SIRUS: A mobile robot for Floating Production Storage and Offloading (FPSO) ship hull inspection Luciano L. Menegaldo * , Melquisedec Santos † , Gustavo Andre Nunes Ferreira †‡ , Rodrigo Guerato Siqueira *† , and Lucas Moscato ‡ * Department of Mechanical and Materials Engineering Military Institute of Engineering, Rio de Janeiro-RJ, Brazil Email: lmeneg@ime.eb.br † Inspectronics Engineering LTD. Rio de Janeiro-RJ, Email: melqui@inspectronics.com.br ‡ Department of Mechatronics, Polytechnic School, University of Sao Paulo Sao Paulo-SP, Brazil Abstract— This paper describes the current development status of a mobile robot designed to inspect the outer surface of large oil ship hulls and Floating Production Storage Offloading (FPSO) platforms. These are usually former oil tanker ships, especially adapted to work as an oil offshore platform. Several mechanisms of corrosion are present in such structures, worsen by the abnormal static operation regime of the vessel and other causes. This situation requires a detailed program of inspection, using several Non Destructive Detection (NDT) techniques, operated manually. Here, a robotic crawler designed to perform such inspections is presented. Locomotion over the hull is provided trough a pair or DC-Motor propelled magnetic tracks, while the system is controlled by two networked PCs and a set of custom hardware to drive the motors, video cameras, ultrasound (US), inertial platform and other devices. Navigation is provided by a Extended Kalman Filter sensor fusion formulation, integrating hodometry and inertial sensors. The current version of the prototype is able to perform ultrasound thickness measurements in the dry part of the hull. I. I NTRODUCTION One of the current Brazilian leading industries is the deep- water offshore oil exploration [1]. Several platform configura- tions are possible, among them the FPSO - Floating Production Storage and Offloading. These vessels are usually former oil tankers that receive a complete pre-processing plant over the deck. According to [2] until year 2004, about 100 FPSOs were operating worldwide, most of them in tropical seas. FPSOs are particularly prone to corrosion [3], either galvanic, chemical and anaerobic (bacterial corrosion) due to: long term anchoring over the production basin, few docked revisions and to the fact that many FPSOs are often built from old and naturally wearied vessels. Deep storage tanks corrosion, that occurs under the petroleum sludge deposits, is also a problem, due to the sea water pumped together with the oil. To manage this situation, periodic inspection, evaluation and repairing activities are performed periodically [4], according to Classification Society Rules like Bureu Veritas [5]: global visual inspection, close-up inspection, thickness measurement in predefined and custom sites and reviewing checks. Sev- eral sets of inspection procedures are performed periodically, usually every 5, 2.5, and 1 year, or when needed. Two main inspection paradigms can possibly adopted: docking, emptying the tanks, cleaning and doing visual inspection, by one side. By the other, applying Non-Destructive Testing (NDT) techniques in situ without discontinue the oil pro- duction operations. The first approach is conservative, safer and more reliable, but requires stopping production, causing a larger economic impact [3]. The second, however, must be performed by specialized personnel like scuba divers and mountaineers for the dry part [6], using NDT probes like ultrasound (US) , x-ray, thermal cameras, electrochemical sensors, and remote magnetic field measurements [7]. Usual measurement sampling is 1 sample per hull square meter [8] what may be not sufficient [9]. A possible strategy to increase reliability is refining the inspection grid, but avoiding to ex- cessively increasing the inspection costs caused by production stop. Doing this manually, in such a huge surface, is also not economically attractive, due to diver and mountaineers cost. Therefore, some attempts can be found in the literature to provide robotic Remotely Operated Vehicle (ROV) or robotic crawlers to perform an automated inspection. Although some specif problems arise for developing a robot specifically for large ship hulls, these crawlers are quite similar to those used to inspect other metallic walls. For large fuel tanks, Neptune [10] is a highly sophisticated tracked robot, developed by Carnegie Mellon University, US Army Corps of Engineers and Ryatheon, Inc, that can be used in explosive environments. Maverick developed by Solex Environmental Systems, Inc. [11] has a similar application, but is propelled by magnetic wheels. Both robots performs US inspections and navigates inside the tank by a sonar posi- tioning system. Sogi [12] and his collaborators developed a magnetic wheel crawler to inspect spherical gas storage tanks. This system uses a Time Of Flight Diffraction Mode (TOFD) ultrasound system, that is specially suitable for finding cracks in welds. Authors claim that the number of working hours was reduced by 1/6 when compared to manual inspection. The robot SURFY [13] was developed at the University of Catania, Italy, and uses eight suction cups to adhere the wall surface, carries US and other NDT sensors. Other examples 978-1-4244-1703-2/08/$25.00 ©2008 IEEE 27 Authorized licensed use limited to: INSTITUTO MILITAR DE ENGENHARIA. Downloaded on September 25, 2009 at 15:10 from IEEE Xplore. Restrictions apply.