Not always. With Multi-Echo, the Scout 137 Gen 3 UTM Payload reads through intact coatings up to 6 mm, so many readings need no surface preparation at all. Where rust, scale or residue sits on the steel, the payload cleans the spot itself in the same docking and measures straight after, with no landing and no tool change. The cleaning is qualified up to ISO 8501 rust grade C.
This question came from an attendee at one of our Live Online Demos.
Why surface condition matters
Ultrasonic Testing (UT) needs clean acoustic contact between probe and metal. The enemy is air: rust, scale and residue trap it, and the ultrasound never crosses into the material. A water-soluble couplant gel bridges the last microscopic gap. It deploys at the probe tip from a 33 ml on-board reservoir.
So the question is not whether the surface must be clean, but whether this particular spot needs work. An intact coating does not: Multi-Echo measures the steel underneath. Loose corrosion or residue does.
How the payload preps the spot
The payload carries a motorised brush. It varies speed to the contamination, and three tool groups of increasing abrasive effect ship with it:
- ScoutBrush SiC for light cleaning
- ScoutBrush Metal for rust and scale, qualified to ISO 8501 rust grade C
- ScoutSleeve abrasive sleeves for hardened coatings and heavy oxide
What rust grade C means. ISO 8501-1 grades the condition of uncoated steel from A to D. Grade C is steel where the mill scale has rusted away or can be scraped off, with slight pitting visible to the naked eye. The ScoutBrush Metal is field-verified to prepare a measurable spot on surfaces up to that grade, and the pilot controls the cleaning time, from light dust through rust grade C.
The rule is gentlest tool first. Start with the lightest head that gives a usable A-scan and step up only when needed, because the abrasive sleeves cut into the substrate itself if overused. Heads swap in seconds.
Once the spot is prepared, the contact sensor confirms the probe is seated and the live A-scan appears in Scout Companion for the NDT technician. The reservoir covers up to 100 readings per flight. The payload is factory calibrated and supports 1- and 2-point field calibration through the app: watch a calibration and measurement run in our Flight Lab.
Proof
In our integrated cleaning and UTM video, the drone approaches a steel plate coated with simulated crude oil residue (paraffin wax), cleans the spot, and measures it immediately. The drone readings were then checked against two independent handheld gauges (Tritex and Cygnus). In another sequence the system performs 10 verified UT measurements in under two minutes, surface preparation included.
Surface preparation and measurement are one task here, not two: that is what makes dense thickness campaigns practical from the air, as in class survey work.
Want to see it on a surface like yours?