HRSG power station inspection

A recently commissioned gas-fired power station with a demanding shutdown

A gas-fired power station in Cork, one of the newest in the country, was heading into a large shutdown that required a great deal of work while the plant was offline. As part of that shutdown, the client asked Engineers With Drones to inspect the heat exchangers within the HRSG system, along with a range of other assets around the site.

HRSG stands for heat recovery steam generation. In practical terms the unit is a very large box, around six or seven stories high and ten to twenty metres wide, containing a series of heat exchangers. Steam from the initial generation passes back through these exchangers to generate even more heat before it is released to the atmosphere.

A six-story interior reached through a manhole-sized door

Almost everything inside the HRSG is accessed through a small door, roughly the size of a manhole cover. Inspecting the full height of the heat exchanger stages means getting up really high within a very confined space, which is quite difficult when it has to be done with scaffolding and similar access equipment.

The alternative was a confined space drone. Engineers With Drones deployed the Flyability Elios, a cage-protected drone built specifically to fly inside enclosed structures, and worked through the HRSG stage by stage.

Stage by stage, from the turbine exit to the top of the stack

The inspection began at the very first stage of the HRSG, just at the exit of the turbine, and captured the whole area around the turbine, a high space with a lot of volume that would otherwise need extensive scaffolding to reach. The team then moved down stage by stage, capturing both the upstream and downstream face of each heat exchange tube element.

Inside each stage the drone covered the heat exchanging tubes, the gas burners, the roof and structure, the pipework, the plating and the deflector plates. Once the HRSG stages were complete, the drone flew up inside the exhaust stack, recording the louvered vents, any protruding probes, suspect areas and the welds in detail.

The external assets, the cooling system and a flexible diaphragm

With the internal work complete, the client asked Engineers With Drones to carry out a series of external inspections: high-level vents on the outside of buildings, the outside of the HRSG stack, a large external cooling system and its ducted fans, and the tops and sides of tanks around the site.

Inside the HRSG building, a flexible diaphragm runs all the way around the unit between the HRSG itself and the stack. The drone inspected the full circumference, and the team found one or two defects on it.

Across the whole job the team were looking for corrosion, missing plates, bent elements and anything else out of the ordinary. In an asset this uniform, much of the inspection comes down to pattern recognition: everything looks the same until it does not, and the moment it looks different is usually where an issue is found. Working alongside an experienced inspector, the drone allowed the team to dial in on those anomalies and verify them close up.

4K video and photography, organised for easy interpretation