Ultrasonic NDT

Navigating through complex inspections using simulation software

Published on 23rd September 2020

Navigating through complex inspections using simulation software


An operator requested advice and a suitable inspection solution to take thickness readings on one of their vertical stacks. There was only one access point on the 16-metre-high asset, which was a small platform that went halfway around the perimeter.

The stack had three fins that spiral around the outside, to the top of the asset. The readings had to be taken along a path between each of these fins. The material of the stack was carbon steel, with a paint coating, there was no information regarding the condition of the material towards the top of the stack.



To complete this scope, a method of taking thickness readings of carbon steel with a paint coating needed to be done. There also needed to be a way of accessing the entire area of inspection.

Access on the stack was limited, as there was no option for rope access, so the inspection had to be conducted from the ground. The platform only covered one side of the stack, which meant access on the opposite side was limited, this meant there was no line of sight during the inspection.

As there were also fins approximately 250mm wide that extended past the platform, accessing the opposite side of the stack was physically obstructed.

Nexxis’ dedicated Engineering team were able to gather all the relevant data on the asset from the asset owner and input this information into Nexxis’ 3D simulation inspection software, nexSIM.

By using nexSIM, the engineers were able to create a simulation of the inspection and decide the perfect solution for the scope.

The simulation also assisted the service provider in planning and carrying out the inspection using Nexxis’ methodology.


This inspection was performed with the use of a magnetic wheeled crawler, due to the limited access of the asset. The crawler that was selected by Nexxis and used by the service provider was designed to have optimal manoeuvrability on a curved surface while maintaining maximum adhesion. The crawler also carried a payload consisting of a twin crystal ultrasonic probe, couplant supply and signal wire, along with the crawler’s own power and communication cable.

To take the measurements on the far side of the stack, just like in the simulation inspection, the crawler was able to negotiate the geometry of the fins or be placed onto a fin and transition onto the surface of the stack.