Research On Ultimate Bearing Capacity Of Pipe With Randomly Distributed Pitting Corrosion

As the main structural form of jacket platform, pipe is constantly eroded and destroyed in the harsh conditions of marine environment including long term effects of winds, waves, flows and ice loads. The load of offshore steel structures can be increased by many reasons including unreasonable design criteria, failing to be repaired timely of damaged members, bar corrosion, the influence of the seabed scour and the growing of marine organisms. Then the bearing capacity is reduced and eventually the whole structure falls down. Many aged platform’s components have appeared different degrees of corrosion and fatigue crack in China. Some platforms have met or exceeded their original design life, reaching their later period of service. The biggest problem to continue service is security of these old platforms. While corrosion affects the ultimate bearing capacity of aged platforms significantly, leading to the failing of the platforms. The change rule of the ultimate bearing capacity of pipe subjected to randomly distributed pitting corrosion under uniaxial compression is studied in this paper. Following research work have been studied specifically:1. The research status of corrosion which effects structural ultimate bearing capacity is analyzed, the basic principles of stochastic finite element is described and the existing modeling methods and rules of random distribution of pitting model are summarized in the paper. Then pipe model with pitting damage systematically is established using ANSYS-APDL. This model realizes the randomness of pitting distribution.2. The changing rule of ultimate bearing capacity of the pipe with randomly distributed pitting is analyzed as pitting parameters including the degree of dispersion and the degree of thickness loss changes. Different forms of corrosion with the same corrosion volume are compared in the paper. The influence of local pitting distributed location and range is discussed and the most influential situation is analyzed.3. The simplified model with randomly distributed pitting is established. It’s confirmed by the equivalent of square pitting and cylindrical pitting and the equivalent of non-simplified model and simplified model. Pitting distributed patterns of simplified model is studied. The changing rule of ultimate bearing capacity with randomly distributed pitting and the influence of pitting distribution on ultimate bearing capacity is also discussed as the pitting parameters including the degree of thickness loss and the density of pitting changes.