Rotating surface coil inspections have undergone remarkable advancements over the years.
The image below captures an Orbitest rotating scanner in use during the late 1960s. This early system featured non-surface-riding pancake coils mounted in an orbiting fixture that rotated around the test material. Even earlier than this, Foerster had pioneered rotating technology, laying the groundwork for modern innovations. By the 1990s, surface-riding rotating coil inspections of bores and tubes had become a mainstay technology, widely adopted across industries.
As probe designs and instrumentation continue to evolve, the ability to extract valuable data from a coil's magnetic field has significantly improved. The images at the bottom showcase some of today’s cutting-edge technology. Directed coils operating in various modes—such as reflection or differential—now provide critical insights into flaw orientation, helping to refine final signal analysis and disposition.
Array probe technology, while not new, has also seen impressive advancements over the decades. These probes, featuring bobbin coils and pancake coils (not limited to pancake coils) distributed around the probe body’s circumference, have become the primary tool for steam generator tube inspections. While array probes are now the industry’s workhorse due to their speed and efficiency, rotating coil inspections still play a critical role when improved flaw disposition is required.
However, rotating coil inspections also have limitations. Despite their ability to provide additional information for certain flaw types, they are inherently slower than array probe testing. The rotating probe must be both indexed and rotated at a constant speed over the material surface, which can be particularly challenging in tight-radius areas, such as U-bends in tubing. These operational constraints mean rotating coils are now used selectively, complementing the broader capabilities of array probes.
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