Three-dimensional crack problems in offshore pipelines under various loadings
Tan, Ying Jian
Date of Issue2016
School of Mechanical and Aerospace Engineering
Offshore pipelines are commonly utilized to transport oil and gas as it is the most direct and economical method. Cracks are often found in the pipe structure due to imperfection in manufacturing processes. Apart from the internal pressure induced by the fluid that the pipe transport, the pipe are subjected bending and tensile loading due to reeling installation and dynamic loading exerted by wave. The combination on these forces on the pipeline may result in the crack to propagate and eventually leading to failure of the pipe. In addition, corrosion on the pipeline causes its material properties to be weakened. The mentioned conditions may cause pipelines to fail earlier than predicted and may result in serious effects such as marine pollution and even loss of life. Hence, this reports aims to study on the behavior of cracks placed in a corroded pipe subjected to various loadings. A series of simulation will be performed on four pipe models with different crack dimension. In the simulation for each case, the model will first be subjected to an internal pressure to a certain degree. Then, either tensile load or bending load will be assigned until a maximum global strain of 3% is reached. In further investigation, a three step simulation in which all three types of loadings will be considered in a single case was performed to simulate extreme condition. After the simulation had been performed, the Crack Tip Opening Displacement values were recorded in order to study the behavior of the cracks under these loadings. The results of the simulation had shown that when the pipelines were subjected to multiple loadings, the increase in hoop stress can lead to an exponential in increase in the Crack Tip Opening Displacement values. In addition, it was also observed that a larger initial crack may yield greater Crack Tip Opening Displacement values under the same set of loadings. Therefore, from the results gathered in this project, it can be concluded that the combination of various types of loadings on the pipeline can have a significant effect on the Crack Tip Opening Displacement.
Final Year Project (FYP)
Nanyang Technological University