Strictly speaking, Castor® casks bodies are not a particularly unusual project for our non-destructive testing experts – after all, this part is essentially just a thick wall steel pipe with a cover to close it off.
The casks are about 6 meters long, have a diameter of about 2.50 meters, a wall thickness of about 500 mm, and are made of ductile cast iron. This results in a weight of about 120 metric tons, which places higher demands on the mechanics of the inspection system. The geometries of the test object variants differ slightly.
The inspection unit we developed and built is called “MUSI-C” (Multichannel Ultrasonic System for Inspection Casks). Using multiple phased-array ultrasonic probes, it checks each Castor® for impermissible inhomogeneities.
The unit is designed as a portal inspection system, in which the respective test object and a reference body can be rotated. The reference body has more than 50 flat-bottom reference holes of 6 mm diameter arranged in all spatial directions. It is used for calibrating the system before and after each inspection.
The inspection uses a total of 13 phased-array ultrasonic probes with a total of 896 inspection channels. This vast electronic complexity is due to both the different inspection directions and the specified inspection time goal.
A cast body with its special microstructure always constitutes a challenge for ultrasonic inspections. Moreover, this inspection necessitated very long sound propagation paths (on the order of one meter). An inspection concept also had to be developed and implemented with a new software environment. Despite the costly and complex development, the inspection unit was completed and accepted by the customer, GNS Gesellschaft für Nuklear-Service mbH, exactly on schedule! Besides providing more reliable results than with manual inspection, the system also achieves significantly shorter inspection times.
The inspection unit’s design is the only one of its kind!