The Fatigue Life Prediction Of Welded Pipe Joint Of One Offshore Platform In Bohai Sea

With the rapid development of the society,the resources on the land are getting less and less and the resources in the ocean are developed.As a result,the offshore platforms emerge.The research object of this paper is the jacket platform which belongs to the offshore platform.The jacket platform stay in the complex ocean environment for a long time,and it always suffer from kinds of various loads.So,a lot of offshore accident occurred.A large number of practice and analysis show that most of the occurrence of the offshore platform accidents are because of the fatigue failure of the offshore platform's tubular joints weld.Therefore,in order to ensure the security and reliability of the jacket platform in the service period,the prediction of the welding joints' fatigue life of jacket platform plays an important role.In this paper,we take a jacket platform in Bohai as the research object,use the ANSYS Workbench as the tool of analysis,and get the stress time history of the hot spot of the jacket platform's tubular joint under the load of the wind and the wave.Then we predict the fatigue life of the hot weld.The specific forecast analysis process mainly includes several parts.Firstly,the load of the jacket platform is analyzed,and the wind load and wave load are simulated by MATLAB.Secondly the static analysis of the jacket platform should be done to determine the hot tube joints.Thirdly,the modal analysis of the jacket platform should be done to get the modes and the frequency of the jacket platform.Fourthly,the transient dynamic analysis of jacket platform should be done to get the stress time history of the hot weld.Lastly,the rain flow counting method should be used to get the stress spectrum of the hot weld,the BS 7608 standard should be used to get the S-N curves of the hot weld,and then the fatigue life of each hot weld can be obtained by combining the linear cumulative damage theory.At the last of this paper,the effect of seawater corrosion on the fatigue life of the welded joint of the jacket platform is analyzed.Through the above work,this paper obtains the fatigue life of the hot spot welded joint of the pipe rack platform successful which is about 21.That is,the forecast fatigue life of the jacket platform is about 21 years,and it is consistent with the design life of the jacket platform.Moreover,in this paper,the fact that the seawater corrosion will greatly reduce the life of jacket platform is verified by the numerical analysis.