A protective method to prevent stray currents from corroding underground pipelines

Abstract

This invention discloses a protective method to prevent stray currents from corroding underground pipelines. After a period of subway operation, the insulation equipment under the rails may become damaged or age, reducing resistance and allowing some rail circuit current to flow underground. This invention provides buried pipelines near the subway with a current of the same magnitude but opposite direction to the stray current from the subway, ensuring that the potential of the buried pipelines remains constant when trains pass. This invention uses a reference electrode to detect the stray current generated when subway vehicles pass and provides the buried pipelines with a current of the same magnitude but opposite direction to the stray current from the subway, ensuring that the potential of the buried pipelines remains constant when trains pass; thus achieving intelligent detection and control of stray current corrosion.

Description

Technical Field

[0001] This invention belongs to the field of underground pipeline protection technology, specifically relating to a protective method for preventing underground pipelines from being corroded by stray currents from railway tracks. Background Technology

[0002] Urban subway lines are becoming increasingly numerous and longer. Although urban subways employ closed-loop systems, meaning subway current can return to the substation via the rails or underground leads, the length of subway lines means that after a period of operation, the insulation equipment under the rails will be damaged or aged, reducing resistance and causing some rail loop current to flow underground. Furthermore, when rails run parallel to underground pipelines, a capacitor-like device is formed between the pipeline and the rails, generating induced current in the underground pipeline. This leakage current or induced current is a stray current that accelerates pipeline corrosion. Especially when the underground pipelines are oil or natural gas pipelines, corrosion can cause leaks and potentially lead to explosions. Protecting adjacent pipelines is not feasible, as some pipelines have been buried underground for many years. Re-laying them would require shutting down the pipelines, inconveniencing residents using oil or gas. Additionally, the cost of excavating underground pipelines is high and uneconomical. Therefore, re-protecting existing underground pipelines, such as applying insulating protective coatings, is highly unreasonable.

[0003] If cathodic protection is used for pipelines adjacent to the subway, and given the intermittent nature of subway operation, the current is high when trains pass, but there is no stray current leakage when trains are not passing, especially at night when most subway lines are closed and no trains are passing, over-protection can occur. Conventional cathodic protection involves supplying a negative potential to the protected underground pipeline. When no subway trains are passing, this negative potential can easily cause hydrogen embrittlement in the underground pipeline. Once hydrogen embrittlement occurs, the underground pipeline can break when a train passes on the surface. This breakage is random and unpredictable, therefore over-protection is also very harmful. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a method for preventing stray current corrosion of underground pipelines. By calculating the potential change caused by stray currents around the track, the opposite potential applied to the pipeline is obtained, so that the pipeline potential remains unchanged, thereby achieving protection against stray current corrosion of underground pipelines.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A protective method for preventing stray currents from corroding underground pipelines is characterized by providing buried pipelines near subways with a current of the same magnitude but opposite direction to the stray currents of the subway, thereby ensuring that the potential of the buried pipelines remains constant when trains pass by.

[0007] Furthermore, the protective device used in the method includes control wires, a control center, reference electrode 1, reference electrode 2, and auxiliary electrodes;

[0008] Reference electrode 1 and reference electrode 2 are respectively connected to the contact column of the control center. The potential measured relative to reference electrode 1 is the initial value of the potential applied to the underground pipeline, and reference electrode 2 is used to monitor the potential applied to the underground pipeline.

[0009] The control wire is connected to the buried pipeline and the control center at both ends, and the connection point between the control wire and the buried pipeline is the control point; the auxiliary electrode is connected to the control center.

[0010] 1) When the buried pipeline is perpendicular to the track:

[0011] Reference electrode 1 and reference electrode 2 are set parallel to each other on one side of the track. Reference electrode 2 is 1-2m away from the buried pipeline, and reference electrode 1 is 1000m away from the buried pipeline. The auxiliary electrode is 1000m away from both the track and the buried pipeline. The control point is in a straight line with reference electrode 1 and reference electrode 2.

[0012] 2) When the buried pipeline is parallel to the track:

[0013] Reference electrode 1 and reference electrode 2 are arranged parallel to each other on one side of the buried pipeline, and the control point is set between reference electrode 1 and reference electrode 2; the line connecting the control point and the auxiliary electrode is perpendicular to the buried pipeline, and the distance between the control point and the auxiliary electrode is 1000m.

[0014] Furthermore, the calculation method for the potential value applied to the surface of the buried pipeline is as follows:

[0015] 1) When the buried pipeline is parallel to the track:

[0016]

[0017] 2) When the buried pipeline is perpendicular to the track:

[0018]

[0019] In the formula: v is the test voltage of reference electrode 1, U is the voltage applied to the pipeline, i.e., the voltage output by the control center, L is the length of the protective pipeline, Rg is the track resistance, Rh is the pipeline resistance, ρ is the soil resistivity, h is the distance between the rail and the pipeline, x is the distance between the control point and the track, and K is the seasonal adjustment coefficient, which is usually taken as 1.

[0020] Furthermore, reference electrode 1 and reference electrode 2 are calomel electrodes, encased in plastic tubing.

[0021] Furthermore, the auxiliary electrode is a cross-shaped copper rod.

[0022] The beneficial effects of this invention are:

[0023] 1) This invention detects stray currents generated when subway vehicles pass by using a reference electrode, and provides buried pipelines with a current of the same magnitude but opposite direction to the stray current of the subway, ensuring that the potential of the buried pipelines remains constant when the train passes by; thus achieving intelligent detection and control of stray current corrosion.

[0024] 2) This invention can automatically and arbitrarily adjust the protection potential and protection current, preventing over-protection from occurring;

[0025] 3) The present invention automatically activates the protective device when the subway is running and automatically deactivates the protective device when the subway stops running, thus reducing protection costs. Attached Figure Description

[0026] Figure 1 Wiring diagram for intelligent protection when the track is perpendicular to the underground pipeline;

[0027] Figure 2 Wiring diagram for intelligent protection when the track is parallel to the underground pipeline;

[0028] Figure 3 This is an auxiliary electrode diagram. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments.

[0030] This invention provides buried pipes near subway stations with a current of the same magnitude but opposite direction to the stray current of the subway, ensuring that the potential of the buried pipes remains constant when a train passes by.

[0031] The protective device used in this invention includes a control wire, a control center, a reference electrode 1, a reference electrode 2, and an auxiliary electrode;

[0032] Reference electrode 1 and reference electrode 2 are respectively connected to the contact post on the control center. Reference electrode 1 is used to detect stray current leaked in the subway, and reference electrode 2 is used to detect the potential applied to the pipeline. The two ends of the control wire are respectively connected to the buried pipeline and the control center. The connection point between the control wire and the buried pipeline is the control point. The auxiliary electrode is connected to the control center.

[0033] Reference electrode 1 and reference electrode 2 are calomel electrodes, and the auxiliary electrode is made of copper, which can be cylindrical or a copper plate; preparation is as follows Figure 3 The cross-shaped copper rod shown should ideally have a diameter greater than 20mm, a copper plate thickness greater than 8mm, and a width greater than 10mm. A plastic tube should be fitted over the calomel reference electrode, with the measuring end exposed. To prevent damage during construction, the reference electrode should be buried at the same depth as the underground pipeline. For pipelines intersecting with tracks, construction can be adjusted to be perpendicular to the pipeline.

[0034] The cross-shaped design of the auxiliary electrode facilitates the application of auxiliary current. Its distance from the rails and pipelines also helps to eliminate interference from the current applied to the auxiliary electrode to other equipment, preventing interference from the auxiliary electrode current to the reference electrode potential and improving the sensitivity of the reference electrode. The auxiliary electrode is made of copper, which both prevents corrosion and improves its current dissipation effect.

[0035] 1) When the buried pipeline is perpendicular to the track:

[0036] like Figure 1 As shown, reference electrode 1 and reference electrode 2 are set parallel to each other on one side of the track. Reference electrode 2 is 1-2m away from the buried pipeline, and reference electrode 1 is 1000m away from the buried pipeline. The auxiliary electrode is 1000m away from both the track and the buried pipeline. The control point is on a straight line with reference electrode 1 and reference electrode 2.

[0037] 2) When the buried pipeline is parallel to the track:

[0038] like Figure 2 As shown, reference electrode 1 and reference electrode 2 are arranged parallel to each other on one side of the buried pipeline, and the control point is set between reference electrode 1 and reference electrode 2; the line connecting the control point and the auxiliary electrode is perpendicular to the buried pipeline, and the distance between the control point and the auxiliary electrode is 1000m.

[0039] The working principle of this invention is as follows:

[0040] When a subway train passes by, the stray current generated is sensed by reference electrode 1 and reference electrode 2 and transmitted to the control center. The control center calculates the potential value that should be applied to the surface of the buried pipeline and applies a potential opposite to the stray current through the control point and auxiliary electrode to keep the potential of the buried pipeline constant. When the two reference electrodes do not sense the current leaked by the train and the ground potential does not change, there is no current between the control point and the auxiliary electrode.

[0041] The calculation method for the potential value applied to the surface of buried pipelines is as follows:

[0042] 1) When the buried pipeline is parallel to the track:

[0043]

[0044] 2) When the buried pipeline is perpendicular to the track:

[0045]

[0046] In the formula: v is the test voltage of reference electrode 1, U is the voltage applied to the pipeline, i.e., the voltage output by the control center, L is the length of the protective pipeline, Rg is the track resistance, Rh is the pipeline resistance, ρ is the soil resistivity, h is the distance between the rail and the pipeline, x is the distance between the control point and the track, and K is the seasonal adjustment coefficient, which is usually taken as 1.

[0047] The applied current is determined by the second reference electrode, ensuring the potential on the pipeline is within ±0.01V relative to when no train is passing. This ±0.01V is essentially instrument error, thus guaranteeing the underground pipeline is free of stray current. As a train approaches and departs, the control center increases or decreases the potential according to the exponential equation of the potential rise / fall curve. This curve is calculated using equations derived from tests of the distribution of stray currents on the track. Reference electrode 1 is the initial value applied to the potential, and reference electrode 2 is the detected value of the applied potential on the pipeline. When the train departs, the current applied to the underground pipeline gradually decreases according to the exponential equation, with the rate of decrease equal to the rate of change of the tested potential between reference electrodes 1 and 2. This design prevents changes in the current on the underground pipeline caused by current leakage as a train approaches, ensures that the leaked stray current matches the opposite current supplied by the control center when a train passes, and solves the protection problems of stray current gradually decreasing exponentially when the train departs and the absence of current in the underground pipeline when rail transit stops or moves away. This means that the system automatically starts when the train is running and automatically shuts off when the train stops, avoiding the problem that conventional cathodic protection cannot automatically adjust the potential and current, and that there is still negative current in the underground pipeline when the train is not running at night. It also prevents hydrogen absorption corrosion that may occur in the underground pipeline due to excessive negative current, thus achieving intelligent detection and corrosion prevention.

[0048] The content of this invention is not limited to the embodiments listed. Any equivalent modifications made by those skilled in the art to the technical solutions of this invention by reading this specification are covered by the claims of this invention.

Claims

1. A method of protecting underground pipes from stray current corrosion by rail tracks, characterised in that: The method provides the same current as the stray current of the subway and in the opposite direction for the buried pipeline near the subway, so that the potential of the buried pipeline is kept constant when the train passes by; The protection device used in the method comprises a control wire, a control center, a reference electrode 1, a reference electrode 2 and an auxiliary electrode; The reference electrode 1 and the reference electrode 2 are connected to the contact column of the control center respectively, the potential tested by the reference electrode 1 is the initial value of the potential applied to the underground pipeline, and the reference electrode 2 is the monitoring of the potential applied to the underground pipeline; The control wire is connected to the buried pipeline and the control center respectively, and the connection point of the control wire and the buried pipeline is a control point; the auxiliary electrode is connected to the control center; 1) when the buried pipeline is perpendicular to the track: The reference electrode 1 and the reference electrode 2 are arranged on one side of the track in parallel, the reference electrode 2 is 1-2 m away from the buried pipeline, the reference electrode 1 is 1000 m away from the buried pipeline; the auxiliary electrode is 1000 m away from the track and the buried pipeline respectively; the control point is in a straight line with the reference electrode 1 and the reference electrode 2; 2) when the buried pipeline is parallel to the track: The reference electrode 1 and the reference electrode 2 are arranged on one side of the buried pipeline in parallel, and the control point is arranged between the reference electrode 1 and the reference electrode 2; the line connecting the control point and the auxiliary electrode is perpendicular to the buried pipeline, and the distance between the control point and the auxiliary electrode is 1000 m; The calculation method of the potential value applied to the surface of the buried pipeline is as follows: 1) when the buried pipeline is parallel to the track: ； 2) when the buried pipeline is perpendicular to the track: ； In the formula, v is the test voltage of the reference electrode 1, U is the voltage applied to the pipeline, that is, the output voltage of the control center, L is the length of the protected pipeline, Rg is the track resistance, Rh is the pipeline resistance, p is the soil resistivity, h is the distance between the track and the pipeline, x is the distance between the control point and the track, K is the seasonal adjustment coefficient, and 1 is taken in general.

2. A method of protecting underground pipes from stray current corrosion according to claim 1, wherein: The reference electrode 1 and the reference electrode 2 adopt mercury-mercury electrodes, which are sleeved with plastic tubes.

3. The method of claim 1, wherein the method further comprises: providing a plurality of conductive strips on the surface of the underground pipeline. The auxiliary electrode adopts a cross-shaped copper rod.

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