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