Packaged FBG sensors for real-time stress monitoring on deep-water riser

Abstract

The safety of under-water risers in drilling platform is of great significance. A packaged fiber Bragg grating (FBG) sensor for real-time stress monitoring is designed for the applications on oil drilling risers under 3000 meters deep water. A copper tube which is the main component of the sensor has a small hole along its axes and a groove at its each end. The bare FBG is passed through the small hole and fixed to its ends by epoxy resin. Then the copper tube is packaged by filling the groove with structural adhesive. In order to avoid that the outer water-pressure is applied on the epoxy resin through the structural adhesive, a gap between the two types of glues is left. The relationships between the stress of the riser and the tension, pressure, temperature of the single sensor are discussed, respectively. The measured tension sensitivity is 136.75 pm/KN while the minimum R-square value is 0.99997. The experimental results also show that there is a good linear response between water-pressure and the Bragg wavelength from 0 to 30MPa, and the sensor can even survive under the pressure more than 30MPa. In addition, the Bragg wavelength shifts linearly with the increasing temperature from 0 to 40°C. So, the pressure and temperature can be easily compensated if another sensor without tension is used.

Study and Test of a New Bundle-Structure Riser Stress Monitoring Sensor Based on FBG

“…The five wavelength curves have downward trends on October 15 when the risers were in laying conditions, and upward trends on 30 November 2014 when risers were in recovery conditions. The previous experimental investigations in the lab [ 22 ] indicated that the wavelength values of FBG sensors are proportional to temperature changes and inversely proportional to water pressure changes. According to the trends of temperature and pressure under seawater in riser working conditions, the downtrends and the uptrends of the curves are consistent with the actual shifts of measured wavelengths.…”

“…In this paper, after applying an all-metal packaging technology [ 22 ], a new bundle-structure sensor for riser stress monitoring was developed to overcome these problems. In cooperation with several departments of the China National Offshore Oil Corporation (CNOOC), a marine test of the sensor was completed on the “hysy-981” ocean oil drilling platform in a sea area of south china sea named Lingshui, which is near the city of Sanya.…”