Prompted by the increasing global demand for oil, the need to reduce environmental risks, and inspired by the advancement in pipeline design and subsea drilling operation systems, energy players in the international market started to turn their attention to the Arctic and other environmentally hostile areas under sub-freezing temperature. Unique conditions in these locations, however, pose significant challenges to offshore pipeline systems. Some of these are the important loading conditions which include the following:
• Ice gouging or scour. First recognized in the 1970s as a challenging condition for Arctic pipelines, ice gouging or scour refers to the grooves in the seabed caused by ice cuts. Usual solutions include the placement of subsea pipeline in a deeper, safer, burial depth.
|Image Source: anewarctic.org|
• Upheaval buckling. This refers to the pipelines’ vertical displacement often caused by high temperature and pressure. Consideration of burial depth and placement of protection against high ice loads may help avoid this threat.
|Image Source: kwltd.com|
• Permafrost thaw settlement or frost heave, or both. This problem causes strain on pipelines often found in locations where the pipeline route is along the line of continuous or discontinuous permafrost. Solutions include installation of pipelines that can withstand strains.
|Image Source: offshore-mag.com|
• Strudel scour. This often occurs during early spring when river outflows inundate the winter sea ice. When the water penetrates through the ice holes, the subsequent erosion of sea floor may expose the buried subsea pipeline. Careful consideration of burial depths of pipelines may be the best protection against strudel scour.
|Image Source: dc190.4shared.com|
Currently, loading conditions are highlighted as among the most crucial challenges in offshore pipeline design, installation, operation, and maintenance. Improvement in these areas must truly be taken into consideration to preserve the pipeline mechanical integrity.
Ali Ghalambor was an American Petroleum Institute endowed professor and is the co-author of the book “Offshore Pipelines: Design, Instillation, and Maintenance.” Visit this Twitter page for more on offshore pipelines.