Application of Mini-ROV Technology for FSO Ballast Tank Inspection and Thickness Gauging
Authors: Thongpool Kittipat , Preeyanurak Thiti , Poonpon Apichat , Insuk Phitsanusak 
Published: October 2015

Conventional methods of Floating Storage and Offloading (FSO) ballast tank inspection and thickness gauging are either by erecting scaffolds inside the tank, rafting or by utilizing rope access team to access the ballast tanks and perform the physical work. These methods pose many risks, including confined space entry, fall from height, work over water, heat stroke and asphyxiation. They are also time-consuming and labor-intensive, which could lead to operation interruption and relatively high cost incurred to PTTEP.

Taking into account the disadvantages mentioned above, PTTEP Marine Engineering team in consultation with Proceanic Engineering Services have come up with a novel and innovative method for FSO ballast tank inspection and thickness gauging. Mini-Remotely Operated Vehicle (ROV) is proposed as a means to perform all physical work inside the ballast tanks. The mini-ROV is connected to the topside via an umbilical link that houses communications cables, information transfer and power source, which allows the controller to be located on the FSO deck without having to enter the confined space. The mini-ROV contains a high-resolution video camera for visual inspection of the ballast tank condition as well as a submersible Ultrasonic Thickness (UT) gauge to perform thickness measurements of the tank structures.

During the ballast tank inspection campaign for PTTEP FSO Pathumabaha (FSO2) life extension study in January 2014, the mini-ROV has been selected as a preferred methodology in terms of safety, efficiency, reliability and cost effectiveness. Since PTTEP is the pioneer in using this method, the surveyor from Classification Society in charge of FSO2, which is American Bureau of Shipping (ABS) has to be present onboard to witness, verify and approve the results. A total of 8 ballast tanks were inspected and gauged by the mini-ROV and the results were verified and approved by ABS, making PTTEP the world's first FSO operator to successfully apply this type of technology for internal tank inspection and thickness gauging and approved by ABS.

Comparing to the conventional methods, the mini-ROV method provides several significant benefits to PTTEP. First and foremost in terms of safety, the mini-ROV eliminates the risk of personnel working inside the ballast tanks (confined space) and working at height. Secondly, the mini-ROV method fares much better in terms of efficiency and, in total, saving 15 working days compared to rope access inspection method with zero interruption to FSO2 operation. Thirdly, the reliability and quality of gauging results and visual inspection data are very high. The real-time, live video feed to the monitor allows easy verification of locations and results by attending Class surveyor. It also provides full video recording of all visual inspection and gauging, which means that the results are traceable and auditable whenever required. Lastly, the work can be performed with minimal people onboard (typically 2) meaning the logistics cost is considerably reduced. An approximate saving of USD 100,000 was achieved when compared to the labor-intensive conventional inspection method with rope access team.