Structural Behavior And Stress Concentration Analysis Of Dented Marine Pipeline

Offshore oil and gas pipeline is an important delivery channel and is one of vulnerable parts. With the useful life growing year by year, pipeline defects also increase, oil and gas pipelines is into an accident-prone stage. The marine environment is complex, once the accident occurs, the accident will cause huge economic losses, ecological damage, even lead to casualties. The marine environment is difficult to recover in coming year or decades after ecological damage. Therefore, the safety of marine pipeline gets widespread concern in the industry.Factors of offshore oil and gas pipeline failure are mainly divided into three categories: corrosion damage, mechanical damage and fatigue damage. A large number of third-party mechanical damage caused by activities on the marine pipelines in the actual production activities, such as subsea pipelines impact may be falling objects, trawling, anchor dragging; Riser may be strike by floating equipment, with deepwater floating production system (FPS) using, collision between a production riser also attracted wide attention of researchers. Structural behavior and stress concentration analysis of dented marine pipeline would help improve the design criteria about collision and the safety assessment of dented pipeline.In the first, introduced the concept of pipeline defects depression, classification and research directions, provide a clear understanding of the indentation of pipeline. The formula of evaluating collision which is recommended by API is introduced. The analysis of structural behavior about dented pipeline is related to the material nonlinearity, the geometric nonlinearity and contact nonlinearity, so the process of analysis must used to model the nonlinear finite element method.The structural behavior of244.5mm pipe subjected lateral loads by the rigid indenter is study through ABAQUS. The result is compared with simple analytical approaches of API; the couple effect of local indentation and global bending is obvious when the length to diameter L/D ratios rise, and the carrying capacity down; and varying diameter to thickness D/t ratios get same results; the pressurized pipes is discussed in the end.In the end, plain spherical dent and plain hoop dent which is based on the structural behavior analysis would carry out parametric analysis without regarding to residual stress. The stress and stress concentration factor is influenced by the depth of dent, diameter to thickness ratio and size of dent, and get the best fitting line of the stress concentration factor and dent depth; the dent don’t consider the axial length and hoop length, get the best line of the stress concentration factor and dent depth and diameter to thickness D/t ratios.