1. Oil and gas transportation field

Requirements for anti-corrosion of underground pipelines:

For buried oil and gas pipelines, due to long-term contact with soil, moisture, salt, microorganisms, etc. in the soil can cause corrosion to the steel pipes. Therefore, it is required that steel pipes have good soil corrosion resistance. Generally, a combination of external anti-corrosion coating and cathodic protection is used. For example, a three-layer polyethylene (3PE) coating is a commonly used external anti-corrosion coating, with the bottom layer being epoxy powder that can bond well with the surface of the steel pipe, the middle layer being adhesive, and the outer layer being polyethylene. This structure can effectively resist the erosion of chemical substances and moisture in the soil. At the same time, by sacrificing anodes (such as magnesium alloy anodes) or applying current cathodic protection systems, the steel pipe is placed in a cathodic state to prevent electrochemical corrosion.

The service life of pipelines is usually required to reach 20-30 years or even longer, so the anti-corrosion performance must be stable for a long time. The thickness of the anti-corrosion layer is generally between 2.5 and 3.7mm, and the continuity and integrity of the coating should be ensured. At the welding site of the pipeline, due to the presence of the welding heat affected zone, the anti-corrosion performance of the coating may be affected. Special anti-corrosion treatment is required for the weld seam, such as using liquid epoxy coating for joint repair, to ensure the anti-corrosion effect of the entire pipeline system.

Anti corrosion requirements for offshore platforms and subsea pipelines:

The marine environment is more complex, and seawater is a strong electrolyte solution containing a large amount of salt, which is extremely corrosive to steel pipes. LSAW Steel Pipes on offshore platforms not only have to withstand the corrosion of seawater, but also the impact of waves and the attachment of marine organisms. For parts exposed to seawater, heavy-duty anti-corrosion coating systems such as thick paste epoxy coatings and glass flake epoxy coatings are usually used. These coatings have a high solid content and thick coating, which can effectively resist the penetration and erosion of seawater.

Subsea oil and gas pipelines face higher pressures, lower temperatures, and more complex corrosive environments. In addition to using high-performance anti-corrosion coatings, it is also necessary to combine cathodic protection technology. Moreover, due to the difficulty in repairing corrosion and leakage in underwater pipelines, the requirements for anti-corrosion performance are extremely strict. For example, some deep-sea pipelines use double-layer anti-corrosion coatings, with an inner layer of corrosion-resistant alloy coating and an outer layer of organic anti-corrosion coating. They are also equipped with intelligent cathodic protection systems to monitor and adjust the protection current in real time, ensuring the pipeline's anti-corrosion performance in harsh underwater environments.

2. Application in the chemical industry

Requirements for anti-corrosion of pipelines transporting corrosive chemicals:

In the chemical industry, LSAW steel pipes may need to transport various highly corrosive chemicals, such as strong acids (sulfuric acid, hydrochloric acid, etc.), strong bases (sodium hydroxide, etc.), organic solvents, etc. For pipelines transporting strong acids, it is required that the steel pipes be lined with acid resistant materials such as polytetrafluoroethylene (PTFE) lining inside. PTFE has excellent chemical stability and hardly reacts with any chemical substances, which can effectively prevent acid from corroding steel pipes. At the same time, the outer surface of the steel pipe also needs to undergo anti-corrosion treatment to prevent chemical substances and moisture in the environment from corroding the steel pipe. Generally, coatings with good chemical resistance such as epoxy phenolic coatings are used.

Pipelines transporting strong alkali can be lined with fiberglass reinforced plastic (FRP), which has good alkali resistance. For pipelines transporting organic solvents, appropriate anti-corrosion materials should be selected based on the properties of the organic solvents, such as using rubber liners with good solvent resistance for some polar organic solvents. The anti-corrosion coating of these pipelines should not only be able to resist the corrosion of chemicals, but also withstand certain temperatures and pressures, as chemical production processes often involve high temperature and high pressure environments.

Requirements for pipeline anti-corrosion in chemical reaction equipment:

In chemical reaction equipment, pipelines need to operate under specific chemical environments and reaction conditions. For example, in some devices involving redox reactions, pipelines may be subjected to strong oxidants or reducing agents. For this situation, steel pipes need to be coated with anti-oxidation and reducing properties, such as ceramic coatings. Ceramic coatings have high hardness, high wear resistance, and good chemical stability, which can maintain good corrosion resistance in complex chemical reaction environments. At the same time, in order to prevent damage to pipelines due to thermal stress, anti-corrosion coatings also need to have a certain degree of thermal stability and be able to adapt to temperature changes during the reaction process.

3. Application in the construction industry

Requirements for anti-corrosion of steel pipes for building structures:

In building structures, LSAW steel pipes are mainly used to support structures such as building frames, bridges, etc. These steel pipes are exposed to the atmospheric environment and need to resist corrosion from pollutants such as moisture, oxygen, and sulfur dioxide in the atmosphere. For general building environments, ordinary anti-corrosion coatings such as alkyd paint, acrylic paint, etc. can meet the requirements. These coatings can form a protective film on the surface of the steel pipe, preventing oxygen and moisture from coming into contact with the steel pipe, thus playing a role in corrosion prevention.

But for some building structures in harsh environments, such as seaside buildings and buildings near chemical parks, better performing anti-corrosion coatings need to be used. For example, fluorocarbon paint has excellent weather resistance and chemical corrosion resistance, which can maintain good appearance and anti-corrosion performance for a long time. The anti-corrosion coating thickness of steel pipes used in building structures is generally between 100 and 200 μ m, and regular inspection and maintenance are required. If any damage or peeling of the coating is found, it should be repaired in a timely manner.

Requirements for anti-corrosion of building water supply and drainage pipelines:

If LSAW steel pipes are used for building water supply and drainage pipelines, the anti-corrosion coating inside the steel pipes must meet the hygiene standards for drinking water. Generally, non-toxic epoxy coatings are used, which not only prevent steel pipes from rusting but also do not pollute water quality. For drainage pipelines, due to the possibility of coming into contact with domestic sewage and industrial wastewater containing various chemicals and microorganisms, anti-corrosion coatings with certain chemical resistance and antibacterial properties, such as epoxy coatings containing fungicides, need to be used.

Selection of anti-corrosion methods for LSAW steel pipes in different applications

1. Oil and gas industry

Land transportation pipeline:

For long-distance land transportation pipelines, a combination of 3-layer polyethylene (3PE) coating and cathodic protection is a commonly used anti-corrosion method. 3PE coating has good impermeability, chemical resistance, and mechanical properties, which can effectively resist the corrosion of steel pipes by moisture, salt, and microorganisms in the soil. Cathodic protection can use sacrificial anodes (such as magnesium alloy anodes) or externally applied current cathodic protection systems to ensure that steel pipes can still be protected in the event of local coating damage. This composite anti-corrosion method has high cost-effectiveness and can meet the 20-year service life requirements of pipelines.

Marine platforms and subsea pipelines:

On offshore platforms, due to issues such as seawater splashing, wave impact, and adhesion of marine organisms, heavy-duty anti-corrosion coating systems such as thick paste epoxy coatings and glass flake epoxy coatings are better choices for steel pipes. These coatings have a high solid content and thick coating, which can effectively resist the penetration and erosion of seawater. At the same time, combined with sacrificial anode cathodic protection system, it provides additional electrochemical protection for steel pipes.

For submarine pipelines, the environment is more harsh and the requirements are higher. Usually, a double-layer anti-corrosion coating is used, with an inner layer of corrosion-resistant alloy coating and an outer layer of organic anti-corrosion coating, such as 3PE coating. And an intelligent cathodic protection system is required to monitor and adjust the protection current in real time to ensure the long-term safe operation of the pipeline in high-pressure, low-temperature, and high salinity underwater environments.

2. Chemical industry

Pipeline for transporting corrosive media:

When transporting strong acids (such as sulfuric acid, hydrochloric acid, etc.), polytetrafluoroethylene (PTFE) lining is usually used inside the pipeline. PTFE has excellent chemical stability and hardly reacts with any chemical substances, which can effectively prevent acid from corroding the steel pipe. For strong alkali (such as sodium hydroxide) transportation pipelines, fiberglass reinforced plastic (FRP) lining is a good choice as it has good alkali resistance. Outside the pipeline, coatings with good chemical resistance such as epoxy phenolic coatings can be used based on the corrosiveness of the surrounding environment to prevent chemical substances in the environment from corroding the steel pipe.

Pipelines in chemical reaction equipment:

In chemical reaction equipment, pipelines need to withstand various complex chemical reaction conditions. For some situations involving high temperature, strong oxidation or strong reduction reactions, ceramic coatings are a better choice. Ceramic coatings have high hardness, high wear resistance, and good chemical stability, which can maintain good corrosion resistance in complex chemical reaction environments. At the same time, in order to prevent damage to pipelines due to thermal stress, anti-corrosion coatings also need to have a certain degree of thermal stability and be able to adapt to temperature changes during the reaction process.

3. Construction industry

Steel pipes for building structures:

In general building environments, such as building frames and bridges in cities, ordinary anti-corrosion coatings such as alkyd paint and acrylic paint can meet the requirements. These coatings can form a protective film on the surface of the steel pipe, preventing oxygen and moisture from coming into contact with the steel pipe, thus playing a role in corrosion prevention. For building structures located in harsh environments, such as seaside buildings and buildings near chemical parks, fluorocarbon paint is a better choice. Fluorocarbon paint has excellent weather resistance and chemical corrosion resistance, which can maintain good appearance and anti-corrosion performance for a long time.

Building water supply and drainage pipelines:

For LSAW steel pipes used for transporting drinking water, it is required that the anti-corrosion coating inside the steel pipe must meet the hygiene standards for drinking water. Generally, non-toxic epoxy coatings are used, which not only prevent rusting of the steel pipe but also do not pollute the water quality. For drainage pipelines, due to the possibility of coming into contact with domestic sewage and industrial wastewater containing various chemicals and microorganisms, anti-corrosion coatings with certain chemical resistance and antibacterial properties, such as epoxy coatings containing fungicides, need to be used.

4. Power industry (mainly thermal power generation)

Steam pipeline:

The steam pipelines in thermal power generation are usually in a high-temperature and high-pressure environment. For this type of pipeline, using high-temperature resistant ceramic coatings or metal ceramic coatings is a better choice. These coatings can withstand the erosion and corrosion of high-temperature steam, while also providing some insulation to reduce heat loss. Outside the pipeline, appropriate anti-corrosion coatings can be used based on the corrosiveness of the surrounding environment, such as a combination of epoxy zinc rich primer and polyurethane topcoat, to prevent the pipeline from being corroded by the surrounding environment.

Circulating water pipeline:

Circulating water pipelines mainly face corrosion from dissolved oxygen, microorganisms, and possible chemical substances in water. The commonly used anti-corrosion method is to use epoxy coating or epoxy glass flake coating, combined with cathodic protection (such as sacrificial anode cathodic protection). This method can effectively resist the corrosion of circulating water and extend the service life of pipelines.