Study On Real-Time Monitoring With Early Warning Conditions Of Aging Jacket Offshore Platforms In Service

Since 1960 s, hundreds of steel jacket platforms have been built and in service in China. Most of these jacket platforms have reached or exceeded their original designed lives. However, the majority of aging jacket platforms has been reformed to serve continuously, for more profits. As these aging jacket platforms have been located in extremely complex and harsh ocean environment for a long time, it is inevitable that they have been suffered from damages and serious material aging. Thus, these aging jacket platforms are in risks in after-designed-life service. In order to ensure the operation security of aging jacket platform and the safety of personnel, the real-time monitoring of the aging jacket platform is in urgent needed and it is in significance to master the situation of the aging jacket platform and issue early warnings correspondingly.In this paper, the structural monitoring methods and early warning conditions were proposed based on the characteristics of the aging jacket platforms, including the monitoring and early warning condition of the displacement, the bearing loads of pile end and the jacket tilt. The main conclusions are as follows:(1) The structural model of a jacket platform has been established using SACS program. Accordingly, static analysis and pushover analysis have been made, considering the interaction of the pile and soil. On the basis of the pushover analysis result, the three kinds of deformations of first brace yield, first pile yield and first joint failure are classified into three degrees of early warnings, namely blue pre-warning, orange pre-warning and red pre-warning correspondingly. On basis of this, the figure of displacement warning conditions can be drawn.(2) A simple method of monitoring the bearing loads of pile end was put forward. Based on the mechanism of load transfer, the bearing loads of pile end can be calculated using the load transfer function and the additional loads of the deck legs, which can be gained by measuring. The early warning condition that the bearing loads of pile end should not exceed half of the ultimate pile capacity was provided according to the API specification(API RP 2A-WSD).(3) The long-term monitoring method of the jacket tilt was presented. The jacket tilt can be calculated using the difference of elevation between any two pile tops, which can be calculated using the stress and tilt angle of the beam between the two piles. The early warning conditions considering the stress and tilt requirements were established, where the tilt should not exceed 0.5%.The monitoring method has been applied to a jacket platform on the South China Sea, and the result illustrates the jacket platform was running fine.