Deepwater Spar Steel Catenary Riser Monitoring Strategy

Steel catenary risers (SCRs) in deepwater environment exhibit complex dynamic dynamic response governed by various factors such as environmental conditions, vessel motions, soil-structure interaction and material degradation. Uncertainties in the SCR design exist in the design data, analysis methodologies, fabrication, and hence a conservative approach has been adopted to overcome these shortfalls. Recent advances in monitoring systems installed on SCRs provide operator the assurance of the integrity of the SCRs in service, verify the SCR design, and enhance basic understanding of the SCR response. This paper outlines a strategy for monitoring the SCRs to characterize the response due to vessel motions, vortex induced vibrations (VIV), and soil-structure interaction. A detailed example of real-time SCR monitoring system with optimized array of motion and strain measurements is presented. The methodology for sensor selection and optimization is based on linear regression analysis. The measured data processing methods include shape matching the response amplitudes with correlating response frequencies. The principles and methods of measured data interpretation to capture global response shape due to wave and vessel motions induced and VIV are presented. The pipe-soil interaction such as soil stiffness, suction, softening and trenching effects characterized using the strain measurements in the touch down zone are presented. In addition, the methods to calibrate the individual vertical, lateral and axial models for pipe-soil interaction are presented.