Multi-field coupling multiple nonlinear vibration model and fatigue failure mechanism of deep-ocean mining hydraulic lifting pipe

In deep-ocean mining operation, the fatigue life of lifting pipe has always been the focus of field operators, and the fatigue failure mechanism has attracted more and more attention of scholars, but it has not been effectively disclosed. Therefore, in this work, a multi-field coupling and multiple nonlinear vibration model of lifting pipe is established, which can accurately determine the alternating stress of deep-ocean lifting pipe. The nonlinear fatigue damage prediction method of lifting pipe based on load interaction effect and residual strength attenuation degradation is established using Corten–Dolan cumulative damage method, which can accurately determine the fatigue life of deep-ocean lifting pipe. Finally, the influences of outflow velocity, buffer station masses and internal flow velocity on the fatigue life of lifting pipe are analyzed. It is found that, firstly, with the increase in the outflow velocity, the fatigue life of the pipe tends to decrease first and then increase, and an external flow rate with the maximum fatigue life appears. However, in real operation, the external flow rate cannot be controlled. Therefore, according to a certain external flow rate, the optimal structure setting can be evaluated by the analysis method established. Secondly, with the increase in the buffer station mass, the fatigue life of the lifting pipe tends to decrease first and then increase. There is an optimal buffer station mass configuration parameter on the site, which is related to the riser structure, ocean flow velocity, internal flow velocity and can be determined by the analysis methodology. Thirdly, with the increase in the lifting flow rate, the fatigue life of the lifting pipe tends to increase first and then decrease. Therefore, when determining to configure the lifting flow rate on-site, it is necessary to use the proposed nonlinear fatigue damage analysis methodology to analyze whether it is in a dangerous state. If it does not meet the site requirements, other parameters can be set, to improve the fatigue life of the lifting pipe.