Top Tension Riser Fatigue Monitoring System

ATP Oil and Gas Corporation (ATP) is utilizing the MinDOC 3 vessel design for their Mirage, Morgus and Telemark fields. The modeling techniques utilized during the design and verification stages of the project suggest that the production top tension risers (TTR) may be affected by a phenomenon known as Wake Induced Oscillation (WIO). The current modeling techniques are insufficient at predicting the expected amplitude the TTRs will experience due to the WIO and what effect the occurrence will have on the overall fatigue performance of the TTR’s. To acquire a thorough understanding of the effects of WIO, ATP has prudently undertaken an extensive assurance initiative with the purpose of assessing and maintaining structural integrity of their TTRs. As part of ATP’s Integrity Management (IM) program, ATP is monitoring localized strain as well as the motion response of the riser at discrete locations. The paper presents, in detail, ATP’s real-time TTR monitoring system deployed on the ATP MinDOC 3 vessel for their Telemark field. Specific topics to be covered are the monitoring system configuration drivers such as; monitoring objectives, instrumentation requirements, specification, and installation. The paper will cover the number and location of monitoring devices and justification for selection. The data acquired will provide state-of-the-art full-scale riser response information especially during significant events such as hurricanes and loop currents. The goals of the project are: 1. To gain a more in depth understanding of WIO with respect to large diameter hull columns and smaller diameter production TTR’s; 2. Bolster the understanding of the fundamental hydrodynamic behaviour of TTRs and, specifically, vessel-motion induced response of TTRs, and VIV of the TTRs with varying levels of strake fouling. 3. To accurately assess the role of WIO in fatigue damage to the TTR(s).