Visual NDT
CASE STUDY: ELIOS 2 DELIVERING SUCCESSFUL POWER STATION MILL INSPECTIONS
Published on 8th March 2021
THE CHALLENGE:
A power generation group was exploring methods to improve the routine maintenance assessment of its assets as it moved into the second half of its expected life cycle. Conventional inspection methods continually rely on CSE (Confined Space Entry) with inadequate data being captured due to the restrictive architecture of the asset. The objectives set out by the client were clear.
- Reduce the requirement of CSE,
- Capture visual data farther than previously possible,
- Data is of sufficient quality to make a clear maintenance assessment,
Several scopes were put forward by the client where it was seeking an improvement.
Inspection of the pulverised fuel mills namely the trifurcation fuel feed ducting.
- These systems contain internal baffling (swirlers) to rotate the fuel feed into the boiler, the pulverised fuel is a wear mechanism and as such these areas encounter a high amount of erosion.
- A specific mill had been flagged for maintenance, to minimise the downtime of the mill which results in a reduction in boiler efficiency and output, an internal inspection was requested to identify the critical areas.
Inspecting the topside of the electrostatic precipitators.
- These systems are a filtration device that removes fine dust particles from gas, the topside has never been inspected due inaccessibility.
Thermal imaging of transformer and HV (high voltage) switching rooms.
- In the case of an emergency, these rooms need to be remotely checked for personnel.
THE SOLUTION:
The platform was capable of achieving the above requirements needed to be compact in size, manoeuvrable, mobile for the inspection engineer and have a payload equipped with a high-quality camera and thermal imaging capability.
Looking through the inventory of inspection equipment it was deemed that the Elios 2 UAV was a perfect candidate to cover the range of challenges put forward.
- The protective cage of the Elios 2 being only 400mm in diameter allowed access through manway entry points, eliminating CSE.
- The uniqueness of the collision tolerant Elios 2 UAV platform is it allows for unrestricted manoeuvrability within a confined space.
- Equipped with optical flow and laser distance sensors, the stability of the Elios 2 is second to none in confined space GPS denied environments.
- The HD streaming to the pilot allows engineers to make assessments in real-time during flight, with the 4k video recording giving the capability of even further analysis post-flight,
- The FLIR thermal camera can display a live thermal image to the pilot for on-the-spot quick safety analysis.
THE OUTCOMES:
In short, the Elios 2 achieved all outcomes that were required in all three scopes.
Trifurcation fuel feed ducting – The small 1400mm diameter ducting that travels vertically 20m along the outside wall of the boilers is not suitable for internal scaffolding and has little to no visual access points. The Elios was able to travel vertically into the trifurcation ducting chutes via access into the mills situated on the first level and visually inspect the bottom side of each of the swirlers.
Post analysis of the video data showed that the erosion on the bottom side of the swirlers was evident on one of the three systems, primarily the system prone to the heavier particles. As a result, the asset owner was able to target which swirler system required maintenance, the specific location and better formulate the repair plan.
Electrostatic precipitators – The topside area of the precipitators have not been inspected since the power station was commissioned, the area of interest is situated 15m vertically above the entrance point and past a network of internal baffling with a narrow 450mm opening. As a result of the precipitators job, the entire system is heavily laden with dust, additionally, with a single unit shutdown, the adjacent precipitator systems create a strong internal draft which must also be overcome.
The Elios successfully completed three flights through the precipitator, navigating past the internal ducting to visually inspect the topside area. The oblique lighting was excellent at minimising the reflection that occurs in an extremely dusty environment. The optical flow sensors assisted with overcoming the internal draft. The engineering maintenance team were on hand watching the live video stream on a secondary display, helping to navigate the pilot to inspect key areas of interest. From these three flights, the maintenance team were able to determine that the asset required immediate attention and identify the reason behind the damages.
Transformer and HV Switching Rooms – In the event of an emergency due to equipment malfunction, the power supply can be cut and as a result, a remote visual assessment must be undertaken to check for injured or trapped personnel and subsequent asset damage. Due to the high voltage nature of these areas, it was questioned whether the Elios 2 could successfully fly without interruption.
It was proven that the Elios was capable of being deployed from a safe location off-site, navigate to each of the two areas to make a visual and thermal assessment with the use of one battery.
