Definition
A method of magnetic particle inspection in which an electric current is passed directly through a part, creating a magnetic field that flows around the part in circular loops at right angles to the current. This field reveals lengthwise (longitudinal) cracks and flaws that lie parallel to the direction of current flow.
Plain English
A way of inspecting a metal part for hidden cracks by sending electricity through it. The electricity creates a magnetic field that wraps around the part in circles, and that field exposes cracks running along its length.
Context Anchor
Seen in magnetic particle inspection of steel aircraft parts, especially when maintenance personnel are checking for cracks that may not be visible on the surface.
Derivation
‘Circular’ comes from the Latin ‘circulus’ meaning a small ring. The name describes the shape of the magnetic field produced — it wraps around the part in rings, rather than running end to end.
Why Pilots Care
Cracks that run lengthwise in a shaft, bolt, or fitting can lead to sudden failure under load. Circular magnetization is one of the standard methods used to find these flaws before a part returns to service.
Analogy
Picture rings around a wire carrying electric current. Circular magnetization is similar: the magnetic field wraps around the current path instead of running straight from one end of the part to the other.
Grounding Statement
During inspection, current is applied and the magnetic field circles around that current path, making certain cracks easier to find.
Intuition Check
“Circular” does not mean the aircraft part has to be round. It means the magnetic field travels in circular paths around the current.
Example Sentence 1
Before reinstalling the crankshaft, the technician used circular magnetization to check for lengthwise cracks.
Example Sentence 2
Circular magnetization is chosen when the inspection focus is on discontinuities parallel to the length of the component.