Real-time health monitoring is an effective method to evaluate the reliability, durability, and safety of ocean offshore platform. Optical fiber sensors show superior potential for structural health monitoring of civil structures to ensure their structural integrity, durability and reliability. Apparent advantages of applying fiber optic sensors to a marine structure include fiber optic sensors' immunity of electromagnetic interference and electrical hazard when used near metallic elements over a long distance. Fiber Bragg grating (FBG) sensors, including strain and temperature sensors, were applied in health monitoring of oil production offshore platform No.CB271, which is located in Bohai Sea. The paper presents the procedure of FBG sensors installation in course of platform construction. FBG strain sensors were placed as strain rosette on the surface of platform's central pillar, and FBG temperature sensors were installed close to those strain sensors for temperature compensation. The sensors have operated for one year without any reduction of working performance. Strain responses induced by impaction of ocean wave and a ship with hundreds tons weight were monitored on-site successfully. The fundamental frequency of platform identified by the results of FBG sensors agrees well with the result obtained by theoretical analysis. From this experiment, FBG sensors exhibit excellent performance and higher tolerance to harsh environment in long-term real-time health monitoring of ocean offshore platform.
The field of structural health monitoring (SHM) is concerned with accurately and reliably assessing the integrity of a given structure in order to reduce ownership costs, increase operational lifetime, and improve safety. The offshore structure, surrounded by a harsh marine environment, must withstand cyclic wave loading, severe storms, sea quakes, and the corrosive effects of sea water. Furthermore, the process of visually inspecting marine structures, especially those in deep water, is much more difficult than for land based structures (Nichols, 2003).