A Scheme Design Of Strength Analysis And Full-scale Fatigue Testing For Marine Risers

Marine riser is a key device connecting offshore platforms and submarine well.The marine riser is susceptible to fatigue failure in the long-term because of the external dynamic load coming from the environment during the process of installation and application and the internal high pressure fluid and gas.Riser fatigue damage is induced by various kinds of alternating stress.The alternating stress can produce and then expand internal and surface cracks in marine risers which can result in fatigue fracture and it will lead to serious production accidents.Therefore,riser fatigue tests and relevant experiments should be carried out in order to calculate and improve riser fatigue life.The parameter derived from fatigue test is useful in the prediction of the riser fatigue life and it can be applied to anti-fatigue design.Riser full-scale fatigue test overcomes the drawbacks of small-scale fatigue test,such as the scale effect,the influence of residual stress and so on.It has been widely used as it more accurately reflects the actual situation of the crack propagation in the riser.Among riser fatigue tests,the widely used is axial tensile fatigue test and resonant bending fatigue test.The former is mainly used in riser material test and the latter is mainly used in riser structure test.This paper is mainly includes the following several aspects:1)The technology status of riser full-scale fatigue test at home and abroad,the advantages and disadvantages of the fatigue test method and test machine and the results from foreign riser full-scale fatigue test are all collected as a reference for the design for riser fatigue test in this paper.2)ANSYS is used to analyze the riser structure to study of the response of marine riser in the marine environment load.The static strength and fatigue performance of risers are analyzed from the angle of stress and deformation.And the simulation analysis results will provide reference data for PHysical model test.The reliability can be inspected by coMparing with the fatigue test results.3)Riser fatigue detection scheme is designed on the basis of fatigue test study at home and abroad and relevant specification.The scheme includes the design of the test load,experiment parameter calculation,the concrete process of the test,the data acquisition and processing,the fatigue life calculation and prediction and the real-time monitoring of the test process.The anatomy of the experiment was carried out to analysis of the structure destruction characteristics and mechanism after the fatigue test.4)Fatigue test machine mentioned above is designed according to API 17B?API 17 J and some other specifications.The first step is drafting the testing machine model with 3D mapping software Inventor.Then Ansys workbench is utilized to do the finite element analysis and calculation on every part of the testing machine which mainly includes modal analysis,static analysis and fatigue analysis.The purpose is to ensure the machine meet the requirements of strength,stiffness and fatigue in fatigue test.