A method for repairing a gas pipeline by using positive and negative pressure lining technology

Abstract

The application discloses a method for repairing a gas pipeline by adopting positive and negative pressure lining technology, and comprises the following steps: S1, cutting off a steel pipe and locally excavating; S2, rusting the inner wall of the steel pipe; S3, lining repair; and S4, secondary connection of the cut-off part. In the step S3, the lining repair is performed by adopting a positive and negative pressure lining elastic polyurethane high-pressure hose technology to repair the inner wall of the in-service pipeline, so that the fouling of the pipeline can be greatly relieved, the risk of leakage caused by the corrosion of the inner wall of the steel pipe is reduced, and the average service life can be prolonged by more than 20 years.

Description

Technical Field

[0001] This invention relates to the field of gas pipeline repair technology, specifically to a method for repairing gas pipelines using positive and negative pressure lining technology. Background Technology

[0002] Gas pipelines, after years of operation, suffer varying degrees of corrosion from H2S and other acidic gases on their inner walls, impacting their lifespan. A common repair method is internal wall spraying, which involves applying a special coating material to repair damaged or corroded sections of the pipeline's inner wall. These coatings typically possess high-temperature resistance and corrosion resistance, providing effective protection and restoring the pipeline's fluid transport capacity. However, internal wall spraying requires thorough cleaning and preparation of the pipeline's inner wall to ensure a firm adhesion of the coating. This includes removing rust, grease, moisture, and other impurities, and performing surface treatment to improve adhesion. This preparation is time-consuming and resource-intensive. Internal wall spraying may not be effective for severely damaged or corroded pipelines. If the pipeline has extensive corrosion, breaks, or dents, internal wall spraying may not provide sufficient protection, necessitating more complex repair methods. While internal wall spraying offers some protection, the coating may wear down or be affected by other environmental factors over time, requiring regular inspection and maintenance. Maintenance involves shutting down pipelines and re-constructing them, which may cause some disruption and costs to operations. Summary of the Invention

[0003] Based on the problems existing in the background technology, the present invention provides a technology for repairing the inner wall of in-service pipelines using positive and negative pressure lined elastic polyurethane high-pressure hoses. The repaired pipeline can greatly alleviate scaling, reduce the risk of leakage caused by corrosion of the inner wall of the steel pipe, and extend the average service life by more than 20 years.

[0004] This invention is implemented through the following technical solutions:

[0005] A method for repairing gas pipelines using positive and negative pressure lining technology includes the following steps:

[0006] S1. Cutting off the steel pipe and partial excavation;

[0007] S2. Rust removal from the inner wall of the steel pipe;

[0008] S3. Lining repair;

[0009] S4. Secondary connection of the cut-off portion.

[0010] Furthermore, the specific operations for cutting off the steel pipe and partial excavation in step S1 are as follows: using line-finding positioning technology, the excavation opening for repairing the steel pipe is located, and the length of the inner lining steel pipe is determined based on the line-finding results. The elbow section needs to be cut off.

[0011] Furthermore, the rust removal of the inner wall of the steel pipe in step S2 can be performed as needed;

[0012] Small-sized (below 168) steel pipes are cleaned using a rotating wire brush and internal air blowing.

[0013] The rotating wire brush is delivered to the cut-off point of the pipeline by a probe (with an internal power cord) using air conveyor. The power cord and drag line are then secured with the drag line before being pulled to the cut-off point, completing all preparations for dragging and power connection. Rust removal of the inner wall is completed during the dragging process by rotating the wire brush (the outer diameter of the wire brush is slightly larger than the inner diameter of the steel pipe, and a connecting ring is welded at the axis for easy connection of the drag rope) with a bearing. This process requires at least two dragging cycles, one forward and one reverse.

[0014] Large-diameter steel pipes (219 and above) are finished by sandblasting and internal air purging.

[0015] Sandblasting (quartz sand) first relies on air conveying to transport the binding cable to the cut-off part of the pipeline. The binding cable is used to fix the air pipe to the built-in carriage (to prevent the carriage from tipping over during operation, three carriages are usually used as a group, evenly distributed along the axial direction of the pipe diameter, and fixed by a bracket at three different points in contact with the pipe wall) (the air pipe nozzle is fixed on one of the built-in carriages). The rust removal of the inner wall of the steel pipe is completed during the carriage dragging process.

[0016] Furthermore, after rust removal in step S2, the debris inside the deposition tube should be blown away using an internal air purging technique. The rust removal effect can be checked by shining a strong flashlight inwards from both sides of the excavation opening.

[0017] Furthermore, the lining repair in step S3 specifically includes the following steps:

[0018] S301. High-pressure hose installation;

[0019] S302. High-pressure hose adheres to steel pipe;

[0020] S303. Adhesive surface cured.

[0021] Further, the specific operation of laying the high-pressure hose in step S301 is as follows: uniformly coat the surface of the high-pressure hose with a composite adhesive, the adhesive layer thickness is 0.1-0.5mm, and use traction technology to pass the high-pressure hose with the adhesive coating on the outer surface through the inner wall of the steel pipe (the diameter of the high-pressure hose is slightly smaller than the inner diameter of the steel pipe, and the high-pressure hose has a certain degree of elasticity). The key to this process is to ensure that the adhesive coating on the hose is uniform, the adhesive layer thickness meets the requirements, keep the high-pressure hose from getting knotted during the crossing, keep the two ends of the high-pressure hose relatively taut, keep the hose from contacting the inner wall of the steel pipe, and proceed smoothly.

[0022] Furthermore, the composite adhesive is characterized by using a polyethylene adhesive with modified maleic anhydride-grafted polyethylene as the main material, and by weight, it comprises the following components: 20-30 parts of maleic anhydride-grafted polyethylene, 10-15 parts of polyacetylene viscoelastic, 3-8 parts of polyester viscoelastic, 1-3 parts of butanediol, 1-2 parts of tetrabutyl titanate, 5-10 parts of butyl rubber, 1-2 parts of antioxidant, and 1-2 parts of peroxide.

[0023] Furthermore, the composite adhesive has a shear strength ≥3.5MPa when bonded to the steel body; an oxidation induction period ≥30min at 200℃; and a viscosity of 12000-15000cps.

[0024] Furthermore, the raw materials of the high-pressure hose contain the following components by weight: 60-70 parts modified polyurethane, 5-10 parts polyurea, 3-8 parts polypropylene, 3-8 parts polyacetylene viscoelastic, 3-5 parts polyisocyanate, and 1-3 parts antioxidant.

[0025] Furthermore, the high-pressure hose is manufactured using a twin-screw extruder blown film forming process in one step;

[0026] The high-pressure hose has a wall thickness of 5-10mm, tensile strength ≥12MPa, nominal strain at break ≥1000%, elastic modulus <0.5Gpa, and oxidation induction period ≥30min at 220℃.

[0027] Furthermore, the bonding of the high-pressure hose to the steel pipe in step S302 specifically includes the following steps:

[0028] S302-1. The laid high-pressure hose is supported by positive pressure technology. The elasticity of the high-pressure hose is used to firmly bond the high-pressure hose to the surface of the steel pipe. After the bond is firm, negative pressure technology is used to test the bonding effect between the high-pressure hose and the steel pipe.

[0029] S302-2. Positive pressure technology is used again to reinforce the adhesion between the high-pressure hose and the steel pipe.

[0030] Furthermore, in step S302-1, the positive pressure technology involves sealing the pipe end and then pressurizing it to a pressure of 1.6 MPa; the negative pressure technology involves sealing the pipe end and using vacuum adsorption technology to evacuate air from inside the steel pipe to a pressure of 1.0 MPa. The negative pressure technology, also known as vacuum adsorption technology, plays a negative destructive role. After positive pressure treatment, the part of the high-pressure hose that is not firmly bonded to the steel pipe will fall off after being treated with negative pressure technology, which facilitates the subsequent secondary reinforcement treatment with positive pressure technology.

[0031] Furthermore, in step S302-2, the positive pressure technology involves sealing the pipe head and then pressurizing it to a pressure of 2.0 MPa. The positive pressure technology secondary reinforcement treatment is actually a repair for the situation where the local high-pressure hose has come off (the negative pressure technology is used to check the adhesion strength).

[0032] In practice, there may not be any local detachment between the high-pressure hose and the steel pipe after negative pressure treatment. However, regardless of whether there is local detachment of the high-pressure hose, a secondary reinforcement treatment with positive pressure technology is required. The secondary reinforcement treatment with positive pressure technology not only repairs the local detachment caused by negative pressure technology, but also enhances the adhesion between the high-pressure hose and the steel pipe.

[0033] Furthermore, in step S303, the bonded surface must be cured, meaning the repaired steel pipe needs to be cured for one week before it can be put into use.

[0034] Furthermore, the specific steps for the secondary connection of the cut-off section in step S4 are as follows: During pipe butt welding, ensure that both ends of the steel pipe have a ceramic lining. Adhere a viscoelastic paste (a soft, freely deformable paste with extremely strong adhesion to metals and non-metals) to the outer surface of the ceramic pipe section to ensure the airtightness of the connection and prevent damage to the ceramic lining during steel pipe welding, thus ensuring the continuity of corrosion protection on the inner wall of the pipe. The external joint is repaired using the same process as the external corrosion protection of the parent pipe.

[0035] The beneficial effects of this invention are:

[0036] 1. This invention uses positive and negative pressure lined elastic polyurethane high-pressure hose technology to repair the inner wall of in-service pipelines. The repair work area is small, and the environmental disturbance is minimal. Moreover, the high-pressure hose lining is cured in situ, so the construction does not affect the strength of the high-pressure hose itself. The repaired pipeline can greatly alleviate scaling, reduce the risk of leakage caused by corrosion of the inner wall of the steel pipe, and extend the average service life by more than 20 years, greatly reducing the project cost.

[0037] 2. The composite adhesive and high-pressure hose used in the method for repairing gas pipelines of the present invention have a similar coefficient of thermal expansion to steel pipes, and will not delaminate due to thermal expansion and contraction.

[0038] 3. In the method for repairing gas pipelines of the present invention, the positive pressure lining can repair the corroded parts of the inner wall of the steel pipe, providing protection and reinforcement for the pipeline; after the positive pressure lining is completed, negative pressure technology is used to test the bonding effect between the high-pressure hose and the steel pipe, and then positive pressure technology is used for secondary reinforcement to repair the local detachment caused by the negative pressure technology and enhance the bonding effect between the high-pressure hose and the steel pipe. Detailed Implementation

[0039] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0040] Example 1

[0041] Preparation of composite adhesives

[0042] By weight, it comprises the following components: 25 parts maleic anhydride-grafted polyethylene, 15 parts polyacetylene viscoelastic, 5 parts polyester viscoelastic, 2 parts butanediol, 2 parts tetrabutyl titanate, 8 parts butyl rubber, 1 part antioxidant, and 1 part peroxide.

[0043] The antioxidant is diphenylamine sulfide phenol; the peroxide is diisopropylbenzene peroxide.

[0044] According to GB / T7124, the shear strength of the composite adhesive bonded to the steel body is 4.2 MPa; the oxidation induction period of the adhesive at 200℃ is 45 min, as tested by differential thermal analysis; and the viscosity of the composite adhesive is 13500 cps, as tested by a viscometer.

[0045] Example 2

[0046] Preparation of high-pressure hoses

[0047] By weight, it contains the following components: 65 parts modified polyurethane, 8 parts polyurea, 5 parts polypropylene, 5 parts polyacetylene viscoelastic, 4 parts polyisocyanate, and 2 parts antioxidant.

[0048] The modified polyurethane, by weight, comprises 50 parts of polypropylene glycol, 38 parts of isoflurane diisocyanate, 12 parts of hydroxyl acrylic resin, and 1 part of p-toluenesulfonic acid. The specific preparation method is as follows: the polypropylene glycol, isoflurane diisocyanate, hydroxyl acrylic resin, and p-toluenesulfonic acid are stirred and mixed evenly, and refluxed at 90°C for 2 hours to obtain the modified polyurethane.

[0049] The antioxidant is diphenylamine sulfophenol; the polyisocyanate is isoflurane diisocyanate.

[0050] The material of the high-pressure hose is mixed to form granular high-pressure hose special material, and then blown into film in one step by a twin-screw extruder at an extrusion temperature of 220℃.

[0051] The wall thickness of the prepared high-pressure hose is 5mm.

[0052] According to the test method in GB / T1040.1-2006, the tensile strength of the high-pressure hose was measured to be 15 MPa, the nominal strain at break was 1000%, the elastic modulus of the high-pressure hose was tested to be 0.3 GPa using the static method, and the oxidation induction period of the adhesive at 200℃ was tested to be 45 min using the differential thermal analysis method.

[0053] Example 3

[0054] Gas pipeline repair

[0055] Repairing the inner wall of in-service pipelines with small gauges (below 168) includes the following steps:

[0056] S1. Cutting off the steel pipe and partial excavation: Using line-finding positioning technology, locate the excavation opening for repairing the steel pipe, and determine the length of the inner lining steel pipe based on the line-finding results. The elbow section needs to be cut off.

[0057] S2. Rust Removal of the Inner Wall of the Steel Pipe: This is accomplished using a rotating wire brush combined with internal air purging. Specifically, the rotating wire brush is conveyed to the cut-off point of the pipe via a probe (connected to a power cord) using airflow. The power cord and towing line are then secured with the towing line before the pipe is pulled to the cut-off point, completing all preparations for pulling and power connection. Rust removal of the inner wall is achieved by rotating the wire brush (whose outer diameter is slightly larger than the inner diameter of the steel pipe, with a welded connecting ring at the axis for easy connection of the towing rope) using a bearing. This process requires at least two forward and reverse pulls. After rust removal, internal air purging is used to remove any remaining debris from the pipe. The rust removal effect is checked by shining a strong flashlight inwards from both sides of the excavation opening.

[0058] S3. Lining repair includes the following steps:

[0059] S301. High-pressure hose laying: Apply a composite adhesive evenly to the surface of the high-pressure hose, with an adhesive layer thickness of 0.1-0.5mm. Using traction technology, pass the high-pressure hose with the adhesive coating through the inner wall of the steel pipe (the diameter of the high-pressure hose is slightly smaller than the inner diameter of the steel pipe, and the high-pressure hose has a certain degree of elasticity). The key to this process is to ensure that the adhesive coating on the hose is uniform, the adhesive layer thickness meets the requirements, keep the high-pressure hose from getting knotted during the crossing, keep both ends of the high-pressure hose taut, keep the hose from contacting the inner wall of the steel pipe, and proceed smoothly.

[0060] S302. Adhesion between high-pressure hose and steel pipe includes the following steps:

[0061] S302-1. The laid high-pressure hose is supported by positive pressure technology. Utilizing the elasticity of the high-pressure hose, it is tightly bonded to the steel pipe surface. After the bond is secure, negative pressure technology is used to test the bonding effect between the high-pressure hose and the steel pipe. The positive pressure technology involves sealing the pipe end and applying pressure at 1.6 MPa. The negative pressure technology involves sealing the pipe end and using vacuum adsorption technology to evacuate air from inside the steel pipe at 1.0 MPa. The negative pressure technology, also known as vacuum adsorption, acts as a negative destructive force. After positive pressure treatment, any weak bonding between the high-pressure hose and the steel pipe will detach when treated with negative pressure, facilitating subsequent secondary reinforcement using positive pressure technology.

[0062] S302-2. The adhesion between the high-pressure hose and the steel pipe is reinforced again using positive pressure technology. The positive pressure technology involves sealing the hose end and then applying pressure of 2.0 MPa. This secondary reinforcement treatment using positive pressure technology is essentially a repair for situations where the high-pressure hose has partially detached (negative pressure technology is used to check the adhesion strength).

[0063] S303. Bonding surface curing: The repaired steel pipe needs to be cured for 1 week before it can be put into use.

[0064] S4. Secondary Connection at the Cut-off Point: When butt-jointing the pipes, ensure that both ends of the steel pipe are lined with ceramic material. Adhere a viscoelastic paste (a soft, freely deformable paste with extremely strong adhesion to both metals and non-metals) to the outer surface of the ceramic pipe section to ensure the airtightness of the connection and prevent damage to the ceramic lining during steel pipe welding, thus ensuring the continuity of corrosion protection on the inner wall of the pipeline. The external joint is repaired using the same process as the external corrosion protection of the parent pipe.

[0065] Test case

[0066] Performance testing was conducted on the repaired gas pipeline.

[0067] According to GB / T23257, the peel strength of the external high-pressure hose and the gas steel pipe at 20℃ and 60℃ are 280N / cm and 180N / cm respectively, which meet the standards specified in GB / T23257.

[0068] Airflow cavitation detection: A 30cm straight section of the repaired gas pipe was selected for testing and connected to a separate premixed gas pipeline. The experimental environment temperature was maintained at 25℃, and the flow rate was adjusted to achieve a flow velocity of 1m / s and a pressure of 0.3MPa in the straight gas pipe. The premixed gas, consisting of methane, air, and hydrogen sulfide in a volume ratio of 1:4:0.05, was kept flowing. The mass loss of the sample pipe was detected at flow times of 720H, 960H, and 1500H. The results were 0.0%, 0.2%, and 0.5%, respectively, indicating that the gas pipeline repaired by this invention has good corrosion resistance and helps to extend the service life of the original gas pipeline.

[0069] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method of repairing a gas pipeline using a positive and negative pressure lining technique, characterized in that, The method comprises the following steps: S1. cutting off the steel pipe and local excavation; S2. rust removal of the inner wall of the steel pipe; S3. inner lining repair: S301. high-pressure hose laying; S302. high-pressure hose adhesion to the steel pipe: S302-1. the laid high-pressure hose is lifted up by positive pressure technology, and the high-pressure hose is tightly adhered to the surface of the steel pipe by the elasticity of the high-pressure hose, and after the adhesion is firm, negative pressure technology is used to test the adhesion effect of the high-pressure hose and the steel pipe; S302-2. the adhesion of the high-pressure hose to the steel pipe is reinforced again by using positive pressure technology twice; S303. curing of the adhesion surface; S4. secondary connection of the cut-off part; In step S302-1, the positive pressure technology is to pressurize after plugging the pipe head, and the pressure value is 1.6 MPa; the negative pressure technology is to plug the pipe end and use vacuum suction technology to pump air in the steel pipe, and the pressure value is 1.0 MPa; In step S302-2, the positive pressure technology is to pressurize after plugging the pipe head, and the pressure value is 2.0 MPa.

2. The method of claim 1, wherein, In step S301, the high-pressure hose laying is specifically operated as follows: a composite adhesive is uniformly coated on the surface of the high-pressure hose, the thickness of the adhesive layer is 0.1-0.5 mm, the high-pressure hose with the coated adhesive on the outer surface is pulled through the inner wall of the steel pipe by traction technology, the high-pressure hose is kept from knotting during the pulling process, the two ends of the high-pressure hose are kept tight, the high-pressure hose is kept from contacting the inner wall of the steel pipe, and the pulling is smoothly performed.

3. The method of claim 2, wherein, The composite adhesive is a polyethylene adhesive mainly made of modified maleic anhydride grafted polyethylene, and comprises the following components by weight: maleic anhydride grafted polyethylene 20-30 parts, polyacetylene viscoelastic body 10-15 parts, polyester viscoelastic body 3-8 parts, butanediol 1-3 parts, tetrabutyl titanate 1-2 parts, butyl rubber 5-10 parts, antioxidant 1-2 parts, and peroxide 1-2 parts.

4. The method of claim 3, wherein, The shear strength of the composite adhesive adhered to the steel body is ≥3.5 MPa, the oxidation induction period at 200℃ is ≥30 min, and the viscosity is 12000-15000 cps.

5. The method as claimed in claim 2, wherein, The raw material of the high-pressure hose comprises the following components by weight: modified polyurethane 60-70 parts, polyurea 5-10 parts, polypropylene 3-8 parts, polyacetylene viscoelastic body 3-8 parts, polyisocyanate 3-5 parts, and antioxidant 1-3 parts.

6. The method as claimed in claim 2, wherein, The high-pressure hose is prepared by one-time forming of film blowing by using a double-screw extruder; The wall thickness of the high-pressure hose is 5-10 mm, the tensile strength is ≥12 MPa, the nominal strain at break is ≥1000%, the elastic modulus is <0.5 Gpa, and the oxidation induction period at 220℃ is ≥30 min.

7. The method of claim 1, wherein, In step S4, the secondary connection of the cut-off part is specifically operated as follows: a high-heat-resistant ceramic pipe with a diameter slightly smaller than the inner diameter of the steel pipe is used as the inner lining material of the connection part, the ceramic material is used as the inner lining of the connection parts at both ends of the steel pipe when the pipes are butt-jointed, the outer surface of the ceramic pipe segment is adhered with viscoelastic body paste material, the airtightness of the connection part is ensured, the inner lining ceramic is not damaged during the welding of the steel pipe, the continuity of the inner wall corrosion protection of the pipeline is ensured, and the external connection part is subjected to joint construction by using the same process as the outer corrosion protection of the parent body.