Study On Corrosion Fatigue In Splash Zone Of Drilling Riser

Drilling riser is an important part of marine equipment and it plays an extremely important role in the process of oil exploitation.In the industry of marine drilling,most of drilling risers have serviced for a long time in our country.The corrosion of drilling risers in the splash zone is serious.The corrosion defects affect the local strength and life of drilling riser,which leads the operation safety and reliability to be reduced.However,only a conservative value is given for the design of the corrosion margin of drilling riser in the related standards such as API RP 581 and SY/T 6558,and the lack of theoretical study which can not be used to evaluate the corroded riser accurately.Therefore,it is necessary to study the corrosion fatigue of drilling riser.The main contents of this paper are as follows:(1)A mechanical analysis model with a hemispherical corrosion defect riser is established by the stress distribution formula of a cylindrical corrosion cylinder under uniaxial tension.Moreover,a method for calculating the stress concentration factor at the defect is proposed.Taking the stress concentration factor SCF caused by the corrosion defect into account,a method for evaluating the fatigue damage of the corroded drilling riser is proposed in this paper..(2)The finite element model of the corroded drilling riser is established by using the finite element software ABAQUS.The stress concentration laws of drilling riser are analyzed under different factors such as the load modes,the distances,angles and depths of the defects.(3)Based on the method of pipe soil interaction(PSI),the integral analysis model of drilling riser is established,and then,the overall dynamic responses of drilling riser are obtained.Finally,by combining the S-N curve of the material and the fatigue damage theory,the fatigue damage analysis and life assessment of drilling riser are carried out.This research further perfects the engineering standards and specifications of drilling riser,besides,it has important guiding significance for the evaluation and use of defective drilling risers.