by Bob Dahlstrom
Drones have become common for remote visual inspection of industrial assets, in part because they provide so much data, including data for things a human sometimes can’t see. These drones with specialty cameras can complete general visual inspections (GVI), close visual inspections (CVI), capture HD video, and store the video as part of a digital data record.
In addition to visual inspections, there are now drone systems that make physical contact with structures to take ultrasonic thickness (UTT) measurements . UTT drones in material evaluation can be used to take exterior measurements in the field on industrial assets such as the shell of aboveground storage tanks (ASTs), including ASTs that contain hazardous or potentially combustible materials.
To collect NDT measurements at height, currently one needs to use a lift, scaffolding, ladders, or other solutions to reach areas on certain assets. This can be time consuming and dangerous, due to the possibility of falls. Using an aerial robotic (drone) platform for contact-based UTT allows workers to remain safely on the ground. Further, with the right safety equipment these systems can be granted hot work permits for hazardous locations such as Class 1 Division 2 (ATEX Zone 2) zones.
API 653 is the standard for UTT on tanks over 50 ft tall or having diameter greater than 30 ft. API 653 covers maintenance, inspection, alteration and repair of steel, and field-erected ASTs built to API 650 or API 12C standards. Part of an API 653 inspection often includes UTT gauging measurements on the exterior shell, sometimes referred to as wall-thickness measurements.
Collecting these measurements on the exterior shell of in-service ASTs with drones is an exciting and revolutionary change and has a multitude of positive benefits applicable directly to you, your career, and the industry. Aerial robotic NDT systems have the potential to improve the inspection, testing, and data collection aspects of coated and uncoated assets, in part, by making the NDT measurement process easier and safer thus allowing for more frequent measurements and/or a larger quantity of measurement samples.
Drone UTT systems have two computer tablets, one for the pilot and one for an observer. The aircraft pilot sees control information for the flight and a single UTT allowing them to ensure valid readings. The observer or engineer sees the full UTT data being streamed while the probe tip is in contact with the surface including the A wave. After landing, the technician can download the full data record which includes the UTT readings, A-scans, HD video, and additional information such as locational coordinate data, weather, environmental data, etc.
These aerial robotic systems can take several hundred measurements per hour at different physical contact locations/corrosion monitoring locations (CMLs) for coated substrates in relatively good condition. These systems have also included an integrated gas monitor (sniffer) which allows it to receive hot work permits to operate in class 1 division 2 (ATEX zone 2) locations where hazardous and potentially flammable and explosive materials may exist.
Human inspectors access ASTs, ships hulls in drydock, elevated sections of flare stacks at oil and gas refineries, and elsewhere to collect UT materials thickness measurements using lifts (such as cherry pickers), scaffolding, ropework, etc. Falls happen, and unfortunately, fall accidents are too common. Heatstroke, excessive sun, and environmental exposures are only a few of the additional risks. Why put people at risk of falls or other injuries when a robotic system can do the work instead?
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Bob Dahlstrom is CEO of Appelix and a US FAA certified drone pilot. r.dahlstrom@Apellix.com
To learn more about how drones increase safety and how they collect UTT at elevation, watch Dahlstrom’s ASNT Virtual Section presentation from July 2022, UT Drones in Materials Evaluation.
For additional information on aerial/robotic inspections, check out this Chat NDT with ASNT podcast and papers from the ASNT NDT Library.
- “Robotic Inspection of Confined spaces,” Chat NDT with ASNT, October 2021
- “Unmanned Aerial Vehicle Use in Nondestructive Testing: An Overview,” Materials Evaluation, April 2019
- “AI-Enabled Robotic NDE for Structural Damage Assessment and Repair,” Materials Evaluation, July 2021, DOI: https://doi.org/10.32548/2021.me-04214
- “Aerial Robots for Contact-Based Ultrasonic Thickness Measurements for Field Inspections,” Materials Evaluation, July 2021, DOI: https://doi.org/10.32548/2021.me-04213
Photos courtesy of Appelix.