ET ASNT Level I Practice Exam 2025 – Your All-in-One Guide to Exam Success!

Narrow coil eddy current test coils are specifically designed to detect small surface defects due to their focused and sensitive nature. The geometry of the narrow coil allows it to penetrate less deeply into the material, which enhances the ability to identify surface anomalies such as cracks, pits, or other irregularities that might be present on or near the surface of the test material.

Eddy current testing operates by inducing electrical currents in conductive materials, and when these currents encounter a defect or variation in the material, they produce changes in the impedance of the coil. Narrow coils excel in this application because they can detect very localized changes, making them ideal for identifying small surface defects that might not be noticeable with broader coils or other testing methods.