Erosion Analysis And Experimental Study Of Elbow Section In Submarine Pipeline

Thinning because of erosion is an important cause of failure and leak accident for submarine pipeline.These accidents not only cause the loss of the offshore oil industry,is also likely to long-term damage to the Marine environment and ecological system.Ocean riser and horizontal pipe section is the the most vulnerable section,and erosion of fluid with sand is the main reason for these accidents.General erosion not only refers to solid particles impacting on the pipe wall at a certain speed and Angle,also including the destructive effect of cavitation erosion caused by cavitation bubbles near the wall.At present,the main method for submarine pipeline to prevent erosion is the use of a simple empirical formula to limit the flow speed of transport media,which hindered the transport capacity of submarine pipeline.In order to make more reasonable anti-submarine pipeline erosion scheme,this paper analyzes the rule of the erosion of the submarine pipeline elbow section and the mechanism of surface injure,based on theoretical calculations and experimental analysis.In the process of numerical calculation,the discrete phase model and cavitation model are respectively introduced into the research of the effect of solid particle and cavitation bubbles on the pipeline erosion.After the simulation of the flow field distribution and the trajectories of particles,it can be found that there is an obvious secondary flow in the elbow,and the particle will collide with the wall on the arch outside part.The distribution and the rate of erosion can be calculated,which shows that the arch outside of elbow and two buccal place of downstream suffer the most serious erosion.Followed by an analysis of the impact of media velocity,solids flow and solid particle size of erosion.The cavitation flow field distribution of the elbow is obtained with the presence of turbulent pressure pulsation and non condensable gas.Through the changes in pressure and volume fraction of gas phase,analysed the formation,growth and collapse of cavitation bubble,determine the location of cavitation damage occurs sidewall surface of the inner arch.Completed the erosion experiments with 5% sand in a self-designed loop piping using coupon weight loss method,and studied damage forms of erosion on the surface of the elbow section in fluid containing quartz sand.Through the scanning electron microscope,observed corrosion pits in the surface morphology of carbon steel coupon which caused by the cavitation erosion,and furrows type of damage,squeezing pits,dents and scratches which caused by the particle erosion.Among them,the pits,dents and scratches are a major injury.Then analyse the damage mechanism of various erosion morphology.By weight-loss method,compares the weightlessness rate of each location in the elbow section,determining the part of the arch out side with severe erosion,which agrees with the result of numerical simulation.Come to the conclusion that the two mechanisms of sand erosion and cavitation bubbles erosion exist at the same time,the sand erosion is severe on arc outside and the bubbles cavitation is severe on arc inside.So the elbow section should distinguish between inside and outside for optimization tactics of the anti-cavitation or anti-erosion.