7 Main Types Of Pipes Used on Marine and Offshore Platform

Utilizing the right pipe materials for offshore platforms is crucial.

Corrosion due to seawater exposure is a major concern that has to be addressed during pipe selection.

It is important to weigh the advantages and disadvantages of different types of seawater pipes in terms of performance and economic viability.

In this article, you will learn about the different types of pipes used in seawater systems and their characteristics.

At present, there are two main pipe series used in seawater systems: metal pipes and non-metal pipes.

The metal pipe series includes: copper-nickel alloy pipe, thick-walled carbon steel pipe, carbon steel pipe with anti-corrosion material, and stainless steel pipe.

The non-metal pipe series includes: steel skeleton plastic composite pipe and fiberglass reinforced pipe.

Metal Pipe Series

Copper-Nickel Alloy Pipe

Copper Nickel Alloy Pipe

Copper Nickel Alloy Pipe (90Cu/10Ni) ,aslo named as cupro nickel pipes,is commonly used in marine platform seawater systems, shipment building.

It has the following advantages as below:

• good seawater corrosion resistance·
• good hydraulic performance·
• no corrosion products·
• good resistance to sea life growth·
• long service life

However, copper-nickel alloy pipes also have their inadequacies because of their high price, poor mechanical strength, and high requirements on the flow rate in the pipe.

The flow rate in continuous use should not exceed 3.36 m/s, and the intermittent use should not exceed 6.72 m/s. This limits the use of copper-nickel alloy pipes to a certain extent.

Copper nickel pipes can be manufactured to copper-nickel pipe fittings.

Copper nickel pipes , flange de cobre e níquel , Conexões para tubos de cobre e níquel and gasket , nuts , others pipe fittings component can form a strong corrosion seawater system.

Carbon Steel Pipe

Carbon Steel Pipe

Carbon Steel Pipe is cheap, and it has mature construction technology and good mechanical performance.

However, the disadvantage of carbon steel pipes is that they are not resistant to seawater corrosion. This significantly reduces the carbon steel pipe’s service life.

Corrosion products can also cause blockage in filters, valves, and nozzles, thus affecting the entire pipeline.

Therefore, the practice of using carbon steel pipe is now rarely applied to seawater pipeline systems.

The commonly used countermeasure method is to treat the carbon steel pipe with anti-corrosion inner plastic coating or with internal galvanizing.

Carbon Steel Pipe with epoxy coating

Carbon Steel Pipe with epoxy coating

The coating treatments can solve the corrosion problem of carbon steel pipe in seawater. However, the installation of this treatment is cumbersome and requires pre-preparation.

It requires pre-treatment and then transportation of the pipelines for installation. The construction process is also complicated. It involves re-cutting, re-patching, and pairing of the pipelines.

Moreover, the inner anti-corrosion layer is relatively fragile. It easily falls off which will cause a local accelerated corrosion condition of the large cathode and the small anode.

Furthermore, the later maintenance, renovation, and pre-fabrication of the pipeline back and forth at sea will be more troublesome.

Hot-dip Galvanized Carbon Steel Pipe

Hot-dip Galvanized Carbon Steel Pipe

The galvanizing process involves coating the steel pipe with zinc.

There are two types of galvanizing methods: cold-dip and hot-dip galvanizing.

However, the hot-dip galvanizing method is the preferred treatment for seawater pipes due to its strong adhesion and good stability.

In the treatment of the carbon steel pipeline, it is necessary to pay attention to the flange at the appropriate length of the pipeline or to disconnect the pipeline with a joint.

Because there is a certain requirement on the length of the pipe section during the anti-corrosion treatment, if the pipe section is too long or there are too many elbows, the effectivity of the anti-corrosion treatment will be affected.

Stainless Steel Pipe

Stainless Steel Pipe

Duplex Stainless Steel Pipe

Stainless Steel Pipe has good corrosion resistance and mechanical properties, but its main disadvantage is that pitting corrosion is easy to occur in seawater medium.

Sulfur in seawater causes pitting corrosion which would lead to perforation and leakage on ordinary stainless steel pipe, thus affecting its service life.

However, the nickel-based alloy duplex stainless steel has better pitting corrosion resistance than the ultra-low carbon alloy steel (316L).

Duplex Stainless Steel Pipe

It has the ability to resist general corrosion, pitting, and crevice corrosion in seawater.  It solves the problem of severe seawater corrosion, but this two-phase stainless steel is expensive which makes it impractical to apply to the seawater system.

Non-Metal Pipe Series

Fiberglass Reinforced Pipe

Fiberglass Reinforced Pipe

Fiberglass Reinforced Pipe has the following characteristics:·

• good corrosion resistance·
• excellent hydraulic performance·
• low thermal conductivity·
• low heat dissipation·
• good anti-freezing,
• anti-fouling
• anti-mite performance
• long service life

It is also light weight and requires simple installation. However, due to its poor heat resistance, flammability, low stiffness, and easy aging due to ultraviolet radiation, the application of glass steel pipes in seawater systems has been limited.

In response to these defects, a UV-resistant material and a fire-retardant coating are added outside the pipe to solve the problem of poor aging and heat resistance of the FRP. It is believed that with this solution and the relatively cheaper prices, the use of FRP in seawater systems will increase.

The glass pipe commonly used in offshore platforms is a filamentary glass pipe. The epoxy resin is used as the substrate. The glass fiber is used as the reinforcement, and the outer layer is filled with the ultraviolet absorber resin.

In terms of pipeline manufacturing, since domestic FRP pipes are not suitable for offshore platforms, the imported glass pipes are generally used on the platforms.

Steel Skeleton Plastic Composite Pipe

Steel Skeleton Plastic Composite Pipe

Steel Skeleton Plastic Composite Pipe is constructed in a way that the corrosion resistance of the plastic is integrated with the high strength of the steel mesh.

The inner and outer plastics of the pipe wall are integrally connected by the metal mesh in the middle of the pipe wall. Aside from good corrosion resistance and high strength, it also has good anti-fouling performance.

The pipeline is light in weight and connected by electrofusion. The construction is very convenient and fast.

The steel skeleton plastic composite pipe has now been localized, and its performance is enough to meet the requirements of various seawater systems on the offshore platform.

At present, many new platforms in China use the steel skeleton plastic composite pipe, which has been found very effective. The price is much cheaper than the metal pipe, and it is easy to operate and maintain.

Overall, it is a very suitable pipe that is worthy of promotion in seawater systems.

Economic and Technical Performance Comparison

Table 1: Pipe Performance

It can be seen from Table 1 that the advantages of steel skeleton plastic composite pipe, glass steel pipe, copper-nickel alloy pipe, and duplex stainless steel pipe are in terms of service life and corrosion resistance.

In terms of price, carbon steel pipe, anti-corrosion carbon steel pipe, fiberglass reinforced pipe, and steel skeleton plastic composite pipe are cheaper.

However, copper-nickel alloy pipes are only suitable for small diameters of less than 3 inches. There are few applications for large diameters, mainly because the price is too expensive. The stainless steel pipe and the duplex stainless steel pipe have the same limitations and are both too expensive.

The fiberglass reinforced pipe has many good properties, and the price is moderate. Therefore, it has been used in many applications. However, due to its poor mechanical properties, poor heat resistance, and easy degradation and aging, the utilization of this material on new offshore platforms has been less in recent years.

For now, most of the seawater fire-fighting pipelines and seawater cooling system pipelines for new offshore platforms use anti-corrosion carbon steel pipes with large diameters and copper-nickel alloy pipes.

You Best Choice For Copper Nickel Pipe – Shihang