Study On The Scour Protection Technology For Pipeline On Slope Seabed Under Wave Condition

The safety of offshore pipeline needs to be valued because of the complex and severe submarine environment;the major cause of offshore pipeline accidents is the fatigue damage of pipeline which is caused by local scour of submarine pipeline.Pipeline scour protection is a problem that Chinese and foreign scholars have been struggling to explore.Seafloor topography,research on slope under the wave action of seabed pipeline protection method,the research of the method of seabed pipeline protection on slope under the wave action,the analysis of the effects on the scour and flushing of pipeline which is caused by all kinds of protection ways is of great significance.The model test which is about the diversion slabs' effects on the submarine pipeline scour and flushing in slope is done in the multi-function wave flume.The effects of the type of spoiler,spoiler length,wave height,period and other parameters on the sandy slope submarine pipeline scour pits' depth,width and shape is analyzed in this paper.The dynamic water pressure distribution of pipeline,the rule of pressure difference in the horizontal and vertical direction is discussed in this paper,thus it can provide a reference for engineering design.Experiment results show that the installation of rigid spoiler makes the pipeline scour pits' depth and width increased,its shape become more sharp,and the vertical direction stress of pipeline became from up to down.These results indicate that the installation of rigid spoiler will cause pipeline buried to protect,but it also can increase the risk of pipeline vibration because of the increasing differential pressure of both side.The shape of pipeline scour pits is extended upwards in the downstream direction after the installation of flexible spoiler.When the spoiler length is less than the critical length,the depth and width of the scour pit begin increased.When the spoiler length exceeded the critical length,the depth and width of it begin to decrease.And the pipeline stress has shown the same rule.These results show that the flexible spoiler which have enough length can protect the sandy bed and decrease the pipeline's vibrating so that we can increase safety performance of pipeline with the flexible spoilers' length increase presented the rule of increasing firstly and decrease latterly.