Conductive earth and method of backfilling to prevent pipeline corrosion from underground stray current

Abstract

The application discloses a conductive soil for preventing underground stray current from corroding pipelines and a filling method. If the underground pipelines of a city are corroded, the harm is immeasurable. The conductive soil comprises the following components in percentage by weight: gypsum powder 55-65%, diatomite or bentonite 20-15%, sodium sulfate 9.5-4.5%, fly ash or carbon residue 15%, and hexamethylene tetramine or thiourea 0.5%. When the pipelines are filled after installation, the pipelines are filled with the conductive soil with a thickness of 100-200 mm, so that the stray current flowing into the ground is transmitted to the ground through the conductive soil preferentially, and does not enter the oil and gas pipelines, thereby achieving the purpose of preventing the corrosion of the stray current on the underground pipelines.

Description

Technical Field

[0001] This invention belongs to the field of underground pipeline corrosion protection technology, specifically relating to a conductive soil and backfilling method for preventing underground stray currents from corroding pipelines. Background Technology

[0002] Underground equipment, especially underground oil and gas pipelines, is becoming increasingly longer and the pressure of these pipelines is increasing. Meanwhile, above-ground rail transit, electrified railways, high-speed railways, and high-voltage and DC power transmission projects generally use the earth as the neutral line, meaning the earth acts as the discharge electrode. As a result, more and more current is being discharged underground. The voltage of this underground current is not only high, but its frequency and direction also vary considerably. This current flowing into the earth is called stray current, and these stray currents are causing increasingly severe corrosion to underground equipment and pipelines.

[0003] Generally speaking, if the current input underground is direct current (DC), underground equipment is subject to accelerated anodic corrosion, but the potential at the current input end is higher than that at the output end, i.e., anodic corrosion occurs at the current input end; the current output end is the cathode, which produces hydrogen evolution corrosion. Anodic corrosion results in thinning and perforation of oil and gas pipelines; hydrogen evolution corrosion at the cathode end makes the pipeline brittle, leading to brittle fracture under gravitational forces. The damage caused by corrosion of underground pipelines in a city is incalculable. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides conductive soil and a backfilling method for preventing underground stray currents from corroding pipelines. This method shields the current flowing into the ground outside the pipeline, and the stray current flowing into the ground is preferentially transmitted to the ground through the conductive soil, preventing it from entering the oil and gas pipeline, thereby achieving the purpose of preventing stray currents from corroding underground pipelines.

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

[0006] A conductive soil for preventing underground stray currents from corroding pipelines is characterized by comprising: 55-65 wt% gypsum powder, 20-15 wt% diatomaceous earth or bentonite, 9.5-4.5 wt% sodium sulfate, 15 wt% fly ash or carbon slag, and 0.5 wt% hexamethylenetetrammonium or thiourea.

[0007] Specifically, it includes 55 wt% gypsum powder, 20 wt% diatomaceous earth, 9.5 wt% sodium sulfate, 15 wt% fly ash, and 0.5 wt% hexamethylenetetramine.

[0008] Specifically, it includes 60 wt% gypsum powder, 17 wt% bentonite, 7.5 wt% sodium sulfate, 15 wt% fly ash or carbon slag, and 0.5 wt% hexamethylenetetramine or thiourea.

[0009] Specifically, it includes 65 wt% gypsum powder, 15 wt% bentonite, 4.5 wt% sodium sulfate, 15 wt% carbon slag, and 0.5 wt% thiourea.

[0010] A method for burying conductive soil to prevent underground stray currents from corroding pipelines, characterized by comprising the following steps:

[0011] Step 1: After the underground pipeline is installed, or when the old underground pipeline is excavated and backfilled, fill the surrounding area with ordinary soil and compact it with an electric tamper to make a gap of 100-200mm between the underground pipeline and the ordinary soil backfill layer.

[0012] Step 2: Take 55-65wt% of gypsum powder with a particle size of 70-120μm, 20-15wt% of diatomaceous earth or bentonite, 9.5-4.5wt% of sodium sulfate, 15wt% of fly ash or carbon slag, and 0.5wt% of hexamethylenetetramine or thiourea. Add water equal to 1 / 3 of the powder weight and mix evenly with a mixer.

[0013] Step 3: Apply the mixture obtained in Step 2 to the surface of the underground pipe;

[0014] Step 4: After ensuring that there is a 100-200mm thick layer of conductive soil around the underground pipeline, fill the conductive soil and underground pipeline with ordinary soil.

[0015] The beneficial effects of this invention are:

[0016] 1) When backfilling the pipeline after installation, the present invention uses conductive soil with a thickness of 100-200mm around the pipeline, so that stray current flowing into the ground is preferentially transmitted to the ground through the conductive soil and does not enter the oil and gas pipeline, thereby preventing the corrosion of underground pipelines by stray current.

[0017] 2) This invention mixes conductive soil and water into a paste, ensuring that the conductive soil can adhere to the pipe. The gypsum powder solidifies quickly, which is convenient for construction and makes the conductive soil less likely to fall off, thus ensuring that there is a tight and uniform conductive soil layer around the pipe.

[0018] 3) The particle size and composition of the conductive soil in this invention ensure the dielectric constant and conductivity of the conductive soil layer, giving it a shielding effect against stray currents; in particular, diatomaceous earth and bentonite are used to fill conductive layers with characteristics similar to capacitors. When the stray current is large, electrons are adsorbed on the surface; when the stray current is small, electrons are released, which helps to balance the electric field around the underground pipeline.

[0019] 4) The conductive soil of the present invention contains sodium sulfate, hexamethylenetetramungsten or thiourea, which improves the corrosion inhibition of the conductive layer and makes the conductive soil a protective layer that prevents the corrosion of underground steel pipes. The conductive soil used for landfilling can not only prevent the corrosion of stray currents, but also prevent the corrosion of underground pipelines by acidic soil, dissolved oxygen and other media in the soil. Attached Figure Description

[0020] Figure 1 This is a comparison diagram showing the effect of conductive soil burial and ordinary soil burial on the external interference current of underground steel pipes according to the present invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments.

[0022] This invention is applicable to the protection of underground pipelines around high-speed railways, subways, and substations. It provides shielding against stray currents and is also suitable for situations where soil corrosion is severe. It is applicable to existing pipelines and new pipelines under construction.

[0023] The conductive soil for preventing stray current corrosion of underground pipelines according to the present invention is composed of the following components: 55-65 wt% gypsum powder with a particle size of 70-120 μm, 20-15 wt% diatomaceous earth or bentonite, 9.5-4.5 wt% sodium sulfate, 15 wt% fly ash or carbon slag and 0.5 wt% hexamethylenetetramine or thiourea.

[0024] The roles of each component in conductive soil backfill:

[0025] Gypsum powder is the main film-forming substance for conductive soil used in landfills. It provides a shaping effect for the conductive soil to adhere to the pipeline. It has a fast curing speed and provides external conditions for the adhesion of a conductive layer with a thickness of 100-200mm. In addition, it stabilizes the dielectric constant of the conductive soil, giving it a certain shielding effect. It is also a neutral material, so it will not cause the problem of accelerated corrosion of steel pipes due to conductive soil adhering to the outside of the steel pipe.

[0026] Diatomaceous earth and bentonite can provide a smooth feel to gypsum powder slurry. In addition, they have high interfacial properties, which can adsorb electrons on the surface when the external potential is high and release electrons when the electrical properties are weak. This makes the conductive soil layer act as a capacitor and maintain the equilibrium potential of the conductive layer. In addition, it is a good dielectric material and can also balance small stray currents by utilizing its dielectric properties, so that underground pipelines are free from stray current interference.

[0027] Sodium sulfate is a conductive salt that acts as a conductive medium, making conductive soil conductive. It can also facilitate the transfer of charge in the charged layers of bentonite and diatomite in conductive soil, and it has good miscibility with diatomite and bentonite.

[0028] Fly ash or carbon slag can provide strength to conductive soil and act as a skeleton support. They are inexpensive and have a synergistic effect on the conductivity of conductive soil.

[0029] Hexamethylenetetramine or thiourea are used as corrosion inhibitors to prevent corrosion of underground steel pipes by corrosive ions in the soil. In other words, even without stray current, chloride ions, hydrogen ions, and solvent oxygen in the soil have a certain corrosive effect on underground steel pipes. When stray current is present, it accelerates corrosion. When there is a conductive soil layer around the steel pipe, the corrosion inhibitor in the conductive soil can effectively prevent soil corrosion. Even if the conductive soil cannot completely shield stray current from causing corrosion, the corrosion inhibitor can still prevent corrosion caused by stray current.

[0030] like Figure 1 As shown, when there is no stray current interference in the underground pipeline, the pipeline potential is a straight line, with a potential of -0.053V relative to the copper sulfate reference electrode. When the simulated subway track has a 5V DC interference current, the potential caused by stray current on the simulated underground steel pipe buried in ordinary soil at a distance of 0.5 meters is 0.05-0.065V. This potential is caused by stray current caused by track leakage. As is well known, stray current accelerates the corrosion of underground steel pipes. Most underground steel pipes transport natural gas, tap water, etc. If the steel pipe leaks after corrosion, it will bring great danger. When the underground pipeline is buried with the conductive soil of this invention, for the same steel pipe, the same location, and the same stray current, the potential change caused by the stray current on the steel pipe is 0.01-0.02V. 0.01-0.02V is 10-20mV, which is within the error range of the corrosion potential of underground equipment. It can be considered that such a small stray current will not accelerate the corrosion of the pipeline. Even if corrosion occurs, the corrosion inhibitor in the conductive soil can prevent it. Actual testing shows that the conductive soil burial technology of this invention achieves the purpose of preventing and shielding underground stray currents, and plays a role in preventing corrosion of underground pipelines by stray currents.

[0031] A method for backfilling conductive soil to prevent underground stray currents from corroding pipelines includes the following steps:

[0032] Step 1: After the underground pipeline is installed, or when the old underground pipeline is excavated and backfilled, fill the surrounding area with ordinary soil and compact it with an electric tamper to make a gap of 100-200mm between the underground pipeline and the ordinary soil backfill layer.

[0033] Step 2: Take 55-65wt% of gypsum powder with a particle size of 70-120μm, 20-15wt% of diatomaceous earth or bentonite, 9.5-4.5wt% of sodium sulfate, 15wt% of fly ash or carbon slag, and 0.5wt% of hexamethylenetetramine or thiourea. Add water equal to 1 / 3 of the powder weight and mix evenly with a mixer.

[0034] Step 3: Apply the mixture obtained in Step 2 to the surface of the underground pipe;

[0035] Step 4: After ensuring that there is a 100-200mm thick layer of conductive soil around the underground pipeline, fill the conductive soil and underground pipeline with ordinary soil.

[0036] The specific implementation method is as follows:

[0037] 1) Example 1

[0038] Stray currents were detected in underground steel pipes along the subway line. Conductive soil was used to fill the pipes to prevent corrosion caused by the stray currents.

[0039] Step 1: After the underground pipeline is installed, the surrounding area is first filled with ordinary soil and compacted with an electric tamper to create a 100mm gap between the pipeline and the ordinary soil filling layer.

[0040] Step 2: Mix 55wt% gypsum powder (70μm), 20wt% diatomaceous earth, 9.5wt% sodium sulfate, 15wt% fly ash, and 0.5wt% hexamethylenetetramine powder with water (1 / 3 of the powder's weight) using a mixer until homogeneous.

[0041] Step 3: Apply the mixture from the previous step to the surface of the pipe;

[0042] Step 4: After ensuring there is a 100mm thick layer of conductive soil around the pipe, fill the conductive soil and pipe with ordinary soil.

[0043] 2) Example 2

[0044] Stray currents were detected in underground steel pipelines along the high-speed railway line. Conductive soil was used to fill the pipelines to prevent corrosion caused by the stray currents.

[0045] Step 1: First, excavate the underground pipeline to expose it, ensuring a 150mm gap between the pipeline and the ordinary soil backfill layer;

[0046] Step 2: Add 60wt% gypsum powder (100μm particle size), 17wt% bentonite, 7.5wt% sodium sulfate, 15wt% fly ash or carbon slag, and 0.5wt% hexamethylenetetramine or thiourea powder to 1 / 3 the weight of the powder and mix evenly with a mixer.

[0047] Step 3: Apply the mixture from the previous step to the surface of the pipe;

[0048] Step 4: After ensuring that there is a 150mm thick layer of conductive soil around the pipe, fill the conductive soil and the pipe with ordinary soil.

[0049] 3) Example 3

[0050] Stray currents were detected in underground steel pipelines around the DC substation. Conductive soil was used to fill the pipelines to prevent corrosion from the stray currents.

[0051] Step 1: After the underground pipeline is installed, the surrounding area is first filled with ordinary soil and compacted with an electric tamper to create a 200mm gap between the pipeline and the ordinary soil filling layer.

[0052] Step 2: Mix 65wt% gypsum powder (120μm), 15wt% bentonite, 4.5wt% sodium sulfate, 15wt% carbon slag, and 0.5wt% thiourea powder with water (1 / 3 of the powder's weight) using a mixer until homogeneous.

[0053] Step 3: Apply the mixture from the previous step to the gap between the pipe and the ordinary soil;

[0054] Step 4: After ensuring that there is a 200mm thick layer of conductive soil around the pipe, fill the conductive soil and the pipe with ordinary soil.

[0055] 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 for burying conductive soil to prevent underground stray currents from corroding pipelines, characterized in that: Includes the following steps: Step 1: After the underground pipeline is installed, or when the old underground pipeline is excavated and backfilled, fill the surrounding area with ordinary soil and compact it with an electric tamper to make a gap of 100-200mm between the underground pipeline and the ordinary soil backfill layer. Step 2: Take 55-65wt% of gypsum powder with a particle size of 70-120μm, 20-15wt% of diatomaceous earth or bentonite, 9.5-4.5wt% of sodium sulfate, 15wt% of fly ash or carbon slag, and 0.5wt% of hexamethylenetetramine or thiourea. Add water equal to 1 / 3 of the powder weight and mix evenly with a mixer. Step 3: Apply the mixture obtained in Step 2 to the surface of the underground pipe; Step 4: After ensuring that there is a 100-200mm thick layer of conductive soil around the underground pipeline, fill the conductive soil and underground pipeline with ordinary soil. The conductive soil comprises 55-65 wt% gypsum powder, 20-15 wt% diatomaceous earth or bentonite, 9.5-4.5 wt% sodium sulfate, 15 wt% fly ash or carbon slag, and 0.5 wt% hexamethylenetetrammonium or thiourea.

2. The method for backfilling conductive soil to prevent underground stray current corrosion of pipelines according to claim 1, characterized in that: The conductive soil comprises 55 wt% gypsum powder, 20 wt% diatomaceous earth, 9.5 wt% sodium sulfate, 15 wt% fly ash, and 0.5 wt% hexamethylenetetrammonium.

3. The method for backfilling conductive soil to prevent underground stray current corrosion of pipelines according to claim 1, characterized in that: The conductive soil comprises 60 wt% gypsum powder, 17 wt% bentonite, 7.5 wt% sodium sulfate, 15 wt% fly ash or carbon slag, and 0.5 wt% hexamethylenetetrammonium or thiourea.

4. The method for backfilling conductive soil to prevent underground stray current corrosion of pipelines according to claim 1, characterized in that: The conductive clay comprises 65wt% gypsum powder, 15wt% bentonite, 4.5wt% sodium sulfate, 15wt% carbon slag, and 0.5wt% thiourea.

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