Bringing navigation precision to petroleum


An autonomous robot equipped with a DVL seeks to revolutionize the inspection of fuel tanks, while eliminating potential operational risks.

Boston-based Square Robot deployed Nortek’s Doppler Velocity Logs (DVLs) already established in subsea applications for this different and harsh environment, develop a robot that can provide detailed assessments of conditions in above-ground oil storage tanks.

Using the robot eliminates the need to empty tanks of liquid so humans can come in to perform detailed inspections – an expensive, time consuming and potentially dangerous procedure still used in most tank assessments.

Founded in 2016, the company took just two years to design and build a very robust autonomous robot certified to operate in these hazardous environments. Five versions of the robot are currently deployed by companies in the US petrochemical storage industry.

The “Square Robot”, from which the company takes its name, is a very robust autonomous robot, loaded with sensors, capable of adapting to the width of 24 inches. “Manway”, the standard-size portal installed at the top of the storage tanks.

The robot is then able to navigate the tank filled with liquid – usually gasoline or diesel – to detect damage such as corrosion on the bottom of the tank. The reservoirs, a familiar sight to many, are typically 10-30m high and 15-80m in diameter.

“The robot is basically doing an inspection of the tank floor that would otherwise have to be done by a human,” said Amy Underwood, senior robotics specialist at Square Robot.

“In a traditional out-of-service inspection, the tank is emptied, cleaned to make it safe for entry, and then inspected by staff. All of this downtime means a significant loss of income for the tank owner. Our robot gets rid of all of that – your tank is still in use and full of product, ”she said.

The vehicle is innovative in that it performs tests in a way that will not damage the tank – known as non-destructive testing (NDT) – using technologies such as ultrasonic testing (UT ), which can characterize the thickness and internal structure of a surface using high-frequency sound waves. In addition, the robot is able to hover, unlike the “crawler” robots sometimes used for basic inspections.

Roboticist Amy Underwood lowers the Square robot through a 24-inch manhole into a storage tank filled with petrochemicals. Image courtesy of Nortek / Square Robot

The Square Robot vehicle with the Nortek DVL1000 four transducer mounted on the far left. The vehicle uses ultrasonic testing, HD cameras and other non-destructive methods to assess tank wear; the evaluation depends on the DVL for precise positioning. Image courtesy of Nortek / Square Robot

But to accurately examine and map areas of concern, the robot needs to know exactly where it is in the tank. This requires accurate speed measurement to make navigation critically easier, which is not easy in a closed tank full of liquid product.

To solve the problem, the company looked to its roots in the underwater industry. The founders of Square Robot and several other members of the team previously worked for a leading AUV developer and had a long career in the underwater industry. So, they already knew what worked well for ocean speed measurement and wondered if it could work in the harsh environment of a storage tank.

“We needed high navigation accuracy and knew that DVLs could provide that to us from our experience in the submarine,” says Underwood.

DVLs use the Doppler effect to calculate velocity by measuring the wavelength shift between acoustic pulses transmitted and reflected by particles in a liquid or a surface such as a seabed.

The team was familiar with Nortek’s Doppler velocity logs. Basically, Nortek’s DVL1000 1 MHz, the instrument chosen by Square Robot, could work accurately at a distance of only about 20 cm from a given surface – often the seabed, but in this case the tank bottom. This is closer to the ground that many other DVLs on the market are able to operate with precision, and a prerequisite for the inspection vehicle to do its job properly.
The fact that this DVL performs so well in such a harsh environment can be attributed to Nortek’s proprietary background tracking algorithm.

Testing the Square Robot vehicle in a test pan filled with water. The DVL1000, seen on the right, is mounted so that it can work without hindrance, while maintaining a minimum distance from the ground.

Square Robot is looking to expand its operations both in the US market, where it currently operates, and internationally. The robot is currently deployed by Veritank, an inspection services subsidiary of Square Robot.

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