There are a wide variety of testing methods that are commonly used within the field of non-destructive testing (NDT) including but not limited to ultrasonic testing, eddy-current testing, dye penetrant testing, and magnetic particle testing. There are many logistical and staging requirements for non-destructive testing projects that are related to physical access to the structure and safety concerns during the inspection. NDT project safety concerns include working at heights and fall protection, scaffolding erection, confined space entry and working in and around hazardous chemicals. In many instances, the staging for NDT exceeds the cost to perform the actual inspection. The staging equipment including scaffolding tends to get rather expensive, especially for longer duration projects. Due to the financial burden of NDT inspection staging, there may be a much lower frequency of tests occurring for many critical infrastructure systems.
Drone Non-destructive Testing - Advantages
Drone based non-destructive testing is an alternative to traditional inspections and a means to minimize the requirement for many NDT staging cost drivers. Drones offer a myriad of advantages. Most notably is the aspect of safety that they provide. Being that many NDT methods require technicians to work at heights, significant risk to the inspector can be eliminated using drone inspections. The use of drones not only eliminates most of the need for such dangerous activity, but also provides many additional services at such heights that humans cannot perform with matching efficiency. Among other notable benefits to drones as it pertains to safety is the ease of avoidance of hazardous atmospheres or potential confined spaces for technicians. Financial advantages of drone NDT include both the tangible and intangible expenses incurred with traditional NDT methods such as scaffolding, confined space entry, and additional liability insurance(s).
Case Study - Drone NDT of Amusement Park Roller Coasters
Visual inspection of roller coaster supporting steel structures is generally performed with extended reach man-lifts and in many cases using rope access technicians. When using man-lifts for amusement park NDT, the process is discontinuous since the manlift must be maneuvered from one location to another. Manlifts also do not provide 100% coverage around a supporting pipe column and single joint may be required to be inspected from 2 or 3 manlift positions to access the entire surface of a typical roller coaster steel pipe columns. The NDT inspection is a 2-3 person job with a qualified operator and NDT technician in the platform and ground personnel for traffic control. Fall protection is required at all times during the inspection. Drone NDT of roller coasters permits the NDT inspector to assess the ride’s critical areas without the need for a man-lift. Cracked joints or suspected crack joints are noted and specified for further investigation using an NDT rope access team and NDT team from a manlift. Significant cost saving can be achieved by using backup NDT inspection methods only for the targeted areas pinointed by the drone nondestructive testing. Additionally, the frequency of inspection can also be increased compared to NDT performed from a man-lift, rope access team, or from a man-lift due to the difference in cost. It should be noted, however, that supplementally inspection will almost always be required to support drone NDT to confirm findings.
Figure 1: Roller coaster fatigue crack observed at a weld joining two pipe support columns.
Case Study - Drone NDT of Remotely Located Agricultural Assets
Remotely located agricultural assets include steel storage tanks, fiberglass storage tanks, irrigation infrastructure, and other production sustaining assets. In addition to being remotely located, access to these assets by land may be risky due to soil conditions. From a safety perspective, it is generally not advisable to work at heights in the case that an accident would occur. For these reasons, TKS now incorporates drone inspections for remotely located agricultural assets. Shown below is a drone surveying and 20,000 gallon FRP tank for perpendicularity, bulging, coating condition, containment area, and shell integrity. The drone screens a tank farm cost effectively and alerts the NDT inspection if more detailed inspections be required.
Figure 2: Drone inspection of storage tank shell
The price point for consumer drones used primarily for recreational purposes typically lands in the range between $100 and $5,000. Thes drones are more tailored for casual users and hobbyists alike. There is, however, an entirely different category of drone consumerism known as commercial drones. Commercial drones contain a considerable amount of additional features as opposed to consumer drones. Among such features include cameras, sensors, heightened flight performance, partial autonomous flight capabilities, and tough design that is capable of taking damage. Commercial drones often have advanced package offerings that include many of the needed materials to conduct high-level NDT. In addition to the drone itself; packages may include replacement parts, an Android tablet for operation, spare cages, extra propellers, and a warranty.
Indoor drones are designed for niche operations in an indoor environment. Consumer indoor drones typically are designed to be smaller in size and weight while also boasting protected propellers. There are a multitude of consumer, recreational indoor drones that are intended to be used as toys or racing drones. Conversely, there is a subset of professional indoor drones that have more specialized uses. They contain many of the features that commercial drones have, however, they are typically smaller in size and are encased in cages to reduce potential damage to an indoor space. They often have high-end cameras for visual inspection and some options for sensor inclusion. Professional indoor drones with cages allow for better access to tight spaces, increased maneuverability, and greater ability to withstand collisions in close quarters.
Commercial and indoor drones both have many of the same useful advantages while also having unique features. Both commercial drones and indoor drones allow for the user to screen the asset for deficiencies that may require a more detailed follow-up inspection. Drone NDT is a worthwhile financial investment that minimizes safety risks to the NDT technician and, in some cases, provides access to critical areas that may not be inspectable by an NDT technician.