Waterproof coating casing pipe

Date:2024-07-23Tags:casing pipe, well pipe casing, casing and tubing

The use of oil casing pipe in oil wells is very common. Due to the complexity of the stress state in the well under different geological conditions, the oil casing pipe must meet high quality standards in the process of bearing tension, compression, bending and torsion stress. Any damage caused by the casing's own defects may lead to a decrease in oil well production or even the scrapping of the entire oil well. Therefore, it is crucial to understand and select the appropriate waterproof coating for the protection of oil casing pipe.


1. Basic characteristics of oil casing pipe

The quality requirements of oil casing pipes are strict. According to the standard SY/T6194-96 for domestic oil casing pipe in China, the casing pipe length ranges from 8 to 13 meters, but casing not shorter than 6 meters can be provided, and its quantity shall not exceed 20%. The production of oil casing pipe needs to comply with the API 5CT standard. In addition, there shall be no defects such as folding, hairline, delamination, cracks, rolling and scarring on the inner and outer surfaces of the casing. These defects must be completely removed, and the removal depth shall not exceed 12.5% of the nominal wall thickness. The outer surface of the coupling shall also be free of defects. The threaded surface of the casing pipe and coupling must be smooth, without burrs, tears and other defects that affect the thread strength and tight connection.

casing pipe

2. Types and functions of waterproof coatings

Waterproof coatings play an important role in protecting oil casing pipe from corrosion and other environmental factors. According to different application environments and requirements, waterproof coatings can be divided into several main types:

Flexible waterproof casing: suitable for structures where pipelines pass through walls, are susceptible to vibration, or have strict waterproof requirements. Its characteristics are that it can adapt to certain pipeline deformations while maintaining excellent waterproof performance.

Civil airtight casing pipe : mainly used in locations that cross air defense zones to ensure waterproof tightness under special environments.

During the pipeline installation process, the selection of waterproof casing pipe is crucial, not only to prevent moisture penetration and protect the internal pipeline, but also to facilitate pipeline maintenance. Waterproof casing can be selected according to rigidity and flexibility:

Rigid waterproof casing: suitable for structures that do not withstand pipeline vibration and expansion and contraction deformation, and can provide good rigid support.

Flexible waterproof casing pipe: suitable for areas with fortification requirements, where pipelines have expansion and contraction deformation and structures with strict waterproof requirements.


3. Anti-corrosion method of waterproof steel casing pipe coating

The anti-corrosion treatment of steel casing pipe is very important. Common anti-corrosion methods include:

External wall anti-corrosion coating: There are many types of coating materials. When choosing, the use conditions and environment of the pipeline should be considered. Common external wall anti-corrosion coatings include epoxy resin, polyethylene, etc. The function of the coating is to isolate the external corrosive medium and prevent the pipeline from rusting and corrosion.

Inner wall anti-corrosion coating: In order to prevent internal corrosion of the pipeline, reduce friction resistance, and increase the output, commonly used coatings include amine-cured epoxy resin and polyamide epoxy resin. The coating thickness is generally between 0.038 and 0.2 mm. In order to ensure that the coating is firmly bonded to the pipe wall, the inner wall must be surface treated.

Anti-corrosion and thermal insulation coating: Especially suitable for medium and small diameter hot crude oil or fuel oil pipelines. Add a composite layer of thermal insulation and anti-corrosion to the outside of the pipeline. Commonly used thermal insulation materials include rigid polyurethane foam plastics, and its operating temperature range is -185℃ to 95℃. In order to enhance the strength, a high-density polyethylene layer is usually added to the outside of the insulation layer to form a composite material structure to prevent groundwater from penetrating into the insulation layer.


4. Anti-corrosion coating materials and applications

The selection of anti-corrosion coating materials depends on the specific environmental conditions and usage requirements. The following are commonly used anti-corrosion coating materials and their applications:

Epoxy resin coating: has excellent anti-corrosion performance and is suitable for various harsh environments. Epoxy resin needs to be carefully handled during coating to ensure the uniformity and adhesion of the coating.

Polyethylene coating: has good chemical corrosion resistance and is usually used for external corrosion protection of pipelines.

Polyurethane coating: commonly used for thermal insulation and corrosion protection of pipelines, especially showing good stability in high temperature environments.

Composite coating: composed of a variety of materials, it can provide excellent anti-corrosion and wear resistance, and is suitable for use in extreme environments.


5. Implementation of coating anti-corrosion

When implementing anti-corrosion coating, the following steps should be considered:

Surface treatment: Remove rust from the pipeline surface to ensure good adhesion of the coating to the pipeline surface. Common methods include sandblasting, polishing, etc.

Coating construction: Select appropriate coating materials and apply according to the coating instructions. Ensure that the coating is uniform and without missing coatings, and complete the coating curing according to the specified drying time.

Quality inspection: After the coating construction is completed, quality inspection is required, including coating thickness, adhesion and uniformity, etc., to ensure the anti-corrosion effect of the coating.


6. Conclusion

The waterproof coating of oil casing pipe is not only the key to protect the pipeline from corrosion, but also an important measure to ensure the stable operation of oil wells. Selecting appropriate waterproof coating and anti-corrosion methods can effectively increase the service life of casing and reduce maintenance costs. With the development of technology, the application of composite materials and new coatings will further enhance the anti-corrosion effect and environmental adaptability. According to the specific application environment, the reasonable selection and implementation of anti-corrosion coating is the key to ensure the long-term stable operation of oil casing pipe.

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