Internal in-service inspection of petrochemical storage tank floors to detect underside corrosion with Non-Destructive Testing Robot

This research develops a new robotics technology for the in-service inspection of floor plates of the majority for the world’s petrochemical storage tanks. The new robotic system aims to decrease inspection cost, reduce human inspector exposure to chemical and hazard environment during the inspection and eliminate tank outage entirely if the floor is found to contain no corrosion.
The research focus is on the design and development of a Non-Destructive Testing Robot (NDTBOT) prototype that uses active buoyancy control for its locomotion mechanism and uses NDT ultrasound to measure floor plate thickness as an indication of corrosion thinning. The NDTBOT hops from one location of the floor to another location to make ultrasound thickness measurements of a tank floor, thus avoiding issues of motion on a dirty tank floor (due to oil sludge). Also, a novel radio frequency (RF) data communication system is investigated and developed that can operate while submerged in oil. This system allows control commands to be sent to the NDTBOT by an operator outside the tank and NDT data to be recovered for analysis. To evaluate the performance of the NDTBOT making thickness measurement in the tank, three types of measurement techniques were used. First, the real thickness was measured using a Vernier caliper, the second method used a standard hand-held ultrasonic thickness measurement instrument and finally the in-service inspection thickness measurements were made with the NDTBOT operating in a water tank. The NDTBOT thickness measurements with an immersion ultrasound probe obtained more accurate results than hand-held contact ultrasonic testing.
Petrochemical storage tank size varies from 20 to 200 meters in diameter, rapid corrosion inspection in such tanks with a swarm of robots requires that a number of NDTBOTs be deployed inside the tank to perform the NDT. Such deployment needs coordination and control work between the robots to send the NDT data to the NDT inspector. Therefore, an investigation and experimental radio frequency wireless transmission is done in order to compare different radio frequency communication. Simulation with commercial software CADFEKO is used to perform simulation of RF wave transmission in petroleum and vegetable oil with selected radio frequencies of 200 MHz, 300 MHz, and 433 MHz. The experimental work and simulation results give confidence. The RF communication in petroleum medium is feasible for both control of NDTBOTs inside the tank and NDT data transmission back to a technician’s console placed outside the tank.