| Under the combined effects of low temperature and environmental loads,the offshore platform welded structures in polar areas are prone to crack propagation and fatigue failure.The existing specifications and standards lack the welding fatigue evaluation theory and design criterion applicable to the polar low temperature conditions.The study of the theories and methods for low-temperature fatigue evaluation of welded structures is critical to ensure the low-temperature reliability of the offshore platform structures.Firstly,the fatigue evaluation theories of welded structures are analyzed,the accuracy and some properties of the structural stress method are studied.Secondly,the low-temperature fatigue properties of welded tube joints are studied by the means of the structural stress method,a low temperature corrected model for the main S-N curve of welded pipe joints is proposed based on a large number of fatigue evaluation data.Finally,the combinatorial spectrum analysis method based on the structural stress is proposed,and the the fatigue evaluation of the multiplanar tube joints is completed.The research results show,the structural stress method can be applied to the fatigue evaluation of welded structures at low temperature,the mesh-insensitive property of the structural stress have been proved;the high structural stress level,the increase of the geometrical scale and the angle of the branch pipe all have adverse effects on the low-temperature fatigue properties of the welded tube joints;the low-temperature fatigue evaluation results obtained by the low temperature corrected model for the main S-N curve are more accurate.The 420 MPa steel has good fatigue properties at low temperature and the results can provide references for the construction of marine platform structure for polar operation;the method of numerical simulation has high application value for low temperature correction of the main S-N curve in the ASME standard. |
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