1.1. Use of subsea pipelines

Offshore pipelines are a main part of any offshore oil and gas project. Marine pipelines transport oil and gas from subsea wells to the platform and subsequetly gas or oil from the platform to the coast for futher process and distribution.There are also large pipeline for the transportation of gas or oil from one country to another.

Pipelines are classified in three categories:

  • Infield Pipelines transport fluids within the field. They are often called flowlines or feeder lines. Infield Pipelines carry a mixture of oil, gas and water from the subsea wells to a manifold or directly from the well to the process platform. A smaller number of infield lines carry processed water from the platform to injection wells for disposal.
  • Export Pipelines transport processed oil or gas from the platform to the coast. If the pipeline carries a mixture of oil and gas  then it is a multi-phase pipeline. If the pipeline carries only oil or only gas, then it is an sigle-phase pipeline.
  • Transmission pipelines carry oil or gas from one coast to another mainly, the same way as a tanker transfers oil for trading purposes.

1.2. Typical pipeline diameters

It is always useful to have a rough idea of typical pipeline diameters for each type of pipeline

  Diameter [Inches] Length [km]
Gas lift flowlines:  2"  
Water injection: 6" sss
Oil production flowlines    
Export Pipelines 14"  
Oil production from manifold 12"  
Water injection to Manifold 10"  
Test flowline 8"  

3.1. Pipeline types

Steel pipelines

Grade from X52 to X70. Diameters from 2'' to 48''. Wall thickness up to 42 mm. Stell pipeline transport products that are aggressive to steel

Flexible pipelines

Composite pipe structure. Diameters from 2'' to 20''. Flexible are used as infield pipelines for aggressive products. Low cost installation in reel-lay. High pipeline manufacturing cost and few suppliers.

Duplex pipelines

Special pipeline which is resistant to aggressive products. Expensive to fabricate and to weld

Cladded or lined with stainless steel

Steel pipeline with liner. Less expensive then Duplex. Fabrication and welding remains expensive

Steel chromium pipelines

Steel with 13%Cr. Less expensive to fabricate. Can withstand aggressive fluids. Expensive welding