Study On The Piping And Flange Joint On The Above Deck Of The Offshore Platform

Sea ice can induce the offshore jacket structure to vibrate in Bohai Sea. Ice-induced vibrations of offshore structure not only could result in the fatigue failure of jacket but also lead the fatigue failure of pipe line and the leakage of flange on the platform. The damage of pipe line of natural gas platforms may make big economic loss and people injury if the leakage of flange was caused. This problem is more prominent in JZ20-2 MSW jacket, because the design of the pipe line was unreasonable, ice-induced vibration was ignored. So it is necessary to perform static and dynamic analysis for the pipe and flange of the JZ20-2 MSW jacket. We study the failure mechanism of the pipe and flange in vibration. The research will improve the safety of platform production in winter and also has a practical guiding meaning to the maintaining of pipe and flange on platform.In the paper, the following subjects were studied through theoretic study, numerical analysis and experimental means:1. On the basis of the project "Sea ice management & Ice induced structures vibration monitoring on the oil platforms", we installed lots of sensors on the piping of the JZ20-2 MSW platform, monitor the pipe and flange vibration induced by ice, the data of vibration were saved2. We analyses dynamic response by ice-induced vibration for gas pipeline system on the jacket based on the data monitored on the JZ20-2 platform in Bohai bay, a mathematical model of structural vibration of pipeline system is built by means of elastic mechanics theory. With finite element modeling, considering the influence of the complex supports, devices and elbows of pipelines, the natural frequencies, the displacement and the amplitude of turning angle response induced by deck vibration are calculated.3. In May, 2005, we participated in the spring repairing work on the JZ20-2 MSW platform. We designed and made the wrench used to measure the moment and stress of bolt ourselves. We totally measured and counted the piping of the platform and have got a lot of data about the leakage in the flange.4. In the present study, through using non-linear three dimensional finite element analysis (FEA), considering the contact in flange to nut and flange to gasket, we accurately computed the stress distribution in the flange joint in the normal work condition. The FEA analysis, incorporating ANSYS software, use pretention179 element to model the preload ofthe bolt. This work will be of realistic significance to guide the design and analysis of flange joint.5. In the lab, we carried out the vibration experiment of the pipe and flange which is subjected to the transverse dynamic excitation. We observed the self-loosening behavior of bolts under transverse vibration and got the relation between the preload of bolt and the dynamic excitation.