Research On Inspection Planning For Deepwater Riser Subjected To Fatigue

The riser system for deepwater drilling is the key to connecting the offshore platform to the subsea wellhead.Due to the influence of marine natural environment,it is in the vibration state for a long time,therefore,risers are prone to have fatigue failure.Fatigue inspection is an important way to prevent riser fatigue failure,but a set of effective fatigue inspection planning method for deepwater drilling riser has not been formed yet.Aiming at this problem,this paper combines the national "13th five-year plan" major science and technology subproject "deep water riser-underwater wellhead life integrity technology and engineering application" and carries out the research on the fatigue inspection planning method of riser in deepwater drilling.The relevant research results provide scientific basis for the riser fatigue inspection program of deepwater drilling in South C hina Sea,which has important academic value and engineering significance.The main research contents and conclusions are as follows:(1)Considering the different modes of riser operation(connection operation,installation operation and suspension operation)and d ifferent fatigue modes(wave induced fatigue and vortex-induced fatigue),the fatigue crack propagation process and fatigue failure state of riser system can be more accurately simulated by establishing comprehensive fatigue analysis model of riser system operation in deepwater drilling.(2)Nondestructive testing method for riser fatigue defects is studied.Based on ACFM testing technology,a nondestructive testing system for risers is developed,and based on traditional POD and precision models,the dual POD model which is considering the fatigue crack length and depth of riser is proposed.By carrying out the research on fatigue crack inspection of riser,the POD model and precision model of riser fatigue crack flaw inspection based on ACFM were established.(3)Based on bayesian network and combined with the fatigue failure analysis model of deepwater riser and defect inspection model,dynamic bayesian model of riser fatigue crack growth and defect inspection is established,which can realize the assessment and update of riser fatigue reliability,and the relationship between different inspection time,different inspection results and the dependent variables in the riser fatigue reliability model could be deeply discussed.(4)Based on the influence diagra m,the establishment of deepwater drilling riser fatigue inspection programming model,taken the riser of the South C hina Sea as an example to carry out the riser fatigue inspection planning analysis,and compared with the traditional riser inspection scheme,the results show that the proposed inspection programming model in this paper can reduce the management cost of riser on the basis of safety,and provides a framework for the fatigue inspection planning of riser,which facilitates the application and implementation of the fatigue inspection planning method.