The Numerical Simulation Analysis Of Marine Pipeline's Smooth Dent In Axial Direction Impacted By Dropped Objects

As we know that marine pipeline is playing a very important role in the transportation of marine oil and gas.Anyway,marine pipeline is a vulnerable part because of that the submarine pipeline is of weakness.So,with the time that the pipeline's being used growing,the defects of the pipeline will become more and more as well as the pipeline will in a situation which is an accident-prone one.The environment in the deep sea is complicated and diversified varied,if a leakage accident happened to the pipeline,it'll do a great damage to the environment and cause huge financial loss,what's worse,it may be the reason that workers loses their lives.And if the marine ecological environment is harmed like this,it cannot be recovered like it's in the old days in a very long period of time.Because of the reason listed above,tie safety of the marine pipeline is widely being concerned by the professionals.The facts the cause the efficacy loses of the marine pipeline are considered in three: fatigue damage,corrosion damage,mechanical damage.There exist lots of third party's activities in the process of actual production which may do mechanical damage to the marine pipeline,the reason may include dropped objects,dropped anchor or marine dragnet etc.Stand pipeline also can be strike by various kinds of facility.In recent years,with the widely use of the Floating Production System(FPS),these impacts between stand pipelines are as well concerned by the professionals.The mechanical damage caused by the third party mainly make the formation of the dent on the pipeline.What this article is going to study is the structure behavior of the dent and stress concentration analysis which may be helpful to the design of pipeline impact and the safety evaluation of dents.The article firstly introduces the conception and classification of the dents as well as the direction of the study,and give an acquaintance of the dents of marine pipelines.And then introduce the recommended evaluation equation of API(America petroleum institute).I use the method of nonlinear finite element to modeling and analyze due to that in the analysis of the dent structure behavior I've used the nonlinear of material,geometry and contact.In this article,ABAQUS is the software I chose by which,in the first place,I modeling a 244.5mm pipeline to study the structure behavior of the dent on it caused by sphere rigid press in a condition of lateral loads.And give a comparison between the results and the Ellinas equation.According to the comparison,the bigger the length to diameter L/D ratios of the pipeline,the more obvious of the couple effect of the entire bending and local indentation.With the reduce of the thickness to diameter D/t ratios,locality of the pipeline's carrying capacity rises.The bigger the internal pressure of the pipeline,the better the carrying capacity of the pipeline,but also internal pressure can accelerate the unstability of the pipeline.I as well have discussed the influence of the weight coating of reinforce concrete and I discover that the thickness of the coating can reinforce the carrying capacity of the pipeline,but when the thickness is big enough,the improvement of carrying capacity will decline.In the end of this chapter,I've conduct a test of sensibility based on the element facts motioned above.First I established a orthogonal list through the method of orthogonal experiment.Then,taking Reactive Force(RF)as the indicator and calculate the sensibility of every element factor by using the Range Method.And the sensibilities of element factors,from large to small,are thickness to diameter D/t ratios,thickness of the weight coating of reinforce concrete,Axial length of the pipeline,internal pressure of the pipeline.And in the next chapter I use a cylindrical rigid press to produce sooth dents in axial direction on a pipeline which's diameter is 500 mm based on the result in the former chapter,and analyze the data without considering the residual stress.And in the analysis,I've discussed how the coefficient of stress concentration is influenced by the depth of the dent,thickness to diameter ratios of the pipeline,axial length of the press and diameter of the press.And with the help of Excel an 1stOpt I can fit the data I got from the ABAQUS,and calculate the equation of dent depth and coefficient of stress concentration.Then I have given the equation among coefficient of stress concentration,depth of dents and ratio of diameter to thickness,axial length of the press without consideration of hoop width and the axial length because the former two are hard to measure.In the end I've conducted a sensitive analysis.I've tested the element factors based on the data motioned above and the indicator factor is the coefficient of stress concentration.And the sensibilities of element factors,from large to small,are axial length of the press,depth of the dent,thickness to diameter D/t ratios,diameter of the press.