Accidental Limit State of Submarine Pipeline: Trawl Gears Pull-Over Loads and Effect of Free Span

Submarine pipelines failures lead to oil spills in water and may even lead to explosions with heavy financial and environmental damages. Trawl gear is one of the main factors in the failure of the submarine pipelines. In this paper, sensitivity analysis is performed on influence of height and span length alternations on the response of pipeline against the traction caused by trawling pull-over load. The FE model is presented using OrcaFlex software including modeling of seabed, pipeline and trawl gear parameters. To model soil and reinforced concrete, nonlinear parameters are considered. To verify the models, DNV-RP-F۱۱۱ and results of modeling by SAGE Profile software is used. The results indicated that increase in span gap resulted in the increase in pipeline responses, but with the increase in span length, only the lateral displacement exhibited a considerable increment. Finally, Maximum time for pipeline to fail and system response to become greater than the standard level has been calculated.

Keywords:

Submarine pipeline , Pull-over load , Free span , Finite element analysis , OrcaFlex