Structural Fatigue Safety Monitoring And Evaluation Of Semi-submersible Production Platform In South China Sea

With the slow growth of the land oil and gas exploration,the deep sea,an area with great potential for oil and gas exploration,has been paid more and more attention,and the development of deep-water oil and gas resources in the South China Sea is also in full swing.The deep-water semi-submersible production platform is the core of a deep-water gas field development project in the South China Sea.Due to the lack of technical support in the longterm safe operation and inspection and maintenance decisions of the hull structure of this type of platform in the South China Sea,this paper takes the deep-water semi-submersible production platform as the target object to conduct structural health monitoring and safety assessment research.Based on the requirements of measurement points,this paper carries out simplified analysis on the overall strength and fatigue damage of the target platform,and determines the high stress point and the larger fatigue damage point of the structure.According to the characteristics of the target platform,the layout method of structural stress monitoring points is mainly studied.The influencing factors of the selection of each monitoring point of the platform are analyzed,the selection principles of each monitoring point are established,and the sensor layout scheme of the overall stress monitoring of the platform structure is formulated.The orthogonal experimental design method based on sea state information change was adopted to optimize the selection of stress and bending moment sensitive monitoring points of the target platform.Considering the selection of monitoring points and hot spots of the difference of location theory based on rules between any two points under the wave load stress response,with the help of a conic criterion proved that stress component meet the elliptical relationship between any two points,and by using the rule innovation put forward a kind of condition identification method and the monitoring point and the point stress component prediction method.The results show that the high stress points are mainly located at the joint pontoon column connection,and the joint of the pontoon transverse and longitudinal bulkhead panels.It is found that the fatigue life of the joint pontoon column joint and its free edge is the minimum,so it is used as a candidate point for fatigue monitoring.In the research and analysis of the sensor sensitive monitoring points,it is found that the closer the node is to the edge line of the column and the bottom line of the pontoon longitudinal bulkhead,the more sensitive it is to the environmental conditions.The non-monitoring point prediction method of platform local structure studied in this paper can better meet the needs of real-time acquisition of hot spot stress state in actual monitoring.According to the conic criterion,it is verified that the stress components satisfy the elliptic relationship.Under different wave heights,the stress components present a cluster of concentric ellipses.The linear relationship between wave height and ellipse parameters has a goodness of fit of nearly 1.Based on the fitting formula,the wave height under the actual working condition is inversed,and the relative error is less than1%.After comparing the predicted and actual stress time history curves,it is found that the two methods are effective.The relative error is less than 10%.