for the thickness range based on the difference between the peak distribution density within and outside any given thickness range. It should be noted that, regarding this first index, in identifying the thickness range where the corrosion product layer is located, the porous and rough nature of the corrosion product layer generates more peaks, resulting in a peak distribution density that differs from that of healthy metal and sediment areas. The first index quantifies this difference by comparing the density difference inside and outside the range, reliably quantifying the probability of any thickness range corresponding to a corrosion product layer in the variation curves at different ultrasonic frequencies.

[0035] When the value of the first index is larger, the difference between the peak distribution density within the thickness range and outside the range is greater, indicating that the probability of the thickness range belonging to the corrosion product layer is higher and the accuracy of range identification is higher; when the value of the first index is smaller, the difference between the peak distribution density within the thickness range and outside the range is smaller, indicating that the probability of the range belonging to the corrosion product layer is lower and the accuracy of range identification is lower. Furthermore, in this embodiment, the rate of reduction of peaks within any thickness range is denoted as the second index. In improving the accuracy of corrosion product layer range identification, the second index utilizes the absorption characteristics of the corrosion product layer to high-frequency ultrasound, providing another dimension of the corrosion product layer thickness range identification basis and solving the problem of insufficient accuracy of a single index. When the second index value is large, the faster the peak reduction rate within the range increases with the ultrasound frequency, the higher the probability that the range belongs to the corrosion product layer, and the more consistent the absorption characteristics to high-frequency ultrasound are with the porous and rough properties of the corrosion product layer compared to the healthy metal layer. When the second index value is small, the slower the peak reduction rate within the range increases with the frequency, the lower the probability that the range belongs to the corrosion product layer, which does not conform to the absorption characteristics of the corrosion product layer to high-frequency ultrasound.

[0036] In summary, this step quantifies the probability of corrosion product layers corresponding to different thickness ranges by defining the first and second indicators based on the frequency change curves. It achieves quantitative characterization of corrosion product layer ranges from two dimensions: differences in peak distribution and peak changes after frequency increases, providing a quantitative basis for subsequent range screening.

[0037] Step S103: Obtain the first interval and the second interval with the maximum overlap. At the same time, the first index obtained by the first interval at the first frequency and the second index obtained by the second interval at the second frequency have maximum values, wherein the second frequency is greater than the first frequency.

[0038] In this embodiment, the screening targets are the first interval and the second interval, so that the first interval and the second interval have the maximum overlap. This process ensures that the thickness range that completely covers the entire corrosion product layer is obtained as much as possible, so that the thickness range is as accurate as possible.

[0039] The first and second intervals satisfy the following conditions: the first index obtained from the first interval has a maximum value, and the second index obtained from the second interval has a maximum value. In this process, when selecting the interval that best matches the characteristics of the corrosion product layer, intervals with non-maximum indices have a lower probability of corresponding to the corrosion product layer and are more likely to contain interfering regions. This process uses the maximum index constraint to select the interval that best matches the response characteristics of the corrosion product layer, thus solving the problem of misjudgment of interfering regions.

[0040] Furthermore, the premise for the first and second indicators of the first and second intervals to have maximum values ​​is that the first and second intervals correspond to different ultrasonic frequencies. This is because if only a single interval is used for identification, it is impossible to combine the response characteristics of low-frequency and high-frequency ultrasound to different positions of the corrosion product layer, and it is impossible to completely cover the thickness range of the entire corrosion product layer, resulting in inaccurate thickness acquisition. This step introduces two intervals corresponding to the identification results at different frequencies, providing a basis for obtaining the complete thickness by combining the characteristics of different frequencies.

[0041] Furthermore, the key factor ensuring that the first index of the first interval at the first frequency and the second index of the second interval at the second frequency have their maximum values ​​is that the second frequency is greater than the first frequency. It should be noted that the first interval is obtained under low-frequency ultrasound. Due to the strong penetrating power of ultrasound and the fact that the side of the corrosion product layer closer to the deposits is more porous, the echo is more pronounced. In this case, the first interval is located on the side of the corrosion product layer closer to the deposits. The second interval is obtained under high-frequency ultrasound. Due to the weak penetrating power of ultrasound, it is rapidly absorbed on the side of the corrosion product layer closer to the healthy metal, resulting in a significant reduction in the echo rate. In this case, the second interval is located on the side of the corrosion product layer closer to the healthy metal. Therefore, when the first and second intervals have maximum overlap, it indicates that the first and second intervals are more likely to completely describe the entire thickness region of the corrosion product layer. Thus, obtaining the corrosion product layer based on the first and second intervals is more reliable.

[0042] In summary, this step maximizes the second index of the second interval under high-frequency ultrasound and the first index of the first interval under low-frequency ultrasound. When the first interval and the second interval have the maximum overlap, the first interval and the second interval can cover the corrosion product layer in a multi-frequency wide range, realizing the accurate screening of the thickness range where the corrosion product layer is located, and providing an accurate data basis for finally determining the corrosion status of the pipe wall.

[0043] Step S104: Determine the thickness of the corrosion product layer inside the pipe wall based on the first interval and the second interval, and use it as the detection result of the pipe wall corrosion status.

[0044] This embodiment uses the thickness of the corrosion product layer inside the pipe wall to describe the corrosion status of the pipe wall. The greater the thickness of the corrosion product layer, the more severe the corrosion of the pipe wall; the smaller the thickness of the corrosion product layer, the less severe the corrosion of the pipe wall.

[0045] In summary, the above steps in this embodiment reliably and accurately describe the corrosion status of the pipe wall by observing the echo behavior of the corrosion product layer at different ultrasonic frequencies.

[0046] As a preferred example, a variable frequency ultrasonic probe is used to perform several A-scans at each detection location on the outer side of the pipe wall, with the ultrasonic frequency of the probe increased after each A-scan. The method includes: Select the pipe to be inspected, first polish the anti-corrosion layer and rust on the designated area to be inspected on the outside of the pipe wall to expose the metallic luster, then apply glycerin-based ultrasonic coupling agent, repeatedly scrape the coupling agent layer to ensure that there is no air gap between the probe and the pipe wall, and control the coupling layer thickness to within 0.1mm; preset multiple detection positions in the area to be inspected, and perform multiple A scans on each detection position in sequence. After each scan, increase the probe frequency according to the preset step size until the preset upper limit value is reached; As an example, the pipe wall being tested is a 20# steel oil pipeline with a nominal wall thickness of h0=8mm. Additionally, one detection point is set every 2cm circumferentially on the outer side of the pipe wall, for a total of 18 detection points covering the entire circumference. A set of circumferential detection points is set every 10cm axially. For a single 1m long section of pipe to be tested, a total of 180 detection points are set, covering the entire area to be tested.

[0047] As an example, when acquiring A-scan data with a variable frequency ultrasonic probe, a longitudinal wave straight probe with an adjustable center frequency range of 2MHz to 18MHz is used. 17 A-scans are performed sequentially at each detection position. The initial frequency is 2MHz. After each scan, the probe frequency is increased by 1MHz until it reaches 18MHz. The sampling rate for each A-scan is set to 100MHz, and the sampling duration is 20μs. Each scan process is repeated 3 times to obtain the average echo value, thus eliminating random noise interference.

[0048] As a preferred example, the first index of the thickness range is determined based on the difference between the peak distribution density within and outside any thickness range, including the following methods: For any thickness interval on the change curve obtained at any ultrasonic frequency, calculate the peak distribution density within that thickness interval, denoted as the first density. The first density is equal to the ratio of the number of effective peaks within that thickness interval to the length L of the thickness interval.

[0049] By stitching together the variation curves outside the thickness range, a spliced ​​curve is obtained, which describes the peak distribution outside the thickness range. Using a sliding interval of length L (i.e., the length of the sliding interval is the same as the thickness range), the lower boundary of this sliding interval is translated along the horizontal axis from the origin of the spliced ​​curve, with a translation step of one unit, until the upper boundary of the sliding interval aligns with the endpoint of the horizontal axis of the spliced ​​curve. After each translation (including before the first translation), the peak distribution density within the sliding interval is obtained, denoted as the second density, which is equal to the ratio of the number of effective peaks within the sliding interval to the length L of the sliding interval.

[0050] In special cases where sliding is not possible, such as when the length of the sliding interval is less than or equal to the horizontal axis length of the splicing curve, the peak distribution density within the sliding interval is equal to the peak distribution density within the splicing curve.

[0051] The maximum value of the second density obtained by all translations is denoted as the third density of the thickness interval, which represents the maximum peak distribution density outside the thickness interval and within an interval of the same length as the thickness interval.

[0052] At any ultrasonic frequency, the first index and the difference between the first density and the third density in this thickness range are positively correlated.

[0053] It should be noted that the echo amplitudes at the splicing points in the spliced ​​curves may not be aligned. In this embodiment, the splicing points are not considered as valid peaks when calculating the second density (i.e., the splicing points are not included in the statistics). In addition, the sampling rate q for each A-scan is set to 100MHz, and the unit length is equal to v×1 / q×1 / 2.

[0054] As an example, methods for obtaining valid peaks include: For any sampling point on any curve, the horizontal axis represents the thickness value and the vertical axis represents the (normalized) echo amplitude. If the echo amplitude of the sampling point is greater than a preset threshold (e.g., 0.2), and the echo amplitudes of the three consecutive sampling points before the sampling point are all less than the echo amplitude of the sampling point, and the echo amplitudes of the three consecutive sampling points after the sampling point are also less than the echo amplitude of the sampling point, then the sampling point is considered a valid peak.

[0055] Specifically, in this example, sampling points within a region with a thickness less than 0.2 mm are not considered valid peaks to avoid interference from the initial wave sidelobes. If there are fewer than three sampling points before and after a given sampling point, then only all sampling points before and after that point are considered.

[0056] As an example, the formula for calculating the first indicator includes: The first index is equal to the ratio of the difference between the first density and the third density to the sum of the first density and the third density. Specifically, when the difference between the first density and the third density is less than 0, the difference between the first density and the third density is set to 0; when the denominator in this formula is 0, the first index is directly set to 0; the purpose of using the sum of the first density and the third density as the denominator to calculate the ratio is to remove dimensions and normalize.

[0057] As a preferred example, the rate of decrease of the peak within any thickness range is denoted as the second index, and the process includes: For any thickness range on the change curve obtained at any ultrasonic frequency, the ultrasonic frequency is denoted as the center frequency, the ultrasonic frequency adjacent to the center frequency (i.e. the ultrasonic frequency during the previous scan) is denoted as the first frequency, and the ultrasonic frequency adjacent to the center frequency (i.e. the ultrasonic frequency during the next scan) is denoted as the second frequency.

[0058] Using the first frequency, center frequency, and second frequency as the abscissa, for each variation curve obtained at the first frequency, center frequency, and second frequency, the number of all effective peaks in each variation curve is denoted as N. The first ratio of the number of effective peaks in the thickness range of each variation curve to (N+1) is calculated. The first ratio of the variation curves obtained at the first frequency, center frequency, and second frequency is used as the ordinate to obtain three coordinate points. The three coordinate points are fitted into a straight line using the least squares method. The second index (i.e., the rate of reduction of peaks) is positively correlated with the absolute value of the slope of the straight line.

[0059] The purpose of using N+1 as the denominator is to remove dimensions and normalize the result, while avoiding a denominator equal to 0.

[0060] Specifically, when the slope of the straight line is greater than 0, it indicates that the peak distribution does not decrease with the increase of ultrasonic frequency. In this case, the thickness range cannot reliably fit or describe the corrosion product layer, and the second index is set to 0.

[0061] The larger the second index, the greater the reduction in the number of wave peaks as the ultrasonic frequency increases.

[0062] As an example, the formula for calculating the second index is: the second index equals the absolute value of the slope of the straight line multiplied by the step size of the ultrasonic frequency (i.e., 1 MHz), the purpose of which is to remove the dimension of the second index. Specifically, if the center frequency has no adjacent previous or next ultrasonic frequency, then there may be a missing coordinate point, with only two coordinate points. In this case, the straight line can be fitted using these two coordinate points.

[0063] As a preferred example, obtaining a first interval and a second interval with the maximum overlap, and simultaneously having a first index obtained in the first interval at a first frequency and a second index obtained in the second interval at a second frequency, where the second frequency is greater than the first frequency, includes the following method: For any two ultrasonic frequencies, the ultrasonic frequency with the smallest value is denoted as the first candidate frequency H1, and the ultrasonic frequency with the largest value is denoted as the second candidate frequency H2. For the two variation curves obtained under H1 and H2, they are denoted as the first curve L1 and the second curve L2, respectively. On the horizontal axis of L1, the closed interval between any two horizontal coordinate points is denoted as the first thickness interval; on the horizontal axis of L2, the closed interval between any two horizontal coordinate points is denoted as the second thickness interval.

[0064] Based on the first index of any first thickness interval in L1 and the second index of any second thickness interval in L2, the corrosion product matching index of any set of first thickness interval and second thickness interval is determined; the corrosion product matching index is positively correlated with the first index and the second index respectively.

[0065] The corrosion product fit index is used to describe whether the ultrasonic echoes in any set of first and second thickness intervals match the absorption and reflection of the corrosion product layer at two different ultrasonic frequencies, H1 and H2. The larger the corrosion product fit index, the better it matches the absorption and reflection.

[0066] The integrity of the corrosion products in the first and second thickness intervals of the group is determined based on the corrosion product fit index and the degree of overlap. The integrity of the corrosion products is positively correlated with both the corrosion product fit index and the degree of overlap.

[0067] The greater the integrity of the corrosion products (i.e., the greater the overlap between the integrity of the corrosion products and the corrosion product matching index), the more the ultrasonic echoes in the first and second thickness intervals not only match the absorption and reflection of the corrosion product layer at two different ultrasonic frequencies, H1 and H2, but also, given that the first thickness interval is located on the side of the corrosion product layer closer to the deposits and the second thickness interval is located on the side of the corrosion product layer closer to the healthy metal, the first and second thickness intervals have sufficient overlap. This indicates that the first and second thickness intervals can more completely and reliably describe the corrosion product layer.

[0068] Thus, the integrity of corrosion products in any set of first and second thickness intervals was evaluated based on the first and second indices of any pair of ultrasonic frequencies (i.e., H1 and H2).

[0069] Furthermore, iterate through all pairs of ultrasonic frequencies, and all combinations of the first and second thickness intervals within each pair of ultrasonic frequencies. Each pair of first and second thickness intervals under any given pair of ultrasonic frequencies corresponds to a corrosion product integrity. Obtain the pair of first and second thickness intervals that maximize corrosion product integrity, and denote them as the first interval and the second interval, respectively.

[0070] Thus, the first interval and the second interval obtained in this example have the first interval and the second interval with the maximum overlap. At the same time, the first index obtained in the first interval at the first frequency and the second index obtained in the second interval at the second frequency have the maximum values ​​respectively.

[0071] Specifically, if the integrity of all corrosion products obtained for all groups of first and second thickness intervals at all ultrasonic frequencies is the same or has small differences (e.g., standard deviation less than 0.1), the first and second intervals cannot be obtained, indicating that there is no corrosion product layer.

[0072] As an optional example, obtaining a first interval and a second interval with the maximum overlap, where the first index obtained in the first interval at a first frequency and the second index obtained in the second interval at a second frequency each have a maximum value, wherein the second frequency is greater than the first frequency, includes the following methods: The above-mentioned preferred example for obtaining the first and second intervals involves a large amount of computation. This optional example reduces the amount of computation by using the following method: The calculation process in this example is similar to that in the preferred example above, except that it traverses all pairs of ultrasonic frequencies and all combinations of the first and second thickness intervals in each pair of ultrasonic frequencies.

[0073] In this example, when the corrosion product layer thickness is less than 0.5 mm, the corrosion of the pipeline is considered minor, and no further subdivision of the corrosion is performed (i.e., when the corrosion product layer thickness is less than 0.5 mm, the specific thickness of the corrosion product layer is no longer considered). When the corrosion product layer thickness is greater than 5 mm, the corrosion of the pipeline is considered to be at its maximum, and no further subdivision of the corrosion is performed (i.e., when the corrosion product layer thickness is greater than 5 mm, the specific thickness of the corrosion product layer is no longer considered). Based on this, this example only needs to obtain the corrosion product layer within the interval [0.5 mm, 5 mm]. Therefore, this example only considers the first or second thickness interval with a length within [0.5 mm, 5 mm]. Other first or second thickness intervals do not need to participate in the calculation of this example (i.e., the first or second thickness interval does not need to be included as a combination result in the calculation of corrosion product integrity).

[0074] Furthermore, in this example, considering that the frequencies that have a significant ultrasonic echo response to the corrosion product layer are distributed within a small range, the maximum value of the difference between the second frequency and the first frequency in this example will not be greater than the preset ultrasonic frequency value k0. Therefore, in this example, only H1 and H2 with differences in the range (0, k0) need to be considered. If there is a case where H2-H1 is greater than or equal to k0 in a pair of ultrasonic frequencies consisting of H1 and H2, then the pair of ultrasonic frequencies will not be included in the calculation of this example (that is, H1 and H2 do not need to be used as an ultrasonic frequency pair and participate in the calculation of the integrity of the corrosion products).

[0075] As an example, k0 is set to 5.2MHz.

[0076] In other examples, methods to further reduce computational load include: considering only the first or second thickness interval with a length within the range of [0.5mm, 5mm], and lengths of 30, 50, 70, ..., 210 units respectively; the purpose is to ensure that the first or second thickness intervals involved in the calculation have a certain typical length difference (i.e., the first or second thickness interval has a certain degree of distinguishability or discreteness). Additionally, when the lower limit of the first or second thickness interval is less than 3mm (i.e., the first or second thickness interval covers one side of the outer wall of the pipe), the first or second thickness interval is not included in the calculation in this example. The purpose is that, considering the corrosion product layer is generally located on the side of the pipe wall closer to the inner wall, for corrosion product layers closer to the outer wall, it is uniformly determined that the pipe has very severe corrosion (more than half of the pipe wall is corroded). For pipes with very severe corrosion, it is no longer necessary to accurately obtain the thickness of the corrosion product layer (i.e., it is unnecessary to obtain the first and second intervals).

[0077] As an example, the formula for calculating the corrosion product compatibility index is: the corrosion product compatibility index is equal to the sum of the first index and the second index.

[0078] As an example, the formula for calculating corrosion product integrity is: corrosion product integrity equals the product of corrosion product fit index and the degree of overlap. The degree of overlap is equal to the crossover ratio of the first thickness interval and the second thickness interval.

[0079] As a preferred example, the method for determining the thickness of the corrosion product layer inside the pipe wall based on the first interval and the second interval includes: Calculate the mean of the lower limits of the first and second intervals, denoted as the first mean *a*. For the upper limit of the first interval, denoted as the first thickness upper limit *b*, on the curve obtained at the minimum ultrasonic frequency, find the segment whose horizontal axis coordinate value (i.e., thickness value) is greater than *b*. Find the horizontal axis coordinate (i.e., the corresponding thickness value) corresponding to the maximum value of this segment, denoted as the second thickness upper limit *c*. The mean of *c* and *b* is denoted as the second mean *d*. The interval [a, d] is taken as the thickness range of the corrosion product layer. The thickness of the corrosion product layer is equal to *da*.

[0080] It should be noted that any variation curve in this embodiment refers to the variation curve within the interval [0, h0], where h0 represents the nominal wall thickness of the pipe (see step S101 for details).

[0081] When the ultrasonic frequency is at its lowest, the ultrasonic penetration is strong, and the acoustic impedance difference between the corrosion product layer and the sediment layer (or between the corrosion product layer and the fluid) is much greater than the acoustic impedance difference between the healthy metal layer and the corrosion product layer. Therefore, the interface between the corrosion product layer and the sediment layer corresponds to a large echo response. Due to the low resolution, it can only be roughly determined that one interface of the corrosion product layer is near c. At the same time, b is also an estimated interface position of the corrosion product layer. Therefore, in this embodiment, the second average of c and b, d, is taken as an interface position of the corrosion product layer (that is, the interface position near the sediment layer or the fluid). a represents the position of the corrosion product layer near the healthy metal layer. Therefore, da represents the thickness of the corrosion product layer, and this thickness is taken as the corrosion detection result.

[0082] In another example, the difference between h0 and d is used as the thinning thickness, representing the reduction in thickness of the pipe's inner wall due to corrosion. In this embodiment, the thinning thickness is always greater than or equal to 0. The thinning thickness is also used as a detection result of the corrosion condition.

[0083] Specifically, when there is no corrosion product layer, the thickness of the corrosion product layer is equal to 0 mm, and the thinning thickness is equal to the difference between h0 and c.

[0084] As an example, the steps to obtain the thickness of the corrosion product layer are as follows: In the above process, the thickness of the corrosion product layer and the thinning thickness were obtained at each detection location on the pipe surface.

[0085] When the thickness of the corrosion product layer is less than 1 mm, the corrosion product layer can be ignored, and the content of the test report generated at the corresponding test location should include: "No obvious corrosion products are found"; when the thinning thickness is less than 1 mm, the content of the test report generated at the corresponding test location should include: "No obvious corrosion thinning of the pipeline".

[0086] When the thickness of the corrosion product layer is greater than the first preset threshold (e.g., 4 mm), the content of the test report generated at the corresponding test location includes: "Corrosion products exceed the standard, repair is required"; when the thinning thickness is greater than the second preset threshold (e.g., 5 mm), the content of the test report generated at the corresponding test location includes: "The pipeline has become significantly thinner due to corrosion, repair is required".

[0087] When the thickness of the corrosion product layer is 1~4mm, or the thinning thickness is 1~5mm, the obtained thickness of the corrosion product layer and the thinning thickness are used as the content of the test report generated at the corresponding test location.

[0088] At this point, test reports for all test locations have been obtained.

[0089] As an example, when all inspection reports for all locations contain a "repair required" field, the selected pipes to be inspected are repaired or replaced to prevent leaks.

[0090] The above description is only 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 principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An ultrasonic testing method for the corrosion condition of a silted pipe section, characterized in that, The method includes the following steps: A series of A-scans were performed at each detection location on the outside of the pipe wall using a variable frequency ultrasonic probe. After each A-scan, the ultrasonic frequency of the probe was increased by one. After each scan, the curve of echo amplitude versus thickness was obtained. In the variation curves obtained at each ultrasonic frequency, the first index of the thickness range is determined based on the difference between the peak distribution density within any thickness range and the peak distribution density outside the thickness range, and the reduction rate of the peak within any thickness range is recorded as the second index. Obtain a first interval and a second interval with the maximum overlap. At the same time, the first index obtained in the first interval at a first frequency and the second index obtained in the second interval at a second frequency each have a maximum value, wherein the second frequency is greater than the first frequency. The thickness of the corrosion product layer inside the pipe wall is determined based on the first and second intervals, and is used as the detection result of the pipe wall corrosion status.

2. The ultrasonic detection method for the corrosion status of a silted pipe section according to claim 1, characterized in that, The specific steps for determining the first index of thickness range based on the difference between the peak distribution density within any thickness range and the peak distribution density outside the thickness range are as follows: For any thickness interval on the change curve obtained at any ultrasonic frequency, calculate the peak distribution density within that thickness interval, denoted as the first density; where the first density is equal to the ratio of the number of effective peaks within that thickness interval to the length of the thickness interval. Calculate the peak distribution density outside the thickness range on the change curve, and denote it as the third density; at any ultrasonic frequency, the first index of the thickness range and the difference between the first density and the third density are positively correlated.

3. The ultrasonic detection method for the corrosion status of a silted pipe section according to claim 1, characterized in that, The rate of decrease of the wave peak within any thickness range is denoted as the second index, and the specific steps involved are as follows: For any thickness range on the change curve obtained at any ultrasonic frequency, the ultrasonic frequency is denoted as the center frequency, the ultrasonic frequency adjacent to the center frequency is denoted as the first frequency, and the ultrasonic frequency adjacent to the center frequency is denoted as the second frequency. The first frequency, center frequency, and second frequency are used as the abscissa, and the number of effective peaks in the thickness range on the change curve obtained at the first frequency, center frequency, and second frequency is used to determine the ordinate. For the straight line formed by all the coordinate points of the abscissa and ordinate, the second index is positively correlated with the absolute value of the slope of the straight line.

4. The ultrasonic detection method for the corrosion status of a silted pipe section according to claim 1, characterized in that, The specific steps for obtaining the first and second intervals with the maximum overlap are as follows: For any pair of ultrasonic frequencies, the ultrasonic frequency with the smallest value is denoted as the first candidate frequency, and the ultrasonic frequency with the largest value is denoted as the second candidate frequency. For the two variation curves obtained under the first candidate frequency and the second candidate frequency, they are denoted as the first curve and the second curve, respectively. On the horizontal axis of the first curve, the closed interval between any two horizontal coordinate points is denoted as the first thickness interval. On the horizontal axis of the second curve, the closed interval between any two horizontal coordinate points is denoted as the second thickness interval. Based on the first index of any first thickness interval in the first curve, the second index of any second thickness interval in the second curve, and the overlap of the first and second thickness intervals, the integrity of the corrosion products of any pair of first and second thickness intervals at ultrasonic frequencies is determined; the integrity of the corrosion products is positively correlated with the first index, the second index, and the overlap, respectively. For all ultrasonic frequencies, the first and second thickness intervals at which the integrity of the corrosion products is maximized are denoted as the first interval and the second interval, respectively.

5. The ultrasonic detection method for the corrosion status of a silted pipe section according to claim 1, characterized in that, The specific steps for determining the thickness of the corrosion product layer inside the pipe wall based on the first and second intervals are as follows: Calculate the average of the lower limits of the first interval and the second interval, and denote it as the first average. The upper limit of the first interval is denoteed as the first upper limit of thickness. On the curve obtained when the ultrasonic frequency is at its minimum, extract the curve segment with a thickness value greater than the first upper limit of thickness, and obtain the thickness value corresponding to the maximum value of the curve segment, which is denoteed as the second upper limit of thickness. The average of the first upper limit of thickness and the second upper limit of thickness is denoteed as the second average. The difference between the second average and the first average is taken as the thickness of the corrosion product layer.

6. The ultrasonic detection method for the corrosion status of a silted pipe section according to claim 5, characterized in that, The difference between the nominal wall thickness of the pipe and the second mean is taken as the thinning thickness, and the thinning thickness is also taken as the detection result of the pipe wall corrosion status.

7. The ultrasonic detection method for the corrosion status of a silted pipe section according to claim 6, characterized in that, When the thickness of the corrosion product layer at any detection location exceeds the first preset threshold or the thinning thickness exceeds the second preset threshold, the pipeline is repaired.

8. The ultrasonic detection method for the corrosion status of a silted pipe section according to claim 2, characterized in that, The specific steps for calculating the peak distribution density outside the thickness range on the variation curve, denoted as the third density, are as follows: The variation curves outside the thickness range are spliced ​​together to obtain a spliced ​​curve. A sliding interval of length L is used to translate and slide on the spliced ​​curve. After each translation and sliding, the peak distribution density within the sliding interval is obtained and recorded as the second density. The maximum value of the second density obtained from all translations and sliding is recorded as the third density of the thickness range. L represents the length of this thickness range.

9. The ultrasonic testing method for the corrosion status of a silted pipe section according to claim 2 or 3, characterized in that, The specific steps for obtaining the effective peak are as follows: For any sampling point on any curve, the horizontal axis of the sampling point is the thickness value and the vertical axis is the normalized echo amplitude. If the echo amplitude of the sampling point is greater than the preset threshold, and the echo amplitudes of several consecutive sampling points before and after the sampling point are all less than the echo amplitude of the sampling point, the sampling point is considered as a valid peak.

10. The ultrasonic detection method for the corrosion status of a silted pipe section according to claim 4, characterized in that, The overlap between the first thickness interval and the second thickness interval is equal to the intersection-to-union ratio of the first thickness interval and the second thickness interval.

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