Drones: Consumable inspection tools with financial benefits

Scott Wambeke, principal HRSG engineer, offered a detailed review of Xcel Energy’s new indoor unmanned aerial system (UAS) tools, a/k/a drones, at the HRSG Forum with Bob Anderson (Fig 1). Although the company has used drones outside to survey transmission systems, pipelines, and other difficult-to-traverse systems, Wambeke’s team concentrates on what’s inside the plant—more specifically what’s inside the boiler. He was at the meeting to explain the experiences, successes, and lessons learned as his crew launched and improved these new inspection tools.

The Xcel team has come a long way in two years of  flying, beginning in large coal-fired units looking at tube-wall slag and burners. Skill and precision have progressed rapidly, and the team is finding comfort and new applications inside the more restrictive HRSGs.

Wambeke clearly labeled drones as consumable inspection tools. In corporate terms the cost is very reasonable. And the savings in time, equipment and labor can be enormous. Scaffolding alone, in a large boiler, can cost up to $100,000 to deploy.

“Our primary purpose is to have a safe, compliant, and efficient internal UAS program that saves both time and money,” he explained. Wambeke’s overview stressed how these systems offer immediate access to information so engineers and maintenance personnel can quickly determine needs and assess what conditions they might be facing. It’s a decision-making tool on whether or not they need to expend further time and effort, and where to focus if they do. 

And it’s nearly spontaneous. When called, the UAS team can be up and running quickly (in as little as 30 minutes).

“We’ve had our challenges,” said Wambeke, “and we know that personnel safety is a primary concern.” The drones can, for example, be pulled by draft into tube walls, or lose power and just drop. They can also veer toward objects and people, and can move horizontally at up to 50 mph. But Xcel adds a “handler” who is equipped to “swat them down.” Think pesky bats.

For the pilot, stress levels can also become high. “Sometimes it’s like driving a car in a snow storm,” stated Wambeke.

But the immediate and recorded inspection results offer great benefits.

Xcel began with a DJI Phantom 3 Pro, modified with carbon-fiber blades, blade guards, and eventually LED lighting. At times, a simple sheet of plywood served well as a launch site.

Most camera systems are reasonably priced, as are memory cards. Wambeke offered a warning on the latter: “Have multiple cards,” he cautioned. “The last thing you want is to lose a memory card in an ash pit or bunker.” So the team replaces cards at each landing. “It’s OK to lose the drone,” he said, “but you don’t want to lose the data.”

There have been other challenges and a few crashes with various causes including HRSG liner bolt snags, draft-induced collision with catalysts, and the occasional yaw malfunction (software-induced). But tabletop repairs can be fairly simple.

Other restrictions become obvious through experience. Examples include:

      • Flight time is 10 to 12 minutes per battery.

      • Minimum space requirement is normally 6 to 12 ft.

      • High dust and ash loading can make flight manipulation a challenge (think snowstorm).

      • Any draft above 5 mph makes flight difficult in tight areas.

      • Standard lighting can be limiting; Xcel has modified and continues to improve theirs (Fig 2).

Challenges. Commercially available drones are designed for outdoor use, and most are equipped with GPS. This positioning system does not work inside a steel boiler. So Xcel is working with others on a possible artificial GPS. They are also working on new object-avoidance software.

Wambeke offered a list of other challenges, including these:

    1. 1. Inspector/operator training and stress can be limiting factors, especially with crew members having other responsibilities and with long intervals between flights.

    2. 2. Safety consciousness around people is critical, and personal protection is required.

    3. 3. Communication between pilot and spotter requires training and coordination.

    4. 4. Drifting in elevation and yaw are nearly unavoidable (at present).

    5. 5. Maintaining a precise position is difficult, especially with ambient drafts.

    6. 6. Compass interference can prevent takeoff; an angle iron near the compass seems to help.

Next generation. Wambeke gave some specific ideas for the next fleet of craft. These included:

      • Continuous lighting improvements.

      • New versions of wall-roller attachments.

      • Upgraded blade guards and unit cages (Fig 3).

      • And eventually, very highly refined, custom-built systems.

Xcel collaborates with universities on some of these developments and shares information with other utilities and users.

Although the possibilities seem endless, Wambeke stressed that drones are still an inspection tool—not (yet) a service and repair tool. But again, the possibilities seem endless.

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