Wireless Communication with Mobile Inspection Robots Operating While Submerged Inside Oil Storage Tanks

Data acquisition during storage tank inspection is one of the most important aspects for petrochemical storage tank owners. Mobile inspection robots designed to enter inside a storage tanks without taking the tank out of service are required to enter through manholes on the roof of the tank with openings as small as 300-millimetre diameter. These robots are controlled via an umbilical cable which supplies power to the robot, sends and receives signals to control robot motion, and transfers inspection data acquired by non-destructive testing (NDT) sensors back to NDT inspectors. It is important to localize a robot inside the tank so that NDT data indicating a defect such as corrosion pitting in tank floors or weld cracks can be mapped for subsequent monitoring and repair. Wireless communication with the robot for NDT data acquisition and localization would enable the minimization of umbilical size and its effective management which is important when a small mobile robot is supplied with a very long umbilical. This paper presents results of a study to develop a wireless communication system that uses radio frequency (RF) signals with low power (< 1W) sent by a transceiver on a robot operating inside an oil storage tank which travel through an oil medium, are transmitted through steel tank walls and are captured by receivers placed in air outside the tank. Simulations using Feko software have been performed to assess the feasibility of using RF for communication in oil storage tanks with laboratory experiments conducted using vegetable oil to validate the simulations. RF signals transmitted by a robot operating inside an oil tank and received by a number of receivers placed in air around the tank has potential application as a robot localization system.