| Lattice boom crane is widely used in various fields of national economic construction. Lattice boom, as an important bearing part, is often subjected to alternating toad effects, fatigue is the main failure mode of damage. According to the design standards, crane design life belongs to the category of high-cycle fatigue, the S-N curve method from fatigue test data is the main method of fatigue assessment. By comparing multiple fatigue standards, such as ABS, DNV, BS7608, IIW, API, AWS ASME, etc., it is significant to find suitable life assessment method for lattice boom welded pipe structural. By combing with K-joint fatigue test data, it is found that Battelle structural stress method based on ASME standard is more suitable for K-joint life assessment than the ABS, DNV, IIW surface interpolation hot spot stress method.25t-level offshore platform crane is selected and studied in this paper. The equivalent structural stress transformed by correction factors is used for the evaluation of stress, combined with the main S-N curve, it is completed for fatigue life assessment of 16 welds in four boom hazardous areas under five different conditions. The main works of this paper are as follows:(1) By comparing multiple fatigue standard documents (such as ABS, DNV, BS7608, IIW, API, AWS, ASME, etc.), the traditional nominal stress S-N curves corresponding to the crane lattice boom pipe joint cannot be found. For pipe joint fatigue assessment, the hot spot stress method is recommended and the corresponding S-N curves are provided in the fatigue standards, such as surface extrapolation interpolation hot spot stress S-N curves in ABS, DNV and BS7608 and the main S-N curve based on Battelle structural stress method in American standard ASME.(2) Based on several different methods in standards, the structural stress along K-joint weld toe is calculated under 6 different grid size modes, which is found that the structural stress is not affected by different methods in standards and the Battelle structural stress method is less sensitive to mesh accuracy. By comparison of Life calculated by different methods and the test results, it is summarized that Battelle structural stress method is more suitable for the life assessment in K-joint, which provides a reference for the life assessment of crane lattice boom.(3) By finite element analysis of 25t-class offshore crane under five kinds of conditions, 4 dangerous high stress zones of the boom are found. The beam elements in the danger zones are replaced by shell element to easily extract the stress along weld toe. The static and dynamic stress test on 25t-class offshore crane is made to verify the reliability for the finite element mode.(4) It is completed for the fatigue life assessment of 16 welds, in 4 boom hazardous areas of 25t-class offshore crane, under five different conditions by using Battelle structure stress method. |
