Boiler inspection is tricky work that most plant staff wish they could avoid. Now they may get their wish. Unmanned craft can provide faster access to high-quality, real-time visual inspection. The technology also has applications for inspection of other fossil power plant systems, wind turbines, and transmission system components.
Mention the word “drone,” and most people will have a mental picture of what a drone is and does. They likely will think first of military drones carrying missiles and other weapons that could malfunction and/or misdirect. In the U.S., there is the perception that if a drone—more formally known as an unmanned aircraft system (UAS)—is in domestic airspace, it is spying on you or otherwise up to no good. However, the reality is that UAS devices are tools; although they can serve military and surveillance goals and may malfunction, how (and how well) they are used depends on the pilot and purpose.
UASs have fascinated and been used by humans for decades. What’s new is the moniker “drone”—as well as enhanced capabilities. Innovations include taking a simple remote-controlled helicopter and adding cameras, lights, vertical landing system equipment, infrared equipment, self-stabilization equipment, material wall thickness calculation capability, and much more. Technology developments, including advanced batteries, have put us in position to increase the payload on UAS devices.
All of those developments are leading to new opportunities in sectors ranging from the military to retail (Amazon, you may have heard, recently announced that it is developing drones for faster delivery of orders) to energy.
United Aerobotics, a division of United Dynamics Advanced Technologies Corp. (UDC), uses a variety of UASs to achieve its goals. We did not create remote-controlled helicopters/drones; however, we took the underlying capabilities, added and developed new (and in some cases cross-pollinated) technology, and made a system that is extremely useful and powerful. We also designed the systems to be affordable and efficient for use in a number of electricity sector applications.
UDC has been in the boiler inspection and condition assessment business since the mid-1970s. Improvements in unit safety, reliability, and overall boiler efficiency have been the company’s specialty since day one.
In the 1980s, John M. Cavote, chairman and CEO of UDC, developed the “CYBER” system, a leading-edge combustion control system designed to read control levels and auto tune for optimal burner function. Fast forward to the 1990s, when UDC recognized a significant deficiency in proper boiler and auxiliary equipment inspection documentation, coupled with a less-than-desirable approach to tracking forced outage and tube leak events. In response, UDC introduced the concept of a boiler tube leak-tracking system, and shortly thereafter developed what was known as the “TRACKER” system. Although it was a little ahead of its time, TRACKER cleared the path for modern software companies to provide systems that track tube leaks, track material wall wastage, mine data, and project wastage rates.
Around the same time, UDC also recognized a fleetwide problem with streamlining reports and maintaining an effective way to archive repair records and inspection findings. As a result, it developed the “GTRACK” system report generator, which is still used by all UDC field reps and their customers for effective report generation and data collection.
After years of performing visual inspections and evaluations on fossil-fueled utility boilers of all makes and sizes, one common problem continued to plague the industry: how to gain quick access to a boiler to take a look.
Previously, we had few options. We could erect scaffolding (see sidebar “Boiler Inspections: A Nasty but Necessary Chore”), we could fly a “sky climber,” or we could simply use binoculars to visually identify problem areas lacking access. These limited, and sometimes costly options, drove us to form United Aerobotics in 2012.
|Boiler Inspections: A Nasty but Necessary Chore
Boiler inspections are no fun. Climbing through a small hole and crawling over tubes covered in ash looking for leaks or abnormal wear is uncomfortable, tiring, and even dangerous. However, the process is important because it helps managers better evaluate the health of one of the plant’s most important assets—the boiler—and assess maintenance and repair options. Correcting problems before equipment fails is important for plant reliability and availability.
I have done my fair share of boiler inspections. While the O&M manager of a biomass-fired power plant, I was the resident boiler inspector. Later, at a coal-fired plant, I also conducted boiler inspections, although in that situation there were more qualified personnel, so we split up the areas and did smaller sections.
Inspections come in various shapes and sizes. During a forced outage, such as following a tube rupture, I generally tried to do as little as possible to save time. It was important to be thorough, however, and inspect enough to ensure you hadn’t missed deficiencies similar to those that had led to the tube rupture that brought the plant down in the first place. There is nothing worse than starting up following a repair and being forced back offline soon after due to a similar problem that could have been corrected during the initial repair.
Inspectors should always do a visual examination of every area opened. That involves looking for obvious signs of trouble. You may see polished areas, which could indicate a steam leak or sootblower erosion. I always inspected for unusual fouling and blocked gas lanes, broken J-hooks, or other types of supports, and any other noticeable issues.
During forced outages, we often needed to hang a swing stage scaffold, which is like what a window washer uses on the outside of a tall building. You hang it from the top of the boiler through small cable ports and run the air motors or electric motors connected to scaffold picks up to the area of concern. During the process, personnel are often suspended in the middle of the boiler 100 or more feet in the air.
On a forced outage you may only open one section of the boiler, specifically where the tube ruptured, but during an extended maintenance outage, you go into everything—starting on the grates and working your way up to the superheater, generating bank, economizer, air heater, scrubber, baghouse, fans, and stack.
Digital cameras gave us the ability to take photos of everything, but I would have welcomed the option of taking those photos using a drone, without having to get inside the boiler.
The time it takes for traditional boiler inspections depends on the situation. You can work for days during a major maintenance period or a few hours when you need to get back online quickly. Efficient and thorough inspections are always the goal.
—Aaron Larson is a POWER associate editor who has worked in nuclear as well as coal- and biomass-fired plants.
Inspection benefits of using United Aerobotics’ UASs include reaching areas not accessible with scaffold erection, being able to evaluate areas without incurring the high cost of scaffolding, evaluating areas when time does not permit for scaffold erection, and accessing areas that are inaccessible due to safety concerns or other regulatory restriction.
United Aerobotics has two drone models (see Table 1). The trademarked MAGNEBOT v1.0 was designed for interior structure evaluations, such as inside the boiler proper, while the ELECTRABOT v1.0 is used outdoors and in areas experiencing drafts.
|Table 1. Comparison of unmanned aircraft system (drone) models. Source: United Aerobotics|
What separates MAGNEBOT and ELECTRABOT from basic remote-controlled helicopters is live, real-time streamed footage, allowing for real-time inspections and reporting. The MAGNEBOT also is capable of landing vertically on a furnace waterwall and can turn off its rotors for energy savings while continuing to operate the camera and lighting system within high-priority inspection areas.
Each drone also comes equipped with a fully functional operating ground station. Although more than one ground station design exists, they all include:
- Pelican case housing to resist the elements
- Flight control electronics to provide support for the flight team
- High-power computer for processing and editing captured footage
- High-definition monitors to provide a live view for the inspector
- High-speed battery charger for continuous flight operations
Ground stations are used by the flight technician as well as lead inspector performing the evaluation. The station used on a given inspection depends on the application and requirements for the flight project, access point (door) dimensions, travel considerations, and other factors.
The larger ground station (Figure 1) was designed to allow for both inspection technician and flight technician to view flight footage with ease, eliminating any interference (crossover) between them. The flight technician can be watching for flight pattern and safety, while the inspector can be viewing for evaluation accuracy. The inspector is evaluating in real time and may ask the flight technician to stop and return the drone to an area based on potential deficiencies that may have been observed. We have learned that technician interference is typically not an issue, which led to the smaller, more transportable and manageable ground stations with one main viewing screen.
|1. Ground control. This photo shows a typical ground station for the drones, with dual screens and dual control. Courtesy: United Aerobotics|
The Technology at Work
Different inspection locations and tasks require different capabilities, which is why the two models have some specialized features.
MAGNEBOT. During any inspection, there are regions or areas on the list that require more attention or time. To best manage inspection of boiler furnace waterwalls, the MAGNEBOT, flown by four rotors, was designed to land vertically (Figure 2).
|2. MAGNEBOT as a boiler wall would see it. Rotors enable the visual inspection tool to move from one area of interest to another. Courtesy: United Aerobotics|
Run time on the MAGNEBOT is approximately 10 to 15 minutes with all attached equipment in operation. The MAGNEBOT has the ability to zone in on a high-priority location for inspection, such as a wall blower opening (Figure 3). Wall blower locations are typically a high-priority item on the inspection checklist due to potential erosion rates and patterns, blower lance head cracking, alignment, and overall deterioration, refractory, wall box fatigue, and the infamous peg fin cracking mechanisms. The only thing the drone cannot do at this point is take an ultrasonic reading on an eroded tube; we can only tell the customer that it is worn. (An upgrade in progress will enable UT readings.) The value to plant managers in seeing burners and wall blowers is that they can determine if they have immediate action items, but in most cases inspections are used to determine parts to be ordered for the next scheduled shutdown.
Due to the enormous amount of energy consumed by the blade motors, having the ability to land the drone on the wall (Figure 4) while eliminating power to the rotors allows for longer, more detailed inspection time. The camera and lighting (Figure 5), including articulation, remain active, allowing the inspection to continue. Once inspection is complete in a particular region, blade rotors can be reenergized for effective and smooth wall departure. Then the drone can be flown to another region for continued inspections.
|4. Climbing the walls. Using both its rotors and rollers, the MAGNEBOT can smoothly travel up a boiler wall, capturing photos or real-time video. Courtesy: United Aerobotics|
|5. Lights, camera… The MAGNEBOT housing box is the “brain center” of the drone and includes both LED lighting and high-definition camera. Courtesy: United Aerobotics|
MAGNEBOT also has the ability to fly with rolling feet, allowing the drone to scroll up and down the wall while experiencing stability throughout the flight. The vertical landing system and roller device are interchangeable on the drone and are utilized based on the application.
The MAGNEBOT was designed considering payload and overall capability in regards to battery life. The MAGNEBOT v1.0 can currently perform inspections all day with a complete battery charge time of 5 minutes, an average flight time of 8 minutes on a fully charged battery, and a battery change-out time of less than 10 seconds. Total battery change-out time is less than 1 minute.
We can run flights all day with consistent battery change-outs and no restriction. Typically, flight crews will lay the inspection out in sections or blocks. They will base the sections or blocks on 5- to 10-minute time spans to achieve the inspection needs (factoring in battery change-outs). Once the battery swap occurs, the drone is reenergized and returns to inspect the next section or block of the evaluation area. This method also helps by easily identifying which block of footage to review for final notes and reporting. This results in a very high duty cycle, which is the foundation of efficiency and cost savings.
ELECTRABOT. The ELECTRABOT v1.0, flown by six rotors, although not as currently productive due to Federal Aviation Administration (FAA) regulations in U.S. air space, is the flashier of the two existing models and currently gets the lion’s share of attention in the industry. Currently, the FAA restricts all unauthorized commercial UAS use in National Air Space (see faa.gov/go/uas). Due to current regulations, the ELECTRABOT has only been used for limited demonstration purposes. All exterior photos were taken by a volunteer pilot during a recreational flight.
ELECTRABOT comes equipped with a zoom-capable high-definition camera (Figure 6) allowing for high-megapixel still shots (Figure 7) as well as high-definition 1080P video capability. The camera rests in a gimbal designed to remain completely balanced regardless of drone position.
|6. Zoom in. The ELECTRABOT high-definition camera’s zoom capability enables the drone to capture high-megapixel shots from a safe distance. Courtesy: United Aerobotics|
|7. Close-up. This shot of high-voltage power line rigging was taken by the camera on the ELECTRABOT from a distance of about 50 feet but is clear thanks to the camera zoom and drone stabilization features. Courtesy: United Aerobotics|
The ELECTRABOT was designed to fly in atmospheric conditions not conducive to operation of its little brother, MAGNEBOT, and can withstand wind gusts up to 35 mph. The rotating gimbal is designed to keep the camera stable during stability-altering flight patterns while allowing for a clean, zoomed-in shot of the inspection location.
The drone comes equipped with attitude control, which allows autonomous control using global positioning systems to stabilize within a locked position when activated. The feature becomes essential when stability is required and wind gusts are screaming through the flight pattern. The ELECTRABOT also has 360-degree camera swivel capability.
This model was designed for external inspections including, but not limited to, power lines, external ductwork, structural supports, hangers, coal conveyors coming from the yard, external stack inspections, and cooling tower inspections.
A flight crew consists of two members: one flight technician and one technical inspection expert for the specified piece of equipment being evaluated. As you can imagine, flying these birds accurately and safely within an enclosed structure such as a boiler furnace cavity requires a high level of skill, experience, and, believe it or not, courage.
UDC has developed and trained flight crews that not only have the skill set to perform the flight and the inspection but also have the ability to perform on-the-move drone maintenance when required. Although every project is equipped with a complete backup drone and repair parts, it is imperative that the crew has the ability to make repair adjustments on the spot in a timely fashion to ensure on-schedule project completion.
Cost and Scheduling Considerations
Cost is always a factor when determining an applicable method of inspection. Aerobotic inspections are not only time beneficial, but they also tend to be easy on the budget when compared with traditional accessibility methods. At a cost of around $5,000 per day and a total cost of roughly $10,000 to $14,000—including mobilization and demobilization—drone inspections compare favorably with the cost and time involved for erecting scaffold or hanging sky climbers.
A typical drone inspection of all burner components takes one to two days; in most cases, time inside the boiler consists of one 10-hour shift, leaving final reporting for day two.
Drone inspections are currently in high demand not only for costs savings; response time and readiness are paramount as well. United Aerobotics teams are prepped and ready for immediate deployment domestically and internationally at any time. A response, and on-site time, can be expected within 12 to 24 hours of initial request (some sites outside of the U.S. may require an additional 24 hours). This inspection program was developed for service purposes, so rapid response time is key.
United Aerobotics was conceived with safety at the top of its requirements. Flying UAS devices for either recreational and/or commercial use comes with potential risks and hazards. It is recommended that only trained and experienced technicians perform flight projects. United Aerobotics’ safety program allows for safe and effective flights. We stress not just flight safety but also flight crew and customer safety.
For example, the MAGNEBOT has been used as an effective visual aid in determining clinker location and position for safe and timely removal. In addition, it can be used to verify that all expected clinkers have been removed.
Although potential damage to structures and objects from a distressed drone is minimal, human safety is paramount. Flight crews are careful to verify that no personnel are within range of the flight pattern, with the exception of the trained flight crew members. Ongoing safety considerations are always being explored and protocol adjustments made to stay on top of the safety curve.
Although United Aerobotics drones have many benefits and applications, there are, of course, some limitations. First and foremost is the current FAA regulation restricting UAS for commercial use in the U.S.
Second, current drone models can only provide a visual inspection. Despite the fact that they can give you unprecedented visual clarity of your asset, they cannot replace human touch. There will always be some advantage to putting your hand on a piece of equipment and performing live nondestructive evaluation (NDE).
The reason we say this is only a current limitation is that research and development is under way to arm drones with limited NDE capability. In addition, action is being taken to equip the drones with full auto pilot system devices to reduce pilot error and ultimately improve safety and efficiency. Third, drones cannot currently perform flights in atmospheric temperatures exceeding 180F and cannot currently fly in “no spark” zones.
United Aerobotics has been in, and serviced, 16 power station units in its first year of operation. Work has ranged from roof/pendant inspections to superheat wrapper tube intersection inspections, waterwall blower (IR port) inspections, burner inspections (including tangentiallly corner–fired and wall-fired burner systems), and bottom ash inspections, to name a few. Following are specifics of two inspections.
Project X. The client in Texas needed to inspect a Combustion Engineering (CE) 800-MW eight-corner furnace with a scope that included CE furnace burners and wall blowers during a short maintenance outage, but they didn’t have the time or funds for scaffolding or buggies.
The United Aerobotics team was able to reach the site within 8 hours and perform an aerial inspection of all components in one shift, using the MAGNEBOT. The inspection scope included 80 burner/air tips and 50 IR ports.
The inspector was able to identify the deterioration of aftermarket ceramic splitter plates in the coal buckets. Due to vibration and overheating, pieces of plate were falling to the slope below, causing tube failures by puncturing the tube wall. The inspector was also able to identify multiple cracked lance heads in the IR ports.
Project Y. This Missouri client needed to inspect a Babcock & Wilcox 750-MW furnace to determine the condition of previous repairs to the membrane on the roof of the boiler as well as determine if there was erosion on the pendants due to adjustments on the IR ports. This project used the MAGNEBOT because its unique design allows it to “land” on the roof and its small size allows it to fit between pendants. The scope included 18 pendants and the seam on the roof line.
The inspector was able to identify missing refractory behind the membrane as well as confirm polishing behind the wrapper tube on all pendants.
Drones Can Provide a Market Edge
New Environmental Protection Agency regulations such as the Mercury and Air Toxics Standards have altered the playing field in regards to emissions control. Consequently, burner performance and condition play an increasingly vital role in the process of maximizing efficiency while helping to meet current and new standards and regulations. Aerial drones can assist in this task by providing quicker burner inspection than traditional methods.
In the power industry, timing is always a concern, from dates and duration of planned maintenance overhauls to the time of year that assets are effectively in operation. On the maintenance side, getting the most work done in the shortest period of time has been the key to success. UASs help streamline the process at multiple levels.
As for external inspections, U.S. FAA flight restrictions are scheduled to lift in the next six to 18 months, allowing for commercial flights to take place in open air space outside of an enclosed structure; however, UASs are commercially utilized in other countries today. (All exterior photos were taken by a volunteer pilot flying the model recreationally. Once FAA restrictions are lifted, we will be ready to provide services to inspect power lines, stack externals, cooling tower externals, wind turbines, towers, and other exterior equipment.)
At the end of the day, UAS inspections are not just high on the cool factor. More importantly, they get the job done. The power industry has been in need of an innovative inspection approach like that offered by drones for decades, and technology has finally caught up with demand. ■
— Jon S. Cavote ([email protected]) is president and COO of United Dynamics Advanced Technologies Corp.