Ground magnetic positioning method for circumferential weld of ultra-buried pipeline

Abstract

The invention discloses a ground magnetic positioning method for a circumferential weld of an ultra-buried pipeline, and relates to the technical field of oil and gas pipeline safety, and the method mainly comprises the following steps: calculating a circumferential weld magnetic anomaly signal of a target pipe section through a finite element method; quantizing the time domain signal characteristics of the circumferential weld signal through an algorithm; applying an excitation signal to the pipeline, collecting an axial magnetic anomaly signal of the pipeline, and completing data noise reduction preprocessing; marking the special condition of the detection pipe section; and identifying and positioning the circumferential weld through a circumferential weld ground positioning method considering the weight. According to the method, accurate ground positioning of the ultra-buried-depth circumferential weld is achieved, solid and reliable ground coordinate support is provided for quality investigation of the circumferential weld, and the cost expenditure of pit expansion and re-drilling caused by inaccurate ground calibration of the circumferential weld is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas pipeline safety, and in particular to a ground magnetic positioning method for girth welds of ultra-deep pipelines. Technical Background

[0002] Girth welds are the weak link in long-distance oil and gas pipelines. They are prone to fracture and failure under the combined effects of internal pressure, temperature difference, and soil load, threatening the safe operation of the pipeline. In recent years, the inspection of pipeline girth weld quality hazards has become an important task that pipeline companies carry out regularly. Through comprehensive excavation along the pipeline, the quality inspection of girth welds will generate a large amount of unnecessary excavation costs. Existing girth weld inspection work usually conducts excavation inspection based on the ground positioning of the girth weld coordinates based on the longitude and latitude coordinates recorded in the internal inspection and as-built data. However, the overlap between the girth weld coordinates calibrated by the internal inspection and as-built data is low, resulting in the unknown true ground coordinates of the girth weld. Blindly excavating the girth weld is likely to result in unnecessary secondary excavation and pit expansion costs. Therefore, there is an urgent need for a precise positioning technology for girth welds to reduce unnecessary excavation costs and improve the efficiency of girth weld quality inspections.

[0003] Pipeline ground positioning technology based on electromagnetic induction has been widely used for locating buried pipelines and has become a mature engineering product. However, this technology only identifies the pipeline route and cannot identify abnormal signals generated by girth welds to facilitate the ground positioning of extremely deep girth welds. Magnetic measurement offers the technical advantages of non-contact testing and a large measurement depth. In theory, it can calibrate the ground coordinates of extremely deep girth welds by capturing the magnetic anomaly signals generated by the weld position.

[0004] However, the ground positioning technology of girth welds based on magnetic measurement has the following defects:

[0005] 1. The burial depth of ultra-deep pipelines is 3 to 5 times that of conventional pipelines. The signal is severely attenuated in space, the signal strength is weak, and it is difficult to pick up the characteristic signal;

[0006] 2. The magnetic anomaly signals generated by abnormal sections such as metal loss, stress concentration, and girth welds have certain similarities. Existing technologies only capture magnetic anomaly signals in general and mark them as abnormal sections. There is no technical method for identifying magnetic anomaly signals generated by girth welds.

[0007] 3. The relationship between the time-domain magnetic anomaly signal waveform of the girth weld and the weld position is unknown, resulting in low accuracy in locating the girth weld through the magnetic anomaly signal. In addition, special sections such as elbows and short pipes can cause distortion of the magnetic anomaly signal, destroying its original waveform characteristics and causing misjudgment or missed judgment. Summary of the Invention

[0008] To address the above-mentioned issues, the present invention proposes a ground magnetic location method for girth welds in ultra-deep pipelines. This method uses alternating excitation to significantly enhance signal strength, overcoming the technical issue of weak signals in ultra-deep pipelines. The method accurately identifies girth welds based on the waveform, width, and amplitude characteristics of the magnetic anomaly signal. Furthermore, the method introduces weighting and uses the entropy-weighted TOPSIS method to overcome signal distortion caused by external factors. The ground magnetic location method for girth welds in ultra-deep pipelines includes the following steps:

[0009] S1. According to the pipe diameter, wall thickness and operating pressure characteristics of the pipeline to be tested, the spatial distribution of the girth weld magnetic signal under alternating excitation conditions is obtained through finite element technology, and the signal is subjected to secondary differentiation to obtain the magnetic tensor signal B. i , the calculation formula is as follows:

[0010]

[0011] Where, B1 is the gradient signal collected on the right side of the magnetic gradiometer at time t0, nT / m; B2 is the gradient signal collected on the left side of the magnetic gradiometer at time t0, nT / m; B3 is the gradient signal collected on the left side of the magnetic gradiometer at time t0, nT / m; 0+1 The gradient signal collected on the right side of the magnetic gradiometer at time t, nT / m; B4 is t 0+1 The gradient signal collected on the left side of the magnetic gradiometer at the moment, nT / m; D is the pipe diameter, m; L is the distance between the signal collection points, m;

[0012] S2. Extract the magnetic anomaly signal of the girth weld along the pipeline axis, eliminate the magnetic gradient tensor signal generated by the pipeline itself, quantify the waveform characteristics of the girth weld magnetic anomaly through characteristic indicators, and realize the mathematical representation of the waveform characteristics;

[0013] S3. Connect the alternating excitation device to the cathodic protection potential test pile via a wire, apply an alternating current at a specific frequency to the pipeline, and the tester moves at a constant speed along the pipeline axis to collect magnetic tensor signals along the pipeline. The collection device has a built-in RTK positioning module that can automatically align the magnetic tensor signals with geographic location information;

[0014] S4. During the detection process, special pipe sections such as elbows and short pipes are occasionally marked in the data set, and the weight ratios of different feature parameters are changed according to the weight division method for different special pipe sections;

[0015] S5. Use a waveform-based girth weld magnetic anomaly recognition method to calibrate the girth weld signal, and locate the girth weld according to the synchronously recorded geographic location information.

[0016] Preferably, in step 2, quantifying the abnormal magnetic waveform characteristics of the girth weld by characteristic indicators includes the following steps:

[0017] S21, remove the magnetic gradient tensor signal generated by the pipeline itself and obtain the girth weld magnetic anomaly signal ΔB i :

[0018] ΔB i =B i -B is (2)

[0019] Where B i is the collected magnetic gradient tensor signal, nT / m; B is is the baseline signal before the signal mutation, nT / m;

[0020] S22, determine the anomaly magnetic signal B of the girth weld iw Characteristic parameters such as fluctuation form (sine wave, single peak), peak-to-peak value F of magnetic anomaly signal, wave width w, kurtosis k, etc.

[0021] Preferably, the weight division method for different special pipe sections described in step S4 includes the following steps:

[0022] S41. If a short pipe appears, adjust the peak-to-peak weight of the magnetic anomaly signal to a s , adjust the magnetic anomaly signal width and kurtosis weight to b s 、c s ;

[0023] S42. If an elbow appears, adjust the peak-to-peak weight of the magnetic anomaly signal to a b , adjust the magnetic anomaly signal width and kurtosis weight to b b 、c b ;

[0024] Preferably, the method for identifying girth weld magnetic anomalies in step S5 comprises the following steps:

[0025] S51, reducing the noise of the collected magnetic tensor signal along the pipeline to eliminate the alternating interference that may occur along the detection process and the high-frequency noise interference inside the instrument;

[0026] S52. Use the depth correction formula to process the signal to the standard height position. The depth correction formula is:

[0027]

[0028] In the formula, d, f, g are unknown coefficients; B i is the collected magnetic tensor signal, nT / m; B ista is the magnetic tensor signal at standard height, nT / m; h is the buried depth of the pipeline, m.

[0029] S53, using the calculated girth weld magnetic anomaly signal as a reference, using a threshold matching template algorithm to determine potential girth weld magnetic anomaly points;

[0030] S54. Extract the characteristic values of the potential girth weld magnetic anomaly points and compare them with the simulation results. Use the AHP (Analytical Hierarchy Process) to obtain the girth weld characteristic comprehensive index. If the girth weld characteristic comprehensive index is less than 0.1, it is determined that a girth weld exists at that location. The calculation method of the girth weld characteristic comprehensive index C is as follows:

[0031]

[0032] Where a, b, and c are weight coefficients; F is the peak-to-peak value of the potential girth weld magnetic anomaly point, nT / m; F sta is the calculated peak-to-peak value of the girth weld magnetic anomaly, nT / m; w is the potential girth weld magnetic anomaly point wave width, m; w sta is the calculated girth weld magnetic anomaly point wave width, m; k is the potential girth weld magnetic anomaly point kurtosis; k sta is the kurtosis of the potential girth weld magnetic anomaly point.

[0033] The beneficial effects of the present invention are:

[0034] 1. The present invention uses magnetic tensor signals as characteristic parameters for identifying girth welds, weakening the influence of the geomagnetic field and the environment, and enhancing signal strength through alternating excitation, thus breaking through the technical limitation of traditional magnetic tomography technology that is not suitable for ultra-deep pipelines.

[0035] 2. The girth weld identification method proposed in the present invention realizes the accurate positioning of the ground position of the girth weld based on the special waveform, wave width, peak-to-peak value, kurtosis and other waveform characteristics unique to the girth weld magnetic gradient tensor, and introduces the weight distribution idea to establish a girth weld identification method suitable for elbows and short pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the examples of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present invention, rather than limiting the present invention.

[0037] Figure 1 The present invention uses finite element technology to obtain the spatial distribution of the ring weld magnetic signal under alternating excitation conditions;

[0038] Figure 2 It is the characteristic signal of the elbow girth weld identified by the recognition algorithm of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiments of the present invention. Unless otherwise defined, the technical terms or scientific terms used in this disclosure should be the ordinary meanings understood by people with ordinary skills in the field to which this disclosure belongs. The words "including" or "comprising" and the like used in this disclosure mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. The present invention is further described below in conjunction with the drawings and embodiments.

[0040] The embodiment selects a short pipe girth weld magnetic anomaly signal for identification and positioning. A pipeline defect ground detection technology based on alternating electromagnetic excitation includes the following steps:

[0041] S1, target pipeline 1016mm, 15.3mm, operating pressure 9.6MPa, using finite element technology to obtain the spatial distribution of the girth weld magnetic signal under alternating excitation conditions, perform secondary difference on the signal, and obtain the magnetic tensor signal ΔB i , the calculation formula is as follows:

[0042]

[0043] Where, B1 is the gradient signal collected on the right side of the magnetic gradiometer at time t0, nT / m; B2 is the gradient signal collected on the left side of the magnetic gradiometer at time t0, nT / m; B3 is the gradient signal collected on the left side of the magnetic gradiometer at time t0, nT / m; 0+1 The gradient signal collected on the right side of the magnetic gradiometer at time t, nT / m; B4 is t 0+1 The gradient signal collected on the left side of the magnetic gradiometer at time t, nT / m;

[0044] S2, extract the magnetic anomaly signal of the girth weld along the pipeline axis and eliminate the magnetic gradient tensor signal generated by the pipeline itself (such as Figure 1 As shown in the figure), the waveform characteristics of the magnetic anomaly of the girth weld are quantified by characteristic indicators, and the waveform characteristics are mathematically quantified;

[0045] S3. Connect the alternating excitation device to the cathodic protection potential test pile via a wire, apply an alternating current at a specific frequency to the pipeline, and the tester moves at a constant speed along the pipeline axis to collect magnetic tensor signals along the pipeline. The collection device has a built-in RTK positioning module that can automatically align the magnetic tensor signals with geographic location information;

[0046] S4. During the detection process, special pipe sections such as elbows and short pipes are marked in the data set, and the weight proportions of different characteristic parameters are changed according to the AHP hierarchical analysis weight division method for different special pipe sections;

[0047] S5. Use the waveform-based girth weld magnetic anomaly recognition method to calibrate the girth weld signal and locate the girth weld according to the synchronously recorded geographical location information (the special girth weld waveform is identified as Figure 2 shown).

[0048] Preferably, in step 2, quantifying the abnormal magnetic waveform characteristics of the girth weld by characteristic indicators includes the following steps:

[0049] S21, remove the magnetic gradient tensor signal generated by the pipeline itself and obtain the anomaly magnetic signal B of the girth weld. iw :

[0050] ΔB i =B i -11000 (2)

[0051] Where B i is the acquired magnetic gradient tensor signal, nT / m;

[0052] S22, determine the anomaly magnetic signal ΔB of the girth weld i The fluctuation is single-peak, the peak-to-peak value F of the magnetic anomaly signal is 1925, the wave width w is 1.34m, the kurtosis k is 2.82, and the girth weld is located just below the signal peak.

[0053] Preferably, the AHP weight division method for different special pipe sections described in step S4 includes the following steps:

[0054] S41. If there is a potential girth weld at the elbow, the peak-to-peak weight of the magnetic anomaly signal is adjusted to 0.8, and the width and kurtosis weights of the magnetic anomaly signal are adjusted to 0.1 and 0.1 respectively;

[0055] Preferably, the method for identifying magnetic anomalies in the girth weld in step S5 comprises the following steps:

[0056] S51. De-noise the collected magnetic tensor signals along the pipeline using a wavelet noise filtering method to eliminate alternating interference that may occur along the detection process and high-frequency noise interference inside the instrument;

[0057] S52. Use the depth correction formula to process the signal to the standard height position. The depth correction formula is:

[0058]

[0059] In the formula, d, f, g are unknown coefficients; B i is the collected magnetic tensor signal, nT / m; B ista is the magnetic tensor signal at standard height, nT / m; h is the buried depth of the pipeline, m.

[0060] S53, using the calculated girth weld magnetic anomaly signal as a reference, using a threshold matching template algorithm to determine potential girth weld magnetic anomaly points;

[0061] S54. Extract the characteristic values of potential girth weld magnetic anomaly points and compare them with the simulation results. Use the AHP method to obtain the girth weld characteristic comprehensive index C. The girth weld characteristic comprehensive index C calculated for the 1# magnetic anomaly point is 0.02, and the girth weld characteristic comprehensive index C calculated for the 2# magnetic anomaly point is 0.28. It is determined that the 1# magnetic anomaly point is a girth weld:

[0062]

[0063] Where F is the peak-to-peak value of the potential girth weld magnetic anomaly point, nT / m; w is the wave width of the potential girth weld magnetic anomaly point, m; k is the kurtosis of the potential girth weld magnetic anomaly point;.

[0064] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A ground magnetic positioning method for ultra-deep pipeline girth welds, characterized in that: The following steps are involved: S1. According to the pipe diameter, wall thickness and operating pressure characteristics of the pipeline to be tested, the spatial distribution of the girth weld magnetic signal under alternating excitation conditions is obtained through finite element technology, and the signal is subjected to secondary differentiation to obtain the magnetic tensor signal B. i , the calculation formula is as follows: Where, B1 is the gradient signal collected on the right side of the magnetic gradiometer at time t0, nT / m; B2 is the gradient signal collected on the left side of the magnetic gradiometer at time t0, nT / m; B3 is the gradient signal collected on the left side of the magnetic gradiometer at time t0, nT / m; 0+1 The gradient signal collected on the right side of the magnetic gradiometer at time t, nT / m; B4 is t 0+1 The gradient signal collected on the left side of the magnetic gradiometer at the moment, nT / m; D is the pipe diameter, m; L is the distance between the signal collection points, m; S2. Extract the magnetic anomaly signal of the girth weld along the pipeline axis, eliminate the magnetic gradient tensor signal generated by the pipeline itself, quantify the waveform characteristics of the girth weld magnetic anomaly through characteristic indicators, and realize the mathematical representation of the waveform characteristics; S3. Connect the alternating excitation device to the cathodic protection potential test pile via a wire, apply an alternating current at a specific frequency to the pipeline, and the tester moves at a constant speed along the pipeline axis to collect magnetic tensor signals along the pipeline. The collection device has a built-in RTK positioning module that can automatically align the magnetic tensor signals with geographic location information; S4. During the detection process, special pipe sections such as elbows and short pipes are occasionally marked in the data set, and the weight ratios of different feature parameters are changed according to the weight division method for different special pipe sections; S5. Use a waveform-based girth weld magnetic anomaly recognition method to calibrate the girth weld signal, and locate the girth weld according to the synchronously recorded geographic location information.

2. The pipeline defect ground detection technology based on alternating electromagnetic excitation according to claim 1 is characterized in that: The weight division method for different special pipe sections in step S4 includes the following steps: S41. If a short pipe appears, adjust the peak-to-peak weight of the magnetic anomaly signal to a s , adjust the magnetic anomaly signal width and kurtosis weight to b s 、c s ; S42. If an elbow appears, adjust the peak-to-peak weight of the magnetic anomaly signal to a b , adjust the magnetic anomaly signal width and kurtosis weight to b b 、c b。 3. The pipeline defect ground detection technology based on alternating electromagnetic excitation according to claim 1 is characterized in that: The method for identifying magnetic anomalies in a girth weld in step S5 includes the following steps: S51, reducing the noise of the collected magnetic tensor signal along the pipeline to eliminate the alternating interference that may occur along the detection process and the high-frequency noise interference inside the instrument; S52. Use the depth correction formula to process the signal to the standard height position. The depth correction formula is: In the formula, d, f, g are unknown coefficients; B i is the collected magnetic tensor signal, nT / m; B ista is the magnetic tensor signal at standard height, nT / m; h is the buried depth of the pipeline, m. S53, using the calculated girth weld magnetic anomaly signal as a reference, using a threshold matching template algorithm to determine potential girth weld magnetic anomaly points; S54. Extract the characteristic values of the potential girth weld magnetic anomaly points and compare them with the simulation results. Use the AHP (Analytical Hierarchy Process) to obtain the girth weld characteristic comprehensive index. If the girth weld characteristic comprehensive index is less than 0.1, it is determined that a girth weld exists at that location. The calculation method of the girth weld characteristic comprehensive index C is as follows: Where a, b, and c are weight coefficients; F is the peak-to-peak value of the potential girth weld magnetic anomaly point, nT / m; F sta is the calculated peak-to-peak value of the girth weld magnetic anomaly, nT / m; w is the potential girth weld magnetic anomaly point wave width, m; w sta is the calculated girth weld magnetic anomaly point wave width, m; k is the potential girth weld magnetic anomaly point kurtosis; k sta is the kurtosis of the potential girth weld magnetic anomaly point.

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