Robotic MFL Sensor and Vibration based Deepwater Riser Monitoring System

Abstract The safety of deepwater risers is essential for successful operation ofoffshore platforms. In this paper, new structural health monitoring (SHM)techniques for deepwater risers is developed to monitor damage due to vibrationand fatigue. The global monitoring is achieved using the proposed blindidentification technique based on vibrations. First, the location of thefatigue damage is determined by the proposed blind identification technique. The global monitoring is used to identify the dominant modes of vibration, fromwhich, the likely location of fatigue damage is estimated. The proposed methodis validated using Gulfstream test data from MIT. Second, extent of damage isdetermined by local monitoring using robotic crawler with magnetic flux leakage(MFL) sensor. The effectiveness of the local monitoring with MFL sensor isverified by experiments. Combining the proposed global and local monitoring techniques can enhancefatigue damage estimation. Local inspection using MFL sensor is power efficientand yields high resolution results that can estimate the extent of damage. Proposed fatigue damage estimation technique can satisfactorily predictlocation of global damage. The proposed SHM techniques are for well suited for deepwater risers. RoboticMFL sensor can be used for in-line inspection for pipelines. Proposed fatiguedamage estimation method can be adapted to other offshore floatingsystems. Introduction Risers are the most important components of offshore oil platforms. Risers arethe conduits between a subsea wellhead and a drilling or production platformfor development, production, gas lift or water injection. They can be eitherrigid or flexible. Risers can be further classified as top tensioned risers(TTR), steel catenary risers, flexible risers and hybrid risers. Mistakes in offshore oil production can be costly; in particular riser failurehas more severe consequences. Any failure incident in the riser would not onlybe an economical and environmental disaster, but also have far reachingconsequences affecting communities. The most recent and severe accidenthappened on April 20, 2010. The Deepwater Horizon, a semi-submersible mobileoffshore drilling unit, experienced a blowout. Deepwater Horizon sank on April22, 2010 and its associated riser collapsed with the platform. 11 workers diedin the explosion. An oil leak ensued from the drill site, which leaked 4.9million barrels of oil into the Gulf of Mexico, making it the largest oil spillrecorded in U.S. history [1] (largest of its kind in the world history [2]). Although disasters of this magnitude are the result of multiple failures, advanced monitoring can be of assistance in detecting such a blowout before itoccurs. SHM systems for risers in offshore deepwater platforms are needed todetermine whether there is damage and to activate contingency plans ormechanisms to initiate damage protection measures or repairs to preventcomplete failure.