Study On Critical Suspended Length Of Pipelines With Corrosion Defects In Shallow Buried Areas Of Rivers

The mileage of oil and gas pipeline which have been in the service for over 40 years is more than 6000 kilometers in our country, buried oil and gas pipeline under the influence of its surrounding complicated geological environment and corrosion medium is prone to corrosion defects, which can cause the thinning of pipe wall and reduce the bearing capacity of the pipeline. When the pipeline in river shallow buried area under the water erosion appeared suspension, the risk of pipeline failure will be aggravated. Therefore, it is necessary to carry out the research on the pipeline with corrosion defects.By means of finite element software ABAQUS, suspended pipeline model containing corrosion defects was established, take stress failure as criterion, by changing the geometric size of the defects, an in-depth study of strength performance of pipeline and the changing law of critical free span between the size of defects when they were located at the mid span and end bearing of the pipe was conducted; analysis of the impact of pressure change on pipeline stress was made; discussion of the variation between the force of the pipeline under the action of water flow loads and critical suspended length.The main conclusions are as follows:(1) When the defects were located at the end of the support, depth variation of thinning had the biggest impact on suspended pipeline stress and its critical suspended length, followed by ring width, axial length is significant in the influence of the pipeline stress in the 0-1.5 interval and, thereafter, decreased with the increasing of axial length; On the other hand, when the defects were located at the mid span, pipeline by force is less affected the changes of axial length, when ring width dimension is small, its effect on the pipeline force is not obvious, but when thinning depth reached 0.5, suspended pipeline was significantly impacted.(2) Wherever defects are, the reduction of the internal pressure will decrease the maximum pipe stress, pipeline pressure and the risk of pipeline failure can be reduced when the pipeline corrosion defects appeared.(3) When thinning defect is located in the middle of the span under water flow load action is more easily cause failure when pipeline is in minor suspension length, simultaneously, flow rate is more than 3m/s, which will accelerate the failure of the pipeline.