What is The Concrete Weight Coating (CWC) Pipe

Concrete weight coating (CWC) is a type of coating used primarily for underwater steel pipelines to provide negative buoyancy (i.e., making the pipe sink in water) and mechanical protection. It also offers a degree of thermal insulation. The concrete coating can be applied over a layer of anti-corrosion coating such as Fusion Bonded Epoxy (FBE), 3LPE (3-layer polyethylene), or 3LPP (3-layer polypropylene) to ensure that the steel pipe is protected from the corrosive underwater environment.

ABTER STEEL provides different types of concrete weight coating (CWC) pipes as follows:

Pipe diameter: 152.4 mm – 1524 mm (6” – 60”)
Pipe thickness: SCH 20, SCH 40, SCH 80, etc.
Applicable standard (steel pipe): API 5L Grade B to Grade 80, ISO 3183 Grade L245 to L555, GB, etc.
Pipe length: Up to 12 meters
Concrete density: 1.8 ton/ m3 – 3.5 ton/ m3 (Concrete formulation can be tailor-made to any specified density as per client requirement)
Concrete thickness: 25 mm – 200 mm
Concrete compressive strength: Up to 50 Mpa
Key features of concrete weight coating (CWC) pipe

Structure

The CWC pipe typically consists of the following layers:

1. Steel Pipe: The primary conduit for the transport of materials.
2. Anti-Corrosion Coating: A layer of anti-corrosion coating (such as FBE, 3LPE, or 3LPP) is applied on the steel pipe to protect it from corrosion.
3. Reinforcement Layer: This layer, often made of felt or fabric, is applied over the anti-corrosion coating to protect it during the application of the concrete coating.
4. Concrete Coating: The outermost layer is a thick layer of concrete that provides negative buoyancy and mechanical protection.

Process

The process of applying the concrete weight coating is as follows:

1. Surface Preparation: The pipe surface is prepared by removing any dirt, rust, or mill scale.
2. Anti-Corrosion Coating Application: An anti-corrosion coating is applied on the pipe.
3. Reinforcement Layer Application: A reinforcement layer is applied over the anti-corrosion coating.
4. Concrete Coating Application: The concrete coating is applied over the reinforcement layer. This is typically done by spraying the concrete onto the pipe in a controlled manner.
5. Curing: The coated pipe is then allowed to cure until the concrete has hardened.

Applications

CWC pipes are primarily used in the oil and gas industry for the laying of underwater pipelines. They are also used in other applications where pipes need to be sunk underwater, such as in offshore wind farms.

Advantages

1. Negative Buoyancy: Ensures that the pipe sinks and remains stable at the seafloor.
2. Mechanical Protection: Protects the pipe from physical damage during installation and service.
3. Thermal Insulation: Offers a degree of thermal insulation, reducing heat loss in hot fluid transportation.
4. Corrosion Protection: When applied over an anti-corrosion coating, it provides protection from the corrosive underwater environment.

Standards

The application of concrete weight coating on pipes is guided by international standards such as:

• ISO 21809-5: Petroleum and natural gas industries — External coatings for buried or submerged pipelines used in pipeline transportation systems — Part 5: External concrete coatings.
• DNVGL-ST-F101: Submarine pipeline systems (previously DNV-OS-F101), which gives requirements for submarine pipeline systems, including CWC.

Concrete weight coating pipe consist of cement, water, aggregates and reinforcement materials, the advantage of CWC pipe is to fix the pipeline stably performances and provides effective mechanical protection. Compared with other insulation type like pipe-in-pipe double-layer steel pipe structure, CWC pipe is more efficient in saving cost, easy the pipeline installation and convenient the operations.