The Simplified Method Of Offshore Platform's Tube Nodes On Damage Crack's Boundary

In recent decades, offshore oil industry has developed rapidly. Therefore, the construction of offshore oil drilling platform got rapid development. And mainly, the semi-submersible offshore platform is supported by the bottom vertical post and the braces tube structure. So in the whole platform structure, the fittings occupy a very important position. In the manufacturing processes of the platform, the pipe and pipe connections are all finish in the form of welding. The most pipe components are near the waterline, and so, they are easier influenced by the corrosion and the loading of the wind. Under the action of the circulating storm load, the welding line on node of the pipe will be plastic deformation. If this kind of plastic deformation reaches a certain degree, it will crack. In this process, although the whole stress is far below the elastic limit, the local stress of the gaps can exceed the yield limit due to the stress concentration. So, local plastic deformation will happen in a very small range. Because the t-tube node is subject to larger concentrate force than others in the offshore platform structure, so it most easily product wall cracks. So, it has great significance to research the wall cracks of the Marine platform t-tube node for the whole platform's safety performance estimation.This thesis uses the finite element method to study the process of the crack's passivation. It uses the ABAQUS software to simulate the passivation of the crack tip, and then contrasts the crack pipes with different sections and different crack sizes. The first chapter describes the necessity and main content of the research. The second chapter introduces the basic principle of the finite element method and the relevant theory about fracture mechanics. The third chapter demonstrates the rationality of the modeling about crack passivation using ABAQUS. Through comparison of CTOD calculate and analytical solution using the method Dugdale, this chapter arrive at that it is possible and applicable to using the finite element simulation software to simulate the process of crack passivation and propagation. The fourth chapter calculates and analyzes the problem that when the section of wall crack is plane, and gives the graph to contrast CTOD calculates about stress distribution. It discusses the difference of CTOD calculates when the crack section is surface or plane. The last chapter compares the CTOD calculate of different pipe node's with t-tube node. Finally, through a series of comparison and summarizing rules, it gets the crack analysis method about simplifying the pipe nodes.