Pipeline Expansion

1) Objective:

To determine pipeline expansion due to changes in temperature and internal pressure of the proposed offshore pipeline section.

2) Introduction:

For long pipeline far away from the platform, there is no expansion as the pipeline is restrained by the soil friction between seabed and pipeline). However, the pipeline near the platform is only partially restrained and it can expand freely towards the platform (vertical riser leg is relatively flexible and does not provide much friction between seabed and pipeline). This pipeline section tends to move when the operating temperature and pressure is higher than the installation / tie-in temperature and pressure.

Longitudinal expansion in a pipeline depends on the following:

• Temperature: thermal expansion force (increase expansion);
• Pressure: End cap force (increase expansion);
• Pressure: Poisson force (decrease expansion);
• Residual lay tension (decrease expansion);
• Soil friction resistance force (decrease expansion).
  

References:

1. A.C. Palmer (1981) Movements of Submarine Pipelines Close to Platforms, Offshore Technology Conference, Houston, Texas, OTC 4067, May 1981.
2. DNV OS-F101 (2007) Submarine Pipeline Systems.

Introduction - Pipeline Expansion Design

Pipeline tends to move when operating temperature and pressure is higher than the temperature and pressure when the pipe is installed and tied in.

For long pipeline far away from the platform, the pipe is constrained so there is no expansion. (This is because the expansion of the pipeline is restrained by soil friction between seabed and pipeline and concrete weight coating.) However, for the pipeline near the platform, the pipe is partially constrained and it can expand freely towards platform. (The vertical riser leg is relatively flexible and does not provide much friction between seabed and pipeline)