Application of Drones in the Field of Non-destructive Testing

Introduction – Drone Non-destructive Testing

Drones, also known as Unmanned Aerial Vehicles (UAVs), have become valuable tools for non-destructive testing (NDT) of various structures due to their ability to access hard-to-reach or hazardous areas, provide high-resolution imagery, and collect data in a safe and efficient manner. This article describes some common drones application in the field on nondestructive testing (NDT).

Overview of Drone Nondestructive Testing (NDT) Applications

TechKnowServ Corp. (TKS) pilots use drones to assist in common non-destructive testing function including visual inspection to capture detailed visual images and videos of structures, allowing inspectors to assess surface conditions, corrosion, cracks, and other defects [1]. Drones may also be mounted with thermal cameras to detect variations in temperature, which can help identify issues such as heat leaks, faulty electrical components, and insulation problems in buildings or industrial equipment in support of mechanical integrity programs [2]. Light detection and ranging (LiDAR) equipped drones use laser technology to create 3D point clouds and digital elevation models, which are valuable for assessing the geometry and condition of structures, as well as detecting deformations and settlements in support of non-destructive testing [3]. Drones with sufficient payload can carry ultrasonic sensors to measure the thickness of materials and identify defects within them. This feature is commonly used to support the nondestructive testing of pipelines, tanks, and bridges [4[. While not directly related to non-destructive testing, drones can play a significant role in environmental monitoring and data support to storage tank containment areas and mapping for Spill Prevention, Control, and Countermeasure (SPCC) plans [5]. Drone-collected data can be processed through advanced software and analytics tools to create detailed reports, including 3D models, heat maps, and defect visualizations, facilitating more informed decision-making.

Drones can be used to efficiently screen above ground storage tanks during external inspection API-653 or STI SP 001 tank and containment area assessments.  From above the drone can visually assess the boundaries of the containment area and screen the tank for containment area deficiencies including large cracks in the concrete or liner tears   Similarly, the drones may be used to assess the general condition of the tank shell and roof.   Areas or paint breakdown and surface corrosion are accurately tracked and a targeted visual inspection is performed based on the initial screening assessment of the tank farm.

Figure 1: Tank farm drone footage is confirmed against site maps to inventory above ground storage tanks. The tank roof, shell, and piping systems withing the containment area are screened for coating breakdown and surface corrosion. These areas are targeted for follow-up visual inspection with standard pit gages and ultrasonic thickness testing.

Figure 2: Tank specific roof footage showing surface corrosion at roof welds. In addition to ultrasonic thickness testing, the welded areas were cleaned, surface pits were measured and the square footage for recoating was calculated.

Common Features of Drones used in Non-destructive Testing

Drones used in non-destructive testing (NDT) often have several standard features and capabilities designed to facilitate efficient and accurate inspections. The main feature is obviously the camera and all drones are equipped with high-resolution cameras, including visible light cameras, which capture detailed visual images and videos of the inspected structure. High-resolution cameras on drones typically have a minimum of 12 MP, but many models have 20 MP or more. Higher megapixels result in sharper and more detailed images. The sensor size can affect image quality and low-light performance. Larger sensors generally capture more light and provide better image quality. Common sensor sizes for drone cameras include 1/2.3", 1-inch, or APS-C. NDT Drone cameras often have fixed lenses designed for aerial photography. The lens type may be wide-angle or zoom, depending on the camera's intended use The aperture size determines the amount of light that enters the camera. A lower f-stop number (e.g., f/2.8) indicates a larger aperture, which is better for low-light conditions. Some NDT drone cameras have adjustable apertures for greater control.

NDT drones often have autonomous flight capabilities, allowing them to follow pre-programmed flight paths or waypoints. This ensures consistent and repeatable data collection.  Many modern NDT drones are equipped with obstacle avoidance sensors (e.g., LiDAR, ultrasonic) to detect and avoid obstacles in their flight path, enhancing safety and reducing the risk of collisions.  NDT drones are designed for stability and may include features such as advanced stabilization systems and wind-resistant capabilities, which are essential for maintaining image quality during inspections.  Extended battery life is crucial for conducting lengthy inspections without frequent interruptions for recharging or battery swaps. Some drones come with swappable batteries for continuous operation.  Drones used in NDT applications should have the ability to carry additional payloads such as sensors, cameras, or testing equipment. Payload capacity varies among different drone models.  Many NDT drones offer real-time data transmission to a ground station or remote operator, allowing inspectors to monitor the inspection in progress and make immediate decisions based on the collected data.  NDT drones are typically operated remotely using a dedicated controller or software interface, which allows inspectors to have full control over the drone's movements and data collection.

Summary

The drone footage shown in this article’s video is an example of how above ground storage tanks can be screened efficiently for targeted inspections.  The NDT drone footage shows that the tank roof is in generally good condition.  A small area of coating breakdown is observed adjacent to the manway and was identified by the API-653 inspector for follow-up NDT.

Drone Non-destructive Testing Technical References

1.     Morgenthal, G.; Hallermann, N. Quality assessment of Unmanned Aerial Vehicle (UAV) based visual inspection of structures. Adv. Struct. Eng. 2014, 17, 289–302. [CrossRef]

2.     Ficapal, A.; Mutis, I. Framework for the detection, diagnosis, and evaluation of thermal bridges using infrared thermography and unmanned aerial vehicles. Buildings 2019, 9, 179.

3.     Wang, J.; Sun, W.; Shou, W.; Wang, X.; Wu, C.; Chong, H.Y.; Liu, Y.; Sun, C. Integrating BIM and LiDAR for real-time construction quality control. J. Intell. Robot. Syst. 2015, 79, 417–432

4.     Mattar, R.A.; Kalai, R. Development of a wall-sticking drone for non-destructive ultrasonic and corrosion testing. Drones 2018, 2, 8.

5.     Hardin, P.J.; Jensen, R.R. Small-scale unmanned aerial vehicles in environmental remote sensing: Challenges and opportunities. GISci. Remote. Sens. 2011, 48, 99–111.