How do you select the most suitable offshore pipeline materials and coatings for different scenarios?

1 Material Selection

The first step in choosing the most suitable offshore pipeline materials is to determine the design requirements and specifications, such as the diameter, wall thickness, length, pressure rating, temperature range, and flow rate of the pipeline. These factors affect the mechanical strength, toughness, fatigue resistance, and weldability of the materials. The second step is to consider the environmental conditions and hazards, such as the seawater chemistry, salinity, oxygen content, microbial activity, cathodic protection, and external loads from waves, currents, and seabed movements. These factors affect the corrosion resistance, erosion resistance, and durability of the materials. The third step is to compare the available options and their costs, benefits, and risks. Some of the common materials used for offshore pipelines are carbon steel, stainless steel, duplex steel, and composite materials.

2 Coating Selection

The second step in choosing the most suitable offshore pipeline materials and coatings is to select the appropriate coating system for the pipeline. The coating system consists of three layers: the anti-corrosion layer, the mechanical protection layer, and the weight coating layer. The anti-corrosion layer is applied directly on the pipe surface to prevent corrosion and provide electrical insulation. The mechanical protection layer is applied over the anti-corrosion layer to protect it from mechanical damage and abrasion. The weight coating layer is applied over the mechanical protection layer to increase the weight and stability of the pipeline on the seabed. The coating selection depends on the pipeline location, function, and service life. Some of the common coating systems used for offshore pipelines are fusion-bonded epoxy (FBE), polyethylene (PE), polypropylene (PP), and concrete.

3 Scenario 1: Shallow Water Pipelines

Shallow water pipelines are typically installed in water depths less than 200 meters. They are exposed to higher wave and current forces, as well as potential fishing and anchor impacts. Therefore, they require more robust materials and coatings than deep water pipelines. For shallow water pipelines, carbon steel is usually the preferred material, as it offers good strength, toughness, and weldability at a relatively low cost. However, carbon steel is susceptible to corrosion and requires a high-performance coating system. FBE or PE coatings are often used as the anti-corrosion layer, while PP or concrete coatings are used as the mechanical protection and weight coating layers.

4 Scenario 2: Deep Water Pipelines

Deep water pipelines are typically installed in water depths greater than 200 meters. They are subjected to higher pressure and temperature variations, as well as lower oxygen levels and microbial activity. Therefore, they require more corrosion-resistant materials and coatings than shallow water pipelines. For deep water pipelines, stainless steel or duplex steel are usually the preferred materials, as they offer high corrosion resistance, strength, and fatigue resistance at a relatively high cost. However, these materials still need a coating system to provide electrical insulation and additional protection. PE or PP coatings are often used as the anti-corrosion layer, while FBE or concrete coatings are used as the mechanical protection and weight coating layers.

5 Scenario 3: Subsea Tie-In Pipelines

Subsea tie-in pipelines are short sections of pipelines that connect subsea wells or manifolds to main pipelines or risers. They are designed to accommodate the movements and stresses of the subsea structures and equipment. Therefore, they require more flexible and durable materials and coatings than other pipelines. For subsea tie-in pipelines, composite materials are usually the preferred option, as they offer high corrosion resistance, flexibility, and strength at a relatively high cost. However, composite materials have limited weldability and require special joining techniques. FBE or PE coatings are often used as the anti-corrosion layer, while PP or concrete coatings are used as the mechanical protection and weight coating layers.

6 Here’s what else to consider

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