How do we detect surface problems with metals used for glass to metal seals?

Eddy current testing (ECT) is a complex process with many interesting aspects and a wide range of applications. It is a widely used and effective method for detecting surface defects of metal components, including round rods, flat strips and strips used in glass-to-metal seals and capillary tubes.

ECT uses electromagnetic induction to detect and characterize surface and sub-surface defects of conductive materials. It is also used for thickness and conductivity measurements. In very basic terms, a coil is used to generate an oscillating magnetic field that, when applied to a conductive test material, induces vortices. Defects in the test object, along with changes in its conductivity and permeability, lead to corresponding changes in the eddy current. ECT measures changes in phase, frequency, amplitude, impedance and other properties to detect defects, including pitting, cracking and corrosion.

There are various ECT techniques, including absolute eddy current testing, in which a probe with a single test coil probe is used to generate eddy currents and detect changes in the current field; Differential eddy current testing, which uses two active coils, is more sensitive to defects; Even combinations of the two, as well as other types of probes and methods.

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