Study On The Mechanism Of Pipeline Deformation Under The External Pressure

With the development of oil and gas pipeline, natural factors along the pipeline such as earthquakes、debris flow、landslide、rockfall; human factors like traffic、pipeline constructions are all increasing the influence on the safe operation of the pipeline. The external effects of these factors on the pipeline are mainly reflects to a force which location and size is difficult to estimated. Under this kind of forces, the dynamic response of pipeline become unknown and whether the pipeline operation satisfied the safety request also become uncertainly. In addition, the structure characteristics of pipeline with large diameter thin thickness make it extremely easy to be deformed. Such external forces on the pipeline aggravated the effects which may cause pipeline failure by deformation. This paper is mainly studied the pipeline deformation mechanism under impacting loads which caused by the rockfall. Finally we provide some theoretical basis avoiding pipeline failure caused by deformation.This paper attempt to explaining the deformation mechanism of pipeline under the action of rockfall, the analysis is separated into two parts:theory calculation and numerical simulation. Some hypothesis is been set up during the progress of theory calculation:first the position where rockfall hitting soil is above the pipeline, second during the progress of collision the law of energy conservation was established. The conclusion based on theory calculation provides convenient for engineering apply, but the hypothesis makes the conclusion differ from the actual conditions. Numerical simulation could reflect the actual condition of the problems, the conclusion based on numerical simulation could be used as a reference for theoretical results. In this paper two analysis methods were used to get the best objective conclusion.In this paper such works have been done:Analyzing the potential motion of rockfall when falling from the slope, then get the collision velocity based on different movement pattern and rockfall volume; According to the law of energy conservation we obtained the impact load when rockfall hitting soil; According to the Boussinesq formula, impacting load transmitted from soil to pipeline was gotten; Axial dynamic response of pipeline based on model of elastic foundation beam was gotten, Lateral dynamic response of pipeline based on model of planar closed curved beam was gotten; We have checked the safety of pipeline according to the strain based principle and found that the stress of pipeline have already over the yield strength and plastically deform happened but pipeline still meet the requirements of safety; Using the finite element analysis software ABAQUS6.11-1to analogy the progress ofcollision, getting the dynamic response of the pipeline;API-5C3is the current standard toevaluating pipeline bucking failure which cross-section is a perfect circle, in fact thecross-section would be deformed under external pressure especially under impacting loads. Inorder to getting the curve between external pressure and sectional ovality we use the methodsof Riks making a bulking analysis about pipeline.