688 M A T E R I A L S E V A L U A T I O N • J U L Y 2 0 2 1 What is measured is known and we can make predictions based on these measurements. These UT thickness measuring aerial robotic systems enable companies to improve the UT thickness measurement process and gather data that didn’t exist before, thus adding to the body of knowledge. The systems can also bring massive efficiencies to the job, including a full auditable data record and information for digital implementation plans, allowing focus on the overall picture to plan and budget accordingly. Further, they help achieve substantial cost savings, particularly when they prevent an asset from being taken out of service or enabling an asset to be returned to service sooner. Finally, they are an elegant safety solution, moving workers from harm’s way and potentially saving lives. Introduction For corrosion or other engineers to take UT thickness measurements at height they may need to utilize a lift, scaffolding, ladders, inspection trucks with elevated baskets, rope work, catwalks, or other solutions. Companies looking to keep personnel out of danger at height or in potentially hazardous locations can adopt aerial robotic systems. However, as with many things, choosing the right system for the job is essential for optimal results. While NDT field inspection programs can dramati- cally increase the safety and integrity of assets, access requirements in performing these inspections in elevated areas introduces risk. Working at height is dangerous, due to the possibility of falls, as well as being time-consuming due to access setup. In certain instances, it may also require taking an asset, such as a flare stack, offline so it can be accessed to take meas- urement readings. Utilizing an aerial robotic system for UT thickness measurements can mitigate these risks and potentially eliminate asset downtime. Drones are commonly used for visual inspections, but it is rare to find them used for contact-based inspections. Researchers have investigated using drones for contact-based NDT (Skaga 2017 Mattar 2018), yet these studies tend to be theoretical and conceptual. The contact-based UT thickness measure- ment drone system presented in this paper is in commercial use and differs from those in the literature in its computer-controlled precision flight while making contact with a structure (using no human pilot/operator), and in that it utilizes the same handheld UT electronic measurement devices that a corrosion or other engineer uses in the field integrated onboard the aircraft with the data streamed live to the engineer or observer on the ground. Further, because these systems are “flying computers” and data-gathering machines, they collect a large amount of data for NDT/NDE. This data can feed NDE 4.0, which is a force multiplier for inspecting, testing, and evaluating industrial assets for their safety, operational effectiveness, and efficacy. NDE 4.0 uses the tools of Industry 4.0–machine ME FEATURE w aerial robots for ut thickness measurements Figure 1. An example of a handheld electronic UT measurement device with a single-element 5 MHz contact transducer. Companies looking to keep personnel out of danger at height or in potentially hazardous locations can adopt aerial robotic systems. Photo credit: DeFelsko Corp.

J U L Y 2 0 2 1 • M A T E R I A L S E V A L U A T I O N 689 learning, artificial intelligence (AI), the Internet of Things (IoT), big data, and so on–to expand and generate knowledge, insights, and understandings that turn data gathered from industrial field inspec- tions, into actionable information to enhance and extend knowledge-based information-driven decision making. These aerial robotic systems help with both the increasing importance of digitalization of assets and data and the use of NDE 4.0 by making it easier to collect information. Aerial Robotic Measurement Collection Methodology Having a computer-controlled heavy-lift multirotor drone outfitted with various sensors and functions to allow precisely controlled flight close to structures is critical in taking contact-based UT thickness measure- ments (see Figure 2). Manual control of such systems is unable to accomplish the precise flying and maneuvers required thus, software-controlled flight is crucial. The aerial robotic system in this paper utilizes existing UT electronics and digital probes to gather measurements. The handheld electronic UT thickness measurement device onboard the aircraft streams all the data (not just what is displayed on the LED view screen) to the computer onboard the aircraft and the pilot and corrosion engineer on the ground. The system works as follows: l The tethered (for power and data transfer) or unteth- ered (battery power and wireless data) aerial robotic system is located close to the structure where UT thickness measurements are to be taken. l The corrosion engineer, using a computer tablet, opens the software interface to begin the test and enters the job information (operator, job name, upper and lower limits for measurements, etc.) and standardizes the handheld UT thickness measure- ment device that is mounted onboard the aircraft, as per the definition of standardization provided by ASTM 1316 (ASTM 2021). l The pilot engages the aerial robotic system’s software and the system takes off vertically to approximately 2 m (6.5 ft) in height, hovers, and completes self-checks. l The pilot then uses a standard handheld radio frequency transmitter to manually fly the system close to the where the UT thickness measurement is to be taken (the “gate” or “window”). (The radio transmitter is the standard operations control for the aircraft. Its sole use in this case is for positioning the aircraft close to the area where the thickness measurements are to be taken. It is also on standby in case manual operational flight controls are needed for example, in case of a failure of the software.) l Once the aerial robotic system is within the “gate” (~2 m [6.5 ft] from the target part of the structure), the pilot selects “start” on the software interface. l The system then operates under full computer control (no manual input). It flies in (while dispensing couplant gel onto the probe), touches the surface, and takes a UT thickness Figure 2. Ultrasonic thickness measurement system in action: (a) on an in-service aboveground storage tank (b) on an in-service active flare stack. (a) (b) Photo credit: ©2020 Apellix, Working Drones Inc. Photo credit: ©2020 Apellix, Working Drones Inc.