Residual Strength Assessment Of Deepwater Risers With Inner Corrosion

Deepwater risers play a very important role in the process of deep-sea oil exploration,production and transportation.The fluid medium inside deepwater risers is highly corrosive,and the corrosion rate increases under the condition of high temperature and high pressure,resulting in corrosion damage from slight to severity inner deep-water risers.When corrosion damage disables such risers for its normal working condition,there is high risk for the risers and is likely to lead to rupture of the riser and oil leak,which can cause serious economic losses and irreversible pollution.Therefore,in order to prevent such incidents,it's very necessary to analyze the law about residual strength of deepwater risers over the change of various parameters.Based on deep sea riser residual strength variation with various factors,the assessment can be made on deepwater riser design,post-maintenance and replacement for better decisions,which can reduce operating costs and ensure deep sea risers safety running.So,the paper makes some preparation such as the following content:First,on the basis of domestic and international data collection and inspection,the paper introduced the development background and trend of the domestic and international deep-sea oil,and described briefly the corrosion risk of the current deepwater risers.In addition,the paper summarized and compared application status of the domestic and foreign corrosion defects assessment of risers,and summed up the corrosion defects research by domestic and foreign scholars with simulation analysis.Based on the above preparation,the research filed and technical route of this paper were proposed.Secondly,after analyzing the corrosion formation mechanism and morphology of marine pipeline,the paper explored the impact such as fluid medium and motion status on corrosion,and determined the object physical models and the factors to be analyzed based on both deep sea risers external environment as well as the above-mentioned aspects.Then,ANSYS workbench was used to analyze residual strength of deepwater risers with inner corrosion defects.Three major factors,namely corrosion shape,working condition(pressure and temperature)and hydrostatic pressure,are respectively analyzed for their influence on risers' ability of bearing pressure.When analyzing corrosion shape and internal pressure,flow rate and hydrostatic pressure,the paper uses fluid-solid coupling method.And in the analysis of different loading forms of pressure,both direct-loading method and fluid-solid coupling method are used.Based on deep sea riser residual strength variation with various factors,some plans are made for application.Finally,the paper made assessment on deepwater riser with inner corrosion according to the usual specification ASME B21-2009,DNV RF101 and PCORRC,and compare the three specifications by Matlab programming.In addition,the case will be simulated with ANSYS workbench,whose result and the outcome calculated by the above three specifications are compared with each other.