Vibration And Fatigue Research Of Free Spanning Submarine Pipeline Considering The Internal Flow

Submarine pipeline is an important part of marine oil and gas exploration system, theyconnect the gathering, storage and transportation systems. Flushed by the sea water, thepipeline would often vibrate with the affection of vortex shedding, i.e., the so-called vortexinduced vibration (VIV) phenomenon, which would result in failure and destruction of thepipe. Failure caused by VIV is the main reason and modes for pipeline destruction. Therefore,the study of vortex-induced vibration of submarine pipeline is very necessary.Many studies of submarine pipeline vibration and fatigue have been made by scholarsboth at home and abroad through theoretical and experimental research，and a lot ofachievements have also been made. The relationship between internal fluid and pipelinevibration has also been studied. Overall, studies of pipeline vibration considering bothexternal and internal fluid are not a lot. In fact, the vibration of submarine pipeline is resultedby complex external and internal fluid.This study combines the basic theory of the flow around a cylinder and summarize andanalyze some parameters which can change the nature frequency of the pipeline，theseparameters includes: pipeline type, spanning length, pipeline diameter, internal fluid and theconstraint conditions of the pipe. The pipeline vibration characteristics has been studied withdifferent spanning length, wall thickness and velocity of external fluid. Meanwhile, this paperalso made research on the pipeline vibration characteristics with the internal fluid considered.With the date gathered from a full-size fluid-structure iteration of submarine pipeline, thefatigue and lifetime analysis of the spanning pipeline using the S-N curves recommend by thecode DNV-RP-C203have been made, this would provide a theoretical basis for designing and operation of the pipeline. Results showed that the nature frequency of the pipeline would beinfluenced by a variety parameters and can be increased by changing these parameters, inorder to avoid sever vortex induced vibration of the pipeline; When3.26≤Ur≤8the pipelinewould vibrate significantly, thicken the wall of the pipe and reduce the spanning length wouldbe helpful to avoid or mitigate vibration; When fluid exists in the pipeline, the pipe wouldreach the maximum amplitude when the reduced velocity Ur increases to about7.96. Whenthere is significant vibration, lifetime of the pipe would rapidly decrease. Therefore, it is veryimportant to optimize the parameters or change the outer surface of the structure as far aspossible during design and construct of the submarine pipeline to avoid or suppress thevibration of it.