By Frédéric REVERDY, Business Development Manager in M2M
Ultrasonic Inspection of nozzles has always been a challenge due to the geometrical complexity of the component, the changing surface curvature and weld profile around the nozzle circumference. During a manual inspection, the operator needs to carefully move the probe around the nozzle circumference constantly adjusting the skew angle to maintain an ultrasonic beam perpendicular to the inspection area.
If the operator finds an indication, it is complicated to position and size this indication within the weld due to the 3D surface and geometrical complexity of the component. Often the operator would mark the external surface with incremental lines to help him position the defects around the nozzle circumference. The operator also has to estimate the local cross-section through the complex shaped component in order to understand the location of received signals and interpret the position of the indications.
It is thus very important to assist operators with tools that can help them position correctly the probe and interpret the data. We have implemented on a portable phased-array unit, GEKKO, an application that allows one to define nozzle type geometries and to use up to 3-axis encoded nozzle scanners. These scanners allow recording of the rotational position around the branch (scan axis), the linear position along the radial direction of the branch (index axis) and the rotational skew of the probe with respect to the radial direction (skew axis). Cross-section overlays are calculated, using the three encoder positions, as the operator moves the probe and superimposed with the ultrasonic data making it possible to position perfectly the probe and to measure the size of indications.
We asked Sonaspection to manufacture a set-on nozzle sample with various defects around the nozzle circumference (the design was made by TWI). The inspection was carried out with a 5L64 phased-array probe with a 0.3-mm pitch attached to the 3-axis nozzle scanner from Phoenix Ltd. The NozzleScan is attached to the branch pipe with magnetic wheels but fixed size clamping rings are available for non ferritic components. GEKKO is compatible with any nozzle scanner.
GEKKO calculates the 3D component for further display.
The following images show results obtained for various defects (lack of penetration, circumferential EDM notch, slag and radial EDM notch). On the left, GEKKO calculates in real time a cross-section overlay of the nozzle (in white) taking into account the positions of the three encoders and superimposes it to a sectorial scan. In the middle, GEKKO displays the sectorial scan in the 3D CAD file of the component and on the right we can see the position of the probe for those defects.
Thanks to the cross-section overlay the operator can calibrate the position of his probe by making sure that the geometry echoes are superimposed to the backwall of the nozzle. As the inspection is encoded, both the circumferential and radial positions of the defects are recorded allowing to accurately position the defects for further repairs.
You can look at the following video to see the real-time display of the cross section superimposed to the sectorial scan.
Even if the operator doesn't have a scanner or cannot use one due to accessibility issues it is still possible to calculate a cross-section overlay by simply entering the position of the probe within the referential of the component. The following image shows a field inspection of a set-through nozzle with little space. The operator enters the position of the probe, GEKKO calculates the cross section and the operator then moves his probe to align the geometry echoes along the cross section.
This application is included with the standard version of GEKKO.