The phased array technique, a good way to inspect for corrosion and cracks on bolts and studs

The bolts no longer need to be disassembled to be inspected properly. Thanks to the phased array technique, scans can be captured and stored for offline interpretation and the technique permits accurate, repeatable inspections for monitoring known defects. Bolt inspection is an in-service inspection application and therefore does not result in downtime of equipment and personnel.

This type of inspection involves a scanner with a phased array probe that is attached to the head or end of a bolt, which is then “blasted” with ultrasound. By means of a sector scan, we can visualise the possible defects for these bolts.

Any corrosion-related degradation of the thread can be observed, as well as any corrosion on the shaft of the bolt. Indications will be visible when they are shaped as linear indications between the toes of the thread.

The phased array technique has multiple applications. For instance, it can be used on crank bolts on taps, where the pieces cannot be disassembled. It can also be used to identify corrosion on bolts or studs that cannot be visually inspected, as well as on heat exchanger bolts. This technique is also useful for periodic surveys on installations with screw connections.

By Leo Schroder